Ultraviolet Fluorescence Spectroscopy Research Articles

River network travel time is correlated with dissolved organic matter composition in rivers of the contiguous United States

AbstractMost terrestrial allochthonous organic matter enters river networks through headwater streams during high flow events. In headwaters, allochthonous inputs are substantial and variable, but become less important in streams and rivers with larger watersheds. As allochthonous dissolved organic matter (DOM) moves downstream, the proportion of less aromatic organic matter with autochthonous characteristics increases. How environmental factors converge to control this transformation of DOM at a continental scale is less certain. We hypothesized that the amount of time water has spent travelling through surface waters of inland systems (streams, rivers, lakes, and reservoirs) is correlated to DOM composition. To test this hypothesis, we used established river network scaling relationships to predict relative river network flow‐weighted travel time (FWTT) of water for 60 stream and river sites across the contiguous United States (3090 discrete samples over 10 water years). We estimated lentic contribution to travel times with upstream in‐network lake and reservoir volume. DOM composition was quantified using ultraviolet and visible absorption and fluorescence spectroscopy. A combination of FWTT and lake and reservoir volume was the best overall predictor of DOM composition among models that also incorporated discharge, specific discharge, watershed area, and upstream channel length. DOM spectral slope ratio (R2 = 0.77) and Freshness Index (R2 = 0.78) increased and specific ultraviolet absorbance at 254 nm (R2 = 0.68) and Humification Index (R2 = 0.44) decreased across sites as a function of FWTT and upstream lake volume. This indicates autochthonous‐like DOM becomes continually more dominant in waters with greater FWTT. We assert that river FWTT can be used as a metric of the continuum of DOM composition from headwaters to rivers. The nature of the changes to DOM composition detected suggest this continuum is driven by a combination of photo‐oxidation, biological processes, hydrologically varying terrestrial subsidies, and aged groundwater inputs.

Quantitation of hydrogen sulfide reference gas mixtures to provide traceability for indoor air quality monitoring

Accurate measurements for the determination of hydrogen sulfide (H2S) are critical for the compliance with legislation in various industries, including natural gas and environmental sectors such as air pollution monitoring. H2S measurements at ambient level are challenging because H2S tends to adsorb on the internal surfaces of the sample collection devices such as gas cylinders and transfer lines. Prolonged exposure to H2S has known health implications to humans, such as irritation to the nose, throat and airways that results in coughing or inflammation, wheezing and shortness of breath around the chest. H2S is mainly monitored for occupational health and safety and indoor air quality monitoring. It is a highly reactive gas that can easily react with oxygen to form sulfur dioxide (SO2) and with water to form sulfuric acid (H2SO4). The traceability of H2S measurements is achieved through the preparation of reference gas mixtures. These gas mixtures are gravimetrically prepared in accordance with International Organization for Standardization (ISO 6142–1:2015). The H2S reference gas mixtures were produced with the highest metrological capability; thus, the molar mass, purity assessment, and the weighing gave an overall gravimetric relative uncertainty which is less than 0.10% (k = 1). One of the biggest challenges in producing a H2S reference gas mixture is the handling of a gas cylinder from the gravimetric preparation process until the verification stage. This work will detail the improved techniques and measurements used to produce the H2S reference gas mixtures. The internal consistency between the mixtures was verified using a non-dispersive ultraviolet (NDUV) spectroscopy analyzer, an ultraviolet fluorescence spectroscopy (UVFS) analyzer and gas chromatography coupled with a pulsed discharged helium ionization detector (GC-PDHID). Our measurement uncertainty results show that the gravimetric value, internal consistency, adsorption, homogeneity, and stability were within a relative uncertainty of 1.2% as compared to our previous uncertainty of 4.4%. This is a significant improvement for the measurements of H2S reference gas mixtures.

