The nature of the AgI...AgI interaction in different Ag(NH3)2 dimers embedded in supramolecular solids.

An isolated silver(I) ammonia monomer, a dimer, and a novel dimer containing an intercalated water molecule have been embedded as guests in supramolecular frameworks, [Ag(NH3)2][(H2thpe)(H3thpe)].MeCN (1), [{Ag(NH3)2}2][(H2thpe)2]4.25 H2O (2), and [{Ag(NH3)2}-H2O-{Ag(NH3)2}][(H2thpe)(2)]benzene (3) (H3THPE=tris(hydroxyphenyl)ethane). The [{Ag(NH3)2}2]2+ dimer is not stable as an isolated entity, but is stabilized by hydrogen bonding in the supramolecular framework. The water-intercalated silver(I) ammonia dimer, which constitutes a novel species, is also subject by hydrogen bonding in concentrated solutions. The destabilization energy of the dimer relative to isolated monomers is calculated to be approximately 300 kJ mol(-1) by both perturbation methods and DFT theory. For the water-intercalated dimer it is calculated to be approximately 200 kJ mol(-1) according to the BSSE-corrected MP2 calculation. The different aggregate states show a dramatic variation of absorption and emission properties, in accordance with the concentration dependent red-shift observed in solutions. Natural-bond-orbital analysis shows that the disilver-ammonium-aquo "sandwich" cation in 3 is stabilized by interaction between the pi lone pair orbital on the oxygen atom of the water molecule and Ag(I)--N sigma antibonding molecular orbital.

Synthesis of a C-linked hyaluronic acid disaccharide mimetic.

The synthesis of a C-disaccharide that is designed as a mimetic for the repeating unit disaccharide of hyaluronic acid is described. The target compound was obtained via the SmI2-promoted coupling reaction of the sulfone, 2-acetamido-4,6-O-benzylidene-3-O-tert-butyldimethylsilyl-1,2-dideoxy-1-pyridinylsulfonyl-beta-D-glucopyranose (6), and the aldehyde, p-methoxyphenyl 2,3-di-O-benzyl-4-deoxy-4-C-formyl-6-O-p-methoxybenzyl-beta-D-glucopyranoside (14).

Mn(dca)2(pym)2 and Mn(dca)2(pym)(H2O) {dca = dicyanamide; pym = pyrimidine}: New coordination polymers exhibiting 1- and 2-D topologies.

Two new coordination polymers comprised of Mn(2+), N(CN)(2)(-) (dicyanamide, herein denoted dca) and pyrimidine (pym) have been synthesized and structurally and magnetically characterized. Mn(dca)(2)(pym)(2), , crystallizes in the orthorhombic space group Pbcn and forms trans bi-bridged Mn-(micro(1,5)-dca)(2)-Mn ribbons that extend along the b-axis of the unit cell. Two terminally bonded pym ligands are trans-coordinated to the Mn center. Adjacent chains interdigitate in an undulating fashion presumably due to a templating effect imposed by the pym ligands where N-atoms of consecutive pym rings stack parallel to the chain axis. Mn(dca)(2)(pym)(H(2)O), , which crystallizes in the monoclinic space group P2(1)/c, has a unique interdigitated 2D network that consists of double-bridged [Mn(2)(dca)(2)(pym)(2)(H(2)O)(2)](2+)"dimers" that are connected via single-bridging dca ligands. Each MnN(5)O octahedron is comprised of a coordinated H(2)O, a monodentate pym ligand, and four micro(1,5)-bridging dca anions. The magnetic data for were fitted to a uniform antiferromagnetic chain model which yielded J/k(B) = -0.34(1) K. In contrast, is best described as an alternating chain owing to the presence of both single- and double-bridging dca anions; a least-squares fit afforded J(a) = -0.43(1) and J(b) = -0.20(2) K, respectively. A transition to long-range magnetic ordering was observed for below approximately 2.4 K in addition to a field-induced spin flop transition at 15.6 kOe (1.7 K).

Ligand-unsupported Au(I) chains with short Au(I)...Au(I) contacts.

