Complexes Of Different Stoichiometry Research Articles

An Inhibitor-Type Competitive Analysis Model for Sensors with Small Sensitive Surface Area

Abstract: A kinetic model for inhibitor-type competitive analysis of sensor systems with surface-type physical transducers having small-area sensitive surfaces (nano- and microsensors) is considered. We calculated the dependencies of sensor response on concentrations of: (i) low-molecular weight analyte to be determined, (ii) its immobilized analog and (iii) macromolecular receptor. This enabled us to advance a method for quantitative determination of low-molecular weight analytes in such systems. Our approach uses polydentate molecular receptors whose area of projection onto the transducer surface depends on the number of occupied recognizing sites. Interrelation between the amounts of analyte−macromolecular receptor complexes of different stoichiometries varies depending on the initial concentration of analyte. This results in variation of the limiting surface concentrations of the corresponding interfacial complexes and, consequently, their amount at the physical transducer surface.

Death Domain Assembly Mechanism Revealed by Crystal Structure of the Oligomeric PIDDosome Core Complex

Proteins of the death domain (DD) superfamily mediate assembly of oligomeric signaling complexes for the activation of caspases and kinases via unknown mechanisms. Here we report the crystal structure of the PIDD DD and RAIDD DD complex, which forms the core of the caspase-2-activating complex PIDDosome. Although RAIDD DD and PIDD DD are monomers, they assemble into a complex that comprises seven RAIDD DDs and five PIDD DDs. Despite the use of an asymmetric assembly mechanism, all DDs in the complex are in quasi-equivalent environments. The structure provided eight unique asymmetric interfaces, which can be classified into three types. These three types of interactions together cover a majority of the DD surface. Mutagenesis on almost all interfaces leads to disruption of the assembly, resulting in defective caspase-2 activation. The three types of interactions may represent most, if not all, modes of interactions in the DD superfamily for assembling complexes of different stoichiometry.

Benzotriazole Complexes with Amines and Phenol: Cooperativity Mediated by Induction Effects in the Crystal State

[structure: see text] Benzotriazole forms complexes of different stoichiometries with amines and phenols. Four of them have been characterized by single-crystal X-ray diffraction. The trends of donor-acceptor hydrogen-bond distances between corresponding molecular entities in the different complexes are related to induction-mediated cooperativity effects.

Fragmentation and skeletal rearrangements of 2‐arylylamino‐5‐aryl‐1,3,4‐oxadiazoles and their noncovalent complexes with cobalt cation and cyclodextrin studied by mass spectrometry

Mass spectrometric fragmentation pathways of title compounds were studied by electron ionization (EI) and electrospray ionization (ESI) as methods of ion generation. To explain the observed complex skeletal rearrangements, tandem mass spectrometry, accurate mass measurement and isotope labeling (compounds containing one 13C atom in oxadiazole ring) were used. Loss of CO, N2 and H atoms under EI conditions led to the formation of 9,10-dihydroacridine-type ions, loss of NH3 under ESI conditions yielded the 4-phenylphthalazinone-type ions and the loss of HNCO under ESI conditions produced N-arylamino-benzonitrilium ions; however, this process can be affected by the electron-donor/electron-withdrawing properties of groups substituted at the phenyl rings. The ESI was used to study the complexes of the compounds with cobalt as well as with cyclodextrin. It was found that the compounds studied tend to form inclusion complexes with cyclodextrin of stoichiometry 1:1 and complexes of different stoichiometries with cobalt, although those of stoichiometry 6:1 and 4:1 are favored and the attachment of counter ion may stabilize the complexes 3:1 and 2:1.

