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Synthesis and characterization of new partially-aggregated water-soluble polyether-triazole linked zinc(II) phthalocyanines as photosensitizers for PDT studies
Synthetic Metals 260 (2020) 116256
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Synthesis and characterization of new partially-aggregated water-soluble polyether-triazole linked zinc(II) phthalocyanines as photosensitizers for PDT studies
T
Yasemin Baygua, Yaşar Gökb,* a b
Tavas Vocational High School, Pamukkale University, Denizli, Turkey Department of Chemical Engineering, Uşak University, Uşak, Turkey
ARTICLE INFO
ABSTRACT
Keywords: Zinc phthalocyanine Partially-aggregation Click reaction PDT Red shift Ester hydrolysis
Peripheral and non-peripheral octa-carboxylated water-soluble zinc(II) phthalocyanines with clicked polyethylene glycol linkers have been prepared. Different multistep reaction pathways have been attempted and compared for the preparation of the phthalonitrile precursors. Novel compounds have been characterized by combination of elemental analysis, 1H and 13C NMR, FT-IR, U–vis and MS spectral data. Both phthalocyanines were proved to be water soluble. Their singlet oxygen generation was determined in both water and DMSO to assess their potential of photosensitizers for photodynamic therapy.
1. Introduction
in water and limit their aggregation. Generally, high solubility and high tendency of aggregation properties of phthalocyanines in water limit their singlet oxygen generation yields and thus significantly restrict their photodynamic therapy potential [7]. Carboxylic acids with triazole groups attached to metallo-phthalocyanines through polyethylene glycol linkers could confer solubility in aqueous media and at the same time overcome aggregation problems water [8]. We report herein the synthesis and characterization of water and DMSO soluble zinc(II) phthalocyanines with octa-substituted carboxylic acid groups attached to the polyether linked triazole moieties. These novel compounds exhibit the characteristic partially-aggregated behavior by UV–vis spectra in aqueous media. Their photochemical properties, especially their singlet oxygen quantum yield, were investigated for PDT applications.
Phthalocyanines and related compounds are one of the largest groups of tetrapyrrolic macrocycles and widely investigated in many areas such as electrochromic and photochromic substances, photosensitizers for dye-sensitized solar cells, liquid crystals, LangmuirBlodgett films, chemical sensors, industrial catalytic systems and material chemistry, semiconductor devices, molecular metals, and photocopying devices [1,2]. In the past few decades, in addition to their traditional uses mentioned above, phthalocyanines strated to appear as ideal second generation photosensitizers for photodynamic therapy (PDT) [3], in particular due to their high singlet oxygen yield and other optical properties [4]. Nonetheless, the low solubility of unsubstituted phthalocyanines in aqueous media and common organic solvents is a strong drawback [5]. An intrinsic advantage of phthalocyanine as PDT photosensitizers is their intense absorption at near-infrared wavelengths (ca. 700 nm), ideal for various types of cancers as it allows to irradiate in the phototherapeutic window. Especially, water soluble phthalocyanines are most promising photosensitizers [6]. Ideally, PDT photosensitizers should exhibit high solubility in water, strong absorption in the 600−800 nm region (deep red) and high singlet oxygen quantum yields. Attachment of carboxylic acid groups attached through triazole moieties to Pcs is expected to significantly increase the solubility of Pcs
⁎
2. Experimental 2.1. General 1
H and 13C NMR spectra were recorded on Varian Mercury plus 300 MHz and on an Agilent-vnmrs 400 spectrometers. CDCl3, DMSO-d6 and D2O were used as the as NMR solvents. FT-IR spectra were recorded on Perkin-Elmer UATR Two spectrometer. The UV–vis absorption spectra were measured on a Shimadzu UV-1601 spectrophotometer which is double-beamed with thermostatically controlled cell block. All
Corresponding author. E-mail address: [email protected] (Y. Gök).
https://doi.org/10.1016/j.synthmet.2019.116256 Received 24 June 2019; Received in revised form 18 November 2019; Accepted 28 November 2019 0379-6779/ © 2019 Elsevier B.V. All rights reserved.
Synthetic Metals 260 (2020) 116256
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measurements were made in 1 mL quartz cuvette. Mass spectra were recorded on a Micromass Quattro Ultima LC–MS/MS and on a Bruker Daltonics Microflex LT MALDI-TOF spectrometers. Elemental analyses were determined on a Costech ECS 4010 instrument. Melting points were determined on an electro thermal melting point apparatus in a sealed capillary and are uncorrected. All reactions were performed under an argon atmosphere using oven-dried glassware. All reagents and solvents were purchased from commercial suppliers and solvents were dried over standard drying agents and procedures prior to use [9]. 1-iodo-3,6,9,12-tetraoxa-pentadec-14-yne [2], S-(3,6,9,12-tetraoxapentadec-14-yn-1-yl) ethanethioate [10], 4,5-dimercaptophtholanitrile [11], 2-azido-etilacetate [12] and 3,6-bis(4’-methyphenyl sulfanyloxy) phtholanitrile [13] were prepared according to the reported procedures. Photo-irradiations were carried out using a General Electric quartz line lamp (300 W). A 600 nm glass cut off filter (Schott) and a water filter were used to filter off ultraviolet and infrared radiations respectively. An interference filter (Intor, 700 nm with a band width of 40 nm) was additionally placed in the light path before the sample. Light intensities were measured with a POWER MAX5100 (Molelectron detector incorporated) power meter.
using dichloromethane as eluent to give desired compound. Cream coloured solid, yield: 2.8 g (83.83 %), mp: 184−185 °C. 1H NMR (400 MHz, CDCl3) δ: 7.52 (s, 2H, Ar-H), 3.46 (s, 6H, CH3), 3.42 (s, 6H, CH3). 13 C NMR (100 MHz, CDCl3) δ: 184.75 (C]S), 153.48, 130.10, 111.72 (C^N), 111.42, 43.74, 39.27. FT-IR (ATR, cm−1): 3074, 3049, 29352879, 2237 (C^N), 1733, 1591, 1552, 1480, 1237, 1101. ESI MS m/z: 335.07 [M+H]+, 352.08 [M+H2O]+, 372.87 [M + K-H]-, 388.90 [M +3H2O]+, 435.94 [M+2 K + Na]+. Anal. calcd. for C14H14N4S2O2: C, 50.28; H, 4.22; N, 16.75. Found: C, 50.01; H, 4.50; N, 17.13. 2.3.2. S,S'-(2,3-dicyano-1,4-phenylene) bis[dimethyl(thiocarbamate)] (4) The precursor compound (3) (1.34 g, 4 mmol) was heated gently and stirred under argon atmosphere at 190° to give melted compound. The melted compound was further heated and stirred at 205 °C for 3 h, then cooled to room temperature. The crude green solid product was triturated with dichloromethane and filtered, washed with dichloromethane and then dried in vacuo. Green solid, yield: 1.06 g (79.34 %), mp: 221 °C. 1H NMR (400 MHz, CDCl3) δ: 7.86 (s, 2H, Ar-H), 3.13 (s, 6H, CH3), 3.05 (s, 6H, CH3). 13C NMR (100 MHz, CDCl3) δ: 162.48 (C]O), 140.18, 136.26, 123.39, 113.89 (C^N), 37.39, 37.09. FT-IR (ATR, cm−1): 3116, 3067, 2927-2888, 2239 (C^N), 1676, 1557, 1477, 1363, 1089. ESI MS m/z: 333.18 [M−H]-, 351.94 [M+H2O-H]-, 356.91 [M + Na-H]-, 389.04 [M+H2O+H]+, 436.01 [M+2 K + Na +H]+. Anal. calcd. for C14H14N4S2O2: C, 50.28; H, 4.22; N, 16.75. Found: C, 50.60; H, 4.57; N, 16.44.
2.2. Singlet oxygen quantum yields Singlet oxygen quantum yield (ΦΔ) determinations were performed in DMSO and in water, using the experimental setup described in literature [14]. Typically, a 3 mL portion of the zinc(II) phthalocyanine solutions (C = 4 × 10−5 M) containing the singlet oxygen quencher was irradiated in the Q band region with the photoirradiation set up [14]. ΦΔ values were determined in air using the relative method and using unsubstituted ZnPc (in DMSO) and ZnPcSmix (in aqueous media) as standards. 1,3-diphenylisobenzofuran (DPBF) and 9,10-antracenediyl-bis(methylene)dimalonoic acid (ADMA) was used as chemical quencher for singlet oxygen in DMSO and aqueous media, respectively. Eq. (1) was employed for the determination of ΦΔ values:
=
Std
R.IStd abs RStd.Iabs
2.3.3. 3,6-dimercaptophthalonitrile (5) A solution of KOH (1.47 g, 26.34 mmol) in dry methanol (36 mL) was added and stirred to a solution of compound (4) (2.0 g, 5.98 mmol) in dry THF (180 mL) at room temperature overnight and monitored TLC [silica gel (chloroform:methanol)(95:5)]. The end of this period, the mixture was poured into cold water (300 mL) and acidified with conc. HCl to pH = 2.0. This reaction mixture was extracted with ethyl acetate (3 × 100 mL) and active carbon was added to the combined organic phase filtered off, washed with ethyl acetate and then dried over anhydrous MgSO4 overnight. The solution was evaporated to dryness under reduced pressure and solidified with diethyl ether. Pale brown solid, yield: 0.82 g (71.32). 1H NMR (DMSO-d6) δ: 7.66 (s, 2H, Ar-H), 2.80 (s, 2H, SH). FT-IR (ATR, cm−1): 3071, 2556 (S-H), 2223 (C^N), 1442, 1201, 1139. Anal. calcd. for C8H4N2S2: C, 49.98; H, 2.10; N, 14.57. Found: C, 49.63; H, 2.45; N, 15.05.
