A study of glutamine interference in the acidified ninhydrin reaction for proline

In the application of the acidified ninhydrin reaction to the estimation of free proline in plant extracts, glutamine was a major source of interference, all others being minor, absent or removable with Permutit. Some characteristics of glutamine interference in this reaction are described. A ratio of linear errors method for the correction of proline values to the glutamine free state is introduced. The glycine and proline concentration in the reaction mixtures are prime factors in obtaining a ratio of linear errors by spectrophotometric measurement at 2 wavelengths.     

On the reaction of ninhydrin with cysteine and its analogues:: A revision

Chemical and spectroscopic evidence leads to the conclusion that the compound described in the literature as 2,3,9,9a-tetrahydro-9a-hydroxy-9-oxo-indeno[2.1]-p-thiazine-3-car☐ylic acid (1), which is formed in the reaction of ninhydrin with L-cysteine, has in fact the isomeric spirane structure (4). Cysteine analogues, such as 3-mercapto-valine and 2-aminoethanethiol, react similarly to give the corresponding condensation products (7 and8).     

A knowledge-based system for the automatic chronopotentiometric elucidation of electrode reaction mechanisms

A knowledge-based system for the elucidation of electrode reaction mechanisms based on chronopotentiometric experiments is described. The system runs the diagnostic experiments and uses the results in the reasoning process. New mechanistic knowledge can be added directly to its knowledge base in the form of production rules. The system is fully modular and its domain- specific modules can easily be changed for application to other electrochemical techniques. Correct operation of the system is demonstrated with the familiar reduction mechanisms of cadmium (II), zinc (II), cystamine and cinnamaldehyde.     

Application of low-temperature rapid-scan techniques in the elucidation of inorganic reaction mechanisms

Reactions that occur too rapidly to be monitored by rapid reaction methods at temperatures at or close to ambient can be investigated kinetically by retarding their reaction rates employing very low temperatures. A selection of reactions studied by this approach (low-temperature stopped-flow spectrophotometry) is reported. Details of the reaction mechanisms have been revealed for peroxide activation involving iron(III) porphyrins and cytochrome P450, superoxide activation involving manganese(II) complexes and iron porphyrin complexes, and dioxygen activation and binding by model mono-, and dinuclear copper(I) complexes and dioxygen activation at mono-, and dinuclear non-heme iron complexes. A final section covers progress in unravelling the mechanism of carbon–hydrogen bond activation by platinum complexes.     

Assay of sialidase activity using ion-exchange chromatography and acidic ninhydrin reaction.

A new assay method for sialidase (EC 3.2.1.18) activity using ion-exchange chromatography and acidic ninhydrin reaction has been developed. Fetuin, 4-methylumbelliferyl-N-acetylneuraminic acid (MUB-NANA), gangliosides and N-acetylneuramin-lactose were examined as substrates. Free sialic acid liberated from these substrates by sialidase reaction was isolated with a Dowex 1-X8 column (trifluoroacetate form, 1.5 cm x 0.5 cm I.D.) and determined by acidic ninhydrin reaction. Among the substrates tested, MUB-NANA was the best in the present method, N-Acetylneuramin-lactose could not be used as the substrate, because it was not separated from liberated sialic acid under the conditions used. The recovery of N-acetylneuraminic acid was above 88%, and the sensitivity of the method was 20 nmol in 300 microliters of the reaction mixture. The method was applied to the sialidase assay during its purification from rat skeletal muscle, and a Michaelis constant of 1.15 mM was obtained with MUB-NANA as the substrate. The method using the acidic ninhydrin reaction was simple and exhibited good reproducibility.     

