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Carbon quantum dots (CQDs) have recently emerged as innovative theranostic nanomaterials, enabling fast and effective diagnosis and treatment. In this study, a facile hydrothermal approach for N-doped biomass-derived CQDs preparation from Citrus clementina peel and amino acids glycine (Gly) and arginine (Arg) has been presented. The gradual increase in the N-dopant (amino acids) nitrogen content increased the quantum yield of synthesized CQDs. The prepared CQDs exhibited good biocompatibility, stability in aqueous, and high ionic strength media, similar optical properties, while differences were observed regarding the structural and chemical diversity, and biological and antioxidant activity. The antiproliferative effect of CQD@Gly against pancreatic cancer cell lines (CFPAC-1) was observed. At the same time, CQD@Arg has demonstrated the highest quantum yield and antioxidant activity by DPPH scavenging radical method of 81.39 ± 0.39% and has been further used for the ion sensing and cellular imaging of cancer cells. The obtained results have demonstrated selective response toward Fe3+ detection, with linear response ranging from 7.0 µmol dm−3 to 50.0 µmol dm−3 with R2 = 0.9931 and limit of detection (LOD) of 4.57 ± 0.27 µmol dm−3. This research could be a good example of sustainable biomass waste utilization with potential for biomedical analysis and ion sensing applications.

Spontaneous precipitation of calcium oxalate monohydrate (COM) in additive-free systems with nearly the same initial supersaturation has been investigated. The influence of thermodynamic parameters such as: temperature (t = 25, 36.5 and 48 °C), calcium concentration range of 5 mmol dm−3 ≤ ci(Ca2+) ≤ 10 mmol dm−3 and pH (5.6, 6.5 and 7.5), on the potential changes in structure, morphology and crystal size of COM have been studied. The values of the initial parameters were varied in a wide range and included values relevant for mimicking the physiological conditions related to those in biological systems and kidney stone formation. The results contributed to the knowledge about the influence of the selected individual parameters as well as their interplay influence on in vitro precipitation of COM. The findings have indicated that COM was the only precipitated phase exhibiting predominant dendritic morphology. The effects on crystal size, structure and morphology are more pronounced at higher temperature, pH and calcium concentration. These results provide basis for future studies of overall mechanism of COM formation and the future studies of kidney stone prevention. This work is licensed under a Creative Commons Attribution 4.0 International License.

Electroactivated disposable pencil graphite electrode (ePGE) was used for hesperidin detection with cv and dpv Electroactivation efficiency of the pencil graphite electrode (PGE) was examined with EIS and SECM. Enhancement of electron transfer kinetics after electroactivation was found. Hesperidin is irreversibly oxidized on ePGE (oxidation was the most pronounced at pH = 5.0). Linear dependence between the peak current and the hesperidin concentration from 5×10‐7 M to 1×10‐5 M was obtained. Determined LOD was 2×10‐7 M. Hesperidin was quantified in pharmaceutical formulation with ePGE and the results were in a good correlation with concentrations determined with HPLC‐DAD (R2 = 0.9462).

Ova studija prikazuje mehanokemijsku sintezu kalcijeva oksalata u planetarnom kugličnom mlinu, bez prisutnosti i uz prisutnost otapala. Dosadašnja istraživanja uglavnom su bila usmjerena na otopinsku sintezu kalcijeva oksalata. U ovom radu opisujemo drugačiji pristup, koji će donijeti nova saznanja o sintezi kristala kalcijeva oksalata, koje su uzrokovane utjecajem mehaničke energije. Cilj istraživanja je sinteza, identifikacija i karakterizacija pojedine oksalatne hidratne faze sintetizirane iz kalcijevih soli (klorida, nitrata i sulfata). Ispitivan je utjecaj brzine mljevenja i praćena je reakcija u ovisnosti o vremenu sinteze. Strukturalna i termička svojstva uzoraka ispitana su spektroskopijom FTIR i termogravimetrijskom analizom (TGA). Morfološke karakteristike kalcijeva oksalata te raspodjela veličine čestica određene su optičkom mikroskopijom i dinamičkim raspršenjem svjetlosti (DLS). Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna., In this work, mechanochemical synthesis of calcium oxalate was done in a planetary ball mill, with and without addition of water as a solvent. Previous research was primarily focused on calcium oxalate synthesis in solution. Here we report a different approach which may contribute to new findings in calcium oxalate crystal synthesis caused by an influence of mechanical energy. The aim of this study was synthesis, identification, and characterization of particular oxalate hydrate phase synthesized with calcium salts (chloride, nitrate and sulphate). The effects of grinding speed and reaction duration regarding the time of synthesis were investigated. Structural and thermal sample properties were studied by FTIR spectroscopy and thermogravimetric analysis (TGA). Morphologic characteristics of calcium oxalate and size distribution were measured by optical microscopy and dynamic light scattering (DLS). This work is licensed under a Creative Commons Attribution 4.0 International License.

