Sequence- and site-specific photodissociation at 266 nm of protonated synthetic polypeptides containing a tryptophanyl residue

Photodissociation at 266 nm of protonated synthetic polypeptides containing a tryptophanyl residue was investigated using a homebuilt tandem time-of-flight mass spectrometer equipped with a matrix-assisted laser desorption/ionization source. Efficient photodissociation of the protonated peptides was demonstrated. Most of the intense peaks in the laser-induced tandem mass spectra were sequence ions. Furthermore, sequence ions due to cleavages at all the peptide bonds were observed; this is a feature of the technique that is particularly useful for peptide sequencing. Fragmentations at both ends of the tryptophanyl residue were especially prevalent, which can be useful for location of the tryptophanyl chromophore in a peptide.     

An electrochemically controllable nanomechanical molecular system utilizing edge-to-face and face-to-face aromatic interactions

[formula: see text] A new molecular system, 2,11-dithio[4,4]metametaquinocyclophane containing a quinone moiety, was designed and synthesized. As the quinone moiety can readily be converted into an aromatic pi-system (hydroquinone) upon reduction, the nanomechanical molecular cyclophane system exhibits a large flapping motion like a molecular flipper from the electrochemical redox process. The conformational changes upon reduction and oxidation are caused by changes of nonbonding interaction forces (devoid of bond formation/breaking) from the edge-to-face to face-to-face aromatic interactions and vice versa, respectively.     

Microwave synthesis,characterization and catalytic properties of titanium-incorporated ZSM-5 zeolite

Titanium-incorporated ZSM-5 zeolites (Si/Al = 50–200 and Si/Ti = 70) were successfully synthesized in a one-step sol-gel process under microwave irradiation. The characteristics of Ti-ZSM-5 zeolites were investigated using X-ray power diffraction, UV/Vis-DRS, FT-IR spectroscopy and solid-state ²⁷Al-NMR to monitor the physico-chemical properties. Simultaneously, the acidic properties were characterized by the NH₃-TPD profile. The characterization results revealed that the Ti⁴⁺ and Al³⁺ ions were well incorporated into the framework of Ti-ZSM-5 zeolite. The prepared zeolite was moderately active but selective in the dehydration of methanol to dimethyl ether.     

Structural basis for inhibition of protein tyrosine phosphatases by Keggin compounds phosphomolybdate and phosphotungstate

Protein-tyrosine phosphatases (PTPs) constitute a family of receptor-like, and cytoplasmic enzymes, which catalyze the dephosphorylation of phosphotyrosine residues in a variety of receptors and signaling molecules. Together with protein tyrosine kinases (PTKs), PTPs are critically involved in regulating many cellular signaling processes. In this study, diverse compounds were screened for PTP inhibition and selectively screened for inhibitors with the end product inhibition properties. Among phosphate analogues and their derivatives for PTP inhibition, Keggin compounds phosphomolybdate (PM) and phosphotungstate (PT) strongly inhibited both PTP-1B and SHP-1, with K(i) values of 0.06-1.2 micromM in the presence of EDTA. Unlike the vanadium compounds, inhibition potencies of PM and PT were not significantly affected by EDTA. PM and PT were potent, competitive inhibitors for PTPs, but relatively poor inhibitors of Ser/Thr phosphatase. Interestingly, PM and PT did not inhibit alkaline phosphatase at all. The crystal structure of PTP-1B in complex with PM, at 2.0 A resolution, reveals that MoO(3), derived from PM by hydrolysis, binds at the active site. The molybdenium atom of the inhibitor is coordinated with six ligands: three oxo-ligands, two apical water molecules and a S atom of the catalytic cysteine residue. In support of the crystallographic finding, we observed that molybdenium oxides (MoO(3), MoO(2), and MoO(2)Cl(2)) inhibited PTP-1B with IC(50) in the range 5-15 micromM.     

