Solute Dipole Moment Research Articles

Partition analysis of dipole moments in solution applied to functional groups in polypeptide motifs.

A partition analysis based on segments is developed for density functional theory defining solute dipole moments of functional groups, and the corresponding induced solvent dipoles representing solvent screening. The accuracy of dipoles from the fragment molecular orbital method is evaluated in comparison to unfragmented values. The analysis is applied to evaluate dipole moments of side chains, amino and carbonyl groups in common polypeptide motifs, α-helixes, β-turns, and random coils in solution. The membrane domain of the ATP synthase (1B9U) is analyzed, revealing the effect of the bend splitting of the α-helix into two pieces.

A self-powered droplet sensor based on a triboelectric nanogenerator toward the concentration of green tea polyphenols.

Self-powered liquid droplet sensors based on triboelectric nanogenerators have attracted extensive attention in the field of biochemical sensing applications. Numerous research studies have investigated the effects of factors such as molecular species, molecular concentration, molecular charge, and molecular dipole moment in solution on the output electrical signals of the sensor. In this study, we prepared a self-powered droplet sensor using conductive copper film tape, polytetrafluoroethylene, and conductive aluminum foil tape. The sensor can continuously output pulsed electrical signals with minimal environmental impact. In comparison with other types of sensors, this sensor boasts a rapid response time of 10 ms and excellent sensitivity. The relationship between the friction-induced output current and voltage of the droplets and the concentration of green tea polyphenols (GTPs) was studied using the self-powered liquid droplet sensor with five different green tea samples. It was found that GTPs were the main factor contributing to the changes in output electrical signals in green tea water droplets. Fluorescence spectroscopy was used to reveal that the magnitude of the output current was inversely proportional to the concentration of GTPs in green tea. These results demonstrate the potential application of self-powered liquid droplet sensors in biochemical sensing applications based on concentration-dependent output signals.

Prediction of cosolvent effect on solvation free energies and analysis of intermolecular forces of tizanidine hydrochloride in ethyl acetate + methanol / ethanol mixtures

The solubility of small molecule drug in solvents can be dramatically affected by addition of a suitable cosolvent, which makes the screening of the best-suited cosolvent an important task for the purification and preparation. The present work aims to improve the fundamental understanding of tizanidine hydrochloride (TIZ HC) solvation by cosolvent. Solubility experimental data from TIZ HCl in mixtures of ethyl acetate + alcohols were obtained at different temperatures with the method of isothermal equilibrium. In the system of ethyl acetate + methanol, the solubility data increased firstly and then decreased with an increase in ethyl acetate content, however, the strictly monotonic decreasing of solubility in ethyl acetate + ethanol mixtures was observed. The solubility correlation fitting was performed with the Jouyban-Acree model and CNIBS/R-K model. The solvent effect analysis indicates that the hydrogen bond acidity, the polarity / polarizability and the cohesive forces of the solvent have a greater influence on the solubility, which was further validated by the local quantitative molecular surface analysis results of electrostatic potential (ESP). The dissolution process of TIZ HCl in systems with different solvent compositions was analyzed in the form of preferential solvation parameters, it was found that methanol is the preferred solvent in the solvation shell of TIZ HCl in methanol-rich and ethyl acetate-rich mixtures but the ethanol is preferred in intermediate compositions and ethyl acetate-rich mixtures. Moreover, the types of intermolecular solute–solvent interactions were discussed on the basis of the structural characteristics of TIZ HCl. The solvation free energy is a key parameter describing solvent effects, which is extremely important for understanding solution chemistry. For this part, with the aid of density functional theory (DFT) and molecular dynamics (MD) simulations, it was found that the cosolvent effect is consistent with the prediction trend of solvation free energy of TIZ HCl in each systems. The effect of the cavity formed by the solvent molecules and dipole moment of solute was calculated accordingly by the solvation model based on density (SMD) for explaining the former behavior.

