Molecules In Aqueous Solution Research Articles

Statistical geometry characterization of local structure of TMAO, TBA and urea aqueous solutions

Recently, we have revealed that trimethylamine-N-oxide (TMAO) molecules in aqueous solutions are distributed generally like random spheres in space (A.V. Anikeenko et al. J. Mol. Liq. 245 (2017) 35–41). We have shown that the variance of the distribution of Voronoi region volumes for the TMAO molecules and the hard random spheres are identical at the corresponding concentrations up to the mole fraction x ~ 0.1 (or packing fraction η ~ 0.2). In the current work, we study clusters in TMAO solutions and calculate the weighted mean cluster size and some topological cluster characteristics. For all these parameters, a great matching of TMAO and random spheres is also observed. The same analysis for tert-butyl alcohol (TBA) and urea aqueous solutions is carried out. These molecules have a tendency to cluster even at very low concentrations. However, basic geometrical features of the clusters are the same both for solutions and for the system of random spheres, indicating that geometrical laws governing the allocation of non-overlapping spheres in space should be taken into account when describing the structure of solutions even at rather low concentrations.

PH-dependent X-ray Photoelectron Chemical Shifts and Surface Distribution of Cysteine in Aqueous Solution.

The distribution and protonation states of amino acids in water droplets are of considerable concern in studies on the formation of clouds in the atmosphere as well as in many biological contexts. In the present work we use the amino acid cysteine as a prototypical example and explore the protonation states of this molecule in aqueous solution, which are strongly affected by the acidity of the environment and also can show different distributions between surface and bulk. We use a combination of X-ray photoelectron chemical shift measurements, density functional theory calculations of the shifts, and reactive force field molecular dynamics simulations of the underlying structural dynamics. We explore how the photoelectron spectra distinctly reflect the different protonation states that are generated by variation of the solution acidity and how the distribution of these protonation states can differ between bulk and surface regions. At specific pH values, we find that the distribution of the cysteine species at the surface is quite different from that in bulk, in particular, for the appearance in the surface region of species which do not exist in bulk. Some ramifications of this finding are discussed.

Interaction of amphotericin B with human and bovine serum albumins: A fluorescence polarization study

Abstract In this study, the interaction of amphotericin B with human and bovine serum albumins has been investigated by fluorescence spectroscopy. Due to the limitations of several analytical methods by the known aggregation of amphotericin B molecules in aqueous solutions, fluorescence polarization technique was employed to determine complex stabilities. Besides the quantitation of reliable stability constants, this method was found to be able determine the stable aggregated amphotericin B fraction in the presence of serum albumins. Our results demonstrate the formation of highly stable albumin-drug complexes, suggesting the significant role of serum albumins regarding the plasma protein binding of amphotericin B.

How does the complexation ability between host endo-functionalized molecular tube and strongly hydrophilic guest molecules in water depend on guest concentration?

We have already shown in our previous work (R. Paul, S. Paul, Synergistic Host-Guest Hydrophobic and Hydrogen Bonding Interactions in the Complexation between Endo-Functionalized Molecular Tube and Strongly Hydrophilic Guest Molecules in Aqueous Solution, Phys. Chem. Chem. Phys. 20 (2018) 16540–16550.) the main factors responsible in the complexation between an endo-functionalized molecular tube and different strongly hydrophilic guest molecules in water. These types of molecular tubes have gained a significant importance for encapsulating many environmentally and biologically important molecules. Here, we have examined how does this type of complexation ability depend on concentration of guest molecules? We use classical molecular dynamics together with MM-PBSA method for this purpose. We examine the effect of concentration of different guest molecules on the host-guest complexation ability by determining different types of hydrogen bond properties, preferential interaction parameter, water-inserted guest interaction energy parameter, host-guest binding free energy and potential of mean force. From the calculated free energy values obtained from MM-PBSA and PMF calculation, it is revealed that as the concentration of guest decreases the free energy becomes less favorable.

