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ABSTRACTThe vibrational absorption spectra of 3'‐Azido‐2'‐deoxythymidine (Zidovudine) have been studied. Thespectra were analysed based on semi‐empirical quantum mechanical (AM1) and (PM3) calculations. Assuming Cspoint symmetry, vibrational assignments for the observed frequencies have been proposed. The spectra exhibitdistinct features originating from low frequency vibrational modes caused by inter‐molecular motion. Normalmodes have been calculated and an assignment of the observed spectra has been proposed.
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Indian Drugs, 45(1), 2008, 16‐25 Spectroscopic and Inter Molecular Studies of Anti AIDS Drug: 3'Azido2'deoxythymidine
Y.P.Singha * and Ratnesh Dasb aDepartment of Physics, Govt. Women’s Polytechnic College , Sagar (MP) 470001 INDIA,.E‐mail: [email protected] bDepartment of Chemistry, Dr. H.S.Gour University, Sagar (MP), INDIA, 470001, E‐mail: [email protected] ABSTRACT The vibrational absorption spectra of 3'‐Azido‐2'‐deoxythymidine (Zidovudine) have been studied. The
spectra were analysed based on semi‐empirical quantum mechanical (AM1) and (PM3) calculations. Assuming Cs
point symmetry, vibrational assignments for the observed frequencies have been proposed. The spectra exhibit
distinct features originating from low frequency vibrational modes caused by inter‐molecular motion. Normal
modes have been calculated and an assignment of the observed spectra has been proposed.
Keywords : Zidovudine, FTIR Spectra, Anti aids drug, HIV, AM1 and MP2 calculations INTRODUCTION
AIDS has ceased to be a mere health
problem and has now acquired dimensions which
perhaps have very few parallels in the history of
mankind. In reality AIDS1 is , not a disease but a
collection of seventy or more conditions which result
from the damage done to the immune system and
other parts of the body as a result of infection by
HIV.
There are a number of drugs that have been
considered as to be anti HIV. The drugs like 3'‐Azido‐
2'‐deoxythymidine (AZT) and ribavirin appear most
promising because both cross the blood‐brain
barrier and can be taken orally, and in early traities
they do not cause serious side effects.
AZT Zidovudine, was the first drug approved for the
treatment of AIDS and HIV infection. Jerome
Horowitz first synthesized AZT in 19642. The crystal
structure of AZT was reported by Alan Howie3 in
1988. In the solid state AZT forms a hydrogen bond
network4.
The study of drug complexes have assumed
much importance, the chemistry of life involves, in
an essential and indispensible way many of the
chemical elements5, 6. The word AIDS inspires fear,
widespread diffusion of information about this
disease has made people aware of its lethal effects.
Nodal research in the medicinal and biological
sciences are being persued all over the world with a
view for achievimg better understanding of AIDS, its
causes, symptoms, mode of spreading, diagnostic
treatment and possible cure. Spectroscopis studies of anti‐AIDS drug have made a significant
contribution of this noble endeavor of striving to
eliminate the fear of this dreadful disease.
The calculation of vibrational frequencies by
computational methods is becoming increasingly
important in many areas7. Infra red and Raman
spetra of molecules in their ground electronic states
were predicted by molecular orbital theory8.
Conformational analysis of AZT structure and other
related drugs have been previously reported at
semi–empirical and ab initio levels of theory 7‐9.
Hernández10 at al reported an ab initio HF and DFT
study of the dipole polarizability of AZT drug.
Thus the present study has been undertaken with a
view to understand the spectroscopy of this drug
and we compared experimental results with
calculated frequencies using force matrix method
and MOPAC method.
Thus the present study has been
undertaken with a view to understand the
spectroscopy of this drug and we compared
experimental results with calculated frequencies
using force matrix method and MOPAC method.
Probably, this is the first time when we are reporting
experimental frequencies with AM1 and PM3
calculated frequencies because we had surveyed lot
of literature but we found nothing.
EXPERIMENTAL
All the chemicals used to prepare
experimental sets were of Analar/BDH grade.
Zidovudine was purchased from Cipla India Ltd.
