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Wetting of water by hexadecane has been investigated by ellipsometry as a function of the concentration of the cationic surfactant dodecyltrimethylammonium bromide (DTAB) in the aqueous phase and temperature. Three phases are identified: a 2-D gas of hexadecane molecules and DTAB molecules, a 2-D liquid comprising a mixed monolayer of hexadecane and DTAB, and a 2-D ‘solid’ phase. Evidence is presented to support the hypothesis that the liquid−solid phase transition is actually a wetting transition in which a surface-frozen layer of pure hexadecane wets the liquid-like mixed monolayer of hexadecane and DTAB. The triple point, at which the three phases coexist, is located at a temperature of 17.3 °C and DTAB concentration of 0.75 mmol kg −1. The slopes of the three phase boundaries are analyzed thermodynamically. [ABSTRACT FROM AUTHOR]

Mechanical forces are critical for regulating many biological processes such as cell differentiation, proliferation, and death. Probing the continuously changing molecular force through integrin receptors provides insights into the molecular mechanism of rigidity sensing in cells; however, the force information is still limited. Here, we built a coil-shaped DNA origami (DNA nanospring, NS) as a force sensor that reports the dynamic motion of single integrins as well as the magnitude and orientation of the force through integrins in living cells. We monitored the extension with nanometer accuracy and the orientation of the NS linked with a single integrin by the shape of the fluorescence spots. We used acoustic force spectroscopy to estimate the force-extension curve of the NS and determined the force with an ∼10% force error at a broad detectable range from subpicoNewtons (pN) to ∼50 pN. We found single integrins tethered with the NS moved several tens of nanometers, and the contraction and relaxation speeds were load dependent at less than ∼20 pN but robust over ∼20 pN. Fluctuations of the traction force orientation were suppressed with increasing load. Our assay system is a potentially powerful tool for studying mechanosensing at the molecular level.

When liquid alkane droplets are placed on a surfactant solution surface having a proper surface density, alkane molecules penetrated into the surfactant-adsorbed film to form a mixed monolayer. Such a mixed monolayer undergoes a thermal phase transition from two-dimensional liquid to solid monolayers upon cooling when surfactant tail and alkane have similar chain lengths. We applied the total-reflection XAFS spectroscopy and surface quasi-elastic light scattering to the mixed adsorbed film of cetyltrimethylammonium bromide and hexadecane to elucidate the impact on the surface phase transition on the counterion distribution of the mixed monolayer. The EXAFS analysis verified that a higher percentage of counter Br - ions were localized in the Stern layer than in the diffuse double layer in the surface solid film compared to the surface liquid film, which resulted in a reduction in the surface elasticity measured by the SQELS. The finding that the surface phase transition accompanies the change in the counterion distribution will be important to consider the future applications of the colloidal systems, in which the coexistence of a surfactant and alkane molecules is essential, such as foams and emulsions.

The surface freezing transition of a mixed adsorbed film containing cetyltrimethylammonium chloride (CTAC) and n -hexadecanol (C16OH) was utilized at the dodecane-water interface to control the stability of oil-in-water (O/W) emulsions. The corresponding surface frozen and surface liquid mixed adsorbed films were characterized using interfacial tensiometry and X-ray reflectometry. The emulsion samples prepared in the temperature range of the surface frozen and surface liquid phases showed a clear difference in their stability: the emulsion volume decreased continuously right after the emulsification in the surface liquid region, while it remained constant or decreased at a much slower rate in the surface frozen region. Compared to the previously examined CTAC-tetradecane mixed adsorbed film, the surface freezing temperature increased from 9.5 to 25.0 °C due to the better chain matching between CTAC and C16OH and higher surface activity of C16OH. This then renders such systems much more attractive for practical applications.

Silica particle (S) stabilized oil-in-water Pickering emulsions are observed in the two-phase region of the critical liquid mixture 2,6-lutidine (L) plus water (W). De-emulsification is found at temperatures below a particle wetting transition temperature T w ( R ) where T w ( R ) decreases toward the lower critical temperature T c for smaller particle radii R . The presence of a Pickering emulsion transition and its dependence upon particle radius can be explained by a competition between destabilizing gravitational forces and stabilizing forces originating from the critical interfacial tension. As a corollary to these observations, the line tension τ at the three-phase SLW contact line is determined as a function of temperature.

A material with anisotropic heat conduction characteristics, which is determined by molecular scale structure, provides a way of controlling heat flow in nanoscale spaces. As such, here, we consider layer-by-layer (LbL) membranes, which are an electrostatic assembly of polyelectrolyte multilayers and are expected to have different heat conduction characteristics between cross-plane and in-plane directions. We constructed models of a poly(acrylic acid)/polyethylenimine (PAA/PEI) LbL membrane sandwiched by charged solid walls and investigated their anisotropic heat conduction using molecular dynamics simulations. In the cross-plane direction, the thermal boundary resistance between the solid wall and the LbL membrane and that between the constituent PAA and PEI layers decrease with increasing degree of ionization (solid surface charge density and the number of electric charges per PAA/PEI molecule). When the degree of ionization is low, the cross-plane thermal conductivity of a constituent layer is higher than that of the bulk state. As the degree of ionization increases, however, the cross-plane thermal conductivity of PAA, a linear polymer, decreases because of the increase in the number of in-plane oriented polymer chains. In the in-plane direction, we investigated the heat conduction of each layer and found the enhancement of effective in-plane thermal conductivity again due to the in-plane oriented chain alignment. The heat conduction in the LbL membrane is three-dimensionally enhanced compared to those in the bulk states of the constituent polymers because of the electrostatic interactions in the cross-plane direction and the molecular alignment in the in-plane direction.

The decyanation of secondary aliphatic nitriles and the 2-fold decyanation of malononitriles leading to alkanes in the presence of 1,3-dimethylimidazol-2-ylidene borane (diMeImd-BH 3 ) are reported. These reactions proceed via a radical mechanism that involves the addition of a borane radical to the nitrile to form an iminyl radical, followed by cleavage of a carbon-carbon bond. Theoretical calculations suggest that the β-cleavage of these iminyl radicals, which affords NHC-BH 2 CN and the corresponding alkyl radicals, is the rate-determining step in this reaction.

