Experimental Dissociation Research Articles

Experimental Data and Predictions of Dissociation Conditions for Ethane and Propane Simple Hydrates in the Presence of Methanol, Ethylene Glycol, and Triethylene Glycol Aqueous Solutions

Experimental dissociation data for ethane and propane simple hydrates in the presence of (0.05 and 0.15) mass fractions of methanol, ethylene glycol, and triethylene glycol aqueous solutions are reported in this work. The experimental data have been measured using an isochoric method. All the experimental data are compared with the predictions of a general correlation (HWHYD correlation) and a thermodynamic model (HWHYD model). The agreements between the experimental and predicted data are generally found acceptable.

Experimental Measurements and Predictions of Dissociation Conditions for Methane, Ethane, Propane, and Carbon Dioxide Simple Hydrates in the Presence of Diethylene Glycol Aqueous Solutions

Experimental gas hydrate dissociation data for methane + 0.066 and 0.168 mass fractions diethylene glycol aqueous solution, ethane + 0.071 and 0.163 mass fractions diethylene glycol aqueous solution, propane + 0.073 and 0.164 mass fractions diethylene glycol aqueous solution, and carbon dioxide + 0.074 and 0.163 mass fractions diethylene glycol aqueous solution systems are reported herein. The new experimental data have been measured using an isochoric method. All the experimental data are compared with the predictions of a general correlation and a thermodynamic model, and the agreements between the experimental and predicted data are found to be generally acceptable.

Can n-Propanol Form Hydrate?

Alcohols are generally considered hydrate inhibitors. The fact that 2-propanol, in addition to tert-butanol can form hydrates, suggests further investigation of this issue is required. In light of this, it was decided to assess the potential for hydrate formation by n-propanol. However, there are at present no data concerning its effects on hydrate stability available in the open literature. Here, we present freezing point data of n-propanol solutions (up to 80 mass %). These data suggest existence of a peritectic point at 263.05 K and formation of clathrate hydrate in the n-propanol−water system. To confirm whether n-propanol, like 2-propanol, forms mixed hydrates with structure I formers at elevated pressures, dissociation conditions were measured for aqueous solution of 10, 16.4, and 25 mass % n-propanol in the presence of methane at pressures up to 40 MPa and natural gas at around 10 MPa. The results show that n-propanol does not display a hydrate inhibition effect, which would be expected from an alcohol and may, in fact, take part in clathrate formation. Consequently, n-propanol has been modeled as a hydrate-forming compound by use of a thermodynamic model. Comparisons between experimental hydrate dissociation data and model predictions suggest that n-propanol may take part in structure II hydrate formation, occupying the large cavity of the hydrate structure.

Kinetic analysis of a human chorionic gonadotropin-β epitope–paratope interaction

Kinetics of protein–protein or ligand–ligate interaction has predominantly been studied by optical spectroscopy (particularly fluorescence) and surface plasmon resonance biosensors. Almost all such studies are based on association kinetics between ligand–ligate and suffer from certain methodological and interpretational limitations. Therefore, kinetic analyses of dissociation data of such interactions become indispensable. In the present investigation, the radiolabeled human chorionic gonadotropin-β (125IhCGβ) was employed as a probe and nitrocellulose (NC) as a solid support to immobilize monoclonal antibody (MAb) G1G10.1. The NC–G1G10.1–125IhCGβ complex (NCcom) was prepared and the dissociation of radiolabeled hCGβ was carried out in the presence of excess unlabeled ligate. From the experimental dissociation data under varying ionic strength, dissociation constants (k− 1), association constants (k+1) and affinity constants (ka) were calculated. The values obtained were utilized in exploring the amino acid residues constituting an epitopic region of hCGβ involved in interaction with the complementary paratope on MAb G1G10.1. Kinetic data of the present study supported our recently published findings [using single step-solid phase radioimmunoassay (SS-SPRIA)] that the core region of hCGβ epitope consists of Arg (94,95) and Asp (99) while a Lys (104) and a His (106) are in proximity to the core epitopic region. Based on the results of present investigation, we conclude that dissociation kinetics coupled with SS-SPRIA unequivocally provides considerable insight into the study of ligand–ligate interactions and epitope analysis.

