Nitrenes are reactive intermediates for many organic reactions, such as Curtius rearrangement. The thermo- or photochemical- decomposition of azides or isocyanates was known to generate nitrenes. We investigated the thermal chemistry of nitrene adsorbed on Cu(111) using benzyl azide (Bz-N=N=N), benzyl isocyanate (Bz-N=C=O) and phenyl isocyanate (ph-N=C=O) as precursors under ultrahigh vacuum conditions using temperature-programmed reaction/desorption (TPR/D), reflectionabsorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS). Our study shows that despite of the isoelectronic functionalities (-N=N=N vs. -N=C=O) these molecules undergo different reaction pathways. For benzyl azide (Bz-N=N=N), the azido group losses N2 ,and the phenyl group migrates from nitrogen to carbon, forming surface bound H2C=N-Ph at 210 K. Eventually, H2 elimination and a carbon-to-nitrogen phenyl shift give the thermally stable ph-CN final product. XPS reveals that benzyl isocyanate (Bz-N=C=O) rearranges to form amide intermediate on the surface, which breaks into CO2, HCN and toluene at 410 K. RAIRs suggests that phenyl isocyanate (ph-N=C=O) undergoes cyclodimerization, cyclotrimerization and condensation to remove CO2 at 170 K, and phenyl group shifts from nitrogen to carbon to produce a metal bound acyl nitrene species (Ph-(C=O)-N---Cu) at 410 K.

Nitromethane is the simplest organic-nitro compound as well as the archetype of an important class of high explosive. Homogeneous nitromethane reactions have been the subject of extensive studies. Particularly the unimolecular isomerization of nitromethane to methyl nitrite is proven to be competitive with simple C-N bond (bond energy 60 kcal/mol) rupture. The activation energy for the rearrangement was measured to be 55.5 kcal/mol and methyl nitrite has a very weak CH3O-NO bond energy 42 kcal/mol lower than that for homolysis. The thermal chemistry of nitromethane on Cu(111) was studied by a combination of temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) techniques. TPD spectra show that the desorption features include the physisorbed multilayer and monolayer of CH3NO2 at 150 and 190 K, respectively. The major decomposition pathway is via cleavage of O-N bond to yield a major product NO, which is characterized by m/z 30(NO+). A possible contribution from isomerization of nitromethane to methyl nitrite (CH3NO2 CH3ONO) on the surface cannot be ruled out at 278 K. In addition to isomerization, the dehydrogenation products CO and CO2 are also unveiled as part of the desorption features at 314 and 455 K, respectively. We can further prove the reactivity of nitromethane on Cu(111) at 367 K by using the deuterated form of nitromethane which reveals the corresponding desorption TPR/D signals of D2, D2O and CD4. However, we find that nitromethane also reacts by dissociating the C-H bond and the O-N bond, however, leaving the C-N bond intact. Along this reaction channel, HCN desorbs as a product above 360 K, as evidenced by a broad desorption feature of m/z 27. Dimerization of CN to C2N2 occurs at 815 K. The RAIR spectroscopy demonstrates that nitromethane is indeed adsorbed on Cu(111) at 100 K. The formation of methoxy and formyl are supported by the observation of desorption of NO at 278 K with the characteristic NO stretching mode found at 1535 cm-1. Moreover, we assign side-bonded CN and aminomethylene (HC-NH2) present on Cu(111). After the surface is annealed to 330 K, a signature band at 2173 cm-1 is assigned to terminal-bounded CN stretching mode. This band eventually fades out above 900 K consistent with the evolution of cyanogen at 815 K.