Using tetraaryllead compounds (PbAr 4 ) as arylating reagents, isocyanides undergo selective diarylation in the presence of palladium catalysts such as Pd(OAc) 2 or Pd(PPh 3 ) 4 to afford imines and/or α-diimines based on the isocyanide employed. With aliphatic isocyanides, imines are obtained preferentially, whereas α-diimines are formed in the case of electron-rich aromatic isocyanides. The differences in imine/α-diimine selectivity can be attributed to the stability of imidoylpalladium intermediates formed in this catalytic reaction. Compared with other arylating reagents, tetraaryllead compounds are excellent candidates for use in the selective transformations to imines and/or α-diimines, especially in terms of inhibiting the oligomerization of isocyanides, which results in a lower product selectivity in many transition-metal-catalyzed reactions of isocyanides.

This feature article addresses a variety of unique macroscopic-scale and colloidal-scale interfacial phenomena, such as wetting transitions of oil droplets into molecularly thin films, spontaneous merging and splitting of oil droplets at air-water interfaces, solid monolayer and bilayer formation in mixed cationic surfactant/alkane adsorbed films, switching of foam-film thickness, and oil-in-water emulsion stability. All of these phenomena can be observed using commercial cationic surfactants, liquid alkanes, and water.

1,4-Hydrogen transfer from the 1-hydroxyallyl radical to give the enoxyl (α-keto) radical is an exothermic process with a high activation energy based on DFT calculations. The lack of experimental examples of such 1,4-H shift reactions lies in the difficulty of generating the 1-hydroxyallyl radical. We have shown that radical carbonylation of alkenyl radicals with CO followed by nucleophilic trapping of the carbonyl portion of the resulting radical by amines gives rise to 1-amino-substituted 1-hydroxyallyl radicals in situ. At the outset of this chemistry, we examined intramolecular trapping reactions via radical carbonylation of alkynylamines mediated by tributyltin hydride. Consequently, α-methylene lactams were obtained, for which the initially formed 1-amino-substituted 1-hydroxyallyl radical underwent a 1,4-H shift followed by subsequent β-scission, which led to the expulsion of a tributyltin radical. A competing pathway of the 1,4-H shift of 1-amino-substituted 1-hydroxyallyl radicals involving hydrogen abstraction was observed, which led to the formation of α-stannylmethylene lactams as a major byproduct. However, in contrast, when intermolecular trapping of α-ketenyl radicals by amines was carried out, the 1,4-H shift from the 1-amino-substituted 1-hydroxyallyl radical became the major pathway, which gave good yields of α,β-unsaturated amides. Thus, we were able to develop three-component reactions comprising terminal alkynes, CO, and amines that led to α,β-unsaturated amides via the 1,4-H shift reaction. DFT calculations support the observation that the 1,4-H shift is more facile when 1-hydroxyallyl radicals have both 1-amino and 3-tin substituents. The choice of substituents on the amine nitrogen is also important, since N-C bond cleavage via an S H 2-type reaction can become a competing pathway. Such an unusual S H 2-type reaction at the amine nitrogen is favored when the leaving alkyl radicals are stable, such as PhC(•)H(CH 3 ) and t-Bu•. Interestingly, even nucleophilic attack of tertiary amines onto α-ketenyl radicals causes cleavage of the C-N bond. For this reaction, DFT calculations predict an indirect homolytic substitution mechanism involving expulsion of alkyl radicals through the zwitterionic radical intermediate arising from nucleophilic amine addition onto the α-ketenyl radical. In contrast, the carbonylation of aryl radicals, generated from aryl iodides, in the presence of amines gave aromatic carboxylic amides in good yields. It is proposed that radical anions originating from acyl radicals and amines undergo electron transfer to aryl iodides to give aminocarbonylation products.

Penetration of alkane molecules into the adsorbed film of a cationic surfactant gives rise to a surface freezing transition at the alkane-water interface upon cooling. In this paper, we show that surface freezing of hexadecyltrimethylammonium chloride (CTAC) at the tetradecane-water interface stabilizes oil-in-water (OW) emulsions. For concentrations of CTAC near the critical micelle concentration, an OW emulsion coalesced readily above the surface freezing transition whereas the OW emulsion was stable in the surface frozen state. There was a discontinuous change in the stability of the OW emulsion at a temperature very close to the surface phase transition temperature as determined by interfacial tensiometry and ellipsometry on a planar oil-water interface. The mechanical elasticity of the surface frozen layer opposes film drainage and density fluctuations that could lead to rupture and is the most likely cause of the enhanced emulsion stability.

The line tension for a nanoparticle (NP) at the air-liquid surface can be determined by examining the variation in NP solution surface tension with bulk NP concentration. In this publication the variation in line tension with liquid solvent is examined for the homologous series of liquids from n-decane through to n-octadecane. Finite-size line tension effects are also studied by examining the variation in line tension with NP size for NPs at the air-octadecane surface. Both the line tension variation with solvent and NP size can be qualitatively explained using an interface displacement model for the line tension.

The Lewis acidic activation of a hypervalent iodine reagent containing a transferable cyano group, 1-cyano-3,3-dimethyl-3-(1H)-1,2-benziodoxole (CDBX), with B(C 6 F 5 ) 3 , to achieve the catalytic electrophilic cyanation of silyl enol ethers is presented. Mechanistic studies indicate that CDBX is activated through coordination of its cyano group to B(C 6 F 5 ) 3 , thus enabling the electrophilic cyanation reaction to occur.

