Use of HPLC in the Determination of the Molar Absorptivity of 4��-Geranyloxyferulic Acid and Boropinic Acid

Natural prenyloxycinnamic acids were shown to exert in vitro and in vivo remarkable and valuable anti-cancer and anti-inflammatory effects. Among these, 4??-geranyloxyferulic acid [3-(4??-geranyloxy-3??-methoxyphenyl)-2-trans-propenoic acid] was discovered as an efficient orally active chemopreventive agent of several types of cancer, and its structural analogue boropinic acid was shown to exert a valuable inhibitory effect both in vitro and in vivo against the growth of Helicobacter pylori. As a continuation of our chemical, chemico-physical, and pharmacological studies on these secondary metabolites, we report herein the comparison between traditional UV/Vis assays and HPLC?CDAD methods for the determination of the molar absorptivity coefficient of 4??-geranyloxyferulic acid (?? ₃₁₀ = 12,950 and ?? ₂₈₈ = 11,910 L mol^?1 cm^?1) and boropinic acid (?? ₃₁₀ = 13,510 and ?? ₂₈₈ = 12,350 L mol^?1 cm^?1). Ferulic acid was merely used as a reference standard to test the possibility of the application of these two assays to the oxyprenylated compounds. The data reported in the present study will represent an essential aid for future studies aimed to better define the pharmacological profile and the mechanism of action of these compounds and are an important starting point to evaluate other natural products where standard powders are not available.     

Synthesis and Characterization of the Terpolymer of Itaconic Acid with Acrylamide and 2-Acrylamido-2-methylpropanesulfonic Acid

The thermal stability of the polymer is of great significance in paper, ceramics and oil industry1. Conventional polymers such as polyanionic cellulose can not meet high temperature limitations2-4. Aggour5-6 and Collette7 etc. have conducted extensive research on synthesis and characterizations of the copolymer or terpolymer containing 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS). Till now, very few research works have been reported on the terpolymer of itaconic acid (IA), acrylamid…     

Study on the Fluorescence System of Oxolinic Acid‐Tb(III) and the Determination of Oxolinic Acid

Abstract

In Tris‐HCl buffer (pH=7.43), Tb³⁺ can react with oxolinic acid (OA) and form a 1:2 complex, which emits the intrinsic fluorescence of Tb³⁺. Based on this, a new fluorimetric method of determination of OA is developed. Under the optimum conditions, the enhanced fluorescence intensity of the system is proportional to the concentration of OA in the range of 1.5×10^?7～2.5×10^?5mol/L, and the detection limit is 5.5×10^?9 mol/L. Recovery test was also satisfactory. The experiments indicated that the luminescence mechanism was attributed to the M*–M luminescence.     

Dielectric Relaxation of the β-Cyclodextrin Complexes with Tridecanoic Acid and 1,13-Tridecanedioic Acid

The frequency and temperature dependence of the real (') and imaginary (') parts of the dielectric permittivity of the polycrystalline complex-cyclodextrin-tridecanoic acid in two hydration forms (with 16.2 and 10.7 water molecules) and -cyclodextrin-1,13-tridecanedioic acid with 16.4 and 10.5 water molecules have been investigated, in the frequency range 0.1–100 kHz and temperature range 120–310 K. The dielectric behavior is described well by Debye-type relaxation dispersion. All systems except for the complex of partially dehydrated monocarboxylic acid, exhibit an additional -dispersion, at low frequencies (f < 1000 Hz). Only one-step was found in the ' vs. Tplots of both complexes in the two hydration forms, a fact indicating that the watermolecules cannot be divided into strongly bound and easily movable molecules. The'vs. T plots, at a fixed frequency (200 Hz), show the characteristic peakattributed to a transition between ordered and disordered -CD hydroxyl groupsand water molecules. The transition temperature was 202.7 K for all systems examinedexcept for the complex -CD-tridecanoic acid.16.2 H₂O (214.5 K). This means that the order to disorder transformation process was unaffected by the dehydration process in the case of the dicarboxylic acid complex, whereas in the case of the monocarboxylic acid, it was unexpectedly facilitated. The relaxation time varies with temperature, in a like curve (in the range 8–14 s), with maximum values located at the corresponding order-disorder transition temperatures. The activation energies of the fully hydrated complexes have absolute values of 5 kJ/mol in the range 1.98–3.82 K_{BT transition} which are higher than the corresponding values of :2 kJ/mol of the dehydrated complexes. A thermal hysteresis observed in all complexes is a result of the order-disorder transformation.     

