Influence of substituent on spectroscopic and acid-base properties of anthraquinone derivatives

A series of 1,4-disubstituted aminoanthraquinones has been prepared from 1,4 ditosyloksyanthraquinone. The potentiometric and UV-spectrophotometric method have been used to study the acid-base properties of obtained compounds. The absorption spectra revealed the presence of vibroelectronic band in visible region for compounds containing two tertiary nitrogen groups. It indicates the separation of vibronic states in the molecule. Determined pKa values in acetonitrile used as a solvent indicate the influence of substitution of amino group on basicity of the anthraquinone moiety

The electrochemical and spectroscopic characterization of 1,4 and 1,8-aminoanthraquinone derivatives

The acid base properties of 1,4 and 1,8-anthraquinone derivatives were determined in methanol and acetonitrile by pH-spectroscopic measurements. The examined compounds was also characterized by electrochemically using cyclic voltammetry in DMSO solutions

Pyrazino[2,3-b]indolizine-10-carbonitrile

In the crystal structure of the title compound, C11H6N4, neighbouring mol­ecules are linked into inversion dimers through pairs of weak C—H⋯N hydrogen bonds, forming an R 2 2(10) ring motif. The dimers forming this motif are further linked by π–π inter­actions. With respective average deviations from planarity of 0.004 (2) and 0.004 (1) Å, the pyrazino[2,3-β]indolizine and cyano fragment are oriented at 0.8 (1)° to each other. The mean planes of the pyrazino[2,3-b]indolizine skeleton either lie parallel or are inclined at an angle of 28.7 (2)° in the crystal

Good Choice of Electrode Material as the Key to Creating Electrochemical Sensors—Characteristics of Carbon Materials and Transparent Conductive Oxides (TCO)

The search for new electrode materials has become one of the goals of modern electrochemistry. Obtaining electrodes with optimal properties gives a product with a wide application potential, both in analytics and various industries. The aim of this study was to select, from among the presented electrode materials (carbon and oxide), the one whose parameters will be optimal in the context of using them to create sensors. Electrochemical impedance spectroscopy and cyclic voltammetry techniques were used to determine the electrochemical properties of the materials. On the other hand, properties such as hydrophilicity/hydrophobicity and their topological structure were determined using contact angle measurements and confocal microscopy, respectively. Based on the research carried out on a wide group of electrode materials, it was found that transparent conductive oxides of the FTO (fluorine doped tin oxide) type exhibit optimal electrochemical parameters and offer great modification possibilities. These electrodes are characterized by a wide range of work and high chemical stability. In addition, the presence of a transparent oxide layer allows for the preservation of valuable optoelectronic properties. An important feature is also the high sensitivity of these electrodes compared to other tested materials. The combination of these properties made FTO electrodes selected for further research

Controlled Silanization of Transparent Conductive Oxides as a Precursor of Molecular Recognition Systems

The search for new molecular recognition systems has become the goal of modern electrochemistry. Creating a matrix in which properties can be controlled to obtain a desired analytical signal is an essential part of creating such tools. The aim of this work was to modify the surface of electrodes based on transparent conductive oxides with the use of selected alkoxysilanes (3-aminopropyltrimethoxysilane, trimethoxy(propyl)silane, and trimethoxy(octyl)silane). Electrochemical impedance spectroscopy and cyclic voltammetry techniques, as well as contact angle measurements, were used to determine the properties of the obtained layers. Here, we prove that not only was the structure of alkoxysilanes taken into account but also the conditions of the modification process—reaction conditions (time and temperature), double alkoxysilane modification, and mono- and binary component modification. Our results enabled the identification of the parameters that are important to ensure the effectiveness of the modification process. Moreover, we confirmed that the selection of the correct alkoxysilane allows the surface properties of the electrode material to be controlled and, consequently, the charge transfer process at the electrode/solution interface, hence enabling the creation of selective molecular recognition systems

In pursuit of ideal chromoionofore

In pursuit for new chromoionophores, it is important to know their functioning, which depends primarily on theirstructure. The structures of chromoionophores were discussed, highlighting the elements that have a significant impact on their operation, i.e. the binding and visualization of metal ion binding. Chromoionophores are composed of a binding and signaling group. Valinomycin, salinomycin and synthetic crown ethers are presented as ionophores. Using the anthraquinone as an example, the function of the chromophore system was defined and discussed. It has been shown that an element connecting the main components of the chromoionophore may also play an important role. The action of chromoionophores is directly related to their acid-base properties, which can influence both ion binding and the visualization of interactions. The examples of aminoanthraquinone derivatives show the influence of the number of groups, position in the anthraquinone ring and the order of amino groups on the basicity of chromoionophores

Acidity Constants of Boronic Acids as Simply as Possible: Experimental, Correlations, and Prediction

The wide use of boronic compounds, especially boronic acids and benzoxaboroles, in virtually all fields of chemistry is related to their specific properties. The most important of them are the ability to form cyclic esters with diols and the complexation of anions. In both cases, the equilibrium of the reaction depends mainly on the acidity of the compounds, although other factors must also be taken into account. Quantification of the acidity (pKa value) is a fundamental factor considered when designing new compounds of practical importance. The aim of the current work was to collect available values of the acidity constants of monosubstituted phenylboronic acids, critically evaluate these data, and supplement the database with data for missing compounds. Measurements were made using various methods, as a result of which a fast and reliable method for determining the pKa of boronic compounds was selected. For an extensive database of monosubstituted phenylboronic acids, their correlation with their Brønsted analogues—namely carboxylic acids—was examined. Compounds with ortho substituents do not show any correlation, which is due to the different natures of both types of acids. Nonetheless, both meta- and para-substituted compounds show excellent correlation. From a practical point of view, acidity constants are best determined from the Hammett equation. Computational approaches for determining acidity constants were also analyzed. In general, the reported calculated values are not compatible with experimental ones, providing comparable results only for selected groups of compounds

Structure and Properties of 1,3-Phenylenediboronic Acid: Combined Experimental and Theoretical Investigations

The structure and properties of 1,3-phenylenediboronic acid are reported. Molecular and crystal structures were determined by single crystal as well as by powder X-ray diffraction methods. Acidity constant, thermal behavior, and NMR characterization of the title compound were also investigated. In addition to the experimental data, calculations of rotational barrier and intermolecular interaction energies were performed. The compound reveals a two-step acid⁻base equilibrium with different pKa values. TGA and DSC measurements show a typical dehydration reaction with formation of boroxine. In crystals, hydrogen-bonded dimers with syn-anti conformation of hydroxyl groups form large numbers of ribbon motifs. The 2D potential energy surface scan of rotation of two boronic groups with respect to phenyl ring reveals that the rotation barrier is close to 37 kJ⋅mol−1, which is higher than the double value for the rotation of the boronic group in phenylboronic acid. This effect was ascribed to intermolecular interaction with C⁻H hydrogen atom located between boronic groups. Furthermore, the molecules in the crystal lattice adopt a less stable molecular conformation most likely resulting from intermolecular forces. These were further investigated by periodic DFT calculations supported by an estimation of dimer interaction energy, and also by topological analysis of electron density in the framework of AIM theory