Kinetics of dimerization of 2-alkylthiopropenals

The rate constants for cyclodimerization of α-alkylthioacroleins were determined. They are two orders of magnitude higher than those for dimerization of α-alkoxyacroleins. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2020–2021, October, 1999.     

Classification Performance of a Low Pressure Differential Mobility Analyzer for Nanometer-sized Particles

Size distribution measurements and classification tests by a low pressure differential mobility analyzer (LPDMA) for nanometer-sized silver particles and cesium iodide particles under low pressure conditions (123–300 Torr) were performed using a transmission electron microscope (TEM) and the tandem DMA technique. When the ratio of the sheath gas flow rate and the aerosol gas flow rate was set at 5 : 1, the targeted sizes calculated from the classification voltage applied to the LPDMA at 160 Torr are found to be in good correlation with the count mean Feret diameter obtained from the TEM observation of the particles collected after a classification ranging from 6 to 25 nm, although the targeted sizes set by the LPDMA were approximately 15% greater than the count mean Feret diameter measured by the TEM after classification. The geometric standard deviations of DMA-classified particles measured by TEM and those obtained from the tandem DMA method ranged from 1.08 to 1.17 and from 1.05 to 1.13, respectively. They were slightly greater than the ideal geometric standard deviations (1.05) of the particles classified with the LPDMA, which was calculated by neglecting the broadening effects due to Brownian diffusion. We experimentally demonstrated the validity of our LPDMA system for size measurements and classification of the nanometer-sized particles under low pressure conditions.     

Swelling of poly(ethylene oxide) gel in aqueous solutions of sodium dodecyl sulfate with added sodium chloride

The swelling behavior of poly(ethylene oxide) (PEO) gels in aqueous solutions of sodium dodecyl sulfate (SDS) with and without NaCl was investigated. In the absence of NaCl, PEO gels with different degrees of cross-linking began to swell from a concentration lower than the critical micelle concentration (cmc) of SDS, then showed sigmoidal enhancements of swelling in a higher SDS concentration region until the degrees of swelling reached maximum values. The SDS concentration at which the swelling began to appear was in reasonable agreement with the critical aggregation concentration (cac) value reported for the aqueous PEO system. For the cases where NaCl was present, the swelling behavior of PEO gel was different from that when NaCl was absent in the following way. The concentrations where the swelling begins to appear, and hence those where the degree of swelling rises steeply, decreased with an increase in NaCl concentration. The ultimate degrees of swelling at higher concentration regions also decreased with an increase in the NaCl concentration. The lowering of the SDS concentrations at which the PEO gel began to swell is in line with the decreases in the cmc of SDS solutions containing NaCl and also with the decreases in the cac of PEO solution. Electronic Publication     

Stereospecificity of 1H, 13C and 15N shielding constants in the isomers of methylglyoxal bisdimethylhydrazone: problem with configurational assignment based on 1H chemical shifts

In the ¹³C NMR spectra of methylglyoxal bisdimethylhydrazone, the ¹³C‐5 signal is shifted to higher frequencies, while the ¹³C‐6 signal is shifted to lower frequencies on going from the EE to ZE isomer following the trend found previously. Surprisingly, the ¹H‐6 chemical shift and ¹J(C‐6,H‐6) coupling constant are noticeably larger in the ZE isomer than in the EE isomer, although the configuration around the –CH═N– bond does not change. This paradox can be rationalized by the C–H?N intramolecular hydrogen bond in the ZE isomer, which is found from the quantum‐chemical calculations including Bader's quantum theory of atoms in molecules analysis. This hydrogen bond results in the increase of δ(¹H‐6) and ¹J(C‐6,H‐6) parameters. The effect of the C–H?N hydrogen bond on the ¹H shielding and one‐bond ¹³C–¹H coupling complicates the configurational assignment of the considered compound because of these spectral parameters. The ¹H, ¹³C and ¹⁵N chemical shifts of the 2‐ and 8‐(CH₃)₂N groups attached to the –C(CH₃)═N– and –CH═N– moieties, respectively, reveal pronounced difference. The ab initio calculations show that the 8‐(CH₃)₂N group conjugate effectively with the π‐framework, and the 2‐(CH₃)₂N group twisted out from the plane of the backbone and loses conjugation. As a result, the degree of charge transfer from the N‐2– and N‐8– nitrogen lone pairs to the π‐framework varies, which affects the ¹H, ¹³C and ¹⁵N shieldings. Copyright © 2012 John Wiley & Sons, Ltd.     

