Remarkable Enhancement of the Rate of Cathodic Reduction of Hydrocarbonate Anions at Palladium in the Presence of Caesium Cations

Steady-state polarization curves, representative of the electrochemical reduction of HCO ions at a smooth palladium cathode, obtained in CsHCO₃ and NaHCO₃ solutions, are compared. The net current densities, associated with the electroreduction of HCO anions, measured in 1M CsHCO₃ solution are shown to be up to 9 times larger than those observed in 1M NaHCO₃ solution. This result is interpreted in terms of a direct involvement of the Cs⁺ cations in the reaction at the cathode through the formation of ion pairs with the HCO anions.     

Stereoselective ring opening of meso bicyclic hydrazines: a straightforward approach to hydrazino cyclopentenic cores

The diastereoselective synthesis of hydrazinocyclopentenes 6 or 7 can be achieved in a straightforward manner from Diels-Alder adduct 4 using an acid-catalyzed rearrangement or a palladium-catalyzed allylic substitution reaction. In the latter case, enantioenriched compounds with ee values up to 58% can be obtained when an appropriate chiral ligand is used. [reaction: see text]     

Revealing Higher Order Protein Structure Using Mass Spectrometry

The development of rapid, sensitive, and accurate mass spectrometric methods for measuring peptides, proteins, and even intact protein assemblies has made mass spectrometry (MS) an extraordinarily enabling tool for structural biology. Here, we provide a personal perspective of the increasingly useful role that mass spectrometric techniques are exerting during the elucidation of higher order protein structures. Areas covered in this brief perspective include MS as an enabling tool for the high resolution structural biologist, for compositional analysis of endogenous protein complexes, for stoichiometry determination, as well as for integrated approaches for the structural elucidation of protein complexes. We conclude with a vision for the future role of MS-based techniques in the development of a multi-scale molecular microscope.

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Impact of Deuteration on the Assembly Kinetics of Transthyretin Monitored by Native Mass Spectrometry and Implications for Amyloidoses

It is well established that the formation of transthyretin (TTR) amyloid fibrils is linked to the destabilization and dissociation of its tetrameric structure into insoluble aggregates. Isotope labeling is used for the study of TTR by NMR, neutron diffraction, and mass spectrometry (MS). Here MS, thioflavin T fluorescence, and crystallographic data demonstrate that while the X‐ray structures of unlabeled and deuterium‐labeled TTR are essentially identical, subunit exchange kinetics and amyloid formation are accelerated for the deuterated protein. However, a slower subunit exchange is noted in deuterated solvent, reflecting the poorer solubility of non‐polar protein side chains in such an environment. These observations are important for the interpretation of kinetic studies involving deuteration. The destabilizing effects of TTR deuteration are rather similar in character to those observed for aggressive mutations of TTR such as L55P (associated with familial amyloid polyneuropathy).     

Octa(p-hydroxy)octakis(propyloxy)calix[8]arene: The First Crystal Structure of a p-Hydroxy Calixarene

Octa(p-ydroxy)octakis(propyloxy)calix[8]arene.9(pyridine).2(H₂O) crystallises in the triclinic space group P-1, a = 14.083(2), b = 14.478(2), c = 15.652(2) Å, = 70.109(4), = 74.146(3), = 75.572(4)°, V = 2843(1) ų, Z = 1. Refinement led to a final R₁ value of 0.0757 for 4693 reflections. The calixarene sits around a crystallographic centre of inversion and is in the `chair-like' conformation. All p-hydroxyl groups form hydrogen bonds with either pyridine or water molecules leading the extended structure to be composed of infinite ribbons parallel to the [1,0,-1] direction.     

Analysis of the structural and dynamic properties of human N-terminal domain of apolipoprotein E by molecular dynamics simulations

Whereas the lipid-free N-terminal domain of apolipoprotein E (apoE-NT) adopts a four-helix bundle, the lipid-bound form is believed to undergo a large conformational change likely to be characterized by the opening of the bundle. ApoE-NT in a water/alcohol mixture was also shown to experience conformational changes exhibiting similarities with those induced upon lipid binding. The structure and dynamics of apoE-NT have been here investigated by analyzing 40 ns and 60 ns molecular dynamics simulations performed in water and in a water/propanol mixture, respectively. The overall structural properties show alterations of the tertiary structure of apoE-NT in the water/alcohol system in agreement with those observed experimentally. In contrast, in the water simulation, the sampled conformations remain closer to the crystal structure that served as a starting point for both simulations. Interestingly, several propanol molecules are seen to penetrate two hydrophobic regions of the bundle interior. One of these regions is enclosed in part by the short helix (H1') connecting helices 1 and 2 of the bundle which has been experimentally shown to be important for modulating lipid binding activity of apoE-NT. Principal component analysis of the water/propanol trajectory confirms that the region including H1' is the locus of the largest motion. Another region involves the loop connecting helix 2 and helix 3 which has been hypothesized to play the role of a hinge in the opening of the bundle.     

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).     

Resolution of the Transport equation subject to constraint

We present a method for solving the Transport equation when its solution has to belong to a constrained set which is not required to be convex. An autonomous formulation of the characteristics method allows us to use the tangency condition which has been introduced for ordinary differential equations. Thus we obtain a sufficient condition for existence of solutions, which shows the interplay between the geometry of the constraints set K   and the velocity field β$\beta$. A numerical method is proposed for solving the problem when the sufficient condition is not satisfied. A numerical experiment is presented showing the efficiency of the algorithm proposed.     

Comprehensive study of the parameters influencing the detection of organotin compounds by a pulsed flame photometric detector in sewage sludge

An investigation of the operating conditions of a pulsed flame photometric detection (PFPD) system for the determination of organotin compounds (OTCs) in sewage sludge is reported. During the analyses, some spectral interferences were observed. For their elimination detector parameters such as gate delay and gate width were investigated. In addition, the applicability of three different internal standards was evaluated. Under optimised analytical conditions (gate delay 3 ms, gate width 2 ms, tripropyltin as internal standard) limits of detection (LOD) were determined. The LOD for butyltins ranged between 8 and 16 ng Sn g(-1), for phenyltins around 8 ng Sn g(-1) and for octyltins between 5 and 10 ng Sn g(-1). Since there is no certified reference material (CRM) available for sewage sludge, the accuracy of the analytical procedure was checked by the analysis of CRM PACS-2 (marine sediment) and a spiked sludge sample. Good agreement between determined and certified values was obtained. Sewage sludge from a local wastewater treatment plant was analysed and the results compared with data from the literature.     

Turbulence: Does Energy Cascade Exist?

To answer the question whether a cascade of energy exists or not in turbulence, we propose a set of correlation functions able to test if there is an irreversible transfert of energy, step by step, from large to small structures. These tests are applied to real Eulerian data of a turbulent velocity flow, taken in the wind grid tunnel of Modane, and also to a prototype model equation for wave turbulence. First we demonstrate the irreversible character of the flow by using multi-time correlation function at a given point of space. Moreover the unexpected behavior of the test function leads us to connect irreversibility and finite time singularities (intermittency). Secondly we show that turbulent cascade exists, and is a dynamical process, by using a test function depending on time and frequency. The cascade shows up only in the inertial domain where the kinetic energy is transferred more rapidly (on average) from the wavenumber \(k_{1}\) to \(k_{2}\) than from \(k_{1}\) to \(k'_{2}\) larger than \(k_{2}\).