Dissociation Reactions Of Complexes Research Articles

Intact Transition Epitope Mapping-Force Interferences by Variable Extensions (ITEM-FIVE).

Investigations on binding strength differences of non-covalent protein complex components were performed by mass spectrometry. T4 fibritin foldon (T4Ff) is a well-studied miniprotein, which together with its biotinylated version served as model system to represent a compactly folded protein to which an Intrinsically Disordered Region (IDR) was attached. The apparent enthalpies of the gas phase dissociation reactions of the homo-trimeric foldon F-F-F and of the homo-trimeric triply biotinylated foldon bF-bF-bF have been determined to be rather similar (3.32 kJ/mol and 3.85 kJ/mol) but quite distinct from those of the singly and doubly biotinylated hetero-trimers F-F-bF and F-bF-bF (1.86 kJ/mol and 1.08 kJ/mol). Molecular dynamics simulations suggest that the ground states of the (biotinylated) T4Ff trimers are highly symmetric and well comparable to each other, indicating that the energy levels of all four (biotinylated) T4Ff trimer ground states are nearly indistinguishable. The experimentally determined differences and/or similarities in enthalpies of the complex dissociation reactions are explained by entropic spring effects, which are noticeable in the T4Ff hetero-trimers but not in the T4Ff homo-trimers. A lowering of the transition state energy levels of the T4Ff hetero-trimers seems likely because the biotin moieties, mimicking intrinsically disordered regions (IDRs), induced asymmetries in the transition states of the biotinylated T4Ff hetero-trimers. This transition state energy level lowering effect is absent in the T4Ff homo-trimer, as well as in the triply biotinylated T4Ff homo-trimer. In the latter, the IDR-associated entropic spring effects on complex stability cancel each other out. ITEM-FIVE enabled semi-quantitative determination of energy differences of complex dissociation reactions, whose differences were modulated by IDRs attached to compactly folded proteins.

Mass Spectrometric ITEM-ONE and ITEM-TWO Analyses Confirm and Refine an Assembled Epitope of an Anti-Pertuzumab Affimer.

Intact Transition Epitope Mapping-One-step Non-covalent force Exploitation (ITEM-ONE) analysis reveals an assembled epitope on the surface of Pertuzumab, which is recognized by the anti-Pertuzumab affimer 00557_709097. It encompasses amino acid residues NSGGSIYNQRFKGR, which are part of CDR2, as well as residues FTLSVDR, which are located on the variable region of Pertuzumab's heavy chain and together form a surface area of 1381.46 Å2. Despite not being part of Pertuzumab's CDR2, the partial sequence FTLSVDR marks a unique proteotypic Pertuzumab peptide. Binding between intact Pertuzumab and the anti-Pertuzumab affimer was further investigated using the Intact Transition Epitope Mapping-Thermodynamic Weak-force Order (ITEM-TWO) approach. Quantitative analysis of the complex dissociation reaction in the gas phase afforded a quasi-equilibrium constant (KD m0g#) of 3.07 × 10-12. The experimentally determined apparent enthalpy (ΔHm0g#) and apparent free energy (ΔGm0g#) of the complex dissociation reaction indicate that the opposite reaction-complex formation-is spontaneous at room temperature. Due to strong binding to Pertuzumab and because of recognizing Pertuzumab's unique partial amino acid sequences, the anti-Pertuzumab affimer 00557_709097 is considered excellently suitable for implementation in Pertuzumab quantitation assays as well as for the accurate therapeutic drug monitoring of Pertuzumab in biological fluids.

Native and compactly folded in-solution conformers of pepsin are revealed and distinguished by mass spectrometric ITEM-TWO analyses of gas-phase pepstatin A - pepsin complex binding strength differences.

