Studies on Kinetics of Colour Formation of Asparagine - Ninhydrin Complex

The complexes of pentacyanoruthenate(II) with 3‐ and 4‐cyanopyridines and benzonitrile are prepared in aqueous solution by mixing (I) with the appropriate ligand.

Electrospray ionization mass spectrometry (ESI-MS) is a valuable and frequently used analytical technique across nearly all branches of chemistry, and has recently seen increasing use in the study of metal-ligand solution equilibria. Despite its prevalence, the method by which ESI produces gas-phase ions from solutions containing metal-ligand complexes is not fully understood, with recent reports showing significant changes to solution equilibria during ESI analysis. This study examines perturbations to the formation kinetics of metal-ligand complexes during the ESI process, showing how quickly new equilibria - reflective of the ionization process and not solution - can be established. Electrospray ionization mass spectrometry (ESI-MS) and ion mobility spectrometry (IMS) are used to examine the well studied Lu-DOTA (1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid) complexation reaction, with collision cross section modeling based on density functional theory (DFT) optimized structures used to aid in the interpretation of the ion mobility results. The electrospray process was found to significantly accelerate the formation kinetics, increasing the formation rate constant by more than an order of magnitude over its previously determined solution-phase value.

Protein-DNA interactions underpin life and play key roles in all cellular processes and functions including DNA transcription, packaging, replication, and repair. Identifying and examining the nature of these interactions is therefore a crucial prerequisite to understand the molecular basis of how these fundamental processes take place. The application of fluorescence techniques and in particular fluorescence resonance energy transfer (FRET) to provide structural and kinetic information has experienced a stunning growth during the past decade. This has been mostly promoted by new advances in the preparation of dye-labeled nucleic acids and proteins and in optical sensitivity, where its implementation at the level of individual molecules has opened a new biophysical frontier. Nowadays, the application of FRET-based techniques to the analysis of protein-DNA interactions spans from the classical steady-state and time-resolved methods averaging over large ensembles to the analysis of distances, conformational changes, and enzymatic reactions in individual Protein-DNA complexes. This chapter introduces the practical aspects of applying these methods for the study of Protein-DNA interactions.

Protein-DNA interactions underpin life and play key roles in all cellular processes and functions including DNA transcription, packaging, replication, and repair. Identifying and examining the nature of these interactions is therefore a crucial prerequisite to understand the molecular basis of how these fundamental processes take place. The application of fluorescence techniques and in particular fluorescence resonance energy transfer (FRET) to provide structural and kinetic information has experienced a stunning growth during the past decade. This has been mostly promoted by new advances in the preparation of dye-labeled nucleic acids and proteins and in optical sensitivity, where its implementation at the level of individual molecules has opened a new biophysical frontier. Nowadays, the application of FRET-based techniques to the analysis of protein-DNA interactions spans from the classical steady-state and time-resolved methods averaging over large ensembles to the analysis of distances, conformational changes, and enzymatic reactions in individual protein-DNA complexes. This chapter introduces the practical aspects of applying these methods for the study of protein-DNA interactions.

In the present work the reversible, bimolecular (1,1) reaction between ethylene and Ag+ in concentrated AgNO3(aq) solutions is analyzed. Due to interactions between the positively charged Ag+ ions and the negatively charged NO3- ions, the silver nitrate is not completely dissociated and the actual free silver ion concentration is considerably lower than the maximum theoretical concentration. Especially at low temperatures and high salt concentrations the reduction in the degree of dissociation is significant. The influence of this degree of dissociation of the silver salt is considered and incorporated in the interpretation of the experimentally obtained results. Physical-chemical characteristics, transport properties of the system, the equilibrium constant of complexation, and the order of magnitude of the kinetic constants of the reaction between Ag+ and ethylene are determined. Subsequent calculation of the enhancement factor shows that the actual enhancement factor is almost equal to the infinite enhancement factor, indicating that the complexation reaction is almost instantaneous. The process is diffusion limited and strongly enhanced by the chemical complexation reaction.

Kinetic studies on complexation reactions of LiI with cryptand C211 in N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)imide (DEMETFSI) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) have been carried out using 7Li NMR. It was found that the reaction rates in both solutions depend on concentrations of free LiI and that their kinetic parameters are almost same. From these results, it is proposed that the LiI complexation reactions in DEMETFSI and EMITFSI solutions proceed though bimolecular mechanism.

