The role of molecular fluorophores in the photoluminescence of carbon dots derived from citric acid: current state-of-the-art and future perspectives.

Carbon dots (CDs), an emerging class of nanomaterials, have attracted considerable attention due to their intriguing photophysical properties. Despite their indisputable potential of utilization in many fascinating areas of research and life, some fundamental aspects concerning their structure and the origin of their photoluminescence (PL) properties still await clarification. The mechanism of PL emission of CDs is associated with their structure, which is dependent on the carbonization process. At the initial stages of CD synthesis via a bottom-up approach, molecular fluorophores are considered to dominate the optical characteristics of the resulting nanomaterials. In this review, the recent progress in the use of molecular state theory for explanation of the structure-property relationship in CDs is summarized. This review focuses exclusively on the molecular fluorophores existing in nanomaterials prepared from citric acid (CA) as one of the most frequent carbon sources reported for the bottom-up synthesis of CDs. Consequently, the most relevant transformations of CA and the history of molecular fluorophores derived from it are described, followed by an in-depth discussion on their relevance in understanding the specific photophysical properties of blue-, green-, and red-emitting CDs. Finally, the challenging issues and future perspectives of molecular state PL mechanism exploration in CDs are highlighted.

Dehydrogenation of Betacyanins in Heated Betalain-Rich Extracts of Red Beet (Beta vulgaris L.).

Betacyanins are a group of water-soluble red-violet compounds containing nitrogen in their structure. These are biosynthesized in red beetroot (Beta vulgaris L.), a widely consumed vegetable that contains significant amounts of nutritious and bioactive compounds which are also found in dietary supplements. This contribution presents results of betacyanin thermal oxidation (resulting in dehydrogenation) interrelated with decarboxylation in selected acetate/phosphate buffers at pH 3-8 and at 85 °C, which may be of particular significance for formulation and performance of foods. Most of the reaction products were detected at the highest concentrations in the acidic solutions (pH 3-4). The main dehydrogenation reaction pathways were monitored by LC-DAD-MS/MS and were associated with decarboxylation of the principal extract pigments, betanin/isobetanin and neobetanin, at carbon positions C-2 and C-17. Additional reactions are accompanied by the 2,15-decarboxylation processes at different dehydrogenation levels with 15-decarboxy-betanin and 2,15-bidecarboxy-betanin, structurally elucidated by NMR analysis, as the distinct indicators of this route type. For other novel pigments detected, 2,15-bidecarboxy-xanbetanin, 2,15-bidecarboxy-xanneobetanin and 2,15,17-tridecarboxy-neobetanin, additional high resolution mass spectrometric analyses were performed and confirmed their molecular formulas.

Nature-Inspired Effects of Naturally Occurring Trace Element-Doped Hydroxyapatite Combined with Surface Interactions of Mineral-Apatite Single Crystals on Human Fibroblast Behavior.

Innovative engineering design for biologically active hydroxyapatites requires enhancing both mechanical and physical properties, along with biocompatibility, by doping with appropriate chemical elements. Herein, the purpose of this investigation was to evaluate and elucidate the model of naturally occurring hydroxyapatite and the effects of doped trace elements on the function of normal human fibroblasts, representing the main cells of connective tissues. The substrates applied (geological apatites with hexagonal prismatic crystal habit originated from Slyudyanka, Lake Baikal, Russia (GAp) and from Imilchil, The Atlas Mountains, Morocco (YAp)) were prepared from mineral natural apatite with a chemical composition consistent with the building blocks of enamel and enriched with a significant F- content. Materials in the form of powders, extracts and single-crystal plates have been investigated. Moreover, the effects on the function of fibroblasts cultured on the analyzed surfaces in the form of changes in metabolic activity, proliferation and cell morphology were evaluated. Apatite plates were also evaluated for cytotoxicity and immune cell activation capacity. The results suggest that a moderate amount of F- has a positive effect on cell proliferation, whereas an inhibitory effect was attributed to the Cl- concentration. It was found that for (100) GAp plate, fibroblast proliferation was significantly increased, whereas for (001) YAp plate, it was significantly reduced, with no cytotoxic effect and no immune response from macrophages exposed to these materials. The study of the interaction of fibroblasts with apatite crystal surfaces provides a characterization relevant to medical applications and may contribute to the design of biomaterials suitable for medical applications and the evaluation of their bioavailability.

Multi-colored shades of betalains: recent advances in betacyanin chemistry.

