Solute-solvent Effects Research Articles

Cyanostyrene derivative with multi-stimuli responsive properties: Multicolor- and high-color-contrast switching in response to force, heat and light

Multi-stimuli responsive luminescent materials are ideal materials for luminescent anti-counterfeiting technology. Currently, it is still challenging to develop excellent multi-stimuli-responsive material that is easy to synthesize and low-cost. Herein, a dicyanostilbenebenzene derivative (α-CFP) with a symmetrical structure was designed and successfully synthesized, which showed obvious AIE and solvent effects in solution. Two polymorphs of it were prepared by controlling the cooling rate, and it was found that green-emitting Form I and blue-emitting Form II can transform into each other by heat and mechanical force. Crystal structure analysis reveals the possible intrinsic mechanism of polymorphism-dependent emission and interconversion. Further studies found that both Form I and Form II could transform into another new polymorph Form III upon heating to 220 °C. Form III can undergo photoinduced [2 + 2] cycloaddition reaction accompanied by discoloration, and it can return to its original state by heating. Finally, three application scenarios were designed and demonstrated, which confirm their potential applications in information encryption and anti-counterfeiting.

Pathway-Controlled Aqueous Supramolecular Polymerization via Solvent-Dependent Chain Conformation Effects

Solute-solvent interactions play a critical role in multiple fields, including biology, materials science, and (physical) organic, polymer, and supramolecular chemistry. Within the growing field of supramolecular polymer science, these interactions have been recognized as an important driving force for (entropically driven) intermolecular association, particularly in aqueous media. However, to date, solute-solvent effects remain poorly understood in the context of complex self-assembly energy landscapes and pathway complexity. Herein, we unravel the role of solute-solvent interactions in controlling chain conformation effects, allowing energy landscape modulation and pathway selection in aqueous supramolecular polymerization. To this end, we have designed a series of oligo(phenylene ethynylene) (OPE)-based bolaamphiphilic Pt(II) complexes OPE2-4 bearing solubilizing triethylene glycol (TEG) chains of equal length on both molecule ends, but a different size of the hydrophobic aromatic scaffold. Strikingly, detailed self-assembly studies in aqueous media disclose a different tendency of the TEG chains to fold back and enwrap the hydrophobic molecular component depending on both the size of the core and the volume fraction of the co-solvent (THF). The relatively small hydrophobic component of OPE2 can be readily shielded by the TEG chains, leading to only one aggregation pathway. In contrast, the decreased capability of the TEG chains to effectively shield larger hydrophobic cores (OPE3 and OPE4) enables different types of solvent quality-dependent conformations (extended, partly back-folded and back-folded), which in turn induce various controllable aggregation pathways with distinct morphologies and mechanisms. Our results shed light on previously underappreciated solvent-dependent chain conformation effects and their role in governing pathway complexity in aqueous media.

Solute-Solvent Interactions in Modern Physical Organic Chemistry: Supramolecular Polymers as a Muse.

Interactions between solvents and solutes are a cornerstone of physical organic chemistry and have been the subject of investigations over the last century. In recent years, a renewed interest in fundamental aspects of solute–solvent interactions has been sparked in the field of supramolecular chemistry in general and that of supramolecular polymers in particular. Although solvent effects in supramolecular chemistry have been recognized for a long time, the unique opportunities that supramolecular polymers offer to gain insight into solute–solvent interactions have become clear relatively recently. The multiple interactions that hold the supramolecular polymeric structure together are similar in strength to those between solute and solvent. The cooperativity found in ordered supramolecular polymers leads to the possibility of amplifying these solute–solvent effects and will shed light on extremely subtle solvation phenomena. As a result, many exciting effects of solute–solvent interactions in modern physical organic chemistry can be studied using supramolecular polymers. Our aim is to put the recent progress into a historical context and provide avenues toward a more comprehensive understanding of solvents in multicomponent supramolecular systems.

