Green and Cost Effective Synthesis of Fluorescent Carbon Quantum Dots for Dopamine Detection

Carbon quantum dots (CQDs) due to its high fluorescent output is evolving as novel sensing material and is considered as future building blocks for nano sensing devices. Hence, in this investigation we report microwave assisted preparation and multi sensing application of CQDs. The microwave derived CQDs are characterized by Dynamic Light Scattering (DLS) experiment and Fourier Infrared spectra (FTIR) to investigate the size distribution and chemical purity respectively. Fluorescent emission spectra recorded at varying pH shows varying fluorescence emission intensities. Further, emission spectra recorded at different temperatures shows that fluorescence emission of CQDs greatly depends on temperature. Therefore, we demonstrate the pH and temperature sensing characteristics of CQDs by fluorescence quenching behaviour. In addition, the interaction and sensing behaviour of CQDs for dopamine is also presented in this work with a detection limit of 0.2 mM. The steady state and time-resolved methods have been employed in fluorescence quenching methods for sensing dopamine through CQDs at room temperature. The bimolecular quenching rate constants for different concentration have been measured. The interaction between CQDs and dopamine indicates fluorescence quenching method is an elegant process for detecting dopamine through CQDs.     

Carbon solubility and superconductivity in MgB2

Successful replacement of B by C in the series MgB_2−xC_x for values of x upto 0.3 is reported. Resistivity and ac susceptibility measurements have been carried out in the samples. Solubility of carbon, inferred from the observed change in the lattice parameter with carbon content indicates that carbon substitutes upto x=0.30 into the MgB₂ lattice. The superconducting transition temperature, T_c measured both by zero resistivity and the onset of the diamagnetic signal shows a systematic decrease with increase in carbon content upto x=0.30, beyond which the volume fraction decreases drastically. The temperature dependence of resistivity in the normal state fits to the Bloch–Gruneisen formula for all the carbon compositions studied. The Debye temperature, θ_D, extracted from the fit, is seen to decrease with carbon content from 900 to 525 K, whereas the electron–phonon interaction parameter, λ, obtained from the McMillan equation using the measured T_c and θ_D, is seen to increase monotonically from 0.8 in MgB₂ to 0.9 in the x=0.50 sample. The ratio of the resistivities between 300 and 40 K versus T_c is seen to follow the Testardi correlation for the C substituted samples. The decrease in T_c is argued to mainly arise due to large decrease in θ_D with C concentration and a decrease in the hole density of states at N(E_F).     

High-performance liquid chromatographic determination of xanthohumol in rat plasma, urine, and fecal samples

Xanthohumol (XN) is the major prenylated flavonoid in hop plants and as such a constituent of beer. Pharmacological studies have shown that XN possesses marked antioxidant and antiproliferative effects. In order to study the resorption and metabolism of this compound, reversed-phase high-performance liquid chromatography is used for the determination of XN in rat plasma, urine, and feces. In session one, rats receive either oral or intravenous (iv) administration (20 mg/kg body weight) of XN. In session two, rats receive oral administration of 50, 100, 200, 400, and 500 mg/kg body weight XN for bioavailability studies at various dose levels. Plasma, urine, and feces are collected at varying time points and assayed for their XN content. Plasma levels of XN fell rapidly within 60 min after iv administration; no XN is detected in plasma after oral administration in either session. XN and its metabolites are excreted mainly in feces within 24 h of administration. The method is a reliable tool for performing studies of XN in different biological material.     

Profiling primaquine metabolites in primary human hepatocytes using UHPLC‐QTOF‐MS with 13C stable isotope labeling

Therapeutic efficiency and hemolytic toxicity of primaquine (PQ), the only drug available for radical cure of relapsing vivax malaria are believed to be mediated by its metabolites. However, identification of these metabolites has remained a major challenge apparently due to low quantities and their reactive nature. Drug candidates labeled with stable isotopes afford convenient tools for tracking drug‐derived metabolites in complex matrices by liquid chromatography‐tandem mass spectrometry (LC‐MS‐MS) and filtering for masses with twin peaks attributable to the label. This study was undertaken to identify metabolites of PQ from an in vitro incubation of a 1:1 w/w mixture of ¹³C₆‐PQ/PQ with primary human hepatocytes. Acquity ultra‐performance LC (UHPLC) was integrated with QTOF‐MS to combine the efficiency of separation with high sensitivity, selectivity of detection and accurate mass determination. UHPLC retention time, twin mass peaks with difference of 6 (originating from ¹³C₆‐PQ/PQ), and MS‐MS fragmentation pattern were used for phenotyping. Besides carboxy‐PQ (cPQ), formed by oxidative deamination of PQ to an aldehyde and subsequent oxidation, several other metabolites were identified: including PQ alcohol, predictably generated by oxidative deamination of PQ to an aldehyde and subsequent reduction, its acetate and the alcohol's glucuronide conjugate. Trace amounts of quinone‐imine metabolites of PQ and cPQ were also detected which may be generated by hydroxylation of the PQ/cPQ quinoline ring at the 5‐position and subsequent oxidation. These findings shed additional light on the human hepatic metabolism of PQ, and the method can be applied for identification of reactive PQ metabolites generated in vivo in preclinical and clinical studies. Copyright © 2013 John Wiley & Sons, Ltd.     

