Molecules In Nonpolar Solvents Research Articles

Recognition of Bis-thiourea Tweezers to Neutral Molecules in Non-Polar Solvent

Recognition of Bis-thiourea Tweezers to Neutral Molecules in Non-Polar Solvent

Vibrational and ultrasonic relaxation spectroscopic study of keto-to-enol tautomerism: The case of acetylacetone

We report on a concentration-dependent Raman and ultrasonic relaxation study of the binary acetylacetone solutions in a wide mole fraction range. We combined vibrational and ultrasonic relaxation spectroscopies with DFT theoretical calculations for the systematic examination of the keto-to-enol tautomerism taking place in acetylacetone solutions with polar and non-polar solvent. Two sets of solutions were prepared with different solvents in terms of polarity. Raman spectra revealed that the keto and enol tautomers of acetylacetone coexist in solution and the keto tautomer is favored as the solvent polarity increases. A single Debye-type relaxation process is detected in the acoustic spectra, which is assigned to the interconversion process between ACAC tautomers. The isentropic volume change associated with the isomerization reaction was estimated from the acoustic data and found to decrease up to x∼0.2, while above this mole fraction reaches an almost constant value of ∼13.6 ml/mol, close to the theoretically estimated value of ΔVtheor,CCl4=12.955 ml/mol in CCl4 solvent environment. The keto-to-enol isomerization in the dilute region was found to be strongly affected by the presence of the non-polar solvent molecules, while for mole fractions higher than x∼0.3 the process is not considerably altered. Several physical properties of the system including density and acoustic properties, as well as the intermolecular free length and polarizability exhibited an inflection point at a specific mole fraction signifying the cross-over of two different regimes related with different tautomerization rates analogous to that observed in the Raman spectra. The results are analyzed and discussed in the framework of the current phenomenological status of the field.

Model of inverse “dry” micelles with coexisting spherical, globular and cylindrical aggregates

A new statistical thermodynamic model of inverse nonionic aggregates of surfactant molecules in nonpolar solvents is considered. This model admits the fluctuation coexistence of inverse spherical, globular, and spherocylindrical aggregates without activation barriers between them. The model is based on the assumption of a uniform bulk density of the number of molecular groups inside the core of an aggregate that can continuously transform into a sphere, a globule, and a spherocylinder. In this model, for any aggregation numbers, the work of aggregation depends not only on the aggregation numbers and the concentration of surfactant monomers, but also on two independent geometric parameters characterizing, at the same aggregation numbers, the deviation from the spherical form of the aggregate towards globular and spherocylindrical forms. Even in the range of small aggregation numbers, this fact leads to a significant difference between the equilibrium distribution function of aggregates, which depends on the aggregation number and two form parameters, and the one-dimensional distribution function in terms of aggregation numbers. It is shown that the optimal values of the form parameters, which minimize the work of aggregation, are in good agreement for spherocylindrical aggregates with the predictions of a purely geometric model of such aggregates under the additional assumption of a uniform surface density of molecular groups at the micelle core. The predictions of a new molecular thermodynamic model for the degrees of surfactant micellization in inverse aggregates of various forms at different surfactant concentrations are considered.

Multiparticle orientational correlations are responsible for the nonlinear dielectric effect: Analysis of temperature-dependent measurements for glycerol.

The nonlinear dielectric effect (NDE) is traditionally viewed as originating from saturation of the response of individual dipoles in a strong electric field. This mean-field view, mathematically described by the Langevin saturation function, predicts enhanced dielectric saturation at lower temperatures. In contrast, recent experiments for glycerol have shown a sharp increase of the NDE with increasing temperature. The formalism presented here splits the NDE into a sum of a term representing binary correlations of dipolar orientations and terms referring to three- and four-particle orientational correlations. Analysis of experimental data shows that the contribution of three- and four-particle correlations strongly increases at elevated temperatures. The mean-field picture of dielectric saturation as the origin of the NDE is inconsistent with observations. A positive NDE (increment of the field-dependent dielectric constant) is predicted for low-concentration solutions of polar molecules in nonpolar solvents. The dependence of the NDE on the concentration of the polar component is polynomial.

