Photochemical activation of a polycarbonate surface for covalent immobilization of a protein ligand

Polycarbonate—a thermostable polymer is activated by a simple and rapid method using a photolinker, 1-fluoro-2-nitro-4-azidobenzene (FNAB) for covalent immobilization of a biomolecule. Horseradish peroxidase (HRP) is used as a model enzyme to check the efficacy of the activated surface. HRP is immobilized on the activated polycarbonate surface without addition of any reagent or catalyst and is found to give 2-2.5-fold increase in absorbance with the substrate as compared to the directly adsorbed enzyme. Photochemical attachment of FNAB to the PC surface is confirmed by X-ray photoelectron spectroscopy (XPS), which shows the presence of nitrogen and fluorine in the ratio of 2:1 in the activated polycarbonate. Disappearance of fluorine peak in the XP spectra of PC bound enzyme further confirms the covalent binding of HRP, through displacement of fluorine moiety of the activated PC by the amino group of the protein. Optimized concentration of the photolinker is found as 6 μmol of FNAB per well and time of photo irradiation is 8 min for activation of a PCR polycarbonate plate. PC bound HRP has shown enhanced thermal and storage stability. Kinetic studies of the immobilized HRP shows improved catalytic activity. The potential application of activated polycarbonate surface includes immobilization of biomolecules for biosensors, immunoassays, and protein and DNA micro-arrays. Due to the stability of the polycarbonate at high temperature, the activated polycarbonate has an advantage for immobilization of thermostable biomolecule such as thermostable enzyme for reaction at elevated temperature.     

Displacement problem and dynamically scheduling aircraft landings

In this paper we define a generic decision problem — the displacement problem. The displacement problem arises when we have to make a sequence of decisions and each new decision that must be made has an explicit link back to the previous decision that was made. This link is quantified by means of the displacement function. One situation where the displacement problem arises is that of dynamically scheduling aircraft landings at an airport. Here decisions about the landing times for aircraft (and the runways they land on) must be taken in a dynamic fashion as time passes and the operational environment changes. We illustrate the application of the displacement problem to the dynamic aircraft landing problem. Computational results are presented for a number of publicly available test problems involving up to 500 aircraft and five runways.     

Queues with postponed work

In this paper a queueing system in which work gets postponed due to finiteness of the buffer is considered. When the buffer is full (capacityK) further arrivals are directed to a pool of customers (postponed work). An arrival encountering the buffer full, will join the pool with probability γ (0<γ<1); else it is lost to the system forever. When, at a departure epoch the buffer size drops to a preassigned levelL−1 (1<L<K) or below, a postponed work is transferred with probabilityp (0<p<1) and positioned as the last among the waiting customers. If at a service completion epoch the buffer turns out to be empty and there is at least one customer in the pool, then the one ahead of all waiting in the pool gets transferred (with probability one) to the buffer and its service commences immediately. This ensures conservation of work. With arrival forming a Poisson process and service time having PH-distribution we study the long run behaviour of the system. Several system performance measures are obtained. A control problem is discussed and some numerical illustrations are provided.     

二氧化硫脲:一锅合成吡喃并[4,3-b] 吡喃类化合物的高效可重复使用有机催化剂（英文）简

A series of pyrano[4,3-b]pyran derivatives have been synthesized in excellent yields by the reaction of aromatic aldehydes with malononitrile or cyanoacetate and 4-hydroxy-6-methylpyran-2-one in water at 80℃, with the transformation being catalyzed by an aqueous solution of thiourea dioxide (TUD). Upon completion of the reaction, the product was isolated by filtration or extraction and the remaining aqueous TUD solution could be reused several times without any discernible impact on its catalytic activity. This procedure offers several advantages over existing procedures, including high yields, operational simplicity, the use of a non-toxic catalyst and solvent, short reaction time and minimum pollution of the environment, making it a useful and attractive process for the preparation of pyrano[4,3-b]pyran derivatives.     

