Laser-Induced Reactions of 4-Aminobenzenthiol Species Adsorbed on Ag, Au, and Cu Plasmonic Structures Followed by SERS Spectroscopy. The Role of Substrate and Excitation Energy - Surface-Complex Photochemistry and Plasmonic Catalysis.

This study focuses on investigating the laser-induced reactions of various surface complexes of 4-aminobenzenethiol on Ag, Au, and Cu surfaces. By utilizing different excitation wavelengths, the distinct behavior of the molecule species on the plasmonic substrates was observed. Density functional theory (DFT) calculations were employed to establish the significant role of chemical enhancement mechanisms in determining the observed behavior. The interaction between 4-aminobenzenethiol (4-ABT) molecules and plasmonic surfaces led to the formation of surface complexes with absorption bands red-shifted into the visible and near-infrared regions. Photochemical transformations were induced by excitation wavelengths from these regions, with the nature of the transformations varying based on the excitation wavelength and the plasmonic metal. Resonance with the electronic absorption transitions of these complexes amplifies surface-enhanced Raman scattering (SERS), enabling the detailed examination of ongoing processes. A kinetic study on the Ag surface revealed processes governed by both first- and second-order kinetics, attributed to the dimerization process and transformation processes of individual molecules interacting with photons or plasmons. The behavior of the molecules was found to be primarily determined by the position and variability of the band between 1170 and 1190 cm-1, with the former corresponding to molecules in the monomer state and the latter to dimerized molecules. Notably, laser-induced dimerization occurred most rapidly on the Cu surface, followed by Ag, and least on Au. These findings highlight the influence of plasmonic surfaces on molecular behavior and provide insights into the potential applications of laser-induced reactions for surface analysis and manipulation.

Nano-FTIR spectroscopy of surface confluent polydopamine films - What is the role of deposition time and substrate material?

Polydopamine (PDA) is a widely used anchoring layer for multiple purposes. While simple to prepare, PDA is characterized by high chemical and topological diversity, which can limit its versatility. Unraveling the formation mechanism and physicochemical properties of continuous confluent layer and adherent nanoparticles on the nanoscale is crucial to further extend the prospective applications of PDA. Utilizing nano-FTIR spectroscopy, we investigate layers of PDA on three different substrates (silicon/silicon dioxide, nitrogen-doped titanium oxide, and gold substrates) at varying times of deposition (ToD). We observed a good correlation between the nano-FTIR and macroscopic FTIR spectra that reflected the changes in the relative abundance of PDA and polymerization intermediates as ToD increased. To gain analytical power, we utilized the principal component analysis (PCA) and extracted additional information from the resulting loadings spectral curves and data distribution in the score plots. We revealed a higher variability of the spectra of ultrathin surface confluent layers compared to the adherent nanoparticles. While the spectra of nanoparticles showed no apparent dependency on either ToD or the substrate material, the spectra of layers were highly affected by the increasing ToD and exhibited a rise in the absorption of PDA. Concomitantly, the spectra of layers grouped according to the substrate material at the lowest ToD point to the fact that the substrate material affects the PDA's initial physicochemical structure. The observed separation gradually diminished with the increasing ToD as the PDA physicochemical structure became less influenced by the substrate material.

Chemoselective Electrochemical Cleavage of Sulfonimides as a Direct Way to Sulfonamides.

A new method for selective cleavage of sulfonimides into sulfonamides in high yields using a simple electrochemical approach is shown. As revealed by the electrochemical study, the aromatic sulfonimides can be selectively cleaved by electrolysis of the starting compound at a given potential (only -0.9 V vs SCE for the nosyl group). The high chemoselectivity was confirmed by preparative electrolysis, and the results were supported with DFT calculations of a set of substances bearing different sulfonimide functions. Moreover, various experimental setups together with other attempts to simplify the procedure were tested. Finally, the removal of the p-nosyl group from the corresponding sulfonimides proceeds smoothly regardless of the number of nosyl groups and the overall shape of the complex molecule. Thus, the method is interesting for use in the field of multifunctional molecules such as calix[n]arenes.

An Insight into Anion Extraction by Amphiphiles: Hydrophobic Microenvironments as a Requirement for the Extractant Selectivity.

