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1.
Anne Fischbeck Nana Bartke Hans-Ulrich Humpf 《Monatshefte für Chemie / Chemical Monthly》2005,20(1):397-410
CD exciton chirality methods are described for the stereochemical assignment of organic compounds containing carboxylic acid groups. Using the chromophoric combination 2-naphthoate or 2-anthroate and 9-anthrylmethyl group the absolute stereochemistry of - and -hydroxy carboxylic acids can be deduced from a single CD measurement. Furthermore, as demonstrated with cyclic and acylic dicarboxylic acids, the direct esterification of sterically hindered carboxyl groups with 2-naphthol also allows the stereochemical assignment via CD spectroscopy. 相似文献
2.
Summary. (A) The origin of exciton interaction and examples of its application to organic stereochemistry are presented. (B) N,N-Carbonyl-bridged dipyrrinones constitute a new class of highly fluorescent chromophores suitable for investigations of stereochemistry and absolute configuration. N,N-Carbonylxanthobilirubic acid esters are strongly fluorescent, with a fluorescence quantum yield (F) 0.8, but produce only weak exciton CD from the trans-1,2-cyclohexanediol template. The ester of an analog with benzoic acid replacing propionic, N,N-carbonyl-8-(4-carboxyphenyl)-3-ethyl-2,7,9-trimethyl-(10H)-dipyrrin-1-one, exhibits strong fluorescence (F=0.68, em=493nm, ex=422nm in CHCl3) and UV-Vis absorption (21000 at 424nm) in organic solvents. Its diester with (1S,2S)-cyclohexanediol is fluorescent and exhibits exciton circular dichroism (=+15dm3·mol–1·cm–1, =432nm; =–4dm3·mol–1cm–1, =380nm) that correlates with the Exciton Chirality Rule. 相似文献
3.
Two types of aromatic polyamide particles were prepared from 4,4′-diphenyldicarbonyl chloride and 3,5-diaminobenzoic acid in a reaction solution containing water or pyridine. Particles obtained using water (PA-water) were coarse spheres containing COOH groups with a diameter of 1 µm. Particles obtained using pyridine (PA-pyridine) were smooth spheres containing COOH and COCl groups with a diameter of 80 nm. The molecular weight of PA-pyridine was less than that of PA-water. During modification of PA-pyridine using 4′-aminobenzo-15-crown-5-ether, the COCl groups reacted with NH2 groups of the crown ether in water, resulting in attachment of the crown ether to the particle surface. 相似文献
4.
Summary. The benzoate 1B region exciton Cotton effects, hitherto unexplored, were analyzed for their use in stereochemical assignments in both acyclic (conformationally flexible) and cyclic molecules. It was found that a strong, allowed 1Ba transition, polarized longitudinally, dominates the 1B region (185–210nm) both in the UV and the CD spectra. The exciton Cotton effects due to this transition have the same sign (but differing magnitude) as those due to the 1La (CT) band. The other component of the nearly degenerate 1B system, i.e. 1Bb transition, polarized orthogonally to the 1Ba transition, gives a Cotton effect in the case of di- and poly(4-chlorobenzoate) chromophoric system, the sign of which is sensitive to the configuration of di- or polyol. In rigid 5-steroid skeleton 1Bb transition couplings appear responsible for strong exciton Cotton effects due to nearly parallelly oriented benzoate chromophores. Whereas 1Ba transition excitation energy appears insensitive to the nature of a substituent in 4-position of the benzoate chromophore, substitution with a donor group (methoxy, dimethylamino) brings about a red shift of the 1Bb band, although less pronounced than the red shift of the 1La (CT) band. 相似文献
5.
Koen Vandyck 《Tetrahedron letters》2005,46(1):75-78
2,3,6,7-Tetrahydro-as-indacene-1,8-dione 4 was prepared in 4 steps starting from 2-methyl-furan by modification of a literature procedure. Appliance of Noyori’s asymmetric transfer hydrogenation, resulted in (1S,8S)-1,2,3,6,7,8-hexahydro-as-indacene-1,8-diol 5 in high yield (81%) and excellent enantioselectivity (>99% ee) or (8S)-8-hydroxy-3,6,7,8-tetrahydro-2H-as-indacen-1-one 6 in moderate yield (58%) and equally high enantioselectivity (98.5% ee), depending on the conditions. The asymmetric reduction was expected to yield the (S)-alcohols using the (S,S)-Ts-DPEN ligand, which was confirmed by the appliance of the exciton chirality method on the corresponding bis(p-dimethylamino)benzoate 7. 相似文献
6.
