Inhibitory effect of safranal and crocin,two principle compounds of <Emphasis Type="Italic">Crocus sativus</Emphasis>, on fibrillation of lysozyme

A key feature in more than twenty amyloid-related diseases is the aggregation of intra-and/or extracellular misfolded proteins as amyloid fibrils. Therefore, preventing or reversing amyloid aggregation by using of small molecules is considered as useful approaches to the treatment of these diseases. We have evaluated the ability of safranal and crocin, to inhibit amyloid self-assembly of hen egg white lysozyme (HEWL), as an in vitro model system. Structural properties of HEWL in the presence of these compounds were investigated individually using thioflavin T, anilinonaphthalene-8-sulfonic acid fluorescence assays, far-UV circular dichroism and scanning electron microscopy as well as docking method. Our results showed that incubation of HEWL with either crocin or safranal at various concentrations leads a significant inhibition in the rate of amyloid formation. Docking analysis revealed crocin and safranal interact with the central hydrophobic region of lysozyme through van der Waals interaction. Hydroxyl group in crocin through hydrogen bonds connected to the several hydrophilic amino acids of lysozyme, while in safranal there are just one aldehyde group that through hydrogen bonds connected to aspartic acid in lysozyme. It can be concluded that both hydrophobic and hydrophilic groups contribute to lower lysozyme fibril accumulation.     

Metric and Complete Metric σ-Frames

A -frame is a lattice in which countable joins exist and binary meets distribute over countable joins. In this paper, the category MFrm, of metric -frames, is introduced, and it is shown to be equivalent to the category MLFrm _u, of metric Lindelöf frames.Finally, it is shown that the complete metric -frames are exactly the cozero parts of complete metric Lindelöf frames.     

Comparison between standard and counterpoise-corrected optimization using some hydrogen and halogen bonded systems

The effect of the counterpoise correction on the geometries, stabilization energies, and vibrational harmonic frequencies of some hydrogen- and halogen-bonded systems (B?=?CH₃CN,?HCN,?NH₃,?N₂,?CO,?H₂O,?H₂S,?PH₃;?HX?=?HF,?HCl,?HBr,?HCN,?HCF₃; XY?=?Br₂,?BrCl,?BrF,?Cl₂,?ClF,?F₂) has been analysed at the MP2 level of theory using the popular 6-311++G(d,p) basis set. The optimized B?···?H and B?···?X bond lengths increase with counterpoise (CP) correction. In some cases standard values and in other cases CP-corrected values are close to experimental data. The absolute values of complexation energies of CP-corrected structures are higher than standard by inclusion of BSSE correction. The effect of CP correction on intermolecular bond lengths and complexation energies of B?···?XY series are usually higher than B?···?HX. Also, this effect is higher for H₂S and PH₃ groups. The CP correction changes the vibrational harmonic frequencies by 0–100%. The changes are frequently lower than 20% for frequencies higher than 300?cm^?1.     

Intramolecular hydrogen bonding in chemoselective synthesized 2-substituted pyrrole stable phosphorus ylide: GIAO, AIM, and NBO approaches

The chemoselectivity of geometrically ylide compounds is often hard to assign from experimental techniques, particular system with intramolecular hydrogen bonding (IHB) are even more challenging. Herein, theoretical calculations were performed to investigate whether theoretical results would provide consistent evidence for the existence of IHB to confirm experimental data and to evaluate strength of the N–H···O IHB from geometrical synthesized 2-substituted pyrrole stable phosphorus ylide (dimethyl 2-(1H-pyrrol-2-yl)-3-(triphenylphosphoranylidene) butanedioate in a single chemoselective compound. Topological parameters at the bond critical points (BCP) of intramolecular hydrogen bonds from Bader’s atoms in molecules (AIM) theory and Winhold’s natural bond orbital (NBO) calculations were analyzed at the B3LYP/6-311++g** level in details. A series of gage-including atomic orbital chemical shift (GIAO c.s.) calculations at the HF and DFT levels of theory were carried out to assign the ¹H NMR chemical shifts. The best prediction of the experimental ¹H NMR values was obtained at the mPW1PW91 levels using the 6-31G** basis set. Theoretical results, in agreement with the experimental data, were confirmed the N–H···O IHB was caused the deshielding of the proton to lower field. The barriers in double bond and single bond rotation were theoretically estimated in detailed and the AIM and NPA approaches were confirmed the loss of charge of the hydrogen atom involving in intramolecular N–H···O hydrogen bonding. The geometrical and topological parameters from AIM and NBO analyses were indicated the medium N–H···O IHB.     

SILICA PHOSPHORIC ACID/NaNO2 AS A NOVEL HETEROGENEOUS SYSTEM FOR THE COUPLING OF THIOLS TO THEIR CORRESPONDING DISULFIDES

Silica phosphoric acid was prepared via reaction of silica chloride (I) and phosphoric acid. Thiols can be readily converted to their corresponding thionitrites with a combination of silica phosphoric acid (II), wet SiO ₂ , and sodium nitrite in dichloromethane at room temperature. Disulfides result from the homolytic cleavage of the sulfur–nitrogen bond of the unstable thionitrite and subsequent coupling of the resultant thiyl radicals.     

