Fatty acid composition of human erythrocyte membranes by capillary gas chromatography-mass spectrometry

Capillary gas chromatographic and gas chromatographic--mass spectrometric methods were employed for profiling total fatty acid content of human erythrocyte membranes. The protocol was designed to efficiently separate, identify, and accurately quantify the fatty acid composition in human erythrocyte membranes. Washed erythrocyte "ghosts" were saponified in aqueous methanolic sodium hydroxide solution and methylated with boron trichloride and acid catalysis. Extracted total fatty acid methyl esters (FAMEs) were analyzed using a highly polar cyanopropylsiloxane SP 2560 fused-silica capillary column. Total run time was 55 min, and 45 FAMEs were tentatively identified by relative retention times compared to those of known FAMEs. Confirmation of identities by mass spectral structure elucidation revealed saturated, mono- and polyunsaturated, and branched-chain FAMEs. The presence of four fatty aldehydes was also confirmed as dimethyl acetal derivatives. Identification of cis/trans isomers was based on relative retention times and characteristic profile of the cis/trans FAME standard. Quantification of FAMEs for normal subjects showed some variation in relative amounts, consistent with expectations based on literature reports on total or phospholipid FAMEs from human erythrocytes. Separation of individual components of fatty acid families (n-3), (n-6), and (n-9) is demonstrated. Losses in relative amounts of polyunsaturated fatty acids upon storing samples were also detectable by this rapid method.     

Dihydrogen activation by a diruthenium analogue of the Fe-only hydrogenase active site

The photochemical reaction of Ru2(S2C3H6)(CO)4(PCy3)2 (1) and H2 gives the dihydride Ru2(S2C3H6)(mu-H)(H)(CO)3(PCy3)2 (2). NMR and crystallographic studies reveal mutually trans basal phosphine ligands and both bridging and terminal hydrides. Ru2(S2C2H4)(CO)4(PCy3)2 behaves similarly. Other HX substrates undergo photoaddition to 1, affording Ru2(S2C3H6)(mu-H)(X)(CO)3(PCy3)2 for X = OTs (3a), Cl (3b), and SPh (3c). Treatment of Ru2(S2C3H6)(mu-H)(H)(CO)3(PCy3)2 with [H(OEt2)]BArF4 (ArF = B(C6H3-3,5-(CF3)2) in CD2Cl2 gives [Ru2(S2C3H6)(mu-H)(CO)3(PCy3)2(H2)]+ (4), which catalyzes H2-D2 exchange. The reaction of 2 with [D(OEt2)]BArF4 gave [Ru2(S2C3H6)(mu-H)(CO)3(PCy3)2(HD)]+ (JH-D = 31 Hz). These studies provide the first models for the Fe-only hydrogenases that bear dihydrogen and terminal hydrido ligands.     

Nuclear multifragmentation, percolation, and the fisher droplet model: common features of reducibility and thermal scaling

It is shown that the Fisher droplet model, percolation, and nuclear multifragmentation share the common features of reducibility (stochasticity in multiplicity distributions) and thermal scaling (one-fragment production probabilities are Boltzmann factors). Barriers obtained, for cluster production on percolation lattices, from the Boltzmann factors show a power-law dependence on cluster size with an exponent of 0.42+/-0.02. The EOS Collaboration Au multifragmentation data yield barriers with a power-law exponent of 0.68+/-0.03. Values of the surface energy coefficient of a low density nuclear system are also extracted.     

Thermophysical Properties of CeB6 and PrB6 at subambient temperatures

Equilibrium adiabatic heat-capacity measurements have been made on zone refined samples of CeB₆ and PrB₆. Companion measurements made on LaB₆, NdB₆, and GdB₆ have been reported elsewhere. These show cooperative lambda-type anomalies associated with antiferro-magnetic ordering. Except for lanthanum hexaboride, Schottky internal crystal field levels result in significant contributions to the thermodynamic functions. The gross thermodynamic properties at 298.15 K heat capacity (C_p/R), entropy increment (Δ^T _0,m S ⁰/R), and Gibbs energy function are correlated with the nature of the lanthanide. For LaB₆, CeB₆, PrB₆, NdB₆, and GdB₆ the three properties are, respectively: {11.654, 12.014, 11.997, 11.916, 11.695} Cp/R; {10.001, 11.803, 12.430, 12.558, 13.982} S⁰/R, and finally {4.379, 5.912, 6.232, 6.451, 7.905}Φ⁰ _m/R. This revised version was published online in August 2006 with corrections to the Cover Date.     

