Characteristic UV-Vis Spectra Research Articles

Tetrabutylammonium-chloride-glycerol of deep eutectic solvent functionalized MnO2: a novel mimic enzyme for the quantitative and qualitative colorimetric detection of L-cysteine.

L-Cysteine is a common amino acid that plays an important role in human livelihood and production. Therefore, a novel method for the simultaneous quantitative and qualitative determination of L-cysteine by a colorimetric detection system is proposed. As a viable oxidase mimic, [N4444]Cl-G/MnO2, which consisted of MnO2 nanosheets functionalized by a tetrabutylammonium chloride-glycerol ([N4444]Cl-G) based deep eutectic solvent (DES) was fabricated. Owing to the oxidation of MnO2 nanosheets, [N4444]Cl-G/MnO2 could oxidize the colorless 3,3',5,5'-tetramethylbenzidine (TMB) into a blue product (oxTMB) with the characteristic UV-vis spectrum absorbance at 652 nm. The oxidation of TMB by DES/MnO2 was inhibited when L-cysteine was introduced, and the absorbance decreased proportionally with the increase in L-cysteine concentration. Due to this inhibition effect, a colorimetric detection system ([N4444]Cl-G/MnO2-TMB) was developed for the quantitative determination of L-cysteine. Under optimal conditions, the assay showed good linearity over the concentration range of 0.125-2.00 μg mL-1 with a low detection limit of 5.96 ng mL-1. A study of the inhibition mechanism demonstrated that the sulfhydryl group of L-cysteine could decompose [N4444]Cl-G/MnO2 into Mn2+, thus limiting the conversion of TMB to oxTMB. In addition, the [N4444]Cl-G/MnO2-TMB system was used in test strips for the visual qualitative detection of L-cysteine. The selectivity and test strip results demonstrated the high selectivity, simple operation, and rapid response of the [N4444]Cl-G/MnO2-TMB system for the qualitative detection of L-cysteine. Given the satisfying performance of the detection strategy, colorimetric sensing based on the [N4444]Cl-G/MnO2-TMB system is considered to have prospective application value in the quantitative and qualitative detection of L-cysteine.

Essential Oil Composition of Aerial Part of Pluchea ovalis (Pers.) DC., Silver Nanoparticles Synthesis, and Larvicidal Activities against Fall Armyworm

In this study, essential oil of the aerial part of Pluchea ovalis (POEO) was isolated and employed for the synthesis of AgNPs (POEO-AgNPs). Then, larvicidal activities of POEO and PEO-AgNPs were evaluated against the larvae of fall armyworm (FAW), Spodoptera frugiderda (J. E. Smith); (Lepidoptera: Noctuidae). The potential medicinal values of P. ovalis and the lack of scientific reports on the applications of essential oils and nanoparticles of the plant species from the ecology of Ethiopia motivated the authors to carry out this research activity. The hydrodistillation technique was used for the isolation of POEO. Characterization of samples was done using gas chromatography/mass spectrometry (GC/MS), ultraviolet–visible spectroscopy (UV–Vis), scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and zeta nanoanalyzer instruments. GC/MS analysis showed that sesquiterpenes (91.27%) are the dominant chemical constituents of POEO. The characteristic UV–Vis spectra absorption of POEO-AgNPs is observed at 428 nm. SEM imaging reveals that POEO-AgNPs have a dominantly spherical shape. A strong peak of EDX at 3.0 keV shows the existence of Ag element in POEO-AgNPs. XRD analysis determines the diffraction peaks of POEO-AgNPs at 2θ of 38.2°, 44.1°, 64.6°, and 77.8° which are indexed to (111), (200), (220), and (311), respectively. The average particle size and surface potential of POEO-AgNPs are 132 nm and −64.7 mV, respectively. POEO-AgNPs were stored at room temperature and 4 °C and showed good stability for about 6 months without aggregation or dissolution. The larvicidal activity was tested at 500, 250, and 125 µg/mL of POEO solution and 100% (full strength = 0.083 g/mL), 50%, and 25% POEO-AgNPs solution against 2nd instar larvae of S. frugiderda for 3 consecutive days. LC50 and LC90 are determined as 154.88 and 11,749.00 µg/mL for POEO and 69.18 and 1318.26% for POEO-AgNPs solutions, respectively. This finding will benefit the applications of POEO and POEO-AgNPs for a sustainable eco-friendly crop pest management method.

