Combined UV-Vis Research Articles

Superparamagnetic iron oxide nanoparticles functionalized with on-demand redox-responsive contractible coordination polymer brush as molecular actuator driven by π-dimerization

Nanomachines require molecular actuators to be coupled to a condensed phase. In this work, a redox responsive 1D contractible coordination polymer (ZnL) used as non-interlocked actuator is grafted onto superparamagnetic iron oxide nanoparticles (SPIONs) in a brush-like configuration. Oxidized rod-like ZnL oligomers have ability to reversibly self-fold upon reduction via π-dimerization of their bis-viologen units. Unlike in usual responsive brushes, ZnL chains behave individually, generating spatially controlled mechanical motion at nanoparticle surface associated to significant variations of particle diameters. ZnL oligomers were “grafted to” SPIONs in a single step. Reduction of colloidal dispersions was perform by visible light illumination with the help of a photoreductant. π-dimerization was assessed by UV–vis–NIR and reversible contraction of ZnL brush was characterized by DLS. Effects of ZnL chains length and grafting density on mechanism and performance of contractibility were studied. ZnL brush can alternately be contracted and extended with excellent reversibility. Combined UV–vis–NIR, DLS and TGA analyses demonstrate that π-dimerization is only intramolecular and that chains behave as independent actuators. Maximal contraction of 22 nm is obtained for largest particles (DH = 86 nm). Full to partial contraction of the brush depends on grafting density with a threshold at ≈ 47 chains per particle.

Characteristics of water dissolved organic matter in Zoige alpine wetlands, China

BackgroundDissolved organic matter (DOM) plays a significant role in the biogeochemical cycle of crucial elements in aquatic ecosystem. However, it is still not clear on the spectral characteristics of water DOM in different types of alpine wetlands, which have less anthropogenic influences and intensive ultraviolet radiation. Here, we collected 107 water samples from marsh, lake, and river wetlands in the Zoige plateau, China, and analyzed the chemical characteristics, compositions, and potential sources of chromophoric DOM by combining UV–vis spectroscopy and excitation–emission matrix fluorescence spectroscopy coupled with parallel factor analysis (EEMs-PARAFAC).ResultsUVC and UVA fulvic-like substances were the prevailing fluorescence components in water DOM, which accounted for 23.74–71.59% and 16.76–30.01% of the total fluorescence intensity, respectively. Compared with the lake and river wetlands, fluoresce intensities of UVC and UVA fulvic-like substances in DOM were higher in marsh wetland. Marsh wetlands possessed the highest SUVA254, E2/E3, E2/E4, and E4/E6 of DOM, suggesting higher humification degree, higher relative molecular nominal size, and higher aromaticity. And the E2/E4 ratios in most water samples were higher than 12, indicating water DOM was mainly derived from autochthonous sources in alpine wetlands.ConclusionsWetland types strongly affected the spectral characteristics of water DOM in Zoige plateau. These findings may be beneficial for sustainable management of alpine wetlands.Graphical

Paper chip-based colorimetric biosensor for glucose by using CuFe2O4@GO as nanozyme

