Low temperature crystal structure of natural diosgenone

The molecular structure of diosgenone, a natural steroidal sapogenin, closely related to diosgenin and isolated from Solanum nudum, was solved by single crystal X-ray diffractometry at 120 K and refined by full-matrix least-squares to an agreement factor, R1 = 0.054. It crystallizes in the monoclinic space group P2(1), with a = 15.1870(4) A, b = 7.2710(2) A, c = 21.2840(6) A, beta = 99.251(1) degrees, and four molecules in the unit cell (Z = 4). The results constitute the first structural report on a steroidal sapogenin from the diosgenin group.

A pyrazine bis-adduct of a binuclear rhodium(II) carboxylate containing 3,4,5-triethoxybenzoate as the equatorial ligand

The title compound, tetrakis(mu-3,4,5-triethoxybenzoato-kappa(2)O:O')bis[(pyrazine-kappa N)rhodium(II)](Rh[bond]Rh), [Rh(2)(C(13)H(17)O(5))(4)(C(4)H(4)N(2))(2)], crystallizes on an inversion centre in the triclinic space group P1. The equatorial carboxylate ligands bridge the two Rh(II) atoms, giving a binuclear lantern-like structure. The pyrazine molecules occupy the two axial coordination sites. The phenyl rings are tilted by ca 10 degrees with respect to the attached carboxylate groups. The pyrazine planes have a torsion angle of ca 19 degrees around the Rh-N bond with respect to the plane of the nearer carboxylate group and are not coplanar with the Rh[bond]Rh bond.

Synthesis and characterization of three new Cu(II)-dipeptide complexes

Three new copper(II) complexes of stoichiometry [Cu(L-dipeptide)].nH(2)O, containing as ligands the dipeptides L-alanine-L-isoleucine, L-alanine-L-threonine and L-alanine-L-tyrosine were prepared. They were characterized by single crystal X-ray diffractometry, and electronic and infrared spectroscopy. In all cases, the Cu(II) cation has essentially the same elongated square pyramidal coordination, being equatorially cis coordinated by a N(2)O(2) arrangement of ligand atoms and axially by a carbonyl oxygen atom. The compounds show rather similar polymeric structures which resemble those recently reported for the [Cu(ala-val)] and [Cu(ala-phe)] complexes. The electronic and infrared spectra are briefly discussed on the basis of the structural peculiarities of the complexes. Superoxide dismutase (SOD)-like activity was also tested for the compounds.

A complex containing three different kinds of Ru-N bonds: ethoxydinitronitrosyl(N,N,N',N'-tetramethylethylenediamine-kappa2N,N')ruthenium(II)

The octahedral title compound, [Ru(C(2)H(5)O)(NO)(NO(2))(2)(C(6)H(16)N(2))], crystallizes in the rhombohedral space group P3(1) with an ethoxy ligand axially coordinated trans to the nitrosyl ligand. The RuII ion is equatorially coordinated by a tetramethylethylenediamine group acting as a bidentate ligand, and to two nitro moieties whose planes are tilted with respect to the mean equatorial plane. Each nitrogen ligand bonded to the metallic centre has a different hybridization state.

Two thiourea-containing gold(I) complexes

The crystal structures of two salts of bis(thiourea)gold(I) complexes, namely bis(thiourea-kappaS)gold(I) chloride, [Au(CH(4)N(2)S)(2)]Cl, (I), and bis[bis(thiourea-kappaS)gold(I)] sulfate, [Au(CH(4)N(2)S)(2)](2)SO(4), (II), have been determined. The chloride salt, (I), is isomorphous with the corresponding bromide salt, although there are differences in the bonding. The Au(I) ion is located on an inversion centre and coordinated by two symmetry-related thiourea ligands through the lone pairs on their S atoms [Au-S 2.278 (2) A and Au-S-C 105.3 (2) degrees ]. The sulfate salt, (II), crystallizes with four independent [Au(CH(4)N(2)S)(2)]+ cations per asymmetric unit, all with nearly linear S-Au-S bonding. The cations in (II) have similar conformations to that found for (I). The Au-S distances range from 2.276 (3) to 2.287 (3) A and the Au-S-C angles from 173.5 (1) to 177.7 (1) degrees. These data are relevant in interpreting different electrochemical processes where gold-thiourea species are formed.

