Showing papers on "Solvent effects published in 2013"
TL;DR: It was found that cohesive solvent-solvent interactions are the major driving force behind apolar association in solution, and theoretical models that implicate important roles for dispersion forces in molecular recognition events should be interpreted with caution in solvent-accessible systems.
Abstract: The emergent properties that arise from self-assembly and molecular recognition phenomena are a direct consequence of non-covalent interactions Gas-phase measurements and computational methods point to the dominance of dispersion forces in molecular association, but solvent effects complicate the unambiguous quantification of these forces in solution Here, we have used synthetic molecular balances to measure interactions between apolar alkyl chains in 31 organic, fluorous and aqueous solvent environments The experimental interaction energies are an order of magnitude smaller than estimates of dispersion forces between alkyl chains that have been derived from vaporization enthalpies and dispersion-corrected calculations Instead, it was found that cohesive solvent-solvent interactions are the major driving force behind apolar association in solution The results suggest that theoretical models that implicate important roles for dispersion forces in molecular recognition events should be interpreted with caution in solvent-accessible systems
211 citations
TL;DR: A negative correlation between ΔEst and efficiency of the delayed fluorescence was observed, ascribed to a lower intersystem crossing rate, kISC, and increased nonradiative decay from S1, k(s)nrs, in polar solvents.
Abstract: Thermally activated delayed fluorescence (TADF) is fluorescence arising from a reverse intersystem crossing (RISC) from the lowest triplet (T1) to the singlet excited state (S1), where these states are separated by a small energy gap (ΔEst), followed by a radiative transition to the ground state (S0). Rate constants relating TADF processes in 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) were determined at four different solvent polarities (toluene, dichloromethane, ethanol, and acetonitrile). We revealed that the rate constant of RISC, kRISC, which is the most important factor for TADF, was significantly enhanced by a reduced ΔEst in more polar solvents. The smaller ΔEst was mainly attributable to a stabilization of the S1 state. This stabilization also induced a Stokes shift in fluorescence through a relatively large change of the dipole moment between S1 and S0 states (17 D). Despite of this factor, we observed a negative correlation between ΔEst and efficiency of the delayed fluorescence (φd). This was ascribed to a lower intersystem crossing rate, kISC, and increased nonradiative decay from S1, k(s)nrs, in polar solvents.
159 citations
31 Jan 2013
TL;DR: In this paper, the acid-base equilibria and salt formation in methanol and aprotic solvents were investigated. But the dissociation constants of methanols and apropositions of acid base strength and acid base acidity were not investigated.
Abstract: 1. Introduction 2. Acid-base equilibria: quantitative treatment 3. Solvation and acid-base strength 4. Determination of dissociation constants 5. Protic solvents 6. High-basicity, aprotic solvents 7. Low-basicity and low-polarity aprotic solvents 8. Acid-base equilibria and salt formation 9. Appendices: Dissociation constants in methanol and aprotic solvents Index
152 citations
TL;DR: A systematic methodology is proposed that quickly identifies improved reaction Solvents by combining quantum mechanical computations of the reaction rate constant in a few solvents with a computer-aided molecular design (CAMD) procedure, and allows the identification of a high-performance solvent within a very large set of possible molecules.
Abstract: Solvents can significantly alter the rates and selectivity of liquid-phase organic reactions, often hindering the development of new synthetic routes or, if chosen wisely, facilitating routes by improving rates and selectivities. To address this challenge, a systematic methodology is proposed that quickly identifies improved reaction solvents by combining quantum mechanical computations of the reaction rate constant in a few solvents with a computer-aided molecular design (CAMD) procedure. The approach allows the identification of a high-performance solvent within a very large set of possible molecules. The validity of our CAMD approach is demonstrated through application to a classical nucleophilic substitution reaction for the study of solvent effects, the Menschutkin reaction. The results were validated successfully by in situ kinetic experiments. A space of 1,341 solvents was explored in silico, but required quantum-mechanical calculations of the rate constant in only nine solvents, and uncovered a solvent that increases the rate constant by 40%.
146 citations
TL;DR: In this paper, the authors investigated the electrocatalytic activity toward the four-electron oxygen reduction-reaction in N-doped graphene quantum dots and found that pyridinic and graphitic nitrogen are the most active sites with overpotentials of 0.55 and 0.79-0.90 V, respectively.
