Interference with ammonium determination by the indophenol-type reaction of salicylate and dichloroisocyanurate

Two widely accepted indophenol-type reactions with ammonium, which use phenol/hypochlorite and salicylate/dichloroisocyanurate as reagents, were compared for possible interferences with other naturally occurring nitrogen-containing compounds. Unlike the first method, the second showed strong interference from all amino acids and peptides tested. As much as 57 mole % of threonine and 49 mole % of serine were degraded to ammonium. Pyrimidines, purines, nucleosides and urea were negative in both reactions. The wide distribution and importance of free and combined amino acids in naturally occurring waters favours the application of the classical phenol/ hypochlorite reaction with ammonium rather than the modified salicylate/dichloroisocyanurate reaction. Received: 20 April 1998 / Revised: 28 May 1998 / Accepted: 5 Juni 1998     

Automated Determination of Ammonia in Natural Freshwaters Using Salicylate-Hexacyanoferrate-Dichloroisocyanurate System

Abstract

An automated method for the determination of ammonia in natural freshwaters was developed with the use of salicylate-hexacyanoferrate-dichloroisocyanurate system. Sodium salicylate is easy to handle and does not produce o-chlorophenol. The use of sodium dichloroisocyanurate as a chlorine donater excludes frequent standarization of chlorine content in sodium hypochlorite solution. Sensitivity in the present method is comparable with that in manual phenol method. The present study suggests that automated salicylate and phenol methods with the need of heating of more than 50°C may not determine the real concentration of ammonia due to the release of ammonia from free amino acids in natural waters.     

水杨酸钠紫外分光光度法测定烟草中的总氮

建立水杨酸钠紫外分光光度法测定烟草中总氮含量的方法。烟草样品经硫酸铜–硫酸钾–浓硫酸消化,用水杨酸钠–二氯异氰尿酸钠显色后用紫外分光光度计检测,并对波长、显色剂用量和反应时间等实验条件进行了优化。总氮的质量浓度在5~60 mg/L范围内与其吸光度呈良好的线性关系,线性相关系数为0.998 8,方法的检出限为0.14 mg/L。样品分析结果的相对标准偏差为3.22%(n=6),样品加标回收率为99.30%~101.62%。该方法具有较高的精密度和准确度,尤其适用于样品量少时对烟草中总氮的测定。     

Structural relationships in small molecule interactions governing gas-phase enantioselectivity and zwitterionic formation

Gas-phase zwitterionic amino acids were formed in complexes of underivatized beta-cyclodextrin through reactions with a neutral base, n-propylamine. The reaction was performed in the analyzer cell of an electrospray ionization-Fourier transform mass spectrometer. Most of the natural amino acids were studied with three cyclodextrin hosts including alpha-, beta-, and gamma-cyclodextrin to understand better the structural features that lead to the stabilization of the zwitterionic complexes. Molecular dynamics calculations were performed to provide insight into the structural features of the complexes. The rate constants of the reactions were obtained through kinetic plots. Examination of both L- and D-enantiomers of the amino acid showed that the reaction was enantioselective. The reaction was then employed to analyze mixtures of Glu enantiomers naturally occurring in the bacteria Bacillus licheniformis.     

Condensation of ammonium ion with acetone

Recrystallization of ammonium anthranilate or ammonium salicylate from acetone-hexane results in conversion of the ammonium salts to diacetoneammonium salts. The reaction is general for the ammonium salts of amino- and hydroxy-substituted benzoic acids, all of which are converted at least in part to diacetoneammonium salts when treated with acetone. Under similar conditions ammonium benzoate is converted to the triacetoneammonium salt. These reactions constitute convenient laboratory procedures for the preparation of diacetoneammonium and triacetoneammonium salts, and explain the frequent incursion of diacetoneamine and triacetoneamine as artifacts when natural systems are extracted with acetone.     

Convenient synthetic approach to 2,4-disubstituted quinazolines

[reaction: see text] 2,4-Dialkyl or aryl quinazolines have been prepared in three steps starting from easily available anilides. A photochemically induced Fries rearrangement of the anilides gave several ortho-aminoacylbenzene derivatives that were acylated at the NH2. These acylamides underwent rapid cyclization to 2,4-disubstituted quinazolines (and benzoquinazolines) in the presence of ammonium formate under microwave activation. This procedure is compatible with different functional groups and allowed also the preparation of new quinazolines derived from naturally occurring amino acids.     

Sensitivity improvement of ammonia determination based on flow-injection indophenol spectrophotometry with manganese(II) ion as a catalyst and analysis of exhaust gas of thermal power plant.

