DFT study of structure, IR and Raman spectra of the first generation dendrimer built from cyclotriphosphazene core with terminal 4-oxyphenethylamino groups

Journal of Molecular Structure 1026 (2012) 17–22

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DFT study of structure, IR and Raman spectra of the first generation dendrimer built from cyclotriphosphazene core with terminal 4-oxyphenethylamino groups V.L. Furer a,⇑, A.E. Vandyukov b, S. Fuchs c, J.P. Majoral c, A.M. Caminade c, V.I. Kovalenko b,⇑ a

Kazan State Architect and Civil Engineering University, Zelenaya, 1, Kazan 420043, Russia A.E. Arbuzov Institute of Organic and Physical Chemistry, Russian Academy of Science, Arbuzov Str., 8, Kazan 420088, Russia c Laboratorie de Chimie de Coordination, CNRS, 205 route de Narbonne, 31077 Toulouse Cedex 4, France b

h i g h l i g h t s " The FTIR and FT-Raman spectra of dendrimer were studied. " Dendrimer molecule has a concave lens structure. " The different types of H-bonds were found.

a r t i c l e

i n f o

Article history: Received 13 February 2012 Received in revised form 19 May 2012 Accepted 21 May 2012 Available online 27 May 2012 Keywords: Dendrimers IR spectra Normal vibrations DFT

a b s t r a c t The FTIR and FT-Raman spectra of the first generation dendrimer G1 built from the cyclotriphosphazene core, six arms AOAC6H4ACH@NAN(CH3)AP(S)< and 12 4-oxyphenethylamino terminal groups AOAC6H4A(CH2)2ANH2 G1 have been recorded. The structural optimization and normal mode analysis were performed for dendrimer G1 on the basis of the density functional theory (DFT). The calculated geometrical parameters and harmonic vibrational frequencies are predicted in a good agreement with the experimental data. It was found that G1 has a concave lens structure with planar AOAC6H4ACH@ NAN(CH3)AP(S)< fragments and slightly non-planar cyclotriphosphazene core. The 4-oxyphenethylamino groups attached to different arms show significant deviations from a symmetrical arrangement relative to the local planes of repeating units. The experimental IR spectra of G1 dendron was interpreted by means of potential energy distributions. Relying on DFT calculations a complete vibrational assignment is proposed. Ó 2012 Published by Elsevier B.V.

1. Introduction Dendrimers are highly branched monodisperse macromolecular compounds [1–3]. A fine control of the shape and properties of dendrimer can be achieved [1–3]. The three structural components of dendrimers, namely an interior core, repeating branching units attached to the core, and functional terminal groups can be tuned at will [1–3]. Dendrimers are inherent multivalent systems thanks to their numerous terminal groups and should play a special role when interacting with biological systems [4]. Phosphorus is a key element, which play crucial roles in all known forms of life. Thus phosphorus-containing dendrimers should play a special role when interacting with biological systems, from DNA and cells to drug delivery [4]. ⇑ Corresponding authors. Tel.: +7 8432 104737; fax: +7 8432 387972 (V.L. Furer), tel.: +7 8432 732283; fax: +7 8432 732253 (V.I. Kovalenko). E-mail addresses: [email protected] (V.L. Furer), [email protected] (V.I. Kovalenko). 0022-2860/$ - see front matter Ó 2012 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.molstruc.2012.05.054

In this paper we report the IR and Raman spectra study combined with DFT calculations of G1 which is the first generation dendrimer built from a cyclotriphosphazene core, six arms AOAC6H4ACH@NAN(CH3)AP(S)< with twelve 4-oxyphenethylamino terminal groups [5]. Such dendrimer was chosen because it was shown that relative compound with amino-bismethylene phosphonic groups may be used for activation of monocytes [6]. This work is an extension of the spectroscopic and quantum chemical studies concerning the structure and reactivity of phosphorus-containing dendrimers [7,8]. The optimized structure parameters of G1 molecules were obtained using DFT techniques. The values of calculated geometric parameters were compared with available experimental data derived by the X-ray analysis [9]. Thus the main aim of this work was to obtain the characteristic spectral features of structural parts of dendrimer: a cyclotriphosphazene core, repeating units and terminal 4-oxyphenethylamino groups based on DFT quantum chemical computation. Analysis of IR and Raman spectra of dendrimer combined with DFT calculations is important for investigation of supramolecular properties

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of dendrimers as containers for different guest molecules. The calculation of electronic density spatial distribution reveals the existence of regions where appropriate environments would attract either ion or a metal atom. The interpretation of IR spectra of non-crystalline dendrimers is important for characterization of their structure. The results that emerge from such an analysis contribute to the understanding of the structure, dynamics and properties of dendrimers.

