Electronic spectra of benzimidazolecarboxylic acids: effect of solvents and acid concentrations

Effect of solvents and acid concentration on the absorption and fluorescence spectra of benzimidazole-2-acetic acid (BIAA), benzimidazole-2-methylacetate (BIAE) and benzimidazole-2-propionic acid have been investigated. The results have indicated that the presence of the methylene group reduces the interaction of BI and −COOH groups. For example, the spectral characteristics of BIAE and BIPA are similar to 2-methylbenzimidazole (MBI). The long wavelength absorption band in BIAA is assigned to the presence of an intramolecular hydrogen-bonded structure and hydrogen bonding is stronger in the S₁ state than in the S₀ state. In aqueous medium, depending upon the pH of the solution, BIAA and BIPA either exist as zwitterion or monoanion. The zwitterion and monoanion of BIAA have a ring structure, whereas those of BIPA have an open structure.     

PHOTOCHEMIE ANOMALER NUCLEINSÄUREBAUSTEINE-VIII. ZUR PHOTOCHEMIE DES 6–AZACYTOSINS UND 6–AZACYTIDINS

Abstract— The photochemical behavior of 6–azacytosine and 6–azacytidine has been investigated by spectrophotometric, polarographic, and chromatographic methods. Both compounds form photohydration products, similar to cytosine and cytidine, but their photosensitivity is about ten fold higher. The greatest stability against u.v. light was found in strong acid and alkaline medium, indicating that under these conditions the electronic density at the reaction center is decreased.
For estimation of the photochemically active excited state triplet-triplet-transfer, experiments and measurements in the presence of paramagnetic metal ions were done. The results show that the photohydration reaction involves the first excited singlet state and the corresponding triplet state probably as well.
The photoproducts of both substances can be reactivated by heat. This reaction in acidic medium is strongly overlapped by a deamination reaction which yields 6–azauracil as a final product. In alkaline solution the ring system of the photohydration product is disrupted in the dark. The kinetic parameters of the heat-reversible reaction of 6–azacytosine and 6–azacytidine are completely identical. This is in contrast to the published results with cytosine and cytidine where the back reaction is lowered for the latter. The differences in the behavior of the normal bases and their azaanalogues can be explained by means of an intramolecular hydrogen bond stabilization of the cytidine photoproduct. An analogous stabilization effect in the case of the 6–azacytidine photoproduct seems to be improbable for sterical reasons.     

Photochemical Processes of Superbase Generation in Xanthone Carboxylic Salts

Photobase generators are species that allow the photocatalysis of various reactions, such as thiol-Michael, thiol-isocyanate, and ring-opening polymerization reactions. However, existing compounds have complex syntheses and low quantum yields. To overcome these problems, photobase generators based on the photodecarboxylation reaction were developed. We synthesized and studied the photochemistry and photophysics of two xanthone photobase, their carboxylic acid precursors, and their photoproducts to understand the photobase generation mechanism. We determined accurate quantum yields of triplet states and photobase generation. The effect of the intermediate radical preceding the base release was demonstrated. We characterized the photophysics of the photobase by femtosecond spectroscopy and showed that the photodecarboxylation process occurred from the second excited triplet state with a rate constant of 2.2×10⁹ s⁻¹.     

Quantitation of tryptophan metabolites in rat feces by thin-layer chromatography.

Indole, skatole, indole-3-acetic acid, indole-3-propionic acid, tryptamine, and free tryptophan have been extracted from rat fecal samples and quantitated by thin-layer chromatography. Additional tryptophan metabolites have been recovered in yields of 87-97% from supplemented fecal samples. Detection limits for all the compounds studied were in the 0.1 mug/g feces range. Quantitation was possible in the mug/g range with an estimated accuracy of plus or minus 10%.     

Binding behavior of amino acid conjugates of indole-3-acetic acid to immobilized human serum albumin

The affinity of indole-3-acetic acid (IAA), indole-3-propionic acid, indole-3-butyric acid and 24 of their amino acid conjugates to immobilized human serum albumin, as expressed by the retention factor k (determined by HPLC), was dependent on (1) lipophilicity, (2) chirality and (3) functional groups in the amino acid moiety; in some cases conformation plays an additional role. Two lipophilicity-related parameters afforded quantitative correlations with k: retention on a C18 reversed-phase column (experimental approach) and the distance between the hydrophilic and hydrophobic poles of the molecules (in silico approach). Most compounds examined are possible metabolic precursors of IAA, an experimental tumor therapeutic.     