Effect of Dissolved CO_2 and Tetrahydrofuran on the Polymerization of Acrylic Acid

Recently,c0mpressedgaseshavebeenusedins0megasantisolventprocesses,suchasfractionati0n0fnaturaIproducts,recrystallization0forganicandin0rganicmaterials,andpolymerpr0cessing'2.WestudiedtheeffectofthedissovledsupercriticaICO=andTHFonthep0lymerizati0n0fAA.Itwasn0tfoundintheliterature.ExperimentalOnemlacrylicacidmonomer,O.O20ginitiator2,2'-azobis(is0butyronitrile)(AlBN),anddesiredam0unt0fTHFwereaddedintoanopticalcelloflOml.CO,wascharged,stirreduntilvap0r-liquidequilibriumwasreachedatabout30…     

Studies on the Interaction of 12-Tungstophosphoric Acid and Diethylene Glycol

The homogeneous system of 12-tungstophosphoric acid and diethylene glycol was studied using IR and NMR spectra. It was found that the protons in 12-tungstophosphoric acid formed proton oxonium ions with the hydroxyl oxygen in diethylene glycol by hydrogen-bonds, and the formed proton oxonium ions could react with the terminal oxygens of heteropoly anions. The dehydration-cyclization mechanism of diethylene glycol in the presence of heteropoly acid was also proposed.     

Preparation and Characterization of Molybdotungstoniobogermanic Acid

Recently,thepreparationandpropertiesofheteropolycomplexeshaveincreasinglyattractedattentioninvariousfieldsofchendstIy,especiallyincatalysicapplicationsfortheiruniqueproperties'.Sincel988,thestudiesoffour-baseheteropolycomplexeswiththeKegginstructurehavebeenreported.Asthespecialbifunctionalcatalyticand.-lantisepsispropertyoftheheteropolycomplexescontainingniobium',andsofarthemolybdotungstoniobogermanicheteropolycomplexesinwhichthecentralatomisgermanium,havenotbeenreportedyet,ennea-tungsto-bi-mo…     

The Preparation of Unsymmetrical Diaminodimethylsilanes and the Cleavage of Silicon-Nitrogen Bonds by Acid Chloride

Ithaslongbeenknownthathesilicon-nitrogenbondinsilyltalnesmnybercadilyconvertedtoavarietyofsilicon-heteroatombondsandthereahonhasbeenextensivelyusedinorghacSynthesisIll.However,verylittleattentionhasbeenpaidtothesilyltalneswhichhavemorethanonetalnogroupwithdiffrentSUbedtUentsonnitrogenatomandsofarasweknow,therelativereactivityofSi-NbondinunmpericaJsilylndnehasnotbeenrePOrtedyetI2].WehavethereforeundertaknthepreparallonofUnSyInmetricalditalnodimethylsilanesandexPloredtheStericaswellaselect…     

Effects of Citric Acid Concentration and Activation Temperature on the Synthesis of Carbon Nanotubes

A series of Ni-La-Mg catalyst samples were prepared by citric acid complex method, and carbonnanotubes were synthesized by catalytic decomposition of CH4 on these catalysts. The effects of the citricacid concentration and the activation temperature on catalytic activity were investigated by CO adsorption,TEM and XRD techniques. The experimental results showed that the particle size of the catalysts preparedthrough gel auto-combustion varied with the concentration of citric acid. Therefore carbon nanotubes with different diameters were obtained correspondingly. The effect of activation temperature on the activity of catalyst was negligible from 500 to 700℃, but it became pronounced at lower or higher temperatures.     

