Rapid Validated RP-HPTLC Method for the Quantification of Major Bioactive Constituents of Crataegus oxyacantha L.

JPC – Journal of Planar Chromatography – Modern TLC - A reverse phase high-performance thin-layer chromatography (RPHPTLC) method was developed for determination of vitexin, hyperoside,...     

On‐chip solid‐phase extraction pre‐concentration/focusing substrates coupled to atmospheric pressure matrix‐assisted laser desorption/ionization ion trap mass spectrometry for high sensitivity biomolecule analysis

Atmospheric pressure matrix‐assisted laser desorption/ionization (AP‐MALDI) has proven a convenient and rapid method for ion production in the mass spectrometric (MS) analysis of biomolecules. AP‐MALDI and electrospray ionization (ESI) sources are easily interchangeable in most mass spectrometers. However, AP‐MALDI suffers from less‐than‐optimal sensitivity due to ion losses during transport from the atmosphere into the vacuum of the mass spectrometer. Here, we study the signal‐to‐noise ratio (S/N) gains observed when an on‐chip dynamic pre‐concentration/focusing approach is coupled to AP‐MALDI for the MS analysis of neuropeptides and protein digests. It was found that, in comparison with conventional AP‐MALDI targets, focusing targets showed (1) a sensitivity enhancement of approximately two orders of magnitude with S/N gains of 200–900 for hydrophobic substrates, and 150–400 for weak cation‐exchange (WCX) substrates; (2) improved detection limits as low as 5 fmol/µL for standard peptides; (3) significantly reduced matrix background; and (4) higher inter‐day reproducibility. The improved sensitivity allowed successful tandem mass spectrometric (MS/MS) sequencing of dilute solutions of a derivatized tryptic digest of a protein standard, and enabled the first reported AP‐MALDI MS detection of neuropeptides from Aedes aegypti mosquito heads. Copyright © 2009 John Wiley & Sons, Ltd.     

Self‐Consistent Theory of Structures and Transitions in Weak Polyampholytes

Weak polyampholytes are charged polymers, where the charge asymmetry can be tuned by varying the solution pH. We determine the size of a randomly charged weak polyampholyte in dilute solution as a function of charge asymmetry, Bjerrum length, salt concentration, pH, and degree of polymerization, using a self‐consistent method. It is known that in the limiting cases of low and high charge asymmetries, polyampholytes behave as neutral polyampholytes and polyelectrolytes, respectively. We explore in detail the regime of intermediate charge asymmetry where a polyampholyte show non‐monotonic change in the chain size as a function of Bjerrum length. A hierarchy of structures exists at different length scales, ranging from ideal coils at low Bjerrum length, extended rod‐like state at intermediate Bjerrum length to globular states at high Bjerrum length. The transition between ideal coil and rod‐like states is continuous, while that between rod‐like and globular states is discontinuous. The addition of salt changes the nature of the rod‐to‐globule transition from discontinuous to continuous. The effective free energy shows a double minimum at intermediate charge asymmetry, indicating the coexistence of globules and extended states. The size as a function of the solution pH shows a minimum at the isoelectric point. The size of neutral polyampholytes at the isoelectric pH increases with the increase in the salt concentration. The size of charge excess polyampholytes far away from the isoelectric pH decreases with the increase in the salt concentration.

     

LET effects following neutron irradiation of lithium formate EPR dosimeters

Lithium formate electron paramagnetic resonance (EPR) dosimeters were irradiated using 60Co gamma-rays or fast neutrons to doses ranging from 5 to 20 Gy and investigated by EPR spectroscopy. Using a polynomial fitting procedure in order to accurately analyze peak-to-peak line widths of first derivative EPR spectra, dosimeters irradiated with neutrons had on average 4.4+/-0.9% broader EPR resonance lines than gamma-irradiated dosimeters. The increase in line width was slightly asymmetrical. Computer simulated first derivative polycrystalline EPR spectra of a *CO2- radical gave very good reconstructions of experimental spectra of irradiated dosimeters. The spectrum simulations could then be used as a tool to investigate the line broadening observed following neutron irradiation. It was shown that an increase in the simulated Lorentzian line width could explain both the observed line broadening and the asymmetrical effect. The ratio of the peak-to-peak amplitude of first derivative EPR spectra obtained at two different microwave powers (20 and 0.5 mW) was 7.8+/-1.2% higher for dosimeters irradiated with neutrons. The dependence of the spectrum amplitude on the microwave power was extensively investigated by fitting observations to an analytical non-linear model incorporating, among others, the spin-lattice (T1) and spin-spin (T2) relaxation times as fitting parameters. Neutron irradiation resulted in a reduction in T(2) in comparison with gamma-irradiation, while a smaller difference in T1 was found. The effects observed indicate increased local radical density following irradiation using high linear energy transfer (LET) neutrons as compared to low LET gamma-irradiation. A fingerprint of the LET may thus be found either by an analysis of the line width or of the dependence of the spectrum amplitude on the microwave power. Lithium formate is therefore a promising material for EPR dosimetry of high LET radiation.     

