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Physiochemical characterization and antimicrobial evaluation of phenylthiourea–formaldehyde polymer (PTF) based polymeric ligand and its polymer metal complexes
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 26–31
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Physiochemical characterization and antimicrobial evaluation of phenylthiourea–formaldehyde polymer (PTF) based polymeric ligand and its polymer metal complexes Tansir Ahamad, Saad M. Alshehri ⇑ Department of Chemistry, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
" A novel polymeric ligand has been
synthesized via polycondensation of phenylthiourea with formaldehyde. " The polymer metal complexes were prepared with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) ions. " All the polymers have been characterized by elemental, spectral and thermogravimetric analyses. " Antimicrobial activities were performed against several bacteria and fungi using agar well diffusion method.
a r t i c l e
i n f o
Article history: Received 18 September 2012 Received in revised form 22 January 2013 Accepted 23 January 2013 Available online 8 February 2013 Keywords: Phenylthiourea Thermogravimetric analysis FTIR Antimicrobial activity
a b s t r a c t Phenylthiourea–formaldehyde polymer (PTF) has been synthesized via polycondensation of phenylthiourea and formaldehyde in basic medium and its corresponding metal complexes [PTF-M(II)] were prepared with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) ions. The synthesized polymers have been characterized by elemental analysis, magnetic susceptibility, UV–visible, FT-IR, 1H NMR, 13C NMR, ESR spectroscopy and thermogravimetric analysis (TGA). Elemental analysis, electronic spectra and magnetic moment measurement indicate that PTF-Mn(II), PTF-Co(II) and PTF-Ni(II) show octahedral geometry, while PTF-Cu(II) and PTFZn(II) show square planar and tetrahedral geometry, respectively. The results of TGA ascribed that all the PTF-M(II) showed better heat-resistance properties than PTF resin. In vitro antimicrobial activities were performed against several bacteria and fungi using agar well diffusion method. The results of microbial activity were compared with Kanamycin and Miconazole as standard antibiotics for antibacterial and antifungal activities respectively. Ó 2013 Elsevier B.V. All rights reserved.
Introduction Polymer metal complexes are a new and interesting class of materials that combine some of the mechanical properties of the ⇑ Corresponding author. Tel.: +966 1 4675971; fax: +966 1 4674018. E-mail address: [email protected] (S.M. Alshehri). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.01.053
organic polymer and some of those of the metal ions. A large number of such polymers have been synthesized and studied and have been found to be of interest because of their biological applications such as antitumor, antibacterial, antiviral and antifungal agents [1– 4]. The biological activities of the polymeric ligands are considered due to their ability to form polymer metal complexes with metal ions. The biological activity of polymer metal complexes is different
T. Ahamad, S.M. Alshehri / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 26–31
from their parental polymeric ligands due to the coordination of metal ions [5–7]. Since few decades, intense research efforts on the synthesis of polymer metal complexes had led to significant efforts due to their potential applications in various fields such as catalysts, biomedical control releasing agents, water treatment agents, solid-state materials such as semiconducting substances and heatresistant materials. Formaldehyde based polymeric ligands are versatile compounds that coordinate with metal ions either as a neutral ligands or as a deprotonated ligands [8,9]. In our previous studies, we have synthesized several polymeric ligands and their polymer metal complexes such as urea–formaldehyde, thiourea–formaldehyde, semicarbazide–formaldehyde, thiosemicatbazide–formaldehyde and other polymeric ligands those exhibited grater antimicrobial activities when compared with their parental polymeric ligands [10–13]. Thiourea, its derivatives and their metal complexes were known to have a wide range of biological activity such as antibacterial, antifungal, antitubercular, antithyoid, antihelmintic, rodenticidal, insecticidal, herbicidal and have plant-growth regulator activity. It had been previously hypothesized that substitution on the aromatic and heterocyclic rings of the thiourea moiety would affect their biological activity [14,15]. In the present manuscript, we have synthesized phenylthiourea–formaldehyde as a polymeric ligand and its polymer metal complexes with transition metal ions. The synthesized polymers have been characterized by elemental analysis, FT-IR, 1H and 13C NMR, UV–visible, ESR spectroscopy, and TGA. In addition, all the synthesized polymers were tested for their antimicrobial activity against six bacteria (Bacillus subtelillis, Bacillus megaterium, Staphylococcu aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi) and six fungi (Candida albicans, Tubercularia species, Aspergillus flavus, Aspergillus niger, Fusarium species, Mucer species). Experimental protocols Materials Phenylthiourea, formaldehyde (37% aqueous solution), acetic acid, sodium hydroxide and Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) chloride (Sigma Aldrich) were used without further purification. Solvent such as acetone, methanol, ethanol, diethyl ether, tetrahydrofuran (THF), dimethylformamide (DMF) and dimethylsulfoxide (DMSO) were purified by standard procedures before use. Tryptic soy agar (TSA) and Tryptic soy broth (TSB) were purchased from Difco Laboratories. All the used strains were kept at 80 °C in a deep freezer. Measurements The elemental analyses of PTF and its PTF-M(II) were carried out on a Perkin Elmer Model-2400 elemental analyzer. The metal contain were determined by complexometric titration against EDTA after decomposing with concentrated nitric acid (HNO3). The FTIR Spectra were recorded over the (4000–400 cm1) range on a Bruker Tensor-27 spectrophotometer by using KBr pallets. The UV– visible spectra were carried on a Simazdu spectrophotometer (UV-1650 PC) by using DMSO as a solvent and the magnetic susceptibility measurements of all the polymer metal complexes were carried out on a Gouy balance using Hg[Co(SCN)4] as a celebrant. 1 H NMR and 13C NMR spectra were recorded on a JEOL–GSX 400MHz FT NMR spectrometer using d6-DMSO as a solvent and tetramethylsilane (TMS) as an internal standard. The X-band electron spin resonance (ESR) spectra of the PTF-M(II) were recorded in DMSO at room temperature on a Varian 112 ESR spectrophotometer. Thermal behaviors of the all the polymers were carried out by SDT Q-600 (TA Instrument) in nitrogen atmosphere at a heating rate of 20 °C/min.
