The accurate crystal structure determinations of MeCbl (1), CNCbl.2LiCl (2), and CNCbl.KCl (3), based on synchrotron diffraction data collected at 100 K and using high-quality single crystals, are reported. Refinements gave R1 indices of 0.0834 (1), 0.0434 (2), and 0.0773 (3). The influence of the water of crystallization and ion content on the crystal packing of these and other cobalamins (XCbl) is discussed, and a relationship between the crystal packing and the corrin side chain conformations is presented. An analysis of the bond lengths within the corrin moiety, based on 13 accurate structures with several X groups, shows that the trend of the C-C and C-N distances can be interpreted in terms of electronic and steric factors. The variation in structural, NMR and IR spectroscopic, and electrochemical properties are compared with those of cobaloximes, the B12 model, when X is varied. This comparison indicates that the pi-back-donation from metal to the CN axial ligand and the transmission of the trans influence of the X ligand are more effective in cobalamins than in cobaloximes. These findings are consistent with a significantly greater availability of electron charge on Co in cobalamins, and, hence, a semiquantitative evaluation of the electronic difference between the cobalt centers in the two systems is allowed.

In the computation of synthetic seismograms by modal summation, when a medium with a sharp lateral discontinuity is considered, a fundamental role is played by a coupling coefficient cj#, The coefficient r;ir is defined via an integral relation involving products between displacements and stresses and can be evaluated both numerically and analytically. The calculation of r;i. can be reduced to the analytical computation of a sum of integrals of elementary functions. The analytical method proved to be particularly convenient for its speed and precision of the results obtained.The energy redistribution within the different modes is illustrated, both in the frequency and in the time domain. Mode conversion cannot be neglected when dealing with higher modes.

High-resolution X-ray structure determinations of chloro- and azidocobalamin·2LiCl, crystallized from concentrated aqueous LiCl solutions, show lithium cations coordinated to the phosphate O atom and to the amidic O atoms of the corrin side chains, and chloride anions held by H-bonds to the corrin amidic N atoms. The structures of the two compounds represent the first structural picture of the interactions of the cobalamin molecule with ionic species.

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