Evidence for complexes of different stoichiometries between organic solvents and cyclodextrins

The influence of the organic solvent on the acid and basic hydrolysis of N-methyl-N-nitroso-p-toluenesulfonamide (MNTS) in the presence of alpha- and beta-cyclodextrins has been studied. The observed rate constant was found to decrease through the formation of an unreactive complex between MNTS and the cyclodextrins. In the presence of dioxane, acetonitrile or DMSO, the inhibitory effect of beta-CD decreased on increasing the proportion of organic cosolvent as a result of a competitive reaction involving the formation of an inclusion complex between beta-CD and the cosolvent. The disparate size of the organic solvent molecules resulted in stoichiometric differences between the complexes; the beta-CD-dioxane and beta-CD-DMSO complexes were 1 : 1 whereas the beta-CD-acetonitrile complex was 1 : 2. The basic and acid hydrolysis of MNTS in the presence of alpha-CD showed a different behavior; thus, the reaction gave both 1 : 1 and 2 : 1 alpha-CD-MNTS complexes, of which only the former was reactive. This result was due to the smaller cavity size of alpha-CD and the consequent decreased penetration of MNTS into the cavity in comparison to beta-CD. The acid hydrolysis of MNTS in the presence of alpha-CD also revealed decreased penetration of MNTS into the cyclodextrin cavity, as evidenced by the bound substrate undergoing acid hydrolysis. In addition, the acid hydrolysis of MNTS in the presence of acetonitrile containing alpha-CD gave 1 : 1 alpha-CD-acetonitrile inclusion complexes, which is consistent with a both a reduced cavity size and previously reported data.

Novel nitrogen containing chelating ligands from aziridines — Preparation, coordination studies, and catalytic application in the cyclopropanation of styrene

Novel ligands have been synthesized by the reaction of readily available aziridines with appropriate nitrogen based nucleophiles under mild conditions. Complexes of different stoichiometry can be readily obtained upon reaction between these ligands and the corresponding copper salts. The enantiomerically pure form of one of the ligands was obtained and applied in the styrene cyclopropanation reaction, where the copper catalyst revealed unexpectedly high diastereoselectivity in comparison with the known systems.Key words: ligands, aziridines, cyclopropanation, copper catalysts, metal complexes.

Cation Complexation by a Lower Rim Calix(4)arene Derivative: Structural, Electrochemical and Thermodynamic Studies

The synthesis and characterization (1H and 13C NMR) of a partially substituted lower rim p-tert-butylcalix(4)arene, namely, 5,11,17,23-tetra-4-tert-butyl-25,27-bis(diethylphosphate amino)ethoxy-26,28-dihydroxycalix[4]arene (1), are reported. The solution thermodynamics of the ligand in a variety of solvents at 298.15 K was investigated through solubility (hence standard Gibbs energy of solution) measurements while the calorimetric technique was used to derive the standard solution enthalpy. These data were used to calculate the standard entropy of solution. An enthalpy–entropy compensation effect is shown and, as a result, slight variations are observed in the transfer Gibbs energies of this ligand from the reference to other solvents. 1H NMR, conductance and calorimetric measurements were carried out to establish the degree of interaction of the ligand with univalent (Li+, Na+, K+, Rb+, Cs+ and Ag+) and bivalent (Mg2+, Ca2+, Sr2+, Ba2+, Pb2+, Cd2+, Hg2+, Cu2+, Zn2+) cations in acetonitrile, methanol, N,N-dimethylformamide and propylene carbonate. No complexation was found between this ligand and univalent cations in these solvents. As far as the bivalent cations are concerned, interaction between 1 and these cations was found only in acetonitrile. The versatile behaviour of this ligand with bivalent cations in this solvent is reflected by the formation of complexes of different stoichiometry. Thus the interaction of 1 with alkaline-earth (Mg2+, Ca2+, Sr2+, Ba2+) and Pb2+ metal cations leads to the formation of 1:2 (cation:ligand) complexes. However, for other bivalent metal cations (Cu2+, Zn2+, Cd2+ and Hg2+) the complex stoichiometry was found to be 1:1. The results are discussed in terms of the key role played by acetonitrile in processes involving calix[4]arene derivatives.

Fluorescence anisotropy of oligomeric proteins

Previous studies of protein oligomerization using time‐resolved fluorescence anisotropy assumed a single fixed probe per oligomeric complex and an identical probe orientation in complexes of different stoichiometry. However, an oligomer consisting of “n” singly labeled monomers must necessarily have “n” probes. Moreover, in the expression for the anisotropy decay, the molecular axes from which the probe orientation is defined are different for complexes that differ in stoichiometry. Here, we derive an expression for the decay of the anisotropy for molecules with any number of fixed probes, and show how an explicit understanding of the probe orientation is necessary to properly assess oligomerization.

