Influence of polyelectrolyte coating conditions on capillary coating stability and separation efficiency in capillary electrophoresis

Polyelectrolytes are widely used in capillary electrophoresis as coating agents of silica capillaries to prevent adsorption phenomena and improve the repeatability of peptide and protein analysis. A systematic study of the coating experimental conditions has been carried out to optimize coating stability and performance. The main experimental parameters studied were the type and concentration of polyelectrolytes used in several monolayer and multilayer coatings, the ionic strength of coating and stabilizing solutions, and the procedures used for coating and capillary storage. Electroosmotic flow magnitude, direction and repeatability were used to monitor coating stability. Coating ability to limit adsorption was investigated by monitoring variations of migration times, time-corrected peak areas and separation efficiency of test peptides. Capillary-to-capillary and batch-to-batch reproducibility was also studied. In addition, the separation performance of polyelectrolyte coatings were compared to those obtained with bare silica capillaries.     

Enzymatic membranes for the selective transport of neutral molecules by electrophoresis

The active and selective transport of glucose and glycerol was carried out using electrophoresis and artificial enzymatic membranes. These positively charged composite membranes carry, on the face adjacent to the donor compartment of an electrophoresis module, a specific kinase (hexokinase or glycerokinase) and, on the opposite face, an alkaline phosphatase (ALP). Phosphorylation of the neutral substrate (glucose or glycerol) on the donor side by the kinase generates a negatively charged phosphorylated substrate, whose transmembrane migration is promoted by an electric field and by the membrane's positive charge. Dephosphorylation of the phosphorylated substrate by ALP on the opposite face regenerates the neutral substrate, which accumulates in the receiver compartment of the electrophoresis module. Using an electrophoresis module specifically designed for this study, our experiments were carried out enabling glucose and glycerol to be concentrated approximately eight- and twelve-fold, respectively, in 8 h.     

Protodesilylation of 2,6-disubstituted silyphosphinines. Experimental and theoretical study

2,6-Disilylphosphinines react with HCl in ethereal solution to cleanly yield the corresponding 2,6-unsubstituted derivatives. DFT calculations allowed rationalization of the mechanism of this protodesilylation.     

A study of the reactive intermediate IF and I atoms with photoelectron spectroscopy

Angle-resolved photoelectron (PE) spectra were recorded for IF and I. These were prepared as primary and secondary products of the F + CH2I2 reaction. PE spectra were recorded with different IF-to-I ratios to evaluate the relative intensities of IF and I photoelectron bands where their bands were overlapped. Improved values were obtained for the vertical and adiabatic ionization energies of the IF(+)(X(2)Pi(3/2)) <-- IF(X(1)sigma(+)) and IF(+)((2)Pi(1/2)) <-- IF(X(1)sigma(+)) ionizations and for the spectroscopic constants omega(e) and omega(e)ex(e) for the two IF ionic states X(2)Pi(3/2) and (2)Pi(1/2). Equilibrium bond lengths r(e) of these IF ionic states were derived from the experimental relative intensities of the vibrational components and calculated Franck-Condon factors. Threshold photoelectron (TPE) spectra were also recorded under the same reaction conditions. On comparing the TPE and PE spectra, the contributions from atomic iodine were much more intense in the TPE spectra. No difference was seen between the vibrational envelopes of the two observed IF bands, and no extra structure was seen associated with the TPE bands of IF as has been observed in TPE spectra of other diatomic halogens. The extra features that were observed in the TPE spectra can be assigned to contributions from autoionization of known I Rydberg states.     

Liquid crystallinity in collagen systems in vitro and in vivo

Collagens are unique triple helical proteins present in large quantities in a fibrillar form in tissues like tendon, bone, skin, cornea, where type I collagen predominates. The passage from triple helical molecules to fibrils obeys to controlled assembly properties, both in vitro by pH raise and in vivo through enzymatic control. The passage from individual fibrils to ordered fibrillar arrays could rely on self-assembly processes as suggested by the liquid crystalline properties of collagen. The present review considers this question recalling the liquid crystalline ordering properties of collagen or procollagen at high concentrations and the question of molecular packing within fibrils. The presence of alignments, undulations and twist at a suprafibrillar level will be described both from basic data in living tissues and recent experiments in self assembled materials. The possible link between laboratory experiences and biological processes will be discussed.     

Ammonia Synthesis at Room Temperature and Atmospheric Pressure from N2: A Boron-Radical Approach

Ammonia, NH₃, is an essential molecule, being part of fertilizers. It is currently synthesized via the Haber–Bosch process, from the very stable dinitrogen molecule, N₂ and dihydrogen, H₂. This process requires high temperatures and pressures, thereby generating ca 1.6 % of the global CO₂ emissions. Alternative strategies are needed to realize the functionalization of N₂ to NH₃ under mild conditions. Here, we show that boron-centered radicals provide a means of activating N₂ at room temperature and atmospheric pressure whilst allowing a radical process to occur, leading to the production of borylamines. Subsequent hydrolysis released NH₄⁺, the acidic form of NH₃. EPR spectroscopy supported the intermediacy of radicals in the process, corroborated by DFT calculations, which rationalized the mechanism of the N₂ functionalization by R₂B radicals.     

Direct time-resolved detection of singlet oxygen in zeolite-based photocatalysts

Singlet oxygen has been characterized spectroscopically as a product of the exposure of suspensions of zeolites containing oxidation catalysts. Spectroscopic and lifetime studies show that a part of the singlet oxygen formed reacts within the zeolite porous structure, while a significant fraction escapes and becomes available for reaction in the bulk media. The liquid phase plays a key role in determining intra- and extracavity dynamics.     

Structural and solvent effects on the 13C and 15N NMR chemical shifts of indoloquinoline alkaloids: experimental and DFT study

Indoloquinoline alkaloids represent an important class of antimalarial, antibacterial and antiviral compounds. They have been shown to bind to DNA via intercalation preferentially at GC-rich sequences containing nonalternating CC sites. The stability of complexes formed with biological macromolecules depends on noncovalent binding. In the present study, the ability of indoloquinolines to form intermolecular interactions with solvents was investigated by using NMR spectroscopy and density functional theory (DFT) (B3LYP/6-31G**) calculations. NMR data measured for indoloquinoline bases and the corresponding hydrochlorides are discussed in relation to the structure. DFT calculations of shielding constants in vacuo and in solution allowed the investigation of the influence of the environment on the NMR parameters. Calculations incorporating solvent effects indicated significant changes in the anisotropy of the electron distribution, reflected in the span of the chemical shielding tensor (Omega = sigma11 - sigma33). Solvent effects on the span of the 13C and 15N shielding tensor depended on the type of atom and the data indicated a significant influence of solute-solvent interactions.