Coupling of electron-deficient urea units with aliphatic chains gives rise to amphiphilic compounds that bind to phosphate and benzoate anions in the hydrogen bonding competitive solvent (DMSO) with KAss = 6 580 M-1 and KAss = 4 100 M-1, respectively. The anchoring of these receptor moieties to the dendritic support does not result in a loss of anion binding and enables new applications. Due to the formation of a microenvironment in the dendrimer, the high selectivity of the prepared compound toward benzoate is maintained even in the presence of aqueous media during extraction experiments. In the presence of binding sites at 5 mM concentration, the amount of benzoate corresponding to the full binding site occupancy is transferred into the chloroform phase from its 10 mM aqueous solution. A thorough investigation of the extraction behavior of the dendrimer reported here, supported by a series of molecular dynamics simulations, provides new insight into the fundamental principles of extraction of inorganic anions by amphiphiles.

Infrared imaging of surface confluent polydopamine (PDA) films at the nanoscale.

Polydopamine (PDA) is one of the most commonly used materials for the preparation of protective adhesive layers for biomedical and tribological applications. Despite its widespread use, the way in which the polymer binds to the substrate is yet to be fully understood. At the nanometre level, the spatial arrangement of individual molecules and the initial growth of PDA layers are expected to be influenced by the utilized substrate material and PDA deposition time. To investigate these hypotheses, we have prepared PDA layers with various times of deposition on surfaces of gold and oxygen-terminated materials (silicon/silicon dioxide and nitrogen-doped titanium oxide). The prepared samples were subsequently analysed using a scattering-type scanning near-field optical microscope utilizing four irradiation energies in the mid-infrared region to detect the chemical contrast originating from vibrational modes of selected chemical moieties. It was found that the polymerization process leads to a formation of a surface confluent PDA layer and deposition of PDA nanoaggregates. The differences in the optical contrast observed at irradiation energies corresponding to the vibrations of indole units of PDA and quinoid groups of polymerization intermediates indicated a slightly different composition of the nanoaggregates and the surrounding confluent layer.

An Electrochemical Sensor for Detection of Neuroblastoma Markers: Complexation Studies as a Tool for the Selection of a Suitable Receptor for Electrode Coating.

Homovanillate (HVA) and vanilmandelate (VMA) are recognized markers of diseases, including neuroblastoma. However, their detection in urine represents a challenging task due to the complexity of the matrix. Here, a design, synthesis and thorough investigation of polymerizable urea-based receptors interacting with HVA and VMA are reported. The selection of receptor with the best anion recognition properties for electrode coating is based on 1 H-NMR and UV-Vis complexation studies. The sensor is prepared by electropolymerization with progress monitoring by cyclic voltammetry. The deposited layer is characterized by IR and scanning electron microscopy. The obtained sensor shows an electrochemical impedance spectroscopy response to VMA with linear range 9.9×10-6 to 1.2×10-3  M and LOD of 3.4×10-6  M. The sensor selectivity was demonstrated by the determination of VMA level in the presence of 16 µM HVA and in artificial urine with and without phosphates, with standard deviations of 0.11, 0.17 and 0.09, respectively.

Application of reverse engineering in the field of pharmaceutical tablets using Raman mapping and chemometrics.

Raman micro-spectroscopy technique offers a combination of relatively high spatial resolution with identification of components or mixtures of components in different sample areas, e.g. on the surface or the cross-section of a sample. This study is focused on the analysis of the tablets from pharmaceutical development with different technological parameters: (1) the manufacturing technology, (2) the particle size of the input API (active pharmaceutical ingredient) and (3) the quantitative composition of the individual excipients. These three mentioned parameters represent the most frequently solved problems in the field of reverse engineering in pharmacy. The investigation aims to distinguish tablets with the above-described technological parameters with limited subjective steps by Raman microscopy. Furthermore, non-subjective methods of Raman data analysis using advanced statistical analysis have been proposed, namely Principal Component Analysis, Soft Independent Modelling of Class Analogy and Linear Discriminant Analysis. The methods successfully distinguished and identified even very small differences in the analysed tablets within our study and provided objective statistic evaluation of Raman maps. The information on component and particle size distribution including their small differences, which is the critical parameter in the development of the original and generic products, was obtained due to combination of these methods. Even though each of these chemometric methods evaluates the data set from a different perspective, their mutual application on the problem of Raman maps evaluation confirmed and specified results on level that would be unattainable with the use of only one them.

Comparison of Four RTK Receivers Operating in the Static and Dynamic Modes Using Measurement Robotic Arm.