The process of complexation of silver(I) ions with thiourea (Tu) in the temperature range 287.16–318.16 K at an ionic strength of 0.11 M (I = 0.1 NaNO3 + 0.01 HNO3) was studied by the potentiometric method using a silver electrode in aqueous solution. The study was performed at a concentration of silver(I) ions CAg+ = 1 · 10–5 and CAg+ = 1 · 10–3 M. The values of the stability constants of AgTui + complexes (i = 1–2) were estimated at CAg+ = 1 · 10–5 M. The AgTu3+ complex constant was determined at CAg+ = 1 · 10–3 M and CTu ≥ 0.01 M. The stability constants of complexes were calculated using the Leden method. The values of the complex constants at 298.16 K are equal to: lgβ1 = 5.59 ± 0.10 (AgTu+), lgβ2 = 10.62 ± 0.03 (AgTu2+) and lgβ3 = 13.05±0.11 (AgTu3+). It is established that the temperature effect does not affect the number of formed particles in the solution; an increase in temperature leads to a decrease in the stability of complexes. The analysis of the values of the stability constants by degrees shows that the step constants AgTu3+ (AgTu2+ + Tu = AgTu3+ + lgβ3 = 2.4) are much smaller than the constants for mono- and bis-coordinated complexes. The complexes thermodynamic parameters (ΔH0, ΔG0, ΔS0) were calculated by the temperature coefficient method. In the system under study, all complexation reactions are exothermic. The largest increase in the value of enthalpy (ΔH0) is observed in the formation of a complex containing two molecules of thiourea. The change in entropy (ΔS0) at the stage of formation of bis- and tris-coordinated complexes is negative, which is most likely due to a decrease in the number of particles in the system under study. It is determined that enthalpy-entropy dependences show a monotonic character. The spontaneous course of complexation reactions is determined by the value of the free Gibbs energy (ΔG0). In degrees G0 decreases (ΔG0)1 < (ΔG0)2 < (ΔG0)3) and has a negative value, which indicates a decrease in the affinity of the complexing agent to the ligand.

The complexation reactions of dicyano monoalkyl tetraaza macrocycle 3b with lithium salts (Li + X -) and the properties of resulting macrocycle 3b-Li + X -complexes were examined in detail by means of 1 H-NMR spectroscopy, because unsymmetrical macrocycle 3b has exhibited intriguing features, such as high selectivity for binding to the Li + ion.The following noticeable facts were found; the reaction rates of complexation are heavily controlled by the properties of anion (X -) and the spectroscopic properties of macrocycle 3b-Li + X -complexes are also changed by the anion.The major origin for the unusual Li + complexation reactions and the specific behavior of Li + complexes would come from the unique properties of metal free macrocycle 3b, because macrocycle 3b has a strong intramolecular hydrogen bond in the macrocyclic ring and the highly strained macrocyclic ring by unsymmetrical structure consisting of nonplanar and planar moieties.

In this study, humic acid-immobilized-amine-modified polyacrylamide/sepiolite (Ha-Am-Paa-Sep) and phytic acid-modified polyacrylamide/sepiolite composites (Phy-Paa-Sep) were prepared and characterized for removal of Cu(II) and Ni(II) from aqueous solutions. The effects of contact time, initial concentration of adsorbent and metal ions, pH and temperature on the adsorption process were investigated. The optimum adsorption of metal ions occurred at pH 5 and 25°C. Ion exchange and complexation reactions were the main mechanisms for adsorption of metal ions. Removal of metal ions followed a pseudo-second-order kinetics and equilibrium occurred after 60 min. The conformity of various adsorption models to the equilibrium data was evaluated among which Freundlich isotherm model gave the best fitting result. The highest monolayer adsorption capacity of Cu(II) and Ni(II) ions were 244 and 250 mg·g −1 for Ha-Am-Paa-Sep and 256.4 and 277 mg·g −1 for Phy-Paa-Sep, respectively, at room temperature. Ultimately, desorption experiments were performed and the results showed approximately 95% of adsorbed metal ions were desorbed.

Central atom exchange reactions in complexes with tetradentate thiominato schiff base ligand

Fluorescence intensity measurements of overall, pseudo-first-order rate constants for two epoxide-containing metabolites of benzo[R]pyrene (BP) were carried out in Tris, EDTA buffer (pH 7.3) without DNA, and in buffer with double-stranded calf thymus DNA (DS ctDNA) and with closed-circular, single-stranded viral M 13mp19 DNA (SS M13 DNA). Highly purified SS M13 DNA was employed in order to avoid polymeric contamination which is present in DNA samples obtained using a standard preparation method relying on phenol extraction and which influences results from measurements of DNA-ligand interactions. The BP metabolites examined were highly carcinogenic (±)-trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[α]pyrene (BPDE) and less genotoxic benzo[α]pyrene 4,5-oxide (BPO)