The sensitivity improvement of a flow-injection spectrophotometric method for the determination of ammonia was examined based on an indophenol blue coloration reaction with salicylate and hypochlorite in the presence of manganese(II) as a reaction promotion catalyst. The optimal conditions for achieving higher sensitivity of ammonia determination were examined using a three-line flow system. The limit of detection corresponding to a signal-to-noise ratio (S/N) of 3 was 0.005 mg l(-1) (approximately equal to 5 ppb) of NH4+. A calibration graph was linear in the range from 5 ppb to 1,000 ppb of ammonium ion. The relative standard deviations (n = 9) for 50 ppb and 100 ppb of ammonium ion were 6.4% and 2.2%, respectively. The proposed method was applied to the determination of ammonia in the exhaust gas of a thermal power plant. Prior to the FIA determination, ammonia in the exhaust gas was absorbed into a boric acid solution; the absorption solution was then analyzed by the proposed FIA.     

A Facile Synthesis of N-Phosphoryl Amino Acids Containing Hydroxy Group

three kinds of N-(diisopropyloxyphosphoryl) amino acids containing hydroxyl group were prepared in high yield by using diisopropyl phosphite as the phosphorylating agent, sodium hypochlorite as the chlorinating agent and tetrabutyl ammonium bromide as the phase transfer catalyst in basic aqueous media.     

Formal Aniline Synthesis from Phenols through Deoxygenative N-Centered Radical Substitution

Phenolic, lignin-derived substrates have emerged as desirable biorenewable chemical feedstocks for coupling reactions. A radical-mediated conversion of phenol derivatives to anilines is reported, using unfunctionalized hydroxamic acids as the N-centered radical source. The applicability of this triethyl phosphite mediated O-atom transfer approach, which tolerates a range of steric and electronic demands to naturally occurring phenols and lignin models, has been demonstrated in this work to access the corresponding aniline derivatives.     

含松香骨架的新型手性季铵盐相转移催化剂的合成及其在不对称环氧化反应中的应用

以天然松香为原料合成了4个新型手性季铵盐类相转移催化剂, 并用于催化不对称查尔酮环氧化反应, 发现这类手性相转移催化剂可以有效地催化查尔酮的不对称环氧化, 环氧化产物ee最高达20%.     

基于天然氨基酸的双环手性季铵盐相转移催化剂的合成及催化性能研究

以L－脯氨酸及L－羟基脯氨酸为原料合成了4个新型手性季铵盐磁相转移催化 剂，并用于催化不对称查耳酮环氧化反应，高产率得到相应环氧化合物，ee最高达 9％。     

Dry state preparation of radioiodine labeled meta-iodobenzylguanidine

Radioiodination of meta-iodobenzylguanidine (MIBG) by the isotopic exchange technique in the dry state has been performed. Benzoic acid, pivalic acid and acetamide have been used as molten protic media to promote isotopic exchange reactions. Ammonium sulphate, diammonium hydrogen ortho-phosphate and ammonium chloride were used as catalysts which provide acidic media to facilitate exchange reactions. Maximum radiochemical yields of 97.1±1.3% and 84.3±1.6% [¹³¹I] MIBG were obtained when ammonium sulphate and benzoic acid were used. High radiochemical yields of 88.3±1.1% and 74.4±1.5% [¹³¹I] MIBG were also obtained in case of diammonium hydrogen orthophosphate and pivalic acid which suggests their successful use as reaction media in the radioiodination of MIBG. The activation energy for the exchange reaction in ammonium sulphate was calculated to be 10.8 kcal/mole.     

Synthetic studies towards cyclic peptides. Concise synthesis of thiazoline and thiazole containing amino acids

Concise and efficient syntheses of optically pure thiazoline and thiazole containing amino acids of the constitution (26) and (27), based on simple condensation reactions between cysteine esters and N-protected imino ethers (22) and (25) derived from chiral amino acids, are described. The synthetic procedures are compatible with a range of amino acid side chains and protecting groups, and allow the preparation of a variety of small optically pure peptides i.e. (32) and (34) suitable for elaboration to naturally occurring cyclic peptides e.g. the lissoclinamides (3) and (4).     

Study of the reactivity of ammonium carboxylates in the synthesis of amides under high-pressure deformation conditions

On deformation under pressures up to 10 GPa the ammonium salts of aliphatic and aromatic acids, as well as mixtures of a free carboxylic acid with the ammonium salts of strong mineral acids, are converted into the corresponding amides. The amide yields increase with pressure, the magnitude of shearing deformation, and temperature. The temperature and pressure coefficients for amide formation are low and have values of 2.5–4 kJ/mole and –1 to –2 cm³/mole, respectively. The reactivity of ammonium salts in the synthesis of amides alternates in the homologous series of aliphatic acids in a similar way to the shear stress of these salts. The reactivity of the ammonium salts of aliphatic acids increases when the reaction is conducted in a matrix of an ammonium salt which possesses plasticity and a high shear stress.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2289–2292, October, 1989.     

Synthesis of 4-hydroxymethyl-2,4-methanoproline

The synthesis of 4-hydroxymethyl-2,4-methanoproline, a novel conformationally restricted amino acid, was performed in four steps. This close analogue of naturally occurring amino acids (i.e., proline, hydroxyproline, serine and threonine) was prepared in good overall yield through two intramolecular recyclization reactions of cyclobutane derivatives.     

