Mass transfer of oxygen in poly(2-hydroxyethyl methacrylate)

The diffusion coefficient of oxygen in poly(2-hydroxyethyl methacrylate) has been explicitly measured using an optical technique based on fluorescence quenching. This measurement represents the first explicit determination of D in PHEMA. A diffusion coefficient of oxygen in PHEMA of 1.36 × 10^?7 cm²/s at 20°C was obtained from this measurement. This value is shown to agree well with permeability data for PHEMA, the free volume theory of diffusion, and with values of D that have been explicitly measured in other methacrylate hydrogels.     

Resolution of the non-steady-state kinetics of the elimination of HBr from 2-(p-nitrophenyl)ethyl bromide in alcohol/alkoxide media

Non-steady-state kinetic studies reveal that the elimination of HBr from 2-(p-nitrophenyl)ethyl bromide in alcohol/alkoxide media, the classical concerted E2 reaction, actually takes place by a two-step mechanism involving the intermediate formation of the carbanion.     

Gas‐phase functionalized carbon‐carbon coupling reactions catalyzed by Ni (II) complexes

Gas‐phase C―C coupling reactions mediated by Ni (II) complexes were studied using a linear quadrupole ion trap mass spectrometer. Ternary nickel cationic carboxylate complexes, [(phen)Ni (OOCR¹)]⁺ (where phen = 1,10‐phenanthroline), were formed by electrospray ionization. Upon collision‐induced dissociation (CID), they extrude CO₂ forming the organometallic cation [(phen)Ni(R¹)]⁺, which undergoes gas‐phase ion‐molecule reactions (IMR) with acetate esters CH₃COOR² to yield the acetate complex [(phen)Ni (OOCCH₃)]⁺ and a C―C coupling product R¹‐R². These Ni(II)/phenanthroline‐mediated coupling reactions can be performed with a variety of carbon substituents R¹ and R² (sp³, sp², or aromatic), some of them functionalized. Reaction rates do not seem to be strongly dependent on the nature of the substituents, as sp³‐sp³ or sp²‐sp² coupling reactions proceed rapidly. Experimental results are supported by density functional theory calculations, which provide insights into the energetics associated with the C―C bond coupling step.     

Free energy of adsorption of water and calcium on the [10 1 4] calcite surface

Molecular dynamics simulations of the calcite-water interface have shown that the free energy of adsorption of water is relatively small compared to the previously calculated enthalpy of adsorption implying a large entropy change and that the free energy profile of a calcium adsorbing on the surface correlates with the solvent density; these calculations allow us to begin to address the rates of adsorption and desorption which are essential for studying growth and dissolution.     

Self-assembly of flexible supramolecular metallacyclic ensembles: structures and adsorption properties of their nanoporous crystalline frameworks

The syntheses, structures, and N2 adsorption properties of six new supramolecular metallacycles are reported. Flexible ditopic linkers, 1-4, with systematically varied lengths and conformational degrees of freedom were synthesized utilizing ester linkages. They were used in combination with (dppp)M(OTf)2, where M = Pt(II) and Pd(II), and cis-(Me3P)2Pt(OTf)2 to form flexible supramolecular metallacycles 5-10 in 88-98% isolated yields. Their structures were characterized via multinuclear NMR and X-ray crystallography. The metallacycles stack to form porous structures in the crystalline state. The pore dimensions depend on both the phosphorus ligands attached to the metals and the flexible linkers. Adsorption studies on the porous materials show that 5a, 6, 8, and 9 held 11.7, 16.5, 5.7, and 6.8 cm3/g STP of N2 at 77 K, respectively. A guest-exchange study with nitromethane and toluene reveals that the nanopore in 5 is flexible, a property which was transferred from the linker to the supramolecular structure in the solid state.     

BSE control: detection of gelatine-derived peptides in animal feed by mass spectrometry

The epidemic of bovine spongiform encephalopathy (BSE) is thought to have resulted from feeding scrapie-infected sheep to cattle. This has led to a ban of feeding animals with "processed animal protein"(PAP). We report a novel approach for the mass spectrometric detection of PAP contamination in animal feedstuffs by detecting gelatine, a derivative of the major animal protein collagen. A method was developed to hydrolyse gelatine standards with hydrochloric acid, followed by detection of the derived hydrolytic peptides at m/z 828, 915, 957 and 1044 by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) and liquid chromatography electrospray ionisation mass spectrometry (LC-ESI-MS-MS). The marker peptides can be detected at concentrations of 100 ng ml(-1) gelatine in water with MALDI. The procedure was adapted to obtain a suitable peptide map of gelatine extracted from spiked feed. The ratio of signal area of the gelatine-derived peptide at m/z 1044 to the internal standard at m/z 556 is shown to relate to the total amount of gelatine present in the sample.     

Tuning azolium azolate ionic liquids to promote surface interactions with titanium nanoparticles leading to increased passivation and colloidal stability

The passivation and stability of suspensions of titanium nanoparticles in azolium azolate ionic liquids can be tuned by introducing metal specific binding sites in the azolate anion.     

193 NM LIGHT INDUCES SINGLE STRAND BREAKAGE OF DNA PREDOMINANTLY AT GUANINE

Irradiation of DNA with 193 nm light results in monophotonic photoionization, with the formation of a base radical cation and a hydrated electron (φ_P1 = 0.048–0.065). Although >50% of the photoionization events initially occur at guanine in DNA, migration of the “hole” from the other bases to guanine occurs to yield predominantly its radical cation or its deprotonated form. From sequence analysis, the data reveal that 193 nm light induces single strand breaks (ssb) in double-stranded DNA preferential 3’ to a guanine residue. However, it has previously been reported that 193 nm light yields very low yields of ssb (<2% of the yield of eaq). The distribution of these ssb at guanine is nonrandom, showing a dependence on the neighboring base moiety. The efficiency of ssb formation at nonguanine sites is estimated to be at least one order of magnitude lower. The preferred cleavage at guanine is consistent with migration and localization of the electron loss center at guanine. It is argued that singlet oxygen and the photoionized phosphate group of the sugar moiety are not major precursors to ssb. At present, the mechanisms of strand breakage are not known although a guanine radical or one of its products remain potential precursors.