X-ray reflectivity and interfacial tension study of the structure and phase behavior of the interface between water and mixed surfactant solutions of CH3(CH2)19OH and CF3(CF2)7(CH2)2OH in hexane

The interface between water and mixed surfactant solutions of CH(3)(CH(2))(19)OH and CF(3)(CF(2))(7)(CH(2))(2)OH in hexane was studied with interfacial tension and X-ray reflectivity measurements. Measurements of the tension as a function of temperature for a range of total bulk surfactant concentrations and for three different values of the molal ratio of fluorinated to total surfactant concentration (0.25, 0.28, and 0.5) determined that the interface can be in three different monolayer phases. The interfacial excess entropy determined for these phases suggests that two of the phases are condensed single surfactant monolayers of CH(3)(CH(2))(19)OH and CF(3)(CF(2))(7)(CH(2))(2)OH. By studying four different compositions as a function of temperature, X-ray reflectivity was used to determine the structure of these monolayers in all three phases at the liquid-liquid interface. The X-ray reflectivity measurements were analyzed with a layer model to determine the electron density and thickness of the headgroup and tailgroup layers. The reflectivity demonstrates that phases 1 and 2 correspond to an interface fully covered by only one of the surfactants (liquid monolayer of CH(3)(CH(2))(19)OH in phase 1 and a solid condensed monolayer of CF(3)(CF(2))(7)(CH(2))(2)OH in phase 2). This was determined by analysis of the electron density profile as well as by direct comparison to reflectivity studies of the liquid-liquid interface in systems containing only one of the surfactants (plus hexane and water). The liquid monolayer of CH(3)(CH(2))(19)OH undergoes a transition to the solid monolayer of CF(3)(CF(2))(7)(CH(2))(2)OH with increasing temperature. Phase 3 and the transition regions between phases 1 and 2 consist of a mixed monolayer at the interface that contains domains of the two surfactants. In phase 3 the interface also contains gaseous regions that occupy progressively more of the interface as the temperature is increased. The reflectivity determined the coverage of the surfactant domains at the interface. A simple model is presented that predicts the basic features of the domain coverage as a function of temperature for the mixed surfactant system from the behavior of the single surfactant systems.     

Self-assembly and odd-even effects of cis-unsaturated carboxylic acids on highly oriented pyrolytic graphite

The self-assembly of several cis-unsaturated carboxylic acids of the structure cis-CH3(CH2)p-1CH=CH(CH2)m-1COOH on highly oriented pyrolytic graphite (HOPG) was studied. The impact of the interior cis-CH=CH group and the molecular chain length on their self-assembled structures was considered. Due to the cis conformation of the -HC=CH- group in the interior of these molecules, they display self-assembled structures significantly different from saturated acids with all-trans configurations. As an example of the class of molecules cis-CH3(CH2)p-1CH=CH(CH2)2n-1COOH (p not equal 2n) (p=8, n=7), cis-CH3(CH2)7CH=CH(CH2)13COOH self-assembles into two kinds of enantiomer domains with opposite 2-D chirality. Due to the steric restriction of the interior cis-HC=CH group, all chains with acid groups are packed at the same side of a lamella, a head-to-head arrangement which is different from the head-to-tail packing of saturated all-trans acids. However, cis-CH3(CH2)7CH=CH(CH2)8COOH, considered as one example of the group cis-CH3(CH2)p-1CH=CH(CH2)2n-2COOH (p not equal 2n-1) (p=8, n=5), does not form any stable self-assembled domain, consistent with the molecular arrangement model. This difference in self-assembly behavior between cis-CH3(CH2)p-1CH=CH(CH2)2n-1COOH (p not equal 2n) and cis-CH3(CH2)p-1CH=CHC2n-2COOH (p not equal 2n-1) shows an odd-even chain-length effect of cis-CH3(CH2)p-1CH=CH(CH2)m-1COOH (p not equal m, m=2n or 2n-1). For another category of molecules, cis-unsaturated acids with equal numbers of all-trans carbon atoms on both sides of the cis-CH=CH group, cis-CH3(CH2)m-1CH=CH(CH2)m-1COOH (m=2n or 2n-1), display another odd-even effect. cis-CH3(CH2)7CH=CH(CH2)7COOH, one example of cis-CH3(CH2)2n-1-CH=CH(CH2)2n-1COOH (n=4), is predicted to form both an enantiomer and a nonchiral racemic structure, which is in accordance with the experimental observation of its self-assembled monolayer. However, cis-CH3(CH2)2n-2CH=CH(CH2)2n-2COOH does not form a stable self-assembled domain due to the same steric repulsion as that seen in the cis-CH3(CH2)7CH=CH(CH2)8COOH structure. These odd-even effects demonstrate that molecular self-assembly can be significantly tailored by slightly changing the molecular chain length.     

