Isomers Research Articles

Synthesis and Chemical Structure of the Cyclic Heptapeptide Stylissamide H.

We investigated the chemical structures and conformational isomers of the cyclic heptapeptides stylissamide H and euryjanicin A isolated from marine sources. Despite sharing the same molecular structure, stylissamide H and euryjanicin A exhibit different conformational isomers in solution and solid states. The main difference arises from the cis/trans configurations of the two Pro residues. We prepared stylissamide H using Fmoc solid-phase peptide synthesis and investigated its chemical structure in the solution state and the solid state via NMR spectroscopy and X-ray crystallography, respectively. The results indicated that the s-trans,cisPro conformer of stylissamide H is more stable in solution, whereas the s-cis,cisPro conformer is more stable in the solid state. We concluded that stylissamide H and euryjanicin A are the same molecules.

Steering diffusion selectivity of chemical isomers within aligned nanochannels of metal-organic framework thin film

The movement of molecules (i.e. diffusion) within angstrom-scale pores of porous materials such as metal-organic frameworks (MOFs) and zeolites is influenced by multiple complex factors that can be challenging to assess and manipulate. Nevertheless, understanding and controlling this diffusion phenomenon is crucial for advancing energy-economic membrane-based chemical separation technologies, as well as for heterogeneous catalysis and sensing applications. Through precise assessment of the factors influencing diffusion within a porous metal-organic framework (MOF) thin film, we have developed a chemical strategy to manipulate and reverse chemical isomer diffusion selectivity. In the process of cognizing the molecular diffusion within oriented, angstrom-scale channels of MOF thin film, we have unveiled a dynamic chemical interaction between the adsorbate (chemical isomers) and the MOF using a combination of kinetic mass uptake experiments and molecular simulation. Leveraging the dynamic chemical interactions, we have reversed the haloalkane (positional) isomer diffusion selectivity, forging a chemical pathway to elevate the overall efficacy of membrane-based chemical separation and selective catalytic reactions.

Analysis of Multivariable Sensor Responses to Multi-Analyte Gas Samples in the Presence of Interferents and Humidity.

This work presents an adaptive sensor signal-processing approach to enable quantification, using a single gas sensor or a small sensor array, of multianalyte mixtures of aromatic hydrocarbons in the presence of various interferents and humidity for environmental-monitoring applications. Dynamic sensor responses are analyzed by extracting multivariable sensing parameters to provide necessary sensitivity and selectivity. This is achieved by integrating the Levenberg-Marquardt-modified, exponentially weighted, recursive-least-squares-estimation (LM-modified EW-RLSE) algorithm and principal-component analysis (PCA). Achieving measured detection limits as low as 3 μg/L (≤1 ppm by volume) for 6 target analytes, the system exhibits excellent PCA cluster separation for all analytes in the mixtures, with reliable identification and accurate quantification, even in the presence of various interferents. Concentration errors of approximately ±5% are obtained for mixtures containing up to 6 BTEX compounds (including chemical isomers) and up to 4 interferents. Additionally, the study investigates the impact of humidity on the polymer/plasticizer-coated shear-horizontal surface acoustic wave (SH-SAW) sensors, demonstrating accurate concentration estimation in a relative humidity range from dry nitrogen to 65%. This sensing-and-multivariate-signal-processing approach is a promising candidate for reliable environmental monitoring in real-world applications.

FGTN: Fragment-based graph transformer network for predicting reproductive toxicity.

