Gallium halide induced heterocycle expansion of dihalodiphosphadiaryldiazanes [(XPNR)2] to the corresponding triphosphatriazanes [(XPNR)3

Reactions of the cyclic diphosphadiazanes (XPNR)(2) (X = Cl, Br; R = 2,6-dimethylphenyl = Dmp, 2,6-diisopropylphenyl = Dipp) with GaX(3) followed by 4-(dimethylamino)pyridine (DMAP) give the corresponding trimers (XPNR)(3). An unusual cyclophosphazanium tetrachlorogallate salt [(DippN)(3)P(3)Cl(2)][GaCl(4)] has been isolated from the reaction of (ClPNDipp)(2) with GaCl(3) and represents an intermediate in the disproportionation process. Dissociation of the gallate ion on reaction of [(DippN)(3)P(3)Cl(2)][GaCl(4)] with DMAP releases a halide ion, which associates with the dicoordinate phosphenium center to give (ClPNDipp)(3). The observations indicate that the presence of medium-sized substituents at nitrogen (R) thermodynamically destabilize the dimer with respect to the trimer, without offering sufficient stabilization of the monomer, as observed for MesNPX (Mes* = 2,4,6-tri-tert-butylphenyl) (Mes* > Dipp > Dmp). Nevertheless, lability of the N-P bond in these derivatives of (XPNR)(2) allows for transformations between dimer and trimer that may include transient existence of the corresponding monomer. Manipulation of substituent steric strain to modify the relative stability of phosphazane oligomers provides a new methodology for diversification of phosphazane chemistry.     

An investigation into the use of platinum ware for silicate analysis

The amount of platinum dissolved from platinum apparatus used for dissolving silicate materials to obtain solutions for analysis has been determined. The study included apparatus made from an alloy containing 95 % platinum and 5 % gold. The affinity of iron and platinum was investigated, together with the problem of removing iron from platinum after the latter has been contaminated during fusions. The behaviour of platinum in a classical scheme for the analysis of silicate materials was investigated and the distribution of the platinum in various precipitates established. Platinum has been found to interfere in commonly used methods for the determination of silica, aluminium, iron, titanium, calcium and magnesium.     

Development of an enantiodivergent strategy for the total synthesis of (+)- and (-)-dragmacidin f from a single enantiomer of quinic Acid

An enantiodivergent strategy for the total chemical synthesis of both (+)- and (-)-dragmacidin F beginning from a single enantiomer of quinic acid has been developed and successfully implemented. Although unique, the synthetic routes to these antipodes share a number of key features, including novel reductive isomerization reactions, Pd(II)-mediated oxidative carbocyclization reactions, halogen-selective Suzuki couplings, and high-yielding late-stage Neber rearrangements.     

Optical sensor for the determination of moisture

Cobalt(II) chloride in gelatin is cast as films on the surface of 600-μm optical fibers. The absorption of these films at 680 nm is measured through the fiber by internal reflection spectroscopy to determine the relative humidity of air between 40% and 80%. The spectrum of cobalt chloride on the fiber is similar to a transmission spectrum rather than an attenuated totla reflection (a.t.r.) spectrum because of the refractive index of the film, which is slightly greater than that of the fiber. Consequently, the spectrum is less sensitive to measurements near the critical angle, and to refractive index changes than is the case with an a.t.r. spectrum. The uptake of water by cobalt chloride at different humidities suggests that the spectral change is due to the formation of hydrates having molecules of bound water similar to those shown by the free salt.     

Factors affecting the solid-state structure and dimensionality of mercury cyanide/chloride double salts, and NMR characterization of coordination geometries

