Thiol addition to t-butyl methyl squarate. Efficient synthesis of novel sulfur-linked squaryl group-containing glutamate analogs

Novel sulfur-linked squaryl group-containing glutamate analogs were synthesized via addition and mono-substitution reactions of thiols to t-butyl methyl squarate (BMSQ: 7) in two steps. A glutamate analog prepared from Boc-l-Cys showed a potent binding affinity to KA/AMPA receptors.     

Synthesis of Orthorhombic Mo‐V‐Sb Oxide Species by Assembly of Pentagonal Mo6O21 Polyoxometalate Building Blocks

Mix and match : The pentagonal [Mo₆O₂₁]^n? polyoxomolybdate building block assembles with other sources of Mo, V, and Sb ions to form an orthorhombic Mo‐V‐Sb oxide. The first single‐crystal X‐ray analysis of an orthorhombic Mo–V‐based oxide, a promising catalyst for light alkane selective oxidation known as the “M1 phase”, revealed the structure of the compound.

     

Unusual temperature dependence of enantioselectivity in asymmetric reductions by chiral NADH models

[reaction: see text] Unusual stereoselectivity changes, i.e., enhancement and inversion of enantioselectivity with increasing temperature, were observed in the asymmetric reduction of methyl benzoylformate with chiral 1,4-dihydropyridines possessing amino acid residues as ligating chiral auxiliaries. The differential activation parameters, DeltaDeltaH(S-R) and DeltaDeltaS(S-R), obtained from the Eyring plots demonstrate that the entropy term controls the enantiodifferentiating step, accounting for the observed unique temperature dependencies.     

High-performance liquid chromatographic determination of free and total polyamines in human serum as fluorescamine derivatives

A highly sensitive and simple fluorimetric method for the determination of free and total polyamines, spermidine, spermine, putrescine and cadaverine, in human serum by high-performance liquid chromatography is described. The polyamines, obtained after clean-up of deproteinized serum by Cellex P column chromatography, are converted to their fluorescamine derivatives in the presence of nickel ion which inhibits the reaction of interfering amines with fluorescamine, and the derivatives are separated simultaneously by reversed-phase chromatography (LiChrosorb RP-18) with a linear gradient elution. The lower limits of detection are 10 and 15 pmole for spermine and the others in 0.5 ml of serum, respectively.     

High-performance liquid chromatographic determination of peptides released by tryptic degradation from opioid peptide precursors in rat brain.

A high-performance liquid chromatographic method involving postcolumn fluorescence derivatization is described for the quantification of five fragment peptides (methionine-enkephalin-Thr-Ser-Glu-Lys, methionine-enkephalin-Lys, methionine-enkephalin-Arg, leucine-enkephalin-Lys and leucine-enkephalin-Arg) released by tryptic digestion from the opioid peptide precursors (proopiomeranocortin and proenkephalins A and B) in rat brain tissues. The tissue proteins containing the precursors are hydrolyzed with trypsin to the fragment peptides. The peptides are separated on an Asahipak ODP-50 column and on-line detected fluorometrically by using hydroxylamine, cobalt(II) and borate buffer reagents. The detection limits (S/N = 3) for the peptides are 0.7-2.8 pmol per 100 microliters injected. The distribution of the precursors in the brain tissues was also discussed on the basis of the determined values of the fragment peptides.     

Identical-location Transmission Electron Microscopy of Pt Nanoparticle Electrocatalysts Using Iridium-coated Au Grids for Fuel Cell Durability Tests Simulating Start-up and Shutdown Conditions

In an identical-location TEM (IL-TEM) analysis of an electrocatalyst, an Au grid is usually selected owing to its chemical stability under potential cycling conditions. A potential cycle between 1.0 and 1.5 V is applied to the catalyst-cast Au grid for cathode durability testing that simulates the start-up and shutdown conditions of fuel cells. Because of the redox potential of Au (1.36 V vs. RHE), the grid dissolves and redeposits on the catalyst under the applied potential, making it complicated to evaluate the catalyst nanoparticle shape and size after degradation. We fabricated an Au grid coated with an iridium oxide layer (Ir-coated Au grid) to suppress the dissolution of Au. The Ir-coated Au grid with carbon support was compared to the Au grid to confirm the effect of the iridium oxide layer. No Au deposition was observed, even after 3000 cycles at 60 °C for the Ir-coated Au grid, but Au was deposited on carbon on the Au grid after 1000 cycles. Consequently, the alkylamine-modified Pt nanoparticle catalyst (unwashed catalyst) was observed along with the Ir-coated Au grid using IL-TEM under durability tests simulating start-up and shutdown conditions. A catalyst with less alkylamine content was prepared by butylamine washing (washed catalyst) and observed using IL-TEM for comparison. The Pt nanoparticles of the washed catalyst aggregated and changed their morphology after 1000 cycles, while the alkylamine-modified nanoparticles of the unwashed catalyst almost maintained their original size and shape up to 1000 cycles. The Ir-coated gold grids allow proper IL-TEM analysis of catalysts in durability tests without the interference of Au dissolution.