Low-lying excited states and nonradiative processes of 9-methyl-2-aminopurine

Trachsel, Maria Angela; Lobsiger, Simon; Schär, Tobias; Leutwyler, Samuel

doi:10.1063/1.4862913

Cited by 7 publications

(4 citation statements)

References 27 publications

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“…52 Analogous excitations of a″ vibrational fundamentals coupled to internal-rotation states have been assigned in the UV spectra of the methyl-rotor molecules 2,6-difluorotoluene 53 and 9-methyl-2-aminopurine. 54 As discussed in section 4.4, the coupled a″ vibrational/internal-rotational levels must be classified in the MS group C 6v (M). A number of possible internal-rotation/a″-vibration combination bands that can arise in this way are indicated in the right half of Figure 9.…”

Section: Resultsmentioning

confidence: 99%

“…(2) Independently, Δv = 1 excitations may occur via coupling of a ′ vibrational fundamentals with suitable θ′ internal-rotation levels . Analogous excitations of a ″ vibrational fundamentals coupled to internal-rotation states have been assigned in the UV spectra of the methyl-rotor molecules 2,6-difluorotoluene and 9-methyl-2-aminopurine . As discussed in section , the coupled a ″ vibrational/internal-rotational levels must be classified in the MS group C 6 v (M).…”

Section: Experimental Resultsmentioning

confidence: 99%

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Modeling the Histidine–Phenylalanine Interaction: The NH···π Hydrogen Bond of Imidazole·Benzene

et al. 2015

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NH···π hydrogen bonds occur frequently between the amino acid side groups in proteins and peptides. Data-mining studies of protein crystals find that ∼80% of the T-shaped histidine···aromatic contacts are CH···π, and only ∼20% are NH···π interactions. We investigated the infrared (IR) and ultraviolet (UV) spectra of the supersonic-jet-cooled imidazole·benzene (Im·Bz) complex as a model for the NH···π interaction between histidine and phenylalanine. Ground- and excited-state dispersion-corrected density functional calculations and correlated methods (SCS-MP2 and SCS-CC2) predict that Im·Bz has a Cs-symmetric T-shaped minimum-energy structure with an NH···π hydrogen bond to the Bz ring; the NH bond is tilted 12° away from the Bz C6 axis. IR depletion spectra support the T-shaped geometry: The NH stretch vibrational fundamental is red shifted by -73 cm(-1) relative to that of bare imidazole at 3518 cm(-1), indicating a moderately strong NH···π interaction. While the S0(A1g) → S1(B2u) origin of benzene at 38 086 cm(–1) is forbidden in the gas phase, Im·Bz exhibits a moderately intense S0 → S1 origin, which appears via the D(6h) → Cs symmetry lowering of Bz by its interaction with imidazole. The NH···π ground-state hydrogen bond is strong, De=22.7 kJ/mol (1899 cm–1). The combination of gas-phase UV and IR spectra confirms the theoretical predictions that the optimum Im·Bz geometry is T shaped and NH···π hydrogen bonded. We find no experimental evidence for a CH···π hydrogen-bonded ground-state isomer of Im·Bz. The optimum NH···π geometry of the Im·Bz complex is very different from the majority of the histidine·aromatic contact geometries found in protein database analyses, implying that the CH···π contacts observed in these searches do not arise from favorable binding interactions but merely from protein side-chain folding and crystal-packing constraints. The UV and IR spectra of the imidazole·(benzene)2 cluster are observed via fragmentation into the Im·Bz+ mass channel. The spectra of Im·Bz and Im·Bz2 are cleanly separable by IR hole burning. The UV spectrum of Im·Bz2 exhibits two 000 bands corresponding to the S0 → S1 excitations of the two inequivalent benzenes, which are symmetrically shifted by -86/+88 cm(-1) relative to the 000 band of benzene

