Mass spectrometric and theoretical study of polyiodides: the connection between solid state, solution, and gas phases

Polyiodides have been transferred intact from acetonitrile solution to the gas phase and analyzed by mass spectrometry. A range of ions were observed, including [I(11)](-), [I(13)](-), and [I(15)](-), which have higher iodine/iodide ratios than any previously characterized ions. Theoretical calculations show that branched structures are strongly favored, a result which is in excellent agreement with with gas phase fragmentation studies (MS/MS) and also previous solid state studies. This study demonstrates the utility of mass spectrometry to provide structural information in the absence of other spectroscopic handles.     

The mechanism of radical-trapping antioxidant activity of plant-derived thiosulfinates

It has long been recognized that garlic and petiveria, two plants of the Allium genus--which also includes onions, leeks and shallots--possess great medicinal value. In recent times, the biological activities of extracts of these plants have been ascribed to the antioxidant properties of the thiosulfinate secondary metabolites allicin and S-benzyl phenylmethanethiosulfinate (BPT), respectively. Herein we describe our efforts to probe the mechanism of the radical-trapping antioxidant activity of these compounds, as well as S-propyl propanethiosulfinate (PPT), a saturated analog representative of the thiosulfinates that predominate in non-medicinal alliums. Our experimental results, which include thiosulfinate-inhibited autoxidations of the polyunsaturated fatty acid (ester) methyl linoleate, investigations of their decomposition kinetics, and radical clock experiments aimed at obtaining some quantitative insights into their reactions with peroxyl radicals, indicate that the radical-trapping activity of thiosulfinates is paralleled by their propensity to undergo Cope elimination to yield a sulfenic acid. Since sulfenic acids are transient species, we complement our experimental studies with the results of theoretical calculations aimed at understanding the radical-trapping behaviour of the sulfenic acids derived from allicin, BPT and PPT, and contrasting the predicted thermodynamics and kinetics of their reactions with those of the parent thiosulfinates. The calculations reveal that sulfenic acids have among the weakest O-H bonds known (ca. 70 kcal mol(-1)), and that their reactions with peroxyl radicals take place by a near diffusion-controlled proton-coupled electron transfer mechanism. As such, it is proposed that the abundance of a thiosulfinate in a given plant species, and the ease with which it undergoes Cope elimination to form a sulfenic acid, accounts for the differences in antioxidant activity, and perhaps medicinal value, of extracts of these plants. Interestingly, while the Cope elimination of 2-propenesulfenic acid from allicin is essentially irreversible, the analogous reaction of BPT is readily reversible. Thus, in the absence of chain-carrying peroxyl radicals (or other appropriately reactive trapping agent), BPT is reformed.     

Adsorption equilibrium of methane and carbon dioxide on porous metal-organic framework Zn-BTB

Porous metal-organic frameworks (MOFs) have emerged over the past decade as an important new class of materials possessing permanent porosities, uniform pore structures, high surface areas, and low crystal densities. MOFs are regarded as promising solid adsorbents for gas storage and separation but have not reached an applied level yet. One impediment to MOF applications is incomplete adsorption information and lack of structure-property relationships. In this paper, we present pure-component adsorption equilibrium data for methane and carbon dioxide at different temperatures on a new three-dimensional Zn-MOF material built from the ligand 1,3,5-tris(4-carboxyphenyl)benzene (H₃BTB) with Zn metal. The data are described by Toth’s equation and Dubinin-Astakhov (D-A) equation. Thermodynamic properties including isosteric heat of adsorption are estimated based on the two models and comparisons are made with other adsorbents. The smaller pore diameters of Zn-MOF compared to related structures MOF-177 and UMCM-1 lead to greater adsorption loadings at 1 bar.     

