Solvophobic Effect Research Articles

Selective Synthesis of Single‐ and Multi‐Walled Supramolecular Nanotubes by Using Solvophobic/Solvophilic Controls: Stepwise Radial Growth via “Coil‐on‐Tube” Intermediates

AbstractNovel hexa‐peri‐hexabenzocoronene (HBC) derivatives, FHBC and FHBC*, which carry perfluoroalkyl segments on one side of the HBC core and long alkyl tails on the other, were synthesized. Their perfluoroalkyl segments are highly solvated in C6F6 (solvophilic effect) and do not assemble, whereas in CH2Cl2, they are excluded (solvophobic effect) and assemble together consequently. For example, the use of C6F6 and CH2Cl2 as assembling media for FHBC leads to the selective formation of single‐ and multi‐walled nanotubes, respectively. When a higher monomer concentration is applied in CH2Cl2, multi‐walled nanotubes with a larger number of walls result. FHBC in CH2Cl2 self‐assembles rather slowly, thereby allowing for the observation of coil‐on‐tube structures, which are possible intermediates for the stepwise radial growth of the nanotubular wall. Casting of the multi‐walled nanotubes onto a quartz plate yields a superhydrophobic thin film with a water contact angle of 161±2°.

Selective Synthesis of Single‐ and Multi‐Walled Supramolecular Nanotubes by Using Solvophobic/Solvophilic Controls: Stepwise Radial Growth via “Coil‐on‐Tube” Intermediates

Novel hexa-peri-hexabenzocoronene (HBC) derivatives, (F) HBC and (F) HBC*, which carry perfluoroalkyl segments on one side of the HBC core and long alkyl tails on the other, were synthesized. Their perfluoroalkyl segments are highly solvated in C6 F6 (solvophilic effect) and do not assemble, whereas in CH2 Cl2 , they are excluded (solvophobic effect) and assemble together consequently. For example, the use of C6 F6 and CH2 Cl2 as assembling media for (F) HBC leads to the selective formation of single- and multi-walled nanotubes, respectively. When a higher monomer concentration is applied in CH2 Cl2 , multi-walled nanotubes with a larger number of walls result. (F) HBC in CH2 Cl2 self-assembles rather slowly, thereby allowing for the observation of coil-on-tube structures, which are possible intermediates for the stepwise radial growth of the nanotubular wall. Casting of the multi-walled nanotubes onto a quartz plate yields a superhydrophobic thin film with a water contact angle of 161±2°.

Quantifying Solvophobic Effects in Nonpolar Cohesive Interactions

The hydrophobic effect plays a central role in determining the structure, activity, and properties of biomolecules and materials. In contrast, the general manifestation of this phenomenon in other solvents—the solvophobic effect—although widely invoked, is currently poorly defined because of the lack of a universally accepted descriptor. Here we have used synthetic molecular balances to measure solvent effects on aromatic, aliphatic, and fluorous nonpolar interactions. Our solvent screening data combined with independent experimental measurements of supramolecular association, single-molecule folding, and bulk phase transfer energies were all found to correlate well with the cohesive energy density (ced) of the solvent. Meanwhile, other measures of solvent cohesion, such as surface tension and internal pressure, gave inferior correlations. Thus, we establish ced as a readily accessible, quantitative descriptor of solvophobic association in a range of chemical contexts.

Solvation of narrow pores of graphene-like plates in simple dipolar liquids: Wetting and dewetting behavior and solvent dynamics for varying pore width and solute–solvent interaction

We have investigated the solvation behavior of two parallel graphene-like plates in a Stockmayer liquid by molecular dynamics simulations for varying inter-plate separation and plate–solvent interactions. The solvent structure, orientation and dynamics around the plates and in their confined pores have been calculated. Layering of Stockmayer molecules with dipole vectors parallel to the surfaces is observed in the vicinity of the nonpolar plates. Density profiles reveal wetting and emptying of the narrow pores depending on the nature of solute–solvent interactions. In the interior and outer surface regions, solvent molecules are found to exhibit a significantly different dynamics than the bulk. From an overall perspective, the solvophobic effects observed here can be considered as the generic behavior of dipolar liquids near nonpolar surfaces without the presence of any specific and complex intermolecular interactions such as hydrogen bonds in water and other protic solvents.

Tetraphenylethene-based star shaped porphyrins: synthesis, self-assembly, and optical and photophysical study.

