Photothermal Detection of Individual Gold Nanoparticles: Perspectives for High‐Throughput Screening

We use photothermal microscopy to detect and image individual gold nanoparticles that are either embedded in a polymer film or immobilized in an aqueous environment. Reducing the numerical aperture of the detection optics allows us to achieve a 200‐fold‐enlarged detection volume while still retaining sufficient detectivity. We characterize the capabilities of this approach for the detection of gold colloids with a diameter of 20 nm, with emphasis on practical aspects that are important for high‐throughput‐screening applications. The extended detection volume in combination with the stability of the photothermal signal are major advantages compared to fluorescence‐based approaches, which are limited by photoblinking and photobleaching. Careful consideration is given to the trade‐off between the maximum increase in local temperature that can be tolerated by a biological specimen and the minimum integration time needed to reliably determine whether a given volume contains a target species. We find that our approach has the potential to increase the detection‐limited flow rate (i.e. the limit given by the detection volume divided by the minimum detection time) by two to three orders of magnitude.     

Thermoreversible gelation of poly(vinylidene fluoride) in phthalates: the influence of aliphatic chain length of solvents

Thermoreversible gelation of poly(vinylidene fluoride) (PVDF) has been studied in a new series of solvents (phthalates), for example, dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), and dihexyl phthalate (DHP) as a function of temperature and polymer concentration, both by test tube tilting and dynamic light scattering (DLS) method. The effect of aliphatic chain length (n) of diesters on the gelation kinetics, structure/microstructure and morphology of PVDF gels has been examined. Gelation rate was found to increase with increasing aliphatic chain length of diester. DLS results indicate that the sol-gel transformation proceeds via two-steps: first, microgel domains were formed, and then the infinite three-dimensional (3D) network is established by connecting microgels through polymer chains. The crystallites are responsible for 3D network for gelation in phthalates, and alpha-polymorph is formed during gelation producing higher amount of crystallinity with increasing aliphatic chain length of diester. Morphology of the networks of dried gels in different phthalates showed that fibril thickness and lateral dimensions decrease with higher homologues of phthalates. The scattering intensity is fitted with Debye-Bueche model in small-angle neutron scattering and suggested that both the correlation length and interlamellar spacing increases with n. A model has been proposed, based on electronic structure calculations, to explain the conformation of PVDF chain in presence of various phthalates and their complexes, which offer the cause of higher gelation rate for longer aliphatic chain length.     

Kinetics of the Oxidation of D‐Glucose and Cellobiose by Acidic Solution of N‐Bromoacetamide Using Transition Metal Complex Species, [RuCl3(H2O)2OH] −, as Catalyst

The kinetics of Ru(III)‐catalyzed and Hg(II)‐co‐catalyzed oxidation of D‐glucose (Glc) and cellobiose (Cel) by N‐bromoacetamide (NBA) in the presence of perchloric acid at 40 °C have been investigated. The reactions exhibit the first order kinetics with respect to NBA, but tend towards the zeroth order to higher NBA. The reactions are the first order with respect to Ru(III) and are fractional positive order with respect to [reducing sugar]. Positive effect of Cl^? and Hg(OAc)₂ on the rate of reaction is also evident in the oxidation of both reducing sugars. A negative effect of variation of H⁺ and acetamide was observed whereas the ionic strength (µ) of the medium had no influence on the oxidation rate. The rate of reaction decreased with the increase in dielectric constant and this enabled the computation of d_AB, the size of the activated complex. Various activation parameters have been evaluated and suitable explanation for the formation of the most reactive activated complex has been given. The main products of the oxidation are the corresponding arabinonic acid and formic acid. HOBr and [RuCl₃(H₂O)₂OH]^? were postulated as the reactive species of oxidant and catalyst respectively. A common mechanism, consistent with the kinetic data and supported by the observed effect of ionic strength, dielectric constant and multiple regression analysis, has been proposed. Formation of complex species such as [RuCl₃·S·(H₂O)OH]^? and RuCl₃·S·OHgBr·OH during the course of reaction was fully supported by kinetic and spectral evidences.     

Stereoselective Synthesis for Potential Isomers of Ticagrelor Key Starting Material

Tartrate salt of carbocyclic amine 2 is one of the key starting materials for the synthesis of Ticagrelor 1 . During the synthesis of 1 , the isomers of 2 also need to be considered as potential impurities and characterized before establishing the specification of product. In the present work, detailed study has been carried out to synthesize the related substances of 2 , and their structure characterization has been discussed.     

Development and validation of a highly sensitive LC‐MS/MS method for simultaneous quantitation of nortriptyline and 10‐hydroxynortriptyline in human plasma: application to a human pharmacokinetic study

A highly sensitive and specific LC‐MS/MS method has been developed for simultaneous estimation of nortriptyline (NTP) and 10‐hydroxynortriptyline (OH‐NTP) in human plasma (250 µL) using carbamazepine as an internal standard (IS). LC‐MS/MS was operated under the multiple reaction‐monitoring mode using the electrospray ionization technique. A simple liquid–liquid extraction process was used to extract NTP, OH‐NTP and IS from human plasma. The total run time was 2.5 min and the elution of NTP, OH‐NTP and IS occurred at 1.44, 1.28 and 1.39 min, respectively; this was achieved with a mobile phase consisting of 20 mm ammonium acetate : acetonitrile (20:80, v/v) at a flow rate of 0.50 mL/min on a HyPURITY C₁₈ column. The developed method was validated in human plasma with a lower limit of quantitation of 1.09 ng/mL for both NTP and OH‐NTP. A linear response function was established for the range of concentrations 1.09–30.0 ng/mL (r > 0.998) for both NTP and OH‐NTP. The intra‐ and inter‐day precision values for NTP and OH‐NTP met the acceptance as per FDA guidelines. NTP and OH‐NTP were stable in a battery of stability studies, i.e. bench‐top, auto‐sampler and freeze–thaw cycles. The developed assay was applied to a pharmacokinetic study in humans. Copyright © 2010 John Wiley & Sons, Ltd.     

