Volume 86, Issue 2

Liquid repellent layers can be fabricated by coating a fractal-like layer of candle soot particles with a silicon oxide layer, combusting the soot at 600 °C and subsequently silanizing with perfluoroalkylsilanes. Drops of different liquids deposited on these so called “superamphiphobic” layers easily roll off thanks to the low liquid-solid adhesion. The lower value of the surface tension of liquids that can be repelled depends on details of the processing. Here, we analyze the influence of the soot deposition duration and height with respect to the flame on the structure and wetting properties of the superamphiphobic layer. The mean diameter of the soot particles depends on the distance from the wick. Close to the wick, the average diameter of the particles varies between 30 and 50 nm as demonstrated by scanning electron microscopy (SEM). Close to the top of the flame, the particles size decreases to 10–20 nm. By measuring the mass of superamphiphobic layers and their thickness by laser scanning confocal microscopy (LSCM) in reflection mode, we could determine that the average porosity is 0.91. The height-dependent structural differences affect the apparent contact and roll-off angles. Lowest contact angles are measured when soot is deposited close to the wick due to wax that is not completely burnt, smearing out the required overhanging structures. The small particle size close to the top of the flame also reduces contact angles, again due to decreasing size of overhangs. Sooting in the middle of the flame led to optimal liquid repellency. Furthermore, for sooting times longer than 45 s the properties of the layer did not change with sooting time, verifying the self-similarity of the layer.

The potassium channel is highly selective for K + over Na + , and the mechanism underlying this selectivity remains unclear. We show the three-dimensional distribution functions (3D-DFs) of small cations (Li + , Na + , and K + ) and the free energy profile of ions inside the open selectivity filter (SF) of the KcsA channel. Our previous results [S. Phongphanphanee, N. Yoshida, S. Oiki, F. Hirata. Abstract Book of 5th International Symposium on Molecular Science of Fluctuations toward Biological Functions, P062 (2012)] indicate that the 3D-DF for K + exhibits distinct peaks at the sites formed by the eight carbonyl oxygen atoms belonging to the surrounding peptide-backbone and residues (the cage site). Li + has sharp distributions in the 3D-DF at the center of a quadruplex composed of four carbonyl oxygen atoms (the plane site). Na + has a rather diffuse distribution throughout the SF region with peaks both in the plane and in cage sites. The results provide microscopic evidence of the phenomenological findings that Li + and Na + are not excluded from the SF region and that the binding affinity alone does not cause the ion selectivity of KcsA. In the present study, with an ion placed explicitly along the pore axis, the free energy profiles of the ions inside the SF were calculated; from these profiles we suggest a new mechanism for selective K + permeation. According to the model, a K + ion must overcome a free energy barrier that is approximately half that of Na + to exit from either of the SF mouths due to the existence of an intermediate local minimum along the route for climbing the barriers.

As a consequence of the ongoing development of enhanced computational resources, theoretical chemistry has become an increasingly valuable field for the investigation of a variety of chemical systems. Simulations employing a hybrid quantum mechanical/molecular mechanical (QM/MM) molecular dynamics (MD) technique have been shown to be a particularly promising approach, whenever ultrafast (i.e., picosecond) dynamical properties are to be studied, which are in many cases difficult to access via experimental techniques. Details of the quantum mechanical charge field (QMCF) ansatz, an advanced QM/MM protocol, are discussed and simulation results for various systems ranging from simple ionic hydrates to solvated organic molecules and coordination complexes in solution are presented. A particularly challenging application is the description of proton-transfer reactions in chemical simulations, which is a prerequisite to study acidified and basic systems. The methodical requirements for a combination of the QMCF methodology with a dissociative potential model for the description of the solvent are discussed. Furthermore, the possible extension of QM/MM approaches to solid/liquid interfaces is outlined.

