Interaction of isomeric forms of xanthophyll pigment zeaxanthin with dipalmitoylphosphatidylcholine studied in monomolecular layers

Two-component monomolecular layers were formed with DPPC and two stereoisomers of zeaxanthin 9-cis and 13-cis at the argon-water interface. Very distinct over-additivity which represents affection of a lipid arrangement in the membrane has been observed in the case of zeaxanthin 9-cis (maximum at 20 mol%) but not in the case of zeaxanthin 13-cis. The differences in the organization of the isomers of zeaxanthin-DPPC monolayers are interpreted in terms of the different orientation of both xanthophylls at the interface observed at relatively high surface pressures (>25 mN/m) comparable to the surface pressures of biomembranes. The results are consistent with the model according to which zeaxanthin 9-cis adopts a vertical orientation at the polar-nonpolar interface in contrast to zeaxanthin 13-cis, which is oriented horizontally owing to the fact that it interacts by two hydroxyl groups with the same hydrophobic-hydrophilic interface in the monolayer. The findings are discussed in comparison with the behavior of zeaxanthin in the conformation all-trans in the same system. Zeaxanthin all-trans forms efficiently molecular aggregates in the mixed monolayers in contrast to cis isomers. Circular dichroism measurements show the formation of molecular structures by zeaxanthin 13-cis that are interpreted as dimers. FTIR measurements show that these dimers are stabilized by van der Waals interactions unlike aggregated structures formed by all-trans zeaxanthin that are stabilized by hydrogen bonding. Physiological importance of the differences in aggregation and orientation of stereoisomers of zeaxanthin in lipid environment is discussed.     

A dispersive model of radical accumulation in irradiated solids

- A dispersive model of radical accumulation in irradiated solids is discussed by the example of hexagonal ice (Ih) and cubic ice (Ic) obtained by annealing of hyperquenched glassy water at 160 K. The model assumes that radical production upon -irradiation is accompanied by their second-order decay, which proceeds according to dispersive kinetics with the time-dependent specific reaction rate k(t) = Bt ^-1, where B = constant and is the dispersion parameter equal to 0.40 for both the hexagonal and cubic ices. The radicals, OH in Ih, and OH plus HO₂ in Ic are produced at the same rate upon -irradiation. The observed enhancement of radical accumulation in ice Ic in comparison with Ih is due to the marked decrease of radical recombination in ice Ic. This is rationalized by the hindrance of radical transport in the lattice of ice Ic containing substantial amounts of Bjerrum-type L-defects.     

Fouling of nanofiltration membranes used for separation of fermented glycerol solutions

In this study, the glycerol solutions were fermented using Lactobacillus casei bacteria. The broths were pre-treated by microfiltration, followed by a further separation with nanofiltration. The latter process was carried out in two stages, using the NF270 and NF90 membranes, respectively. The concentrates thus obtained were enriched with citric acid (first stage) and then with lactic acid and glycerol (second stage). By means of SEM and AFM microscopy, as well as ATR-FTIR analysis, the intensity of membrane-fouling was studied. The colloidal fouling and bio-fouling caused a more than two-fold decrease in the permeate flux during microfiltration of the broth. This pre-treatment stage was effective, and a permeate turbidity of less than 0.2 NTU was obtained. However, the nanofiltration membranes exhibited a 30 % flux decline over the course of the process, mainly due to the organic fouling.     

Thermal and spectroscopic properties of light lanthanides (III) and sodium complexes of 2,5-pyridinedicarboxylic acid

Pyridine-2,5-dicarboxylic acid, known as isocinchomeric acid is one of six isomers containing two carboxylic groups. Light lanthanide (III) complexes with pyridine-2,5-dicarboxylic acid with general formula Ln₂L₃·nH₂O, where n = 8, 9, were obtained. Their thermal and spectroscopic properties were studied. Sodium salt was obtained as Na₂L·H₂O. Hydrated complexes of La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III) and Gd(III) are stable to 313–333 K, whereas Na₂L·H₂O is stable to about 333 K. Dehydration process for all compounds runs in one stage, next they decompose into appropriate lanthanide oxalates, oxocarbonates carbonates and finally to metal oxides. Bands of νCOOH vibrations at 1736 and 1728 cm⁻¹ disappear on complex spectra and ν_as and ν_s of COO⁻ groups appear thus indicating that complexation process took place.     

LDI and ESI MS as well as low energy CID of a self-assembling nanorod-forming fullerene derivative

An amphiphatic fullerene derivative (8-(N-Methyl-Fullero-Pyrrolidinium-1-yl-chloride)-3,6-Dioxaoctan-1-Ammonium Chloride (MFPDAC)), which is of great interest in nanotechnology due to the fact that it forms self-assembling fullerenic nanorods, has been structurally characterized with emphasis to its purity and thermal treatment of a formed nanorod film (on a LDI target) by means of laser desorption/ionization (LDI) coupled with high-resolution curved field reflectron time-of-flight (TOF) mass spectrometry, and by low energy MS/MS as well as in-source fragmentation experiments applying an quadrupole ion trap (QIT) combined with a two-stage reflectron TOF analyzer. The interpretation of LDI results has been supplemented by ESI QIT MS(n) (n = 1-3), as well as high-resolution ESI reflectron TOF mass spectrometric experiments. Based on the experimental data obtained by both desorption/ionization techniques, various types of analyzers and sample treatments, we could completely characterize MFPDAC and further found out that the investigated sample was not entirely free of impurities. Furthermore, the envisaged loss of the derivative sidechain upon the heat treatment in vacuum of the self-assembled nanorod sample film on a metallic substrate could be successfully monitored by LDI MS.     