3. Computational method Calculations of IR spectrum of G1 were carried out using the gradient-correlated density functional theory with Perdew Burke Ernzerhof exchange correlation functional (DFT/PBE) [10]. This functional is very satisfactory from the theoretical point of view, because it verifies a lot of the exact conditions for the exchange correlation hole and it does not contain any fitting parameters [11]. The comparison of the computed with PBE functional binding energies, geometries and dynamical properties of different molecules shows the best agreement with experiment [12,13]. Calculations were performed using three exponential basis with two polarizing functions (TZ2P) [14,15]. This basis set was chosen in order to obtain the most advantageous relation of accuracy and computation time. Its peculiarity is that the same set of exponents is used for all values of angle moment in atom. The program PRIRODA was used to perform DFT calculations [16]. The minima of the potential surface were found by relaxing the geometric parameters with standard optimization methods. All stationary points were characterized as minima by analysis of Hessian matrices. The software package SHRINK [17] was used for the transformation of quantum mechanical Cartesian force constants to the matrix in the dependent internal coordinates and calculation of potential energy distribution. No scaling procedure of frequencies or force constants was applied. The selected functional and basis set was

2. Experimental The synthesis and main characteristics of dendrimer G1 were described earlier [5]. The molecule G1 contains a hexafunctional cyclotriphosphazene core (NP)3, six bifunctional repeating units AOAC6H4ACH@NAN(CH3)AP(S)<, and 12 terminal 4-oxyphenethylamino groups AOAC6H4A(CH2)2ANH2 (Fig. 1). The studied dendrimer is amorphous solid compound. IR spectra in the region 4000–400 cm1 have been recorded with a Vector 22 Bruker FTIR spectrometer. The spectral resolution was set at 4 cm1. Sixty-four scans were added for each spectrum. The studied samples were placed between the KBr plates. The Raman spectra in the region 3500–10 cm1 were excited by Nd: YAG laser line 1064 nm with power at sample 50 mW and were recorded with an FTIR-spectrometer Vertex 70 equipped with RAM II Bruker FT-Raman module.

H2N

H2N

NH2 H2N O S O P N H3C N

H2N

N CH

CH

O O P

S CH 3 N

O

N H C

N

O P O

H2N

O P

N

O S

H2N

C N H CH3

O O P S N CH

3

NH2

O P N

H3C

N

C N H

P O O

CH N

S O

N P

O

NH2 CH3 S P O O

N

NH2 H2N

NH2 Fig. 1. Structure of dendrimer molecule G1.

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V.L. Furer et al. / Journal of Molecular Structure 1026 (2012) 17–22

checked by calculation of geometry and IR spectra of dendrimers [18]. Spectra were generated from a list of frequencies and intensities using Gaussian band shape and width at half-height of 20 cm1 for each of vibration modes calculated. An assignment of bands was fulfilled on the basis of calculated potential energy distribution (PED). 4. Results and discussion The dendrimer G1 is amorphous and lacks long-range order in the condensed phase. Thus, its molecular structure is impossible to determine by X-ray diffraction. But we can use the geometric parameters of relative phenethylamino and cyclotriphosphazene molecules in crystalline state defined by X-ray diffraction method [9,19]. It was shown that the cyclotriphosphazene ring is slightly non-planar, with two nitrogen atoms displaced by 0.15 Å in opposite directions from the plane of the other four (three phosphorous and one nitrogen) atoms [19]. There are no differences among chemically equivalent bond lengths [19]. Although the comparison between gas phase and condensed phase structures is not direct, we can observe a reasonable agreement between theoretical calculations of G1 and the experimental X-ray diffraction data for the crystal phase of hexaphenoxycyclotriphosphazene [19] and hexakis(4-N0 (-dichloro(thio)phosphonyl)N0 -methyl-diazobenzene)cyclotriphospha-zene [9] (Table 1 and Fig. 2). Full optimization yielded the conformer of G1 with slightly non-planar cyclotriphosphazene ring. The calculated dihedral angles of cyclotriphosphazene ring are less than 30°. Our data correspond to recent ab initio calculations of phosphazenes [20]. It was shown that most of cyclotriphosphazene derivatives have planar ring conformations [20]. From DFT calculations it follows that each AOAC6H4ACH@ NAN(CH3)AP(S)< arm is planar. Thus, the molecular conformation is defined by the dihedral angles N(1)AP(1)AO(1)AC(1) and P(1)AO(1)AC(1)AC(2) which determine the orientation of arms.