In this article, we discuss how the relation between interactions and structure in ionic liquids (ILs) can be probed at a molecular level using ab initio and molecular dynamics (MD) methodologies. The first part of the discussion will focus on the unique and complex properties of ILs as pure substances including the existence of an extended and flexible polar network and the possibility of a second nanosegregated subphase containing the nonpolar residues of the molecular ions that constitute some ILs. The discussion will then be extended to IL plus molecular species mixtures/solutions. In this context the concept of ILs as charge templates for the electronic make-up of the molecular species will be analyzed at length. Finally, that concept will be extended to ILs adsorbed over solid substrates.

The properties of N -methylacetamide (NMA) molecules encapsulated in the reverse micelles (RMs) formed by anionic surfactant aerosol OT (AOT), are studied with vibrational spectroscopy and computation. Vibrational spectra of the amide I′ mode of the fully deuterated NMA- d 7 show gradual increase of peak frequencies and line broadening as the size of RMs decreases. Analyses of the spectral features reveal the presence of three states of NMA- d 7 that correspond to NMA located in the core of water phase (absorption frequency of 1606 cm –1 ) and two types of interfacial NMA near the surfactant layer (1620 and 1644 cm –1 ). In larger RMs with water content w 0 = [D 2 O]/[AOT] ≥ 10, only the first two states are observed, whereas in smaller RMs, the population of the third state grows up to 25 % at w 0 = 2. These results indicate the general validity of the two-state core/shell model for the confined aqueous solution of NMA, with small modifications due to the system-dependent solute-interface interaction. However, simulations of small RM systems with w 0 ≤ 15 show continuous variations of the population, frequency shifts, and the solute-solvent interaction strengths at solute-interface distance less than 4 Å. Thus, the distinction of solute core/shell states tends to be blurred in small RMs but is still effective in interpreting the average spectroscopic observables.

Various Pd–C complexes have been developed to date, affording deep insights into the reaction intermediates in useful catalytic reactions in organic syntheses. Cyclopalladation is one of the most famous Pd–C bond formation reactions to generate the palladacycles. Indole is an electron-rich aromatic ring involved in the side chain of an essential amino acid, tryptophan (Trp), and Trp and its derivatives are important in biological systems, such as electron transfer in protein, cofactors for conversion of biological molecules and so on. Pd catalysts are also useful for syntheses of such indole derivatives, and the mechanisms are considered to be through the Pd–C intermediates. However, the detailed properties and formation mechanisms of Pd–indole species are still unclear. With these points in mind, we focus on Pd(II)–indole-C2 carbon bond formations using various Pd(II) complexes having an indole moiety, especially on the recent studies on the kinetic analyses for these cyclopalladation reactions and their detailed mechanisms.

The Cu(II)-phenoxyl radical formed during the catalytic cycle of galactose oxidase (GO) attracted much attention, and the structures and properties of a number of metal-phenoxyl radical complexes have been studied. Some of the functional model systems of GO reported previously have shown that the Cu complexes oxidize primary alcohols to aldehydes and that the Cu(II)-phenoxyl radical species is formed in the catalytic cycle. Many Cu(II)-phenoxyl radical species have been produced by one-electron oxidation of the Cu(II)-phenolate complexes. On the other hand, one-electron oxidation of a Cu(II)-phenolate complex has the possibility to give different electronic structures, one of which is the Cu(III)-phenolate. From these points of view, this micro review is focused on the one-electron oxidized square-planar Cu(II) complexes of the salen-type ligands. Introduction of substituents into the phenolate moieties and conversion from a 5- to a 6-membered chelate backbone alter the electronic structure of the one-electron oxidized Cu(II) complexes and give rise to a different reactivity of benzyl alcohol oxidation. The relationship between the electronic structure and the reactivity is herein discussed.

Periodic entanglements of filaments and networks, which resemble sponge-like materials, are often found as self-assembled materials. The interaction between the geometry of the assembly and a solvent in its interstices can dictate the geometric configuration of the structure as well as influence macroscopic properties such as swelling and mechanics. In this paper, we show the calculation of the solvation free energy as a function of the solute–solvent interaction from hydrophilic to hydrophobic, for a candidate entanglement of filaments. We do this using the morphometric approach to solvation free energy, a method that disentangles geometric properties from thermodynamic coefficients, which we compute via density functional theory.