Ground State Potential Energy Curve and Dissociation Energy of MgH

New high-resolution visible emission spectra of the MgH molecule have been recorded with high signal-to-noise ratios using a Fourier transform spectrometer. Many bands of the A 2Pi-->X 2Sigma+ and B' 2Sigma+-->X 2Sigma+ electronic transitions of 24MgH were analyzed; the new data span the v' = 0-3 levels of the A 2Pi and B'2Sigma+ excited states and the v''=0-11 levels of the X 2Sigma+ ground electronic state. The vibration-rotation energy levels of the perturbed A 2Pi and B' 2Sigma+ states were fitted as individual term values, while those of the X 2Sigma+ ground state were fitted using the direct-potential-fit approach. A new analytic potential energy function that imposes the theoretically correct attractive potential at long-range, and a radial Hamiltonian that includes the spin-rotation interaction were employed, and a significantly improved value for the ground state dissociation energy of MgH was obtained. The v''=11 level of the X 2Sigma+ ground electronic state was found to be the highest bound vibrational level of 24MgH, lying only about 13 cm(-1) below the dissociation asymptote. The equilibrium dissociation energy for the X 2Sigma+ ground state of 24MgH has been determined to be De=11104.7+/-0.5 cm(-1) (1.37681+/-0.00006 eV), whereas the zero-point energy (v''=0) is 739.11+/-0.01 cm(-1). The zero-point dissociation energy is therefore D0=10365.6+/-0.5 cm(-1) (1.28517+/-0.00006 eV). The uncertainty in the new experimental dissociation energy of MgH is more than 2 orders of magnitude smaller than that for the best value available in the literature. MgH is now the only hydride molecule other than H2 itself for which all bound vibrational levels of the ground electronic state are observed experimentally and for which the dissociation energy is determined with subwavenumber accuracy.

Experimental Data and Predictions of Dissociation Conditions for Ethane and Propane Simple Hydrates in the Presence of Distilled Water and Methane, Ethane, Propane, and Carbon Dioxide Simple Hydrates in the Presence of Ethanol Aqueous Solutions

Experimental gas hydrate dissociation data for ethane + distilled water, propane + distilled water, methane + 0.05 and 0.1 mass fraction ethanol aqueous solution, ethane + 0.05 and 0.1 mass fraction ethanol aqueous solution, propane + 0.05 and 0.1 mass fraction ethanol aqueous solution, and carbon dioxide + 0.05 and 0.1 mass fraction ethanol aqueous solution systems are reported herein. The new experimental data have been measured using an isochoric method. All the experimental data are compared with the predictions of a general correlation and a thermodynamic model. The agreements between the experimental and predicted data are generally found to be acceptable. The hydrate dissociation data for ethane + distilled water and propane + distilled water systems are also compared with some experimental data reported in the literature, and acceptable agreements between the data indicate the reliability of the experimental technique used in this study.

Accurate studies on dissociation energies of diatomic molecules

The molecular dissociation energies of some electronic states of hydride and N2 molecules were studied using a parameter-free analytical formula suggested in this study and the algebraic method (AM) proposed recently. The results show that the accurate AM dissociation energies D e AM agree excellently with experimental dissociation energies D e expt , and that the dissociation energy of an electronic state such as the 23Δg state of 7Li2 whose experimental value is not available can be predicted using the new formula.

Ground states of the Mo2, W2, and CrMo molecules: A second and third order multireference perturbation theory study

The potential energy curves of the molecules Mo(2), W(2), and CrMo have been studied ab initio using large basis sets and the "n-electron valence state perturbation theory" up to the third order in the energy. The third order results for Mo(2) and W(2) reproduce the equilibrium distances r(e) and the harmonic frequencies omega(e) in fairly good accordance with the experimental values but tend to underestimate the dissociation energy. The CrMo molecule, for which experimental dissociation energy data do not exist yet, is predicted to have a value for D(e) of approximately 2.5 eV.

Experimental dissociation of neural circuits underlying conditioned avoidance and hypophagic responses to lithium chloride

We previously reported that noradrenergic (NA) neurons in the nucleus of the solitary tract (NST) are necessary for exogenous CCK octapeptide to inhibit food intake in rats. To determine whether NST NA neurons also are necessary for lithium chloride (LiCl) to inhibit food intake and/or to support conditioned avoidance behavior, saporin toxin conjugated to an antibody against dopamine beta hydroxylase (DSAP) was microinjected bilaterally into the NST to ablate resident NA neurons. DSAP and sham control rats subsequently were tested for the ability of LiCl (0.15M, 2% body wt) to inhibit food intake and to support conditioned flavor avoidance (CFA). LiCl-induced hypophagia was significantly blunted in DSAP rats, and those with the most extensive loss of NST NA neurons demonstrated the most attenuated LiCl-induced hypophagia. Conversely, LiCl supported a robust CFA that was of similar magnitude in sham control and DSAP rats, including rats with the most extensive NA lesions. A terminal c-Fos study revealed intact LiCl-induced c-Fos expression in the lateral parabrachial nucleus and central amygdala in DSAP rats, despite significant loss of NST NA neurons and attenuated c-Fos activation of corticotropin-releasing hormone-positive neurons in the paraventricular nucleus of the hypothalamus (PVN). Thus, NST NA neurons contribute significantly to LiCl-induced hypophagia and recruitment of stress-responsive PVN neurons but appear to be unnecessary for CFA learning and expression. These findings support the view that distinct central nervous system circuits underlie LiCl-induced inhibition of food intake and conditioned avoidance behavior in rats.

