The concerted use of ab initio time-dependent density functional theory (TDDFT) calculations of transparent spectral region optical rotation and of circular dichroism has recently become practicable, permitting the concerted use of transparent spectral region optical rotation and circular dichroism in determining the absolute configurations of chiral molecules. Here, we report concerted TDDFT calculations of the transparent spectral region specific rotations and of the circular dichroism spectra originating in n --> pi C=O group excitations of four bicyclo[3.3.1]nonane diones, 1-4. Comparison to experiment yields absolute configurations for 1-4. For each dione, specific rotations and circular dichroism spectra give identical absolute configurations. Our results are consistent with previous work, with the exception of the Octant Rule-derived absolute configuration of the 2,9-dione.

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In an approach to helical self-aggregation, C2-symmetric cavity compounds based on the fusion of the bicyclo[3.3.1]nonane and indole framework and incorporating two 2-pyridone hydrogen-bonding motifs, compounds (-)-4 (pyrrole N-butyl) and (-)-5 (pyrrole N-decyl), have been synthesized. The 2-pyridone AD-DA hydrogen-bonding motif failed to operate in the solid state as demonstrated by X-ray diffraction analysis of (-)-4. Instead, the hydrogen-bonded (D-A) chains ...O=C-N-H...O=C-N-H...O=C-N-H..., interconnecting columnar stacks, comprise helices of the right-handed (P) chirality motif. In solution, the aggregation of (-)-5 was studied by NMR, electronic, and CD spectroscopies, and VPO measurements. These investigations strongly suggest that (-)-5 associates to oligomers in CHCl3 and CH2Cl2 using the 2-pyridone motif, fitting the equal K model, and that pi-stacking can be ruled out as a mode of aggregation. We conclude that the so formed aggregates of (-)-5 have a helical structure, based on the fact that only helical tubular structures can result when enantiomerically pure 5 uses its 2-pyridone AD-DA hydrogen-bonding motifs for aggregation.

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Different cysteamine (H2N-CH2-CH2-SH) ionization forms have been studied by polarized Raman spectroscopy in solutions prepared with H2O and D2O and by DFT calculations at the B3LYP/6-31++G(d,p) level. To account for solvation effects, we employed the integral equation formalism polarizable continuum model (IEFPCM) option and explicit water molecules. Calculated relative energies and Raman spectra revealed that gauche rotamers around the C-C bond are the most stable conformers in solution. The experimental pKa values and Raman spectra of various ionization forms were best predicted by using a model with three explicit water molecules and the IEFPCM option. In general, the use of IEFPCM tends to lower the calculated frequencies for a few bands, but in some cases (S-H stretching mode) this effect is expressed very strongly. Potential energy distribution (PED) analysis of gauche conformers of various cysteamine ionization forms provided the possibility of discriminating spectroscopically methylene groups adjacent to sulfur, (CH2)S, and nitrogen, (CH2)N, sites. In general, stretching and scissoring modes as well as wagging and twisting vibrations of the (CH2)N group were found to be at higher frequencies. The influence of ionization of SH and NH2 groups on the vibrational spectrum is discussed, and Raman markers for further amine group ionization studies are suggested.

This paper experimentally verifies the idea presented earlier that the contact of nonpolar clusters located on the surface of protein molecules with water destabilizes proteins. It is demonstrated that protein stabilization can be achieved by artificial hydrophilization of the surface area of protein globules by chemical modification. Two experimental systems are studied for the verification of the hydrophilization approach.1. The surface tyrosine residues of trypsin are transformed to aminotyrosines using a two-step modification procedure: nitration by tetranitromethane followed by reduction with sodium dithionite. The modified enzyme is much more stable against irreversible thermoinactivation: the stabilizing effect increases with the number of aminotyrosine residues in trypsin and the modified enzyme can become even 100 times more stable than the native one.2. a-Chymotrypsin is covalently modified by treatment with anhydrides or chloroanhydrides of aromatic carboxylic acids. As a result, different numbers of additional carboxylic groups (up to five depending on the structure of the modifying reagent) are introduced into each Lys residue modified. Acylation of all available amino groups of cr-chymotrypsin by cyclic anhydrides of pyromellitic and mellitic acids results in a substantial hydrophilization of the protein as estimated by partitioning in an aqueous Ficoll-400/Dextran-70 biphasic system. These modified enzyme preparations are extremely stable against irreversible thermal inactivation at elevated temperatures (65 -98 "C); their thermostability is practically equal to the stability of proteolytic enzymes from extremely thermophilic bacteria, the most stable proteinases known to date.Applications of enzymatic catalysis in biotechnology, fine organic synthesis, analysis, medicine, and other areas are often hindered because many enzymes, if isolated from their natural environment in vivo, become unstable and rapidly inactivate (denature); for review, see [l, 21. For these reasons the problem of enzyme stabilization has received considerable attention in recent years [3 -81.The analysis of the structure-stability relationships in the protein leads us to the conclusion [S] that the structure of proteins is not optimal with regard to their stability. There are still some reverses for stabilization which are used by nature for the production of extremely stable proteins, such as, for example, enzymes from thermophilic microorganisms ; for review, see [S, 91. Reserves of such a kind may be useful for artificial stabilization of enzymes. We shall discuss here, from this viewpoint, how to improve the protein structure in order to make enzymes more stable.According to X-ray crystallographic data, about one half of the surface area of proteins is occupied by nonpolar amino Corre2pondence to K. Martinek, Ustav OrganickC Chemie a Biochemie, Ceskoslovenska Akademie Vtid, Flemingovo nimEsti 2, CS-166-10 Praha, CzechoslovakiaThe authors wish to dedicate this paper to the memory of their teacher and friend. Professor...

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