Determination and study on refractive indices and viscosities of aqueous solutions of citric acid, (citric acid + glycerol), and (citric acid + d-sorbitol) at T = 293.15 K–323.15 K and atmospheric pressure

Citric acid, glycerol, and d-sorbitol are used as important food additives. In this research work, viscosities and refractive indices (the physico-chemical properties) for aqueous solution of citric acid, as well as ternary solutions of (water + d-sorbitol + citric acid) and (water + glycerol + citric acid) were measured in mass fractions of citric acid (0.03–0.21) and at temperatures (T = 293.15, 303.15, 313.15, and 323.15) K and atmospheric pressure. For these solutions, the experimental refractive indices were fitted using a semi-empirical equation which its constant, Kr, was introduced by Koohyar in 2011. This constant can be applied to investigate the power of interactions between solute and solvent molecules in aqueous solutions. Also, the experimental viscosities were fitted by the Jones-Dole and Arrhenius-like equations. Obtained data of this research work can be applied in food industries.

Study of Strength of Interaction between Solute and Solvent Molecules in Aqueous Solutions of Ethylene Glycol, D-Mannitol, D-Fructose, Sucrose, and Maltose at 294.15, 298.15, and 303.15 K and Atmospheric Pressure using Refractometry

In this research work, we measured the refractive indices for aqueous solutions of ethylene glycol, D-mannitol, D-fructose, sucrose, and maltose at T = 294.15, 298.15, and 303.15 K and atmospheric pressure entire wide range of molar concentrations. These measurements were done in order to investigate the power of interactions between solute and solvent molecules as well as the effect of temperature in these interactions. For these mixtures, the experimental values of refractive index were correlated with experimental equation and constants of this equation (Kr) were applied to investigate on power of interactions between solute species in solutions of this study.

Self-assembly kinetics of debranched short-chain glucans from waxy maize starch to form spherical microparticles and its applications.

Starch microparticles (SMPs) of well-defined size and morphology were synthesized through pullulanase-mediated debranching of waxy maize starch followed by spontaneous re-assembly of the resulting short-chain glucan molecules in aqueous solution. Enzymatic debranching of amylopectins from native starch generated two major fractions corresponding to a smaller glucan and partially digested larger amylopectin molecules. The ratio of short-chain glucan (SCG) over partially digested amylopectin (PDAp) turned out to be the deterministic factors for the size and crystallinity of SMPs, of which the ratio could be controlled by the concentration of debranching enzyme. The PDAp fraction was closely associated with the creation of nuclei, determining the growth kinetics of SMPs which led to the formation of SMPs with a diameter ranging from 0.52.5 μm. In addition, we demonstrated that iron oxide nanoparticles (IONPs) were successfully incorporated into the starch microstructure by introducing them during the self-assembly reaction, conferring desired functionality onto the final SMPs. The incorporated IONPs rendered the SMPs an excellent magnetic sensitivity, which were successfully applied for the separation and concentration of target bacteria upon conjugation of specific antibody on the surface of SMPs. The simple processes and biocompatible nature of starch would make this approach attractive for many applications in the area of food, medicine and other related materials sciences.

ISFET Based DNA Sensor: Current-Voltage Characteristic and Sensitivity to DNA Molecules

Dependency of both source-drain current and current sensitivity of nanosize ISFET biosensor vs. concentration of DNA molecules in aqueous solution theoretically is investigated. In calculations it is carried out effects concerning charge carriers distribution in current channel and concerning carriers’ mobility behavior in high electrical fields in the channel. The influence of DNA molecules on the work of ISFET biosensors is manifested by a change in the magnitude of the gate surface charge. Starting with fairly low concentrations of DNA, ISFET sensors respond to the presence of DNA molecules in an aqueous solution which is manifested by modulation of channel conductance and therefore the source-drain current changes of the field-effect transistor. It is shown that the current sensitivity with respect to concentration of DNA molecules linearly depends on the source-drain voltage and reaches high values.

Supramolecular nanostructures constructed by rod-coil molecular isomers: effect of rod sequences on molecular assembly.