(1)
where is the singlet oxygen quantum yields for the standard ZnPc ( Std = 0.67 in DMSO) [15] and ZnPcSmix ( Std = 0.45 in aqueous media) [16], R and RStd are the DPBF (or ADMA) photo-bleaching rates in the presence of the respective samples (ZnPc-I and ZnPc-II) and standards, respectively. Iabs and IStd abs are the rates of light absorption by the samples (ZnPc-I and ZnPc-II) and standards, respectively. To avoid chain reactions induced by DPBF (or ADMA) in the presence of singlet oxygen [17], the concentration of quenchers (DPBF or ADMA) was lowered to ∼3 × 10−5 M. Solutions of sensitizer (absorbance = 1 at the irradiation wavelength) containing DPBF (or ADMA) were prepared in the dark and irradiated in the Q band region using the setup described above. DPBF degradation at 417 nm and ADMA degradation at 380 nm were monitored. The light intensity 6.21 × 1015 photons s-1 cm-2 was used for ΦΔ determinations. Std
2.3.4. 3,6,9,12-tetraoxapentadec-14-yne-1-thiol (7) A solution of H2SO4/H2O (4.2 mL) (1:1) was added to a solution of compound 6 (1.35 g, 4.65 mmol) in methanol (35 mL) under argon atmosphere and refluxed for 10 h. The reaction was monitored by TLC [silica gel (dichloromethane:methanol) (97:3)]. The mixture was then allowed to cool at room temperature and was poured into water (150 mL) and then extracted with dichloromethane (3 × 75 mL). Collected organic phases were washed with water (150 mL) and dried over anhydrous MgSO4 and then evaporated to dryness under vacuum. The resulting brown oil compound was purified by column chromatography using chloroform as eluent. Pale yellow oil, yield:1.0 g (86.96 %). 1H NMR (400 MHz, CDCl3) δ: 4.14 (s, 2H, HCCCH2O-), 3.65-3.53 (m, 14H, -OCH2CH2O-), 2.72-2.64 (m, 2H, -OCH2CH2SH), 2.40 (d, 1H, HCCCH2O-), 1.54 (t, 1H, -OCH2CH2SH). 13C NMR (100 MHz, CDCl3) δ: 78.65 (C^CH), 73.65 (^CH), 71.85-68.07 (eCH2CH2), 57.37 (CH2C^), 23.25 (CH2SH). FT-IR (ATR, cm−1): 3251 (^CH), 2866 (OCH2CH2O-), 2558 (eSH), 2113 (C^C), 1094.
2.3. Synthesis 2.3.1. O,O'-(2,3-dicyano-1,4-phenylene) bis[dimethyl(thiocarbamate)] (3) Dimethylthiocarbamoyl chloride (3.2 g, 26 mmol) was added to a solution of 2,3-dicyano hydroquinone (1) (1.6 g, 10 mmol) and DABCO (2) (5.78 g, 50 mmol) in dry DMF (20 mL) under argon atmosphere at room temperature. The reaction mixture was stirred at 75 °C for 2 h, then cooled to room temperature and poured into water (80 mL). The suspension was mixed with ethyl acetate (80 mL) and then water phase extracted with ethyl acetate. Combined organic phases were washed with brine (60 mL), dried over anhydrous MgSO4 and concentrated. The crude product was purified by a silica gel column chromatography
2.3.5. 3,6-bis((3,6,9,12-tetraoxapentadec-14-yn-1-yl)thio)phthalonitrile (10) 2.3.5.1. Method A. A solution of compound 8 (2.56 g, 5.48 mmol) and compound 7 (3.4 g, 13.7 mmol) in dry DMSO (60 mL) was stirred under argon atmosphere at room temperature for 15 min. and then dry K2CO3 (3.02 g, 21.94 mmol) was added to this mixture. The reaction mixture 2
Synthetic Metals 260 (2020) 116256
Y. Baygu and Y. Gök
was stirred at the same condition for 3 days and monitored by TLC [silica gel (dichloromethane:methanol)(98:2)]. The end of this period, the reaction mixture was poured into water (400 mL) and extracted with dichloromethane (3 × 140 mL). Collected organic phases were washed with water (200 mL) and dried over anhydrous MgSO4 overnight and then evaporated to dryness under reduced pressure. The yellow oil crude product was purified by column chromatography [silica gel (dichloromethane: methanol)(98:2)] to give yellow oil product. Yield: 1.16 g (34.14 %). 1H NMR (400 MHz, CDCl3) δ: 7.65 (s, 2H, Ar-H), 4.17 (s, 4H, OCH2C), 3.73-3.60 (m, 28H, eOCH2CH2O), 3.22 (t, 4H, SCH2), 2.42 (s, 2H, ^CH). 13CNMR (100 MHz, CDCl3) δ: 141.10, 132.92, 117.18, 113.84 (C^N), 79.63 (C^CH), 74.59 (^CH), 70.55-69.09, 58.37, 33.65. FT-IR (ATR, cm−1): 3280-3250 (^CH), 3071, 2908-2865, 2224 (C^N), 2113 (C^C), 1441, 1092. ESI (+) MS m/z: 638.2 [M+H2O]+, 621.2 [M+H]+. Anal. calcd. for C30H40N2S2O8: C, 58.04; H, 6.49; N, 4.51. Found: C, 57.70; H, 6.20; N, 4.86.
125.80, 109.92, 70.81-67.31, 62.85, 58.68, 55.10, 42.63. FT-IR (ATR, cm−1): 3259, 3136, 2912-2864, 1701, 1620, 1558, 1462, 1368, 1283, 1085. UV–vis (H2O): λmax (log ε) : 776 (4.90), 687 (4.34), 321 (4.66). MS MALDI-TOF m/z: 3307.708 [M-CO2H-H]-, 3366.606 [M(C5H6N3O2)+Matrix]+, 3429.632 [M+3H2O + Na-H]-, 3460.820 [M +6H2O-H]-, 3517.58 [M + K-7H2O-H]-, 3615.283 [M+2MatrixCO2H-H]-. Anal. calcd. for C136H184N32S8O48Zn: C, 48.66; H, 5.52; N, 13.35. Found: C, 48.38; H, 5.85; N, 13.54. 2.3.8. 4,5-bis(3,6,9,12-tetraoxapentadec-14-yn-1-ylthio)phthalonitrile (15) 2.3.8.1. Method A. 4,5-Dichloro phthalonitrile (13) (0.45 g, 2.3 mmol) and compound 7 (1.25 g, 5.04 mmol) was dissolved and stirred with dry DMF (150 mL) containing excess amount of dry K2CO3 (1.11 g, 8.05 mmol) under argon atmosphere at 50 °C for overnight. The reaction process was checked by TLC [silica gel (chloroform:methanol)(99:1)]. After cooling to room temperature, the reaction mixture was filtered off and evaporated to dryness under reduced pressure. Purification of the crude product was carried out by column chromatography on silica gel using chloroform as eluent to give compound 15. Colourless solid, yield: 0.88 g (62.03 %), mp: 49−50 °C. 1H NMR (400 MHz, CDCl3) δ: 7.62 (s, 2H, Ar-H), 4.18 (s, 4H, OCH2C), 3.79-3.64 (m, 28H, OCH2CH2O), 3.23 (t, 4H, SCH2), 2.42 (s, 2H, ^CH). 13C NMR (100 MHz, CDCl3) δ: 143.95, 129.39, 115.50, 111.47, 79.65 (C^CH), 74.52 (^CH), 70.75-70.59, 69.10, 58.38, 32.72. FT-IR (ATR, cm−1): 3266, 3223, 3072, 2907-2868, 2231 (C^N), 2106 (C^C), 1565, 1462, 1348, 1094. MS MALDI-TOF m/z: 638.01 [M+H2O]+, 642.98 [M + Na-H]-, 643.89 [M + Na]+, 658.88 [M + K-H]-. Anal. calcd. for C30H40 N2S2O8: C, 58.04; H, 6.49; N, 4.51. Found: C, 57.78; H, 6.20; N, 4.88.
2.3.5.2. Method B. 3.6-Dimercaptophthalonitrile (5) (0.76 g, 4 mmol) was dissolved in dry acetone (120 mL) in the presence of dry K2CO3 (1.64 g, 12 mmol) under argon atmosphere at room temperature for 35 min. A solution of compound 9 (3.0 g, 8.8 mmol) in dry acetone (20 mL) was added and stirred at room temperature overnight. The reaction was monitored by thin layer chromatography [silica gel (dichloromethane:methanol)(96:4)]. At the end of this period, the reaction mixture was evaporated to dryness under reduced pressure and then mixed with chloroform:water mixture [(400 mL)(1:1)]. Organic phase was collected, dried over anhydrous MgSO4 overnight and then purified by column chromatography (silica gel) using dichloromethane as eluent. Pale yellow oil, yield: 1.04 g (41.95 %).
2.3.8.2. Method B. 4.5-Dimercapto phthalonitrile (14) (0.44 g, 2.28 mmol) was dissolved and stirred with dry acetone (60 mL) containing excess amount of dry K2CO3 (0.94 g, 6.84 mmol) under argon atmosphere at room temperature for 35 min. At the end of this period, a solution of compound 9 (1.70 g, 5 mmol) in dry acetone (10 mL) was added above solution and stirred at room temperature for overnight. The reaction was monitored by TLC [silica gel (chloroform:methanol)(97:3)]. The reaction mixture was filtered off, washed with chloroform and evaporated to dryness under reduced pressure. Purification of the crude product was carried out by column chromatography on silica gel using chloroform/methanol (97:3) as eluent to afford compound 15. Colorless solid, yield: 0.66 g (46.69 %), mp: 48−50 °C
2.3.6. Diethyl 2,2'-[(2,3-dicyano-1,4-phenylene)bis(thio-2,5,8,11-tetraoxatridecane-13,1-diyl-1H-1,2,3-triazole-4,1-diyl)]diacetate (12) A orange suspension of sodium-L-ascorbate (0.30 g, 1.5 mmol) and copper(II) acetate monohydrate (0.144 g, 0.72 mmol) in water (14 mL) was added to a solution of 10 (1.16 g, 1.87 mmol) and 2-azido ethyl acetate (11) (0.96 g, 7.48 mmol) in a mixture of tert-butanol (14 mL) and DMF (16 mL) under argon atmosphere at room temperature overnight, then poured into water (100 mL) and extracted with chloroform (3 × 40 mL). Collected organic extracts were washed with brine (60 mL) and dried over anhydrous MgSO4 and then purified by column chromatography [silica gel (dichloromethane:methanol) (95:5)] to give pale yellow oil, yield: 1.18 g (71.87 %). 1H NMR (400 MHz, CDCl3) δ: 7.70 (s, 2H, CH]C), 7.63 (s, 2H, Ar-H), 5.13 (s, 4H, NCH2C), 4.68 (d, 4H, OCH2C), 4.23 (m, 4H, OCH2CH3), 3.71-3.57 (m, 24H, -OCH2CH2O), 3.19 (t, 4H, OCH2), 2.84 (m, 4H, SCH2), 1.27 (t, 6H, CH3). 13C NMR (100 MHz, CDCl3) δ: 166.28 (C]O), 145.47, 141.07, 132.94, 124.11, 117.05, 113.89 (C^N), 70.56-69.53, 64.50, 62.35, 50.80, 38.37, 33.62, 14.05. FT-IR (ATR, cm−1): 3142, 3079, 2972-2867, 2224 (C^N), 1749 (C]O), 1443, 1211, 1093. ESI MS m/z: 878.050 [M]+. Anal. calcd. for C38H54N8S2O12: C, 51.92; H, 6.19; N, 12.75. Found: C, 52.29; H, 5.91; N, 13.08.
