To establish a detailed reaction mechanism for the condensation between a boronic acid, RB(OH)2, and a diol, H2L, in aqueous solution, the acid dissociation constants (${K{{{\rm BL}\hfill \atop {\rm a}\hfill}}}$ ) of boronic acid diol esters (HBLs) were determined based on the well‐established concept of conditional formation constants of metal complexes. The pKa values of HBLs were 2.30, 2.77, and 2.00 for the reaction systems, 2,4‐difluorophenylboronic acid and chromotropic acid, 3‐nitrophenylboronic acid and alizarin red S, and phenylboronic acid and alizarin red S, respectively. A general and precise reaction mechanism of RB(OH)2 with H2L in aqueous solution, which can serve as a universal reaction mechanism for RB(OH)2 and H2L, was proposed on the basis of (a) the relative kinetic reactivities of the RB(OH)2 and its conjugate base, that is, the boronate ion, toward H2L, and (b) the determined pKa values of HBLs. The use of the conditional formation constant, K′, based on the main reaction: RB(OH)2+H2L ${{\mathop \leftrightarrow \limits ^{K{_{1}}}_{}}}$ RB(L)(OH)?+H3O+ instead of the binding constant has been proposed for the general reaction of uncomplexed boronic acid species (B′) with uncomplexed diol species (L′) to form boronic acid diol complex species (esters, BL′) in aqueous solution at pH 5–11: B′+L′ ${{\mathop \leftrightarrow \limits ^{K{^\prime}}_{}}}$ BL′. The proposed reaction mechanism explains perfectly the formation of boronic acid diol ester in aqueous solution. 相似文献
Lactic acid and 2‐hydroxyglutaric acid are chiral metabolites that have two distinct d‐ and l ‐enantiomers with distinct biochemical properties. Perturbations of a single enantiomeric form have been found to be closely related to certain diseases. Therefore, the ability to differentiate the d and l enantiomers is important for these disease studies. Herein, we describe a method for the separation and determination of lactic acid and 2‐hydroxyglutaric acid enantiomers by chiral derivatization (with l‐ menthol and acetyl chloride) combined with gas chromatography and mass spectrometry. The two pairs of above‐mentioned enantiomers exhibited linear calibration curves with a correlation coefficient (R2) exceeding 0.99. The measured data were accurate in the acceptable recovery range of 88.17–102.30% with inter‐ and intraday precisions (relative standard deviations) in the range of 4.23–17.26%. The limits of detection for d‐ lactic acid, l‐ lactic acid, d‐ 2‐hydroxyglutaric acid, and l‐ 2‐hydroxyglutaric acid were 0.13, 0.11, 1.12, and 1.16 μM, respectively. This method was successfully applied to analyze mouse plasma. The d‐ lactic acid levels in type 2 diabetes mellitus mouse plasma were observed to be significantly higher (P < 0.05, t‐test) than those of normal mice, suggesting that d‐ lactic acid may serve as an indicator for type 2 diabetes mellitus. 相似文献
Ethylenediaminotetramethylenephosphonic acid (EDTMP, H8L) was prepared and its complexes with some lanthanide ions (La, Eu, Gd and Sm) were isolated under various conditions. IR spectra and thermal stabilities of EDTMP and its complexes were studied. The experimental conditions of the preparation influence to the composition of the complexes were shown. In alkaline solution (pH=8) deprotonated (P(O)(O–)2), and in acidic solution (pH=3–4) deprotonated and partly protonated (P(O)(O–)(OH)) and non-protonated (P(O)(OH)2) phosphonic groups are present in the complexes. All the complexes contain coordinated water molecules. The complexes containing a protonated phosphonic group contain coordinated and hydrogen-bonded water molecules.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
Six new triorganotin complexes ( 1a – 1c and 2a – 2c ) of 5‐(salicylideneamino)salicylic acid, [5‐(3‐X‐2‐HOC6H3CH═N)‐2‐HOC6H3COO]SnR3 (X = H, 1 ; CH3O, 2 ; R = Ph, a ; Cy, b ; CH2C(CH3)2Ph, c ), have been synthesized by one‐pot reaction of 5‐aminosalicylic acid, salicylaldehyde and triorganotin hydroxide and characterized using elemental analysis and infrared and NMR (1H, 13C and 119Sn) spectra. The crystal structures of 1a , 1b , 2a ·CH3OH, 2b ·CH3OH and 2c ·CHCl3 have been determined using single‐crystal X‐ray diffraction. In non‐coordinated solvent CDCl3, the tin atoms in the complexes are all four‐coordinated. In the crystalline state, these compounds adopt a four‐ or five‐coordination mode. Complex 1a exhibits a 44‐membered macrocyclic tetrameric structure with trigonal bipyramidal geometry around the tin atoms in which the axial positions are occupied by the oxygen atom of carboxylate group of the ligand and the phenolic oxygen atom from the adjacent ligand. The coordination geometry of tin atom in 1b and 2c ·CHCl3 is a distorted tetrahedron shaped by three carbon atoms of alkyl groups and a carboxylate oxygen atom of the ligand. In 2a ·CH3OH and 2b ·CH3OH, the tin atom has a distorted trans‐C3SnO2 trigonal bipyramidal geometry formed by three alkyl groups, a monodentate carboxylate group and a coordinated methanol molecule. The molecules of 2a ·CH3OH and 2b ·CH3OH are linked via O─H···O hydrogen bonds into a one‐dimensional supramolecular chain and a centrosymmetric R44(22) macrocycle, respectively. Bioassay results against two human tumor cell types (A549 and HeLa) show the complexes are efficient cytostatic agents and may be explored as potential antitumor drugs. 相似文献
