Construction of a new interface for comprehensive supercritical fluid chromatography x reversed phase liquid chromatography (SFC x RPLC)

The design of a new interface to hyphen high efficiency supercritical fluid chromatography (SFC) and fast RPLC in a comprehensive configuration is described. SFC x RPLC is a viable alternative to normal phase (NP) LC x RPLC and is characterized by high orthogonality. Compared to NPLC x RPLC an additional advantage is the expansion of supercritical carbon dioxide (CO(2)) when exposed to atmospheric pressure leading to fractions consisting of solvents that are miscible with the second dimension RPLC mobile phase. The interface consists of a two-position/ten-port switching valve equipped with two packed octadecyl silica (C(18)) loops for effective trapping and focusing of the analytes after elution from the SFC dimension. The addition of a water make-up flow to the SFC effluent prior to entering the loops is of fundamental importance to efficiently focus the solutes on the C(18) material and to reduce interferences of expanded CO(2) gas on the second dimension separation. The features of the system are illustrated with the analysis of a lemon oil sample.     

Evaluation of a combined fractionation and speciation approach for study of size-based distribution of organotin species on environmental colloids

Results relating to the first original application of an analytical approach combining asymmetric flow field-flow fractionation (As-Fl-FFF) with multi-detection and chemical speciation for determination of organotins in a landfill leachate sample are presented. The speciation analysis involved off-line head-space solid-phase microextraction (HS-SPME)–gas chromatography with pulsed-flame photometric detection (GC–PFPD) performed after three consecutive collections of five different fractions of interest from the As-Fl-FFF system and cross-flow part (assumed to be representative of the <10 kDa phase). After 0.45 μm filtration and without preconcentration before fractionation and speciation analysis, limits of detection (LOD) were 4–45 ng (Sn) L⁻¹ in the sample, with relative standard deviations (RSD) of 3–23%. The As-Fl-FFF fractionation of this sample enables characterization of two distinct populations—organic-rich and inorganic colloids with gyration radius up to 120 nm. Total Sn and mono and dibutyltins (MBT and DBT) appear to be distributed over the whole colloidal phase. Tributyl, monomethyl, monooctyl, and diphenyltins (TBT, MMT, MOcT, and DPhT) were also detected. Quantitative speciation analysis performed on the two colloidal populations and in the <10 kDa phase revealed concentrations from 130 ± 10 (MMT) to 560 ± 50 ng (Sn) L⁻¹ (DPhT).     

Synthetic studies towards 4,10-diaza-1,7-dioxaspiro[5.5]undecanes: access to 3-aza-6,8-dioxabicyclo[3.2.1]octan-2-one and 2H-1,4-oxazin-3(4H)-one frameworks

Synthetic approaches towards 4,10-diaza-1,7-dioxaspiro[5.5]undecanes starting from 1,3-dichloroacetone and solketal derivatives are explored. The method relies on the preparation of a key bis-substituted dihydroxy-protected oxime, which would undergo a final acidic deprotection-spiroacetalization process. Although the desired diazaspiroketal framework could not be obtained, our conditions led to the unexpected 3-aza-6,8-dioxabicyclo[3.2.1]octan-2-one 18 or to the oxazinone 32 in good yields.     

Novel polymerizable surfactants from 1:1 mixtures of alkylcarboxylic acids and norbornene methylenamine

A new family of polymerizable surfactants was synthesized starting from a 1:1 mixture of alkylcarboxylic acids (C(10) to C(16)) and norbornene methyleneamine. The ion-paired surfactants exhibited cloud temperatures, surface activity, and critical aggregation concentrations that differed according to the chain length, with a variation indicating a strongly associated ion pair. Light-scattering measurements and electron microscopy observations confirmed the spontaneous formation of stable vesicles (90 nm < d < 370 nm). Also, NMR experiments showed the enclosing of the norbornene part inside the vesicle membrane. Moreover, the addition of sodium chloride allowed the formation of a tubular structure leading to a viscous or gel-like solution. Finally, a preliminary vinylic polymerization test proved the polymerizable character of these ion-paired surfactants by an organometallic catalysis, leading to partially polymerized vesicles.     

Homochiral oligopeptides via a lattice-controlled polymerisation in racemic crystals of valine N-carboxyanhydride suspended in aqueous solutions