Influence of RE-Gd3+ ion substitution on structure, morphology, optical, and magnetic analysis of Cu-Cd based nano ferrites synthesized by low-temperature citrate sol–gel auto combustion method

The current study focused on the influence on physical, thermal, spectral, optical, and magnetic properties with the replacement of Fe3+ ions by large ionic radii rare-earth Gd3+ ions in CuCdFe2O4 nano-ferrites. The Gd3+ doped CuCdFe2O4 ferrite samples with chemical composition Cu0.8Cd0.2GdxFe2-xO4 (x = 0, 0.025, 0.05, 0.075 and 0.1) were produced by citrate sol–gel auto combustion route from the metal nitrates of the corresponding compounds. With the help of Thermo-gravimetric and differential thermal (TG-DTA) analysis, the temperature-dependent spinel phase formation and weight loss percentages were examined. The results of Powder X-ray diffraction patterns and FTIR spectra revealed the development of a cubic single-phase structure with α-Fe2O3 secondary phase, and stretching of metal ion bonds with the addition of Gd3+ ion in CuCdFe2O4 ferrites. From XRD data the observed lattice parameter was in the range of 8.323–8.469 Å and the average crystalline size was increased from 13 to 18 nm. “Field emission scanning electron microscopy” (FE-SEM) and “high-resolution transmission electron microscopy” (HR-TEM) analysis was used to give the particle size, shape, clear agglomeration, and dense structure of Gd3+ doped Cu-Cd nanoparticle. The semiconducting nature of the fabricated samples were confirmed from the characteristic UV–Vis spectra and the respective optical band gap values (1.70–1.74 eV). Electron spin resonance spectroscopy (ESR) analysis was provided the information about the various factors including g-value, peak to peak line width (ΔHPP), resonance field (Hr), and time relaxation (T2). The magnetic characteristic hysteresis loops of synthesised samples at 300 K and 15 K temperatures were obtained by VSM. The results showed that all Gd3+ doped samples exhibited a ferromagnetic nature at 300 K and enhanced hard magnetic nature at 15 K. The maximum saturation magnetisation (MS) was observed for x = 0.025 at both the temperatures (31.66 emu/g at 300 K and 39.65 emu/g at 15 K). The HC values were found in the range of 169.23–557.29 Oe at 300 K and 374.69–749.85 Oe at 15 K. The observed SQR (Mr/Ms) values revealed the single domain structure of prepared samples.

Single-step purified R-phycoerythrin transmits cellular imaging functionalities in vitro

A single-step and rapid chromatographic method-based purification of Gracilaria corticata (J. Agardh) R-phycoerythrin (R-PE) was attained using polyacrylamide gel electrophoresis (PAGE) technique without affecting structural integrity. The purified R-PE had a characteristic UV–Vis spectrum with three absorbance maxima at 496, 535, and 565 nm, and fluorescence at 575 nm. R-PE was obtained with a purity index of 4.2 and a recovery yield of 44.3%. SDS-PAGE analysis exhibited three sub-units i.e., 18, 21, and 31 kDa, which corresponds to α, β, and γ, respectively. This report's purification process was considered less time-consuming and could be efficiently applied to purify phycobiliproteins. The purified R-PE showed optimal stability up to 6 h at pH 7.0 when exposed to light (3000 lx), while the temperature at which the maximum stability was retained was at 20 °C. The cellular imaging property of R-PE was effectively implemented to evaluate its credentials without affecting the cell proliferation of Vero and Hep-2 cell lines with the higher IC50 concentrations in vitro. Under fluorescence microscopy and flow cytometry analysis, purified R-PE displayed the characteristic affinity towards cell imaging functions in preliminary in vitro studies.