茚三酮对B-Z振荡反应的影响

研究了茚三酮对B Z振荡体系的影响,考察了振幅和周期的改变值与茚三酮浓度的关系。结果表明,在6.9×10-7～4.2×10-2mol/L范围内,第一振幅改变值与茚三酮浓度有良好的线性关系,相关系数为0.9977。依据FKN模型,对此反应机理进行了初步探讨。     

Quantitative reaction cascades of ninhydrin in the solid state

Crystalline ninhydrin (1) undergoes waste-free solid-state cascade reactions with dimedone, L-proline, three o-phenylenediamines, o-mercaptoaniline, two ureas, three thioureas, and methyl 3-aminocrotonate. The yields are quantitative and give pure crystalline products without workup just by milling stoichiometric mixtures of the crystalline reagents. The structures of the new and the previously obtained products with lower yields from solutions are established or confirmed by spectroscopic data and density functional calculations at the B3LYP/6-31G* level. The success of 3- and 4-cascade reactions in the crystal without melting is unusual and of unmatched atom economy. They are mechanistically investigated with atomic force microscopy techniques (AFM) on six different faces of 1 when o-phenylenediamine was the reagent (substitution, elimination, cyclization, elimination) and interpreted on the basis of known crystal structure data. Strict correlations to the crystal packings are observed. The characteristic surface features grow to microm heights in some cases at distances of 0.5 mm from the contact edge of the reacting crystals. The waste-free and easy syntheses of highly functionalized (C=O; O-H; C=N) heterocycles or of a tetraketone are also of interest for synthetic use.     

Expeditious reaction of ninhydrin with active methylene compounds on montmorillonite K10 clay

Abstract  Ninhydrin reacted expeditiously with thirteen active methylene compounds on montmorillonite K10 clay at room temperature to furnish, in 5 min, a Knoevenagel condensate in one case, aldols in six cases, aldol-derived cyclic hemiketals in three cases, and interesting products in the remaining three cases. Almost identical results were obtained, but faster, when the reactions were carried out in water on steam-bath. The structures of two novel products were also confirmed by single-crystal X-ray diffraction analysis. Graphical abstract        

Coupling real-time surface-enhanced raman spectroscopy with linear-sweep voltammetry : Application to elucidation of electrochemical mechanisms

The broad-based utilization of real-time surface-enhanced Raman spectra, obtained by using an intensified diode-array detector, to examine interfacial redox transformations under cyclic voltammetric conditions is exemplified for the oxidation at gold electrodes of irreversibly adsorbed benzidine and the reduction of adsorbed azoxybenzene. The first reaction, involving a pair of irreversible one-electron oxidation steps, enabled a quantitative comparison to be made between the extent of oxidation of the adsorbed layer during the potential sweep and the simultaneous spectral response. Although relatively slow (10–50 mV s^?1) sweeps are required in order to yield spectral sequences having a suitably narrow (?50 mV) potential interval, the spectral data acquisition requires only a single potential perturbation. This “single-shot” spectroelectrochemical approach, desirable for the examination of irreversible interfacial systems, differs from conventional time-resolved methods that involve signal integration over numerous repetitive perturbations.     

Transparent formal methods for reducing the combinatorial abundance of conceivable solutions to a chemical problem : Computer-assisted elucidation of complex reaction mechanisms

Restraining the combinatorial flood of conceivable solutions to chemical problems by formal means is discussed. An algebraic model of the logical structure of constitutional chemistry not only serves as the theoretical foundation of the inference engines in strictly logic-orientated chemical computer programs, but also provides a conceptual framework for non-arbitrary, transparent procedures for reducing the combinational abundance of conceivable solutions to given chemical problems. Diverse procedures are available to provide efficient guidance on routes from a chemical problem to its chemically most meaningful solutions. The division of problems into subsidiary problems, the bilateral alternative to monolateral approaches, and the hierarchic classification of results, prior to selecting individual solutions, is highly effective in computer-assisted problem-solving.     

A Synthesis of Two Novel Benzo[f]ninhydrin Analogs: 6-Methoxybenzo[f]ninhydrin and Thieno[f]ninhydrin

Improved methodology for the synthesis of benzo[f]ninhydrin (1) is described. The generality of this approach is illustrated with the synthesis of two novel analogs, 6-methoxybenzo[f]ninhydrin (3) and thieno[f]ninhydrin (4).     