Solvent-Assisted Li-Ion Transport and Structural Heterogeneity in Fluorinated Battery Electrolytes.

The electrolytes diluted with fluorinated solvents show promising properties toward better battery technology than existing ones. The transport of Li ions in these fluorinated electrolytes is essential to access the performance of a battery. It is believed that the transport of the Li ion in these electrolytes occurs through polar solvents in the matrix of nonpolar solvent molecules. The atomistic details of this mechanism are yet to be proved using the dynamics of these mixtures. In this study, we performed classical molecular dynamics simulations at various temperatures to probe this mechanism through the structure and dynamics of electrolytes at the atomic level. Here, we have shown that the polar fluorinated solvents assist the Li-ion transport in a region of nonpolar solvent. Highly polar molecules also solvate the Li ion at a lower temperature. The nonpolar solvent solvates the Li ion weakly as compared to others. The calculated values of the ionic conductivity from the Green-Kubo relation provide a better match than that from an experimental conductivity meter. Furthermore, we probed the heterogeneity in the dynamics of the electrolytes by calculating the non-Gaussian parameter. We also show that the transport mechanism of the Li ion in diluted concentrated electrolytes is different than a few of the other reported electrolytes. We have also calculated the ion-pair and ion-cage lifetimes to see the most and least lived ion/ion-solvent pairs. The mechanism given from the present study may help to design the fluorinated electrolytes for Li-ion batteries.

Features of the Electronic Structure of Excited Quadrupolar Molecules in Non-Polar Solvents

Interactions of the electronic subsystem of the quadrupolar fluorophore with intramolecular highfrequency antisymmetric vibrations and solvent polarization are responsible for charge transfer symmetry breaking (SB), which is observed after optical excitation of such molecules in polar solvents. It is known that although these two interactions are mathematically described in similar ways, only the interaction of the fluorophore with solvent orientational polarization can create a state with broken symmetry if this interaction is strong enough. Nevertheless, the interaction of a quadrupolar fluorophore with intramolecular highfrequency antisymmetric vibrations in nonpolar solvents leads to a considerable reconstruction of the electronic subsystem. The analysis of the excited state of quadrupolar molecules in nonpolar solvents performed in this study reveals that such molecules can behave like quantum twostate systems, that is, as a quasispin s = 1/2, having an electric dipole moment instead of a magnetic one. This feature of excited quadrupolar molecules may be of interest to emerging technologies of molecular electronics.

Direct Measurement of the Selective Microwave-Induced Heating of Agglomerates of Dipolar Molecules: The Origin of and Parameters Controlling a Microwave Specific Superheating Effect.

Agglomerates of polar molecules in nonpolar solvents are selectively heated by microwave radiation. The magnitude of the selective heating was directly measured by using the temperature dependence of the intensities of the Stokes and anti-Stokes bands in the Raman spectra of p-nitroanisole (pNA) and mesitylene. Under dynamic heating conditions, a large apparent temperature difference (ΔT) of over 100 °C was observed between the polar pNA solute and the nonpolar mesitylene solvent. This represents the first direct measurement of the selective microwave heating process. The magnitude of the selective microwave heating was affected by the properties of the agglomerated pNA. As the concentration of the pNA increases, the magnitude of the selective heating of the pNA was observed to decrease. This is explained by the tendency of the pNA dipoles to orient in an antiparallel fashion in the aggregates as measured by the Kirkwood g value, which decreased with increasing concentration. This effect reduces the net dipole moment of the agglomerates, which decreases the microwave absorption. After the radiation was terminated, the effective temperature of the dipolar molecules returned slowly to that of the medium. The slow heat transfer was modeled successfully by treating the solutions as a biphasic solvent/solute system. Based on modeling and the fact that the agglomerate can be heated above the boiling temperature of the solvent, an insulating layer of solvent vapor is suggested to form around the heated agglomerate, slowing convective heat transfer out of the agglomerate. This is an effect unique to microwave heating.