As part of our program on the biochirogenesis of homochiral peptides, we report the formation of racemic parallel (p) beta sheets composed of alternating R and S chains of up to 14-15 repeat units of the same handedness through the polymerisation of (R,S)-valine N-carboxyanhydride (NCA) crystals suspended in aqueous solutions of a primary amine as the initiator. The occurrence of such a lattice-controlled reaction accompanied by a reduction in volume implies the operation of a mechanism that differs from that of the common solid-state polymerisation in vinyl systems. The topotacticity of the reaction is explained through the operation of a multistep nonlinear process comprising lattice control coupled with an asymmetric induction in the formation of homochiral short peptides followed by their self-assembly into racemic p beta sheets, which operate as efficient templates in the ensuing process of enantioselective chain elongation at the polymer/crystal interface. The composition of the diastereoisomeric libraries of oligopeptides was determined by MALDI-TOF and MALDI-TOF-TOF MS analyses of the products obtained from monomers enantioselectively labelled with deuterium. The structure of the p beta sheets could be determined by initiating the polymerisation reaction with water-soluble esters of enantiopure alpha-amino acids or short peptides. The same reaction performed with the monomer crystals suspended in hexane yielded a complex mixture of diastereoisomeric oligopeptides, thus highlighting the indispensable role played by water in controlling the stereoselectivity of the reaction. By contrast, polymerisation of (R,S)-leucine NCA crystals, with a different packing arrangement that presumably does not endorse the formation of periodic peptide templates, yielded, both in aqueous and hexane suspensions, libraries of peptides dominated by heterochiral diastereoisomers.     

Photogeneration of two metastable NO linkage isomers with high populations of up to 76% in trans-[RuCl(py)4(NO)][PF6]2.1/2H2O

Two light-induced metastable NO linkage isomers with oxygen-bound (SI) and side-on configuration (SII) of NO are generated in trans-[RuCl(py)(4)(NO)][PF(6)](2).(1/2)H(2)O. Irradiation by light in the blue-green spectral range (450-530 nm) leads to the population of SI. A further irradiation by near infrared light (920-1100 nm) transfers SI into SII at temperatures below 150 K. The heat release during the thermal decay of the linkage isomers shows that SI and SII are separated from the ground state (GS) by potential barriers of E(A)(SI) = 0.70(3) eV and E(A)(SII) = 0.38(3) eV, and are energetically situated at 1.42(6) eV and 1.07(7) eV above the ground state, respectively. Maximum populations of 76% for SI and of 56% for SII can be generated, as determined by the decrease of the nu(NO) stretching absorption band of the ground state. The nu(NO) stretching vibration shifts to lower energies by 143 cm(-1) in SI and by 300 cm(-1) in SII, indicating that the linkage isomers are of the same type as found in other octahedrally coordinated transition-metal nitrosyl complexes. The experimental observations are in agreement with results from calculations by the density functional theory, which predict that the metastable states correspond to a side-on bonded (SII) and an isonitrosyl (SI) configuration of the NO ligand. The calculations provide the energy minima of the ground state and the metastable states SI and SII as well as the saddle points along the reaction coordinate Q. This reaction coordinate corresponds to a rotation of the NO ligand by about 90 degrees (SII) and 180 degrees (SI), and therefore allows the comparison between observed and calculated activation energies.     

Conformational substates of horse heart cytochrome c exhibit different thermal unfolding of the heme cavity

The charge transfer (CT) band at 695 nm in the spectrum of ferri-cytochrome c is highly asymmetric, indicating conformational heterogeneity due to the coexistence of different conformational substates. We have measured the respective band profile of horse heart ferri-cytochrome c as a function of temperature between 283 K (10 degrees C) and 333 K (60 degrees C) and found that the well-known decrease of the absorptivity is wavenumber-dependent and exhibits a biphasic behavior. This indicates that the underlying conformational substates differ in their thermodynamic stability with respect to the structural changes associated with the disappearance of the 695 nm band, which eventually (at high temperatures) involves the replacement of M80 by a nearby lysine residue. Our data further indicates that the thermal unfolding process involves two structurally different intermediate states.     

Anomalous diffusion of water in [BMIM][TFSI] room-temperature ionic liquid

We have studied the self-diffusion properties of butyl-methyl-imidazolium bis(trifluoromethylsulfonyl)-imide ([BMIM][TFSI]) + water system. The self-diffusion coefficients of cations, anions, and water molecules were determined by pulsed field gradient NMR. These measures were performed with increased water quantity up to saturation (from 0.3 to 30 mol %). Unexpected variations have been observed. The self-diffusion coefficient of every species increases with the quantity of water but not in the same order of magnitude. Whereas very similar evolutions are observed for the anion and cation, the increase is 25 times greater for water molecules. We interpret our data by the existence of phase separation at microscopic scale.     

Asymmetric syntheses of 1-aryl-2,2,2-trifluoroethylamines via diastereoselective 1,2-addition of arylmetals to 2-methyl-N-(2,2,2-trifluoroethylidene)propane-2-sulfinamide

Condensation of N-tert-butanesulfinamide (S)-1 with trifluoroacetaldehyde hydrate 2a afforded 2-methyl-N-(2,2,2-trifluoroethylidene)propane-2-sulfinamide 3. Without isolation and purification, imine 3 was added to various aryllithium reagents to give highly diastereomerically enriched adducts 5a-g. Acidic methanolysis of 5a-g provided the desired 1-aryl-2,2,2-trifluoroethylamine hydrochloride compounds 6a-g. [reaction: see text].