The role of anionic substances in removal of textile dyes from solutions using cationic flocculant

The mechanism of dye removal from textile waste water using polyquaternary ammonium salt as a flocculant has been proposed. It was shown that the cationic polymer tends to react with anionic textile finishing chemicals and auxiliaries (anionic detergents, dispersing agents, thickeners), forming intermolecular complexes of different stoichiometry. Under controlled conditions these complexes are able to incorporate the dye ions or molecules and precipitate together. Formation of triple complexes is postulated to be the only possible way for non-ionic dyes to be precipitated. The nature of forces causing the transfer of the dyes to a polymeric matrix has been revealed. The necessity of an anionic polyfunctional compound with a proper chemical structure to play the role of disperse dye carrier is emphasised. The mechanism of incorporation of dye ions into triple complexes, the possibility of competitive reactions, and the problems of stability and reduced cationic functionality of nonstoichiometric complexes are discussed.

Resolution of the Association Equilibria of 2-(p-Toluidinyl)-naphthalene-6-sulfonate (TNS) with β-Cyclodextrin and a Charged Derivative

The importance of possible electrostatic effects in the complexation of cyclodextrins has been investigated. The complexation features of the anionic guest molecule, 2-(p-toluidinyl)naphthalene-6-sulfonate (TNS), with the positively charged cyclodextrin, 6-deoxy-6-amino-β-cyclodextrin (NH3+CD), and with the neutral β-cyclodextrin (β-CD) were compared. Although TNS is a widely used fluorescent probe for the studies of complexation with cyclodextrins, its behavior is still not completely understood. In this paper we show that the complexation of TNS with β-CD involves the simultaneous formation of two different 1:1 complexes, resulting from inclusion of the toluidin moiety or the naphthalenesulfonate moiety in a cyclodextrin unit, and a 1:2 complex, which is due to the complexation of the two aromatic moieties of TNS with two cyclodextrin molecules. In the complexation of TNS with NH3+CD, the same species and equilibria are present, although significant structural differences of their complexes and variations in the values of the association constants are observed. Such differences can be explained by the electrostatic interaction between the sulfonate anion of TNS and the positively charged amino group of NH3+CD. The resolution of these complicated systems, with four emitting species and four association equilibria, could be achieved only by careful and systematic analysis of both steady-state and time-resolved fluorescence data, together with direct structural information from NMR experiments. Moreover, principal components global analysis (PCGA) is presented as an objective method for the detection of complexes of different stoichiometries and for the precise determination of the involved association constants.

Anodic stripping voltammetry in the complexation study of the peptide Lys-Cys-Thr-Cys-Cys-Ala [56–61] MT I and cadmium: application in determination of the complexing capacity and stability constant

A study of Cd complexation with the peptide Lys-Cys-Thr-Cys-Cys-Ala thionein fragment [56–61] MT I (FT) was performed in the differential pulse anodic stripping voltammetric (DPASV) mode. Amperometric titrations of FT with cadmium standard solution were performed in 0.59 mol dm −3 NaCl at pH 7.9, and at a constant temperature of 25.0°C. The signal of FT without cadmium has the peak potential at E p(FT)=−0.52 V (vs. an Ag ∣ AgCl electrode). As the titration with CdCl 2 proceeds, a signal related to CdFT complex appears at the potential E p(CdFT)=−0.67 V. When the available complexing sites on FT are saturated the signal of ionic Cd appears. From the amperometric titration data the capacity of FT to complex Cd ( C L) and the apparent stability constant of the CdFT complex ( K′) using a modified van den Berg–Ružić–Lee method were determined. The mean value of the stability constant corrected for the partition of the hydrated Cd 2+ ion within the ionic cadmium concentration is 5.3×10 10 dm 3 mol −1. In addition, titration of the constant Cd 2+ concentration with FT was performed. Due to the excess of cadmium over the FT and vice versa the existence of complexes of different stoichiometry are proposed to cause the poorly resolved signal.

