M.R. Udupa

Abstract: Preparation, crystal and molecular structure of creatininium tetrachlorocuprate(II) is described. The structure was solved by X-ray diffraction studies and was refined by least-squares methods to R = 0.041 for 1344 reflections. The compound is monoclinic, space group, P21/c. The unit cell parameters are a = 8.080(3), b = 7.831(2), c = 13.922(3) A, β = 113.77(2)°, V = 806.2 A3, dc = 1.786, dm = 1.77(1) g cm−3, Z = 2. The [CuCl4]2− ion is centrosymmetric and the copper atom is surrounded by four Cl atoms (CuCl1 2.233(1), CuCl2 2.268(1)) in a square planar arrangement. The creatininium cation is almost planar and each cation is linked to [CuCl4]2− units through hydrogen bonding involving the amino and imino nitrogen atoms.

Abstract: Tris(thiourea)silver(I) perchlorate, Ag[SC(NH2)2]3ClO4, is monoclinic with cell parameters a = 19.537(8), b = 13.436(6), c = 10.791(5) A, β = 103.57(5)°. The space group is C2/c with Z = 8, dc = 2.102 g. cm−3 and dm = 2.090 g.cm−3. The crystal structure was determined from three-dimensional diffractometer data and refined by least-squares methods with anisotropic thermal parameters to a conventional R factor of 0.048 for 2202 observed reflections. The structure is ionic and consists of binuclear complexes (Ag2[SC(NH2)2]6)2+ with C2 symmetry and perchlorate anions. The sulphur atoms of four thiourea molecules form a distorted coordination tetrahedron (SAgS angles range from 100.5(1) to 115.9 (1)°) around each Ag. Two of the six sulphur atoms of the binuclear complex cation act as bridging ligands in a four-membered AgSAgS ring (bridge bond lengths 2.663(2) and 2.684(2) A), the remaining four are terminal (AgS bond lengths 2.524(2) AND 2.570 (2) A). The bond angle AgSAg is 64.3(1), the Ag… Ag distance in the binuclear complex is 2.845(1) A. The bonding of the complex cation is different from the corresponding copper(I) complex. The orientation of the thiourea molecules suggests use of electron pairs of pπ sulphur-carbon MO's in the terminal as well as (together with sulphur sp2 orbitals) in the bridge AgS bonds.

Abstract: The polarized X-ray absorption cross section of the ls → 3d transition in a square planar CuCl2−4 complex has been measured with respect to rotation about an axis normal to the CuCl4 The cross section exhibits four-fold periodicity about this axis, indicating that the transition is primarily due to coupling with the electric quadrupole component of the radiation The vibronically allowed dipole transition is approximately one-third as the quadrupolar cross section These observations are in agreement with SCF Xα multiple-scattered wave calculations, and may have implications for the intepretation of other X-ray absorption spectra The half-filled d orbital is shown to have the angular characteristics of dx2−y2

Abstract: To elucidate the origin of the shoulder structure which is known to appear about half-way up the Cu K-edge in the X-ray absorption spectra of Cu(II) compounds, polarized X-ray absorption spectra were measured on the single crystal of (creatinium)2CuCl4 by using synchrotron radiation. The transition responsible for the shoulder structure was found to be exclusively polarized in the direction normal to the molecular plane of the CuCl42− ion. The polarization dependence of other structures in the XANES spectra was also examined and compared with the results of ab initio SCF CI calculation. It is shown that the structure half-way up the Cu K-edge is due to the shake-down accompanying the 1s-4p= excitation, arising from the ligand-to-metal charge transfer induced by the core-hole creation. Structures attributable to the shake-down accompanying the 1s-4pσ and 1s-5p=, σ excitations were also found.

Abstract: Attack by reactive oxygen species leads to a decay in phycoerythrin fluorescence emission. This phenomenon provides a versatile new assay for small molecules and macromolecules that can function as protective compounds. With 1-2 x 10(-8) M phycoerythrin, under conditions where peroxyl radical generation is rate-limiting, the fluorescence decay follows apparent zero-order kinetics. On reaction with HO., generated with the ascorbate-Cu2+ system, the fluorescence decays with apparent first-order kinetics. Examination of the major components of human urine in this assay confirms that at physiological concentrations, urate protects against both types of oxygen radicals. A novel finding is that creatinine protects efficiently by a chelation mechanism against radical damage in the ascorbate-Cu2+ system at creatinine, ascorbate, and Cu2+ concentrations comparable to those in normal urine. Urate and creatinine provide complementary modes of protection against reactive oxygen species in the urinary tract.

Abstract: The syntheses and crystal structures of a family of silver cyanide complexes of thiourea and substituted thioureas are reported. The sulfur ligands include thiourea (tu), 1-methyl-2-thiourea (mtu), 1,3-dimethyl-2-thiourea (dmtu), 1,1,3,3-tetramethyl-2-thiourea (tmtu), and 2-imidazolidinethione (N,N‘-ethylenethiourea, etu). Synthesis was effected by dissolving AgCN in an aqueous solution of ligand. Two different complexes were obtained by the reaction of AgCN with tu. Complex 1a: (AgCN)(tu), monoclinic, P21/c, a = 9.3851 (6) A, b = 8.2782 (5) A, c = 7.1178 (5) A, β = 94.591 (1)°, and Z = 4. Complex 1b: (AgCN)(tu)2, triclinic, P1, a = 7.9485 (14) A, b = 9.431 (2) A, c = 12.771 (2) A, α = 85.695 (3)°, β = 81.210 (4)°, γ = 77.987 (2)°, and Z = 4. Complex 2: (AgCN)(mtu), triclinic, P1, a = 4.113 (2) A, b = 9.472 (4) A, c = 9.679 (4) A, α = 113.918 (5)°, β = 98.188 (6)°, γ = 97.725 (6)°, and Z = 2. Complex 3 (AgCN)2(dmtu)2, monoclinic, P21/m, a = 7.1482 (7) A, b = 14.776 (2) A, c = 7.3366 (7) A, β = 92.418...