Supramolecular self-assembly and self-organization are simple and convenient ways to design and create controlled assemblies with organic molecules, and they have provoked great interest due to their potential applications in various fields, such as electronics, photonics, and light-energy conversion. Herein, we describe the synthesis of two π-conjugated porphyrin molecules bearing tetraphenylethene moieties with high fluorescence quantum yield. Photophysical and electrochemical studies were conducted to understand the physical and redox properties of these new materials, respectively. Furthermore, these derivatives were used to investigate self-assembly via the solvophobic effect. The self-assembled aggregation was performed in nonpolar and polar organic solvents and forms nanospheres and ring-like nanostructures, respectively. The solution based aggregation was studied by means of UV-vis absorption, emission, XRD, and DLS analyses. Self-assembled ring-shape structures were visualized by SEM and TEM imaging. This ring-shape morphology of nanosized macromolecules might be a good candidate for the creation of artificial light-harvesting nanodevices.

Wetting behavior of nonpolar nanotubes in simple dipolar liquids for varying nanotube diameter and solute-solvent interactions.

Atomistic simulations of model nonpolar nanotubes in a Stockmayer liquid are carried out for varying nanotube diameter and nanotube-solvent interactions to investigate solvophobic interactions in generic dipolar solvents. We have considered model armchair type single-walled nonpolar nanotubes with increasing radii from (5,5) to (12,12). The interactions between solute and solvent molecules are modeled by the well-known Lennard-Jones and repulsive Weeks-Chandler-Andersen potentials. We have investigated the density profiles and microscopic arrangement of Stockmayer molecules, orientational profiles of their dipole vectors, time dependence of their occupation, and also the translational and rotational motion of solvent molecules in confined environments of the cylindrical nanopores and also in their external peripheral regions. The present results of structural and dynamical properties of Stockmayer molecules inside and near atomistically rough nonpolar surfaces including their wetting and dewetting behavior for varying interactions provide a more generic picture of solvophobic effects experienced by simple dipolar liquids without any specific interactions such as hydrogen bonds.

Heterometallic complexes with gold(I) metalloligands: self-assembly of helical dimers stabilized by weak intermolecular interactions and solvophobic effects.

New gold(I) alkynyl metalloligands bpylCCAuL, bpyl'CCAuPPh3 , and PPN[Au(CCbpyl')2 ] (bpyl or bpyl'=2,2'-bipyridin-5-yl or -4-yl, respectively; L=PMex Ph3-x (x=1-3), P(C6 H3 Me2 -3,5)3 , PCy3 , XyNC) have been synthesized. Ligands bpylCCH and metalloligands bpylCCAuL (L=PPh3 , PMePh2 , PCy3 , CNXy) react with MX2 (M=Fe, Zn, X=ClO4 ; M=Co, X=BF4 ) to give complexes [M(bpylCCZ)3 ]X2 (Z=H or AuL). In most cases, these complexes are mixtures of fac and mer isomers in a statistical distribution, in both CH2 Cl2 and MeCN. However, for L=PPh3 , the fac isomer is dominant in MeCN. NMR and ESI-MS studies, together with the crystal structure of [Co(bpylCCAuPPh3 )3 ](BF4 )2 , suggest that this solvent dependence is originated by the formation of helical dimers between two fac complexes in MeCN. These dimers are stabilized by solvophobic effects and multiple intermolecular interactions. Complex [Fe(Ph3 PAuCCbpdiylCCAuPPh3 )3 ](ClO4 )2 (bpdiyl=2,2'-bipyridin-5,5'-diyl) was obtained by reaction of three diauro diethynylbipyridines and Fe(ClO4 )2 .

Partitioning Solvophobic and Dispersion Forces in Alkyl and Perfluoroalkyl Cohesion

AbstractFluorocarbons often have distinct miscibility properties compared to their nonfluorinated analogues. These differences may be attributed to van der Waals dispersion forces or solvophobic effects, but their contributions are notoriously difficult to separate in molecular recognition processes. Here, molecular torsion balances were used to compare cohesive alkyl and perfluoroalkyl interactions in a range of solvents. A simple linear regression enabled the energetic partitioning of solvophobic and van der Waals forces in the self‐association of apolar chains. The contributions of dispersion interactions in apolar cohesion were found to be strongly attenuated in solution compared to the gas phase, but still play a major role in fluorous and organic solvents. In contrast, solvophobic effects were found to be dominant in driving the association of apolar chains in aqueous solution. The results are expected to assist the computational modelling of van der Waals forces in solution.

Partitioning solvophobic and dispersion forces in alkyl and perfluoroalkyl cohesion.