Pepsin, because of its optimal activity at low acidic pH, has gained importance in mass spectrometric proteome research as a readily available and easy-to-handle protease. Pepsin has also been study object of protein higher-order structure analyses, but questions about how to best investigate pepsin in-solution conformers still remain. We first determined dependencies of pepsin ion charge structures on solvent pH which indicated the in-solution existence of (a) natively folded pepsin (N) which by nanoESI-MS analysis gave rise to a narrow charge state distribution with an 11-fold protonated most intense ion signal, (b) unfolded pepsin (U) with a rather broad ion charge state distribution whose highest ion signal carried 25 protons, and (c) a compactly folded pepsin conformer (C) with a narrow charge structure and a 12-fold protonated ion signal in the center of its charge state envelope. Because pepsin is a protease, unfolded pepsin became its own substrate in solution at pH 6.6 since at this pH some portion of pepsin maintained a compact/native fold which displayed enzymatic activity. Subsequent mass spectrometric ITEM-TWO analyses of pepstatin A - pepsin complex dissociation reactions in the gas phase confirmed a very strong binding of pepstatin A by natively folded pepsin (N). ITEM-TWO further revealed the existence of two compactly folded in-solution pepsin conformers (Ca and Cb) which also were able to bind pepstatin A. Binding strengths of the respective compactly folded pepsin conformer-containing complexes could be determined and apparent gas phase complex dissociation constants and reaction enthalpies differentiated these from each other and from the pepstatin A - pepsin complex which had been formed from natively folded pepsin. Thus, ITEM-TWO turned out to be well suited to pinpoint in-solution pepsin conformers by interrogating quantitative traits of pepstatin A - pepsin complexes in the gas phase.

Mass Spectrometric Analysis of Antibody-Epitope Peptide Complex Dissociation: Theoretical Concept and Practical Procedure of Binding Strength Characterization.

Electrospray mass spectrometry is applied to determine apparent binding energies and quasi equilibrium dissociation constants of immune complex dissociation reactions in the gas phase. Myoglobin, a natural protein-ligand complex, has been used to develop the procedure which starts from determining mean charge states and normalized and averaged ion intensities. The apparent dissociation constant 3.60 × 10−12 for the gas phase heme dissociation process was calculated from the mass spectrometry data and by subsequent extrapolation to room temperature to mimic collision conditions for neutral and resting myoglobin. Similarly, for RNAse S dissociation at room temperature a 4.03 × 10−12 was determined. The protocol was tested with two immune complexes consisting of epitope peptides and monoclonal antibodies. For the epitope peptide dissociation reaction of the FLAG peptide from the antiFLAG antibody complex an apparent gas phase dissociation constant 4.04 × 10−12 was calculated. Likewise, an apparent 4.58 × 10−12 was calculated for the troponin I epitope peptide—antiTroponin I antibody immune complex dissociation. Electrospray mass spectrometry is a rapid method, which requires small sample amounts for either identification of protein-bound ligands or for determination of the apparent gas phase protein-ligand complex binding strengths.

Formation and dissociation reactions of complexes involving interstitial carbon and oxygen defects in silicon

We present a detailed first-principles study which explores the configurational space along the relevant reactions and migration paths involving the formation and dissociation of interstitial carbon-oxygen complexes, $\mathrm{C_{i}O_{i}}$ and $\mathrm{C_{i}O_{2i}}$, in silicon. The formation/dissociation mechanisms of $\mathrm{C_{i}O_{i}}$ and $\mathrm{C_{i}O_{2i}}$ are found as occurring via capture/emission of mobile $\mathrm{C_{i}}$ impurities by/from O-complexes anchored to the lattice. The lowest activation energies for dissociation of $\mathrm{C_{i}O_{i}}$ and $\mathrm{C_{i}O_{2i}}$ into smaller moieties are 2.3 eV and 3.1 eV, respectively. The first is compatible with the observed annealing temperature of $\mathrm{C_{i}O_{i}}$ , which occurs at around 400 $^{\circ}$C, and below the threshold for $\mathrm{O_{i}}$ diffusion. The latter exceeds significantly the measured activation energy for the annealing of $\mathrm{C_{i}O_{2i}}$ ($E_{\mathrm{a}}=2.55$ eV). We propose that instead of dissociation, the actual annealing mechanism involves the capture of interstitial oxygen by $\mathrm{C_{i}O_{2i}}$, thus being governed by the migration barrier of $\mathrm{O_{i}}$ ($E_{\mathrm{m}}=2.53$ eV). The study is also accompanied by measurements of hole capture cross sections and capture barriers of $\mathrm{C_{i}O_{i}}$ and $\mathrm{C_{i}O_{2i}}$. In combination with previously reported data, we find thermodynamic donor transitions which are directly comparable to the first-principles results. The two levels exhibit close features, conforming to a model where the electronic character of $\mathrm{C_{i}O_{2i}}$ can be described by that of $\mathrm{C_{i}O_{i}}$ perturbed by a nearby O atom.

