18205-99-7Relevant articles and documents
Redox regulation of protein tyrosine phosphatase 1B (PTP1B): A biomimetic study on the unexpected formation of a sulfenyl amide intermediate
Sarma, Bani Kanta,Mugesh, Govindasamy
, p. 8872 - 8881 (2007)
The effect of steric and electronic environments around the sulfur and nitrogen atoms and the role of nonbonded S...O/N interactions on the cyclization reactions of amide substituted benzene sulfenic acids are described. The reaction profiles and the role
Electron paramagnetic resonance spectroscopy as a probe of hydrogen bonding in heme-Thiolate proteins
Dent, Matthew R.,Milbauer, Michael W.,Hunt, Andrew P.,Aristov, Michael M.,Guzei, Ilia A.,Lehnert, Nicolai,Burstyn, Judith N.
, p. 16011 - 16027 (2019/11/28)
Despite utilizing a common cofactor binding motif, hemoproteins bearing a cysteine-derived thiolate ligand (heme-Thiolate proteins) are involved in a diverse array of biological processes ranging from drug metabolism to transcriptional regulation. Though the origin of heme-Thiolate functional divergence is not well understood, growing evidence suggests that the hydrogen bonding (H-bonding) environment surrounding the Fe-coordinating thiolate influences protein function. Outside of X-ray crystallography, few methods exist to characterize these critical H-bonding interactions. Electron paramagnetic resonance (EPR) spectra of heme-Thiolate proteins bearing a six-coordinate, Fe(III) heme exhibit uniquely narrow low-spin (S = 1/2), rhombic signals, which are sensitive to changes in the heme-Thiolate H-bonding environment. To establish a well-defined relationship between the magnitude of g-value dispersion in this unique EPR signal and the strength of the heme-Thiolate H-bonding environment, we synthesized and characterized of a series of six-coordinate, aryl-Thiolate-ligated Fe(III) porphyrin complexes bearing a tunable intramolecular H-bond. Spectroscopic investigation of these complexes revealed a direct correlation between H-bond strength and g-value dispersion in the rhombic EPR signal. Using density functional theory (DFT), we elucidated the electronic origins of the narrow, rhombic EPR signal in heme-Thiolates, which arises from an Fe-S pI-dI bonding interaction. Computational analysis of the intramolecularly H-bonded heme-Thiolate models revealed that H-bond donation to the coordinating thiolate reduces thiolate donor strength and weakens this Fe-S interaction, giving rise to larger g-value dispersion. By defining the relationship between heme-Thiolate electronic structure and rhombic EPR signal, it is possible to compare thiolate donor strengths among heme-Thiolate proteins through analysis of low-spin, Fe(III) EPR spectra. Thus, this study establishes EPR spectroscopy as a valuable tool for exploring how second coordination sphere effects influence heme-Thiolate protein function.
Amidation of Carboxylic Acids with Amines by Nb2O5 as a Reusable Lewis Acid Catalyst
Ali,Siddiki,Onodera, Wataru,Kon, Kenichi,Shimizu, Ken-Ichi
, p. 3555 - 3561 (2015/11/10)
Among 28 types of heterogeneous and homogenous catalysts tested, Nb2O5 shows the highest yield for direct amidation of n-dodecanoic acid with a less reactive amine (aniline). The catalytic amidation by Nb2O5 is applicable to a wide range of carboxylic acids and amines with various functional groups, and the catalyst is reusable. A comparison of the results of the catalytic study and an infrared study of the acetic acid adsorbed on the catalyst suggests that activation of the carbonyl group of the carboxylic acid by Lewis acid sites on Nb2O5 is responsible for the high activity of the Nb2O5 catalyst. Kinetic studies show that Lewis acid sites on Nb2O5 are more water-tolerant than conventional Lewis acidic oxides (Al2O3, TiO2). In comparison with the state-of-the-art homogeneous Lewis acid catalyst for amidation (ZrCl4), Nb2O5 undergoes fewer negative effects from basic additives in the solution, which indicates that Nb2O5 is a more base-tolerant Lewis acid catalyst than the homogeneous Lewis acid catalyst.