Covering: 2001 to 2021Betacyanins cover a class of remarkable natural red-violet plant pigments with prospective chemical and biological properties for wide-ranging applications in food, pharmaceuticals, and the cosmetic industry. Betacyanins, forming the betalain pigment group together with yellow betaxanthins, have gained much attention due to the increasing social awareness of the positive impact of natural products on human health. Betalains are commercially recognized as natural food colorants with preliminarily ascertained, but to be further investigated, health-promoting properties. In addition, they exhibit a remarkable structural diversity based on glycosylated and acylated varieties. The main research directions for natural plant pigments are focused on their structure elucidation, methods of their separation and analysis, biological activities, bioavailability, factors affecting their stability, industrial applications as a plant-based food, natural colorants, drugs, and cosmetics as well as methods for high-yield production and stabilization. This review covers period of the last two decades of betacyanin research. In the first part of the review, we present an updated classification of all known betacyanins and their derivatives identified by chemical means as well as by mass spectrometric and NMR techniques. In the second part, we review the current research reports focused on the chemical properties of the pigments (decarboxylation, oxidation, conjugation, and chlorination reactions as well as the acyl group migration phenomenon) and describe the semi-synthesis of natural and artificial fluorescent betalamic acid conjugates, showing various prospective research directions.

Advancements in structure-property correlation studies of cross-linked citric acid-based elastomers from the perspective of medical application.

Herein, a renewed prominence towards the synthesis of poly(alkylene citrate) (PAC) biomaterials and their detailed chemical, structural and mechanical characterization has been reported. Based on the modifications to the PAC synthesis protocol introduced in this study, the fabrication process was significantly streamlined, the reaction yields were increased, and the homogeneity of the final materials was found to be substantially improved. Comprehensive nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS) studies of the fabricated prepolymers shed light on the mechanism of the PAC cross-linking process and supported the design of materials with enhanced biocompatibility. Therefore, the initial molar ratio of the reagents involved in the synthesis of PAC materials was found to be pivotal to both the biological and mechanical properties of the final products. Moreover, cell viability and proliferation assays revealed enhanced biocompatibility of the materials formulated with a molar ratio of diol over citric acid (3 : 2 mol/mol) in comparison to the most commonly described 1 : 1 analogue without affecting the possibility of further functionalization. Furthermore, this work creates a new paradigm for prospective studies on the properties of modified PAC materials and their application in medicine and tissue engineering.

Nature of Linear Spectral Properties and Fast Electronic Relaxations in Green Fluorescent Pyrrolo[3,4-c]Pyridine Derivative.

The electronic nature of 4-hydroxy-1H-pyrrolo[3,4-c]pyridine-1,3,6(2H,5H)-trione (HPPT) was comprehensively investigated in liquid media at room temperature using steady-state and time-resolved femtosecond transient absorption spectroscopic techniques. The analysis of the linear photophysical and photochemical parameters of HPPT, including steady-state absorption, fluorescence and excitation anisotropy spectra, along with the lifetimes of fluorescence emission and photodecomposition quantum yields, revealed the nature of its large Stokes shift, specific changes in the permanent dipole moments under electronic excitation, weak dipole transitions with partially anisotropic character, and high photostability. Transient absorption spectra of HPPT were obtained with femtosecond resolution and no characteristic solvate relaxation processes in protic (methanol) solvent were revealed. Efficient light amplification (gain) was observed in the fluorescence spectral range of HPPT, but no super-luminescence and lasing phenomena were detected. The electronic structure of HPPT was also analyzed with quantum-chemical calculations using a DFT/B3LYP method and good agreement with experimental data was shown. The development and investigation of new pyrrolo[3,4-c]pyridine derivatives are important due to their promising fluorescent properties and potential for use in physiological applications.

Selective Cytotoxicity of Complexes with N,N,N-Donor Dipodal Ligand in Tumor Cells.

The present article demonstrates selective cytotoxicity against cancer cells of the complexes [Co(LD)2]I2∙CH3OH (1), [CoLD(NCS)2] (2) and [VOLD(NCS)2]∙C6H5CH3 (3) containing the dipodal tridentate ligand LD = N,N-bis(3,5-dimethylpyrazol-1-ylmethyl)amine), formed in situ. All tested complexes expressed greater anticancer activities and were less toxic towards noncancerous cells than cisplatin. Cobalt complexes (1 and 2) combined high cytotoxicity with selectivity towards cancer cells and caused massive tumour cell death. The vanadium complex (3) induced apoptosis specifically in cancer cells and targeted proteins, controlling their invasive and metastatic properties. The presented experimental data and computational prediction of drug ability of coordination compounds may be helpful for designing novel and less toxic metal-based anticancer species with high specificities towards tumour cells.

Electro-Fenton approach in oxidative degradation of dimethyl phthalate - The treatment of aqueous leachate from landfills.

