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In this work, we describe a combined experimental and theoretical study focused on the solvatochromic effects of eight different solvents on the UV absorption spectrum of three distinct oxo-centered carbonyl-triruthenium clusters of general formula [Ru3O(CH3COO)6(CO)(L)2], where L= (1) 2,6-dimethylpyrazine (dmpz), (2) pyridine (py), and (3) 4-aminopyridine (ampy). Due to the nature of the ancillary ligands, the charge transfer (CT) absorption band of each complex have a different shift as the solvent polarity/polarizability increases. These shifts have been rationalized using a combined Density Functional/Time-Dependent Density Functional theory and two popular solvatochromic scales: the Catalan and the Kamlet–Taft models. According to the Kamlet–Taft method, the ability of the solvent to donate a proton in a solvent–solute hydrogen bond is more essential on describing the solvatochromic properties of 3 than 1, being also more relevant than solvent polarity. The employed solvatochromic scales also corroborate the preferential solvation behavior of these complexes.

Asphaltenes (Asps) are operationally defined as the toluene-soluble but n-pentane- or n-heptane-insoluble fractions, e.g., of crude oils. Therefore, there is intense interest in determining the concentration of n-heptane required to precipitate Asps from their solutions in particular media (solvents, solvent mixtures, and maltenes). Here, we report on the dependence of Asp dissolution in binary mixtures of n-heptane (solvent 1, S1)/organic solvent (solvent 2, S2) over the entire mole fraction range of S2, χS2, and in few selected maltene models (n-heptane + S2 + benzothiazole + n-octyl-1-napthoate). The S2 employed were benzonitrile, cyclohexanone, ethyl benzoate, 1-methylnaphthalene, tetrahydropyran, and toluene. For all S2 and model maltenes, the dependence of wt % dissolved Asp (determined by mass and UV/vis absorbance) on χS2 was nonlinear. We attribute this nonlinear, i.e., nonideal dissolution behavior to “preferential solvation” of the Asp by a component(s) of the medium (binary solvent mixtures an...

Interactions concerning the high SO2 absorption capacity of tricyanomethanide ionic liquids were investigated. Solutions of SO2 in 1-butyl-3-methyilimidazolium tricyanomethanide (BMITCM) were analyzed through Raman spectroscopy. The SO2 symmetric stretching band, νs(SO2), remained equal in shape and wavenumber regardless the SO2 molar fraction, suggesting no specific interaction between TCM and SO2. However, by increasing the Raman excitation energy from 568 to 405 nm, a pre-resonance condition was reached, where a shifting and broadening of νs(SO2) were observed. Such results evidence solvation states where charge transfer interactions between TCM and SO2 prevail, corroborating the high absorption capacity of TCM ionic liquids.

In this work is presented a spectrophotometry investigation focused on the solvatochromic effects upon Methylene Blue (MB). Measurements were carried out in four different water/organic solvent mixtures: low polarity protic solvent (ethanol), polar non-protic solvent (acetonitrile), highly polar protic solvent (glycerol), and non-polar solvent (dioxane). The results showed that the photophysical behavior of MB is highly affected by self-aggregates formation at 80% of water/organic solvent blends. Besides polarity, the protic character and the coordinating properties of the solvent molecules are the key parameters for its photophysical behavior, since the sulfur atom of the cationic structure can act as a coordination center due to its Lewis acid character. In fact, water and acetonitrile coordinating properties have proved to be important to determine MB interactions intensity and its spectroscopic properties as singlet oxygen emission. It was observed that an increase of the amount of the organic solvent resulted in an enhancement of the singlet oxygen emission intensity. The presence of the water increases the dielectric constant of the medium and favors the self-aggregation process. Besides, the water molecules can act as a quencher and it decreases the quantum yield of the fluorescence of MB. DOI: http://dx.doi.org/10.17807/orbital.v9i4.996

Molecular docking is an important tool for the discovery of new biologically active molecules given that the receptor structure is known. An excellent environment for the development of new methods and improvement of the current methods is being provided by the rapid growth in the number of proteins with known structure. The evaluation of the solvation energies outstands among the challenges for the modeling of the receptor-ligand interactions, especially in the context of molecular docking where a fast, though accurate, evaluation is ought to be achieved. Here we evaluated a variation of the desolvation energy model proposed by Stouten (Stouten P.F.W. et al, Molecular Simulation, 1993, 10: 97-120), or SV model. The SV model showed a linear correlation with experimentally determined solvation energies, as available in the database FreeSolv. However, when used in retrospective docking simulations using the benchmarks DUD, charged-matched DUD and DUD-Enhanced, the SV model resulted in poorer enrichments when compared to a pure force field model with no correction for solvation effects. The data provided here is consistent with other empirical solvation models employed in the context of molecular docking and indicates that a good model to account for solvent effects is still a goal to achieve. On the other hand, despite the inability to improve the enrichment of retrospective simulations, the SV solvation model showed an interesting ability to reduce the number of molecules with net charge -2 and -3 e among the top-scored molecules in a prospective test.