Experimental observation by high-resolution microwave dielectric spectroscopy of hydration properties of alkali halide ions, adenosine phosphate ions, and F-actin revealed the existence of hypermobile water (HMW) molecules around those solutes. To understand the molecular process of HMW, two theoretical approaches are reviewed here. One is based on a statistical mechanical approach to analyze the rotational freedom of water molecules around a charged particle. Another approach reports direct calculation of dielectric relaxation process of water molecules around an ion. Experimentally observed HMW molecules are theoretically explained with the significance of multi-correlations among an ion and water molecules.

We briefly summarize the recent progress in tuning protein interactions as well as phase behavior in protein solutions using multivalent metal ions. We focus on the influence of control parameters and the mechanism of reentrant condensation, the metastable liquid–liquid phase separation and classical vs. non-classical pathways of protein crystallization.

Emulsion templates containing monomers in both emulsion phases were used to manufacture polystyrene- co -divinylbenzene based polymerized high internal phase emulsions (polyHIPEs) which have been reinforced by poly(methacrylic acid) (polyMAA) and poly(dimethyl aminoethyl methacrylate) (polyDMAEMA). The morphology of the hydrogel-filled polyHIPEs is affected by the hydrogels synthesized in the aqueous emulsion phase. The pore structure of polyMAA-filled polyHIPEs is highly interconnected indicating the formation of a methacrylic acid- co -styrene copolymer at the oil/water interface of the emulsion templates during synthesis. However, polyDMAEMA-filled polyHIPEs are predominately closed celled and the pore walls are covered by grafted hydrogel. The ability of the hydrogel-filled polyHIPEs to absorb water decreased with increasing crosslinking density of the hydrogels. The dry hydrogel reinforced the polyHIPE scaffolds possessed higher elastic moduli and crush strengths than the control polyHIPEs. The reinforcing ability of the dry hydrogels was further enhanced by increasing their degree of crosslinking. However, the reinforcement could be “switched off” simply by hydrating the hydrogels. The switchable mechanical properties of the hydrogel-filled polyHIPEs could potentially be utilized in smart humidity sensor technology.

A series of molecular dynamics (MD) simulations has been undertaken to investigate the effective interaction between vesicles including PC (phosphatidylcholine) and PE (phosphatidylethanolamine) lipids using the Shinoda–DeVane–Klein coarse-grained force field. No signatures of fusion were detected during MD simulations employing two apposed unilamellar vesicles, each composed of 1512 lipid molecules. Association free energy of the two stable vesicles depends on the lipid composition. The two PC vesicles exhibit a purely repulsive interaction with each other, whereas two PE vesicles show a free energy gain at the contact. A mixed PC/PE (1:1) vesicle shows a higher flexibility having a lower energy barrier on the deformation, which is caused by lipid sorting within each leaflet of the membranes. With a preformed channel or stalk between proximal membranes, PE molecules contribute to stabilize the stalk. The results suggest that the lipid components forming the membrane with a negative spontaneous curvature contribute to stabilize the stalk between two vesicles in contact.

The enthalpies of solution of alcohols were determined by calorimetry in HEPES and (HEPES + trehalose) at 298.15 K. The used methodology and experiment’s design allowed us to extract from a single titration experiment the enthalpy of solution (Δ sol H m ), the limiting solubility of the alcohol in each aqueous media, and an estimation of the enthalpy of solution of water in the alcohol phase. From these values the changes in Gibbs energy (Δ sol G m ) and in entropy (Δ sol S m ) of solution were derived. A decrease in solubility for 1-butanol and 1-pentanol in the crowded media (HEPES + trehalose) was observed which is driven by a significant decrease in the favorable enthalpy of solution. The partial molar heat capacity, in each media was determined in our heat capacity drop calorimeter, also at 298.15 K. A significant decrease of the partial molar heat capacity was observed for both alcohols in (HEPES + trehalose), which together with the obtained decrease in favorable Δ sol H m , is consistent with a decrease in hydrophobic solvation, as a result of a decrease in free solvent availability induced by the trehalose. Finally, we tentatively predict that in the aqueous media of the crowded solutions that characterize cells and biological fluids, solutes with low aqueous solubility will be more soluble, whereas the solubility of highly polar solutes will be reduced.