2.3.9. Diethyl 2,2'-[(4,5-dicyano-1,2-phenylene)bis(thio-2,5,8,11-tetraoxatridecane-13,1-diyl-1H-1,2,3-triazole-4,1-diyl)]diacetate (16) A suspension of copper(II) acetate monohydrate (0.147 g, 0.73 mmol) and sodium-L-ascorbate (0.3 g, 1.51 mmol) in water (15 mL) was added to a solution of compound 15 (1.17 g, 1.89 mmol) and 2-azido acetate (11) (0.99 g, 7.56 mmol) in a mixture of tert-butanol and THF (30 mL)(1:1) under argon atmosphere at room temperature for 2 days. Reaction was monitored by using TLC [silica gel (chloroform:methanol) (95:5)]. The reaction mixture was poured into water (60 mL) and extracted with chloroform (3 × 45 mL), washed with brine solution (60 mL) and then dried over anhydrous MgSO4 overnight. The solution was filtered off, washed with chloroform and evaporated to dryness under reduced pressure. Yellow oil crude product was purified by column chromatography on silica gel using as eluent a mixture of chloroform/ methanol (gradient 100:0 →98:2) to yield compound 16 as a colorless oil. Yield: 0.9 g (54.24 %). 1H NMR (400 MHz, CDCl3) δ: 7.71 (s, 2H, triazole), 7.62 (s, 2H, Ar-H), 5.14 (s, 4H, NCH2C), 4.68 (s, 4H, OCH2C), 4.24 (m, 4H, OCH2-CH3), 3.76 (m, 24H, OCH2CH2), 3.62 (m, 4H, CH2CH2-O), 3.22 (t, 4H, SCH2), 1.28 (t, 6H, CH3). 13C NMR (100 MHz, CDCl3) δ: 166.31 (C]O), 145.52, 143.95, 129.38, 124.10, 115.58, 111.35 (C^N), 70.61-70.48, 69.67-69.32, 64.53, 62.36, 50.82, 32.67, 14.06. FT-IR (ATR, cm−1): 3140, 3099, 3060, 2982-2867, 2229 (C^N),
2.3.7. ZnPc-I In a Schlenk system, 3,6-disubstitue phthalonitrile (12) (0.40 g, 0.46 mmol) and zinc acetate dihydrate (0.10 g, 0.46 mmol) in dimethyl ethanolamine (2.5 mL) was heated and stirred at 155 °C, under argon atmosphere for 20 h. After cooling to room temperature, the reaction mixture was evaporated to dryness under vacuum and the reaction mixture was poured into methanol (20 mL) and then centrifuged to give desired product. The solid product was filtered off, washed with methanol and then dried under vacuo. Brown solid, yield: 0.077 g (20.05 %), mp > 300 °C. 1H NMR (400 MHz, D2O δ: 7.81 (s, 8H, CH = C), 7.44 (s, 8H, Ar-H), 4.88 (16H, NCH2C), 4.68 (m, 16H, OCH2C), 3.92 (d, 16H, OCH2), 3.76-3.13 (m, 96H, OCH2CH2), 2.78 (s, 16H, SCH2). 13C NMR (100 MHz, D2O) δ: 172.76 (C]O), 157.16, 143.71, 143.50, 135.20, 3
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1748 (C]O), 1565, 1460, 1212, 1092. MS MALDI-TOF m/z: 878.889 [M]+, 917.411 [M + K]+. Anal. calcd. for C38H54N8S2O12: C, 51.92; H, 6.19; N, 12.75. Found: C, 52.23; H, 5.86; N, 12.42.
lower yield than the first pathway by a base-catalyzed nucleophilic aromatic substitution of compound 7 with 3,6-bis(4’-methyl phenylsulfoxyloxy) phthalonitrile (8) [21] based on the high nucleophilic property of –SH moieties in dry DMSO in the presence of K2CO3 with moderate yield of 34.14 %. The precursor compound 7 was synthesized as reported in the literature with a slightly different strategy [20]. The hydrolysis reaction of this compound was performed in methanol medium with trace amount of H2SO4/H2O (1/1), at reflux temperature for 10 h. Conversion was achieved in high yields (86.96 %). The disapearance of chemical shifts belonging to acetate protons at δ = 2.31 ppm in 1H NMR and carbonyl carbon resonance of 13C NMR spectrum at δ =196.21 ppm, together with the appearance of a signal at δ =1.54 ppm related –SH group also confirmed the formation of compound 7. Cu-catalyzed Huisgen 1,3-dipolar cycloaddition reaction [22] between compound 10 and 2-azido ethyl acetate (11) in an aqueous solution of copper(II) acetate monohydrate and sodium-L-ascorbate at room temperature was carried out to obtain compound 12. Compound 12 was isolated and then purified by using column chromatography with high yield (71.87 %). 1H NMR spectrum of 12 confirmed the formation of the dinitrile derivative with the presence of characteristic triazole resonance at δ =7.70 ppm. The peak at δ =166.28 ppm in 13C NMR spectrum can be attributed to the C]O group of ethyl carboxylate. The formation of the desired compound was also confirmed by the molecular ion peak at m/z = 878.050 [M]+. Peripheral analogue (15) was synthesized in two different routes, as shown in Scheme 2. One of these routes is based on the thiol intermediate that contains alkyl linked polyethylene glycol moieties (7) and 4,5-dichloro phthalonitrile (13) through a large excess base (K2CO3) which promoted condensation reaction in 62.03 % yield. The structure of the novel compound was confirmed by NMR and MALDI-TOF mass spectrometry data. 1H NMR spectrum of 15 indicates the presence of novel resonances for the alkyne and polyether protons at δ = 2.42 and 3.79-3.64 ppm, respectively, and the disappearance of the –SH resonances, which support the formation of the expected peripheral substituted dicyano derivative. On the 13C NMR spectrum of this compound, characteristic resonances corresponding to the alkyne and nitrile carbon atoms at δ = 79.65 and 115.50 ppm, respectively. Compound 15 displayed the expected molecular ion peaks at m/z = 638.01 [M+H2O]+, 642.98 [M + Na-H]− and 643.89 [M + Na]+. The synthesis of compound 15 in the presence of compound 14 and 9 was an alternative procedure employed with success to synthesize the target compound. The yield of the condensation reaction between compound 14 [23] and 9 in dry acetone in the presence of excess amount of K2CO3 was more convenient than the other route. The NMR, FT-IR, MS spectra and elemental analysis data of this compound were in accordance with previously synthesized compound. The Huisgen 1,3-dipolar cycloaddition reaction was performed between 2-azido ethyl acetate (11) and alkyne substituted phthalonitrile compound (15) in a tert-butanol/THF/water mixture under argon atmosphere at room temperature. This reaction was catalyzed by Cu(I), which was produced by copper(II) acetate monohydrate and sodium-Lascorbate. At the end of the reaction, compound 16 was obtained with a lower yield (54.24 %) than non-peripheral analogue. 1H NMR, 13C NMR, FT-IR and MALDI-TOF MS were used to verify the proposed structure. Absence of the characteristic resonance of alkyne groups from at δ = 2.42 ppm and presence of triazole proton resonances at δ =7.71 ppm from 1H NMR spectrum of 16 confirmed the formation triazole rings. 13C NMR of compound 16 showed different chemical shifts of carbon resonances due to the formation of triazole and ester groups as expected. The novel carbon resonances at δ = 145.52, 124.10 and 166.31 ppm, respectively, could be attributed to the proposed structure. The absence of alkyne, azide and presence of triazole aromatic CeH and C]O vibrations in FT-IR spectrum of compound 16 at 3140 and 1748 cm−1, respectively, also supported the proposed structure (Scheme 2). The MALDI-TOF spectral data for this compound
2.3.10. ZnPc-II 4,5-Disubstituted phthalonitrile (16) (0.40 g, 0.46 mmol) and zinc acetate dihydrate (0.10 g, 0.46 mmol) in dimethylethanolamine (2.5 mL) were stirred at 155 °C in a Schlenk apparatus under argon atmosphere for 20 h. After cooling to room temperature, the reaction mixture was evaporated to dryness under vacuum and the reaction mixture was stirred with chloroform. The product was filtered off and dried under vacuo. Dark green solid, yield: 0.055 g (14.26 %), mp > 300 °C. 1 H NMR (400 MHz, D2O) δ: 7.86 (s, 8H, CH]C), 7.43-7.36 (s, 8H, ArH), 4.90 (s, 16H, NCH2C), 4.68 (m, 16H, OCH2C), 3.92 (d, 16H, OCH2), 3.68-3.37 (m, 96H, OCH2CH2O), 3.14 (m, 16H, SCH2). 13C NMR (100 MHz, D2O) δ: 173.06 (C]O), 155.14, 143.72, 136.10, 127.24, 126.02, 115.17, 69.55-67.36, 55.54, 53.78, 53.06, 32.22-31.90. FT-IR (ATR, cm−1): 3346, 3142, 3093-3037, 2904-2866, 1621, 1463, 1378, 1292. UV–vis (H2O): λmax (log ε): 701 (4.88), 664 (4.99), 359 (5.04). MS MALDI-TOF m/z: 3369.38 [M+H2O-2 H]-2. Anal. calcd. for C136H184N32S8O48Zn: C, 48.66; H, 5.52; N, 13.35. Found: C, 48.98; H, 5.85; N, 13.08. 3. Results and discussions Schemes 1 and 2 describe the synthetic routes used to prepare octasubstituted non-peripheral and peripheral zinc(II) phthalocyanines. Different synthetic pathways were attempted for the synthesis of precursor compounds and metallo-phthalocyanines. The precursor compound 5 was synthesized through multistep reaction sequence (Scheme 1). The starting compound O,O'-(2,3-dicyano-1,4-phenylene) bis[dimethyl(thiocarbamate)] (3) [9] was prepared from 2,3-dicyano hydroquinone (1) and dimethylthiocarbamoyl chloride (2) in the presence of strong tertiary amine base such as DABCO (1,4-Diazabicyclo[2.2.2] octane) in high yield (83.83 %). This compound was converted to dimethyl carbamate moiety (4) [18] in high yield (79.34 %) by thermal rearrangement reaction at 205 °C. The hydrolysis reaction of S-aryl dimethylthiocarbamate with some reagents such as 10 % aqueous NaOH, methanolic KOH or LiAlH4 [19] in H2O or MeOH media is well-known. In this study, 3,6-dimercaptophthalonitrile is a crucial intermediate that was obtained by a hydrolysis reaction of S,S'-(2,3-dicyano-1,4-phenylene) bis[dimethyl (thiocarbamate)] in THF and dry methanolic KOH solution at room temperature with moderate yield of 71.32 %. As expected, the significant diversity of the FT-IR and 13C NMR spectra of intermediates 3 and 4 is very high, due to the exchange of C]S and C]O groups, whereas their respective 1H NMR spectra are very similar. The 1H NMR and FT-IR spectra of 5 showed characteristic resonances for –SH protons and –SH stretching vibrations at δ = 2.80 ppm and 2556 cm−1, respectively. The disappearance of characteristic resonances belonging to C]S and eCH3 moieties in the 1H and 13C NMR spectra indicate that the hydrolysis reaction was completed. As outlined in Scheme 1, the synthesis of compound 10 was achieved by using two different routes. In the first pathway, 3,6-dimercaptophthalonitrile (5) was reacted with compound 9 [20] in dry acetone containing excessive amount of dry K2CO3 atmosphere at room temperature for overnight with moderate yield of 41.95 %. In the 1H NMR spectrum of 10, expected peaks corresponding to SCH2, OCH2C, OCH2CH2O-, HC^C and aromatic protons gave significant resonances at δ = 3.22, 4.17, 3.73-3.60, 2.42 and 7.65 ppm, respectively. In the 13 C NMR spectrum of this compound, characteristic signals were observed at δ = 79.63, 74.59, 33.65 and 113.84 ppm, attributed to ^CeH, C^C, SCH2 and C^N moieties. These results are in accordance with starting compounds (5, 9). In addition, ESI mass spectra of this compound at m/z = 638.2 [M+H2O]+ also support the proposed formula. In the second route, compound 10 was synthesized with a 4
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Scheme 1. Synthesis of ZnPc-I.
