Collective diffusion coefficient of proteins with hydrodynamic, electrostatic, and adhesive interactions

A theory is presented for lambdaC, the coefficient of the first-order correction in the density of the collective diffusion coefficient, for protein spheres interacting by electrostatic and adhesive forces. An extensive numerical analysis of the Stokesian hydrodynamics of two moving spheres is given so as to gauge the precise impact of lubrication forces. An effective stickiness is introduced and a simple formula for lambdaC in terms of this variable is put forward. A precise though more elaborate approximation for lambdaC is also developed. These and numerically exact expressions for lambdaC are compared with experimental data on lysozyme at pH 4.5 and a range of ionic strengths between 0.05M and 2M.     

A comparative study of ECNC and CNC suspensions: effect of salt on rheological properties

This paper addresses the effect of monovalent (Na⁺) and divalent (Ca²⁺) ions on the shear viscosity and viscoelastic properties of two different aqueous suspensions of nanoparticles, cellulose nanocrystals (CNCs), and electrosterically stabilized nanocrystals of cellulose (ECNCs). ECNC is similar as CNC, but with carboxylated cellulose chains protruding from both endcaps. The different suspensions were studied in the semi-dilute regime, which corresponded to concentrations ranging from 0.5 to 8 wt% for CNCs and from 0.6 to 9 wt% for ECNCs. As the charges on CNCs are presumably distributed all along the crystal domains and the CNC have a twist in their backbone structure, their suspensions shifted to a cholesteric state as the volume fraction increased while ECNC suspensions did not. This is because the charges on ECNCs are mainly distributed at the endcaps of the particles and the protruding chains expel each other. On the one hand, it was demonstrated that at moderate ionic strength (I = 20 mM), CNC suspensions formed gels even at really low concentrations due to agglomeration. Calcium chloride (CaCl₂) had a greater effect than sodium chloride (NaCl) on both shear and viscoelastic properties due to stronger network formation. On the other hand, ECNCs could withstand much higher ionic strengths than CNCs. NaCl had no effect other than making the ECNC particles precipitate above a concentration of 200 mM, while CaCl₂ made ECNC suspensions turn into gels due to a bridging effect with their carboxylic acid groups at a concentration of [Ca2+] ≈ [COOH]/2.     

Azin­yl sulfides. LXXXI. 14‐Phen­yl‐7‐thia­pyrano[2,3‐c;6,5‐c′]diquinoline‐14‐carbonitrile

The mol­ecules of the title compound, C₂₆H₁₅N₃S, have a penta­cyclic ring system which is almost planar, with the central ring in a flattened boat conformation. The folding angle between the two quinoline rings is 6.75 (7)°. The 14‐phen­yl substituent is in a quasi‐axial conformation, while the 14‐cyano substituent is in a quasi‐equatorial conformation with respect to the thio­pyran ring. The S⋯C—C_phen­yl and S⋯C—C_CN angles are 116.8 (2) and 129.3 (2)°, respectively. The plane of the phen­yl group is nearly coplanar with the plane bis­ecting the dihedral angle of the penta­cyclic ring system.     

Photoisomerisation in single molecules of nitroprusside embedded in mesopores of xerogels

Photoswitchable hybrid materials are successfully prepared by embedding guanidinium nitroprussides (GuNP, (CN₃H₆)₂[Fe(CN)₅NO]) into mesopores of transparent xerogel monoliths. The such prepared hybrid materials exhibit a higher photostability than the corresponding GuNP solutions, whereby the chemical stability of the [Fe(CN)₅NO]²⁻-anion in titania gel is nearly infinite. By irradiation with light in the blue-green spectral range one nitrosyl isomer is formed by a 180° rotation of the NO ligand changing the Fe–NO into a Fe–ON coordination (SI), which is detected by the shift of the ν(NO) stretching vibration from 1945 cm⁻¹ (Fe–NO) to 1820  cm⁻¹ (Fe–ON). Consequently there is enough space around the NO-ligand for such movement in xerogel mesopores. The embedding in silica xerogels increases the achievable population of the isomeric nitrosyl configuration to about 15% with respect to a single crystalline powder where only 9% are reached.     

