Search PubMed⌕ Search

Biomedical subjects

V G Young

Publications and source records attributed to V G Young.

29 records · Page 2Linked to original sources
PubMed2000

Addition and metathesis reactions of zirconium and hafnium imido complexes.

The zirconium and hafnium imido metalloporphyrin complexes (TTP)M = NArtPr (TTP = meso-5,10,15,20-tetra-p-tolylporphyrinato dianion; M = Zr (1), Hf; AriPr = 2,6-diisopropylphenyl) were used to mediate addition reactions of carbonyl species and metathesis of nitroso compounds. The imido complexes react in a stepwise manner in the presence of 2 equiv of pinacolone to form the enediolate products (TTP)M[OC(tBu)CHC(tBu)(Me)O] (M = Zr (2), Hf (3)), with elimination of H2NAriPr. The bis(mu-oxo) complex [(TTP)ZrO]2 (4) is formed upon reaction of (TTP)Zr = NAriPr with PhNO. Treatment of compound 4 with water or treatment of compound 2 with acetone produced the (mu-oxo)bis(mu-hydroxo)-bridged dimer [(TTP)Zr]2(mu-O)(mu-OH)2 (5). Compounds 2, 4, and 5 were structurally characterized by single-crystal X-ray diffraction.

Journal Article↗
PubMed2000

Syntheses and structures of quinuclidine-stabilized amido- and azidogallanes.

Quinuclidine-stabilized amido- and azidogallanes, HGa[N(TMS)2]2(quin) (1), H2Ga[N(TMS)2](quin) (2), HGa-[N(H)(2,6-iPr2C6H3)]2(quin) (3), and H2GaN3(quin) (4), were synthesized from the quinuclidine adducts of mono- and dichlorogallane. Structural determinations revealed that all compounds were monomeric with four-coordinate gallium centers. Reactions of the five-coordinate compound, HGaCl2(quin)2, with 2 equiv of Li[N(TMS)2] or Li[N(H)(2,6-iPr2C6H3)] resulted in the isolation of compound 1 or 3. A ligand redistribution during the reaction of H2GaCl(quin) with Li[N(H)(2,6-iPr2C6H3)] produced compound 3 and H3Ga(quin) in a 1:1 molar ratio.

Journal Article↗
PubMed2000

LiEuPSe4 and KEuPSe4: novel selenophosphates with the tetrahedral [PSe4]3- building block.

LiEuPSe4, the first quaternary lithium-containing selenophosphate, was synthesized as red polyhedra by reacting Eu with a molten mixture of Li2Se/P2Se5/Se at 750 degrees C. Similarly, the reaction of Eu with a molten mixture of K2Se/P2Se5/Se at 495 degrees C produced red polyhedral crystals of KEuPSe4. Both compounds are unstable in moist air. In addition, both compounds were plagued with crystal twinning. Acceptable crystal structure refinements could only be obtained by identifying the type of twinning and taking it into account in the final refinement. LiEuPSe4 crystallizes in the noncentrosymmetric space group Ama2 (no. 40) with a = 10.5592 (9) A, b = 10.415 (1) A, c = 6.4924(7) A, and Z = 4. The structure is three-dimensional and composed of EuSe8 distorted square antiprisms and PSe4 tetrahedral building blocks that create tunnels, running down the a axis, in which the Li ions reside. The Li ions are in a highly distorted tetrahedral coordination. KEuPSe4 crystallizes in the space group P2(1)/m (no. 11) with a = 6.8469(6) A, b = 6.9521(6) A, c = 9.0436(8) A, beta = 107.677(2) degrees, and Z = 2. The structure has two-dimensional character with layers composed of EuSe6 trigonal prisms and PSe4 tetrahedral units. Between the [EuPSe4]nn- layers the K ions reside in a bicapped trigonal prism of Se atoms. The structure of the [EuPSe4]nn- framework is similar to that found in CsPbPSe4. Both compounds are semiconductors with band gaps of 2.00 and 1.88 eV, respectively. Differential thermal analysis and infrared spectroscopic characterization are also reported.

Journal Article↗
PubMed2000

Antineoplastic agents 430. Isolation and structure of cribrostatins 3, 4, and 5 from the republic of maldives cribrochalina species.

