Room-Temperature Formation Pathway for CdTeSe Alloy Magic-Size Clusters

Little is known about the pathway of room-temperature formation of ternary CdTeSe magic-size clusters (MSCs) obtained by mixing binary CdTe and CdSe induction period samples containing binary precursor compounds (PCs) of MSCs, monomers (Ms), and fragments (Fs). Also, unestablished are dispersion effects that occur when as-mixed samples (without incubation) are placed in toluene (Tol) and octylamine (OTA) mixtures. The resulting ternary MSCs, exhibiting a sharp optical absorption peak at 399 nm, are labelled CdTeSe MSC-399, and their PCs are referred to as CdTeSe PC-399. When the amount of OTA is relatively small, single-ensemble MSC-399 evolved without either binary CdTe or CdSe MSCs. When the OTA amount is relatively large, CdTe MSC-371 appeared initially and then disappeared, while single-ensemble MSC-399 developed more deliberately. The larger the OTA amount, the more slowly these changes proceeded. The substitution reaction of CdTe PC + CdSe M/F↔CdTeSe PC-399 + CdTe M/F is proposed to be rate-determining for the MSC-399 formation in a Tol and OTA mixture. This study provides further understanding of the transformation pathway between MSCs.     

Development and validation of a LC-MS/MS assay for quantitation of plasma citrulline for application to animal models of the acute radiation syndrome across multiple species

The potential risk of a radiological catastrophe highlights the need for identifying and validating potential biomarkers that accurately predict radiation-induced organ damage. A key target organ that is acutely sensitive to the effects of irradiation is the gastrointestinal (GI) tract, referred to as the GI acute radiation syndrome (GI-ARS). Recently, citrulline has been identified as a potential circulating biomarker for radiation-induced GI damage. Prior to biologically validating citrulline as a biomarker for radiation-induced GI injury, there is the important task of developing and validating a quantitation assay for citrulline detection within the radiation animal models used for biomarker validation. Herein, we describe the analytical development and validation of citrulline detection using a liquid chromatography tandem mass spectrometry assay that incorporates stable-label isotope internal standards. Analytical validation for specificity, linearity, lower limit of quantitation, accuracy, intra- and interday precision, extraction recovery, matrix effects, and stability was performed under sample collection and storage conditions according to the Guidance for Industry, Bioanalytical Methods Validation issued by the US Food and Drug Administration. In addition, the method was biologically validated using plasma from well-characterized mouse, minipig, and nonhuman primate GI-ARS models. The results demonstrated that circulating citrulline can be confidently quantified from plasma. Additionally, circulating citrulline displayed a time-dependent response for radiological doses covering GI-ARS across multiple species.     

Effects of the standardization of quantitative fluorometry on the automated evaluation of platelet antibodies

An automated fluorescence invertoscope featuring a computer-controlled scanning stage with plate inserts for multiple samples, a photomultiplier tube and software controlling every function of the microscope were used to collect the fluorescence data after analog-to-digital conversion. Principal differences between this method and qualitative platelet tests include the standardization of all test reagents and the quantitative evaluation of possible autofluorescence. The automated data acquisition permitted the separate evaluation of the fluorescence intensities of all materials to ensure low background fluorescence and optimal fluorochrome concentrations. EDTA-anticoagulated platelets of 100 donors were incubated with serum, subsequently with fluorescein- or rhodamine-treated IgG, washed, counted in PBS-glycerol, and mounted on thin glass plates. Each plate contained 5000 cells per test and negative and positive controls.     

Synthesis of 3-azido-2,3,6-trideoxy-beta-D-arabino-hexopyranosyl pyranonaphthoquinone analogues of medermycin

The synthesis of an isomeric mixture of 4-O-acetyl-3-azido-2,3,6-trideoxy-beta-D-arabino-hexopyranosyl analogues 6 of the C-glycosylpyranonaphthoquinone antibiotic medermycin is described. The key 3-acetyl-6-(4-O-acetyl-3-azido-2,3,6-trideoxy-beta-D-arabino- hexopyranosyl)-5-methoxy-1,4-naphthoquinone 8 was prepared via Stille coupling of 6-(3-azido-2,3,6-trideoxy-beta-D-arabino-hexopyranosyl)-3-bromo-1,4- naphthoquinone 17 with (alpha-ethoxyvinyl)tributyl-stannane followed by hydrolysis and oxidation of the resultant hydroquinone 18. Bromonaphthoquinone 17 in turn was afforded by oxidative demethylation of 6-(4-O-acetyl-3-azido-2,3,6-trideoxy-beta-D-arabino-hexopyranosyl)-3- bromo-1,4,5-trimethoxynaphthalene 16 formed by regioselective bromination of 6-(4-acetyl-3-azido-2,3,6-trideoxy- beta-D-arabino-hexopyranosyl)-1,4,5-trimethoxynaphthalene 10. This latter naphthalene 10 was prepared via direct C-glycosylation of naphthol 12 with glycosyl donor 11 using BF3.Et2O in acetonitrile. The regioselectivity of the bromination of naphthalene 10 was independently determined by reductive monomethylation of the 6-(4-O-acetyl-3-azido-2,3,6-trideoxy-beta-D-arabino- hexopyranosyl)-5-methoxy-1,4-naphthoquinone 22 to naphthol 23 followed by selective ortho bromination to bromide 24 and methylation to 16. Attempts to effect acetylation of 6-(4-O-acetyl-3-azido-2,3,6-trideoxy-beta-D-arabino- hexopyranosyl)-3-bromo-1,4,5-trimethoxynaphthalene 16 and 3-bromo-6-(3-dimethylamino-2,3,6-trideoxy-beta-D-arabino- hexopyranosyl)-1,4,5-trimethoxynaphthalene 26 via Stille coupling with (alpha-ethoxyvinyl)tributylstannane were low yielding thereby establishing the necessity to use an azido group as a latent dimethylamino group and a more electrophilic bromonaphthoquinone as the coupling partner for the Stille reaction. Addition of 2-trimethylsilyloxyfuran 9 to 3-acetyl-6-(4-O-acetyl-3-azido-2,3,6-trideoxy-beta-D-arabino-hexopyranosyl)- 5-methoxy-1,4-naphthoquinone 8 afforded the furofuran adducts 7 and 19 as an inseparable mixture of diastereomers. Oxidative rearrangement of this diastereomeric mixture using ceric ammonium nitrate afforded the inseparable diastereomeric furonaphthopyrans 6 and 20.     

