Investigations of the local distortions and EPR parameters for Cu2+ in xNa2O‐(30–x)K2O‐70B2O3 (5 ≤ x ≤ 25 mol%) glasses

The local distortions and electron paramagnetic resonance parameters for Cu²⁺ in the mixed alkali borate glasses xNa₂O‐(30–x)K₂O‐70B₂O₃ (5 ≤ x ≤ 25 mol%) are theoretically studied with distinct modifier Na₂O compositions x. Owing to the Jahn–Teller effect, the octahedral [CuO₆]¹⁰⁻ clusters show significant tetragonal elongation ratios p ~19% along the C₄ axis. With the increase of composition x, the cubic field parameter Dq and the orbital reduction factor k exhibit linearly and quasi‐linearly decreasing tendencies, respectively, whereas the relative tetragonal elongation ratio p has quasi‐linearly increasing rule with some fluctuations, leading to the minima of g factors at x = 10 mol%. The composition dependences of the optical spectra and the electron paramagnetic resonance parameters are suitably reproduced by the linear or quasi‐linear relationships of the relevant quantities (i.e., Dq, k, and p) with x. The above composition dependences are analyzed from mixed alkali effect, which brings forward the modifications of the local crystal‐fields and the electronic cloud distribution around Cu²⁺ with the variation of the composition of Na₂O.     

Cadmium O‐alkylxanthates as CVD precursors of CdS: a chemical characterization

Cadmium bis(O‐alkylxanthates) are potential single‐source molecular precursors for the chemical vapor deposition (CVD) of Cd(II) sulfide thin films. In this work, a multi‐technique characterization of Cd(O‐RXan)₂ compounds [where O‐RXan is CH₃CH₂OCS₂ (O‐EtXan) or (CH₃)₂CHOCS₂ (O‐ⁱPrXan)] is performed by means of several analytical methods (extended x‐ray absorption fine structure, Raman, Fourier transform infrared and optical absorption, spectroscopics ¹H and ¹³C NMR, thermal analysis and mass spectrometry) for a thorough investigation of their structure and chemical–physical properties. The most important results concerning the chemical behavior under different experimental conditions, with particular attention to relevant properties for CVD applications, are presented and discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

A system for predicting the retentions of O-alkyl, n-(1-methylthioethylideneamino) phosphoramidates on RP-HPLC

Summary By using factor analysis, cluster analysis and multiple linear regression methods, two parameters, FHF and ECCR, were selected from eight solute-related structure parameters as showing the best correlation with retention data. The relationship between the retention data (k) and these two structure parameters were established for ten O-alkyl, O-(1-methylthioethylideneamino) phosphoramidate compounds under the experimental conditions studied. Retention data (k) for six other compounds that have a high correlation with structure parameters were predicted using these QSRR equations. The system was evaluated by comparing the experimentalk values with the predicted ones. Good agreement was obtained between the experimental and predictedk values.     

Synthesis and NMR characterization of 6‐Phenyl‐6‐deoxy‐2,3‐di‐O‐methylcellulose

Cellulose ( 1 ) was converted for the first time to 6‐phenyl‐6‐deoxy‐2,3‐di‐O‐methylcellulose ( 6 ) in 33% overall yield. Intermediates in the five‐step conversion of 1 to­ 6 were: 6‐O‐tritylcellulose ( 2 ), 6‐O‐trityl‐2,3‐di‐O‐methylcellulose ( 3 ), 2,3‐di‐O‐methylcellulose ( 4 ); and 6‐bromo‐6‐deoxy‐2,3‐di‐O‐methylcellulose ( 5 ). Elemental and quantitative carbon‐13 analyses were concurrently used to verify and confirm the degrees of substitution in each new polymer. Gel permeation chromotography (GPC) data were generated to monitor the changes in molecular weight (DP_w) as the synthesis progressed, and the compound average decrease in cellulose DP_w was ～ 27%. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to characterize the decomposition of all polymers. The degradation temperatures ( °C) and percent char at 500 °C of cellulose derivatives 2 to 6 were 308.6 and 6.3%, 227.6 °C and 9.7%, 273.9 °C and 30.2%, 200.4 °C and 25.6%, and 207.2 °C and 27.0%, respectively. The glass transition temperature (T_g) of­6‐O‐tritylcellulose by dynamic mechanical analysis (DMA) occurred at 126.7 °C and the modulus (E′, Pa) dropped 8.9 fold in the transition from ?150 °C to + 180 °C (6.6 × 10⁹ to 7.4 × 10⁸ Pa). Modulus at 20 °C was 3.26 × 10⁹ Pa. Complete proton and carbon‐13 chemical shift assignments of the repeating unit of the title polymer were made by a combination of the HMQC and COSY NMR methods. Ultimate non‐destructive proof of carbon–carbon bond formation at C6 of the anhydroglucose moiety was established by generating correlations between resonances of CH₂6 (anhydroglucose) and C1′, H2′, and H6′ of the attached aryl ring using the heteronuclear multiple‐bond correlation (HMBC) method. In this study, we achieved three major objectives: (a) new methodologies for the chemical modification of cellulose were developed; (b) new cellulose derivatives were designed, prepared and characterized; (c) unequivocal structural proof for carbon–carbon bond formation with cellulose was derived non‐destructively by use of one‐ and two‐dimensional NMR methods. Copyright © 2002 John Wiley & Sons, Ltd.     