Simultaneous Electrochemical Determination of Indole-3-acetic Acid and Salicylic Acid in Pea Roots using a Multiwalled Carbon Nanotube Modified Electrode

Indole-3-acetic acid and salicylic acid are essential phytohormones with profound effects on growth and development as well as stress responses of plants. Accumulating evidence has suggested that these compounds mediate the same biological process by collaboration or antagonistic actions. Simultaneous determination of indole-3-acetic acid and salicylic acid may significantly improve the understanding on mechanisms of their interaction. In this study, the simultaneous determination of these analytes was electrochemically performed using a multiwalled carbon nanotubes-chitosan modified glassy carbon electrode. Based on differential pulse voltammetry, indole-3-acetic acid and salicylic acid were determined from 0.67 to 48.82 micromolar with detection limits of 0.1 micromolar. In addition, no interferences were observed from other molecules. This method was employed for the simultaneous determination of the analytes in pea root extracts. The approach may be extended for additional study of the interaction of indole-3-acetic acid and salicylic acid in plants.     

Investigating the CO2 uncaging mechanism of nitrophenylacetates by means of fs-IR spectroscopy and quantum chemical calculations

Caged compounds are widely utilized for light-triggered control of biological and chemical reactions. In our study we investigated the photo-induced decarboxylation of all three constitutional isomers of nitrophenylacetate (NPA), which can be regarded as caged-CO(2). UV-pump/IR-probe spectroscopy was used to directly observe the nascent CO(2) in the region of 2340 cm(-1). Together with quantum chemical calculations the reaction models for all three components could be obtained. For meta- and para-NPA the main decarboxylation pathway proceeds via a triplet state with a lifetime of 0.2 ns. In the case of ortho-NPA the photodecarboxylation reaction is suppressed by an H(+)- or H˙-transfer reaction in the excited state as a result of the proximity of the nitro and acetate substituents. Nevertheless, the photodecarboxylation can be investigated due to the isolated spectral position of the CO(2) band. The analysis of the data reveals that a weak ultrafast release channel (<300 fs) represents the main photodecarboxylation reaction pathway for ortho-NPA. The detailed understanding of the molecular mechanisms of CO(2) uncaging should provide general guidelines for the design of systematically improved nitrobenzyl cages.     

Identification and quantitation of auxins in plants by liquid chromatography/electrospray ionization ion trap mass spectrometry

Auxin is an important phylohormone, which regulates specific physiological responses such as division, elongation and differentiation of cells. A new method using liquid chromatography/electrospray ionization ion trap mass spectrometry (LC/ESI-ITMS) has been developed for identification and quantitation of four auxins. Under the optimum conditions, four auxins (indole-3-acetic acid, indole-3-propionic acid, indole-3-butyric acid and 1-naphthylacetic acid) were completely separated and quantitated within 7 min with a minimum detection limit of 8.0 ng mL(-1) with relative standard deviations lower than 5.0%. This method also has been applied to analysis of auxins in Chinese cabbage where, even with a complicated serious background perturbation due to the natural biological matrix, the mean recoveries ranged from 77.5% to 99.8%. Finally, we discuss the MS-relevant properties of the identified auxins in detail.     

Determination and Application of Nineteen Monoamines in the Gut Microbiota Targeting Phenylalanine,Tryptophan, and Glutamic Acid Metabolic Pathways

