We report one-step in situ laser-induced synthesis of the conductive copper microstructures doped with iron, zinc, nickel, and cobalt with highly developed surface area. It was observed that the ...presence of chlorides of the aforementioned metals in the solutions used in our experiments increases the deposition rate and the amount of copper in the resulting deposits; it also leads to the deposit miniaturization. The laser deposition from solutions containing cobalt (II) chloride of concentration more than 0.003 M results in fabrication of copper microelectrode with better electrochemical properties than those deposited from solutions containing chlorides of other metals of the same concentration. Moreover, copper microelectrode doped with cobalt has demonstrated good reproducibility and long-run stability as well as sensitivity and selectivity towards determination of hydrogen peroxide (limit of detection-0.2 μM) and d-glucose (limit of detection-2.2 μM). Thus, in this article we have shown the opportunity to manufacture two-phase microcomposite materials with good electrical conductivity and electrochemical characteristics using in situ laser-induced metal deposition technique. These materials might be quite useful in development of new perspective sensors for non-enzymatic detection of such important analytes as hydrogen peroxide and glucose.
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•We propose one-step laser-induced synthesis of bimetallic microcomposite sensors.•Doping with iron, zinc, nickel, and cobalt decreases the copper electrode size.•Doping with iron, zinc, nickel, and cobalt increases the copper deposition rate.•Copper doped with cobalt reveals the best electrochemical and sensor properties.
•Discusses the stages of development of questioned document analysis techniques.•The transformation of chromatographic methods is shown.•The prospects for the development of spectral methods are ...described.•Examples of successful work to multidimensional data processing area are given.
Dating an inscription on a sheet of paper by analyzing the dye is one of the most important and complex forensic tasks. To date, the task of analyzing the limitation of document details has not been fully resolved.
Currently, the main research trend in the field of dating is the use of various chromatography methods. They are based on the study of the evaporation dynamics of volatile ink components. Basically, such methods are used within 2 years of the stroke of the writing composition. In addition to traditional gas chromatography, researchers use all known separation methods to determine the age, including ion chromatography, high-performance liquid chromatography, thin-layer chromatography, and gas chromatography-mass spectrometry. The review analyzes the most authoritative European studies in this area and discusses the reasons behind the limitations of chromatographic methods. An alternative to chromatographic studies of volatile components are spectral methods for the analysis of dyes. The most interesting works carried out by the methods of mass spectrometry, microspectrophotometry, Raman spectroscopy, diffusion of luminescence in the near-infrared and visible regions, laser-induced breakdown spectroscopy, Fourier-transform infrared spectroscopy, etc. are described. Despite a number of successful works in this area, the desired result has also not yet been achieved in terms of the accuracy and reliability of the results. The advantages and disadvantages of the methods are analyzed. Modern researchers are beginning to actively use new methods of mathematical processing of digital signal arrays. Examples of the use of chemometric data processing, including principal component analysis, are presented.
Azobenzene/tetraethyl ammonium photochromic ligands (ATPLs) are photoactive compounds with a large variety of photopharmacological applications such as nociception control or vision restoration. ...Absorption band maximum and lifetime of the less stable isomer are important characteristics that determine the applicability of ATPLs. Substituents allow to adjust these characteristics in a range limited by the azobenzene/tetraethyl ammonium scaffold. The aim of the current study is to find the scope and limitations for the design of ATPLs with specific spectral and kinetic properties by introducing para substituents with different electronic effects. To perform this task we synthesized ATPLs with various electron acceptor and electron donor functional groups and studied their spectral and kinetic properties using flash photolysis and conventional spectroscopy techniques as well as quantum chemical modeling. As a result, we obtained diagrams that describe correlations between spectral and kinetic properties of ATPLs (absorption maxima of
and
isomers of ATPLs, the thermal lifetime of their
form) and both the electronic effect of substituents described by Hammett constants and structural parameters obtained from quantum chemical calculations. The provided results can be used for the design of ATPLs with properties that are optimal for photopharmacological applications.