A liquid crystal derived from ruthenium(II,III) and a long-chain carboxylate

The title compound, catena-poly[[tetrakis(mu-decanoato-kappa(2)O:O')diruthenium(II,III)(Ru-Ru)]-mu-octanesulfonato-kappa(2)O:O'], [Ru(2)(C(10)H(19)O(2))(4)(C(8)H(17)O(3)S)], is an octanesulfonate derivative of the mixed-valence complex diruthenium tetradecanoate. The equatorial carboxylate ligands are bidentate, bridging two Ru atoms to form a dinuclear structure. Each of the two independent dinuclear metal complexes in the asymmetric unit is located at an inversion centre. The octanesulfonate anion bridges the two dinuclear units through axial coordination. The alkyl chains of the carboxylate and sulfonate ligands are arranged in a parallel manner. The global structure can be seen as infinite chains of polar moieties separated by a double layer of non-polar alkyl groups, without interdigitation of the alkyl chains.

1,2,5-Oxadiazole N-oxide derivatives as potential anti-cancer agents: synthesis and biological evaluation. Part IV

Several new 1,2,5-oxadiazole N-oxide derivatives and some deoxygenated analogues were synthesized to be tested as potential selective hypoxic cell cytotoxins. Compounds prepared were designed in order to gain insight into the mechanism of action of this kind of cytotoxin. Compounds were tested in oxia and hypoxia and they proved to be non-selective. 3-Cyano-N(2)-oxide-4-phenyl-1,2,5-oxadiazole showed the best cytotoxic activity in oxia. The cytotoxicity observed for these derivatives could be explained in terms of the electronic characteristics of the 1,2,5-oxadiazole substituents. Electrochemical and ESR studies were performed on the more cytotoxic derivative.

Synthesis, structure and magnetic properties of tetrakis-mu-carboxylato-bis(dodecylnicotinato)dicopper(II) complexes; crystal and molecular structure of the decyl carboxylate derivative

Dodecylnicotinate bis-adducts of binuclear copper carboxylates, of the general formula Cu2(O2CC(n-1)H(2n-1))4(C5H4NCOOC12H25)2, were synthesized for n = 10, 12, 14, 16, 18 and 20, and their crystal structure, thermal behavior and magnetic properties studied. The molecular structure of the decyl derivative has been determined from single-crystal X-ray diffraction data. The dimer is centrosymmetric with the CuII ions in a square-pyramidal coordination with four O-alkyl O atoms [average d(Cu-O) 1.960 (6) A] in the basal plane and the nicotine N atom at apical positions [d(Cu-N) 2.183 (3) A]. The copper ions, 2.615 (1) A apart, are bridged by four O-alkyl carboxylate groups. Both the n = 20 and n = 18 homologues exhibit lamellar phases, which can be related to the supramolecular arrangement found in the n = 10 derivative. The magnetic behavior of the decyl and octadecyl dimers was studied in the 2-300 K temperature range. They exhibit a strong intramolecular antiferromagnetic interaction (Cu-Cu superexchange coupling constant J = -347 cm(-1) for the decyl derivative), which can be attributed to a large overlap of the metal 3d orbitals and the oxygen lone pair orbitals of the linking carboxylate groups.

Characterization of bis(isoorotato)diaquamagnesium(II) dihydrate: a potentially useful complex for magnesium supplementation

The synthesis and crystal structure of a new Mg(II) complex of stoichiometry [Mg(isoor)2(H2O)2].2H2O, where isoor is the monoanion of 5-carboxyuracil (isoorotic acid), are reported. The structure, solved by single-crystal X-ray diffractometry, shows that it crystallizes in the triclinic space group P(-1) with Z = 1. The electronic, IR and Raman spectra of the complex are briefly discussed. Its thermal behavior was also investigated by means of thermal gravimetry (TG) and differential thermal analysis (DTA) measurements in an oxygen atmosphere. Dissolution studies support the usefulness of the compound for magnesium supplementation.

The 6-A crystal structure of delta 5-3-ketosteroid isomerase. Architecture and location of the active center

The crystal structure of the dimeric steroid metabolizing enzyme, delta 5-3-ketosteroid isomerase (EC 5.3.3.1), has been solved to 6-A resolution by multiple isomorphous replacement, augmented by real space direct methods. The unit cell is hexagonal (space group P6122) with dimensions a = b = 65.4 A, c = 504 A, and contains four identical 13,400-dalton protomers in each of its 12 asymmetric units. The 504-A c axis required double focusing mirrors (Franks optics) to resolve the reflections. The complexity of the combined local and lattice symmetry necessitated direct methods to establish the positions of heavy atoms in even the simplest of the isomorphous derivatives. The electron density map clearly showed both (a) the elaborate packing scheme of protomers, which accounts for this large and complicated unit cell, and (b) the coarse features of the functional dimer. The steroid-binding site has been established by imaging the bound inhibitor, 4-acetoxymercuriestradiol, in a difference Fourier map. Each of the dimer's two steroid-binding sites lies completely within one subunit but close enough to the opposing subunit that functional interactions may be possible.