Adduct under Field—A Qualitative Approach to Account for Solvent Effect on Hydrogen Bonding

The location of a mobile proton in acid-base complexes in aprotic solvents can be predicted using a simplified Adduct under Field (AuF) approach, where solute–solvent effects on the geometry of hydrogen bond are simulated using a fictitious external electric field. The parameters of the field have been estimated using experimental data on acid-base complexes in CDF3/CDClF2. With some limitations, they can be applied to the chemically similar CHCl3 and CH2Cl2. The obtained data indicate that the solute–solvent effects are critically important regardless of the type of complexes. The temperature dependences of the strength and fluctuation rate of the field explain the behavior of experimentally measured parameters.

Investigation of Solution pKa and Thermodynamic Values of Lamivudine and Pefloxacin Drugs by Ab initio and DFT Methods

In this work we investigate the thermodynamic properties and pKa value of lamivudine and pefloxacin drugs, in aqueous solutions, by ab initio and density functional theory (DFT) methods at different temperatures. Molecular structures and solute–solvent effects of the anions, cations, and neutral molecules of lamivudine and pefloxacin were studied by the polarizable continuum model (PCM). The calculation was done at the DFT-B3LYP/6-31+G(d) level of theory using Tomasi’s method to analyze the formation of intermolecular hydrogen bonds (IHB) in aqueous solution. The pKa1 values of lamivudine and pKa2 values of pefloxacin increase with temperature increase. In contrast, the pKa1 values of pefloxacin decrease when the temperature increases. Further, the thermodynamic properties of the ionization processes (∆H, ∆S and ∆G) of the drugs in aqueous solution were determined and discussed. The results of this work are in good agreement with the literature data at 298.15 K.

Predicting Nucleation of Isonicotinamide from the Solvent-Solute Interactions of Isonicotinamide in Common Organic Solvents.

The interactions of isonicotinamide (INA) with seven common solvents (acetic acid, acetonitrile, acetone, chloroform, ethyl acetate, and methanol) have been studied to examine solute-solvent effects on the nucleation of INA from these solvents. In a simple model of 1:1 solute-solvent interactions, the strongest INA-solvent interaction is with acetic acid (binding energy, Δ Ebind = -64.05 kJ mol-1) and the weakest is with chloroform (Δ Ebind = -24.85 kJ mol-1). This arises since acetic acid and INA form a hydrogen-bonding motif containing two moderate strength N-H···O hydrogen bonds, while chloroform and INA have a single weak C-H···O hydrogen bond. Taking acetic acid, chloroform, and methanol, the solvents with the strongest, the weakest, and an intermediate strength INA-solvent binding energy, the solvation of INA was studied to compare it with the 1:1 model. Acetic acid has the strongest binding energy (-872.24 kJ mol-1) and solvation energy (-341.20 kJ mol-1) with chloroform binding energy (-517.72 kJ mol-1) and solvation energy (-199.05 kJ mol-1). Methanol has intermediate binding energy (-814.19 kJ mol-1) and solvation energies (-320.81 kJ mol-1). These results further confirm the recent the findings which indicate that the key trends in solvent-solute interactions can be determined from a simple and efficient 1:1 dimer model and can be used to predict ease of nucleation with stronger binding energies correlating to slower, more difficult nucleation. A limit of this model is revealed by considering alcohol and acid solvents with longer alkyl chains.

Dispersion and Hydrogen Bonding Rule: Why the Vaporization Enthalpies of Aprotic Ionic Liquids Are Significantly Larger than those of Protic Ionic liquids.

It is well known that gas-phase experiments and computational methods point to the dominance of dispersion forces in the molecular association of hydrocarbons. Estimates or even quantification of these weak forces are complicated due to solvent effects in solution. The dissection of interaction energies and quantification of dispersion interactions is particularly challenging for polar systems such as ionic liquids (ILs) which are characterized by a subtle balance between Coulomb interactions, hydrogen bonding, and dispersion forces. Here, we have used vaporization enthalpies, far-infrared spectroscopy, and dispersion-corrected calculations to dissect the interaction energies between cations and anions in aprotic (AILs), and protic (PILs) ionic liquids. It was found that the higher total interaction energy in PILs results from the strong and directional hydrogen bonds between cation and anion, whereas the larger vaporization enthalpies of AILs clearly arise from increasing dispersion forces between ion pairs.