A new series of solids with ligand-unsupported Au(I) chains with short Au...Au contacts were synthesized; as Ag compounds with the same structure are known, the new phases now allow unbiased comparison of Ag...Ag and Au...Au metallophilic bonds not supported by bridging ligands, which shows the latter to be consistently shorter by 0.03-0.04 A.

Investigation into factors influencing stereoselectivity in the reactions of heterocycles with donor-acceptor-substituted rhodium carbenoids.

Rhodium-catalyzed decomposition of aryldiazoacetates in the presence of pyrroles or furans results in mono- or biscyclopropanation of the heterocycle, but with opposite enantioinduction. In the absence of sterically encumbering groups, the cyclopropanation of furan occurs with initial bond formation at the 2-position. If this pathway is sterically blocked, cyclopropanation can occur with initial bond formation at the 3-position of the furan ring; in this case, the cyclopropanation reaction takes place on the opposite face of the heterocycle, and the opposite enantioinduction is observed. Upon extension of this methodology to benzofurans, a highly enantioselective monocyclopropanation reaction occurs to furnish a product derived from initial bond formation at the 2-position of the benzofuran. When this reaction pathway is inhibited by sterically encumbering substituents on the benzofuran, no cyclopropanation of the furan ring is observed, and instead, double cyclopropanation of the benzene ring occurs. Double cyclopropanation of the benzene ring was also observed in reactions with indoles.

Stimulation of P-glycoprotein ATPase by analogues of tetramethylrosamine: coupling of drug binding at the "R" site to the ATP hydrolysis transition state.

The multidrug resistance efflux pump P-glycoprotein (Pgp) couples drug export to ATP binding and hydrolysis. Details regarding drug trajectory, as well as the molecular basis for coupling, remain unknown. Nearly all drugs exported by Pgp have been assayed for competitive behavior with rhodamine123 transport at a canonical "R" drug binding site. Tetramethylrosamine (TMR) displays a relatively high affinity for Pgp when compared to other rhodamines. Here, we present the construction and characterization of a library of compounds based upon the TMR scaffold and use this set to assess the determinants of drug binding to the "R" site of Pgp. This set contained modifications in (1) the number, location, and conformational mobility of hydrogen-bond acceptors; (2) the heteroatom in the xanthylium core; and (3) the size of the substituent in the 9-position of the xanthylium core. Relative specificity for coupling to the distal ATP catalytic site was assessed by ATPase stimulation. We found marked ( approximately 1000-fold) variation in the ATPase specificity constant within the library of TMR analogues. Using established methods involving ADP-Vi trapping by wild-type Pgp and ATP binding by catalytic carboxylate mutant Pgp, these effects can be extended to ATP hydrolysis transition-state stabilization and ATP occlusion at a single site. These data support the idea that drugs trigger the engagement of ATP catalytic site residues necessary for hydrolysis. Further, the nature of the drug binding site and coupling mechanism may be dissected by variation of a drug-like scaffold. These studies may facilitate development of novel competitive inhibitors at the "R" drug site.

Electron and nuclear positions in the short hydrogen bond in urotropine-N-oxide.formic acid.

The crystal structure of urotropine-N-oxide.formic acid, as determined from multiple temperature single-crystal X-ray diffraction experiments in the range 123-295 K and from neutron diffraction at 123 K, is reported. There is a strong hydrogen bonding interaction between the OH of formic acid and the N-oxide of urotropine, with the oxygen-oxygen distance ranging from 2.4300(10) to 2.4469(10) A. The electron density of the hydrogen atom associated with this interaction was located in the Fourier difference maps of the spherical atom refinement after all heavy atom positions were determined. The maximum of the electron density associated with the hydrogen bond is located approximately 1.16 A from the formate segment, though the distribution of electron density is very broad. The electron density associated with the H atom is thus shown by these accurate X-ray diffraction experiments to be approximately centered at all temperatures studied. This was conclusively confirmed by single-crystal neutron diffraction data obtained at 123 K, from which statistically equivalent O-H distances of 1.221(7) and 1.211(7) A were obtained.

On the solid state structure of 4-iodobenzoic acid.