m/z = 878.889 [M]+ also strongly supported the proposed structure. The targeted phthalocyanines ZnPc-I and ZnPc-II were prepared as shown in Schemes 1 and 2. Heating the phthalonitriles (12, 16) in appropriate solvents such as n-pentanol, DMF with anhydrous Zn(II) acetate and catalytic amounts of DBU leads to the phthalocyanines and
then subsequent hydrolysis of the ester groups in NaOH/MeOH [24], LiOH/MeOH-H2O [25], HCl/H20 [26]. As an alternative and a very convenient synthetic procedure for ZnPc-I and ZnPc-II, we performed the target compound formation of Zn(II) phthalocyanines and hydrolysis of ester groups under the same reaction conditions [27]. 5
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Scheme 2. Synthesis of ZnPc-II.
Cyclotetramerization reaction was carried out by using related phthalonitriles (12, 16) in dimethylethanolamine in the presence of Zn (CH3COO)2.2H2O at 155 °C. Zn(CH3COO)2.2H2O was chosen as metallo cyclotetramerization process instead of anhydro species to convert simultaneously zinc(II) phthalocyanines and the ester function into the corresponding octacarboxylic acid forms as in situ. In this reaction condition, phthalocyanine formation and hydrolysis of all ester groups were performed in yields of 20.05 % (ZnPc-I) and 14.26 % (ZnPc-II). Phthalocyanines proved to be extraordinary soluble in water due to their eight carboxylic acid groups and the triazole rings which considerably reduce their aggregation tendency and increase their water solubility. The 1H NMR spectra of zinc(II) phthalocyanines were recorded in deuterium oxide. All expected peaks corresponding to the substituents were observed in their respective region and were almost identical with those of the precursor dinitrile compounds (12, 16). The significant difference between 12, 16 and related zinc phthalocyanines are the disappearance of the ethyl protons belonging to the esters moieties. The carboxylic acid protons resonances could not be observed due to its easy exchangeability with deuterium oxide solvent and fast exchangeability during NMR [28]. The disappearance of C^N and appearance of C]N resonances at δ = 157.16 and 155.14 ppm in the 13 C NMR spectra of ZnPc-I and ZnPc-II, respectively, indicate the tetracyclomerization reaction of related dicyano compounds. The sharp
peaks in the FT-IR spectra for the C^N stretching vibrations at the region of 2224−2229 cm−1 disappeared after the formation of zinc phthalocyanines, are also indication of their formation. The MALDITOF mass spectra of peripheral and non-peripheral metallo-phthalocyanines confirmed the proposed structures because of the peaks at m/z = 3307.708 [M−CO2H-H]-, 3366.606 [M-2(NC2O2H3)+Matrix]+, 3429.632 [M+3H2O-H]-, 3460.820 [M+6H2O-H]- and 3369.38 [M +H2O-2 H]-2 related to ZnPc-I and ZnPc-II, respectively. The zinc(II) phthalocyanines were found to be soluble in both water and DMSO, but insoluble in other common organic solvents. The UV–vis spectra of ZnPc-I in water and DMSO is shown in Fig. 1. ZnPc-I and ZnPc-II were dissolved in water at room temperature as infinite. Non-peripheral and peripheral phthalocyanines showed characteristic absorptions in the Q band derived from HOMO-LUMO transition at λ = 776, 701 nm in water and λ = 773, 708 in DMSO, respectively. The single narrow absorptions the Q band region ZnPc-I in aqueous medium should be related to the π→ π* transition of the Pc core. These absorptions also indicate the monomeric and non-aggregated behavior of ZnPc-I species due to its D4h symmetry [29]. The broad Q band of ZnPc-II in aqueous medium is typical of aggregated species because of strong π → π stacking between the planar phthalocyanine cores and hydrogen bonding with carboxyl groups [27,30]. On the contrary, the sharp absorption peak is observed in the 6
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Fig. 1. UV–vis spectra of a) ZnPc-I and b) ZnPc-II (4 × 10−5 M in DMSO and H2O at room temperature).
UV–vis spectrum of ZnPc-II (Fig. 1) in DMSO, probably related to the monomeric and reduced non-aggregated species [7,31]. Peripheral substituted phthalocyanine showed, as expected, blue-shifted Q band absorption in the same solvents. It is well known that the position of substituents are crucial factor in shifting the Q band absorptions to blue or red region. This shift to higher energy region could be attributed to H-type aggregates [32,33].The substituents at β and α positions of the Pc skeleton indicate the high degree of aggregation in water by reducing their aggregation tendency in DMSO media. The Q band absorption of non-peripheral substituted phthalocyanine is significantly redshifted relative to peripheral substituted phthalocyanine because of the attachment of the electron-donating sulfur-linked polyether groups at the α position [34]. The B band region of ZnPc-I is fairly different according to ZnPc-II analogue. It is well known that absorbance in range of 200−350 nm contains four absorption bands, namely, N, L, C and B. The B band region is normally the most intense and is observed as a broad absorption [35]. This band region is not clear, although there is a trend that substitution at non-peripheral positions broadens the band [36]. The broadening of the B, N, L and C bands has been attributed to the presence of underlying n→π* transitions from inner nitrogens, and because of the closeness of the energies of these absorptions considerable configurational interaction is expected [37]. The broadening in the UV region of the spectra of phthalocyanine makes identification of the individual transitions from absorption spectra alone very difficult. In order to assess their potential as PDT photosensitizers, the singlet oxygen generation quantum yields (ΦΔ) of ZnPc-I and ZnPc-II were determined in both water and DMSO. The results of can be related to the position of substituents on the phthalocyanine skeleton. The singlet oxygen quantum yields (ΦΔ) of ZnPc-I and ZnPc-II were determined as 0.34 and 0.11 in water and 0.60 and 0.36 in DMSO media, respectively. It is known that the aggregation of the phthalocyanines reduce their photocatalytic activities such as PDT. It is well documented that some solvents such as DMSO and DMF efficiency reduce the aggregation of phthalocyanines [38]. The singlet oxygen results of this study are also a good example for this phenomenon. The singlet oxygen quantum yield value of the ZnPc-I (0.34) is higher than the value of ZnPc-II (0.11)
Table 1 Singlet oxygen quantum yields of ZnPc-II and ZnPc-I in DMSO and water. Compound
Solvent
ΦΔ
ZnPc-II
DMSO Water DMSO Water DMSO Water
0.36 0.11 0.60 0.34 0.67 0.45
ZnPc-I ZnPc ZnPcSmix
(Table 1). Indeed, while the ZnPc-II showed aggregation in water, the ZnPc-I did not show any aggregation in this media. For this reason, the singlet oxygen generation of the ZnPc-I is higher than ZnPc-II as we expected. The aggregation in phthalocyanines also decreased the photosensitizers properties due to non-radiative energy relaxation therefore decreasing their photosensitizing efficiency [39]. The singlet generation of the synthesized zinc(II) phthalocyanines were found to be lower than those of the ZnPcSmix. But only singlet oxygen generation ability of a photosensitizer is not enough for determination of its PDT activity. Especially absorption wavelength is also important for this purpose. The absorption wavelength values of the synthesized phthalocyanines are higher than ZnPcSmix. The absorption energy of each of these ZnPcs is lower than ZnPcSmix and it means these Pcs are less harmful for healthy cells. On the other hand, the cell uptake behavior of the photosensitizers is also very important. The cell uptake study on these phthalocyanines will be evaluated in further studies and these Pcs can show better cell uptake than ZnPcSmix. 4. Conclusions In this study, symmetrically octa carboxylic acid substituted peripheral and non-peripheral zinc(II) phthalocyanines bridged with triazole attached to tetraethylene glycol linkers have been prepared as potential photosensitizers for PDT. The synthetic procedure which employs peripheral and non-peripheral alkyl sulfur donors can be used to synthesize various reactions of substitution and addition. The 7
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reaction sequence implied the preparation of 3,6-dimercapto phthalonitrile, a very important novel reactant. The infinite solubility of phthalocyanines in aqueous media is due to the triazole-linked octa carboxylic groups. Higher aggregation of ZnPc-II in aqueous media than ZnPc-I phthalocyanine could be attributed to the positions of substituents (α, β). Strong aggregation capabilities of synthesized phthalocyanines decreased their singlet oxygen quantum yield in aqueous media. However, the higher ΦΔ values in DMSO than aqueous media exhibit that Zn(II) phthalocyanines can be used as photodynamic therapy photosensitizers.
[12] [13] [14] [15] [16] [17] [18]
Acknowledgements
[19] [20]
This study was supported by TÜBİTAK. Y. Baygu acknowledges The Scientific and Technological Research council of Turkey, AnkaraTurkey for financial support in Project (Project No: 114Z441).