The protonation properties of amines are of particular interest for the development of thermodynamic models representative of CO 2 dissolution in aqueous solutions. This paper reports experimental equilibrium constants of protonation of alkanolamines (2-aminoethanol, 2,2′-iminodiethanol, 2-[bis(2-hydroxyethyl)amino]ethanol, 2-amino-2-methylpropan-1-ol, 2,2′-(methylimino)diethanol and cyclic amines (morpholine, 4-methylmorpholine, pyridine, 1-methyl-piperidine, 2-methyl-piperidine, 2,6-dimethylpiperidine). The equilibrium constants of protonation were determined by potentiometric technique up to 353.15 K and extrapolated up to 373.15 K using experimental enthalpies of protonation.

The transfer coefficient α is a quantity that is commonly employed in the kinetic investigation of electrode processes. In the 3 rd edition of the IUPAC Green Book, the cathodic transfer coefficient α c is defined as –( RT / nF )( d ln k c /d E ), where k c is the electroreduction rate constant, E is the applied potential, and R, T , and F have their usual significance. This definition is equivalent to the other, -( RT / nF )( d ln| j c |/d E ), where j c is the cathodic current density corrected for any changes in the reactant concentration at the electrode surface with respect to its bulk value. The anodic transfer coefficient α a is defined similarly, by simply replacing j c with the anodic current density j a and the minus sign with the plus sign. It is shown that this definition applies only to an electrode reaction that consists of a single elementary step involving the simultaneous uptake of n electrons from the electrode in the case of α c , or their release to the electrode in the case of α a . However, an elementary step involving the simultaneous release or uptake of more than one electron is regarded as highly improbable in view of the absolute rate theory of electron transfer of Marcus; the hardly satisfiable requirements for the occurrence of such an event are examined. Moreover, the majority of electrode reactions do not consist of a single elementary step; rather, they are multistep, multi-electron processes. The uncritical application of the above definitions of α c and α a has led researchers to provide unwarranted mechanistic interpretations of electrode reactions. In fact, the only directly measurable experimental quantity is d ln| j |/d E , which can be made dimensionless upon multiplication by RT / F , yielding ( RT / F )( d ln| j |/d E ). One common source of misinterpretation consists in setting this experimental quantity equal to αn , according to the above definition of the transfer coefficient, and in trying to estimate n from αn , upon ascribing an arbitrary value to α , often close to 0.5. The resulting n value is then identified with the number of electrons involved in a hypothetical rate-determining step or with that involved in the overall electrode reaction. A few examples of these unwarranted mechanistic interpretations are reported. In view of the above considerations, it is proposed to define the cathodic and anodic transfer coefficients by the quantities α c = –( RT / F )( d ln| j c |/d E ) and α a = ( RT / F )( d ln j a /d E ), which are independent of any mechanistic consideration.

The transfer coefficient α is a quantity that is commonly employed in the kinetic investigation of electrode processes. An unambiguous definition of the transfer coefficient, independent of any mechanistic consideration and exclusively based on experimental data, is proposed. The cathodic transfer coefficient α c is defined as –( RT / F )(dln| j c |/d E ), where j c is the cathodic current density corrected for any changes in the reactant concentration on the electrode surface with respect to its bulk value, E is the applied electric potential, and R, T , and F have their usual significance. The anodic transfer coefficient α a is defined similarly, by simply replacing j c with the anodic current density and the minus sign with the plus sign. This recommendation aims at clarifying and improving the definition of the transfer coefficient reported in the 3 rd edition of the IUPAC Green Book.