Molecular dynamics study of water rotational relaxation in saccharide solution for the development of bioprotective agent

Saccharides are often used as bio-protective agent owing to their unique interactions with the solvent water to change the water dynamics which dominate biomolecule deterioration. In this work, we present some basic laws for controlling water rotational relaxation time by performing molecular dynamics (MD) simulations of saccharide solutions. It is revealed that the water rotational relaxation time in saccharide solution is exponentially proportional to its residence time. Interestingly, the larger the solute dipole moment, the smaller the prerequisite residence time to obtain a tenfold retardation of the water relaxation time (the decuple-retarding period), which means the higher the increasing rate of the relaxation time vis-à-vis the residence time. We also find that water residence time exhibits a Gaussian distribution for various sugar solutions. This random walk of water within the solution further suggests that the larger ratio of the hydration layer volume to the overall water accessible space results in a longer residence time, thus a longer relaxation time distribution. We finally conclude that the protective agent with a large specific surface area and a large dipole moment is effective to retard the water rotational relaxation.

Hydration of the neurotransmitter [formula omitted]-aminobutyric acid and its isomer [formula omitted]-aminobutyric acid

Room-temperature aqueous solutions of the neurotransmitter γ-aminobutyric acid (GABA) and its isomer α-aminobutyric acid (AABA) were studied with broad-band dielectric relaxation spectroscopy (DRS) and statistical mechanics (1D-RISM and 3D-RISM) calculations. Comparison of the first-shell coordination numbers from 3D-RISM with the total effective hydration numbers from DRS revealed that for both solutes only about half of the H2O molecules in direct contact with the solute are affected in their dynamics. Whereas for GABA ∼10 of them are moderately retarded by a factor of ∼2–3 compared to bulk water and only ∼1–2 effectively frozen at vanishing solute concentration, AABA appears to be more strongly hydrated with only ∼6 moderately retarded but ∼6 H2O frozen by the solute molecule. This is reflected in the effective solute dipole moments.

Typical at glance but interesting when analyzed in detail: A story of Tris hydration.

This paper provides results of dielectric relaxation (DR) spectroscopy of aqueous solutions of tris(hydroxymethyl)aminomethane (Tris) covering frequencies of 0.05 ≤ ν/GHz ≤89. The DR spectra can be well fit by a sum of Cole-Cole relaxation, assigned to the solute, and 2Debye modes already observed for neat water. Analysis of the amplitudes reveals that Tris is hydrated by 7 H2Os up to its solubility limit. However, the rather high effective solute dipole moment of ≈12D suggests that H2O dipoles in contact with Tris should reorient independently from it. Accordingly, an alternative description of the DR spectra with a superposition of 4Debyerelaxations was attempted. In this model, the slowest mode at ∼4GHz arises from solute reorientation and that at ∼8GHz was assigned to dynamically retarded hydration water, whereas relaxations at ∼18 and ∼500GHz are again those of (rather unperturbed) bulk water. Analysis of the solvent-related modes shows that Tris indeed slows down 7-8 H2O molecules. However, the solute-solvent interaction strength is rather weak, excluding the rotation of an alleged Tris-(7-8) H2O cluster as an entity. The now derived effective dipole moment of (6.3 ± 0.5) D for the bare Tris molecule allows speculations on its conformation. With the help of computational methods, we suggest that Tris dissolved in water most likely possesses an intramolecular H-bond between the nitrogen and hydrogen atoms of amino and hydroxyl groups, respectively. In addition, computational results indicate that the seven hydration H2Os found by DR bind directly to the Tris OH groups.

Fullerene C60 spectroscopy in [BMIM][PF6] ionic liquid: Molecular dynamics study using polarization effects

We employ molecular dynamics (MD) simulations to assess the electrical behavior of the atomic charges of a fullerene immersed in an ionic liquid (and water). From solute-solvent configurations and DFT calculations, we obtained the atomic charges and the dipole moment in each stage of MD-simulation. Through an iterative process alternating MD-simulations and DFT calculations we obtained the convergence of the C60 dipole moment in solution. A complete analysis of the behavior of atomic charges is presented comparing the impact on the solute-solvent structure, where we highlight the importance of the complete polarization of the solute in solution. To observe the impact of electronic C60-solvente interaction on spectroscopy results we performed nuclear magnetic resonance (NMR) and absorption spectra quantum calculations, using GIAO-DFT and TD-DFT methodology. The results indicate a smaller chemical shift, δ(13C) and a more intense electronic transition band for the fully polarized C60 in solution.