A Simple and Efficient Procedure for Synthesis of Optically Active 1,2,4‐Triazolo‐[3,4‐b]‐1,3,4‐Thiadiazole Derivatives Containing l‐Amino Acid Moieties

Some new and optically active 1,2,4‐triazolo thiadiazoles bearing N‐phthaloyl‐l ‐amino acids were synthesized by reaction of 4‐amino‐5‐(3‐ or 4‐)pyridyl‐3‐mercapto‐(4H)‐1,2,4‐triazoles with N‐phthaloyl‐l ‐amino acids in the presence of phosphorus oxychloride. All the newly synthesized compounds were confirmed by IR, ¹H NMR, ¹³C NMR and elemental analysis.     

Solid Phase Extraction and Simultaneous Spectrophotometric Determination of Trace Amounts of Copper and Iron Using Mixture of Ligands

 A novel sensitive and simple method for rapid and selective extraction, preconcentration and determination of iron (as its bathophenanthroline complex) and copper (as its neocuproine complex) using octadecyl silica cartridges and dual wavelength spectrophotometry is presented. The dual wavelength method (533 nm for the iron-bathophenanthroline and 454 nm for the copper-neocuproine as the analytical wavelength) is used to eliminate spectral interferences. Extraction efficiency and the influence of flow rates of sample solution and eluent, pH, amount of neocuproine, bathophenanthroline and hydroxylamine hydrochloride, type and least amount of eluent for elution of iron and copper complexes from cartridge, break-through volume and limit of detection are evaluated. The effects of various cationic and anionic interferences on percent recovery of iron and copper are also studied. Extraction efficiencies >95% are obtained by elution of cartridges with minimal amount of organic solvent. Iron and copper were determined in the range of 3–100 ng mL⁻¹. The limits of detection are 0.98 and 1.13 ng mL⁻¹ for iron and copper, respectively. The proposed method is applied successfully to the determination of both analytes in river, tap and well water samples. Author for correspondence. E-mail: yyamini@modares.ac.ir Received September 18, 2002; accepted December 12, 2002 Published online May 5, 2003     

A simple method for derivation of the rovibrational Hamiltonian: application to orthogonal radau coordinate systems as special cases

The molecular Hamiltonian of polyatomic molecules has been obtained. A general choice of internal coordinates depending on external parameters was considered. The rovibrational Hamiltonian for this set of coordinate system was derived in general terms as a function of the external parameters a and b. This procedure is also applicable to various kinds of internal coordinates in a straightforward way. The rovibrational Hamiltonian of triatomic molecules is considered as an application of this general formulation. In addition, orthogonal Radau coordinates are considered as cases of this new approach     

Optimized ultrasound‐assisted extraction procedure for the analysis of opium alkaloids in papaver plants by cyclodextrin‐modified capillary electrophoresis

This study investigated the use of ultrasound‐assisted extraction to improve the extraction efficiency of morphine, codeine and thebaine from the papaver plants. Extraction conditions such as type of solvent, temperature, duration, frequency and power level of ultrasonic were optimized and the influences of different parameters on resolution of alkaloids in CE were studied. The optimized condition for CE separation includes a sodium phosphate buffer (100 mM, pH 3.0) containing 5 mM α‐CD. The optimized extraction conditions for ultrasound‐assisted extraction was an extraction time of 1 h, an ultrasonic frequency of 60 kHz with water–methanol (80:20) at 40°C as the extraction solvent. The LOD for alkaloids was found to be 0.1 μg/mL at a signal‐to‐noise ratio of 3:1. The RSDs for peak areas were in the range of 1.4–4.4%. The amounts of opium alkaloids (mg/100 g dried sample) in four Iranian papaver plants were found to be in the range of 7.8–8.7 (morphine), 5.5–9.5 (codeine) and 1.4–10.4 (thebaine). It should be emphasized that no cleanup of the filtered extract was required; hence, direct determination after extraction drastically simplifies the analytical process.     

In vitro selection and characterization of deoxyribonucleic acid aptamers for digoxin

The low therapeutic index of digoxin necessitates careful monitoring of its serum levels. Most of digoxin immunoassays suffer from interferences with digoxin-like immunoreactive substances. Since aptamers have been shown to be highly specific for their targets, the aim of this study was to develop DNA aptamers for this widely used cardiac glycoside. Digoxin was coated onto the surface of streptavidin magnetic beads. DNA aptamers against digoxin were designed using Systematic Evolution of Ligands by Exponential enrichment method (SELEX) by 11 iterative rounds of incubation of digoxin-coated streptavidin magnetic beads with synthetic DNA library, DNA elution, electrophoresis and PCR amplification. The PCR product was cloned and sequenced. Binding affinity was determined using digoxin–BSA conjugate, coated onto ELISA plate. Inhibitory effect of anti-digoxin aptamer was conducted using isolated guinea-pig atrium. Three aptamers (D1, D2 and D3) were identified. Binding studies of fluorescein-labeled truncated (without primer binding region) D1 and D2 and full length D1 anti-digoxin aptamers were performed and their corresponding dissociation constants values were 8.2 × 10⁻⁹, 44.0 × 10⁻⁹ and 17.8 × 10⁻⁹ M, respectively. This is comparable to what other workers have obtained for interaction of monoclonal antibodies raised against digoxin. There was little difference in binding affinity between full length and truncated anti-digoxin D1 aptamer. D1 anti-digoxin aptamer also inhibited the effects of digoxin on the isolated guinea-pig atrium. D1 anti-digoxin aptamer distinguished between digoxin and ouabain in both tissue study and binding experiments. Our finding indicated that D1 anti-digoxin aptamer can selectively bind to digoxin. Further studies might show its suitability for use in digoxin assays and as a therapeutic agent in life-threatening digoxin toxicity.