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121.
Alexander Czaja Samer Awad Olga E. Eremina Augusta Fernando Cristina Zavaleta 《Journal of Raman spectroscopy : JRS》2024,55(5):566-580
Surface-enhanced Raman scattering nanoparticles (SERS NPs) offer powerful optical contrast features for imaging assays. Their gold core enhances the inelastic scattering cross section, allowing highly sensitive and rapid detection, and their characteristic sets of narrow spectral bands give them unsurpassed multiplexing capabilities. Multiplexed hyperspectral images are commonly unmixed using a compensation matrix of reference spectra to produce quantitative image channels illustrating the distribution of each material. It is these unmixed channels that are fit for interpretation from assays utilizing SERS NP contrast agents. Some factors that may impact SERS NP quantitative and dynamic range capabilities may include endogenous background heterogeneity, the ability of unmixing algorithms to account for signal variances, and linear system conditioning imposed by contrast agent signals. We report on hyperspectral Raman imaging of mixtures of SERS NPs from an expanded library of contrast agents. We study increasing plexity and varying degrees of system conditioning as inputs to a diverse set of classical, non-negatively constrained, and regularized regression algorithms to investigate which signal features and unmixing methods deliver the most promising quantitation performance with the least error. Raman imaging of SERS NP mixtures is performed on controlled substrates and representative biological specimens, and experimental results are compared against ground truth data. We evaluate spectral fitting fidelity, quantitation, and specificity correlations with system conditioning. Spectral unmixing with a regularized hybrid of least squares regression with principal component analysis (HLP) algorithm approximated spectra with 3.5× better fitting fidelity and 3× better quantitation robustness with tissue background compared with simpler unmixing routines. 相似文献
122.
Raika Milde Arianne Schnabel Toni Ditfe Wolfgang Hoehenwarter Carsten Proksch Bernhard Westermann Thomas Vogt 《Molecules (Basel, Switzerland)》2022,27(20)
Capsaicin, produced by diverse Capsicum species, is among the world’s most popular spices and of considerable pharmaceutical relevance. Although the capsaicinoid biosynthetic pathway has been investigated for decades, several biosynthetic steps have remained partly hypothetical. Genetic evidence suggested that the decisive capsaicin synthase is encoded by the Pun1 locus. Yet, the genetic evidence of the Pun1 locus was never corroborated by functionally active capsaicin synthase that presumably catalyzes an amide bond formation between trans 8-methyl-6-nonenoyl-CoA derived from branched-chain amino acid biosynthesis and vanilloylamine derived from the phenylpropanoid pathway. In this report, we demonstrate the enzymatic activity of a recombinant capsaicin synthase encoded by Pun1, functionally expressed in Escherichia coli, and provide information on its substrate specificity and catalytic properties. Recombinant capsaicin synthase is specific for selected aliphatic CoA-esters and highly specific for vanilloylamine. Partly purified from E. coli, the recombinant active enzyme is a monomeric protein of 51 kDa that is independent of additional co-factors or associated proteins, as previously proposed. These data can now be used to design capsaicin synthase variants with different properties and alternative substrate preferences. 相似文献
123.
E. A. Mareeva M. A. Orlova V. V. Doseeva D. B. Loginov A. G. Galkin I. G. Gazarina V. I. Tishok 《Applied biochemistry and biotechnology》1996,61(1-2):13-23
Two horseradish peroxidase C (HRPC) mutants with substitutions in the active center, i.e., Phe41→ His and Phel43→ Glu, were
compared to the wild-type recombinant enzyme expressed in Escherichia coli in terms of the enzymatic activity and stability
under irradiation. Both mutations caused a significant decrease in activity, but it was still possible to follow the effect
of mutations on the key steps of the reaction mechanism. Phe41 can be considered a nonpolar barrier separating histidine residues
in the active center and providing a firm noncovalent binding with the highly hydrophobic porphyrin ring. The replacement
of Phe41 with the ionizable His residue destabilizes the enzyme. The Phel43→ Glu replacement creates a negative charge at
the entrance of the heme-binding pocket, and protects the latter from both donor substrates and free radicals.