Photo-physical study of coumarins in aqueous organic solvents: An experimental and theoretical approach

In the present work, we have studied the spectroscopic behavior of four structurally similar coumarin dyes and ground (μg) and excited state (μe) dipole moments in aqueous DMSO as well as aqueous DMA using absorption and fluorescence emission spectroscopy. The μg and μe have been determined using the Bilot-Kawski method. The experimental results show that the dipole moments of solutes are influenced by solute-solvent interaction. The increase in solvent polarity leads to an increase in Stokes shift in both the aqueous mixtures while a decrease in Stokes shift has been observed for C519 and C523 in aqueous DMA. The μe is observed to be higher than that of the μg in all the solvents indicating the intramolecular charge transfer (ICT). To support experimental results, the electronic structure and spectroscopic properties of Coumarins have been investigated in gas and different solvent phases by DFT/ TD-DFT calculations. The HOMO-LUMO, molecular electrostatic potential map (MEP), and Natural Bond Orbital (NBO) analysis have been carried out to study the intermolecular charge transfer process.

Computational and Spectral Means for Characterizing the Intermolecular Interactions in Solutions and for Estimating Excited State Dipole Moment of Solute

The results obtained both in quantum chemical computation and in solvatochromic study of pyridinium di-carbethoxy methylid (PCCM) are correlated in order to estimate the electric dipole moment in the excited state of this molecule. This estimation is made by a variational method in the hypothesis that the molecular polarizability does not change in time of the absorption process. Ternary solutions of PCCM in protic binary solvents are used here, both establishing the contribution of each type of interaction to the spectral shift and to characterize the composition of the first solvation shell of PCCM. Results are compared with those obtained before for other binary solvents. The difference between the interaction energies in molecular pairs of PCCM-active solvent and PCCM-less active solvent was also estimated based on the cell statistical model of the ternary solutions.

Unlabeled lysophosphatidic acid receptor binding in free solution as determined by a compensated interferometric reader

Native interactions between lysophospholipids (LPs) and their cognate LP receptors are difficult to measure because of lipophilicity and/or the adhesive properties of lipids, which contribute to high levels of nonspecific binding in cell membrane preparations. Here, we report development of a free-solution assay (FSA) where label-free LPs bind to their cognate G protein-coupled receptors (GPCRs), combined with a recently reported compensated interferometric reader (CIR) to quantify native binding interactions between receptors and ligands. As a test case, the binding parameters between lysophosphatidic acid (LPA) receptor 1 (LPA1; one of six cognate LPA GPCRs) and LPA were determined. FSA-CIR detected specific binding through the simultaneous real-time comparison of bound versus unbound species by measuring the change in the solution dipole moment produced by binding-induced conformational and/or hydration changes. FSA-CIR identified KD values for chemically distinct LPA species binding to human LPA1 and required only a few nanograms of protein: 1-oleoyl (18:1; KD = 2.08 ± 1.32 nM), 1-linoleoyl (18:2; KD = 2.83 ± 1.64 nM), 1-arachidonoyl (20:4; KD = 2.59 ± 0.481 nM), and 1-palmitoyl (16:0; KD = 1.69 ± 0.1 nM) LPA. These KD values compared favorably to those obtained using the previous generation back-scattering interferometry system, a chip-based technique with low-throughput and temperature sensitivity. In conclusion, FSA-CIR offers a new increased-throughput approach to assess quantitatively label-free lipid ligand-receptor binding, including nonactivating antagonist binding, under near-native conditions.

Determination of excited state dipole moments in solution via thermochromic methods

The method basically combines the existing ideas of excited state dipole moment determination via thermochromic fluorescence spectroscopy with the determination of the solvent cavity volume via concentration dependent density measurements of the solution densities at different weight fractions. Additionally, the determination of the cavity volume in dependence of the solvent temperature is included here, which provides a better accuracy of the excited state dipole moment determination. With this step two major sources of errors are eliminated: the use of the very imprecise Onsager radius and the assumption, that the cavity size is temperature independent.•Thermochromic absorption and fluorescence spectroscopy.•Cavity volume determination by density measurements.•Temperature dependent cavity volume determination.