The development of nanomaterials with notable enzyme-like activity is of great significance to the field of bioanalysis. Herein, a nanomaterial composed of copper ferrite nanoparticles (CuFe2O4 NPs) and graphene oxide (GO) was successfully prepared (CuFe2O4@GO). The obtained CuFe2O4@GO was proved to have peroxidase-like (POD-like) activity, which could catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to generate oxidized TMB (ox-TMB) in the presence of H2O2 with an obvious color change. On this basis, a colorimetric biosensor using a UV–vis spectrometer as readout and a paper chip-based colorimetric biosensor using a smartphone as readout was constructed for glucose detection, respectively, as glucose oxidase (GOD) could oxidize glucose to form H2O2. The UV–vis spectrometer-based approach exhibits a linear range of 0 to 1000 μM and a limit of detection (LOD) of 0.79 μM for glucose. The smartphone-based method shows a linear range of 0.1 to 50 mM and a LOD of 0.04 mM for glucose. Moreover, the fabricated colorimetric biosensors have good selectivity towards glucose and the sample matrixes cannot affect the detection of glucose. Finally, the concentration of glucose in human serum samples was successfully detected using two different ways, and the results are close to the clinical values. The proposed method embraces several good merits. Firstly, the colorimetric biosensors combining UV–vis spectrometer and smartphone offer precise results, which could effectively prevent the occurrence of false events. Secondly, paper-based microfluidic analytical device (μPAD) as analytical platform and smartphone as readout provides a versatile approach for constructing sensitive, cost-effective, and simple colorimetric biosensor for the visual monitoring of glucose. Lastly, except for glucose detection, this work also shows great application prospects for other small molecules detection that could generate H2O2.

Surface DBD in moist air for nitrogen fixation: a comparative study of pulsed versus amplitude-modulated AC powered discharge

Surface DBD (SDBD) discharge maintained in moist air in the immediate vicinity of the water surface is an effective source of reactive species for the production of plasma-activated water (PAW). In this work, we investigated the water activation process for two different DBD energization methods; i.e. using periodic HV pulses with nanosecond risetimes and amplitude-modulated HV AC. We combined UV–vis–NIR ICCD spectroscopy with electrical characteristics to determine the basic characteristics of SDBD microfilaments. Formation of N2O5/NO2/N2O/H2O2/NO2 −/NO3 − species was followed and the production yields of species generated in PAW (H2O2/NO2 −/NO3 −) were determined in a flow-through reactor under well-defined and stable discharge conditions. Both energization methods reached comparable energy efficiencies of nitrogen fixation in the range of 1–6 g kWh−1 with minimal concentrations of H2O2 (10 s μM). However, the AC-powered SDBD produced mainly NO3 − with minimal NO2 − (1/10 of NO3 −), while in the case of pulsed SDBD the better-balanced NO2 −/NO3 − ratio was achieved.

The Functionality of the DC Pair in a Rhodopsin Guanylyl Cyclase from Catenaria anguillulae

Rhodopsin guanylyl cyclases (RGCs) belong to the class of enzymerhodopsins catalyzing the transition from GTP into the second messenger cGMP, whereas light-regulation of enzyme activity is mediated by a membrane-bound microbial rhodopsin domain, that holds the catalytic center inactive in the dark. Structural determinants for activation of the rhodopsin moiety eventually leading to catalytic activity are largely unknown. Here, we investigate the mechanistic role of the D283-C259 (DC) pair that is hydrogen bonded via a water molecule as a crucial functional motif in the homodimeric C. anguillulae RGC. Based on a structural model of the DC pair in the retinal binding pocket obtained by MD simulation, we analyzed formation and kinetics of early and late photocycle intermediates of the rhodopsin domain wild type and specific DC pair mutants by combined UV–Vis and FTIR spectroscopy at ambient and cryo-temperatures. By assigning specific infrared bands to S-H vibrations of C259 we are able to show that the DC pair residues are tightly coupled. We show that deprotonation of D283 occurs already in the inactive L state as a prerequisite for M state formation, whereas structural changes of C259 occur in the active M state and early cryo-trapped intermediates. We propose a comprehensive molecular model for formation of the M state that activates the catalytic moiety. It involves light induced changes in bond strength and hydrogen bonding of the DC pair residues from the early J state to the active M state and explains the retarding effect of C259 mutants.