This work is focused on a practical procedure by which pure and well-formed COD crystals were obtained. The effect of different type of stirring on the precipitation process and properties of COD crystals is studied. Mechanical and magnetic stirring are two common stirring types for precipitation of calcium oxalate and method using ultrasonic irradiation is newly described. The precipitation processes are systematically investigated varying solution stoichiometry (defined as a ratio of concentrations of the constituent ions in solution, (Ca+/(C2O42−) and concentration of additive (citrate). The differences of the structure, morphology and crystals properties between precipitates were investigated by SEM, FT-IR, TG and PXRD. In the ultrasonically stirred systems, COD was the only precipitated phase regardless of solution stoichiometry. Pure and well formed COD crystals with well-formed planes were obtained in the system with c(Ca2+)/c(C2O42−) = 3.86 and c(citrate) = 0.009 mol dm−3. The results demonstrate that ultrasonically assisted precipitation could be a new way in synthesis of COD crystals having different potential applications (in the fields of medicine and biotechnology).

The main goal of this study was to investigate complexation of L-carnosine and its constituent amino acids beta-alanine and L-histidine with copper (II) in a buffer at pH = 10. For this study the following methods were used: potentiometry, cyclic and differential pulse voltammetry and UV/VIS spectroscopy. The results have shown that L-histidine and L- carnosine formed a complex with copper in a 1:1 ratio, while no complexation with beta-alanine was observed.

In this Special Issue, we focus on biomineralization/pathological biomineralization systems and the synthesis of bioinspired materials. This Special Issue promotes the current trend of “green chemistry”, and, as such, in all published papers, only aqueous solutions and eco- friendly additives were used for the production of well-characterized bioinspired materials. This Special Issue contains four papers: three original research papers and one review. Here, a brief introduction of these papers is provided.

The search for an efficient drug or inhibitor in the formation process of kidney stones has been a promising research topic towards reducing the risks of the formation of disease. However, several challenges have been faced in investigating the most common constituents of kidney stones, calcium oxalate and its hydrate forms (COM, COD and COT). This study focuses on the preparation and structural characterization (TG, XRD, FTIR, SEM) of calcium oxalate hydrates in the presence of gallic acid (GA) and by varying operating parameters such as temperature (25 °C, 36.5 °C and 48 °C), pH (5.6, 6.5 and 7.5) and amount of added GA (ranging from 100 mg to 1000 mg). Response surface methodology was applied in order to evaluate the effects of operating parameters in the formation of COM and COD, and for the process optimization towards maximizing their content in samples. The results indicated that GA inhibited the formation of COM (0–100%) and promoted the formation of COD (0 ≤ 99%), while a medium pH and the amount of added GA showed a significant effect in the process of COD formation. In order to investigate the interactions established in the formation process and the possible adsorption between GA and the formed crystals, electrochemical measurements were performed.

In this study, glassy carbon electrode modified with nano gold-crystal violet film has been used to detect arsenite (As (III)) in a model system and in groundwater samples. The modified electrode was characterized by scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). Using voltammetric measuring technique, linear response was obtained in a concentration range of 2.0-22.0 uM. The arsenite concentrations in groundwater samples varied between 2.4 uM to 4.8 uM. The sensitivity of the modified electrode for As (III) detection was 5.6 uA/ uM cm2 and 0.8 uM concentration was found as lower limit of detection (LOD). The accuracy of the method was checked with standard method anodic stripping voltammetry (ASV). Groundwater samples were characterized with dynamic (DLS) and electrophoretic (ELS) light scattering measurements which have shown that particles present in different samples differ in size distribution and zeta potential which did not interfere with As (III) detection.