Fluorine-fluorine interactions in the solid state: an experimental and theoretical study

The solid state structures of three compounds that contain a perfluorinated chain, CF(3)(CF(2))(5)CH(2)CH(CH(3))CO(2)H, CF(3)(CF(2))(5)(CH(2))(4)(CF(2))(5)CF(3) and {CF(3)(CF(2))(5)CH(2)CH(2)}(3)P═O have been compared and a number of C-F···F-C and C-F···H-C interactions that are closer than the sum of the van der Waals radii have been identified. These interactions have been probed by a comprehensive computational chemistry investigation and the stabilizing energy between dimeric fragments was found to be 0.26-29.64 kcal/mol, depending on the type of interaction. An Atoms-in-Molecules (AIM) study has confirmed that specific C-F···F-C interactions are indeed present, and are not due simply to crystal packing. The weakly stabilizing nature of these interactions has been utilized in the physisorption of a selected number of compounds containing long chain perfluorinated ponytails onto a perfluorinated self-assembled monolayer, which has been characterized by IRRAS (Infrared Reflection Absorption Spectroscopy).     

Dehydration reaction of hydroxyl substituted alkenes and alkynes on the Ru(2)S(2) complex

A variety of inter- and intramolecular dehydration was found in the reactions of [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)(mu-S(2))](CF(3)SO(3))(4) (1) with hydroxyl substituted alkenes and alkynes. Treatment of 1 with allyl alcohol gave a C(3)S(2) five-membered ring complex, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCH(2)CH(2)CH(OCH(2)CH=CH(2))S]](CF(3)SO(3))(4) (2), via C-S bond formation after C-H bond activation and intermolecular dehydration. On the other hand, intramolecular dehydration was observed in the reaction of 1 with 3-buten-1-ol giving a C(4)S(2) six-membered ring complex, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2) [mu-SCH(2)CH=CHCH(2)S]](CF(3)SO(3))(4) (3). Complex 1 reacts with 2-propyn-1-ol or 2-butyn-1-ol to give homocoupling products, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCR=CHCH(OCH(2)C triple bond CR)S]](CF(3)SO(3))(4) (4: R = H, 5: R = CH(3)), via intermolecular dehydration. In the reaction with 2-propyn-1-ol, the intermediate complex having a hydroxyl group, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCH=CHCH(OH)S]](CF(3)SO(3))(4) (6), was isolated, which further reacted with 2-propyn-1-ol and 2-butyn-1-ol to give 4 and a cross-coupling product, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCH=CHCH(OCH(2)C triple bond CCH(3))S]](CF(3)SO(3))(4) (7), respectively. The reaction of 1 with diols, (HO)CHRC triple bond CCHR(OH), gave furyl complexes, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SSC=CROCR=CH]](CF(3)SO(3))(3) (8: R = H, 9: R = CH(3)) via intramolecular elimination of a H(2)O molecule and a H(+). Even though (HO)(H(3)C)(2)CC triple bond CC(CH(3))(2)(OH) does not have any propargylic C-H bond, it also reacts with 1 to give [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCH(2)C(=CH(2))C(=C=C(CH(3))(2))]S](CF(3)SO(3))(4) (10). In addition, the reaction of 1 with (CH(3)O)(H(3)C)(2)CC triple bond CC(CH(3))(2)(OCH(3)) gives [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(2)][mu-S=C(C(CH(3))(2)OCH(3))C=CC(CH(3))CH(2)S][Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)]](CF(3)SO(3))(4) (11), in which one molecule of CH(3)OH is eliminated, and the S-S bond is cleaved.     

Study on water evaporation through 1-alkanol monolayers by the thermogravimetry method

The influence of 1-alkanol monolayers on the rate of water evaporation has been studied by measuring water loss per unit time using thermogravimetry. The evaporation rate of water from the surface covered by an insoluble monolayer for each of four saturated 1-alkanols (C(13)OH, C(15)OH, C(17)OH, and C(19)OH) was measured as a function of temperature and alkyl chain length, where the monolayer was under equilibrium spreading pressure. The evaporation rate decreased with increasing alkyl chain length or increasing molecular interaction among 1-alkanol molecules in the insoluble monolayer. Using the Arrhenius equation, the activation energy for the water evaporation was calculated from the temperature dependence of the evaporation rate, which showed that the activation energy decreased with increasing temperature. On the other hand, the activation energy increased with increasing alkyl chain length, which indicates that the activation energy includes the energy to cross the insoluble monolayer at the air/water interface. This energy increased almost linearly with alkyl chain length, when the length is longer than a dodecyl group. This means that water molecules need more energy to escape from the liquid to the gaseous phase across a membrane of longer 1-alkanols, which becomes more evident at lower temperatures. The temperature dependence of the activation energy was slightly larger for longer 1-alkanols than for shorter ones.     

