1,3-substituted imidazolidine-2,4,5-triones: synthesis and inhibition of cholinergic enzymes

A series of novel and highly active acetylcholinesterase and butyrylcholinesterase inhibitors derived from substituted benzothiazoles containing an imidazolidine-2,4,5-trione moiety were synthesized and characterized. The molecular structure of 1-(2,6-diisopropyl-phenyl)-3-[(1R)-1-(6-fluoro-1,3-benzothiazol-2-yl)ethyl]-imidazolidine-2,4,5-trione (3g) was determined by single-crystal X-ray diffraction. Both optical isomers are present as two independent molecules in the triclinic crystal system. The lipophilicity of the compounds was determined as the partition coefficient log K(ow) using the traditional shake-flask method. The in vitro inhibitory activity on acetylcholinesterase from electric eel and butyrylcholinesterase isolated from equine serum was determined. The inhibitory activity on acetylcholinesterase was significantly higher than that of the standard drug rivastigmine. The discussed compounds are also promising inhibitors of butyrylcholinesterase, as some of the prepared compounds inhibit butyrylcholinesterase better than the internal standards rivastigmine and galanthamine. The highest inhibitory activity (IC?? = 1.66 μmol/L) corresponds to the compound 1-(4-isopropylphenyl)-3-[(R)-1-(6-fluorobenzo[d]thiazol-2-yl)ethyl]imidazolidine-2,4,5-trione (3d). For all the studied compounds, the relationships between the lipophilicity and the chemical structure as well as their structure-activity relationships are discussed.     

Surface sticking and lateral diffusion of lipids in supported bilayers

The diffusion of fluorescently labeled lipids in supported bilayers is studied using two different methods: Z-scan fluorescence correlation spectroscopy (z-scan FCS) and two-focus fluorescence correlation spectroscopy (2f-FCS). It is found that the data can be fitted consistently only when taking into account partial sticking of the labeled lipids to the supporting glass surface. A kinetic reaction-diffusion model is developed and applied to the data. We find a very slow sticking rate which, however, when neglected, leads to strongly varying estimates of the free diffusion coefficient. The study reveals a strong sensitivity of FCS on even slight binding/unbinding kinetics of the labeled molecules, which has significance for related diffusion measurements in cellular lipid membranes.     

The elimination of magnetic susceptibility artifacts in the micro-image of liquid-solid interfaces: internal gradient modulation by the CPMG RF train

Distortions of magnetic resonance images near solid-liquid interface appear as the result of the restriction to spin self-diffusion in the proximity of impermeable boundary as well as of a susceptibility difference. The spectral analysis of spin echo enables to resolve, in a simple way, how various RF-gradient pulse sequences reduce the effect of the internal magnetic field induced by the susceptibility difference at interfaces. The 1D diffusion-weighted imaging of water in the narrow notch tested efficiency of some sequence. The notch was milled in a piece of Plexiglas. The method can be used to distinguish the susceptibility effect from the effects of applied gradients when investigating the transport of fluid through a porous structure.     

Magnetic resonance imaging of single rice kernels during cooking

The RARE imaging method was used to monitor the cooking of single rice kernels in real time and with high spatial resolution in three dimensions. The imaging sequence is optimized for rapid acquisition of signals with short relaxation times using centered out RARE. Short scan time and high spatial resolution are critical factors in the investigation of the cooking behavior of rice kernels since time and spatial averaging may lead to erroneous results. The results are confirming the general pattern of moisture ingress that has been suspected from previous (more limited) studies. Water uptake as determined by analysis of the MRI time series recorded during cooking compares well with gravimetric studies. This allows using these real-time MRI data for developing and validating models that describe the effect of kernel microstructure on its cooking behavior.     

Preparation and characterisation of ribonuclease monolithic bioreactor

In gene therapy and DNA vaccination, RNA removal from DNA preparations is vital and is typically achieved by the addition of ribonuclease into the sample. Removal of ribonuclease from DNA samples requires an additional purification step. An alternative is the implementation of immobilized ribonuclease. In our work, ribonuclease was covalently coupled onto the surface of methacrylate monoliths via epoxy or imidazole carbamate groups. Various immobilization conditions were tested by changing immobilization pH. Ribonuclease immobilized on the monolith via imidazole carbamate groups at pH 9 was found to be six times more active than the ribonuclease immobilized on the monolith via epoxy groups. Under optimal immobilization conditions the Michaelis-Menten constant, Km, for cytidine-2,3-cyclic monophosphate, and turnover number, k3 were 0.52 mM and 4.6s(-1), respectively, and mirrored properties of free enzyme. Enzyme reactor was found to efficiently eliminate RNA contaminants from DNA samples. It was active for several weeks of operation and processed 300 column volumes of sample. Required residence time to eliminate RNA was estimated to be around 0.5 min enabling flow rates above 1 column volume per min.     