I.R. Spectrum has been recorded using KBr
disc in solid phase in the range 400‐4000cm‐1 on
Perkin‐Elmer spectrometer Model 397.
Preparation of KBr Pallets: A small amount
of finally grounded solid sample was intimately
mixed with about 100 times or more than its weight
of Potassium bromide powder. The finely ground
mixture was than pressed under very high pressure
in a press (about 10/cm2) to form a small pallet
(about 1‐2 mm thick and 1cm in diameter).
The accuracy of the measurements was
estimated to be within 3cm‐1 and the resolution was
better than 2cm‐1 through the entire spectra.
Figure 1: Structure and Formula of Zidovudine
RESULTS and DISCUSSIONS
Zidovudine is one of the complex structured
drugs. The infra red spectrum of this drug is
presented in figure 2.
The theoretical prediction of vibrational
spectra is of practical importance for the
identification of known and unknown compounds,
and has become an important part of spectro‐
chemical and quantum chemical investigations11.
We can get information from computational
vibrational spectra only when we compare it with
experimental spectrum. The values of bond angle in
angstroms, bond angles in degrees and Cartesian
coordinates are presented in Table 1. The
experimental results are compared with those
obtained by AM1 and PM3 method. These
calculations are done on the basis of precise set. The
calculated bond distances and bond angles comes
out to be in agreement with the experimental one as
reported by Roey et al12.
C 3 C 5
C 7
C 1
O 1 9 N 4 H 2 0
N 2
C 8
H 2 2
H 2 3
H 2 1
C 1 2C 6
O 9
H 2 6
H 2 5
N 1 4
N 1 6
C 1 3
H 2 4H 2 7
H 2 8
N 3 2
H 1 8
O 1 7
H 3 0 H 2 9
O 1 5
H 3 1
3'‐Azido‐2'‐deoxythymidine or Zidovudine
Empirical Formula C10H13N5O4
Molecular Weight 267.24
The vibrational infrared frequencies were
also calculated on the basis of AM1 and PM3 precise
set of MOPAC as shown in table 3. 3'‐Azido‐2'‐
deoxythymidine contains 32 atoms so that it has 90
normal modes. The calculated normal modes are
distributed among 60 a΄ and 30 a΄΄ species of Cs
symmetry group.
The table 3 also shows that PED
contributions for 90 normal modes. These
assignments are partly based on the calculated
frequencies. As the table 3 is self‐explanatory, we
shall discuss here only some important points.
Only the frequencies from 300cm‐1 to
2200cm‐1 have been taken into consideration. The
experimental bands are shown in figure 2. All spectra
exhibit fine structures. Experimental O‐H stretching
bands are not shown; only theoretically calculated
frequencies are taken into account.
Figure 3 and 4 shows agreement between
the experimental and calculated wave numbers
(AM1 and PM3). The graph is linear which shows
that theoretical and experimental results are in good
agreement.
CONCLUSIONS Theoretical semi‐empirical quantum
mechanical AM1 and PM3 calculations of the
geometry and vibrational frequencies of the AZT
drug are presented in this paper and compared with
infrared spectra. The calculated geometries and
frequencies agree well with the experimental ones,
but there are some differences between frequencies
mainly due to intermolecular interactions,
anharmonicity and computational basis set.
ACKNOWLEDGEMENTS The authors are grateful to Director, DTE‐
Madhya Pradesh, Bhopal and Head, Department of
Chemistry, Dr. H.S.Gour University, Sagar (MP),
India.
REFRENCES
1. Dossier P, AIDS and Thirld World, The Panon Institute of London (1988)
2. Yarchoan R, Mitsuya H, Broder S. AIDS therapies. Sci Am, 259(4):110‐9, (1988)
3. Alan Howie, [email protected], www.abdn.ac.uk/chemistry/research/rah/rah.hti, (2006)
4. I.D. Dyer, J.N.Low, P.T.Tollin, H.R. Wilson and R. Alan Howie; Structure of 3'‐Azido‐2'‐deoxythymidine, AZT; Acta Crystal,; C44, 767‐769, (1988)
5. A.P.Scott, L.J.Radom,; Harmonic vibrational frequencies: An evaluation of HF, MP, Quadratic configuration Interaction, DFT and Semiempirical scale factors; J. Phys Chem A;; 100, 16502‐16513, (1996)