Fluorocarbons often have distinct miscibility properties compared to their nonfluorinated analogues. These differences may be attributed to van der Waals dispersion forces or solvophobic effects, but their contributions are notoriously difficult to separate in molecular recognition processes. Here, molecular torsion balances were used to compare cohesive alkyl and perfluoroalkyl interactions in a range of solvents. A simple linear regression enabled the energetic partitioning of solvophobic and van der Waals forces in the self-association of apolar chains. The contributions of dispersion interactions in apolar cohesion were found to be strongly attenuated in solution compared to the gas phase, but still play a major role in fluorous and organic solvents. In contrast, solvophobic effects were found to be dominant in driving the association of apolar chains in aqueous solution. The results are expected to assist the computational modelling of van der Waals forces in solution.

Tert-Butyl chloride as a probe of the solvophobic effects

Relationships between the Gibbs free energy and enthalpy of solvation of tert-butyl chloride in various protic solvents are considered in order to compare the strength of the solvophobic effects from solvent to solvent. The values of thermodynamic functions of solvation are determined experimentally using titration calorimetry and gas chromatographic headspace analysis techniques. Positions of the data points on the ΔG vs ΔH plot indicate that the solvophobic effects take place in various mono- and dihydric alcohols, acetic acid, and acid amides. The excess positive contribution into free energy of solvation of tert-butyl chloride in self-associated solvents is used to characterize their strength quantitatively. It is shown that the solvophobic effects are stronger when the concentration of the hydrogen bonds in a solvent is larger.

Thermodynamics of solvation in propylene glycol and methyl cellosolve

Limiting activity coefficients of low-polar substances: aliphatic and aromatic hydrocarbons, including alkanes, cycloalkanes, alkylbenzenes, and halobenzenes in two solvents, propylene glycol and methyl cellosolve, were measured at temperature T=298.15K using gas chromatographic headspace analysis technique. The Gibbs free energies of solvation were calculated from these data and analyzed together with the enthalpies of solvation for the same systems. It was shown that the Gibbs free energies of solvation in propylene glycol are significantly lower than in its homologue ethylene glycol, and in methyl cellosolve they are lower than in propylene glycol. This difference is mainly due to the solvophobic effect, which strength is decreasing in the same order: ethylene glycol>propylene glycol>methyl cellosolve. The contribution of the solvophobic effect into the Gibbs free energies of solvation can be determined using a Gibbs free energy versus enthalpy of solvation plot. This contribution is shown to grow up linearly with the molecular volume of a solute in propylene glycol and methyl cellosolve, as well as in ethylene glycol and in monohydric alcohols.

Nano-droplet Systems by Surfactant Self-assembly and Applications in the Pharmaceutical Industry

Liquid systems containing droplets with size in the nanoscale range are attractive from both scientific and technological points of view as they have many current and potential applications in several industries and products. The formation and stabilization of nano-droplet systems are mostly based on the self-assembly of surfactant (amphiphilic) molecules at interfaces, driven by the solvophobic effect. Surfactants are involved in both top-bottom (high energy) and bottom- up (low energy) methods. Several devices have also been developed to aid in liquid fragmentation down to the nanometer scale. Nano-droplet systems can be both thermodynamically stable (microemulsions) or metastable (nanoemulsions), and appropriate formulation is a key for optimum product design in terms of droplet size, maximum solubilization, colloidal stability, and optical and rheological properties, among others. Such characteristics are determined by molecular packing, interfacial curvature, droplet-droplet interactions, film elasticity and nature of the dispersed and continuous phase. These properties can be engineered by proper understanding of the molecular structure and phase behavior of the multicomponent systems involved and by a range of experimental characterization techniques. Nano-droplet systems can help to solve specific issues in pharmaceutical products such as processing, limitations in drug solubility or stability, control on drug release, drug targeting and absorption; there are many examples to prove that. However, several practical aspects should be considered for preclinical and clinical tests and product development.

ChemInform Abstract: Pillararene‐Based Assemblies: Design Principle, Preparation and Applications

AbstractReview: 109 refs.

Quaternary ammoniums and a cationic sodium complex as supramolecular catalysts in ring-opening of epoxides by amines

Supramolecular ionic organocatalysts and a metal-based catalyst were investigated in the ring-opening of epoxides by amines, without any artifice to enhance conversion (i.e., solvophobic effect, extended reaction time, heating, excess of amine, high catalyst loading). Different β-amino-alcohols were obtained in satisfying conversion (50–80%) in 24 h, under mild conditions.