Hydroxylporphyrin/NiO nanosheet nanocomposite with strong interfacial interaction for highly efficient hydrogen generation

Hexagonal nickel oxide nanosheet (NiO) was surface modified with various amounts of tetrahydroxylphenyl porphyrin (THPP) to form a series of THPP/NiO nanosheet photocatalysts. The interacted mechanism between THPP and NiO was studied in detail by ultraviolet spectroscopy and fluorescence spectroscopy. Furthermore, the photocatalytic activity for hydrogen production and electron transfer mechanism over the THPP/NiO nanosheet nanocomposite were investigated by fluorescence spectra, UV–vis spectra and electrochemical measurements. The results showed that the special coordination interaction between THPP and NiO had an important influence on the photocatalytic performance of the nanocomposite, and a photocatalyst with high and stable photocatalytic activity can be achieved by controlling the interaction between porphyrin and NiO-like metal oxides. It will provide a new idea for fabricating highly efficient photocatalysts for hydrogen production.

Synthesis of Fluorescent Carbon Dots and Their Application in Ascorbic Acid Detection.

Water-soluble fluorescent carbon dots (CDs) were synthesized by a hydrothermal method using citric acid as the carbon source and ethylenediamine as the nitrogen source. The repeated and scale-up synthetic experiments were carried out to explore the feasibility of macroscopic preparation of CDs. The CDs/Fe3+ composite was prepared by the interaction of the CDs solution and Fe3+ solution. The optical properties, pH dependence and stability behavior of CDs or the CDs/Fe3+ composite were studied by ultraviolet spectroscopy and fluorescence spectroscopy. Following the principles of fluorescence quenching after the addition of Fe3+ and then the fluorescence recovery after the addition of asorbic acid, the fluorescence intensity of the carbon dots was measured at λex = 360 nm, λem = 460 nm. The content of ascorbic acid was calculated by quantitative analysis of the changing fluorescence intensity. The CDs/Fe3+ composite was applied to the determination of different active molecules, and it was found that the composite had specific recognition of ascorbic acid and showed an excellent linear relationship in 5.0–350.0 μmol·L−1. Moreover, the detection limit was 3.11 μmol·L−1. Satisfactory results were achieved when the method was applied to the ascorbic acid determination in jujube fruit. The fluorescent carbon dots composites prepared in this study may have broad application prospects in a rapid, sensitive and trace determination of ascorbic acid content during food processing.

Characterization of dissolved organic matter derived from coal gangue packed in underground reservoirs of coal mines using fluorescence and absorbance spectroscopy.

Organic and nitrogen pollutants in mine water could be removed effectively during the storage and transport of water in a coal mine underground reservoir packed with coal gangue through various water-rock interactions. However, little is known about the effect of the released dissolved organic matter (DOM) derived from the packed matrix on their removal. Column experiments were performed at a Darcy flux of 1.56 cm·h-1 at 25 °C to investigate the characteristics of DOM derived from Jurassic and Permian coal gangue individually packed in underground reservoirs of Bulianta (BL1) and Baode (BD2) coal mines. Chemical characteristics of the DOM were analyzed by using the ultraviolet and visible (UV-Vis) absorbance and fluorescence spectroscopy techniques. Results showed that the values of dissolved organic carbon (DOC) and electricity (EC) in the outlet of column packed with BL1 were obviously higher than those from BD2 due to the higher permeability of BL1 with more complex mineralogical and chemical compositions. The parallel factor analysis (PARAFAC) indicated that the fluorescence components in the DOM derived from BL1 and BD2 were individually dominated by the humic-like and tryptophan-like substances. Thus, the higher aromaticity, hydrophobicity, and humification indicated by the specific ultraviolet absorbance at 254 nm (SUVA254) and 260 nm (SUVA260) and humification index (HIX) were observed in the DOM from the younger Jurassic BL1, implying that the DOM may contain more plant-derived precursors. Meanwhile, the higher values of fluorescence index (FI) and biological/autochthonous index (BIX) confirmed the stronger autochthonous characterization of DOM originated from the earlier Permian BD2. The observed characterization of DOM will further extend the understanding of purification mechanism of mine water during its storage and transport in coal mine underground reservoirs packed with coal gangue of different geologic ages.