The Role of Computational Chemistry in the Experimental Determination of the Dipole Moment of Molecules in Solution.

The methods for the experimental determination of electric dipole moment of molecules in solution from measurements of dielectric permittivity and refractive index are traditionally based on the classical Onsager model. In this model the molecular solute is approximated as a simple polarizable point dipole inside a spherical or ellipsoidal cavity of a dielectric medium representing the solvent. However, the inadequacies of the model resulting from the assumption of a simple shape of the cavity, for the evaluation of the cavity field effect, and from the uncertainty of the polarizability of the molecular solute influences the results and hampers the comparison with the electric dipole moments computed from quantum chemical solvation models. In this article we propose a new method for the experimental determination of the electric dipole moment in solution in which information from the Polarizable Continuum Model calculations are used in place of the Onsager model. The new method overcomes the limitations of this latter model regarding both the cavity field effect and the polarizability of the molecular solutes, and thus allows a coherent comparison between experimental and computed dipole moments of solvated molecules. © 2019 Wiley Periodicals, Inc.

The Structure of Cis-2,2′-Azopyridine in the Solid State

Descriptions of azoheteroaromatic compounds in their cis-isomeric form in the solid state are almost non-existent. Cis-2,2′-azopyridine is a known compound which structure differentiates from the trans-isomer based on spectroscopic evidence (UV–Vis absorption, 1H, and 13C NMR spectroscopy) and with studies regarding its stability, thermal reversion to the trans-isomer, and dipole moment in solution. However, the structure of this compound in the solid state has been unresolved. Herein, we present the crystal structure of cis-2,2′-azopyridine that forms red prismatic crystals in the monoclinic space group C2/c. The unit cell parameters are: a = 23.485 (4), b = 5.9241 (12), c = 21.656 (4) A, and V = 2717.1 (9) A3 with 12 molecules per unit cell. Molecules are arranged as two helical conformers (P and M) with C–N=N–C torsion angles and aromatic ring planes’ angles comparable to those reported for cis-azobenzene. The rare structural determination of an azoheteroaromatic cis-isomer of 2-azopyridine that was synthesized, isolated and crystallized is presented. X-ray structure analysis reveals that the molecule forms dimeric complexes containing both M- and P-helical conformers as well as infinite stacked columns in the solid state through a combination of C–H⋯N hydrogen bonds, C–H⋯π interactions and lone pair⋯π contacts.

Toward the Understanding of Micro-TLC Behavior of Various Dyes on Silica and Cellulose Stationary Phases Using A Data Mining Approach.

Planar chromatography and related techniques [micro-planar chromatography, micro-TLC, or paper-based microfluidic devices (μPADs)] present several advantages in analytical applications, such as simplicity, low cost of analysis, and the ability to work with raw complex samples without the involvement of time-consuming prepurification steps. By using commonly applied planar chromatographic systems and μPADs devices, stationary phases (silica and cellulose based), different solvent mixtures (methanol-water and dichloromethane-methanol), and proportions varying from 0 to 100% (v/v), micro-TLC migration profiles of several dyes described in terms of characteristic of chromatographic parameters (retardation factor, peak base width, and asymmetry factor) were investigated. Combining these results with some quantum mechanics calculated properties for each solute (dipole moment, polarizability), and by using the data mining approach, we modeled this overall chromatographic behavior in order to describe experimental data. With this approach, we were able to predict with reasonable confidence some chromatographic properties. This effort its crucial in order to (1) optimize solute elution, (2) increase mixture resolution, and (3) identify some molecular properties of analytes for designing simple micro-TLC. It is hoped that the presented nonhypothesis-driven data-mining approach can be helpful for understanding the chromatographic behavior of dyes on silica and cellulose adsorbents using the simplest mobile phases. This should be helpful for further designing the micro-TLC separation systems or μPADs quantification devices based on cellulose and related biopolymers and considering dye compounds as analytes for separation and sensing molecules.

The Interplay of Methyl-Group Distribution and Hydration Pattern of Isomeric Amphiphilic Osmolytes.

