Interaction of hydrogen chloride with ice surfaces: the effects of grain size, surface roughness, and surface disorder

Characterization of the interaction of hydrogen chloride (HCl) with polar stratospheric cloud (PSC) ice particles is essential to understanding the processes responsible for ozone depletion. The interaction of HCl with ice was studied using a coated-wall flow tube with chemical ionization mass spectrometry (CIMS) between 5x10(-8) and 10(-4) Torr HCl and between 186 and 223 K, including conditions recently shown to induce quasi-liquid layer (QLL) formation on single crystalline ice samples. Measurements were performed on smooth and rough (vapor-deposited) polycrystalline ice films. A numerical model of the coated-wall flow reactor was used to interpret these results and results of studies on zone-refined ice cylinders with grain sizes on the order of several millimeters (reported elsewhere). We found that HCl adsorption on polycrystalline ice films typically used in laboratory studies under conditions not known to induce surface disordering consists of two modes: one relatively strong mode leading to irreversible adsorption, and one relatively weak binding mode leading to reversible adsorption. We have indirect experimental evidence that these two modes of adsorption correspond to adsorption to sites at crystal faces and those at grain boundaries, but there is not enough information to enable us to conclusively assign each adsorption mode to a type of site. Unlike what was observed in the zone-refined ice study, there was no strong qualitative contrast found between the HCl uptake curves under QLL versus non-QLL conditions for adsorption on smooth and vapor-deposited ices. We also found indirect evidence that HCl hexahydrate formation on ice between 3x10(-7) and 2x10(-6) Torr HCl and between 186 and 190 K is a process involving hydrate nucleation and propagation on the crystal surface, rather than one originating in grain boundaries, as has been suggested for ice formed at lower temperatures. These results underscore the dependence of the HCl-ice interaction on the characteristics of the ice substrate.     

Synthesis, structure and reactivity of cuboidal-type cluster aqua complexes with W3PdS4 4+ core

The reaction of PdCl(2) with [W3S4(H2O)9]4+ in the presence of hypophosphorous acid in 2 M HCl gives cuboidal cluster [W3(PdCl)S4(H2O)9]3+ (1) which undergoes condensation and crystallises from Hpts solutions as edge-linked double cubane cluster [{W3PdS4(H2O)9}2](pts)(8).19H2O (pts = p-toluenesulfonate) (1'). The substitution of Cl- in (1) by different ligands was explored. The Pd atom in the cluster shows an exceptionally high reactivity in the isomerisation of the hydrophosphoryl H2P(O)(OH), HP(O)(OH)2, HPPh(O)(OH) and HPPh2(O) molecules into the corresponding hydroxo tautomers HP(OH)2, P(OH)3, PhP(OH)2 and Ph2P(OH) stabilised by coordination at Pd. The reactions were followed by UV-Vis spectrophotometry and 31P NMR. Formation constants of the 1 : 1 coordination of [M3(PdCl)S4(H2O)9]3+ (M = Mo, W) with HP(OH)2 and As(OH)3 were obtained. The structures of cucurbit[6]uril (C36H36N24O12, CUC[6]) adducts [W3(PdP(OH)3)S4(H2O)8Cl]-(C36H36N24O12)Cl3.12.5H2O (2), and [W3Pd(PhP(OH)2)S4(H2O)7Cl2]2(C36H36N24O12)Cl4.9H2O (3) were determined by single-crystal X-ray diffraction.     

Separation of suspended particles by arrays of obstacles in microfluidic devices

The stochastic transport of suspended particles through a periodic pattern of obstacles in microfluidic devices is investigated by means of the Fokker-Planck equation and numerical simulations. Asymmetric arrays of obstacles have been shown to induce the continuous separation of DNA molecules, with particles of different size migrating in different directions within the microdevice (vector separation). We show that the separation of tracer particles only occurs in the presence of a permeating driving force with a nonzero normal component at the surface of the solid obstacles, and arises from differences in the local Peclet number of the particles. On the other hand, finite-size particles also exhibit nonzero, but small, migration angles in the case of nonpermeating fields. Monte Carlo simulations for different driving fields agree with the solutions to the Fokker-Planck equation.     

