The doublet at 850 and 830 cm-1 in the Raman spectra of proteins containing tyrosyl residues has been examined as to its origin and the relation of its components to the environment of the phenyl ring, the state of the phenolic hydroxyl group, and the conformation of the amino acid backbone. Raman spectral studies on numerous model molecules related to tyrosine, including certain deuterium derivatives, show that the doublet is due to Fermi resonance between the ring-breathing vibration and the overtone of an out-of-plane ring-bending vibration of the para-substituted benzenes. Further examination of the effects of pH and solvents on the Fermi doublet and of the crystallographic data demonstrates that the intensity ratio of the two components depends on changes in the relative frequencies of the two vibrations. These in turn are found to be sensitive to the nature of the hydrogen bonding of the phenolic hydroxyl group of its ionization, but much less so to the environment of the phenyl ring and the conformation of the amino acid backbone. By use of the relative intensities of the doublet in model systems where the phenolic hydroxyl group is strongly hydrogen-bonded, weakly hydrogen-bonded, free or ionized, the reported Raman intensities of the doublets observed in the Raman spectra of several proteins have been interpreted. The results are compared with those obtained by other techniques.

Interpretation of the doublet at 850 and 830 cm-1 in the Raman spectra of tyrosyl residues in proteins and certain model compounds.

We present an alternative approach to the derivation of scaled quantum mechanical (SQM) force fields involving the direct scaling of individual primitive valence force constants from a full set of redundant valence coordinates. Our approach is completely general and more flexible than previous SQM schemes. Optimal scaling factors for various primitive stretching, bending, and torsional force constants are derived from a training set of 30 molecules containing C, O, N, H, and Cl and used to scale force constants for a further 30 molecules. Calculated vibrational frequencies are compared with experimental values for over 1500 fundamentals. Using the hybrid three-parameter B3-LYP density functional with the split-valence 6-31G* basis set, our scaling procedure gives an average error of less than 8.5 cm-1 in the scaled frequencies. The average percentage error is under 1%.

Direct Scaling of Primitive Valence Force Constants: An Alternative Approach to Scaled Quantum Mechanical Force Fields

Vibrational spectra of phenol are calculated with ab initio Hartree−Fock and MP2 methods as well as with density functional theory (DFT) using the 6-31G(d,p) basis set. A clear-cut assignment of th...

Density Functional, Hartree−Fock, and MP2 Studies on the Vibrational Spectrum of Phenol

In the search of Ni based metal–organic frameworks (MOFs) containing paddle-wheel type building units, three chemical systems Ni2+/HnL/base/solvent with HnL = H3BTC (1,3,5-benzenetricarboxylic acid), H3BTB (4,4′,4′′,-benzene-1,3,5-triyl-tris(benzoic acid)), and H2BDC (terephthalic acid) were investigated using high-throughput (HT) methods. In addition to the conventional heating, for the first time HT microwave assisted synthesis of MOFs was carried out. Six new compounds were discovered, and their fields of formation were established. In the first system, H3BTC was employed and a comprehensive HT-screening of compositional and process parameters was conducted. The synthesis condition for the Ni paddle-wheel unit was determined and two compounds [Ni3(BTC)2(Me2NH)3]·(DMF)4(H2O)4 (1a) and [Ni6(BTC)2(DMF)6(HCOO)6] (1b) were discovered (Me2NH = dimethylamine, DMF = dimethylformamide). In the second system, the use of the extended tritopic linker H3BTB and the synthesis conditions for the paddle-wheel units le...

Investigation of Porous Ni-Based Metal–Organic Frameworks Containing Paddle-Wheel Type Inorganic Building Units via High-Throughput Methods

The infrared and Raman spectra of several dialkyl disulfides were measured and their conformations were discussed in relation with the characteristic S–S and C–S stretching vibrations. The infrared spectra in the solid state and the temperature dependence of Raman spectra were measured for ethyl methyl disulfide and diethyl disulfide. For ethyl methyl disulfide, the gauche-gauche isomer was more stable than the trans-gauche isomer by about 0.9 kcal/mol while for diethyl disulfide the gauche-gauche-gauche isomer was more stable than the trans-gauche-gauche isomer by about 0.6 kcal/mol in the liquid state. Only the gauche-gauche form for ethyl methyl disulfide and only the gauche-gauche-gauche form for diethyl disulfide were observed in the solid state.

W. Kynaston

Papers

Vibrational spectra of benzene derivatives—XIV: Mono substituted phenols

Vibrational spectra of benzene derivatives—XII 1,2,4-trisubstituted compounds

Vibrational spectra of benzene derivatives—XI 1,3,5- and 1,2,3-trisubstituted compounds

The vibrational spectra of the dimethylpyridines

The vibrational spectra of propanal, 1-deuteropropanal and 2,2-dideuteropropanal