Behavioural evidence for separating components within visuo-spatial working memory

Several different sources of evidence support the idea that visuo-spatial working memory can be segregated into separate cognitive subsystems. However, the nature of these systems remains unclear. Recently we reported data from neurological patients suggesting that information about visual appearance is retained in a different subsystem from information about spatial location. In this paper we report latency data from neurologically intact participants showing an experimental double dissociation between memory for appearance and memory for location. This was achieved by use of a selective dual task interference technique. This pattern provides evidence supporting the segregation of visuo-spatial memory between two systems, one of which supports memory for stimulus appearance and the other which supports memory for spatial location.

Infrared photodissociation of a water molecule from a flexible molecule-H2O complex: Rates and conformational product yields following XH stretch excitation

Infrared-ultraviolet hole-burning and hole-filling spectroscopies have been used to study IR-induced dissociation of the tryptamine.H2O and tryptamine.D2O complexes. Upon complexation of a single water molecule, the seven conformational isomers of tryptamine collapse to a single structure that retains the same ethylamine side chain conformation present in the most highly populated conformer of tryptamine monomer. Infrared excitation of the tryptamine.H2O complex was carried out using a series of infrared absorptions spanning the range of 2470-3715 cm-1. The authors have determined the conformational product yield over this range and the dissociation rate near threshold, where it is slow enough to be measured by our methods. The observed threshold for dissociation occurred at 2872 cm-1 in tryptamine.H2O and at 2869 cm-1 in tryptamine.D2O, with no dissociation occurring on the time scale of the experiment (approximately 2 micros) at 2745 cm-1. The dissociation time constants varied from approximately 200 ns for the 2869 cm-1 band of tryptamine.D2O to approximately 25 ns for the 2872 cm-1 band of tryptamine.H2O. This large isotope dependence is associated with a zero-point energy effect that increases the binding energy of the deuterated complex by approximately 190 cm-1, thereby reducing the excess energy available at the same excitation energy. At all higher energies, the dissociation lifetime was shorter than the pulse duration of our lasers (8 ns). At all wavelengths, the observed products in the presence of collisions are dominated by conformers A and B of tryptamine monomer, with small contributions from the other minor conformers. In addition, right at threshold (2869 cm-1), tryptamine.D2O dissociates exclusively to conformer A in the absence of collisions with helium, while both A and B conformational products are observed in the presence of collisions with helium. Using resolution-of-identity approximation to second-order Moller-Plesset binding energies extrapolated to the complete basis set limit and harmonic vibrational frequencies and transition states calculated at the density functional limit B3LYP/6-31+G* level of theory, Rice-Ramsperger-Kassel-Marcus (RRKM) predictions for the dissociation, isomerization, and water shuttling rates as a function of energy are made. At threshold, the experimental dissociation rate is almost 10(3) faster than RRKM predictions. Reasons for this apparent non-RRKM behavior will be discussed.

Sphingosine 1-phosphate p Ka and binding constants: Intramolecular and intermolecular influences

The dissociation constant for an ionizable ligand binding to a receptor is dependent on its charge and therefore on its environmentally-influenced p K a value. The p K a values of sphingosine 1-phosphate (S1P) were studied computationally in the context of the wild type S1P 1 receptor and the following mutants: E3.29Q, E3.29A, and K5.38A. Calculated p K a values indicate that S1P binds to S1P 1 and its site mutants with a total charge of −1, including a +1 charge on the ammonium group and a −2 charge on the phosphate group. The dissociation constant of S1P binding to these receptors was studied as well. The models of wild type and mutant proteins originated from an active receptor model that was developed previously. We used ab initio RHF/6-31+G(d) to optimize our models in aqueous solution, where the solvation energy derivatives are represented by conductor-like polarizable continuum model (C-PCM) and integral equation formalism polarizable continuum model (IEF-PCM). Calculation of the dissociation constant for each mutant was determined by reference to the experimental dissociation constant of the wild type receptor. The computed dissociation constants of the E3.29Q and E3.29A mutants are three to five orders of magnitude higher than those for the wild type receptor and K5.38A mutant, indicating vital contacts between the S1P phosphate group and the carboxylate group of E3.29. Computational dissociation constants for K5.38A, E3.29A, and E3.29Q mutants were compared with experimentally determined binding and activation data. No measurable binding of S1P to the E3.29A and E3.29Q mutants was observed, supporting the critical contacts observed computationally. These results validate the quantitative accuracy of the model.