Many studies about porphyrins have emerged in recent years, including studies using porphyrins as building blocks for supramolecular assemblies. Understanding new solid state forms of porphyrins and the elucidation of their structures can have remarkable benefits for nanoscience and synthetic biology. In this study, a new pseudopolymorph of cobalt (II) meso-tetraphenylporphyrin, (CoTPP), was synthesized in a known one-pot reaction, rather than using many-step conventional methods, was isolated and was characterized for the first time by low-temperature single crystal X-ray diffraction. It is a nonstoichiometric solvate assembled into dichloromethane channels. The most striking feature of this structure is the conformation adopted by the porphyrin macrocycle. In contrast to the non-solvated form of CoTPP that exhibits a ruffled core distortion and crystallizes in the tetragonal space group I-42d, this solvated form has been crystallized in the triclinic space group Pī and shows a distinct saddle-shaped macrocycle distortion. In the triclinic form, the conformation of one of the four phenyl rings is remarkably different from the others. A potential energy surface scan of the torsional angles around the bonds between this phenyl moiety and the macrocycle of CoTPP in both the non-solvated and the solvate forms demonstrates that the saddle-shaped macrocycle distortion depends on the unusual phenyl conformation. The distortion is responsible for the symmetry decrease in the channel solvate form, causing a loss of the 4-fold rotoinversion axis observed in the non-solvated tetragonal phase, which has identical phenyl conformations.

Single and double protonated (E)-1,4-diamine-2-butenes were evaluated as a model system to probe isomerization during the ESI processes employing infrared multiple-photon dissociation (IRMPD) spectroscopy and density function theory (DFT) calculations, including implicit and explicit solvation models. Our results show that the preferential protonation takes place at the amines for singly protonated species and that the double bond is not protonated even under double protonation, as expected from known pKa values. This behavior was shown to reflect the (E)-(Z) interconversion rate, as no interconversion was observed nor predicted by implicit solvation model based on density (SMD) calculations even by the olefin protonation pathway. Explicit solvent calculations show that the singly protonated (E) configuration observed in the gas phase is also the most stable configuration in solution due to molecular interactions with the solvent that are absent for the (Z) configuration. The explicit solvation calculation reverts the supposed gas-phase stability of the (Z) configuration in comparison to (E) from -9 kcal mol-1 (in relative Gibbs free energy) in the gas phase to +89 kcal mol-1 (in total potential energy) as depicted by explicit Monte Carlo (MC) simulations. Together with previous results for the saturated 1,4-diamines from Morton and coworkers that show the (Z) configuration related conformation to be the most stable geometry in the gas-phase due to intermolecular hydrogen bonding, our experiments clearly show that conformational reorganizations can take place during the ESI process. These results suggest that gas-phase experiments and vacuum calculations may not be valid as evidence for conformations in solution without prior testing to check for isomerization during the ESI process.

Titanium dioxide was obtained by hydrolysis of the corresponding ethoxide, followed by washing, drying, and calcination at 80, 160, 240, 320, 400, and 700 °C, respectively. The following surface properties of the solids obtained were determined as a function of the calcinations temperature: TCalcn; area by the BET method; Bronsted acidity by titration with sodium hydroxide; empirical polarity, ET(30); Lewis acidity, αSurf; Lewis basicity, βSurf; and dipolarity/polarizability πSurf*, by use of solvatochromic indicators. Except for βSurf whose value increased slightly, heating the samples resulted in a decrease of all of the above-mentioned surface properties, due to the decrease of surface hydroxyl groups. This conclusion has been corroborated by FTIR. Values of ET(30), αSurf, and πSurf* are higher than those of water and alcohols; the Bronsted and Lewis acidities of the samples correlate linearly. The advantages of using solvatochromic indicators to probe the surface properties and relevance of the result...