714 research outputs found
Catalysts on Demand: Selective Oxidations by Laboratory-Evolved Cytochrome P450 BM3
Efficient catalysts for selective oxidation of C-H bonds using atmospheric oxygen are highly desirable to decrease the economic and environmental costs associated with conventional oxidation processes. We have used methods of directed evolution to generate variants of bacterial cytochrome P450 BM3 that catalyze hydroxylation and epoxidation of a wide range of nonnative substrates. This fatty acid hydroxylase was converted to a propane monooxygenase (PMO) capable of hydroxylating propane at rates comparable to that of BM3 on its natural substrates. Variants along the PMO evolutionary lineage showed broadened substrate scope; these became the starting points for evolution of a wide array of enzymes that can hydroxylate and derivatize organic scaffolds. This work demonstrates how a single member of enzyme family is readily converted by evolution into a whole family of catalysts for organic synthesis
Enzymatic functionalization of carbon-hydrogen bonds
The development of new catalytic methods to functionalize carbonâhydrogen (CâH) bonds
continues to progress at a rapid pace due to the significant economic and environmental benefits
of these transformations over traditional synthetic methods. In nature, enzymes catalyze regio- and
stereoselective CâH bond functionalization using transformations ranging from hydroxylation to
hydroalkylation under ambient reaction conditions. The efficiency of these enzymes relative to
analogous chemical processes has led to their increased use as biocatalysts in preparative and
industrial applications. Furthermore, unlike small molecule catalysts, enzymes can be systematically
optimized via directed evolution for a particular application and can be expressed in vivo to
augment the biosynthetic capability of living organisms. While a variety of technical challenges
must still be overcome for practical application of many enzymes for CâH bond functionalization,
continued research on natural enzymes and on novel artificial metalloenzymes will lead to improved
synthetic processes for efficient synthesis of complex molecules. In this critical review, we discuss the
most prevalent mechanistic strategies used by enzymes to functionalize non-acidic CâH bonds, the
application and evolution of these enzymes for chemical synthesis, and a number of potential
biosynthetic capabilities uniquely enabled by these powerful catalysts (110 references)
4-Methylcyclohexanemethanol Acute Toxicity to Daphnia and Its Effects on General Esterase and Glutathione S-Transferase Activity in Fathead Minnows
In 2014, 10,000 gallons of crude MCHM spilled into the Elk River in West Virginia. Due to a paucity of information about the toxicity of this chemical prior to the spill, our research aimed to verify the published 48-h EC50 for Daphnia magna (Daphnia) examine the effects of MCHM on two enzyme detoxification systems, general esterase and glutathione S-transferase, in Pimephales promelas (Fathead Minnow). We used pure MCHM instead of the crude form used in Eastmanâs toxicity tests because the composition of crude MCHM is variable. The EC50 we obtained for pure MCHM did not differ significantly from the EC50 provided by Eastman for the crude form. We exposed Fathead Minnows to sublethal environmentally-relevant concentrations of MCHM for 96 h prior to performing the enzyme assays. The experimental groups in these assays did not show significant difference from control groups. Although our results add to the toxicity information, there is still a concerning deficit in chronic toxicity testing because of possible prolonged human exposure following the spill
Photoemission study of poly(dA)-poly(dT) DNA : Experimental and theoretical approach to the electronic density of states
We present results of an ultraviolet photoemission spectroscopy study of
artificially synthesized poly(dA)-poly(dT) DNA molecules on -type Si
substrates. For comparison, we also present the electronic density of states
(DOS) calculated using an \emph{ab initio} tight-binding method based on
density-functional theory (DFT). Good agreement was obtained between experiment
and theory. The spectra of DNA networks on the Si substrate showed that the
Fermi level of the substrate is located in the middle of the band gap of DNA.
The spectra of thick ( nm) DNA films showed a downward shift of eV compared to the network samples.Comment: 4 pages, 4 figure
Should We Provide a Clinical Diagnosis for People with Shoulder Pain? Absolutely, Maybe, Never! The Ongoing Clinical Debate Between Leavers and Retainers
[No abstract available
âRestoring that Faith in my Shoulderâ: A Qualitative Investigation of how and why Exercise Therapy Influenced the Clinical Outcomes of Individuals with Rotator Cuff-Related Shoulder Pain
Chemoenzymatic elaboration of monosaccharides using engineered cytochrome P450_(BM3) demethylases
Polysaccharides comprise an extremely important class of biopolymers
that play critical roles in a wide range of biological processes,
but the synthesis of these compounds is challenging because of
their complex structures. We have developed a chemoenzymatic
method for regioselective deprotection of monosaccharide substrates
using engineered Bacillus megaterium cytochrome P450
(P450_(BM3)) demethylases that provides a highly efficient means
to access valuable intermediates, which can be converted to a
wide range of substituted monosaccharides and polysaccharides.
Demethylases displaying high levels of regioselectivity toward a
number of protected monosaccharides were identified using a
combination of protein and substrate engineering, suggesting that
this approach ultimately could be used in the synthesis of a wide
range of substituted mono- and polysaccharides for studies in
chemistry, biology, and medicine
Measurement of the Electrical Resistance of n-Type Si Microwire/p-Type Conducting Polymer Junctions for Use in Artificial Photosynthesis
The junction between n-type silicon microwires and p-type conducting polymer PEDOT:PSS (poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)) was investigated using a soft contact method. Dopant levels within the microwires were varied during growth to give a highly-doped region for improved contact and a low-doped region for light absorption. The low-doped region of the microwires had a dopant density of 5 X 10(17) cm(-3) while the highly-doped region had an increased dopant density of 5 X 10(18) cm(-3) over similar to 20 mu m. Uniform, highly-doped microwires, with a dopant density of 4 X 10(19) cm(3), were used as a comparison. Regions of highly-doped n-type Si microwires (N-D = 5 X 10(18) cm(-3) and 4 X 10(19) cm(-3)) contacted by PEDOT:PSS showed a significantly lower junction resistance compared to the low-doped (3 X 10(17) cm(-3)) regions of the microwire. Junctions incorporating the metal catalyst used during growth were also investigated. Microwires with copper at the interface had similar currentvoltage characteristics to those observed for the highly-doped microwire/conducting polymer junction; however, junctions that incorporated gold exhibited significantly lower resistances, decreasing the iR contribution of the junction by an order of magnitude with respect to the total voltage drop in the entire structure
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