Abstract: First-principles investigations of the electrocatalytic activity toward the four-electron oxygen reduction-reaction in N-doped graphene quantum dots reveal that pyridinic and graphitic nitrogen are the most active sites with overpotentials of 0.55 and 0.79–0.90 V, respectively. This agrees with experimental findings. Our calculations account for van der Waals interactions, solvent effects, and describe the electrochemistry using standard hydrogen electrode model. The results show correlations between OH*, OOH*, and O* binding energies that impose a lower limit on the oxygen reduction overpotential.
133 citations
TL;DR: The results demonstrate that the choice of the exchange-correlation functional and of the PCM model is critical to reproduce the experimental data in the most accurate way and shows that the formation of an accessible TICT state is possible for C152.
Abstract: Time-dependent B3LYP and CAM-B3LYP calculations have been used to investigate the absorption and emission energies as well as to shed light on the formation of the twisted intramolecular charge transfer state (TICT) in Coumarin-152 (C152) embedded in cyclohexane, acetonitrile, and water solvents. The bulk solvent effects have been included by using the linear-response (LR) and State-Specific (SS) models in the framework of the so-called polarizable continuum method (PCM). The results demonstrate that the choice of the exchange-correlation functional and of the PCM model is critical to reproduce the experimental data in the most accurate way. In particular, it has been observed that both the solvatochromic and Stokes' shifts are well reproduce by CAM-B3LYP/SSPCM calculations performed on the S0 and S1 geometries of C152 optimized at the B3LYP/LRPCM level of theory, whereas not accurate Stokes' shifts are computed with CAM-B3LYP/SSPCM calculations carried out on the CAM-B3LYP/LRPCM optimized structures. This is attributed to the incorrect (underestimated) solvation energy provided by LRPCM, which could lead to misleading results especially for charge-transfer excited state structures in polar solvents. Instead, B3LYP/LRPCM excited state optimizations seem to provide a reasonable geometry for a simple 'error cancellation' effect due to the balance among the B3LYP overstabilization of charge transfer states and the LRPCM underestimation of the solute-solvent binding energy when the former is in a polar solvent. Finally, CAM-B3LYP/SSPCM calculations, in very good agreement with experimental evidence, show that the formation of an accessible TICT state is possible for C152 and that the crossing between S0 and S1 states at a dihedral angle of around 70° occurs only in polar solvents.
128 citations
TL;DR: The effect of surrounding solvents on the photoluminescence (PL) of MoS2 monolayers on Si/SiO2 substrates is studied and blueshift and intensity increase are observed.
Abstract: The effect of surrounding solvents on the photoluminescence (PL) of MoS2 monolayers on Si/SiO2 substrates is studied. A redshift (up to -60 meV) is observed for MoS2 monolayers with nonhalogenated solvent surroundings. A blueshift (up to 60 meV) and intensity increase (2-50 times) are observed for monolayers with halogenated solvent surroundings.
126 citations
TL;DR: It is found that the interactions between the pyridylpyrazole headgroups and the solvents could subtly change the stacking of the molecules and, hence, their self-assembled nanostructures and the structure and properties of a gel.
Abstract: The self-assembly of a low-molecular-weight organogelator into various hierarchical structures has been achieved for a pyridylpyrazole linked L-glutamide amphiphile in different solvents. Upon gel formation, supramolecular chirality was observed, which exhibited an obvious dependence on the polarity of the solvent. Positive supramolecular chirality was obtained in nonpolar solvents, whereas it was inverted into negative supramolecular chirality in polar solvents. Moreover, the gelator molecules self-assembled into a diverse array of nanostructures over a wide scale range, from nanofibers to nanotubes and microtubes, depending on the solvent polarity. Such morphological changes could even occur for the xerogels in the solvent vapors. We found that the interactions between the pyridylpyrazole headgroups and the solvents could subtly change the stacking of the molecules and, hence, their self-assembled nanostructures. This work exemplifies that organic solvents can significantly involve the gelation, as well as tune the structure and properties, of a gel.
122 citations
TL;DR: It is argued that both contributions to the change of the solute's charge distribution after excitation should be taken into account, and most previous implementations of comparable continuum solvation models only include either of both effects.