While the existing research provides a wealth of information about the static properties of RTK receivers, less is known about their dynamic properties, although it is clear that the vast majority of field operations take place when the machine is moving. A new method using a MRA for the evaluation of RTK receivers in movement with a precise circular reference trajectory (r = 3 m) was proposed. This reference method was developed with the greatest possible emphasis on the positional, time and repeatable accuracy of ground truth. Four phases of the measurement scenario (static, acceleration, uniform movement and deceleration) were used in order to compare four different types of RTK receiver horizontal operation accuracy over three measurement days. The worst result of one of the receivers was measured at SSR = 13.767% in dynamic movement. Since the same "low-cost" receiver without an INS unit had SSR = 98.14% in previous static measurements, so it can be assumed that the motion had a very significant effect on the dynamic properties of this receiver. On the other hand, the best "high-end" receiver with an INS unit had SSR = 96.938% during the dynamic testing scenarios. The median values of the deviations were always better during uniform movements than during acceleration or braking. In general, the positioning accuracy was worse in the dynamic mode than in the static one for all the receivers. Error indicators (RMSerr and Me) were found several times higher in the dynamic mode than in the static one. These facts should be considered in the future development of modern agricultural machinery and technology.

Optimization of Electrochemical Visualization of Latent Fingerprints with Poly(Neutral Red) on Brass Surfaces.

This study is focused on the visualization of latent fingerprints on brass surfaces using the method of electrochemical deposition of a polymer film based on poly(neutral red) (PNR). The experiment included (i) optimization of conditions of electrochemical deposition of PNR on brass surfaces, (ii) ATR-FTIR spectroscopic characterization of PNR-modified substrates, and (iii) identification of characteristic details on visualized fingerprints on fired brass cartridges. For electrochemical visualization, it is necessary to keep in mind both kind and "story" substrates. Experimental findings showed that electrochemical visualization carried out on brass plates is a step forward before known findings described in the literature and gives simultaneously a new approach for criminalists in the fight against crime.

Unraveling the influence of substrate on the growth rate, morphology and covalent structure of surface adherent polydopamine films.

Polydopamine (PDA), also known as synthetic melanin, is widely used as a biomimetic anchoring layer for the modification of various solid substrates. PDA is utilized for a wide range of biomedical, sensing and tribological applications, even though the polymer's precise covalent structure has not been completely revealed yet. Even more, it is not evident to which extent the chemical nature of the substrate, on which the layer is formed, influences and predetermines the covalent structure of resulting PDA. In this contribution, we have studied the growth of PDA using various surface-sensitive techniques such as spectroscopic ellipsometry, atomic force microscopy and X-ray photoelectron spectroscopy. We supplemented grazing angle attenuated total reflection FTIR spectroscopy with multivariate statistical analysis to further gain analytical power. We have particularly focused on the effects of polymerization time and substrate on the PDA structure. We found notable differences in the chemical composition of PDA formed on gold and on surfaces terminated with oxides/reactive hydroxides such as silicon and N-dopped-TiO2 in the early stages of the layer formation. At the later stages of layer formation, a merely unified chemical structure was observed independently on the type of substrate.

Methodology of deconvolution of total solute retention on chemically modified stationary phases to structure specific contributions of bound compounds.

The total solute retention by a chemically modified stationary phase (CMSP) has been shown several times to be a potential tool for studying the binding abilities of the bound compound. In this article, we present a methodology for the deconvolution of the total retention into structure-specific contributions. Three complementary silica-based CMSPs were prepared: 1) non-modified silica, 2) silica modified by syn-bis-Tröger's base (a molecular tweezer) and 3) silica modified by anti-bis-Tröger's base (a non-tweezer molecule). These were characterized by elemental analysis and Raman spectroscopy, and used to assemble liquid chromatography (LC) columns. The total retention factors were estimated for electron-deficient nitro- and cyano-derivatives of benzene in both normal and reverse elution modes. The total retention factor was considered to be the sum of structure-specific retention factors, each related to the affinity (the binding constant) of a specific structure (the binding site), and its content in the modified silica, as defined for weak-affinity chromatography (WAC). The obtained structure-specific contributions are in line with the binding studies of ligands in solution. They reveal details of the retention mechanism, suggesting a more suitable attachment of ligands, and expose the shortcomings of evaluations based solely on the total retentions.

Immobilization of green-synthesized silver nanoparticles for micro- and nano-spectroscopic applications: What is the role of used short amino- and thio-linkers and immobilization procedure on the SERS spectra?