Effect of aliphatic solvents on the reverse self-assembly of lecithin and calcium chloride mixtures

Reverse spherical micelles are formed by self-assembly of lecithin molecules in nonpolar solvents. They are transformed into reverse cylindrical micelles when inorganic salts such as CaCl2 are added to lecithin solutions. When the reverse cylindrical micelles are long enough to be entangled, the solution viscosity increases significantly, forming organogels. In this study, we investigate the effects of aliphatic solvents on the reverse self-assembly of lecithin and CaCl2 mixtures. When the hydrocarbon chain length of the aliphatic solvents increases, the viscosities of lecithin and CaCl2 mixtures increase. In addition, for the same hydrocarbon chain length, mixtures in alkanes have higher viscosities than those in alkenes. Small-angle X-ray scattering (SAXS) results suggest that the viscosities of the mixtures are correlated with the length of the reverse cylindrical micelles. Herein, Fourier transform infrared spectroscopy was used to investigate the interactions between lecithin headgroups and CaCl2, which play a significant role in forming the reverse cylindrical micelles.

Enhancing compatibility in epoxy/vulcanized natural rubber (VNR)/Graphene nano-platelets (GNP) system using epoxidized natural rubber (ENR-50)

This paper reports the effect of epoxidized natural rubber (ENR-50) as a compatibilizer on the mechanical, thermal, and electrical performances of epoxy/VNR and epoxy/VNR/GNP systems. Fixed blend ratios at 95/5 and 80/20 vol% of epoxy/VNR were studied. Epoxy/VNR and epoxy/VNR/GNP systems were prepared using magnetic stirring method, with ENR-50 contents varied at 0, 5, and 10 vol%. Flexural strength and modulus of two systems have successfully improved with 5 vol% of ENR-50 content. With the incorporation of ENR-50, the distribution of VNR phases in epoxy matrix was more homogenous, thus improving the compatibility of the system. Nevertheless, the toughness properties of the compatibilized system were lower as compared to the non-compatibilized system, albeit higher than pure epoxy. Thermal stability (Tmax) of the compatibilized system was lower as compared to non-compatibilized system, which was attributed to the low thermal stability of oxygen-containing groups (epoxide groups) on ENR-50. The incorporation of ENR-50 decreased the electrical conductivity of compatibilized system. This was supported by the d-spacing values, as obtained from the XRD results. The compatibilized system also shows high cross-link density as compared to the non-compatibilized system, where ENR-50 inhibited the penetration of non-polar solvent molecules into the cross-linked network structure.

Inspecting fluctuation and coordination around chromophore inside green fluorescent protein from water to nonpolar solvent.

Green fluorescent protein (GFP) is a widely used biomarker that demands systematical rational approaches to its structure function redesign. In this work, we mainly utilized atomistic molecular dynamics simulations to inspect and visualize internal fluctuation and coordination around chromophore inside GFP, from water to nonpolar octane solvent. We found that GFP not only maintains its β-barrel structure well into the octane, but also sustains internal residue and water coordination to position the chromophore stably while suppress dihedral fluctuations of the chromophore, so that functional robustness of GFP is achieved. Our accompanied fluorescence microscope measurements accordingly confirmed the GFP functioning into the octane. Furthermore, we identified that crucial water sites inside GFP along with permeable pores on the β-barrel of the protein are largely preserved from the water to the octane solvent, which allows sufficiently fast exchanges of internal water with the bulk or with the water layer kept on the surface of the protein. By additionally pulling GFP from bulk water to octane, we suggest that the GFP function can be well maintained into the nonpolar solvent as long as, first, the protein does not denature in the nonpolar solvent nor across the polar-nonpolar solvent interface; second, a minimal set of water molecules are in accompany with the protein; third, the nonpolar solvent molecules may need to be large enough to be nonpermeable via the water pores on the β-barrel.