Abstract: The conductor-like screening model (COSMO) is used to treat solvent effects on excited states within a correlated method based on the algebraic-diagrammatic construction through second-order ADC(2). The origin of solvent effects is revisited, and it is pointed out that two types of contributions have to be considered. One effect is due to the change of the solute’s charge distribution after excitation, which triggers a reorganization of the solvent. Initially, only the electronic degrees of freedom adapt to the new charge distribution (nonequilibrium case); for sufficiently long-lived states, the reorientation of the solvent molecules contributes, as well (equilibrium case). The second effect is the coupling of the transition densities to the fast (purely electronic) response of the solvent molecules, which can be viewed as excitonic coupling between solute and solvent molecules. This interaction is also responsible for the screening of excitonic couplings between spatially separated chromophores. While m...
118 citations
TL;DR: In this article, the effect of solvent polarity on the rate of SET activation was visualized by adding methyl 2-bromopropionate (MBP) initiator to the disproportionation mixture and monitoring the disappearance of the nascent Cu(0) nanoparticles.
113 citations
TL;DR: The results from this study offer insights for the design of new surfactant-containing low-molecular-mass gelators with predefined gelating abilities and hydrogen-bonding between glucono units and π-π stacking between pyrenyl groups are important in the formation and maintenance of the gel networks.
Abstract: A series of glucono-appended 1-pyrenesulfonyl derivatives containing α,ω-diaminoalkane spacers (Pn, where n, the number of methylene units separating the amino groups, is 2, 3, 4, 6, 7, and 8) have...
TL;DR: Rate constants of activation (kact) for the reactions of tertiary alkyl halides with the ATRP catalyst CuIBr/1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) have been determined in 14 different solvents and the effect of increasing amounts of monomer in a solvent on the activation rate has been analyzed.
Abstract: Rate constants of activation (kact) for the reactions of tertiary alkyl halides with the ATRP catalyst CuIBr/1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) have been determined in 14 different solvents. The measurements have been performed at 25 °C by spectrophotometrically following the time-dependent absorbances of the CuII species. A large excess of 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO), which quantitatively trapped the alkyl radicals, ensured the irreversible generation of CuII. The rate constant for the least active solvent butanone is 30 times smaller than that of the most active solvent DMSO. In addition, the effect of increasing amounts of monomer in a solvent on the activation rate has been analyzed. A linear correlation of activation rate constants with previously determined equilibrium constants (KATRP) provides a Leffler–Hammond coefficient of 0.45. However, the activation rate constants do not correlate with dielectric constants and Dimroth’s and Reichardt’s ET(30) values. Appl...
TL;DR: Noncatalytic reactions of D-fructose were kinetically investigated in dimethylsulfoxide (DMSO), water, and methanol as a function of time at temperatures of 30-150 °C by applying in situ (13)C NMR spectroscopy.
Abstract: Noncatalytic reactions of d-fructose were kinetically investigated in dimethylsulfoxide (DMSO), water, and methanol as a function of time at temperatures of 30–150 °C by applying in situ 13C NMR spectroscopy. The products were quantitatively analyzed with distinction of isomeric species by taking advantage of site-selective 13C labeling technique. In DMSO, d-fructose was converted first into 3,4-dihydroxy-2-dihydroxymethyl-5-hydroxymethyltetrahydrofuran having no double bond in the ring, subsequently into 4-hydroxy-5-hydroxymethyl-4,5-dihydrofuran-2-carbaldehyde having one double bond through dehydration, and finally into 5-hydroxymethyl-2-furaldehyde (5-HMF) having two double bonds. No other reaction pathways were involved, as shown from the carbon mass balance. In water, 5-HMF, the final product in DMSO, was generated with the precursors undetected and furthermore transformed predominantly into formic and levulinic acids and slightly into 1,2,4-benzenetriol accompanied by polymerization. d-Glucose was a...
04 Dec 2013
TL;DR: Tautomerization is a well-studied technique in the field of physics as mentioned in this paper, and it has been used in a variety of applications in the past few decades, such as the analysis of Tautomeric Equilibria.