Reproductive toxicity is one of the important issues in chemical safety. Traditional laboratory testing methods are costly and time-consuming with raised ethical issues. Only a few in silico models have been reported to predict human reproductive toxicity, but none of them make full use of the topological information of compounds. In addition, most existing atom-based graph neural network methods focus on attributing model predictions to individual nodes or edges rather than chemically meaningful fragments or substructures. In current studies, we develop a novel fragment-based graph transformer network (FGTN) approach to generate the QSAR model of human reproductive toxicity by considering internal topological structure information of compounds. In the FGTN model, the compound is represented by a graph architecture using fragments to be nodes and bonds linking two fragments to be edges. A super molecule-level node is further proposed to connect all fragment nodes by undirected edges, obtaining global molecular features from fragment embeddings. The FGTN model achieved an accuracy (ACC) of 0.861 and an area under the receiver operating characteristic curve (AUC) value of 0.914 on nonredundant blind tests, outperforming traditional fingerprint-based machine learning models and atom-based GCN model. The FGTN model can attribute toxic predictions to fragments, generating specific structural alerts for the positive compound. Moreover, FGTN may also have the capability to distinguish various chemical isomers. We believe that FGTN can be used as a reliable and effective tool for human reproductive toxicity prediction in contribution to the advancement of chemical safety assessment.

Julian Hirniak, an early proponent of periodic chemical reactions

In this article we present and discuss the work and scientific legacy of Julian Hirniak, the Ukrainian chemist and physicist who published two articles in 1908 and 1911 about periodic chemical reactions. Over the last 110+ years, his theoretical work has often been cited favorably in connection with Alfred Lotka’s theoretical model of an oscillating reaction system. Other authors have pointed out thermodynamic problems in Hirniak’s reaction scheme. Based on English translations of his 1908 Ukrainian and 1911 German articles, we show that Hirniak’s claim (that a cycle of inter-conversions of three chemical isomers in a closed reaction vessel can show damped periodic behavior) violates the Principle of Detailed Balance (i.e., the Second Law of Thermodynamics), and that Hirniak was aware of this Principle. We also discuss his results in relation to Lotka’s first model of damped oscillations in an open system of chemical reactions involving an auto-catalytic reaction operating far from equilibrium. Taking hints from both Hirniak and Lotka, we show that the mundane case of a kinase enzyme catalyzing the phosphorylation of a sugar can satisfy Hirniak’s conditions for damped oscillations to its steady state flux (i.e., the Michaelis–Menten rate law), but that the oscillations are so highly damped as to be unobservable. Finally, we examine historical and factual misunderstandings related to Julian Hirniak and his publications.

Modulating the Reaction Pathway of Ni2P/Al2O3 by Introducing Different Noble Metals for Hydrodesulfurization of Diesel.

Regulating the reaction pathway of a hydrodesulfurization (HDS) catalyst to achieve ultradeep desulfurization of diesel is a low-energy-consumption yet effective strategy but remains a tricky challenge. Herein, we present a Ni2P/Al2O3 catalyst with mesoporous properties synthesized by a facile hydrothermal-temperature-programmed reduction and normal impregnation (TPRI) method, and then different precious metals with similar loadings were introduced to prepare M-Ni2P/Al2O3 (M = Pt, Pd) catalysts through incipient wetness impregnation. Their structures were analyzed by a series of characterization methods, and their catalytic performances were examined for 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS. The correlation characterization results revealed that the kind of precious metals significantly affected the surface acidity and then the metal-support interaction (MSI) between Ni2P and Al2O3. Among them, the Pt-Ni2P/Al2O3 catalyst exhibits superior HDS activity with 88.5% 4,6-DMDBT conversion to Pd-Ni2P/Al2O3 (76.3%) and pristine Ni2P/Al2O3 (58.6%) catalysts under reaction conditions of 3.4 MPa, 340 °C, and LHSV = 4.8 h-1. This should be due to the introduction of Pt, which significantly facilitates the dissociation rate of H2 and the subsequent generation of more active hydrogen species than Pd, thereby promoting the formation of Brønsted acid sites, remarkably facilitating the isomerization (ISO) pathway, and markedly enhancing the 4,6-DMDBT HDS conversion of Pt-Ni2P/Al2O3. This work provides an efficient protocol to tame the reaction pathway and thereafter the catalytic performance of the HDS catalyst in the future.

Metabolic profiling of the flower of Citrus aurantium L. var. amara Engl. in rats using ultra-high-performance liquid chromatography coupled to quadrupole time-of-flight tandem mass spectrometry with data mining strategy.

