LIFETIME AND ACTIVATION ENERGY OF THE PHOTOINDUCED QUINOID INTERMEDIATE IN PYRIDOXAL CATALYSIS

Abstract— The lifetime of the p -quinoid intermediate of transamination was determined through photoinduction in the metal-ion model system. From the dependence of the lifetime on temperature, the Arrhenius activation energy for proton transfer was 4.2–8.4 kJ/mol (1-2 kcal/mol). The activation energy correlated well with the R group of the amino acid and demonstrated that native substrates have a very labile proton.     

The effect of the physical and chemical characteristics of activated carbons on the adsorption energy and affinity coefficient of Dubinin equation

The dependency of adsorption energy (E) and affinity coefficient (beta) of Dubinin equations (Dubinin-Radushkevich (DR) or Dubinin-Astakhov (DA)) on surface chemistry and porosity of activated carbons was investigated by analyzing adsorption of nitrogen, benzene, trichloroethylene (TCE), and water vapor by several surface-modified activated carbons and carbon fibers. For all studied nonpolar adsorbates, carbons with smaller average micropores showed higher adsorption energies independent of their surface chemistry. For water vapor, carbons with higher surface polarities showed higher adsorption energies due to specific adsorbate-adsorbent interactions. Adsorption energies increased with decreasing average micropore widths. betaN2,DR for different carbons were observed to vary in the 0.292-0.539 range. Carbons with higher degrees of mesoporosity had higher betaN2,DR values, while no dependency was observed between betaN2,DR and surface chemistry. A comparison of DR and DA cases indicates that: (1) the average value of betaN2,DA is considerably above the classical value of this parameter; and (2) the range of betaN2,DA values were smaller compared to betaN2,DR, despite a wide range of mesoporosity of carbons examined. Obtained beta(TCE,DR) values varied in the 0.952-1.243 range, with an average value of 1.085+/-0.083, independent of surface chemistry or porosity of activated carbons. A similar result was observed for beta(TCE,DA). betaH2O,DR values of different granular and fibrous activated carbons changed in the range of 0.081-0.271. They depended more on the carbon surface chemistry and less on the porosity. A similar result was obtained when DA equation was considered.     

Separation and identification of organic and organometallic compounds by use of a liquid chromatography-particle beam-glow discharge mass spectrometry combination

Evaluation of the particle beam glow discharge mass spectrometry (PB-GDMS) system as a detector for liquid chromatography (LC) is described for the analysis of polycyclic aromatic hydrocarbons, steroids, selenoamino acids, and alkyllead compounds. A particle beam interface is used to introduce analyte species from the LC into a glow discharge source for subsequent vaporization and ionization. Mass spectra display classic EI fragmentation patterns for the organic compounds, as well as elemental and molecular information for the organometallic compounds. Chromatographic separations display good temporal correlation between UV and PB-GDMS detection modes. Detection limits for Pb in lead nitrate, triethyllead, and triphenyllead fall in the sub-ppb (ng) range.     

Novel approach to bismuth modifying procedure for voltammetric thick film carbon containing electrodes

The novel bismuth modifying technique for disposable thick film carbon containing sensors (TFCC) by means of a surface synthesis of the modifier (bismuth phosphate) have been developed. The optimal composition and the method of cathodic reduction (“activation”) of the modifying BiPO₄ layer has been proposed. These conditions provided the structure of a modifying layer with the bismuth nano particles of size less than 0.1 μm. On the important analytical parameters (sensitivity, accuracy, tolerance to surfactant fouling effect, particularly for Zn), sensor developed (TFCC/BiPO₄) surpasses TFCC with electrolytic bismuth films. The detection limit of 8 nM for zinc, 4 nM for cadmium and 2 nM for lead was achieved after a 2 min accumulation. Therefore, the developed non-toxic and low cost disposable sensor excludes the necessity of mechanical pretreatment of a working surface and can be used in field, laboratory and automatic systems for environmental monitoring (at the trace level inclusive).     