From the potential energy scans of the internal rotations around PAO and CAO bonds, molecule was predicted to exist predominantly in the only one of low-energy stable conformation of AOAC6H4ACH@NAN(CH3)AP(S)< arms. The most stable is the conformer of G1 molecule with calculated N(1)AP(1)AO(1)AC(1) and P(1)AO(1)AC(1)AC(2) dihedral angles: 170.1° and 158.8° (Fig. 2 and Table 1). The corresponded experimental dihedral angles are equal to 174.7° and 172.8°. Full optimization yielded that conformer of terminal 4-oxyphenethylamino groups AOAC6H4A(CH2)2ANH2 with C(13)AC(22)AC(23)AN(6) and C(22)AC(23)AN(6)AH(23) dihedral angles: 63.7° and 46.8° (Fig. 2 and Table 1) is the predominant. The 4-oxyphenethylamino groups attached to different arms show significant deviations from a symmetrical arrangement relative to the local SPNN planes of repeating units. These deviations may be ascribed to intermolecular interactions. The calculated bond distances (in Å) P(1)AN(3) (1.606), P(1)AO(1) (1.649), C(1)AO(1) (1.388) in G1 molecule correspond well to the experimental values 1.576, 1.585, 1.401. The theoretical bond angles (in degrees) N(1)AP(2)AN(2) (121.2), P(1)AN(1)AP(2) (119.2), O(1)AP(1)AN(1) (103.0), P(1)AO(1)AC(1) (126.2) are also in close agreement with the experimental values 117.6, 122.0, 110.8, 128.7. Our calculations show that G1 molecule has a concave lens structure with planar AOAC6H4ACH@NAN(CH3)AP(S)< fragments and slightly non-planar cyclotriphosphazene core. The 4-oxyphenethylamino groups attached to different arms show significant deviations from a symmetrical arrangement relative to the local planes of repeating units. The dendrimers shape can be characterized by ratios I1/I3 and I2/ I3 of principal moments of gyration tensor. The difference of these ratios from 1 characterizes the deviation of dendrimers shape from the sphere. For the studied dendrimer the calculated values of ratios I1/I3 and I2/I3 of principal moments of gyration tensor are 0.22 and 0.98. Thus the G1 molecule has highly asymmetric shape

Table 1 0 Experimental and calculated bond distances (Å A) and bond angles (°) of G1. Exp. [9,19]

Calc.

Exp. [9,19]

1.578 1.576 1.585 1.572 1.573 1.574 1.575 1.899 1.634

1.606 1.606 1.649 1.610 1.609 1.608 1.612 1.926 1.646

N(4)AC(7) N(4)AN(5) N(5)AC(8) O(2)AC(10) N(6)AC(23) C(1)AO(1) C(13)AC(22) C(22)AC(23) P(4)AO(3)

1.401 1.465 1.465 1.585

1.292 1.368 1.462 1.400 1.466 1.388 1.509 1.552 1.653

Angles N(1)AP(1)AN(3) N(1)AP(2)AN(2) N(2)AP(3)AN(3) P(1)AN(1)AP(2) P(1)AN(3)AP(3) P(2)AN(2)AP(3) P(1)AO(1)AC(1) O(1)AC(1)AC(2) P(4)AO(2)AC(10)

117.3 117.6 116.6 122.0 121.3 122.4 128.7 118.8 124.4

120.6 121.2 121.1 119.2 119.2 118.6 126.2 115.5 131.1

N(4)AN(5)AP(4) N(4)AN(5)AC(8) N(5)AN(4)AC(7) C(1)AC(3)AC(4) C(4)AC(5)AC(7) O(1)AC(1)AC(3) O(1)AP(1)AN(1) S(1)AP(4)AN(5)

105.2 121.7 119.4 118.8 119.9 124.1 110.8 115.6

114.6 122.8 119.0 118.9 118.9 123.9 103.0 114.9

Dihedral angles P(1)AN(1)AP(2)AN(2) P(1)AN(3)AP(3)AN(2) P(1)AO(1)AC(1)AC(2) P(2)AN(1)AP(1)AN(3) P(2)AN(2)AP(3)AN(3) P(3)AN(2)AP(2)AN(1) N(1)AP(1)AN(3)AP(3) P(4)AO(2)AC(10)AC(11) C(13)AC(22)AC(23)AN(6)