Chemical Exchange Reaction Effect on Polarization Transfer Efficiency in SLIC-SABRE.

Signal Amplification By Reversible Exchange (SABRE) is a new and rapidly developing hyperpolarization technique. The recent discovery of Spin-Lock Induced Crossing SABRE (SLIC-SABRE) showed that high field hyperpolarization transfer techniques developed so far were optimized for singlet spin order that does not coincide with the experimentally produced spin state. Here, we investigated the SLIC-SABRE approach and the most advanced quantitative theoretical SABRE model to date. Our goal is to achieve the highest possible polarization with SLIC-SABRE at high field using the standard SABRE system, IrIMes catalyst with pyridine. We demonstrated the accuracy of the SABRE model describing the effects of various physical parameters such as the amplitude and frequency of the radio frequency field, and the effects of chemical parameters such as the exchange rate constants. By fitting the model to the experimental data, the effective life time of the SABRE complex was estimated, as well as the entropy and enthalpy of the complex-dissociation reaction. We show, for the first time, that this SLIC-SABRE model can be useful for the evaluation of the chemical exchange parameters that are very important for the production of highly polarized contrast agents via SABRE.

Mutual effects of equatorial and axial ligands on the stability of praseodymium(III) and samarium(III) phthalocyanine complexes

The nature of axial ligand in lanthanide(III) phthalocyanine complexes markedly affects their physicochemical properties. The role of axially coordinated anion in the stability of coordination sphere was determined by the example of praseodymium(III) and samarium(III) phthalocyanine complexes (X)LnPc (X = Cl–, Br–, AcO–). The synthesis and the results of dissociation kinetics study of the complexes under the action of AcOH in ethanol solution were presented. Stability parameters for the complexes, kinetic equations, and activation parameters for the dissociation of coordination centers were determined. Effect of the axial ligand on the strength of macrocycle binding and the stoichiometric mechanism of complex dissociation reaction was considered. The state of axial bond in the complexes was shown to determine the value of reaction order toward acid (1 or 2) and the nature of rate-limiting step of the reaction: with participation of molecule or ionized in the axial direction complex.

Composition and Properties of Saturated Vapor over NaBr-LnBr3 (Ln = La, Lu) Binary Systems

The NaBr−LnBr3 (Ln = La, Lu) binary systems and their individual components NaBr, LaBr3 and LuBr3 were studied by the Knudsen effusion cell mass spectrometry (KEMS) and the density functional theory (DFT). The complex molecules NaLnBr4, Na2LnBr5 and both positive Na2LnBr4 +, Na3LnBr5 + and negative NaLnBr5 − complex ions have been observed in saturated vapor along with the molecules and ions inherent to the pure components. Molecular parameters and energy characteristics of species were obtained by quantum-chemical calculations. The partial pressures of molecules have been obtained. The equilibrium constants of dissociation reactions of complexes were determined and the enthalpies of reactions have been calculated using the second and third laws of thermodynamics. The enthalpies of formation of complex molecules and ions have been obtained.