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Section: Resultsmentioning

confidence: 99%

Section: Experimental Resultsmentioning

confidence: 99%

Modeling the Histidine–Phenylalanine Interaction: The NH···π Hydrogen Bond of Imidazole·Benzene

et al. 2015

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“…This dependence results from the fact that the conical intersections that mediate IC occur at molecular geometries that differ strongly from ground state minimum geometries. Therefore, the excited state dynamics of nucleobases can differ drastically for different derivatives, − analogues, − and even tautomers. − Many derivatives and analogues of the canonical nucleobases that could serve as alternative bases lack the UV protection afforded by rapid internal conversion. This difference suggests a possible prebiotic photochemical selection of nucleobases on an early earth.…”

Section: Introductionmentioning

confidence: 99%

Excited State Dynamics of 6-Thioguanine

et al. 2017

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Here we present the excited state dynamics of jet-cooled 6thioguanine (6-TG), using resonance-enhanced multiphoton ionization (REMPI), IR−UV double resonance spectroscopy, and pump−probe spectroscopy in the nanosecond and picosecond time domains. We report data on two thiol tautomers, which appear to have different excited state dynamics. These decay to a dark state, possibly a triplet state, with rates depending on tautomer form and on excitation wavelength, with the fastest rate on the order of 10 10 s −1 . We also compare 6-TG with 9-enolguanine, for which we observed decay to a dark state with a 2 orders of magnitude smaller rate. At increased excitation energy (∼+500 cm −1 ) an additional pathway appears for the predominant thiol tautomer. Moreover, the excited state dynamics for 6-TG thiols is different from that recently predicted for thiones.

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“…A mixed symmetric quartic-harmonic potential of the form V = z 4 + Bz 2 (in reduced coordinates) has been used . Such a form of the potential has been successfully applied for ring puckering modes active in the vibronic spectrum of many systems. − The existence of two symmetry equivalent distorted structures implies that only even levels (Δν = 0, 2, 4, ...) of such vibrational modes are active in the excitation from a planar ground state. In the case of high inversion barrier, pairs of these levels are practically degenerate and spacing of low-energy levels is well approximated by harmonic frequency calculations within one of two minima.…”

Section: Resultsmentioning

confidence: 98%

Supersonic Jet Spectroscopy and Density Functional Theory Study of Isomeric Diazines: 1,4- and 1,8-Diazatriphenylene. Why Do They Differ So Deeply?

et al. 2016

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We report on laser-induced fluorescence excitation and dispersed fluorescence spectra of two isomeric compounds: 1,4- and 1,8-diazatriphenylene (1,4- and 1,8-DAT) isolated in supersonic molecular jets, and their 1:1 complexes with protic solvents. We found that the ground and excited state vibronic patterns of bare 1,4-DAT differ significantly from those of 1,8-DAT, and those of the complexes of both isomers. A marked activity of several out-of-plane vibrations in 1,4-DAT and the symptoms of the distortion of the S excited molecule were diagnosed from the vibronic spectra, whereas planar structures were predicted for 1,8-DAT in S and S states. An anharmonic double-minimum potential along an out-of-plane coordinate has been derived and used to predict higher overtones of the S state vibration at 113 cm. Large enhancement of fluorescence was observed upon formation of 1:1 complexes of 1,4-DAT with water or methanol, which is explained in terms of an increased separation of interacting (n,π*) and (π,π*) electronic states in the H-bonded complexes, and/or a suppression of the intersystem crossing process.

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Low-lying excited states and nonradiative processes of 9-methyl-2-aminopurine

Cited by 7 publications

References 27 publications

Modeling the Histidine–Phenylalanine Interaction: The NH···π Hydrogen Bond of Imidazole·Benzene

Modeling the Histidine–Phenylalanine Interaction: The NH···π Hydrogen Bond of Imidazole·Benzene

Excited State Dynamics of 6-Thioguanine

Supersonic Jet Spectroscopy and Density Functional Theory Study of Isomeric Diazines: 1,4- and 1,8-Diazatriphenylene. Why Do They Differ So Deeply?

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