HPTLC–densitometric and HPTLC–MS methods for analysis of flavonoids

HPTLC silica gel plates without and with fluorescence indicator F₂₅₄ in combination with n-hexane–ethyl acetate–formic acid (20:19:1, v/v/v) as a developing solvent were explored for the HPTLC–densitometric and HPTLC–MS/(MSⁿ) analyses of flavonoids. Pre-development of the plates with chloroform–methanol (1:1, v/v) was needed for reliable HPTLC–densitometric analyses of flavonoid aglycones in the whole R_F range, while 2-step pre-development (1^st methanol–formic acid (10:1, v/v), 2^nd methanol), that decreased background signals of formic acid adducts, was required for HPTLC–MS analyses. Optimization with conditioning of the adsorbent layer with water before development and saturation of the twin trough chamber resulted in required decrease of the R_F values of studied flavonoids (flavone, apigenin, luteolin, chrysin, quercetin dihydrate, myricetin, kaempferide, kaempferol, naringenin, pinocembrin).

Detection was performed based on fluorescence quenching (on the plates with F₂₅₄), natural fluorescence and after post-chromatographic derivatization with natural product reagent without or with further enhancement and stabilization of fluorescent zones with polyethylene glycol (PEG 400 or PEG 4000) or paraffin–n-hexane reagents. For all three reagents, drying temperature and time passed after drying influenced the intensity, which was increasing the first 20?min, and the stability (less than 2?h for PEGs and at least 24?h for paraffin–n-hexane) of the standards’ zones.

Optimal wavelengths for densitometric evaluation were selected based on in-situ absorption spectra scanned before and after derivatization and after stabilization. The developed method was tested via analyses of propolis, roasted coffee, rose hip, hibiscus, rosemary and sage crude extracts. To further increase the reliability of the obtained densitometric results HPTLC–MS/(MSⁿ) analyses of all crude extracts were performed. Several phenolic and non-phenolic compounds were tentatively identified.

Some possible interferences with phenolic acids (chlorogenic acid, rosmarinic acid, protocatechuic acid, gallic acid, syringic acid, ellagic acid, trans-cinnamic acid, o-coumaric acid, m-coumaric acid, p-coumaric acid, caffeic acid, ferulic acid, sinapic acid) that are often present in the extracts together with flavonoids were also examined.     

Herbicidal activity of pure compound isolated from rhizosphere inhabiting Aspergillus flavus

In the quest for bioactive natural products of fungal origin, Aspergillus flavus was isolated from rhizosphere of Mentha piperita using Potato Dextrose Agar (PDA) and Czapec Yeast Broth (CYB) nutrient media for metabolites production. In total, three different metabolites were purified using HPLC/LCMS and the structures were established using 500 Varian NMR experiments. Further the isolated metabolites in different concentrations (10, 100, 1000 μg/mL) were tested for herbicidal activity using Completely Randomized design (CRD) against the seeds of Silybum marianum and Avena fatua which are major threats to wheat crop in Pakistan. Among the isolated metabolites, one compound was found active against the test weed species whose activity is reported in the present work. The chemical name of the compound is 2-(1, 4-dihydroxybutan-2-yl)-1, 3-dihydroxy-6, 8-dimethoxyanthracene-9, 10(4aH, 9aH)-dione with mass of 388. Results showed that all seeds germinated in control treatment; however, with the metabolite treated, the growth was retarded to different levels in all parts of the weeds. At a dose of 1000 μg/mL of the pure compound, 100% seeds of S. marianum and 60% seeds of A. fatua were inhibited. Interestingly, the pure compound exhibited less inhibition of 10% towards the seeds of common wheat (Triticum aestivum).     

Structure of adsorption layers and conformation transformations of ethylhydroxyethylcellulose on surfaces of titanium and iron oxides

Regularities of the adsorption of ethylhydroxyethylcellulose (EHEC) hydrophilic polymer on a surface of inorganic pigments of TiO₂ and Fe₂O₃ were investigated by infrared spectroscopy. It was found that the adsorption interaction between EHEC and a surface of oxides is accompanied by conformation transformations of the adsorbed molecules of EHEC. The means by which macromolecules bind with active centers on a surface of metal oxides and the influence of the oxides’ nature on the EHEC macromolecule conformation transformations determining the structure of the adsorption layer upon adsorption were established.     

Effect of water on the temperatures of human immunoglobulin conformation transitions

A differential thermal analysis of native and denaturated human immunoglobulin (G isotype) and mixtures of the native protein with water over the temperature range of 80–570 K is conducted. Temperatures of the protein conformational transitions and the effect of water on them are investigated. The limit of water solubility in the native protein is determined calorimetrically from the enthalpy of excess water phase melting. A physical state diagram of the immunoglobulin-water system over a wide range of temperatures and component concentrations is built and analyzed.     

