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Five isomers of monomeric cytosine and their interconversions induced
Lapinski, Leszek; Igor Reva, Igor Reva; Nowak, Maciej J.; Fausto, RuiPhotoisomerization processes involving five isomers of cytosine were induced by narrowband tunable UV irradiation of matrix-isolated monomers of the compound. Irradiation of an argon matrix containing cytosine monomers with UV l = 313 nm laser light resulted in syn2anti photoisomerizations between the two imino–oxo forms, whereas the substantially more populated amino–hydroxy and amino–oxo forms stayed intact. ...
Infrared Spectra and Photochemistry of Matrix-Isolated Pyrrole-2-carbaldehyde
Giuliano, Barbara Michela; Reva, Igor; Fausto, RuiMonomeric pyrrole-2-carbaldehyde (P2C) was isolated in low-temperature argon and xenon matrices, and its UV-induced photochemistry was studied. The structures of the reagent as well as the reaction photoproducts were characterized by FTIR spectroscopy. Interpretation of the experimental results was assisted by theoretical calculations carried out at the MP2 and DFT (B3LYP) levels with the 6-311++G(d,p) basis se...
Thermal and Photoinduced Control of Relative Populations of 4-Methoxybenzaldehy...
Kus, Nihal; Sharma, Archna; Reva, Igor; Lapinski, Leszek; Fausto, RuiTwo almost isoenergetic conformers of 4-methoxybenzaldehyde (p-anisaldehyde), O-trans and O-cis, are nearly equally populated in gas phase at room temperature. The existence of these two conformers of similar energy makes p-anisaldehyde an attractive molecule for conformational investigations, in which the relative populations of the two forms might be subjected to optical control. In the present study, monomer...
Positive Identification of UV-Generated, Non-Hydrogen-Bonded Isomers of o-Hydro...
Lapinski, Leszek; Rostkowska, Hanna; Reva, Igor; Fausto, Rui; Nowak, Maciej J.Non-hydrogen-bonded isomers were photogenerated by UV (λ > 335 nm) irradiation of o-hydroxybenzaldehyde (salicylaldehyde) and o-hydroxyacetophenone monomers isolated in low-temperature Ar matrixes. These photoisomerizations were found to be photoreversible. Upon shorter wavelength (λ > 235 nm or λ > 270 nm) UV irradiation, the initial forms of the compounds (with intramolecular hydrogen bonds) were partially re...
Infrared spectra of methyl isocyanate isolated in Ar, Xe and N2 matrices
Reva, Igor; Lapinski, Leszek; Fausto, RuiThe infrared spectra of methyl isocyanate monomer isolated in cryogenic argon, xenon and nitrogen matrices were studied. Interpretation of the experimental results was supported by harmonic and anharmonic calculations carried out at the DFT, MP2 and CCSD levels of approximation. Spectral indicators of the molecule structural flexibility were examined, the most striking of these being the multiplet structure of ...
NIR-laser-induced selective rotamerization of hydroxy conformers of cytosine
Lapinski, Leszek; Nowak, Maciej J.; Reva, Igor; Rostkowska, Hanna; Fausto, RuiThe relative populations of two amino-hydroxy conformers of cytosine, differing in rotation of the OH group by 180°, were selectively and repeatedly manipulated with narrowband, near-infrared laser light. For cytosine monomers isolated in a low-temperature Ar matrix, laser irradiations at 7013 cm−1 and at 7034 cm−1 were found to induce effective transformations of the two conformers into each other.
Photoisomerization and Photochemistry of Matrix-Isolated 3-Furaldehyde
Kuş, Nihal; Reva, Igor; Fausto, Rui3-Furaldehyde (3FA) was isolated in an argon matrix at 12 K and studied using FTIR spectroscopy and quantum chemistry. The molecule has two conformers, with trans and cis orientation of the O═C—C═C dihedral angle. At the B3LYP/6-311++G(d,p) level of theory, the trans form was computed to be ca. 4 kJ mol−1 more stable than the cis form. The relative stability of the two conformers was explained using the natural...
Conformational Cooling Dynamics in Matrix-Isolated 1,3-Butanediol
Rosado, Mário T. S.; Jesus, António J. Lopes; Reva, Igor D.; Fausto, Rui; Redinha, José S.The complete conformational space of monomeric 1,3-butanediol has been characterized theoretically, and 73 unique stable conformers were found at the MP2/6-311++G(d,p) level. These were classified into nine families whose members share the same heavy atom backbone configurations and differ in the hydrogen atom orientations. The first and third most populated backbone families are governed by the formation of an...
Conformational Switching Induced by Near-Infrared Laser Irradiation
Sharma, Archna; Reva, Igor; Fausto, RuiThis work describes a molecular system where it is possible to effectively control the interconversion between two different stable conformational states, using selective narrow-band near-infrared irradiation. Monomers of hydroxyacetone (HA) isolated in low temperature argon matrices at 15 K exist exclusively in the conformational ground state Cc. Narrow-band near-infrared vibrational excitation of the first OH...
Matrix-Isolation Study and Ab Initio Calculations of the Structure and Spectra ...
Sharma, Archna; Reva, Igor; Fausto, RuiThe structure of hydroxyacetone (HA) isolated in an argon matrix (at 12 K) and in a neat solid phase (at 12−175 K) was characterized by using infrared (IR) spectroscopy. The interpretation of the experimental results was supported by high-level quantum chemical calculations, undertaken by using both ab initio (MP2) and density functional theory methods. A potential-energy surface scan, carried out at the MP2/6-...
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