The phase transition and domain formation of the adsorbed film of two kinds of hybrid alcohols (CF3(CF2)m-1(CH2)nOH, FmHnOH), 2-perfluorooctylethanol (F8H2OH) and 2-perfluorohexylhexanol (F6H6OH), as a mixture at the hexane/water interface was investigated by interfacial tensiometry and X-ray reflection. The interfacial tension γ versus total molality m curve of pure F8H2OH has a break point at high concentration, and thus, the mean area per molecule A changes discontinuously at high interfacial pressure π, corresponding to the phase transition between expanded and condensed films. The Fresnel divided reflectivity R/RF versus Qz plots in the expanded state was well-fitted by the domain model for incoherent interference to determine the interfacial coverage, which is the fraction of the interface covered by the condensed phase. This indicates that the expanded film is heterogeneous and consists of a condensed F8H2OH domain, the size of which is larger than the X-ray coherence length (∼5 μm). In the mixed system, the discontinuous change in A at the phase transition point becomes small with increasing the bulk composition of F6H6OH X2 in the mixture, and eventually the A value changes continuously; i.e, the phase transition becomes obscure in X2 ≥ 0.6. This behavior was linked to an increase in interfacial coverage with X2. Furthermore, the R/RF versus Qz plot was fitted by the domain model for coherent interference, suggesting that the size of the domain is smaller than 5 μm. These results are probably due to the reduction of domain line tension by preferential adsorption of F6H6OH at the F8H2OH domain boundary.

Penetration of alkane molecules into the adsorbed film gives rise to a surface freezing transition of cationic surfactant at the alkane-water interface. To examine the effect of the alkane chain length and counterion on the surface freezing, we employed interfacial tensiometry and ellipsometry to study the interface of cetyltrimethylammonium bromide and cetyltrimethylammonium chloride aqueous solutions against dodecane, tetradecane, hexadecane, and their mixtures. Applying theoretical equations to the experimental results obtained, we found that the alkane molecules that have the same chain length as the surfactant adsorb preferentially into the surface freezing film. Furthermore, we demonstrated that the freezing transition temperature of cationic surfactant adsorbed film was independent of the kind of counterion.

A novel quadraphasic phase-vanishing system in which acetylene is evolved from calcium carbide and directly applied in situ to the Sonogashira coupling reaction was developed. This method, which provides a safe, convenient, and one-pot means to utilize gaseous reagents without special equipment, was also applied to a Cu-catalyzed azide-alkyne cycloaddition (CuAAC) reaction and a three-component aldehyde-alkyne-amine (A(3)) coupling reaction with excellent results.

For hexadecane oil droplets at an aqueous-air surface, the surface film in coexistence with the droplets exhibits two-dimensional gaseous (G), liquid (L), or solid (S) behavior depending upon the temperature and concentration of the cationic surfactant dodecyltrimethylammonium bromide. In the G (L) phase, oil droplets are observed to coalesce (fragment) as a function of time. In the coalescence region, droplets coalesce on all length scales, and the final state is a single oil droplet at the aqueous-air surface. The fragmentation regime is complex. Large oil droplets spread as oil films; hole nucleation breaks up this film into much smaller fluctuating and fragmenting or metastable droplets. Metastable droplets are small contact angle spherical caps and do not fluctuate in time; however, they are unstable over long time periods and eventually sink into the bulk water phase. Buoyancy forces provide a counterbalancing force where the net result is that small oil droplets (radius r < 80 μm) are mostly submerged in the bulk aqueous medium with only a small fraction protruding above the liquid surface. In the G phase, a mechanical stability theory for droplets at liquid surfaces indicates that droplet coalesce is primarily driven by surface tension effects. This theory, which only considers spherical cap shaped surface droplets, qualitatively suggests that in the L phase the sinking of metastable surface droplets into the bulk aqueous medium is driven by a negative line tension and a very small spreading coefficient.

The effect of molecular orientation on the miscibility and structure of the adsorbed film of the 1H,1H,10H,10H-perfluorodecane-1,10-diol (FC10diol)-1H,1H,2H,2H-perfluorodecanol (FC10OH) mixture at the hexane/water interface were examined by interfacial tension and X-ray reflectivity measurements. The interfacial tension and X-ray reflectivity at the hexane solution/water interface were measured as a function of total molality m and composition of FC10OH in the mixture X2 under atmospheric pressure at 298.15 K. The interfacial pressure vs mean area per molecule curves showed that two kinds of condensed monolayers (C1 and C2) and multilayer (M) states appeared depending on m and X2. In the pure component systems, it was found that FC10OH forms condensed monolayer in which the molecules orient almost normally to the interface, and FC10diol orients parallel and is densely packed in the condensed monolayer and then piles spontaneously to form multilayer. In the mixed system, the phase diagram of adsorption indicated that FC10OH molecules are richer in C2 than in C1 state. The X-ray reflectivity measurements manifest that the condensed monolayer below X2 = 0.985 is heterogeneous in which the normal- and parallel-oriented domains coexist at the interface (C1 state), and that above X2 = 0.985 seems to be homogeneous with normal molecular orientation (C2 state). The structure of M state depends on those of condensed monolayers, on which the molecules pile spontaneously. The heterogeneous structure in C1 state is compared to that previously observed in the mixed system of FC10diol-FC12OH (1H,1H,2H,2H-perfluorododecanol), where FC12OH has longer fluorocarbon chain length than FC10OH and is discussed in terms of domain line tension.

Cyanoborohydrides are efficient reagents in the reductive addition reactions of alkyl iodides and electron-deficient olefins. In contrast to using tin reagents, the reaction took place chemoselectively at the carbon-iodine bond but not at the carbon-bromine or carbon-chlorine bond. The reaction system was successfully applied to three-component reactions, including radical carbonylation. The rate constant for the hydrogen abstraction of a primary alkyl radical from tetrabutylammonium cyanoborohydride was estimated to be <1 × 10(4) M(-1) s(-1) at 25 °C by a kinetic competition method. This value is 3 orders of magnitude smaller than that of tributyltin hydride.

