Effects of Heavy Iodine Atoms and π-Expanded Conjugation on Charge Transfer Dynamics in Carboxylic Acid BODIPY Derivatives as Triplet Photosensitizers

Borondipyrromethene (BODIPY) chromophores are composed of a functional-COOH group at meso position with or without a biphenyl ring, and their compounds with heavy iodine atoms at −2, −6 positions of the BODIPY indacene core were synthesized. The photophysical properties of the compounds were studied with steady-state absorption and fluorescence measurements. It was observed that the absorption band is significantly red-shifted, and fluorescence signals are quenched in the presence of iodine atoms. In addition to that, it was indicated that the biphenyl ring does not affect the spectral shifting in the absorption as well as fluorescence spectra. In an attempt to investigate the effect of π-expanded biphenyl moieties and heavy iodine atoms on charge transfer dynamics, femtosecond transient absorption spectroscopy measurements were carried out in the environment of the tetrahydrofuran (THF) solution. Based on the performed ultrafast pump-probe spectroscopy, BODIPY compounds with iodine atoms lead to intersystem crossing (ISC) and ISC rates were determined as 150 ps and 180 ps for iodine BODIPY compounds with and without π-expanded biphenyl moieties, respectively. According to the theoretical results, the charge transfer in the investigated compounds mostly appears to be intrinsic local excitations, corresponding to high photoluminescence efficiency. These experimental findings are useful for the design and study of the fundamental photochemistry of organic triplet photosensitizers.     

Effect of the presence of strong and weak electrolytes on the existence of uniaxial and biaxial nematic phases in lyotropic mixtures

The lyotropic mixture of potassium laurate/decanol/water presenting only the uniaxial nematic calamitic phase was doped with one strong (potassium chloride, KCl) and 11 weak electrolytes with phenyl-rings (DL-mandelic acid, benzoic acid, DL-phenyllactic acid, phenylacetic acid, phenol and phenylmethanol) and with cyclohexyl-ring (RS-hexahydromandelic acid, cyclohexanecarboxylic acid, cyclohexaneacetic acid, cyclohexanol and cyclohexylmethanol), separately. We also chose two nonpolar dopant molecules, benzene and cyclohexane, for the comparison of them with weak electrolytes, since they are located in the hydrocarbon core of the micelle. The nematic phase sequences, in particular the presence of the biaxial nematic phase, were investigated as a function of the dopant molar concentration and temperature. The laser conoscopy and small-angle X-ray scattering techniques were used to characterise the different nematic phases. Weak electrolytes having –COOH group as polar part were found to be very effective in stabilising the three nematic phases (two uniaxial and a biaxial). Guest molecules with only the –OH group did not show any effect on the stabilisation of other nematic phases. The experimental results are interpreted considering the screening effect of the hydrophilic parts of the dopants on the repulsion between the polar heads of the main amphiphilic molecules at micelle surfaces. This process favours the increase of the more flat micellar surfaces of micelles, which triggers the orientational fluctuations responsible for the biaxial and discotic nematic phases.     

Investigation of electrochemical behavior and development of a validated adsorptive stripping square wave voltammetry method for 3-nitrotyrosine in human plasma and cerebrospinal fluid

An adsorptive stripping square wave voltammetric (AdSqW) method was developed for the determination of 3-nitrotyrosine (3-NT), a biomarker of in vivo oxidative damage in Alzheimer, ALS, Parkinson’s, cardiovascular diseases and cancer, in some biological fluids. Voltammetric measurements were performed in 0.30 M (pH 9.0) phosphate solution as supporting electrolyte, a reduction peak was observed at–0.487 V (vs. Ag/AgCl–3 M KCl) with a hanging mercury drop electrode by square wave voltammetry. Cyclic voltammetric measurements showed that the current was adsorption-controlled. LOD and LOQ values were as 0.25 and 1.5 nM, respectively, for the AdSqW method. 3-NT was determined in plasma and cerebrospinal fluid using AdSqW method, which allowed to work at low concentrations. Recovery value was measured as 96.3 ± 2.3%.     

Synthesis of positively charged silver nanoparticles via photoreduction of AgNO3 in branched polyethyleneimine/HEPES solutions

Branched polyethyleneimine (BPEI) and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) were used collaboratively to reduce silver nitrate under UV irradiation for the synthesis of positively charged silver nanoparticles. The effects of molar ratio of the ingredients and the molecular weight of BPEI on the particle size and distribution were investigated. The mechanism for the reduction of Ag+ ions in the BPEI/HEPES mixtures entails oxidative cleavage of BPEI chains that results in the formation of positively charged BPEI fragments enriched with amide groups as well as in the production of formaldehyde, which serves as a reducing agent for Ag+ ions. The resultant silver nanoparticles are positively charged due to protonation of surface amino groups. Importantly, these positively charged Ag nanoparticles demonstrate superior SERS activity over negatively charged citrate reduced Ag nanoparticles for the detection of thiocyanate and perchlorate ions; therefore, they are promising candidates for sensing and detection of a variety of negatively charged analytes in aqueous solutions using surface-enhanced Raman spectroscopy (SERS).     

