Double-walled carbon nanotube based carbon paste electrode as xanthine biosensor

We describe the first usage of a double walled carbon nanotube (DWCNT) modified carbon paste electrode as biosensor transducer. Xanthine was chosen as a substrate for evaluation of the electrode performance. Proper amount of DWCNT and xanthine oxidase enzyme were mixed with proper amount of graphite and mineral oil for attaining the xanthine biosensor. Results were compared with previous work that includes multi-walled carbon nanotube and single-wall carbon nanotube based carbon paste electrode xanthine biosensors. A linearity was obtained in the concentration range between 2–50 μM xanthine under the response time of 150 s with the equation of y?=?0.0441x + 0.2013 and RSD value of 4.20%. This system was applied to the determination of xanthine in canned tuna fish samples and recovery was calculated as 99.20%?±?0.07.     

Ab initio studies of crystal field effects. VII. Structure of 2,3-diketopiperazine using a 13-molecule cluster,a calculation involving 1092 basis functions

The structure of 2,3-diketopiperazine in a crystal phase (P2₁/c), modeled by a 13-molecule cluster surrounded by point charges, was completely optimized using standard gradient procedures. The (ab initio) MIA approach was used to perform the SCF step, which using a 4-21G basis set, involves calculations using 1092 basis functions. Results are in very good agreement with experimental (X-ray) data, in contrast to a previous study in which a model was used consisting of only point charges. © 1993 John Wiley & Sons, Inc.     

Thermal analysis of binary liquid crystalline mixtures

Two series of binary mixtures composed of bent shaped and rod like molecules are reported. The first star shaped bent core molecules were synthesized and used as a component of binary mixtures. The chiral rod like compounds having commensurable length with the arms of the bent core compounds have been chosen for these mixtures. The resulted compositions show various thermotropic liquid crystalline phases that are characteristic to both types of liquid crystalline materials. In case of mixing the rod like molecules to the bent core compound the B2, B7 and induced B1 phases have been observed. While using the star-shaped bent core and chiral rod like compounds in mixture, the paraelectric smectic A, ferroelectric smectic C* and orthogonal hexatic smectic B phases were preferred. The appearing mesophases were investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction methods.     

Centri‐Voltammetric Folic Acid Detection

The need for practical detection of folic acid (FA) has been increased day by day. For this reason in this work, a two steps electroanalytical technique, centri‐voltammetry was utilized for FA detection for the first time. In order to get rid of the slow electrode kinetics of FA oxidation, the working electrode was modified with graphene‐Pt hibrid nanomaterial. Also for increasing the sensitivity, 1‐Chloro‐2‐[2‐(2‐methoxyethoxy) ethoxy]ethane (TEG?Cl) and 1,2‐di{2‐[2‐(2‐methoxyethoxy)ethoxy] ethoxy}‐4‐nitrobenzene (4NC?NO₂) was used as a carrier material. After the characterization of graphene‐Pt hybrid nanomaterial, experimental parameters like, 4NC?NO₂ amount, adsorption time, centri‐voltammetric parameters like centrifuge time and speed were optimized. After that, analytical characteristics such as linear range, relative standard deviation (R.S.D), limit of detection (LOD) and limit of quantification (LOQ) values were found. In this manner, linear range was obtained for FA between 1.0 μM–1000 μM with the equations of (R²=0.9977). R.S.D value was calculated for 0.83 mM FA (n=3) as 1.86 % while LOD and LOQ values were found as 1.00 μM and 3.34 μM respectively. After the examination of interference effect of substances like ascorbic acid and uric acid, established centri‐voltammetric technique was enforced for FA detection in pharmateutical tablets. As a result, the recovery value was calculated as 96.4 %.     

Structural study of α-lactose monohydrate subjected to microwave irradiation

The aim of this work was to investigate the influence of different levels of microwave irradiation on the structure and particle size characteristics of α-lactose monohydrate. The structural study of the samples was carried out by XRD, the presence of lactose polymorphs in the test samples was determined by DSC and the particle size distribution was measured by laser diffraction. The samples subjected to microwave irradiation retained their original X-ray patterns. No significant differences in thermal transition characteristics and particle size were observed. Hence, neither the occurrence of crystalline-amorphous transition resulted by microwave irradiation nor the presence of lactose polymorphs in the test samples can be assumed. The unmodified properties can be attributed to the fact that the water of crystallization is very difficult to remove from the crystal structure and is not free to move during microwave treatment, which results in stability to microwaves.     

Novel quantitative electrophoretic analysis of endotoxins on microchips

A novel microchip electrophoresis method was developed and applied for sensitive detection and quantitative analysis of endotoxins extracted from Gram-negative bacteria. The method provides a fast and quantitative differentiation of smooth and rough endotoxins based on the solubilization and complexation of the lipopolysaccharides with dodecylsulfate, and then with a fluorescent dye. The migration of the complexes was followed by LIF detection. The novel method is able to replace the SDS-PAGE with the advantage of high speed and better sensitivity, and by avoiding the laborious gel-preparation and silver staining.     

Inhibitory Effect of Multivalent Rhamnobiosides on Recombinant Horseshoe Crab Plasma Lectin Interactions with Pseudomonas aeruginosa PAO1

To evaluate the molecular interaction of recombinant horseshoe crab plasma lectin (rHPL) with Pseudomonas aeruginosa PAO1, multivalent rhamnobioside derivatives were designed. Eight rhamnoclusters with three or four α(1–3)‐rhamnobiosides attached to different central cores, such as methyl gallate, pentaerythritol, and N‐Boc Tris, through either an ethylene glycol or a tetraethylene glycol linker, were assembled in two consecutive azide–alkyne cycloaddition click reactions. The synthetic method embraced the preparation of two α(1–3)‐rhamnobiosides with different linker arms and their conjugation, in stoichiometric or substoichiometric amounts, to propargyl ether‐functionalized tri‐ or tetravalent scaffolds. A divalent derivative and two self‐assembling rhamnobiosides were also prepared. The different architectures and valences of the rhamnoclusters provided an opportunity to evaluate the impact of topology and valency on the binding properties toward rHPL. Inhibitory ELISA data showed that all covalently linked rhamnoclusters could inhibit P. aeruginosa PAO1 recognition activity of rHPL with high efficacy. Trivalent rhamnobiosides showed a stronger inhibitory effect on P. aeruginosa PAO1 binding, and the more flexible clusters on a pentaerythritol or a Tris core were superior to the less flexible methyl gallate‐based clusters. Interestingly, the length of the linker arms had a very low impact on the binding ability of the rhamnoclusters. Herein, the two trivalent derivatives on an N‐Boc protected Tris central core were the best inhibitors. The self‐assembling amphiphilic rhamnobioside derivatives were found to display no multivalent effect.     

Comparison of resolution methods for racemic 8-(phenylsulfinyl)-1-naphthoic acid

Despite of the fact that resolution is an extremely important process in the pharmaceutical and agrochemical industries, the development of the separation of enantiomers is still based on trial-and-error experiments. In order to compare the different procedures, the resolution of 8-(phenylsulfinyl)-1-naphthoic acid 1 was carried out by chiral organic bases using heat facilitated diastereomeric crystallization, enantioselective liquid–liquid extraction and chiroselective transport. The results give valuable information about the interactions in the racemate/resolving agent/solvent system, which helps with the understanding and development of resolution processes. Diastereomeric crystallization with brucine as a resolving agent afforded enantiomerically pure (?)-1.