The surface freezing (SF) of liquid n-heptadecane (C17)-n-octadecane (C18) and 1-perfluorooctyl decane (F8H10)-C18 mixtures were studied by surface tension and external reflection absorption FTIR (ERA-FTIR) measurements. The surface tension versus temperature curves of all pure liquids show a sharp break point at Ts corresponding to a surface liquid (SL)-SF transition. The entropy of surface formation is very negative, indicating a well-ordered structure of the SF layer. The ERA-FTIR spectra in the SF state suggested that the C18 molecules are densely packed in the solid state, while the packing of the hydrocarbon (HC) part of F8H10 is a little looser than the fluorocarbon (FC) part because of the difference in the cross-sectional area. In the C17-C18 mixture, the SL-SF transition was found at all bulk compositions. The estimation of the surface composition suggested that two components are miscible both in SL and SF states. The excess entropy of the surface is almost zero in both states, and thus, it was concluded that the two components are mixed almost ideally at the surface. In the case of the F8H10-C18 system, on the other hand, the SL layer is enriched in F8H10 with lower surface tension than C18 compared to bulk liquid. The surface composition in the SF state is almost zero or unity, indicating that F8H10 and C18 molecules are practically immiscible mainly due to the weak interaction between different components. Furthermore, the negative excess entropy in the SL layer suggests domain formation of F8H10 molecules at the surface.

A dyad consisting of a tripod-shaped trithiol with an adamantane core and a terminal ferrocenyl group linked through ap-phenyleneethynylene bridge was synthesized. The trithiol formed a stable self-assembled monolayer (SAM) on Au(111), wherein each molecule is bound to the surface by three-point adsorption using all sulfur atoms, with confirmation by PM-IRRAS and XPS analyses. Cyclic voltammetry of the SAM showed a line shape typical of an ideal adsorbed system, that is, a monolayer with negligible electrostatic interaction among the terminal ferrocenyl groups. Thus, a rare SAM was achieved, in which the component molecules were isolated from adjacent molecules without the coadsorption of nonelectroactive molecules.

Alkanes on surfactant solutions can form three distinct phases at the air-solution interface, a liquid phase (L), a solid monolayer phase (S1), and a hybrid bilayer phase (S2). Phase coexistence between any two, or all three, of these phases has been observed by Brewster angle microscopy of tetradecane, hexadecane, and their mixtures on solutions of tetradecyltrimethylammonium bromide. The morphologies of the domains depend on the competition between line tension and electrostatic interactions, which are essentially different depending on the pair of phases in contact. Domains of S1 in the L phase are long and thin; however, long, thin domains of L in an S1 phase are not stable but break up into a string of small circular domains. The bilayer S2 domains are always circular, owing to the dominance of line tension on the morphology.

Novel multilayer formation of fluorocarbon compounds at the hexane/water interface was investigated from the viewpoint of intermolecular interaction and miscibility of molecules in the adsorbed film. The two kinds of mixed systems were employed: 1H,1H,2H,2H-perfluorododecanol (FC12OH)-1H-perfluorodecane (HFC10) (System A) and 1-icosanol (C20OH)-HFC10 (System B). The interfacial tension γ between the hexane solution and water was measured as a function of total concentration m and the composition of HFC10 in the mixture X(2) at 298.15 K under atmospheric pressure. X-ray reflectivity (XR) measurement was performed at BL37XU in SPring-8 as a function of scattering vector Q(z). In both systems, the γ vs m curves except for the pure HFC10 system have a break at low concentrations, which corresponds to the gaseous-condensed monolayer transition for System A and the expanded-condensed monolayer for System B. The remarkable difference between the two systems was that the curves in a limited bulk composition range (0.45 ≤ X(2) ≤ 0.9) of System A show another break at high concentrations close to the solubility limit. The total interfacial density above this break point was around 7-11 μmol m(-2), suggesting the spontaneous molecular piling to form a multilayer. The phase diagrams of adsorption in the condensed monolayer indicated that the film composition of HFC10 is negative in System B but definitely positive above X(2) ≥ 0.45 in System A. This clearly shows that HFC10 molecules are miscible with FC12OH but immiscible with C20OH in the condensed monolayer. Thus, it is likely that the mixing of HFC10 with FC12OH in the condensed monolayer induces multilayer formation. The X-ray reflectivity normalized by Fresnel reflectivity R/R(F) vs Q(z) plot in the condensed monolayer of System A was fitted by a one-slab model with uniform electron density and thickness. The electron density profile was almost the same as that of the pure FC12OH system. The plot in the multilayer, on the other hand, was fitted well by the two-slab model with different electron densities and thicknesses. The electron density profile showed that the multilayer consists of two layers, one of which has slightly higher electron density than the bulk hexane phase and piles on the lower layer with almost the same electron density as the condensed FC12OH monolayer.

Unsaturated lactones undergo reductive radical cyclizations upon treatment with SmI(2)-H(2)O to give decorated cycloheptanes in a single highly selective operation during which up to three contiguous stereocenters are generated. Furthermore, cascade processes involving lactones bearing two alkenes, an alkene and an alkyne, or an allene and an alkene allow "one-pot" access to biologically significant molecular scaffolds with the construction of up to four contiguous stereocenters. The cyclizations proceed by the trapping of radical anions formed by electron transfer reduction of the lactone carbonyl.

Lactones bearing two alkenes or an alkene and an alkyne undergo reductive cyclization cascades upon treatment with SmI(2)-H(2)O, giving decorated azulene motifs in excellent yields with good diastereocontrol.

The surface tension γ of the aqueous solution of 1H,1H,6H,6H-perfluorohexane-1,6-diol (FC₆diol) and 1H,1H,8H,8H-perfluorooctane-1,8-diol (FC8diol) mixtures was measured as a function of total molality m and composition of FC₈diol in the mixture X₂ at 293.15 K under atmospheric pressure. The γ vs m curves except at X₂ = 0 and 0.05 have a distinct break point due to a phase transition in the adsorbed film. The surface pressure π vs mean area per adsorbed molecule A curves consist of two parts connected by a discontinuous change. The curve was almost vertical just below the phase transition, and the variation of the A value with film composition X(2)(H) was linear corresponding to the fact that FC₆diol and FC₈diol molecules orient parallel to the surface and are densely packed with the same areas of individual condensed films. Above the phase transition, the A value further decreases to around 0.12-0.19 nm² which is much smaller than the cross-sectional area of the fluorocarbon chain, indicating the multilayer formation at the surface. The phase diagram of adsorption (PDA) in the condensed film showed that the m vs film composition X(2)(H) curve is almost linear and the excess Gibbs energy of adsorption g(HE)/RT is at most 0.01, manifesting the ideal mixing of molecules. This is in contrast to a positive deviation (g(HE)/RT ~0.12) observed in the condensed film of the mixture of 1H,1H,2H,2H-perfluorodecanol (FC₁₀OH) and 1H,1H,2H,2H-perfluorododecanol (FC₁₂OH) with perpendicular molecular orientation. The loss of dispersion interaction between different species having different chain lengths is more appreciable in the perpendicular condensed films and thus leads to less miscibility of FC₁₀OH and FC₁₂OH. In the parallel condensed film, on the other hand, FC₆diol and FC₈diol molecules can arrange their position as close as possible to minimize the loss of dispersion interaction. The X(2)(H) value in the multilayer is close to unity, and thus, the multilayer consists of almost FC₈diol molecules which form a multilayer in the single-component system. Furthermore, the condensed monolayer-multilayer phase transition was accompanied by a large increase in surface density of FC₈diol and a small decrease in that of FC₆diol, indicating that FC₈diol molecules pile preferentially to form a multilayer.