Facile allylic C-H bond activation on the bridging disulfide ligand in the Ru(III) dinuclear complex having a conjugated RuSSRu core

Treatment of [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)(mu-S(2))](CF(3)SO(3))(4) (1), which is prepared by the reaction of [[RuCl(P(OCH(3))(3))(2)](2)(mu-S(2))(mu-Cl)(2)] (2) with 4 equiv of AgCF(3)SO(3), with terminal alkenes such as 1-pentene, allyl ethyl ether, allyl phenyl ether, 1,4-hexadiene, and 3-methyl-1-butene, resulted in the formation of complexes carrying a C(3)S(2) five-membered ring, [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCH(2)CH(2)CR(1)R(2)S]](CF(3)SO(3))(4) (3, R(1) = CH(2)CH(3), R(2) = H, 40%; 4, R(1) = OCH(2)CH(3), R(2) = H, 60%; 5, R(1) = OC(6)H(5), R(2) = H, 73%; 6, R(1) = CH=CHCH(3), R(2) = H, 48%; 7, R(1) = R(2) = CH(3), 40%). Reaction of 1 with methylenecycloalkanes was found to give several different types of products, depending on the ring size of the substrates. A trace of [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-SCH(CH(2)CH(2))CH(CH(3))S]](CF(3)SO(3))(4) (9) having a C(2)S(2) four-membered ring to bridge the two Ru atoms was obtained by the reaction of 1 with methylenecyclobutane, whereas the reaction with methylenecyclohexane gave [[Ru(P(OCH(3))(3))(2)(CH(3)CN)(3)](2)[mu-S(CH(2)(C=CHCH(2)CH(2)CH(2)CH(2))S)](CF(3)SO(3))(3) (10) in 69% yield via C-S bond formation and elimination of a proton. Throughout these reactions with alkenes giving a variety of products, the activation of the allylic C-H bond is always the essential and initial key step.     

Quaternary salts containing the pentafluorosulfanyl (SF5) group

The first quaternary salts of pyridine (2), N-methyl imidazole (3), N-propyl triazole (4), and pyridazine (5) that contain the pentafluorosulfanyl (SF(5)) group were prepared and characterized. Neat reactions of the aromatic nitrogen compounds with SF(5)(CF(2))(n)(CH(2))(m)I (n = 2 or 4, m = 2 or 4) gave quaternary iodides 6a-c, 7a-c, 8a, and 9a,b, which were metathesized with LiN(SO(2)CF(3))(2) to form the bis(trifluoromethylsulfonyl)amides 10a-c, 11a-c, 12a, and 13a,b, in high yields. With the exception of the pyridine bis(trifluoromethylsulfonyl)amide salts, the compounds melted or exhibited a T(g) at <0 degrees C. The methylimidazolium, pyridinium, and pyridazinium salts exhibited densities of approximately 2 g/cm(3). Particularly striking was the density of CF(3)(CF(2))(5)(CH(2))(2)-pyridazinium N(CF(3)SO(2))(2) measured at 2.13 g/cm(3); however, an atypically high density for the 1-CF(3)(CF(2))(5)(CH(2))(2)-3-methyl imidazolium amide (14) was also observed at 1.77 g/cm(3). All quaternary salts were characterized via IR, (19)F, (1)H, and (13)C NMR spectra and elemental analyses.     

Biophysical investigation of the interfacial properties of cationic fluorocarbon/hydrocarbon hybrid surfactant: mimicking the lung surfactant protein C