M. tuberculosis copper-sensitive operon repressor (Mtb CsoR) is the founding member of a new metalloregulatory protein family in prokaryotes that regulates the transcription of the cso operon in response to copper toxicity. Mtb CsoR tetramer binds 1 monomer mol equiv of Cu(I) with very high affinity (log KCu=18.0) via three conserved residues, Cys36, His61' and Cys65'. Binding of Cu(I) allosterically inhibits the CsoR binding to the DNA operator (CsoO) overlapping the cso promoter (DeltaGc=+3.6 kcal/mol, pH 7.0, 25 oC). These findings are consistent with a role of CsoR as a transcriptional repressor with Cu(I) binding inducing transcriptional derepression. To explore the mechanism of this regulation, His61 was substituted with 1-methylhistidine (MeH) or Beta- (2-thiazolyl)-alanine (Thz) using a native chemical ligation strategy. The CsoO binding affinities of the resultant H61MeH and H61Thz CsoRs are both refractory to inhibition by Cu(I) binding despite the fact that each forms a high affinity 3-coordinate complex with Cu(I). This suggests that while Cu(I) is coordinated by the N?11 atom of His61, the N?22 atom plays an critical role in driving this allosteric switch. Evidence in support of a formation of a hydrogen bonding network involving the N?1 face of His61 and two conserved "second coordination shell" residues, Glu81' and Tyr35, is presented. Remarkably, this mechanism is analogous to that proposed for the Zn(II) sensor CzrA from S. aureus. To test this, we employed the same native chemical ligation approach to substitute the key Zn(II) ligand His97 with 1-methylhistidine; with the preliminary findings fully consistent with an intersubunit allosteric switch involving the N?2 face of this key His97 residue in CzrA. Two predicted homologs of Mtb CsoR were also biochemically characterized to obtain additional support for the hypothesis that CsoR is a key Cu(I) regulatory protein in many bacterial species. B. subtilis CsoR, known to regulate the transcription of the copZA operon, was found to have biochemical properties similar to those of Mtb CsoR as to Cu(I) binding, DNA binding and Cu(I)-dependent allosteric regulation. Interestingly, Bsu CsoR also binds other divalent metal ions (Zn, Ni) with high affinity but with metal coordination geometries distinct from that of Cu(I). Binding of these divalent metal ions only weakly regulates copZA operator binding in vitro, suggesting that coordination number and geometry are most closely related to the allosteric regulation. Finally, a putative CsoR from the pathogenic S. aureus Newman strain was identified and characterized, and was found to exhibit biochemical properties similar to those of Mtb and Bsu CsoRs. Parallels between Cu(I)-sensing CsoRs and functional orthologs in the CsoR/RcnR family are further discussed in the context of the mechanism and evolutionary divergence of this new family of regulatory proteins.

Membrane separations provide a potentially attractive technology over conventional processes due to their advantages, such as low capital cost and energy consumption. The goal of this thesis is to design hybrid membranes that facilitate specific gas separations, especially olefin/paraffin separations. This thesis focuses on the designing dendrimer-based hybrid membranes on mesoporous alumina for reverse-selective separations, synthesizing Cu(I)-dendrimer hybrid membrane to facilitate olefin/paraffin separations, particularly ethylene/methane separation, and investigating the influence of solvent, stabilizing ligands on facilitated transport membrane. Reverse-selective gas separations have attracted considerable attention in removing the heavier/larger molecules from gas mixtures. In this study, dendrimer-based chemistry was proved to be an effective method by altering dendrimer structures and generations. G6-PIP, G4-AMP and G3-XDA are capable to fill the alumina mesopores and slight selectivity are observed. Facilitated transport membranes were made to increase the olefin/paraffin selectivity based on their chemical interaction with olefin molecules. Two approaches were explored, the first was to combine facilitator Cu(I) with dendrimer hybrid membrane to increase olefin permeance and olefin/paraffin selectivity simultaneously, and second was to facilitate transport membrane functionality by altering solvents and stabilizing ligands. Promising results were found by these two approaches, which were: 1) olefin/paraffin selectivity slightly increased by introducing facilitator Cu(I), 2) the interaction between Cu(I) and dendrimer functional groups are better known.

This study was to investigate the effect on conversion, deactivation of long-term, selectivity of product, and kinetics in deep oxidation of toluene over copper catalyst. The copper catalyst is supported on honeycomb of ceramic monolith (400 cell/inch2). The operation parameters in heterogeneous reactor were performed as follows: 1000 ppm initial concentration of toluene, temperature of reaction in ranging from 200 ¢J to 400 ¢J, 15 % of oxygen concentration, and 4000 hr-1 of space velocity. In the selection of catalyst, we decided to use 20% Cu catalyst for its high conversion, high selectivity and low cost in oxidation of toluene. The conversion of toluene in catalytic reaction was increased with the increasing both of reaction temperature and influent concentration of oxygen, and decreased with the going up of initial concentration of toluene and of space velocity. In the catalyst stability of long-term test, Cu catalysts had a good stability after 7 days reaction in heterogeneous reactor. The tests such as BET, SEM and EA were also determined to verify the stability from surface of catalyst. The kinetics of heterogeneous reactor over Cu catalyst supported on ceramic honeycomb in oxidation of toluene was found that a pseudo-first order could be described by both Power-rate law and Mars-Van Krevelen model. The apparent reaction order and activated energy were obtained in this work.

