Development and validation of an HPLC-DAD analytical procedure for quality control of damiana (Turnera diffusa), using an antioxidant marker isolated from the plant

Damiana is a shrub used as a dietary supplement and as an additive in several foods. This report presents the first validated analytical method for QC of products made from damiana. Through bioassay-guided fractionation, the compound showing the best antioxidant activity, determined using 2,2-diphenyl-1-picryl-hydrazyl assay in TLC, was purified and identified as 8-C-beta-[6-deoxy-2-O-(alpha-1-rhamnopyranosyl)-xylo- hexopyranos-3-uloside] (Cl50 5.56 g/mL). This is the only natural source from which this compound has been reported, and has been found in all native damiana samples analyzed. Therefore, it was used as a biomarker to develop an HPLC-diode-array detection analytical procedure using the first-order derivative of the chromatograms. Separation was achieved using an AccQ Tag C18 150 x 3.9 mm (4 microm) column, with a gradient of methanol and 0.1% trifluoroacetic acid in water. The method was shown to be accurate, sensitive, and reproducible, providing a useful quantitative means to apply QC to damiana products.     

Ionic liquids as desorption solvents and memory effect suppressors in heterocyclic aromatic amines determination by SPME–HPLC fluorescence

The beneficial effects of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF₄) ionic liquid (IL) as mobile phase additive, desorption solvent, and memory effect suppressor in solid-phase microextraction (SPME)–high-performance liquid chromatography with fluorescence detection for the determination of six heterocyclic aromatic amines have been evaluated for the first time. Several chromatographic parameters have been evaluated in the presence or absence of IL or using triethylamine as the most common mobile phase additive, with a Nova-Pak® C18 stationary phase. This IL was found to be clearly superior to triethylamine for efficiency as well as peak shape enhancement and sensitivity increase. SPME was chosen because it is faster than conventional extraction techniques and allowed us to minimize the use of organic solvents. However, memory effect may become a problem when a high-sensitivity detector is used. The appropriate conditions for the desorption step and to eliminate the memory effect involving BMIm-BF₄ were established and optimized. The method was applied for the determination of these compounds in commercial meat extracts.     

Existence and uniqueness of best proximity points in geodesic metric spaces

A mapping T:A∪B→A∪B such that T(A)⊆B and T(B)⊆A is called a cyclic mapping. A best proximity point x for such a mapping T is a point such that d(x,Tx)= dist(A,B). In this work we provide different existence and uniqueness results of best proximity points in both Banach and geodesic metric spaces. We improve and extend some results on this recent theory and give an affirmative partial answer to a recently posed question by Eldred and Veeramani in [A.A. Eldred, P. Veeramani Existence and convergence of best proximity points, J. Math. Anal. Appl. 323 (2) (2006) 1001-1006].     

Leucoxol,a new diterpenoid from acacia leucophloea. X-ray structure determination

From $\text{Acacia leucophloea}$ (Roxb.) Willd. (Mimosaceae) the new diterpenoid 11α, 16-epoxy-1β, 15$\text{R}$-dihydroxy-isopimar-8(14)-ene (leucoxol) has been isolated. Its structure was determined by X-ray diffraction analysis.     

Photoprotective properties of a hydrophilic extract of the fern Polypodium leucotomos on human skin cells

The effect of a hydrophilic extract of the fern Polypodium leucotomos (PLE) has been investigated in terms of photoprotection against UV-induced cell damage. PLE efficiently preserved human fibroblast survival and restored their proliferative capability when the cells were exposed to UVA light. This effect was specific and dose-dependent. Photoprotection was not restricted to fibroblasts, as demonstrated by its effect on survival and proliferation of the human keratinocyte cell line HaCat. Finally, treatment of the cells with PLE prevented UV-induced morphological changes in human fibroblasts, namely disorganisation of F-actin-based cytoskeletal structures, coalescence of the tubulin cytoskeleton and mislocalization of adhesion molecules such as cadherins and integrins. Our in vitro results demonstrate the photoprotective effect of PLE on human cells and support its use in the preventive treatment of sunburning and skin pathologies associated with UV-mediated damage.     

Density and wave function analysis of actinide complexes: what can fuzzy atom, atoms-in-molecules, Mulliken, Lowdin, and natural population analysis tell us?