The interfacial behavior of the newly designed Fluorocarbon Hydrocarbon Cationic Lipid (FHCL or CH(3)(CH(2))(17)N(+)(C(2)H(5))(2)(CH(2))(3)(CF(2))(7)CF(3)I(-)) and its mixtures with a phospholipid (DPPC, Dipalmitoylphosphatidylcholine) at different mole fractions were investigated. This new molecule was synthesized to mimic the selected properties of lung surfactant, which is a natural lipid-protein mixture which is known to play important roles in the process of respiration, by considering the structure/function relation of lung surfactant protein (SP-C). Each segment in the molecular structure was selected to affect the molecular level interaction at the interface whereas the keeping the overall structure as simple as possible. The surface pressure area isotherms obtained for the mixtures of DPPC/FHCL indicated that there was repulsive interaction between DPPC and FHCL molecules. Due to the molecular level interaction, specifically at mole fraction 0.3, the isotherm obtained from that mixture resembled the isotherm obtained from the DPPC monolayer in the presence of SP-C. High elasticity of the interface was one of the important parameters for the respiration process, therefore, shear and dilatational elasticities of two-component systems were determined and they were found to be similar to the case where SP-C protein is present. Fluorescence microscopy images were taken in order to investigate the monolayer in details. The FHCL was able to fluidize the DPPC monolayer even at high surface pressures effectively. In addition, the cyclic compression-expansion isotherms were obtained to understand the spreading and re-spreading ability of the pure FHCL and the mixed DPPC/FHCL monolayers. At a specific mole fraction, X(FHCL)=0.3, the mixture exhibited good hysteresis in area, compressibility, recruitment index and re-spreading ability at the interface. All these results point out that FHCL can fulfill the selected features of the lung surfactant that are attributed to the presence of SP-C protein when mixed with DPPC, even if the molecular structure of the FHCL is quite simple.     

Phase behaviour and conductivity study of electrolytes in supercritical hydrofluorocarbons

The purpose of this work was to characterise supercritical hydrofluorocarbons (HFC) that can be used as solvents for electrodeposition. The phase behaviour of CHF(3), CH(2)F(2), and CH(2)FCF(3) containing [NBu(n)(4)][BF(4)], [NBu(n)(4)][B{3,5-C(6)H(3)(CF(3))(2)}(4)] and Na[B{3,5-C(6)H(3)(CF(3))(2)}(4)] was studied and the conditions for forming a single supercritical phase established. Although all three HFCs are good solvents for [NBu(n)(4)][BF(4)] the results show that the CH(2)F(2) system has the lowest p(r) for dissolving a given amount of [NBu(n)(4)][BF(4)]. The solubility of Na[B{3,5-C(6)H(3)(CF(3))(2)}(4)] in CH(2)F(2) was found to be unexpectedly high. Studies of the phase behaviour of CH(2)F(2) containing [NBu(n)(4)][BF(4)] and [Cu(CH(3)CN)(4)][BF(4)] showed that the copper complex was unstable in the absence of CH(3)CN. For CHF(3), [Cu(hfac)(2)] was more soluble and more stable than [Cu(CH(3)CN)(4)][BF(4)] and only increased the phase-separation pressure by a moderate amount. Studies of the conductivity of [NBu(n)(4)][B(C(6)F(5))(4)], [NBu(n)(4)][B{3,5-C(6)H(3)(CF(3))(2)}(4)], [NR(f)Bu(n)(3)][B{3,5-C(6)H(3)(CF(3))(2)}(4)] (R(f) = (CH(2))(3)C(7)F(15)), and Na[B{3,5-C(6)H(3)(CF(3))(2)}(4)] were carried out in scCH(2)F(2). The results show that these salts are more conducting than [NBu(n)(4)][BF(4)] under the same conditions although the increase is much less significant than that reported in previous work in supercritical CO(2) + CH(3)CN. Consequently, either [NBu(n)(4)][BF(4)] or the corresponding BARF salts would be suitable background electrolytes for electrodeposition from scCH(2)F(2).     

Electronic structure of iron chlorins: characterization of bis(l-valine methyl ester)(meso-tetraphenylchlorin)iron(III)triflate and bis(l-valine methyl ester)(meso-tetraphenylchlorin)iron(II)

The synthesis and characterization of the two iron chlorin complexes [Fe(III)(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) and Fe(II)(TPC)[(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2))](2) (2) are reported. The crystal structure of complex 1 has been determined. The X-ray structure shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(4), 2.034(4) A, and to the pyrrole trans to it N(2), 2.012(4) A, are longer than the distances to the two remaining nitrogens [N(1), 1.996(4) A, and N(3), 1.984(4) A], leading to a core-hole expansion of the macrocycle due to the reduced pyrrole. The (1)H NMR isotropic shifts at 20 degrees C of the different pyrrole protons of 1 varied from -0.8 to -48.3 ppm according to bis-ligated complexes of low-spin ferric chlorins. The EPR spectrum of [Fe(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) in solution is rhombic and gives the principal g values g(1) = 2.70, g(2) = 2.33, and g(3) = 1.61 (Sigmag(2) = 15.3). These spectroscopic observations are indicative of a metal-based electron in the d(pi) orbital for the [Fe(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) complex with a (d(xy))(2)(d(xz)d(yz))(3) ground state at any temperature. The X-ray structure of the ferrous complex 2 also shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(4), 1.991(5) A, and to the pyrrole trans to it N(2), 2.005(6) A, are slightly different from the distances to the two remaining nitrogens [N(1), 1.988(5) A, and N(3), 2.015(5) A], leading to a core-hole expansion of the macrocycle due to the reduced pyrrole.     