Identifying the Role of Brønsted and Lewis Acid Sites in the Diels-Alder Cycloaddition of 2,5-DMF and Ethylene

The role of Lewis and Brønsted acid sites in the Diels-Alder cycloaddition (DAC) of ethylene to 2,5-dimethylfuran (2,5-DMF) to p-xylene was investigated. Amorphous silica catalysts containing Al³⁺ (ASA), Ga³⁺ (ASG), and In³⁺ (ASI) were prepared via homogeneous deposition-precipitation. Silica modified with Zr⁴⁺ (ASZ) was prepared by impregnation. Their acidic properties were characterized by various IR and NMR spectroscopic techniques. Measurements using pyridine as a probe molecule highlighted the presence of mostly Lewis acid sites (LAS) in all materials. Using CO as a probe, in contrast, demonstrated the existence of Brønsted acid sites (BAS) in ASA and ASG, which were nearly absent in ASI and ASZ. Differences in basic strength can explain the contrast in results observed between the two probe molecules. The highest p-xylene yield (~20 %) in the DAC reaction, could be achieved with ASA and ASG. The lack of BAS in ASI and ASZ resulted in inferior performance in the DAC, with p-xylene yields below 5 %. These results indicate the importance of BAS for the DAC reaction. Several other heterogeneous and homogeneous catalysts were explored for the DAC reaction to show the generality of our conclusion that BAS play a critical role in obtaining p-xylene from 2,5-DMF and ethylene.     

Studies on the Total Synthesis of Crotocembreneic Acid and Neocrotocembreneic Acid:A Perchloric Acid-induced Lactonization Reaction of Epoxy Ester

Cembranoids, a large family of diterpenoid natural products characterized by the presence of fourteen-membered ring, have been isolated from various marine sources as well as some terrestrial organisms since the 1960's1. Crotocembraneic acid 1 and neocrotocembraneic acid 2 have been isolated from the stem bark of Croton oblongifolius Roxb. (Euphorbiaceae)2. In our studies on the total synthesis of 1 and 2, we find a novel perchloric acid-induced lactonization reaction of epoxy ester 9 (Scheme…     

Esterification of Glycerol by Oleic Acid and Selective Hydrogenation of Oleic Acid Methylester Over Acid and Ru-Sn-B Supported Mesoporous AlMCM-41

Demand for large pore size molecular sieves has given rise to great interests in a new family of silica-based mesoporous materials designated as M41s, which expand typical molecular sieves into an extra-large pore range and generate the potential for the applications of these materials in catalysis and sorption for very bulky molecules1-6. MCM-41 possesses a hexagonal arrangement of uniform mesopore ranging from 15 to 100 ? and can be prepared with varied Si/Al ratios. The investigations of …     

Improved One-pot Synthesis of 4,6-Dihydroxyisophthalic Acid and 2,3-Dihydroxyterephthalic Acid

An improved method for the large-scale preparation of 4,6-dihydroxyisophthalic acid and 2,3-dihydroxyterephthalic acid has been developed.Compared to the previous procedures,this new process-requires much lower CO2 pressure of 0.3 Mpa and shorter reaction time.thus providing a convenient access for large-scale synthesis.The yield is high （93% and 65%,respectively）, and the oxidation of phenol is nearly inhibited,neither decolorization nor further chromatographic purification is required.     

Purification and Structure Identification of Hyaluronic Acid

Polysaccharide produced by mutated strain of Streptococcus zooepidemicus was purified by the procedures including Savage method, quaternary ammonium compound precipitation, DEAE-cellulose(DE52) chromatography and Sephadex G-75 gel filtration. The structure of the purified polysaccharide has been characterized by means of chemical composition analysis,13C NMR spectrum, infrared spectrum and circular dichroism (CD). All the results showed that the purified polysaccharide was hyaluronic acid (HA). The single helix conformation of the purified HA was determined by Congo red experiment. The molecular weight of the HA was about 1.16×106D, which was measured by viscosity method.     

Synthesis of L-Aspartic Acid and Lactone Copolymers

Recently,thesynthesisandapplications0fbiodegradablepolydepsipeptides,alternatingcopolymersofa-aminoacidanda-hydroxyacidwithfunctionalside-chaingroupshavedrawnmoreandmoreattentionl'2.Thisisbecausethefunctionalizedpendantgroups0fthep0lydepsipeptidesmakethemusefulf0rthepreparationofavarietyofpolymer-drugconjugates.However,thepolymerizati0nofdepsipeptideswithfuncti0nalgr0upsisratherdifficultduetotheirbigstructuresandsterichindrance.Furthermore,high-molecular-weightpr0ductsofsuitablephysicalpropert…     

Crystal and Molecular Structure of Cyanuric Acid

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Thermodynamic Study of the Three Isomers of Bromobenzoic Acid