Coil-rod-coil molecules, composed of flexible oligoether chains and conjugated rod blocks, have a well-known ability to produce various nanostructures in bulk and in aqueous solution. Herein we report the synthesis and self-assembly of coil-rod-coil molecules based on the sequence of the rod building block and the type of oligoether coil chain. These molecules consist of conjugated rod segments, which are composed of biphenyl, terphenyl, and acetylenic bonds, with chiral oligoether chains as flexible coil segments. The experimental results imply that the sequence of the rod segments markedly influences the self-assembled nanostructures of coil-rod-coil molecules in the bulk state, and that the type of coil chain strongly affects the morphology of the supramolecular nanoassemblies of these molecules in aqueous solution. In the bulk state, molecules 1a and 1b, which contain biphenyl units connected to the end of the coil segments self-organize into a hexagonal perforated lamellar phase, and oblique columnar and body-centred tetragonal structures, respectively. However, molecules 2a and 2b bearing terphenyl units linked to the end of the coil segments self-assemble into lamellar, hexagonal perforated lamellar and hexagonal columnar structures. In aqueous solution, rod-coil molecular isomers with linear chiral oligoether chains self-assemble into helical nanofibres of various lengths. Meanwhile, isomers with chiral oligoether dendron chains self-organize into sheet-like nanoribbons of different sizes.

Time-resolved photoelectron spectroscopy of organic molecules in aqueous solutions

We use time-resolved photoelectron spectroscopy with wavelength-selected XUV femtosecond pulses to study photoinduced dynamics of organic molecules in solutions at millimolar concentrations. Upon electronic excitation we observe relaxation processes, such as excited state intramolecular proton transfer and trans-cis isomerization.

Исследование спектральных свойств нековалентных комплексов водорастворимого полизамещенного производного фуллерена С-=SUB=-60-=/SUB=- и хлорина е6 в полярных растворителях

The formation of non-covalent electrostatic complexes based on the water-soluble fullerene derivative (WSFD) and chlorin e6, dissolved in water or in ethanol was showed by absorption and fluorescent spectroscopy methods. As a result of the formation of such complexes, the chlorine e6 absorption spectrum changed with a bathochromic shift and its fluorescence was effectively quenched. The Stern-Volmer constants of complex are 7.3·10^5 and 2·10^5 M^-1 in water and ethanol, respectively. It was found that complex consists of 1 molecule of WSFD and 3 dye molecules in aqueous solution, while in ethanol this ratio is 1:1.

Self-assembly of phospholipid molecules in solutions under shear flows: Microstructures and phase diagrams.

Shear-induced microstructures and their phase diagrams were investigated for phospholipid molecules in aqueous solution by dissipative particle dynamic simulation. Self-assembled microstructures, including spherical and cylindrical micelles, spherical vesicles, lamellae, undulated lamellae, perforated lamellae, and continuous networks, were observed under various shear flows and phospholipid concentrations, where the spatial inhomogeneity and symmetry were analysed. A series of phase diagrams were constructed based on the chain lengths under various phospholipid concentrations. The phase distributions showed that the structures with spherical symmetry could be shear-induced to structures with cylindrical symmetry in the dilute solutions. In the semi-concentrated solutions, the lamellae were located in most spaces under zero shear flows, which could be shear-induced into undulated lamellae and then into cylindrical micelles. For the concentrated solutions, the strong shear flows oriented the directions of multilayer lamellae and phase transitions appeared between several cylindrical network structures. These observations on shear-induced microstructures and their distributions revealed a promising approach that could be used to design bio-microstructures based on phospholipid molecules under shear flows.

Surface-enhanced infrared attenuated total reflection spectroscopy via carbon nanodots for small molecules in aqueous solution.

In this study, carbon nanodots (CNDs) with excellent aqueous dispersibility, narrow size distribution, and oxygen-rich functional groups have been prepared via a green electrochemical method. Graphite electrodes were directly electrolyzed at ambient temperatures to form uniform CNDs in deionized water, which is free from additional oxidant/reductant. As-synthesized CNDs have been applied to coat an attenuated total reflection (ATR) waveguide enabling surface-enhanced infrared absorption (SEIRA) spectroscopic studies for detecting a variety of analytes in aqueous phase with remarkably enhanced IR band intensities. Finally, the proposed ATR-SEIRA strategy enabled quantitatively analyzing adenine in aqueous solution after optimizing the amount of CNDs, the solution pH, and potential CND aggregation. Graphical abstract.