Cation Sensing Capabilities of A Nitrophenyl Cinnamaldehyde Derivative

The cationic chemosensor based on organic compound bearing an aminophenol moiety as a receptor for metal analyte and a cinnamaldehyde moiety as chromophoric fragment has been developed. In this work, we report the colorimetric sensing of nitrophenyl cinnamaldehyde derivative, namely methyl-3-(2-hidroxy-5-nitrophenyl amino)-3-phenylpropanoate, towards a variety of metal cations, such as Cu2+, Fe3+, Ni2+ and Zn2+. The cation sensing abilities of the sensor were observed for Cu2+and Fe3+ with a color change from colorless to pink and faint yellow, respectively, The characteristic UV-Vis spectra changes were observed upon addition of Cu2+and Fe3+ cations. The hypsochromic absorption spectra shifts were obtained, indicating the cations and sensor complexations had formed. A metal-to-ligand-charge-transfer (MLCT) had occurred and the charge density of the sensor changed resulting in appearance of new absorption peaks in the UV-Vis spectra and color changes of the sensor solution upon addition of the Cu2+and Fe3+.

Methyl-3-(2-hidroxy-5-nitrophenyl amino)-3-phenylpropanoate Based Colorimetric Sensor for Oxyanions

A colorimetric anion sensor of methyl-3-(2-hydroxy-5-nitrophenyl amino)-3-phenylpropanoate bearing –OH and –NH groups as binding sites and nitrophenyl as a signaling unit, has been successfully accomplished. The compound functioned as a colorimetric chemosensor for H2PO4– and AcO–, in particular, the sensor showed significant naked-eye detectable color change from colorless to light yellow. In contrast, no color change was detected upon addition of other anions such as SO42–, NO3–, and CIO4–. The anion sensing ability of the sensor was further investigated by UV-Vis absorption spectroscopy in acetone. Characteristic UV-Vis spectra changes were revealed upon addition of H2PO4– and AcO–.

Characterization of the pigment in naturally yellow-colored domestic silk

Naturally colored silks are not durable and apt to fade during fabric processing and home laundering due to the unstable pigment composition and the accumulation of pigment in the surface sericin layer. In this study, the pigment of naturally yellow-colored silk was isolated, characterized and quantified. A dominant pigment composition identified by NMR analysis was all-trans-lutein and other five components were identified as all-trans-neoxanthin, all-trans-violaxanthin, all-trans-α-carotene, all-trans-β-carotene and 9-cis-β-carotene, according to their characteristic UV–Vis spectra and EI-MS data. All six carotenoids were accumulated in sericin layer and exhibited a remarkable decrease in total content in the outer layer (220 μg/g), middle layer (117 μg/g) and inner layer (50 μg/g) of the cocoon shell as determined by analyzing the reeled fiber from one end to the other.

A combined kinetic and computational study of the reactions of transient germylenes with oxiranes and thiiranes in solution

The reactions of dimethyl- and diphenylgermylene (GeMe2and GePh2, respectively) with cyclohexene oxide (CHO) and propylene sulfide (PrS) have been studied in hydrocarbon solvents at 25 °C by laser flash and steady-state photolysis methods using appropriately substituted germacyclopent-3-ene derivatives as germylene precursors. GeMe2reacts with CHO and PrS with rate constants in the range of 1.2–1.7 × 1010M−1s−1in hexanes at 25 °C to form new transient products that are assigned to the corresponding Lewis acid-base complexes of the germylene with the substrates. The complexation reactions were found to be reversible and are characterized by equilibrium constants of KC= (3.7 ± 0.8) × 103M−1and (3 ± 1) × 104M−1for complexation of GeMe2with CHO and PrS, respectively. The complexes decay over approximately 10 μs with the concomitant formation of tetramethyldigermene (Ge2Me4), identifiable by its characteristic UV-vis spectrum centered at λmax= 370 nm. Diphenylgermylene behaves analogously, reacting rapidly and reversibly with the two substrates to form the corresponding Lewis acid-base complexes (λmax≈ 355 nm) that decay over several tens of microseconds with the concomitant growth of the characteristic UV-vis spectrum of tetraphenyldigermene (Ge2Ph4) (λmax= 440 nm). Steady-state photolysis of the germylene precursors in the presence of CHO afforded germanium-containing oligomers but showed no evidence of oxygen abstraction or the formation of substrate-derived product(s). Similar photolyses in the presence of PrS also afforded germanium-containing oligomers, but as well yielded propene in 20%–30% yield and (in the case of the GePh2precursor) minor amounts of low molecular weight compounds that appear to be derived from the corresponding germanethione. Density functional theory calculations of the chalcogen abstraction reactions of GeMe2with oxirane and thiirane in the gas phase have been carried out at the B3LYP/6-311+G(d,p) level of theory and are in good qualitative agreement with the experimental data.