Real-Time Quantum Dynamics Reveals Complex, Many-Body Interactions in Solvated Nanodroplets.

Electronic excitations in the liquid phase are surprisingly rich and considerably more complex than either gas-phase or solid-state systems. While the majority of physical and biological processes take place in solvent, our understanding of nonequilibrium excited-state processes in these condensed phase environments remains far from complete. A central and long-standing issue in these solvated environments is the assessment of many-body interactions, particularly when the entire system is out of equilibrium and many quantum states participate in the overall process. Here we present a microscopic picture of solute-solvent electron dynamics and solvatochromic effects, which we uncover using a new real-time quantum dynamics approach for extremely large solvated nanodroplets. In particular, we find that a complex interplay of quantum interactions underlies our observations of solute-solvent effects, and simple macroscopic solvatochromic shifts can even be qualitatively different at the microscopic molecular level in these systems. By treating both the solvent and the solute on the same footing at a quantum-mechanical level, we demonstrate that the electron dynamics in these systems are surprisingly complex, and the emergence of many-body interactions underlies the dynamics in these solvated systems.

A combined TD-DFT and spectroscopic investigation of the solute–solvent interactions of efavirenz

Efavirenz, commercially known as Sustiva® or Stocrin®, is a first-line antiretroviral treatment for HIV/AIDS. The clinical efficacy of efavirenz is, however, hindered by its solubility. We sought to investigate the solute–solvent effects of efavirenz by means of a combined qualitative study implementing UV–visible spectrophotometry, 1H NMR spectroscopy and time-dependent density functional theory (TD-DFT) calculations. The UV spectrum displayed two main absorbance maxima, band I and band II at 246–260 and 291–295nm, respectively. A general bathochromic shift was noticed from the non-polar solvent cyclohexane to the most polar solvent DMSO (≈13.69nm) in band I and a smaller bathochromic (≈2.17nm) and hyperchromic shift was observed in band II. We propose that these observations are due to the role of the amino (NH) and carbonyl (CO) functionalities which induce charge-transfer and intra- and inter-molecular hydrogen bonding. The aromatic and amine protons showed the most deshielded effects in the observed chemical shifts (δ) in the more polar DMSO-d6 solvent relative to CDCl3. The 1H NMR chemical shifts observed are due to the increased delocalization of the lone pair electrons of the amino nitrogen with increased polarity of the more polar DMSO solvent. The theoretical reproduction of the UV and 1H NMR spectra by means of TD-DFT is in good agreement with the experimental results.

Low concentrated hydroxyectoine solutions in presence of DPPC lipid bilayers: A computer simulation study

The influence of hydroxyectoine on the properties of the aqueous solution in presence of DPPC lipid bilayers is studied via semi-isotropic constant pressure (NPT) Molecular Dynamics simulations. We investigate the solvent–co-solute behavior in terms of Kirkwood–Buff integrals as well as hydrogen bond life times for an increasing hydroxyectoine concentration up to 0.15mol/L. The observed preferential exclusion mechanism identifies hydroxyectoine as a kosmotropic osmolyte. Our findings with regard to the DPPC lipid bilayer indicate an increase of the surface pressure as well as the solvent accessible surface area in presence of higher hydroxyectoine concentrations. The results are in agreement to the outcome of recent experiments. With this study, we are able to validate the visibility of co-solute–solute–solvent effects for low and physiologically relevant osmolyte concentrations.