Tin hydride mediated radical addition of organic halide to 2-(2,2,2-trifluoroethylidene)-1,3-dithiane 1-oxide has been devised. The reaction is equivalent to an unrealizable radical addition to trifluoromethylketene, providing useful α-trifluoromethyl carbonyl equivalents. The trifluoromethyl and the sulfoxide groups of the substrate play key roles for the success of the radical addition, lowering the barrier of the radical addition step and controlling the stereoselectivity of the reaction, which DFT calculations have elucidated.

The adsorption of 1H,1H,10H,10H-perfluorodecane-1,10-diol (FC10diol) at the hexane solution/water interface was investigated by the measurement of interfacial tension gamma as a function of pressure p and concentration m1 and the thermodynamic data analysis. The results obtained were compared with those of 1H,1H,2H,2H-perfluorodecanol (TFC10OH) in order to clarify the effect of molecular orientation on the structure and property of the adsorbed film from the viewpoint of volume change of adsorption. The interfacial pressure pi versus mean area per adsorbed molecule A curve revealed two types of phase transitions among expanded, parallel condensed, and multilayer states. The A value in the condensed state and the transition pressure between the expanded and condensed states were larger for FC10diol than for TFC10OH, which manifests the different molecular orientation that the dispersion interaction between hydrophobic chains is weaker in the parallel orientation of FC10diol than in the perpendicular orientation of TFC10OH. The partial molar volume of FC10diol in the condensed state nu1H.C is slightly larger than that of TFC10OH, although the partial molar volume in the hexane solution is much smaller for FC10diol than for TFC10OH. This supports the view that the fluorocarbon chains of FC10diol remain in their contact with hexane even in the condensed film because of the parallel molecular orientation. The partial molar volume in the nu1H,M was very close to the molar volume of solid FC10diol nu1S and smaller than that of nu1H.C at the condensed-multilayer phase transition, and increased gradually with molecular piling. This substantiates that FC10diol molecules are densely packed in a first few layers just above the phase transition and a little loosely packed in the upper layers of the multilayer with increasing molecular piling. Furthermore, the volume change associated with adsorption from the solid FC10diol Delta(nu)(S) evaluated from the gamma versus p curve under the existence of solid deposit was positive and showed a minimum against concentration for the multilayer state. This is primarily due to the minimum in interfacial density at the solubility limit Gamma1H,S and thus due to the minimum in nu1H,M.

Although simple aliphatic esters and lactones have long been thought to lie outside the reducing range of SmI(2), activation of the lanthanide reagent by H(2)O allows some of these substrates to be manipulated in an unprecedented fashion. For example, the SmI(2)-H(2)O reducing system shows complete selectivity for the reduction of 6-membered lactones over other classes of lactones and esters. The kinetics of reduction has been studied using stopped-flow spectrophotometry. Experimental and computational studies suggest that the origin of the selectivity lies in the initial electron-transfer to the lactone carbonyl. The radical intermediates formed during lactone reduction with SmI(2)-H(2)O can be exploited in cyclizations to give cyclic ketone (or ketal) products with high diastereoselectivity. The cyclizations constitute the first examples of ester-alkene radical cyclizations in which the ester carbonyl acts as an acyl radical equivalent.

The miscibility and distribution of Br(-) and BF(4)(-) ions of imidazolium ionic liquid mixtures, 1-hexyl-3-methylimidazolium bromide (HMIMBr) + 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF(4)), at the air/water surface were investigated by surface tensiometry and the total-reflection XAFS (TRXAFS) method. Tensiometry showed that the surface density of BF(4)(-) was much larger than that of Br(-), the adsorbed films of the HMIMBr-HMIMBF(4) mixture were greatly enriched in BF(4)(-) at all surface tensions, and the excess Gibbs energy of adsorption was positive. However, TRXAFS revealed that the Br ions were all in the free-Br state solvated by six water molecules in the mixed adsorbed film. Entropy-originated nonideal mixing, where a kind of segregation of the counterion distribution takes place in the interfacial region, was suggested in the mixture.

We measured the surface tension of aqueous solutions of octanol-butandiyl-1,4-bis(decyldimethylammonium bromide) using the drop-volume technique at 298.15 K under atmospheric pressure as a function of the total molality and bulk composition. The results of the surface tension measurements, which were analyzed by originally developed thermodynamic equations, suggested that octanol molecules filled the spaces among the hydrophobic chains of gemini surfactants and formed a densely packed monolayer with them in the adsorbed film. The turbidity of aqueous solutions was also measured to construct the concentration-composition diagram with the surface tension data. A transmission electron microscope was used to determine the aggregate morphology in the aqueous solutions. Disc-like micelle and microemulsion regions were found on the diagram prior to the spherical micelle formation; nevertheless, the butandiyl-1,4-bis(decyldimethylammonium bromide) itself formed only spherical (or small ellipsoid) micelles in the concentration range measured. We also studied the relationship between synergism and molecular packing in the aggregates.

