Theoretical study of valance photoelectron spectra of hypoxanthine, xanthine, and caffeine using direct symmetry‐adapted cluster/configuration interaction methodology

Farrokhpour, Hossein; Fathi, F.

doi:10.1002/jcc.21832

Cited by 21 publications

(18 citation statements)

References 27 publications

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“…For comparison with the TDDFT results, the CC2 vertical excitation energies of the lowest energy conformer A of caffeine calculated at CC2-optimized S 0 geometry are also given in Table 2. Reported photoelectron spectra 40,45 and NBO calculations also show that the HOMO in caffeine molecule is formed mainly from p C4-C5 bonding orbital, and shape of the HOMO of hypoxanthine, xanthine and caffeine were found very similar. 40 B3LYP-TDDFT and CC2 VEE for the optically bright lowest singlet excited state predicted at 4.51-4.60 eV and 4.58 eV respectively (with an oscillator strength $0.14), are found consistent with the longer wavelength absorption peak of caffeine at 4.54 eV.…”

Section: Vertical Excitation Energies Of Caffeinementioning

confidence: 86%

“…The observed UV-absorption peaks 9 are analyzed and assigned well by TD-DFT/CC2 vertical electronic excitation energies (VEE), and molecular orbital calculations of caffeine. 40 The energy gap between HOMO and LUMO of the most stable conformer A was found to be 5.09 eV at B3LYP/TZVP and DFT-D/ TZVP levels of theory. 9,12 The highest occupied molecular orbital (HOMO) of caffeine is a p-orbital.…”

Section: Vertical Excitation Energies Of Caffeinementioning

confidence: 97%

“…† As seen in Table 1, the relative energy obtained by DFT employing M06-2X functional is found more near to MP2 value in comparison to other DFT (X3LYP, B3LYP, B3PW91) values. 40 Caffeine has two carbonyl groups, C 2 -O 11 (isolated carbonyl) and C 6 -O 13 (conjugated carbonyl), joined to N 1 atom, as shown in Fig. 1.…”

Section: Ground-state Optimized Geometries Of Caffeinementioning

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: Vertical Excitation Energies Of Caffeinementioning

confidence: 86%

Section: Vertical Excitation Energies Of Caffeinementioning

confidence: 97%

Section: Ground-state Optimized Geometries Of Caffeinementioning

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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“…This leads to remarkable changes in the electronic structure. The most obvious one is the extraordinary increase in acidity (p K

≈ 5.7) compared to all common other purine bases (e.g., p K

≈ 9.2 for guanosine), which has been shown in investigations of the gas and solution phase structures [ 3 , 4 , 5 , 6 , 7 , 8 , 9 ] and in experimental [ 10 , 11 , 12 , 13 ] and theoretical [ 14 ] investigations of its electronic properties.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast Electronic Deactivation Dynamics of Xanthosine Monophosphate

et al. 2017

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Ultrafast energy dissipation is a crucial factor for the photostability of DNA and RNA, but even some of the key electronic deactivation pathways in monomeric nucleic acid building stones are still controversial. Here, we report on the excited-state dynamics of the rare nucleotide xanthosine monophosphate as a function of deprotonation state (XMP vs. XMP−) and excitation wavelength (λpump= 278–243 nm) by femtosecond time-resolved fluorescence and absorption spectroscopy. We show that the predominating relaxation channel leads to a return of the photo-excited molecules to the electronic ground state in τ∼1 ps. The mechanism likely involves an out-of-plane deformation of the five-membered ring, different from the main electronic deactivation pathways in the canonical purine bases adenine and guanine. The results are discussed in terms of the structural and electronic differences of XMP compared to the canonical nucleotides.

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“…Vianna and Machado [8] show that the recent experience of forming a new political agreement at federal level revealed the importance of the federal administration in the formulation and regulation of public policies--something that it not incompatible with sectoral decentralization policies.…”

Section: Introductionmentioning

confidence: 99%

Human resources for health and decentralization policy in the Brazilian health system

Pierantoni

García

2011

Hum Resour Health

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BackgroundThe Brazilian health reform process, following the establishment of the Unified Health System (SUS), has had a strong emphasis on decentralization, with a special focus on financing, management and inter-managerial agreements. Brazil is a federal country and the Ministry of Health (MoH), through the Secretary of Labour Management and Health Education, is responsible for establishing national policy guidelines for health labour management, and also for implementing strategies for the decentralization of management of labour and education in the federal states. This paper assesses whether the process of decentralizing human resources for health (HRH) management and organization to the level of the state and municipal health departments has involved investments in technical, political and financial resources at the national level.MethodsThe research methods used comprise a survey of HRH managers of states and major municipalities (including capitals) and focus groups with these HRH managers - all by geographic region. The results were obtained by combining survey and focus group data, and also through triangulation with the results of previous research.ResultsThe results of this evaluation showed the evolution policy, previously restricted to the field of 'personnel administration', now expanded to a conceptual model for health labour management and education-- identifying progress, setbacks, critical issues and challenges for the consolidation of the decentralized model for HRH management. The results showed that 76.3% of the health departments have an HRH unit. It was observed that 63.2% have an HRH information system. However, in most health departments, the HRH unit uses only the payroll and administrative records as data sources. Concerning education in health, 67.6% of the HRH managers mentioned existing cooperation with educational and teaching institutions for training and/or specialization of health workers. Among them, specialization courses account for 61.4% and short courses for 56.1%.ConclusionsDue to decentralization, the HRH area has been restructured and policies beyond traditional administrative activities have been developed. However, twenty years on from the establishment of the SUS, there remains a low level of institutionalization in the HRH area, despite recent efforts of the MoH.

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Theoretical study of valance photoelectron spectra of hypoxanthine, xanthine, and caffeine using direct symmetry‐adapted cluster/configuration interaction methodology

Cited by 21 publications

References 27 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

Ultrafast Electronic Deactivation Dynamics of Xanthosine Monophosphate

Human resources for health and decentralization policy in the Brazilian health system

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