Single Alcohol Molecule Research Articles

Density functional theory study of the adsorption of MeOH and EtOH on the surface of Pt-decorated graphene

The adsorption energies and orientation of single alcohol molecule (methanol and ethanol) on the surface of Pt-decorated graphene (PtG) were determined from first-principles density functional (DFT) calculations. We found the same adsorption energies as well as connecting distances upon adsorption of MeOH and EtOH on PtG surface, in which at their relaxed structures, the O atom of alcohol is closed to the Pt of PtG surface. We found high adsorption energies, low connecting distances, and high orbital hybridizing upon adsorption of EtOH and MeOH molecules on PtG surface. There are significant shifts in the location of both the HOMO and LUMO, in addition to variation in the charge transfer when the MeOH and EtOH are adsorbed on PtG surface.

Cooperative hydrophobe aggregation mediated by interfacially active alcohols

The aggregation of isobutane and toluene in aqueous solutions of 5wt% alcohols of varying polarity is studied using molecular dynamic simulations. In the absence of alcohol these hydrophobes are predominantly monomeric in water with minimal clustering. Simple alcohols like methanol and ethanol barely perturb the hydrophobe cluster size distribution. More complex alcohols with added carbon and hydroxyl units, on the other hand, can induce cooperative aggregation of the hydrophobic solutes and alcohols, with mean cluster sizes greater than that observed for the hydrophobes or alcohols alone. The tendency for an alcohol to induce cooperative aggregation is strongly correlated with its affinity for sitting at an oil/water interface, as quantified by the free energy of transferring a single alcohol molecule from bulk water to a water/octane interface. The onset of aggregation occurs over a narrow range of adsorption free energies centered about −3.2kcal/mol. Alcohols with adsorption free energies below this value tend to promote hydrophobic aggregation, and alcohols with adsorption free energies above this value are indifferent to aggregation. The tendency for alcohols to induce hydrophobic aggregation is also correlated with their tendency to lower the size selective barrier to transport of cargo greater than ∼30kDa in mass across the nuclear pore complex in eukaryotic cells, which regulates traffic between the nucleus and cytoplasm. The transport barrier within the central channel of the nuclear pore complex is composed of tangled natively unfolded proteins with repeat sequences rich in leucine and phenyalanine, which isobutane and toluene are side chain analogs of. Our results suggest interfacial active alcohols promote leucine and phenyalanine aggregation, subsequently opening holes within the nuclear pore complex’s transport barrier to provide alternate routes for cargo translocation.

Mesoscopic structuring and dynamics of alcohol/water solutions probed by terahertz time-domain spectroscopy and pulsed field gradient nuclear magnetic resonance.

Terahertz and PFG-NMR techniques are used to explore transitions in the structuring of binary alcohol/water mixtures. Three critical alcohol mole fractions (x1, x2, x3) are identified: methanol (10, 30, 70 mol %), ethanol (7, 15, 60 mol %), 1-propanol (2, 10, 50 mol %), and 2-propanol (2, 10, 50 mol %). Above compositions of x1 no isolated alcohol molecules exist, and below x1 the formation of large hydration shells around the hydrophobic moieties of the alcohol is favored. The maximum number of water molecules, N0, in the hydration shell surrounding a single alcohol molecule increases with the length of the carbon chain of the alcohol. At x2 the greatest nonideality of the liquid structure exists with the formation of extended hydrogen bonded networks between alcohol and water molecules. The terahertz data show the maximum absorption relative to that predicted for an ideal mixture at that composition, while the PFG-NMR data exhibit a minimum in the alkyl chain self-diffusivity at x2, showing that the alcohol has reached a minimum in diffusion when this extended alcohol-water network has reached the highest degree of structuring. At x3 an equivalence of the alkyl and alcohol hydroxyl diffusion coefficients is determined by PFG-NMR, suggesting that the molecular mobility of the alcohol molecules becomes independent of that of the water molecules.

FTIR and DFT-D investigation of the structure of ruthenium pentacarbonyl in small alcohol solvents

The equilibrium structure of Ru(CO)5 in butanol, ethanol and isopropanol has been investigated using FTIR spectroscopy and DFT-D calculations. It was determined that 88–100% of the Ru(CO)5 molecules form a weak hexacoordinated complex with a single alcohol molecule under ambient conditions. Complexation of Ru(CO)5 is more favorable than Fe(CO)5 in all solvents studied. The DFT-D calculations predict that the complex formation occurs via electron donation from the complexing alcohol molecule to Ru(CO)5 at an equilibrium distance of ∼375pm from the metal center to the hydroxyl oxygen.