The synthesis of conductive gold and copper-gold microstructures with high developed surface based on the method of laser-induced metal deposition from solution was developed. The topology and ...crystallization phase of these structures were observed by means of scanning electron microscopy and X-ray diffraction, respectively. The electrochemical properties of the synthesized materials were investigated using cyclic voltamperometry and amperometry. According to the obtained results, it was found out that copper-gold microstructures demonstrate a linear dependence of Faraday current vs. concentration from 0.025 to 5µM for D-glucose and from 0.025 to 10µM for hydrogen peroxide. In turn, gold deposit exhibits a linear dependence of Faraday current vs. concentration from 0.025 to 50µM for D-glucose and from 0.025 to 1µM for hydrogen peroxide. Moreover, the synthesized materials reveal low detection limits (0.025µM) with respect to the aforementioned analytes, which is quite promising for their potential application in design and fabrication of new non-enzymatic biosensors.
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•The method for synthesis of copper-gold and gold microelectrodes was proposed.•The produced conductive metal structures have highly developed surface area.•These structures reveal high selectivity towards D-glucose and hydrogen peroxide.•Copper-gold and gold electrodes exhibit rather good reproducibility and stability.
Rhodopsins are seven α-helical membrane proteins that are of great importance in chemistry, biology, and modern biotechnology. Any in silico study on rhodopsin properties and functioning requires a ...high-quality three-dimensional structure. Due to particular difficulties with obtaining membrane protein structures from the experiment, in silico prediction of the three-dimensional rhodopsin structure based only on its primary sequence is an especially important task. For the last few years, significant progress was made in the field of protein structure prediction, especially for methods based on comparative modeling. However, the majority of this progress was made for soluble proteins and further investigations are needed to achieve similar progress for membrane proteins. In this paper, we evaluate the performance of modern protein structure prediction methodologies (implemented in the Medeller, I-TASSER, and Rosetta packages) for their ability to predict rhodopsin structures. Three widely used methodologies were considered: two general methodologies that are commonly applied to soluble proteins and a methodology that uses constraints that are specific for membrane proteins. The test pool consisted of 36 target-template pairs with different sequence similarities that was constructed on the basis of 24 experimental rhodopsin structures taken from the RCSB database. As a result, we showed that all three considered methodologies allow obtaining rhodopsin structures with the quality that is close to the crystallographic one (root mean square deviation (RMSD) of the predicted structure from the corresponding X-ray structure up to 1.5 Å) if the target-template sequence identity is higher than 40%. Moreover, all considered methodologies provided structures of average quality (RMSD < 4.0 Å) if the target-template sequence identity is higher than 20%. Such structures can be subsequently used for further investigation of molecular mechanisms of protein functioning and for the development of modern protein-based biotechnologies.
Nanocomposite membranes have been actively developed in the last decade. The involvement of nanostructures can improve the permeability, selectivity, and anti-fouling properties of a membrane for ...improved filtration processes. In this work, we propose a novel type of ion-selective Glass/Au composite membrane based on porous glass (PG), which combines the advantages of porous media and promising selective properties. The latter are achieved by depositing gold nanoparticles into the membrane pores by the laser-induced liquid phase chemical deposition technique. Inside the pores, gold nanoparticles with an average diameter 25 nm were formed, which was confirmed by optical and microscopic studies. To study the transport and selective properties of the PG/Au composite membrane, the potentiometric method was applied. The uniform potential model was used to determine the surface charge from the experimental data. It was found that the formation of gold nanoparticles inside membrane pores leads to an increase in the surface charge from -2.75 mC/m
to -5.42 mC/m
. The methods proposed in this work allow the creation of a whole family of composite materials based on porous glasses. In this case, conceptually, the synthesis of these materials will differ only in the selection of initial precursors.