HEU measurements of holdup and recovered residue in the deactivation and decommission activities of the 321-M Reactor Fuel Fabrication Facility at the Savannah River Site

Summary This paper contains a summary of the holdup and material control and accountability (MC&A) assays conducted for the determination of highly enriched uranium (HEU) in the deactivation and decommissioning (D&D) of the Reactor Fuel Fabrication Facility at the Savannah River Site (SRS). The facility was used to fabricate HEU fuel assemblies, lithium-aluminum target tubes, neptunium assemblies, and miscellaneous components for the SRS production reactors. The facility operated for more than 35 years. During this time thousands of uranium-aluminum alloy (U-Al) production reactor fuel tubes were produced. After the facility ceased operations in 1995, all of the easily accessible U-Al was removed from the building, and only residual amounts remained. The bulk of this residue was located in the equipment that generated and handled small U-Al particles and in the exhaust systems for this equipment (e.g., chip compactor, casting furnaces, log saw, lathes A & B, cyclone separator, Freon?cart, riser crusher, …, etc). The D&D project is likely to represent an important example for D&D activities across SRS and across the Department of Energy weapons complex. The Savannah River National Laboratory was tasked to conduct holdup assays to quantify the amount of HEU on all components removed from the facility prior to placing in solid waste containers. The ²³⁵U holdup in any single component of process equipment must not exceed 50 g in order to meet the container limit. This limit was imposed to meet criticality requirements of the low level solid waste storage vaults. Thus, the holdup measurements were used as guidance to determine if further decontamination of equipment was needed to ensure that the quantity of ²³⁵U did not exceed the 50 g limit and to ensure that the waste met the Waste Acceptance Criteria (WAC) of the solid waste storage vaults. Since HEU is an accountable nuclear material, the holdupassays and assays of recovered residue were also important for material control and accountability purposes. In summary, the results of the holdup assays were essential for determining compliance with the Waste Acceptance Criteria, Material Control & Accountability, and to ensure that administrative criticality safety controls were not exceeded. This paper discusses theg-ray assay measurements conducted and the modeling of the acquired data to obtain measured holdup in process equipment, exhaust components, and fixed geometry scrap cans. It also presents development work required to model new acquisition configurations and to adapt available instrumentation to perform the assays.     

Automated multi-attribute method sample preparation using high-throughput buffer exchange tips

Rationale

The multi-attribute method (MAM) has become a valuable mass spectrometry (MS)-based tool that can identify and quantify the site-specific product attributes and purity information for biotherapeutics such as monoclonal antibodies (mAbs) and fusion molecules in recent years. As we expand the use of the MAM at various stages of drug development, it is critical to enhance the sample preparation throughput without additional chemical modifications and variability.

Methods

In this study, a fully automated MAM sample preparation protocol is presented, where rapid desalting in less than 15 minutes is achieved using miniaturized size-exclusion chromatography columns in pipette tips on an automated liquid handler. The peptide samples were analyzed using an electrospray ionization (ESI) orbitrap mass spectrometer coupled to an ultra-high-performance liquid chromatography (UHPLC) system with a dual column switching system.

Results

No significant change was observed in product attributes and their quantities compared with manual, low-artifact sample preparation. The sample recovery using the buffer exchange tips was greatly enhanced over the manual spin cartridges while still demonstrating excellent reproducibility for a wide variety of starting sample concentrations. Unlike a plate desalting system, the individual columns provide flexibility in the number of samples prepared at a time and sample locations within plates.

Conclusions

This automated protocol enables the preparation of up to 96 samples with less “at-bench” time than the manual preparation of a smaller batch of samples, thereby greatly facilitating support of process development and the use of the MAM in quality control.

