Relaxation In Aqueous Solutions Research Articles

Relaxation of Aqueous Solutions in Successive Dilutions of Antibodies to S100 Protein According to Luminescence Data

Relaxation of Aqueous Solutions in Successive Dilutions of Antibodies to S100 Protein According to Luminescence Data

Identical Water Dynamics in Acrylamide Hydrogels, Polymers, and Monomers in Solution: Ultrafast IR Spectroscopy and Molecular Dynamics Simulations.

The dynamics and structure of water in polyacrylamide hydrogels (PAAm-HG), polyacrylamide, and acrylamide solutions are investigated using ultrafast infrared experiments on the OD stretch of dilute HOD/H2O and molecular dynamics simulations. The amide moiety of the monomer/polymers interacts strongly with water through hydrogen bonding (H-bonding). The FT-IR spectra of the three systems indicate that the range of H-bond strengths is relatively unchanged from bulk water. Vibrational population relaxation measurements show that the amide/water H-bonds are somewhat weaker but fall within the range of water/water H-bond strengths. A previous study of water dynamics in PAAm-HG suggested that the slowing observed was due to increasing confinement with concentration. Here, for the same concentrations of the amide moiety, the experimental results demonstrate that the reorientational dynamics (infrared pump-probe experiments) and structural dynamics (two-dimensional infrared spectroscopy) are identical in the three acrylamide systems studied. Molecular dynamics simulations of the water orientational relaxation in aqueous solutions of the acrylamide monomer, trimer, and pentamer are in good agreement with the experimental results and are essentially chain length independent. The simulations show that there is a slower, low-amplitude (<7%) decay component not accessible by the experiments. The simulations examine the dynamics and structure of water H-bonded to acrylamide, in the first solvent shell, and beyond for acrylamide monomers and short chains. The experiments and simulations show that the slowing of water dynamics in PAAm-HG is not caused by confinement in the polymer network but rather by interactions with individual acrylamide moieties.

Impact of Measurement Uncertainty on Modeling of Dielectric Relaxation in Aqueous Solutions

Uncertainty analysis is performed on a coaxial probe-based dielectric spectroscopy measurement platform, and its impact on the modeling of dielectric relaxation in an aqueous solution is further analyzed. Based on the characterization theory and calibration principle of the platform, uncertainty due to the different available expressions and parameters of the calibration liquid is calculated. Then, repeatability uncertainty related to drift of the measurement platform, environment change, position variation of the probe immersed in the liquid under test (LUT), and so on is analyzed. Next, three types of water–alcohol mixtures and one group of glucose solutions are measured using the platform. Based on the measurement results, the best model is chosen to analyze the frequency dependence of the solutions’ relaxation properties. In addition, based on the uncertainty analysis, appropriate mathematical formulas are provided to model the composition dependence of the solutions’ relaxation parameters, which can be used as a liquid detection technique for chemical and biological applications.

Hydration and dielectric properties of aqueous solutions of protonated diallylmethylammonium polymer: transition from monomer to polymer

The high-frequency dielectric relaxation of aqueous solutions of protonated diallylammonium polyelectrolyte, namely poly(diallylmethylammonium trifluoroacetate) has been studied at the maximum water dispersion frequencies, 7.5–25 GHz, and temperatures of 288, 298, and 308 K. Dielectric relaxation parameters have been calculated and compared with similar characteristics of aqueous solutions of monomer, diallylmethylammonium trifluoroacetate, and pyrrolidinium trifluoroacetate salt simulated structure of pyrrolidinium polymer link. It has been concluded that although the monomer features hydrophobic hydration, its polymer exhibits hydrophilic hydration properties. This change is related to conformation of hydrophilic-hydrophobic polycations in aqueous solutions and the change in the structure of polymer links.

Super-High-Frequency Permittivity and Relaxation of Aqueous Solutions of Aluminum Chloride

The super-high-frequency dielectric properties of aqueous solutions of aluminum chloride were measured at five frequencies (13–25 GHz) at 298 K. The static permittivities and the times and other parameters of dielectric relaxation of the solutions were calculated. The concentration dependences of the hydration properties of the solutions within various concentration ranges were studied.

