Measuring the Electrode Kinetics of Vitamin B2 at a Constant Time Window of a Square Wave Voltammetric Experiment

The electrode kinetics of vitamin B2 was measured at a constant scan rate of a square‐wave (SW) voltammetric experiment by recently introduced method based on alteration of the height (amplitude) of the SW potential pulses. The electrode reaction mechanism was analyzed in the light of the simplified model considering two‐electron one step surface electrode mechanism, as well as to more appropriate EE surface reaction pathway consisting of two successive one‐electron quasireversible reactions. Theoretical analysis indicated that the evolution of the voltammetric response under variation of the SW amplitude enables estimation of the rate determining step of the EE mechanism.     

Substituent effects on the electrophilic activity of nitroarenes in reactions with carbanions

The effect on electrophilic activity of substituents located para, ortho, and meta to the nitro group of nitrobenzenes was determined by using vicarious nucleophilic substitution of hydrogen (VNS) with the carbanion of chloromethyl phenyl sulfone (1) as the model process. Values for the relative activities of substituted nitroarenes are given relative to nitrobenzene, which was taken as the standard. This process was chosen as a model reaction because it meets key criteria, such as the wide range of substituents that can be present on the nitrobenzene ring, a low sensitivity to steric hindrance, and in particular the possibility of ensuring conditions in which the overall relative rates of reaction in competitive experiments are equal to the relative rates of nucleophilic addition. The values of relative rates of addition, which were taken to be a measure of electrophilic activity, were determined by competitive experiments in which pairs of nitroarenes competed for the VNS reaction with carbanion of 1. A comprehensive set of data for effects of substituents on the electrophilic activity of nitroarenes is presented for the first time.     

Cationic agents for DNA compaction

Fluorescence microscopy was used to investigate the conformational changes of individual T4 DNA molecules induced by different compacting agents, namely the cationic surfactants, cetyltrimethylammonium bromide (CTAB) and chloride (CTAC), iron(III), lysozyme, and protamine sulfate. A protocol for establishing size estimates is suggested to obtain reproducible results. Observations show that in the presence of lysozyme and protamine sulfate, DNA molecules exhibit a conformational change from an elongated coil structure to compact globules, usually interpreted as a first-order transition. The maximum degree of compaction that is attained when iron(III) or CTAB (CTAC) are used as compacting agents is considerably smaller, and intermediate structures (less elongated coils) are visible even for high concentrations of these agents. Dynamic light scattering experiments were carried out, for some of the systems, to assess the reliability of size estimates from fluorescence microscopy.     

Bond- and site-selective loss of H- from pyrimidine bases

Electron attachment to gas phase thymine and uracil leads to H- loss within a broad and structured feature in the energy range between about 5 and 12 eV consisting of 4 overlapping resonances. By using thymine and uracil methylated at the N1 and N3 positions, respectively, and taking into account recent results from partly deuterated thymine, we find that by tuning the electron energy, H- loss turns out to be not only bond selective, i.e., (C-H) versus (N-H) bonds, but also site selective (N1 versus N3 site). Such a bond and site selectivity by energy has not been observed before in dissociative electron attachment. Implications for the mechanism of strand breaks observed in plasmid DNA are considered.     

Proliferative and antioxidant activity of Symphytum officinale root extract

The root of Symphytum officinale L. is commonly used in folk medicine to promote the wound healing, reduce the inflammation and in the treatment of broken bones. The objective of our investigation was to analyse the extract from S. officinale in term of its antioxidant activity and the effect on cell viability and proliferation of human skin fibroblast (HSF). Moreover, the quantification of main phenolics and allantoin was conducted using HPLC–DAD method. Five compounds were found: rosmarinic, p-hydroxybenzoic, caffeic, chlorogenic and p-coumaric acid. DPPH, FRAP and TPC assay showed the high antioxidant activity of the extract. MTT test proved the stimulatory effect on cell metabolism and viability of HSF cells. Moreover, no changes in cytoskeleton structure and cells shape were observed. The obtained results indicate that non-toxic extract from S. officinale root has strong antioxidant potential and a beneficial effect on human skin fibroblasts.     

Mesogenic behaviour of isomeric bent-core 6-oxoverdazyls: 1,3-vrs 1,5-substitution pattern

Two series of isomeric bent-core derivatives of 6-oxoverdazyl, with alkyl and partially fluorinated alkyl chains, were investigated by thermo-optical, powder X-ray diffraction and electron paramagnetic resonance methods in the pure state and binary mixtures. The results revealed that the substitution position of the arms at the verdazyl ring (1,5 vs. 1,3) strongly affects mesogenic behaviour. Steric (torsion and bending angles) and dipolar factors in both isomers are considered.     

Crystallographic and computational studies of a new organoarsenate compound: o‐anisidinium dihydroarsenate

The crystal structure and the results of theoretical calculations for the new organoarsenate salt o‐anisidinium dihydroarsenate (systematic name: 2‐methoxyanilinium dihydrogen arsenate), C₇H₁₀NO⁺·H₂AsO₄^?, are reported. The salt, crystallizing in the triclinic space group P, was synthesized using a solution method and was characterized by single‐crystal X‐ray diffraction analysis. It possesses a layered supramolecular architecture in the crystal. The intermolecular interactions were studied using Hirshfeld surface analysis which confirmed that hydrogen bonds and H…H contacts play dominant roles in the crystal structure of the investigated system. An analysis of the electronic structure and molecular modelling using charge distribution confirms the good electrophilic reactivity of the title compound.     

Reactions of carbanions derived from α-substituted-methyl tolyl sulfones with quinone methides as Michael acceptors

Nucleophilic addition of α-halo-4-tolylsulfonyl methyl anions to quinone methides and subsequent reactions were studied. Three kinds of consecutive reaction products were isolated, depending on the substrate structures and reaction conditions. Two of them were identified as rearrangement products and one as the vicarious nucleophilic substitution (VNS) product. An unexpected 1,2-migration of the tosyl group was observed. The mechanism of the reactions is briefly discussed.     

Effect of Different Surface Treatment Methods on Bond Strength of Dental Ceramics to Dental Hard Tissues: A Systematic Review

For long-term successful use of ceramic materials in dental procedures, it is necessary to ensure reliable bonding of restorations to dental substrates. This can be achieved by the application of a proper luting cement and through additional surface conditioning. The present systematic review summarizes the most up-to-date evidence on the use of different surface modification methods to enhance the bond strength of dental ceramics to the hard tissues of the teeth. The authors of the review searched the Web of Science, Scopus, and MEDLINE databases to identify relevant articles published between 1 January 2010 and 1 January 2020. A total of 4892 records were identified, and after screening, the full text of 159 articles was evaluated, which finally resulted in the inclusion of 19 studies. The available reports were found to be heterogeneous in terms of materials and methodology, and therefore, only within-studies comparison was performed instead of comparison between studies. A statistically significant difference in the bond strength between the samples treated with different methods of surface conditioning, or between conditioned and nonconditioned samples, was revealed by most of the studies. Predominantly, the studies showed that a combination of mechanical and chemical methods was the most effective way of enhancing bond strength. Artificial aging and luting cement were also identified as the factors significantly influencing bond strength.