XAFS spectral analysis of the cadmium coordination geometry in cadmium thiolate clusters in metallothionein

We report the combination of measurement and prediction of X-ray absorption fine structure (XAFS) data, where the term XAFS refers to the overall spectrum that encompasses both the X-ray Absorption Near Edge Structure (XANES) region as well as the Extended X-ray Absorption Fine Structure (EXAFS) region, to evaluate the cadmium thiolate cluster structures in the metalloprotein metallothionein. XAFS spectra were simulated using coordinates from molecular models of the protein calculated by molecular mechanics/molecular dynamics (MM3/MD), from NMR analyses, and from analysis of X-ray diffraction data. XAFS spectra were also simulated using the coordinates from X-ray crystallographic data for [Cd(SPh)4]2-, CdS, [Cd2(mu-SPh)2(SPh)4]2-, and [Cd4(mu-SPh)6(SPh)4]2-. The simulated XAFS data that were calculated using the FEFF8 program closely resemble the experimental data reported for [Cd(SPh)4]2-, CdS, [Cd2(mu-SPh)2(SPh)4]2-, [Cd4(mu-SPh)6(SPh)4]2-, rabbit liver metallothionein cadmium alpha-domain (Cd4-alpha MT), and cadmium rabbit liver betaalpha metallothionein (Cd7-betaalpha MT). MM3 force field parameters were modified to include cadmium-sulfur bonding and were initially set to values derived from published X-ray diffraction and EXAFS experimental data. The force field was further calibrated and adjusted through comparison between experimental spectra taken from the literature and simulated XAFS spectra calculated using the FEFF8 program in combination with atomic coordinates from MM3/MD energy minimization. MM3/MD techniques were used with the calibrated force field to predict the high-resolution structure of the metal clusters in rabbit liver Cd7-MT. Structures for Cd3S9 (beta) MT and Cd4S11 (alpha) MT domains from MM3/MD calculations and those previously reported for Cd7-MT on the basis of 1H and 113Cd NMR data were compared. Structural differences between the different models for these cadmium thiolate clusters were evident. Combining the measurement and simulation of XAFS data provides an excellent method of assessing, modeling, and predicting metal-binding sites in metalloproteins when X-ray absorption spectroscopy (XAS) data are available.     

Poly(alkyl α-chloroacrylates). V. Preparation and properties of methyl,ethyl, and isopropyl polymers of varied tacticity

Polymers of different tacticities, from highly isotactic to highly syndiotactic, were prepared from methyl, ethyl, and isopropyl α-chloroacrylates. These polymers were characterized for tacticity by infrared spectroscopy and 100 and 300 MHz nuclear magnetic resonance (NMR) and for thermal properties by differential scanning calorimetry (DSC). After corrections were made for molecular weight effects, the observed glass temperature-tacticity results were analyzed, and it was determined that the maximum differences in glass temperatures of the purely isotactic compared to the purely syndiotactic polymers should be 92°C for the methyl ester, 86°C for the ethyl ester, and 68°C for the isopropyl ester polymers. The highly isotactic polymers of all three esters were crystalline. Possible polymerization reaction mechanisms are discussed on the basis of the triad and tetrad tacticity values observed and the calculated propagation statistics.     

Enriched copper isotope tracer for dietary copper incorporation into hair using neutron activation analysis in conjunction with direct-current argon plasma spectrometry

A method is described for labeling and measuring the incorporation of dietary copper into hair using the enriched (99.61 atomic-%) ⁶⁵Cu isotope. Natural isotope abundant copper exists as ⁶⁵Cu (30.86 atomic-%) and ⁶³Cu (69.17 atomic-%), but enriched (99.61 atomic-%) ⁶⁵Cu isotope may be obtained commercially and administered to change deliberately the natural isotope abundance of copper to “label” the copper source. Natural isotope abundant copper and the enriched (99.61 atomic-%) ⁶⁵Cu isotope were mixed into rat feed and administered daily by gavage. The isotope concentration was determined by neutron activation analysis (NAA). The copper concentration was determined by direct-current argon plasma (DCP) spectrometry.The measured copper isotope ratios (⁶⁵Cu/Cu_tot)_for the natural isotope abundant copper in National Bureau of Standards Standard Reference Materials (NBS SRM) 1571 Orchard Leaves and 1577a Bovine Liver were 0.3201 ± 0.0039 and 0.3187 ± 0.0089, respectively. Measured copper isotope ratios in rat hair were 0.3100 ± 0.0606, 0.4580 ± 0.2495 and 0.2712 ± 0.0645 from rats given a standard feed that contained natural isotope abundant copper, a daily supplement of natural isotope abundant copper sulfate mixed into the standard feed and a daily supplement of copper sulfate administered by gavage, respectively. The copper isotope ratio increased to 0.5251 ± 0.2860 and 0.7235 ± 0.0704 in hair from rats given enriched ⁶⁵Cu in their feed and by gavage, respectively. The statistically significant increase in the ⁶⁵Cu isotope when administered by gavage demonstrates strates successful labeling of dietary copper in the hair.