Kinetic studies on the deaquation-anation of aquapentammine-cobalt(III) chloride

Summary The deaquation-anation of solid aquapentamminecobalt(III) chloride was studied isothermally and non-isothermally. Kinetic data were obtained from t.g.a. and were analysed using 17 rate laws known for solid state reactions. This reaction, long interpreted as S_N2, was found to obey an A1.5 rate law from both types of experiments. From the isothermal experiments, an E _a of 97.0 kJ mol^-1 was found.     

Surface enrichment of proteins at quartz/water interfaces: a neutron reflectivity study

Neutron reflectivity (NR) was used to study the adsorption of human serum albumin and human fibrinogen on quartz. The proteins were individually and sequentially adsorbed from heavy water and heavy water/methanol mixtures at pH 4 and 7.0. The technique allows for the subnanometer resolution of the adsorbed layer thickness and gross morphology. Under the conditions of our measurements we found that fibrinogen formed a distinct layer that we interpret as a mat of the protein three layers thick whereas albumin formed only diffuse layers. The adsorption pattern of the two proteins changed radically when one protein was adsorbed on top of the other (previously adsorbed). In general our measurements indicate that the adsorbed protein layers on quartz are rather loosely bound and that these layers, incorporating as much as 80% water, extend further into the bulk fluid than might have been expected.     

The assembly of organic radical anions between metal-borate scaffolds

Metal-organic frameworks based on the Pb[B(Im)(4)](+) unit form layered structures analogous to those observed in clays and double layered hydroxide minerals. These layers can act as scaffolds for the organization of anionic organic guests. In this report, we use this scaffold to assemble TEMPO and PROXYL carboxylates in the interlayer spacings of Pb[B(Im)(4)](4-carboxy-TEMPO) 1 and Pb[B(Im)(4)](3-carboxy-PROXYL)(H(2)O)2, respectively. The resultant materials are paramagnetic, and the organization of the radical units differs between the two compounds. This results in changes in electronic structure of the radical unit, as observed by EPR spectroscopy.     

Terephthalamide derivatives as mimetics of helical peptides: disruption of the Bcl-x(L)/Bak interaction

A series of Bcl-x(L)/Bak antagonists, based on a terephthalamide scaffold, was designed to mimic the alpha-helical region of the Bak peptide. These molecules showed favorable in vitro activities in disrupting the Bcl-x(L)/Bak BH3 domain complex (terephthalamides 9 and 26, K(i) = 0.78 +/- 0.07 and 1.85 +/- 0.32 microM, respectively). Extensive structure-affinity studies demonstrated a correlation between the ability of terephthalamide derivatives to disrupt Bcl-x(L)/Bak complex formation and the size of variable side chains on these molecules. Treatment of human HEK293 cells with the terephthalamide derivative 26 resulted in disruption of the Bcl-x(L)/Bax interaction in whole cells with an IC(50) of 35.0 microM. Computational docking simulations and NMR experiments suggested that the binding cleft for the BH3 domain of the Bak peptide on the surface of Bcl-x(L) is the target area for these synthetic inhibitors.     

ZIF-8 degrades in cell media,serum, and some—but not all—common laboratory buffers

ABSTRACT

Drug delivery using metal-organic frameworks (MOF) has elicited interest in their biocompatibility; however, few studies have been conducted on their stability in common buffers, cell media, and blood proteins. In particular, the use of ZIF-8, a MOF interconnected by Zn and methylimidazole, has been frequently employed. In this study, we tested single crystals of ZIF-8 with common laboratory buffers, cell media, and serum, and noted several issues. Buffers containing phosphate and bicarbonate alter the appearance and composition of ZIF-8; however, these buffers do not appear to cause cargo to leak out even when the ZIF-8 itself is displaced by phosphates. On the other hand, serum dissolves ZIF-8, causing premature cargo release. Our results show that ZIF-8 undergoes surface chemistry changes that may affect the interpretation of cellular uptake and cargo release data. On the other hand, it provides a rational explanation as to how ZIF-8 neatly dissolves in vivo.     

Analysis for sulfur as hydrogen sulfide incorporating zirconia pretreatment and preconcentration

The method of analysis for sulfate by reduction of high oxidation state sulfur to hydrogen sulfide, followed by spectrophotometric analysis, has the advantages of allowing small quantities to be measured and some interfering species to be removed. However, it has been found that acid digested samples cannot be analysed by this method due to destruction of the reduction mixture. A column of zirconium(IV) oxide was successfully used to both, remove interfering ions (H(+), Cl(-) and NO(-)(3)) from a sediment digest, as well as perform preconcentration of sulfate. Recoveries from digests of standard sulfur samples were 101 +/- 1%, and from preconcentration solutions 98.8 +/- 1.2%. Comparison of results with independent analyses confirmed that not all sulfur species are detected with the same efficiency by the combined zirconia/reduction-spectrophotometric method.