Improved direct diabatization and coupled potential energy surfaces for the photodissociation of ammonia

Diabatic potential energy surfaces are a convenient starting point for dynamics calculations of photochemical processes, and they can be calculated by the fourfold way direct diabatization scheme. Here we present an improved definition of the reference orbital for applying the fourfold way direct diabatization scheme to ammonia. The improved reference orbital is a geometry-dependent hybrid orbital that allows one to define consistent dominant configuration lists at all geometries important for photodissociation. Using diabatic energies calculated with the new reference orbital and consistent dominant configuration lists, we have refitted the analytical representations of the ground and the first electronically excited singlet-state potential energy surfaces and the diabatic coupling surface. Improved functional forms were used to reproduce the experimental dissociation energies and excitation energies, which will be important for subsequent simulations of photochemical dynamics. We find that the lowest-energy conical intersection point is at 5.16 eV, with C 2v symmetry.

Ab Initio Study of Bonding between Nucleophilic Species and the Nitroso Group

The bonding between anionic nucleophiles and the nitroso group has been studied in the common nitrosating agents nitroso chloride (ONCl), nitroso bromide (ONBr), nitroso thiocyanate (ONSCN), and dinitrogen trioxide (N2O3) in aqueous solution. A variety of theoretical methods were employed, including ab initio, density functional theory (DFT), and composite theoretical techniques, with solvent effects described using the polarizable continuum model (PCM). Experimental nitroso bond heterolytic dissociation free energies were accurately reproduced with a number of composite theoretical methods, the most successful being CBS-Q and G2MP2, with average errors of 3.1 and 3.4 kJ mol(-1), respectively. Using the MP2 and B3LYP methods, calculations were made with correlation consistent basis sets up to quadruple-zeta, extrapolated to the complete basis set (CBS) limit. The MP2/CBS calculations were accurate to around 10 kJ mol(-1), while the B3LYP/CBS calculations routinely overpredicted experimental bond free energies by ca. 40 kJ mol(-1). It is therefore highly recommended that B3LYP energies are not used for nitroso compounds, although other results demonstrate that the B3LYP method provides a good account of nitroso compound geometries, frequencies, and entropies. Single-point CBS energy calculations using MP2/aug-cc-pVQZ geometries and frequencies showed that the MP4(SDTQ) and QCISD(T) methods provide a slight improvement over MP2 at the CBS limit, although the inclusion of triple excitations is necessary to achieve this improvement in accuracy. Enthalpy-entropy compensation was also discovered, with an average isoequilibrium temperature of 825 K. This relatively large isoequilibrium temperature indicates that enthalpic effects dominate over entropic ones.

Multiple memory systems

The term multiple memory systems describes the idea that there are several independent parallel systems of neural structures each of which is specialized to process and store a different kind of information. A major form of evidence for this idea is experimental dissociations of brain structures and memory types in humans and rats. In both species, damage to the medial temporal lobes (hippocampus and related structures) impairs declarative memory but leaves procedural (skill) memory and emotional memory (Pavlovian conditioning) intact. Damage to the basal ganglia (caudate nucleus) impairs only procedural memory, and damage to the amygdala impairs only emotional memory. Other evidence shows that the outputs of the systems interact to control behavior both cooperatively and competitively.

Temporal information processing and pitch discrimination as predictors of general intelligence.

In the present study, the relationship between performance on temporal and pitch discrimination and psychometric intelligence was investigated in a sample of 164 participants by means of an experimental dissociation paradigm. Performance on both temporal and pitch discrimination was substantially related to psychometric intelligence (r=.43 and r =.39). Regression analysis and structural equation modeling suggested that both psychophysical domains can be considered as valid predictors of psychometric intelligence. Both predictor variables contributed substantial portions of both shared and unique variance to the prediction of individual differences in psychometric intelligence. Thus, the present study yielded further evidence for a functional relationship between psychometric intelligence and temporal as well as pitch discrimination acuity. Eventually, findings are consistent with the notion that temporal discrimination - in addition to general aspects of sensory discrimination shared with pitch discrimination reflects specific intelligence-related aspects of neural information processing.

