TY - JOUR

T1 - Theoretical density functional and ab initio computational study of the tautomeric, vibrational and H-bond properties of 1,7-di-CH3-guanine

T2 - A comparison with FT-IR data from matrix isolation experiments

AU - Smets, J.

AU - Schoone, K.

AU - Ramaekers, R.

AU - Adamowicz, L.

AU - Maes, G.

N1 - Funding Information:
This work was supportedb y the ECC ("S&T Cooperation with Central and Eastern European Countries") Research Project (ERB CIPA-CT 93-0108) and by the NATO InternationaCl ollaboration Grant INT-9313268. L. Adamowicz acknowledges the Office of Health and EnvironmentaRl esearch, the Office of Energy Research, Departmento f Energy (Grant No. DEFG 0393ERG1605)G. . Maes and K. Schoone ackowledgeth e Flemish FWO for their ResearchF ellowships.

PY - 1998/2/3

Y1 - 1998/2/3

N2 - In this work we report the results of a combined matrix-isolation FT-IR and theoretical computational DFT and ab initio study of the tautomeric and vibrational characteristics of 1,7-dimethyl-guanine (17DMG). The HF, MP2 and DFT methods are all in agreement in predicting that the amino-oxo tautomer of 17DMG is the most stable form, and that the imino-oxo tautomer, which can exist in two different geometrical isomers, is the second most stable form. The energy difference between the amino-oxo and amino-oxo tautomer is rather large: 23, 25 and 33 kJ mol-1, for the HF, DFT and MP2 methods, respectively. The imino-hydroxy tautomer is, according to the calculations, by far the least stable form (ΔE > 180 kJ mol-1). The FT-IR spectra of 17DMG isolated in an argon matrix are in agreement with the theoretical calculation indicating that only the amino-oxo tautomer should be present in the gas phase in detectable amounts. The experimental IR frequencies agree quite well with the theoretical values. When a single scaling factor is applied to approximately correct the calculated frequencies for various systematic errors in theoretical approach, the mean frequency deviations for the HF/6-31++G**, DFT /6-31G** and DFT/6-31++G** calculated spectra are 17.5 cm-1, 12.2 cm-1 and 16.3 cm-1, respectively. The DFT mean-frequency-deviations decrease to 8.1 cm-1 and 10.1 cm-1 when variable factors are applied. The stabilities of the different water complexes of the amino-oxo tautomer of 17DMG are investigated by optimizing the complexes at the HF/6-31++G** level of theory and calculating the MP2 energies at these optimized geometries. The N3...HO-H complex, which has a close structure with two H-bonds, is predicted to be the most stable structure. The MP2 calculated energy differences between the most stable complex and the C6=O...HO-H, the H-NH...OH2 and the H2N...HO-H hetero-dimers are 14.28 kJ mol-1, 1954 kJ mol-1 and 20.73 kJ mol-1, respectively.

AB - In this work we report the results of a combined matrix-isolation FT-IR and theoretical computational DFT and ab initio study of the tautomeric and vibrational characteristics of 1,7-dimethyl-guanine (17DMG). The HF, MP2 and DFT methods are all in agreement in predicting that the amino-oxo tautomer of 17DMG is the most stable form, and that the imino-oxo tautomer, which can exist in two different geometrical isomers, is the second most stable form. The energy difference between the amino-oxo and amino-oxo tautomer is rather large: 23, 25 and 33 kJ mol-1, for the HF, DFT and MP2 methods, respectively. The imino-hydroxy tautomer is, according to the calculations, by far the least stable form (ΔE > 180 kJ mol-1). The FT-IR spectra of 17DMG isolated in an argon matrix are in agreement with the theoretical calculation indicating that only the amino-oxo tautomer should be present in the gas phase in detectable amounts. The experimental IR frequencies agree quite well with the theoretical values. When a single scaling factor is applied to approximately correct the calculated frequencies for various systematic errors in theoretical approach, the mean frequency deviations for the HF/6-31++G**, DFT /6-31G** and DFT/6-31++G** calculated spectra are 17.5 cm-1, 12.2 cm-1 and 16.3 cm-1, respectively. The DFT mean-frequency-deviations decrease to 8.1 cm-1 and 10.1 cm-1 when variable factors are applied. The stabilities of the different water complexes of the amino-oxo tautomer of 17DMG are investigated by optimizing the complexes at the HF/6-31++G** level of theory and calculating the MP2 energies at these optimized geometries. The N3...HO-H complex, which has a close structure with two H-bonds, is predicted to be the most stable structure. The MP2 calculated energy differences between the most stable complex and the C6=O...HO-H, the H-NH...OH2 and the H2N...HO-H hetero-dimers are 14.28 kJ mol-1, 1954 kJ mol-1 and 20.73 kJ mol-1, respectively.

KW - Ab initio calculation

KW - Density functional theory

KW - Hydrogen bonding

KW - Tautomerism

KW - Vibration spectrum

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U2 - 10.1016/S0022-2860(97)00334-7

DO - 10.1016/S0022-2860(97)00334-7

M3 - Article

AN - SCOPUS:0032477923

VL - 442

SP - 201

EP - 220

JO - Journal of Molecular Structure

JF - Journal of Molecular Structure

SN - 0022-2860

IS - 1-3

ER -