Ferrocene-based small molecules for dual-channel sensing of heavy- and transition-metal cations

The synthesis, electrochemical, optical, and cation-sensing properties of ferrocene-pentakis(phenylthio)benzene dyads, linked through a putative cation-binding 2-azadiene bridge, are presented. Dyad 5 behaves as a highly selective dual-redox and chromogenic chemosensor molecule for Pb(2+) cations; the oxidation redox peak is anodically shifted (DeltaE(1/2) = 125 mV), and the low energy band of the absorption spectrum is red-shifted (Delta lambda = 119 nm) upon complexation with this metal cation. Linear sweep voltammetry and spectroelectrochemical studies revealed that Cu(2+) and Hg(2+) metal cations induced oxidation of the ferrocene unit. The isomeric dyad 7, in which the nitrogen atom and the ferrocene unit are in closer proximity, has shown its ability for sensing both Pb(2+) and Hg(2+) ions; the oxidation redox peak is anodically higher shifted (DeltaE(1/2) = 340 mV), and the low energy band of the absorption spectrum is lower red-shifted (Delta lambda = 61 nm) that those found for dyad 5. The changes in the absorption spectra are accompanied by dramatic color changes which allow the potential for "naked eye" detection. A further exciting property of dyad 7 is that it behaves as an electrochemically induced switchable chemosensor for Pb(2+) and Hg(2+) because of the low metal-ion affinity of the oxidized 7(*+) species for these metal cations. The experimental data and conclusions about the ion-sensing properties are supported by DFT calculations.     

External polyacrylate-coating as alternative material for preparation of photopolymerized sol-gel monolithic column

Photopolymerized sol-gel monolithic columns for use in capillary electrochromatography were prepared in 125 microm i.d. polyacrylate-coated fused-silica capillaries. The polyacrylate-coating, unlike the polyimide one, is transparent to the radiation used (approximately 370 nm), and thus, no coating removal is necessary. This is a very important particularity since intrinsic capillary column characteristics, such as flexibility and mechanical resistance, are unchanged. A mixture containing metacryloxypropyltrimethoxysilane (MPTMS) as the polymeric precursor, hydrochloric acid as the catalyst, toluene as the porogen and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Irgacure 819) as the photoinitiator was irradiated at 370 nm for 20 min inside the capillaries to prepare the columns through sol-gel approach. The versatility and viability of the use of polyacrilate as a new capillary external coating were shown through preparation of two columns under different conditions, which were tested in electrochromatography for separation of standard mixture containing thiourea (marker compound), propylbenzene, phenanthrene and pyrene.     

Synthesis and Photophysical Characterizations of Pyrroloquinolone Photosensitizers for Singlet Oxygen Production†

A series of pyrroloquinolone photosensitizers bearing different halogen substituents (Cl, Br, I) on the heterocyclic framework was studied. These structures were readily prepared through a multi-step synthetic sequence involving an oxidative protocol as an important step to access the quinolone framework. Spectroscopic characterizations and computational investigations were carried out to study the dyes before and after the oxidative step. Interestingly, the fluorescence emission was significantly reduced upon oxidation. In spite of a low photostability under UV light, the pyrroloquinolone photosensitizers proved effective to produce singlet oxygen. Higher singlet oxygen quantum yields were obtained with photosensitizers bearing halogen atoms with a higher atomic number.     