In the reaction of organic monocationic chlorides or coordinatively saturated metal-ligand complex chlorides with linear, neutral Hg(CN)(2) building blocks, the Lewis-acidic Hg(CN)(2) moieties accept the chloride ligands to form mercury cyanide/chloride double salt anions that in several cases form infinite 1-D and 2-D arrays. Thus, [PPN][Hg(CN)(2)Cl].H(2)O (1), [(n)Bu(4)N][Hg(CN)(2)Cl].0.5 H(2)O (2), and [Ni(terpy)(2)][Hg(CN)(2)Cl](2) (4) contain [Hg(CN)(2)Cl](2)(2-) anionic dimers ([PPN]Cl = bis(triphenylphosphoranylidene)ammonium chloride, [(n)Bu(4)N]Cl = tetrabutylammonium chloride, terpy = 2,2':6',6' '-terpyridine). [Cu(en)(2)][Hg(CN)(2)Cl](2) (5) is composed of alternating 1-D chloride-bridged [Hg(CN)(2)Cl](n)(n-) ladders and cationic columns of [Cu(en)(2)](2+) (en = ethylenediamine). When [Co(en)(3)]Cl(3) is reacted with 3 equiv of Hg(CN)(2), 1-D [[Hg(CN)(2)](2)Cl](n)(n-) ribbons and [Hg(CN)(2)Cl(2)](2-) moieties are formed; both form hydrogen bonds to [Co(en)(3)](3+) cations, yielding [Co(en)(3)][Hg(CN)(2)Cl(2)][[Hg(CN)(2)](2)Cl] (6). In [Co(NH(3))(6)](2)[Hg(CN)(2)](5)Cl(6).2H(2)O (7), [Co(NH(3))(6)](3+) cations and water molecules are sandwiched between chloride-bridged 2-D anionic [[Hg(CN)(2)](5)Cl(6)](n)(6n-) layers, which contain square cavities. The presence (or absence), number, and profile of hydrogen bond donor sites of the transition metal amine ligands were observed to strongly influence the structural motif and dimensionality adopted by the anionic double salt complex anions, while cation shape and cation charge had little effect. (199)Hg chemical shift tensors and (1)J((13)C,(199)Hg) values measured in selected compounds reveal that the NMR properties are dominated by the Hg(CN)(2) moiety, with little influence from the chloride bonding characteristics. delta(iso)((13)CN) values in the isolated dimers are remarkably sensitive to the local geometry.     

Preparation and study of cyclic polynuclear ferrocenes derived from (C6H5)2PCH2CH2Si(CH3)2C5H4Li as a bridging ligand

The synthesis of the potential bridging ligand (C₆H₅)₂PCH₂CH₂Si(CH₃)₂C₅H₄ (3) is described. The ferrocene (6 derived from 3 has been found to form macrocyclic complexes with metal fragments NiCl₂, NiBr₂, and Co₂(CO)₆. Although monomeric, bimetallic products might have been expected based upon the reduced steric demands of ligand 3 relative to an analogous ligand, (C₆H₅)₂PCH₂Si(CH)₃)₂C₅H₄ (1), it appears that the increased flexibility in 3 is the overriding factor leading to a preference for inter- rather than intramolecular coordination of the second phosphine function in 6.     

Water superstructures within organic arrays; hydrogen-bonded water sheets, chains and clusters

A strategy for encouraging the formation of extended water arrays is presented, in which molecules that contain a 1,4-dihydroquinoxaline-2,3-dione core are used as supramolecular hosts for the accommodation of guest water molecules and arrays. These molecules were selected as they contain a hydrophilic oxalamide-based "terminus" that allows water molecules to hydrogen-bond to the host organic molecules as well as to each other. The host molecules also contain a hydrophobic "end" based upon an aromatic ring, which serves to encourage the formation of discrete water clusters in preference to three-dimensional networks, as the water molecules cannot form strong hydrogen bonds with this part of the molecule. A systematic study of several hydrated structures of four organic molecules based on 1,4-dihydroquinoxaline-2,3-dione (qd) is discussed. The organic molecules, qd, 6-methyl-1,4-dihydroquinoxaline-2,3-dione (mqd), 6,7-dimethyl-1,4-dihydroquinoxaline-2,3-dione (dmqd) and 1,4-dihydrobenzo[g]quinoxaline-2,3-dione (Phqd), act as supramolecular crystal hosts for the clusters of water, with zero-, one- and two-dimensional arrays of water being observed. The hydrogen bonding in the structures, both within the water clusters and between the clusters and organic molecules, is examined. In particular, the structure of dmqd6 H2O contains a two-dimensional water sheet composed of pentagonal and octagonal units. Phqd3 H2O forms a hydrophilic extended structure encouraging the formation of one-dimensional chains consisting entirely of water. Both qd2 H2O and dmqd2 H2O can be considered to form one-dimensional chains, but only by utilising bridging carbonyl groups of the oxalamide moieties to form the extended array; if only the water is considered, zero-dimensional water tetramers are observed. The remaining hydrated structures, [Na+dmqd-]dmqdH2O, dmqd1/3H2O and mqd1/2H2O, all contain discrete water molecules but do not form extended water structures.     