6. M.W.Wong; Vibrational frequencies prediction using DFT; Chem Phys. Lett;; 256, 391‐399, (1996)
7. M. Sabio, S. Topiol; A conformational analysis of 3'‐Azido‐2'‐deoxythymidine; J. Comput. Chem, 13, 478–491, (1992).
8. M. T. Baumgartner, M. I. Motura, R. H. Contreras, A. B. Pierini, M. C. Brión; Conformational studies of novel antiretroverial analogs of Zidovudine; Nucl.eos. Nucleot. & Nucleic Acids, 22, 45–62, (2003).
9. H. Xinjuan, H. Mingbao, Y. Dayu; Density function of 3'‐Azido‐2'‐deoxythymidine; Sci. China Serie B: Chemistry, 45, 470–474, (2002).
10. Javier Hernández, Humberto Soscún,and Alan Hinchliffe, The dipole polarazibility of the most stable conformation of 3'‐Azido‐2'‐deoxythymidine; Internet Electronic Journal of Molecular Design, Volume 2, Number 9, Pages 589–598, (2003).
11. M. Szafran, J. Koput, Z. Dega, A. Katrusiak , M. Pankowski and K. Stobiecka ; X‐ray, MP2, DFT studies of the structure and vibrational
spectra of trigonelliniumchloride; Chemical Physics, 289, 201‐219, (2003)
12. V.P. Roey, J.M. Salerno, W.L. Duax, C.K.Chu, M.K.Ahn, R.F. Schinazi; Solid state conformation of anti human
immunodeficiency virus type‐1 agents: Crystal structure of three AZT; J. Am. Soc, 110, 2277‐2282, (1988)
Fig 2: I. R. Spectra of 3'‐Azido‐2'‐deoxythymidine/ Zidovudine (AZT) Table 1. Optimized bond distances (in Angstrom Å), bond angles and torsion angles (in degrees °)of AZT.
Bond length ( A0 )
Bond Angle ( Degree )
Bond Experimental14
AM1 Calculation
PM3 Calculation
Bond Angle Experimental14 AM1 Calculation PM3 Calculation
C1‐N2 N2‐C3 C3‐N4 C5‐N4 C5‐C7 C7‐C1 C1‐O17 C7‐C8 C8‐H21 N2‐H18 C3‐O19 C5‐H20 N4‐C10 C10‐O9 C10‐C6 C6‐C12 C12‐C11 C11‐O9 C11‐C13 C13‐O15 C12‐N14 N14‐N16 N16‐N32 N32‐N14
1.384 1.368 1.372 1.386 1.332 1.197 1.503 1.201 1.463 1.391 1.535 1.529 1.414 1.515 1.405 1.467 1.231 1.100
1.391 1.391 1.391 1.391 1.391 1.391 1.107 1.542 1.694 1.095 1.095 1.095 1.456 1.401 1.598 1.581 1.946 1.511 1.591 1.483 1.492 1.316 1.245 1.729
1.3911.391 1.391 1.391 1.391 1.391 1.113 1.557 1.703 1.109 1.116 1.115 1.498 1.451 1.603 1.608 1.993 1.549 1.612 1.506 1.507 1.359 1.281 1.937
C1‐N2‐C3C1‐N2‐H18 N2‐C1‐O17 N2‐C3‐O19 C3‐N4‐C5 C7‐C8‐H21 H21‐C8‐H22 C7‐C5‐H20 C5‐N4‐C10 N4‐C10‐H27 N4‐C10‐O9 H27‐C10‐C6 C11‐O9‐C10 C10‐C6‐C12 C10‐C6‐H26 O9‐C11‐C12 C11‐C12‐C6 C11‐C13‐O15 C13‐O15‐H31 H30‐C13‐O15 C6‐C12‐N14 C5‐C7‐C1 C5‐C7‐C8 C13‐C11‐O9 N4‐C10‐C6 N14‐N16‐N32 N16‐N32‐N14 N32‐N14‐N16 N2‐C3‐N4