Recent advances in computational methods have made it possible to calculate the wave functions for a wide variety of simple actinide complexes. Equally important is the ability to analyze the information contained therein and produce a chemically meaningful understanding of the electronic structure. Yet the performance of the most common wave function analyses for the calculation of atomic charge and bond order has not been thoroughly investigated for actinide systems. This is particularly relevant because the calculation of charge and bond order even in transition metal complexes is known to be fraught with difficulty. Here we use Mulliken, Lowdin, natural population analysis, atoms-in-molecules (AIM), and fuzzy atom techniques to determine the charges and bond orders of UO(2)(2+), PuO(2)(2+), UO(2), UO(2)Cl(4)(2-), UO(2)(CO)(5)(2+), UO(2)(CO)(4)(2+), UO(2)(CN)(5)(3-), UO(2)(CN)(4)(2-), UO(2)(OH)(5)(3-), and UO(2)(OH)(4)(2-). This series exhibits a clear experimental and computational trend in bond lengths and vibrational frequencies. The results indicate that Mulliken and Lowdin populations and bond orders are unreliable for the actinyls. Natural population analysis performs well after modification of the partitioning of atomic orbitals to include the 6d in the valence space. The AIM topological partitioning is insensitive to the electron donating ability of the equatorial ligands and the relative atomic volume of the formally U(VI) center is counterintuitively larger than that of O(2-) in the UO(2)(2+) core. Lastly, the calibrated fuzzy atom method yields reasonable bond orders for the actinyls at significantly reduced computational cost relative to the AIM analysis.     

Repair of guanyl radicals in plasmid DNA by electron transfer is coupled to proton transfer

By using gamma-irradiation in the presence of thiocyanate ions, we have generated guanyl radicals in plasmid DNA. These can be detected by using an Escherichia coli base excision repair endonuclease to convert their stable end products to strand breaks. The yield of enzyme-sensitive sites is strongly attenuated by the presence of micromolar concentrations of one of a series of singly substituted phenols, and it is possible to derive bimolecular rate constants for the reduction of DNA guanyl radicals by these phenols. More strongly reducing phenols were found to react more rapidly. This electron-transfer reaction also involves a proton transfer. By comparing the expected energetics of the reaction with the observed rate constants, the electron transfer is found to be mechanistically coupled with the proton transfer.     

Interaction of epothilone analogs with the paclitaxel binding site: relationship between binding affinity, microtubule stabilization, and cytotoxicity

The interactions of epothilone analogs with the paclitaxel binding site of microtubules were studied. The influence of chemical modifications in the C15 side chain and in C12 on binding affinity and microtubule elongation was characterized. Modifications favorable for binding affinity are (1). a thiomethyl group at C21 of the thiazole side chain, (2). a methyl group at C12 in S configuration, (3). a pyridine side chain with C15 in S configuration, and (4). a cyclopropyl moiety between C12 and C13. The same modification in different ligands has similar effect on affinity, allowing good structure-affinity characterization. The correlation between binding, microtubule stabilization, and cytotoxicity of the compounds has been determined, showing differential effects of the modifications. The binding constants correlate well with IC(50) values, demonstrating that affinity measurements are a useful tool for drug design.     

Simultaneous Determination of Vitamins D3 (Calcitriol,Cholecalciferol) and K2 (Menaquinone-4 and Menaquinone-7) in Dietary Supplements by UHPLC

The content and composition of dietary supplements is of great interest due to their increasing consumption and variety of available brand offered in the market. Accurate determination of vitamins is important for the improvement of dietary supplement quality and nutrition assessments. In this regard, the simultaneous determination of vitamin D3 (calcitriol—CT and cholecalciferol—CHL) and K2 (menaquinone-4—MK-4 and menaquinone-7—MK-7) in dietary supplements was developed by using ultra-high-pressure liquid chromatography (UHPLC). The overall runtime per sample was above 35 min, with the retention times of 2.40, 6.59, 7.06, and 32.6 min for vitamin D3 (CT and CHL) and vitamin K2 (MK-4 and MK-7), respectively. The limits of detection and limits of quantification for the target nutritional compounds ranged between 0.04–0.05 µg/mL, respectively. The validation results indicated that the method had reasonable linearity (R² ≥ 0.9990), good recovery (>82%), satisfactory intra-day precision (≤1.9%) and inter-day precision (≤3.5%), and high selectivity and specificity. The validated UHPLC method was demonstrated to be precise, accurate, and robust for the simultaneous determination of vitamins D3 (CT and CHL) and K2 (MK-4 and MK-7) in dietary supplements.