The coupling constant polarizability and hyperpolarizabilty of 1J(NH) in N-methylacetamide, and its application for the multipole spin-spin coupling constant polarizability/reaction field approach to solvation

We present a benchmark study of a combined multipole spin-spin coupling constant (SSCC) polarizability/reaction field (MJP/RF) approach to the calculation of both specific and bulk solvation effects on SSCCs of solvated molecules. The MJP/RF scheme is defined by an expansion of the SSCCs of the solvated molecule in terms of coupling constant dipole and quadrupole polarizabilities and hyperpolarizabilities derived from single molecule ab initio calculations. The solvent electric field and electric field gradient are calculated based on data derived from molecular dynamics (MD) simulations thereby accounting for solute-solvent dynamical effects. The MJP/RF method is benchmarked against polarizable QM/MM calculations for the one-bond N-H coupling constant in N-methylacetamide. The best agreement between the MJP/RF and QM/MM approaches is found by truncating the electric field expansion in the MJP/RF approach at the linear electric field level. In addition, we investigate the sensitivity of the results due to the choice of one-electron basis set in the ab initio calculations of the coupling constant (hyper-)polarizabilities and find that they are affected by the basis set in a way similar to the coupling constants themselves.

DFT study of the hydrogen bond strength and IR spectra of formic, oxalic, glyoxylic and pyruvic acids in vacuum, acetone and water solution

The molecular geometries of the possible conformations of formic, oxalic, glyoxylic and pyruvic acids have been fully optimized at DFT B3LYP/6-311++G(d,p) levels of calculation in vacuum as well as in water and acetone solution. Solutions were treated according to the SCRF PCM approach but some formic acid–water and formic acid–acetone clusters as well as adducts of oxalic acid with two or four water molecules were also taken into account for testing the importance of specific solute–solvent effects. All the most stable isomers of the title compounds are characterized by weak intramolecular hydrogen bonds, whose strengths (EHB) cannot be correctly estimated as stability difference between the open and chelate forms since the energy of the former isomer is, in turn, stabilized by a weak hydrogen bridge due to the formic acid moiety. Following the Rotation Barrier Method (RBM), proposed some years ago, EHB in the examined molecules (gas phase) falls in the range of 18–22 kJ/mol for oxalic acid (9.6 kJ/mol for the c-C-t isomer), 16.8 kJ/mol for glyoxylic acid and 19.8 kJ/mol for pyruvic acid. Most of them disappear at all, or nearly at all, both in acetone and aqueous solution, in consequence of the solvent effect. The frequencies of the OH and CO stretching modes, calculated according to the anharmonic oscillator model, are in very good agreement with the experimental literature data, where available. Copyright © 2009 John Wiley & Sons, Ltd.

Prediction of SAMPL-1 Hydration Free Energies Using a Continuum Electrostatics-Dispersion Model

The SAMPL-1 hydration free energy blind prediction challenge data set includes 63 compounds that are more chemically diverse, polyfunctional, drug-like, and with examples of transfer free energies and molecular weights larger than ever before seen in previously tabulated data sets of neutral compounds. For the prospective SAMPL-1 study, we employed a continuum model including a boundary element solution of the Poisson equation to describe electrostatic solvation, a molecular surface area-based cost of cavity formation in water, and a continuum Lennard-Jones potential to account for dispersion-repulsion solute-solvent effects. For the latter contribution, continuum van der Waals atom-type coefficients were calibrated and validated on previously available hydration data sets. In the prospective study, this continuum hydration model yielded SAMPL-1 predictions highly correlated with experimental data, albeit with a slope of slightly above 0.5, suggesting a valid model but with a systematic error. Analysis of the major outliers, all overestimating the experimental hydration data, highlights a common structural theme as a possible cause of the prediction errors: densely polar and hydrogen-bond-capable structures, featuring primarily substituted (sulfon)amide groups, often in conjugated systems. By examining analog pairs within the SAMPL-1 data set, it was also noted that certain solvation trends are captured neither by chemical sense nor by our hydration model, which seem too additive. A retrospective analysis of model transferability between hydration data sets as a function of its parameters and complexity indicates that the electrostatic component of the model is fairly transferrable across data sets, but the nonelectrostatic terms are less so. For the chemical space covered in SAMPL-1, absolute prediction errors indicate that the simpler transferrable electrostatics-only model outperforms the more complex model including cavity and continuum dispersion terms. Possible directions to further improve this continuum hydration model are proposed.