A zwitterionic heterocyclic boronic acid based on 4-isoquinolineboronic acid (IQBA) exhibits the highest reported binding affinity for sialic acid or N-acetylneuraminic acid (Neu5Ac, K=5390±190 m −1) through the formation of a cyclic boronate ester complex under acidic conditions (pH 3). This anomalous pH-dependent binding enhancement does not occur with common neutral saccharides (e.g., glucose, fructose, sorbitiol), because it is mediated via selective complexation to a α-hydroxycarboxylate moiety forming a stable ion pair and ternary complex with Neu5Ac in phosphate buffer. IQBA expands biorecognition beyond classical vicinal diols under neutral or alkaline buffer conditions, which enables the direct analysis of Neu5Ac by native fluorescence with sub-micromolar detection limits. 相似文献
Random copolymers of N-isopropylacrylamide (NIPA) and 4-vinylphenylboronic acid (VPBA) were obtained by solution polymerization using 2,2′-azobisizobutyronitrile as the initiator in ethanol at 65 °C. NIPA-co-VPBA copolymer exhibited both temperature- and pH-sensitivity. Thermally reversible phase transitions were observed both in the acidic and alkaline pH region for the copolymers produced with different VPBA/NIPA feed ratios. The pH dependency of the lower critical solution temperature (LCST) was stronger for the copolymers produced with higher VPBA feed concentrations. RNA was selected as a model biomolecule having vicinal-diol and amino groups that were potentially reactive with the boronic acid groups of NIPA-co-VPBA copolymer. The effect of RNA concentration on the LCST of NIPA-co-VPBA copolymer was investigated in aqueous media at different pHs. Although no significant effect was observed at pH 4, 7 or 10.5, the LCST decreased linearly with increasing RNA concentration at a pH approximately equal to the pKa of boronic acid. This behavior was explained by considering the binding of RNA onto the copolymer chains to occur via two types of complex formation. For the formation of these complexes, the amino and vicinal-diol groups of RNA should react with the boronic acid groups of the copolymer in the tetrahedral anionic form. The results indicated that NIPA-co-VPBA copolymer could be utilized as a new reagent for the determination of RNA concentration in aqueous media. The proposed method was valid for the RNA concentration range of 0–4 g · mL−1.
The schematical representation of the possible interactions between NIPA-co-VPBA copolymer and RNA. (A) A typical structure of single-stranded RNA. (B) Tetrahedral anionic form of boronic acid groups. (C) The interaction between the amino groups of the unpaired bases of RNA and the boronic acid groups of the copolymer. (D) Cyclic borate ester formation by the interaction between vicinal diol groups located at the 3′-end of RNA and boronic acid groups of the copolymer. 相似文献
We describe the pH response of a set of isomeric water-soluble fluorescent probes based on both the 6-aminoquinolinium and boronic acid moieties. These probes show spectral shifts and intensity changes with pH, in a wavelength-ratiometric and colorimetric manner. Subsequently, changes in pH can readily be determined around the physiological level.Although boronic acid containing probes are known to exhibit pH sensitivity along with an ability for saccharide binding/chelating, the new probes reported here are considered to be unique and show an unperturbed pH response, even in the presence of high concentrations of background saccharide, such as with glucose and fructose, allowing for the predominant pH sensitivity. The response of the probes is based on the ability of the boronic acid group to interact with strong bases like OH−, changing from the neutral form of the boronic acid group, R-B(OH)2, to the anionic ester, R-B−(OH)3, form, which is an electron donating group. The presence of an electron deficient quaternary heterocyclic nitrogen center and a strong electron donating amino group in the 6-position of the quinolinium backbone, provides for the spectral changes observed upon OH− complexation. In addition, by comparing the results obtained with systems separately incorporating 6-methoxy or 6-methyl substituents, the suppressed response towards monosaccharides, such as with glucose and fructose, can clearly be observed for these systems. Finally we compare our results to those of a control compound, BAQ, which does not contain the boronic acid group, allowing a rationale of the spectral changes to be made. 相似文献