In this study, three different precipitation systems of increasing complexities were used to study formation of calcium oxalate hydrates under hyperoxaluria conditions. For this purpose, three different precipitation systems have been studied: a) a simple system (a system containing constituent ions), b) NaCl system (a system consisted of constituent ions and 0.3 mol dm−3 NaCl), and c) artificial urine system (a system containing constituent ions that are of the type and quantity mimicking real urine) at initial pH (pHi = 6.5) value, with and without added vitamin C. The vitamin C has been extensively tested for its ability to inhibit or promote the process of calcium oxalate precipitation or the formation of specific hydrate modification. In order to determine whether calcium oxalate crystallization could be affected by the presence of vitamin C in precipitation systems with increasing complexity, different amounts of vitamin C (in the mass range from 100 mg to 1000 mg) were added to the precipitation systems.The results indicated that in all investigated simple systems, calcium oxalate monohydrate (COM) is observed to be dominant precipitated hydrate phase, while in NaCl systems precipitation of COM and calcium oxalate trihydrate (COT) mixture occurrs, except in reference NaCl system (without addition of vitamin C) where COM precipitated exclusively. In reference artificial urine system, calcium oxalate dihydrate (COD) was observed to be dominant precipitated hydrate phase, while addition of vitamin C promoted precipitation of COT. Significant differences are mainly observed in crystal morphology and the content of individual hydrate phases. Electrochemical measurements have indicated the existence of electrostatic interactions between seed crystals and ascorbic acid, even at low masses of added vitamin C.

This work focuses on systematic research of spontaneous precipitation of calcium oxalate in model systems mimicking the chemical conditions typical for hyperoxaluria. For this purpose, model systems of three different complexities (simple, NaCl and artificial urine system) and two initial pH (pHi = 5.0 and pHi = 9.0) at 37 ºC are studied. In all investigated systems, dominant precipitation of calcium oxalate monohydrate (COM) is observed, except in artificial urine system at pHi = 9.0, ci(C2O42-) ≥ 6.0 mmol dm-3 and ci(Ca2+) ≥ 7.5 mmol dm-3 where precipitation of a mixture of calcium oxalate monohydrate and calcium oxalate dihydrate (COD) occurrs. The significant difference is mainly observed in COM crystal morphology. In a simple system, COM precipitates in a dendritic form, in NaCl system dendritic form and irregular shapes are found, while in the artificial urine, prismatic hexagonal and aggregated COM crystals precipitate.

In this work oxido-reduction properties of L-histidine were studied by cyclic and differential pulse voltammetry in a pH range from pH 4–10. The results have shown that L-histidine is not electroactive in a pH range from pH 4 to pH 9, while oxidation peak of L-histidine’s imidazole ring at pH 10 was detected with differential pulse voltammetry. It has been found that the oxidation peak current of L-histidine increased with the increase of its concentration in a solution. Adsorption of oxidation product of L-histidine on a glassy carbon electrode surface was also detected. Voltammetric techniques (cyclic and differential pulse voltammetry) and UV/VIS spectroscopy were used to study formation of L-histidine complexes with transition metals. It has been found that L-histidine formed octahedral complex with metal ion (Co2+ and Ni2+) in a 1 : 1 ratio. This work is licensed under a Creative Commons Attribution 4.0 International License.

The scientific conference The 1st Young Scientist Day – PhD Conference was held on 14th June 2018 in Osijek at Aula of Josip Juraj Strossmayer University of Osijek. Scientific lectures were held by the PhD students and postdoc fellows from Josip Juraj Strossmayer University of Osijek, Faculty of Food Technology Osijek, Faculty of Agriculture Osijek, Faculty of Medicine Osijek, Department of Chemistry and Department of Biology. The main idea was the presentation of experimental results between young scientists, PhD students and postdoc fellows of the Josip Juraj Strossmayer University of Osijek, with the aim of promoting new ideas and knowledge, sharing experiences, as well as acquiring competencies in the multidisciplinary fields of science, and with the purpose of future collaboration establishing.