The flower of Citrus aurantium L. var. amara Engl. (FCAVA), an edible tea and herbal medicine with anti-obesity effect, has attracted great attention in China. The structural elucidation of chemical components in FCAVA has been realized in our previous work. It is well known that metabolic profiling provided a structural basis to discover potential anti-obesity ingredients in FCAVA. Nevertheless, there are no reports about in vivo metabolic profiles of FCAVA. Therefore, it is necessary to comprehensively identify in vivo substances of FCAVA. The identification of in vivo substances of FCAVA remains a challenge due to the strong interference of complex chemical components, biological matrices and metabolite isomers. In this work, ultra-high-performance liquid chromatography coupled to quadrupole time-of-flight tandem mass spectrometry (UHPLC-QTOF-MS/MS) analysis with a data mining strategy was established and applied for the metabolic profiling of FCAVA in rats. The data mining strategy, including diagnostic product ions and neutral loss filtering, improved structural elucidation of xenobiotics in rats after oral administration of FCAVA. A total of 228 xenobiotics, including 80 prototypes (10 unambiguous confirmed with reference standards) and 148 metabolites, were tentatively characterized in rat plasma, urine and fecal samples. Among them, 35 xenobiotics were found in plasma, 124 in urine and 156 in feces. The main biotransformation pathway of FCAVA metabolism was deglycosylation, methylation, glucuronidation and sulfation. The main compounds absorbed into the blood were neohesperidin and naringin, which have been reported to show significant anti-obesity effect. Collectively, this present study would be conducive to the discovery of active ingredients of FCAVA for the treatment of obesity and the development of quality control of FCAVA.

Optimization of dendritic TS-1/Silica micro–mesoporous composites for efficient hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene

A novel composite material (TD) composed of TS-1 microcrystalline and dendritic mesoporous silica nanospheres (DMSNs) was successfully prepared. The TD composite material had open pore structure and large specific surface area, which was conducive to the mass transfer of reactants and products. The Ti element in TS-1 could be used as an electron assistant, and the spillover d-electrons were conducive to the improvement of the sulfidation and dispersion of MoS2, thereby forming more type II MoS2 active phases. The incorporation of Ti could bring more Brønsted (B) and Lewis (L) acid, which was conducive to the hydrogenation pathway (HYD) selectivity (41.2%) of dibenzothiophene (DBT) hydrodesulfurization (HDS) and isomerization (ISO) route selectivity (21.9%) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS, thus improve the HDS activity of DBT and 4,6-DMDBT. NiMo/TD-70 (Aging temperature = 70 °C) had the best HDS activities of DBT (99.0%) and 4,6-DMDBT (93.7%) due to its large open pore structure, good acidity, suitable metal-support interaction (MSI) and perfect dispersion of the metallic active sites.

Volume-Corrected Free Energy as a New Criterion for Structural Elucidation in Chemical-Tagging-Based Metabolomics.

Chemical tagging via possible derivatization reagents alters metabolites' retention times, leading to different retention behavior during liquid chromatography-mass spectrometry (LC-MS) analysis. Incorporation of the retention time dimension can dramatically reduce false-positive structural elucidation in chemical-tagging-based metabolomics. However, few studies predict the retention times of chemically labeled metabolites, especially requiring a simple, easy-to-access, accurate, and universal predictor or descriptor. This pilot study demonstrates the application of volume-corrected free energy (VFE) calculation and region mapping as a new criterion to describe the retention time for structure elucidation in chemical-tagging-based metabolomics. The universality of VFE calculation is first evaluated with four different types of submetabolomes including hydroxyl-group-, carbonyl-group-, carboxylic-group-, and amino-group-containing compounds and oxylipins with similar chemical structures and complex isomers on reverse-phase LC. Results indicate a good correlation (r > 0.85) between VFE values and their corresponding retention times using different technicians, instruments, and chromatographic columns, describing retention behavior in reverse-phase LC. Finally, the VFE region mapping is described for identifying 1-pentadecanol from aged camellia seed oil using three proposed steps, including public database searching, VFE region mapping for its 12 isomers, and chemical standard matching. The possibility of VFE calculation of nonderivatized compounds in retention time prediction is also investigated, demonstrating its effectiveness on retention times with different influence factors.