Selective C70 encapsulation by a robust octameric nanospheroid held together by 48 cooperative hydrogen bonds

Self-assembly of multiple building blocks via hydrogen bonds into well-defined nanoconstructs with selective binding function remains one of the foremost challenges in supramolecular chemistry. Here, we report the discovery of a enantiopure nanocapsule that is formed through the self-assembly of eight amino acid functionalised molecules in nonpolar solvents through 48 hydrogen bonds. The nanocapsule is remarkably robust, being stable at low and high temperatures, and in the presence of base, presumably due to the co-operative geometry of the hydrogen bonding motif. Thanks to small pore sizes, large internal cavity and sufficient dynamicity, the nanocapsule is able to recognize and encapsulate large aromatic guests such as fullerenes C60 and C70. The structural and electronic complementary between the host and C70 leads to its preferential and selective binding from a mixture of C60 and C70.

Probing Solvation Dynamics around Aromatic and Biological Molecules at the Single-Molecular Level.

Solvation processes play a crucial role in chemical reactions and biomolecular recognition phenomena. Although solvation dynamics of interfacial or biological water has been studied extensively in aqueous solution, the results are generally averaged over several solvation layers and the motion of individual solvent molecules is difficult to capture. This review describes the development and application of a new experimental approach, namely, picosecond time-resolved pump-probe infrared spectroscopy of size- and isomer-selected aromatic clusters, in which for the first time the dynamics of a single individual solvent molecule can be followed in real time. The intermolecular isomerization reaction is triggered by resonant photoionization (pump), and infrared photodissociation (probe) at variable delay generates the spectroscopic signature of salient properties of the reaction, including rates, yields, pathways, branching ratios of competing reactions, existence of reaction intermediates, occurrence of back reactions, and time scales of energy relaxation processes. It is shown that this relevant information can reliably be decoded from the experimental spectra by sophisticated molecular dynamics simulations. This review covers a description of the experimental strategies and spectroscopic methods along with all applications to date, which range from aromatic clusters with nonpolar solvent molecules to aromatic monohydrated biomolecules.

The Existence of Two Types of Colloidal Solutions of Molecules Fullerene C60

The last thirty years scientists carried out an active search of universal parameter of solvent C60 for predicting the solubility of fullerenes. However, this parameter was not found up to these days. In this paper it has been found an explanation of the impossibility of detection of such parameter. In present paper the features of the solubility of fullerene C60 molecules in nonpolar solvents have been studied. The molecule state diagram of the fullerene С60 molecules in solution at temperatures 265+308 K and pressure range 1+100 MPa indicating the existence field of β and γ-modifications, has been constructed. Moreover, it has been shown that in the solutions of fullerenes C60 in the γ-state the solubility decreases with a rise in temperature since the chemical activity of fullerene molecule increases. For this reason during extraction procedure the temperature rise causes the value of extraction rate to increase, but solubility – to decrease, i.e. to diminish the concentration of fullerenes molecules in the solvent volume.

Aggregates of poly-functional amphiphilic molecules in water and oil phases

The solvation and aggregate formation of complex amphiphilic molecules such as tetra-acids in polar and nonpolar phases are studied via Molecular Dynamics simulations. The nonpolar core of tetra-acid molecules is found to be effectively impermeable for water molecules resulting in a low solubility in the polar solvent, while nonpolar solvent molecules sufficiently solvate the amphiphilic molecules considered, enabling an open conformation of their molecular structure. The rigidity of the core region of the tetra-acid molecules has been found to play a crucial role in their behavior in both polar and nonpolar phases. In the polar phase, simulations have shown that tetra-acids form micelle-like structures with a small aggregation number, confirming previous experimental work. The identification of a case of study in which micelle-like structures can form only with a small aggregation number enables the study via Molecular Dynamics of micelle-micelle interactions. Micelle stability and dispersion in the polar phase under different conditions can be therefore investigated. In the nonpolar phase, the preferential interactions between carboxyl groups, the affinity of the tetra-acids with the solvent molecules, and the structural characteristics of the central core moiety of the tetra-acids have been found to possibly induce a web like array, or network.