[21] [22] [23]
Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.synthmet.2019. 116256.
[24] [25]
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Synthesis and characterization of new partially-aggregated water-soluble polyether-triazole linked zinc(II) phthalocyanines as photosensitizers for PDT studies
T
Yasemin Baygua, Yaşar Gökb,* a b
Tavas Vocational High School, Pamukkale University, Denizli, Turkey Department of Chemical Engineering, Uşak University, Uşak, Turkey
ARTICLE INFO
ABSTRACT
Keywords: Zinc phthalocyanine Partially-aggregation Click reaction PDT Red shift Ester hydrolysis
Peripheral and non-peripheral octa-carboxylated water-soluble zinc(II) phthalocyanines with clicked polyethylene glycol linkers have been prepared. Different multistep reaction pathways have been attempted and compared for the preparation of the phthalonitrile precursors. Novel compounds have been characterized by combination of elemental analysis, 1H and 13C NMR, FT-IR, U–vis and MS spectral data. Both phthalocyanines were proved to be water soluble. Their singlet oxygen generation was determined in both water and DMSO to assess their potential of photosensitizers for photodynamic therapy.
1. Introduction
in water and limit their aggregation. Generally, high solubility and high tendency of aggregation properties of phthalocyanines in water limit their singlet oxygen generation yields and thus significantly restrict their photodynamic therapy potential [7]. Carboxylic acids with triazole groups attached to metallo-phthalocyanines through polyethylene glycol linkers could confer solubility in aqueous media and at the same time overcome aggregation problems water [8]. We report herein the synthesis and characterization of water and DMSO soluble zinc(II) phthalocyanines with octa-substituted carboxylic acid groups attached to the polyether linked triazole moieties. These novel compounds exhibit the characteristic partially-aggregated behavior by UV–vis spectra in aqueous media. Their photochemical properties, especially their singlet oxygen quantum yield, were investigated for PDT applications.
Phthalocyanines and related compounds are one of the largest groups of tetrapyrrolic macrocycles and widely investigated in many areas such as electrochromic and photochromic substances, photosensitizers for dye-sensitized solar cells, liquid crystals, LangmuirBlodgett films, chemical sensors, industrial catalytic systems and material chemistry, semiconductor devices, molecular metals, and photocopying devices [1,2]. In the past few decades, in addition to their traditional uses mentioned above, phthalocyanines strated to appear as ideal second generation photosensitizers for photodynamic therapy (PDT) [3], in particular due to their high singlet oxygen yield and other optical properties [4]. Nonetheless, the low solubility of unsubstituted phthalocyanines in aqueous media and common organic solvents is a strong drawback [5]. An intrinsic advantage of phthalocyanine as PDT photosensitizers is their intense absorption at near-infrared wavelengths (ca. 700 nm), ideal for various types of cancers as it allows to irradiate in the phototherapeutic window. Especially, water soluble phthalocyanines are most promising photosensitizers [6]. Ideally, PDT photosensitizers should exhibit high solubility in water, strong absorption in the 600−800 nm region (deep red) and high singlet oxygen quantum yields. Attachment of carboxylic acid groups attached through triazole moieties to Pcs is expected to significantly increase the solubility of Pcs
⁎
2. Experimental 2.1. General 1
H and 13C NMR spectra were recorded on Varian Mercury plus 300 MHz and on an Agilent-vnmrs 400 spectrometers. CDCl3, DMSO-d6 and D2O were used as the as NMR solvents. FT-IR spectra were recorded on Perkin-Elmer UATR Two spectrometer. The UV–vis absorption spectra were measured on a Shimadzu UV-1601 spectrophotometer which is double-beamed with thermostatically controlled cell block. All
Corresponding author. E-mail address: [email protected] (Y. Gök).
https://doi.org/10.1016/j.synthmet.2019.116256 Received 24 June 2019; Received in revised form 18 November 2019; Accepted 28 November 2019 0379-6779/ © 2019 Elsevier B.V. All rights reserved.
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measurements were made in 1 mL quartz cuvette. Mass spectra were recorded on a Micromass Quattro Ultima LC–MS/MS and on a Bruker Daltonics Microflex LT MALDI-TOF spectrometers. Elemental analyses were determined on a Costech ECS 4010 instrument. Melting points were determined on an electro thermal melting point apparatus in a sealed capillary and are uncorrected. All reactions were performed under an argon atmosphere using oven-dried glassware. All reagents and solvents were purchased from commercial suppliers and solvents were dried over standard drying agents and procedures prior to use [9]. 1-iodo-3,6,9,12-tetraoxa-pentadec-14-yne [2], S-(3,6,9,12-tetraoxapentadec-14-yn-1-yl) ethanethioate [10], 4,5-dimercaptophtholanitrile [11], 2-azido-etilacetate [12] and 3,6-bis(4’-methyphenyl sulfanyloxy) phtholanitrile [13] were prepared according to the reported procedures. Photo-irradiations were carried out using a General Electric quartz line lamp (300 W). A 600 nm glass cut off filter (Schott) and a water filter were used to filter off ultraviolet and infrared radiations respectively. An interference filter (Intor, 700 nm with a band width of 40 nm) was additionally placed in the light path before the sample. Light intensities were measured with a POWER MAX5100 (Molelectron detector incorporated) power meter.
using dichloromethane as eluent to give desired compound. Cream coloured solid, yield: 2.8 g (83.83 %), mp: 184−185 °C. 1H NMR (400 MHz, CDCl3) δ: 7.52 (s, 2H, Ar-H), 3.46 (s, 6H, CH3), 3.42 (s, 6H, CH3). 13 C NMR (100 MHz, CDCl3) δ: 184.75 (C]S), 153.48, 130.10, 111.72 (C^N), 111.42, 43.74, 39.27. FT-IR (ATR, cm−1): 3074, 3049, 29352879, 2237 (C^N), 1733, 1591, 1552, 1480, 1237, 1101. ESI MS m/z: 335.07 [M+H]+, 352.08 [M+H2O]+, 372.87 [M + K-H]-, 388.90 [M +3H2O]+, 435.94 [M+2 K + Na]+. Anal. calcd. for C14H14N4S2O2: C, 50.28; H, 4.22; N, 16.75. Found: C, 50.01; H, 4.50; N, 17.13. 2.3.2. S,S'-(2,3-dicyano-1,4-phenylene) bis[dimethyl(thiocarbamate)] (4) The precursor compound (3) (1.34 g, 4 mmol) was heated gently and stirred under argon atmosphere at 190° to give melted compound. The melted compound was further heated and stirred at 205 °C for 3 h, then cooled to room temperature. The crude green solid product was triturated with dichloromethane and filtered, washed with dichloromethane and then dried in vacuo. Green solid, yield: 1.06 g (79.34 %), mp: 221 °C. 1H NMR (400 MHz, CDCl3) δ: 7.86 (s, 2H, Ar-H), 3.13 (s, 6H, CH3), 3.05 (s, 6H, CH3). 13C NMR (100 MHz, CDCl3) δ: 162.48 (C]O), 140.18, 136.26, 123.39, 113.89 (C^N), 37.39, 37.09. FT-IR (ATR, cm−1): 3116, 3067, 2927-2888, 2239 (C^N), 1676, 1557, 1477, 1363, 1089. ESI MS m/z: 333.18 [M−H]-, 351.94 [M+H2O-H]-, 356.91 [M + Na-H]-, 389.04 [M+H2O+H]+, 436.01 [M+2 K + Na +H]+. Anal. calcd. for C14H14N4S2O2: C, 50.28; H, 4.22; N, 16.75. Found: C, 50.60; H, 4.57; N, 16.44.
2.2. Singlet oxygen quantum yields Singlet oxygen quantum yield (ΦΔ) determinations were performed in DMSO and in water, using the experimental setup described in literature [14]. Typically, a 3 mL portion of the zinc(II) phthalocyanine solutions (C = 4 × 10−5 M) containing the singlet oxygen quencher was irradiated in the Q band region with the photoirradiation set up [14]. ΦΔ values were determined in air using the relative method and using unsubstituted ZnPc (in DMSO) and ZnPcSmix (in aqueous media) as standards. 1,3-diphenylisobenzofuran (DPBF) and 9,10-antracenediyl-bis(methylene)dimalonoic acid (ADMA) was used as chemical quencher for singlet oxygen in DMSO and aqueous media, respectively. Eq. (1) was employed for the determination of ΦΔ values:
=
Std
R.IStd abs RStd.Iabs
2.3.3. 3,6-dimercaptophthalonitrile (5) A solution of KOH (1.47 g, 26.34 mmol) in dry methanol (36 mL) was added and stirred to a solution of compound (4) (2.0 g, 5.98 mmol) in dry THF (180 mL) at room temperature overnight and monitored TLC [silica gel (chloroform:methanol)(95:5)]. The end of this period, the mixture was poured into cold water (300 mL) and acidified with conc. HCl to pH = 2.0. This reaction mixture was extracted with ethyl acetate (3 × 100 mL) and active carbon was added to the combined organic phase filtered off, washed with ethyl acetate and then dried over anhydrous MgSO4 overnight. The solution was evaporated to dryness under reduced pressure and solidified with diethyl ether. Pale brown solid, yield: 0.82 g (71.32). 1H NMR (DMSO-d6) δ: 7.66 (s, 2H, Ar-H), 2.80 (s, 2H, SH). FT-IR (ATR, cm−1): 3071, 2556 (S-H), 2223 (C^N), 1442, 1201, 1139. Anal. calcd. for C8H4N2S2: C, 49.98; H, 2.10; N, 14.57. Found: C, 49.63; H, 2.45; N, 15.05.