Photoprotection of folic acid upon encapsulation in food-grade amaranth (Amaranthus hypochondriacus L.) protein isolate – Pullulan electrospun fibers

In this work, the ability of amaranth protein isolate (API):pullulan structures obtained through electrospinning for the photoprotection of bioactive compounds was studied. The model bioactive compound encapsulated was folic acid, due to its great sensitivity to UV light exposure. Addition of 100 mg of folic acid per g of biopolymer to the biopolymeric solution used for electrospinning resulted in increased apparent viscosity and, thus, in thicker electrospun fibers. Very high encapsulation efficiency was obtained (>95%) using this encapsulation technology and no specific chemical interactions were established between the vitamin and the matrix materials as inferred from FTIR analysis. Encapsulation within the API:pullulan structures increased thermal stability of folic acid, which may be useful for food processing applications. Furthermore, no degradation of the encapsulated compound was observed after 2 h of UV exposure, while the characteristic UV–Vis spectrum from the photodegradation compounds of folic acid was observed after UV irradiation of the unprotected vitamin.

Pattern-Based Sensing of Peptides and Aminoglycosides with a Single Molecular Probe

A coumarin-based molecular probe can be used for the sensing of peptides and aminoglycoside antibiotics. The probe reacts with the primary amine group(s) of the analytes to give a mixture of covalent adducts with distinct colors. Each analyte gives rise to a characteristic UV-vis spectrum. A pattern-based analysis of the spectra allows identifying structurally related analytes. Furthermore, it is possible to obtain information about the quantity and the purity of the analytes.

Quinacrine reactivity with prion proteins and prion-derived peptides

Quinacrine is a drug that is known to heal neuronal cell culture infected with prions, which are the causative agents of neurodegenerative diseases called transmissible spongiform encephalopathies. However, the drug fails when it is applied in vivo. In this work, we analyzed the reason for this failure. The drug was suggested to "covalently" modify the prion protein via an acridinyl exchange reaction. To investigate this hypothesis more closely, the acridine moiety of quinacrine was covalently attached to the thiol groups of cysteines belonging to prion-derived peptides and to the full-length prion protein. The labeled compounds were conveniently monitored by fluorescence and absorption spectroscopy in the ultraviolet and visible spectral regions. The acridine moiety demonstrated characteristic UV-vis spectrum, depending on the substituent at the C-9 position of the acridine ring. These results confirm that quinacrine almost exclusively reacts with the thiol groups present in proteins and peptides. The chemical reaction alters the prion properties and increases the concentration of the acridine moiety in the prion protein.

Examination of black inkjet printing inks by capillary electrophoresis

Counterfeiting of documents is a common phenomenon in the modern world. A large proportion of forgeries relates to inkjet printed documents. Hence there is an evident need to develop an effective and reliable method for the differentiation and identification of inkjet inks on questioned documents. The aim of the presented study was to investigate the possibility of applying micellar electrokinetic capillary chromatography (MECC) to forensic analysis of inkjet inks extracted from black and white printouts.In order to achieve the above aim, a capillary electrophoresis system equipped with a diode array detector was used. The separation was performed using a fused silica capillary (60/50cm total/effective length, 75μm i.d.) with a background electrolyte composed of 40mM sodium borate, 20mM SDS and 10% (v/v) acetonitrile (pH 9.5) at 25°C and 30kV. Ink samples were extracted from black inkjet printouts with the use of dimethyl sulphoxide (DMSO).Differentiation of inks was based on the number of significant peaks at different wavelengths, the relative migration times and the characteristic UV–Vis spectra. The electropherograms of the inks extracted from paper showed patterns which in most cases were distinctly different from each other. The greatest diversity of electrophoretic profiles was revealed for documents printed by Hewlett-Packard inkjet technology. A database of electrophoretic separation results of inks has been constructed for further forensic use.