Determination of nitrate esters in water samples Comparison of efficiency of solid-phase extraction and solid-phase microextraction

This paper deals with comparison of efficiency of extraction techniques (solid-phase extraction, SPE and solid-phase microextraction, SPME) used for extraction of nitrate esters (ethyleneglycoldinitrate, EGDN and nitroglycerin, NG), representing the first step of the method of quantitative determination of trace concentrations of nitrate esters in water samples. EGDN and NG are subsequently determined by means of high-performance liquid chromatography with ultraviolet detection (HPLC-UV). Optimization of SPE and SPME conditions was carried out using model water samples. Seven SPE cartridges were tested and the conditions were optimized (type of sorbent, type and volume of solvent to be used as eluent). For both nitrate esters the limit of detection (LOD) and the limit of quantification (LOQ) obtained using SPE/HPLC-UV were 0.23 microg mL(-1) and 0.70 microg mL(-1), respectively. Optimization of SPME conditions: type of SPME fibre (four fibres were tested), type and time of sorption/desorption, temperature of sorption. PDMS/DVB (polydimethylsiloxane/divinylbenzene) fibre coating proved to be suitable for extraction of EGDN and NG. For this fibre the LOD and the LOQ for both nitrate esters were 0.16 microg mL(-1) and 0.50 microg mL(-1), respectively. Optimized methods SPE/HPLC-UV and SPME/HPLC-UV were then used for quantitative determination of nitrate esters content in real water samples from the production of EGDN and NG.     

Electrochemical determination of Ag-ions in environment waters and their action on plant embryos

We utilized liquid chromatography coupled with electrochemical detector (HPLC-ED) for analyzing of silver ions. The optimization of basic chromatographic parameters has been done. The detection limit (3 S/N) obtained were 20 nmol/dm(3). Influence of different interferences (anions and cations) on current response of silver ions has been described. Moreover, we used HPLC-ED to analyze waters of different purity including photographic emulsion, which naturally contained silver ions. We found out that content of silver ions in the emulsion was 1.57 x 0.03 mmol/dm(3). Moreover, we investigated influence of silver ions on early somatic embryos of Blue Spruce. We were interested in the issue how much silver ions can embryos uptake during four days long treatment. For this purpose, we used optimized HPLC-ED technique. The content increased with increasing treatment time and applied concentration. We also studied how silver ions can influence thiols content in the treated embryos. For these purposes we used adsorptive transfer stripping voltammetry in connection with differential pulse voltammetry--Brdicka reaction. It clearly follows from the obtained results that content of thiols increased with increasing treatment time and applied concentration.     

Facile synthesis of optically active imidazole derivatives

Five optically active imidazole derivatives have been synthesized via a facile 4-step reaction sequence starting from commercially available and inexpensive N-Cbz amino acids. While microwave assisted condensation was unsuccessful, the condensation of the corresponding alpha-bromoketones with formamidine acetate in liquid ammonia was revealed to be a useful method for the synthesis of such imidazole derivatives. The derivatives thus prepared are structurally-related to histamine.     

Effect of protein denaturation on void fraction in foam separation column

Foam fractionation is a cost-effective process that uses air to extract protein from a liquid (in this case “crude” dilute egg-albumin solution). This article deals with how the void fraction (fraction of air in the aerated solution) of foam is affected by heat denaturation of the protein. A 2-mm glass tube was used to sample the foam-liquid interface fluid in a 35-mm-diameter column in order to detect small changes in void fraction and foam production, which are not easily detected directly from the bulk foam. The main control variablein this study was the protein solution preheating time. As the preheating time increased, the initial void fraction in the column decreased. The initial void fraction of the undenatured solution ranged from about 0.73 to 0.80, and the void fraction for significant preheating times of 5 min ranged from approx 0.68 to 0.72. Furthermore, the period of foam production increased from 5 to 7 min for undenatured proteins in solution to as long 15 min for 5-min preheated solutions. Side-port sampling through a small capillary tube has the potential to be used as a rapid and inexpensive way to determine the level of protein denaturation by directly determining the void fraction and then estimating the effect of denaturation from a protein denaturation calibration curve of the void fraction.