Collision induced dissociation of deprotonated guanine: Fragmentation of pyrimidine ring and water adduct formation

This investigation of collision induced dissociation of deprotonated guanine was conducted by using sequential ion trap tandem mass spectrometry and isotopically labelled guanine analogs to clarify the complex dissociation reactions of pyrimidine ring of deprotonated guanine. The fragmentation patterns confirmed that the gas-phase dissociation processes are initiated from the pyrimidine ring through charge site controlled reactions involving charge redistribution, proton transfer and nucleophilic attack to generate the three primary fragment products by the elimination of ammonia, cyanamide and isocyanic acid. Our findings shed light on the process of pyrimidine ring opening and closure prior to the decomposition of deprotonated guanine and therefore the identity of N1 and exocyclic N 2 is lost in deprotonated guanine as a result of scrambling. Intriguing association products of water addition to fragment ions have been structurally characterized to establish the role of ketene group in the selective gas-phase reaction of water addition and the formation of water adducts. The elimination of CO 2 from negatively charged water adducts provides evidence for the covalent attachment of water to the ketene moiety. The established mechanisms of the dissociation reactions of pyrimidine ring should provide a basis for the structural elucidation of guanine relevant species modified on its active sites. To lend support for our proposals, collision induced dissociation study of 8-phenyl-2′-deoxyguanosine adduct was performed.

Copper(II) complexes of tetraaza macrocycles bearing pendant arms: syntheses, structures and properties

A new difunctionalized tetraaza macrocycle, 1,8-bis(2-hydroxyethyl)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, H2L2 has been synthesized in one step by the reaction of ethylene oxide and C-rac-5,5,7,12,12, 14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (L1). The crystal structure of [Cu(H2L2)][ClO4]2 1 shows the metal ion in tetragonally elongated octahedral geometry, co-ordinated by the oxygen atoms of the pendant arms in the trans-axial position. Copper(II) complexes were also synthesized and characterized from other 1,8-disubstituted macrocyclic ligands L3, L4, HL5, H2L6, L8 and H2L9. The molecular structure of [CuL3][ClO4]2 2 (R1 = R2 = CH2CH2CN) and [CuL5]ClO4, 4 (R1 = H, R2 = CH2CO2–) shows the macrocycle in trans-I configuration with square planar and distorted square pyramidal geometries respectively at the metal centers. The structures of complexes [CuL8][ClO4]2 6 [L8 = 1,8-bis(2-cyanoethyl)-4,7,11,14-tetramethyl-1,4,8,11-tetraazacyclotetradecane] and [Cu(H2L9)][ClO4]2 7 (corresponding CH2CO2H derivative) show the macrocyclic ligand in the trans-III configuration. Interestingly the two pendant acetic acid groups of H2L9 in 7 remain protonated and co-ordinate through the carbonyl oxygen atoms in trans-octahedral geometry. The cyclic voltammetric studies of the complexes revealed that the copper(I) oxidation state is highly stabilized by the ligands L3 and L8. The pH dependent co-ordination geometry changes of complexes 4, [CuL6] 5 (R1 = R2 = CH2CO2–) and 7 based on the changes in their electronic spectra are discussed. The kinetics of acid promoted dissociation reactions of complexes 2 and 6 has been studied in HCl–NaCl solutions (I = 5.0 M). The possible mechanisms of the reactions, the factors influencing the rate and the relative importance of the solvent separation and protonation pathways are discussed.

Kinetics of actinide complexation reactions

We report herein a summary of what is known about actinide complexation kinetics. The systems include actinide ions in the four principal oxidation states (III, IV, V, and VI) and complex formation and dissociation rates with both simple and complex ligands. Complex formation reactions tend to be rapid, accessible only to rapid-scan and equilibrium perturbation techniques. Complex dissociation reactions exhibit a wider range of rates and are generally more accessible using standard analytical methods. Literature results are described and correlated with the known properties of the individual ions.

Complex formations of silver(I) trifluoroacetate and trifluoromethanesulfonate with benzene and cyclohexene

An apparatus for measurements of equilibrium ligand vapor pressure has been applied in order to determine the stoichiometry of benzene and cyclohexene complexes of silver(I) trifluoroacetate (AgCF 3CO 2) and silver(I) trifluoromethanesulfonate (silver(I) triflate, AgCF 3SO 3) in the solid state. It has been found that the equilibrium leads the formation of such complexes as: (AgCF 3CO 2) 2(C 6H 6), (AgCF 3CO 2) 2(C 6H 10), (AgCF 3CO 2) 2(C 6H 10) 3, (AgCF 3SO 3) 2(C 6H 6), (AgCF 3SO 3)(C 6H 6), (AgCF 3SO 3)(C 6H 10) and (AgCF 3SO 3)(C 6H 10) 2. The temperature dependence of the gas-solid equilibrium ligand pressure has also been examined for these complexes, and the enthalpy and entropy changes according to the following complex dissociation reactions were estimated: (AgCF 3CO 2)L m (s) ⇄ AgCF 3CO 2 (s)+mL (g): and (AgCF 3SO 3)L n (s) ⇄ AgCF 3SO 3 (s)+nL (g), where L's are benzene and cyclohexene. On the basis of the thermodynamic data obtained, the effects of the counter anion as well as the ligand on the complex stability are discussed.