SmI(2)-H(2)O reduces cyclic 1,3-diesters to 3-hydroxyacids with no over-reduction. Furthermore, the reagent system is selective for cyclic 1,3-diesters over acyclic 1,3-diesters and esters. Experimental and computational studies suggest that the origin of the selectivity lies in the initial electron transfer to the ester carbonyl and the anomeric stabilization of the resulting radical-anion intermediate. Radicals formed by one-electron reduction of the ester carbonyl group have been exploited in intramolecular additions to alkenes.

Radicals containing the histidine residue have been generated in the gas phase by femtosecond electron transfer to protonated histidine-N-methylamide (1H+), Nalpha-acetylhistidine-N-methylamide (2H+), Nalpha-glycylhistidine (3H+), and Nalpha-histidylglycine (4H+). Radicals generated by collisional electron transfer from dimethyldisulfide to ions 1H+ and 2H+ at 7 keV collision energies were found to dissociate completely on the microsecond time scale, as probed by reionization to cations. The main dissociations produced fragments from the imidazole side chain and the cleavage of the C(alpha)CO bond, whereas products of NCalpha bond cleavage were not observed. Electron transfer from gaseous potassium atoms to ions 3H+ and 4H+ at 2.97 keV collision energies not only caused backbone NCalpha bond dissociations but also furnished fractions of stable radicals that were detected after conversion to anions. Ion structures, ion-electron recombination energies, radical structures, electron affinities, and dissociation and transition-state energies were obtained by combined density functional theory and Møller-Plesset perturbational calculations (B3-PMP2) and basis sets ranging from 6-311+G(2d,p) to aug-cc-pVTZ. The Rice-Ramsperger-Kassel-Marcus theory was used to calculate rate constants on the B3-PMP2 potential energy surfaces to aid interpretation of the mass spectrometric data. The stability of Nalpha-histidylglycine-derived radicals is attributed to an exothermic isomerization in the imidazole ring, which is internally catalyzed by reversible proton transfer from the carboxyl group. The isomerization depends on the steric accessibility of the histidine side chain and the carboxyl group and involves a novel cation radical-COO salt-bridge intermediate.

The adsorption behavior of 1,1,2,2,-tetrahydroheptadecafluorodecanol (FC10OH), 1-eicosanol (C20OH), and their mixtures at the hexane solution/water interface is summarized briefly and examined from the viewpoints of interfacial tensions in the presence of domains, domain formation, and the correlation between the phase transition and the miscibility of film forming substances in the adsorbed films. The two-dimensional analogue of the Laplace equation showed that the interfacial tension is always higher in the presence of domains than that in the absence of them. The higher tendency of domain formation of FC10OH compared to C20OH is mainly ascribed to the excess Gibbs energy of mixing of fluorocarbon chains and hydrocarbon solvent being positive and to the interaction energy between domains being more stable against cohesion for FC10OH than for C20OH. The thermodynamic equations derived here suggested the heteroazeotropy in the phase diagram of adsorption and the temperature dependence of interfacial tension at the phase transition points, which are in accord with the experimental findings qualitatively.

The surface tension of the aqueous solution of 1H,1H,8H,8H-perfluorooctane-1,8-diol (FC(8)diol) was measured as a function of temperature and concentration under atmospheric pressure. The interfacial density and the entropy and energy of adsorption were evaluated and compared to those obtained for the adsorption of 1H,1H,10H,10H-perfluorodecane-1,10-diol (FC(10)diol) at the hexane solution/water interface. The surface tension curves show a break point corresponding to a phase transition of the adsorbed FC(8)diol film. The value of mean area per adsorbed molecule A just below the phase transition indicated the formation of a parallel condensed monolayer, and that above the phase transition suggested the spontaneous formation of a multilayer. The multilayer of FC(8)diol is less compressible and shows a smaller increase in layering with pi compared to FC(10)diol. This is probably because the surface force is repulsive for the hexane/FC/water interface, while it is attractive for the air/FC/water interface. The partial molar entropy change of adsorption is positive in the condensed FC(8)diol film, while it is negative in the condensed FC(10)diol film, which is reasonably explained in terms of the difference in entropy change accompanied by desolvation around the hydrophobic chain. From the viewpoints of the energetic stabilization accompanied by adsorption for the FC(8)diol system, the contribution from the replacement of air/water contact with air/fluorocarbon and fluorocarbon/water contacts and that from the molecular ordering in the adsorbed film is almost equal in case of the condensed monolayer, while in the multilayer the latter is comparatively larger than the former due to the hydrogen bonding between hydroxyl groups and the dispersion interaction among the ordered hydrophobic chains.

Aggregate formation of a didodecyldimethylammonium bromide (DDAB) and didodecyldimethylammonium chloride (DDAC) mixture in aqueous solution was investigated. The concentration vs composition diagram of aggregate formation was constructed by analyzing the surface tension, turbidity, and electrical conductivity data. The cryogenic transmission electron microscopy was applied to several representative points in the diagram and provided information of the morphology of aggregates. The sequence of monomer (m) - m + small aggregate (A) - m + A + vesicle (V) - m + V was concluded with increasing total concentration of surfactants at all mixing ratios. The compositions of counterions in A and V were estimated on the basis of thermodynamic consideration and examined from the viewpoint of asymmetry of constituents and uneven distribution between outer and inner monolayers of a vesicle bilayer. Vesicle surfaces were suggested to abound in chloride ions compared to bulk solution, which is opposite to spherical micelle surfaces.

Wetting of water by hexadecane has been investigated by ellipsometry as a function of the concentration of the cationic surfactant dodecyltrimethylammonium bromide (DTAB) in the aqueous phase and temperature. Three phases are identified: a 2-D gas of hexadecane molecules and DTAB molecules, a 2-D liquid comprising a mixed monolayer of hexadecane and DTAB, and a 2-D 'solid' phase. Evidence is presented to support the hypothesis that the liquid-solid phase transition is actually a wetting transition in which a surface-frozen layer of pure hexadecane wets the liquid-like mixed monolayer of hexadecane and DTAB. The triple point, at which the three phases coexist, is located at a temperature of 17.3 degrees C and DTAB concentration of 0.75 mmol kg (-1). The slopes of the three phase boundaries are analyzed thermodynamically.

