Supercoiled circular DNA retention in nonequilibrium chromatography: viscosity and velocity dependence--behavior difference with proteins

This study demonstrates that the retention behavior of various circular double-stranded DNA molecules (3, 5, and 10 kb) increases over the entire flow-rate range (0.02-1.8 mL/min) at all the mobile phase viscosities (h). The transition between the two well-known nonequilibrium chromatography methods (slalom and hydrodynamic chromatography) is clearly visualized for proteins and does not appear for plasmids because of their strong compact structure. Also, the optimal conditions for F and h are determined to obtain the most efficient separation of these three plasmids in a minimum analysis time.     

Straightforward synthesis of conductive graphene/polymer nanocomposites from graphite oxide

The reduction of graphite oxide (GO) in the presence of reactive poly(methyl methacrylate) (PMMA), under mild biphasic conditions, directly affords graphene grafted with PMMA. The resulting nanocomposite shows excellent electrical conductivities resulting from the optimal dispersion and exfoliation of graphene in the polymer matrix.     

Design of cross-linked semicrystalline poly(ε-caprolactone)-based networks with one-way and two-way shape-memory properties through Diels-Alder reactions

Cross‐linked poly(ε‐caprolactone) (PCL)‐based polyesterurethane (PUR) systems have been synthesized through Diels–Alder reactions by reactive extrusion. The Diels–Alder and retro‐Diels–Alder reactions proved to be useful for enhancing the molecular motion of PCL‐based systems, and therefore their crystallization ability, in the design of cross‐linked semicrystalline polymers with one‐way and two‐way shape‐memory properties. Successive reactions between α,ω‐diol PCL (PCL₂), furfuryl alcohol, and methylene diphenyl 4,4′‐diisocyanate straightforwardly afforded the α,ω‐furfuryl PCL‐based PUR systems, and subsequent Diels–Alder reactions with N,N‐phenylenedimaleimide afforded the thermoreversible cycloadducts. The cross‐linking density could be modulated by partially replacing PCL‐diol with PCL‐tetraol. Interestingly, the resulting PUR systems proved to be semicrystalline cross‐linked polymers, the melting temperature of which (close to 45 °C) represented the switching temperature for their shape‐memory properties. Qualitative and quantitative measurements demonstrated that these PUR systems exhibited one‐way and two‐way shape‐memory properties depending on their cross‐linking density.     

The stimulating adventure of KRN 7000

Associated with the CD1d protein, KRN 7000, a potent synthetic α-galactosylceramide, is known to activate the invariant NKT immune cells. This stimulation then leads to the production of different cytokines modulating a T(H)1/T(H)2 immune response balance involved in protection against several pathologies such as autoimmune diseases and cancers. Various efforts have been made toward the synthesis of simple and more functionalized analogues in order to selectively induce T(H)1 or T(H)2-type cytokine production. Since the discovery of KRN 7000, structure-activity relationships, crystallographic and modelling studies have pointed to the potential of several GalCer analogues in term of selective bioactivity, and have highlighted interesting elements in order to better understand the recognition and activation mechanisms of immune iNKT cells. By presenting an up-to-date library of analogues, collecting recent breakthroughs done in crystallography and molecular modelling, and relating them to the available biological results, we hope that this review will highlight and help the scientific community in their KRN research.     

Cryogenic Chemistry and Quantitative Non-Thermal Desorption from Pure Methanol Ices: High-Energy Electron versus X-Ray Induced Processes

X-Ray irradiation of interstellar ice analogues has recently been proven to induce desorption of molecules, thus being a potential source for the still-unexplained presence of gaseous organics in the coldest regions of the interstellar medium, especially in protoplanetary disks. The proposed desorption mechanism involves the Auger decay of excited molecules following soft X-ray absorption, known as X-ray induced electron-stimulated desorption (XESD). Aiming to quantify electron induced desorption in XESD, we irradiated pure methanol (CH₃OH) ices at 23 K with 505 eV electrons, to simulate the Auger electrons originating from the O 1s core absorption. Desorption yields of neutral fragments and the effective methanol depletion cross-section were quantitatively determined by mass spectrometry. We derived desorption yields in molecules per incident electron for CO, CO₂, CH₃OH, CH₄/O, H₂O, H₂CO, C₂H₆ and other less abundant but more complex organic products. We obtained desorption yields remarkably similar to XESD values.     

UV photodesorption of interstellar CO ice analogues: from subsurface excitation to surface desorption

Carbon monoxide is after H(2) the most abundant molecule identified in the interstellar medium (ISM), and is used as a major tracer for the gas phase physical conditions. Accreted at the surface of water-rich icy grains, CO is considered to be the starting point of a complex organic--presumably prebiotic--chemistry. Non-thermal desorption processes, and especially photodesorption by UV photons, are seen as the main cause that drives the gas-to-ice CO balance in the colder parts of the ISM. The process is known to be efficient and wavelength-dependent, but, the underlying mechanism and the physical-chemical parameters governing the photodesorption are still largely unknown. Using monochromatized photons from a synchrotron beamline, we reveal that the molecular mechanism responsible for CO photoejection is an indirect, (sub)surface-located process. The local environment of the molecules plays a key role in the photodesorption efficiency, and is quenched by at least an order of magnitude for CO interacting with a water ice surface.     

Primärreaktionen des oxydativen Abbaues während der Autooxydation von Poly(oxytetramethylen) bei 25°C. 1. Mitt. Charakterisierung der Äthylenbildung

Ohne Zusammenfassung     

Chiral discrimination of phenoxypropionic acid herbicides on teicoplanin phase: Effect of mobile phase modifier

Summary The chiral recgonition mechanism for a series of phenoxypropionic acid herbicides was investigated in reversed phase liquid chromatography (RPLC) on a teicoplanin stationary phase over a wide range of column temperatures. Thermodynamic constants, of the transfer of an enantiomer from the mobile to the teicoplanin stationary phases were determined. The van't Hoff plots for all solutes had a break at a critical temperature T^* showing a variation in the enantiomer retention mechanism due to a change in the conformational state of the teicoplanin, structure. Additionally, enthalpy-entropy compensation confirmed both the change in enantiomer interaction mechanism observed for regions T<T^* and T>T^* and the independence of this mechanism from (i) herbicide molecular structure,s i.e. the position of the chloro group on the phenol ring and (ii) the carbon absolute configuration. Moreover, the increasing enantioselectivity with increasing methanol fraction in the mobile phase was attributed to restriction of the solute association in the teicoplain, stationary phase, leading to favorable stereoselective interactions. This behavior was used to optimize chromatographic conditions for separation of herbicide enantiomers on teicoplanin.     

Novel approach to the study of the chiral discrimination mechanism in a series of dansyl amino acids.

With poly(octadecylsiloxane) as the liquid chromatographic stationary phase, phosphate buffer as the mobile phase, a series of D- and L-dansyl amino acids as solutes, and beta-cyclodextrin as the chiral selector, a study was conducted of the hydrophobic effect on both the solute complexation with the chiral selector and chiral discrimination mechanisms by varying the sucrose concentration in the mobile phase and the column temperature. The number of sucrose molecules excluded during the solute complexation with the chiral selector proved to be a good marker of the solute inclusion in the cavity. Gibbs Helmotz parameters delta(deltaH) and delta(deltaS) between D- and L-enantiomers were determined from plots of the logarithm of the intrinsic selectivity versus the reciprocal of the temperature. The results obtained predicted that the enantioselectivity was related to the bulkiness of the solute. This numerical approach is a valuable tool in the exploration of the steric effects implied in the formation of the host-guest complex.