Abstract: Preface TAUTOMERISM: INTRODUCTIN, HISTORY, AND RECENT DEVELOPMENTS IN EXPERIMENTAL AND THEORETICAL METHODS The Definition and Scope of Tautomerism: Principles and Practicalities Causes of Reversal in Tautomeric Form: Aromatic Resonance Causes of Reversal in Tautomeric Form: Lone-Pair and Dipolar Repulsion Causes of Reversal in Tautomeric Form: Selective Stabilization Through "Far" Intramolecular Hydrogen Bonding Changes in Tautomeric Form Brought About by Electronegative Substituents The Influence of Solvent on Tautomeric Form Tautomeric Equilibrium: Historical Overview of an Analytical Problem Short Historical Overview of Tautomerization Dynamics Conclusions and Outlook ABSORPTION UV-vis SPECTROSCOPY AND CHEMOMETRICS: FROM QUALITATIVE CONCLUSIONS TO QUANTITATIVE ANALYSIS Introduction Quantitative Analysis of Tautomeric Equilibria Analysis of Real Tautomeric Systems Concluding Remarks STUDIES OF PHOTOINDUCED NH TAUTOMERISM BY STATIONARY AND TIME-RESOLVED FLUORESCENCE TECHNIQUES Introduction Photoinduced Proton/Hydrogen Atom Transfer Fluorescence Techniques for Studying Tautomerism Tautomerism in Bifunctional NH/N Azaaromatics Ab initio and DFT Computational Methods NH Tautomerism as a Tool in Biophysics Concluding Remarks FEMTOSECOND PUMP-PROBE SPECTROSCOPY OF PHOTOINDUCED TAUTOMERISM Introduction Ultrafast Pump-Probe Spectroscopy Dynamics from Pump-Probe Spectroscopy Reaction Mechanism Reaction-Path-Specific Wavepacket Dynamics in Double ESIPT Internal Conversion Summary and Conclusions NMR SPECTROSCOPY STUDY OF TAUTOMERISM IN SOLUTION AND IN THE SOLID STATE Introduction Methodologies of NMR Spectroscopy to Study Tautomerism Types of Tautomerism Studied by NMR Spectroscopy Conclusions and Outlook ISOTOPE EFFECTS ON CHEMICAL SHIFTS AS A TOOL IN THE STUDY OF TAUTOMERIC EQUILIBRIA Introduction Experimental Requirements Isotope Effects on Chemical Shifts Secondary Equilibrium Isotope Effects on CS Primary Isotope Effects Solid State Theoretical Calculations Examples Overview TAUTOMER-SELECTIVE SPECTROSCOPY OF NUCLEOBASES, ISOLATED IN THE GAS PHASE Introduction Techniques Guanine Adenine Cytosine Uracil and Thymine Base Pairs Outlook DIRECT EVIDENCE OF SOLID-STATE TAUTOMERISM BY DIFFRACTION METHODSD: ISOMERS, EQUILIBRIA, AND KINETICS Application of X-Ray Diffraction to Study Tautomerism Examples of X-Ray Diffraction Analysis of Proton Transfer Other Diffraction Methods Used to Study Proton Transfer Reactions DYNAMICS OF GROUND- AND EXCITED-STATE INTRAMOLECULAR PROTON TRANSFER REACTIONS Introduction Transition State Theory Two Examples of Tautomerization The Role of the Solvent Solvent Friction and Solvent Dynamics The Solvent Coordinate: Basics Polarization Fluctuations The Solvent Coordinate: An Application Electronic Rearrangement The Rug that Ties the (Classical) Room Together Quantum and Classical Quantum Decay Coupling Quantum and Classical Motion: A Simple Example Nonlinear Optics Femtochemistry Concluding Remarks FORCE FIELD TREATMENT OF PROTON AND HYDROGEN TRANSFER IN MOLECULAR SYSTEMS Introduction Computational Approaches to Proton Transfer Proton Transfer Reactions with MMPT Applications of MMPT Discussion and Outlook THE SCOPE AND LIMITATIONS OF LSER IN THE STUDY OF TAUTOMER RATIO Introduction The Taft-Kamlet LSER Methodology LSER Case Histories in the Field of Tautomerism Overview THE "BASICITY METHOD" FOR ESTIMATING TAUTOMER RATIO: A RADICAL RE-APPRAISAL Introduction Experimental Protocol The Derivation of Correction Factors Regularities Revealed by Correction Factors Complicating Factors in the Use of the "Basicity Method" Tautomeric Problems to Which the "Basicity Method" Is Inapplicable Overview QUANTUM CHEMICAL CALCULATION OF TAUTOMERIC EQUILIBRIA Introduction Computational Procedures Solvent Effects Applications of Quantum Chemical Methods to Tautomeric Equilibria Concluding Remarks Index
TL;DR: It is suggested that a N-doped h-BN monolayer can demonstrate catalytic properties for the ORR under the condition that electron transport to the catalytically active center is provided.