8.7 9.9 172.8 9.3 4.8 11.8 16.6 81.9 71.2

0.5 1.7 158.8 2.1 0.1 0.5 2.6 69.7 63.7

N(1)AP(1)AO(1)AC(1) C(4)AC(5)AC(7)AN(4) O(1)AC(1)AC(2)AC(6) O(1)AP(1)AN(1)AP(2) C(5)AC(7)AN(4)AN(5) C(1)AC(2)AC(6)AC(5) C(2)AC(6)AC(5)AC(7) S(1)AP(4)AN(5)AN(4) C(22)AC(23)AN(6)AH(23)

174.7 175.8 174.1 116.8 179.5 0.7 176.9 179.9 49.3

170.1 176.3 179.0 124.3 179.4 0.5 179.6 179.1 46.8

Bond distances P(1)AN(1) P(1)AN(3) P(1)AO(1) P(2)AN(1) P(2)AN(2) P(3)AN(2) P(3)AN(3) S(1)AP(4) P(4)AO(2)

Calc. 1.263 1.471 1.459 1.404

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V.L. Furer et al. / Journal of Molecular Structure 1026 (2012) 17–22

Fig. 2. Optimized geometry and atom numbering for G1.

calculated absorption curve of isolated molecule of G1 is much simpler than the experimental IR spectrum the intensity of most prominent bands is reproduced by our computations (Fig. 3). Thus DFT calculations may be used for interpretation of spectra of dendrimers. The assignment of bands was fulfilled by calculation of potential energy distribution (PED) (Table 2). The strong complex band at 1687 cm1 in the experimental IR spectrum of G1 is assigned to stretching vibrations of C@O bonds of CF3COOH groups which are present due to synthesis of dendrimer. The band at 1632 cm1 which is NH2 deformation has medium intensity in the IR spectrum of G1. The intense bands at 1606 and 1505 cm1 in the IR spectrum of G1 refer to CCar stretch and CCH bending vibrations of aromatic ring. In the Raman spectrum of G1 lines at 1604, and 1577 cm1 reveal their self in this region. The rather weak bands at 1469, 1441, 1429 cm1 in the IR spectrum of G1 are connected with HCH bending vibrations. The corresponded line at 1431 cm1 is observed in the Raman spectrum of G1. The rather weak lines at 1307 and 1372 cm1 in the Raman spectrum of G1 are assigned to NCH and CCH bend. The corresponded 2.0

2

1.5

Absorbance

and possesses open structures. The shape of dendrimers molecules defines their capability to self-assembling or self-ordering in various hierarchical structures [21]. This concave lens shape of G1 molecules should induce the cavities, large enough to accommodate guest molecules. The determining factor in the host guest systems is electrostatic interactions. In order to evaluate the interactions between dendrimers and various active substances such as drugs, pesticides and perfumes, we calculated electronic density spatial distribution for the core, repeating units and terminal groups. From our calculations it follows that the studied G1 dendrimer incorporates CAN polar bonds in the cyclotriphosphazene core with Hirshfeld charges (in a.u.) on atoms [22] N(1) (0.31), P(1) (0.39). The nitrogen atom of the terminal group N(6) also has negative charge 0.18. Dendrimer G1 contains P@S polar bonds in repeated unit with charges on atoms S(1) (0.25) and P(4) (0.36). The charges on atoms O(1) and O(2) are about 0.12. Other atoms of repeated unit and terminal groups have charges less than 0.1. Thus in the case of the phosphorus-containing dendrimers macromolecules have a hydrophobic interior and there are active sites for reaction and interaction in the core of dendrimer and in the terminal groups. Dipole moments may be used for characterization of dendrimers structure. The calculated in gas phase dipole moment of G1 molecule is equal to 4.17 D. Thus G1 dendrimer has a significant dipole moment which may be attributed to a non-symmetrical distribution of the lone pairs of the nitrogen atoms. The branches of this dendrimer induce a great influence upon the core in terms of isolation and polarity. Lipophilicity is a very important molecular descriptor that often correlates well with the bioactivity of chemicals [23]. The logarithm of the partition coefficient (log P) correlates with water solubility [23]. Lipophilicity can be measured by log P, which reflects the equilibrium partitioning a molecule between an apolar and a polar phase. In the present study we calculate log P for G1 molecules with HyperChem software [24] and obtained the rather high value 35.54. Thus the dendrimer of the first generation G1 has a strongly positive log P value and it is lipophilic. The lipophilicity of this dendrimer has a tremendous importance for its geometry and shape in water. Our results demonstrate that the internal structure of dendrimers plays a crucial role when considering biological properties. The experimental IR and Raman spectra of studied dendrimer, obtained in this work, are represented in Figs. 3–5. Although the

1.0

1

0.5

0.0 1800

1600

1400

1200

1000

800

600

Wavenumber/cm-1 Fig. 3. Theoretical (1) and experimental (2) IR spectra of G1.