Gas−Phase Hydration and Alcohol Addition Reactions of Complexes Composed of Ag+ and a Single Alcohol Molecule

The reactivity of mono-alcohol/Ag+ complexes (methanol, ethanol, n-propanol, n-butanol, and tert-butyl alcohol) when stored, without collisional activation, in an ion trap mass spectrometer for periods ranging from 1 to 1000 ms was investigated. During the isolation/reaction time, association reactions between the complex ions and adventitious water and alcohol present within a He bath gas occurred to varying degrees. While the free Ag+ ion was unreactive, complexes composed of Ag+ coordinated by a single alcohol molecule demonstrated reactivity consistent with the following reactions: (1) formation of an adduct by the addition of a single water molecule, (2) formation of a bis-alcohol complex by the addition of a second alcohol molecule, and (3) formation of the bis-alcohol complex via the exchange of a water molecule for alcohol when investigated under similar experimental conditions. The trend in reactivity followed the order n-butanol > n-propanol > ethanol > methanol. To quantify observed trends in hydration reactivity, experimental kinetic plots were modeled stochastically. Reasonable fits to experimental reaction kinetic plots were achieved using a model that included forward and, in some cases, apparently reverse reactions, consistent with the addition of either water or alcohol in nondissociative fashion. Pseudo-first-order reaction rate constants were generated using stochastic kinetic simulations that provide insight into the relative reactivity of the mono-alcohol/Ag+ complexes. To rationalize the observed trends in reactivity, the lowest energy conformations and molecular orbital geometries were determined using Hartree−Fock and density functional theory calculations. Our results show that the hydration and alcohol addition reactivity of Ag+ may be influenced by the degree to which electron density can be delocalized within a coordinating ligand and to which the electron density within a hybridized orbital on Ag+ is decreased by bonding to an alcohol molecule.

Metastable Decomposition of {ROH}nH+ Cluster Ions (Where R = CH3 or CH3CH2)

We have studied the metastable decomposition of protonated alcohol cluster ions employing a reflectron time-of-flight mass spectrometer. Loss of a single alcohol molecule is observed as the dominant decomposition channel in all of these cluster ions. From the daughter ion spectra, we find experimental evidence that the {ROH}6H+ cluster ions possess a unique stability relative to the parent cluster ion. Theoretical calculations were performed to interpret the cause for this special stability and to indicate several possible isomeric structures for this cluster ion. The energetic ordering of the isomers can be interpreted in terms of hydrogen bonding and delocalization of charge.

Orientation of molecules of aliphatic alcohols adsorbed on a mercury electrode surface analysis of steric factors of inhibited electrode reactions and quantum-chemical calculations

The orientation of adsorbed aliphatic alcohols on mercury electrode surface is discussed on the basis of literature data concerning steric factors of electrochemical reactions inhibited by these alcohols and on quantum chemical calculations using the mopac program. Steric factors were evaluated from dependences of rate constants of electrochemical reactions of several model systems on alcohol concentration at total surface coverage. Theoretical calculations were made for a single alcohol molecule interacting with a 28-atomic mercury cluster. These two sets of data point to a vertical orientation of adsorbed alcohol molecules, even at incomplete coverage of the electrode surface.

Solute–solvent interaction in the photoinduced tautomerization of 7-azaindole in various alcohols and in mixtures of cyclohexane and ethanol

The evolution of the fluorescence of 7-azaindole in several alcohols, in mixtures of cyclohexane and etheanol and in mixtures of 1,4-dioxane and hexafluoropropanol has been investigated by excitation with a 25 ps (u.v.) laser pulse, followed by detection with a streak camera. We show that adiabatic keto–enol tautomerization of the compound in its lowest electronically excited singlet state in these solvents proceeds via double proton transfer in a well defined complex of a single alcohol molecule and the excited solute molecule. Unlike previous authors, we conclude that viscosity and solvent aggregation are not the important factors determining the rate of intramolecular adiabatic excited-state double proton transfer in this compound. Within the series of alcohols the variation of the rate constant for this process can be attributed satisfactorily to the variation in the acidity of the alcohols. A temperature-independent kinetic isotope effect has been observed for the complexes of 7-azaindole with ethanol (OH) and ethanol(OD). Our previous explanation for such kinetic behaviour also applies here. It involves thermally activated isotope independent formation of a specific (cyclic doubly hydrogen bounded) solute–solvent complex from an (open singly hydrogen bonded) precursor complex, followed by thermally unassisted proton transfer in the specific complex.

Exciplex formation in alcohol and water solutions of 7-azaindole

The unusual long-wavelength shift and bandwidth of the fluorescence spectra of 7-azaindole in alcohol and water solutions compared with hydrocarbon solution is demonstrated to be the result of exciplex formation between the 7-azaindole and the hydroxylic solvent molecules. The technique of monitoring the fluorescence band position, intensity, and half-width (fwhm) in alcohol-hydrocarbon solutions as developed by Walker et al. has been used to distinguish the exciplex model from other existing models. Aggregation effects and the dependence of the exciplex fluorescence yield on alcohol acidity have led to a model attributing excited-state charge transfer between the nonbonding oxygen electrons in the alcohol and the lowest vacant ..pi.. orbital of excited 7-azaindole. It also has been demonstrated that excited-state double proton transfer between 7-azaindole and a single alcohol molecule occurs, independent of the exciplex formation, for molecules that form a cyclic hydrogen-bonded complex in the ground state.