A thermally stable Pt/Y-based metal-organic framework: Exploring the accessibility of the metal centers with spectroscopic methods using H2O, CH3OH, and CH3CN as probes

A metal-organic framework (MOF) based on Pt, Y, and 2,2'-bipyridine-5,5'-dicarboxylate (BPDC), stable up to 400 degrees C, has been synthesized and characterized. In this MOF, the Pt centers are coordinated to Cl and the N atoms of the BPDC unit, giving a local environment similar to that found in a series of Pt-organic complexes with catalytic activity toward C-H bond cleavage of alkanes. This new material is a heterogeneous counterpart to the corresponding metal-organic complex. The structure, determined by single-crystal XRD data, is the repetition of three covalently bonded layers. These layers form a block, which is stacking as an (a)(b)(c) sequence along the crystallographic b-axis. Each layer contains the Pt-organic unit, while Y atoms represent the connection between adjacent layers. No covalent connection is present between layer (a) of a block and layer (c) of an adjacent block. EXAFS (BM29 at the ESRF) analysis supports the XRD data. As this MOF crystallizes under hydrothermal conditions, water acts both as solvent and as a direct ligand of Y. Accessibility to the metal centers is demonstrated by reversible water desorption/readsorption, as determined by TPA/TPD, FTIR, UV-vis, EXAFS, and XANES. Importantly, the results show that the as-synthesized material will not suffer a permanent loss in porosity upon solvent removal. In addition to water, methanol, ethanol, and acetonitrile can also access the internal void of the dehydrated phase.     

Screening of fluoroquinolones in environmental waters using disk-based solid-phase extraction combined to microplate fluorimetric determination and LC-MS/MS

Fluoroquinolones are in the order of the day concerning environmental contamination through anthropogenic activities, resulting in increased risk for antibiotic resistance dissemination. In this context, accessible, low-cost analytical methods are required for implementation of comprehensive surveillance and screening schemes. In this work, we propose a down-scaled disk-based solid-phase extraction system from which the eluate can be first screened by miniaturized fluorimetric reading, followed by individual determination of target fluoroquinolones (ciprofloxacin, norfloxacin, and enrofloxacin) by liquid chromatography combined to tandem mass spectrometry. The fluorimetric measurement is based on the intrinsic fluorescence of fluoroquinolones. Disk-based retention was performed after sample acidification (pH 4.0) by mixed-mode cation exchange using polystyrene divinylbenzene sulphonated sorbent. Sample loading was precisely controlled in a dedicated flow system operating at 4.0 mL min^?1. Different eluent compositions were tested, with elution performed by 1.00 mL of methanol-ammonium hydroxide (98:2, v/v), with subsequent reading of eluate in both detectors. Quantification was attained for 2–25 µg L^?1 range, with LOD values at 1 µg L^?1. The proposed approach was successfully applied to estuarine waters from the Douro River, with comparable results to a conventional SPE-LC-MS/MS procedure.     

Characterization of the Phytochemical Profiles and Biological Activities of Ajuga chamaepitys subsp. chia var. chia and Ajuga bombycina by High-Performance Liquid Chromatography–Electrospray Ionization–Tandem Mass Spectrometry (HPLC–ESI–MSn)

This study investigates into the pharmacological potential of three solvent extracts (ethyl acetate, methanol, and water) of two Ajuga species (Ajuga chamaepitys subsp. chia var. chia and Ajuga bombycina) based on their antioxidant activity and enzyme inhibitory effects along with establishing the phytochemical profile. Spectrophotometric and high-performance liquid chromatography–electrospray ionization–tandem mass spectrometry (HPLC–ESI–MSⁿ) were used to determine the total and individual phytocompounds, respectively. Antioxidant potential was assessed using different assays such as DPPH, ABTS, CUPRAC, FRAP, phosphomolybdenum, and metal chelation. Enzyme inhibitory effects were studied against acetylcholinesterase, butyrylcholinesterase, tyrosinase, α-amylase, and α-glucosidase. The aqueous extract of both plants showed better ABTS scavenging, FRAP, and metal chelating activities. The methanol extracts displayed the highest tyrosinase inhibitory and antioxidant activity in the phosphomolybdenum assay while the ethyl acetate extracts of both plants showed better butyrylcholinesterase (BChE), α-amylase, and α-glucosidase inhibition. The total phenolic content was highest in the aqueous extract of A. chamaepitys while the methanolic extract of A. bombycina showed the highest flavonoid content. Identification by HPLC–ESI–MSⁿ revealed the presence of some individual compounds including phenolic acids, flavonoids, iridoid glycosides, phenylethanoid glycosides, and other compounds. To conclude, both A. chamaepitys and A. bombycina can be considered as rich sources of phytocompounds to manage chronic diseases.     

Modified Brans–Dicke theory of gravity from five-dimensional vacuum

We investigate, in the context of five-dimensional (5D) Brans–Dicke theory of gravity, the idea that macroscopic matter configurations can be generated from pure vacuum in five dimensions, an approach first proposed by Wesson and collaborators in the framework of 5D general relativity. We show that the 5D Brans–Dicke vacuum equations when reduced to four dimensions (4D) lead to a modified version of Brans–Dicke theory in 4D. As an application of the formalism, we obtain two 5D extensions of 4D O’Hanlon and Tupper vacuum solution and show that they lead two different cosmological scenarios in 4D.     