Horseradish peroxidase compound I as a tool to investigate reactive protein-cysteine residues: from quantification to kinetics

Proteins containing reactive cysteine residues (protein-Cys) are receiving increased attention as mediators of hydrogen peroxide signaling. These proteins are mainly identified by mining the thiol proteomes of oxidized protein-Cys in cells and tissues. However, it is difficult to determine if oxidation occurs through a direct reaction with hydrogen peroxide or by thiol–disulfide exchange reactions. Kinetic studies with purified proteins provide invaluable information about the reactivity of protein-Cys residues with hydrogen peroxide. Previously, we showed that the characteristic UV–Vis spectrum of horseradish peroxidase compound I, produced from the oxidation of horseradish peroxidase by hydrogen peroxide, is a simple, reliable, and useful tool to determine the second-order rate constant of the reaction of reactive protein-Cys with hydrogen peroxide and peroxynitrite. Here, the method is fully described and extended to quantify reactive protein-Cys residues and micromolar concentrations of hydrogen peroxide. Members of the peroxiredoxin family were selected for the demonstration and validation of this methodology. In particular, we determined the pKa of the peroxidatic thiol of rPrx6 (5.2) and the second-order rate constant of its reactions with hydrogen peroxide ((3.4±0.2)×107 M−1 s−1) and peroxynitrite ((3.7±0.4)×105 M−1 s−1) at pH 7.4 and 25°C.

Synthesis and Structure of 16 π Octaalkyltetraphenylporphyrins

The oxidized octaethyltetraphenylporphyrin (1, OETPP) and the corresponding newly prepared octaisobutyltetraphenylporphyrin (3, OisoBuTPP) could be isolated from the reaction of OETPPLi2 (or OisoBuTPPLi2) with SOCl2. The X-ray analysis and the characteristic UV-vis spectra of 1 and 3 revealed that these are the first examples of 16 pi nonaromatic porphyrins.

Antagonists Mo and Cu in a heterometallic cluster present on a novel protein (orange protein) isolated from Desulfovibrio gigas

An orange-coloured protein (ORP) isolated from Desulfovibrio gigas, a sulphate reducer, has been previously shown by extended X-ray absorption fine structure (EXAFS) to contain a novel mixed-metal sulphide cluster of the type [S2MoS2CuS2MoS2] [J. Am. Chem. Soc. 122 (2000) 8321]. We report here the purification and the biochemical/spectroscopic characterisation of this novel protein. ORP is a soluble monomeric protein (11.8 kDa). The cluster is non-covalently bound to the polypeptide chain. The presence of a MoS42− moiety in the structure of the cofactor contributes with a quite characteristic UV–Vis spectra, exhibiting an orange colour, with intense absorption peaks at 480 and 338 nm. Pure ORP reveals an Abs480/Abs338 ratio of 0.535. The gene sequence coding for ORP as well as the amino acid sequence was determined. The putative biological function of ORP is discussed.

Inactivation of copper-containing amine oxidases by turnover products.

For bovine serum amine oxidase, two different mechanisms of substrate-induced inactivation have been proposed. One consists of a slow oxidation by H2O2 of a conserved residue in the reduced enzyme after the fast turnover phase [Pietrangeli, P., Nocera, S., Fattibene, P., Wang, X.T., Mondovì, B. & Morpurgo, L. (2000) Biochem. Biophys. Res. Commun.267, 174-178] and the other of the oxidation by H2O2 of the dihydrobenzoxazole in equilibrium with the product Schiff base, during the catalytic cycle [Lee, Y., Shepard, E., Smith, J., Dooley, D.M. & Sayre, L.M. (2001) Biochemistry40, 822-829]. To discriminate between the two mechanisms, the inactivation was studied using Lathyrus cicera (red vetchling) amine oxidase. This, in contrast to bovine serum amine oxidase, formed the Cu+-semiquinolamine radical with a characteristic UV-vis spectrum when oxygen was exhausted by an excess of any tested amine in a closed cuvette. The inactivation, lasting about 90 min, was simultaneous with the radical decay and with the formation of a broad band (shoulder) at 350 nm. No inactivation occurred when a thousand-fold excess of amine was rapidly oxidized in an L. cicera amine oxidase solution stirred in open air. Thus, the inactivation is a slow reaction of the reduced enzyme with H2O2, following the turnover phase. Catalase protected L. cicera amine oxidase from inactivation. This effect was substrate-dependent, varying from full protection (benzylamine) to no protection (putrescine). In the absence of H2O2, a specific inactivating reaction, without formation of the 350 nm band, was induced by some aldehydes, notably putrescine. Some mechanisms of inactivation are proposed.

