Functional Groups Assisted Tunable Dielectric Permittivity of Guest-Free Zn-Based Coordination Polymers for Gate Dielectrics

The dielectric properties of coordination polymers has been a topic of recent interest, but the role of different functional groups on the dielectric properties of these polymers has not yet been fully addressed. Herein, the effects of electron-donating (R=NH₂) and electron-withdrawing (R=NO₂) groups on the dielectric behavior of such materials were investigated for two thermally stable and guest-free Zn-based coordination polymers, [Zn(L₁)(L₂)]_n ( 1 ) and [Zn(L₁)(L₃)]_n ( 2 ) [L₁=2-(2-pyridyl) benzimidazole (Pbim), L₂=5-aminoisophthalate (Aip), and L₃=5-nitroisophthalate (Nip)]. The results of dielectric studies of 1 revealed that it possesses a high dielectric constant (κ=65.5 at 1 kHz), while compound 2 displayed an even higher dielectric constant (κ=110.3 at 1 kHz). The electron donating and withdrawing effects of the NH₂ and NO₂ substituents induce changes in the polarity of the polymers, which is due to the inductive effect from the aryl ring for both NO₂ and NH₂. Theoretical results from density functional theory (DFT) calculations, which also support the experimental findings, show that both compounds have a distinct electronic behavior with diverse wide bandgaps. The significance of the current work is to provide information about the structure-dielectric property relationships. So, this study promises to pave the way for further research on the effects of different functional groups on coordination polymers on their dielectric properties.     

Rapid Protein Hydrolysis by Microwave Irradiation Using Heat-Resistant Teflon-Pyrex Tubes

A rapid peptide-bond hydrolysis by means of microwave irradiation is introduced for the facile preparation of protein hydrolysates used for amino acid analysis. The optimal hydrolysis condition has been determined using several enzymes with known amino acid compositions. The effects of hydrolysis time on the recovery of various labile and hydrophobic amino acids are also exemplified in the microwave heating of standard amino acids. The method has been applied to the complete amino acid analysis with a single nonvolatile solvent of methanesulfonic acid with good recovery of tryptophan and half-cystine. It provides a radical expedition of protein and peptide hydrolysis via commercial microwave ovens and specially-designed Teflon-Pyrex tubes, circumventing the tedious procedures using vacuum-sealed pyrex lubes heating at 110°C for more than 24 h. This novel type of microwave chemistry associated with rapid peptide-bond cleavage is of great potential in the automation of the complete process of amino acid analysis starting from the preparation of protein hydrolysates.     

Probing stereoselective inhibition of the acyl binding site of cholesterol esterase with four diastereomers of 2'-<Emphasis Type="Italic">N</Emphasis>-α-methylbenzylcarbamyl-1, 1'-bi-2-naphthol

Background  

Recently there has been increased interest in pancreatic cholesterol esterase due to correlation between enzymatic activity in vivo and absorption of dietary cholesterol. Cholesterol esterase plays a role in digestive lipid absorption in the upper intestinal tract, though its role in cholesterol absorption in particular is controversial. Serine lipases, acetylcholinesterase, butyrylcholinesterase, and cholesterol esterase belong to a large family of proteins called the α/β-hydrolase fold, and they share the same catalytic machinery as serine proteases in that they have an active site serine residue which, with a histidine and an aspartic or glutamic acid, forms a catalytic triad. The aim of this work is to study the stereoselectivity of the acyl chain binding site of the enzyme for four diastereomers of an inhibitor.     

Pt Nanoparticle‐modified Carbon Fiber Microelectrode for Selective Electrochemical Sensing of Hydrogen Peroxide

We report a simple approach to the production of carbon fiber‐based amperometric microbiosensors for selective detection of hydrogen peroxide (H₂O₂), which was achieved by electrometallization of carbon fiber microelectrodes (CFMs) by electrodeposition of Pt nanoparticles. The Pt‐carbon hybrid sensing interface provided a sensitivity of 7711±587 μA ? mM^?1 ? cm^?2, a detection limit of 0.53±0.16 μM (S/N=3), a linear range of 0.8 μM–8.6 mM, and a response time of <2 sec. The morphologies of the Pt nanoparticle‐modified CFMs were characterized by scanning electron microscopy. To achieve selectivity, permseletive layers, polyphenylenediamine (PPD) and Nafion, were deposited resulting in exclusion of the anionic and cationic interferents, ascorbic acid and dopamine, respectively, at their physiologically relevant concentrations. The resultant sensors displayed a sensitivity to hydrogen peroxide of 1381±72 μA ? mM^?1 ? cm^?2, and a detection limit of 0.86±0.19 μM (S/N=3). This simple and rapid metallization method converts carbon fiber microelectrodes, which are readily accessible, to microscale Pt electrodes in 2 min, providing a platform for oxidase‐based amperometric biosensors with improved spatial resolution over more commonly used platinum electrode array microprobes.     