Identification of Students' Misconceptions on Hydrocarbon Material Using a Four-Tier Multiple Choice Diagnostic Test

As one of the sciences, some students consider chemistry complex and abstract, so many misconceptions arise. One of the chemistry topics that cause many misconceptions is hydrocarbons. A misconception is an understanding of concepts in students' minds that are contrary to scientific concepts. This research aimed to identify the student’s understanding and misconception of hydrocarbon. The study was qualitative descriptive research. Qualitative descriptive research was used to identify student misconceptions using the four-tier test. The sample of the research was 24 students. The instruments used in this research are four test levels which include (1) multiple-choice, (2) confidence rating of the answer beliefs, (3) reason for the answer, and (4) confidence rating of the reasoning. The result shows that 24,7% of students well-understood hydrocarbon concepts, 32,1% do not understand, and 43,2% have misconceptions. Misconceptions in this research are divided into three categories: low, moderate, and high. The students experience misconceptions with high criteria on the concept reaction of hydrocarbon (66,7%), moderate criteria on the concept of determining hydrocarbon compound (31,3%), the nomenclature of hydrocarbon compound (56,3%), types atom carbon (37,5%), Physical and Chemical Properties (45,8%), isomers (47,9%) and low criteria on the concept of characteristics of carbon atoms (16,7%).

Targeted profiling of polar metabolites in cancer metabolic reprogramming by hydrophilic interaction liquid chromatography-tandem mass spectrometry

Metabolic reprogramming of cancer cells is a hallmark of cancer, in which the polar metabolites involving aerobic glycolysis, pentose phosphate pathway (PPP), tricarboxylic acid (TCA) cycle, and glutaminolysis play a crucial role in the occurrence and development of cancer. Therefore, targeted analysis of the polar metabolites in these pathways is of great value for understanding cancers, finding diagnostic biomarkers, and identifying therapeutic targets. However, it is still challenging to directly determine polar metabolites in these pathways without derivatization due to their diverse chemical properties, isomers, and strong polarity. Herein, a highly selective and sensitive HILIC-MS/MS method was developed for direct determination of the polar metabolites in aerobic glycolysis, PPP, TCA cycle, and glutaminolysis pathways. Without derivatization, 19 polar metabolites and their isomers with carbonyl, carboxyl, or phosphoryl groups in human plasma and cell extracts of prostate cancer (PC) were determined with strong retention and high resolution. This method has been widely verified by measuring linearity, precision, sensitivity, repeatability, matrix effect, and accuracy. The analysis of plasma samples by HILIC-MS/MS revealed distinct PC-specific metabolic signatures compared to a healthy control. In addition, this method could also be used to screen the targets of metabolic inhibitors at the cellular level. We conclude that the developed HILIC-MS/MS method provides a valuable means to study the cancer metabolic reprogramming or energy metabolism in living organisms.

Structural Elucidation of Agrochemicals and Related Derivatives Using Infrared Ion Spectroscopy.

Agrochemicals frequently undergo various chemical and metabolic transformation reactions in the environment that often result in a wide range of derivates that must be comprehensively characterized to understand their toxicity profiles and their persistence and outcome in the environment. In the development phase, this typically involves a major effort in qualitatively identifying the correct chemical isomer(s) of these derivatives from the many isomers that could potentially be formed. Liquid chromatography-mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy are often used in attempts to characterize such environment transformation products. However, challenges in confidently correlating chemical structures to detected compounds in mass spectrometry data and sensitivity/selectivity limitations of NMR frequently lead to bottlenecks in identification. In this study, we use an alternative approach, infrared ion spectroscopy, to demonstrate the identification of hydroxylated derivatives of two plant protection compounds (azoxystrobin and benzovindiflupyr) contained at low levels in tomato and spinach matrices. Infrared ion spectroscopy is an orthogonal tandem mass spectrometry technique that combines the sensitivity and selectivity of mass spectrometry with structural information obtained by infrared spectroscopy. Furthermore, IR spectra can be computationally predicted for candidate molecular structures, enabling the tentative identification of agrochemical derivatives and other unknowns in the environment without using physical reference standards.

