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101.
102.
The amino groups of purified least acidic xylanase (LAX) isomer and carboxyl groups of purified highly acidic xylanase (HAX)
isomer fromScopulariopsis sp. were chemically modified, resulting in charge neutralization and reversal. Modification of the second amino group was
accompanied by the complete loss of enzyme activity in both the absence and presence of xylose. Multiple alignments of family
10 and 11 xylanases revealed that there is a pair of fully conserved Lys residues only in family 10 members. Xylanase structures
from family 10 members showed that one of the conserved Lys residues is found near the active-site cleft that makes an H-bond
with the substrate. The LAX and HAX isoenzymes in which one amino and three to four carboxyl groups were modified were subjected
to kinetic and thermodynamic characterization. There were no differences in pH optima between the native and modified HAX,
but there was a broadening of pH optimum toward the alkaline range for charge-neutralized LAX and a double pH optimum for
charge-reversed LAX. TheV
max/K
m of both modified LAX and HAX decreased relative to the native species. The thermodynamics of xylan hydrolysis showed that
the decrease in the catalytic activity of modified LAX enzymes was entropically driven. When compared with native enzyme,
the thermostabilities of modified LAX enzymes increased in the presence and decreased in the absence of substrate. The thermodynamics
of kinetic stability for modified LAX enzymes revealed that this increase in thermolability was owing to the decrease in ΔH# with a concomitant increase in ΔS# compared with native LAX. The thermostabilities of all the modified HAX species decreased except that of charge-neutralized
HAX, whose half-life significantly increased in 50% (v/v) aqueous dioxan. These results suggest that the altered properties
of the modified enzymes were a result of the conformational changes brought about by chemical modification.
An erratum to this article is available at . 相似文献
103.
Electrochemical Investigation of Metal Oxide Conducting Electrodes for Direct Detection of Sulfide 下载免费PDF全文
This study examined the performance of four conducting metal oxide electrodes for the direct electrochemical analysis of sulfide; the electrode materials studied were indium tin oxide (ITO), fluorine doped tin oxide (FTO), aluminum doped zinc oxide (AZO) and gallium doped zinc oxide (GZO). Cyclic voltammetry (CV) results obtained using the ITO, AZO, GZO and FTO electrodes showed direct electrooxidation peak potential of sulfide at 381, 507, 400, and 850 mV vs. Ag/AgCl, respectively; however, the less positive oxidation potential and high catalytic current response of the ITO electrode made it the electrode of choice for the direct oxidation of sulfide. The effects of different electrolytes and buffer solutions on the CV responses were also evaluated. A linear concentration range up to 350 µM and a detection limit of 8.0 µM were achieved. CV response was highly reproducible, remaining unaffected even after 50 measurements. The sensor was found to have good selectivity, with no interference from sulfite, sulfate or chloride ions. The present findings demonstrate that the bare ITO electrode can be used as the basis of an inexpensive, sensitive, selective and robust sulfide sensor. 相似文献
104.
Muhammad Z. Rana Mazhar Mehmood Jamil Ahmad Muhammad Aslam Syed K. Hasanain Sohail Hameed 《Journal of nanoparticle research》2011,13(1):375-384
We report a novel technique for the formation of metal nanoparticles, based on electrolysis of the alcogels containing metal
chlorides. The alcogel was formed from TEOS, water, ethanol, and nickel chloride, and subjected to galvanostatic electrolysis.
This resulted in successful formation of Ni nanoparticles inside the silica gel. Average particle size of FCC Ni lies between
18 and 20 nm. The formation of tetragonal nickel (a sub-oxide of nickel) as well as NiO were also detected by XRD and SAED.