130.4 123.1 119.1 117.9 107.8 110.2 98.8 104.7 105.6 113.5 111.1 120.0 120.0 120.4 162.3 113.0
120.000 120.000 120.000 120.000 120.000 77.245 69.517 120.000 118.953 120.269 108.329 77.519 111.538 99.157 106.681 103.184 105.995 114.382 141.357 39.462 113.346 121.634 119.924 120.996 160.534 57.165 69.378 56.00 110.0
120.000120.000 120.010 120.00 120.060 78.058 70.349 121.658 119.359 121.647 109.264 76.927 112.327 100.062 106.992 104.194 104.367 115.216 140.581 40.421 114.624 120.347 120.068 120.624 159.458 58.619 70.058 55.0274 111.621
Table 2: Cartesian Coordinates
AM1 PM3
NO. ATOM X Y Z 1 C .0000 .0000 .0000 2 N 1.4008 .0000 .0000 3 C 2.1006 1.2117 .0000 4 N 1.4002 2.4246 .0000 5 C .0010 2.4250 .0000 6 C 4.2036 2.5236 .7786 7 C ‐.6994 1.2119 .0000 8 C ‐1.8025 1.2121 .0000 9 O 4.7145 1.1446 1.2160 10 C 5.0983 3.5291 1.5247 11 C 6.2287 1.3673 1.3141 12 C 6.3343 2.7396 1.9949 13 C 5.8960 .0270 1.3141 14 N 7.2137 4.1369 1.9949 15 O 6.5882 ‐1.0034 1.3141 16 N 6.4851 5.2408 1.9949 17 O ‐.5515 ‐.9553 .0000 18 H 1.9522 ‐.9554 .0000 19 O 3.2037 1.2117 .0000 20 H ‐.5504 3.3804 .0000 21 H ‐2.3927 .3261 .0000 22 H ‐2.9386 1.4685 .0000 23 H ‐2.7141 2.1686 .0000 24 H 7.1433 1.6133 1.3141 25 H 5.8477 2.2723 .3594 26 H 5.1078 2.5105 .3594 27 H 5.2926 4.3952 1.5247 28 H 3.6686 3.8305 .7786 29 H 5.1802 ‐.8574 1.3141 30 H 4.9213 .2590 1.3141 31 H 7.9281 ‐1.6039 1.3141 32 N 5.0070 6.0841 1.9949
NO. ATOM X Y Z 1 C .0000 .0000 .0000 2 N 1.4008 .0000 .0000 3 C 2.1006 1.2117 .0000 4 N 1.4002 2.4246 .0000 5 C .0010 2.4250 .0000 6 C 2.2467 3.4319 .8402 7 C ‐.6994 1.2119 .0000 8 C ‐1.8025 1.2121 .0000 9 O 2.8323 2.2889 1.6796 10 C 3.4668 4.2561 .3927 11 C 4.1331 1.9632 .9355 12 C 4.6962 3.3511 .5971 13 C 4.5736 1.1318 .9355 14 N 5.3458 3.6474 .5971 15 O 5.5266 .6188 .9355 16 N 5.1056 4.8577 .5971 17 N 4.5477 4.4753 .5971 18 O ‐.5515 ‐.9553 .0000 19 H 1.9522 ‐.9554 .0000 20 O 2.7078 1.1640 .0000 21 H ‐.5504 3.3804 .0000 22 H ‐1.7139 ‐.0315 .0000 23 H ‐2.3664 .4990 .0000 24 H ‐2.0873 1.9235 .0000 25 H 4.7343 2.5012 .9355 26 H 3.9969 2.8504 .5971 27 H 3.0875 3.5391 .2340 28 H 3.8512 4.6240 .3927 29 H 2.6679 3.9207 .8402 30 H 3.7636 .7315 .9355 31 H 5.2904 1.4621 .9355 32 H 6.4823 .6999 .9355