Effects of AAEMs on formation of heavy components in bio-oil during pyrolysis at various temperatures and heating rates

Heavy components (molecular weight > 200 Da) in bio-oil affect the thermal conversion of bio-oil significantly. The inherent alkali/alkaline earth metal species (AAEMs) in biomass affect the formation of heavy components in bio-oil due to its catalytic effects. In order to investigate the effects of AAEMs on the formation of heavy components in bio-oil during biomass pyrolysis, the heavy components in bio-oil were characterized with the Fourier transform ion cyclotron resonance mass (FT-ICR MS) spectrometer and the ultraviolet fluorescence (UV-F) spectroscopy. The roles of K and Ca were also investigated. The results showed that AAEMs promoted the breakage of active oxygen-containing functional groups in heavy phenolics and inhibited their formation during pyrolysis, as well as the formation of heavy carbohydrates. The total content of heavy components decreased due to the catalytic effects of AAEMs. The catalytic effects of K on the decomposition of large molecular weight compounds (> 500 Da) in heavy components were stronger than those of Ca. K increased the content of single ring aromatic components in bio-oil for 1.5 times, while Ca decreased the content of the 2–3 rings aromatic components in bio-oil for more than 50%, compared to the bio-oil generated from the pyrolysis without AAEMs.

Impact of hydrophyte decomposition on the changes and characteristics of dissolved organic matter in lake water

Abstract Hydrophyte decomposition can generate a large amount of decomposed organic matter that results in potential risks to water quality. Dissolved organic matter (DOM) collected from lake water induced by hydrophyte decomposition may play a key role in understanding the change in the water quality. Spectroscopic techniques can reveal the spectral properties of DOM and their impact on the water quality under oligotrophic and eutrophic growth conditions, such as the application of ultraviolet visible (UV–vis) spectra and fluorescence spectroscopy in combination with parallel factor analysis (PARAFAC) method. The results indicated that dissolved organic carbon (DOC), a350, and UV absorption in a unit of TOC at 254 nm (SUVA254) values under eutrophic growth conditions in summer are generally higher than those under oligotrophic conditions in winter. Five fluorescent components, including one humic-like substance (C4), one fulvic-like material (C3) and three protein-like materials (C1, C2 and C5) were obtained by PARAFAC analysis from hydrophyte-derived DOM samples under different growth conditions and in different seasons. The Fmax of the different fluorescent components were greatly influenced by hydrophyte decomposition, and varied under these different conditions. The results of water quality parameters also showed that dissolved oxygen (DO), chemical oxygen demand (COD), total phosphorus (TP), and total nitrogen (TN) concentrations for oligotrophic and eutrophic conditions in the summer (OS and ES) samples were generally higher than those in the winter samples. The characterization of hydrophyte decomposition DOM is of great importance in eutrophic lake management. Thus, much effort should be put into the study of hydrophyte-derived DOM characteristics and their potential risks as a carrier of hazardous pollutants. The study provides scientific guidance for lake clean water management.

L-Arginine Modified Magnetic Nanoparticles (RMNPs): Ameliorative Effects on Lysozyme Structure and Efficiency