N–N 2 state to state vibrational-relaxation and dissociation rates based on quasiclassical calculations

Interpolation formulas are presented to reproduce the rate coefficients for vibrational–translational energy exchange and dissociation for the N + N 2 collision process. The original data have been obtained by quasiclassical method in a detailed way, including the effect of molecular rotation. The fitting procedure results are compared with original data and the related error is evaluated. Comparison with global experimental dissociation results is also presented.

The use of recurrent signals about adaptation for subsequent saccade programming depends on object structure

Executing sequences of accurate saccadic eye movements supposes the use of signals carrying information about the first saccade for updating the predetermined motor plan of the subsequent saccades. The present study examines the signals used in planning a second saccade when subjects made two successive saccades towards one long or two short peripheral objects displayed before the first saccade execution. Different first eye movement signals could be used: desired eye movement signals, representing the movement necessary for attaining the intended target, or actual eye movement signals, representing the movement actually executed. Experimental dissociation of desired and actual eye movement signals is made possible by adaptive modifications of the first saccade, obtained by transfer of single saccade adaptation, during which the motor vector was progressively modified in response to the systematic intra-saccadic step of a single target. Whether the second saccade used the actual eye movement signal to compensate or not for the adaptive changes in the first saccade depended on which object properties were relevant for saccade planning. Compensation was observed for saccades that aimed for a new object (between-object saccades) because adaptation modifies relative object location. No compensation was observed for saccades that explored an extended object (within-object saccades). Implications for the on-line control of subsequent eye movements are discussed.

Experimental Gas Hydrate Dissociation Pressures for Pure Methane in Aqueous Solutions of MgCl2 and CaCl2 and for a (Methane + Ethane) Gas Mixture in an Aqueous Solution of (NaCl + MgCl2)

Gas hydrate dissociation pressures along the hydrate−liquid−gas equilibrium line in the temperature range (273 to 292) K and for pressures up to 23 MPa have been determined for methane in aqueous unsaturated magnesium chloride solutions w = (1, 5, 10, and 15) % of MgCl2, in a calcium chloride solution w = 17.05 % of CaCl2, and for a (methane + ethane) mixture in an aqueous solution of sodium chloride and magnesium chloride w(NaCl) = 5 % + w(MgCl2) = 6.09 % applying an isochoric method. For the methane system, it is shown that considerable deviation from “ideal” behavior occurs at high MgCl2 concentrations. A gas hydrate calculation model has been applied being able to reproduce the experimental dissociation pressures to within ± 2 % as well as efficiently predicting the dissociation pressures and the inhibiting effects of various other electrolyte solutions for gas hydrate systems with pure gases and gas mixtures.

Development of thermodynamic models for simulating probe dissociation profiles in fluorescence in situ hybridization

Stringency in ribosomal RNA (rRNA)-targeted fluorescence in situ hybridization (FISH) is typically adjusted with formamide, and the optimum formamide concentration at which the probe can hybridize with the target rRNA, but not with rRNAs with mismatches, is to be found experimentally. This is a difficult task when target or closest non-target organisms are not available in pure culture, or when there are numerous non-targets of concern. The objective of this work was to formulate mechanistic models capable of simulating the effect of formamide on probe dissociation. Using a previously described equilibrium model of FISH [Yilmaz and Noguera (2004) Applied and Environmental Microbiology 70(12):7126-7139] as the basis, the effect of formamide on free energy changes of probe-target duplex formation (DeltaG(1)(0)) and folding of target region (DeltaG(3)(0)) was simulated to be linear, and models differing in the definitions of the slopes of these relationships (m(1) and m(3)) were calibrated using experimental dissociation profiles for 27 probes targeting the 16S rRNA of Escherichia coli (E. coli). A good level of predictive power was obtained when m(1) was linearly related to probe length and when m(3) was made proportional to DeltaG(3)(0). The effect of single mismatches on probe dissociation with formamide was also studied, although at a preliminary level. The expected changes in DeltaG(1)(0) with the introduction of mismatches were not sufficient to capture the overall trends of mismatched dissociation profiles. In conclusion, this study offers the first theoretical method to calculate dissociation profiles for perfectly matched probes, and suggests a direction to systematically evaluate the effect of formamide on mismatched probes.