Kinetics of the chromium(III)/l‐glutamic acid complexation reaction: Formation,decay, and UV‐vis spectrum of a long‐lived intermediate

The kinetics of the aqueous reaction of Cr(III) with either l ‐glutamic acid or sodium hydrogen l ‐glutamate at pH 2.46‐5.87 have been followed by means of absorbance readings. The rate of formation of the reaction products showed acceleration‐deceleration periods, caused by the accumulation and posterior decay of an intermediate in nonnegligible concentration. A double‐exponential integrated rate law allowed obtaining two rate constants for each absorbance‐time experimental series, associated with the appearance (k₁) and decay (k₂) of the long‐lived intermediate. An increase of the initial concentrations of either hydrogen l ‐glutamate (apparent kinetic orders < 1) or hydroxide (kinetic orders = 1) ions resulted in an increase of both k₁ and k₂, but addition of an inert electrolyte (KNO₃) resulted in opposite effects on k₁ (decrease) and k₂ (increase). The experimental activation energies were 83 ± 10 (for k₁) and 95 ± 5 (for k₂) kJ mol⁻¹. The electronic spectrum of the low reactivity detected intermediate resembled more closely to that of the blue/green reactant than that of the violet reaction product. The low number of protons set free by the complexating hydrogen l ‐glutamate ligand seems to suggest that some polymerization of the coordinated amino acid (to form a di‐ or tripeptide) might take place. The available experimental data indicate that the coordination of the organic ligand must be preceded by the breakdown of a strong Cr(III)–H₂O chemical bond in the slow steps of the mechanism.     

Simultaneous determination of 7‐O‐succinyl macrolactin A and its active major metabolite,macrolactin A in dog plasma using high‐performance liquid chromatography with UV detection

We developed a method for the simultaneous quantification of 7‐O‐succinyl macrolactin A and its active metabolite, macrolactin A, in dog plasma. After protein precipitation with acetonitrile including flufenamic acid as an internal standard, 7‐O‐succinyl macrolactin A, macrolactin A, and flufenamic acid were chromatographed on a reverse‐phase C₁₈ analytical column. The mobile phase, consisting of 20 mM acetate buffer and acetonitrile, was eluted using a gradient program at 1 mL/min, and the UV absorbance was measured at 230 nm. The retention times of 7‐O‐succinyl macrolactin A, flufenamic acid, and macrolactin A were 3.4, 4.8, and 6.9 min, respectively. The coefficient of variation in the assay precision for both substances was less than 6%, and the accuracy ranged from 96 to 105%. This method was used to measure the concentrations of 7‐O‐succinyl macrolactin A and macrolactin A in dog plasma following an intravenous administration of a single dose (25 mg/kg) of 7‐O‐succinyl macrolactin A salt.     

Alkyl‐Tethered Bis‐Phosphoryl Compounds with two 1,3,2‐Benzodiazaphosphorinone Units; Oxidation,Complexation, and X‐Ray Structure Analysis of Selected Compounds

The reaction of the bis‐chlorophosphines 1 a – 1 d with bis(2‐chloroethyl)amine hydrochloride in the presence of triethylamine and with various trimethylsilylamines led to a new class of bis‐phosphorus ligands 2 a – 2 c and 3 a – 3 g . ³¹P‐NMR studies suggested that the bis‐phosphorus ligands undergo rotation reactions about the alkyl bridge in polar solvents. Compounds 2 a – 2 c showed initially only one sharp singlet each in their ³¹P‐NMR spectra. After a few days at room temperature, two signals were observed. Similar results were observed for 3 a – 3 g . In the solid state, the two phosphorus atoms in 2 c are not equivalent, as was confirmed by the observation of two signals in the solid state ³¹P‐NMR spectrum. Oxidation reactions of 2 a – 2 c by the hydrogen peroxide‐urea 1 : 1 adduct (NH₂)₂C(:O) · H₂O₂ led to the formation of the corresponding phosphoryl compounds 4 a – 4 c . Reaction of 2 a and 3 a with Pt[COD]Cl₂ (COD = 1.5‐Cyclooctadiene) furnished the complexes 5 and 6 . The NMR spectra suggested that the two chlorine atoms are in cis position. X‐ray structure analyses were conducted for 2 a , which exhibits twofold symmetry; 2 c , which is linked into dimers by hydrogen bonds C–H…O; and 6 , confirming the cis configuration.     

