Coupling order and conductivity. Liquid crystalline conjugated polymers

Acetylenic and diacetylenic liquid crystalline monomers have been prepared in order to obtain conjugated polymers with an orientational character. Unlike the polydiacetylene derivatives obtained and which do not exhibit any mesomorphic behaviour, a smectic phase, stable over a large temperature range, occurs in the case of all the polyacetylenes. This mesophase appears to be stabilized by an in situ polymerization of the monomers oriented in the nematic state. After iodine doping, a nematic phase appears in the polymer in addition to the smectic phase. AC complex conductivity measurements, realized over a large frequency range. are reported for some doped and undoped polyacetylenes. Preliminary results concern both non-oriented polymers and an undoped polymer in which the mesogenic groups have been oriented after polymerization.     

A new sensor architecture based on carbon Printex 6L to the electrochemical determination of ranitidine

A glassy carbon electrode (GCE) modified with carbon Printex 6L (Printex6L/GCE) as a novel sensor is proposed. A morphological study was carried out using scanning electron microscopy, and an electrochemical characterization of the proposed electrode was performed by cyclic voltammetry (CV) using [Fe(CN)₆]^4? as a redox probe. With the incorporation of the carbon Printex 6L film onto the GCE surface, the [Fe(CN)₆]^4? analytical signal was substantially increased and the difference between the oxidation and reduction potentials (ΔE _p) decreased, a characteristic of the electrocatalytic effect. Furthermore, the use of carbon Printex 6L film resulted in an 84 % increase in the oxidation current and a 123 % increase in the reduction current. Faster charge transfer was observed at the proposed electrode/electrolyte interface during CV when compared with GCE. The Printex6L/GCE was tested for ranitidine (RNT) sensing and showed a decrease in the working potential and an increase in the analytical signal, when compared with GCE, again demonstrating an electrocatalytic effect. Under optimized experimental conditions, the developed square-wave adsorptive anodic stripping voltammetry (SWAdASV) method presented an analytical curve that was linear in RNT concentration range from 1.98 × 10^?6 to 2.88 × 10^?5 mol L^?1 with a detection limit of 2.44 × 10^?7 mol L^?1. The developed Printex6L/GCE was successfully applied to the determination of RNT concentrations in human body fluid samples (urine and serum).     

Protocell Communication through the Eyes of Synthetic Organic Chemists

The bottom-up fabrication of synthetic cells (protocells) from molecules and materials, is a major challenge of modern chemistry. A significant breakthrough has been the engineering of protocells capable of chemical communication using bio-derived molecules and ex situ stabilised cell machineries. These, however, suffer from short shelf-lives, high costs, and require mild aqueous conditions. In this Concept Article we analyse the chemistry at the heart of protocell communication to highlight new opportunities for synthetic chemists in protocell engineering. Specifically, we (i) categorise the main bio-derived chemical communication machineries in enzyme cascades, DNA strand displacement, and gene-mediated communication; (ii) review the chemistries of these signal transduction machineries; and (iii) introduce new types of bio-inspired, fully synthetic artificial enzymes to replace their natural counterparts. Developing protocells that incorporate synthetic analogues of bio-derived signal transduction machineries will improve the robustness, stability, and versatility of protocells, and broaden their applications to highly strategic fields such as photocatalysis and fine chemicals production.     

Prediction of Cassava Starch Edible Film Properties by Chemometric Analysis of Infrared Spectra

Cassava starch has been shown to make transparent and colorless flexible films without any previous chemical treatment. The functional properties of edible films are influenced by starch properties, including chain conformation, molecular bonding, crystallinity, and water content. Fourier‐transform infrared (FTIR) spectroscopy in combination with attenuated total reflectance (ATR) has been applied for the elucidation of the structure and conformation of carbohydrates. This technique associated with chemometric data processing could indicate the relationship between the structural parameters and the functional properties of cassava starch–based edible films. Successful prediction of the functional properties values of the starch–based films was achieved by partial least squares regression data. The results showed that presence of the hydroxyl group on carbon 6 of the cyclic part of glucose is directly correlated with the functional properties of cassava starch films.     