The Co-Cu nanoparticles is one of the magnetic materials that have considerable potential for a variety of industrial applications, including giant magnetoresistance (GMR) digital storage devices and have therefore attracted a great deal of attention in recent years. For this reason, it will be an important reference to the development of the magnetic digital storage devices if we can go deep into study the material properties of the Co-Cu nanoparticles. This study uses molecular dynamics simulations to investigate the crystalline process of Co-Cu nanoparticles of high and low Co concentrations (5~25 %) during the annealing process. The modified many-body tight binding potential is adopted to accurately model the Cu-Cu, Co-Co, and Co-Cu pair inter-atomic interactions. The structural transformations at the upper and lower melting points are observed by the radial distribution function (RDF), the angle correction function (ACF) and the average bond lengths. finally, we employs molecular dynamics simulations to predict the distribution function of diluted magnetic Co atoms in a Cu host and then uses the the Ruderman-Kittel-Kasuya-Yosida (RKKY) theory and quantum magnetism theory to calculate the magnetic properties of the Co-Cu alloys at different temperature, including their Curie temperature.

In organometallic study, activation of C-F bond is an interesting subject, especially in fluoro-substituted propyl groups, because of their different reactivityn from fluoro-substituted methyl and ethyl groups. In this thesis, fluorinated propyl groups were studied on a Cu(111) surface under ultrahigh vacuum (UHV) conditions. We have examined the kinetics of the £]-elimination reaction in CF3CF2CH2-Cu, CHF2CF2CH2-Cu, and CF3CH2CH2-Cu. These species all decompose via £]-elimination to give CF3CF=CH2, CHF2CF=CH2, and CF3CH=CH2. The first two species undergo £]-fluoride elimination and the third one undergoes £]-hydride elimination. The difference in activation energies between the first two accounts for the charge separation (R-C£]+£_¡KF−£_¡KM+£_) in the transition state proposed by Gellman. The activation energies for £]-hydride elimination (CF3CH2CH2-Cu) and £]-fluoride elimination (CF3CF2CH2-Cu) was also compared. The activation energy for £]-fluoride elimination is found to be lower than that of £]-hydride elimination. In the studies of reaction pathways for perfluoropropyl groups (n-C3F7-Cu and i-C3F7-Cu) on Cu(111), we discovered novel chemistry in TPD. n-C3F7-Cu undergoes Cu-C homolytic cleavage (radical desorption) at 340 K, whereas i-C3F7-Cu eliminates the £]-fluorine at 365 K. By changing the Cu-C bond length in the i-C3F7-5Cu models their IR spectra was calculated. We discover that the IR of i-C3F7-5Cu with shorter Cu-C bond (1.728Å) is more similar to the experimental IR spectra. That demonstrates the bond strength of Cu-C bond of i-C3F7-Cu is too strong to undergo Cu-C homolytic cleavage at 340 K. Hence, £]-F decomposition becomes the favorite pathway to i-C3F7-Cu because there are more £]-F atoms available in this moiety.

none

The main purpose of this research is to utilize the FEMLAB multiphysics software as to analyze the thermal stress of Cu/Diamond/Cu three-layered heat spreader device. The alteration of film thickness under different temperatures(allowing the device to increase from room temperature of 27¢XC to 100¢XC, 200¢XC and 300¢XC), with upper Cu layer of 2µm, altered middle diamond layer(20µm, 50µm 100µm), and lower Cu layer(100µm, 200µm, 300µm)(assuming that there is no residual stress produced after the manufacture of heat spreader device), is regarded as the conditional parameter of heat spreader device in analyzing the deformation rate and stress variation produced. After simulation of the research, it was found out that a maximum shear stress is attained under a fixed temperature load. And, when the film thickness is altered and under a fixed thick of Cu layer, the shear stress will become bigger due to the thickness of the diamond layer increases, when the diamond layer is 50-70µm, stress increases slowly; but it is considered to be the greatest effect when the heat transfer of diamond is at 100µm; thus selection of 70µm would be a better option in this paper suggestion, and that the alteration of the thickness of lower Cu layer will not cause great effect to max shear stress.) After stabilizing the thickness of upper Cu layer and middle diamond layer, the maximum deformation rate will become smaller when the thickness of lower Cu layer increases.

No description available.