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Synthesis Synthesis of polymeric ligand (PTF) In a 250 mL round-bottom flask, phenylthiourea (15.2 g, 10 mmol) was dissolved in 30 mL of ethanol then 37% aqueous solution of formaldehyde (15 mL, 0.2 mol) were mixed and pH of the mixture was adjusted 8–9 using aqueous solution of NaOH. The mixture was refluxed with continuous stirring at 80 °C for 5 h and progress of the reaction was monitored by thin layer chromatography (TLC). The excess amount of the solvents was removed using rotary evaporator under reduced pressure. The resulting light yellow color viscous product was washed with deionized water and ethanol respectively and dried in vacuum oven to remove trapped solvents to give phenylthiourea–formaldehyde resin (PTF) in 75% yield. Synthesis of polymer metal complexes [PTF-M(II)] In a 250 mL three necked round bottom flask, PTF (20 mmol) was dissolved in 50 mL of THF and than metal chloride (10 mmol) dissolved in 30 mL of ethanol were mixed in this solution and stirred at 70 °C for 5 h. The excess amount of the solvents was removed using rotary evaporator under reduced pressure. The reaction mixture was cooled and precipitated into a 75/50 (v/v) water/acetone mixture. The colored precipitate was filtered, and then re-precipitated from DMF into methanol. Finally, the product of the polymer metal complexes was dried in a vacuum oven to remove trapped solvents and gave color powder of PTF-M(II) in 70–80% yield. Antimicrobial activity Antibacterial activity The antibacterial activity of the PTF and its PTF-M(II) were carried out against Bacillus subtiis, B. megaterium, S. aureus, E. coli, P. aeruginosa and S. typhi using agar well diffusion method [16]. All the synthesized polymers were dissolved in DMSO separately to prepare 50 lg/mL concentration solutions. Bacterial strains were nourished in a nutrient broth (Difco) and incubated on Mueller– Hinton agar for 24 h. The wells were dug in the media with the help of a sterile steel borer and then 0.1 mL of each sample was introduced in the corresponding well. The petri dishes were incubated at 37 °C and the inhibition zones were recorded in mm after 24 h of incubation with the help of vernier caliper. Each experiment was repeated three times. The antibacterial activity of the solvent (DMSO) and a common standard antibiotic Kanamycin was also recorded to maintain positive and negative controls respectively. Antifungal activity The synthesized polymers, blank (DMSO solvent) and the standard drug Miconazole were screened for their antifungal activity against various fungi viz. C. albicans, T. species, A. flavus, A. niger, F. species, and M. species. The solution concentrations 100 lg/mL of each compound were prepared in DMSO. The fungus strains were nourished in a malt extract broth (Difco) and incubated for 48 h on Sabouraud dextrose agar. The wells were dug in the media with the help of a sterile steel borer and then 0.1 mL of each sample was introduced in the corresponding well. Other wells were supplemented with solvent (DMSO) for positive control and standard drug, (Miconazole) for negative control. The petri dishes were incubated at 30 °C and the inhibition zones were recorded in mm after 72 h of incubation. Results and discussions The polycondensation reaction between phenylthiourea and formaldehyde was carried out in a nitrogen atmosphere resulting
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Table 1 Elemental analysis of PTF and its polymer metal complexes. Abbreviations (color)
Yield in (%)
PTF (light yellow) PTF-Mn(II) (light yellow) PTF-Co(II) (pink) PTF-Ni(II) (light green) PTF-Cu(II) (blue) PTF-Zn(II) (light yellow)
75 75 80 78 70 74
Elemental analysis Carbon
Hydrogen
Nitrogen
Sulfur
58.51 51.53 51.26 51.27 53.50 53.36
4.91 4.59 4.57 4.57 4.21 4.20
17.06 15.02 19.94 14.95 15.60 15.56
19.52 17.20 17.10 17.11 17.85 17.81
(58.55) (51.53) (51.25) (51.28) (53.56) (53.32)
(4.94) (4.54) (4.56) (4.58) (4.24) (4.24)
(17.08) (15.06) (19.94) (14.94) (15.58) (15.57)
Metal (19.56) (17.18) (17.11) (17.14) (17.83) (17.86)
– 7.37 7.86 7.83 8.83 9.08
(7.35) (7.85) (7.82) (8.85) (9.05)
The calculated (found) values.
a light yellow viscous product was obtained as PTF resin. The polymer metal complexes [PTF-M(II)] were prepared with metal ions as shown in Scheme 1 (Supplementary Fig. 1). All the PTF-M(II) were insoluble in water, methanol, ethanol and other common organic solvents but soluble in THF, DMF and DMSO. The molecular weight of PTF was estimated from GPC (gel permeation chrometography) measurement using THF as a solvent and polystyrene as a standard. The results were indicating that the molecular weight was found to be 16,800 Dalton. The molecular weight of polymer metal complexes were not determine due to the insolubility in THF. The elemental analysis and color of the synthesized polymers is summarized in Table 1. The slight deviation in the elemental analysis results may have been due to the polymeric nature of the compounds, as the value of the end groups were not taken into account for the theoretical calculations. The analysis of the PTF indicated that the molar ratio of phenylthiourea and formaldehyde was 1:2 and the micro-analytical data of PTF-M(II) showed that the PTF and metals chloride were in a 2:1 M ratio. The analytical data of PTF-M(II) also revealed that the polymer Mn(II), Co(II) and Ni(II) complexes were coordinated with two water molecules, but the polymer Cu(II) and Zn(II) complexes did not have coordinated water, which was further supported by the TGA results.
FTIR spectra FTIR spectroscopy was used characterized the structure of PTF and its PTF-M(II) and illustrated in Fig. 1. In the spectrum of PTF, the presence of the methylene group in all the synthesized compounds is confirmed by the appearance of two strong bands at 2945–2835 cm1 of mCH2 sym and asym stretching and a band between 1480 and 1450 cm1 due to CH2 bending mode the bond formed during the condensation reaction with formaldehyde. A very broad band is observed in 3350–3250 cm1 regions due to asymmetric and symmetric mNAH. The broadening in this region suggests intermolecular hydrogen bonding [17] which is possible between the sulfur of the thionyl group and the hydrogen of the amide group. The C@S stretching frequency of PTF appears between 1680 and 1695 cm1, while in PTF-M(II) a major shift to lower wave number by 25–30 cm1 have been found (1650– 1655) cm1 and support the coordination with metal ions [18]. The presence of coordination water molecules in the spectra of PTF-Mn(II), PTF-Co(II) and PTF-Ni(II) was further supported by the appearance of absorption bands in the region 1610– 1520 cm1 for HAOAH deformation and between 670 and 650 cm1 for rocking mode of coordination water, while these bands were disappear in the spectra of PTF-Cu(II) and PTF-Zn(II).
Fig. 1. FTIR spectra of polymeric ligand (PTF) and its polymer metal complexes [PTF-Mn(II)].
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T. Ahamad, S.M. Alshehri / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 26–31 Table 2 Magnetic moment and electronic spectral data of polymeric metal complexes. Magnetic moment in B.Ma.
Abbreviations
PTF-Mn(II)
5.76
PTF-Co(II)
4.42
PTF-Ni(II)
2.86
PTF-Cu(II) a
1.96
ESR gII/g\
–
–
–
2.360/2.069
Electronic spectral data Electronic transition (cm1)
Assignment
10Dq (cm1)
B (cm1)
b
b0 (%)
24,840 22,630 17,480
4
6
8496
765
0.82
18
4
6
4
6
20,270 14,160 4780
4
4
T1g (F) T1g(F) 4 T1g(F)
11,236
786
0.84
16
23,690 16,180 13,820
3
2
8960
872
0.78
22
24,840 16,260
A1g(G) T2g(G) T1g(G)
T1g(P) A2g(F) 4 T2g(F) 4
T1g(P) T1g(F) 3 T2g(F) 3
A1g(F) A1g(F) A1g(F)
4
A2g(F) A2g(F) 3 A2g(F) 3
Charge-transfer 2 A1g B1g
2
Bohr magneton.