Thermodynamics of the formation of complexes between aniline derivatives and proton acceptors in solution

Abstract The M(0),, M(1) and 2(M (2) ) 1 2 spectral moments of the v(NH) bands of aniline derivatives as well as their complexes with various proton acceptors in solution were determined in the temperature range 285–330K. Studied compounds were: aniline; 4-metoxytetrafluoraniline; 2,3,5,6-tetrafluoraniline and 4-aminotetrafluorpyridine. The coefficients of linear Y=aT+b regression of the spectral moments M(0),, M(1) and 2( M (2) ) 1 2 with temperature were determined for the free amino groups as well as for 1:1 complexes with various proton acceptors in CCl4 solutions. An analysis of the influence of temperature on the spectral characteristics of monomers and their 1:1 complexes with various proton acceptors was performed. The heat formation (ΔH1) of the 1:1 complexes with proton acceptors was determined using the dependence of the equilibrium constants on temperature. On the basis of the “rule of intensity”: -Δ H = αΔ B 1 2 , the ΔH2 for the complexes of 1:2 stoichiometry was calculated, allowing the estimation of the relation ΔH1/ΔH2 It was shown that ΔH1 is larger than ΔH2 recalculated for a single bond. Comparison of the dynamics characteristics of the N-H bonds in amino groups in complexes of different stoichiometry proves that the hydrogen bonds in 1:1 complexes is stronger than in the complexes of 1:2 stoichoimetry.

Aspects of the interactions between indomethacin and nicotinamide in solid dispersions

A series of indomethacin/nicotinamide binary system-melts were prepared as models to study some aspects of the potential physico-chemical interactions between indomethacin and nicotinamide. The comparative analysis of the data from FT-IR- and UV spectroscopy, DSC, X-ray diffractometry and equilibrium solubility study showed that formation of complexes of different stoichiometry can take place in the solid state and in solution. The aqueous solubility of the assumed complexes of drug/carrier molar ratio above 1:1 (M/M) did not exceed the solubility of the pure indomethacin (IND) (treated), which was prepared as the model melts. The melts with a low drug content (e.g. 7.5 and 9.1% melts) were found to be in a metastable physical state probably due to the amorphous nature of the indomethacin or its complex. They can be in situ transformed into 1% indomethacin aqueous solution.

Characterization by Potentiometric Procedures of the Acid−Base and Metal Binding Properties of Two New Classes of Immobilized Metal Ion Affinity Adsorbents Developed for Protein Purification

The acid-base protonation constants of two recently introduced chelating ligands for protein purification, O-phosphoserine and 8-hydroxyquinoline immobilized onto Sepharose CL-4B, and the stability constants of their derived immobilized metal ion chelate complexes have been determined by potentiometric methods. The data confirm that immobilization thermodynamically constrains the ligands, with the electron-withdrawing characteristics of the group linking the ligand to the support material affecting the magnitude of the stability constant of the immobilized metal ion complex vis-à-vis the free ligand-metal ion complex in solution. The influence of buffer composition, ionic strength, and pH on the stability constant of the immobilized hard metal ion chelate complexes has also been examined. Collectively, the results have confirmed that coordination complexes with stoichiometries other than the simply 1:1 ML-type exist with these systems, with hard metal ions exhibiting a preference for hydrolytic M(OH)(m)L(n) complexes where m or n > 1. These findings on the participation of coordination complexes of different stoichiometry depending on the characteristics of the chelating ligand and metal ion have fundamental implications for the interpretation of immobilized metal ion affinity chromatographic separation of proteins.

The Oxidation of Gold Powder by Me3El2 (E  P, As) under Ambient Conditions; Structures of [AuI3(PMe3)2], [AuI3(AsMe3)], and [(Me3PO)2H][AuI2

Unactivated gold powder readily reacts with Me3EI2 (E  P, As) in diethyl ether to form the planar complex [AuI3(AsMe3)] and, surprisingly, the trigonal-bipyramidal complex [AuI3-(PMe3)2] (structure shown on the right); the latter readily hydrolyzes to form [(Me3PO)2H][AuI2]. The oxidation of this noble metal to Au3+ and the production of complexes of different stoichiometries and structures illustrates the oxidizing power and the subtlety of these Me3EI2 reagents.