It has been reported that monoamine neurotransmitters can be produced by gut microbiota, and that several related metabolites of amino acids in these pathways are associated with nervous system (NVS) diseases. Herein, we focused on three pathways, namely, phenylalanine (Phe), tryptophan (Trp), and glutamic acid (Glu), and established an underivatized liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for the quantification of nineteen monoamine neurotransmitters and related metabolites in the gut microbiota. The neurotransmitters and related metabolites included Phe, tyrosine (Tyr), l-dopa (Dopa), dopamine (DA), 3-methoxytyramine, Trp, hydroxytryptophan, 5-hydroxytryptamine (5-HT), 5-hydroxyindole-3-acetic acid (5-HIAA), kynurenine (KN), kynurenic acid (KYNA), melatonin, tryptamine (TA), indole-3-lactic acid (ILA), indole-3-acetic acid (IAA), indolyl-3-propionic acid (IPA), Glu, gamma-aminobutyric acid (GABA), and acetylcholine (Ach). A fluoro-phenyl bonded column was used for separation, and the mobile phase consisted of methanol:acetonitrile (1:1) and water, with 0.2% formic acid in both phases. The compounds exhibited symmetric peak shapes and sufficient sensitivity under a total analysis time of 8.5 min. The method was fully validated with acceptable linearity, accuracy, precision, matrix effect, extraction recovery, and stability. The results showed that neurotransmitters, such as Dopa, DA, 5-HT, GABA, and Ach, were present in the gut microbiota. The metabolic pathway of Trp was disordered under depression, with lower levels of 5-HT, 5-HIAA, KN, KYNA, TA, ILA, IAA, IPA, and Glu, and a higher ratio of KYNA/KN. In addition, some first-line NVS drugs, such as sertraline, imipramine, and chlorpromazine, showed regulatory potential on these pathways in the gut microbiota.     

A theoretical study on the acid catalysed hydration of excited state acetylene

That significant modification in the acid/base behavior of aromatic molecules can be induced by electronic excitation is common knowledge. A recent application of this phenomenon is the acid catalyzed photohydration of aromatic acetylenes: ArCCH. The energetics of proton transfer and subsequent hydration of acetylene, as indicated by ab initio MO methods, suggests that this property of enhanced excited state basicity is not uniquely characteristic of the Ar substituent.     

Microwave-Assisted Rapid Preparation of Substituted Carbazole-9-acetic and Propionic Acids and their Absorption and Fluorescence Spectra

 A rapid one-pot synthesis of substituted carbazole-9-acetic and -propionic acids under microwave irradiation is described. N-Alkylation and hydrolysis was carried out in DMF without catalyst. The absorption and fluorescence spectroscopic characteristics of the title compounds are discussed.     

Simultaneous determination of four plant hormones in bananas by molecularly imprinted solid-phase extraction coupled with high performance liquid chromatography

A highly selective molecularly imprinted solid-phase extraction (MISPE) combined with liquid chromatography-ultraviolet detection was developed for the simultaneous isolation and determination of four plant hormones including indole-3-acetic acid (IAA), indole-3-propionic acid (IPA), indole-3-butyric acid (IBA) and 1-naphthaleneacetic acid (NAA) in banana samples. The new molecularly imprinted microspheres (MIMs) prepared by aqueous suspension polymerization using 3-hydroxy-2-naphthoic acid and 1-methylpiperazine as mimic templates performed with high selectivity and affinity for the four plant hormones, and applied as selective sorbents of solid-phase extraction could effectively eliminate the interferences of the banana matrix. Good linearity was obtained in a range of 0.04-4.00 μg g(-1) and the recoveries of the four plant hormones at three spiked levels ranged from 78.5 to 107.7% with the relative standard deviations (RSD) of less than 4.6%. The developed MISPE-HPLC protocol obviously improved the selectivity and eliminated the effect of template leakage on quantitative analysis, and could be applied for the determination of plant hormones in complicated biological samples.     

Enantioselective stable isotope analysis (ESIA) of polar herbicides

Assessing the environmental fate of chiral micropollutants such as herbicides is challenging. The complexity of aquatic systems often makes it difficult to obtain hydraulic mass balances, which is a prerequisite when assessing degradation based on concentration data. Elegant alternatives are concentration-independent approaches like compound-specific isotope analysis or enantiospecific concentration analysis. Both detect degradation-induced changes from ratios of molecular species, either isotopologues or enantiomers. A combination of both—enantioselective stable isotope analysis (ESIA)—provides information on ¹³C/¹²C ratios for each enantiomer separately. Recently, Badea et al. demonstrated for the first time ESIA for the insecticide α-hexachlorocyclohexane. The present study enlarges the applicability of ESIA to polar herbicides such as phenoxy acids: 4-CPP ((RS)-2-(4-chlorophenoxy)-propionic acid), mecoprop (2-(4-chloro-2-methylphenoxy)-propionic acid), and dichlorprop (2-(2,4-dichlorophenoxy)-propionic acid). Enantioselective gas chromatography–isotope ratio mass spectrometry was accomplished with derivatization prior to analysis. Precise carbon isotope analysis (2σ?≤?0.5‰) was obtained with ≥7 ng C on column. Microbial degradation of dichlorprop, 2-(2,4-dichlorophenoxy)-propionic acid by Delftia acidovorans MC1 showed pronounced enantiomer fractionation, but no isotope fractionation. In contrast, Badea et al. observed isotope fractionation, but no enantiomeric fractionation. Hence, the two lines of evidence appear to complement each other. They may provide enhanced insight when combined as ESIA.     

