Trace-Level Determination of Oxolinic Acid and Flumequine in Soil,River Bed Sediment,and River Water Using Microwave-Assisted Extraction and High-Performance Liquid Chromatography with Fluorimetric Detection

This work presents the optimization of analytical procedures for the determination of two antibiotics, oxolinic acid (OA) and flumequine (FL), in bed sediment, river water, and soil samples. Three extraction methods (microwave-assisted extraction (MAE), ultrasonication, and reflux) were tested, and the highest recoveries were obtained with MAE (94 ± 3% and 95 ± 3% for OA and FL, respectively). A solid-phase extraction (SPE) clean-up step was optimized by comparing two polymeric sorbents: Oasis HLB and Oasis MAX. The final extracts were analyzed by liquid chromatography with fluorimetric detection. Limits of detection (LOD) obtained for OA and FL in soil and sediment ranged from 0.3 to 0.5 µg kg^?1. Meanwhile, a novel SPE procedure was also implemented for OA and FL determination in river water samples. It also relied on the use of Oasis MAX, and recovery rates were in the range 90–94%; LODs were 2 ng L^?1 for both OA and FL. These methods were applied for the analysis of samples taken in the Seine River basin (France). The obtained results demonstrated the widespread occurrence of OA and FL, at ng L^?1 and µg kg^?1 levels in water and sediment/soil, respectively, and their persistence in the environment.     

Entropy-driven mechanism of an E3 ligase

Ubiquitin-like modifications are macromolecular chemistry for which our understanding of the enzymatic mechanisms is lacking. Most E3 ligases in ubiquitin-like modifications do not directly participate in chemistry but are thought to confer allosteric effects; however, the nature of the allosteric effects has been elusive. Recent molecular dynamics simulations suggested that an E3 binding enhances the population of the conformational states of the E2·SUMO thioester that favor reactions. In this study, we conducted the first temperature-dependent enzyme kinetic analysis to investigate the role of an E3 on activation entropy and enthalpy. The small ubiquitin-like modifier (SUMO) E3, RanBP2, confers unusually large, favorable activation entropy to lower the activation energy of the reaction. Mutants of RanBP2, designed to alter the flexibilities of the E2·SUMO thioester, showed a direct correlation of their favorable entropic effects with their ability to restrict the conformational flexibility of the E2·SUMO thioester. While the more favorable activation entropy is consistent with the previously suggested role of E3 in conformational selection, the large positive entropy suggests a significant role of solvent in catalysis. Indeed, molecular dynamics simulations in explicit water revealed that the more stable E2·SUMO thioester upon E3 binding results in stabilization of a large number of bound water molecules. Liberating such structured water at the transition state can result in large favorable activation entropy but unfavorable activation enthalpy. The entropy-driven mechanism of the E3 is consistent with the lack of structural conservation among E3s despite their similar functions. This study also illustrates how proteins that bind both SUMO and E2 can function as E3s and how intrinsically unstructured proteins can enhance macromolecular chemistry in addition to their known advantages in protein--protein interactions.     

Computational studies of adsorption in metal organic frameworks and interaction of nanoparticles in condensed phases

In this review, we describe recent efforts to systematically study nano-structured metal organic frameworks (MOFs), also known as metal organic heat carriers, with particular emphasis on their application in heating and cooling processes. We used both molecular dynamics and grand canonical Monte Carlo simulation techniques to gain a molecular-level understanding of the adsorption mechanism of gases in these porous materials. We investigated the uptake of various gases such as refrigerants R12 and R143a. We also evaluated the effects of temperature and pressure on the uptake mechanism. Our computed results compared reasonably well with available measurements from experiments, thus validating our potential models and approaches. In addition, we investigated the structural, diffusive and adsorption properties of different hydrocarbons in Ni₂(dhtp). Finally, to elucidate the mechanism of nanoparticle dispersion in condensed phases, we studied the interactions among nanoparticles in various liquids, such as n-hexane, water and methanol.     

Dichroic Optical Properties of Uniaxially Oriented Gold Nanorods in Polymer Films

Applications based on the optical excitation of the longitudinal surface plasmon resonance of gold nanorods (AuNRs) work at highest efficiency if all component AuNRs can be maximally excited simultaneously. This can be achieved in aligned AuNR structures, such as those embedded in uniaxially stretched polymer films. Since too high heating temperatures during film stretching cause reshaping and alteration of optical properties of the rods, a maximum allowable heating temperature is determined. The alignment of the rods is quantified by an orientational order parameter of 0.92 based on a statistically significant sample of assumed t distributed means and obtained by scanning electron microscopy. We show that a stretched AuNRs-PVA composite film has optical properties that approach the dichroic properties of an idealized ensemble of fully aligned, identical, and non-interacting AuNRs embedded in a PVA film. The idealized system is provided by FDTD simulations of a single AuNR, which we carried out using the size- and shape-adapted dielectric function of gold and the software RSOFT.     