Another band in the region 1387–1228 cm1 is attributed to CAN stretching. The formation of PTF-M(II) is further supported by the appearance of MAS and MAN stretching vibrations between 640–630 and 510–507 cm1. 1
H NMR and
13
C NMR spectra
The 1H NMR spectra of PTF and PTF-Zn(II) were recorded in DMSO and presented in S. Figs. 2–3. The resonance signals of thioamide group, ArANH and CH2ANH signals appear at 8.32 and 7.15 ppm respectively in the spectra of PTF, which had actually shifted downfield from its original position because of the intermolecular and intramolecular hydrogen bonding between the NH and C@S groups. The resonance signal at 7.15 ppm in the spectra of PTF-Zn(II) is almost disappeared due to deprotonation with meta metal ions [19]. The presence methylene group presence in different environment of PTF and PTF-Zn(II) show resonance signal at 5.46 ppm, 5.37 ppm, 5.14 ppm, 5.08 ppm, 4.84 ppm and 3.43 ppm for ArANACH2ANAAr, ArANHACH2ANAAr ArANHACH2ANHAAr, ArANHACH2ANHAC@S, S@CANACH2ANAC@S and S@C NHACH2ANHAC@S respectively. The aromatic protons of the PTF show signals at 6.93 ppm, 7.23 ppm and 7.31 ppm. These aromatic bands become broad and less intense due to the drifting of ring electrons towards the metal ions and show resonance signal between 6.92 and 7.15 ppm. In the 13C NMR spectra of PTF is shown in S. Fig. 4 (Supplementary Fig. 4), the signals for the CH2 groups of ArANACH2ANAAr, ArANHACH2ANAAr, ArANHACH2ANHAAr, ArANACH2ANHAC S, S@CANACH2ANAC@S and S@CANHACH2ANHAC@S appear at 82.3 ppm, 76.5 ppm, 74.2 ppm, 70.5 ppm, 68.4 ppm, 66.7 ppm, respectively. The resonance signals around 176.2 ppm and 172.4 ppm are assigned to thionyl carbon in two different environments for ArANHACSAN and ArANACSAN, respectively [20]. A downfield shift of the carbonyl carbon signal in the case of diamagnetic metal complex is an indication of complexation process viz a significant carbonyl Cd+ Sd contribution to the stability of the complexes and resultant reduction in the electron density. The aromatic carbons show resonance signals in different environment at 126.4 ppm, 128 ppm, 129.2 ppm, 130 ppm, 132 ppm and 140.2 ppm. It is also observed for both (1H NMR and 13C NMR) spectra that the solvent (DMSO) did not have any coordinating effect in the spectra of PTF and PTF-Zn(II). Electronic, magnetic and ESR studies of PTF-M(II) Electronic spectra of the polymer Mn(II), Co(II), Ni(II) and Cu(II) complexes were taken in DMSO and their magnetic properties are depicted in Table 2. The magnetic moment of PTF-Mn(II) was found
Fig. 2. Thermogravimetric analysis of polymeric ligand and its polymer metal complexes.
to be 5.76 B.M., which indicate the presence of five unpaired electrons suggesting octahedral geometry [21]. The electronic spectra exhibited three absorption bands, at 17,480, 22,630 and 6 6 24,840 cm1, due to 4T1g(G) A1g(F), 4T2g(G) A1g(F) and 4A1g 6 A1g(F) transitions respectively. The spectral data were used to calculate the crystal field parameter (Dq), Racah parameter (B), nephelauxetic effect (b) and the covalency parameter (b0) values. The 10Dq, B, b and b0 were found to be 8496 cm1, 765 cm1, 0.82% and 18% respectively, that indicate indicated the covalent nature of the compound. PTF-Co(II) with magnetic moment of 4.42 B.M., corresponding to four unpaired electrons. Three absorption bands was observed in this spectra at 9780, 14,160 and 4 4 20,270 cm1, due to 4T2g(F) T1g(F) (m1), 4A2g(F) T1g(F) and 4 4 T1g(P) T1g(F) transitions, respectively. These values were consistent with the octahedralgeometry of Co(II) ions. The spectral parameters 10Dq, B and b were found to be 11,236 cm1, 786 cm1 and 0.84. The reduction of the Racah parameter from the free ion value of 971–786 cm1 and the value of b indicate the presence of covalence in the compound. The PTF-Ni(II) was found to be paramagnetic nature with 2.86 B.M. magnetic moment [22]. The electronic spectra showed three bands at 13,820, 16,180 and 23,690 cm1 due to the spin-allowed transitions 3T2g(3 3 3 F) A2g(F), 3T1g(F) A2g(F) and 3T1g(P) A2g(F) respectively, and represent octahedral geometry. The spectral parameters 10Dq, B and b were found to be 8960 cm1, 872 cm1 and 0.78 and the b0 value was 22% respectively. The Racah parameter reduced from the free ion value 1080–872 cm1 indicate the covalent
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Table 3 Antibacterial activity of PTF and its PTF-M(II). Abbreviations
PTF PTF-Mn(II) PTF-Co(II) PTF-Ni(II) PTF-Cu(II) PTF-Zn(II) Kanamycinb DMSOc a b c
Zone of inhibitiona (mm) 50 lg/disk B. subtilis
B. megaterium
S. aureus
E. coli
P. aeruginosa
S. typhi
17 18 19 19 20 19 29 –
17 19 20 19 20 20 29 –
17 18 19 19 20 21 27 –
18 19 20 20 22 21 29 –
14 17 18 18 19 21 30 –
16 16 18 20 22 24 29 –
18–30 mm = significantly active; 10–17 mm moderately active; <10 mm = weakly active. Standard drug (positive control). Solvent (negative control).
Table 4 Antifungal activity of PTF and its PTF-M(II). Abbreviations
PTF PTF-Mn(II) PTF-Co(II) PTF-Ni(II) PTF-Cu(II) PTF-Zn(II) Miconazoleb DMSOc a b c
Zone of inhibitiona (mm) 100 lg/disk C. albicans
T. species
A. flavus
A. niger
F. species
M. species
14 17 16 17 18 16 22 –
16 18 17 18 20 20 25 –
13 14 16 16 22 18 25 –
12 16 19 17 22 20 25 –
14 16 17 19 22 18 25 –
16 17 18 20 22 14 25 –
18–30 mm = significantly active; 10–17 mm moderately active; <10 mm = weakly active. Standard drug (positive control). Solvent (negative control).
