Novel nucleophilic substitution of alkyl bromo-2(1H)-pyridones

Nucleophilic substitution of certain alkyl bromo-2(1H)-pyridones gave some unexpected products where the alkyl group is substituted and the ring bromine is replaced by hydrogen. The expected ring substituted product is also formed, but only as the minor product in most cases. Many reactions are cited with various nucleophiles, and a plausible mechanism is also presented.     

A novel photoaddition of 2-phenylbenzimidazole

Irradiation of 2-phenylbenzimidazole ( 3 ) in the presence of methyl acrylate (20 equivalents) using a medium pressure mercury lamp gives methyl 2-(2-phenylbenzimidazol-1-yl)propionate ( 4 ) (75%) whose structure has been confirmed by an X-ray analysis. A similar reaction using acrylonitrile gave only a low yield (1%) of the corresponding propionitrile derivative 5 . A mechanism involving photoexcitation of 2-phenylbenzimidazole ( 3 ) followed by sequential single electron transfer, proton transfer and radical coupling is proposed to account for the formation of the novel photoadducts 4 and 5 .     

Polysulfonylamine. CLX [1] Kristallstrukturen von Metall‐di(methansulfonyl)amiden. 10 [2] Die dreidimensionalen Koordinationspolymere M[(CH3SO2)2N] mit M = Kalium,Rubidium, Caesium (isotype Strukturen für M = K,Rb)

Polysulfonylamines. CLX. Crystal Structures of Metal Di(methanesulfonyl)amides. 10. The Three‐Dimensional Coordination Polymers M[(CH₃SO₂)₂N], where M is Potassium, Rubidium, Cesium (Isotypic Structures for M = K, Rb) Low‐temperature X‐ray crystal structures are reported for KA (monoclinic, space group P2₁/c, Z′ = 1), RbA (isotypic and isostructural with KA), and CsA (monoclinic, P2₁/n, Z′ = 1), where A^— denotes the anion obtained by deprotonation of the strong nitrogen acid (MeSO₂)₂NH. In KA and RbA, the anion is distorted into a rare C₁ conformation, whereas the standard C₂ conformation is retained in the cesium complex. The structures consist of three‐dimensional coordination networks, in which each cation adopts an irregular (O₆N)‐heptacoordination by forming close contacts to one (O, N)‐chelating, one (O, O)‐chelating and three κ¹O‐bonding ligands; however, the coordination number for Cs⁺ is effectively increased to 8 by a very short Cs···Cs contact distance of 422.5 pm. The crystal packings of the isotypic compounds KA and RbA display lamellar layer substructures that involve six independent ligand‐metal bonds and comprise an internal cation lamella and peripheral regions built up from anion monolayers; the 3D framework is completed by one independent M—O bond cross‐linking the layer substructures. In contrast, CsA features anion monolayers that intercalate planar zigzag chains of cations (Cs···Cs alternatingly 422.5 and 487.5 pm, Cs···Cs···Cs 135.7°), whereby each chain is surrounded and coordinated by four anion stacks and each anion stack connects two cation chains. All structures exhibit close C—H···A interanion contacts consistent with weak hydrogen bonding.     

Swelling and network parameters of crosslinked thermoreversible hydrogels of poly(N-ethylacrylamide)

Samples of Poly(N-ethylacrylamide) (PEA) have been synthesized by free radical polymerization in water using N,N′-methylene bis-acrylamide (BIS) as crosslinker. Hydrogels obtained by swelling them in water, 15 wt% KCl and 1 wt% sodium dodecyl sulphate (SDS) were examined by gravimetric, dimensional and compression-strain measurements to afford values of swelling ratio, polymer-solvent interaction parameters, elastic moduli and effective crosslinking density ν_e. Crosslinking inefficiency is evidenced by the low value (0.23) of ν_e relative to the theoretical crosslinking density ν_t based on the content of BIS in the synthesis. A small but finite extrapolated value of ν_e at ν_t = 0 is indicative of hydrophobic physical interactions. In water at 298 K increasing the content of BIS leads to a decrease in swelling and increases in values of elastic moduli and polymer-water interaction parameter. At a fixed content of BIS the values of ν_e and the elastic moduli exhibit an unusual increase with temperature, the crosslinking thus being thermally reversible. It is proposed that this results from a balance between hydrophobic interaction and breakage of hydrophilic hydrogen bonding. Although KCl in the medium decreases the swelling compared with that in water, the opposite effect occurs on incorporation of SDS, which is assumed to confer some polyelectrolyte character to the PEA chains. The finding, that these two swelling media reduce the values of ν_e and elastic moduli cf the value in water, has not been resolved satisfactorily.     

Chemically modified "polar patch" mutants of subtilisin in peptide synthesis with remarkably broad substrate acceptance: designing combinatorial biocatalysts

A significant enhancement of the applicability of the serine protease subtilisin Bacillus lentus (SBL) in peptide synthesis was achieved by using the strategy of combined site-directed mutagenesis and chemical modification to create chemically modified mutant (CMM) enzymes. The introduction of polar and/or homochiral auxiliary substituents, such as X=oxazolidinones, alkylammonium groups, and carbohydrates at position 166 at the base of the primary specificity S(1) pocket created SBL CMMs S166C-S-X with strikingly broad structural substrate specificities. These CMMs are capable of catalyzing the coupling reactions of not only L-amino acid esters but also D-amino acid esters as acyl donors with glycinamide to give the corresponding dipeptides in good yields. These powerful enzymes are also applicable to the coupling of L-amino acid acyl donors with alpha-branched acyl acceptor, L-alaninamide. Typical increases in isolated yields of dipeptides of 60-80 % over SBL-WT (e.g. 0 % yield of Z-D-Glu-GlyNH(2) using SBL-WT-->74 % using S166C-S-(CH(2))(2) NMe(3) (+)) demonstrate the remarkable synthetic utility of this "polar patch" strategy. Such wide-ranging systems displaying broadened and therefore similarly high, balanced yields of products (e.g. 91 % Z-L-Ala-GlyNH(2) and 86 % yield of Z-D-Ala-GlyNH(2) using S166C-S-(3R,4S)-indenooxazolidinone) may now allow the use of biocatalysts in parallel library synthesis.     

Initiation of polymer degradation via transfer of infectious species

A novel dual stage chemiluminescence detection system incorporating individually controlled hot stages has been developed and applied to probe for material interaction effects during polymer degradation. Utilization of this system has resulted in experimental confirmation for the first time that in an oxidizing environment a degrading polymer A (in this case polypropylene, PP) is capable of infecting a different polymer B (in this case polybutadiene, HTPB) over a relatively large distance. In the presence of the infectious degrading polymer A, the thermal degradation of polymer B is observed over a significantly shorter time period. Consistent with infectious volatiles from material A initiating the degradation process in material B it was demonstrated that traces (micrograms) of a thermally sensitive peroxide in the vicinity of PP could induce degradation remotely. This observation documents cross-infectious phenomena between different polymers and has major consequences for polymer interactions, understanding fundamental degradation processes and long-term aging effects under combined material exposures.     

Geometric and electronic structure of clusters

The interplay between electronic and geometric structure is investigated for covalently bonded phosphorus clusters. We use a modification of the molecular dynamics/ density functional (MD/DF) method of Car and Parrinello, describing the electronic structure by a simplified linear combination of atomic orbitals (LCAO) approach. The results show clearly the tendency of phosphorus to threefold coordination, and substantial variations in bond angles lead to a large variety of isomers.