HPLC–MS/MS studies of brimonidine in rabbit aqueous humor by microdialysis

Aim: The pharmacokinetic study of the brimonidine tartrate in situ gel in the anterior chamber of the rabbit eye was studied by microdialysis technique, and samples were analyzed by HPLC–MS/MS. Materials & methods: It was monitored in ESI mode at transition 291.9→212.0 and 296.0→216.0 for brimonidine and internal standard, respectively. Acetonitrile and 0.1% aqueous formic acid (50:50, v/v) were used as the mobile phase at 0.4 ml/min. Results & conclusion: It showed a good linear correlation between 5 and 5000 ng/ml in microdialysis solution, and the inter- and intra-day precision (relative standard deviation) was less than 4.0%. The pharmacokinetic study showed that the AUC(0-t) of in situ gel was 3.5-times than that of eyedrops, which significantly improve the bioavailability of brimonidine.

Carbon Dot Functionalized Papers for the Selective Detection of 2,4,6-Trinitrophenol in Aqueous Solutions

The development of probes for the testing of the carcinogenic pollutant 2,4,6-trinitrophenol (TNP) is of great importance for environmental protection and human health. In this paper, a new rapid and sensitive fluorescence detection method based on carbon dots (CDs) was designed for the detection of TNP. The CDs were synthesized by simple pyrolysis using citric acid as raw material and characterized by various advanced techniques. The addition of TNP caused a significant turn off in the fluorescence of the CDs. The fluorescence quench intensity and TNP concentration exhibited a good linear correlation in the range of 0–80 μM with a minimum detection limit of 0.48 μM and a related coefficient of 0.994. The analytical method was applied to the determination of trace TNP in river water and tap water with recoveries in the range of 98%–110% and relative standard deviations less than 5%. Importantly, carbon dots functionalized papers (CDFPs) were prepared using the synthesized CDs and successfully applied to the determination of TNP in aqueous solutions, demonstrating the promising application of the method.

Eco-friendly fluorimetric approaches for the simultaneous estimation of the co-administered ternary mixture: etoposide, moxifloxacin and nalbuphine

Antineoplastic drugs, etoposide (ETO), are widely used in leukaemia. A patient with leukaemia has a relative infection with pneumonia treated by fluoroquinolones as moxifloxacin HCL (MOX). Because opioid analgesic as nalbuphine HCL (NAL) does not have a ceiling dose, it is used to manage the distasteful sensory in leukaemia. Consequently, green methods for synchronous spectrofluorimetric quantification of a ternary mixture of ETO, MOX and NAL were developed. The first approach relies simply on the estimation of MOX at 371 nm by conventional synchronous fluorimetric technique (Δ λ of 60 nm). The second approach depends on applying the first derivative synchronous fluorimetric technique (Δ λ of 60 nm) for simultaneous estimation of ETO and NAL at 257 and 273 nm, respectively. A good linear correlation was obtained in the ranges of 0.04–0.40, 0.10–1.00 and 0.50–5.00 µg ml −1 for MOX, ETO and NAL, respectively. Moreover, the proposed approaches were successfully applied for the estimation of the studied drugs in the pharmaceutical dosage forms. Additionally, the synchronous assessment of ETO, MOX and NAL in the spiked human urine was successfully attained by the facile protein precipitation technique. The mean % recoveries in spiked human urine were 99.49, 98.07 and 98.48 for MOX, ETO and NAL, respectively.

Effect of Graphene Nanoplatelets (GNPs) on Fatigue Properties of Asphalt Mastics

To investigate the effect of graphene on the fatigue properties of base asphalt mastics, graphene nanoplatelets (GNPs)-modified asphalt mastics and base asphalt mastics were prepared. A dynamic shear rheometer (DSR) was used to conduct the tests in the stress-controlled mode of a time-sweep test. The results showed that GNPs can improve the fatigue life of asphalt mastic. Under a stress of 0.15 MPa, the average fatigue life growth rate (ω¯) was 17.7% at a filler-asphalt ratio of 0.8, 35.4% at 1.0, and 45.2% at 1.2; under a stress of 0.2 MPa, the average fatigue life growth rate (ω¯) was 17.9% at a filler-asphalt ratio of 0.8, 25.6% at 1.0, and 38.2% at 1.2. The growth value (ΔT) of fatigue life of GNPs-modified asphalt mastics increased correspondingly with the increase of filler–asphalt ratio, the correlation coefficient R2 was greater than 0.95, and the growth amount showed a good linear relationship with the filler–asphalt ratio. In the range of 0.8~1.2 filler–asphalt ratio, the increase of mineral powder can improve the fatigue life of asphalt mastics, and there is a good linear correlation between filler–asphalt ratio and fatigue life. The anti-fatigue mechanism of GNPs lies in the interaction between GNPs and asphalt, as well as its own lubricity and thermal conductivity.

Modelling the Microphone-Related Timbral Brightness of Recorded Signals

Brightness is one of the most common timbral descriptors used for searching audio databases, and is also the timbral attribute of recorded sound that is most affected by microphone choice, making a brightness prediction model desirable for automatic metadata generation. A model, sensitive to microphone-related as well as source-related brightness, was developed based on a novel combination of the spectral centroid and the ratio of the total magnitude of the signal above 500 Hz to that of the full signal. This model performed well on training data (r = 0.922). Validating it on new data showed a slight gradient error but good linear correlation across source types and overall (r = 0.955). On both training and validation data, the new model out-performed metrics previously used for brightness prediction.