Solvent- and guest-responsive supramolecular self-assembly of 1,3,5-tris(10-carboxydecyloxy) benzene by scanning tunneling microscopy

• TCDB can entrap solvent molecules or π-electron-conjugated guest molecules. • We calculate hydrogen bonding which is crucial to stabilize the assembly networks. • Structural properties rely on the solvent- and guest-responsive assembly. • Kinetics and thermodynamics explain the morphology character of polarity. Two-dimensional hydrogen-bonded networks formed in the self-assembly of 1,3,5-tris(10-carboxydecyloxy) benzene (TCDB) show regular solvent- and guest-induced supramolecular structural properties, which have been presented by scanning tunneling microscopy at the liquid–solid interface at ambient conditions. TCDB acting as a host template can entrap solvent molecules or π-electron-conjugated guest molecules to fabricate the flexible co-adsorption architectures, which are subject to the balance between the hydrogen bonding of the host lattice and the van der Waals forces between the host and the guest molecules. Hydrogen bonding among TCDB molecules is crucial to stabilize the host networks to settle the system into a global minimum of Gibbs free energy. We also find a strong correlation between the structural parameters and the physical properties of the solvent. Statistical analysis shows that the unit cell volume of TCDB dissolved in nonpolar 1-phenylotane and n -tetradecane shrank significantly compared with that of host–guest system, which fully reflects the coadsorption effect of nonpolar solvent molecules. Our results identify that the kinetic effect of adsorption/desorption as well as the solvent viscosity comes into play in tuning the two-dimensional self-assembled structures. Furthermore, mechanical calculations demonstrate that TCDB incline to adsorb with a larger dipole configuration in nonpolar solvents due to its dissolvability. It is believed that the results are of significance to supramolecular host–guest chemistry and surface science.

Dipole moment calculation in solution for some liquid crystalline molecules

Theoretical and experimental studies were used to determine the dipole moment for four liquid crystalline materials. Ab initio calculations in vacuum led to elimination of a few potential conformers in each molecule. These results were used as initial data to obtain the geometry of the molecules in non-polar solvent according to Onsager’s or PCM model. After employing both models, slight increase of the dipole moment was noticed for all the molecules. The results are similar for both the models, with one exception for the strongly polar molecule where the Onsager’s model led to much higher dipole moment. The dipole moment was also determined experimentally for all the materials. The experimental data were compared with the results from calculations. For the nematic materials, the theoretically predicted sign of the dielectric anisotropy was compared with experimental results.

Application of melt-blown technology in the manufacturing of a solvent vapor-sensitive, non-woven fabric composed of poly(lactic acid) loaded with multi-walled carbon nanotubes

We evaluated a solvent vapor-sensitive, non-woven fabric made from a biodegradable, poly(lactic acid) (PLA) polymer loaded with multi-walled carbon nanotubes. The sensory properties of the fabric were obtained by optimizing the process parameters for manufacturing the melt-blown, non-woven fabric composed of 98% PLA 4060D (Nature Works) and 2% multi-walled carbon nanotubes (Nanocyl®). The diffusion of polar and non-polar solvent molecules influenced the electron flow between the separated carbon nanotubes in percolation paths built into the PLA, resulting in an increase of the resistance of the melt-blown, non-woven fabrics. The statistically significant differences between the mean values of electrical resistance before and after the influence of the tested solvent vapors were achieved for the non-woven fabrics manufactured at high air velocity and low extruder screw speed, taking the values of 30 m3/h and 20 rpm, respectively. The results obtained for the non-woven fabric manufactured in the optimal conditions show that methanol vapor response has the lowest amplitude of 15%, whereas for benzene, acetone and toluene sensitivity reaches values of 60%, 40%, and 35%, respectively. The values of the relative resistance amplitude correspond with Flory–Huggins interaction parameters κPLA\benzene < κPLA\acetone < κPLA\toluene < κPLA\methanol.

