Ab initio and DFT studies of the structure and vibrational spectra of anhydrous caffeine

Srivastava, Santosh K.; Singh, Vipin Bahadur

doi:10.1016/j.saa.2013.06.005

Cited by 32 publications

(44 citation statements)

References 40 publications

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“…Calculated DFT-B3LYP/6-311++G(d,p) vibrational wave numbers are found to be slightly larger than the fundamental modes. 12 Changes in the harmonic wave numbers of NH and carbonyl stretching modes due to different conformations of caffeine were found to be about 2-3 cm À1 , however symmetric CH 3 stretching vibrations were appreciably changed by 7 cm À1 . However, our earlier report 12 is in good agreement with Pavel et al 42 and Nyquist and Feidler 43 experimental results (observed in solutions and condensed phase), in which the two C]O groups couple into an in phase C]O stretching vibration and an out of phase stretching vibrations.…”

Section: Ground-state Optimized Geometries Of Caffeinementioning

confidence: 90%

“…In the last decade, photochemistry of nucleic acid bases and related molecular systems have been extensively studied with experimental and theoretical methods. Caffeine (1,3,7trimethyl-xanthine), the most widely consumed psychoactive stimulant [12][13][14] in the world, has the shortest life time (0.54 ps) 9 in the studied lowest excited state ( 1 pp*) among all the methyl xanthine compounds. 1,6 In this regard photo dynamics of nucleic acid analogue, xanthine (3,7-dihydro-purine-2,6-dione), plays an important role with the goal of transferring the experience obtained in these simpler systems to more complex situation found in DNA.…”

Section: Introductionmentioning

confidence: 99%

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Spectroscopic signatures and structural motifs in isolated and hydrated caffeine: a computational study

Singh

2014

RSC Adv.

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The conformational landscapes of neutral caffeine and its hydrated complex have been investigated by MP2 and DFT methods. The ground state geometry optimization yields six lowest energy structures for bare caffeine and five lowest energy conformers of the caff 1 -(H 2 O) 1 complex at the MP2/6-311++G(d,p) level of theory for the first time. We investigated the low-lying excited states of bare caffeine by means of coupled cluster singles and approximate doubles (CC2) and TDDFT methods and a satisfactory interpretation of the electronic absorption spectra (Phys. Chem. Chem. Phys., 2012, 14, 10677-10682) is obtained. The difference between the S 0 -S 1 transition energy due to the most stable and the least stable conformation of caffeine was found to be $859 cm À1 . One striking feature is the coexistence of the blue and red shift of the vertical excitation energy of the optically bright state S 1 ( 1 pp*) of caffeine upon forming a complex with a water at isolated and conjugated carbonyl sites, respectively. The lowest singlet pp* excited-state of the caff 1 -(H 2 O) 1 complex involving isolated carbonyl is strongly blue shifted which is in agreement with the result of R2PI spectra of singly hydrated caffeine (J. Chem. Phys., 2008, 128, 134310). While for the most stable and the second most stable caff 1 -(H 2 O) 1 complexes involving conjugated carbonyl, the lowest singlet pp* excited-state is red shifted. The effect of hydration on the S 1 ( 1 pp*) excited state due to the bulk water environment was mimicked by a combination of a polarizable continuum solvent model (PCM) and a conductor like screening model (COSMO), which also shows a blue shift in accordance with the result of electronic absorption spectra in an aqueous solution (Phys.Chem. Chem. Phys., 2012, 14, 10677-10682). This hypsochromic shift is expected to be the result of the changes in the p-electron delocalization extent of the molecule because of hydrogen bond formation. † Electronic supplementary information (ESI) available: The structural parameters, selected harmonic wave number and rotational constants of all six conformers caffeine at MP2/6-311++G(d,p) level. See

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Section: Ground-state Optimized Geometries Of Caffeinementioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Spectroscopic signatures and structural motifs in isolated and hydrated caffeine: a computational study

Singh

2014

RSC Adv.

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“…Similar to caffeine 42,43 , theophylline possesses three main sites for hydration, into which a water molecule can bind strongly: (1) the C(6) carbonyl group (2) the C(2) carbonyl and (3) the N 9 atom. Figure Table 2.We find that M06-2X method give energy value more near to MP2 in comparison to other DFT functionals and can perform much better for H-bonded systemss.…”

Section: Optimized Geometries Of Monohydrated Complexes Of Theophmentioning

confidence: 99%

“…As mentioned in the earlier section 3.1 that the two 9 C=O groups in theophylline is coupled into an in-phase (C=O) 2 stretching vibration and an out of phase (C=O) 2 stretching vibration modes and the out of phase (C=O) 2 stretching mode is observed at a lower frequency than the in-phase mode. 42 It seems that the C 6 -O 13 carbonyl, stretching mode strongly mixes with the C=C stretching mode to give rise out of phase ( lower frequency) C=O stretching band. It was reported that the valence bond electron delocalization through the central N 1 atom favors lower energy for the coupled out of phase (C=O) 2 stretching mode in caffeine.…”

Section: Optimized Geometries Of Monohydrated Complexes Of Theophmentioning

confidence: 99%

Spectroscopic signatures and structural motifs in isolated and hydrated theophylline: a computational study

Singh

2015

RSC Adv.