Thermodynamic study of proton transfer reactions of Re(V) trans-dioxocomplexes in aqueous solution

The thermodynamics of protonation of trans-[Re(V)O(2)L(2)](+) (L = aliphatic di and polyamines) complexes in aqueous solution was studied by using experimental and theoretical approaches. The complexes containing diamines undergo protonation on the oxo ligands, whereas those containing polydentate amines protonate on uncoordinated amino groups. The protonation reactions were studied experimentally by microcalorimetric techniques, in all cases exothermic with |DeltaH degrees | ranging from 7 to 50 kJ/mol. For complexes containing diamines, the exothermicity was in concordance with the basicities in some cases, while in others no systematic behaviour was found. For complexes with polydentate amines, the enthalpy dominates with a modest influence on the entropy. Theoretically, Density Functional Theory (DFT) methods were employed in the gas phase, and bulk solvent effects were treated by means of the Polarizable Continuum Model. Direct solute-solvent effects were considered adding explicit water molecules. The enthalpy change calculated in the gas phase was in marked disagreement with the experimental results due to the relevancy of solvation/desolvation processes. The explicit inclusion of water molecules led to a good improvement. A discrete-continuum model was also employed, for which DeltaG degrees was overestimated in all cases. Further investigations, both experimental and theoretical are necessary to get a more complete picture of the proton transfer reactions of these complexes. The experimental values herein determined constitute the first step to construct a set of data to which it is possible to benchmark new theoretical approaches to compute the thermodynamics of proton transfer reactions of metal complexes in aqueous solution.

A theoretical thermochemical study of solute-solvent dielectric effects in the displacement of codon-anticodon base pairs

Quantum-chemical solvent effect theories describe the electronic structure of a molecular subsystem embedded in a solvent or other molecular environment. The solvation of biomolecules is important in molecular biology, since numerous processes involve proteins interacting in changing solvent-solute systems. In this theoretical study, we focus on mRNA-tRNA base pairs as a fundamental step in protein synthesis influenced by hydrogen bonding between two antiparallel trinucleotides, namely, the mRNA codon and tRNA anticodon. We use the mean reaction field theories, which describe electrostatic and polarization interactions between solute and solvent in the AAA, UUU, AAG, and UUC triplex sequences optimized in various solvent media such as water, dimethylsulfoxide, methanol, ethanol, and cyclopean using the self-consistent reaction field model. This process depends on either the reaction potential function of the solvent or charge transfer operators that appear in solute-solvent interaction. Because of codon and anticodon biological criteria, we performed nonempirical quantum-mechanical calculations at the BLYP and B3LYP/3-21G, 6-31G, and 6-31G* levels of theory in the gas phase and five solvents at three temperatures. Finally, to obtain more information, we calculated thermochemical parameters to find that the dielectric constant of solvents plays an important role in the displacement of amino acid sequences on codon-anticodon residues in proteins, which can cause some mutations in humans.

Nuclear Magnetic Shielding of the 113Cd(II) Ion in Aqua Solution: A Combined Molecular Dynamics/Density Functional Theory Study

We present a combined molecular dynamics simulation and density functional theory investigation of the nuclear magnetic shielding constant of the (113)Cd(II) ion solvated in aqueous solution. Molecular dynamics simulations are carried out for the cadmium-water system in order to produce instantaneous geometries for subsequent determination of the nuclear magnetic shielding constant at the density functional theory level. The nuclear magnetic shielding constant is computed using a perturbation theory formalism, which includes nonrelativistic and leading order relativistic contributions to the nuclear magnetic shielding tensor. Although the NMR shielding constant varies significantly with respect to simulation time, the value averaged over increasing number of snapshots remains almost constant. The paramagnetic nonrelativistic contribution is found to be most sensitive to dynamical changes in the system and is mainly responsible for the thermal and solvent effects in solution. The relativistic correction features very little sensitivity to the chemical environment, and can be disregarded in theoretical calculations when a Cd complex is used as reference compound in (113)Cd NMR experiments, due to the mutual cancelation between individual relativistic corrections.