Spectral properties of phytochrome Agp2 from Agrobacterium tumefaciens are specifically modified by a compound of the cell extract

Phytochromes are widely distributed photoreceptors that are converted by light between the red absorbing Pr and the far-red absorbing Pfr form. The soil bacterium Agrobacterium tumefaciens contains two phytochromes, Agp1 and Agp2, which act as light-regulated histidine kinases. Whereas most phytochromes are stable in the Pr form, Agp2 and few other phytochromes convert into Pfr in darkness. We have shown in a previous publication that the spectral properties of recombinant Agp2 are modified by compounds of the cell extract from an Agrobacterium agp1(-)/agp2(-) double knockout mutant. In the present work we performed concentration series which show that the interaction is specific and that the modifying factor has a concentration of ca. 0.2 microM. We have also performed a series of mixing experiments with the truncated protein Agp2-M2, which consists of the N-terminal chromophore module (501 amino acids). The cell extract inhibited the photoconversion of Agp2-M2 in an unspecific way. In concentration series, this negative effect was less pronounced when lower concentrations of Agp2-M2 were used. In the presence of excess Agp2-M2 apoprotein, the cell extract did no longer modify the spectral properties of Agp2. The data suggest that the factor of the cell extract interacts specifically with the N-terminal moiety of Agp2.     

Distribution of urocanic acid isomers between aqueous solutions and n-octanol, liposomes or bovine serum albumin

The distribution of urocanic acid (UCA) isomers between aqueous solutions and n-octanol, egg yolk phosphatidylcholine (eggPC) liposomes or bovine serum albumin (BSA) has been evaluated. Regarding its partitioning between water and n-octanol, the behaviour of both isomers is very similar, and the amount incorporated to the organic solvent is mostly determined by the fraction of the compound that, in the aqueous phase, is present as uncharged species. This implies that the highest hydrophobicity occurs near the isoelectric point. cis- and trans-UCA are readily incorporated into eggPC unilamellar liposomes. A simple pseudophase treatment of ultrafiltration data renders a binding constant of 0.20+/-0.04mL/mg for the trans isomer at pH 7.4. The binding constant decreases, by a factor two, at pH 5.0, suggesting that the negatively charged species is more favourably bound to the liposomes than the neutral species, which is mostly present as zwitterions. The cis-isomer, at both pHs, is less incorporated to the bilayers. trans-UCA and cis-UCA readily bind to BSA at pH 7.4, with binding constants of 3400M(-1) and 6900M(-1), respectively. This result suggests that, as in the octanol/water partitioning, hydrophobic interactions predominate and the degree of binding is determined by the fraction present as uncharged species. A smaller binding constant at pH 5.0 indicates that the charge of the protein is also plying a relevant role.     

Ion-selective sensors for determining Au(CN)<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> with membranes based on the ionic liquid tetradecylphosphonium dicyanoaurate

A polymeric membrane for an ion-selective electrode is proposed on the basis of supramolecular systems including a polymeric compound (polyvinyl chloride, PVC) and an ionophore (ionic liquid tetradecylphosphonium dicyanoaurate) in which ionic liquid is simultaneously used as a PVC plasticizer. The selectivity, linear response range, and potential stability of ion-selective electrodes with the optimum membrane composition are measured. The detection limit for Au(I) with the developed electrode is 4.5 × 10^?7 M.     

Asymmetric Synthesis of Monofluorinated Carbocyclic Alcohols and Vicinal Difluorinated Heterocycles and Carbocycles

A straightforward method to access novel families of enantioenriched cis-monofluorinated carbocyclic alcohols has been developed through ATH/DKR in up to 97 % yield, up to 99 : 1 dr and enantioinductions up to 97 % ee. Trans-difluorinated indans, tetrahydronaphthalenes, tetrahydroquinolines and chromans have been synthesized as well by deoxofluorination of the corresponding cis-fluoro alcohols. The reaction was performed on a series of variously substituted 3-fluorochromanols, 3-fluorotetrahydroquinolinols, 2-fluoro inden-1-ols and 2-fluoro 1,2,3,4-tetrahydronaphthalen-1-ols in up to 86 % yields, with diastereoselectivities up to 97 : 3 and enantioselectivities up to >99 % ee.