Novel Method for HPLC Analysis of Triterpenic Acids Using 9-Anthryldiazomethane Derivatization and Fluorescence Detection

Triterpenic acids are a group of secondary plant metabolites which are part of the cuticular waxes covering fruits, leaves, and flowers. To date, quantitative analysis of these compounds has often been conducted using high-performance liquid chromatography coupled with spectrophotometric detection or mass spectrometry; however, these methods have some major drawbacks. This paper reports a new method of analysis implementing derivatization with 9-anthryldiazomethane and fluorescence detection. The method consists of the extraction of analytes from a matrix, purification with anion exchanging SPE columns, and an optional step of the alkaline hydrolysis of triterpenic acid esters. The paper also describes a fast and easy method for the synthesis of the derivatization agent. The detection limits of the method presented are approximately 100-fold lower than in a similar method using ultraviolet spectrophotometry as the mode of detection. The recovery and repeatability of the method are at satisfactory levels.     

Effects of unsteadiness of the rates of flow on the dynamics of formation of droplets in microfluidic systems

Oscillations of the input rates of flow have a significant impact on the dynamics of formation of droplets in microfluidic systems and on the quality of generated emulsions.     

The -Cys-Cys- motif in Helicobacter pylori's Hpn and HspA proteins is an essential anchoring site for metal ions

The Hpn and HspA proteins from H. pylori are significant for nickel homeostasis and protect the cells from higher concentrations of external metal ions. Both proteins have a unique histidine- and cysteine-rich domain at the C terminus. The interactions of Ni(2+), Bi(3+), Zn(2+) and Cd(2+) ions with C-terminal Ac-CCSTSDSHHQ-NH(2) and Ac-EEGCCHGHHE-NH(2) fragments from Hpn and the Ac-GSCCHTGNHD-NH(2) sequence from HspA were studied by potentiometry, mass spectrometry, circular dichroism and UV-Vis spectroscopy. Ac-CC-NH(2) was used as a reference peptide. The studies have shown that nickel ions form planar complexes with a {2S(-),N(-)} binding mode. The thiol sulfurs of the -Cys-Cys- motif are also the anchoring sites for Bi(3+), Zn(2+) and Cd(2+) ions. The studied protein fragments have the highest affinity for Bi(3+) ions. The thermodynamic stability of Ni(2+) is much higher then that of Zn(2+).     

Theoretical search for alternative nine-electron ligands suitable for superhalogen anions

The calculations performed at the OVGF/6-311++G(3df,3pd)//MP2/6-311++G(d,p) level for the representative NaX(2)(-) and AlX(4)(-) anions matching the MX(k+1)(-) superhalogen formula and utilizing 9-electron systems (i.e., consisting of various possible combinations of atoms containing nine electrons when brought together) revealed that the OH, Li(2)H(3), and NH(2) groups might be considered as alternative ligands X due to their thermodynamic stability and large values of electron binding energy (approaching or even exceeding 6 eV in some cases). All aluminum-containing AlX(4)(-) anions (excluding Al(HBLi)(4)(-)) were predicted to be thermodynamically stable, whereas the NaX(2)(-) anions for X = CH(3), HBLi, CLi, BeB, and H(2)BeLi were found to be susceptible to the fragmentations leading to Na(-) loss. Among the MX(k+1)(-) (M = Na, Al; X = Li(2)H(3), OH, H(2)BeLi, BeB, NH(2), HBLi, CH(3), Be(2)H, CLi) anions utilizing systems containing 9 electrons (and thus isoelectronic with the F atom) the largest vertical electron detachment energy of 6.38 eV was obtained for Al(OH)(4)(-).     

Hydrophilic Microspheres Containing αα-tert Butoxy-ωω-vinylbenzyl-polyglycidol for Immunodiagnostics: Synthesis,Properties and Biomedical Applications