In recent years, there is great attention on the L-Arginine (Arg) which is a unique, non-toxic, and biocompatible green material because it can be utilized as an agent for the functionalization then stabilization of magnetite [Fe3O4] nanoparticles (MNPs) against oxidation and aggregation during or after synthesis procedure. Our studies demonstrate that Arg has two great impacts on the MNPs which include increasing and decreasing its stability and particle size respectively. Besides, saturation magnetization and electrostatic interactions of Arg-coated magnetic nanoparticles (RMNP) have a direct impact on the biological molecules such as proteins and genes. Therefore, controlling Arg concentration gives a great chance to accurate control above mentioned characterizations which is a useful tool for applications such as antibody connecting, catalyst, drug loading, and MNPs stability modifier. In the current study, RMNPs with different arginine concentrations aka 0.42μg, 1.62μg, and 2.29μg per mg in three synthesized RMNPs (as named \U0001d45d0.5, \U0001d45d1, and \U0001d45d1.5) on the surface of MNPs based on a colorimetric determination, has been successfully synthesized through the simple co-precipitation method. Besides, as-synthesized RMNP powders were characterized by XRD, SEM/EDAX, FT-IR, VSM, and Zeta Potential analyser. The effect of these nanoparticles on the stability of lysozyme protein as a model protein was investigated; also the secondary structure and stability of lysozyme along with these nanoparticles were detected by Ultraviolet (UV) spectroscopy, circular dichroism (CD), fluorescence spectroscopy and enzymatic activity measurements. The results show that magnetic nanoparticles capped with arginine, improve the properties of magnetite (biocompatibility, prevent aggregation of nanoparticles, reduce the size of nanoparticles) and improve the secondary structure of the protein, as well as increase the stability and protein activity. Results from XRD, SEM, and FT-IR was argued that arginine was completely capped to magnetite nanoparticles. Also, the results of VSM showed that, with increasing amount of arginine, magnetite saturation magnetization decreased due to the increase in the diameter of the coating. Finally, the results of bioassay tests proven stability and protein efficiency.Keywords: Arginine, Arginine coated magnetic nanoparticles, Co-precipitation, Lysozyme.1-Bagherpour AR, Kashanian F, Ebrahimi SS, Habibi-Rezaei M. L-arginine modified magnetic nanoparticles: green synthesis and characterization. Nanotechnology. 2018 Jan 15;29(7):075706.2-Alimohammadi V, Kashanian F, Seyyed Ebrahimi SA, Habibi Rezaei M, Bagherpour A. Synthesis and characterization of functionalizedmagnetite nanoparticles by alkyl group (Fe3O4@ TMOS). Metallurgical Engineering. 2019;21(4):275-83.3-Kashanian F, Habibi-Rezaei M, Bagherpour AR, Seyedarabi A, Moosavi-Movahedi AA. Magnetic nanoparticles as double-edged swords: concentration-dependent ordering or disordering effects on lysozyme. RSC Advances. 2017;7(86):54813-22.4-Kashanian F, Habibi-Rezaei M, Moosavi-Movahedi AA, Bagherpour AR, Vatani M. The ambivalent effect of Fe3O4 nanoparticles on the urea-induced unfolding and dilution-based refolding of lysozyme. Biomedical Materials. 2018 May 15;13(4):045014.5-Bagherpour AR. Magnetic Nanoparticles As a Biological Sensors for Early Diagnosis and Treatment of Cancer Cells. InMeeting s 2019 Sep 1 (No. 52, pp. 2290-2290). The Electrochemical Society.

Multi-sensing function integrated nitrogen-doped fluorescent carbon dots as the platform toward multi-mode detection and bioimaging

In this work, nitrogen-doped carbon dots (N-CDs) were successfully utilized as a photoluminescent platform for multi-mode sensing of chromium(VI) [Cr(VI)], 2,4,6-trinitrophenol (TNP) and ascorbic acid (AA). The N-CDs with green fluorescent emission were synthesized via one-pot method using p-phenylenediamine and ammonia as precursors. The structure and optical properties were characterized by Fourier transform infrared spectroscopy, ultraviolet visible spectroscopy and fluorescence spectroscopy, respectively. Cr(VI) and TNP were able to absorb the excitation band and emission band of N-CDs and decreased the photoluminescence of N-CDs from internal filtration effect (IFE). Besides, the construction of N-CDs/Cr(VI) mixture can implement as a fluorescence platform for further detection of AA on the basis of the oxidation-reduction reactions between Cr(VI) and AA. Meanwhile, as-prepared N-CDs exhibit strong photostability, low toxicity and great biocompatibility. Moreover, the as-fabricated N-CDs have been smoothly achieved bioimaging in SMMC7721 cells owing to its low toxicity. It is prospective that N-CDs can be applied as a rapid multi-function sensing platform to biosensing and biomedical optical imaging.

Probing the structural interactions between methotrexate and dexamethasone with muscle cystatin: a biophysical study

Drug protein interactions have gained considerable attention over the past many years. In the current communication the association of muscle cystatin (MC) with anti-rheumatic drugs methotrexate and dexamethasone was studied by thiol proteinase inhibitor assay, ultra violet (UV) absorption, fluorescence spectroscopy, and fluorescence transform infra-red spectroscopy (FTIR). A static pattern of quenching was noticed between muscle cystatin and methotrexate (MTX). Binding constant (K a) of methotrexate to muscle cystatin was found to be 1 × 10−7 M−1 and the stoichiometry of binding was calculated to be one. Fluorescence measurement of the emission quenching reveals that the quenching process of cystatin by dexamethasone (DXN) was also static. The stoichiometry of binding and binding constant was also obtained. Additional evidence regarding MTX–MC and DXN–MC was obtained from UV spectroscopy and FTIR spectroscopic results. Such spectroscopic studies would help in modelling new candidate drugs for rheumatoid arthritis based on their cystatin binding profile. Communicated by Ramaswamy H. Sarma