(1)
where is the singlet oxygen quantum yields for the standard ZnPc ( Std = 0.67 in DMSO) [15] and ZnPcSmix ( Std = 0.45 in aqueous media) [16], R and RStd are the DPBF (or ADMA) photo-bleaching rates in the presence of the respective samples (ZnPc-I and ZnPc-II) and standards, respectively. Iabs and IStd abs are the rates of light absorption by the samples (ZnPc-I and ZnPc-II) and standards, respectively. To avoid chain reactions induced by DPBF (or ADMA) in the presence of singlet oxygen [17], the concentration of quenchers (DPBF or ADMA) was lowered to ∼3 × 10−5 M. Solutions of sensitizer (absorbance = 1 at the irradiation wavelength) containing DPBF (or ADMA) were prepared in the dark and irradiated in the Q band region using the setup described above. DPBF degradation at 417 nm and ADMA degradation at 380 nm were monitored. The light intensity 6.21 × 1015 photons s-1 cm-2 was used for ΦΔ determinations. Std
2.3.4. 3,6,9,12-tetraoxapentadec-14-yne-1-thiol (7) A solution of H2SO4/H2O (4.2 mL) (1:1) was added to a solution of compound 6 (1.35 g, 4.65 mmol) in methanol (35 mL) under argon atmosphere and refluxed for 10 h. The reaction was monitored by TLC [silica gel (dichloromethane:methanol) (97:3)]. The mixture was then allowed to cool at room temperature and was poured into water (150 mL) and then extracted with dichloromethane (3 × 75 mL). Collected organic phases were washed with water (150 mL) and dried over anhydrous MgSO4 and then evaporated to dryness under vacuum. The resulting brown oil compound was purified by column chromatography using chloroform as eluent. Pale yellow oil, yield:1.0 g (86.96 %). 1H NMR (400 MHz, CDCl3) δ: 4.14 (s, 2H, HCCCH2O-), 3.65-3.53 (m, 14H, -OCH2CH2O-), 2.72-2.64 (m, 2H, -OCH2CH2SH), 2.40 (d, 1H, HCCCH2O-), 1.54 (t, 1H, -OCH2CH2SH). 13C NMR (100 MHz, CDCl3) δ: 78.65 (C^CH), 73.65 (^CH), 71.85-68.07 (eCH2CH2), 57.37 (CH2C^), 23.25 (CH2SH). FT-IR (ATR, cm−1): 3251 (^CH), 2866 (OCH2CH2O-), 2558 (eSH), 2113 (C^C), 1094.
2.3. Synthesis 2.3.1. O,O'-(2,3-dicyano-1,4-phenylene) bis[dimethyl(thiocarbamate)] (3) Dimethylthiocarbamoyl chloride (3.2 g, 26 mmol) was added to a solution of 2,3-dicyano hydroquinone (1) (1.6 g, 10 mmol) and DABCO (2) (5.78 g, 50 mmol) in dry DMF (20 mL) under argon atmosphere at room temperature. The reaction mixture was stirred at 75 °C for 2 h, then cooled to room temperature and poured into water (80 mL). The suspension was mixed with ethyl acetate (80 mL) and then water phase extracted with ethyl acetate. Combined organic phases were washed with brine (60 mL), dried over anhydrous MgSO4 and concentrated. The crude product was purified by a silica gel column chromatography
2.3.5. 3,6-bis((3,6,9,12-tetraoxapentadec-14-yn-1-yl)thio)phthalonitrile (10) 2.3.5.1. Method A. A solution of compound 8 (2.56 g, 5.48 mmol) and compound 7 (3.4 g, 13.7 mmol) in dry DMSO (60 mL) was stirred under argon atmosphere at room temperature for 15 min. and then dry K2CO3 (3.02 g, 21.94 mmol) was added to this mixture. The reaction mixture 2
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was stirred at the same condition for 3 days and monitored by TLC [silica gel (dichloromethane:methanol)(98:2)]. The end of this period, the reaction mixture was poured into water (400 mL) and extracted with dichloromethane (3 × 140 mL). Collected organic phases were washed with water (200 mL) and dried over anhydrous MgSO4 overnight and then evaporated to dryness under reduced pressure. The yellow oil crude product was purified by column chromatography [silica gel (dichloromethane: methanol)(98:2)] to give yellow oil product. Yield: 1.16 g (34.14 %). 1H NMR (400 MHz, CDCl3) δ: 7.65 (s, 2H, Ar-H), 4.17 (s, 4H, OCH2C), 3.73-3.60 (m, 28H, eOCH2CH2O), 3.22 (t, 4H, SCH2), 2.42 (s, 2H, ^CH). 13CNMR (100 MHz, CDCl3) δ: 141.10, 132.92, 117.18, 113.84 (C^N), 79.63 (C^CH), 74.59 (^CH), 70.55-69.09, 58.37, 33.65. FT-IR (ATR, cm−1): 3280-3250 (^CH), 3071, 2908-2865, 2224 (C^N), 2113 (C^C), 1441, 1092. ESI (+) MS m/z: 638.2 [M+H2O]+, 621.2 [M+H]+. Anal. calcd. for C30H40N2S2O8: C, 58.04; H, 6.49; N, 4.51. Found: C, 57.70; H, 6.20; N, 4.86.
125.80, 109.92, 70.81-67.31, 62.85, 58.68, 55.10, 42.63. FT-IR (ATR, cm−1): 3259, 3136, 2912-2864, 1701, 1620, 1558, 1462, 1368, 1283, 1085. UV–vis (H2O): λmax (log ε) : 776 (4.90), 687 (4.34), 321 (4.66). MS MALDI-TOF m/z: 3307.708 [M-CO2H-H]-, 3366.606 [M(C5H6N3O2)+Matrix]+, 3429.632 [M+3H2O + Na-H]-, 3460.820 [M +6H2O-H]-, 3517.58 [M + K-7H2O-H]-, 3615.283 [M+2MatrixCO2H-H]-. Anal. calcd. for C136H184N32S8O48Zn: C, 48.66; H, 5.52; N, 13.35. Found: C, 48.38; H, 5.85; N, 13.54. 2.3.8. 4,5-bis(3,6,9,12-tetraoxapentadec-14-yn-1-ylthio)phthalonitrile (15) 2.3.8.1. Method A. 4,5-Dichloro phthalonitrile (13) (0.45 g, 2.3 mmol) and compound 7 (1.25 g, 5.04 mmol) was dissolved and stirred with dry DMF (150 mL) containing excess amount of dry K2CO3 (1.11 g, 8.05 mmol) under argon atmosphere at 50 °C for overnight. The reaction process was checked by TLC [silica gel (chloroform:methanol)(99:1)]. After cooling to room temperature, the reaction mixture was filtered off and evaporated to dryness under reduced pressure. Purification of the crude product was carried out by column chromatography on silica gel using chloroform as eluent to give compound 15. Colourless solid, yield: 0.88 g (62.03 %), mp: 49−50 °C. 1H NMR (400 MHz, CDCl3) δ: 7.62 (s, 2H, Ar-H), 4.18 (s, 4H, OCH2C), 3.79-3.64 (m, 28H, OCH2CH2O), 3.23 (t, 4H, SCH2), 2.42 (s, 2H, ^CH). 13C NMR (100 MHz, CDCl3) δ: 143.95, 129.39, 115.50, 111.47, 79.65 (C^CH), 74.52 (^CH), 70.75-70.59, 69.10, 58.38, 32.72. FT-IR (ATR, cm−1): 3266, 3223, 3072, 2907-2868, 2231 (C^N), 2106 (C^C), 1565, 1462, 1348, 1094. MS MALDI-TOF m/z: 638.01 [M+H2O]+, 642.98 [M + Na-H]-, 643.89 [M + Na]+, 658.88 [M + K-H]-. Anal. calcd. for C30H40 N2S2O8: C, 58.04; H, 6.49; N, 4.51. Found: C, 57.78; H, 6.20; N, 4.88.
2.3.5.2. Method B. 3.6-Dimercaptophthalonitrile (5) (0.76 g, 4 mmol) was dissolved in dry acetone (120 mL) in the presence of dry K2CO3 (1.64 g, 12 mmol) under argon atmosphere at room temperature for 35 min. A solution of compound 9 (3.0 g, 8.8 mmol) in dry acetone (20 mL) was added and stirred at room temperature overnight. The reaction was monitored by thin layer chromatography [silica gel (dichloromethane:methanol)(96:4)]. At the end of this period, the reaction mixture was evaporated to dryness under reduced pressure and then mixed with chloroform:water mixture [(400 mL)(1:1)]. Organic phase was collected, dried over anhydrous MgSO4 overnight and then purified by column chromatography (silica gel) using dichloromethane as eluent. Pale yellow oil, yield: 1.04 g (41.95 %).
2.3.8.2. Method B. 4.5-Dimercapto phthalonitrile (14) (0.44 g, 2.28 mmol) was dissolved and stirred with dry acetone (60 mL) containing excess amount of dry K2CO3 (0.94 g, 6.84 mmol) under argon atmosphere at room temperature for 35 min. At the end of this period, a solution of compound 9 (1.70 g, 5 mmol) in dry acetone (10 mL) was added above solution and stirred at room temperature for overnight. The reaction was monitored by TLC [silica gel (chloroform:methanol)(97:3)]. The reaction mixture was filtered off, washed with chloroform and evaporated to dryness under reduced pressure. Purification of the crude product was carried out by column chromatography on silica gel using chloroform/methanol (97:3) as eluent to afford compound 15. Colorless solid, yield: 0.66 g (46.69 %), mp: 48−50 °C
2.3.6. Diethyl 2,2'-[(2,3-dicyano-1,4-phenylene)bis(thio-2,5,8,11-tetraoxatridecane-13,1-diyl-1H-1,2,3-triazole-4,1-diyl)]diacetate (12) A orange suspension of sodium-L-ascorbate (0.30 g, 1.5 mmol) and copper(II) acetate monohydrate (0.144 g, 0.72 mmol) in water (14 mL) was added to a solution of 10 (1.16 g, 1.87 mmol) and 2-azido ethyl acetate (11) (0.96 g, 7.48 mmol) in a mixture of tert-butanol (14 mL) and DMF (16 mL) under argon atmosphere at room temperature overnight, then poured into water (100 mL) and extracted with chloroform (3 × 40 mL). Collected organic extracts were washed with brine (60 mL) and dried over anhydrous MgSO4 and then purified by column chromatography [silica gel (dichloromethane:methanol) (95:5)] to give pale yellow oil, yield: 1.18 g (71.87 %). 1H NMR (400 MHz, CDCl3) δ: 7.70 (s, 2H, CH]C), 7.63 (s, 2H, Ar-H), 5.13 (s, 4H, NCH2C), 4.68 (d, 4H, OCH2C), 4.23 (m, 4H, OCH2CH3), 3.71-3.57 (m, 24H, -OCH2CH2O), 3.19 (t, 4H, OCH2), 2.84 (m, 4H, SCH2), 1.27 (t, 6H, CH3). 13C NMR (100 MHz, CDCl3) δ: 166.28 (C]O), 145.47, 141.07, 132.94, 124.11, 117.05, 113.89 (C^N), 70.56-69.53, 64.50, 62.35, 50.80, 38.37, 33.62, 14.05. FT-IR (ATR, cm−1): 3142, 3079, 2972-2867, 2224 (C^N), 1749 (C]O), 1443, 1211, 1093. ESI MS m/z: 878.050 [M]+. Anal. calcd. for C38H54N8S2O12: C, 51.92; H, 6.19; N, 12.75. Found: C, 52.29; H, 5.91; N, 13.08.
