Effectiveness of the suzuki-miyaura cross-coupling reaction for solid-phase peptide modification

The Suzuki-Miyaura (SM) cross-coupling reaction has recently become one of the most efficient methods for C-C bond construction opening a wide range of opportunities in organic synthesis. This study focused on the evaluation of the use of the SM reaction to modify peptides using a solid-phase synthesis approach, an avenue that was still not investigated intensively. We used as a peptide model [Ala (1,2,3), Leu (8)]Enk linked to a polystyrene support on which it was previously assembled. The aromatic residues Tyr (4) and Phe (7) of [Ala (1,2,3), Leu (8)]Enk were respectively substituted with p-iodo-Phe, and an SM-related strategy was developed. Results indicated that the reaction conditions involving K 3PO 4 or Na 2CO 3 (base), DMF (solvent), Pd(PPh 3) 4 (catalyst), and temperatures ranging from 50 to 80 degrees C during 20 h were found as optimal. Finally applying those optimal conditions, a series of [Ala (1,2,3), Leu (8)]Enk analogs modified at Tyr (4) or Phe (7) positions was synthesized using diverse boronic acid derivatives.     

Recent innovations in protein separation on microchips by electrophoretic methods

Microchips for analytical purposes have attracted great attention over the last 20 years. In the present review, we focus on the most recent development of microchips for electrophoretic separation of proteins. This review starts with a short recalling about the microchips covering the basic microchip layout for CE and the commercial chips and microchip platforms. A short paragraph is dedicated to the surface treatment of microchips, which is of paramount importance in protein analysis. One section is dedicated to on-line sample pretreatment in microchips and summarizes different strategies to pre-concentrate or to purify proteins from complex matrixes. Most of the common modes used for CE of proteins have already been adapted to the chip format, while multidimensional approaches are still in progress. The different routes to achieve detection in microchip are also presented with a special attention to derivatization or labeling of proteins. Finally, several recent applications are mentioned. They highlight the great potential of electrophoretic separations of proteins in numerous fields such as biological, pharmaceutical or agricultural and food analysis. A bibliography with 151 references is provided covering papers published from 2000 to the early 2007.     

LIF detection of peptides and proteins in CE

CE- and microchip-based separations coupled with LIF are powerful tools for the separation, detection and determination of biomolecules. CE with certain configurations has the potential to detect a small number of molecules or even a single molecule, thanks to the high spatial coherence of the laser source which permits the excitation of very small sample volumes with high efficiency. This review article discusses the use of LIF detection for the analysis of peptides and proteins in CE. The most common laser sources, basic instrumentation, derivatization modes and set-ups are briefly presented and special attention is paid to the different fluorogenic agents used for pre-, on- and postcapillary derivatization of the functional groups of these compounds. A table summarizing major applications of these derivatization reactions to the analysis of peptides and proteins in CE-LIF and a bibliography with 184 references are provided which covers papers published to the end of 2005.     

Amine-induced growth of an In2O3 shell on colloidal InP nanocrystals

A simple and rapid method for the growth of an In2O3 shell on colloidal InP nanocrystals is described, increasing their fluorescence efficiency by one order of magnitude.     

REGULATION OF PROTOCHLOROPHYLL(IDE) LEVELS IN DARK-GROWN NON-DIVIDING Euglena—II. INFLUENCE OF UTILIZABLE SUBSTRATES AND INHIBITORS OF PROTEIN SYNTHESIS*

Dark-grown cells of Euglena gracilis var. bacillaris incubated on resting medium for 7 days lose half of their extractable and phototransformable protochlorophyll(ide) [Pchl(ide)]. The readily-utilized substrates glutamate and malate bring about a regeneration of both pools of Pchl(ide) to the levels found in growing cells, without causing cell division during the period of regeneration. Light does not cause a regeneration of total extractable Pchl(ide) to the levels found in growing cells, and the complete regeneration of phototransformable Pchl(ide) seen probably results from conversion of non-transformable Pchl(ide) to transformable Pchl(ide). Optimal glutamate, malate, and light in any combination are no better in causing phototransformable Pchl(ide) regeneration than any one treatment alone, indicating that the Pchl(ide) pool size is limited by other factors. The regeneration of phototransformable Pchl(ide) induced by light or substrates is insensitive to inhibitors of protein synthesis on 80 S cytoplasmic ribosomes (cycloheximide) or on 70 S chloroplast ribosomes (streptomycin). Cycloheximide, however, induces the regeneration of phototransformable Pchl(ide) in darkness in the absencc of externally-added substrates. Since cycloheximide is known to induce paramylum breakdown under the same conditions, it is likely that this process can provide internal substrates and/or reducing power for phototransformable Pchl(ide) regeneration. Possible mechanisms of regulation of formation of Pchl(ide)₆₃₅ in Euglena are discussed and compared with regulation of Pchl(ide)₆₅₀ in higher plants.     