The reduction of the Rieske iron–sulfur cluster in naphthalene dioxygenase by X-rays

Naphthalene 1,2 dioxygenase (NDO) displays characteristic UV–Vis spectra depending on the oxidation state of the Rieske center. Investigations on crystals of NDO grown for X-ray diffraction experiments showed spectra characteristic of the oxidized form. Crystals reduced in an anaerobic glovebox using sodium-dithionite showed a characteristic reduced spectrum. Spectra of crystals (cooled to 100 K) after being exposed to X-rays for data collection showed spectra corresponding to a reduced Rieske iron center, demonstrating the ability of X-rays to change the oxidation state of the Rieske iron–sulfur cluster in NDO.

Identification of Cu+ as the effective reagent in nitric oxide formation from S-nitrosothiols (RSNO)

Decomposition of S-nitrosothiols (RSNO) in aqueous solution at pH 7.4 is brought about by copper ions, either present as an impurity or specifically added. The primary products are nitric oxide and the disulfide. In the presence of the specific Cu+ chelator, neocuproine, reaction is progressively inhibited as the [neocuproine] is increased, the reaction eventually stopping completely. The characteristic UV–VIS spectrum of the Cu+ adduct can be obtained from the reaction solutions. This shows clearly that Cu+ and not Cu2+ is the effective catalyst. Two limiting kinetic conditions can be identified for a range of S-nitrosothiols at specific copper ion concentrations (a) a first-order dependence and (b) a zero-order dependence upon [RSNO]. Normally both situations also have a short induction period. This induction period can be removed by the addition of the corresponding thiol RSH. A mechanism is proposed in which Cu+ is formed by reduction of Cu2+ by thiolate anion via an intermediate, possibly RSCu+. Loss of nitric oxide from RSNO is then brought about by Cu+, probably via another intermediate in which Cu+ is bound to the nitrogen atom of the NO group and another electron-rich atom (such as nitrogen from an amino group, or oxygen from a carboxylate group) involving a six-membered ring. As well as NO this produces both RS– and Cu2+ which then are part of the cycle regenerating Cu+. Thiolate ion is oxidised to RS˙ which dimerizes to give the disulfide. Depending on the structure (and hence reactivity) of RSNO either Cu+ formation or its reaction with RSNO can be rate-limiting. Computer modelling of the reaction scheme allows the generation of absorbance time plots of the same forms as those generated experimentally, i.e. first- or zero-order, both with or without induction periods. We suggest that the thiolate ion necessary to bring about Cu2+ reduction is either present as a thiol impurity or is generated in small quantities by partial hydrolysis of the nitrosothiol, which results in an induction period. Addition of small quantities of thiol removes the induction period and leads to catalysis but larger quantities bring about a rate reduction by, it is suggested, complexation of the Cu2+. For two very unreactive substrates, S-nitrosoglutathione and S-nitroso-N-acetylcysteine very large induction periods were observed, typically three hours. This results, we suggest, from competitive re-oxidation of Cu+ to Cu2+ by the dissolved oxygen. Experiments carried out anaerobically confirm this, since there is then no induction period. Addition of hydrogen peroxide extends the induction period ever further. The results are discussed in terms of the biological properties of S-nitrosothiols which are related to nitric oxide release.

Reactions of platinum in oxygen- and hydrogen-treated [formula omitted] catalysts : II. Ultraviolet-visible studies, sintering of platinum, and soluble platinum

Pt γ-Al 2O 3 catalysts treated in oxygen between 100 and 600 °C and in hydrogen at 500 °C were studied by uv-vis reflectance spectroscopy. The formation of different oxidized Pt surface species previously indicated by TPR studies [H. Lieske, G. Lietz, H. Spindler, and J. Völter, J. Catal. 81, 8 (1983)] was confirmed by characteristic uv-vis spectra. The results are used as the basis for a model describing the types of surface reactions and details of the platinum surface species formed in oxygen and in hydrogen, and for a model of the sintering in oxygen. The amount of soluble platinum was found to correspond with the amount of highly dispersed platinum. Hence, only surface platinum atoms are soluble.