Summary: Synthesis, characteristics and medical diagnostic application of core-shell poly(styrene/α-tert-butoxy-ω-(vinylbenzyl)polyglycidol) (P(S/PGL)) microspheres are described. The particles were prepared by soap-free emulsion polymerization of styrene and α-tert-butoxy-ω-(vinylbenzyl)polyglycidol macromonomer (PGL) initiated with potassium persulfate. The polymerization in water yielded microspheres with diameters in the range from 220 to 650 nm, depending on concentration of the macromonomer. Polydispersity was usually below 1.06. The fraction of PGL in interfacial layer of microspheres ranged from 0 to 42 mol.% (estimated by XPS). Microspheres suspended in NaCl solutions manifested fully reversible swelling-deswelling properties of their interfacial layer with characteristic transition temperature (T_t) slightly dependent on NaCl concentration. The adsorption of human serum albumin on the surface of P(S/PGL) microspheres was highly reduced when the PGL surface fraction exceeded 40 mol.%. P(S/PGL) microspheres with immobilized antigens Helicobacter pylori were used for detection of antibodies against. The test was based on monitoring differences in electrophoretic mobility of P(S/PGL) microspheres covalently bound H. pylori antigens and antibodies against H. pylori in blood serum.     

Development in Synthesis,Electrochemistry, LB Moieties of Phenothiazine Based Units

A convenient and higher yielding synthetic route to N‐alkyl‐bis(thiophene)phenothiazine derivatives is reported and their aggregation, electrochemical properties and polymerization are characterized. The key step in the synthesis of this group of compounds has been the Stille type coupling reaction between the N‐alkyldibromophenothiazine and tin derivatives of thiophene as the best way for preparation of conjugated N‐alkylphenothiazine derivatives. For this group of compounds we also present an electrochemical polymerization effect and widely adopted approach to prepare structurally ordered thin, electroconducting films by Langmuir–Blodgett technique.     

Lower Bounds on the Lowest Spectral Gap of Singular Potential Hamiltonians

We analyze Schr?dinger operators whose potential is given by a singular interaction supported on a sub-manifold of the ambient space. Under the assumption that the operator has at least two eigenvalues below its essential spectrum we derive estimates on the lowest spectral gap. In the case where the sub-manifold is a finite curve in two dimensional Euclidean space the size of the gap depends only on the following parameters: the length, diameter and maximal curvature of the curve, a certain parameter measuring the injectivity of the curve embedding, and a compact sub-interval of the open, negative energy half-axis which contains the two lowest eigenvalues. Dedicated to Krešimir Veselić on the occasion of his 65^th birthday. Submitted: February 20, 2006; Accepted: May 8, 2006     

Bioinspired Nanodevice Based on the Folic Acid/Titanium Dioxide System

A new bioinspired nanomaterial has been obtained by chemisorption of folic acid onto nanocrystalline titanium dioxide. The organic chromophore is linked with the semiconductor surface via the glutamate chain and anchored with the carboxylate group. The geometry and electronic structure of the chromophore was studied in detail with DFT. Photoelectrochemical studies revealed photosensitization of the new material towards visible light. The photoelectrodes composed of the folic acid/titanium dioxide hybrid material generated photocurrent over a 300–600‐nm window. Moreover, the direction of the photocurrent could be changed from anodic to cathodic and vice versa by application of the appropriate photoelectrode potential. Photoelectrochemical and spectroscopic studies allowed the elucidation of the mechanism of photocurrent switching. Photoelectrodes composed of folate‐modified titanium dioxide may serve as a simple model of optoelectronic switches and may constitute the basis for molecular photoelectronic devices.     

Molecular mechanical devices based on quinone-pyrrole and quinone-indole dyads: a computational study

A set of intramolecularly connected dyads consisting of a quinone unit and a pyrrole or indole moiety have been designed and evaluated in quantum-chemical calculations. It is shown computationally for several systems, depending on the length and attachment points of the interconnecting chains, that a reduction of the quinone to the semiquinone radical anion or quinolate dianion state leads to a reversible intramolecular reorientation from a pi-stacked to a T-stacked arrangement. In the rearranged structures, a hydrogen bond from the pyrrole or indole N-H function to the semiquinone or quinolate pi-system is created upon reduction. In some systems, hydrogen bonds to the semiquinone or quinolate oxygen atoms are partly feasible and will be preferred over T-stacking. The choice of systems has been based on recent computational observations related to photosystem I. Systems with pyrrole or indole units should provide a better basis for the envisioned molecular motor than recently proposed quinone-benzene dyads. The intramolecular interactions modify the quinone redox potentials. Electronic g-tensors have been computed for the semiquinone states. These reflect characteristically the presence and nature of hydrogen bonds to the semiquinone and represent suitable electron paramagnetic resonance spectroscopic probes for the preferred structures. Intramolecular proton transfer is possible in the dianionic state.