Aqueous solvation of amphiphilic solutes: concentration and temperature dependent study of the ultrafast polarisability relaxation dynamics

An understanding of the influence of hydrophilic and hydrophobic interactions on the dynamics of solvating water molecules is important in a diverse range of phenomena. The polarisability anisotropy relaxation dynamics of aqueous solutions of the amphiphiles TBA (t-butyl alcohol) and TMAO (trimethylamine N-oxide) have been measured as a function of concentration and temperature. TMAO is shown to have a greater effect on the picosecond relaxation dynamics of water than TBA. This result is consistent with hydrophilic interactions being mainly responsible for the slowing down the polarisability relaxation in aqueous solutions. The room temperature Raman spectral densities of the two solutions are remarkably similar to that of bulk water, an effect which is tentatively ascribed to the formation of nanoscale structure in the solutions, allowing the formation of bulk-like water pools. The temperature dependent spectral density of TMAO remains similar to that of bulk water at all temperatures, while that for TBA shows a marked decrease in the amplitude of the response usually ascribed to a water-water stretch with increasing temperature. This is discussed in terms of the temperature dependent structure of TBA aggregates in solution.

Multiple‐Frequency and Variable‐Temperature EPR Study of Gadolinium(III) Complexes with Polyaminocarboxylates: Analysis and Comparison of the Magnetically Dilute Powder and the Frozen‐Solution Spectra

AbstractAn electron paramagnetic resonance (EPR) study of glasses and magnetically dilute powders of [Gd(DTPA)(H2O)]2−, [Gd(DOTA)(H2O)]−, and macromolecular gadolinate(1−) complexes P792 was carried out at the X‐ and Q‐bands and at 240 GHz (DTPA=diethylenetriaminepentaacetato; DOTA=1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetato). The results show that the zero‐field splitting (ZFS) parameters for these complexes are quite different in a powder as compared to the frozen aqueous solution. In several complexes, an inversion of the sign of the axial component D of the zero field splitting is observed, indicating a significant structural change. In contrary to what was expected, powder samples obtained by lyophilization do not allow a more precise determination of the static ZFS parameters. The results obtained in glasses are more relevant to the problem of electron spin relaxation in aqueous solution than those obtained from powders.

Dielectric constant and dielectric relaxation in aqueous solutions of K2[PdCl4] and K2[PtCl4

The MW-dielectric properties of aqueous solutions of K2[PtCl4] (I) and K2[PdCl4] (II) were studied at 298 and 313 K in the frequency range (12–25 GHz) corresponding to the maximum dielectric constant dispersion for water and aqueous solutions of these salts. The low-frequency conductivities were measured. The static dielectric constant, the dielectric relaxation time, and the enthalpy of activation of the dielectric relaxation of the solutions were determined. Compared to pure water, in solutions of salts I and II, the orientational mobility of water molecules is increased and the network of H-bonds is violated more strongly than that of most other ions with hydrophilic hydration. It was demonstrated for the first time that dielectric spectroscopy can be used for analyzing complexation processes in systems containing aqua and hydroxo chloride complexes of metals.

Deviations from a simple Debye relaxation in aqueous solutions of differently flexible polyions induced by polymer concentration

The electrical conductivity of aqueous solutions of differently flexible polymers has been measured in the frequency range from 1 MHz to 2 GHz. This note evidences how the shape parameter alpha of the conductivity relaxation associated with the orientational polarization of the aqueous phase depends on the polymer concentration and, moreover, reflects the different concentration regimes of the polymer solution (dilute, semidilute entangled and nonentangled, and concentrated regimes). The relevance of this dependence, as far as the microscopic environment of water molecules is concerned, is briefly discussed.

The temperature dependences and methods for the functional representation of the rates of proton magnetic relaxation in aqueous solutions of electrolytes

The paper presents the results of temperature dependence measurements for the rate of proton relaxation (1/T1) in sea water with salinity 35‰ over the temperature range −22−+120°C at atmospheric pressure and in some salt solutions at two concentrations (0.5 and 1 mol/l). The possibility of approximating the temperature dependences of magnetic relaxation rates by various functions in pure water, sea water, and solutions of salts with various concentrations was studied. The parameters of these dependences and trends of their variations under the influence of salt components are reported. The most well grounded method for the functional representation of the temperature dependences of 1/T1 is the use of the sum of exponents with the number of terms depending on solution concentration. This representation takes into account structural changes in solutions as the concentration grows and corresponds to the Frenkel model of the thermal motion of molecules in aqueous solutions of electrolytes. The combined use of the parameters of the temperature dependences of the rate of relaxation represented by various functions can be a mutually augmenting method for studying the dynamic properties of aqueous solutions of electrolytes with low and moderate concentrations.

Dielectric properties of aqueous hydrochloric acid solutions

The structure-breaking effect of HCl molecules is established on the basis of the data on dielectric relaxation in aqueous solutions.

