Measurement of radioactive samples in Marinelli beakers by gamma-ray spectrometry

Radioactivity measurement of environmental samples is frequently assayed by gamma-ray spectrometry using Marinelli beakers. In this work, self-absorption and coincidence summing effects arising in activity measurements for Marinelli beaker geometry have been studied with a Ge detector. Three types of Marinelli beakers which have capacities of 450 mL, 1 L, and 2 L were developed. Self-attenuation effects for density variation of radioactive samples in each type of the Marinelli beakers were measured as a function of gamma-ray energy, and also the results were compared with calculated values by mathematical model. Meanwhile, the coincidence summing effects of¹²⁵Sb and¹⁵⁴Eu nuclides were obtained from the determination of the full-energy peak and total efficiencies for a Ge detector.     

Fragmentation mechanisms of oligodeoxynucleotides: Effects of replacing phosphates with methylphosphonates and thymines with other bases in T-rich sequences

This article reports another step in an ongoing effort to understand the fragmentation of T-rich oligodeoxynucleotides. We extended an earlier investigation of T-rich 4-mers to T-rich 6-mers, 8-mers and 10-mers by using four different tandem mass spectrometric methods. The methods include low-energy collisionally activated decomposition (CAD) of electrospray ionization (ESI)-produced ions, source-CAD of ESI-produced ions, post-source decay (PSD), and CAD of matrix assisted laser desorption ionization (MALDI)-generated ions. The most abundant fragment ions produced from [M - 2H]2- precursors upon low-energy CAD in an ion trap are the [a - B]- and their complementary w ions. The predominant cleavage sites for T-rich oligodeoxynucleotides are always the 3' C-O bonds adjoining a non-T nucleobase (i.e., a base with a higher proton affinity (PA) than that of T). The relative abundance of [a - B]- correlates with the PAs of the nucleobases, underscoring the importance of proton transfer to the base. The propensity to form [a - B]- ions falls in the order of G > C approximately A > T. Structural isomers up to 10-mers can be readily sequenced and distinguished with each of the four tandem mass spectrometric methods applied. The fragmentation of oligodeoxynucleotides in which various phosphates were replaced with methylphosphonate is a measure of the participation of the phosphate proton in the formation of [a - B] ions. For 4 and 5-mers, transfer of an acidic proton from the 5'-phosphate to the departing base is the initiating step in the formation of [a - B]- ions.     

Catalytic Asymmetric Propionate Aldol Reactions via Acyl Halide-Aldehyde Cyclocondensations

Catalyzed asymmetric acyl halide-aldehyde cyclocondensation (AAC) reactions afford highly enantiomerically enriched 3,4-disubstituted-2-oxetanones. These reactions constitute catalytic asymmetric propionate aldol additions. An optically active Al(III)-triamine complex (10 mol %) catalyzes the di(isopropyl)ethylamine-mediated cyclocondensation of propionyl bromide and a variety of aldehydes to afford beta-lactone adducts with uniformly high enantioselection (90 --> 98% ee), diastereoselection (74 --> 98% de), and chemical yields (78-90%). Lactone ring opening reveals that the enantiomerically enriched beta-lactones act as surrogates for syn propionate aldol adducts.     

Quantitative interrogation of protein co-aggregation using multi-color fluorogenic protein aggregation sensors

Co-aggregation of multiple pathogenic proteins is common in neurodegenerative diseases but deconvolution of such biochemical process is challenging. Herein, we developed a dual-color fluorogenic thermal shift assay to simultaneously report on the aggregation of two different proteins and quantitatively study their thermodynamic stability during co-aggregation. Expansion of spectral coverage was first achieved by developing multi-color fluorogenic protein aggregation sensors. Orthogonal detection was enabled by conjugating sensors of minimal fluorescence crosstalk to two different proteins via sortase-tag technology. Using this assay, we quantified shifts in melting temperatures in a heterozygous model protein system, revealing that the thermodynamic stability of wild-type proteins was significantly compromised by the mutant ones but not vice versa. We also examined how small molecule ligands selectively and differentially interfere with such interplay. Finally, we demonstrated these sensors are suited to visualize how different proteins exert influence on each other upon their co-aggregation in live cells.

A little leak will sink a great ship! We prepared a series of multi-color protein aggregation sensors and developed a dual-color thermal shift assay to simultaneously and quantitatively report on protein co-aggregation of two different proteins.     