Static and kinetic studies of calmodulin and melittin complex.

Ca2+ binding to calmodulin triggers conformational change of the protein which induces exposure of hydrophobic surfaces. Melittin has been believed to bind to Ca(2+)-bound calmodulin through the exposed hydrophobic surfaces. However, tryptophan fluorescence measurements and gel chromatography experiments with the melittin-calmodulin system revealed that melittin bound to calmodulin at zero salt concentration even in the absence of Ca2+; addition of salt removed melittin from Ca(2+)-free calmodulin. This means not only the hydrophobic interaction but also the electrostatic interaction contributes to the melittin-calmodulin binding. The fluorescence stopped-flow studies of the dissociation reaction of melittin-calmodulin complex revealed that Ca2+ removal from the complex induced a conformational change of calmodulin, resulting in reduction of the hydrophobic interaction between melittin and calmodulin, but the electrostatic interaction kept melittin still bound to calmodulin for a subsecond lag period, after which melittin dissociated from calmodulin. The fluorescence stopped-flow experiments on the dissociation reaction of complex of melittin and tryptic fragment(s) of calmodulin revealed that the lag period of the melittin dissociation reaction was attributable to the interaction between the C-terminal half of calmodulin and the C-terminal region of melittin.

Creep deformation and fracture of a two-phase TiAl alloy

This paper reports that gamma TiAl (L1{sub 0} structure), which is structurally stable up to about 1460{degrees}C and exhibits good specific strength, modulus, and oxidation resistance at high temperature, is a potential candidate structural material for high temperature service such as required for heat engines. Due to it inherent brittleness at ambient temperature, extensive efforts have been made in recent years to develop more ductile alloys. This was primarily done through additions of Cr, V, Mn, Nb, and Ta, and manipulation of microstructure for two-phase (gamma + alpha-2) alloys based on Ti. Depending upon heat treatments, these alloys exhibit four different types of microstructure: fully-lamellar, nearly-lamellar, duplex, and nearly-gamma. Fully-lamellar structures consisting of large grains with alternating gamma and alpha-2 platelets are know to yield high toughness and creep resistance, and duplex microstructures result in the highest ductility at room temperature. A number of researchers have studied the deformation behavior of single-phase TiAl alloys, while there are only limited number of reports on the deformation behavior of two-phase alloys. The results show that in single phase (gamma) Ti-(52-54) at.% Al binaries, the slip systems are {l brace}111{r brace} planes and dislocation of a/2 {l angle}110{r angle}, a {l angle}101{r angle}more » and a/2 {l angle}112{r angle} types are present. The a{l angle}101{r angle} and a/2 {l angle}112{r angle} dislocations are superdislocations, which were found to undergo complex dissociation reactions, creating sessile faulted dipoles and contributing to the brittleness of TiAl alloys. For two-phase alloys, only the easy-slip type unit dislocation a/2 {l angle}110{r angle} and {l brace}111{r brace} twins were present after tensile deformation at room temperature.« less

Thermochemical properties of some f-electron element β-diketonates, and metal-oxygen bond energies. lanthanum(III)β-diketonates

The standard molar enthalpies of formation of the crystalline lanthanum(III) chelate complexes with pentane-2,4-dione (acetylacetone, Hacac) and 1-phenylbutane-1,3-dione (benzoylacetone, Hbzac) were determined by the solution calorimetry method. The following values ofΔH f(s) 0 (kJ mol−1) were obtained: La(acac)3', −1916.2±7.0; La(bzac)3 · 2H2O, −2099.1 ±9.7. The enthalpies of the hypothetical complex dissociation reactions in the gaseous phase: $$LaL_{3(g)} = La_{(g)} + 3L_{(g)} and LaL_{3(g)} = La_{(g)}^{ + 3} + 3L_{(g)}^ - $$ were calculated as a measure of the mean bond dissociation energy, <D>(La-O), and the mean coordinate bond dissociation energy, <DCB>(La-O), respectively.