Photoinduced Reaction of Hydrogen-End-Capped Polyynes with Iodine Molecules

Hydrogen-end-capped polyynes, H(C≡C)(n)H (n = 5-7), were photoirradiated in the presence of iodine molecules in nonpolar solvents to find a dramatic change in the UV/vis absorption spectrum. Absorption bands of polyynes in the UV and the band of I(2) in the visible region disappeared, whereas weaker bands of polyynes were intensified in the near UV region. The emerging features are associated with vibronic bands in the symmetry-forbidden transition of the linear polyyne molecule. Stoichiometry for the reaction, i.e., C(12)H(2) + nI(2) → C(12)H(2)I(2n), was determined to be n = 3 from the concentration-dependence experiment. (13)C NMR spectra for 1:3 mixture of polyyne and iodine molecules, namely C(10)H(2)/3I(2) and C(12)H(2)/3I(2), exhibited five and six lines, respectively, all shifted to lower fields compared to those in the case without iodine. After removing excess I(2) by reductive reagent of Na(2)SO(3), recovery of the missing absorption bands for the components of C(10)H(2) and I(2) was observed. These observations strongly support the formation of an unique molecular complex of C(2n)H(2)I(6) (n = 5-7) upon photoabsorption by an I(2) molecule within a cluster of polyyne and iodine molecules, C(2n)H(2)(I(2))(m) (m ≥ 3).

Studies on [3]pseudorotaxane formation from a bis-azacrown derivative as host and imidazolium ion-derivatives as guest

A new host molecule, having two azacrown derivatives bridged by luminescent naphthalene diimide functionality, is found to form a [3]pseudorotaxane derivative with imidazolim ion-based guest molecules in non-polar solvents through hydrogen-bonded adduct formation. Depending upon the length of the covalent linker that links the imidazolium ion and the luminescent naphthalene fragment in the guests, the [3]pseudorotaxane adducts adopt different conformation or orientation with varying π-π/donor-acceptor interaction. The mechanism for the naphthalene-based luminescence quenching by NDI fragment on adduct formation was found to be a combination of static, as well as dynamic with static quenching as the dominant one.

Solvation of hydrophobes in water and simple liquids

The solvation of nonpolar molecules in water and that in simple liquids are compared and contrasted. First, solvation thermodynamics is reviewed in a way that focuses on how the enthalpy and entropy of solvation depend on the choice of microscopic volume change v in the solvation process--including special choices v being zero (fixed-volume condition) and v being the partial molecular volume of a solute molecule (fixed-pressure condition)--and how the solvation quantities are related with temperature derivatives of the solvation free energy. Second, the solvation free energy and the solvation enthalpy of a Lennard-Jones (LJ) atom in model water are calculated in the parameter space representing the solute size and the strength of the solute-solvent interaction, and the results are compared with those for an LJ atom in the LJ solvent. The solvation diagrams showing domains of different types of solvation in the parameter space are obtained both for the constant-volume condition and for the constant-pressure condition. Similarities between water and the simple liquid are found when the constant-volume solvation is considered while a significant difference manifests itself in the fixed-pressure solvation. The domain of solvation of hydrophobic character in the parameter space is large in the constant-volume solvation both for water and for the simple liquid. When switched to the constant-pressure condition accompanying a microscopic volume change, the hydrophobic domain remains large in water but it becomes significantly small in the simple liquid. The contrasting results are due to the smallness of the thermal pressure coefficient of water at low temperatures.