Xue‐Hua ZHANG Yi‐Shan YAO Chao LI Wei‐Bo WANG Xue‐Xin CHENG Xue‐Song WANG Bao‐Wen ZHANG 《中国化学》2008,26(5):929-934
Three electron donor‐?? bridge‐electron acceptor (D‐π‐A) organic dyes bearing two carboxylic acid groups were applied to dye‐sensitized solar cells (DSSC) as sensitizers, in which one triphenylamine or modified triphenylamine and two rhodanine‐3‐acetic acid fragments act as D and A, respectively. It was found that the introduction of t‐butyl or methoxy group in the triphenylamine subunit could lead to more efficient photoinduced intramolecular charge transfer, thus improving the overall photoelectric conversion efficiency of the resultant DSSC. Under global AM 1.5 solar irradiation (73 mW·cm?2), the dye molecule based on methoxy‐substituted triphenylamine achieved the best photovoltaic performance: a short circuit photocurrent density (Jsc) of 12.63 mA·cm?2, an open circuit voltage (Voc) of 0.55 V, a fill factor (FF) of 0.62, corresponding to an overall efficiency (η) of 5.9%. 相似文献
7.
Noriaki Nishiguchi Takafumi Kinuta Yoko Nakano Dr. Takunori Harada Dr. Nobuo Tajima Tomohiro Sato Prof. Dr. Michiya Fujiki Prof. Dr. Reiko Kuroda Prof. Dr. Yoshio Matsubara Dr. Yoshitane Imai 《化学:亚洲杂志》2011,6(4):1092-1098
The solid‐state chiral optical properties of a 4‐(2‐arylethynyl)‐benzoic acid/amine supramolecular organic fluorophore can be controlled by changing the arylethynyl group of the achiral 4‐(2‐arylethynyl)‐benzoic acid component molecule rather than the chirality of the amine component molecule. 相似文献
8.
9.
《Analytical letters》2012,45(3):585-600
Abstract The intensity of the radiation emitted by humic acid (HA) in the presence of SO5 2? in basic medium was used to determine HA in the range up to 20.0 mg l?1. The detection limit was 0.24 mg l?1. The addition to the sample of 50 mg l?1 of Co(II) or Mn(II), as EDTA complexes or chloride salts, enhanced the radiation emission as a result of the formation of strong oxidant radicals such as SO5 ??, SO4 ??, and HO?. In the presence of these metal ions, the oxidation of HA and the catalytic decomposition of SO5 2? occur simultaneously. Low concentration of HA in natural waters can be detected. HA was replaced by some model organic compounds. The marked chemiluminescent (CL) signals followed the order: phloroglucinol>fulvic acid>humic acid>resorcinol>pyrogallol>cathecol>hydroquinone. 相似文献
10.
11.
Ning Jin Shouyu Zhang Shibo Sun Minghuo Wu Xiaojing Yang Jianqiang Xu Kun Ma Shui Guan Weiping Xu 《Molecules (Basel, Switzerland)》2022,27(7)
Industrial processing of raspberry juice and wine generates considerable byproducts of raspberry pomace. Ellagic acids/ellagitannins, being characterized by their antioxidant and antiproliferation properties, constitute the majority of polyphenolics in the pomace and are valuable for recovery. In the present study, we developed a novel procedure with sodium bicarbonate assisted extraction (SBAE) to recover ellagic acid from raspberry wine pomace. Key parameters in the procedure, i.e., sodium bicarbonate concentration, temperature, time and solid/liquid (S/L) ratio, were investigated by single factor analysis and optimized subsequently by Response Surface Methodology (RSM). Optimal parameters for the SBAE method here were found to be 1.2% (w/v) NaHCO3, 1:93 (w/v) S/L ratio, 22 min and 100 °C. Under these conditions, the ellagic acid yield was 6.30 ± 0.92 mg/g pomace with an antioxidant activity of 79.0 ± 0.96 μmol Trolox eq/g pomace (DPPH assay), which are 2.37 and 1.32 times the values obtained by extraction with methanol–acetone–water solvent, respectively. The considerable improvement in ellagic acid extraction efficiency could be highly attributed to the reactions of lipid saponification and ellagitannin hydrolysis resulted from sodium bicarbonates. The present study has established an organic solvent-free method for the extraction of ellagic acid from raspberry wine pomace, which is feasible and practical in nutraceutical applications. 相似文献
12.