Radicals formed by electron transfer to protonated arginine have been predicted by theory to undergo an inverse migration of the hydrogen atom from the C(alpha) position to the guanidine carbon atom. Experiments are reported here that confirm that a fraction of arginine and arginine amide radicals undergo such an inverse hydrogen migration. The rearranged arginine and arginine amide C(alpha) radicals are detected as stable anions after charge inversion by collisions with Cs atoms of precursor cations at 3 and 50 keV kinetic energies. RRKM calculations on the B3-PMP2/aug-cc-pVTZ potential energy surface indicate that arginine radicals undergo rapid rotations of the side chain to reach conformations suitable for C(alpha)-H transfer, which is calculated to be fast (k > 10(9) s(-1)) in radicals formed by electron transfer. By contrast, H-atom transfer from the guanidine group onto the carboxyl or amide C=O groups is >50 times slower than the C(alpha)-H atom migration. The guanidine group in arginine radicals is predicted to be a poor hydrogen-atom donor but a good H-atom acceptor and thus can be viewed as a radical trap. This property can explain the frequent observation of nondissociating cation radicals in electron capture and electron transfer mass spectra of arginine-containing peptides.

The total-reflection XAFS measurement possessing bromide ion selectivity at the interfacial region was applied to the adsorbed film of hexadecyltrimethylammonium chloride (HTAC) and dodecyltrimethylammonium bromide (DTAB) mixture. The surface compositions XjH of individual ions j ( j = HTA+, Cl(-), DTA+, and Br (-)) were evaluated by combining the surface excess concentration of Br(-) estimated from the XAFS with the surface composition of the respective surfactants from the surface tension results. It is clearly shown that HTA+ and Br(-) are preferentially adsorbed to DTA+ and Cl(-) at the air/water interface. The preferential adsorption was estimated numerically in terms of activity coefficient fi+/-(H,p) of component i and excess Gibbs energy of adsorption ĝprH,E. Then, the magnitude of ĝprH,E was compared with that of ĝprH,E attributable to intrinsic interaction between ions.

Ab initio and DFT calculations reveal that acyl radicals add to imines and electron-rich olefins through simultaneous SOMO --> pi*, pi --> SOMO, and HOMO --> pi*C=O interactions between the radical and the radicalophile. At the CCSD(T)/aug-cc-pVDZ//QCISD/cc-pVDZ level, energy barriers of 15.6 and 17.9 kJ mol(-1) are calculated for the attack of the acetyl radical at the carbon and nitrogen ends of methanimine, respectively. These barriers are 17.1 and 20.4 kJ mol(-1) at BHandHLYP/cc-pVDZ. In comparison, barriers of 34.0 and 23.4 kJ mol(-1) are calculated at BHandHLYP/cc-pVDZ for reaction of the acetyl radical at the 1- and 2-positions in aminoethylene, repectively. Natural bond orbital (NBO) analysis at the BHandHLYP/6-311G** level of theory reveals that SOMO --> pi*imine, pi imine--> SOMO, and LPN --> pi*C=O interactions are worth 90, 278, and 138 kJ mol-1, respectively, in the transition state (2) for reaction of acetyl radical at the nitrogen end of methanimine; similar interactions are observed for the chemistry involving aminoethylene. These multiorbital interactions are responsible for the unusual motion vectors associated with the transition states involved in these reactions. NBO analyses for the remaining systems in this study support the hypothesis that the acetyl radical is ambiphilic in nature.

We report a combined experimental and computational study of the proline effect in model dipeptides Pro-Gly and Gly-Pro. Gas-phase protonated peptide ions were discharged by glancing collisions with potassium or cesium atoms at 3 keV collision energies, and the peptide radical intermediates and their dissociation products were analyzed following collisional ionization to anions. The charge reversal (+CR-) mass spectra of (Pro-Gly + H)+(1a+) and (Gly-Pro + H)+ (2a+) showed dramatic differences and thus provided a sensitive probe of ion structure. Whereas 1a+ completely dissociated upon charge inversion, 2a+ gave a nondissociated anion as the most abundant product. Ab initio and density functional theory calculations provided structures and vertical recombination energies (REvert) for 1a+ and 2a+. The recombination energies, REvert = 3.07 and 3.36 eV for 1a+ and 2a+, respectively, were lower than the alkali metal ionization energies and indicated that the collisional electron transfer to the peptide ions was endoergic. Radical 1a* was found to exist in a very shallow local energy minimum, with transition state energies for loss and migration of H indicating very facile dissociation. In contrast, radical 2a* was calculated to spontaneously isomerize upon electron capture to a stable dihydroxycarbinyl isomer (2e*) that can undergo consecutive and competitive isomerizations by proline ring opening and intramolecular hydrogen atom transfers to yield stable radical isomers. Radical 2e* and its stable isomers were calculated to have substantial electron affinities and thus can form the stable anions that were observed in the +CR- mass spectra. The calculated TS energies and RRKM kinetic analysis indicated that peptide N-C alpha bond dissociations compete with pyrrolidine ring openings triggered by radical sites at both the N-terminal and C-terminal sides of the proline residue. Open-ring intermediates were found in which loss of an H atom was energetically preferred over backbone dissociations. This provided an explanation for the proline effect causing low incidence of electron capture dissociations of N-C alpha bonds adjacent to proline residues in tryptic peptides and also for some peculiar behavior of proline-containing protein cation-radicals.

Free-radical chemistry has come a long way in a relatively short period of time. The synthetic practitioner takes for granted the wealth of mechanistic and rate constant data now available and can apply free-radical techniques to the synthesis of many different classes of target molecule with confidence. Despite this, there are still mechanistic anomalies that need to be addressed. This Account highlights recent work involving nucleophilic radicals with low-lying unoccupied orbitals, such as acyl, oxyacyl, silyl, stannyl, and germyl radicals. Through interesting singly occupied molecular orbital (SOMO)-pi* and highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) interactions during these reactions, the radicals involved are able to mask as electrophiles, providing high levels of regiocontrol and efficient methods for the synthesis of important heterocycles.