Axially chiral 2-arylimino-3-aryl-thiazolidine-4-one derivatives: enantiomeric separation and determination of racemization barriers by chiral HPLC

Axially chiral 2-arylimino-3-aryl-thiazolidine-4-ones have been synthesized as racemic mixtures, and each mixture with the exception of 2-(o-chlorophenyl)imino-3-(o-chlorophenyl)-thiazolidine-4-one has been converted to the corresponding 5-benzylidene-2-arylimino-3-aryl-thiazolidine-4-one racemates by reaction with benzaldehyde. The thermally interconvertible enantiomers of each compound have been obtained by enantioselective HPLC separation on columns Chiralpak AD-H and Chiralcel OD-H, and the barriers to racemization have been found to be 98.1-114.1 kJ/mol. The barriers determined were compared to those of structurally related compounds to provide evidence for the stereochemistry of the aryl imino bond.     

Probabilistic evolution theory for the solution of explicit autonomous ordinary differential equations: squarified telescope matrices

Probabilistic evolution theory (PREVTH) is used for the solution of initial value problems of first order explicit autonomous ordinary differential equation sets with second degree multinomial right hand side functions. It is an approximation method based on Kronecker power series: a rewriting of multivariate Taylor series using matrices having certain flexible parameters. Kronecker power series have matrices which are called telescope matrices: \(n \times n^{j+1}\) matrices where j is the index of summation. The additive terms of each telescope matrix is formed through Kronecker product from both sides by Kronecker powers of identity matrices. Recently, squarification is proposed in order to avoid the growing of the matrices in size at each additive term of the series. This paper explains the squarification procedure: the procedure used in order to avoid Kronecker multiplications within PREVTH so that the sizes of the matrices do not grow and so that the amount of necessary computation is reduced. The recursion between squarified matrices is also given. As a numerical application, the solution of a Hénon–Heiles system is provided.     

A lysozyme and magnetic bead based method of separating intact bacteria

As a response to environmental stress, bacterial cells can enter a physiological state called viable but noncultivable (VBNC). In this state, bacteria fail to grow on routine bacteriological media. Consequently, standard methods of contamination detection based on bacteria cultivation fail. Although they are not growing, the cells are still alive and are able to reactivate their metabolism. The VBNC state and low bacterial densities are big challenges for cultivation-based pathogen detection in drinking water and the food industry, for example. In this context, a new molecular-biological separation method for bacteria using point-mutated lysozymes immobilised on magnetic beads for separating bacteria is described. The immobilised mutated lysozymes on magnetic beads serve as bait for the specific capture of bacteria from complex matrices or water due to their remaining affinity for bacterial cell wall components. Beads with bacteria can be separated using magnetic racks. To avoid bacterial cell lysis by the lysozymes, the protein was mutated at amino acid position 35, leading to the exchange of the catalytic glutamate for alanine (LysE35A) and glutamine (LysE35Q). As proved by turbidity assay with reference bacteria, the muramidase activity was knocked out. The mutated constructs were expressed by the yeast Pichia pastoris and secreted into expression medium. Protein enrichment and purification were carried out by SO₃-functionalised nanoscale cationic exchanger particles. For a proof of principle, the proteins were biotinylated and immobilised on streptavidin-functionalised, fluorescence dye-labelled magnetic beads. These constructs were used for the successful capture of Syto9-marked Microccocus luteus cells from cell suspension, as visualised by fluorescence microscopy, which confirmed the success of the strategy.     

Optimal timing of regime switching in optimal growth models: A Sobolev space approach

This paper analyses the optimal timing of switching between alternative and consecutive regimes in optimal growth models. We derive the appropriate necessary conditions for such problems by means of standard techniques from the calculus of variations and some basic properties of Sobolev spaces.     

LC/MS method using cloud point extraction for the determination of permitted and illegal food colors in liquid, semiliquid, and solid food matrixes: single-laboratory validation

A cloud point extraction method is reported using LC/MS for the determination of regulated water-soluble food colors (Allura Red, Sunset Yellow, erythrosine, and tartrazine) and banned fat-soluble synthetic azo dyes (Sudan I, II, III, and IV; Red B; 7B; Black B; Red G; Metanil Yellow; and Rhodamine B). The extraction of all 14 colors was carried out with cloud point extraction using the nonionic surfactant Triton X 114. Optimized conditions for cloud point extraction were 3% Triton X 114 (w/v), 0.1 M ammonium acetate, and heating at 50 degrees C for 30 min. This approach proved effective in giving quantitative recoveries from a diverse range of food matrixes, and optimized LC gave baseline chromatographic separation for all colors including Sudan IV and Red B. Single-laboratory validation was performed with spiking into liquid matrixes (wine and homemade wine), semiliquid matrixes (sauce and homemade paprika paste), and solid matrixes (spice and homemade chili powder) using the respective blank matrixes for matrix-matched calibration. The LOQ values for water-soluble colors were in the range of 15-150 mg/kg, and for the fat-soluble colors, 0.1-1.5 mg/kg. The mean recovery values were in the range of 69.6-116.0% (except Allura Red and Sunset Yellow in wine, for which recoveries were lower). The mean RSDs for colors were in the range of 4.0-14.8%. A small survey was conducted of samples of confectionery products, dried fruits, wines, bitter sodas, juices, sauces, pastes, and spices, which demonstrated the applicability of the method to a diverse selection of real food samples. Allura Red was detected in strawberry jelly and Sunset Yellow in artificial saffron.     

Development and Evaluation of Europium-Based Quantitative Lateral Flow Immunoassay for the Chronic Kidney Disease Marker Cystatin-C

Journal of Fluorescence - This study aimed to establish a Europium label time-resolved fluorescence immunoassay (TRFIA) to detect the chronic kidney disease (CKD) biomarker Cystatin-C. An Europium...