Liquid chromatography–mass spectrometry for the simultaneous determination of the catalpol‐related iridoid glucosides,verproside, isovanilloylcatalpol,catalposide and 6‐O‐veratroyl catalpol in rat plasma

Verproside, isovanilloylcatalpol, catalposide and 6‐O‐veratroyl catalpol are bioactive iridoid glucosides isolated from in a number of folk medicinal plants. A rapid, sensitive and selective liquid chromatography/mass spectrometric (LC/MS) method for the simultaneous determination of verproside, isovanilloylcatalpol, catalposide and 6‐O‐veratroyl catalpol in rat plasma was developed. The analytes were extracted from 50 µL of rat plasma with ethyl acetate using 7‐carboxymethyloxy‐3',4',5‐trimethoxyflavone as internal standard and analyzed on an X‐Bridge C₁₈ column within 6.5 min with 40% methanol in 10 mm ammonium formate (pH 3.0). The analytes were quantified using an electrospray ionization mass spectrometry in the selected ion monitoring mode. The standard curves were linear over the concentration ranges of 10–2000 ng/mL for verproside, isovanilloylcatalpol and catalposide and 20–2000 ng/mL for 6‐O‐veratroyl catalpol. The coefficients of variation and relative errors of verproside, isovanilloylcatalpol, catalposide and 6‐O‐veratroyl catalpol for intra‐ and inter‐assay at four quality control levels were 2.5–8.0 and–4.0–6.6%, respectively. This method was successfully applied to the pharmacokinetic study of verproside and its possible metabolite isovanilloylcatalpol after intravenous administration of verproside, a candidate anti‐asthma drug, in male Sprague–Dawley rats. Copyright © 2009 John Wiley & Sons, Ltd.     

A New Hydrolyzable Tannin from Balanophora harlandii with Radical‐Scavenging Activity

One new hydrolyzable tannin, 1‐O‐[(E)‐p‐coumaroyl]‐3‐O‐galloyl‐β‐D ‐glucopyranose ( 1 ), was isolated from the rhizome of Balanophora harlandii, together with 18 known phenolic compounds. Their structures were determined by detailed spectroscopic analysis. Of the known compounds, 3‐O‐caffeoyl‐D ‐glucopyranose ( 6 ) was obtained as a natural product for the first time, and compounds 2 – 6 and 8 – 19 were identified for the first time from this plant. The radical‐scavenging activity of the isolated compounds was tested by a DPPH assay.     

‘Click Synthesis’ of Some Novel O‐Substituted Oximes Containing 1,2,3‐Triazole‐1,4‐diyl Residues as New Analogs of β‐Adrenoceptor Antagonists

The ‘click synthesis’ of some novel O‐substituted oximes, 7a – 7t , which contain 1,2,3‐triazolediyl residues, as new analogs of β‐adrenoceptor antagonists is described (Schemes 1–4). The synthesis of these compounds was achieved in four to five steps. The formation of oximes of 9H‐fluoren‐9‐one and benzophenone, i.e., 9a and 9b , respectively, followed by their reaction with propargyl bromide, afforded O‐propargyl oximes 10a and 10b , respectively, which by a subsequent CuI‐catalyzed Huisgen cycloaddition with prepared β‐azido alcohols 11a – 11j (Schemes 2 and 3), led to the target compounds 7a – 7t in good yields.     

Generation of Aryl(2‐lithiophenyl)methanone O‐Methyl Oximes and Their Use for the Synthesis of N‐(3‐Alkyl‐1‐aryl‐ or 1,3‐diaryl‐1H‐isoindol‐1‐yl)‐O‐methylhydroxylamines via the Reaction with Nitriles

An efficient two‐step procedure for the preparation of a new type of 1H‐isoindoles, i.e., N‐(3‐alkyl‐1‐aryl‐ or 1,3‐diaryl‐1H‐isoindol‐1‐yl)‐O‐methylhydroxylamines 5 , from readily available aryl(2‐bromophenyl)methanones 1 has been developed. Aryl(2‐bromophenyl)methanone O‐methyloximes 2 , derived from the corresponding ketones, were treated with BuLi in Et₂O at 0° to generate novel lithium compounds, aryl(2‐lithiophenyl)methanone O‐methyloximes 3 , which were allowed to react with nitriles to give the desired products 5 in moderate‐to‐fair yields.     