Aggregation properties of cationic gemini surfactants with partially fluorinated spacers in aqueous solution

The aggregation properties of cationic gemini surfactants alkanediyl-alpha,omega-bis(dodecyldimethylammonium bromide), [C(12)H(25)(CH(3))(2)N(CH(2))(m)(CF(2))(n)(CH(2))(m))N(CH(3))(2)C(12)H(25)]Br(2) [where 2m + n = 12 and n = 0, 4, and 6; designated as 12-12-12, 12-12(C(4)(F))-12, and 12-12(C(6)(F))-12, respectively] have been studied by microcalorimetry, time-resolved fluorescence quenching, and electrical conductivity. Compared with a fully hydrocarbon spacer of 12-12-12, the fluorinated spacer with a lower ratio of CF(2) to CH(2) in 12-12(C(4)(F))-12 tends to disfavor the aggregation, leading to larger critical micelle concentration (cmc), lower micelle aggregation number (N), and less negative Gibbs free energy of micellization (DeltaG(mic)). However, the fluorinated spacer with a higher ratio of CF(2) to CH(2) in 12-12(C(6)(F))-12 may prompt the aggregation, resulting in lower cmc, higher N, and more negative DeltaG(mic). It is also noted that enthalpy change of micellization (DeltaH(mic)) for 12-12(C(4)(F))-12 is the most exothermic, but the values of DeltaH(mic) for 12-12-12 and 12-12(C(6)(F))-12 are almost the same. These results are rationalized in terms of competition among the enhanced hydrophobicity and the rigidity of the fluorinated spacer, and the variation of immiscibility of the fluorinated spacer with the hydrocarbon side chains.     

Chiral fluorous dialkoxy-diamino zirconium complexes: synthesis and use in stereospecific polymerization of 1-hexene

New catalysts for the isospecific polymerization of 1-hexene based on cationic zirconium complexes incorporating the tetradentate fluorous dialkoxy-diamino ligands [OC(CF(3))(2)CH(2)N(Me)(CH(2))(2)N(Me)CH(2)C(CF(3))(2)O](2-) [(ON(2)NO)(2-)] and [OC(CF(3))(2)CH(2)N(Me)(1R,2R-C(6)H(10))N(Me)CH(2)C(CF(3))(2)O](2-) [(ON(Cy)NO)(2-)] have been developed. The chiral fluorous diamino-diol [(ON(Cy)NO)H(2), 2] was prepared by ring-opening of the fluorinated oxirane (CF(3))(2)COCH(2) with (R,R)-N,N'-dimethyl-1,2-cyclohexanediamine. Proligand 2 reacts cleanly with [Zr(CH(2)Ph)(4)] and [Ti(OiPr)(4)] precursors to give the corresponding dialkoxy complexes [Zr(CH(2)Ph)(2)(ON(Cy)NO)] (3) and [Ti(OiPr)(2)(ON(Cy)NO)] (4), respectively. An X-ray diffraction study revealed that 3 crystallizes as a 1:1 mixture of two diastereomers (Lambda-3 and Delta-3), both of which adopt a distorted octahedral structure with trans-O, cis-N, and cis-CH(2)Ph ligands. The two diastereomers Lambda-3 and Delta-3 adopt a C(2)-symmetric structure in toluene solution, as established by NMR spectroscopy. Cationic complexes [Zr(CH(2)Ph)(ON(2)NO)(THF)(n)](+) (n=0, anion=[B(C(6)F(5))(4)](-), 5; n=1, anion=[PhCH(2)B(C(6)F(5))(3)](-), 6) and [Zr(CH(2)Ph)(ON(Cy)NO)(THF)](+)[PhCH(2)B(C(6)F(5))(3)](-) (7) were generated from the neutral parent precursors [Zr(CH(2)Ph)(2)(ON(2)NO)] (H) and [Zr(CH(2)Ph)(2)(ON(Cy)NO)] (3), and their possible structures were determined on the basis of (1)H, (19)F, and (13)C NMR spectroscopy and DFT methods. The neutral zirconium complexes H and 3 (Lambda-3/Delta-3 mixture), when activated with B(C(6)F(5))(3) or [Ph(3)C](+)[B(C(6)F(5))(4)](-), catalyze the polymerization of 1-hexene with overall activities of up to 4500 kg PH mol Zr(-1) h(-1), to yield isotactic-enriched (up to 74 % mmmm) polymers with low-to-moderate molecular weights (M(w)=4800-47 200) and monodisperse molecular-weight distributions (M(w)/M(n)=1.17-1.79).     