Dielectric Relaxation in Aqueous Solutions of Hydrazine and Hydrogen Peroxide: Water Structure Implications

We report dielectric relaxation studies of aqueous solutions of two water-like molecules, hydrazine and hydrogen peroxide, in the neighborhood of their glass transition temperatures, Tg. These solutions behave in a rather simple manner, reminiscent of the diols and diamines of which they are the limiting cases. Their relaxations near Tg are more nearly exponential than in most other cases, and they show essentially no secondary relaxations. Supercooled hydrazine solutions are the more stable. At the composition 20 mol % N2H4, the liquid exhibits precise time−temperature-superposition (TTS) behavior. At higher N2H4 contents, a weak deviation from TTS appears. The temperature dependence of the relaxation time follows the Vogel−Fulcher−Tammann (VFT) equation, and the strength parameter, D, is similar to that of glycerol, a liquid of intermediate fragility. The VFT divergence temperature, T0, lies close to the Kauzmann temperature, TK, determined earlier from calorimetric studies implying that the thermodynamic and kinetic measures of fragility are very similar. Tg values assessed from T(τ=100s) agree well with observed calorimetric, Tg's. Extrapolation of the relaxation time behavior to pure water would imply a Tg for water of 135−140 K; however, the dielectric behavior of amorphous solid water in the temperature range 130−160 K is completely different from that of the solutions showing no sign of the loss peak exhibited by all the solutions. Based on the solution behavior, water controversially must either remain glassy up until the temperature of crystallization or be an almost ideally strong liquid above 136 K. Having shown elsewhere how this implies glassy character up to LDA crystallization and a Tg above 160 K, we now examine the implications for water structure reorganization on dissolution of solutes, certain glycols excepted. It appears that the water in these solutions behaves like ice III rather than ice I.

Field-dependent proton relaxation in aqueous solutions of some manganese(II) complexes: a new interpretation.

Field-dependent measurements of the paramagnetic relaxation enhancement for water protons in the presence of Mn(II) complexes ( S=5/2), reported recently, are re-interpreted using theoretical models that take into consideration the fact that the relaxation of the electron spin for S>1 is multiexponential (even in the Redfield limit) and that are valid for an arbitrary relation between the electronic Zeeman interaction and the zero-field splitting in the complex.

Dielectric permittivity and relaxation in aqueous solutions of alkali metal sulfates and nitrates in the temperature range 288–313 K

The temperature dependencies of microwave dielectric permittivity and losses of nitrate and sulfate alkali metal aqueous solutions are studied at 288–313K in wide concentration ranges. The dielectric constant ϵ s and dielectric relaxation time τ are determined. It is shown that the order of the decrease of ϵ s for sulphate and nitrate solutions is identical: Li + > Na + > K + > Cs +. The concentration changes of ϵ s in sulphate and nitrate solutions for the same alkali metals (except lithium) are equal when the ionic strength is used instead of salt concentration. The distinctions in temperature and concentration dependencies of ϵ s are observed between the diluted and the concentrated solutions. The temperature changes of ϵ s are absent in concentrated solutions of salts. The changes of dielectric relaxation time are different for sulfate and nitrate solutions. At initial concentrations the relaxation time decreases negative to positive in concentrated Li 2SO 4 solutions. The order of τ changes in concentrated sulfate solutions is Li + > Na + ≈ H 2O > K + > Cs +. The decrease of relaxation time is observed in the alkali metal nitrate solutions. The difference for various alkali metal cations is practically absent in this case. Thus the influence of different anions on water molecule mobility in hydration spheres of cations is shown.

Anomalous nuclear magnetic relaxation of aqueous solutions of ferritin: an unprecedented first-order mechanism.

Ferritin, the iron-storing protein, speeds up proton transverse magnetic relaxation in aqueous solutions. This T(2) shortening is used in MRI to quantify iron in the brain and liver. Current theoretical models underestimate the relaxation enhancement by ferritin at imaging fields, and they do not predict the measured dependence of the rate enhancement on the magnetization of the particles. Here it is shown that a proton exchange dephasing model (PEDM) overcomes these limitations by allowing a first-order relaxation mechanism. The PEDM considers proton exchange between bulk water and exchangeable protons located at the surface of the hydrated iron oxide nanometric core of the protein. Relaxation is shown to depend on the distribution of the frequency shifts of the adsorption sites; the observed properties agree with a Lorentzian distribution. Computer simulations utilizing recent Mössbauer spectroscopy data show that the distribution of these shifts is effectively Lorentzian.

