A Wavenumber,Intensity, and Resolution Standard for High Resolution Ultraviolet/Visible Fourier Transform Spectroscopy

Abstract

The Re I (527. 55 nm, 18955 cm^?1) emission line from a hollow cathode lamp (HCL) is proposed as a standard for wavenumber accuracy and precision, resolution accuracy and precision and intensity precision. The Los Alamos Fourier transform spectrometer measured the HCL emission at high resolution (0. 026 cm^?1). The advantages of this spectral line to other emission standards is discussed.     

Microwave-assisted organic synthesis of a high-affinity pyrazolo-pyrimidinyl TSPO ligand

We herein report a dramatically improved total synthesis of the high-affinity translocator protein (TSPO) ligand DPA-714, featuring microwave-assisted organic synthesis (MAOS). Compared with previously described approaches, our novel MAOS method dramatically reduces overall reaction time without adversely effecting reaction yields. We envision that the described MAOS protocol may be suitably applied to high-throughput, diversity-oriented synthesis of novel compounds based on the pyrazolo-pyrimidinyl scaffold. Such an approach could accelerate the development of focused libraries of novel TSPO ligands with potential for future development as molecular imaging and therapeutic agents.     

Discovery of a substrate selectivity switch in tyrosine ammonia-lyase, a member of the aromatic amino acid lyase family

Tyrosine ammonia-lyase (TAL) is a recently described member of the aromatic amino acid lyase family, which also includes phenylalanine (PAL) and histidine ammonia-lyases (HAL). TAL is highly selective for L-tyrosine, and synthesizes 4-coumaric acid as a protein cofactor or antibiotic precursor in microorganisms. In this report, we identify a single active site residue important for substrate selection in this enzyme family. Replacing the active site residue His89 with Phe in TAL completely switched its substrate selectivity from tyrosine to phenylalanine, thereby converting it into a highly active PAL. When a corresponding mutation was made in PAL, the enzyme lost PAL activity and gained TAL activity. The discovered substrate selectivity switch is a rare example of a complete alteration of substrate specificity by a single point mutation. We also show that the identity of the amino acid at the switch position can serve as a guide to predict substrate specificities of annotated aromatic amino acid lyases in genome sequences.     

DFTMP, an NMR reagent for assessing the near-neutral pH of biological samples

A new NMR chemical shift standard and pH indicator, difluorotrimethylsilanylphosphonic acid (DFTMP), is described, and the utility of this reagent is demonstrated for in situ determination of pH in complex biofluids. The pH dependence of this reagent allows accurate in situ determination of aqueous solution pH to within an RMSE of 0.02 pH units over a pH range of 5 to 8. Advantages of this reagent over previously described pH-sensitive components include (1) lack of metal binding affinity, (2) minimal disturbance of endogenous spectral regions, and (3) the potential to function as a multinuclear pH indicator and chemical shift reference point for 19F, 1H, and 31P nuclei. This reagent will be generally useful for NMR experiments on biological systems where the pH needs to be accurately measured at the moment of data acquisition.     

C-H activation as a strategic reaction: enantioselective synthesis of 4-substituted indoles

A method is described for the asymmetric synthesis of 4-substituted indoles from the Rh2(S-DOSP)4-catalyzed decomposition of vinyldiazoacetates in the presence of N-Boc-4-acetoxy-6,7-dihydroindole. The reaction proceeds via a combined C-H activation/Cope rearrangement-elimination mechanism resulting in good yields and very high asymmetric induction.     

Eine Notiz zur Methoxyl-Bestimmung

Ohne Zusammenfassung     

Synthesis of tetrahydropyridazino[1,2-a][1,2,4] benzotriazin-6-one derivatives. A novel heterocyclic system

Synthesis of pyridazino[1,2-a][1,2,4]benzotriazin-6-one derivatives involving reaction of either 1,2,3,6-tetra-hydropyridazine ( 9 ) or hexahydropyridazine 14 with 2-fluoro-5-nitrophenylisocyanate ( 5 ) to give, via intramolecular cyclization, 3a and 16 respectively is described. Compound 3a was converted to 18 via methylation and hydroxylation to give 20 followed by conversion to the acetonide derivative 18 . Both 16 and 18 were reduced to the amino derivatives 17 and 19 respectively.     

Ozone Decomposition Data for Kinetics Exercises

The goal of this paper is to provide data that can be used in a variety of exercises ranging from kinetics in general chemistry to advanced problems in physical chemistry. The data provided relates to ozone-decay kinetics in various atmospheres (O₂, N₂, Ar) as measured by ultraviolet/visible absorbance spectroscopy (UV/vis) at 254 nm. The absorbance of ozone is monitored over a 75-min time period, and by using Beers law the concentration is calculated. Nine data sets, each repeated three times, of absorbance measurements are provided for student exercises, and prelaboratory and postlaboratory questions are suggested.     

Regiospecificity in the reaction of [Fe2(η-C5H5)2(CO)4-n(CNMe)n] (n  02) with mercury(II) halides

The reactions of [Fe₂(η-C₅H₅)₂(CO)₂(L)(CNMe)] (L  CO or CNME) with HgX₂ (X  Cl, Br or I) give [Fe(η-C₅H₅)(CO)₂HgX] and [Fe(η-C₅H₅)(L)-(CNMe)X] as the sole products in ca. quantitative yields; this is consistent with the previously proposed mechanism for the reactions of electrophiles with polynuclear metal carbonyl derivatives.     

Palladium(II) Pyridinecarboxaldimine Complexes Derived from Unsaturated Amines

Pyridinecarboxaldimines (N–N′) derived from pyridin-2-ylcarboxaldehydes and unsaturated amines add to [PdCl₂(coe)]₂ (coe = cis-cyclooctene) to give complexes of the type PdCl₂(N–N′) in moderate yields. The palladium complexes have been investigated as substrates for hydroboration reactions and as antifungal agents against Aspergillus niger, A. flavus, Candida albicans, and Saccharomyces cerevisiae.