400

21

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V.L. Furer et al. / Journal of Molecular Structure 1026 (2012) 17–22

1.0

Table 2 Experimental and corresponded calculated frequencies m (cm1) and intensity I (km/ mol) of bands in the IR spectra of G1 in the region 400–1800 cm1. Experiment IR

Raman

m

m

1505 1469 1441 1429 1411 1387 1384 1368 1324 1304 1291 1266

0.0 1800

1600

1400

641 601 969

1200

886

1102

1371

1431

1220

0.5

1166

Intensity

1577

1632 1606

1000

800

600

400

Wavenumber/cm-1

1198 1181 1164 1140

1604 1577

1431

1372 1307 1251 1220 1181 1166 1101

Fig. 4. Experimental Raman spectrum of G1.

2941

2

3040

1.5

3436

2.0

2858

2995

3072

1.0

1

0.5

0.0 3600

3400

3200

3000

2800

2600

Wavenumber/cm-1

1017 946 929 892 837 799 785 755 722 698 673 655 646 639 626 597 574 562 543 533 519 508 498 480 475 463 456 434 425 412 412

968 886

641

602

407

Calculation

m

I

Assignment

1609 1604 1573 1491 1461 1440 1432 1416 1403 1387 1355 1330 1296 1294 1244 1226 1200 1183 1161 1146 1102 1015 943 927 895 844 800 778 757 725 690 675 657 639 634 631 597 566 561 545 525 504 479 473 472 459 456 445 435 433 412 409

41.8 71.1 5.6 142.6 59.4 2.9 7.0 5.7 1.6 17.3 37.8 6.6 7.4 2.5 135.5 762.1 85.4 1233.3 148.1 11.0 29.0 126.3 143.8 47.2 317.1 201.0 180.8 275.5 381.7 28.8 23.5 12.9 2308 4.9 37.2 17.6 56.5 14.3 10.0 41.6 10.2 122.6 130.9 23.6 15.8 12.9 96.7 59.4 117.0 52.9 24.1 6.1

36 d(HNH), 23 d(CNH), 21 m(CCar) 49 m(CCar), 23 m(C@N), 18 d(CCH) 72 m(CCar), 14 d(CCH), 8 d(CCC) 53 d(CCH), 32 m(CCar), 7 m(CAO) 71 d(HCH), 21 d(NCH) 60 d(HCH), 17 d(CCH) 83 d(HCH), 9 d(NCH) 52 m(CCar), 36 d(CCH) 47 d(NCH), 28 d(HCH), 8 d(CCH) 47 d(NCH), 30 d(CCH), 12 m(CAC) 31 d(NCH), 29 d(CCH), 17 d(CNH) 66 m(CCar), 8 m(CAC), 5 d(NCH) 37 d(CCH), 20 d(CNH), 15 d(NCH) 87 d(CCH), 9 m(CCar), 5 d(CCC) 39 m(PN), 25 m(CAO), 13 m(CCar) 19 d(CCH), 19 m(PN), 14 m(CAC) 15 m(PN), 15 d(NCH), 14 m(CCar) 30 m(CAO), 20 m(PN), 13 d(CCH) 67 d(CCH), 13 m(CCar), 11 m(CAO) 95 m(PN) 55 d(CCH), 16 m(CCar), 6 d(NCH) 33 m(CAN), 28 d(CCH), 11 m(CCar) 44 m(PO), 10 m(PN) 41 q(CH), 7 m(CAC) 52 m(PO), 12 m(CO), 7 m(PN) 36 d(CNH), 11 m(CC), 6 d(HNH) 65 q(CH), 5 m(CC), 4 m(CCar) 58 m(PO), 234 m(PN), 5 d(PNP) 20 d(CCH), 12 q(CH), 11 m(PS) 29 q(CH), 27 v(CC), 7 m(PO) 25 m(PO), 13 d(CCC), 7 m(CO) 40 m(PN), 13 m(PO), 12 d(PNP) 43 d(CCC), 9 d(CCH), 7 d(OCC) 60 d(CCC), 20 d(CCH), 6 d(OCC) 57 d(CCC), 14 d(CCH), 4 d(OCC) 23 d(CCC), 16 m(PO), 14 m(P@S) 23 d(POC), 20 d(CCC), 9 d(OCC) 40 d(POC), 16 q(CH), 8 d(CCC) 16 d(CCC), 12 d(OCC), 9 d(POC) 16 d(PNP), 13 d(CCC), 11 d(OPO) 58 q(CH), 13 v(CN), 12 v(CC) 36 q(CH), 16 v(PO), 14 v(CC) 20 d(CNN), 13 d(NPO), 11 d(CCC) 24 v(PN), 24 d(NPO), 8 d(CNN) 17 v(PO), 11 q(CH), 8 d(CCC) 8 d(OPO), 8 d(CNP), 8 d(CCC) 22 v(PO), 15 d(NPO), 8 v(PN) 40 v(PO), 31 d(OPO), 10 d(PNP) 18 d(POC), 11 v(CC), 10 v(PO) 17 v(PO), 14 v(CC), 14 d(NPO) 30 v(CC), 21 v(PO), 16 d(NPO) 26 d(NPO), 22 v(PO), 14 v(PN)

