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81.
The stability (affinity, association, binding, complexation, formation) constant characterizes binding interaction between the analyte and the complexing agent. Knowledge of the stability constant makes possible the prediction and estimation of the binding behavior of constituents (amino acids, peptides, proteins, drugs, antibiotics, enzymes, enantiomers) to their partners, and the finding of a suitable partner for the given analyte to form a stable complex. The present paper summarizes the stability constant determination methods and the approaches used to evaluate the experimental data. Further, the paper recapitulates the published stability constant values determined, mainly, by capillary electrophoretic methods, taken from the Web of Science database covering the last decade. Details of the experimental conditions employed for the determination of the stability constants are also given. The review attempts to give a critical evaluation of the problems that accompany the determination of stability constant and discusses their solution. 相似文献
82.
The production of octahydrocoumarin, which can serve as a replacement for toxic coumarin, was investigated using 5% Ru on active carbon (Ru/C) as the catalyst for the hydrogenation of couma-rin. The hydrogenation was studied by optimizing the reaction conditions (pressure, solvent and coumarin concentration). The activity and selectivity of the Ru/C catalyst were compared for dif-ferent solvents. The mechanism of coumarin hydrogenation was deduced. The formation of side products was explained. The optimal hydrogenation reaction conditions were: 130 °C, 10 MPa, 60 wt% coumarin in methanol, and 0.5 wt% (based on coumarin) of Ru/C catalyst. At the complete conversion of coumarin, the selectivity to the desired product was 90%. 相似文献
83.
From Dibismuthenes to Three‐ and Two‐Coordinated Bismuthinidenes by Fine Ligand Tuning: Evidence for Aromatic BiC3N Rings through a Combined Experimental and Theoretical Study 下载免费PDF全文
Iva Vránová Dr. Mercedes Alonso Dr. Rabindranath Lo Dr. Robert Sedlák Dr. Roman Jambor Prof. Aleš Růžička Prof. Frank De Proft Prof. Pavel Hobza Dr. Libor Dostál 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(47):16917-16928
The reduction of N,C,N‐chelated bismuth chlorides [C6H3‐2,6‐(CH?NR)2]BiCl2 [where R=tBu ( 1 ), 2′,6′‐Me2C6H3 ( 2 ), or 4′‐Me2NC6H4 ( 3 )] or N,C‐chelated analogues [C6H2‐2‐(CH?N‐2′,6′‐iPr2C6H3)‐4,6‐(tBu)2]BiCl2 ( 4 ) and [C6H2‐2‐(CH2NEt2)‐4,6‐(tBu)2]BiCl2 ( 5 ) is reported. Reduction of compounds 1 – 3 gave monomeric N,C,N‐chelated bismuthinidenes [C6H3‐2,6‐(CH?NR)2]Bi [where R=tBu ( 6 ), 2′,6′‐Me2C6H3 ( 7 ) or 4′‐Me2NC6H4 ( 8 )]. Similarly, the reduction of 4 led to the isolation of the compound [C6H2‐2‐(CH?N‐2′,6′‐iPr2C6H3)‐4,6‐(tBu)2]Bi ( 9 ) as an unprecedented two‐coordinated bismuthinidene that has been structurally characterized. In contrast, the dibismuthene {[C6H2‐2‐(CH2NEt2)‐4,6‐(tBu)2]Bi}2 ( 10 ) was obtained by the reduction of 5 . Compounds 6 – 10 were characterized by using 1H and 13C NMR spectroscopy and their structures, except for 7 , were determined with the help of single‐crystal X‐ray diffraction analysis. It is clear that the structure of the reduced products (bismuthinidene versus dibismuthene) is ligand‐dependent and particularly influenced by the strength of the N→Bi intramolecular interaction(s). Therefore, a theoretical survey describing the bonding situation in the studied compounds and related bismuth(I) systems is included. Importantly, we found that the C3NBi chelating ring in the two‐coordinated bismuthinidene 9 exhibits significant aromatic character by delocalization of the bismuth lone pair. 相似文献
84.
A family consisting of quadrature formulas which are exact for all polynomials of order ?5 is studied. Changing the coefficients, a second family of quadrature formulas, with the degree of exactness higher than that of the formulas from the first family, is produced. These formulas contain values of the first derivative at the end points of the interval and are sometimes called “corrected”. 相似文献
85.