Although a catalyst does not shift the position of equilibrium but it does markedly change the reaction rate, because the catalyst lowers the activation energy of a reaction providing an alternative favorable route for the formation of the products. The reacted catalyst is regenerated and is repeatedly involved in an indicator reaction. When the rate depends on the concentration of the catalyst, it can be determined by measuring the change in the physical properties of the reactants and/or products in the indicator reaction. The change in a physical property such as absorbance, fluorescence, chemiluminescence (CL) or electrode potential of a reaction system is usually monitored with time. This methodology is called catalytic methods or kinetic–catalytic methods of analysis.Kinetic–catalytic methods of analysis based on catalyzed reactions have progressed recently and have been applied to trace analyses for various catalysts (element) because of their extremely high sensitivity, low limit of detection and selectivity. Several reactions such as redox, ligand substitution and complexation reactions have been utilized as indicator reactions for the development of kinetic–catalytic methods of trace analyses. Most of the catalysts in redox reactions are metal ions or inorganic anions having different oxidation states such as cobalt, copper, chromium, iron, manganese, vanadium, selenium, iodide, bromide and nitrite. Oxidants capable of regenerating the catalyst are hydrogen peroxide, chlorate, bromate, periodate and dissolved oxygen. Reductants include ascorbic acid, hydroxylamine, hypophosphorous acid, alkali sulfides, dithiothreitol and tin(II).Certain substances significantly increase the rate of catalyzed reactions. These substances are referred to as activators and have been defined as substances that do not catalyze the indicator reaction but enhance the catalytic effect of the catalyst. Activators provide high sensitivity and selectivity in kinetic–catalytic methods. Such improved specificity can be expected to eliminate the preliminary separation in many instances.As the measurement includes time as an experimental variable, care is needed to ensure that mixing of reagents takes place at regular time intervals to obtain highly accurate results using a manual procedure. Such disadvantages in the manual system can be overcome by using flow‐injection analysis (FIA), in which the reaction time can easily be controlled by varying the flow rate of the solutions and the length of the reaction coil.Kinetic–catalytic methods allow the determination of various elements at nanogram and picogram levels (10−11 M) with a simple and reasonable equipment. The detection limits (DLs) of the methods are of the order of picograms per milliliter with good accuracy and precision and are almost equal to those for inductively coupled plasma mass spectrometry (ICPMS).The application of catalytic effects of metal ions in titrimetry has been recognized for a long time. This methodology is called catalytic titration and involves two consecutive reactions, i.e. titration reaction and indicator reaction. The determinable concentration is almost 10−6 M of the metal ions.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetic studies of the aquopentaamminecobalt(III)/- and aquopentaamminechromium(III)/hydrogen chromate complexation reactionMichael R. Grace and Peter A. TregloanCite this: Inorg. Chem. 1992, 31, 22, 4524–4529Publication Date (Print):October 1, 1992Publication History Published online1 May 2002Published inissue 1 October 1992https://pubs.acs.org/doi/10.1021/ic00048a016https://doi.org/10.1021/ic00048a016research-articleACS PublicationsRequest reuse permissionsArticle Views47Altmetric-Citations7LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

A system of β-cyclodextrin and l-isoleucine in aqueous solution was studied by the ultrasonic relaxational method to obtain kinetic parameters for the complexation reaction at 25 °C. Ultrasonic absorption coefficients were measured as a function of frequency in the range 0.8−95 MHz and solute concentration at three different pH's. The frequency dependence of the absorption observed as a function of frequency was analyzed by a Debye-type equation with a single relaxation time at neutral pH. The cause of the relaxation was attributed to a perturbation of a chemical equilibrium due to formation of inclusion complex consisting of β-cyclodextrin and l-isoleucine. The forward and backward rate constants, the equilibrium constant, and the standard volume change of the reaction were determined from the ultrasonic parameters. Comparing these obtained results with those at low pH, it was found that the complexation reaction at low pH is the same as that at neutral pH range. However, at the high pH, another reaction...

In this study, the effect of acetonitrile (AN)—dimethylsulfoxide (DMSO) binary solutions on the complexation reaction between Fe2+, Cu2+, and Zn2+ cations with 4,4′,4″,4‴-(porphine-5,10,15,20-tetrayl) tetrakis (benzoic acid) (TBAP) and 15-crown-5 (15C5) ligands has been studied at different temperatures using conductometric method. The stability constant of complexes is obtained from fitting of molar conductivity data using GENPLOT computer program, also in all cases, the stoichiometry of the complexes was obtained 1: 1 [M: L]. The results show that the order of stability constant for (TBAP.Cu2+), (TBAP.Zn2+), (15C5.Cu2+) and (15C5.Zn2+) complexes in pure organic solvents is: AN > DMSO. A non-linear behavior was observed for changes of the stability constant of complexes versus the composition of AN-DMSO binary solutions. The selectivity order of 15C5 ligand for these cations in AN-DMSO (AN = 25, 50 and 75 mol %) binary solutions was obtained: Fe2+ > Cu2+ > Zn2+ but in the case of TBAP ligand in AN-DMSO (AN = 50 and 75 mol %) binary solutions were found: Fe2+ > Zn2+ > Cu2+. The values of thermodynamic parameters (ΔHC°) and (ΔSC°) for formation of complexes were obtained from temperature dependence of stability constants of complexes using the Van’t Hoff plots. Moreover, the results show a non-monotonic relationship between these thermodynamic quantities and the solvent composition.