Terbium Oxalatophosphonate as Efficient Multiresponsive Luminescent Sensors for Chromate Anions and Tryptophan Molecules.

A stable 2D terbium oxalatophosphonate with green luminescence, namely, [Tb2(H3L)(C2O4)3(H2O)4]·2H2O (1), has been hydrothermally obtained by using (4-carboxypiperidyl)-N-methylenephosphonic acid (H3L) and oxalate ligand. The luminescent investigation indicates that the emission behavior of compound 1 shows high water and pH stabilities. It can be applied as a multiresponsive luminescent probe with high selectivity, high sensitivity, recycling capability, and fast sensing of CrO42–, Cr2O72– anions and tryptophan (Trp) molecules in aqueous solution through the luminescence quenching effect. Moreover, the sensing results can be distinguished by the naked eye under the irradiation of UV light of 254 nm. In addition, the probable mechanisms for the quenching behavior are also discussed, which can be mainly attributed to the competitive absorption of excitation energy between compound 1 and the analytes.

New Hybrid Method for the Calculation of the Solvation Free Energy of Small Molecules in Aqueous Solutions.

The ability to accurately predict the solvation free energies of ionic species using the appropriate thermodynamic cycle is of great importance in many areas of chemistry and biochemistry. To improve the accuracy of calculating solvation free energies, we devised a hybrid cluster-continuum approach, where explicit solvent molecules are added to the traditionally employed continuum model. Our computational workflow consists of the following steps: First, the minimum number of explicit water molecules beyond which additional water molecules no longer improve the accuracy of the cluster-continuum model is carefully established. Next, the convergence values for fully relaxed molecular configurations are compared with those obtained by sampling thermally disordered configurations using single-point calculations. We find that the dielectric constant does not have a significant influence on the solvation free energy, while accounting for the placement of a counterion is necessary for the accurate calculation of the solvation free energy.

The effect of the side chain structures on the energy of intermolecular interactions of α-amino acids with some formamides in aqueous solutions at T = 298.15 K

To evaluate the effect of amino acid side chains on the thermodynamics of their interaction with the formamides molecules in aqueous solutions, we expanded the range of amino acids by studying in the present investigation the thermodynamics of the dissolution of glutamine in mixed solvents {water + (formamide, N‑methylformamide and N,N‑dimethylformamide)} at T = 298.15 K and organic solvent mole fractions up to x2 ~ 0.3. The standard enthalpies of solution (ΔsolH°) and transfer (ΔtrH°) of l-glutamine from water to a mixed solvent as well as the enthalpy coefficients of pairwise interactions (hxy) were calculated. The interrelation between enthalpic characteristics of l-glutamine dissolution (transfer) and the composition of water-organic mixtures was determined. Using the enthalpic coefficients of pairwise interactions of l-glutamine and five more amino acids (glycine, dl-α-alanine, l-valine, l-methionine, and l-threonine), the enthalpic contributions of the side chains of these amino acids to their interparticle interactions with the molecules of formamides were calculated.

A facile route for the preparation of silver nanoparticles-graphene oxide nanocomposites and their interactions with pyronin Y dye molecules

We report a facile synthesis of silver nanoparticles-graphene oxide (AgNPs-GO) nanocomposites and their interactions with Pyronin Y (PyY) molecules studied by UV-Vis absorption, steady-state and time-resolved fluorescence spectroscopy techniques in aqueous solution. With this aim, firstly, monodisperse AgNPs with two different sizes (4 and 6 nm) were synthesized by using a surfactant-assisted organic solution phase protocol comprising the consecutive thermal decomposition and reduction of silver (I) acetate. Secondly, AgNPs were anchored into GO nanoflakes via using liquid self-assembly method to prepare AgNPs-GO nanocomposites. The morphology and structure of both colloidal AgNPs and the AgNPs-GO nanocomposites were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and absorption spectroscopy. Finally, AgNPs-GO nanocomposites were interacted with PyY molecules in aqueous solution and the photophysical properties of PyY were studied by UV-Vis absorption and fluorescence (steady-state and time-resolved) spectroscopy techniques. The spectroscopic results revealed that the photophysical properties of the dye were dramatically changed after its interaction with AgNPs-GO nanocomposites in aqueous solution.