Abstract: The catalytic activity for the oxygen reduction reaction (ORR) of both the pristine and defect-possessing hexagonal boron nitride (h-BN) monolayer and H-terminated nanoribbon have been studied theoretically using density functional theory It is demonstrated that an inert h-BN monolayer can be functionalized and become catalytically active by nitrogen doping It is shown that the energetics of adsorption of O2, O, OH, OOH, and H2O on N atom impurities in the h-BN monolayer (NB@h-BN) is quite similar to that known for a Pt(111) surface The specific mechanism of destructive and cooperative adsorption of ORR intermediates on the surface point defects is discussed It is demonstrated that accounting for entropy and zero-point energy (ZPE) corrections results in destabilization of the ORR intermediates adsorbed on NB@h-BN, while solvent effects lead to their stabilization Therefore, entropy, ZPE and solvent effects partly cancel each other and have to be taken into account simultaneously Analysis of the free energy changes along the ORR pathway allows us to suggest that a N-doped h-BN monolayer can demonstrate catalytic properties for the ORR under the condition that electron transport to the catalytically active center is provided
TL;DR: Although the effect of all organic solvents on various properties on lipase is qualitatively similar, the study suggest that magnitudes of effects do not appear to follow bulk solvent properties like polarity and the solvent effects are apparently dictated by specific and local interactions of solvent molecule(s) with the protein.
Abstract: Studying alterations in biophysical and biochemical behavior of enzymes in the presence of organic solvents and the underlying cause(s) has important implications in biotechnology. We investigated the effects of aqueous solutions of polar organic solvents on ester hydrolytic activity, structure and stability of a lipase. Relative activity of the lipase monotonically decreased with increasing concentration of acetone, acetonitrile, and DMF but increased at lower concentrations (upto ∼20% v/v) of dimethylsulfoxide, isopropanol, and methanol. None of the organic solvents caused any appreciable structural change as evident from circular dichorism and NMR studies, thus do not support any significant role of enzyme denaturation in activity change. Change in 2D [15N, 1H]-HSQC chemical shifts suggested that all the organic solvents preferentially localize to a hydrophobic patch in the active-site vicinity and no chemical shift perturbation was observed for residues present in protein's core. This suggests that activity alteration might be directly linked to change in active site environment only. All organic solvents decreased the apparent binding of substrate to the enzyme (increased Km); however significantly enhanced the kcat. Melting temperature (Tm) of lipase, measured by circular dichroism and differential scanning calorimetry, altered in all solvents, albeit to a variable extent. Interestingly, although the effect of all organic solvents on various properties on lipase is qualitatively similar, our study suggest that magnitudes of effects do not appear to follow bulk solvent properties like polarity and the solvent effects are apparently dictated by specific and local interactions of solvent molecule(s) with the protein.
TL;DR: In this article, three different empirical solvatochromic models are assessed against 13 coumarins, and a combinatorial approach to determine the best-fit equations in all of the empirical models is applied; this involves both statistical best-fits and the physical validation of the resulting parameters.
Abstract: Coumarins often function in the solution phase for a diverse range of optoelectronic applications. The associated solvent effects on the UV–vis absorption and/or fluorescence spectral shifts of coumarins need to be understood in order that their photochemistry can be controlled. To this end, three different empirical solvatochromic models are assessed against 13 coumarins. The two generalized solvent scales developed by Catalan and co-workers demonstrate comparable performance to the popular Taft–Kamlet solvatochromic comparison method. A combinatorial approach to determine the best-fit equations in all of the empirical models is applied; this involves both statistical best-fits and the physical validation of the resulting parameters, based on the molecular structures of solvents and solutes and their corresponding interactions. The findings of this approach are used to extract useful information about different aspects of solvent effects on the solvatochromism of coumarins.
TL;DR: It is demonstrated that supramolecular assembly and subsequent enhancement of charge transport characteristics of conjugated polymers can be facilitated simply by adding small amounts of a more volatile poor solvent, which can hydrogen bond with the majority solvent.