Synthesis,characterization, spectroscopy and thermal analysis of rare earth picrate complexes with <Emphasis Type="Italic">L</Emphasis>-leucine

Rare earth picrate complexes with L-leucine (Leu) were synthesized and characterized. Elemental analysis (CHN), EDTA titrations and thermogravimetric data suggest a general formula RE(pic)₃2Leu⋅5H₂O (RE=La–Lu, Y and pic=picrate). IR spectra indicate the presence of water and suggest that L-leucine is coordinated to the central ion through the nitrogen of the aminogroup. The absorption spectrum of the solid Nd compound indicates that the metal-ligand bonds show a weak covalent character. Emission spectra and biexponential behavior of the luminescence decay of the Eu compound suggest the existence of polymeric species. Thermal analysis results indicate that all the compounds present a similar behavior, with five major thermal decomposition steps. The final products are rare earth oxides. A slow heating rate is necessary to observe all decomposition steps.     

A molecular dynamics study of human endostatin and its synthetic fragments with antiangiogenic properties

Human endostatin is one of the better characterized endogenous angiogenesis inhibitors, and its ability to modulate vascularization of tumours could be of great therapeutic interest. These properties are not exclusive to the full-length protein, but are shared by some of its synthetic fragments. A number of research groups have partitioned human endostatin in different peptides and have investigated their activity, in order to collect a body of experimental data which could be important in shedding new light on their structure-activity relationships. It was also reported that a small active fragment can become inactive when contained in a larger fragment, revealing an apparent discrepancy in the experimental results. Very few studies have been devoted to the computational analysis of these systems and to the rationalization of their properties using molecular modelling. Through molecular dynamics simulations of human endostatin and of four synthetic fragments, we have been able to rationalize the experimental findings. In particular, we have identified a pattern consisting of six amino acids, namely R-R(G)-A-D-R-A, which appears to be an active epitope if it is properly exposed to the solvent. Interestingly, this pattern can be already present in sequential order in the primary structure, or it can be generated by the spatial approach of two groups of residues, far apart in the primary structure, as an effect of the peptide folding. Comparing the structural features and the time evolution of all the simulated peptides we provide a coherent explanation of their activity or inactivity.     

A low-cost automated flow analyzer based on low temperature co-fired ceramic and LED photometer for ascorbic acid determination

An automated flow analyzer based on low temperature co-fired ceramic (LTCC), a solid-phase reactor (SPR) and a low-cost photometer was designed for ascorbic acid (AA) determination in pharmaceutical formulations. It consists of a peristaltic pump, three-way solenoid valves, SPR to chemically convert Cu(II) into Cu(I), and a LTCC device for mixing the liberated copper with bathocuproine and detection. The flow cell in the LTCC employed an ultrabright LED — photodiode photometer. The analyzer successfully determined AA in pharmaceutical formulations. The analytical curve from 8.5×10^?6 to 7.0×10^?4 M gave a detection limit of 7.0×10^?7 M and a RSD of 2.1% for a 2.0×10^?4 M AA solution (n = 10). A high sampling frequency of 102 h^?1 and low reagent and sample consumption (150 µL) resulted.      

Variational transition state theory rate constants and H/D kinetic isotope effects for CH3 + CH3OCOH reactions

The rate constants and H/D kinetic isotope effect for hydrogen abstraction reactions involving isotopomers of methyl formate by methyl radical are computed employing methods of the variational transition state theory (VTST) with multidimensional tunneling corrections. The energy paths were built with a dual-level method using the moller plesset second-order perturbation theory (MP2) method as the low-level and complete basis set (CBS) extrapolation as the high-level energy method. Benchmark calculations with the CBS_D-T approach give an enthalpy of reaction at 0 K for R1 (−4.5 kcal/mol) and R2 (−4.2 kcal/mol) which are in good agreement with the experiment, that is, −4.0 and − 4.8 kcal/mol. For the reactional paths involving the isotopomers CH₃ + CH₃OCOH → CH₄ + CH₃OCO and CH₃ + CH₃OCOD → CH₃D + CH₃OCO, the value of k^H/k^D (T = 455 K) using the canonical VTST/small-curvature tunneling approximation method is 6.7 in close agreement with experimental value (6.2). © 2019 Wiley Periodicals, Inc.     

A new efficient route to imidazo[4,5-c]pyrazol-5-ones

The synthesis of imidazo[4,5-c]pyrazol-5-ones ( 6 ) is reported. 5-Amino-4-ethoxycarbonylaminopyra-zoles 3a-g when heated at 200° for 2 hours afford 6a-g. In a similar manner imidazo[4,5-c]pyrazol-5-one ( 6a ) is readily obtained from 4-amino-5-ethoxycarbonylaminopyrazole ( 5a ).