The electrical properties of chemically obtained barium titanate improved by attrition milling

Barium titanate ceramics were prepared using the nanopowder resulting from a polymeric precursor method, a type of modified Pechini process. The obtained nanopowder was observed to agglomerate and in order to de-agglomerate the powder and enhance the properties of the barium titanate the material was attrition milled. The impact of this attrition milling on the electrical properties of the barium titanate was analysed. The temperature dependence of the relative dielectric permittivity showed three structural phase transitions that are characteristic for ferroelectric barium titanate ceramics. The relative dielectric permittivity at the Curie temperature was higher for the attrition-treated sample than for the non-treated barium titanate. The dielectric losses were below 0.04 in both barium titanate ceramics. The grain and grain-boundary contributions to the total resistivity were observed using impedance analyses for both ceramics. A well-defined ferroelectric hysteresis loop and piezoelectric coefficient d₃₃ = 150 pC/N were obtained for the ceramics prepared from the de-agglomerated powder. In this way we were able to demonstrate that by attrition milling of chemically obtained powders the ferroelectric and piezoelectric properties of the ceramics could be enhanced.     

Low-temperature versus oxygen plasma treatment of water-based TiO2 paste for dye-sensitized solar cells

High-temperature treatment steps in fabrication process of dye sensitized solar cell (DSSC) significantly contribute to the manufacturing costs and limit the use of temperature sensitive substrates. Therefore our aim was to develop a simple method for the preparation of water-based TiO₂ paste. The paste is based on peroxotitanic acid (PTA) sol–gel matrix and commercial TiO₂ nanoparticles (P25). Two fabrication processes to decompose/transform the PTA matrix in the printed TiO₂ layer are explored and combined: annealing at temperatures up to 250 °C and/or oxygen plasma treatment. The results show that the PTA matrix in the paste converts to anatase phase and to some extent also attaches to the TiO₂ nanoparticles P25 acting as an interconnecting network within TiO₂ layer. The transformation of the PTA matrix occurs around 250 °C, but in the presence of TiO₂ nanoparticles P25 it starts already at 120 °C. In addition the results reveal that the crystallization is achievable also solely with the oxygen plasma treatment. The efficiency of the TiO₂ layers, exposed to different post-deposition treatments, is evaluated in DSSCs. The results show that oxygen plasma treatment of the TiO₂ layers could efficiently replace temperature curing at 250 °C. Within this study the DSSCs with the efficiency up to 4.2 % measured under standard test conditions (1,000 W/m², AM1.5, 25 °C) were realized.     

Novel approach to the synthesis of 3-acyl substituted indolizines. The synthesis of 3-(indolizinyl-2)alanine and 4-(indolizinyl-3) homoalanine derivatives

A novel approach to the synthesis of 3-acylindolizines and the transformations of some acids into tryptophane analogues are described. Reaction of ethyl 2-pyridinylacetate and methyl 2-quinolinylacetate with N-trifluoroacetyl-5-bromo-4-oxonorvaline methylester led to N-trifluoroacetyl-3-(1-ethoxycarbonylindolizinyl-2) alanine methyl ester and N-trifluoroacetyl-3-(3-methoxycarbonylpyrrolo [1,2-a]quinolinyl-2) alanine methyl ester, respectively. Treatment of ethyl 2-pyridinylacetate and 2-pyridinylacetonitrile, first with N,N-dimethylformamide dimethyl acetal (DMFDMA), followed by reaction with phenacyl bromide, gave the corresponding 3-benzoylindolizines, while the reaction of ethyl 2-pyridinylacetate and 2-pyridinylacetonitrile with DMFDMA, followed by treatment with (S)-N-trifluoroacetyl-5-bromo-4-oxonorvaline methyl ester, gave the corresponding N-trifluoroacetyl-4-oxo-4-(indolizinyl-3)homoalanine methyl esters.     

Cyclization vs. Elimination Reactions of 5‐Aryl‐5‐hydroxy 1,3‐Diones: One‐Pot Synthesis of 2‐Aryl‐2,3‐dihydro‐4H‐pyran‐4‐ones

2‐Aryl‐2,3‐dihydro‐4H‐pyran‐4‐ones were prepared in one step by cyclocondensation of 1,3‐diketone dianions with aldehydes. The use of HCl (10%) for the aqueous workup proved to be very important to avoid elimination reactions of the 5‐aryl‐5‐hydroxy 1,3‐diones formed as intermediates. The TiCl₄‐mediated cyclization of a 2‐aryl‐2,3‐dihydro‐4H‐pyran‐4‐one with 1,3‐silyloxybuta‐1,3‐diene resulted in cleavage of the pyranone moiety and formation of a highly functionalized benzene derivative.     

The thermochemical characteristics of cellulose and its mixtures with water

The heat capacity of cotton microcrystalline cellulose was measured on an adiabatic vacuum calorimeter over the temperature range 80–330 K, and the differential thermal analysis data on the substance were obtained from 80 to 550 K. The enthalpy of cellulose interaction with water was measured at 303 K using a differential microcalorimeter. The standard enthalpies of combustion and formation of microcrystalline cellulose and wood celluloses with different crystallinity indices were determined. The concentration of saturated water solution in microcrystalline cellulose at 273 K was determined calorimetrically from the enthalpy of fusion of the excess water phase.