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361.
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363.
Laurie Carrier Charles-Émile Fecteau Paul A. Johnson 《International journal of quantum chemistry》2020,120(15):e26255
Eigenvectors of a Hamiltonian solvable by a Bethe ansatz (BA) are employed as a variational trial wavefunction for electrons. Energy expressions are developed showcasing the methods of BA. Numerical results are presented for atomic systems as well as molecular dissociations, which are numerically identical with the restricted Hartree-Fock (HF) results. The present contribution serves as a bridge between HF and other BA wavefunctions to be employed as mean-field methods for strongly correlated electrons. 相似文献
364.
These velocity map imaging experiments characterize the photolytic generation of one of the two radical intermediates formed when OH reacts via an addition mechanism with allene. The CH2CCH2OH radical intermediate is generated photolytically from the photodissociation of 2-chloro-2-propen-1-ol at 193 nm. Detecting the Cl atoms using [2+1] resonance-enhanced multiphoton ionization evidences an isotropic angular distribution for the Cl+CH2CCH2OH photofragments, a spin-orbit branching ratio for Cl(2P1/2):Cl(2P3/2) of 0.28, and a bimodal recoil kinetic energy distribution. Conservation of momentum and energy allows us to determine from this data the internal energy distribution of the nascent CH2CCH2OH radical cofragment. To assess the possible subsequent decomposition pathways of this highly vibrationally excited radical intermediate, we include electronic structure calculations at the G3//B3LYP level of theory. They predict the isomerization and dissociation transition states en route from the initial CH2CCH2OH radical intermediate to the three most important product channels for the OH+allene reaction expected from this radical intermediate: formaldehyde+C2H3, H+acrolein, and ethene+CHO. We also calculate the intermediates and transition states en route from the other radical adduct, formed by addition of the OH to the center carbon of allene, to the ketene+CH3 product channel. We compare our results to a previous theoretical study of the O+allyl reaction conducted at the CBS-QB3 level of theory, as the two reactions include several common intermediates. 相似文献
365.
Yikilmaz E Porta J Grove LE Vahedi-Faridi A Bronshteyn Y Brunold TC Borgstahl GE Miller AF 《Journal of the American Chemical Society》2007,129(32):9927-9940
The active site metal ion of superoxide dismutase (SOD) is reduced and reoxidized as it disproportionates superoxide to dioxygen and hydrogen peroxide. Thus, the reduction midpoint potential (Em) is a critical determinant of catalytic activity. In E. coli Fe-containing SOD (FeSOD), reduction of Fe3+ is accompanied by protonation of a coordinated OH-, to produce Fe2+ coordinated by H2O. The coordinated solvent's only contact with the protein beyond the active site is a conserved Gln residue. Mutation of this Gln to His or Glu resulted in elevation of the Em by 220 mV and more than 660 mV, respectively [Yikilmaz et al., Biochemistry 2006, 45, 1151-1161], despite the fact that overall protein structure was preserved, His is a chemically conservative replacement for Gln, and neutral Glu is isostructural and isoelectronic with Gln. Therefore, we have investigated several possible bases for the elevated Em's, including altered Fe electronic structure, altered active site electrostatics, altered H-bonding and altered redox-coupled proton transfer. Using EPR, MCD, and NMR spectroscopies, we find that the active site electronic structures of the two mutants resemble that of the WT enzyme, for both oxidation states, and Q69E-FeSOD's apparent deviation from WT-like Fe3+ coordination in the oxidized state can be explained by increased affinity for a small anion. Spontaneous coordination of an exogenous anion can only stabilize oxidized Q69E-Fe3+SOD and, therefore, cannot account for the increased Em of Q69E FeSOD. WT-like anion binding affinities and active site pK's indicate that His69 of Q69H-FeSOD is neutral in both oxidation states, like Gln69 of WT-FeSOD, whereas Glu69 appears to be neutral in the oxidized state but ionized in the reduced state of Q69E-FeSOD. A 1.1 A resolution crystal structure of Q69E-Fe2+SOD indicates that Glu69 accepts a strong H-bond from coordinated solvent in the reduced state, in contrast to the case in WT-FeSOD where Gln69 donates an H-bond. These data and DFT calculations lead to the proposal that the elevated Em of Q69E-FeSOD can be substantially explained by (1) relief from enforced H-bond donation in the reduced state, (2) Glu69's capacity to provide a proton for proton-coupled Fe3+ reduction, and (3) strong hydrogen bond acceptance in the reduced state, which stabilizes coordinated H2O. Our results thus support the hypothesis that the protein matrix can apply significant redox tuning via its influence over redox-coupled proton transfer and the energy associated with it. 相似文献
366.