nature of the compound. The electronic spectra of PTF-Mn(II), PTFCo(II) and PTF-Ni(II) indicates octahedral geometry around the central metal ion due to the coordination with two H2O molecules. The polymer Cu(II) complex has magnetic moment 1.96 B.M. which shows the presence of one unpaired electron. This value is lower than the spin-only value which is due to mixing of orbital angular momentum from excited state via spin–orbit coupling and shows d–d transition bands at 16,260 cm1, 24,840 cm1 as2 signed to 2A1g B1g transition and charge-transfer spectra respectively, which supports square-planar geometry [23]. The ESR spectrum of PTF-Cu(II) is anisotropic with resolved hyperfine structure shows gII > g\ with the following values gII = 2.360, g\ = 2.096. These values indicate that the ground state of Cu(II) is predominately dx2y2, which supports a square planar structure. The covalent character of a bond becomes more pronounced when the parameters gII and g\ are decreased. The most sensitive parameter is the gII, the variation in the gII value is the best indication about the covalent character. According to Kivelson and Neimen, for ionic environment the gII value is normally >2.3 and for the covalent character the value is less than 2.3. The g-values can be used to calculate the G value, with this factor indicating that the ligand is a weak field or strong field ligand. The equation used is as follows:
main degradation stage (200–500 °C) and third is carbonization stage (>500 °C) of the polymers. In first an initial 2–3% weight loss were found at 100 °C in all the synthesized polymers, this decomposition is mainly due to absorbed water and other solvent. 8–10% weight loss was found with PTF-Mn(II), PTF-Co(II) and PTF-Ni(II) at 200 °C corresponding to coordinated water molecules [26], while in the case of PTF and other polymer complexes 4–5% weight loss was observed and support the absence of coordination water molecules. In the second stage the about 70% of weight is observed up to 500 °C in the case of PTF, and it decomposed completely into volatile products up to 575 °C. On the other hand, PTF-M(II) are not completely decomposed up to 800 °C. The PTF-M(II) show two-step degradation in second stage, where the first step was faster than the second. This may be due to the fact that non-coordinated part of the complexes decomposes first, while the actually coordinated part of all the polymer metal complexes decomposes later [27]. The results of thermogravimetric analysis revealed that the PTF-Cu(II) is comparatively more thermally stable than that of other PTF-M(II) due to the higher stability constant of Cu(II) ions. The order of thermal stability on the basis of thermal residual weight at 800 °C appear to be PTF-Cu(II) > PTF-Zn(II) > PTF-Ni(II) > PTF-Co(II), and this order matches with Irving–Williams order of stability for the complexes of divalent metal ions.
G ¼ ðg II 2:002Þ=ðg ? 2:002Þ where G is less than 4.0, the ligand forming Cu2+ complex is regarded as a strong field ligand. In this case, the G value is 5.18, which is indicating the formation of a weak field ligand [24,25]. Thermal analysis The TGA curves of PTF and PTF-M(II) are represented in Fig. 2. The thermal degradation is divided into three stages, first stage is drying stage and removal of coordination water (<200 °C), second stage is
Antimicrobial assay The antibacterial activity of PTF and PTF-M(II) was studied against several bacteria and the results are summarized in Table 3. PTF show zone of inhibition value 17 mm against B. megaterium, S. aureus, and Bacillus subtilis. The highest and lowest inhibition zone values, i.e. 18 and 14 mm, were measured in E. coli, and P. aeruginosa. The PTF-Cu(II) show highest inhibition zone value 22 mm, against E. coli and S. typhi when compared with other polymer metal complexes with corresponding bacteria in this study. The
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results of antibacterial activities revealed that the PTF-M(II) show higher zone of inhibition than PTF due to the coordination of metal ions. Comparison with a standard drug, Kanamycin (30 lg), showed that the inhibition effect of the polymer metal complexes on bacterial growth was significantly active. The antifungal activity of the polymeric ligand and its polymer metal complexes was studied and the results are presented in Table 4. The polymeric ligand show zone of inhibition values, i.e. 16, 13 and 12 mm were measured against M. species, A. flavus and A. niger, respectively. The PTF-Co(II) show promising zone of inhibition values, 17, 19 and 18 mm against T. species, A. niger, and M. species respectively, while PTF-Zn(II) show zone of inhibition 20 mm against these microbes. PTF-Cu(II) show highest zone of inhibition values, i.e. 22 mm, against M. species, F. species, A. flavus and A. niger, respectively. This investigation revealed that the antimicrobial activity of the compounds increased after metal chelation. This is because chelation reduces the polarity of the central metal ion by partial sharing of its positive charge with the donor groups. This process increases the lipophilic nature of the central metal ion, which in turn favors its permeation to the lipid layer of the membrane [28]. These new polymer metal complexes are not expected to have any toxic behavior for humans; however, a toxicity study should be carried out before their use in vivo. Although allergies may develop due to the presence of formaldehyde, in general, it should not be a concern for formaldehyde-based polymers. Conclusions The new polymeric resin (PTF) has been synthesized via polycondensation of phenylthiourea with formaldehyde in basic medium. The PTF also coordinated with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) to give amorphous colored PTF-M(II). The results of elemental analyses, electronic spectra and magnetic moment measurement indicate that PTF-Mn(II), PTF-Co(II) and PTF-Ni(II) show octahedral geometry, while PTF-Cu(II) and PTF-Zn(II) show square planar and tetrahedral geometry, respectively. All the synthesized polymers showed excellent antimicrobial activity against several bacteria and fungi. The results of antimicrobial evaluation indicate that the PTF-M(II) show higher antimicrobial activity than the PTF. The PTF-Cu(II) showed highest antibacterial as well as antifungal activity then other polymers due to higher stability constant of Cu(II) ions. Since these polymers showed promising antibacterial as well as antifungal activity against several microbes, they can be used for medical and biomaterial applications in future.
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Acknowledgment This work is supported by Research Center, College of Science, King Saud University, Riyadh. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.saa.2013.01.053. References [1] IF. Abu-Awwad, FI. Khalili, BA. Sweileh, Solvent Extr. Ion Exch. 28 (2010) 682– 705. [2] T. Ahamad, S.M. Alshehri, Bioinorg. Chem. Appl. (2010), http://dx.doi.org/ 10.1155/2010/976901. [3] N. Chantarasiri, N. Sutivisedsak, C. Pouyuan, Eur. Polym. J. 37 (2001) 2031– 2038. [4] K.C. Gupta, H.K. Abdulkadir, J. Macromol. Sci. A 45 (2008) 53–64. [5] B.L. Rivas, N.A. Maureira, S.C. Guzmán, Macromol. Symp. 287 (2010) 69–79. [6] T. Ahamad, V. Kumar, N. Nishat, J. Biomed, Mater. Res. A 88 (2009) 288–294. [7] S. Hasnain, M. Zulfequar, N. Nishat, Polym. Adv. Technol. 23 (2012) 1002–1010. [8] N. Nishat, M. Zulfequar, A. Asma, S. Hasnain, J. Coord. Chem 63 (2010) 1273– 1281. [9] N. Nishat, R. Rasool, S.A. Khan, S. Parveen, J. Coord. Chem. 64 (2011) 4054– 4063. [10] N. Nishat, S. Ahmad, R. Ddin, T. Ahamad, J. Appl. Polym. Sci 100 (2) (2006) 928– 936. [11] T. Ahamad, V. Kumar, N. Nishat, Polym. Int. 55 (2006) 1398–1406. [12] N. Nishat, T. Ahamad, S.M. Alshehri, S. Parveen, Eur. J. Med. Chem. 45 (2010) 1287–1294. [13] S. Parveen, T. Ahamad, N. Nishat, Appl. Organomet. Chem. 22 (2008) 70–77. [14] T.K. Venkatachalam, C. Mao, F.M. Uckun, Biochem. Pharmacol. 67 (2004) 1933–1946. [15] T.K. Venkatachalam, E. Sudbeck, F.M. Uckun, J. Mol. Struct. 751 (2005) 41–50. [16] D.P. Singh, K. Kumar, C. Sharma, Eur. J. Med. Chem. 44 (2009) 3299–3304. [17] T. Ahamad, N. Nishat, S. Parveen, J. Coord. Chem. 61 (2008) 1963–1972. [18] N. Nishat, T. Ahamad, S. Ahmad, S. Parveen, J. Coord. Chem. 64 (2011) 2639– 2648. [19] P.F. Kelly, A.M.Z. Slawin, R.A. Soriano, J. Chem. Soc., Dalton Trans. 1 (1996) 53– 59. [20] I.H. Hall, S.Y. Chen, B.J. Barnes, D.X. West, Met. Based Drugs 6 (1999) 143–147. [21] V. Kumar, T. Ahamad, N. Nishat, J. Coord. Chem. 61 (2008) 1036–1045. [22] Y. Patel, J. Shah, Indian J. Chem. 24 (1985) 8000–8005. [23] T. Ahamad, N. Nishat, J. Appl. Polym. Sci. 107 (2008) 2280–2289. [24] D. Kivelson, R. Neiman, J. Chem. Phys. 35 (1985) 149–155. [25] K. Narang, V. Singh, Trans. Met. Chem. 21 (1996) 507–511. [26] N.S. Bhave, A.S. Aswar, Colloid Polym. Sci. 269 (1991) 547–552. [27] N.S. Bhave, A.S. Aswar, Asian J. Chem. 4 (1992) 65–73. [28] N. Nishat, R. Rasool, S.A. Khan, S. Parveen, J. Coord. Chem. 64 (2011) 4054– 4065.
