Crystallization of Arthrobacter sp. strain 1C N-(1-D-carboxyethyl)-L-norvaline dehydrogenase and its complex with NAD+

The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres.     

Molecular orbital calculations of iron(II) complexes of diimine ligands

Summary Molecular orbital calculations using-, the INDO method have been carried out fm the [FeL(CN)₄]² and [FeLH(CN)₄] complexes, as well as for the tree ligands, with L 2 × pyridine, 1,10-phenanthroline.2,2-bipyridyl. 2,2-rimidine, 2, 3,3-bipyridazine and 4.4-bipyrimidine. Calculations of residual charge at carbon atoms in the ligand rings. correlating with relative nucleophilicity of the compounds, corresponds with observed differences of rate of reaction of the complex [FeI;]² With nucleophiles.     

Many-particle tracking with nanometer resolution in three dimensions by reflection interference contrast microscopy

We have developed and characterized a method, based on reflection interference contrast microscopy, to simultaneously determine the three-dimensional positions of multiple particles in a colloidal monolayer. To evaluate this method, the interaction of 6.8 microm (+/-5%) diameter lipid-derivatized silica microspheres with an underlying planar borosilicate substrate is studied. Measured colloidal height distributions are consistent with expectations for an electrostatically levitated colloidal monolayer. The precision of the method is analyzed using experimental techniques in addition to computational bootstrapping algorithms. In its present implementation, this technique achieves 16 nm lateral and 1 nm vertical precision.     

The Electronic Structure of Bis-(π-cyclobutadiene)nickel

INDO SCF MO calculations have been carried out for the title complex, and comparisons with similar results for π-cyclopentadienyl-π-cyclobutadienecobalt, and π -cyclopentadienyl-π-cyclopropenyl-nickel, are used to shed light on the mode of bonding of the cyclobutadiene ligand to the metal.     

Molecular orbital calculations on complexes with strongly Jahn-Teller unstable transition metals: The hexanitro-copper(II) and cobalt(II) ions

INDO-LCAO-MO calculations have been performed for the complex cations [T^II(NO₂)₆]^4- (T^II: Cu²⁺, Co²⁺), in order to analyse the T-N bond properties and the Jahn-Teller distortion of the TN₆ octahedra as well as the high-spin low-spin behaviour of Co²⁺. While the essential features of the electronic structure and the coordination geometry of the TN₆ polyhedra resulting from the calculations are well in line with the experimental data for nitrocomplexes A₂^IM^IIT^II(NO₂)₆, the quantitative agreement is only approximate.     

Molecular orbital calculations on transition metal complexes : XX. The π-cyclopentadienyl-π-benzene complexes of chromium and manganese

INDO SCF MO calculations are reported for the complexes (C₅H₅)M(C₆H₆) (M = Cr and Mn) and for the corresponding cations. A ²A₁ ground state is correctly predicted for the neutral Cr system, and other experimental quantities are satisfactorily reproduced. The dominantly metal d-levels yield the H^core sequence e₂ < a₁ < _e1 and the principal interactions were found to be those between the metal e₁ level and the π-orbitals of the C₅H₅ ligand, and between the metal e₂ level and the ligand C₆H₆ π-orbitals. From the state energies of the formally 3d⁵ species estimates were made of the one-electron 3d splittings in the ligand field model, and comparisons made with similar results for M(C₅H₅)₂, M(C₆H₆)₂, and (C₅H₅)M(C₇H₇) systems: these indicated the general validity of the bonding scheme in which the extent of the metal—ligand interaction via the e₁ and e₂ 3d levels varied systematically with the sizes of the ligand rings.