Preparation of nitrogen-doped reduced graphene oxide and its use in a glassy carbon electrode for sensing 4-nitrophenol at nanomolar levels

We describe a novel procedure for the synthesis of nitrogen-doped reduced graphene oxide (N-rGO). It is based on the thermal reduction of GO (dispersed in water) with sodium diethyldithiocarbamate that acts as both the reducing agent and the source for nitrogen. The surface morphology of the N-rGO is characterized using high resolution transmission electron microscopy. X-ray photoelectron spectroscopy was carried out to study the composition of their surface, and Raman spectroscopy was performed to study the level of doping with nitrogen and the structural order. The N-rGO was deposited on a glassy carbon electrode (GCE), and the resulting electrode utilized as a sensing platform for 4-nitrophenol (4-NP). The modified GCE exhibits a well-defined oxidation peak current that is about ten times larger when compared to that of a bare GCE. The electron transfer number, proton transfer number and electron transfer rate constant (k_s 1.046 s^?1) were determined. At optimized conditions, the oxidation peak current is linearly related to the concentration of 4-NP in the 20–500 nM range, with a correlation coefficient of 0.9917. The detection limit (at an SNR of 3) is 7 nM. The method was successfully applied to the analysis of waters spiked with 4-NP. Recoveries range from 97.8 to 102.6 %, and no interferences are found for common inorganic cations and anions. Figure

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Silica-supported perchloric acid (HClO4–SiO2): a mild, reusable and highly efficient heterogeneous catalyst for multicomponent synthesis of 1,4-dihydropyridines via unsymmetrical Hantzsch reaction

Facile synthesis of some 1,4-dihydropyridine derivatives via Hantzsch reaction of 5,5-dimethyl-1,3-cyclohexanedione (dimedone), 1,3-diphenyl-2-propen-1-one derivatives and ammonium acetate under solvent-free condition in the presence of silica-supported perchloric acid (HClO₄–SiO₂) is described. The catalyst is easily prepared, stable, reusable and efficient under the reaction conditions.     

Numerical analysis of(s, S) inventory systems with repeated attempts

This paper deals with a continuous review (s,S) inventory system where arriving demands finding the system out of stock, leave the service area and repeat their request after some random time. This assumption introduces a natural alternative to classical approaches based either on lost demand models or on backlogged models. The stochastic model formulation is based on a bidimensional Markov process which is numerically solved to investigate the essential operating characteristics of the system. An optimal design problem is also considered. AMS subject classification: 90B05 90B22     

Role of nitrogen substitution in phenyl ring on excited state intramolecular proton transfer and rotamerism of 2-(2'-hydroxyphenyl)benzimidazole: a theoretical study

A comparative study of 2-(2'-hydroxy-3'-pyridyl)benzimidazole (2',3'-HPyBI), 2-(3'-hydroxy-4'-pyridyl)benzimidazole (3',4'-HPyBI), 2-(4'-hydroxy-3'-pyridyl)benzimidazole (4',3'-HPyBI), 2-(3'-hydroxy-2'-pyridyl)benzimidazole (3',2'-HPyBI), and 2-(5'-hydroxy-4'-pyrimidinyl)benzimidazole (5',4'-HPymBI) with 2-(2'-hydroxyphenyl)benzimidazole (HPBI) was performed theoretically to evaluate the effect of nitrogen substitution in the phenolic ring on the photophysics and rotamerism of HPBI. Density functional theory (DFT) and configuration interaction singles (CIS) combined with time-dependent DFT were employed for ground and excited state studies, respectively. Different possible molecular forms were considered for each molecule viz., cis-enol, trans-enol, open-enol, and keto forms. The computational results revealed that cis-enol is the most stable form in the ground state for all the molecules except in 2',3'-HPyBI. In 2',3'-HPyBI, K-2 keto is the most stable form. Water molecule assisted interconversions between different forms of 2',3'-HPyBI were examined theoretically. Excitation and emission energies for all the forms have been calculated theoretically and the values are in good agreement with the available experimental data. The calculations show that intramolecular proton transfer (ESIPT) is endothermic in the ground state while it is exothermic in the first excited singlet state (except 5',4'-HPymBI). The barrier for the excited state ESIPT reaction increases with nitrogen substitution. Torsional rotation between the benzimidazole and the pyridinyl∕pyrimidinyl rings in the S(1) state depicts that twisted-keto structures involve charge transfer from the hydroxypyridinyl∕hydoxypyrimidinyl to the benzimidazole ring. However, the formation of twisted-keto is not energetically favored in these systems.