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Physiochemical characterization and antimicrobial evaluation of phenylthiourea–formaldehyde polymer (PTF) based polymeric ligand and its polymer metal complexes Tansir Ahamad, Saad M. Alshehri ⇑ Department of Chemistry, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
" A novel polymeric ligand has been
synthesized via polycondensation of phenylthiourea with formaldehyde. " The polymer metal complexes were prepared with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) ions. " All the polymers have been characterized by elemental, spectral and thermogravimetric analyses. " Antimicrobial activities were performed against several bacteria and fungi using agar well diffusion method.
a r t i c l e
i n f o
Article history: Received 18 September 2012 Received in revised form 22 January 2013 Accepted 23 January 2013 Available online 8 February 2013 Keywords: Phenylthiourea Thermogravimetric analysis FTIR Antimicrobial activity
a b s t r a c t Phenylthiourea–formaldehyde polymer (PTF) has been synthesized via polycondensation of phenylthiourea and formaldehyde in basic medium and its corresponding metal complexes [PTF-M(II)] were prepared with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) ions. The synthesized polymers have been characterized by elemental analysis, magnetic susceptibility, UV–visible, FT-IR, 1H NMR, 13C NMR, ESR spectroscopy and thermogravimetric analysis (TGA). Elemental analysis, electronic spectra and magnetic moment measurement indicate that PTF-Mn(II), PTF-Co(II) and PTF-Ni(II) show octahedral geometry, while PTF-Cu(II) and PTFZn(II) show square planar and tetrahedral geometry, respectively. The results of TGA ascribed that all the PTF-M(II) showed better heat-resistance properties than PTF resin. In vitro antimicrobial activities were performed against several bacteria and fungi using agar well diffusion method. The results of microbial activity were compared with Kanamycin and Miconazole as standard antibiotics for antibacterial and antifungal activities respectively. Ó 2013 Elsevier B.V. All rights reserved.
Introduction Polymer metal complexes are a new and interesting class of materials that combine some of the mechanical properties of the ⇑ Corresponding author. Tel.: +966 1 4675971; fax: +966 1 4674018. E-mail address: [email protected] (S.M. Alshehri). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.01.053
organic polymer and some of those of the metal ions. A large number of such polymers have been synthesized and studied and have been found to be of interest because of their biological applications such as antitumor, antibacterial, antiviral and antifungal agents [1– 4]. The biological activities of the polymeric ligands are considered due to their ability to form polymer metal complexes with metal ions. The biological activity of polymer metal complexes is different
T. Ahamad, S.M. Alshehri / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 26–31
from their parental polymeric ligands due to the coordination of metal ions [5–7]. Since few decades, intense research efforts on the synthesis of polymer metal complexes had led to significant efforts due to their potential applications in various fields such as catalysts, biomedical control releasing agents, water treatment agents, solid-state materials such as semiconducting substances and heatresistant materials. Formaldehyde based polymeric ligands are versatile compounds that coordinate with metal ions either as a neutral ligands or as a deprotonated ligands [8,9]. In our previous studies, we have synthesized several polymeric ligands and their polymer metal complexes such as urea–formaldehyde, thiourea–formaldehyde, semicarbazide–formaldehyde, thiosemicatbazide–formaldehyde and other polymeric ligands those exhibited grater antimicrobial activities when compared with their parental polymeric ligands [10–13]. Thiourea, its derivatives and their metal complexes were known to have a wide range of biological activity such as antibacterial, antifungal, antitubercular, antithyoid, antihelmintic, rodenticidal, insecticidal, herbicidal and have plant-growth regulator activity. It had been previously hypothesized that substitution on the aromatic and heterocyclic rings of the thiourea moiety would affect their biological activity [14,15]. In the present manuscript, we have synthesized phenylthiourea–formaldehyde as a polymeric ligand and its polymer metal complexes with transition metal ions. The synthesized polymers have been characterized by elemental analysis, FT-IR, 1H and 13C NMR, UV–visible, ESR spectroscopy, and TGA. In addition, all the synthesized polymers were tested for their antimicrobial activity against six bacteria (Bacillus subtelillis, Bacillus megaterium, Staphylococcu aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi) and six fungi (Candida albicans, Tubercularia species, Aspergillus flavus, Aspergillus niger, Fusarium species, Mucer species). Experimental protocols Materials Phenylthiourea, formaldehyde (37% aqueous solution), acetic acid, sodium hydroxide and Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) chloride (Sigma Aldrich) were used without further purification. Solvent such as acetone, methanol, ethanol, diethyl ether, tetrahydrofuran (THF), dimethylformamide (DMF) and dimethylsulfoxide (DMSO) were purified by standard procedures before use. Tryptic soy agar (TSA) and Tryptic soy broth (TSB) were purchased from Difco Laboratories. All the used strains were kept at 80 °C in a deep freezer. Measurements The elemental analyses of PTF and its PTF-M(II) were carried out on a Perkin Elmer Model-2400 elemental analyzer. The metal contain were determined by complexometric titration against EDTA after decomposing with concentrated nitric acid (HNO3). The FTIR Spectra were recorded over the (4000–400 cm1) range on a Bruker Tensor-27 spectrophotometer by using KBr pallets. The UV– visible spectra were carried on a Simazdu spectrophotometer (UV-1650 PC) by using DMSO as a solvent and the magnetic susceptibility measurements of all the polymer metal complexes were carried out on a Gouy balance using Hg[Co(SCN)4] as a celebrant. 1 H NMR and 13C NMR spectra were recorded on a JEOL–GSX 400MHz FT NMR spectrometer using d6-DMSO as a solvent and tetramethylsilane (TMS) as an internal standard. The X-band electron spin resonance (ESR) spectra of the PTF-M(II) were recorded in DMSO at room temperature on a Varian 112 ESR spectrophotometer. Thermal behaviors of the all the polymers were carried out by SDT Q-600 (TA Instrument) in nitrogen atmosphere at a heating rate of 20 °C/min.