Immobilization of nanoparticles (NPs) is a technique suitable for the preparation of large-scale substrates for surface-enhanced vibrational spectroscopy including micro- and nano-spectroscopic applications. The developed immobilization method provides the enhancing properties of the roughened substrate surface to be maintained for techniques like surface-enhanced Raman scattering (SERS) spectroscopy, however, at the same time the morphology is not limiting for related near-field (scanning probe) techniques. The study is focused on the comparison of different immobilization procedures of Ag nanoparticles and finding the relationship between preparation procedures leading to convenient surface morphology and the quality of the observed signal of the model analyte (riboflavin) using SERS. Amino-linker (3-aminopropyl)trimethoxysilane (APTMS) and four thio-linkers (cysteine, 3-mercaptopropanoic acid, 2-mercaptoethanol, and 2,2'-oxydiethanthiol) using five immobilization procedures at three different temperatures (23 °C, 40 °C, and 70 °C) were compared. Surface morphology was monitored by scanning electron microscopy and atomic force microscopy. The SERS spectra of riboflavin were evaluated in terms of the intensity and the resolution of individual bands. The spectral dataset was inspected by multivariate statistical methods - principal component analysis and discriminant analysis. The evaluation of spectra and statistical models show the influence of the used linker and AgNPs immobilization procedure on the spectral output. APTMS linker is less suitable; much more appropriate are thio-linkers deposited on an evaporated Au layer on a glass slide. The best spectral parameters were obtained for 2,2'-oxydiethanthiol and 23 °C.

Role of TiO2 Nanoparticles and UV Irradiation in the Enhancement of SERS Spectra To Improve Levamisole and Cocaine Detection on Au Substrates.

The original goal of this study was the employment of surface-enhanced Raman spectroscopy (SERS) for the analysis of real cocaine samples (containing adulterants) on composite Au-TiO2 nanomaterials to achieve low detection limits suitable for the analysis of illicit drugs and controlled substances and to exploit the photodegradation activity of TiO2 to recycle the SERS substrate for repeated analyses. The photodegradation (self-cleaning) effects of the Au-TiO2 composite nanomaterials by ultraviolet (UV) radiation are known. These effects were investigated on large-area SERS substrates immersed in the TiO2 nanoparticle aqueous suspension. The cocaine samples were measured on electrochemically gold-plated platinum targets. Surprisingly, the intensity of SERS spectra of the pure cocaine did not change after immersion in a suspension of TiO2 under UV irradiation. However, for some real cocaine samples, the overall intensity of the SERS spectra was even higher after the treatment by TiO2 and UV radiation as compared to the usual Au substrate. This unexpected signal amplification (valuable for illicit drug detection) was found to be caused mainly by the contained levamisole, which is used as a medical drug and is one of the frequent adulterants of cocaine. Both the sole effect of TiO2 on the levamisole spectrum intensity and the role of UV irradiation were inspected separately. Finally, an investigation of both the TiO2 and UV radiation treatments was performed, demonstrating (i) the necessity of both factors for selective SERS signal enhancement of the adulterant and (ii) the revision of general anticipation of the role of TiO2 in SERS systems.

New designed special cells for Raman mapping of the disintegration process of pharmaceutical tablets.

The goal of this study was the methodological development of Raman microscopy application for advanced and reliable monitoring of pharmaceutical tablets disintegration in aqueous media. First step of the development involved new design and testing of static, flow cell and tablet holders. On-line Raman mapping method enables observation of the tested tablet interphase changes, particularly the changes of tablet composition during interaction of the solid-state drug form with disintegration medium. Furthermore, the quantitative information of tablet components (% w/w) from Raman maps was calculated. Second part of this study performs off-line Raman mapping, which was focused on the mapping of disintegrated tablet residua. Time-dependent Raman chemical maps provide an understanding of the role of several synergic processes, e.g. solvation, solvent penetration, both active pharmaceutical ingredient and excipient dissolution etc., which occur simultaneously on the surface of dissolving tablet. Raman data of disintegration process were evaluated by a chemometric method - Principal Component Analysis (PCA).

The use of infrared spectroscopic techniques to characterize nanomaterials and nanostructures: A review.

Recent advances in nanotechnology have opened a lot of new possibilities for nanomaterials application in wide variety of industrial, pharmaceutical, medicinal and environmental applications. This review aims to description of various Fourier Transform Infrared (FTIR)-based spectroscopic techniques suitable to characterize (i) different types of nanomaterials and (ii) various macroscopic samples at their nanoscale. In the introductory section, nanomaterials are classified according to their crucial properties, i.e. chemical composition, size and surface morphology. Application of traditional FTIR techniques, such as Attenuated Total Reflection (ATR), Diffuse Reflection (DRIFT) and infrared micro (spectro)scopy, for characterization of nanomaterials and nanostructures is compared with novel optical nanoscopic techniques derived from scanning probe microscopy which enable to overcome the diffraction limit and to characterize nanomaterials at molecular scale.

SERS study of riboflavin on green-synthesized silver nanoparticles prepared by reduction using different flavonoids: What is the role of flavonoid used?