Fig. 5. Experimental Raman (1) and IR (2) spectra of G1.

bands at 1304 and 1368 cm1 reveal their self in the IR spectrum of G1. The very strong and complex bands in the experimental IR spectrum of G1 at 1164, 1181, 1198 cm1 refer to the CAO, PAN and CAC stretch. The Raman spectrum of G1 in this region shows lines at 1166 and 1181 cm1. Band at 1017 cm1 is connected with CAN stretch. The strong band at 946 cm1 in the experimental IR spectrum of G1 is assigned to PAO stretch. The medium-intensity band at 837 cm1 in the IR spectrum of G1 refers to the symmetric COC stretch. The band at 646 cm1 in the IR and Raman spectra of G1 include contribution of CCC, CCH and OCC bend. The band at 574 cm1 in the IR spectrum of G1 refers to POC bend.

Band at 3436 cm1 arising from NH2 antisymmetric stretch is observed in the IR spectrum of G1. Four CAH stretching modes should be expected in the 3120–3000 cm1 region of the parasubstituted benzene derivatives. In the experimental IR spectra of G1 the bands at 3040, 3000 and 2941 cm1 appears in this region (Fig. 5). In the experimental Raman spectrum of G1 lines at 3072, 2995 and 2858 cm1 are observed (Fig. 5). Bands at 3070, 3000 cm1 refer to aromatic CAH stretch. Bands at 2941 and 2858 cm1 may be assigned to antisymmetric and symmetric CH2 stretch vibrations of methylene group. Thus, the dendrimer core (NP)3, reveals itself by band at 1266 cm1 in the IR spectra of G1 assigned to PAN stretch. The 4-oxyphenethylamino terminal groups are characterized by the well defined band at 3436 cm1 assigned to NH2 antisymmetric

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stretch. The line at 1577 cm1 in the Raman spectrum of G1 may be assigned to m(C@N) vibrations of repeating units. 5. Summary The IR and Raman spectra of G1 dendrimer built from a cyclotriphosphazene core with 4-oxyphenethylamino terminal groups have been recorded. The structural optimization and vibrational analysis were made for G1 by DFT method. The intensity of the most prominent bands in the IR spectrum of G1 is reproduced by our calculations. The calculated absorption curves of G1 as a whole corresponds to the experimental IR spectrum in the wide frequency region. Thus the employed DFT method enables one to calculate the structure, charges on atoms, and reproduce the experimental IR spectrum of the dendrimer with cyclotriphosphazene core and 4-oxyphenethylamino end groups. The 4-oxyphenethylamino terminal groups of G1 are out of the repeating group plane. The calculated ratios of principal moments of gyration tensor reveal that G1 molecule has highly asymmetric shape. IR spectroscopy combined with quantum chemical DFT computation provides unique detailed information about the structure of the technologically relevant materials, which could not be obtained before by any other technique. The analysis of IR and Raman spectra of dendrimer enables one to distinguish the bands of a cyclotriphosphazene core, repeating units, 4-oxyphenethylamino terminal groups. Acknowledgment Authors are grateful to supercomputer center of collective use of Kazan Scientific Center RAS for access to computer resources.

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