Nikita M. Podvalnyy Alexander I. Zinin Nelly N. Malysheva Roman A. Kunetskiy 《Journal of carbohydrate chemistry》2013,32(5):213-224
A convenient synthesis and separation of α- and β-anomers of methyl (phenyl 3,5-dideoxy-2-thio-5-trifluoroacetamido-D-glycero-D-galacto-nonulopyranosid)onate (6a and 6b) on a multigram scale was developed. Both α- and β-isomers of 6 were obtained as crystals suitable for safe storage. The β-isomer forms a crystalline solvate with methanol. Fully O-trichloroacetylated and O-trifluoroacetylated N-trifluoroacetyl thiosialosides were synthesized in an efficient manner from the β-tetraol 6b. 相似文献
13.
提出了计算多元弱酸(或碱)溶液pH的新方法.该计算方法具有以下特点:限制条件简单,即多项式中某一项小于最大项的5%即可忽略该项贡献;计算过程和步骤清晰易记;通用性好,一元或多元弱酸(碱)溶液pH计算均可适用. 相似文献
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15.
It is the first time that boron has been used as a chromogenic agent to determine aminomethylbenzoic acid (PAMBA) by the fading spectrophotometric method in this paper. The study indicates that at pH 10.00 the absorbance of PAMBA decreases when boric acid (BA) is added to the solution. A simple, rapid, sensitive and reliable novel method based on the product of PAMBA and BA is obtained. The stoichiometric ratio of the product is 1:2. Beer's law is obeyed in the range of PAMBA concentrations of 0.13 ? 38.40 μg/mL at a wavelength of 242 nm (ε242 is 8.1 × 104 L/mol/cm). The equation of linear regression is A = ‐0.06635 – 0.02914C (× 10?5 M), with a linear correlation coefficient of 0.9974. The detection limit is 0.12 μg/mL and RSD 0.11%. The method is successfully applied to the determination of PAMBA in pharmaceutical samples, and average recoveries from pharmaceutical samples and urine samples were between 98.4 ? 102.5%. The other components in these samples do not interfere with the determination by the proposed method. 相似文献
16.
Kishore K. Tiwari 《中国化学会会志》2010,57(1):105-110
A new simple and sensitive and selective spectrophotometric method has been developed for the determination of ascorbic acid (AA) at trace level using a new reagent, leuco malachite green (LMG). AAreacts with potassium iodide‐iodate solution under acidic conditions to liberate iodine and the liberated iodine selectively oxidizes LMG to MG dye. The colour of the dye was measured at 620 nm. Beer's law is obeyed over the concentration range of 0.8–8 iμg μAA per 25 mL of final solution (0.032–0.32 ppm). The apparent molar absorptivity and Sandell's sensitivity of the method were found to be 2.98 × 105 l mol−1 cm−1, 0.0042 μg cm−2, and respectively. Statistical treatment of the experimental results indicates that the method is precise and accurate. The method is free from interference of common ions and many of the ingredients commonly found in pharmaceuticals. The reliability of the method was established by parallel determination against Leucocrystal violet (LCV) method. The method described was satisfactorily applied for the determination of AA in fruit juices, pharmaceuticals and biological samples. 相似文献
17.
