Thermal activation of the co-chaperonins GroES and gp31 probed by mass spectrometry

Many biological active proteins are assembled in protein complexes. Understanding the (dis)assembly of such complexes is therefore of major interest. Here we use mass spectrometry to monitor the disassembly induced by thermal activation of the heptameric co-chaperonins GroES and gp31. We use native electrospray ionization mass spectrometry (ESI-MS) on a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer to monitor the stoichiometry of the chaperonins. A thermally controlled electrospray setup was employed to analyze conformational and stoichiometric changes of the chaperonins at varying temperature. The native ESI-MS data agreed well with data obtained from fluorescence spectroscopy as the measured thermal dissociation temperatures of the complexes were in good agreement. Furthermore, we observed that thermal denaturing of GroES and gp31 proceeds via intermediate steps of all oligomeric forms, with no evidence of a transiently stable unfolded heptamer. We also evaluated the thermal dissociation of the chaperonins in the gas phase using infrared multiphoton dissociation (IRMPD) for thermal activation. Using gas-phase activation the smaller (2-4) oligomers were not detected, only down to the pentamer, whereafter the complex seemed to dissociate completely. These results demonstrate clearly that conformational changes of GroES and gp31 due to heating in solution and in the gas phase are significantly different.     

First generation poly(propyleneimine) dendrimers functionalised with 1,8-naphthalimide units as fluorescence sensors for metal cations and protons

The synthesis of two new green fluorescent poly(propyleneimine) dendrimers from first generation has been described. The new materials are comprised of a 1,8-naphthalimide fluorophore having a substituent at C-4 position. The substituent in the first case is a N,N-dimethylaminoethylamino group while in the second one it is N-methylpiperazine. The spectroscopic and photophysical characteristics of the new dendrimers determined in organic solvent of different polarity have been presented. Both dendrimers show substantial increases in their fluorescence intensity in the presence of metal cations (Zn²⁺, Co²⁺, Ni²⁺, Pb²⁺, Mn²⁺, Cu²⁺, Fe³⁺ and Ag⁺) and protons. The influence of the photoinduced electron transfer on their sensing properties has been discussed.     

Tunable single-mode fiber-VCSEL using an intracavity polymer microlens

We report a tunable, single-mode vertical cavity surface-emitting laser (VCSEL) format suitable for array operation, power scaling, fiber coupling, and operation in isolated environments such as those required by atom optics. The devices are fiber VCSELs, consisting of a semiconductor gain and mirror structure separated from a mirror-coated optical fiber by an air (or vacuum) gap. The gain structure has polymer microlenses fabricated on its surface, of characteristics suitable to focus the oscillating mode on both cavity mirrors, ensuring stable fundamental mode emission and high fiber coupling efficiency. We demonstrate such devices in continuous-wave operation at 1.03 microm at room temperature, with a single-mode tuning range of 13 nm, laser threshold as low as 2.5 mW, and a maximum fiber-coupled output power of 10 mW.     

Sharp Sobolev inequalities in the presence of a twist

Let be a smooth compact Riemannian manifold of dimension . Let also be a smooth symmetrical positive -tensor field in . By the Sobolev embedding theorem, we can write that there exist such that for any ,

where is the standard Sobolev space of functions in with one derivative in . We investigate in this paper the value of the sharp in the equation above, the validity of the corresponding sharp inequality, and the existence of extremal functions for the saturated version of the sharp inequality.

     

Joint Venture of Metal Cluster and Amphiphilic Cationic Minidendron Resulting in Near Infrared Emissive Lamellar Ionic Liquid Crystals

Inorganic red-NIR emissive materials are particularly relevant in many fields like optoelectronic, bioimaging or solar cells. Benefiting from their emission in devices implies their integration in easy-to-handle materials like liquid crystals, whose long-range ordering and self-healing abilities could be exploited and influence emission. Herein, we present red-NIR emissive hybrid materials obtained with phosphorescent octahedral molybdenum cluster anions electrostatically associated with amphiphilic guanidinium minidendrons. Polarized optical microscopy and X-ray analysis show that while the minidendron chloride salts self-organize into columnar phases, their association with the dianionic metal cluster leads to layered phases. Steady-state and time-resolved emission investigations demonstrate the influence of the minidendron alkyl chain length on the phosphorescence of the metal cluster core.     