Long-acting photocatalytic degradation of crude oil in seawater via combination of TiO2 and N-doped TiO2/reduced graphene oxide

ABSTRACT N-doped TiO2/ reduced graphene oxide (N/TiO2/rGO) composite was prepared and used together with the commercial TiO2 for comparative research on photocatalytic degradation of crude oil in seawater. Five test conditions were designed including a combined catalyst of TiO2 and N/TiO2/rGO (4:1) under UV-A light irradiation with a duration of 28 days. The changing trend of the water-soluble fraction (WSF) of crude oil in seawater was monitored by ultraviolet spectroscopy and fluorescence spectroscopy as well as dissolved organic carbon (DOC) measurement. The SARA fractions of oil residues were analysed by column chromatography, and the chemical composition changes of saturates and aromatics were investigated by gas chromatography-mass spectroscopy (GC-MS). The results reveal that although it had high efficiency in the degradation of aromatics, the nano-TiO2 tended to self-agglomerate, which enhanced agglomeration of crude oil, causing its catalytic process actually terminating within seven days. By comparison, the N/TiO2/rGO composite consistently dispersed crude oil in the whole experimental duration, subsequently, it presented a higher photocatalytic degradation rate than TiO2. The combination of TiO2 and N/TiO2/rGO (4:1) shows concerted catalysis on photocatalytic degradation of crude oil, and the oil degradation rate reached to 54.80% while the aromatic degradation rate was 74.83%. The fluorescent components in WSFs were preferentially degraded, and the degradation products of aromatic fraction were CO2 and H2O as well as saturates, mainly C20∼C31 alkanes. Considering its long-acting photocatalysis, the N/TiO2/rGO composite possesses practical utilization potentiality together with TiO2 in spilled oil treatment in the marine environment.

A Turn‐On Fluorescence Probe for Rapid Detection of Hypochlorite in Living Cells and in Vitro

AbstractA turn on fluorescence probe for the rapid detection of hypochlorite (ClO−) was prepared successfully. The detection performances of this probe were studied by virtue of ultraviolet absorption and fluorescence spectroscopy. The results demonstrated that this probe displayed excellent colorimetric and noteworthy fluorescence enhancement after interaction with hypochlorite (ClO−) and showed good selectivity and sensitivity for ClO− over other analytes in solution. Due to the short reaction time, high selectivity and sensitivity, this probe was successfully used in the detection of ClO− in living cells and water samples.

Transglutaminase-catalysed cross-linking eliminates Penaeus chinensis tropomyosin allergenicity by altering protein structure

ABSTRACT Transglutaminase (TG) is a major food processing enzyme that induces protein cross-linking. Tropomyosin (TM) is a major shellfish allergen that is responsible for at least 80% of the shrimp allergic incidents. The aim of this research was to investigate the effect of TG on TM allergenicity and reveal the involvement of TM structure alternation. After treated with TG for different time, the allergenicity of TM was assessed by indirect ELISA with shrimp allergic patients’ sera, and the structure of TM was characterized by circular dichroism (CD) spectroscopy, ultraviolet (UV) absorption spectroscopy and fluorescence spectroscopy. Results showed that the allergenicity slightly decreased at the early stage of reaction and dramatically decreased at the late stage, which is tightly correlated with the increment of β-turn content and UV absorption. In conclusion, TG modification is an effective and promising food processing method to eliminate TM allergenicity with significant prospect of industrial application.

Studies on the Interaction between Angiotensin-Converting Enzyme (ACE) and ACE Inhibitory Peptide from Saurida elongata.

Angiotensin-converting enzyme (ACE) inhibitory peptides derived from food protein exhibited antihypertensive effects by inhibiting ACE activity. In this work, the interaction between ACE inhibitory peptide GMKCAF (GF-6) and ACE was studied by isothermal titration calorimetry (ITC), molecular docking, ultraviolet absorption spectroscopy, fluorescence spectroscopy, and circular dichroism spectroscopy. Experimental results revealed that the binding of GF-6 to ACE was a spontaneous exothermic process driven by both enthalpy and entropy. The interaction occurred via a static quenching mechanism and involved the alteration of the conformation of ACE. In addition, ITC and molecular docking results indicated binding of GF-6 to ACE via multiple binding sites on the protein surface. This study could be deemed helpful for the better understanding of the inhibitory mechanism of ACE inhibitory peptides.