Glycosylated hemoglobin (HbA1c) detection is performed routinely in hospitals as it is the most widespread confirmatory diagnosis of diabetes mellitus. Here we present a novel CE method for measuring HbA1c by introducing silica nanoparticles (NPs) modified with a boronic acid derivative (sugar loadings of 51 ± 2 μg/mg) as pseudo‐stationary phase. Before the sample injection, SiO2NP─B(OH)2 were introduced via pressure. Electrophoretic separation was explored through variation of the buffer pH and separation voltage, being the best separation, resolution and shorter separation time achieved with a 25 mM phosphate buffer pH 6.5. The calibration curve obtained was expressed as Area = 182.05%−1 × HbA1c − 377.02; R2 = 0.9826, using a UV/VIS absorbance detector at 415 nm (diode array). No interferences were observed from carbamylated or acetylated hemoglobin and the method shows a noteworthy stability. A paired t‐test was applied to compare the developed CE method with a commercial HbA1c test and no significant variations have been observed at a 90% significance level. 相似文献
The existence of homoserine lactone in Pisum sativum seedlings is demonstrated. L-Homoserine lactone reacts with hydroxylamine, at neutral or alkaline pH, to form homoserine hydroxamic acid. Procedures are described for preparing L-homoserine lactone and L-homoserine hydroxamic acid. The hydroxamic acid yields a color with maximum absorbance at 492 nm with Fe3+ in 0.25 N HCl. This reaction permitted assay for total homoserine and homoserine lactone. Six-day old Pisum sativum seedlings, with cotyledons removed, were extracted with 90% ethanol. Evaporation of the ethanol and addition of Na2SO4 solution and toluene and centrifugation removed protein lipids and esters. After clarification with activated charcoal, homoserine lactone content was estimated by reaction with NH2OH and Fe3+ reagents. For total homoserine, protein precipitation was with 2 N HCl and toluene. Evaporation to dryness at 60 °C under vacuum converted all homoserine to the lactone. The values found for total homoserine (μmols/g, wet weight) and preformed lactone (%) with the various growth media used were as follows: nitrate 87.4 (14.7%), NH2OH 75.2 (6.3%), water 70.5 (7.9%), urea 56.4 (18.9%). Acetic anhydride added to homoserine hydroxamic acid forms acetohydroxamic acid, which yields a color with maximum absorbance at 505 nm with Fe3+. This color reaction is seven times as sensitive as the reaction of Fe3+ with homoserine hydroxamic acid itself. 相似文献
Eight disubstituted benzyltin complexes, i.e., {[R(O)C=N‐N=C (Me)COO]R'2Sn(CH3OH)}n ( 1a and 2b ), {[R(O)C=N‐N=C (Me)COO]R'2Sn(CH3OH)}2 ( 1b and 1d ) and {[R(O)C=N‐N=C (Me)COO]R'2Sn}n ( 1c , 2a , 2c , and 2d ) (R = C4H3O‐, C4H3S‐, p–t‐Bu‐C6H4‐ or p‐MeO‐C6H4‐; R' = o‐Cl‐C6H4CH2‐ or o‐Me‐C6H4CH2‐), were prepared from the reaction of arylformylhydrazine, pyruvic acid and disubstituted benzyltin dichloride with microwave irradiation. All complexes were characterized by FT‐IR spectroscopy, 1H, 13C and 119Sn NMR spectroscopy, HRMS, elemental analysis, X‐ray single‐crystal diffraction and TGA. The in vitro antitumour activities of all complexes were evaluated by an MTT assay against three human cancer cell lines (NCI‐H460, HepG2, and MCF7). 2b exhibited strong antitumour activity on HepG2 cells and was expected to be a suitable platform for further chemical optimization to develop as anticancer therapeutics. The DNA binding of 2b was studied by UV–visible absorption spectrometry, fluorescence competitive assays, viscosity measurements and gel electrophoresis. Molecular docking was used to predict the binding between 2b and DNA, and the results show that 2b can become embedded in the double helix of DNA and cleave DNA. 相似文献