Continued investigation of cancer-cell growth-inhibitory constituents of the blue marine sponge Cribrochalina sp. has led to discovery of cribrostatins 3 (4a), 4 (5), and 5 (4b) in 10(-5) to 10(-7) % of the wet weight. The structure of cribrostatin 3 (4a) was determined by results of high field (500 MHz) (1)H and (13)C NMR and HRMS interpretations. The same general approach to the structures of cribrostatins 4 (5) and 5 (4b) was completed by X-ray crystal structure determinations. Cribrostatins 3, 4, and 5 provided significant cancer cell line inhibitory activities. Cribrostatins 1 and 2(2) and the newly isolated cribrostatins 3-5 displayed antibacterial and/or antifungal activities.

Animals↗
PubMed1999

Solid-state behavior of cromolyn sodium hydrates.

Cromolyn sodium (CS, disodium cromoglycate) is an antiasthmatic and antiallergenic drug. The solid-state behavior of CS is still not completely understood. CS forms nonstoichiometric hydrates and sorbs and liberates water in a continuous manner, although with hysteresis. The reported continuous changes in crystal lattice parameters of CS, which are associated with the changes in water stoichiometry, renders CS physically variable, which may complicate formulation and processing. In addition, controversies still remain as to whether CS exists as different stoichiometric hydrates, mainly because of its variable powder X-ray diffraction (PXRD) patterns (Cox, J. S. G. et al. J. Pharm. Sci. 1971, 60, 1458-65), which indicates a variable crystal structure. The objectives of this study are (a) to understand this unusual water uptake in the light of the molecular and crystal structures of CS, (b) to understand the relationship between the crystal structure and the PXRD patterns using Rietveld analysis, and (c) to investigate whether CS exists as different stoichiometric hydrates. The crystal structure of CS containing 6.44 molecules of water per molecule of CS was determined at 295 and 173 K. The packing arrangements in these structures (space group P1) are similar to those in a previous report, in which the water stoichiometry is 5 to 6, but the bond lengths, bond angles, and lattice parameters are different, reflecting the different water stoichiometries. In the crystal structure solved at 295 K, the position of only one of the two sodium ions could be determined. In the crystal structure solved at 173 K, the previously undetermined sodium ion is disordered over three sites, while four of eight water positions are partially occupied. The 2-hydroxy-propane chain that links the two cyclic moieties of CS was found to be flexible, perhaps allowing the CS crystal to accommodate variable amounts of water. The lack of a fixed coordination site for the second sodium ion may contribute to the disorder of the water molecules. The nonstoichiometric water content of CS is mainly attributed to the water molecules that are associated with the two unoccupied sodium sites. From the PXRD patterns of CS powder, equilibrated at various relative humidities, the various lattice parameters, including previously unreported alpha, beta, and gamma values, were calculated using Rietveld analysis. The peak shifts in these PXRD patterns are quantitatively explained by slight changes in the unit cell parameters. The recently described solid forms of CS were prepared and were found to correspond to the original crystalline CS, described by Cox et al. (1971), but with contamination by the known M mesophase in various proportions. The present results support a variable crystal structure and not the existence of different stoichiometric hydrates of CS.

Anti-Asthmatic Agents↗
PubMed1997

Physicochemical characterization of nedocromil bivalent metal salt hydrates. 3. Nedocromil calcium.

