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91.
92.
J. F. Lawrence R. W. Frei 《International journal of environmental analytical chemistry》2013,93(4):317-325
The fluorigenic labelling of several N-methyl carbamates is carried out using 1-dimethyl-aminonaphthalene-5-sulfonyl chloride (dansyl chloride). Prior to chromatography the carbamates are reacted in aqueous solution with the dansyl chloride. The derivative is extracted from the solution with n-hexane and subsequently spotted on a thin-layer plate for chromatography. For each N-methyl carbamate, two highly fluorescent spots are obtained. One is common to all N-methyl carbamates studied, whereas the other is characteristic of each individual carbamate. N.m.r. and infrared spectroscopic data indicate that the common spot is the methylamine derivative, and the second spot is the derivative from the phenyl moiety of each carbamate. The sensitivity of the method is less than one nanogram and has been successfully applied to the analysis of natural water samples. 相似文献
93.
94.
Kätchen K. Lachmayr Charlotte M. Wentz Prof. Lawrence R. Sita 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(4):1537-1542
“One-component” soft material Frank–Kasper (FK) phases are an intriguing structural form of matter that possess periodically ordered structures arising from the self-reconfiguration and close packing of an initial assembly of identical “deformable” spheres into two or more size- or shape-distinct sets of particles. Significant challenges that must still be addressed to advance the field of soft matter FK phases further, however, include their rare and unpredictable occurrence, uncertain mechanisms of solid-state assembly, and low thermodynamic stability. Here we show that a readily-accessible sugar–polyolefin conjugate quantitatively produces an exceptionally stable solid-state FK A15 phase through a rapid and irreversible thermotropic order–order transition, which contrary to other prevailing proposed mechanisms, does not require mass transfer between particles or large structural reorganization in the bulk to establish unit cell non-equivalency. Our results provide the basis for a realistic strategy for obtaining practical and scalable quantities of a diverse range of sugar–polyolefin FK A15 phases with unique intrinsic physical properties and chemical reactivities not previously seen in such systems. 相似文献
95.
Saikat Banerjee Waqas Rasheed Ruixi Fan Dr. Apparao Draksharapu Dr. Williamson N. Oloo Prof. Dr. Yisong Guo Prof. Dr. Lawrence Que Jr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(41):9608-9613
The [FeIV(O)(Me3NTB)]2+ (Me3NTB=tris[(1-methyl-benzimidazol-2-yl)methyl]amine) complex 1 has been shown by Mössbauer spectroscopy to have an S=1 ground state at 4 K, but is proposed to become an S=2 trigonal-bipyramidal species at higher temperatures based on a DFT model to rationalize its very high C−H bond-cleavage reactivity. In this work, 1H NMR spectroscopy was used to determine that 1 does not have C3-symmetry in solution and is not an S=2 species. Our results show that 1 is unique among nonheme FeIV=O complexes in retaining its S=1 spin state and high reactivity at 193 K, providing evidence that S=1 FeIV=O complexes can be as reactive as their S=2 counterparts. This result emphasizes the need to identify factors besides the ground spin state of the FeIV=O center to rationalize nonheme oxoiron(IV) reactivity. 相似文献
96.
Prof. Dr. Jevgenij A. Raskatov Dr. Scott Virgil Dr. Hsiau-Wei Lee Dr. Lawrence M. Henling Ka Chan Ariel J. Kuhn Alejandro R. Foley 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(20):4467-4470
Methionine (Met) oxidation is an important biological redox node, with hundreds if not thousands of protein targets. The process yields methionine oxide (MetO). It renders the sulfur chiral, producing two distinct, diastereomerically related products. Despite the biological significance of Met oxidation, a reliable protocol to separate the resultant MetO diastereomers is currently lacking. This hampers our ability to make peptides and proteins that contain stereochemically defined MetO to then study their structural and functional properties. We have developed a facile method that uses supercritical CO2 chromatography and allows obtaining both diastereomers in purities exceeding 99 %. 1H NMR spectra were correlated with X-ray structural information. The stereochemical interconversion barrier at sulfur was calculated as 45.2 kcal mol−1, highlighting the remarkable stereochemical stability of MetO sulfur chirality. Our protocol should open the road to synthesis and study of a wide variety of stereochemically defined MetO-containing proteins and peptides. 相似文献
97.
98.
Fuyu Guan Cornelius E. Uboh Lawrence R. Soma Mary Robinson George A. Maylin Xiaoqing Li 《Analytical and bioanalytical chemistry》2013,405(14):4707-4717
Dermorphin is a unique opioid peptide that is 30–40 times more potent than morphine. It was misused and went undetected in horse racing until 2011 when intelligence obtained from a few North American race tracks suggested its use. To prevent such misuse, a reliable analytical method became necessary for detection and identification of dermorphin in post-race horse samples. This paper describes the first liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for such a purpose. Equine plasma and urine samples were pre-treated with ethylenediamine tetra-acetic acid and urea prior to solid-phase extraction (SPE) on Oasis MCX cartridges. Resulting eluates were dried under vacuum and analyzed by LC–MS/MS for dermorphin. The matrix effect, SPE efficiency, intra-day and inter-day accuracy and precision, and stability of the analyte were assessed. The limit of detection was 10 pg/mL in plasma and 20 pg/mL in urine, and the limit of confirmation was 20 pg/mL in plasma and 50 pg/mL in urine. Dermorphin in plasma is stable at ambient temperature, but its diastereomer is unstable. With isotopically labeled dermorphin as an internal standard, the quantification range was 20–10,000 pg/mL in plasma and 50–20,000 pg/mL in urine. The intra-day and inter-day accuracy was from 91 % to 100 % for the low, intermediate, and high concentrations. The intra-day and inter-day coefficients of variation were less than 12 %. The method differentiates dermorphin from its diastereomer. This method is very specific for identification of dermorphin in equine plasma and urine, as assessed by BLAST search and targeted SEQUEST search, and by MS/MS spectrum library search. The method has been successfully applied to analysis of samples collected following dermorphin administration to research horses and of official post-race samples. Figure
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99.
A practical synthesis of optically pure 1-[(3R,4R)-1-cyclooctylmethyl-3-ethoxycarbonyl-4-piperidinyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (J-113397) was developed that avoids the use of chiral columns. 相似文献
100.
Graham E. O'Mahony Kevin S. Eccles Robin E. Morrison Alan Ford Simon E. Lawrence Anita R. Maguire 《Tetrahedron》2013
Steric and electronic effects in the copper-catalysed asymmetric oxidation of aryl benzyl, aryl alkyl and alkyl benzyl sulfides have been investigated. The presence of an aryl group directly attached to the sulfur is essential to afford sulfoxides with high enantioselectivities, with up to 97% ee for 2-naphthyl benzyl sulfoxide, the highest enantioselectivity achieved to date for copper-catalysed asymmetric sulfoxidation. In contrast, the benzyl substituent can be replaced by sterically comparable groups with no effect on enantioselectivity. Copper-mediated oxidation of substituted aryl benzyl sulfides display modest steric and electronic effects resulting in comparable or lower enantioselectivities to those obtained with the unsubstituted benzyl phenyl sulfide. 相似文献