Conductance study of some 1-1 electrolytes in dimethyl sulfoxide and hexamethylphosphoramide

Conductance measurements of 1-1 electrolytes were made in HMPT and DMSO at 25°C. The limiting conductances and the association constants were evaluated and discussed in terms of solvation. A great similarity is observed between these dipolar aprotic solvents. For sodium and potassium ions, the results can be explained in terms of classic ion-dipole interactions. For other ions such as tetraalkylammonium, tetraphenylboride, chlorate, and perchlorate, the solvation cosphere effects increase the mobilities and the short-range attractions between anions and cations.     

Diiron dithiolato carbonyls related to the H(ox)CO state of [FeFe]-hydrogenase

Oxidation of the electron-rich (E(1/2) = -175 vs Ag/AgCl) ethanedithiolato complex Fe2(S2C2H4)(CO)2(dppv)2 (1) under a CO atmosphere yielded [Fe2(S2C2H4)(mu-CO)(CO)2(dppv)2](+) ([1(CO)](+)), a model for the H(ox)(CO) state of the [FeFe]-hydrogenases. This complex exists as two isomers: a kinetically favored unsymmetrical derivative, unsym-[1(CO)](+), and a thermodynamically favored isomer, sym-[1(CO)](+), wherein both diphosphines span apical and basal sites. Crystallographic characterization of sym-[1(CO)](+) confirmed a C2-symmetric structure with a bridging CO ligand and an elongated Fe-Fe bond of 2.7012(14) A, as predicted previously. Oxidation of sym-[1(CO)](+) and unsym-[1(CO)](+) again by 1e(-) oxidation afforded the respective diamagnetic diferrous derivatives where the relative stabilities of the sym and unsym isomers are reversed. DFT calculations indicate that the stabilities of sym and unsym isomers are affected differently by the oxidation state of the diiron unit: the mutually trans CO ligands in the sym isomer are more destabilizing in the mixed-valence state than in the diferrous state. EPR analysis of mixed-valence complexes revealed that, for [1](+), the unpaired spin is localized on a single iron center, whereas for unsym/sym-[1(CO)](+), the unpaired spin was delocalized over both iron centers, as indicated by the magnitude of the hyperfine coupling to the phosphine ligands trans to the Fe-Fe vector. Oxidation of 1 by 2 equiv of acetylferrocenium afforded the dication [1](2+), which, on the basis of low-temperature IR spectrum, is structurally similar to [1](+). Treatment of [1](2+) with CO gives unsym-[1(CO)](2+).     

Lewis vs. Brønsted-basicities of diiron dithiolates: spectroscopic detection of the "rotated structure" and remarkable effects of ethane- vs. propanedithiolate

The new complexes Fe2(S2CnH2n)(CO)2(dppv)2 (n = 2, 3; dppv = cis-1,2-C2H2(PPh2)2) form adducts with AlBr3 and B(C6F5)3, which adopt the "rotated structure" proposed for the active site of the Fe-only hydrogenases--the propanedithiolate is significantly more Lewis basic due to nonbonded interactions between the dithiolate strap and the ligands on Fe.     

Emerging optofluidic technologies for point-of-care genetic analysis systems: a review

This review describes recently emerging optical and microfluidic technologies suitable for point-of-care genetic analysis systems. Such systems must rapidly detect hundreds of mutations from biological samples with low DNA concentration. We review optical technologies delivering multiplex sensitivity and compatible with lab-on-chip integration for both tagged and non-tagged optical detection, identifying significant source and detector technology emerging from telecommunications technology. We highlight the potential for improved hybridization efficiency through careful microfluidic design and outline some novel enhancement approaches using target molecule confinement. Optimization of fluidic parameters such as flow rate, channel height and time facilitates enhanced hybridization efficiency and consequently detection performance as compared with conventional assay formats (e.g. microwell plates). We highlight lab-on-chip implementations with integrated microfluidic control for “sample-to-answer” systems where molecular biology protocols to realize detection of target DNA sequences from whole blood are required. We also review relevant technology approaches to optofluidic integration, and highlight the issue of biomolecule compatibility. Key areas in the development of an integrated optofluidic system for DNA hybridization are optical/fluidic integration and the impact on biomolecules immobilized within the system. A wide range of technology platforms have been advanced for detection, quantification and other forms of characterization of a range of biomolecules (e.g. RNA, DNA, protein and whole cell). Owing to the very different requirements for sample preparation, manipulation and detection of the different types of biomolecules, this review is focused primarily on DNA–DNA interactions in the context of point-of-care analysis systems.     

Assessment of submicron particle zeta potential in simple electrokinetic microdevices

The present communication illustrates the use of simple electrokinetic devices for the assessment of the zeta potential of submicron polystyrene particles. A combination of manual and automatic particle tracking was employed. This approach allows for characterizing particles in the same conditions and devices in which they can be separated, e.g. dielectrophoretic separations; making the resulting data readily applicable.