2.3.9. Diethyl 2,2'-[(4,5-dicyano-1,2-phenylene)bis(thio-2,5,8,11-tetraoxatridecane-13,1-diyl-1H-1,2,3-triazole-4,1-diyl)]diacetate (16) A suspension of copper(II) acetate monohydrate (0.147 g, 0.73 mmol) and sodium-L-ascorbate (0.3 g, 1.51 mmol) in water (15 mL) was added to a solution of compound 15 (1.17 g, 1.89 mmol) and 2-azido acetate (11) (0.99 g, 7.56 mmol) in a mixture of tert-butanol and THF (30 mL)(1:1) under argon atmosphere at room temperature for 2 days. Reaction was monitored by using TLC [silica gel (chloroform:methanol) (95:5)]. The reaction mixture was poured into water (60 mL) and extracted with chloroform (3 × 45 mL), washed with brine solution (60 mL) and then dried over anhydrous MgSO4 overnight. The solution was filtered off, washed with chloroform and evaporated to dryness under reduced pressure. Yellow oil crude product was purified by column chromatography on silica gel using as eluent a mixture of chloroform/ methanol (gradient 100:0 →98:2) to yield compound 16 as a colorless oil. Yield: 0.9 g (54.24 %). 1H NMR (400 MHz, CDCl3) δ: 7.71 (s, 2H, triazole), 7.62 (s, 2H, Ar-H), 5.14 (s, 4H, NCH2C), 4.68 (s, 4H, OCH2C), 4.24 (m, 4H, OCH2-CH3), 3.76 (m, 24H, OCH2CH2), 3.62 (m, 4H, CH2CH2-O), 3.22 (t, 4H, SCH2), 1.28 (t, 6H, CH3). 13C NMR (100 MHz, CDCl3) δ: 166.31 (C]O), 145.52, 143.95, 129.38, 124.10, 115.58, 111.35 (C^N), 70.61-70.48, 69.67-69.32, 64.53, 62.36, 50.82, 32.67, 14.06. FT-IR (ATR, cm−1): 3140, 3099, 3060, 2982-2867, 2229 (C^N),
2.3.7. ZnPc-I In a Schlenk system, 3,6-disubstitue phthalonitrile (12) (0.40 g, 0.46 mmol) and zinc acetate dihydrate (0.10 g, 0.46 mmol) in dimethyl ethanolamine (2.5 mL) was heated and stirred at 155 °C, under argon atmosphere for 20 h. After cooling to room temperature, the reaction mixture was evaporated to dryness under vacuum and the reaction mixture was poured into methanol (20 mL) and then centrifuged to give desired product. The solid product was filtered off, washed with methanol and then dried under vacuo. Brown solid, yield: 0.077 g (20.05 %), mp > 300 °C. 1H NMR (400 MHz, D2O δ: 7.81 (s, 8H, CH = C), 7.44 (s, 8H, Ar-H), 4.88 (16H, NCH2C), 4.68 (m, 16H, OCH2C), 3.92 (d, 16H, OCH2), 3.76-3.13 (m, 96H, OCH2CH2), 2.78 (s, 16H, SCH2). 13C NMR (100 MHz, D2O) δ: 172.76 (C]O), 157.16, 143.71, 143.50, 135.20, 3
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1748 (C]O), 1565, 1460, 1212, 1092. MS MALDI-TOF m/z: 878.889 [M]+, 917.411 [M + K]+. Anal. calcd. for C38H54N8S2O12: C, 51.92; H, 6.19; N, 12.75. Found: C, 52.23; H, 5.86; N, 12.42.
lower yield than the first pathway by a base-catalyzed nucleophilic aromatic substitution of compound 7 with 3,6-bis(4’-methyl phenylsulfoxyloxy) phthalonitrile (8) [21] based on the high nucleophilic property of –SH moieties in dry DMSO in the presence of K2CO3 with moderate yield of 34.14 %. The precursor compound 7 was synthesized as reported in the literature with a slightly different strategy [20]. The hydrolysis reaction of this compound was performed in methanol medium with trace amount of H2SO4/H2O (1/1), at reflux temperature for 10 h. Conversion was achieved in high yields (86.96 %). The disapearance of chemical shifts belonging to acetate protons at δ = 2.31 ppm in 1H NMR and carbonyl carbon resonance of 13C NMR spectrum at δ =196.21 ppm, together with the appearance of a signal at δ =1.54 ppm related –SH group also confirmed the formation of compound 7. Cu-catalyzed Huisgen 1,3-dipolar cycloaddition reaction [22] between compound 10 and 2-azido ethyl acetate (11) in an aqueous solution of copper(II) acetate monohydrate and sodium-L-ascorbate at room temperature was carried out to obtain compound 12. Compound 12 was isolated and then purified by using column chromatography with high yield (71.87 %). 1H NMR spectrum of 12 confirmed the formation of the dinitrile derivative with the presence of characteristic triazole resonance at δ =7.70 ppm. The peak at δ =166.28 ppm in 13C NMR spectrum can be attributed to the C]O group of ethyl carboxylate. The formation of the desired compound was also confirmed by the molecular ion peak at m/z = 878.050 [M]+. Peripheral analogue (15) was synthesized in two different routes, as shown in Scheme 2. One of these routes is based on the thiol intermediate that contains alkyl linked polyethylene glycol moieties (7) and 4,5-dichloro phthalonitrile (13) through a large excess base (K2CO3) which promoted condensation reaction in 62.03 % yield. The structure of the novel compound was confirmed by NMR and MALDI-TOF mass spectrometry data. 1H NMR spectrum of 15 indicates the presence of novel resonances for the alkyne and polyether protons at δ = 2.42 and 3.79-3.64 ppm, respectively, and the disappearance of the –SH resonances, which support the formation of the expected peripheral substituted dicyano derivative. On the 13C NMR spectrum of this compound, characteristic resonances corresponding to the alkyne and nitrile carbon atoms at δ = 79.65 and 115.50 ppm, respectively. Compound 15 displayed the expected molecular ion peaks at m/z = 638.01 [M+H2O]+, 642.98 [M + Na-H]− and 643.89 [M + Na]+. The synthesis of compound 15 in the presence of compound 14 and 9 was an alternative procedure employed with success to synthesize the target compound. The yield of the condensation reaction between compound 14 [23] and 9 in dry acetone in the presence of excess amount of K2CO3 was more convenient than the other route. The NMR, FT-IR, MS spectra and elemental analysis data of this compound were in accordance with previously synthesized compound. The Huisgen 1,3-dipolar cycloaddition reaction was performed between 2-azido ethyl acetate (11) and alkyne substituted phthalonitrile compound (15) in a tert-butanol/THF/water mixture under argon atmosphere at room temperature. This reaction was catalyzed by Cu(I), which was produced by copper(II) acetate monohydrate and sodium-Lascorbate. At the end of the reaction, compound 16 was obtained with a lower yield (54.24 %) than non-peripheral analogue. 1H NMR, 13C NMR, FT-IR and MALDI-TOF MS were used to verify the proposed structure. Absence of the characteristic resonance of alkyne groups from at δ = 2.42 ppm and presence of triazole proton resonances at δ =7.71 ppm from 1H NMR spectrum of 16 confirmed the formation triazole rings. 13C NMR of compound 16 showed different chemical shifts of carbon resonances due to the formation of triazole and ester groups as expected. The novel carbon resonances at δ = 145.52, 124.10 and 166.31 ppm, respectively, could be attributed to the proposed structure. The absence of alkyne, azide and presence of triazole aromatic CeH and C]O vibrations in FT-IR spectrum of compound 16 at 3140 and 1748 cm−1, respectively, also supported the proposed structure (Scheme 2). The MALDI-TOF spectral data for this compound
2.3.10. ZnPc-II 4,5-Disubstituted phthalonitrile (16) (0.40 g, 0.46 mmol) and zinc acetate dihydrate (0.10 g, 0.46 mmol) in dimethylethanolamine (2.5 mL) were stirred at 155 °C in a Schlenk apparatus under argon atmosphere for 20 h. After cooling to room temperature, the reaction mixture was evaporated to dryness under vacuum and the reaction mixture was stirred with chloroform. The product was filtered off and dried under vacuo. Dark green solid, yield: 0.055 g (14.26 %), mp > 300 °C. 1 H NMR (400 MHz, D2O) δ: 7.86 (s, 8H, CH]C), 7.43-7.36 (s, 8H, ArH), 4.90 (s, 16H, NCH2C), 4.68 (m, 16H, OCH2C), 3.92 (d, 16H, OCH2), 3.68-3.37 (m, 96H, OCH2CH2O), 3.14 (m, 16H, SCH2). 13C NMR (100 MHz, D2O) δ: 173.06 (C]O), 155.14, 143.72, 136.10, 127.24, 126.02, 115.17, 69.55-67.36, 55.54, 53.78, 53.06, 32.22-31.90. FT-IR (ATR, cm−1): 3346, 3142, 3093-3037, 2904-2866, 1621, 1463, 1378, 1292. UV–vis (H2O): λmax (log ε): 701 (4.88), 664 (4.99), 359 (5.04). MS MALDI-TOF m/z: 3369.38 [M+H2O-2 H]-2. Anal. calcd. for C136H184N32S8O48Zn: C, 48.66; H, 5.52; N, 13.35. Found: C, 48.98; H, 5.85; N, 13.08. 3. Results and discussions Schemes 1 and 2 describe the synthetic routes used to prepare octasubstituted non-peripheral and peripheral zinc(II) phthalocyanines. Different synthetic pathways were attempted for the synthesis of precursor compounds and metallo-phthalocyanines. The precursor compound 5 was synthesized through multistep reaction sequence (Scheme 1). The starting compound O,O'-(2,3-dicyano-1,4-phenylene) bis[dimethyl(thiocarbamate)] (3) [9] was prepared from 2,3-dicyano hydroquinone (1) and dimethylthiocarbamoyl chloride (2) in the presence of strong tertiary amine base such as DABCO (1,4-Diazabicyclo[2.2.2] octane) in high yield (83.83 %). This compound was converted to dimethyl carbamate moiety (4) [18] in high yield (79.34 %) by thermal rearrangement reaction at 205 °C. The hydrolysis reaction of S-aryl dimethylthiocarbamate with some reagents such as 10 % aqueous NaOH, methanolic KOH or LiAlH4 [19] in H2O or MeOH media is well-known. In this study, 3,6-dimercaptophthalonitrile is a crucial intermediate that was obtained by a hydrolysis reaction of S,S'-(2,3-dicyano-1,4-phenylene) bis[dimethyl (thiocarbamate)] in THF and dry methanolic KOH solution at room temperature with moderate yield of 71.32 %. As expected, the significant diversity of the FT-IR and 13C NMR spectra of intermediates 3 and 4 is very high, due to the exchange of C]S and C]O groups, whereas their respective 1H NMR spectra are very similar. The 1H NMR and FT-IR spectra of 5 showed characteristic resonances for –SH protons and –SH stretching vibrations at δ = 2.80 ppm and 2556 cm−1, respectively. The disappearance of characteristic resonances belonging to C]S and eCH3 moieties in the 1H and 13C NMR spectra indicate that the hydrolysis reaction was completed. As outlined in Scheme 1, the synthesis of compound 10 was achieved by using two different routes. In the first pathway, 3,6-dimercaptophthalonitrile (5) was reacted with compound 9 [20] in dry acetone containing excessive amount of dry K2CO3 atmosphere at room temperature for overnight with moderate yield of 41.95 %. In the 1H NMR spectrum of 10, expected peaks corresponding to SCH2, OCH2C, OCH2CH2O-, HC^C and aromatic protons gave significant resonances at δ = 3.22, 4.17, 3.73-3.60, 2.42 and 7.65 ppm, respectively. In the 13 C NMR spectrum of this compound, characteristic signals were observed at δ = 79.63, 74.59, 33.65 and 113.84 ppm, attributed to ^CeH, C^C, SCH2 and C^N moieties. These results are in accordance with starting compounds (5, 9). In addition, ESI mass spectra of this compound at m/z = 638.2 [M+H2O]+ also support the proposed formula. In the second route, compound 10 was synthesized with a 4
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Scheme 1. Synthesis of ZnPc-I.