Long-term trend in CHF2Cl (HCFC-22) from high spectral resolution infrared solar absorption measurements and comparison with in situ measurements

The average tropospheric volume mixing ratio of CHF₂Cl (HCFC-22) has been retrieved from a time series of high spectral resolution ground-based infrared solar absorption spectra recorded with the McMath Fourier transform spectrometer located at the U.S. National Solar Observatory facility on Kitt Peak in southern Arizona (31.9°N, 111.6°W, 2.09 km altitude) for the time period October 1987–November 2002. The retrievals are based on fits to the well-isolated, unresolved 2ν₆ Q branch at 829.05 cm⁻¹ and the SFIT2 retrieval algorithm. The measured daily averages show a near linear rise per year in the mean tropospheric volume mixing ratio as a function of time with a best fit yielding an average increase rate of (5.66±0.15) parts per trillion (10⁻¹²) by volume per year, corresponding to (6.47±0.17)%yr⁻¹, 1 sigma, at the beginning of the time series. The tropospheric mixing ratios retrieved from the solar spectra have been compared with monthly average surface flask sampling measurements from the Climate Monitoring and Diagnostic Laboratory (CMDL) station at Niwot Ridge, Colorado (40.0°N, 105.5°W, 3013 m altitude), archived measurement from the same location, and early CMDL northern hemisphere Pacific cruise measurements. The average ratio of the retrieved tropospheric mixing ratio relative to the CMDL surface mixing ratio is 1.053 for the overlapping 1987 to 2002 time period. The retrieved mean tropospheric mixing ratio is consistent with the surface measurements within the errors estimated for the remote sensing observations.     

First measurements of the HCFC-142b trend from atmospheric chemistry experiment (ACE) solar occultation spectra

The first measurement of the HCFC-142b (CH₃CClF₂) trend near the tropopause has been derived from volume mixing ratio (VMR) measurements at northern and southern hemisphere mid-latitudes for the 2004–2008 time period from spaceborne solar occultation observations recorded at 0.02 cm⁻¹ resolution with the ACE (atmospheric chemistry experiment) Fourier transform spectrometer. The HCFC-142b molecule is currently the third most abundant HCFC (hydrochlorofluorocarbon) in the atmosphere and ACE measurements over this time span show a continuous rise in its volume mixing ratio. Monthly average measurements at northern and southern hemisphere mid-latitudes have similar increase rates that are consistent with surface trend measurements for a similar time span. A mean northern hemisphere profile for the time span shows a near constant VMR at 8–20 km altitude range, consistent on average for the same time span with in situ results. The nearly constant vertical VMR profile also agrees with model predictions of a long lifetime in the lower atmosphere.     

New and efficient synthesis of azabicyclo[4.4.0]alkane amino acids by Rh-catalyzed cyclohydrocarbonylation

[reaction: see text] Highly efficient syntheses of azabicyclo[4.4.0]alkane amino acids were achieved by Rh-catalyzed cyclohydrocarbonylation of dipeptides bearing a terminal olefin moiety and a heteroatom nucleophile.     

Production of l-DOPA by tyrosinase immobilized on modified polystyrene

Mushroom tyrosinase was immobilized on modified polystyrene—polyaminostyrene (PSNH) and polymethylchloridestyrene (PSCL)—to produce l-DOPA from l-tyrosine. Glutaraldehyde was used as an activating agent for the PSNH to immobilize the tyrosinase and 10% (w/v) glutaraldehyde was optimal in conferring the highest specific activity (11.96 U/g) to the PSNH. Methylchloride on the PSCL was directly linked with the tyrosinase, and 1.5 mmol of Cl/g was optimal in attaining the specific activity of 17.0 U/g. The temperature and optimal acidity were, respectively, 60°C and pH 5.5 for the PSNH, and 70°C and pH 3.0 for the PSCL. In a 50-mL batch reactor working over 36 h, the l-DOPA production rate at 30°C was 1.44 mg/(L·h) for the PSNH and 2.33 mg/(L·h) for the PSCL. The production rate over 36 h was 3.86 mg/(L·h) for the PSNH at 60°C and 5.54 mg/(L·h) for the PSCL at 70°C. Both of the immobilized enzymes showed a remarkable stability with almost no change in activity after being stored wet. The operational stability study indicated a 22.4% reduction in l-DOPA production for the PSNH and an 8.63% reduction for the PSCL over seven runs (each run was for 144h at 30°C) when the immobilized enzymes were used under turnover conditions. The immobilized tyrosinase was more stable on the PSCL than on the PSNH.     

A hybrid approach for optimal design of signalized road network

For a signalized road network with expansions of link capacity, the maximum possible increase in travel demands is considered while total delays for travelers are minimized. Using the concept of reserve capacity of signal-controlled junctions, the problem of finding the maximum possible increase in travel demand and determining optimal link capacity expansions can be formulated as optimization programs. In this paper, we present a new solution approach for simultaneously solving the maximum increase in travel demands and minimizing total delays of travelers. A projected Quasi-Newton method is proposed to effectively solve this problem to the KKT points. Numerical computations and comparisons are made on real data signal-controlled networks where obtained results outperform traditional methods.     

Multipoint parallel excitation and CCD-based imaging system for high-throughput fluorescence detection of biochip micro-arrays

We report the development and the characterization of a multipoint parallel excitation and CCD-based imaging system for high-throughput fluorescence detection of biochip micro-arrays. A two-dimensional array of (19×19) points with uniform intensity distribution, generated by a holographic array generator, was used for parallel excitation of two-dimensional micro-arrays of fluorescence samples. A CCD-based imaging system was used for high-throughput parallel detection and quantitative analysis of the fluorescence output. Micro-array samples of cyanine (Cy5) dye dots on silicon wafers and on glass substrates with varying concentration were used to evaluate the performance of the system. Results of fluorescence intensity measurements with varying concentration of dye and with different image acquisition time are presented. We have demonstrated that this novel approach will, in general, outperform the conventional approach in the excitation efficiency, the signal-to-noise ratio, and the throughput. The limitations and the potential improvements of the present method are discussed.