Electrochemical preparation of the bis(ruthenocenium) dication

The electrochemical oxidation of ruthenocene (1) in CH(2)Cl(2)/[NBu(4)]A, where A = [B(C(6)F(5))(4)](-) or [B(C(6)H(3)(CF(3))(2))(4)](-), gives the dimeric dication [(RuCp(2))(2)](2+), 2(2+), in equilibrium with the 17-electron ruthenocenium ion 1(+). At room temperature the rapid equilibrium accounts for the quasi-Nernstian cyclic voltammetry (CV) behavior (E(1/2) = 0.41 V vs FeCp(2), A = [B(C(6)F(5))(4)](-)). Direct electrochemical evidence for 2(2+) is seen by CV and by bulk electrolysis at 243 K. The bis(ruthenocenium) dication undergoes a highly irreversible two-electron cathodic reaction at E(pc) ca. 0 V. Anodic electrolysis of 1 at 243 K using [B(C(6)H(3)(CF(3))(2))(4)](-) as the supporting electrolyte, followed by cathodic electrolysis of 2(2+), regenerates half of the original 1. Precipitation of 2(2+) occurs when the supporting electrolyte is [B(C(6)F(5))(4)](-), allowing facile isolation of [(RuCp(2))(2)][B(C(6)F(5))(4)](2). A second, unidentified, anodic product also reduces to give back ruthenocene. Digital simulations of the CV curves of 1 at 243 K give a dimerization equilibrium constant of 9 x 10(4) M(-1) for K(eq) = [(RuCp(2))(2)(2+)]/2 [RuCp(2)](+) in CH(2)Cl(2)/0.1 M [NBu(4)][B(C(6)F(5))(4)].     

Alkyl 2,2,2-Trifluoroethanesulfonates (Tresylates): Elimination-Addition vs Bimolecular Nucleophilic Substitution in Reactions with Nucleophiles in Aqueous Media(1)

Alkyl 2,2,2-trifluoroethanesulfonate esters (tresylates), ROSO(2)CH(2)CF(3), react with aqueous base (pH >/= 9) to give the (alkoxysulfonyl)acetic acid, ROSO(2)CH(2)COOH; with the further addition of either a primary or secondary amine or of an alkanethiol, the product is the either the corresponding amide, ROSO(2)CH(2)C(O)NR(1)R(2), or a mixture in which the ketene dithioacetal, ROSO(2)CH=C(SR(1))(2), or the thioorthoester, ROSO(2)CH(2)C(SR(1))(3), may predominate. Kinetic and product studies are consistent with the following: (a) the reaction of tresylates with water is the normal sulfonic ester hydrolysis and (b) reaction with hydroxide is an (E1cB)(rev) process with loss of HF to yield the alkyl 2,2-difluoroethenesulfonate, ROSO(2)CH=CF(2), which rapidly yields the observed products. Benzyl 2,2,2-trifluoroethyl sulfone reacts analogously. The relationship between these observation with small molecules and those of earlier workers with tresyl agarose is discussed.     

Scope and mechanism of the intermolecular addition of aromatic aldehydes to olefins catalyzed by Rh(I) olefin complexes

Rhodium (I) bis-olefin complexes Cp*Rh(VTMS)(2) and CpRh(VTMS)(2) (Cp* = C(5)Me(5), Cp = C(5)Me(4)CF(3), VTMS = vinyl trimethylsilane) were found to catalyze the addition of aromatic aldehydes to olefins to form ketones. Use of the more electron-deficient catalyst CpRh(VTMS)(2) results in faster reaction rates, better selectivity for linear ketone products from alpha-olefins, and broader reaction scope. NMR studies of the hydroacylation of vinyltrimethylsilane showed that the starting Rh(I) bis-olefin complexes and the corresponding Cp*/Rh(CH(2)CH(2)SiMe(3))(CO)(Ar) complexes were catalyst resting states, with an equilibrium established between them prior to turnover. Mechanistic studies suggested that CpRh(VTMS)(2) displayed a faster turnover frequency (relative to Cp*Rh(VTMS)(2)) because of an increase in the rate of reductive elimination, the turnover-limiting step, from the more electron-deficient metal center of CpRh(VTMS)(2). Reaction of Cp*/Rh(CH(2)CH(2)SiMe(3))(CO)(Ar) with PMe(3) yields acyl complexes Cp*/Rh[C(O)CH(2)CH(2)SiMe(3)](PMe(3))(Ar); measured first-order rates of reductive elimination of ketone from these Rh(III) complexes established that the Cp ligand accelerates this process relative to the Cp* ligand.     