Electronic structure that gives rise to the optical properties of zinc, cadmium and silver hexacyanocobaltates(III)

Transition metal hexacyanocobaltates(III) correspond to coordination polymers that present physical properties that can be used for technological applications. In this sense, properties like spin-crossover under different physical stimuli (light, temperature, pression, etc) or the colossal mechanical negative thermal expansion has been reported as astonishing properties of these materials (Goodwin et al., 2008; Goodwin et al., 2008; Avila et al., 2022) [1–3]. In this contribution, the electronic properties of hexacyanocobaltates(III) that contain Zn2+, Cd2+ and Ag1+ as metal ions, with a closed d-shell electronic configuration, are studied by means of combined UV–Vis spectroscopy and ab-initio calculations. The influence of the outer metals (Zn, Cd, Ag) when forming the coordination polymers as well as the effect of the inner octahedral moiety [Co(CN)6]3- have on the macroscopic electronic properties is discussed. Metal to ligand charge transfer transitions that produce the optical behavior are also clarified. Furthermore, the origin of the band gap transitions for Zn and Cd hexacyanocobaltates(III) is reported for the first time and supported by ab-initio calculations. New optical band gap energy values are proposed from a combined Urbach and Tauc analysis. Finally, the effects of metal substitution in Prussian blue analogues and the structural phase shift towards a zeolite-like phase on the band gap are analyzed.

Colorimetric evaluation of total antioxidant capacity based on peroxidase-like nonstoichiometric Cu2-xSe nanoparticles

Antioxidants can help trap and neutralize free reactive oxygen species to reduce their damage. Thus, it is important to evaluate the content of antioxidants in foods and drugs. In this paper, a simple and sensitive colorimetric sensing platform for total antioxidant capacity (TAC) detection was developed based on the peroxidase-like nanozyme of nonstoichiometric copper selenide nanoparticles (Cu2-xSe NPs). The Cu2−xSe NPs with copper vacancy structures can accelerate intramolecular charge transfer and effectively catalyze the oxidation of chromogenic substrate colorless 3,3′5,5′-tetramethylbenzidine (TMB) into blue oxidized TMB (oxTMB), exhibiting that they had good peroxidase-like activity. Base on the good activity of Cu2−xSe NPs peroxidase mimics, a colorimetric sensing array combining UV–vis spectrometer, naked eye and smartphone-based digital image analysis for three typical antioxidant acids (ascorbic acid (AA), gallic acid (GA) and citric acid (CA)) were realized and the platform was successfully used for evaluating the TAC in the medical tablets, beverages and fruit juices.

The "Tethered Solvent" Effect - H-Bonding-Controlled Thermo-Halochromism of a Push-Pull Azo Chromophore via Its Secondary Amidoalkyl Acrylamide Side Chain.

The fascinating field of thermo-halochromism of azo chromophores still astounds with unexplored facets nourished by the intricate relationship between molecular structure variations and their spectroscopic signatures. In this respect, we investigated the thermally dependent absorption behaviour of acrylamide derivatives of o-methyl red, characterised by two secondary amide linkages with hydrogen bonding-active protons in the pendant alkyl substituent. The systems were studied by a combination of UV-vis, derivative, and difference, as well as 2D-NMR (Nuclear Overhauser Effect Spectroscopy, NOESY) spectroscopy. These experiments show that the thermo-halochromism is specifically influenced by hydrogen bonding interaction of the secondary amidoalkyl acrylamide side chain with the azobenzene core in dependence of the spacer length. Apparently, the substituent acts like a solvent, which is directly tethered to the chromophore and where the tether length determines the interaction by conformational freedom. We refer to this novel phenomenon as "H-bonding-controlled thermo-halochromism".

