Near infrared spectra (4000-10 500 cm-1) of phenol-OH and phenol-OD in carbon tetrachloride.

The near infrared spectra (3800-10 500 cm(-1) of phenol-OH and phenol-OD are studied in carbon tetrachloride solution. The bandwidth of the v(OH) and v(OD) stretching vibrations increases with the vibrational quantum number in contrast to results obtained by nonresonant ionization spectroscopy (S.I. Ishiuchi et al., Chem. Phys. Lett. 283 (1998) 243). The bandwidth of the v(CH) vibrations obtained by a deconvolution procedure also increases with the frequencies associated with the vibrational transitions. The anharmonicity of the v(CH) vibrations ranges between 51 and 72 cm(-1). Numerous absorptions are observed in the near infrared spectra. These absorptions are tentatively assigned to combinations involving the fundamental transitions which have been recently calculated at different levels of theory (D. Michalska et al., J. Phys. Chem. 100 (1996) 17786). The experimental, theoretical and harmonic v(OH) and vi(CH) frequencies are compared.

Theoretical and experimental study of the vibrational spectrum of N-acetyl-L-alanine.

The energies, vibrational frequencies and IR intensities of cis- and trans-N-acetyl-L-alanine (NAAL) are computed using the density functional theory (B3LYP) combined with the 6-311G(d, p) basis set. The trans conformer is characterized by an intramolecular NH ... O hydrogen bond leading to the formation of a five-membered ring and is by 23 kJ mol(-1) more stable than the cis conformer. The difference between the vibrational frequencies and IR intensities computed for the two conformers is discussed. The IR spectra at different temperatures and the Raman spectra of solid NAAL and its deuterated counterpart are investigated and discussed. The frequencies of the v(OH) vibration and the isotopic ratio suggest the formation of short OH ... O hydrogen bonds in the solid state. The NH group seems also to be involved in a weak hydrogen bond.

Theoretical and Experimental (400-10 000 cm-1) Study of the Vibrational Spectrum of Pentachlorophenol.

Geometric and vibrational spectroscopic data (bond distances and angles, vibrational frequencies, infrared intensities) of pentachlorophenol-OH (PCP-OH) and pentachlorophenol-OD (PCP-OD) are calculated by density functional theory (B3LYP) using the 6-311G(d, p) basis set. Except for the vibrations involving the OH bond, the agreement between the experimental and calculated fundamental frequencies between 3600 and 400 cm-1 is very good. The theoretical method failed, however, to reproduce quantitatively the experimental intensities. The infrared spectra between 3600 and 10 000 cm-1 are studied, and the overtones or combination bands are assigned by comparing the spectra of PCP-OH and PCP-OD. The difference between the experimental and theoretical frequencies of the nu(OH) and nu(OD) frequencies can be mainly accounted for by the neglect of the anharmonicities of these vibrations in calculations. The binary or ternary combinations characterized by the highest coupling constants and the highest intensities are those involving the nu(OH), delta(OH), gamma(OH), and nu(C-O) vibrations. Copyright 1999 Academic Press.

Assignment of the Vibrations in the Near-Infrared Spectra of Phenol-OH(OD) Derivatives and Application to the Phenol-Pyrazine Complex

The near-infrared spectra (7200-3800 cm-1 ) of seven phenols OH-OD (4-CH3 , H, 4-Cl, 4-Br, 3-Br, 3,4-diCl, 3-5-diCl) are investigated at room temperature in carbon tetrachloride. The mid-infrared spectra of some phenol-OD have also been studied. Beside the first overtone of the nu(OH) stretching vibration, six absorptions disappear upon deuteration. The absorptions are assigned to combinations involving the nu(OH) stretching mode and aromatic ring vibrations, the nu(C-O) mode, or the delta(OH) mode. The anharmonicity and coupling constants are discussed. The isotopic ratio of the nu(OH) stretching fundamentals, of their first overtone, and the ratio of the anharmonicity constants are very insensitive to the nature of the phenol. The stability constants of complexes between phenols and base can be computed from several near-infrared absorptions and this is illustrated for the 3,5-dichlorophenol-pyrazine complex.

The reaction of nitrite with the haemocyanin of the Roman snail (Helix pomatia).

The reaction of nitrite at pH 5.0-7.0 with the deoxyhaemocyanin of a mollusc, the Roman snail (Helix pomatia), yielded nitrosylhaemocyanin (CuIA.NO+ CuIIB), in contrast with the formation of methaemocyanin with the deoxyhaemocyanin of the crustacean Astacus leptodactylus (mud crayfish). With Helix haemocyanin 1 NO was thereby liberated per active site, as shown by m.s., as against 2 NO with Astacus haemocyanin. Helix nitrosylhaemocyanin was characterized in c.d. by the negative extremum at 336 nm (CuIA.NO+) and by the mononuclear e.p.r. signal at g = 2 (CuIIB). Binuclear e.p.r. signals have been observed after the addition of nitrite to methaemocyanins. With Astacus methaemocyanin, no further reaction occurred, whereas with Helix methaemocyanin the mononuclear e.p.r. signal, characteristic for nitrosylhaemocyanin gradually appeared. This formation of Helix nitrosylhaemocyanin implicates the binding, most likely on CuIIA, of a second nitrite besides a bridging nitrite, so that a dismutation into NO and NO2 can occur there. A further dismutation of NO2 yields nitrite and nitrate. The formation of the latter was demonstrated by Raman spectrometry. The reaction rate of Helix methaemocyanin with nitrite decreased with increasing pH according to the Henderson-Hasselbalch equation with a pKa value of 6.77, attributed to a mu-aquo bridging ligand, which can be exchanged for nitrite, in equilibrium with a mu-hydroxo ligand which cannot. These data also favour the formulation of the final reaction product as nitrosylhaemocyanin instead of semi-methaemocyanin, with or without bound nitrite.

Infrared study of the interaction between caffeine and hydroxylic derivatives.

The interaction between caffeine and hydroxylic derivatives (phenols, water) has been studied by infrared (IR) spectroscopy in 1,2-dichloroethane. The formation constants, enthalpies, and entropies of complex formation have been determined. The IR spectra in the vOH and vc=o ranges indicate that hydrogen bond formation occurs at the carbonyl functions, approximately 70% of the complexes being formed at the O6 atom. These results are compared with 1,3-dimethyluracil complexes and discussed as a function of the ionization potential of the two oxygen atoms. In the solid hydrate, the spectroscopic results show that the interaction of water takes place on the N9 atom of the imidazole ring in agreement with earlier X-ray results. The different interaction sites in solution and in the solid state are briefly discussed.