Catalytic asymmetric addition of alkylzinc and functionalized alkylzinc reagents to ketones

We describe our full report of the catalytic asymmetric addition of simple and functionalized dialkylzinc reagents to a broad range of saturated ketones and enones. The functionalized organozinc reagents contain esters, silyl ethers, alkyl chlorides, and alkyl bromides. In general, the resulting tertiary alcohol products are isolated with high ee's. With some substrates, yields are low as a result of the formation of aldol byproducts. Most substrates undergo additions with good yields reaching as high as 91%.     

镍基气凝胶催化CH4-CO2重整制取合成气反应的研究 Ⅲ.影响催化剂积碳性能因素的探讨

考察了823K焙烧的干凝胶xNCA550、气凝胶aNCA550及浸渍型催化剂iNCA550在923K、1073K、1173K反应温度下的积碳行为，对催化剂表面碳的活性及类型进行了分析，并探讨了影响催化剂积碳的因素。实验结果表明，随反应温度的提高，催化剂的积碳能力减弱，尤以气凝胶催化剂aNCA550明显。催化剂的积碳主要发生在反应的初期，反应温度越高，到达积碳量相对稳定期所需要的时间越短；随着反应时间的延续，催化剂积碳量缓慢增长，并且表面碳的活性降低。催化剂的酸性和镍晶粒大小是影响其积碳性能的主要内在因素，而它们对积碳的影响程度受反应温度的影响，反应温度越高，催化剂表达酸性中心利于积碳的作用越小，小晶粒镍抑制催化剂积碳的能力越强。     

Photochemical deuterium exchange of the m-methyl group of 3-methylbenzophenone and 3-methylacetophenone in acidic D2O

Photolysis of the title compounds in acidic aqueous solution results in "activation" of the distal m-methyl group, resulting in deuterium exchange (Phi approximately 0.1) when D(2)O is used. The reaction is not observed in neutral aqueous solution or in deuterated organic solvents such as CD(3)CN. The reaction is best rationalized by a mechanism involving initial protonation at the carbonyl oxygen of the triplet excited state. [reaction: see text]     

Fourier transform infrared spectroscopy study of the effect of pH on anion and cation adsorption onto poly(acrylo‐amidino diethylenediamine)

The role of hydrogen bonding in the chemistry of transition‐metal complexes remains a topic of intense scientific and technological interest. Poly(acrylo‐amidino diethylenediamine) was synthesized to study the effects of hydrogen bonding on complexes at different pHs. The polymer was synthesized through the coupling of diethylene triamine with polyacrylonitrile fiber in the presence of AlCl₃ · 6H₂O addition. The adsorption capacity of this polymer was 11.4 mequiv/g. The ions used for the adsorption test were CrO, PO, Cu²⁺, Ni²⁺, Fe²⁺, and Ag⁺. All experiments were confirmed with Fourier transform infrared. In the study of anion adsorption, at low pHs, only ionic bonds existed, whereas at high pHs, no bonds existed. However, in the middle pH region, both ionic bonds and hydrogen bonds formed between poly(acrylo‐amidino diethylenediamine) and the chromate ion or phosphate ion. When poly(acrylo‐amidino diethylenediamine) and metal ions (Cu²⁺, Ni²⁺, Fe²⁺, and Ag⁺) formed complexes, a hydrogen‐bonding effect was not observed with Fourier transform infrared. The quantity of metal ions adsorbed onto poly(acrylo‐amidino diethylenediamine) followed the order Ag⁺ > Cu²⁺ > Fe²⁺ > Ni²⁺. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2010–2018, 2004     

Cob(I)alamin-Catalyzed Skeletal Migrations Observed during the Reduction of 4β-(tert-Butyl)-1α-(1-methylvinyl)cyclohexanecarbaldehyde

The cob(I) alamin (1(I)) -catalyzed² transformation of the aldehyde 2 has been studied (cf. Table 1). Kinetic examinations showed a rapid isomerization of 2 to 3 (cf. Fig. 1 and 2). From the transformations in glacial AcOH, the two cyclopropanols 5 and 7 were isolated as main products (cf. Tables 1–3 and Fig. 1 and 2). Using large amounts of 1(I) , the aldehyde 4 was very slowly transformed. Accepting the intermediate formation of 6 interconnected Co-complexes, i. e. A , B , C , D , E and F (cf. Scheme), the generation of all the products observed can be explained.