Encapsulation of phthalocyanine-C$_{60}$ fullerene conjugates into metallosupramolecular subphthalocyanine capsules: a turn of the screw

In this communication, encapsulation studies between metallosupramolecular capsule 1, formed by 2 subphthalocyanines (SubPcs) coordinated to 3 metallic centers, and phthalocyanine (Pc)-C_{60} fullerene conjugates 2--5 have been carried out. It was shown that the encapsulation of the C_{60} moiety by the SubPc cage occurred exclusively for dyads 2--4, whereas it was not observed in the case of triad 5. The rigidity of the linker between the Pc and the fullerene unit proved to have an important impact in the complex formation. Complex formation was tested in 2 different solvents, where the importance of solvophobic effects was highlighted. The resulting multicomponent supramolecular systems represent a unique combination of photoactive moieties where covalent and supramolecular chemistry coexist.

Solvophobic effects: Qualitative determination and quantitative description

Solvophobic effects strongly influence the thermodynamic properties of solutions and are one of the driving forces of self-assembly processes of supramolecular structures. However, the generally accepted definition and a quantitative measure of these effects have so far been absent. Based on the analysis of a large set of experimental data on the thermodynamic functions of solvation in various systems, we propose a qualitative criterion allowing us to judge about whether the solvophobic effects are manifested in the solution or not, and also a method to determine their contributions to the thermodynamic functions of solvation. A feature of the solvophobic effect is a violation of the linear relationship between the Gibbs free energy and the enthalpy of solvation, which is fulfilled for the solutions of different compounds in many non-associated solvents. It is shown that in self-associated solvents the solvophobic effect is observed for any dissolved compounds, including well soluble ones, resulting in an increase in the Gibbs energy of solvation. Previously proposed solvophobicity parameters are considered and compared with our results.

Pillararene‐Based Assemblies: Design Principle, Preparation and Applications

In this review, we highlight recent advancements on pillararene-based assemblies. The driving forces for the formation of the pillararene-based assemblies are discussed first. The host-guest interactions are deemed as not only general strategy for constructing assemblies but also essential components for preventing the assemblies from the dissociation. Solvent effect is also important in the assembling process, since it could influence the host-guest interactions and provide solvophobic effect on pillararenes for the assembly. Then, several pillararene-based assembly architectures are introduced, including pillararene-based interlocked structures, such as (poly)pseudorotaxanes, (poly)rotaxanes, and daisy chains, classified by their topological structures and synthetic strategy. The morphologies of the supramolecular assemblies are divided into several types, for example, nanospheres, nanotubes and supramolecular polymers. Furthermore, the functions and potential applications are summarized accompanied with related assembly structures. The review not only provides fundamental findings, but also foresights future research directions in the research area of pillararene-based assemblies.

Molecular Dynamics and Principal Component Analysis for a Self-assembled Nanocube in Aqueous Solution

Abstract Molecular dynamics (MD) simulations in aqueous solution were performed for hexameric nanocubes of methylated (16) and demethylated (26) gear-shaped amphiphiles. To elucidate the difference between these nanocubes, the principal component analysis for the MD simulation results in aqueous solution and the normal mode analysis in the gas phase were also applied to the nanocube, 16 and 26. The structural fluctuation of the lowest-frequency motion on 26 is larger than that on 16 around the triple π stacking of 3-pyridyl groups. For the structural stability and fluctuation of the nanocube, interactions among the constituent gear-shaped molecules play more important roles than the solvophobic effect due to solvent molecules.

Solvent-Dependent Disassembly of Amphiphilic OPE-Based Tricarboxamides

A series of water-compatible C3-symmetric tricarboxamides endowed with a large number of EO side chains separated from the amide groups by different paraffinic linkers has been synthesized. The addition of a small amount of water breaks the N-H···O═C amide H-bonds but induces the formation of aggregates by a solvophobic effect. The lack of highly directional H-bonding interactions results in an isodesmic supramolecular polymerization with a calculated Gibbs free energy of -31.26 and -36.79 kJ mol(-1) for 1 and 3, respectively.

Conformational Analysis of Chiral Supramolecular Aggregates: Modeling the Subtle Difference between Hydrogen and Deuterium

A detailed analysis of the conformational states of self-assembled, stereoselectively deuterated benzene-1,3,5-tricarboxamides ((S,S,S)-D-BTAs) reveals four different conformers for the supramolecular polymers. The relative amount of the conformers depends on the solvent structure and the temperature. With the help of a model, the thermodynamic parameters that characterize the different conformational states were quantified as well as the amount of the species that occur at different stages of the polymerization process. The results show that small changes in the stability between different types of conformers formed by (S,S,S)-D-BTAs—in the order of a few J mol(–1)—arise from the combination of interactions between the solvent/supramolecular aggregate, temperature, and solvent structure. While the introduction of a deuterium label allows to sensitively probe the solvophobic effects in the supramolecular aggregation, a rationalization of the observed effects on a molecular level is not yet straightforward but is proposed to result from subtle effects in the vibrational enthalpy and entropy terms of the isotope effect.