Rapid Quality Control Assessment of Adeno-Associated Virus Vectors Via Stunner

As recombinant adeno-associated virus (AAV) vectors expand the availability of gene therapy; high-speed low-volume analytical methods become more vital for manufacturing. Current approaches for characterization are time consuming and sample consuming. Stunner combines ultraviolet–visible (UV–Vis) spectroscopy, static light scattering (SLS), and dynamic light scattering (DLS) to characterize up to 96 samples in <1 h, using 2 μL per sample. These data can be used to precisely quantify critical AAV titer, empty/full ratio, size, and aggregation. This study compares this technique with quantitative real-time PCR (qPCR), enzyme-linked immunoassay (ELISA), transmission electron microscopy, and analytical ultracentrifugation using AAV vectors with multiple serotypes, genome sizes, and purification strategies. Recommended sample criteria were established to provide guidelines on the suitability of Stunner analysis on a per-sample basis. The data presented herein lay the groundwork in establishing the use of combined UV–Vis, SLS, and DLS as a powerful and flexible analytical tool for AAV gene therapy vector development and manufacturing.

Organelle-selective near-infrared fluorescent probes for intracellular microenvironment labeling

The design, synthesis, and bio-applicability of a series of 8 near-infrared (NIR) molecular probes with tunable hydrophilic/hydrophobic properties are described in this paper. The title dyes comprise of symmetric heptamethine cyanines with various N-quaternary heterocyclic moieties including indole, benzo[e]indol, benzothiazole and naphtho[1,2-d]thiazole, along with an extra positive charge in close proximity to the polymethine backbone. Combined UV–Vis and spectrofluorimetric techniques in both organic and aqueous-buffered solutions were employed to investigate the optical properties of the NIR chromophores. Two of the fluorophores emerged remarkable fluorescence quantum yield (Φ = 0.083), while their brightness was found up to 3-fold that of the FDA approved Indocyanine green – ICG (Φ = 0.027). What is more, two of the dyes appear to outperform the later clinical benchmark fluorophore in terms of photostability. While the ICG was completely faded after 1 h of constant irradiation, nearly 70% of the original emission signal could be observed for one of the novel molecular probes. The log Pow values determined by a combination of HPLC and UV–Vis (partition between 1-octanol/water) cover a relatively large range, from −2.14 up to 7.92. Investigation on the cytotoxicity by means of the MTT assay revealed, that present dyes are suitable for bioanalytical purposes and are safe to use. This paper also includes fluorescence imaging and cellular applications, such as labeling of HeLa cervical cancer cells. The results from the confocal microscopy reveal the superior staining capability of current heptamethines since they show significantly brighter signal than the commercial ICG probe. An organelle-selective fluorescent staining was achieved depending on the dye chemical structure. Co-localization within the intracellular microenvironment (linear or granular - cytosol, mitochondria, lysosome, endoplasmatic reticulum or Golgi apparatus) was confirmed without interference, employing several conventional organelle dye trackers. To the best of our knowledge, heptamethine dyes represent the first example of a series NIR emitting probes, that exhibit rational structural modifications aiming to fine-tune the hydrophilic/hydrophobic properties furnishing organelle-targeted staining.

Intermolecular interactions of tetracyanoethylene (TCNE) and fumaronitrile (FN) with minor amines: A combined UV-Vis and EPR study.

In this paper, the nature of interactions between two cyanocarbons-tetracyanoethylene (TCNE) and fumaronitrile (FN)-and a series of four secondary amines possessing a general formula C4HxN (x = 5-11) is thoroughly scrutinized. For all of the TCNE-amine pairs, tricyanovinylation (TCV) reaction is observed; however, only for pyrrole, it is accompanied with a visible charge-transfer (CT) complex formation-no such chemical individuals, characteristic for TCNE, have been noticed for aliphatic and alicyclic amines. On the contrary, FN forms such complexes with all the amines studied. Interestingly, a rather unexpected reaction of FN with alicyclic amines has been observed. The recorded electron paramagnetic resonance (EPR) spectra indicate the presence of both TCNE●- and FN●- radicals in the analyzed samples, assigned to a complete charge (electron) transfer process within the CT complexes, whose efficiency can be additionally enhanced by photoirradiation. The origination of the former radical, whose presence is observed also in the TCNE-diethylamine mixture, is as well proposed to result indirectly from the TCV reaction, occurring for this system. Finally, the superhyperfine structure of EPR spectra, indicating the existence of some secondary interactions of the radicals with surrounding compounds, is discussed. Formation of CT complexes and tricyanovinylates has been investigated and characterized with UV-Vis spectroscopy, while the presence of (cyano)radicals in the analyzed mixtures has been evidenced by (photoinduced) EPR measurements. Interpretation of the experimental results is also supplemented with computer simulations including density functional theory calculations.