The intermolecular interactions and dynamics of aqueous 1,1-dimethyurea (1,1-DMU) solutions were studied by examining the concentration dependence of the solvent and solute relaxations detected by dielectric spectroscopy. Molecular dynamics simulations were carried out to facilitate interpretation of the dielectric data and to get a deeper insight into the behavior of the system components at the microscopic level. In particular, the simulations allowed for explaining the main differences between the dielectric spectra of aqueous solutions of 1,1-DMU and of its structural isomer 1,3-DMU. Similar to the previously studied compounds urea and 1,3-DMU, 1,1-DMU forms rather stable hydrates. This is evidenced by an effective solute dipole moment that significantly exceeds the value of a neat 1,1-DMU molecule, indicating pronounced parallel alignment of the solute dipole with two to three H2O moments. The MD simulations revealed that the involved water molecules form strong hydrogen bonds with the carbonyl group. However, in contrast to 1,3-DMU, it was not possible to resolve a "slow-water" mode in the dielectric spectra, suggesting rather different hydration-shell dynamics for 1,1-DMU as confirmed by the simulations. In contrast to aqueous urea and 1,3-DMU, addition of 1,1-DMU to water leads to a weak decrease of the static permittivity. This is explained by the emergence of antiparallel dipole-dipole correlations among 1,1-DMU hydrates with rising concentration.

Excited State Dipole Moments in Solution: Comparison between State-Specific and Linear-Response TD-DFT Values.

We compare different response schemes for coupling continuum solvation models to time-dependent density functional theory (TD-DFT) for the determination of solvent effects on the excited state dipole moments of solvated molecules. In particular, linear-response (LR) and state-specific (SS) formalisms are compared. Using 20 low-lying electronic excitations, displaying both localized and charge-transfer character, this study highlights the importance of applying a SS model not only for the calculation of energies, as previously reported ( J. Chem. Theory Comput. , 2015 , 11 , 5782 , DOI: 10.1021/acs.jctc.5b00679 ), but also for the prediction of excited state properties. Generally, when a range-separated exchange-correlation functional is used, both LR and SS schemes provide very similar dipole moments for local transitions, whereas differences of a few Debye units with respect to LR values are observed for CT transitions. The delicate interplay between the response scheme and the exchange-correlation functional is discussed as well, and we show that using an inadequate functional in a SS framework can yield to dramatic overestimations of the dipole moments.

The chemical potential of a dipole in dipolar solvent at infinite dilution: Mean spherical approximation and Monte Carlo simulation

A new analytical expression was derived for the chemical potential of a hard sphere dipole in hard sphere dipole fluid at infinite dilution of the solute using the mean spherical approximation (MSA). A set of Monte Carlo (MC) simulations has been carried out to investigate the scope of applicability of the derived equation. The mean reaction field (MRF) approach was used in our MC computations. Two different MC methods (Widom particle insertion and thermodynamic integration) were applied for obtaining the chemical potential change associated with the dipole creation at the solute particle to provide adequate accuracy of the MC simulations. Also, corresponding changes in the mean potential energy were calculated by direct method and by thermodynamic integration. The solvation energies have been obtained for the systems of dipolar hard spheres with reduced dipole moment 1.0 at the reduced densities 0.2, 0.5, and 0.8. Computations have been made for solute particles with the reduced dipole moment varied from 0.0 to 1.5 and the hard sphere diameter varied from 0.5 to 2.0. The variation of those quantities with the molecular parameters was analyzed and compared with the MSA equation and Kirkwood classical expressions. It was found that the MSA calculations agree relatively well with MC simulations at densities less than 0.5 and solute dipole moment less than 1.0.