Kinetic aspects of l-quinuclidinyl benzilate interaction with muscarinic receptor

l-Quinuclidinyl benzilate is undoubtedly the most widely used radioactive reporter ligand for studies on muscarinic receptor. In the present Commentary the kinetic aspects of the interaction of this ligand with muscarinic receptor are summarized. On the basis of these results a kinetic mechanism has been proposed involving consequential isomerization of the receptor-ligand complex and cooperative regulation of this process by the excess of the ligand. In addition, the data give evidence of at least two different types of binding sites on the receptor. Owing to the solubilization of the receptor protein there occur remarkable changes in its kinetic properties. The kinetic analysis points to inadequacy of the simple one-step equilibrium binding scheme for l-quinuclidinyl benzilate interaction with muscarinic receptor, which may explain the apparently contradictory data in the literature, such as the large scattering of the K(d) values and the different regularities described in the case of the receptor-ligand complex dissociation reaction. That points to the conclusion that l-quinuclidinyl benzilate is an "inconvenient" ligand for receptor studies, which call for true equilibrium conditions of the system.

Kinetic analysis of actinides using differential spectrophotometry

The kinetic method developed allowed us to analyse of two-component actinide mixtures without separation. The concentration changes in the system where complex dissociation reaction takes place were determined by spectrophotometry.

A photoion–photoelectron coincidence (PIPECO) study of fragmentation rates and kinetic energy release in energy selected metastable ions

The absolute fragmentation rates and kinetic energy releases associated with the unimolecular dissociation reactions of energy selected halo-hydrocarbon ions have been investigated by photoion–photoelectron coincidence (PIPECO) spectroscopy in which nominally zero kinetic energy electrons are detected in coincidence with their corresponding fragment ions. The reactions investigated were HCl loss from C2H5Cl+ and ClCH2CH2Cl+, Cl loss from C3H3Cl+ (propargyl chloride) and Br loss from C3H3Br+ (propargyl bromide). Although the kinetic energy released in the HCl loss from C2H5Cl+ reaction is small, the other three reactions have large energy release values associated with them. We found that X loss from C3H3X+ proceeds via two paths yielding different isomeric forms of C3H3+ with markedly different kinetic energy release values. The most unusual feature in these complex dissociation reactions is that the rate of fragmentation cannot be described by a single exponential decay function but rather must be expressed as the sum of at least two exponentials. Possible explanations for two-component decay rates and their implications for the statistical theory of unimolecular decay are discussed.

The effect of 'impure' pore fluids on metamorphic dissociation reactions

Summary Comparison of experimental data from the systems MgO-CO2-H2O (closed) and MgO-CO2-A (simulating an open system) shows that the effects of H2O and A on the dissociation of magnesite are almost identical; both behave as inert components reducing the partial pressure of CO2. The dissociation temperature at constant total pressure is lowered according to the proportion of inert volatiles in the initial vapour phase. The dissociation is completed at one temperature (univariant) in an open system but in a closed system it proceeds through a temperature interval (divariant) because the vapour phase changes composition. The amount of dissociation remains small until the upper limit of the interval is reached. More complex dissociation reactions in the systems CaO-MgO-CO2-H2O and CaO-SiO2-CO2-H2O are described; they follow similar patterns. Under closed or partially open metamorphic conditions non-reacting pore fluid components (inert) have to be treated as one additional component for application of the mineralogical phase rule. Comparison of the pattern of metamorphic parageneses with the patterns of reactions occurring under known experimental conditions may provide information about metamorphic processes. Metamorphic reactions can be represented within a petrogenetic model with axes P, T, and pore fluid composition varying between H2O and CO2.