Table 3 Experimental, Calculated Frequencies and Potential Distribution in Zidovudine (AZT)
Assignment Experimental Frequencies
(in cm1−)
MOPAC Calculated Frequencies (in cm1−) Potential Energy
Distributionb
AM1 PM3 Atom Pair / Energy Contribution
(in %)a
Species a’
1 3468.99 3485.70 O15‐ H31 (99.5) νs (Hydroxyl Group) 2 3451.41 3356.85 N2‐H18 (99.3) νa (Thymine Ring) 3 3331.98 3294.36 015‐H31 (99.5) νa (Hydroxyl Group) 4 3190.12 3166.24 C10‐H27 (97.7) νa (Azide Ring) 5 3143.81 3087.32 C8‐H22 (32.9)
C8‐H21 (29.2) C8‐H23 (24.7)
νs (Thymine Ring)
6 3142.39 3077.40 C5 – H20 (86.0) νs (Thymine Ring) 7 3094.79 3073.82 C11‐H24 (54.9) νs 8 3084.79 3069.05 C6‐H26 (70.1)
C6‐H28 (28.4) νs (Furancose Ring)
9 3072.90 2993.62 C13‐H29 (92.1) νs (Hydroxyl Group) 10 3055.24 2988.79 C8‐H22 (55.8)
C8‐H21 (39.2) νs (Thymine Ring)
11 3039.39 2907.71 C8‐H23 (66.4) C8‐H21 (26.5)
νa (Thymine Ring)
12 3020.78 2805.41 C11‐H24 (38.8) νa (Furancose Ring)
13 3015.48 2639.90 C6‐H28 (68.4) C6‐H26 (29.8)
νa (Furancose Ring)
14 2512.86 2622.94 N16‐N32 (71.7) N14‐N16 (28.0)
νa (Azide Ring)
15 2170 2162.78 2163.94 C12‐N14 (23.6) νs (Furancose Ring) 16 1887 1842.68 1949.16 C10‐H27(42.2)
C12‐N14 (16.7) C11‐C12 (15.5)
β s + νs + νs (Furancose Ring)
17 1801 1811.70 1894.66 C5‐C7 (21.7) C3‐C5 (15.7) C3‐N4 (10.7)
β s + β s + νs (Thymine Ring)
18 1725 1728.36 1720.75 C3‐N4 (19) C3‐O19 (14.1)
β s + νs (Thymine Ring)
19 1623 1653.82 1605.83 C3‐N4 (14.8) C3‐O19 (18.1)
β a + νa (Thymine Ring)
20 1552.48 1543.15 N4‐C5 (24.1) C5‐C7 (15.6)
νs + νs (Thymine Ring)
21 1549.01 1532.50 O15‐H31 (50.3) C13‐H29 (11.5) C13‐O15 (11.1)
β s + β s + νs (Hydroxyl Group)
22 1539.82 1500.53 C12‐N14 (35.3) N14‐N16 (29.4)
νs + νs (Azide Ring)
23 1483 1479.92 1472.42 C13‐O15 (22.6) C11‐C13 (18.4) C13‐H29 (15.5)
νa + νa + β a (Hydroxyl Group)
24 1476.10 1469.10 C7‐C8 (25.7) C1‐C7 (15.0) C5‐C7 (13.2)
νs + νs+ νs (Thymine Ring)
25 1460.51 1451.15 C6‐H26 (20.1) C6‐C10 (16.8) C6‐H28 (15.8)
β s+ νs + β s (Furancose Ring)
26 1437.58 1425.70 N2‐H18 (29.2) N2‐C3 (10.4)
β s+ νs (Thymine Ring)
27 1436.61 1419.17 C11‐C12 (21.5) νs (Furancose Ring) 28 1414 1412.89 1429.43 C1‐C7 (13.1)
C8‐H22 (10.7) N2‐H18 (10.6)
νs + β s+ β s (Thymine Ring)
29 1395.64 1382.55 C6‐H28 (12.5) C6‐H26 (12.4)
β s+ β s (Furancose Ring)
30 1384.84 1377.64 C11‐H24 (17.9) β s (Furancose Ring)
31 1377.14 1370.14 C11‐H24 (14.9) β a (Furancose Ring)