Herein, the dimethyl phthalate (DMP) contamination, as an emerging pollutant, has been cost-effectively removed from landfill leachate through an advanced oxidation process, that is the electro-Fenton (EF) process. For this purpose, a quadratic polynomial model was developed via response surface methodology (RSM). Furthermore, the analysis of variance (ANOVA) was performed for evaluating the significance of the proposed assumptions. The actual removal rate of 99.1% was obtained with optimal values of 4 mg L-1 of initial DMP concentration, 50 mM Na2SO4, 600 µL L-1 H2O2, 8-minute electrolytic time, solution pH 3 and 6 mA cm-2 current density for the process variables and was consistent with the expected 99.6% removal rate. Satisfactory correlation coefficients were obtained, and a non-significant value of 0.0618 for model mismatch confirmed that the proposed model is extremely important and can successfully predict the effectiveness of DMP removal. The kinetics of the process and the effect of the presence of some radical scavengers were studied to understand the exact mechanism of DMP degradation. Therefore, it was observed that the reaction of hydroxyl radicals with DMPs followed the first-order kinetics model. Moreover, it was established that the optimal ratio of H2O2/Fe2+ mole was 1.6 and the electricity consumption was 0.157 kWh m-3. The elaborated treatment model used to remove DMP from landfill leachate showed that DMP contamination was effectively removed with a 95.6% removal efficiency in the investigating process.

The Responses of Bioactive Betanin Pigment and Its Derivatives from a Red Beetroot (Beta vulgaris L.) Betalain-Rich Extract to Hypochlorous Acid.

Neutrophils produce hypochlorous acid (HOCl) as well as other reactive oxygen species as part of a natural innate immune response in the human body; however, excessive levels of HOCl can ultimately be detrimental to health. Recent reports suggest that betacyanin plant pigments can act as potent scavengers of inflammatory factors and are notably effective against HOCl. Comparison of the in vitro anti-hypochlorite activities of a novel betalain-rich red beetroot (Beta vulgaris L.) extract with its pure betalainic pigments revealed that the extract had the highest anti-hypochlorite activity, far exceeding the activity of all of the betalainic derivatives and selected reference antioxidants. This suggests that it may be an important food-based candidate for management of inflammatory conditions induced by excessive HOCl production. Among all pigments studied, betanidin exhibited the highest activity across the pH range.

Fluorescence assay for the determination of glutathione based on a ring-fused 2-pyridone derivative in dietary supplements.

Herein, a novel fluorescent method for the determination of GSH levels in aqueous solutions involving the utilization of citric acid as a derivatization reagent was developed. Therefore, the crucial parameters of the derivatization process were established from what has resulted in the development of a sensitive, reproducible, and accurate GSH assay. The method was validated, and its applicability in the characterization of the GSH concentration in dietary supplements concerning the selectivity in the determination of GSH over GSSG was both confirmed. The chemical structure of the new fluorophore 3-[(carboxymethyl)carbamoyl]-5-oxo-2,3-dihydro-5H-[1,3]thiazolo[3,2-a]pyridine-7-carboxylic acid - CTPC was elucidated using detailed NMR: one-dimensional (1H, 13C), as well as two-dimensional NMR spectra (1H-1H COSY, 1H-13C HSQC, 1H-13C HMBC, 1H-15N HSQC, 1H-15N HMBC) experiments. Besides, the essential optical, biological and antioxidative properties of CTPC were investigated.

Recovery and Characterization Studies of Post-Production Alloy Waste from the Automotive Industry.

Superalloys provide high corrosion resistance and are widely used as high-performance materials in aerospace, automotive, chemical, and other industries. Herein, the investigation into the characteristics and properties of alloy waste; Inconel 625, Inconel 718, and Titanium Grade 5, from the automotive industry, was introduced as a result of a recovery in various processes. For this reason, the following procedures were carried as follows; the washing process to remove oil from the swarf was evaluated using several commercial agents and for the process of thermal disposal of processing fluids, a temperature of 900 °C was used in a muffle furnace without air access. The presented studies show that the commercially available series of washing agents did not modify the composition of the surface. However, the high temperatures during the calcination of oil residues are affecting the elemental composition of the alloys. According to the results of the analyses, it is not possible to remove 100% of the oil residues from alloy waste using washing agents based on light organic fractions; however, the effectiveness of this method reaches 99%. In this report, accurate SEM-EDS analyses show changes that occur on the surface after machining and removal of processing fluids. The NMR and GC/MS investigations indicate contaminants as a mixture of aliphatic and cycloaliphatic hydrocarbons with carbon numbers from C8-C30.