Ultrafast excited-state dynamics of CuCl42- in acetonitrile is studied by femtosecond broadband transient absorption spectroscopy following excitation of the complex into all ligand-field (LF or d-d) ...states and into the two ligand-to-metal charge transfer (LMCT) states corresponding to the most intense steady-state absorption bands. The LF excited states are found to be nonreactive. The lowest-lying 2E LF excited state has a lifetime less than 150 fs, and the lifetimes of the second (2B1) and the third (2A1) LF excited states are 1 and 5 ps, respectively. All three LF states decay directly into the ground 2B2 state. Such significant differences in excited-state decay time constants were rationalized computationally through time-dependent density functional theory (TD-DFT) computations. TD-DFT mapping of the relaxation pathway along the symmetric Cl-Cu-Cl umbrella bending vibration gives evidence for a conical intersection between the 2E excited state and the ground 2B2 state. The LMCT states decay within 200 fs with the primary deactivation mode consistent to be Cu-Cl stretch. A fraction of the CuCl42- complexes excited into the LMCT states undergoes ionic dissociation to form products that survive longer than 1 ns. The remaining fraction undergoes internal conversion, which can be viewed as back electron transfer, populating the lower vibrationally hot LF states. The LF states populated from the LMCT states exhibit the same lifetimes as the Franck-Condon LF states and likewise decay directly into the ground state.
This work is devoted to the extremely popular but poorly developed scientific and forensic problem of the estimation of the actual dates of inscriptions placed on paper and made by ballpoint pens. It ...is shown that the degradation of writing inks with time may be controlled via Raman spectroscopy and gas chromatography. The time intervals for the implementation of each of these methods were determined using the ratios of the Raman peak intensities as degradation characteristics rather than their absolute values. In turn, this eliminates the effect of the concentration of a dye. The mutual influence of the volatile components and dyes of writing inks was also investigated and the time interval within which such influence is critical was found. According to the obtained results, a new methodological scheme for determining the age of documents, which were created at least 40 months ago, was proposed.
In the current paper, in situ laser-induced synthesis of gas sensing microcomposites based on molybdenum and its oxides is discussed. The influence of pH of the solutions used for deposition and ...optical characteristics of a dielectric substrate on electrical conductivity and sensor properties of the synthesized microdeposits is also studied. It was shown that the phase distribution in the obtained materials is consistent with temperature level in the thermal zones of the laser beam focused on the surface of a dielectric substrate of different type. In turn, highly developed surface area of these microsensors is directly responsible for their high sensitivity, short response time, and low temperature of regeneration with respect to hydrogen sulfide and ammonia. Indeed, the highest sensitivity was observed for detection of small concentration (≤50 ppm) of hydrogen sulfide at temperatures of 300–350 °C, whereas at temperatures of 300 °C or less, the deposited molybdenum-containing microstructures are applicable for the ammonia sensing. Thus, this work demonstrates that the method of laser-induced metal deposition is a promising and perspective approach for fabrication of new effective standalone micro-sized gas sensors.
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The durability against light and aging dynamics of heteroatomic aromatic dyes and pigments containing nitrogen atoms used in writing inks was studied using Raman spectroscopy. The mechanisms of their ...thermal and photo-decomposition were proposed and the rates of these processes were determined. According to Raman spectroscopy, it was found that depending on the presence of one or another colorant, there are three main types (Type A, Type B and Type C) of blue dye inks used in ballpoint, gel and capillary pens which were studied in this work. Each type is characterized by a certain set of signals in Raman spectra. Time dependencies of Raman signal intensities for each type revealed the dynamics of the processes occurred with colorants included in the studied inks from the moment when they were printed on paper. Thus, the results obtained in this study can be used for the age estimation of the paper documents up to 15 years.
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•The Raman studies of natural and artificial ink aging process were performed.•The dye degradation model was proposed.•The age of the paper documents up to 15 years can be estimated.
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