Natural J coupling (NJC) analysis of the electron lone pair effect on NMR couplings: 2. The anomeric effects on 1 J (C, H) couplings and its dependence on solvent

The electronic origin of the influence of the anomeric effect (negative hyperconjugative interaction, NHI) on the Fermi contact (FC) term of 1 J(C, H) couplings has been studied from a theoretical point of view at the DFT-B3LYP level. The HN=CH2, molecule was chosen as the primary model compound, in which both FC 1 J(C, H) couplings were decomposed into bond contributions with the natural J coupling dissection approach (NJC). Differences between the 1 J (C, H)FC couplings for C——H bonds in synperiplanar and antiperiplanar orientations with respect to the nitrogen non-bonding electron pair closely follow the experimental trend. They are made up chiefly of three NJC contributions: ‘bond’, ‘direct lone pair’ and the ‘carbon-core orbitals’. The NHI influence on these terms was studied by applying the natural bond orbital (NBO) deletion procedure to the charge transfer interaction into the antiperiplanar (C——H) antibond (n(N)→(C——H)*) prior to the NJC dissection calculation. The dielectric solvation effect on both the total FC terms and the respective NJC contributions was estimated by carrying out the calculations using the polarization continuum model. Inhibition of the anomeric effect is evident when the solvent polarity is increased. NHI saturates rapidly with increasing solvent dielectric. Specific solute-solvent interaction effects on 1 J(C, H) couplings were estimated by evaluating molecular complex models of the form CH2=HN…S (S = H2O and DMSO).

Solute–Solvent effects on the Dissociation of Oxalic Acid in Aqueous Mixtures of Ethylene Glycol Solvent at Different Temperatures

The dependence of the dissociation constants of oxalic acid on temperature and composition of ethylene glycol–water binary mixtures have been studied. Thermodynamic and extrathermodynamic analysis of the obtained results have been examined. The p K values have been correlated with the dielectric constant of the medium according to Born's electrostatic equation.

Time-resolved fluorescence of polarizable chromophores

The paper reports an exact solution for spectral profiles of time-resolved fluorescence following a broad-band excitation producing changes in both the chromophore’s dipole moment and the polarizability. The problem is formulated in terms of a two-state chromophore with a bilinear coupling to a Gaussian solvent mode. Closed-form solutions for the time-dependent spectral shift and width are obtained. These two transient spectral moments are sufficient to generate transient, non-Gaussian band-shapes by using the proposed formalism. An approximately linear relation between the normalized shift and width time correlation functions is found. The Stokes shift correlation function is virtually insensitive to the nonlinear solute–solvent effects, in spite of dramatic transient changes in the spectral width. Depending on chromophore’s parameters, the transient line shape can be well approximated by a nonstationary Gaussian process or shows clearly non-Gaussian statistics. The model is extended to treat heterogeneous solvent dynamics.

Solute-solvent interactions probed by picosecond transient Raman spectroscopy: S1trans-4,4′-diphenylstilbene in aromatic solvents

The picosecond transient Raman spectra of S1 trans-4,4′-diphenylstilbene (DPS) in benzene and toluene at an excitation wavelength of 310 nm and probe wavelengths of 630 and 660 nm are presented. No significant dynamic variations between benzene and toluene in the change in peak position of vibrational modes in S1 DPS with delay were observed. These data indicate that vibrational relaxation occurs at similar rates in both solvents. The vibrational relaxation dynamics of S1 DPS in the aromatic solvents were also compared with those in dioxane and methylene chloride. It is suggested that specific solute–solvent effects contribute to vibrational relaxation in these solvents. It was found that the relative intensities of Raman bands that contain contributions from the phenyl–phenyl stretch are different for S1 DPS in toluene compared with S1 DPS in benzene. The difference in relative intensities is attributed to an equilibrium conformation in S1 DPS that is perturbed by the methyl group on toluene, giving rise to a variation in the conformation of the biphenyl group in S1 DPS. Copyright © 2000 John Wiley & Sons, Ltd.