Sol-gel-derived prussian blue-silicate amperometric glucose biosensor

A new type of inorganic biosensor is introduced. The sensor comprises glucose oxidase enzymes encapsulated in a sol-gel-derived Prussian blue-silicate hybrid network. Glucose is detected by the biocatalytic reduction of oxygen followed by catalytic reduction of hydrogen peroxide by the Prusian blue catalyst. The sol-gel silicate entails a rigid encapsulating matrix, the Prussian blue provides chemical catalysis and charge mediation from the reduction site to the supporting electrode, and the enzyme is responsible for the biocatalysis. The feasibility of a dual optical/electrochemical mode of analysis is also demonstrated.     

Validation and clinical application of an LC‐ESI‐MS/MS method for simultaneous determination of tolmetin and MED5, the metabolites of amtolmetin guacil in human plasma

A highly sensitive, rapid assay method has been developed and validated for the simultaneous estimation of tolmetin (TMT) and MED5 in human plasma with liquid chromatography coupled to tandem mass spectrometry with electrospray ionization in the positive‐ion mode. A simple solid‐phase extraction process was used to extract TMT and MED5 along with mycophenolic acid (internal standard, IS) from human plasma. Chromatographic separation was achieved with 0.2% formic acid–acetonitrile (25:75, v/v) at a flow rate of 0.50 mL/min on an X‐Terra RP₁₈ column with a total run time of 2.5 min. The MS/MS ion transitions monitored were 258.1 → 119.0 for TMT, 315.1 → 119.0 for MED5 and 321.2 → 207.0 for IS. Method validation and clinical sample analysis were performed as per FDA guidelines and the results met the acceptance criteria. The lower limit of quantitation achieved was 20 ng/mL and the linearity was observed from 20 to 2000 ng/mL, for both the anlaytes. The intra‐day and inter‐day precisions were in the range 3.27–4.50 and 5.32–8.18%, respectively for TMT and 4.27–5.68 and 5.32–8.85%, respectively for MED5. This novel method has been applied to a clinical pharmacokinetic study. Copyright © 2010 John Wiley & Sons, Ltd.     

High‐Level Incorporation of Silver in Gold Nanoclusters: Fluorescence Redshift upon Interaction with Hydrogen Peroxide and Fluorescence Enhancement with Herbicide

High‐level incorporation of Ag in Au nanoclusters (NCs) is conveniently achieved by controlling the concentration of Ag⁺ in the synthesis of bovine serum albumin (BSA)‐protected Au NCs, and the resulting structure is determined to be bimetallic Ag₂₈Au₁₀‐BSA NCs through a series of characterizations including energy‐dispersive X‐ray spectroscopy, mass spectroscopy, and X‐ray photoelectron spectroscopy, together with density functional theory simulations. Interestingly, the Ag₂₈Au₁₀ NCs exhibit a significant fluorescence redshift rather than quenching upon interaction with hydrogen peroxide, providing a new approach to the detection of hydrogen peroxide through direct comparison of their fluorescence peaks. Furthermore, the Ag₂₈Au₁₀ NCs are also used for the sensitive and selective detection of herbicide through fluorescence enhancement. The detection limit for herbicide (0.1 nm ) is far below the health value established by the U.S. Environmental Protection Agency; such sensitive detection was not achieved by using AuAg NCs with low‐level incorporation of Ag or by using the individual metal NCs.     

An alternative synthetic strategy for (3R),(5R)-5-hydroxy-de-O-methyllasiodiplodin and its epimer

A concise total synthesis of (3R),(5R)-5-hydroxy-de-O-methyllasiodiplodin and its epimer have been synthesized from commercially available (R)-propylene oxide and Orsellinic acid as starting materials. The key steps involved in the synthesis are Wittig reaction, epoxide ring opening with 1,3-dithiane intermediate and Yamaguchi macrolactonization.