Nathalie Laronze Jean-François Moisan Catherine Roch-Marchal Feng-Xian Liu Gilbert Hervé 《Journal of Cluster Science》2002,13(3):355-368
Transition metal salts of heteropolyacids have been prepared taking into account the strong acidic and cation exchanging properties of the solid heteropolyacids. The exchange between protons and the transition metal cation is carried out by stirring a suspension of the hydrated heteropolyacid in a solution of the metal acetylacetonate complex in toluene. The exchange occurs on the surface of the solid particles and diffusion of protons and metal cations into the hydrated lattice leads to the substitution of all the protons. The method can be utilized in order to prepare supported vanadyl and copper molybdophosphates from supported heteropolyacids and they have been studied in the catalysis of the oxidative dehydrogenation of isobutyric acid. The effect of vanadyl counter-ions on the catalytic behavior is the same as observed with bulk catalysts but, on the contrary, copper supported molybdophosphate shows an acid catalytic activity not observed with bulk catalysts. 相似文献
18.
The oscillating reaction involving organic gallic acid (GA), potassium bromate, and a metal ion complex has been reinvestigated. In contrast to other previous reports, this oscillating reaction is catalyzed by the [Fe(phen)n]2+ ion (phen = 1,10-o-phenanthroline, n=1, 2, 3) rather than by the cerium ion. The characteristics of the oscillations depend on the temperature and on the concentrations of the potassium bromate, gallic acid, [Fe(phen)n]2+, and sulfuric acid. A cyclic voltammetric study indicates that the redox potential and the reversibility of the [Fe(phen)n]2+/3+ couple play a major role in catalyzing this oscillating system. 相似文献
19.
Salicylic acid is a key compound in nonsteroidal anti-inflammatory drugs that has been recently used for preventing the risk of hospitalization and death among COVID-19 patients and in preventing colorectal cancer (CRC) by suppressing two key proteins. Understanding drug–drug interaction pathways prevent the occurrence of adverse drug reactions in clinical trials. Drug–drug interactions can result in the variation of the pharmacodynamics and pharmacokinetic of the drug. Inhibition of the Cytochrome P450 enzyme activity leads to the withdrawal of the drug from the market. The aim of this paper was to develop and validate an HPLC-UV method for the quantification of 4′-hydroxydiclofenac as a CYP2C9 metabolite using salicylic acid as an inhibitor in rat liver microsomes. A CYP2C9 assay was developed and validated on the reversed phase C18 column (SUPELCO 25 cm × 4.6 mm × 5 µm) using a low-pressure gradient elution programming at T = 30 °C, a wavelength of 282 nm, and a flow rate of 1 mL/min. 4′-hydroxydiclofenac demonstrated a good linearity (R2 > 0.99), good reproducibility, low detection, and quantitation limit, and the inter and intra-day precision met the ICH guidelines (<15%). 4′-hydroxydiclofenac was stable for three days and showed an acceptable accuracy and recovery (80–120%) within the ICH guidelines in a rat liver microsome sample. This method will be beneficial for future applications of the in vitro inhibitory effect of salicylic acid on the CYP2C9 enzyme activity in rat microsomes and the in vivo administration of salicylic acid in clinical trials. 相似文献
20.
Constantine D. Stalikas Alexandros Ch. Pappas Miltiades I. Karayannis Panayotis G. Veltsistas 《Mikrochimica acta》2003,142(1-2):43-48
Squaric acid (1,2-dihydroxy-3,4-diketo-cyclobutene) is used in a specific reaction with Fe(III) for the spectrophotometric
determination of Fe(III) and total iron content. The optimization of the experimental parameters leads to the establishment
of a simple, fast and accurate analytical method. The analytical procedure includes mixing ammonium squarate (40 mM), prepared
in a phthalate buffer solution of pH 2.7, with the sample and measuring the absorbance at 515 nm. The molar absorptivity of
the colored product is 3.95×103 L·mol−1·cm−1, at 515 nm. Calibration graphs for Fe(III) are rectilinear for 0.5–20 mgL−1, with a detection limit of 0.3 mgL−1 and r.s.d. not exceeding 2.5%, for five replicates of a 3.0 mgL−1 standard solution. The method has been successfully applied to the determination of iron (III) and the total iron content
after quantitative oxidation of iron (II). The results for several analyzed samples when compared with those acquired by using
the FAAS technique, were found to be in satisfactory agreement.
Author for correspondence: University of Ioannina, Department of Chemistry, Laboratory of Analytical Chemistry, Ioannina 451
10, Greece. E-mail: panavelt@cc.uoi.gr
Received July 27, 2002; accepted December 20, 2002
Published online April 11, 2003 相似文献