A crystalline pentahydrate and a crystalline 8/3 hydrate of nedocromil calcium (NC) were prepared. The relationships between these solid phases and the nature of the water interactions in their structures were studied through characterization by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Karl Fischer titrimetry (KFT), hot-stage microscopy (HSM), ambient- or variable-temperature powder X-ray diffraction (PXRD), Fourier-transform infrared (FTIR) spectroscopy, solid-state nuclear magnetic resonance (SSNMR) spectroscopy, water uptake at various relative humidities (RH), intrinsic dissolution rate (IDR) and solubility measurements. The solubility and intrinsic dissolution rate of the pentahydrate in water at 25 degrees C are approximately 17% greater than the corresponding values for the 8/3 hydrate, corresponding to a greater Gibbs free energy of only 380 J.mol-1 (91 cal.mol-1) for the pentahydrate. The results of DSC, TGA, and FTIR and SSNMR spectroscopy indicate that the water of hydration is more loosely bound in the pentahydrate than in the 8/3 hydrate. On increasing the temperature in open-pan DSC and TGA, the water in the pentahydrate is released in four steps (three steps in crimped pans), whereas the water in the 8/3 hydrate is released in three steps (three steps also in crimped pans). These three stepwise dehydrations are fundamentally explained by their different water environments in the crystal structure of the 8/3 hydrate, which was determined by single-crystal XRD [crystal data: triclinic, space group P1, a = 13.2381(3) A, b = 13.3650(2) A, c = 17.8224(2) A, alpha = 68.202(1) degrees, beta = 86.894(1) degrees, gamma = 82.969(1) degrees, Z = 6]. The asymmetric unit contains three nedocromil anions and three calcium cations associated with eight water molecules. The nedocromil anions act as polyfunctional ligands to the Ca2+ ions, coordinating through both the carbonyl oxygen and the carboxylate oxygen atoms. The molecular conformations of the three nedocromil anions in the asymmetric unit are almost identical. However, the crystal structure contains two different calcium environments, one of which has the Ca2+ ion hydrated by four water molecules in the equatorial plane and by two carbonyl oxygens in its axial coordination sites. In the second environment, the Ca2+ ion has four carboxylate oxygen atoms in its equatorial plane and two water molecules in its axial coordination sites. Two of the carboxylate ligands are twisted out of the tricyclic ring, and the other two carboxylate ligands are nearly coplanar with the tricyclic ring. All of the eight water molecules in the 8/3 hydrate are linked to calcium and carboxylate ions and none are linked to other water molecules.

Calcium↗
PubMed1996

Reversible cleavage and formation of the dioxygen O-O bond within a dicopper complex.

A key step in dioxygen evolution during photosynthesis is the oxidative generation of the O-O bond from water by a manganese cluster consisting of M2(mu-O)2 units (where M is manganese). The reverse reaction, reductive cleavage of the dioxygen O-O bond, is performed at a variety of dicopper and di-iron active sites in enzymes that catalyze important organic oxidations. Both processes can be envisioned to involve the interconversion of dimetal-dioxygen adducts, M2(O2), and isomers having M2(mu-O)2 cores. The viability of this notion has been demonstrated by the identification of an equilibrium between synthetic complexes having [Cu2(mu-eta2:eta2-O2)]2+ and [Cu2(mu-O)2]2+ cores through kinetic, spectroscopic, and crystallographic studies.

Chemical Phenomena↗
PubMedDate not supplied

Crystal structures of a family of silver cyanide complexes of thiourea and substituted thioureas.

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, P2(1)/c, a = 9.3851 (6) A, b = 8.2782 (5) A, c = 7.1178 (5) A, beta = 94.591 (1) degree, 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, alpha = 85.695 (3) degrees, beta = 81.210 (4) degrees, gamma = 77.987 (2) degrees, and Z = 4. Complex 2: (AgCN)(mtu), triclinic, P1, a = 4.113 (2) A, b = 9.472 (4) A, c = 9.679 (4) A, alpha = 113.918 (5) degrees, beta = 98.188 (6) degrees, gamma = 97.725 (6) degrees, and Z = 2. Complex 3 (AgCN)2(dmtu)2, monoclinic, P2(1)/m, a = 7.1482 (7) A, b = 14.776 (2) A, c = 7.3366 (7) A, beta = 92.418 (2) degrees, and Z = 2. Complex 4: (AgCN)(tmtu), orthorhombic, P2(1)2(1)2(1), a = 8.823(6) A, b = 10.209 (2) A, c = 10.362 (2) A, and Z = 4. Complex 5: (AgCN)2(etu)2, triclinic, P1, a = 6.8001 (2) A, b = 8.6154 (1) A, c = 13.4747 (3) A, alpha = 71.720 (1) degree, beta = 79.906 (1) degree, gamma = 75.885 (2) degrees, and Z = 2. All of the structures involve either one- or two-dimensional polymeric arrays held together by bridging S and CN groups. There is, however, no similarity between any two of the arrays. Four of the five ligands used also form similar complexes with CuCN. For one ligand, tmtu, the structures are isomorphous. For the other three, not only are the structures not isomorphous, the m/n ratio in (MCN)mLn when M is Ag is different from that when M is Cu.

Journal Article↗