‘Click Synthesis’ of Some Novel Benzimidazol Oxime Ethers Containing Heterocycle Residues as Potential ß‐Adrenergic Blocking Agents

The ‘click synthesis’ of some novel O‐substituted oximes, 5a – 5j , which contain heterocycle residues, as new analogs of ß‐adrenoceptor antagonists is described (Scheme 1). The synthesis of these compounds was achieved in four steps. The formation of (E)‐2‐(1H‐benzo[d]imidazol‐1‐yl)‐1‐phenylethanone oxime, followed by their reaction with 2‐(chloromethyl)oxirane, afforded mixture of oil compounds 3 and 4 , which by a subsequent tetra‐n‐butylammonium bromide (TBAB)‐catalyzed reaction with N H heterocycle compounds (Scheme 1), led to the target compounds 5a – 5j in good yields.     

Computation of the binding affinities of catechol‐O‐methyltransferase inhibitors: Multisubstate relative free energy calculations

Alchemical free energy simulations are amongst the most accurate techniques for the computation of the free energy changes associated with noncovalent protein–ligand interactions. A procedure is presented to estimate the relative binding free energies of several ligands to the same protein target where multiple, low‐energy configurational substates might coexist, as opposed to one unique structure. The contributions of all individual substates were estimated, explicitly, with the free energy perturbation method, and combined in a rigorous fashion to compute the overall relative binding free energies and dissociation constants. It is shown that, unless the most stable bound forms are known a priori, inaccurate results may be obtained if the contributions of multiple substates are ignored. The method was applied to study the complex formed between human catechol‐O‐methyltransferase and BIA 9‐1067, a newly developed tight‐binding inhibitor that is currently under clinical evaluation for the therapy of Parkinson's disease. Our results reveal an exceptionally high‐binding affinity (K_d in subpicomolar range) and provide insightful clues on the interactions and mechanism of inhibition. The inhibitor is, itself, a slowly reacting substrate of the target enzyme and is released from the complex in the form of O‐methylated product. By comparing the experimental catalytic rate (k_cat) and the estimated dissociation rate (k_off) constants of the enzyme‐inhibitor complex, one can conclude that the observed inhibition potency (K_i) is primarily dependent on the catalytic rate constant of the inhibitor's O‐methylation, rather than the rate constant of dissociation of the complex. © 2012 Wiley Periodicals, Inc.     

Synthesis and characterization of zinc bis(O‐isopropylxanthate) as a single‐source chemical vapor deposition precursor for ZnS

The utilization of single‐source molecular precursors in chemical vapor deposition (CVD) experiments requires a deep knowledge of their chemico‐physical properties, with particular regard to thermal stability and fragmentation pattern. This study describes the synthesis and characterization of zinc bis(O‐isopropylxanthate), Zn(O‐ⁱPrXan)₂, [O‐ⁱPrXan = (CH₃)₂CHOCS₂], a single‐source precursor for the CVD of zinc(II) sulfide thin films and nanorods. Several analytical methods yielding complementary information (extended X‐ray absorption fine structure, Raman, FT‐IR, UV–Vis optical absorption, ¹H and ¹³C NMR, thermogravimetric analysis, differential scanning calorimetry as well as mass spectrometry techniques, i.e. electrospray and electron ionization, mass‐analyzed ion kinetic energy) are adopted for a comprehensive investigation of purity, structure, thermal behavior and decomposition pathways of the molecule. The most significant results are discussed critically and the properties useful for CVD applications are highlighted. Copyright © 2005 John Wiley & Sons, Ltd.     