Abstract: We demonstrate that supramolecular assembly and subsequent enhancement of charge transport characteristics of conjugated polymers can be facilitated simply by adding small amounts of a more volatile poor solvent, which can hydrogen bond with the majority solvent. Addition of up to 2 vol % acetone to a precursor solution of poly(3-hexylthiophene) (P3HT) in chloroform leads to approximately a 4-fold increase in P3HT field-effect mobility. The improvement is associated with hydrogen bonding interactions between acetone and chloroform which decrease the evaporation rate of the mixed solvent. P3HT is less soluble in the binary solvent than in the more readily vaporized chloroform component, and this characteristic enables the supramolecular assembly of P3HT chains at the nanoscale. Two-dimensional molecular ordering of the polymer film was controlled by varying the quantity of poor solvent added to the precursor solution, and the correlation between field-effect mobility and molecular ordering was investigated...
TL;DR: In this paper, the aqueous phase adsorption free energy of the neutral form is comparable to that of the deprotonated form, which suggests that for imidazole, because of its more basic nature, neutral form and for triazole and tetrazole their deproptonated forms are the active species for inhibiting corrosion.
TL;DR: The interactions of iodoperfluoroarenes and -alkanes with anions in organic solvent were studied and indicated that favorable halogen-bonding interactions exist between halide anions and the monodentate model compounds C(6)F(5)I and C(8)F (17)I.
Abstract: The interactions of iodoperfluoroarenes and -alkanes with anions in organic solvent were studied. The data indicates that favorable halogen-bonding interactions exist between halide anions and the monodentate model compounds C(6)F(5)I and C(8)F(17)I. These data served as a basis for the development of preorganized multidentate receptors capable of high-affinity anion recognition. Several new receptor architectures were prepared, and the multidentate-iodoperfluorobenzoate-ester design, as described in a preliminary communication, was evaluated in more detail. Computation was employed to better interpret the structure-activity relationships arising from these studies. Investigations of the thermodynamics of anion binding (by van't Hoff analysis) and solvent effects reveal details of these halogen bonding interactions.
TL;DR: Ethanol was proven to be the most suitable solvent to convert C. pyrenoidosa into bio- oil from the yield and economic points of view and temperature is the most influential factor on the products yield and properties of the bio-oil.
TL;DR: The mechanism, solvent effects, and origins of selectivities in Ru(II)-catalyzed intramolecular (5+2) cycloaddition and ene reaction of vinylcyclopropanes (VCPs) and alkynes have been studied using density functional theory.
Abstract: The mechanism, solvent effects, and origins of selectivities in Ru(II)-catalyzed intramolecular (5+2) cycloaddition and ene reaction of vinylcyclopropanes (VCPs) and alkynes have been studied using density functional theory. B3LYP/6-31G(d)/LANL2DZ optimized structures were further evaluated with the M06 functional, 6-311+G(2d,p) and LANL2DZ basis sets, and the SMD solvent model. The favored mechanism involves an initial ene-yne oxidative cyclization to form a ruthenacyclopentene intermediate. This mechanism is different from that found earlier with rhodium catalysts. The subsequent β-hydride elimination and cyclopropane cleavage are competitive, determining the experimental selectivity. In trans-VCP, the cyclopropane cleavage is intrinsically favored and leads to the (5+2) cycloaddition product. Although the same intrinsic preferences occur with the cis-VCP, an unfavorable rotation is required in order to generate the cis-double bond in seven-membered ring product, which reverses the selectivity. Acetone solvent is found to facilitate the acetonitrile dissociation from the precatalyst, destabilizing the resting state of the catalyst and leading to a lower overall reaction barrier. In addition, the origins of diastereoselectivities when the allylic hydroxyl group is trans to the bridgehead hydrogen are found to be the electrostatic interactions. In the pathway that generates the favored diastereomer, the oxygen lone pairs from the substituent are closer to the cationic catalyst center and provide stabilizing electrostatic interactions. Similar pathways also determine the regioselectivities, that is, whether the more or less substituted C-C bond of cyclopropane is cleaved. In the trans-1,2-disubstitued cyclopropane substrate, the substituent from the cyclopropane is away from the reaction center in both pathways, and low regioselectivity is found. In contrast, the cleavage of the more substituted C-C bond of the cis-1,2-disubstituted cyclopropane has steric repulsions from the substituent, and thus higher regioselectivity is found.
TL;DR: In this article, the authors used n-heptane solvent and Ir ReOx/SiO2 catalyst for hydrogenolysis of trans-1,2-cyclohexanediol.