The role of molecular chaperonins in warm ischemia and reperfusion injury in the steatotic liver: A proteomic study

ABSTRACT: BACKGROUND: The molecular basis of the increased susceptibility of steatotic livers to warm ischemia/reperfusion (I/R) injury during transplantation remains undefined. Animal model for warm I/R injury was induced in obese Zucker rats. Lean Zucker rats provided controls. Two dimensional differential gel electrophoresis was performed with liver protein extracts. Protein features with significant abundance ratios (p < 0.01) between the two cohorts were selected and analyzed with HPLC/MS. Proteins were identified by Uniprot database. Interactive protein networks were generated using Ingenuity Pathway Analysis and GRANITE software. RESULTS: The relative abundance of 105 proteins was observed in warm I/R injury. Functional grouping revealed four categories of importance: molecular chaperones/endoplasmic reticulum (ER) stress, oxidative stress, metabolism, and cell structure. Hypoxia up-regulated 1, calcium binding protein 1, calreticulin, heat shock protein (HSP) 60, HSP-90, and protein disulfide isomerase 3 were chaperonins significantly (p < 0.01) down-regulated and only one chaperonin, HSP-1was significantly upregulated in steatotic liver following I/R. CONCLUSION: Down-regulation of the chaperones identified in this analysis may contribute to the increased ER stress and, consequently, apoptosis and necrosis. This study provides an initial platform for future investigation of the role of chaperones and therapeutic targets for increasing the viability of steatotic liver allografts.     

Substituent effects on Ni-S bond dissociation energies and kinetic stability of nickel arylthiolate complexes supported by a bis(phosphinite)-based pincer ligand

Pincer complexes of the type [2,6-(R(2)PO)(2)C(6)H(3)]NiSC(6)H(4)Z (R = Ph and i-Pr; Z = p-OCH(3), p-CH(3), H, p-Cl, and p-CF(3)) have been synthesized from [2,6-(R(2)PO)(2)C(6)H(3)]NiCl and sodium arylthiolate. X-ray structure determinations of these thiolate complexes have shown a somewhat constant Ni-S bond length (approx. 2.20 ?) but an almost unpredictable orientation of the thiolate ligand. Equilibrium constants for various thiolate exchange (between a nickel thiolate complex and a free thiol, or between two different nickel thiolate complexes) reactions have been measured. Evidently, the thiolate ligand with an electron-withdrawing substituent prefers to bond with "[2,6-(Ph(2)PO)(2)C(6)H(3)]Ni" rather than "[2,6-(i-Pr(2)PO)(2)C(6)H(3)]Ni", and bonds least favourably with hydrogen. The reactions of the thiolate complexes with halogenated compounds such as PhCH(2)Br, CH(3)I, CCl(4), and Ph(3)CCl have been examined and several mechanistic pathways have been explored.     

Construction of a Microstructured Collagen Membrane Mimicking the Papillary Dermis Architecture and Guiding Keratinocyte Morphology and Gene Expression

A papillary‐structured collagen fibril membrane is created, mimicking the 3D‐architecture of the human papillary dermis. Primary human keratinocytes cultured to confluency on papillar‐structured films are compared to keratinocytes cultured on flat membranes. Microscopical evaluation reveals the presence of morphologically distinct cells at the base of the papillar structures that are not observed on flat membranes. Gene expression microarrays and RT‐qPCR indicate that these cells are in a more proliferative/migrational state, whereas cells on flat membranes have a more differentiated expression profile. Immunohistochemical stainings confirm these results. In conclusion, specific collagen architecture can direct keratinocyte behavior, and this may be used to further improve skin regeneration.

     

Novel Gas Separation Membranes Containing Covalently Bonded Fullerenes

Summary: In this work, we report superior mass transport properties of polymers prepared by the covalent coupling of supermolecular carbon cages (e.g., fullerenes, bucky balls) to a poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) polymer. Dispersing the bucky balls into the polymer reduces gas permeability, whereas covalent bonding enhances permeability up to 80% in comparison to the pure PPO. Gas pair selectivity, however, is not compromised and stays constant.

Schematic representation of the PPO polymer membrane and the PPO‐covalently bonded C₆₀ polymer membrane.     

Adsorption Equilibrium of Alkanes on a High Surface Area Activated Carbon Prepared from Brazilian Coconut Shells

Adsorption equilibria of methane, ethane, and n-butane on a high surface area activated carbon prepared from Brazilian coconut shells is examined in this study. The material shows high capacities for the alkanes tested. A group-contribution theory is used to predict adsorption isotherms for all three components with very good accuracy employing one set of model parameters. The theory is also used to observe trends in isosteric heat of adsorption as a function of loading at various temperatures.