二氧化硅负载磷钨酸铵催化苯酚氧化溴代反应

以溶胶-凝胶法制备的二氧化硅负载磷钨酸铵为催化剂,溴化钾为溴源,双氧水为氧化剂,冰醋酸为溶剂,实现了苯酚的催化氧化溴代反应。 探讨了催化剂负载量、催化剂用量和反应时间等反应参数对氧化溴代反应的影响。 结果表明,溶胶-凝胶法制备的负载磷钨酸铵仍具有典型的Keggin结构;在室温的温和条件下,该催化剂表现出较强的催化苯酚氧化溴代反应活性和较高的对溴苯酚选择性,在实验优化条件下,苯酚转化率达到95.4%,对邻比达到3.2;而且催化剂易回收,重复4次使用后,催化活性有所降低,苯酚转化率为87.4%,对邻比为1.6。     

Ceric ammonium nitrate (CAN) mediated esterification of N-Boc amino acids allows either retention or removal of the N-Boc group

Reaction of N-Boc amino acids with ceric ammonium nitrate in an alcohol as the solvent at room temperature resulted in the esterification of N-Boc amino acids with Boc group retention. When the reaction was conducted at reflux temperature, esterification was accompanied with simultaneous removal of the Boc group. Both reactions gave the desired products in good yields.     

ELECTRONIC EFFECTS ON THE FLUORESCENCE OF TYROSINE IN SMALL PEPTIDES

Abstract— It is shown for a series of tyrosine-derivatives and tyrosine-containing peptides that the amide group in combination with electron-withdrawing substituents quenches the fluorescence of the phenol moiety. The ammonium group has the strongest electron-withdrawing effect and thus the largest influence on the quenching rate. The peptide group itself does not quench the fluorescence. In a series of peptides with an increasing number of alanines the decreasing quenching efficiency or the peptide group due to the greater distance of the ammonium group is demonstrated. In tyrosine-containing di- and tripeptides a linear correlation between the ¹³C-NMR chemical shift δ of the C₂ atom of various aliphatic amino acids and the fluorescence-quenching constant confirms the hypothesis that electron-withdrawing and donating groups are modulating the fluorescence-quenching efficiency of the peptide group. In small peptides the fluorescence lifetime of tyrosine is characteristic for the neighboring amino acids. Using model substances the redox properties of a peptide group and the phenol ring were studied electrochemically. The highest occupied molecular orbital of the tyrosine (1.4 V vs saturated calomel electrode [SCE]) and the lowest unoccupied molecular orbital of the peptide group (-3.12 V vs SCE) have appropriate energies for a photoinduced electron transfer reaction. For solute-quenching experiments quencher molecules can be systematically selected.     

Yb(OTf)3-catalyzed reactions of 5-alkylidene Meldrum's acids with phenols: one-pot assembly of 3,4-dihydrocoumarins, 4-chromanones, coumarins, and chromones

[reaction: see text] The Yb(OTf)3-catalyzed annulation reactions of phenols with 5-alkylidene Meldrum's acids enabled the synthesis of structurally diverse heterocycles in high isolated yields. A series of 4-substituted 3,4-dihydrocoumarins, 2,2-disubstituted 4-chromanones, coumarins, and 2-substituted chromones were readily and efficiently assembled, including the naturally occurring coumarins citropten, scoparone, and ayapin. Addition of phenols to biselectrophilic 5-alkylidene Meldrum's acids proceeded through two distinct multibond-forming modes: Friedel-Crafts C-alkylation/O-acylation and Friedel-Crafts C-acylation/O-alkylation. The regioselectivity of the catalytic annulation reaction was controlled by the degree of substitution on the alkylidene moiety.     

Development and validation of a hydrophilic interaction ultra‐high‐performance liquid chromatography with triple quadrupole MS/MS for the absolute and relative quantification of amino acids in Sophora alopecuroides L.†

Amino acids are naturally occurring compounds in many edible or medicinal plants, which possess a variety of pharmacological effects on humans. The aim of this study is to develop and validate a hydrophilic interaction LC coupled with MS/MS method for the absolute and relative quantification of amino acids without derivatization. The application of this method has been proven through 20 naturally occurring amino acids in 21 samples from different parts and phenological growth stage of Sophora alopecuroides. The method was performed on an ultra‐high performance LC separation system coupled with ESI‐MS on a triple quadrupole mass spectrometer. The proposed absolute quantitative method was fully validated in terms of linearity, sensitivity, precision, repeatability as well as recovery. The analysis results showed that S. alopecuroides is rich in free amino acids. In addition, relative quantitative determination of amino acids with several amino acids selected for the best accuracy was investigated. The accuracies of relative quantitative method for amino acids determinations suggest that it is feasible to quantify amino acids by the proposed relative quantitative determination method, which contributes to breaking through the choke point of lack of standards.