Phytochemical Molecules from the Decarboxylation of Gomphrenins in Violet Gomphrena globosa L.-Floral Infusions from Functional Food.

Herein, the generation of decarboxylated derivatives of gomphrenin pigments exhibiting potential health-promoting properties and the kinetics of their extraction during tea brewing from the purple flowers of Gomphrena globosa L. in aqueous and aqueous citric acid solutions were investigated. Time-dependent concentration monitoring of natural gomphrenins and their tentative identification was carried out by LC-DAD-ESI-MS/MS. The high content of acylated gomphrenins and their principal decarboxylation products, 2-, 15-, 17-decarboxy-gomphrenins, along with minor levels of their bidecarboxylated derivatives, were reported in the infusions. The identification was supported by the determination of molecular formulas of the extracted pigments by liquid chromatography coupled with high-resolution mass spectrometry (LCMS-IT-TOF). The influence of plant matrix on gomphrenins' stability and generation of their derivatives, including the extraction kinetics, was determined by studying the concentration profiles in the primary and diluted infusions. Isolated and purified acylated gomphrenins from the same plant material were used for the preliminary determination of their decarboxylated derivatives. The acylated gomphrenins were found to be more stable than nonacylated ones. Citric acid addition had a degradative influence on natural gomphrenins mainly during the longer tea brewing process (above 15 min); however, the presence of plant matrix significantly increased the stability for betacyanins' identification.

Fluorescence Assay for the Determination of d-Panthenol Based on Novel Ring-Fused 2-Pyridone Derivative.

Herein, a novel fluorescent method for the determination of d-panthenol (DP) level in solutions with no separate hydrolysis step has been revealed based on the utilization of citric acid (CA) as a derivatizing agent. Consequently, the essential parameters of the derivatization process were established, resulting in the development of sensitive, repeatable, and accurate determination of panthenol. The method was approved, and its usefulness in characterizing the concentration of DP in pharmaceutical formulations and selectivity in the determination of DP were validated. The chemical structure of the new fluorophore formulating in the reaction in DP with CA, i.e., 6-oxo-3,4-dihydro-2H,6H-pyrido[2,1-b][1,3]oxazine-8-carboxylic acid (ODPC), was elucidated using detailed NMR experiments: one-dimensional (1H, 13C) as well as two-dimensional NMR spectra (1H-1H COSY, 1H-13C HSQC, 1H-13C HMBC, 1H-15N HSQC, 1H-15N HMBC).

Anti-Hypochlorite, Antioxidant, and Catalytic Activity of Three Polyphenol-Rich Super-Foods Investigated with the Use of Coumarin-Based Sensors.

The anti-hypochlorite activity of açaí (Euterpe oleracea Mart.), goji (Lyciumbarbarum L.) and schisandra (Schisandrachinensis) fruit extracts were assessed by determining the reactive chlorine species (RCS)-scavenging ability of these three "super-food" berries. In addition, the aqueous extracts obtained were employed as both the media and the catalyst in a green chemistry approach to the synthesis of a coumarin-based fluorescence turn-off sensor, which was then used for anti-hypochlorite activity testing. The aqueous extracts were also assessed for total phenolic content (TPC), using the Folin-Ciocalteu method, and the antioxidant activity using the ABTS+• assay. Moreover, the main water-soluble polyphenolic constituents of the extracts were identified by the HPLC-PDA-ESI-MS technique. Among the extracts tested, açaí demonstrated the highest anti-hypochlorite and antioxidant activities, while the highest TPC value was found for the goji extract. All extracts demonstrated modest catalytic activity as Knoevenagel condensation catalysts.

Cyclodextrin-modified poly(octamethylene citrate) polymers towards enhanced sorption properties.

Herein, we describe the synthesis of poly(1,8-octamethylene citrate) materials modified in the bulk with 2-hydroxypropyl-ß-cyclodextrin (cPOCCD), biodegradable elastomers with intrinsic sorption properties for drug delivery. The chemical structure, physicochemical properties, in vitro drug loading and release profiles of cPOCCD were investigated. Thus, cPOCCD polyesters absorb the studied drugs more effective and release them for a longer period of time than poly(1,8-octamethylene citrate) materials not containing cyclodextrins.

Luminescence phenomena of carbon dots derived from citric acid and urea - a molecular insight.

In this report, we present the results of our investigations into the elucidation of the chemical structure of moieties responsible for the blue and green luminescence of CDs derived from the microwave-assisted pyrolysis of citric acid in the presence of urea. The molecular fluorophore that forms during the synthesis of green fluorescing CDs is 4-hydroxy-1H-pyrrolo[3,4-c]pyridine-1,3,6(2H,5H)-trione (HPPT).