ABSTRACT
A carbohydrate-derivative alkylcobalt carbonyl,([(1,2:5,6-di-O,O-isopropylidene-alpha-D-glucofuranos-3-yl)oxycarbonyl]methyl)cobalt tricarbonyl triphenylphosphene(3) was prepared and characterized by IR, NMR, and CD spectra, as well as by X-ray diffraction. The supramolecular chemistry in the crystalline P2(1)2(1)2(1) (chiral) phase and in solution was analyzed and compared. The bulky carbohydrate-based ligand stabilized one chiral conformation, which, however, is less ordered than for analogous compounds with more flexible and less bulky chiral groups. Intermolecular, H-bond interactions are more important in the P2(1)2(1)2(1) phase of complex 3 than at other analogous compounds.
Subject(s)
Carbohydrates/chemistry , Cobalt/chemistry , Glucose/chemistry , Organometallic Compounds/chemistry , Carbohydrate Conformation , Crystallography, X-Ray , Furans/chemical synthesis , Furans/chemistry , Glucose/analogs & derivatives , Glucose/chemical synthesis , Molecular Structure , Organometallic Compounds/chemical synthesis , Organophosphorus Compounds/chemical synthesis , Organophosphorus Compounds/chemistry , StereoisomerismABSTRACT
Chiral conformations of flexible molecules may develop in a concerted manner if the molecule is crowded enough to assure sufficient level of through-the-space contacts. Higher number (> 4) of groups connected to the same atom, as in many coordination compounds, can be advantageous in this respect. The case study of R,S-[(sec-butoxycarbonyl)methyl]cobalt tricarbonyl triphenylphosphine is presented here. X-ray diffraction shows that the possible number of enantiomeric and diastereomeric conformations is reduced by 75% (from 8 to 2) by concerted development of the molecular conformations in crystalline phase.
Subject(s)
Cobalt/chemistry , Molecular Conformation , Phosphines/chemistry , Stereoisomerism , Isomerism , Magnetic Resonance Spectroscopy , Models, Molecular , Molecular Structure , Spectrophotometry, Infrared , X-Ray DiffractionABSTRACT
Voltage-dependent calcium channels are located in the plasma membrane and form a highly selective conduit by which Ca2+ ions enter all excitable cells and some nonexcitable cells. Extensive characterization studies have revealed the existence of one low (T) and five high-voltage-activated calcium channel types (L, N, P, Q, and R). The high voltage-activated calcium channels have been found to exist as heteromultimers, consisting of an alpha1, beta, alpha2/delta, and gamma subunit. Molecular cloning has revealed the existence of 10 channel transcripts, and expression of these cloned calcium channel genes has shown that basic voltage-activated calcium channel function is strictly carried by the corresponding alpha1 subunits. In turn, the auxiliary subunits serve to modulate calcium channel function by altering the voltage dependence of channel gating, kinetics, and current amplitude, thereby creating a likelihood for calcium channels with multiple properties. Although for calcium channels to be effective, Ca2+ ions must enter selectively through the pore of the alpha1-subunit, bypassing competition with other extracellular ions. The structural determinants of this highly selective Ca2+ filter reside within the four glutamic acid residues located at homologous positions within each of the four pore-forming segments. Together, these residues form a single or multiple Ca2+ affinity site(s) that entrap calcium ions, which are then electrostatically repulsed through the intracellular opening of the pore. This mechanism of high-selectivity calcium filtration, the spatial arrangement of pore glutamic acid residues, and the coordination chemistry of calcium binding are discussed in this review.