Spectroscopy of surface-enhanced Raman scattering (SERS) is nowadays widely used in the field of bio-science and medicine. These applications require new enhancing substrates with special properties. They should be non-toxic, environmentally friendly and (bio-) compatible with examined samples. Flavonoids are natural antioxidants with many positive effects on human health. Simultaneously, they can be used as reducing agent in preparation procedure of plasmonic enhancing substrate for SERS spectroscopy. The best amplifiers of Raman vibrational spectroscopic signal are generally silver nanoparticles (AgNPs). In this study, several flavonoids (forming a logical set) were used as reducing agent in AgNPs preparation procedures. Reactivity of 10 structurally arranged flavonoids (namely flavone, chrysin, apigenin, luteolin, tricetin, 3-hydroxyflavone, galangin, kaempferol, quercetin and myricetin) was compared and SERS-activity of prepared AgNPs was tested using model analyte riboflavin. Riboflavin was detected down to concentration 10-9mol/l.

Immobilized strychnine as a new chiral stationary phase for HPLC.

A new ion-exchanger type chiral stationary phase for high-performance liquid chromatography was prepared. The synthetic protocol is based on derivatization of silica with (3-iodopropyl)trimethoxysilane in the first step followed by immobilization of strychnine via quaternization of nitrogen atom of the alkaloid strychnine. The synthesized chiral stationary phase was chromatographically characterized. The main effort was headed towards the evaluation of the enantioselectivity of the novel sorbent. For that purpose a set of suitable chiral probes, specifically, binaphthyl derivatives, was employed. The influence of methanol content, concentration of aqueous ammonium acetate buffer, and its pH on retention factors, separation selectivity, and resolution of the atropoisomers of the mentioned chiral solutes was studied in detail. It was demonstrated that the new chiral stationary phase was capable to separate atropoisomers of four out of seven testing compounds. Despite the strong influence of the above mentioned variables on retention, their impact on selectivity and resolution was rather moderate. Concerning retention mechanism, it seems that electrostatic interaction between the positively charged quaternary nitrogen of the chiral stationary phase and anionic solute participates significantly in the retention process.

Study of plasmonic nanoparticles interactions with skin layers by vibrational spectroscopy.

The healing effects of silver and gold nanoparticles (AgNPs, AuNPs) are already known from ancient times. In addition considering to their antibacterial and anti-inflammatory effects speculations are being lead with respect to these nanoparticles (NPs) also about enhancement of skin penetration properties. In this work the interactions of pig skin (PS) layers and ointments with additions of AgNPs or AuNPs prepared by standard procedures and also by "green" synthesis in a different weight proportion by vibrational spectroscopy were studied. Spectra of untreated skin and skin treated by pure ointment were measured, as well as by ointment modified by vitamins without addition of NPs or with different proportion of NPs. Kinetics of interactions of modified ointments with skin was monitored during two hours with a five-minutes interval between each two consecutive measurements. The obtained series of spectra were analyzed by multivariate statistical methods namely Partial Least Squares (PLS), Principal Component Analysis (PCA) and Soft Independent Modelling of Class Analogy (SIMCA) which revealed observation of spectral changes in time-dependent spectra and variations of the peak intensity ratios. The study showed that the effects of quantity and type of NPs on skin penetration characteristics are evident.

The Eighth Central European Conference "Chemistry towards Biology": Snapshot.

The Eighth Central European Conference "Chemistry towards Biology" was held in Brno, Czech Republic, on August 28-September 1, 2016 to bring together experts in biology, chemistry and design of bioactive compounds; promote the exchange of scientific results, methods and ideas; and encourage cooperation between researchers from all over the world. The topics of the conference covered "Chemistry towards Biology", meaning that the event welcomed chemists working on biology-related problems, biologists using chemical methods, and students and other researchers of the respective areas that fall within the common scope of chemistry and biology. The authors of this manuscript are plenary speakers and other participants of the symposium and members of their research teams. The following summary highlights the major points/topics of the meeting.

Synthesis and characterization of a helicene-based imidazolium salt and its application in organic molecular electronics.

Herein we demonstrate the synthesis of a helicene-based imidazolium salt. The salt was prepared by starting from racemic 2-methyl[6]helicene, which undergoes radical bromination to yield 2-(bromomethyl)[6]helicene. Subsequent treatment with 1-butylimidazole leads to the corresponding salt 1-butyl-3-(2-methyl[6]helicenyl)-imidazolium bromide. The prepared salt was subsequently characterized by using NMR spectroscopy and X-ray analysis, various optical spectrometric techniques, and computational chemistry tools. Finally, the imidazolium salt was immobilized onto a SiO2 substrate as a crystalline or amorphous deposit. The deposited layers were used for the development of organic molecular semiconductor devices and the construction of a fully reversible humidity sensor.