Three hydroxamic acid ligands (HL1 = acetohydroxamic acid; HL2 = benzohydroxamic acid; HL3 = N-phenylbenzohydroxamic acid), have been used to synthesize series of mono- or dialkyltin(IV) complexes, which include (i) the carboxyl acid hybrid five-coordinated dialkyltin complexes (C4H9)2SnL1L4 (1), [(CH3)2SnL2L5]·0.5C6H6 (2), (HL4 = acetic acid; HL5 = benzoic acid); (ii) the six-coordinated mono-n-butyltin complexes (C4H9)SnL1·Cl2·H2O (3), (C4H9)SnL2·Cl2·H2O (4), [(C4H9)SnL3·Cl2·H2O]·H2O (5), [(C4H9Sn)2(L3)2·Cl2·(OCH3)2] (6); and (iii) the alkali metal-mingled seven-coordinated mono-n-butyltin complexes [(C4H9Sn)3L2Na]+·Cl−·(CH3CH2)2O (7), [(C4H9Sn)3L2K]+·Cl−·CH2Cl2 (8). All complexes were characterized by elemental analyses, IR, 1H, 13C, 119Sn NMR and X-ray single crystal diffraction. In these complexes, hydroxamic acids present bidentate coordination modes with the carbonyl O atom and the hydroxyl O atom binding to tin center. In complexes 1-6, each tin atom is coordinated by one hydroxamic acid ligand. However, in complexes 7 and 8, tin atom is surrounded by three hydroxamic acid ligands, and all hydroxyl O atoms of the ligands also bind to the alkali metal center (Na or K). This kind of organotin(IV) framework containing one alkali metal is found for the first time. Furthermore, the supramolecular structures of 1, 3, 4 and 6 have been found to consist of 1D linear molecular chains formed by intermolecular N-H···X or C-H···X (X = O, N or Cl) hydrogen bonds. For complex 2, an interesting macrocyclic tetramer has been built by the intermolecular N-H···O hydrogen bonds. Fascinatingly, two unique symmetric dimeric structures are recognized in complexes 7 and 8, which is individually bridged by intermolecular N-H···Cl and N-H···O hydrogen bonds. In addition, for 8, the dimeric cycles have been further connected into a 1D supramolecular chain. 相似文献
The structure of the title compound, C7H6BNO3, a new boron heterocycle, prepared by the condensation of (2‐ethoxycarbonylphenyl)boronic acid and hydroxylamine, reveals the specific mode of intramolecular condensation between a phenylboronic acid and an ortho hydroxamic acid substituent. The crystal structure shows that dehydration occurs to form a planar oxazaborinine ring possessing both phenol‐like B—O—H and lactam functional groups. In the extended structure, intermolecular hydrogen bonding generates a 14‐membered ring. To our knowledge, this is the first crystal structure determination involving a six‐membered ring that exhibits consecutive B—OH, O, NH, and C=O functional groups. 相似文献
Density functional theory (DFT) calculations were made on the hydrolysis of hydantoin (2,4-imidazolidinedione). In the neutral hydrolysis, reacting systems composed of hydantoin and (H2O)n with n = 1+3, 2+3, 3+3, and 4+3 were adopted. Three water molecules (“+3”) participate in the in-plane hydrogen-bond circuit, and the n–3 = 1, 2, 3 or 4 water cluster works for the out-of-plane nucleophilic attack onto the carbonyl carbon of hydantoin. Transition states (TSs) involving bond interchanges prompted by proton transfers were determined. The reaction path with n = 3+3 containing N-carbamoyl glycine, N-carboxy glycine and three tetrahedral intermediates was found to be most likely. In the acid-catalyzed hydrolysis, a reacting system composed of hydantoin and H3O+(H2O)7 was employed. Ten TSs and nine intermediates were obtained. N-carbamoyl glycine and N-carboxy glycine were confirmed to be detectable stable species. The product consists of glycine, carbonic acid (not CO2), NH4+, and (H2O)5. It has the exothermic energy, whereas the product in the neutral hydrolysis is of the endothermic one for all n values. For both neutral (n = 3+3) and acid-catalyzed hydrolyses, the rate-determining steps were calculated to be for formation of the tetrahedral intermediate, HOOC-CH2-NH-C(OH)2NH2. The pattern of proton transfers along hydrogen bonds was carefully investigated. 相似文献
Two dual fluorescent receptors (1 and 2) for monosaccharides based on 4-dialky(alkyl=methyl and n-butyl) containing boronic acid group at the amido aniline were synthesized and their spectral properties were investigated. These receptors exhibited dual fluorescence with the long-wavelength band displaying strong solvent-polarity dependence, indicating the occurrence of the excited-state intramolecular charge transfer (ICT).With increasing pH value in aqueous solutions, the hybridization of the boron atom changed from sp^2 to sp^3, inducing a decrease in the total fluorescence quantum yield. The experimental results indicated that the anionic form of the boronate group acted as an electron donor and the benzanilide-like charge transfer was promoted upon hybridization change. In the presence of monosaccharides, the boronic acid in 1 and 2 changed from neutral to anionic form. The intensity of the locally excited (LE) state emission decreased in the presence of sugars while a slight increase in the intensity at the charge transfer (CT) emission occurred. Based on the change in the CT to LE intensity ratios of 1 and 2 due to sugar binding, ratiometric fluorescent assays for monosaccharide sensing were established. 相似文献