Identification and Quantitation of Aqueous Single- and Multianalyte Solutions of the Isomers Ethylbenzene, m-, p-, and o-Xylene Using a Single Specifically Tailored Sensor Coating and Estimation Theory-Based Signal Processing.

The isomer-specific detection and quantitation of m-, p-, and o-xylene and ethylbenzene, dissolved singly and as mixtures in aqueous solutions at concentrations from 100 to 1200 ppb by volume, is reported for a specifically designed polymer-plasticizer coating on a shear-horizontal surface acoustic wave (SH-SAW) device. The polystyrene-ditridecyl phthalate-blend coating was designed utilizing Hansen solubility parameters and considering the dipole moment and polarizability of the analytical targets and coating components to optimize the affinity of the sensor coating for the four chemical isomers. The two key coating sorption properties, sensitivity and response time constant, are determined by the (slightly different) dipole moments and polarizabilities of the four target analytes: as analyte dipole moment decreases, coating sensitivity increases; as analyte polarizability decreases, coating response time lengthens. Using the measured sensitivities and time constants for the targets, sensor signals were processed with exponentially weighted recursive-least-squares estimation (EW-RLSE) to identify (with near 100% accuracy) and quantify (with ± 5-7% accuracy) the isomers. This impressive performance was achieved by combining the specifically tailored, high-sensitivity coating and an SH-SAW platform (yielding a detection limit of 5 ppb for the analytes) and using the EW-RLS estimator, which estimates unknown parameters accurately even in the presence of measurement noise and for analytes with only minor differences in response. Identification of the xylene isomers is important for applications including environmental monitoring and chemical manufacturing.

Direct infusion electrospray ionization-ion mobility-mass spectrometry for rapid metabolite marker discovery of medicinal Phellodendron Bark

Ion-mobility mass spectrometry (IM-MS) currently serves as a powerful tool for the structural identification of numerous biological compounds and small molecules. In this work, rapid metabolomic analysis of closely-related herbal medicines by direct injection ion mobility-quadrupole time-of-flight mass spectrometry (DI-IM-QTOF MS) was established. Phellodendron chinense Bark (PC) and Phellodendron amurense Bark (PA) were studied as a case. Thirty-three batches of PC and twenty-two batches of PA have been directly injected in electrospray ionization-IM-QTOF MS in positive mode. Without chromatographic separation, each run was completed within 3 min. After data alignment and statistical analysis, a total of seven chemical markers were found (p-value < 0.05, VIP > 1.00). Among them, the ion m/z 342.17 and m/z 356.18 present a single peak in the drift spectrum, respectively, but their drift time has a certain deviation compared with the pure substance of known compounds. In addition, the MS/MS spectra also confirmed that the single peak includes two chemical isomers. To investigate the composition ratio of individual isomers, the calibration curves of relative drift time (rDT) based on the standard superposition method were established, which were found to fit the least square regression. The ion [M]+m/z 342.17 was recognized consisting of magnoflorine (MAG) and phellodendrine (PHE), and their composition ratio in PA and PC samples was calculated. The results were compared with those obtained by the HPLC quantitative method, which produced equivalent quantification results. Our DI-IM-QTOF MS methodology provides an additional methodology for the relative quantification of unresolved isomers in drift tube IM-MS and offers DI-IM-QTOF MS based metabolomics.