The formation mechanism for OPAHs during the cellulose thermal conversion in inert atmosphere at different temperatures based on ESI(−) FT-ICR MS measurement and density functional theory (DFT)

Oxygenated polycyclic aromatic hydrocarbons (OPAHs) are an important group of components produced from the thermal conversion of cellulose. Through using gas chromatography mass spectrometry (GC–MS), Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) and ultraviolet fluorescence spectroscopy (UV-F), the information for the evolution of OPAHs is obtained in this study. The tar produced at low temperature mainly contains light components such as homologues of pyran and furan, while the components in the tars at 700 °C and 900 °C show high double bond equivalent (DBE) values, indicating the existence of large aromatic structures.High temperature promote condensation reactions during cellulose thermal conversion, thus leading to a higher percentage of OPAHs in the tar at higher temperature process. According to Density Functional Theory (DFT) calculation, the energy barrier of Diels-Alder reaction (302.65 kJ/mol) is lower than the dehydration (583.26 kJ/mol), which means that Diels-Alder reaction could be the main route for OPAH formation rather than dehydration reaction. High reaction temperature is calculated to be favorable for the formation of naphthol during the cellulose thermal conversion because of the high energy barrier of dehydration between phenol and furan. It is consistent with the ESI FT-ICR MS result that there is a higher content of naphthol in the tar at 700 °C than that at 500 °C.

Effect of the pre-reforming by Fe/bio-char catalyst on a two-stage catalytic steam reforming of bio-oil

Ni-based catalyst is prone to the deactivation by coke deposition during the catalytic steam reforming of bio-oil. In order to optimize catalytic activity of the Ni-based catalyst, a two-stage catalytic reforming scheme was proposed whereby a low-temperature (350–600 °C) pre-reforming process with a less expensive catalyst was introduced prior to the Ni-based catalyst. To study this scheme, the reforming experiments with different combinations of Fe/bio-char (in the first stage) and Ni-Ca/γ-Al2O3 (in the second stage) were conducted. In addition to the quantification of product yields, the tar and gas were characterized with an ultraviolet (UV) fluorescence spectroscopy, a gas chromatography/mass spectrometer (GC/MS) and a gas chromatography (GC). The results indicate that significant proportions of naphthalenes and polycyclic aromatics in the intermediate volatiles turned into furans, phenols and non-aromatics, which are easier to be reformed on Ni-based catalysts, via the Fe/bio-char pre-reforming, resulting in the increase of the final H2 and CO yields of the overall process. At high pre-reforming temperatures (550–600 °C), the coke formation on Ni-based catalyst was significantly inhibited due to the Fe/bio-char pre-reforming. In addition, the results indicate that the spent Ni-based catalyst had more free NiO and NiAl2O4 spinel than the fresh one, suggesting that the increase in the catalytic activity of Ni-based catalyst during the reforming process was promoted by Fe/bio-char pre-reforming.

Effects of heating rate on the evolution of bio-oil during its pyrolysis

Bio-oil from the fast pyrolysis of biomass can be converted to solid carbon materials, chemicals and syngas by various thermochemical conversion methods. As a first step in all of these processes, bio-oil undergoes drastic components changes due to its exposure to the elevated temperature. Understanding the effects of heating rate on bio-oil transformation during its pyrolysis is therefore crucial for effective utilization of bio-oil. In this study, a bio-oil sample produced from the fast pyrolysis of rice husk at 500 °C was pyrolyzed in a fixed-bed reactor at temperatures between 300 and 800 °C at three different heating rates: fast (≈200 °C/s), medium (≈20 °C/s), and slow (≈0.33 °C/s). In addition to the quantification of coke and tar yields, the tar was characterized with an ultraviolet (UV) fluorescence spectroscopy, a gas chromatography/mass spectrometer (GC/MS) and a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). Our results indicate that slow heating rates promote polymerization of bio-oil components, particularly at low temperatures (<500 °C), resulting in higher primary coke yields than that of the fast heating rates. Decomposition reaction was found to be pronounced at fast heating rates, causing decreases in the tar yields and abundance of light compounds. The increases in the yields of the secondary coke, the formations of more condensed aromatic structures and macromolecules (m/z > 500) were also promoted at fast heating rates via the more intense secondary reactions.