The binaural intelligibility level difference in hearing-impaired listeners: the role of supra-threshold deficits

Reduced binaural performance of hearing-impaired listeners may not only be caused by raised hearing thresholds (reduced audibility), but also by supra-threshold coding deficits in signal cues. This question was investigated in the present study using binaural intelligibility level difference (BILD) comparisons: the improvement of speech-reception threshold scores for N(0)S(π) relative to N(0)S(0) presentation conditions. Investigated was what types of supra-threshold deficits play a role in reducing BILDs in hearing-impaired subjects. BILDs were investigated for 25 mild to moderate sensorineural hearing-impaired listeners, under conditions where optimal audibility was assured. All stimuli were bandpass filtered (250-4000 Hz). A distortion-sensitivity approach was used to investigate the sensitivity of subjects BILDs to external stimulus perturbations in the phase, frequency, time, and intensity domains. The underlying assumption of this approach was that an auditory coding deficit occurring in a signal cue in a particular domain will result in a low sensitivity to external perturbations applied in that domain. Compared to reference data for listeners with normal BILDs, distortion-sensitivity data for a subgroup of eight listeners with reduced BILDs suggests that these reductions in BILD were caused by coding deficits in the phase and time domains.     

The Garfield and Uley nontronites--an infrared spectroscopic comparison

FTIR and Infrared emission spectroscopy (IES) has been used to characterise the Uley (Australian) and Garfield nontronites. These clay minerals are characterised by a strong emission band at 3570 cm(-1) attributed to the FeFeOH unit. Dehydroxylation is followed by the loss of intensity of this band as a function of temperature. Dehydroxylation is also followed by the loss of intensity of the FeFeOH deformation vibration at 843 cm(-1). IES shows that the dehydroxylation occurs as a continuous process in comparison to DTA/TGA studies where the dehydroxylation occurs abruptly at 425 degrees C. Water in these high iron bearing smectites have been observed through the stretching mode at 3430 cm(-1) and the bending mode at 1630 cm(-1). Different types of water are identified in the nontronite structure by the analysis of the band profile in the 1590-1680 cm(-1) region. Low frequency vibrations show that the Uley green nontronite is similar to the Garfield nontronite. The brown Uley nontronite is closer to the Hohen-Hagen nontronite. The Uley nontronites may, therefore, be used spectroscopically to replace other nontronites as a reference clay mineral.     

Near-infrared spectroscopic study of nontronites and ferruginous smectite

The existence of life on planets such as Mars depend upon the presence of water. This water may not necessarily be as liquid or crystalline water but may be as interlayer water such as is found in smectitic clays. One group of smectites, relevant to the search for interplanetary life are those which have a high iron content, known as nontronites. Near-IR reflectance spectroscopy has been used to show the presence of water and hydroxyl units in these minerals. Three near-IR spectral regions are identified, (a) the high frequency region between 6400 and 7400 cm(-1) attributed to the first overtone of the hydroxyl stretching mode; (b) the 4800-5400 cm(-1) region attributed to water combination modes; and (c) the 4000-4800 cm(-1) region attributed to the combination of the stretching and deformation modes of the FeFeOH units of nontronite. Two types of hydroxyl groups were identified using near-IR spectroscopy, hydroxyl units coordinated to the iron, and hydroxyl groups from water in the nontronite structure. The first hydroxyls are characterised by several bands, firstly in the 7055-7098 cm(-1) region assigned to the first overtone of the AlFeOH stretching unit, secondly in the 6958-6878 cm(-1) region attributed to the FeFeOH unit. The overtone of the hydroxyl stretching frequency of water was observed at around 6800 cm(-1). These observations show that nontronites can be a source of water that may support life.     

On the possible catalysis by single water molecules of gas-phase hydrogen abstraction reactions by OH radicals

The gas phase hydrogen abstraction reaction between OH and CY(2)XH, where X = H, F, OH, or NH(2) and Y = H, CH(3) or F, in the absence and presence of a single water molecule is investigated using both density function theory, B3LYP, and explicitly correlated coupled cluster theory, CCSD(T)-F12. We find that a single water molecule could have a catalytic effect at low temperatures possible in laboratory experiments, but does not seem to catalyze these reactions at 298 K, and will not play a role under relevant atmospheric conditions.     

Quantification of asenapine and three metabolites in human plasma using liquid chromatography-tandem mass spectrometry with automated solid-phase extraction: application to a phase I clinical trial with asenapine in healthy male subjects

The development and validation of methods for determining concentrations of the antipsychotic drug asenapine (ASE) and three of its metabolites [N-desmethylasenapine (DMA), asenapine-N(+) -glucuronide (ASG) and 11-O-sulfate-asenapine (OSA)] in human plasma using LC-MS/MS with automated solid-phase extraction is described. The three assessment methods in human plasma were found to be acceptable for quantification in the ranges 0.0250-20.0 ng/mL (ASE), 0.0500-20.0 ng/mL (DMA and OSA) and 0.250-50.0 ng/mL (ASG).