Copolymerization Kinetics of Dopamine Methacrylamide during PNIPAM Microgel Synthesis for Increased Adhesive Properties.

Combining stimuli-responsive properties of gels with adhesive properties of mussels is highly interesting for a large field of applications as, e.g., in life science. Therefore, the present paper focuses on the copolymerization of poly(N-isopropylacrylamide) (PNIPAM) microgels with dopamine methacrylamide (DMA). A detailed understanding of reaction kinetics is crucial to figure out an optimized synthesis strategy for tailoring microgels with adhesive properties. The present study addresses the influence of relevant synthesis parameters as the injection time of DMA during the microgel synthesis and the overall reaction time of the microgel. Reaction kinetics were studied by mass spectrometry of time samples taken during the microgel synthesis. This allowed us to determine the monomer consumption of NIPAM, the cross-linker N,N'-methylenebisacrylamide (BIS), and DMA. A second-order reaction kinetics was found for DMA incorporation. The amount of DMA incorporated in the resulting microgel was successfully determined by a combination of UV-vis and NMR spectroscopy to level off limitations of both methods. The dependence of the hydrodynamic radius on temperature was determined by DLS measurements for the microgels. While an early injection of DMA stops the PNIPAM polymerization due to scavenging, it greatly enhances the reaction speed of DMA. The faster reaction of DMA and the incomplete NIPAM and BIS conversion also compensate for shorter reaction times with respect to the incorporated amount of DMA. On the contrary, a later injection of DMA leads to a full NIPAM monomer and BIS cross-linker consumption. An overall reaction time of 60 min ensures the DMA incorporation. Longer reaction times lead to clumping. First adhesion tests show an increased adhesion of P(NIPAM-co-DMA) microgels compared to pure PNIPAM microgels, when mechanical stress is applied.

Iodide vs Chloride: The Impact of Different Lead Halides on the Solution Chemistry of Perovskite Precursors

Controlled perovskite growth from solution is crucial for efficient optoelectronic applications and requires a deep understanding of the perovskite precursor chemistry. The so-called “chlorine route” to lead–iodide perovskite, using PbCl2 or MACl additive as a precursor, is frequently employed to form homogeneous perovskite layers by retarding perovskite crystallization. To understand the role of chlorine-containing lead precursors in solution, we analyze the chemical interaction of PbCl2 and PbI2 precursors with commonly employed solvents (γ-butyrolactone (GBL), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO)) by combining first-principles simulations and experimental UV–vis spectroscopy in diluted precursor solutions. Ab initio molecular dynamics simulations reveal reduced solvation and an increased free energy barrier of lead-halide bond dissociation of PbCl2 compared to PbI2 with chlorine acting as a stronger ligand, which, in turn, limits the solvent coordination. In contrast to PbI2, PbCl2 absorption spectra lack signatures of high-valent [PbCln]2–n complexes and show low sensitivity on the employed solvent, as confirmed by combined UV–vis and excited-state time-dependent density functional theory (TD-DFT) analysis. Altogether, our data suggest the presence of residual chlorine coordinated to Pb even in the presence of high iodine excess, which may retard the perovskite growth and could also lead to chlorine incorporation within the lead–iodide perovskite crystal.