Abstract: Hydrogenolysis of alcohols was carried out using n-heptane solvent and Ir ReOx/SiO2 catalyst, which has been known to be active in water solvent. Hydrogenolysis of trans-1,2-cyclohexanediol proceeded more smoothly in n-heptane than in water. The maximum yield of cyclohexanol was 74%, and at longer reaction time cyclohexane was selectively formed (>80% yield). Stronger adsorption of substrate on catalyst surface in n-heptane than in water is one of factors in obtaining the good yields. Alkane solvent was also advantageous to water solvent in hydrogenolysis of mono-alcohols. The reaction route via acid-catalyzed dehydration and subsequent hydrogenation is enhanced in alkane solvent. On the other hand, the “direct” hydrogenolysis driven by the hydride-like species is suppressed in alkane solvent, leading lower activity in n-heptane for hydrogenolysis of tetrahydrofurfuryl alcohol or 1,2-hexanediol, which smoothly react over Ir ReOx/SiO2 catalyst in water.
TL;DR: The proposed method is regarded as a reliable hydroxyl radical-scavenging assay, suitable for all types of antioxidants, and shows that any organic solvent should be completely evaporated before measurement.
TL;DR: Findings suggest that microfibril twisting is favored by vdW interactions, and counteracted by both intrachain hydrogen bonds and solvent effects at the microFibril surface.
Abstract: Molecular dynamics (MD) simulations of cellulose microfibrils are pertinent to the paper, textile, and biofuels industries for their unique capacity to characterize dynamic behavior and atomic-level interactions with solvent molecules and cellulase enzymes. While high-resolution crystallographic data have established a solid basis for computational analysis of cellulose, previous work has demonstrated a tendency for modeled microfibrils to diverge from the linear experimental structure and adopt a twisted conformation. Here, we investigate the dependence of this twisting behavior on computational approximations and establish the theoretical basis for its occurrence. We examine the role of solvent, the effect of nonbonded force field parameters [partial charges and van der Waals (vdW) contributions], and the use of explicitly modeled oxygen lone pairs in both the solute and solvent. Findings suggest that microfibril twisting is favored by vdW interactions, and counteracted by both intrachain hydrogen bonds and solvent effects at the microfibril surface.
TL;DR: This work visualize the electron transfer to water using ultrafast fluorescence spectroscopy with polychromatic detection from the ultraviolet to the visible region, upon photo-excitation of the so-called charge transfer to solvent states of aqueous iodide.
Abstract: Electron transfer from solute to solvent has a crucial role in chemistry, but this process has not yet been visualized in real time. Messina et al. provide the first real-time observation of the dynamic rearrangement of water cages around aqueous halides before full electron ejection.
TL;DR: The solvent effect on the Grignard reaction of benzyl, aryl and heteroaromatic substrates has been systematically evaluated based on reaction efficiency, ease of subsequent work-up, safety and greenness as discussed by the authors.
TL;DR: In this article, the authors used quantitative solid-state high-resolution nuclear magnetic resonance to show that the main cause of irreversible capacity is not the decomposition of lithium salt but the degradation of electrolyte solvent with the formation of non lithiated carbon species as polymer or oligomers.
TL;DR: Magnetic studies reveal that both 1 and 2 show thermally activated magnetization relaxation as expected for single-molecule magnets.
Abstract: A new dysprosium(III) phosphonate dimer {Dy(notpH4)(NO3)(H2O)}2·8H2O (1) [notpH6=1,4,7-triazacyclononane-1,4,7-triyl-tris(methylenephosphonic acid)] that contains two equivalent Dy(III) ions with a three-capped trigonal prism environment is reported. Complex 1 can be transformed into {Dy(notpH4)(NO3)(H2O)}2 (2) in a reversible manner by desorption and absorption of solvent water at ambient temperature. This process is accompanied by a large dielectric response. Magnetic studies reveal that both 1 and 2 show thermally activated magnetization relaxation as expected for single-molecule magnets. Moreover, the magnetic dynamics of the two compounds can be manipulated by controlling the number of solvent molecules at room temperature.
TL;DR: In this paper, the effects of substituents and solvents on the ground state molecular geometry, dipole moments, polarizabilities and frontier orbital energies of aniline, N-methylaniline (NMA), NEA, DMA and DEA were computed by using the ab initio restricted HF-DFT self-consistent field method (B3LYP) with 6-31G* basis set in vacuum, ethanol and tetrahydrofuran.