New forced degradation products of vildagliptin: Identification and structural elucidation using LC-MS,with proposed formation mechanisms

Abstract

A new and simple RP-HPLC-UV method was developed for well-separation of vildagliptin raw material and its degradation products at different conditions; it uses of ammonium acetate buffer at pH= 7.5 and methanol with Athena C18 -WP (250?mm) column. Results show that six degradants have been identified using LC–MS technique, in addition to the NMR approach in some cases. One degradant at relative retention time (RRT) 1.3 was formed under acidic condition and designated as 2-((1R, 3S, 5R, 7S)-3-hydroxyadamantan-1-yl) hexahydropyrrolo[1,2-a]pyrazine-1,4-dione at m/z = 304. Three degradants were formed under various conditions of basic hydrolysis at RRTs 1.2, 0.6 and 0.4 with following names and molar masses (m/z), respectively: 1-(((1S, 3S, 5S, 7S)-1,3-dihydroxyadamantan-2-yl)glycyl)pyrrolidine-2-carboxamide at m/z = 337.2, 1-(((1R, 3S, 5R, 7S)-3-hydroxyadamantan-1-yl)glycyl)pyrrolidine-2-carboxamide at m/z = 321.1 and (1,4-dioxo-1,4,6,7,8,8a-hexahydropyrrolo[1,2-a]pyrazin-3-yl)glycylproline at m/z = 322.6. Another three degradants were also formed under oxidative oxidations of vildagliptin, one at RRT 0.38 and designated as N-hydroxy-N-((1R, 3S, 5R, 7S)-3-hydroxyadamantan-1-yl) glycinate with m/z 241.1, the second one was identical to that formed under basic hydrolysis at RRT 0.6 and the last one has RRT 0.8 and was identified as (1S, 3R, 5R, 7S)-3-(hydroxyamino)adamantan-1-ol at m/z 183.1. Formation mechanisms for the degradation products were described.     

Headspace single-drop microextraction and cuvetteless microspectrophotometry for the selective determination of free and total cyanide involving reaction with ninhydrin

Headspace single-drop microextraction has been used for the determination of cyanide with ninhydrin in combination with fibre-optic-based cuvetteless microspectrophotometry which accommodates sample volume of 1 μL placed between the two ends of optical fibres, and has been found to avoid salient drawbacks of batch methods. This method involved hydrocyanic acid formation in a closed vial, and simultaneous extraction and reaction with 2 μL drop of ninhydrin in carbonate medium suspended at the tip of a microsyringe needle held in the headspace of the acidified sample solution. The method was linear in range 0.025-0.5 mg L⁻¹ of cyanide. The headspace reaction was free from the interference of substances, e.g., thiocyanate, hydrazine sulphate, hydroxylammonium chloride and ascorbic acid. Sulphide was masked by cadmium sulphate, nitrite by sulphamic acid, sulphite by N-ethylmaleimide, and halogens by ascorbic acid. The limit of detection was found to be 4.3 μg L⁻¹ of cyanide which was comparable to existing most sensitive methods for cyanide. However, the present method is far more simple. The method was applied to acid-labile and metal cyanides complexes by treatment with sulphide when metal sulphides were precipitated setting cyanide ion free, and to iron(II) and (III) cyanide complexes by their decomposition with mercury(II), the mercury(II) cyanide formed was then determined. These pre-treatment methods avoided cumbersome pre-separation of cyanide by methods such as distillation or gas diffusion. The overall recovery of cyanide in diverse samples was 97% with RSD of 3.9%.     

Investigations of the reaction mechanisms of 1,2-indanediones with amino acids.

The reaction mechanisms of amino acids with a new class of fluorogenic reagents were investigated. The structures of colored and fluorescent species formed in these reactions were partially confirmed by experimental evidence. Reaction intermediates, C-N-C 1,3-dipoles derived from imines, were trapped with dipolarophiles in 3 + 2 cycloadditions to form spiropyrrolidines.     

茚三酮显色法测定壳聚糖含量

本研究根据壳聚糖与茚三酮作用显色的特性,建立可见光分光光度法测定壳聚糖含量的方法,并对该测定方法的适宜条件及工作曲线进行确定。实验结果表明,壳聚糖与茚三酮在p H5.5的HAc-Na Ac缓冲体系中显色稳定,在0.004~0.040 g·L-1浓度范围内,其复合物在570nm处吸光度与壳聚糖浓度线性关系良好(r2=0.9981)。进一步对该方法的稳定性、重现性和回收率进行考察,表明该方法操作简单,结果可靠,可满足样品中微量壳聚糖含量的常规检测需要。