Refractive index dependence of solvatochromism

Abstract Refractive index (n) function ϕ(n2) (ϕ(n2) = (n2 − 1)/(n2 + 2)) stands for average electronic polarizability density of the matter. Sets of nonpolar and highly polar (e ≥ 25) liquids were used in parallel for recording the ϕ(n2) dependence of absorption and fluorescence spectra of several push-pull chromophores. Fluorescence maxima of Nile Red (NR) and laser dye 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) shift much less in polar solvents (coefficient corresponding to the sensitivity to ϕ(n2), p ∼ −4000 cm−1). Fluorescence in nonpolar solvents, as well as absorption in both solvent sets has almost constant and much larger p of ∼−8000 cm−1. Similarly, zwitter-ionic Betaine 30 has also different p values in nonpolar and highly polar media for absorption (Renge, J. Phys. Chem. A 114 (2010) 6250). The ϕ(n2) dependent induction shift is a function of solute dipole moments squared (μg2 − μe2). This shift is suppressed in polar environment, if the dipole of the initial state is large (μe for fluorescence, μg for absorption), in qualitative agreement with Li theory of non-equilibrium solvation (Huang et al., J. Theor. Comput. Chem. 5 (2006) 355). As compared to absorption, conspicuous fluorescence bandwidth narrowing by a factor of ∼2 takes place in highly polar liquids for NR and DCM. The unusual narrowing indicates a dramatic molecular structure change in the excited state affecting the Franck-Condon factors for vibronic coupling. The reaction field created by the large dipole of solute in polar liquid exceeding 109 V/m can modulate the bond alternation in a conjugated polymethine system. Dipole moments μg, μe and the polarizability difference Δα were estimated for NR as 14 ± 3 D, 18 ± 3 D, and 38 ± 10 A3, respectively. Finally, a set of guidelines for solvatochromic data assessment is proposed.

A dynamic look on molecular symmetry

J.H. van’t Hoff’s seminal paper variously titled as either: Chemistry in Space, The Placement of Atoms in Space or other with similar wording, depending on the language it was published in, suggested that the structure of a molecule would be independent of its physical state: solid, liquid, vapor, gaseous, or in solution. However, this is definitely not true so much so that during the last decades many examples have accumulated showing that the structure of a molecule in a crystalline solid can differ substantially from its structure in solution. This would have important consequences not only on how molecules are structurally described and the way they react, but also that molecular symmetry may not be a static property and has to be considered from a dynamic point of view. To add additional evidence to this conception, we took advantage of a family of trans-1,4-di- and tetra-substituted cyclohexane derivatives that appear to have a centre of symmetry but show a substantial dipole moment in solution. In the present work, we used the trans-1,4-dicarboxymethylcyclohexane and its 1,4-dibrominated derivative and were able, through dipole moment determinations IR, Raman, NMR studies, and computational calculations with the SpinWorks, MOPAC, and MOLDEN programs, to confirm our assumption that the molecular symmetry and the molecular structure are dependent on the environment.

Multiparametric Characterization of Single, Unlabeled Proteins in Solution

With large diversity in structure and function, as well as clinical relevance, proteins represent an important target for biophysical characterization. Resistive pulse-based nanopore sensing is a compelling platform for this task, as it provides information about individual proteins during their translocation through the zeptoliter sensing volume inside of a nanopore. Previous work in our group used lipid-coated synthetic nanopores to extract five distinct protein descriptors by analyzing modulations in ionic current, ΔI, resulting from the translocation and rotation of individual lipid-tethered proteins [1]. However, while coating of nanopore walls with fluid lipid bilayers and tethering proteins with lipid anchors is useful for preventing non-specific protein adsorption, extending translocation times, and increasing specificity, it is technically demanding and its success depends on nanopore diameter, geometry, and surface chemistry. This work explores the possibility of using the detergent Tween-20 for nanopore surface coating [2] combined with high bandwidth recording electronics to characterize freely translocating, untethered proteins on a single molecule level. Here, we utilize the dependence of ΔI on the orientation of non-spherical proteins transiting a nanopore to determine their intrinsic shapes, volumes, and dipole moments in solution. The ability to thoroughly examine unlabeled, natively-folded proteins in an aqueous sample on a single molecule level signifies an important step toward the use of nanopores for proteomic and diagnostic applications.[1] Yusko, E.C., et al., Real-time shape approximation and 5-D fingerprinting of single proteins. arXiv preprint arXiv:1510.01935, 2015.[2] Hu, Rui, et al. Intrinsic and membrane-facilitated α-synuclein oligomerization revealed by label-free detection through solid-state nanopores. Scientific reports 6, 2016.