Relapse of pathological angiogenesis: functional role of the basement membrane and potential treatment strategies

Blinding eye diseases such as corneal neovascularization, proliferative diabetic retinopathy, and age-related macular degeneration are driven by pathological angiogenesis. In cancer, angiogenesis is key for tumor growth and metastasis. Current antiangiogenic treatments applied clinically interfere with the VEGF signaling pathway—the main angiogenic pathway—to inhibit angiogenesis. These treatments are, however, only partially effective in regressing new pathologic vessels, and the disease relapses following cessation of treatment. Moreover, the relapse of pathological angiogenesis can be rapid, aggressive and more difficult to treat than angiogenesis in the initial phase. The manner in which relapse occurs is poorly understood; however, recent studies have begun to shed light on the mechanisms underlying the revascularization process. Hypotheses have been generated to explain the rapid angiogenic relapse and increased resistance of relapsed disease to treatment. In this context, the present review summarizes knowledge of the various mechanisms of disease relapse gained from different experimental models of pathological angiogenesis. In addition, the basement membrane—a remnant of regressed vessels—is examined in detail to discuss its potential role in disease relapse. Finally, approaches for gaining a better understanding of the relapse process are discussed, including prospects for the management of relapse in the context of disease.Subject terms: Inflammation, Experimental models of disease     

Simulation study of the coil-globule transition of a polymer in solvent

Molecular dynamics simulations are used to study the coil-globule transition for a system composed of a bead-spring polymer immersed in an explicitly modeled solvent. Two different versions of the model are used, which are differentiated by the nature of monomer-solvent, solvent-solvent, and nonbonded monomer-monomer interactions. For each case, a model parameter lambda determines the degree of hydrophobicity of the monomers by controlling the degree of energy mismatch between the monomers and solvent particles. We consider a lambda-driven coil-globule transition at constant temperature. The simulations are used to calculate average static structure factors, which are then used to determine the scaling exponents of the system in order to determine the theta-point values lambdatheta separating the coil from the globule states. For each model we construct coil-globule phase diagrams in terms of lambda and the particle density rho. The results are analyzed in terms of a simple Flory-type theory of the collapse transition. The ratio of lambdatheta for the two models converges in the high density limit exactly to the value predicted by the theory in the random mixing approximation. Generally, the predicted values of lambdatheta are in reasonable agreement with the measured values at high rho, though the accuracy improves if the average chain size is calculated using the full probability distribution associated with the polymer-solvent free energy, rather than merely using the value obtained from the minimum of the free energy.     

Solvophobic acceleration of Diels-Alder reactions in supercritical carbon dioxide

The rate of the Diels-Alder reaction between N-ethylmaleimide and 9-hydroxymethylanthracene in supercritical carbon dioxide (scCO(2)) was determined by following the disappearance of 9-hydroxymethylanthracene with in situ UV/vis absorption spectroscopy. The reaction conditions were 45-75 degrees C and 90-190 bar, which correspond to fluid densities (based on pure carbon dioxide) ranging between approximately 340 and 730 kg m(-3). The measured reaction rate at low scCO(2) fluid densities was nearly 25x faster than that reported in acetonitrile at the same temperature (45 degrees C). An inverse relationship between reaction rate and fluid density/pressure was observed at all temperatures in scCO(2). The apparent activation volumes were large and positive (350 cm(3) mol(-1)) and only a weak function of reduced temperature. A solvophobic mechanism analogous to those observed in conventional solvents is postulated to describe (a) the rate acceleration observed for this reaction in scCO(2) relative to that in acetonitrile, (b) the observed relationship between reaction rate and pressure/temperature/density, and (c) the large, positive activation volumes. Solubility measurements in scCO(2), rate measurements in conventional solvents, and an empirical correlation are used to support this theory. Our results advance the general understanding of reactivity in supercritical fluids and provide a rationale for selecting reactions which can be accelerated when conducted in scCO(2).