The gas phase tropospheric removal of fluoroaldehydes (CxF2x+1CHO, x = 3, 4, 6)

The rate coefficient of the OH reaction with the perfluoroaldehydes C(3)F(7)CHO and C(4)F(9)CHO have been determined in the temperature range 252-373 K using the pulsed laser photolysis-laser induced fluorescence (PLP-LIF) method: k(C(3)F(7)CHO+OH) = (2.0 +/- 0.6) x 10(-12) exp[-(369 +/- 90)/T] and k(C(4)F(9)CHO+OH) = (2.0 +/- 0.5) x 10(-12) exp[-(356 +/- 70)/T] cm(3) molecule(-1) s(-1), corresponding to (5.8 +/- 0.6) x 10(-13) and (6.1 +/- 0.5) x 10(-13) cm(3) molecule(-1) s(-1), respectively, at 298 K. The UV absorption cross sections of these two aldehydes and CF(3)(CF(2))(5)CH(2)CHO have been measured over the range 230-390 nm at 298 K and also at 328 K for CF(3)(CF(2))(5)CH(2)CHO. The obtained results for C(3)F(7)CHO and C(4)F(9)CHO are in good agreement with two recent determinations but the maximum value of the absorption cross section for CF(3)(CF(2))(5)CH(2)CHO is over a factor of two lower than the single one recently published. The photolysis rates of C(3)F(7)CHO, C(4)F(9)CHO and CF(3)(CF(2))(5)CHO have been measured under sunlight conditions in the EUPHORE simulation chamber in Valencia (Spain) at the beginning of June. The photolysis rates were, respectively, J(obs) = (1.3 +/- 0.6) x 10(-5), (1.9 +/- 0.8) x 10(-5) and (0.6 +/- 0.3) x 10(-5) s(-1). From the J(obs) measurements and calculated photolysis rate J(calc), assuming a quantum yield of unity across the atmospheric range of absorption of the aldehydes, quantum yields J(obs)/J(calc) = (0.023 +/- 0.012), (0.029 +/- 0.015) and (0.046 +/- 0.028) were derived for the photodissociation of C(3)F(7)CHO, C(4)F(9)CHO and CF(3)(CF(2))(5)CHO, respectively. The atmospheric implication of the data obtained in this work is discussed. The main conclusion is that the major atmospheric removal pathway for fluoroaldehydes will be photolysis, which under low NO(x) conditions, may be a source of fluorinated carboxylic acids in the troposphere.     

Rational aspect ratio and suitable antibody coverage of gold nanorod for ultra-sensitive detection of a cancer biomarker

We report a simple, ultra-sensitive, and straightforward method for non-labeling detection of a cancer biomarker, using Rayleigh light scattering spectroscopy of the individual nanosensor based on antibody-antigen recognition and localized surface plasmon resonance (LSPR) λ(max) shifts. By experimentally measuring the refractive index sensitivity of Au nanorods, the Au nanorod with an aspect ratio of ~3.5 was proven optimal for the LSPR sensing. To reduce the steric hindrance effect as well as to immobilize a large amount of ligand on the nanoparticle surface, various mixtures containing different molar ratios of HS(CH(2))(11)(OCH(2)CH(2))(6)OCH(2)COOH and HS(CH(2))(11)(OCH(2)CH(2))(3)OH were applied to form different self-assembled monolayer surfaces. The results showed that the best molar ratio for antibody conjugation was 1 : 10. When using individual Au nanorod sensors for the detection of prostate specific antigen (PSA), the lowest concentration recorded was ~1 aM (~6 × 10(5) molecules), corresponding to LSPR λ(max) shifts of ~4.2 nm. These results indicate that sensor miniaturization down to the nanoscale level, the reduction of steric hindrance, and optimization of size, shape, and aspect ratio of nanorods have led to a significant improvement in the detection limit of sensors.     

Photodegradation of toluene over TiO(2-x)N(x) under visible light irradiation

We report the photooxidation of toluene over nitrogen doped TiO(2) (TiO(2-x)N(x)) under visible light irradiation. The photocatalytic oxidation of toluene in air over TiO(2-x)N(x) powders was studied using diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS), gas chromatography (GC), ion chromatography (IC), and gas chromatography mass spectrometry (GC-MS), focusing on the photocatalytic decomposition processes of toluene. Results obtained indicate that toluene, weakly adsorbed on the catalyst surface, is initially photooxidized to benzaldehyde which adsorbs onto the TiO(2-x)N(x) surface more strongly, leading to the formation of ring-opening products such as carboxylic acids and aldehydes. No gaseous intermediates were detected during the photooxidation. Major intermediates adsorbed at the catalyst surface were oxalic acid, (COOH)(2), acetic acid, CH(3)COOH, formic acid, HCOOH, and pyruvic acid, CH(3)COCOOH, whereas more complicated carboxylic species, including propionic acid, CH(3)CH(2)COOH, isovaleric acid, (CH(3))(2)CHCH(2)COOH, and succinic acid, (CH(2)COOH)(2), were also found in the early stage of the photooxidation. These intermediate products were gradually photodegraded to CO(2) and H(2)O under visible light irradiation.     