Thin-layer chromatography-densitometric measurements for determination of N-(hydroxymethyl)nicotinamide in tablets and stability evaluation in solutions

A thin-layer chromatography (TLC)-densitometric method was developed to determine N-(hydroxymethyl)nicotinamide in tablets and basic solutions along with nicotinic acid. Analysis was performed on silica gel F254 plates using chloroform-ethanol (2 + 3, v/v) mobile phase. The densitometric observations were made at 260 nm. The results showed good precision and accuracy; relative standard deviation was 2.37%, and recovery ranged from 97.60 to 100.82%. The limit of detection was 0.1 microg/spot, while the linearity range was from 0.2 to 1.75 microg/spot. Applicability of the newly developed method was tested for determination of N-(hydroxymethyl)nicotinamide in the preparation Cholamid. Densitometric measurements were used to evaluate stability of N-(hydroxymethyl)nicotinamide in basic solutions. It was found that decomposition corresponded to first-order reaction kinetics. The computed kinetic and thermodynamic parameters at 30 degrees C were as follows: k = 0.00675/min, t0,5 = 1.71 h, t0,1 = 0.26 h, and Ea = 44.75 kJ/mol.     

Synthesis and reactivity of bis(cycloamidinium-2-yl)alkane bromide tribromides, brominating agents and tectons for molecular engineering

Bis(cycloamidine-2-yl)alkanes easily form bromide tribromide salts in the reduction-oxidation processes with bromine. Bis(tetrahydroimidazolium-2-yl)ethane and bis(hexahydropyrimidinium-2-yl)-ethane bromide tribromides are such new convenient brominating agents for aromatic amides in chemo- and regioselective electrophilic substitutions and α-bromination reactions.     

Sequential homo-coupling Diels-Alder/retro Diels-Alder reaction of 5,5′-bi-1,2,4-triazine-containing thiamacrocycles as a new route to thiacrown ethers incorporating a 2,2′-bipyridine subunit

A new route to thiacrown ethers 5a-d and 6a-d incorporating a 2,2′-bipyridine subunit is elaborated using, (1) homo-coupling of 1,2,4-triazine sulfides 3a-d tethered to poly(ethylene glycol) chains with potassium cyanide and (2) Diels-Alder/retro Diels-Alder reaction with norbornadiene or 1-pyrrolidino-1-cyclopentene as the key steps.     

Optimized derivatization of acidic herbicides with trimethylsilyldiazomethane for GC analysis

In the present study, the preparation of methyl esters of chlorophenoxy acids with trimethylsilyldiazomethane (TMSD) is reported. TMSD is a mild and safe alternative to the highly toxic, thermally labile, and explosive diazomethane. Due to the novelty of this method, the characteristics of the reaction were investigated and the derivatization procedure was screened for statistically significant factors. The parameters identified as influential are the amount of methanol as well as reaction time and temperature. A careful optimization by a complete factorial response surface design was carried out to generate optimal reaction conditions with respect to maximum recovery and reaction yield. Special emphasis has been given to an accurate validation of the derivatization procedure. LODs were determined between 4.1 and 8.1 ng/mL for the enriched sample and linearity was proofed for more than five orders of magnitude. The applicability of the method was demonstrated by the analyses of quality control material including sample preparation with SPE. Polar herbicides investigated in the study belong to acetic acid (2,4-D, MCPA, and 2,4,5-T), butanoic acid (MCPB), and propanoic acid (mecoprop). An efficient, fast, and high-throughput method for the determination of polar herbicides including the potential for automation is proposed.     

Gold nanoparticle-enhanced target for MS analysis and imaging of harmful compounds in plant,animal tissue and on fingerprint

Gold nanoparticle-enhanced target (AuNPET) was used for detailed investigation of various materials of biological origin – human fingerprint, onion bulb and chicken liver. Analysis of these objects was focused on toxic and harmful compounds – designer drug containing pentedrone, diphenylamine in onion and potentially cancerogenic metronidazole antibiotic in liver. Detection of large quantity of endogenous compounds from mentioned objects is also shown. Most of analyzed compounds were also localized with MS imaging and relationship between their function and location was discussed. Detected compounds belong to a very wide range of chemical compounds such as saccharides, ionic and non-ionic glycerides, amino acids, fatty acids, sulfides, sulfoxides, phenols etc. Fingerprint experiments demonstrate application of AuNPET for detection, structure confirmation and also co-localization of drug with ridge patterns proving person-drug contact.