Systematic characterization of flavonoids from Siraitia grosvenorii leaf extract using an integrated strategy of high‐speed counter‐current chromatography combined with ultra high performance liquid chromatography and electrospray ionization quadrupole time‐of‐flight mass spectrometry

The chemical constituents of the Siraitia grosvenorii leaf extract were studied. Firstly, high‐speed counter‐current chromatography was applied to the one‐step separation of four compounds from S. grosvenorii leaf extract with the solvent system composed of 0.01% acetic acid water/n‐butanol/n‐hexane/methanol (5:3:1:1, v/v/v/v). In this work, 270 mg of crude sample yielded four compounds, a new kaempferol O‐glycoside derivative, kaempferol 3‐O‐α‐L‐[4‐O‐(4‐carboxy‐3‐hydroxy‐3‐methylbutanoyl)]‐rhamnopyranoside‐7‐O‐α‐L‐rhamnopyranoside, named kaempferitrin A (2.1 mg, 90%), and three known compounds, grosvenorine (3.4 mg, 93%), kaempferitrin (14.4 mg, 99%) and afzelin (4 mg, 98%), and the structures of these compounds were identified by NMR spectroscopy and mass spectrometry. Then, ultra high performance liquid chromatography with electrospray ionization quadrupole time‐of‐flight mass spectrometry was used to illustrate the dominant flavonoids in S. grosvenorii leaf extract. 34 flavonoids including 19 kaempferol O‐glycosides, 4 quercetin O‐glycosides, 6 flavanone derivatives, and 5 polymethoxyflavones, were accurately or tentatively identified by carefully comparing their retention times, UV data, precise masses, the typical fragments of the standards and literature data. Most of these compounds were reported for the first time. This study establishes a foundation for the further development and utilization of S. grosvenorii leaves in future.     

O-氯丙基和O-氰丙基间苯二酚杯芳烃的合成，晶体结构和电化学性质

四烃基和四二茂铁基间苯二酚杯芳烃在丙酮回流条件和碳酸钾存在下用1-溴-3-氯丙烷或4-氯丁腈进行烃基化反应分别生成全取代的O-氯丙基和O-氰丙基间苯二酚杯芳烃,晶体结构测定表明烷基间苯二酚杯芳烃倾向于以全顺式构型存在,而芳基间苯二酚杯芳烃倾向于以顺-反-反式构型存在。本文还已经了四二茂铁基间苯二酚杯芳烃的电化学性质。     

Xanthone O‐Glycosides from the Roots of Pteris Multifida

Two new xanthone glycosides and six known compounds were isolated from the roots of Pteris multifida. Based on spectroscopic and chemical methods, the structures of the new compounds were elucidated as 1‐hydroxy‐4,7‐dimethoxy‐8‐(3‐methyl‐2‐butenyl)‐6‐O‐α‐L‐rhamnopyranosyl‐(1→2)‐[β‐D‐glucopyranosyl‐(1→3)]‐β‐D‐glucopyranosylxanthone ( 1 ), and 1,3‐dihydroxy‐7‐methoxy‐8‐(3‐methyl‐2‐butenyl)‐6‐O‐α‐L‐rhamnopyranosyl‐(1 →2)‐[β‐D‐glucopyranosyl‐(1→3)]‐β‐D‐glucopyranosylxanthone ( 2 ), respectively.     

Antioxidant and Antiradical Activity of Hydroxy‐Substituted 4‐Thiaflavanes

The antioxidant activities of several hydroxy‐substituted 4‐thiaflavanes, compounds 1 – 3 , were determined by measuring their ability of inhibiting the autoxidation of styrene or cumene. On this basis, the role played by the number and position of OH groups and by the oxidation state of the S‐atom was quantified and rationalized. With these data, it should be possible to optimize the structural features of these ‘double‐faced’ antioxidants for structure? activity‐relationship studies. A comparison between the kinetic data (k_inh) reported in this paper and the previously reported values of the antiradical activities (SC₅₀), measured by the DPPH^. bleaching method, for 1 – 3 is made (Table).     

A simple and sensitive HPLC‐UV determination of 7‐O‐succinyl macrolactin A in rat plasma and urine and its application to a pharmacokinetic study

A simple, sensitive and reproducible isocratic reversed‐phase (C₁₈) high‐performance liquid chromatography (HPLC) method was developed to determine 7‐O‐succinyl macrolactin A (SMA) in rat plasma and urine samples using UV detector set at 230 nm. Lamotrigine was used as internal standards (IS) to ensure the precision and accuracy of the method. The retention times of SMA and IS for the plasma sample were 9.2 and 4.4 min, respectively, and those for the urine samples were 7.9 and 4.3 min, respectively. The intra‐ and inter‐day variations of the analytical responses, expressed in terms of relative standard deviation, were less than 14.9%. The accuracy, in terms of average analytical recovery, ranged from 90.4 to 119%. The lower limits of quantification of SMA in rat plasma and urine samples were 0.02 and 0.1 µg/mL, respectively. This method is applicable for the pharmacokinetic studies of SMA in rats. Copyright © 2012 John Wiley & Sons, Ltd.