Stochastic moment problem and hedging of generalized Black-Scholes options

In mathematical finance one is interested in the quadratic error which occurs while replacing a continuously adjusted portfolio by a discretely adjusted one. We first study higher order approximations of stochastic integrals. Then we apply the results to quantify quadratic error which occurs in estimating the discretely adjusted hedging risk in pricing European options in a generalized Black-Scholes market.     

Large deviations in testing fractional Ornstein–Uhlenbeck models

The paper obtains the explicit form of fine large deviation theorems for the log-likelihood ratio in testing models with fractional Ornstein–Uhlenbeck processes with Hurst parameter bigger than half and obtains the explicit rates of decrease of the error probabilities of Neyman–Pearson, Bayes and minimax tests.     

Base-Catalyzed Dehydration of 3-Substituted Benzene cis-1,2-Dihydrodiols: Stabilization of a Cyclohexadienide Anion Intermediate by Negative Aromatic Hyperconjugation

Evidence that a 1,2-dihydroxycyclohexadienide anion is stabilized by aromatic "negative hyperconjugation" is described. It complements an earlier inference of "positive" hyperconjugative aromaticity for the cyclohexadienyl cation. The anion is a reactive intermediate in the dehydration of benzene cis-1,2-dihydrodiol to phenol. Rate constants for 3-substituted benzene cis-dihydrodiols are correlated by σ(-) values with ρ = 3.2. Solvent isotope effects for the reactions are k(H(2)O)/k(D(2)O) = 1.2-1.8. These measurements are consistent with reaction via a carbanion intermediate or a concerted reaction with a "carbanion-like" transition state. These and other experimental results confirm that the reaction proceeds by a stepwise mechanism, with a change in rate-determining step from proton transfer to the loss of hydroxide ion from the intermediate. Hydrogen isotope exchange accompanying dehydration of the parent benzene cis-1,2-dihydrodiol was not found, and thus, the proton transfer step is subject to internal return. A rate constant of ～10(11) s(-1), corresponding to rotational relaxation of the aqueous solvent, is assigned to loss of hydroxide ion from the intermediate. The rate constant for internal return therefore falls in the range 10(11)-10(12) s(-1). From these limiting values and the measured rate constant for hydroxide-catalyzed dehydration, a pK(a) of 30.8 ± 0.5 was determined for formation of the anion. Although loss of hydroxide ion is hugely exothermic, a concerted reaction is not enforced by the instability of the intermediate. Stabilization by negative hyperconjugation is proposed for 1,2-dihydroxycyclohexadienide and similar anions, and this proposal is supported by additional experimental evidence and by computational results, including evidence for a diatropic ("aromatic") ring current in 3,3-difluorocyclohexadienyl anion.     

Detailed investigation of a γ-cyclodextrin inclusion complex with l-thyroxine for improved pharmaceutical formulations

Thyroxine is a naturally occurring human hormone produced by the thyroid gland. Clinical applications of thyroxine to treat several chronic disorders are limited by poor water solubility and instability under physiological conditions. An inclusion complex of levo-thyroxine (l-thyroxine), the active form of the hormone with gamma cyclodextrin (γ-CD) has been obtained and studied with the aim of improving oral delivery rather than the injection formulation of the sodium salt. In addition to greater patient acceptability, inclusion complexes often improve aqueous solubility and bioavailability, stability, and reduce toxicity of drugs, thus providing enhanced pharmaceutical formulations. Physicochemical characterization of the inclusion complex was carried out using Fourier transform infrared spectroscopy, X-ray diffractometry, differential scanning calorimetry, scanning electron microscopy and proton nuclear magnetic resonance spectroscopy. Intermolecular dipolar interactions for the inclusion complex were also studied using 2 dimensional ROESY experiments. Formation of the inclusion complex between the protons H3 and H5 of cyclodextrin with aromatic protons of thyroxine was confirmed by their dipolar interaction. Molecular modelling was used to understand the basis for the complex formation and predict the formation of other complexes. Interestingly, we found that l-thyroxine forms an inclusion complex only with the larger γ-CD and not with other available alpha and beta forms.     

Poly(ethylene glycol) (400) as superior solvent medium against ionic liquids for catalytic hydrogenations with PtO2

Adams' catalyst in poly(ethylene glycol) (PEG) (400) has been found to be a superior solvent over the ionic liquids by severalfold in promoting the hydrogenation of various functional groups. Both the catalyst and PEG were recycled efficiently over 10 runs without loss of activity, and substrate cross contamination was not observed despite a change in the substrate four times.