ANALYSIS OF PURINIC ALKALOIDS BY XRD AND MOLECULAR MODELING METHODS

Theophylline, theobromine and caffeine, are purine-based alkaloids in which the main differentiation in the molecular structure is the presence of methyls, one, two and three, respectively in these substances. This study presents an analysis by XRD and molecular modeling methods of the alkaloid’s caffeine and theobromine. The crystalline structure of caffeine was characterized as a monoclinic system, and the diffractogram of the caffeine crystals showed peaks with regions of greater intensity at 2θ = 11.7616 ° (d = 7.51 Å; I% = 80.13) and 2θ = 11.9416 ° (d = 7.40 Å; I% = 98.14). In the diffractogram of the theobromine crystal sample, peaks of greater intensity occurred in the regions 2θ = 13.4616 ° (d = 6.57 Å; I% = 98.92) and 2θ = 27.0816 ° (d = 3, 28 Å; I% = 67.23). Results obtained by XRD for caffeine and theobromine were compatible with standard cards of the X’Pert High Score Plus® program. The presence of an extra methyl in the structure of the caffeine purine base, suggests, a shift in the values ​​of the angle 2 θ for the main peaks of theobromine, as well as an increase in intensity, mainly in 27.016, theobromine also presents a peak in the region 10.6 which does not occur in caffeine. Statistical results reveal that the linear models for data of peaks of specific angles in 2θ of the samples, presented good linear correlation (R2> 98%) and satisfactory results after the procedure of cross validation. caffeine and theobromine also showed important differences in interactions with adenosine A2AR, particularly in hydrophobic and hydrogen interactions.

Substituent effects and Mechanism Studies in CO2 Transformation to Benzoxazinone Derivatives as Worthwhile N-containing Heterocycles: insight from DFT simulation

Investigation of CO2 transformation into value-added organic molecules is an interesting purpose in scientific communities. Here, the substitute effect exploration in CO2 incorporation reaction toward benzoxazinones formation, as a bioactive heterocyclic compound, is the main studied issue. A profound understanding of the substituent effect is helpful toward the investigation of the kinetic and thermodynamic aspects of the reaction. The substituted arynes, an imine compound, and atmospheric CO2 have been reported as the starting reactants. The substituted functional groups show substantial consequences on the studied mechanisms. The obtained results show that mechanism A, in which the imine compound is added as a nucleophile to arynes, is the most probable mechanism. The Energetic Span Model (ESM) was used in the kinetic studies, which indicates the turnover-frequency determining intermediate (TDI) and turnover-frequency determining transition state (TDTS) in the reaction progress. Also, Electron localization function (ELF) analyses reveal that the electron density of a developing monosynaptic basin on the carbon atom (V(C)) at the transition state shows a good linear correlation with the calculated energy values of TDTS. Electron-withdrawing and electron-releasing characters of the substituents have the main effects on the electron density of the developing basin at the transition states which change the TDTS energies.

Fabrication of an Extremely Cheap Poly(3,4-ethylenedioxythiophene) Modified Pencil Lead Electrode for Effective Hydroquinone Sensing

Hydroquinone (HQ) is one of the major deleterious metabolites of benzene in the human body, which has been implicated to cause various human diseases. In order to fabricate a feasible sensor for the accurate detection of HQ, we attempted to electrochemically modify a piece of common 2B pencil lead (PL) with the conductive poly(3,4-ethylenedioxythiophene) or PEDOT film to construct a PEDOT/PL electrode. We then examined the performance of PEDOT/PL in the detection of hydroquinone with different voltammetry methods. Our results have demonstrated that PEDOT film was able to dramatically enhance the electrochemical response of pencil lead electrode to hydroquinone and exhibited a good linear correlation between anodic peak current and the concentration of hydroquinone by either cyclic voltammetry or linear sweep voltammetry. The influences of PEDOT film thickness, sample pH, voltammetry scan rate, and possible chemical interferences on the measurement of hydroquinone have been discussed. The PEDOT film was further characterized by SEM with EDS and FTIR spectrum, as well as for stability with multiple measurements. Our results have demonstrated that the PEDOT modified PL electrode could be an attractive option to easily fabricate an economical sensor and provide an accurate and stable approach to monitoring various chemicals and biomolecules.

The fluorescence of a mercury probe based on osthol

The ability of osthol (OST) to recognize mercury ions in aqueous solution was studied using fluorescence, UV–vis spectrophotometry, mass spectrometry, and 1H NMR spectroscopy, and the recognition mechanism is discussed. The results showed that OST and Hg2+ can form a complex with a stoichiometric ratio of 1:1. The binding constant was 1.552 × 105 L∙mol−1, having a highly efficient and specific selectivity for Hg2+. The fluorescence intensity of OST showed a good linear correlation with the Hg2+ concentration (6.0 × 10−5 to 24.0 × 10−5 mol∙L−1, R 2 = 0.9954), and the detection limit of the probe was 5.04 × 10−8 mol∙L−1, which can be used for the determination of Hg2+ traces.

Analysis of citric acid and D-isoascorbic acid in beverages by High performance liquid chromatography

In this study, high performance liquid chromatography (HPLC) was used to analysis the content of citric acid and D-isoascorbic acid in beverages. The samples were separated by C18 chromatography column, 0.1 % phosphoric acid solution was used as the mobile phase with the flow rate of 0.5 mL/min, the column temperature was 35 °C, and the detection wavelength was 210 nm. The results showed that the content of citric acid and D-isoascorbic acid has a good linear correlation (r>0.99) within the range of 50 μg to 200 μg. The selectivity, recovery and precision of citric acid and D-isoascorbic acid were suitable. Meanwhile, this method could be used to detect the content of citric acid and D-isoascorbic acid in beverages.