Circadian dysfunction in response to in?vivo treatment with the mitochondrial toxin 3-nitropropionic acid

Sleep disorders are common in neurodegenerative diseases including Huntington''s disease (HD) and develop early in the disease process. Mitochondrial alterations are believed to play a critical role in the pathophysiology of neurodegenerative diseases. In the present study, we evaluated the circadian system of mice after inhibiting mitochondrial complex II of the respiratory chain with the toxin 3-nitropropionic acid (3-NP). We found that a subset of mice treated with low doses of 3-NP exhibited severe circadian deficit in behavior. The temporal patterning of sleep behavior is also disrupted in some mice with evidence of difficulty in the initiation of sleep behavior. Using the open field test during the normal sleep phase, we found that the 3-NP-treated mice were hyperactive. The molecular clockwork responsible for the generation of circadian rhythms as measured by PER2::LUCIFERASE was disrupted in a subset of mice. Within the SCN, the 3-NP treatment resulted in a reduction in daytime firing rate in the subset of mice which had a behavioral deficit. Anatomically, we confirmed that all of the treated mice showed evidence for cell loss within the striatum but we did not see evidence for gross SCN pathology. Together, the data demonstrates that chronic treatment with low doses of the mitochondrial toxin 3-NP produced circadian deficits in a subset of treated mice. This work does raise the possibility that the neural damage produced by mitochondrial dysfunction can contribute to the sleep/circadian dysfunction seen so commonly in neurodegenerative diseases.     

Novel Characterization and Live Imaging of Schlemm's Canal Expressing Prox-1

Schlemm''s canal is an important structure of the conventional aqueous humor outflow pathway and is critically involved in regulating the intraocular pressure. In this study, we report a novel finding that prospero homeobox protein 1 (Prox-1), the master control gene for lymphatic development, is expressed in Schlemm''s canal. Moreover, we provide a novel in vivo method of visualizing Schlemm''s canal using a transgenic mouse model of Prox-1-green fluorescent protein (GFP). The anatomical location of Prox-1⁺ Schlemm''s canal was further confirmed by in vivo gonioscopic examination and ex vivo immunohistochemical analysis. Additionally, we show that the Schlemm''s canal is distinguishable from typical lymphatic vessels by lack of lymphatic vessel endothelial hyaluronan receptor (LYVE-1) expression and absence of apparent sprouting reaction when inflammatory lymphangiogenesis occurred in the cornea. Taken together, our findings offer new insights into Schlemm''s canal and provide a new experimental model for live imaging of this critical structure to help further our understanding of the aqueous humor outflow. This may lead to new avenues toward the development of novel therapeutic intervention for relevant diseases, most notably glaucoma.     

Genome-Wide Investigation of DNA Methylation Marks Associated with FV Leiden Mutation

In order to investigate whether DNA methylation marks could contribute to the incomplete penetrance of the FV Leiden mutation, a major genetic risk factor for venous thrombosis (VT), we measured genome-wide DNA methylation levels in peripheral blood samples of 98 VT patients carrying the mutation and 251 VT patients without the mutation using the dedicated Illumina HumanMethylation450 array. The genome-wide analysis of 388,120 CpG probes identified three sites mapping to the SLC19A2 locus whose DNA methylation levels differed significantly (p<3 10⁻⁸) between carriers and non-carriers. The three sites replicated (p<2 10⁻⁷) in an independent sample of 214 individuals from five large families ascertained on VT and FV Leiden mutation among which 53 were carriers and 161 were non-carriers of the mutation. In both studies, these three CpG sites were also associated (2.33 10⁻¹¹<p<3.02 10⁻⁴) with biomarkers of the Protein C pathway known to be influenced by the FV Leiden mutation. A comprehensive linkage disequilibrium (LD) analysis of the whole locus revealed that the original associations were due to LD between the FV Leiden mutation and a block of single nucleotide polymorphisms (SNP) located in SLC19A2. After adjusting for this block of SNPs, the FV Leiden mutation was no longer associated with any CpG site (p>0.05). In conclusion, our work clearly illustrates some promises and pitfalls of DNA methylation investigations on peripheral blood DNA in large epidemiological cohorts. DNA methylation levels at SLC19A2 are influenced by SNPs in LD with FV Leiden, but these DNA methylation marks do not explain the incomplete penetrance of the FV Leiden mutation.     

越南冷水花属(荨麻科)一新记录种

报道了越南荨麻科(Urticaceae)冷水花属(Pilea Lindl.)一新记录种——基心叶冷水花(P.basicordata W.T.Wang ex C.J.Chen)。该种在越南Pu Hu自然保护区发现,与产自越南北部的P.balansae Gagnep.相似,主要区别在于其雄花序聚伞圆锥状,托叶大,叶先端渐尖或短尾状渐尖。