Manipulation of nuclear isomers with lasers: mechanisms and prospects

Over one hundred years have passed since the nuclear isomer was first introduced, in analogy with chemical isomers to describe long-lived excited nuclear states. In 1921, Otto Hahn discovered the first nuclear isomer $^{234m}$Pa. After that, step by step, it was realized that different types of nuclear isomers exist, including spin isomer, K isomer, seniority isomers, and ``shape and fission'' isomer. The spin isomer occurs when the spin change $\Delta I$ of a transition is very large. The larger $\Delta I$, the lower the electromagnetic transition rates, the longer the half-lives. The K-isomer exists due to the significant change in K, where K is the projection of the total angular momentum on the symmetry axis. The seniority isomers arise due to a very small transition probability in seniority conserving transitions around semi-magic nuclei, where the seniority, which corresponds to the number of unpaired nucleons, is a reasonably pure quantum number. For a so-called shape isomer, the inhibition of the decay transition comes from the associated shape changes. It is caused by that a nucleus is trapped in a deformed shape which is its secondary minimum and is hard to decay back to its ground state.

Nanobodies for Accurate Recognition of Iso-tenuazonic Acid and Development of Sensitive Immunoassay for Contaminant Detection in Foods.

The accurate analysis of chemical isomers plays an important role in the study of their different toxic effects and targeted detection of pollutant isomers in foods. The Alternaria mycotoxins tenuazonic acid (TeA) and iso-tenuazonic acid (ITeA) are two isomer mycotoxins with the lack of single analysis methods due to the similar structures. Antibody-based immunoassays exhibit high sensitivity and superior application in isomer-specific determination. Previously, various kinds of antibodies for TeA have been prepared in our group. Herein, highly specific nanobodies (Nbs) against ITeA mycotoxin were selected from immune nanobody phage display library, and one of Nbs, namely Nb(B3G3) exhibited excellent affinity, thermal stability as well as organic solvent tolerance. By molecular simulation and docking technology, it was found that stronger interaction between Nb(B3G3) and ITeA lead to higher affinity than that for its isomer TeA. Furthermore, a sensitive indirect competitive enzyme-linked immunosorbent assay (icELISA) was established with a limit of detection (LOD) of 0.09 ng/mL for ITeA mycotoxin. The recovery rate of ITeA in spiked samples was analyzed with 84.8%-89.5% for rice, 78.3%-96.3% for flour, and 79.5%-90.7% for bread. A conventional LC-MS/MS method was used to evaluate the accuracy of this proposed icELISA, which showed a satisfactory consistent correlation. Since the convenient strategy for nanobody generation by phage display technology, this study provide new biorecognition elements and sensitive immunoassay for analysis of ITeA in foods.

An integrated chemical analysis and network pharmacology approach to identify quality markers of Actinidia eriantha Benth radix on gastric cancer.

Actinidia eriantha Benth radix (AEBR) is one of the most commonly used medicines by the She people in China, used primarily for the treatment of tumours of the digestive tract. There is currently limited to no data on the quality control of AEBR. The aim of this study was to identify quality markers of AEBR. An ultra-performance lquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) method was used to identify and analyse the components of AEBR from water extracts. An ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was also established for the simultaneous determination of 13 active components in the water extracts. The network pharmacology method was used to screen for quality markers of AEBR in gastric cancer. This study tentatively identified 199 chemical constituents and isomers, including 67 pentacyclic triterpenoids, 20 flavonoids, 39 phenolic acids, 18 coumarins, and other compounds. The 13 active components in the water extracts were successfully determined using a validated UPLC-MS/MS method. Based on the network pharmacology method, four compounds were selected as quality markers of AEBR. This study provides an important reference for the quality control of AEBR. Chemical analysis combined with network pharmacology provides an effective strategy for the discovery of quality markers in traditional Chinese/herb medicine.

Hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene over NiMo supported on yolk-shell silica catalysts with adjustable shell thickness and yolk size

Mesoporous yolk-shell silica spheres with different shell thicknesses and yolk sizes (YxSy) were synthesized by incubating mesostructured silica nanospheres with water. Al-modified YxSy-supported NiMo catalysts were prepared and applied to hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The shell thickness and yolk size have a large effect on the HDS activities. Among the as-made catalysts, NiMo/Al-Y30S13 catalyst with relatively low shell thickness (13 nm), yolk size (30 nm) and proper structural stability exhibit the highest activities for HDS of DBT and 4,6-DMDBT at the weight time of 1.39–13.76 g min mol−1, of which its DBT conversion at 1.39 g min mol−1 (50.4%) is 1.5 times as that of the reference NiMo/Al2O3 (33.6%), four times as that of NiMo/Al-Y83S28 (12.3%) and what’s more, the HDS conversion of Al-Y30S13 could reach 99.5% at 13.76 g min mol−1 (about 2.5 ppm S remained). Its 4,6-DMDBT conversion at 1.39 g min mol−1 (27.1%) is almost 2 times as that over NiMo/Al2O3 (13.8%), and 2.7 times as that over NiMo/Al-Y83S28 (9.9%). Additionally, the 95.7% HDS conversion (about 16.6 ppm S remained) of Al-Y30S13 could be obtained at 13.76 g min mol−1. The good HDS performance of the NiMo/Al-Y30S13 catalyst could be derived from the synergistic effect of moderate shell thickness and relatively small yolk size, proper structural stability, appropriate acidity, moderate metal-support interaction (MSI), suitable dispersion and desirable stacking morphology of the Ni and Mo species. DBT HDS over the NiMo/Al-Y30S13 catalyst shows the lowest direct desulfurization (DDS)/hydrodesulfurization (HYD) ratio (2.70), demonstrating that the increase of HYD proportion could improve the ability of ultra-deep desulfurization of catalysts. 4,6-DMDBT HDS over the NiMo/Al-Y30S13 catalyst shows the highest selectivity of isomerization (ISO) route (69%), illustrating that the ISO route is the dominant pathway. Furthermore, the mechanisms of DBT and 4,6-DMDBT HDS are proposed over NiMo/Al-YxSy materials.

DEGRADATION OF ANTIBIOTIC SULFAMETHOXAZOLE IN AQUEOUS MEDIA BY UVA/TiO2 PURE-BROOKITE PHOTOCATALYSIS

The appearance of antibiotic sulfamethoxazole (SMX) in natural environments poses a potential risk to human health and ecology. Among many developed treatment techniques to remove and degrade SMX from an aqueous environment, photodegradation using the phase-pure TiO2 nanoparticles (NPs) in brookite structure as an active photocatalyst could be considered as a novel and effective strategy. The photocatalytic degradation of SMX in aqueous media followed an apparent first-order kinetics under the simulated UV-A irradiation. The higher the photocatalysts load, the higher photocatalytic efficiency. The SMX photodegradation over brookite nanoparticles depended on the pH of the SMX solution that was related to changes in chemical isomers of SMX molecules in the range of pH values between 2.0 and 10.0. The degradation efficiency was highest at pH 10.0 (up to 88 % after 180 min under UV-A irradiation) when SMX was in anionic form. With real matrices, the presence of metal ions (in mineral water) and fact-finding organic matter (in surface water) had a small effect on photodegradation efficiency due to either the complexation between SMX with metal ions or the inhibition of free radicals. The obtained results confirmed that the nano-sized TiO2 brookite photocatalyst has a high potential for water and wastewater remediation.

Topoisomerase: An Overview

The structure of DNA is a double-stranded helix, where the four bases are paired and stored in the center of this helix. The two strands of DNA are intertwined and this would require the two strands to be untwisted in order to access the information stored. Topoisomerases catalyze and guide the unknotting of DNA by creating transient breaks in the DNA using a conserved Tyrosine as the catalytic residue. Two classes of Topoisomerses are identified yet. Since the overall chemical composition and connectivity of the DNA does not change, the tangled and untangled DNAs are chemical isomers, differing only in their global topology, hence the enzymes are named as Topoisomerases. The insertion of viral DNA into chromosomes and other forms of recombination also require the action of topoisomerases. Topoisomerase inhibitors are agents designed to interfere with the action of topoisomerase enzymes, which control the changes in DNA structure by catalyzing the breaking and rejoining of the phosphodiester backbone of DNA strands during the normal cell cycle. Thus they are found to be important tools for treatment of cancer.