The resistivity measurements showed that the nickel nanoparticles were separated from each other by Ni(O) present between
them. Magnetic studies based on ZFC and FC measurements below room temperature (up to 5 K) and above room temperature (up
to 700 K) were conducted using SQUID and Magnetic TGA, respectively, which showed strong magnetic irreversibility as attributable
to exchange interaction between metallic and oxide phases and mutual interactions among metallic particles in the network
structure. The blocking temperature (~600 K) of the samples was above room temperature. M–H studies based on VSM showed an
increase in magnetic coercivity with the formation of NiO. A magnetic transition associated with tetragonal nickel was seen
at 10 K. 相似文献
105.
106.
PoonamPratibha Kumari Sohail AhmadShive Murat Singh Chauhan 《Tetrahedron letters》2011,52(52):7083-7086
A series of functional metallophthalocyanines have been synthesized to study their role as a catalyst towards the reductive dechlorination of atrazine using sodium borohydride as a mild reducing agent. The cobalt(II) phthalocyanine bearing nitro groups at the peripheral position is the most efficient catalyst with exceptionally high catalytic activity in comparison to other functional cobalt(II) phthalocyanines. 相似文献
107.
108.
Thermal rectification, the origin of which lies in modifying the thermal resistance in a nonlinear manner, could significantly improve the thermal management of a wide range of nano-devices (both electronic and thermoelectric), thereby improving their efficiencies. Since rectification requires a material to be inhomogeneous, it has been typically associated with solids. However, the structure of solids is relatively difficult to manipulate, which makes the tuning of thermal rectification devices challenging. Since liquids are more amenable to tuning, this could open up new applications for thermal rectification. We use molecular dynamics simulations to demonstrate thermal rectification using liquid water. This is accomplished by creating an inhomogeneous water phase, either by changing the morphology of the surface in contact with the liquid or by imposing an arbitrary external force, which in practice could be through an electric or magnetic field. Our system consists of a bulk fluid that is confined in a reservoir that is bounded by two walls, one hot and the other cold. The interfacial (Kapitza) thermal resistance at the solid-fluid interface and the density gradient of the bulk fluid both influence the magnitude of the thermal rectification. However, we find that the role of the interfacial resistance is more prominent than the application of an external force on the bulk fluid. 相似文献
109.
The chain elongation of the deoxy-nitroribose 6 by a Michael addition to the vinyl-phosphonate 7 followed by a solvolysis gave the heptulosephosphonate 11 (87%). From 11 , the key intermediates 15 and 16 (77%) were obtained by a highly diastereoselective reduction, followed by detritylation, periodate cleavage, and silylation. Methoxycarbonylation of 15 and 16 gave 17 and 18 which were converted into methyl shikimate ( 21 ; 79%) by intramolecular olefination and partial deprotection. Similarly, phosphonoylation of 16 gave 22 (99%) which was transformed into the diethyl phosphashikimate 2 (53% from 6). 相似文献
110.
Electrocatalytic Properties of a Gold Nanoseed Particle‐modified Indium Tin Oxide Electrode: Comparison of the Shape and Preparation Methods 下载免费PDF全文
Md. Abdul Aziz Manzar Sohail M. Nasiruzzaman Shaikh Munetaka Oyama 《Electroanalysis》2016,28(5):1119-1125
Gold nanostructures are the most commonly used nanostructures for fabricating electrochemical sensors and biosensors. In this study, we compared the catalytic performances of three types of gold nanoseed particles having two different morphologies, upon attachment to an amino‐functionalized ITO electrode surface. The ITO electrode surface was modified with 3‐aminopropyltrimethoxysilane (APTMS) and (1) gold nanoseed spheres (AuNSS), prepared using the ion capture and successive reduction method (ICR), (2) commercially available 5 nm AuNSS, and (3) a newly synthesized gold nanoseed wire (AuNSW). The electrocatalytic properties of the three electrodes were evaluated. Among the three electrodes, the AuNSW/APTMS/ITO was found to be the electrode of choice and exhibited excellent electrocatalytic properties toward the biologically important analytes glucose, uric acid, and serotonin. 相似文献