Construction of fish-scale tubular carbon nitride-based heterojunction with boosting charge separation in photocatalytic tetracycline degradation and H2O2 production

A fish-scale tubular carbon nitride (FTCNso) and its heterojunction ZnIn2S4/FTCNso were constructed to enhance the ability of photocatalytic tetracycline degradation and H2O2 production under visible light. The photocatalysts were analyzed through a variety of techniques. Firstly, the surface of FTCNso was composed of fish-scale nanoplatelets with abundant structural defects by SEM. Secondly, the results of UV–vis and theoretical calculation proved the improvement of visible light absorption performance of ZnIn2S4/FTCNso. Thirdly, the electrochemical tests confirmed the ZnIn2S4/FTCNso effectively inhibited the recombination of photogenerated e−-h+ pairs. Meanwhile, the electronic-structural properties and photocatalytic mechanism were systematically and deeply studied by combining UV–vis, XPS valence band, theoretical calculations and capture experiments of active species in different pH solution. ZnIn2S4/FTCNso exhibited excellent performance in photocatalytic tetracycline degradation and H2O2 production under visible light due to the special structure and the existence of heterojunction. This work provides guidance for the development and design of new multifunctional carbon nitride-based materials.

Reaction, structure and spectroscopic properties of bis(cyano) cobalt(III) porphyrin complexes

Cyanocobalamin and analogues have drawn much attention for the promising applications in photovoltaic and photocatalytic systems. In this study, two low spin bis(cyano) cobalt(III) porphyrin complexes [K(222)][Co[Formula: see text](TPP)(CN)2] and [K(222)][Co[Formula: see text](TMP)(CN)2] (222 = 4,7,13,16,21,24-hexaoxo-1,10-diazabicyclo[8.8.8]hexacosane, TPP = meso-tetraphenylporphyrin dianion, TMP = meso-tetramesitylporphyrin dianion), which were isolated from the reactions between [Co[Formula: see text](Porph)] (Porph = Porphyrin) and [K(222)(CN)], are characterized by a single crystal X-ray diffraction, FT-IR and UV-vis spectroscopies. Combined UV-vis and electron paramagnetic resonance (EPR) investigations have been conducted to understand the reaction mechanisms. The work gives new insights into the reactivities and spectroscopic properties of cyano cobalt macrocyclic complexes.

Phase diagrams of temperature-responsive copolymers p(MEO2MA-co-OEGMA) in water

Random copolymers of 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and oligo(ethylene glycol) methacrylate (OEGMA) have a temperature-induced phase transition in aqueous solutions, which can be tuned for different temperatures from ca. 20 °C to 90 °C, by changing their monomer ratio. Here, we explore a novel approach combining UV–Vis measurements (light scattering) with standard and modulated-temperature differential scanning calorimetry (DSC), to obtain the phase diagrams of copolymers with different compositions over an unprecedented wide concentration range (0.7–800 mg/mL). We used three copolymers synthesized by RAFT polymerization with very low size dispersity, and containing 6, 8 and 11 mol% of OEGMA. The change in their phase transition temperature with concentration show that they reach different lower critical solution temperature (LCST) in the concentration interval 20–30 mg/mL. Our results offer new insights on the influence of concentration, in particular for high concentrations, on the temperature, the reversibility and the kinetics of the phase transition. This information can be used to assist the design of copolymers with predetermined temperature response.

An easy and green amine-based microextraction strategy combined UV–Vis spectrophotometric detection for mercury in natural water samples

An amine-based microextraction method was established for preconcentration of mercury by forming a 1-(2-pyridylazo)-2-naphthol (PAN) chelate complex. The Hg (II)-PAN hydrophobic complex was extracted into the N,N-dimethyl-n-octylamine phase at pH 9.5, after the pre-concentration of Hg (II), the absorption spectrum was taken with UV–Vis spectrophotometer at 555.0 nm. The effects of important analytical parameters such as pH, PAN amount, N,N-dimethyl-n-octylamine volume, sample volume and matrix effects for quantitative recovery were investigated and optimized. 0.05% (w/v) PAN volume, N,N-dimethyl-n-octylamine volume, vortex time and centrifugation time were optimized as 0.4 mL, 0.1 mL, 1 min and 15 min, respectively. The validity of the developed liquid phase micro-extraction method was checked by standard addition-recovery experiments. The presented microextraction method was successfully applied for mercury determination in natural water samples. The mercury concentration in natural water samples ranged from 0.20 to 1.42 µg mL-1. The limit of detection (LOD), limit of quantification (LOQ) and preconcentration factor (PF) were found as 0.035 μg L−1, 0.12 μg L−1 and 26.67, respectively.