Visible light active platinum-ion-doped TiO2 photocatalyst

Platinum-ion-doped TiO2 (Pt(ion)-TiO2) was synthesized by a sol-gel method, and its visible light photocatalytic activities were successfully demonstrated for the oxidative and reductive degradation of chlorinated organic compounds. Pt(ion)-TiO2 exhibited a yellow-brown color, and its band gap was lower than that of undoped TiO2 by about 0.2 eV. The flat band potential of Pt(ion)-TiO2 was positively shifted by 50 mV compared with that of undoped TiO2. X-ray absorption spectroscopy and X-ray photoelectron spectroscopy analyses showed that the Pt ions substituted in the TiO2 lattice were present mainly in the Pt(IV) state with some Pt(II) on the sample surface. Pt(ion)-TiO2 exhibited higher photocatalytic activities than undoped TiO2 under UV irradiation as well. The visible light activity of Pt(ion)-TiO2 was strongly affected by the calcination temperature and the concentration of Pt ion dopant, which were optimal at 673 K and 0.5 atom %, respectively. Under visible irradiation, Pt(ion)-TiO2 degraded dichloroacetate and 4-chlorophenol through an oxidative path and trichloroacetate via a reductive path. The activity of Pt(ion)-TiO2 was not reduced when used repeatedly under visible light. However, visible-light-illuminated Pt(ion)-TiO2 could not degrade substrates such as tetramethylammonium and trichloroethylene, which are degraded with UV-illuminated TiO2. The characteristics and reactivities of Pt(ion)-TiO2 as a new visible light photocatalyst were investigated in various ways and discussed in detail.     

Catalytic carbonylation for the synthesis of chemical intermediates

Chemistry related to three catalytic carbonylation reactions is discussed. Synthesis of diphenylurea from nitrobenzene, aniline, and CO gives isolated yields above 98% at 100–120 °C and 15–60 bar of CO in the presence of a palladium (II) complex, PPh₃ and NEt₄Cl. Experimental evidence was provided to prove a new reaction stoichiometry and involvement of a carbamoyl intermediate. In carbonylation of HCHO over ion exchange resin catalysts, reaction temperature, time, pressure, and solvent were important variables to obtain high yields of methyl glycolate. Carbonylation of isobutylphenylethanol at 120°C and 40 bar of CO in the presence of PdCl₂−PPh₃−HCl gives 98% yield of α-(4-isobutylphenyl) propionic acid (ibuprofen). Each catalyst component had a definite role that is indispensable for an efficient overall reaction.     

Fast visible dye staining of proteins in one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gels compatible with matrix assisted laser desorption/ionization-mass spectrometry

A fast and matrix assisted laser desorption/ionization-mass spectrometry (MALDI-MS) compatible protein staining method in one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (1- and 2-D SDS-PAGE) is described. It is based on the counterion dye staining method that employs oppositely charged two dyes, zincon (ZC) and ethyl violet (EV) to form an ion-pair complex. The protocol, including fixing, staining and quick washing steps, can be completed in 1-1.5 h depending upon gel thickness. It has a sensitivity of 4-8 ng, comparable to that of colloidal Coomassie Brilliant Blue G (CBBG) staining with phosphoric acid in the staining solution. The counterion dye stain does not induce protein modifications that complicate interpretation of peptide mapping data from MS. Considering the speed, sensitivity and compatibility with MS, the counterion dye stain may be more practical than any other dye-based protein stains for routine proteomic researches.     

Fluorescence-based nitric oxide detection by ruthenium porphyrin fluorophore complexes

The ruthenium(II) porphyrin fluorophore complexes [Ru(TPP)(CO)(Ds-R)] (TPP = tetraphenylporphinato dianion; Ds = dansyl; R = imidazole (im), 1, or thiomorpholine (tm), 2) were synthesized and investigated for their ability to detect nitric oxide (NO) based on fluorescence. The X-ray crystal structures of 1 and 2 were determined. The Ds-im or Ds-tm ligand coordinates to an axial site of the ruthenium(II) center through a nitrogen or sulfur atom, respectively. Both exhibit quenched fluorescence when excited at 368 or 345 nm. Displacement of the metal-coordinated fluorophore by NO restores fluorescence within minutes. These observations demonstrate fluorescence-based NO detection using ruthenium porphyrin fluorophore conjugates.