High‐throughput experimentation in atom transfer radical polymerization: A general approach toward a directed design and understanding of optimal catalytic systems

High‐throughput experimentation (HTE) was successfully applied in atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) for the rapid screening and optimization of different reaction conditions. A library of 108 different reactions was designed for this purpose, which used four different initiators [ethyl 2‐bromoisobutyrate, methyl 2‐bromopropionate, (1‐bromoethyl)benzene, and p‐toluenesulfonyl chloride], five metal salts (CuBr, CuCl, CuSCN, FeBr₂, and FeCl₂), and nine ligands (2,2′‐bipyridine and its derivatives). The optimal reaction conditions for Cu(I) halide, CuSCN, and Fe(II) halide‐mediated ATRP systems with 2,2′‐bipyridine and its 4,4′‐dialkyl‐substituted derivatives as ligands were determined. Cu(I)‐mediated systems were better controlled than Fe(II)‐mediated ones under the examined conditions. A bipyridine‐type ligand with a critical length of the substituted alkyl group (i.e., 4,4′‐dihexyl 2,2′‐bipyridine) exhibited the best performance in Cu(I)‐mediated systems, and p‐toluenesulfonyl chloride and ethyl 2‐bromoisobutyrate could effectively initiate Cu(I)‐mediated ATRP of MMA, resulting in polymers with low polydispersities in most cases. Besides, Cu(I) halide‐mediated ATRP with 4,5′‐dimethyl 2,2′‐bipyridine as the ligand and p‐toluenesulfonyl chloride as the initiator proved to be better controlled than those with 4,4′‐dimethyl 2,2′‐bipyridine as the ligand, and polymers with much lower polydispersities were obtained in the former cases. This successful HTE example opens up a way to significantly accelerate the development of new catalytic systems for ATRP and to improve the understanding of structure–property relationships of the reaction systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1876–1885, 2004     

Interaction of a chirally functionalised porphyrin derivative with chiral micellar aggregates

The functionalisation of a porphyrin derivative with a chiral functionality results in a selective interaction with chiral micellar aggregates.     

Liquid chromatography-mass spectrometry of spiroketal stereoisomers of pectenotoxins and the analysis of novel pectenotoxin isomers in the toxic dinoflagellate Dinophysis acuta from New Zealand

The acid-catalyzed inter-conversion of spiroketal isomers of pectenotoxins PTX1, PTX6 and PTX2 were studied by liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-MS-MS). Using a C8-silica reversed-phase column and a mobile phase of aqueous acetonitrile containing 2 mM ammonium formate and 50 mM formic acid, the known spiroketal stereoisomers of PTX1 eluted in order of PTX1, PTX4 and PTX8, while those of PTX6 eluted in the order PTX6, PTX7 and PTX9. Acid treatment of PTX2 yielded two novel spiroketal stereoisomers, which have been named PTX2b and PTX2c. LC-MS-MS spectra obtained for the [M+NH4]- ions of PTX2, PTX2b and PTX2c were essentially identical. As an application of the LC-MS-MS methodology, a sample of the toxic dinoflagellate Dinophysis acuta collected from the coast of New Zealand was analyzed for pectenotoxins. PTX2 and a new pectenotoxin, which has been named PTX11, were detected as the most predominant compounds. Novel PTX2 and PTX11 isomers were also found in the D. acuta although the levels of these compounds were low.     

Perturbation results of critical elliptic equations of Caffarelli-Kohn-Nirenberg type

We find for small ε positive solutions to the equation

     

REMOVAL OF THYMINE-CONTAINING PYRIMIDINE DIMERS FROM UV LIGHT-IRRADIATED DNA BY S1 ENDONUCLEASE

Abstract— S₁ endonuclease was shown to remove thymine-containing pyrimidine dimers from UV-irradiated human DNA, although efficient removal could be demonstated only by using long digestion times, relatively high enzyme concentrations, and irradiation sufficient to yield dimer substitutions in DNA of 1 per 1W300 (dimers/base pair). Neutral and alkaline sucrose gradient analysis of strand break induction by S, of UV-irradiated DNA suggests that recognition of the dimer by S, is the limiting factor in its removal and dimer removal usually results from attack on the dimer containing DNA strand without the induction of a double-strand break.     

Experiments on the Total Synthesis of Lysolipin I. Part I. On Configuration and Conformation of 5-Substituted 1,2,3,4,4a,9,10,10a-Ocathydrophenanthrene-4,9-diones

The substituted 1,2,3,4,4a,9,10,10a-octahydrophenanthrene-4,9-dione 2 , synthesized from the cyclohexanone 8 and quinone 11 (Scheme 2), was found by X-ray analysis adn ¹H-NMR studies to be the isomer with cis-junction of the saturated rings. The cis-fusion could also be determined from the ¹H-NMR data of the related compound 17 (Scheme 4), which was previously considered to be trans-fused. In contrary to previous argumentations, the interaction of the C(4)-carbonyl O-atom of trans-fused octahydrophenanthenes is more severe with a 5-methoxy than with a 5-methyl substituent.     

Unexpected Acetylation of Endogenous Aliphatic Amines by Arylamine N‐Acetyltransferase NAT2

N‐Acetyltransferases play critical roles in the deactivation and clearance of xenobiotics, including clinical drugs. NAT2 has been classified as an arylamine N‐acetyltransferase that mainly converts aromatic amines, hydroxylamines, and hydrazines. Herein, we demonstrate that the human arylamine N‐acetyltransferase NAT2 also acetylates aliphatic endogenous amines. Metabolomic analysis and chemical synthesis revealed increased intracellular concentrations of mono‐ and diacetylated spermidine in human cell lines expressing the rapid compared to the slow acetylator NAT2 phenotype. The regioselective N⁸‐acetylation of monoacetylated spermidine by NAT2 answers the long‐standing question of the source of diacetylspermidine. We also identified selective acetylation of structurally diverse alkylamine‐containing drugs by NAT2, which may contribute to variations in patient responses. The results demonstrate a previously unknown functionality and potential regulatory role for NAT2, and we suggest that this enzyme should be considered for re‐classification.     

Dating of hot springs at Attri,Tarabalo and Athmalik sites in Odisha,India using radiocarbon technique

Journal of Radioanalytical and Nuclear Chemistry - In this study environmental radioisotopes of water (3H and 14C) were used to determine the residence time of thermal waters. The temperature of...     

Chemical Synthesis of Native S-Palmitoylated Membrane Proteins through Removable-Backbone-Modification-Assisted Ser/Thr Ligation

The preparation of native S-palmitoylated (S-palm) membrane proteins is one of the unsolved challenges in chemical protein synthesis. Herein, we report the first chemical synthesis of S-palm membrane proteins by removable-backbone-modification-assisted Ser/Thr ligation (RBM^GABA-assisted STL). This method involves two critical steps: 1) synthesis of S-palm peptides by a new γ-aminobutyric acid based RBM (RBM^GABA) strategy, and 2) ligation of the S-palm RBM-modified peptides to give the desired S-palm product by the STL method. The utility of the RBM^GABA-assisted STL method was demonstrated by the synthesis of rabbit S-palm sarcolipin (SLN) and S-palm matrix-2 (M2) ion channel. The synthesis of S-palm membrane proteins highlights the importance of developing non-NCL methods for chemical protein synthesis.