     

Electroreductive polymerization of trans-[RuCl 2(vpy) 4] on Nd-Fe-B magnets: electrochemical impedance spectroscopy interpretation, Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy analysis

The electropolymerization of trans-[RuCl₂(vpy)₄] (vpy=4-vinylpyridine) monomer on Nd-Fe-B magnets was studied by electrochemical impedance spectroscopy (EIS). Impedance diagrams obtained during the polymerization process were used to monitor film formation. The EIS results gave insight into the electrochemical phenomena occurring at the magnet surface as the polymerization process progressed. The film structure and morphology were also studied by X-ray photoelectron spectroscopy, scanning electron microscopy and Raman spectroscopy. The Raman spectroscopy results showed that the polymerization takes place at the vinyl groups of the monomer and also that the redox polymer structure is very similar to that of the monomer. The ratio of the intensity of the XPS peaks for fluorine (from the electrolyte PF₆ ^–) and ruthenium present in the film showed that the polymer on Nd-Fe-B contained an equal proportion of Ru²⁺ and Ru³⁺, indicating that part of the film is positively charged, i.e. {[RuCl₂(vpy)₄]⁺} _n .     

Density Functional Theory and Low-Temperature Matrix Investigations of CO-Loss Photochemistry from [(C<Subscript>5</Subscript>R<Subscript>5</Subscript>)Ru(CO)<Subscript>2</Subscript>]<Subscript>2</Subscript> (R = H,Me) Complexes

The photochemical CO-loss products of the diruthenium complexes [CpRu(CO) ₂]₂ (5; Cp = ⁵-C₅H₅), [Cp*Ru(CO)₂]₂ (5*; Cp* = ⁵-C₅(CH₃)₅) and CpCp*[Ru(CO)₂]₂ (5) have been studied experimentally in low-temperature (96 K) matrices in 3-methylpentane by using IR spectroscopy. It is proposed that all three complexes undergo single-CO-loss chemistry but that the products have different structures. The single-CO-loss product from 5 is proposed to have one bridging and two terminal carbonyl ligands, whereas 5* and 5 generate triply bridged CO-loss products similar to that observed from [CpFe(CO)₂]₂ and [Cp*Fe(CO)₂]₂. Double-CO-loss from 5* and 5* 9 is also apparently observed. Relativistic DFT calculations have been carried out on various isomers of the starting materials and on potential CO-loss products from 5. The calculations suggest that the triply bridged product Cp₂Ru₂(-CO)₃ (6) might have a singlet ground state in contrast to the corresponding diiron complex Cp₂Fe₂(-CO)₃ (3), which has a triplet ground state.     

Excess enthalpy and entropy of aqueous tetramethylguanidinium methanesulfonate and trifluoromethanesulfonate solutions

Relative apparent molal heat contents, φ_L, are reported for the tetramethylguanidinium salts of methanesulfonic (MS) and trifluoromethanesulfonic (TFMS) acids. Relative partial molal heat contents, L?₂, are calculated and combined with previously reported activity coefficient data, to yield excess entropies. It is found that the values of L?₂ make the principal contribution to the excess entropies of Me₄GuMS solutions while the excess free energies, as calculated from activity coefficients, make the greatest contribution to the excess entropies of Me₄GuTFMS solutions.     

Preparation and structural characterization of a hexanuclear molybdenum (II) cluster containing carboxylate ligands (Bu4N)2[Mo6(μ3-Cl)8(O2CMe)6]

The hexamolybdenum cluster complex [Mo₆(₃-Cl)₈(O₂CMe)₆]^2–, 1 was isolated as the Bu₄N⁺ salt in 71% yield from the reaction of (Bu₄N)₂[Mo₆(₃-Cl)₈Cl₆] with AgO₂CMe in CH₂Cl₂ solvent. The compound was characterized by single crystal X-ray diffraction analysis. The cluster contains an octahedral arrangement of six molybdenum atoms with eight chloride ligands bridging the eight trianglar faces and six carboxylate ligands terminally coordinated through one oxygen atom to each of the six molybdenum atoms. Crystal data: space group =P2₁/n,a=10.713(3)Å,b=14.43(1)Å,c=21.919(4)Å, =94.37(2)°,Z=2, 1965 reflections,R=0.036.