27
Synthesis Synthesis of polymeric ligand (PTF) In a 250 mL round-bottom flask, phenylthiourea (15.2 g, 10 mmol) was dissolved in 30 mL of ethanol then 37% aqueous solution of formaldehyde (15 mL, 0.2 mol) were mixed and pH of the mixture was adjusted 8–9 using aqueous solution of NaOH. The mixture was refluxed with continuous stirring at 80 °C for 5 h and progress of the reaction was monitored by thin layer chromatography (TLC). The excess amount of the solvents was removed using rotary evaporator under reduced pressure. The resulting light yellow color viscous product was washed with deionized water and ethanol respectively and dried in vacuum oven to remove trapped solvents to give phenylthiourea–formaldehyde resin (PTF) in 75% yield. Synthesis of polymer metal complexes [PTF-M(II)] In a 250 mL three necked round bottom flask, PTF (20 mmol) was dissolved in 50 mL of THF and than metal chloride (10 mmol) dissolved in 30 mL of ethanol were mixed in this solution and stirred at 70 °C for 5 h. The excess amount of the solvents was removed using rotary evaporator under reduced pressure. The reaction mixture was cooled and precipitated into a 75/50 (v/v) water/acetone mixture. The colored precipitate was filtered, and then re-precipitated from DMF into methanol. Finally, the product of the polymer metal complexes was dried in a vacuum oven to remove trapped solvents and gave color powder of PTF-M(II) in 70–80% yield. Antimicrobial activity Antibacterial activity The antibacterial activity of the PTF and its PTF-M(II) were carried out against Bacillus subtiis, B. megaterium, S. aureus, E. coli, P. aeruginosa and S. typhi using agar well diffusion method [16]. All the synthesized polymers were dissolved in DMSO separately to prepare 50 lg/mL concentration solutions. Bacterial strains were nourished in a nutrient broth (Difco) and incubated on Mueller– Hinton agar for 24 h. The wells were dug in the media with the help of a sterile steel borer and then 0.1 mL of each sample was introduced in the corresponding well. The petri dishes were incubated at 37 °C and the inhibition zones were recorded in mm after 24 h of incubation with the help of vernier caliper. Each experiment was repeated three times. The antibacterial activity of the solvent (DMSO) and a common standard antibiotic Kanamycin was also recorded to maintain positive and negative controls respectively. Antifungal activity The synthesized polymers, blank (DMSO solvent) and the standard drug Miconazole were screened for their antifungal activity against various fungi viz. C. albicans, T. species, A. flavus, A. niger, F. species, and M. species. The solution concentrations 100 lg/mL of each compound were prepared in DMSO. The fungus strains were nourished in a malt extract broth (Difco) and incubated for 48 h on Sabouraud dextrose agar. The wells were dug in the media with the help of a sterile steel borer and then 0.1 mL of each sample was introduced in the corresponding well. Other wells were supplemented with solvent (DMSO) for positive control and standard drug, (Miconazole) for negative control. The petri dishes were incubated at 30 °C and the inhibition zones were recorded in mm after 72 h of incubation. Results and discussions The polycondensation reaction between phenylthiourea and formaldehyde was carried out in a nitrogen atmosphere resulting
28
T. Ahamad, S.M. Alshehri / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 26–31
Table 1 Elemental analysis of PTF and its polymer metal complexes. Abbreviations (color)
Yield in (%)
PTF (light yellow) PTF-Mn(II) (light yellow) PTF-Co(II) (pink) PTF-Ni(II) (light green) PTF-Cu(II) (blue) PTF-Zn(II) (light yellow)
75 75 80 78 70 74
Elemental analysis Carbon
Hydrogen
Nitrogen
Sulfur
58.51 51.53 51.26 51.27 53.50 53.36
4.91 4.59 4.57 4.57 4.21 4.20
17.06 15.02 19.94 14.95 15.60 15.56
19.52 17.20 17.10 17.11 17.85 17.81
(58.55) (51.53) (51.25) (51.28) (53.56) (53.32)
(4.94) (4.54) (4.56) (4.58) (4.24) (4.24)
(17.08) (15.06) (19.94) (14.94) (15.58) (15.57)
Metal (19.56) (17.18) (17.11) (17.14) (17.83) (17.86)
– 7.37 7.86 7.83 8.83 9.08
(7.35) (7.85) (7.82) (8.85) (9.05)
The calculated (found) values.
a light yellow viscous product was obtained as PTF resin. The polymer metal complexes [PTF-M(II)] were prepared with metal ions as shown in Scheme 1 (Supplementary Fig. 1). All the PTF-M(II) were insoluble in water, methanol, ethanol and other common organic solvents but soluble in THF, DMF and DMSO. The molecular weight of PTF was estimated from GPC (gel permeation chrometography) measurement using THF as a solvent and polystyrene as a standard. The results were indicating that the molecular weight was found to be 16,800 Dalton. The molecular weight of polymer metal complexes were not determine due to the insolubility in THF. The elemental analysis and color of the synthesized polymers is summarized in Table 1. The slight deviation in the elemental analysis results may have been due to the polymeric nature of the compounds, as the value of the end groups were not taken into account for the theoretical calculations. The analysis of the PTF indicated that the molar ratio of phenylthiourea and formaldehyde was 1:2 and the micro-analytical data of PTF-M(II) showed that the PTF and metals chloride were in a 2:1 M ratio. The analytical data of PTF-M(II) also revealed that the polymer Mn(II), Co(II) and Ni(II) complexes were coordinated with two water molecules, but the polymer Cu(II) and Zn(II) complexes did not have coordinated water, which was further supported by the TGA results.
FTIR spectra FTIR spectroscopy was used characterized the structure of PTF and its PTF-M(II) and illustrated in Fig. 1. In the spectrum of PTF, the presence of the methylene group in all the synthesized compounds is confirmed by the appearance of two strong bands at 2945–2835 cm1 of mCH2 sym and asym stretching and a band between 1480 and 1450 cm1 due to CH2 bending mode the bond formed during the condensation reaction with formaldehyde. A very broad band is observed in 3350–3250 cm1 regions due to asymmetric and symmetric mNAH. The broadening in this region suggests intermolecular hydrogen bonding [17] which is possible between the sulfur of the thionyl group and the hydrogen of the amide group. The C@S stretching frequency of PTF appears between 1680 and 1695 cm1, while in PTF-M(II) a major shift to lower wave number by 25–30 cm1 have been found (1650– 1655) cm1 and support the coordination with metal ions [18]. The presence of coordination water molecules in the spectra of PTF-Mn(II), PTF-Co(II) and PTF-Ni(II) was further supported by the appearance of absorption bands in the region 1610– 1520 cm1 for HAOAH deformation and between 670 and 650 cm1 for rocking mode of coordination water, while these bands were disappear in the spectra of PTF-Cu(II) and PTF-Zn(II).