A simple, robust and reliable analytical procedure for the determination of 28 selected elements, namely Al, As, Ba, Be, Bi, Ca, Cd, Co, Cr, Cu, Fe, K, Hg, Mg, Mn, Mo, Na, Ni, Pb, Sc, Si, Se, Sn, Sm, Sr, Tl, V, and Zn in textile materials by inductively coupled plasma optical emission spectrometry (ICP-OES) after microwave digestion of samples was optimized and validated in this work. The total amount of elements present in textile samples was determined after microwave digestion of materials in 7 mol/L nitric acid within the optimal working program: 5 min at 150 °C (power 250 W), 15 min 180 °C (300 W) and 20 min at the maximum temperature of 200 °C (350 W). For the quality control reasons, which were ascertained by analysis of the certified cotton trace elements reference material IAEA-V9, the ICP-OES method was optimized through several parameters: by comparing Meinhard and Gemcone Low Flow nebulizers efficiency, ranging nebulizer gas flows from 0.6 to 1.0 L/min, ranging sample flows from 0.8 to 1.2 mL/min, testing RF power from 1200 to 1400 W, detecting data acquisition time (read time) from 0 to 527 s, ranging washing (delay) time from 0 to 408 s, as well as by checking the occurring interferences for the optimal line selection. Validation included determination of linearity, selectivity, accuracy, reproducibility, precision and limits of detection calculated for all 28 selected elements of interest. The developed analytical procedure was successfully applied on textile fibers (cotton, flax and hemp) as well as on standard knitted textile sample materials (cotton and wool). 相似文献
86.
Iva Rezi? 《Trends in analytical chemistry : TRAC》2011,30(7):1159
Textile materials with engineered nanoparticles (ENPs) have excellent properties as they are antibacterial, antimicrobial, water resistant and protective. The textile industry has recognized the importance and the advantages of ENPs, so they comprise one of the fastest developing branches of processing.The most important sources of ENPs released to the environment from textiles are textile-industry wastewaters and waters from large hospital or hotel laundries. In addition, waste textile materials coated with ENPs present a threat to the environment, if such materials are not properly handled and disposed of after use.Currently, the toxicity and the potential harm of ENPs widely applied on textiles are not thoroughly investigated and/or eliminated. Consequently, there is an urgent need to define the most appropriate analytical methods for monitoring ENPs on textiles.This review presents the most important techniques for monitoring ENPs on textile materials and in textile-wastewater samples, from the perspective of protecting the environment and human health. 相似文献
87.
JPC – Journal of Planar Chromatography – Modern TLC - A novel method is proposed for optimization of simultaneous thinlayer chromatographic separation of seven amino acids. For this... 相似文献
88.
Cationic and amphiphilic polymers are known to exert broad-spectrum antibacterial activity by a putative mechanism of membrane disruption. Typically, nonspecific binding to hydrophobic components of the complex biological milieu, such as globular proteins, is considered a deterrent to the successful application of such polymers. To evaluate the extent to which serum deactivates antibacterial polymethacrylates, we compared their minimum inhibitory concentrations in the presence and absence of fetal bovine serum. Surprisingly, we discovered that the addition of fetal bovine serum (FBS) to the assay media in fact enhances the antimicrobial activity of polymers against Gram-positive bacteria S. aureus, whereas the opposite is the case for Gram-negative E. coli. Here, we present these unexpected trends and develop a hypothesis to potentially explain this unusual phenomenon. 相似文献
89.
Simona Hybelbauerová Jan Sejbal Martin Dračínský Iva Rudovská Bohumír Koutek 《Helvetica chimica acta》2009,92(12):2795-2801
The two previously unreported esters 1 and 2 of pentane‐2,4‐diol and p‐coumaric acid (=3‐(4‐hydroxyphenyl)prop‐2‐enoic acid) along with 13 known compounds including 6 oleanane‐ and ursane‐type triterpenoids were isolated from MeOH extracts of the stems of Vaccinium myrtillus. The structures of the new compounds were assigned as (2S,4R)‐4‐(β‐D ‐glucopyranosyloxy)pentan‐2‐yl (2E)‐p‐coumarate ( 1 ) and its aglycone 2 on the basis of 1D‐ and 2D‐NMR spectroscopic analyses of the isolated and synthesized compounds and molecular modelling experiments. This is the first report on the occurrence of a chiral pentane‐2,4‐diol linker between the phenol‐derived acid and a glycoside part in natural products. 相似文献