32 1376.39 1364.90 C8‐H22 (34.9) C8‐H23 (21.5)
U (Thymine Ring)
33 1372.71 1360.08 C3‐O19 (11.5) β s (Thymine Ring) 34 1324 1320.69 1330.35 C13‐H29 (25.1)
C11‐C13 (13.8) β s + νs (Hydroxyl Group)
35 1318.57 1316.84 C1‐N2 (30.0) C1‐O17 (13.3) C1‐C7 (12.6)
νs + νs+ νs (Thymine Ring)
36 1286.42 1280.66 C5‐H20 (28.1) N2‐C3 (12.7) N4‐C5 (11.7)
β s + νs+ νs (Thymine Ring)
37 1281.31 1278.95 C13‐H29 (17.6) C12‐N14 (14.2)
β s (Hydroxyl Group) νs (Azide Ring)
38 1275.97 1269.91 C6‐H28 (23.8) C13‐H29 (22.6)
β s (Furancose Ring) β s (Hydroxyl Group)
39 1172.30 1174.33 C13‐H29 (19.6) C6‐H28 (10.0)
β a (Furancose Ring) β a (Hydroxyl Group)
40 1151 1171.21 1169.71 C11‐H24 (16.9) C11‐C13 (14.0)
β s (Furancose Ring) β s (Hydroxyl Group)
41 1118.52 1112.05 C11‐C13 (18.9) C11‐H24 (17.8)
β a (Hydroxyl Group) β a (Furancose Ring)
42 1106 1103.83 1110.50 C5‐H20 (22.5) C1‐N2 (14.4) C3‐N4 (14.3)
νs+ β s + νs (Thymine Ring)
43 1072.51 1062.79 C8‐H23 (36.6) C8‐H21 (21.0) C8‐H22 (17.3)
β s + β s+ β s (Thymine Ring)
44 1058.95 1049.28 C8‐H23 (11.5) C8‐H21 (24.7) C8‐H22 (26.8)
β a + β a+ β a (Thymine Ring)
45 1050.84 1034.86 C6‐C10 (19.5) C10‐H27 (10.6)
νs + β s (Furancose Ring)
46 1013 1012.02 1006.45 C6‐C10 (18.6) C6‐H26 (17.2) C6‐H28 (15.9)
νs+ β s+ β s (Furancose Ring)
47 1001 966.26 976.38 C11‐H24 (24.1) C11‐C12 (19.2)
β s+ νs (Furancose Ring)
48 927 922.03 931.15 C1‐C7 (12.9) β s (Thymine Ring) 49 854.58 863.26 C5‐C7 (13.6) β a (Thymine Ring)
50 694.90 715.21 C6‐C10 (11.0) β s (Furancose Ring)
51 574 574.24 562.87 C13‐O15 (18.7) C11‐C13 (16.2)
rocking (Hydroxyl Group)
52 482 490.62 450.83 C1‐C7 (10.5) β s (Thymine Ring) 53 456.07 417.07 O15‐H31 (22.4) β s (Hydroxyl Group) 54 417.19 402.02 N14‐N16 (11.8) νs (Azide Group) 55 367.44 354.55 C3‐015 (37.0) β s (Hydroxyl Group) 56 322.41 362.60 N14‐N16 (21.9) β a (Azide Group) 57 311 305.67 317.91 C6‐C10 (14.5)
C6‐H28 (21.1) C6‐H26 (18.9)
β s + β s+ β s (Furancose Ring)
58 236.18 225.89 C6‐C10 (24.5) C6‐H28 (20.1) C6‐H26 (19.9)
β a + β a+ β a (Furancose Ring)
59 144.79 15.47 C6‐C10 (13.4) C10‐H27 (13.0)
β s+ βs (Furancose Ring)
60 112.24 77.84 C7‐C8 (24.5) C8‐H21 (21.2) C8‐H22 (20.5)
β a + β a (Thymine Ring)
Assignment Experimental Frequencies
(in cm1−)
MOPAC Calculated Frequencies (in cm1−) Potential Energy
Distribution
AM1 PM3 Atom Pair / Energy Contribution (in %)