Reaction mechanisms and structural characterization of the reactive intermediates observed after the photolysis of 3-(hydroxymethyl)benzophenone in acetonitrile, 2-propanol, and neutral and acidic aqueous solutions

Nanosecond time-resolved resonance Raman (ns-TR(3)) spectroscopy was employed to investigate the photoinduced reactions of 3-(hydroxymethyl)benzophenone (1) in acetonitrile, 2-propanol, and neutral and acidic aqueous solutions. Density functional theory calculations were utilized to help the interpretation of the experimental spectra. In acetonitrile, the neutral triplet state 1 [denoted here as (m-BPOH)(3)] was observed on the nanosecond to microsecond time scale. In 2-propanol this triplet state appeared to abstract a hydrogen atom from the solvent molecules to produce the aryphenyl ketyl radical of 1 (denoted here as ArPK of 1), and then this species underwent a cross-coupling reaction with the dimethylketyl radical (also formed from the hydrogen abstraction reaction) to form a long-lived light absorbing transient species that was tentatively identified to be mainly 2-(4-(hydroxy(3-(hydroxymethyl)phenyl)methylene)cyclohexa-2,5-dienyl)propan-2-ol. In 1:1 H(2)O:CH(3)CN aqueous solution at neutral pH, (m-BPOH)(3) reacted with water to produce the ArPK of 1 and then underwent further reaction to produce a long-lived light absorbing transient species. Three photochemical reactions appeared to take place after 266 nm photolysis of 1 in acidic aqueous solutions, a photoreduction reaction, an overall photohydration reaction, and a novel photoredox reaction. TR(3) experiments in 1:1 H(2)O:CH(3)CN aqueous solution at pH 2 detected a new triplet biradical species, which is associated with an unusual photoredox reaction. This reaction is observed to be the predominant reaction at pH 2 and seems to face competition from the overall photohydration reaction at pH 0.     

Microwave-Assisted Rapid Preparation of Substituted Carbazole-9-acetic and Propionic Acids and their Absorption and Fluorescence Spectra

Summary.  A rapid one-pot synthesis of substituted carbazole-9-acetic and -propionic acids under microwave irradiation is described. N-Alkylation and hydrolysis was carried out in DMF without catalyst. The absorption and fluorescence spectroscopic characteristics of the title compounds are discussed. Received January 31, 2000. Accepted (revised) March 7, 2000     

Analysis of plant hormones by microemulsion electrokinetic capillary chromatography coupled with on-line large volume sample stacking

A novel method of microemulsion electrokinetic capillary chromatography (MEEKC) coupled with on-line large volume sample stacking was developed for the analysis of six plant hormones including indole-3-acetic acid, indole-3-butyric acid, indole-3-propionic acid, 1-naphthaleneacetic acid, abscisic acid and salicylic acid. Baseline separation of six plant hormones was achieved within 10 min by using the microemulsion background electrolyte containing a 97.2% (w/w) 10 mM borate buffer at pH 9.2, 1.0% (w/w) ethyl acetate as oil droplets, 0.6% (w/w) sodium dodecyl sulphate as surfactant and 1.2% (w/w) 1-butanol as cosurfactant. In addition, an on-line concentration method based on a large volume sample stacking technique and multiple wavelength detection was adopted for improving the detection sensitivity in order to determine trace level hormones in a real sample. The optimal method provided about 50-100 fold increase in detection sensitivity compared with a single MEEKC method, and the detection limits (S/N = 3) were between 0.005 and 0.02 μg mL(-1). The proposed method was simple, rapid and sensitive and could be applied to the determination of six plant hormones in spiked water samples, tobacco leaves and 1-naphthylacetic acid in leaf fertilizer. The recoveries ranged from 76.0% to 119.1%, and good reproducibilities were obtained with relative standard deviations (RSDs) less than 6.6%.     