Novel Bi2S3/Bi2WO6 nanomaterials with 2D/3D spatial structure stably degrade veterinary antibiotics under visible light

In this study, nano-flowers Bi2S3/Bi2WO6 nanomaterial photocatalyst was fabricated by the mild solvothermal-hydrothermal method, which can effectively and stably degrade tetracycline(TC). The crystal structure, element composition chemical, valence state and microscopic morphology of the nanomaterials were characterized by XRD, XPS and SEM. Besides, PL and EIS analysis showed the composites have low recombination rate and impedance. The degradation rate of optimal(30%)Bi2S3/Bi2WO6 to TC is as high as 91.4%, which much higher than pure Bi2WO6 at visible-light. Particularly, the repetitive experiments demonstrated that the photocatalytic activity of Bi2S3/Bi2WO6 can still reach 84.3% and the photocatalyst has no changes in morphology and structure. Combining UV–vis DRS spectrum, Mott-Schottky curve and free radical trapping experiments, a Z-scheme photocatalytic mechanism suitable for this photocatalytic system was deduced. In general, the heterojunction formed by the unique spatial structure promotes the excitation, migration and separation of photo-generated carriers. Finally, this structure can provide more reference when dealing with antibiotics in wastewater.

Detection of honey adulteration – The potential of UV-VIS and NIR spectroscopy coupled with multivariate analysis

Honey is usually adulterated by cheaper, commercially available sugar syrups with similar chemical composition. Adulterated honeys are frequently marked as natural and are valued in the same way as pure honeys and as a result, there is a growing need for rapid, simple, and accurate analytical methods to evaluate their characteristics and authenticity. In this work potential of UV-VIS and NIR spectroscopy coupled with PLS modelling and ANN modelling was analysed for the detection of adulteration and quantification of the physical and chemical proprieties of pure and adulterated honey samples. Acacia honey samples from Krapina-Zagorje County (Croatia) were adulterated by corn syrup (10–90%). The results indicate that PLS models developed in this work, except that for moisture content, can be used efficiently for screening (7<RER<20). ANN modelling provided accurate and simultaneous prediction of the properties of honey with correlation coefficients for validation above 0.8 so that these results show significant performance of ANNs modelling in the prediction of the physical and chemical properties of pure honey samples and adulterations based on combined UV-VIS NIR spectra.

Spectroelectrochemical Experiment for Studying Water Oxidation with a Nickel Oxide Catalyst

Electrochemical and spectroelectrochemical techniques are very important for characterizing energy materials. In the search for new sources of renewable energy, water splitting for hydrogen production and CO2 reduction is attracting significant attention. These applications require efficient and durable catalysts and a detailed understanding of the underlying catalytic mechanism. Here, we experimentally study electrodeposited nickel oxide as a catalyst for electrochemical water oxidation by combining UV–vis and electrochemical techniques, with emphasis on revealing the interplay between catalytic activity and physical changes in the catalyst. Specifically, the spectroelectrochemical characterization of the catalyst at different pH enables students to establish correlations between catalytic activity, pH, and physical changes in the catalyst. Students are also introduced to fundamental principles of electrocatalysis such as Tafel plots, TOF (turnover frequency), and midpoint potential. Moreover, they are guided toward the reliable interpretation of optical absorption and electrochemical data, along with the conceptual aspects behind these techniques.