Interaction of some barbituric acid derivatives with hydroxypropyl-β-cyclodextrin

The interaction between 39 barbituric acid derivatives and hydroxypropyl-β-cyclodextrin (HPβCD) was studied by reversed-phase charge-transfer thin-layer chromatography. Except for one derivative, each barbiturate formed inclusion complexes with HPβCD, the complex always being more hydrophilic than the uncomplexed drug. The intensity of interaction significantly increased with increasing lipophilicity of the guest molecule proving the preponderant role of hydrophobic interactions in inclusion complex formation. The di- and trisubstituted derivatives probably formed complexes of different stoichiometry. Free-Wilson analysis proved that the intensity of interaction increases with increasing size of the substituents at least in the studied range.

Fourier transform infrared studies on charge-transfer interactions of plastoquinones and α-tocopherol quinone with their hydroquinone forms and monog

Fourier transform infrared (FTIR) spectra of plastoquinone-9 (PQ-9), plastoquinone-3 (PQ-3), α-tocopherol quinone (α-TQ), their reduced forms, monogalactosyldiacylglycerol (MGDG), quinone-hydroquinone Q-QH 2) and Q-QH 2-MGDG mixtures in thin films have been measured. The spectra were recorded directly on samples evaporated from hexane and after precooling at liquid nitrogen temperature. It was found that pure QH 2 molecules are hydrogen bonded and occur mainly in polymeric forms, but in mixtures with corresponding quinones, they show only the presence of dimers. The quinones in Q−QH 2 mixtures in a liquid state do not form hydrogen bonds, but after solidification most of their carbonyl groups are hydrogen bound to hydroquinones, which facilitates the formation of charge-transfer (CT) complexes. Hydrogen bonds in CT complexes between PQ-9 and PQH 2-9 were found to occur also in MGDG matrix. There were also some indications found on Q−QH 2 interactions in a liquid state. The peak responsible for C−O stretching vibrations of hydroxyl groups in liquid Q−QH 2 mixtures is strongly reduced, and after solidification there appeared two new peaks due to stretching vibrations as a result of hydrogen bonding. Only for PQ-9 and PQH 2-9 in solid state did crystallization bands appear below 900 cm −1, which originate from skeletal vibrations of the isoprenoid side chain of both compounds. The possibility of the existence of CT complexes of different stoichiometry in apolar solutions is also considered.

Study of mutual influence of hydrogen bonds in complicated complexes by low-temperature 1H NMR spectroscopy

1H NMR spectra of various acid-base complexes of different stoichiometry at 100–120K in freon mixtures have been obtained. The separate signals of non-equivalent OH-protons, involved in different H-bonds, have allowed us to consider the problem of the mutual influence of these bonds, using a correlation between the δ OH chemical shift and the AΔ H H-bond enthalpy. The mutual strengthening of H-bonds in complexes of the AH⋯AH⋯B type and their weakening in AH⋯B⋯HA complexes have been found, the value of the effect being about 10–30%

Affinity electrophoresis used for determination of binding constants for antibody-antigen reactions

The use of affinity electrophoresis in agarose gels for determination of binding constants for the interaction of antigens with monoclonal antibodies is exemplified for monoclonal anti-human serum albumin and anti- α 1-fetoprotein antibodies. The calculated binding constants are verified by independent binding assays. The electrophoretic separation of antigen-antibody complexes of different stoichiometry is also demonstrated. Thus, affinity electrophoresis represents an alternative method for both qualitative and quantitative assessment of antigen-antibody interactions.

ChemInform Abstract: Metal Complexes of Alkylating Agents. Part 5. Complexes of Phosphoramide Mustard Derivatives.

AbstractThe title ligands (I) and (II) (preparation described) react with a variety of metal perchlorates (metal: Al, Ba, Co, Cu, La, Li, Mg, Mn, Ni) to give complexes of different stoichiometries (tables).