The irregular demand and communication network disruption that are characteristics of situations demanding humanitarian logistics, particularly after large-scale earthquakes, present a unique challenge for relief inventory modelling. However, there are few quantitative inventory models in humanitarian logistics, and assumptions inherent in commercial logistics naturally have little applicability to humanitarian logistics. This paper develops a humanitarian disaster relief inventory model that assumes a uniformly distributed function in both lead-time and demand parameters, which is appropriate considering the limited historical data on relief operation. Furthermore, this paper presents different combinations of lead-time and demand scenarios to demonstrate the variability of the model. This is followed by the discussion of a case study wherein the decision variables are evaluated and sensitivity analysis is performed. The results reveal the presence of a unique reorder level in the inventory wherever the order quantity is insensitive to some lead-time demand values, providing valuable direction for humanitarian relief planning efforts and future research. 相似文献
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368.
Laurie Cavey Margaret Kinzel Sharon Walen Kathleen Rohrig 《School science and mathematics》2015,115(4):168-178
This study examines data from college students who worked in pairs to make decisions about a list of potential definitions of prime number. Analysis focused on the evidence each student pair cited when they decided whether or not a statement could be used as a definition for prime number. The purpose of this paper is to describe patterns in the ways students used the evidence they cited. Findings suggest that students attend to important features of mathematical definitions, with some students giving preference to usability and others giving preference to definitions that are unambiguous. 相似文献
369.
The successful development of novel bio-inspired devices requires the ability to place specific biomolecules on a substrate with nanometre precision, in such a way so that their bioactivity is retained. A method is required that can verify this bio-modification. Scanning probe microscopy (SPM) can image and probe a surface in a liquid environment with nanometre resolution. Using short chain complementary oligonucleotides as the bioactive molecules we have modified continuous and patterned gold substrates and SPM probes. We demonstrated that the attached oligonucleotides retained their biological activity after surface attachment with a hybridization interaction force that varies between 50 and 400pN as measured by SPM force measurements. Finally, the position of the attached oligonucleotides was determined with nanometre resolution. Thus we have demonstrated the capabilities of SPM in the application of the development of substrates and templates suitable for forming the basis of novel and innovative devices. 相似文献
370.
Rubel Chakravarty Meera Venkatesh Ashutosh Dash 《Journal of Radioanalytical and Nuclear Chemistry》2011,290(1):45-51
A novel electrochemical process to avail clinical grade 99mTc from (n,γ)99Mo has been demonstrated. The electrochemical parameters were optimized to maximize the 99mTc yield with minimal 99Mo contamination. 99Mo/99mTc generators containing up to 29.6 GBq (800 mCi) 99Mo were developed and their performance were extensively evaluated for 10 days without changing the operating conditions.
Very high radioactive concentration of 99mTcO4
− of acceptable quality, commensurate with hospital radiopharmacy requirements could be availed from the system with >90% yield.
The compatibility of the product for the formulation of 99mTc labeled radiopharmaceuticals such as 99mTc-DMSA and 99mTc-EC was found to be satisfactory in terms of high labeling yields. The proposed route represents an important step for enhancing
the scope of accessing clinical grade 99mTc from low specific activity (n, γ)99Mo. 相似文献