Fig. 1. FTIR spectra of polymeric ligand (PTF) and its polymer metal complexes [PTF-Mn(II)].
29
T. Ahamad, S.M. Alshehri / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 26–31 Table 2 Magnetic moment and electronic spectral data of polymeric metal complexes. Magnetic moment in B.Ma.
Abbreviations
PTF-Mn(II)
5.76
PTF-Co(II)
4.42
PTF-Ni(II)
2.86
PTF-Cu(II) a
1.96
ESR gII/g\
–
–
–
2.360/2.069
Electronic spectral data Electronic transition (cm1)
Assignment
10Dq (cm1)
B (cm1)
b
b0 (%)
24,840 22,630 17,480
4
6
8496
765
0.82
18
4
6
4
6
20,270 14,160 4780
4
4
T1g (F) T1g(F) 4 T1g(F)
11,236
786
0.84
16
23,690 16,180 13,820
3
2
8960
872
0.78
22
24,840 16,260
A1g(G) T2g(G) T1g(G)
T1g(P) A2g(F) 4 T2g(F) 4
T1g(P) T1g(F) 3 T2g(F) 3
A1g(F) A1g(F) A1g(F)
4
A2g(F) A2g(F) 3 A2g(F) 3
Charge-transfer 2 A1g B1g
2
Bohr magneton.
Another band in the region 1387–1228 cm1 is attributed to CAN stretching. The formation of PTF-M(II) is further supported by the appearance of MAS and MAN stretching vibrations between 640–630 and 510–507 cm1. 1
H NMR and
13
C NMR spectra
The 1H NMR spectra of PTF and PTF-Zn(II) were recorded in DMSO and presented in S. Figs. 2–3. The resonance signals of thioamide group, ArANH and CH2ANH signals appear at 8.32 and 7.15 ppm respectively in the spectra of PTF, which had actually shifted downfield from its original position because of the intermolecular and intramolecular hydrogen bonding between the NH and C@S groups. The resonance signal at 7.15 ppm in the spectra of PTF-Zn(II) is almost disappeared due to deprotonation with meta metal ions [19]. The presence methylene group presence in different environment of PTF and PTF-Zn(II) show resonance signal at 5.46 ppm, 5.37 ppm, 5.14 ppm, 5.08 ppm, 4.84 ppm and 3.43 ppm for ArANACH2ANAAr, ArANHACH2ANAAr ArANHACH2ANHAAr, ArANHACH2ANHAC@S, S@CANACH2ANAC@S and S@C NHACH2ANHAC@S respectively. The aromatic protons of the PTF show signals at 6.93 ppm, 7.23 ppm and 7.31 ppm. These aromatic bands become broad and less intense due to the drifting of ring electrons towards the metal ions and show resonance signal between 6.92 and 7.15 ppm. In the 13C NMR spectra of PTF is shown in S. Fig. 4 (Supplementary Fig. 4), the signals for the CH2 groups of ArANACH2ANAAr, ArANHACH2ANAAr, ArANHACH2ANHAAr, ArANACH2ANHAC S, S@CANACH2ANAC@S and S@CANHACH2ANHAC@S appear at 82.3 ppm, 76.5 ppm, 74.2 ppm, 70.5 ppm, 68.4 ppm, 66.7 ppm, respectively. The resonance signals around 176.2 ppm and 172.4 ppm are assigned to thionyl carbon in two different environments for ArANHACSAN and ArANACSAN, respectively [20]. A downfield shift of the carbonyl carbon signal in the case of diamagnetic metal complex is an indication of complexation process viz a significant carbonyl Cd+ Sd contribution to the stability of the complexes and resultant reduction in the electron density. The aromatic carbons show resonance signals in different environment at 126.4 ppm, 128 ppm, 129.2 ppm, 130 ppm, 132 ppm and 140.2 ppm. It is also observed for both (1H NMR and 13C NMR) spectra that the solvent (DMSO) did not have any coordinating effect in the spectra of PTF and PTF-Zn(II). Electronic, magnetic and ESR studies of PTF-M(II) Electronic spectra of the polymer Mn(II), Co(II), Ni(II) and Cu(II) complexes were taken in DMSO and their magnetic properties are depicted in Table 2. The magnetic moment of PTF-Mn(II) was found
Fig. 2. Thermogravimetric analysis of polymeric ligand and its polymer metal complexes.
to be 5.76 B.M., which indicate the presence of five unpaired electrons suggesting octahedral geometry [21]. The electronic spectra exhibited three absorption bands, at 17,480, 22,630 and 6 6 24,840 cm1, due to 4T1g(G) A1g(F), 4T2g(G) A1g(F) and 4A1g 6 A1g(F) transitions respectively. The spectral data were used to calculate the crystal field parameter (Dq), Racah parameter (B), nephelauxetic effect (b) and the covalency parameter (b0) values. The 10Dq, B, b and b0 were found to be 8496 cm1, 765 cm1, 0.82% and 18% respectively, that indicate indicated the covalent nature of the compound. PTF-Co(II) with magnetic moment of 4.42 B.M., corresponding to four unpaired electrons. Three absorption bands was observed in this spectra at 9780, 14,160 and 4 4 20,270 cm1, due to 4T2g(F) T1g(F) (m1), 4A2g(F) T1g(F) and 4 4 T1g(P) T1g(F) transitions, respectively. These values were consistent with the octahedralgeometry of Co(II) ions. The spectral parameters 10Dq, B and b were found to be 11,236 cm1, 786 cm1 and 0.84. The reduction of the Racah parameter from the free ion value of 971–786 cm1 and the value of b indicate the presence of covalence in the compound. The PTF-Ni(II) was found to be paramagnetic nature with 2.86 B.M. magnetic moment [22]. The electronic spectra showed three bands at 13,820, 16,180 and 23,690 cm1 due to the spin-allowed transitions 3T2g(3 3 3 F) A2g(F), 3T1g(F) A2g(F) and 3T1g(P) A2g(F) respectively, and represent octahedral geometry. The spectral parameters 10Dq, B and b were found to be 8960 cm1, 872 cm1 and 0.78 and the b0 value was 22% respectively. The Racah parameter reduced from the free ion value 1080–872 cm1 indicate the covalent
30
T. Ahamad, S.M. Alshehri / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 26–31
Table 3 Antibacterial activity of PTF and its PTF-M(II). Abbreviations
PTF PTF-Mn(II) PTF-Co(II) PTF-Ni(II) PTF-Cu(II) PTF-Zn(II) Kanamycinb DMSOc a b c
Zone of inhibitiona (mm) 50 lg/disk B. subtilis
B. megaterium
S. aureus
E. coli
P. aeruginosa
S. typhi
17 18 19 19 20 19 29 –
17 19 20 19 20 20 29 –
17 18 19 19 20 21 27 –
18 19 20 20 22 21 29 –
14 17 18 18 19 21 30 –
16 16 18 20 22 24 29 –
18–30 mm = significantly active; 10–17 mm moderately active; <10 mm = weakly active. Standard drug (positive control). Solvent (negative control).