The enthalpies of sublimation and fusion and triple-point temperatures of 2-bromo-. 3-bro-mo- and 4-bromobenzoic acids have been determined precisely by sublimation calorimetry, drop calorimetry and differential thermal analysis. The measurements of sublimation enthalpy of the three acids were made at 333, 348 and 363 K, respectively, using a Tian-Calvet microcalorimeter equipped with Knudsen effusion cells. The derived standard molar enthalpies of sublimation at 298.15 K are (95. 94±0. 41), (99. 20± 0.18), and (103. 08±0. 59) kJ · mol-1for the 2-bromo-, 3-bromo- and 4-bromobenzoic acids, respectively. In addition, the saturated vapour pressure of these compounds was also calculated on the basis of the sublimation experiments. The enthalpy of fusion, the triple-point temperatures and the mole fraction purities of the samples of the investigated substances were measured using the mean temperature version DTA apparatus developed by the CTM of the CNRS in Marseille. The triple-point temperature and the     

Effect of Mn（Ⅱ） and Ce（Ⅳ） Ions on the Oxidation of Lactic Acid by Chromic Acid

The kinetics and mechanism of lactic acid oxidation in the presence of Mn（Ⅱ） and Ce（Ⅳ） ions by chromic acid were studied spectrophotometrically. The oxidation of lactic acid by Cr（Ⅵ） was found to proceed in two measurable steps, both of which gave pyruvic acid as the primary product in the absence of Mn（Ⅱ）.2Cr（Ⅵ）＋2CH3CHOHCOOH→2CH3COCOOH＋Cr（Ⅴ）＋C（Ⅲ） Cr（V）＋CH3CHOHCOOH→Cr（Ⅲ）＋CH3COCOOHThe observed kinetics was explained due to the catalytic and inhibitory effects of Mn（Ⅱ） and Ce（Ⅳ） on the lactic acid oxidation by Cr（Ⅵ）. The reactivity of lactic acid depends upon the experimental conditions. It acts as a two- or three- equivalent reducing agent in the absence or presence of Mn（Ⅱ）. It was examined that Cr（Ⅲ） products resulting from the direct reduction of Cr（Ⅵ） by three-equivalent reducing agents. The oxidation of lactic acid follows the complex order kinetics with respect to [lactic acid]. The activation parameters Eo, △H^#, and AS^# were calculated and discussed.     

Substituent Effects on the Low-Frequency Vibrational Modes of Benzoic Acid and Related Compounds

Well-resolved absorption spectra of benzoic acid and its derivatives with one hydrogen atom replaced by a substituent group CH3, OH, NH2 or NO2 were reported in the frequency region between 6 and 67 cm^-1 at room temperature with terahertz time-domain spectroscopy （THz-TDS）. These substances can be distinguished easily based on the terahertz absorption spectra. The measurements suggested that even minor changes in the molecular configuration and chemical composition lead to distinct differences in THz spectrum. Density functional theory （DFT） method was used to assist the analysis and assignment of the individual THz absorption spectra of benzoic acid and its methyl derivatives. Observed THz responses of samples can be assigned to the collective vibrations associated with intermolecular hydrogen bonds.     

Chemical Reactions of Surfactants with Acid–Base Dyes and Determination of Imidazolines in the Air of the Working Area

Reactions of acid–base monoazo dyes with polyamine surfactants were studied. The ratios of components in the resulting compounds were determined; the stability constants and molar absorptivities were calculated. A mechanism was proposed for the reaction of monoazo dyes with amine and imidazoline surfactants with the formation of macroheterocycles. Approaches to predicting analytical reactions between monoazo dyes and surfactants were substantiated. The dependence of the extraction of these compounds on the pH of the aqueous phase and the concentrations of NaCl and ethanol was studied. The optimal conditions for extraction separation were found, and a procedure was developed for the spectrophotometric determination of 1-(-hydroxyethyl)-2-heptadecenyl-2-imidazoline (Imidazoline 17) and 1,1"-bis(-hydroxyethyl)-2-heptadecenyl-2-imidazolonium chloride (Imidastat O) in the air of the working area using Methyl Orange as the reagent. The determination limits were 0.025 and 0.12 g/mL, respectively. A sampling procedure was developed for the determination of Imidazoline 17 and Imidastat O in the air with determination limits of 0.05 and 0.25 mg/m³, respectively, for sampling 15 L of air to 60% ethanol.