The radiolytic inactivation of the wild-type and mutant forms of recombinant HRP suggested different binding sites for iodide,
2,2′-bis(3-ethylbenzothiasoline-6-sulfonate (ABTS), guaiacol, and o-phenylene diamine. The study of kinetics and inactivation
is in agreement with the direct binding of iodide to the heme porphyrin ring. The results also suggest that the ABTS binding
site is less accessible than that for o-phenylene diamine. 相似文献
124.
Biscatechol-hydroxamate and catechol-bishydroxamate chelators of similar architecture were synthesized by a small set of acylation reactions, Michael additions, and domino Wittig alkenations and they were tested for siderophoric activity in various receptor-deficient mutants of Escherichia coli under iron starvation. Growth promotion occurred only in mutants featuring catecholate recognizing receptors. Simplified mimics of the natural siderophores parabactin and agrobactin, carrying an o-hydroxybenzamide instead of the 2-(o-hydroxyphenyl)oxazoline ligand, were prepared analogously. Unlike the originals these mimics are fully functional siderophores in E. coli. 相似文献
125.
Shagidullina R. A. Zakharova L. Ya. Valeeva F. G. Kudryavtseva L. A. 《Russian Chemical Bulletin》2001,50(7):1181-1185
The micellar effect of cationic surfactants in alkaline hydrolysis of O-alkyl-O-aryl-chloromethyl phosphonates involves a positive contribution of concentrating the reagents and a negative effect of the micellar environment due to a loss in the activation entropy. The reactivity of substrates in micelles depends on both electronic and hydrophobic characteristics of substituents in the aryl group. 相似文献
126.
筋骨草甾酮C是分布于植物中的植物甾酮类化合物,具有抗氧化的作用.本文标定了该化合物中所有的碳信号,并通过13C-1HCOSY和1H-1HCOSY技术纠正了文献中氢信号归属的错误. 相似文献
127.
Dong ZY Huang X Mao SZ Liang K Liu JQ Luo GM Shen JC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(13):3575-3579
To elucidate the relationships between molecular recognition and catalytic ability, we chose three assay systems using three different thiol substrates, glutathione (GSH), 3-carboxyl-4-nitrobenzenethiol (CNBSH), and 4-nitrobenzenethiol (NBSH), to investigate the glutathione peroxidase (GPx) activities of 2,2'-ditellurobis(2-deoxy-beta-cyclodextrin) (2-TeCD) in the presence of a variety of structurally distinct hydroperoxides (ROOH), H2O2, tert-butyl peroxide (tBuOOH), and cumene peroxide (CuOOH), as the oxidative reagent. A comparative study of the three assay systems revealed that the cyclodextrin moiety of the GPx mimic 2-TeCD endows the molecule with selectivity for ROOH and thiol substrates, and hydrophobic interactions are the most important driving forces in 2-TeCD complexation. Furthermore, in the novel NBSH assay system, 2-TeCD can catalyze the reduction of ROOH about 3.4 x 10(5) times more efficiently than diphenyl diselenide (PhSeSePh), and its second-order rate constants for thiol are similar to some of those of native GPx. This comparative study confirms that efficient binding of the substrate is essential for the catalytic ability of the GPx mimic, and that NBSH is the preferred thiol substrate of 2-TeCD among the chosen thiol substrates. Importantly, the proposed mode of action of 2-TeCD imitates the role played by several possible noncovalent interactions between enzymes and substrates in influencing catalysis and binding. 相似文献
128.
Moshe Kress Kyle Y. Lin Roberto Szechtman 《Mathematical Methods of Operations Research》2008,68(3):539-549
A target is hidden in one of several possible locations, and the objective is to find the target as fast as possible. One
common measure of effectiveness for the search process is the expected time of the search. This type of search optimization
problem has been addressed and solved in the literature for the case where the searcher has imperfect sensitivity (possible
false negative results), but perfect specificity (no false positive detections). In this paper, which is motivated by recent
military and homeland security search situations, we extend the results to the case where the search is subject to false positive
detections. 相似文献
129.
130.
L. Ya. Zakharova F. G. Valeeva R. A. Shagidullina L. A. Kudryavtseva 《Russian Chemical Bulletin》2000,49(10):1696-1698
The reactivity of alkyl aryl chloromethylphosphonates in alkaline hydrolysis in the sodium bis(2-ethylhexyl)sulfosuccinate—decane—water
reverse micellar system is mainly determined by the electronic properties of substituents and depends only slightly on their
hydrophobicity.
Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1712–1715, October, 2000. 相似文献