The solid-state structure of 4-iodobenzoic acid has been confirmed by variable temperature X-ray diffraction, variable temperature solid-state NMR and differential scanning calorimetry. 4-iodobenzoic acid crystallizes in the space group P2(1)/n, and dimerizes in the solid state about a center of inversion. Using extensive X-ray crystallographic data collections, the placement of the carboxylate H atoms from the residual electron density in difference Fourier maps was determined. The position of the electron density associated with the proton is found to vary with temperature in that the population of the disordered sites changes with varying temperature. Determination of the crystal structure between the temperatures of 248 and 198 K was not possible due to a phase transition, an endothermic event occurring at 230.77 K. The phase transition is also indicated by a change in the relaxation time of the ring carbon atoms in the solid-state NMR data. Though the dominating force in the dimeric unit in the solid state is the presence of strong hydrogen bonds, there are also van der Waals forces present between the iodine atoms. In the layered structure, the iodine-iodine distance is within the van der Waals contact radii, an interaction which causes a deformation in the electron density of the iodine atoms.

A pair of epimeric 13-hydroxy-2,3,6,7-tetramethoxy-8b,11,12,12a,13,13a-hexahydro-9H-9a-azacyclopenta[b]triphenylene-10-ones.

The structures of two compounds which are intermediates in the synthesis of phenanthroindolizidine alkaloids have been determined. (8bS,13aS,14R,14aR)-8b,9,11,12,13,13a,14,14a-Octahydro-14-hydroxy-2,3,6,7-tetramethoxydibenzo[f,h]pyrrolo[1,2-b]isoquinolin-11-one acetone solvate, C24H27NO6.C3H6O, (II), crystallizes in a chiral space group with one solvent molecule (acetone) present in the asymmetric unit. On the other hand, (8bS,13aS,14S,14aR)-8b,9,11,12,13,13a,14,14a-octahydro-14-hydroxy-2,3,6,7-tetramethoxydibenzo[f,h]pyrrolo[1,2-b]isoquinolin-11-one, C24H27NO6, (III), crystallizes in a centrosymmetric space group with two molecules in the asymmetric unit and with no solvent present. The two molecules in the asymmetric unit of (III) are structurally the same. Compounds (II) and (III) are epimers at the C atom carrying the OH group; otherwise they are very similar in structure.

Tetrakis(tetrahydrofuran-kappaO)lithium mer-tris(carbazolyl-kappaN)-trans-dichloro(tetrahydrofuran-kappaO)zirconate.

In the title compound, [Li(C(4)H(8)O)(4)][ZrCl(2)(C(12)H(8)N)(3)(C(4)H(8)O)], the environment of the Zr atom is pseudo-octahedral, with the three carbazolyl ligands in a mer configuration. The counter-ion of the zirconium complex is composed of an Li atom surrounded by four tetrahydrofuran (THF) molecules. The THF molecule attached to the Zr atom is disordered over two sites, as are two of the THF molecules in the lithium moiety. All bond distances and angles are consistent with those in complexes with similar structural entities. The Zr-N bond distances are 2.2185 (18) and 2.167 (3) A.

Trans-dichloro-cis-bis(3,6-dimethylcarbazolyl)-cis-bis(tetrahydrofuran)zirconium(IV) benzene sesquisolvate.

In the title compound, [ZrCl(2)(C(14)H(12)N)(2)(C(4)H(8)O)(2)].1.5C(6)H(6), the Zr atom is pseudo-octahedral, with two Cl atoms in trans positions and two tetrahydrofuran molecules in cis positions. The two 3,6-dimethylcarbazolyl ligands are in cis positions and are canted with respect to one another. The two Zr-N distances are 2.1148 (18) and 2.1236 (18) A, and the N-Zr-N angle is 95.08 (7)degrees. The title compound crystallizes as the benzene solvate, with one of the benzene molecules positioned on an inversion center.

(Tetrahydrofuran)potassium mer-trans-tris(carbazolyl)dichloro(tetrahydrofuran)zirconate.

In the title compound, [K(C(4)H(8)O)][ZrCl(2)(C(12)H(8)N)(3)(C(4)H(8)O)], the Zr atom is pseudo-octahedral, with two Cl ligands in trans positions. There is extensive interaction between the potassium cation and two of the aromatic carbazolyl ligands in eta(6) [C.K = 3.167 (3)-3.331 (3) A] and eta(2) [C.K = 3.147 (3)-3.268 (2) A] fashions.