m/z = 878.889 [M]+ also strongly supported the proposed structure. The targeted phthalocyanines ZnPc-I and ZnPc-II were prepared as shown in Schemes 1 and 2. Heating the phthalonitriles (12, 16) in appropriate solvents such as n-pentanol, DMF with anhydrous Zn(II) acetate and catalytic amounts of DBU leads to the phthalocyanines and
then subsequent hydrolysis of the ester groups in NaOH/MeOH [24], LiOH/MeOH-H2O [25], HCl/H20 [26]. As an alternative and a very convenient synthetic procedure for ZnPc-I and ZnPc-II, we performed the target compound formation of Zn(II) phthalocyanines and hydrolysis of ester groups under the same reaction conditions [27]. 5
Synthetic Metals 260 (2020) 116256
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Scheme 2. Synthesis of ZnPc-II.
Cyclotetramerization reaction was carried out by using related phthalonitriles (12, 16) in dimethylethanolamine in the presence of Zn (CH3COO)2.2H2O at 155 °C. Zn(CH3COO)2.2H2O was chosen as metallo cyclotetramerization process instead of anhydro species to convert simultaneously zinc(II) phthalocyanines and the ester function into the corresponding octacarboxylic acid forms as in situ. In this reaction condition, phthalocyanine formation and hydrolysis of all ester groups were performed in yields of 20.05 % (ZnPc-I) and 14.26 % (ZnPc-II). Phthalocyanines proved to be extraordinary soluble in water due to their eight carboxylic acid groups and the triazole rings which considerably reduce their aggregation tendency and increase their water solubility. The 1H NMR spectra of zinc(II) phthalocyanines were recorded in deuterium oxide. All expected peaks corresponding to the substituents were observed in their respective region and were almost identical with those of the precursor dinitrile compounds (12, 16). The significant difference between 12, 16 and related zinc phthalocyanines are the disappearance of the ethyl protons belonging to the esters moieties. The carboxylic acid protons resonances could not be observed due to its easy exchangeability with deuterium oxide solvent and fast exchangeability during NMR [28]. The disappearance of C^N and appearance of C]N resonances at δ = 157.16 and 155.14 ppm in the 13 C NMR spectra of ZnPc-I and ZnPc-II, respectively, indicate the tetracyclomerization reaction of related dicyano compounds. The sharp
peaks in the FT-IR spectra for the C^N stretching vibrations at the region of 2224−2229 cm−1 disappeared after the formation of zinc phthalocyanines, are also indication of their formation. The MALDITOF mass spectra of peripheral and non-peripheral metallo-phthalocyanines confirmed the proposed structures because of the peaks at m/z = 3307.708 [M−CO2H-H]-, 3366.606 [M-2(NC2O2H3)+Matrix]+, 3429.632 [M+3H2O-H]-, 3460.820 [M+6H2O-H]- and 3369.38 [M +H2O-2 H]-2 related to ZnPc-I and ZnPc-II, respectively. The zinc(II) phthalocyanines were found to be soluble in both water and DMSO, but insoluble in other common organic solvents. The UV–vis spectra of ZnPc-I in water and DMSO is shown in Fig. 1. ZnPc-I and ZnPc-II were dissolved in water at room temperature as infinite. Non-peripheral and peripheral phthalocyanines showed characteristic absorptions in the Q band derived from HOMO-LUMO transition at λ = 776, 701 nm in water and λ = 773, 708 in DMSO, respectively. The single narrow absorptions the Q band region ZnPc-I in aqueous medium should be related to the π→ π* transition of the Pc core. These absorptions also indicate the monomeric and non-aggregated behavior of ZnPc-I species due to its D4h symmetry [29]. The broad Q band of ZnPc-II in aqueous medium is typical of aggregated species because of strong π → π stacking between the planar phthalocyanine cores and hydrogen bonding with carboxyl groups [27,30]. On the contrary, the sharp absorption peak is observed in the 6
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Fig. 1. UV–vis spectra of a) ZnPc-I and b) ZnPc-II (4 × 10−5 M in DMSO and H2O at room temperature).
UV–vis spectrum of ZnPc-II (Fig. 1) in DMSO, probably related to the monomeric and reduced non-aggregated species [7,31]. Peripheral substituted phthalocyanine showed, as expected, blue-shifted Q band absorption in the same solvents. It is well known that the position of substituents are crucial factor in shifting the Q band absorptions to blue or red region. This shift to higher energy region could be attributed to H-type aggregates [32,33].The substituents at β and α positions of the Pc skeleton indicate the high degree of aggregation in water by reducing their aggregation tendency in DMSO media. The Q band absorption of non-peripheral substituted phthalocyanine is significantly redshifted relative to peripheral substituted phthalocyanine because of the attachment of the electron-donating sulfur-linked polyether groups at the α position [34]. The B band region of ZnPc-I is fairly different according to ZnPc-II analogue. It is well known that absorbance in range of 200−350 nm contains four absorption bands, namely, N, L, C and B. The B band region is normally the most intense and is observed as a broad absorption [35]. This band region is not clear, although there is a trend that substitution at non-peripheral positions broadens the band [36]. The broadening of the B, N, L and C bands has been attributed to the presence of underlying n→π* transitions from inner nitrogens, and because of the closeness of the energies of these absorptions considerable configurational interaction is expected [37]. The broadening in the UV region of the spectra of phthalocyanine makes identification of the individual transitions from absorption spectra alone very difficult. In order to assess their potential as PDT photosensitizers, the singlet oxygen generation quantum yields (ΦΔ) of ZnPc-I and ZnPc-II were determined in both water and DMSO. The results of can be related to the position of substituents on the phthalocyanine skeleton. The singlet oxygen quantum yields (ΦΔ) of ZnPc-I and ZnPc-II were determined as 0.34 and 0.11 in water and 0.60 and 0.36 in DMSO media, respectively. It is known that the aggregation of the phthalocyanines reduce their photocatalytic activities such as PDT. It is well documented that some solvents such as DMSO and DMF efficiency reduce the aggregation of phthalocyanines [38]. The singlet oxygen results of this study are also a good example for this phenomenon. The singlet oxygen quantum yield value of the ZnPc-I (0.34) is higher than the value of ZnPc-II (0.11)
Table 1 Singlet oxygen quantum yields of ZnPc-II and ZnPc-I in DMSO and water. Compound
Solvent
ΦΔ
ZnPc-II
DMSO Water DMSO Water DMSO Water
0.36 0.11 0.60 0.34 0.67 0.45
ZnPc-I ZnPc ZnPcSmix
(Table 1). Indeed, while the ZnPc-II showed aggregation in water, the ZnPc-I did not show any aggregation in this media. For this reason, the singlet oxygen generation of the ZnPc-I is higher than ZnPc-II as we expected. The aggregation in phthalocyanines also decreased the photosensitizers properties due to non-radiative energy relaxation therefore decreasing their photosensitizing efficiency [39]. The singlet generation of the synthesized zinc(II) phthalocyanines were found to be lower than those of the ZnPcSmix. But only singlet oxygen generation ability of a photosensitizer is not enough for determination of its PDT activity. Especially absorption wavelength is also important for this purpose. The absorption wavelength values of the synthesized phthalocyanines are higher than ZnPcSmix. The absorption energy of each of these ZnPcs is lower than ZnPcSmix and it means these Pcs are less harmful for healthy cells. On the other hand, the cell uptake behavior of the photosensitizers is also very important. The cell uptake study on these phthalocyanines will be evaluated in further studies and these Pcs can show better cell uptake than ZnPcSmix. 4. Conclusions In this study, symmetrically octa carboxylic acid substituted peripheral and non-peripheral zinc(II) phthalocyanines bridged with triazole attached to tetraethylene glycol linkers have been prepared as potential photosensitizers for PDT. The synthetic procedure which employs peripheral and non-peripheral alkyl sulfur donors can be used to synthesize various reactions of substitution and addition. The 7
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reaction sequence implied the preparation of 3,6-dimercapto phthalonitrile, a very important novel reactant. The infinite solubility of phthalocyanines in aqueous media is due to the triazole-linked octa carboxylic groups. Higher aggregation of ZnPc-II in aqueous media than ZnPc-I phthalocyanine could be attributed to the positions of substituents (α, β). Strong aggregation capabilities of synthesized phthalocyanines decreased their singlet oxygen quantum yield in aqueous media. However, the higher ΦΔ values in DMSO than aqueous media exhibit that Zn(II) phthalocyanines can be used as photodynamic therapy photosensitizers.
[12] [13] [14] [15] [16] [17] [18]
Acknowledgements
[19] [20]
This study was supported by TÜBİTAK. Y. Baygu acknowledges The Scientific and Technological Research council of Turkey, AnkaraTurkey for financial support in Project (Project No: 114Z441).
[21] [22] [23]
Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.synthmet.2019. 116256.
[24] [25]
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