Sensitivity of silver(I) complexes of a pyrimidine-hydrazone ligand to solvent, counteranion, and metal-to-ligand ratio changes

Metal complexation studies were performed with AgSO(3)CF(3) and AgBF(4) and the ditopic pyrimidine-hydrazone ligand 6-(hydroxymethyl)pyridine-2-carboxaldehyde (2-methylpyrimidine-4,6-diyl)bis(1-methylhydrazone) (1) in both CH(3)CN and CH(3)NO(2) in a variety of metal-to-ligand ratios. The resulting complexes were studied in solution by NMR spectroscopy and in the solid state by X-ray crystallography. Reacting either AgSO(3)CF(3) or AgBF(4) with 1 in either CH(3)CN or CH(3)NO(2) in a 1:1 metal-to-ligand ratio produced a double helicate in solution. This double helicate could be converted into a linear complex by increasing the metal-to-ligand ratio; however, the degree of conversion depended on the solvent and counteranion used. Attempts to crystallize the linear AgSO(3)CF(3) complex resulted in crystals with the dimeric structure [Ag(2)1(CH(3)CN)(2)](2)(SO(3)CF(3))(4) (2), while attempts to crystallize the AgSO(3)CF(3) double helicate from CH(3)CN resulted in crystals of another dimeric complex, [Ag(2)1(SO(3)CF(3))(CH(3)CN)(2)](2)(SO(3)CF(3))(2)·H(2)O (3). The AgSO(3)CF(3) double helicate was successfully crystallized from a mixture of CH(3)CN and CH(3)NO(2) and had the structure [Ag(2)1(2)](SO(3)CF(3))(2)·3CH(3)NO(2) (4). The linear AgBF(4) complex could not be isolated from the double helicate in solution; however, crystals grown from a solution containing both the AgBF(4) double helicate and linear complexes in CH(3)CN had the structure [Ag(2)1(CH(3)CN)(2)](BF(4))(2) (5). The AgBF(4) double helicate could only be crystallized from CH(3)NO(2) and had the structure [Ag(2)1(2)](BF(4))(2)·2CH(3)NO(2) (6).     

Syntheses and reactivities of disubstituted and trisubstituted fluorous pyridines with high fluorous phase affinities: solid state,liquid crystal,and ionic liquid-phase properties

Reactions of 2,6-dibromo-, 3,5-dibromo-, and 2,4,6-tribromopyridine with IZnCH(2)CH(2)R(f8) (R(f8) = (CF(2))(7)CF(3)) in THF at 65 degrees C in the presence of trans-Cl(2)Pd(PPh(3))(2) (5 mol %) gave the fluorous pyridines 2,6- and 3,5-NC(5)H(3)(CH(2)CH(2)R(f8))(2) (1 and 2; 85%, 31%) and 2,4,6-NC(5)H(2)(CH(2)CH(2)R(f8))(3) (3, 61%). Reaction of 2,6-pyridinedicarboxaldehyde with [Ph(3)PCH(2)CH(2)R(f8)](+)I(-)/K(2)CO(3) (p-dioxane/H(2)O, 95 degrees C) gave 2,6-NC(5)H(3)(CH[double bond]CHCH(2)R(f8))(2) (95%; 70:30 ZZ/ZE), which was treated with H(2) (1 atm, 12 h) and 10% Pd/C to yield 2,6-NC(5)H(3)(CH(2)CH(2)CH(2)R(f8))(2) (5, 95%), a higher homologue of 1. Longer reaction times afforded piperidine cis-2,6-HNC(5)H(8)(CH(2)CH(2)CH(2)R(f8))(2) (6, 98%). The stereochemistry was established by NMR analysis of the N-benzylpiperidine. Pyridines 1-3 and 5 are low-melting white solids with CF(3)C(6)F(11)/toluene partition coefficients (24 degrees C) of 93.8:6.2, 93.9:6.1, >99.7:<0.3, and 90.4:9.6, respectively (6, 93.6:6.4). Reaction of 1 and CF(3)SO(3)H gave a pyridinium salt, and Cl(2)Pd(NCCH(3))(2) (0.5 equiv) yielded trans-Cl(2)Pd(1)(2). The crystal structure of the former, which also exhibited liquid crystalline and ionic liquid phases, was determined.