Rapid and sensitive detection of auxins and flavonoids in plant samples by high-performance liquid chromatography coupled with tandem mass spectrometry

Simultaneous determination of indole-3-acetic acid and methyl indole-3-acetic acid ester in small amounts of plant tissue is essential for elucidating their mutual transformation mechanism and the in vivo function of methyl indole-3-acetic acid ester. Rapid quantification of flavonoids in the same sample is important for clarifying their roles in the transport of auxins and other phytohormones. Herein, we describe a simple method for the simultaneous determination of indole-3-acetic acid and its methyl ester in the roots of the Arabidopsis thaliana seedlings and a protocol for the rapid extraction and quantification of quercetin and kaempferol in these seedlings. High-performance liquid chromatography coupled with electrospray ionization time-of-flight tandem mass spectrometry was used for the detection of all the compounds. Negative data for indole-3-acetic acid and positive data for methyl indole-3-acetic acid ester were collected in two successive files with a single injection of the extracted sample. Under optimized conditions, the limit of detection for the four compounds was 2 ng/mL for indole-3-acetic acid, 0.5 ng/mL for methyl indole-3-acetic acid ester, 5 ng/mL for quercetin, and 1 ng/mL for kaempferol, respectively. Because of the high sensitivity of the assay, only 2-10 mg of the plant material was required to obtain quantitative results.     

Synthesis of Calix[4]arene Derivatives Containing a Nucleobase and their Interaction with Complementary Nucleosides at the Air–Water Interface

Amphiphilic calix[4]arene derivatives with a nucleobase on the lower rim have been synthesized in good yields by the condensation of calix[4]arenediamine {5,11,17,23-tetra-tert-butyl-25,27-bis(2-aminoethoxy)-26,28-dihydroxycalix[4]arene} with uracilo-N-acetic acid, thymino-N-acetic acid and adenino-N-propionic acid in the presence of CDI in DMF. Monolayers of the amphiphilic calix[4]arene-nucleobase derivatives on the surface of pure water, the aqueous subphases containing complementary nucleosides, were studied by film balance measurement and relaxation experiments. LB films deposited from all subphases were investigated by UV spectra and FT-IR spectroscopy. All the results indicate that the interaction between the nucleobases in the headgroup of amphiphilic p-tert-butylcalix[4]arene derivatives and the complementary nucleosides in the subphase takes place through multiple hydrogen bonding and the nucleosides can be transferred to solid substrates along with their monolayers.     

全自动在线固相萃取-液相色谱-串联质谱法同时检测水稻中6种内源性植物激素

建立了同时检测水稻中6种内源性植物激素脱落酸( Abscisic acid,ABA)、吲哚-3-乙酸( Indole-3-acetic acid, IAA)、水杨酸( Salicylic acid,SA)、茉莉酸( Jasmonic acid,JA)、吲哚-3-丙酸( Indole-3-propionic acid, IPA)和吲哚-3-丁酸( Indole-3-butyric acid,IBA)的全自动在线固相萃取-液相色谱-串联质谱方法。植物样品经过甲醇提取,采用C18固相萃取柱富集净化,流动相将待测物洗脱至C18分析色谱柱进行分离,最终使用串联四极杆质谱进行检测。方法的线性范围为8~320μg/L,相关系数为R2≥0.99;方法的检出限(S/N=3)范围为0.1~0.8μg/kg;实际样品中方法回收率范围为71.2%~126%,RSD<13%。应用本方法快速、准确地检测了水稻幼穗中多种内源性植物激素的含量,并与目前植物学领域内常用的检测方法进行了比较。同时,本方法对水稻受伤叶片的内源植物激素含量变化进行了定量分析,其含量随受伤时间的变化趋势与其生物背景的实验结果相吻合。     

Molecular structures, hydrogen bonding and electrostatic interactions of 3-(2-bromo-pyridinium)-propionic acid and 3-(pyridinium)-pivalic acid halides

Intra- and intermolecular interactions and the conformations of 3-(2-bromo-pyridinium)-propionic acid bromide (1) and 3-(pyridinium)-pivalic acid chloride (2) have been studied by X-ray diffraction and theoretically. In these complexes, Br⁻ and Cl⁻ anions are H-bonded to the COOH group and interact electrostatically with the positively charged nitrogen atoms of neighbouring molecules. To analyse these interactions theoretically, the structures of monomers and dimers in various configurations were optimized by PM3 and BLYP/6-31G(d,p) methods. The analysis confirmed the vital role of both the H-bonds and electrostatic interactions (intra- and intermolecular) for the molecular conformation and the ionic aggregation in the solid state.