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The spectra and structures of theophylline monomer and dimer and their hydrated complex have been investigated by MP2 and DFT methods. The ground state geometry optimization yield five lowest energy conformers of Tph 1 -(H 2 O) 1 complex at the M06-2X/6-311++G(d,p) level of theory for the first time. We investigated the low-lying excited states of bare theophylline by means of coupled cluster singles and approximate doubles (CC2) and TDDFT methods and a satisfactory interpretation of the electronic absorption spectra (Phys. Chem. Chem. Phys., 2012,14,10677-10682) is obtained. One striking feature is the coexistence of the blue and red shift of the vertical excitation energy of the optically bright state S 1 ( 1 ππ* ) of theophylline upon forming complex with a water at C 2 =O and C 6 =O carbonyl sites, respectively. The optimized structure of newly characterized theophylline dimer Form IV,computed the first time by MP2 and DFT methods. The binding energy of this dimer linked by double N-H…O=C hydrogen bonds was found to be 88 kj/mole at the MP2/6-311++G(d,p) level of theory. The geometry optimization of dimer Form M has also been performed and found that further stability is being conferred to the dimer IV after hydration. Computed IR spectra is found in remarkable agreement with the experiment (Cryst. Growth Des. 2010, 10, 3879-3886) and the out of phase (C=O) 2 stretching mode shows tripling of intensity upon dimerisation. The vertical excitation energy of the optically bright state S 1 ( 1 ππ* ) of theophylline monomer upon forming dimer IV is shifted towards red as well as blue.

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“…This molecule show many important biological and pharmacological activities, which was the point of interest for several theoretical studies, using DFT, Hartree-Fock (HF) and second-order perturbation theory (MP2) to analyze its vibrational spectrum, molecular structure, electronic excitation energies, density maps, and NMR. [7][8][9][10][11][12] We investigated the effects of several methods and basis set in quantum chemical descriptors, i.e., ionization potential, electron affinity, chemical hardness, chemical potential and global philicity index for the caffeine molecule, C 8 H 10 N 4 O 2 . Principal component analysis (PCA) was used to correlate the descriptors used in this work.…”

mentioning

confidence: 99%

Chemical Reactivity Indices of the Caffeine Molecule

Almeida¹,

Barbosa²,

Santos³

et al. 2016

Revista Virtual De Química

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Resumo: Apresentamos neste trabalho uma análise da molécula de cafeína usando funções de base difusas e polarizadas, 6-31++G(d,p) e aug-cc-pVDZ, assim como a função de base D95V, combinadas com os métodos HF, MP2 e DFT. O objetivo foi investigar os efeitos destes métodos e funções de base nos descritores químico-quânticos, potencial de ionização, afinidade eletrônica, dureza química, potencial químico e filicidade global da molécula de cafeína, C 8 H 10 N 4 O 2 . A análise de componentes principais foi realizada para correlacionar os resultados. Também realizamos análise de cargas atômicas calculadas com os métodos de Mulliken, MerzKollman e orbitais atômicos naturais.Palavras-chave: NBO; reatividade química; MP2; DFT. AbstractIn this paper we present an analysis of the caffeine molecule using diffuse and polarized basis functions, 6-31++G(d,p) and aug-cc-pVDZ, as well as theD95V basis set, combined with the HF, MP2 and DFT methods. The aim was to investigate the effects of these methods and basis sets in quantum chemical descriptors, e.g., ionization potential, electron affinity, chemical hardness, chemical potential and global philicity index of the caffeine molecule, C 8 H 10 N 4 O 2 . A principal component analysis was performed to correlate the results. We have also carried out population analysis of atomic charges with Mulliken, Merz-Kollman and Natural Atomic Orbital methods.

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Ab initio and DFT studies of the structure and vibrational spectra of anhydrous caffeine

Cited by 32 publications

References 40 publications

Spectroscopic signatures and structural motifs in isolated and hydrated caffeine: a computational study

Spectroscopic signatures and structural motifs in isolated and hydrated caffeine: a computational study

Spectroscopic signatures and structural motifs in isolated and hydrated theophylline: a computational study

Chemical Reactivity Indices of the Caffeine Molecule

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