Finite element modelling of cold drawing for high-precision tubes

Cold tube drawing is a metal forming process that allows manufacturers to produce high-precision tubes. The dimensions of the tube are reduced by pulling it through a conical converging die with or without inner tool. In this study, finite element modelling has been used to give a better understanding of the process.This paper presents a model that predicts the final dimensions of the tube with very high accuracy. It is validated thanks to experimental tests. Moreover, five studies are performed with this model, such as investigating the influence of the die angle on the drawing force or the influence of relative thickness on tube deformation.     

Early stage expansion and time-resolved spectral emission of laser-induced plasma from polymer

In the nanosecond laser ablation regime, absorption of laser energy by the plasma during its early stage expansion critically influences the properties of the plasma and thus its interaction with ambient air. These influences can significantly alter spectral emission of the plasma. For organic samples especially, recombination of the plasma with the ambient air leads to interfering emissions with respect to emissions due to native species evaporated from the sample. Distinguishing interfering emissions due to ambient air represents a critical issue for the application of laser-induced breakdown spectroscopy (LIBS) to the analysis of organic materials. In this paper, we report observations of early stage expansion and interaction with ambient air of the plasma induced on a typical organic sample (nylon) using time-resolved shadowgraph. We compare, in the nanosecond ablation regime, plasmas induced by infrared (IR) laser pulses (1064 nm) and ultraviolet (UV) laser pulses (266 nm). Nanosecond ablation is compared with femtosecond ablation where the post-ablation interaction is absent. Subsequent to the early stage expansion, we observe for each studied ablation regime, spectral emission from CN, a typical radical for organic and biological samples. Time-resolved LIBS allows identifying emissions from native molecular species and those due to recombination with ambient air through their different time evolution behaviors.     

Dynamic chemical devices: photoinduced electron transfer and its ion-triggered switching in nanomechanical butterfly-type bis(porphyrin)terpyridines

A series of butterfly-type molecular constructs has been prepared in good yield by using a double Stille coupling synthetic protocol. They are composed of a terpyridine (terpy) scaffold and two wings composed of appended porphyrins that are capable of switching from an extended W geometry to a compact U geometry upon cation coordination of the terpy unit. The porphyrin moieties exist in the constructs either as free bases or they can be sequentially metallated, thus giving rise to wings of different "colours". Stationary and time-resolved emission studies of the HZn, ZnAu and Zn2Au constructs show that the electronic properties are strongly dependent on the geometry. In the extended W conformation an energy-transfer process is seen from the free base to the Zn-metallated porphyrin. In the U conformation in Zn2Au the donor luminescence resulting from the singlet excited state of the Zn wing is strongly, quenched not only due to the heavy atom effect but also due to a fast electron-transfer process to the ground state of the Au wing. Furthermore, the binding of (alpha,omega)-diamine substrates to the Zn(II)-porphyrin sites can also influence the conformation of the system. For the Zn2Zn construct, single-crystal diffraction experiments with synchrotron radiation allowed the structure to be solved by direct methods and fully refined; it shows the expected U conformation. The central Zn atom is six-coordinate, whereby the zinc atom is coordinated by the eta3-terpy ligand as well by monodentate and semi-chelating acetate anions. The structure is made rigid by hydrogen bonds involving the aqua ligands on the outer Zn centres and acetate oxygen atoms. The present system thus represents a double-trigger-modulated optomechanical switching device with selective substrate binding for either metal atoms or tailored ligands. Both energy- and electron-transfer processes can be controlled opening a means of improving the on/off ratio in future constructs.