Excess Si concentration dependence of the photoluminescence of Si nanoclusters in SiO2 fabricated by ion implantation

A method for the fabrication of luminescent Si nanoclusters in an amorphous SiO₂ matrix by ion implantation and annealing, and the detailed mechanisms for the photoluminescence are reported. We have measured the implanted ion dose, annealing time and excitation energy dependence of the photoluminescence from implanted layers. The samples were fabricated by Si ion implantation into SiO₂ and subsequent high-temperature annealing. After annealing, a photoluminescence band below 1.7 eV has been observed. The peak energy of the photoluminescence is found to be independent of annealing time and excitation energy, while the intensity of the luminescence increases as the annealing time and excitation energy increase. Moreover, we found that the peak energy of the luminescence is strongly affected by the dose of implanted Si ions especially in the high dose range. These results indicate that the photons are absorbed by Si nanoclusters, for which the band-gap energy is modified by the quantum confinement effects, and the emission is not simply due to direct electron–hole recombination inside Si nanoclusters, but is related to defects probably at the interface between Si nanoclusters and SiO₂, for which the energy state is affected by Si cluster–cluster interactions. It seems that Si nanoclusters react via a thin oxide interface and the local concentrations of Si nanoclusters play an important role in the peak energy of the photoluminescence.     

Laccase-catalysed reaction between Meldrum's acid and catechols/hydroquinones – An investigation

Enzymatic oxidation of catechols/hydroquinones in the presence of Meldrum's acid as a nucleophile in aqueous solution has been investigated in detail by applying laccase as a catalyst. Optimization of the reaction through the use of HBT/ABTS/HPI as a mediator allowed a yield of more than 65% of the isolated product. We derived some new compounds with catechol/hydroquinone ring with moderate yields based on enzymatic synthesis in environmentally benign aqueous solution. These types of reactions represent a milestone along the path to future sustainable green chemistry.     

On the Number of Linearly Separable Subsets of Finite Sets in R n

Let X be a finite set of cardinality m in general position in R ^n. For n=3 we show that if X is in convex position, the number of k-sets in X is given by Γ _k =2k(m-k)-m+2. In general odd dimension we obtain ; here convexity is not required. Received January 18, 1995, and in revised form January 21, 1997.     

Pyrene: a probe to study protein conformation and conformational changes

The review focuses on the unique spectral features of pyrene that can be utilized to investigate protein structure and conformation. Pyrene is a fluorescent probe that can be attached covalently to protein side chains, such as sulfhydryl groups. The spectral features of pyrene are exquisitely sensitive to the microenvironment of the probe: it exhibits an ensemble of monomer fluorescence emission peaks that report on the polarity of the probe microenvironment, and an additional band at longer wavelengths, the appearance of which reflects the presence of another pyrene molecule in spatial proximity (~10 ?). Its high extinction coefficient allows us to study labeled proteins in solution at physiologically relevant concentrations. The environmentally- and spatially-sensitive features of pyrene allow monitoring protein conformation, conformational changes, protein folding and unfolding, protein-protein, protein-lipid and protein-membrane interactions.     

Development of a new polypropylene-based suture: plasma grafting, surface treatment, characterization, and biocompatibility studies

Polypropylene sutures (PP) are already used in surgery. Because microbial infection leads to complications, we developed antimicrobial PP suture by plasma-induced graft polymerization of acrylic acid followed by chitosan binding on the remaining carboxyl groups. Mechanical properties and surface morphologies were analyzed on these sutures. Tetracycline hydrochloride (TC) or nanosilver (NS) was then immobilized to PP. The resulting PP sutures evidenced drug release properties and antimicrobial activity in vitro. PP implanted in vivo for 30 days in the muscle of rats showed the absence of adverse effects and a tissue organization. This new polypropylene suture with suitable antimicrobial features appears to be a promising macromolecular material for clinical and cosmetic applications.