Table 4 Antifungal activity of PTF and its PTF-M(II). Abbreviations
PTF PTF-Mn(II) PTF-Co(II) PTF-Ni(II) PTF-Cu(II) PTF-Zn(II) Miconazoleb DMSOc a b c
Zone of inhibitiona (mm) 100 lg/disk C. albicans
T. species
A. flavus
A. niger
F. species
M. species
14 17 16 17 18 16 22 –
16 18 17 18 20 20 25 –
13 14 16 16 22 18 25 –
12 16 19 17 22 20 25 –
14 16 17 19 22 18 25 –
16 17 18 20 22 14 25 –
18–30 mm = significantly active; 10–17 mm moderately active; <10 mm = weakly active. Standard drug (positive control). Solvent (negative control).
nature of the compound. The electronic spectra of PTF-Mn(II), PTFCo(II) and PTF-Ni(II) indicates octahedral geometry around the central metal ion due to the coordination with two H2O molecules. The polymer Cu(II) complex has magnetic moment 1.96 B.M. which shows the presence of one unpaired electron. This value is lower than the spin-only value which is due to mixing of orbital angular momentum from excited state via spin–orbit coupling and shows d–d transition bands at 16,260 cm1, 24,840 cm1 as2 signed to 2A1g B1g transition and charge-transfer spectra respectively, which supports square-planar geometry [23]. The ESR spectrum of PTF-Cu(II) is anisotropic with resolved hyperfine structure shows gII > g\ with the following values gII = 2.360, g\ = 2.096. These values indicate that the ground state of Cu(II) is predominately dx2y2, which supports a square planar structure. The covalent character of a bond becomes more pronounced when the parameters gII and g\ are decreased. The most sensitive parameter is the gII, the variation in the gII value is the best indication about the covalent character. According to Kivelson and Neimen, for ionic environment the gII value is normally >2.3 and for the covalent character the value is less than 2.3. The g-values can be used to calculate the G value, with this factor indicating that the ligand is a weak field or strong field ligand. The equation used is as follows:
main degradation stage (200–500 °C) and third is carbonization stage (>500 °C) of the polymers. In first an initial 2–3% weight loss were found at 100 °C in all the synthesized polymers, this decomposition is mainly due to absorbed water and other solvent. 8–10% weight loss was found with PTF-Mn(II), PTF-Co(II) and PTF-Ni(II) at 200 °C corresponding to coordinated water molecules [26], while in the case of PTF and other polymer complexes 4–5% weight loss was observed and support the absence of coordination water molecules. In the second stage the about 70% of weight is observed up to 500 °C in the case of PTF, and it decomposed completely into volatile products up to 575 °C. On the other hand, PTF-M(II) are not completely decomposed up to 800 °C. The PTF-M(II) show two-step degradation in second stage, where the first step was faster than the second. This may be due to the fact that non-coordinated part of the complexes decomposes first, while the actually coordinated part of all the polymer metal complexes decomposes later [27]. The results of thermogravimetric analysis revealed that the PTF-Cu(II) is comparatively more thermally stable than that of other PTF-M(II) due to the higher stability constant of Cu(II) ions. The order of thermal stability on the basis of thermal residual weight at 800 °C appear to be PTF-Cu(II) > PTF-Zn(II) > PTF-Ni(II) > PTF-Co(II), and this order matches with Irving–Williams order of stability for the complexes of divalent metal ions.
G ¼ ðg II 2:002Þ=ðg ? 2:002Þ where G is less than 4.0, the ligand forming Cu2+ complex is regarded as a strong field ligand. In this case, the G value is 5.18, which is indicating the formation of a weak field ligand [24,25]. Thermal analysis The TGA curves of PTF and PTF-M(II) are represented in Fig. 2. The thermal degradation is divided into three stages, first stage is drying stage and removal of coordination water (<200 °C), second stage is
Antimicrobial assay The antibacterial activity of PTF and PTF-M(II) was studied against several bacteria and the results are summarized in Table 3. PTF show zone of inhibition value 17 mm against B. megaterium, S. aureus, and Bacillus subtilis. The highest and lowest inhibition zone values, i.e. 18 and 14 mm, were measured in E. coli, and P. aeruginosa. The PTF-Cu(II) show highest inhibition zone value 22 mm, against E. coli and S. typhi when compared with other polymer metal complexes with corresponding bacteria in this study. The
T. Ahamad, S.M. Alshehri / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 108 (2013) 26–31
results of antibacterial activities revealed that the PTF-M(II) show higher zone of inhibition than PTF due to the coordination of metal ions. Comparison with a standard drug, Kanamycin (30 lg), showed that the inhibition effect of the polymer metal complexes on bacterial growth was significantly active. The antifungal activity of the polymeric ligand and its polymer metal complexes was studied and the results are presented in Table 4. The polymeric ligand show zone of inhibition values, i.e. 16, 13 and 12 mm were measured against M. species, A. flavus and A. niger, respectively. The PTF-Co(II) show promising zone of inhibition values, 17, 19 and 18 mm against T. species, A. niger, and M. species respectively, while PTF-Zn(II) show zone of inhibition 20 mm against these microbes. PTF-Cu(II) show highest zone of inhibition values, i.e. 22 mm, against M. species, F. species, A. flavus and A. niger, respectively. This investigation revealed that the antimicrobial activity of the compounds increased after metal chelation. This is because chelation reduces the polarity of the central metal ion by partial sharing of its positive charge with the donor groups. This process increases the lipophilic nature of the central metal ion, which in turn favors its permeation to the lipid layer of the membrane [28]. These new polymer metal complexes are not expected to have any toxic behavior for humans; however, a toxicity study should be carried out before their use in vivo. Although allergies may develop due to the presence of formaldehyde, in general, it should not be a concern for formaldehyde-based polymers. Conclusions The new polymeric resin (PTF) has been synthesized via polycondensation of phenylthiourea with formaldehyde in basic medium. The PTF also coordinated with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) to give amorphous colored PTF-M(II). The results of elemental analyses, electronic spectra and magnetic moment measurement indicate that PTF-Mn(II), PTF-Co(II) and PTF-Ni(II) show octahedral geometry, while PTF-Cu(II) and PTF-Zn(II) show square planar and tetrahedral geometry, respectively. All the synthesized polymers showed excellent antimicrobial activity against several bacteria and fungi. The results of antimicrobial evaluation indicate that the PTF-M(II) show higher antimicrobial activity than the PTF. The PTF-Cu(II) showed highest antibacterial as well as antifungal activity then other polymers due to higher stability constant of Cu(II) ions. Since these polymers showed promising antibacterial as well as antifungal activity against several microbes, they can be used for medical and biomaterial applications in future.
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