Steady-State and Time-Resolved Fluorescence Spectroscopic Studies on Interaction of the N-terminal Region with the Hairpin Loop of the Phytocystain Scb

The steady-state and time-resolved fluorescece spectroscopy is one of the most powerful method to detect and analyze subtle conformation change and interaction between peptide elements in protein. Phytocystatin Scb isolated from sunflower seeds includes a single Trp residue at position 85. In an attempt to investigate the interaction of the N-terminal region of Scb with the first and second hairpin loops by fluorescence spectroscopy of Trp residue, two Scb mutants in which single Trp locates at position 52 and 58, respectively, and their N-terminal removed mutants were generated. The N-terminal truncation changed the fluorescence decay kinetics of Trp52 from the triple exponential to double. Furthermore, the time-resolved fluorescence anisotropy residue indicated that the segmental motion of Trp52 was significantly enhanced by its N-terminal truncation. In contrast, Trp58 and Trp85 had little influence. The N-terminal successive truncations of Scb and its mutants resulted in the weaken inhibitors to papain. These results suggested that the N-terminal region of Scb interacts with the peptide segment preceding the first hairpin loop, thereby stabilizing the conformation of the hairpin loop structure.     

Magnetic behavior of Fe0.2Mg0.8TiO3 and Fe0.3Mg0.7TiO3 probed by Mössbauer timescale

Magnetization and Mössbauer measurements have been made on a diluted antiferromagnets Fe_xMg_1?xTiO₃ with x=0.2, 0.3 and 0.7. It has been demonstrated that this system exhibits a spin glass or a reentrant spin glass like behavior in the samples with x around the percolation concenrration x_c≈0.25. It has been shown that various sizes of magnetic clusters are formed well above the transition temperatures determined by the magnetization measurements in the samples with x near x_c. The behavior of Fe_0.2Mg_0.8TiO₃ is discussed as a typical cluster glass.     

Buffers to suppress sodium dodecyl sulfate adsorption to polyethylene oxide for protein separation on capillary polymer electrophoresis

Although polyethylene oxide (PEO) offers several advantages as a sieving polymer in SDS capillary polymer electrophoresis (SDS-CPE), solution properties of PEO cause deterioration in the electrophoresis because PEO in solution aggregates itself, degrades into smaller pieces, and forms polymer-micelle complexes with SDS. We examined protein separation on SDS-CPE with PEO as a sieving matrix in four individual buffer solutions: Tris-CHES, Tris-Gly, Tris-Tricine, and Tris-HCl buffers. The solution properties of PEO as a sieving matrix in those buffers were examined by dynamic light scattering (DLS) and by surface tension. Preferential SDS adsorption onto PEO disturbed protein-SDS complexation and impaired the protein separation efficiency. Substantial adsorption of SDS to PEO was particularly observed in Tris-Gly buffer. The Tris-CHES buffer prevented SDS from adsorbing onto the PEO. Only Tris-CHES buffer achieved separation of six proteins. This study demonstrated efficient protein separation on SDS-CPE with PEO.     

Abnormal phospholipids distribution in the prefrontal cortex from a patient with schizophrenia revealed by matrix-assisted laser desorption/ionization imaging mass spectrometry

Schizophrenia is one of the major psychiatric disorders, and lipids have focused on the important roles in this disorder. In fact, lipids related to various functions in the brain. Previous studies have indicated that phospholipids, particularly ones containing polyunsaturated fatty acyl residues, are deficient in postmortem brains from patients with schizophrenia. However, due to the difficulties in handling human postmortem brains, particularly the large size and complex structures of the human brain, there is little agreement regarding the qualitative and quantitative abnormalities of phospholipids in brains from patients with schizophrenia, particularly if corresponding brain regions are not used. In this study, to overcome these problems, we employed matrix-assisted laser desorption/ionization imaging mass spectrometry (IMS), enabling direct microregion analysis of phospholipids in the postmortem brain of a patient with schizophrenia via brain sections prepared on glass slides. With integration of traditional histochemical examination, we could analyze regions of interest in the brain at the micrometric level. We found abnormal phospholipid distributions within internal brain structures, namely, the frontal cortex and occipital cortex. IMS revealed abnormal distributions of phosphatidylcholine molecular species particularly in the cortical layer of frontal cortex region. In addition, the combined use of liquid chromatography/electrospray ionization tandem mass spectrometry strengthened the capability for identification of numerous lipid molecular species. Our results are expected to further elucidate various metabolic processes in the neural system.