We have investigated the tripod-shaped bromo adamantane trithiol (BATT) molecule on Au(111) using scanning tunneling microscopy (STM) at 4.7 K. Adsorption of BATT leads to formation of highly ordered self-assembled monolayers (SAMs) with three-point contacts on Au(111). The structure of these SAMs has been found to have a two-tiered hierarchical chiral organization. The self-assembly of achiral monomers produces chiral trimers, which then act as the building blocks for chiral hexagonal supermolecules. SAMs begin to form from the racemic mixture of assembled molecules in ribbon-shaped islands, followed by the transformation to enantiomeric domains when SAM layers develop two-dimensionally across hcp domains. Such a chiral phase transition at the two-dimensional domain can arise from a subtle balance between molecule-substrate and intermolecular interactions. Two structural factors, the S atom (stabilization) and the methylene groups (chirality) located just above the S atom, induce the chiral ordering of BATT on Au(111).

The concentration vs composition diagram of aggregate formation of the dodecyltrimethylammonium bromide (DTAB) and didodecyldimethylammonium bromide (DDAB) mixture in aqueous solution at rather dilute region was constructed by analyzing the surface tension, turbidity, and electrical conductivity data and inspected by cryo-TEM images and dynamic light scattering data. Although the aqueous solution of DTAB forms only micelles, the transition from monomer to small aggregates and then to vesicle was found at 0.1 < X2

The total-reflection X-ray absorption fine structure (XAFS) method previously employed for the adsorption of dodecyltrimethylammonium bromide (DTAB) at the air/water interface was applied to that in the presence of NaBr. The surface concentration of the bromide ions Gamma(X)(B) of DTAB and NaBr was evaluated by using the Br K-edge absorption jump values of the total-reflection XAFS spectra and was compared to the corresponding value Gamma(H)(B) estimated from the dependence of surface tension on the bulk concentrations of DTAB m(1) and NaBr m(2). The Gamma(X)(B) values trace almost perfectly the Gamma(X)(B) versus m(1) curve up to a concentration near the critical micelle concentration (cmc) and deviate gradually above the concentration. This behavior is basically similar to that of the single DTAB system and ensures that the XAFS method is also applicable to the DTAB system, even in the presence of NaBr. In addition, this method was extended to the single nonionic amphiphile with covalently bonded bromine, and the surface concentrations of 6-bromo-1-hexanol (BrC6OH), Gamma(X)(1) and Gamma(H)(B), were evaluated and compared with each other. It was found that the Gamma(X)(1) value almost perfectly traces the Gamma(H)(1) versus m(1) curve, even at high surface concentrations. The excellent coincidence confirmed that the total-reflection XAFS method can be applied to the nonionic amphiphile system as well as a cationic surfactant with or without an added salt system. Finally, the difference between the Gamma(X)(B) and Gamma(H)(B) values observed in the DTAB with and without an added salt system is briefly described.

The surface conformational states of the Gibbs monolayer of ethylene glycol mono-n-dodecyl ether (C(12)E(1)) at the air/water interface was studied using dynamic surface tension, external reflection-absorption FT-IR spectroscopy (ERA FT-IR), and two-dimensional infrared (2D IR) correlation methods at constant temperature. The dynamic surface tensions were measured at different bulk concentrations of C(12)E(1), and it was observed that a constant surface tension region appears at approximately 38.5 mN m(-1) in a dynamic surface tension profile at concentrations higher than 11 micromol kg(-1). This constant surface tension region corresponds to the surface phase transition from liquid expanded (LE) to liquid condensed (LC). Two sets of ERA FT-IR spectra were collected, one at different bulk concentrations but after equilibrium time (equilibrium measurements) and another at constant bulk concentration (m = 16 micromol kg(-1)) but at different times (dynamic measurements). The first set of these measurements show that the peak area increases in the range of 11 < m < or = 16 micromol kg(-1), which means the increase in the number of surfactant molecules at the air/water interface. Also, the wavenumber of antisymmetric CH(2) stretching decreases gradually from approximately 2923 cm(-1) (for 10 and 11 micromol kg(-1)) to approximately 2918 cm(-1) (for m > or = 16 micromol kg(-1)) with increasing concentration. The wavenumbers of 2923 and 2918 cm(-1) were assigned to LE and LC phases, respectively, and the decrease of wavenumber in the concentration range of 11 < m < or = 16 micromol kg(-1) were correlated to the surface phase transition (LE --> LC), or in other words, in the mentioned concentration range, two phases coexist. The dynamic ERA FT-IR measurements at 16 micromol kg(-1) also confirm the surface phase transition from LE to LC. The 2D IR correlation method was applied to the both equilibrium and dynamic IR spectra of the C(12)E(1) monolayer. The synchronous correlation maps show two strong autopeaks at approximately 2922 and approximately 2851 cm(-1) and also show a strong correlation (cross-peaks) between antisymmetric CH(2) stretching (nu(a)) and symmetric CH(2) stretching (nu(s)). The asynchronous correlation maps show that both observed bands of nu(a) and nu(s) in one-dimensional IR split into two components with the characteristic of overlapped bands, which reveals the coexistence of two phases (LE and LC) at the interface at 11 < m < or = 16 micromol kg(-1). The synchronous and asynchronous maps that were obtained from dynamic IR spectra closely resembled the equilibrium map.

Acyl radicals generated by the addition of alkyl or vinyl radicals to carbon monoxide cyclized onto the C-N bonds of imines and oxazoline with perfect 6-endo selectivity, driven by a preference for attack at nitrogen.

To evaluate the effect of preferential surface adsorption of bromide ions on the synergism of homologous cationic surfactant mixtures reported previously, the surface tension of the aqueous solutions of the hexadecyltrimethylammonium chloride (HTAC)-dodecyltrimethylammonium bromide (DTAB) system was measured as a function of the total molality of surfactants and the relative proportion of DTAB at 298.15 +/- 0.05 K under atmospheric pressure. The excess Gibbs energies calculated from them were -2.6 kJ mol(-)(1) in the mixed adsorbed film and -2.0 kJ mol(-)(1) in the mixed micelle, respectively. A useful analytical procedure to evaluate the composition of individual ions (hexadecyltrimethylammonium, dodecyltrimethylammonium, chloride, and bromide ions) in the adsorbed film and micelle was developed and applied.