Consequences of 129Xe–1H Cross Relaxation in Aqueous Solutions

We have investigated the transfer of polarization from 129Xe to solute protons in aqueous solutions to determine the feasibility of using hyperpolarized xenon to enhance 1H sensitivity in aqueous systems at or near room temperatures. Several solutes, each of different molecular weight, were dissolved in deuterium oxide and although large xenon polarizations were created, no significant proton signal enhancement was detected in l-tyrosine, α-cyclodextrin, β-cyclodextrin, apomyoglobin, or myoglobin. Solute-induced enhancement of the 129Xe spin–lattice relaxation rate was observed and depended on the size and structure of the solute molecule. The significant increase of the apparent spin–lattice relaxation rate of the solution phase 129Xe by α-cyclodextrin and apomyoglobin indicates efficient cross relaxation. The slow relaxation of xenon in β-cyclodextrin and l-tyrosine indicates weak coupling and inefficient cross relaxation. Despite the apparent cross-relaxation effects, all attempts to detect the proton enhancement directly were unsuccessful. Spin–lattice relaxation rates were also measured for Boltzmann 129Xe in myoglobin. The cross-relaxation rates were determined from changes in 129Xe relaxation rates in the α-cyclodextrin and myoglobin solutions. These cross-relaxation rates were then used to model 1H signal gains for a range of 129Xe to 1H spin population ratios. These models suggest that in spite of very large 129Xe polarizations, the 1H gains will be less than 10% and often substantially smaller. In particular, dramatic 1H signal enhancements in lung tissue signals are unlikely.

The ultrasonic relaxation in aqueous solutions of N-ethylacetamide

Measurements are reported of the ultrasonic absorption in the frequency range 10–100 MHz in aqueous solutions of N-ethylacetamide (NEAA). The occurrence of a relaxation process due to forming and to breaking of molecular complexes is demonstrated. Relaxation parameters of the discovered process have been calculated. The value of the activation enthalpy of the process indicates that molecular complexes composed of H2O–NEAA are formed through the hydrogen bond. The theoretical model of ultrasonic absorption in aqueous solutions of nonelectrolytes developed by Andreae, Edmonds, and McKellar, is applied.

Field-Dependent Proton NMR Relaxation in Aqueous Solutions of Ni(II) Ions. A New Interpretation

A new model is presented for nuclear-spin relaxation in paramagnetic transition metal complexes in solution, allowing the electron-spin relaxation to be outside the Redfield limit. The novel feature is that the transient zero-field splitting (ZFS), modulated by distortions of the solvation shell, is allowed to be of rhombic rather than cylindrical symmetry. The model, which assumes that the static ZFS is absent, is applicable to aqueous solutions of transition metal ions. The magnetic-field dependence of the proton spin–lattice relaxation rate enhancement in aqueous solution has been investigated, and calculations are presented for anS= 1 system such as Ni2+(aq), using different degrees of rhombicity of the ZFS and different motional conditions (Redfield limit and slow-motion regime). The new model is also applied to fit the previously reported data for the field dependence of proton relaxation in aqueous solution of Ni(ClO4)2at low pH [J. Kowalewski, T. Larsson, and P.-O. Westlund,J. Magn. Reson.74, 56 (1987)]. The inclusion of rhombicity, motivated by recent theoretical work, provides a model which performs as well as the earlierad hocmodel.

Spin dynamics under the Hamiltonian varying with time in discrete steps: Molecular dynamics-based simulation of electron and nuclear spin relaxation in aqueous nickel(II)

A method of calculating the time correlation functions for electron spin is proposed, based on solving the time-dependent Schrödinger equation for a spin Hamiltonian that contains a term varying randomly in discrete time steps. It is applied to the study of electron spin relaxation in aqueous solution of nickel(II) ions with S=1. The random term in the spin Hamiltonian in this case is the zero-field splitting (ZFS) interaction. The method is evaluated by an application to a model system (the pseudorotation model) for which an analytical solution to the electron spin relaxation problem is known. The same method is then employed to study the electron and nuclear spin dynamics in a system where the time variation of the zero-field splitting is obtained by a combination of ab initio quantum chemistry and molecular dynamics simulations.

Spectral characteristics of 4-aminodiphenyl ether in different solvents and at various pH values

The solvatochromic shifts are found to be mainly due to the interaction of solvents with the amino group of 4-aminodiphenyl ether (ADPE). There is an increase in Stokes' shift with the increase in polarity and hydrogen bonding ability of solvents. The abnormal red shift in the fluorescence spectrum on protonation of ADPE is neither due to the amino group becoming more basic nor due to large solvent relaxation in aqueous solution but is due to monocation-solvent exciplex formation. The monocation of ADPE in cyclohexane followed the normal blue shift in the fluorescence spectrum. Contrary to other aromatic amines, ADPE does not undergo proton-induced quenching.