Species a’’́
1 1387 1381.07 1373.55 C8‐H21 (47.9) C8‐H23 (35.4)
γs (Thymine Ring)
2 1350.60 1363.73 C6‐H28 (17.3) C6‐H26 (15.0)
γs (Furancose Ring)
3 1246.77 1274.74 C13‐H29 (54.1) O15‐H31 (12.7)
γs + γs (Hydroxyl Group)
4 1191 1213.16 1206.15 C6‐H26 (27.1) C10‐H27 (11.8) C13‐H29 (11.8)
γa (Furancose Ring) γa (Hydroxyl Group)
5 914 944.84 981.27 C5‐H20 (65.0) γs (Thymine Group) 6 857.71 885.26 C6‐C10 (11.9) γs (Furancose Ring) 7 817 815.85 813.62 C10‐H27 (24.8)
C6‐H26 (13.9) C6‐H28 (13.7)
γs (Furancose ring)
8 741 752.51 797.30 C1‐C7 (31.7) C1‐N2 (21.6) C1‐O17 (21.5)
γs (Thymine Group)
9 696.64 699.38 C3‐N4 (27.3) N2‐C3 (21.3) C3‐O19 (20.8)
γs (Thymine Group)
10 696.22 671.40 N2‐H18 (80.2) γs (Thymine Group) 11 607 624.34 647.93 C1‐N2 (21.1)
N2‐C3 (14.8) C1‐C7 (13.8)
γa (Thymine Group)
12 563.95 562.70 C3‐C5 (14.5) Rocking (Thymine Ring)
13 537.38 555.47 C6‐C10 (11.6) γa (Furancose Ring)
14 486.23 489.36 C11‐H24 (11.3) γs Scissoring (Furancose Ring)
15 461.91 453.46 C12‐N14 (12.0) C11‐C12 (10.2)
γa Scissoring (Furancose Ring)
16 441 448.37 432.65 N16‐N32 (52.0) N14‐N16 (41.6)
γs Scissoring (Azide Ring)
17 406 427.19 412.02 N14‐N16 (11.8) γa Scissoring (Azide Ring)
18 355 344.89 394.32 O15‐H31 (21.8) N14‐N16(13.2)
γs (Hydroxyl Group) γs (Azide Ring)
19 337.41 377.95 C7‐C8 (20.5) N4‐C5 (13.0)
γs (Thymine Ring)
20 180.47 191.89 O9‐C110 (12.1) O9‐C11 ( 11.4)
γs (Furancose Ring)
21 167.09 183.81 C1‐N2 (20.3) N2‐C3 (20.0) N2‐H18 (17.7)
γa (Thymine Ring)
22 106.61 116.5 C11‐C12 (21.4) C11‐C13 (20.6) C11‐H24 (18.8)
γs (Furancose Ring)
23 81.07 71.33 C3‐O19 (13.6) γs (Thymine Ring) 24 50.97 47.41 C13‐O15 (19.0)
C11‐C13 (16.2) O15‐H31 (11.9)
γa ( Hydroxyl Group)
25 38.55 33.11 C13‐O15 (17.5) C11‐C13 (12.9)
Rocking (Hydroxyl Group)
26 29.21 27.21 C7‐C1 ( 19.8) C7‐C5 (17.3) C7‐C8 (12.6)
Rocking (Thymine Ring)
27 28.56 26.8 C10‐O9 (18.6) C10‐C6 (16.5) C10‐H27 (12.9)
Rocking (Azide Ring)
28 17.86 18.42 C8‐H21(15.6) C8‐H23 (14.9) C8‐C7 (11.60
Rocking (Thymine Ring)
29 12.50 13.6 Twisting 30 10.10 10.8 Twisting
a Only contributions > 10% are listed b ν = stretching,β= in‐plane bending, γ=out‐of‐plane bending, s= symmetric, a= asymmetric
Fig 3: Correlation Diagram for Experimental Vs Calculated Frequencies (AM1 method)
Fig :4 Correlation Diagram for Experimental Vs Calculated Frequencies (PM3 method)