Aqueous MADIX/RAFT polymerization of diallyldimethylammonium chloride: Extension to the synthesis of poly(DADMAC)‐based double hydrophilic block copolymers

Macromolecular design by interchange of xanthates/reversible addition fragmentation chain transfer polymerization (MADIX/RAFT) of diallyldimethylammonium chloride (DADMAC) using the hydrophobic O‐ethyl‐S‐(1‐methoxycarbonyl) ethyl dithiocarbonate MADIX/RAFT mediating agent, Rhodixan A1, was investigated. Attempts to obtain an efficient control of DADMAC polymerization in a water/ethanol mixture failed because of significant chain transfer to ethanol. The use of a water‐soluble Rhodixan A1‐terminated acrylamide oligomer as the MADIX/RAFT agent enabled the controlled polymerization of DADMAC in water at 50 °C using the cationic azo initiator V‐50. An excellent agreement was found between experimental and theoretical M_n values throughout polymerization and over a broad range of initial concentration of xanthate. Polydispersity indexes (PDIs) at the end of the polymerization were abnormally high for a process showing a linear increase of M_n with monomer conversion (1.8 < PDI < 2.0). This feature was explained by the measurement of a high transfer constant to xanthate (C_x = 18.8 ± 1.6) but a low interchange transfer constant (C_ex = 1.5). Nevertheless, poly(acrylamide)–poly(DADMAC) double hydrophilic block copolymers (DHBCs) of controlled M_n and composition could be successfully synthesized for the first time. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Controlled synthesis of polyepichlorohydrin with pendant cyclic carbonate functions for isocyanate‐free polyurethane networks

Poly(allyl glycidyl ether) and poly(allyl glycidyl ether‐co‐epichlorohydrin) were prepared by monomer‐activated anionic polymerization. Quantitative and controlled polymerization of allyl glycidyl ether (AGE) giving high molar mass polyether was achieved in a few hours at room temperature in toluene using tetraoctylammonium salt as initiator in presence of an excess of triisobutylaluminum ([i‐Bu₃Al]/[NOct₄Br] = 2?4). Following the same polymerization route, the copolymerization of AGE and epichlorohydrin yields in a living‐like manner gradient‐type copolymers with controlled molar masses. Chemical modification of the pendant allyl group into cyclic carbonate was then investigated and the corresponding polymers were used as precursors for the isocyanate‐free synthesis of polyurethane networks in presence of a diamine. Formation of crosslinked materials was followed and characterized by infrared and differential scanning calorimetry. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

IR thermometry: a new tool for contactless in situ investigations of metal–insulator transition

In the present work, we focus on an original study of metal–insulator transition in LaNiO₃ (LNO) compound by IR camera mounted on a pulsed laser deposition chamber. IR thermometry is based on the measurement of the radiated energy that is a function of the surface temperature and the emissivity (ε) of a material. Thus, at a fixed high temperature in an oxygen equilibrium state and by fixing arbitrary an emissivity value, we can follow the evolution of the “measured temperature” linked to the change of the real emissivity value during a reduction/reoxygenation treatment. The variation of emissivity is correlated to the change in optical constants, e.g. to the conductivity measured simultaneously by an in situ spectroscopic ellipsometry. The combination of both techniques offers a convenient way to observe in situ and contactless changes from metallic to insulator behavior and vice versa.     

The rhombohedral-cubic transition in the IV-VI semiconductor GeTe under high pressure

Abstract

The IV-VI semiconductor GeTe was studied at room temperature as a function of pressure in a truly hydrostatic medium up to 8 GPa and in a quasi-hydrostatic environment, silicone grease, up to 25 GPa