Study of spatial inhomogeneity in inverted all‐polymer solar cells: Effect of solvent and annealing

The efficiency optimization of bulk heterojunction solar cells requires the control of the local active materials arrangement in order to obtain the best compromise between efficient charge generation and charge collection. Here, we investigate the large scale (10–100 μm) inhomogeneity of the photoluminescence (PL) and the external quantum efficiency (EQE) in inverted all‐polymer solar cells (APSC) with regioregular poly(3‐hexylthiophene) (P3HT):poly(9,9‐dioctylfluorene‐co‐benzothiadiazole) (F8BT) active blends. The morphology and the local active polymer mixing are changed by depositing the active layer from four different solvents and by thermal annealing. The simultaneous PL and EQE mapping allowed us to inspect the effects of local irregularities of active layer thickness, polymer mixing, polymer aggregation on the charge generation and collection efficiencies. In particular, we show that the increase of the solvent boiling point affects the EQE non‐uniformity due to thickness fluctuations, the density non‐uniformity of rrP3HT aggregate phase, and the blend components clustering. The thermal annealing leads to a general improvement of EQE and to an F8BT clustering in all the samples with locally decrease of the EQE. We estimate that the film uniformity optimization can lead to a total EQE improvement between 2.7 and 6.3 times. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 804–813     

Immunosensor for electrodetection of the C-reactive protein in serum

Epidemiological studies have demonstrated an association between the risk of cardiovascular events and increasing C-reactive protein (CRP) concentration. This paper reports the development of an immunosensor for the assessment of the cardiovascular process using anti-C-reactive protein antibody immobilized onto a gold-printed screen electrode. Positive and negative human sera were successfully evaluated using electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), and atomic force microscopy (AFM). EIS results show that, after the incubation with positive serum for myocardial infarction, the resistance increased about two times in relation to the negative serum. A linear range from 6.25 to 50 μg mL^?1 and detection limit of 0.78 μg mL^?1 using DPV were obtained. The immunosensor developed for the CRP detection using gold electrode revealed efficacy and a potential use for the diagnosis and monitoring of the progression of cardiovascular diseases.     

MSPD procedure for determining buprofezin,tetradifon, vinclozolin,and bifenthrin residues in propolis by gas chromatography–mass spectrometry

A simple and effective extraction method based on matrix solid-phase dispersion (MSPD) was developed to determine bifenthrin, buprofezin, tetradifon, and vinclozolin in propolis using gas chromatography–mass spectrometry in selected ion monitoring mode (GC–MS, SIM). Different method conditions were evaluated, for example type of solid phase (C₁₈, alumina, silica, and Florisil), the amount of solid phase and eluent (n-hexane, dichloromethane, dichloromethane–n-hexane (8:2 and 1:1, v/v) and dichloromethane–ethyl acetate (9:1, 8:2 and 7:3, v/v)). The best results were obtained using 0.5 g propolis, 1.0 g silica as dispersant sorbent, 1.0 g Florisil as clean-up sorbent, and dichloromethane–ethyl acetate (9:1, v/v) as eluting solvent. The method was validated by analysis of propolis samples fortified at different concentration levels (0.25 to 1.0 mg kg⁻¹). Average recoveries (four replicates) ranged from 67% to 175% with relative standard deviation between 5.6% and 12.1%. Detection and quantification limits ranged from 0.05 to 0.10 mg kg⁻¹ and 0.15 to 0.25 mg kg⁻¹ propolis, respectively.     

Bovine serum albumin adsorption onto 316L stainless steel and alumina: a comparative study using depletion,protein radiolabeling,quartz crystal microbalance and atomic force microscopy

The importance of protein adsorption on biomaterials is widely recognized, but the dependence of the adsorption results on the chosen technique has not been much addressed. The objective of this work is to compare adsorption data obtained using several techniques under experimental conditions as closely as possible. Two case studies were investigated: adsorption of bovine serum albumin (BSA) onto 316L stainless steel (SS) and onto alumina. Both materials were used as powders and plates, whose characterization was done through zeta potential (ZP) measurements. The experimental techniques were depletion, protein radiolabeling, quartz crystal microbalance with dissipation (QCM‐D) and atomic force microscopy (AFM). The adsorption isotherms obtained with depletion and QCM‐D techniques, although quantitatively different, present some similarities in shape. Both techniques suggest the existence of a compact end‐on monolayer of protein on the SS surface, while on the alumina surface a less dense side‐on monolayer is formed at lower BSA concentration, followed by a second layer at higher concentration. AFM topographical characterization of the protein films adsorbed on both materials confirms those findings. Further use of AFM in determining the thickness of the film adsorbed on SS yielded values in good agreement with the QDM‐D results. Different surface charges measured on powders and plates do not seem to affect adsorption. Protein radiolabeling seems to be the least reliable technique because it yields, for both materials, adsorption values higher than those from the other techniques. In the case of SS, the difference amounts to one order of magnitude. Copyright © 2008 John Wiley & Sons, Ltd.