Investigation into micro-physicochemical interaction between sodium dodecylbenzene sulfonate (SDBS) and partially hydrolyzed polyacrylamide (HPAM) utilizing electron probe microanalysis method

After adding a surfactant to the polymer solution, the interaction between them has a significant influence on the oil recovery of polymer/surfactant (SP) flooding. The study of the micro-physicochemical interaction between sodium dodecylbenzene sulfonate (SDBS) and partially hydrolyzed polyacrylamide (HPAM) can contribute toward an understanding of the action of SP flood. In this paper, the characteristic interaction parameter (CAC and PSP) was determined by tensiometry, the microstructure of HPAM and SP solution was observed with electron probe microscope, then the distribution of SDBS in the mixtures of HPAM and SDBS was determined based on the characteristic of Sulfur. Results show HPAM and SDBS begin to aggregate after the CAC and HPAM is saturated by SDBS above the PSP. HPAM molecules in aqueous solution have a multilayer three-dimensional network structure in the form of aggregates. Most structures are hexahedral, in which there are solid backbones attached with thin branches, the mesh is from 10 μm to 100 μm. Compared with HPAM, the size of the mesh in the sample of SP solution has no noticeable change, but the network layer is reduced, the density of mesh is decreased, the rough skeleton becomes more substantial, and the branch is less. The thin films occasionally scattered in the mixtures of HPAM and SDBS. Approximate 50% of the SDBS in the solution formed aggregates with HPAM molecules by hydrophobic interaction.

CO2-controllable smart nanostructured fluids in a pseudo Gemini surfactant system

A novel CO2 responsive anionic smart wormlike micelles (SWLMs) was constructed by simply mixing sodium oleate (NaOA) and the small organic counterion 2, 6, 10-trimethyl-2, 6, 10-triazaundecane (TMTAD) in a 3:1 M ratio without complex organic synthesis. After bubbling CO2, TMTAD and NaOA molecules in aqueous solution, a pseudo Gemini surfactant is formed in situ due to electrostatic interactions. This system shows two obvious performance transitions when CO2 is continuously introduced, from a water-like solution to a viscoelastic fluid and then a milky solution. Such transitions reflect the continuous transformation of the self-assembled structure from spherical micelles to wormlike micelles and then vesicle or spherical micelles. Additionally, this system can exhibit two similar sequential transformations when the pH changes in the reverse process.

Structure, Dynamics, and Hydration Free Energy of Carbon Dioxide in Aqueous Solution: A Quantum Mechanical/Molecular Mechanics Molecular Dynamics Thermodynamic Integration (QM/MM MD TI) Simulation Study.

The solvation of carbon dioxide in solution represents a key step for the capture and fixation CO2 in nature, which may be further influenced by the formation of (bi)carbonate species and/or the formation of CO2 clusters in solution. The latter processes are strongly dependent on the exact environment of the liquid state (e.g., pH value, solvated ions, etc.) and may interfere with the experimental determination of structural, dynamical, and thermodynamic properties. In this work a hybrid quantum mechanical/molecular mechanical (QM/MM) simulation approach at correlated ab initio level of theory resolution-of-identity second-order Møller-Plesset Perturbation Theory (RI-MP2) has been applied in the framework of thermodynamic integration (TI) to study structure, dynamics, and the hydration free energy of a single carbon dioxide molecule in aqueous solution. A detailed analysis of the individual QM/MM potential energy contributions demonstrate that the overall potential remains highly consistent over the entire sampling phase and that no artificial contributions are influencing the determination of the hydration free energy. The latter value of 0.01 ± 0.92 kcal/mol was found in very good agreement with the values of 0.06 and 0.24 kcal/mol obtained via quasi-chemical theory and experimental measurements, respectively. In order to obtain detailed information about the C- and O C-water interaction, conically restricted regions with respect to the main axis of the CO2 molecule have been employed in structural analysis. The presented data not only provide detailed information about the hydration properties of CO2 but act as a critical validation of the simulation technique, which will be beneficial in the study of nonaqueous solvents such as pure and aqueous NH3 solutions, which have been suggested as potential candidates to capture CO2 from anthropogenic sources.