Investigation of the interaction between benzaldehyde thiosemicarbazone compounds and xanthine oxidase

A series of substituted benzaldehyde thiosemicarbazide compounds (1–7) were synthesized as xanthine oxidase (XO) inhibitors, and the interactions between substituted benzaldehyde thiosemicarbazide compounds (1–7) and XO were studied by ultraviolet spectroscopy, fluorescence spectroscopy, and molecular docking. It was found that the hydrogen bond and hydrophobicity were the main interactions between substituted benzaldehyde thiosemicarbazide compounds and XO, and introducing OH at the para position of the benzene ring and a Ph- or Me-group at the amino terminal of compound 4 increased the modifier's inhibitory activity. The results suggest that the newly introduced benzene ring interacted with the hydrophobic cavity of XO by means of the π-π stacking force between the newly introduced benzene ring and the aromatic amino acid residues, such as the Phe residue, which greatly increased the modifier's inhibitory activity. We conclude that introducing the Ph-group at the amino terminal of compound 4 and the OH group at the para position of the benzene ring was a good route to obtain novel XO inhibitors. Fluorescence spectroscopy assisted by 8-anilino-1-naphthalenesulfonic acid fluorescence probing and molecular docking were helpful for achieving a preliminary and relatively clear understanding of the interactions between target compounds and XO, which deserve further study.

Study on the structural evolution of semi-chars and their solvent extracted materials during pyrolysis process of a Chinese low-rank coal

The structural evolution of coal during pyrolysis process has been studied for a long time but remains unclear, mainly due to the extraordinary complexity of coal structure. The present study aimed to further identify the chemical structural evolution of different parts in the semi-chars obtained by low-temperature pyrolysis of a Chinese low-rank coal (Shenfu coal). Semi-chars and their solvent extracted materials (oil, resin, asphaltene and preasphaltene) were analyzed by 13C nuclear magnetic resonance (NMR) mass spectrometry, diffuse reflectance Fourier transform-infrared spectroscopy (DRIFTs) and ultraviolet (UV) fluorescence spectroscopy, separately. The results showed that 23.8% weight loss occurred during the whole pyrolysis process at 435 °C and half of the weight loss was achieved in the initial five minutes. By contrast, amount of the extracts in semi-chars (solvent extracted metaplast materials) decreased more dramatically in the initial stage of the pyrolysis, and 51.8% of the extracts disappeared in the initial one minute. Oil and preasphaltene showed higher thermal sensitivity than asphaltene and resin. Considerable content of metaplast materials with 1–2 rings (especially in oil and/or asphaltene) were produced along with the pyrolysis process. Condensed aromatic structures in semi-chars were relatively stable and mainly decomposed in the initial stage of pyrolysis which could be attributed to the dramatically decomposition of some active aromatic structures with ≥ 4 rings (especially the components in extracts such as preasphaltene). The results provided a new insight into the structural evolution of coal during low-temperature pyrolysis process, which specially considered the detailed information of the solvent extractable metaplast materials in semi-chars.

Detecting aromatic compounds on planetary surfaces using ultraviolet time-resolved fluorescence spectroscopy

Many aromatic organic molecules exhibit strong and characteristic fluorescence when excited with ultraviolet radiation. As laser excitation in the ultraviolet generates both fluorescence and resonantly enhanced Raman scattering of aromatic vibrational modes, combined Raman and fluorescence instruments have been proposed to search for organic compounds on Mars. In this work the time-resolved fluorescence of a suite of 24 compounds composed of 2–5 ringed alternant, non-alternant, and heterocyclic PAHs was measured. Fluorescence instrumentation with similar specifications to a putative flight instrument was capable of observing the fluorescence decay of these compounds with a sub-ns resolution. Incorporating time-resolved capabilities was also found to increase the ability to discriminate between individual PAHs. Incorporating time-resolved fluorescence capabilities into an ultraviolet gated Raman system intended for a rover or lander can increase the ability to detect and characterize PAHs on planetary surfaces.