Energy Elasticity of Tie Molecules in Semicrystalline Polymers

Elastic response of the disordered phase between crystal lamellae in semicrystalline polymers is modelled on the assumption that the stress is transferred by bridging (tie) molecules. The deformation characteristics of short poly(methylene) (PM) bridges were computed by using two methods: (a) the single‐molecule loading by molecular mechanics (MM) calculations and (b) the chain‐ensemble averaging by lattice simulations. The energy elastic functions ensuing from both methods differ considerably. In MM the loading of chains containing numerous gauche defects by an external force F yields the sawtooth‐like profile of the force (F)–length (R) functions brought about by the stress‐induced gauche–trans conformational transitions. The Young's moduli E of PM chains containing several gauche defects can be less than 1% of the all‐trans value E_T; by elimination of the defects the moduli steeply increase. In contrast, the ensemble‐averaging approach gives a smooth increase of the (positive) elastic force f with chain length R and a decrease of the (negative) energy component of the elastic force f_U with R. Both energy deformation mechanisms, single‐chain loading (by F) and statistical (by f_U), are complementary and can simultaneously be operative in the interlamellar (IL) phase. Their proportion in the stretching process should depend on the chain mobility and structural homogeneity (history) of the sample, particularly on the presence of the so‐called rigid amorphous fraction in the IL phase.     

Eine Methode zur Mikroeiwei?bestimmung

Ohne Zusammenfassung     

Inversion of enantioselectivity in quinine-mediated desymmetrization of glutaric meso-anhydrides

An unexpected inversion of enantioselectivity, dependent on the degree of quinine loading, was observed during the desymmetrization of glutaric meso-anhydrides. Decrease in catalyst loading from 1.6 equiv to 0.1 equiv caused a clear inversion of stereochemistry—from about 40% ee of (R)-configuration to about 40% ee of the opposite enantiomer. The effect of various carboxylic acid additives was also studied.     

Thermolysis of 1-homoadamantyl hypoiodite. Convenient synthesis of 10-homoprotoadamantan-4-one (tricyclo [4.3.2.03,8]undecan-4-one)

Thermolysis of 1-homoadamantyl hypoiodite followed by intramolecular cyclizatlon yields 74% of the hitherto unknown $\text{10-homo}$aprotoadamantan-4-one; $\text{the hypoiodite thermoIysis-cyclization sequence}$ appears to be an excellent method for the preparation of adamantanoid ketones.     

D‐Glucosamine in iron‐catalysed cross‐coupling reactions of Grignards with allylic and vinylic bromides: application to the synthesis of a key sitagliptin precursor

A sustainable D ‐glucosamine ligand is successfully introduced into iron‐catalysed C ? C cross‐coupling reactions for the first time. The Fe(acac)₂/D ‐glucosamine·HCl/Et₃N catalytic system was effective at 5 mol% loading in coupling reactions of Grignard reagents with organic bromides. Moderate to high efficiency was achieved with preserved stereochemistry when allyl (Csp³) or alkenyl (Csp²) bromides were coupled with phenylmagnesium (Csp²) or benzylmagnesium (Csp³) bromides. The catalytic system developed was also successfully applied for the novel and economic preparation of a Michael‐acceptor‐like starting material used in an alternative synthesis of the drug sitagliptin, a known blockbuster for the treatment of type II diabetes mellitus. Copyright © 2015 John Wiley & Sons, Ltd.     

Corona discharge as a temperature probe of atmospheric air microwave plasma jet

We developed and tested a new method for temperature measurements of near-LTE air plasmas at atmospheric pressure. This method is specifically suitable for plasmas at relatively low gas temperature (800–1700 K) with no appropriate radiation for direct spectroscopic temperature measurements. Corona discharge producing cold non-equilibrium plasma is employed as a source of excitation and is placed into the microwave plasma jet. The gas temperature of the microwave plasma jet is determined as the rotational temperature of N₂? produced in the corona discharge. The corona probe temperature measurement was tested by the use of a thermocouple. We found a fairly good agreement between the two methods after correcting the thermocouple measured temperatures for radiative losses. The corona probe method can be generally applied to determine the temperature of the near-LTE plasmas and contrary to the thermocouple it can be used for higher plasma temperatures and is not affected by radiative losses and problems of interaction with the microwave plasma and electromagnetic fields.     

syn/anti Diastereoselectivity in the Aldol Reaction of Aldehydes with the C(3) Carbanion of 1,3‐Dihydro‐2H‐1,4‐benzodiazepin‐2‐one

The aldol reaction of the C(3) carbanion of 7‐chloro‐1,3‐dihydro‐1‐methyl‐5‐phenyl‐2H‐1,4‐benzodiazepin‐2‐one ( 2 ) with a series of aromatic and aliphatic aldehydes at −78° afforded threo/erythro diastereoisomers 3 – 16 of 7‐chloro‐1,3‐dihydro‐3‐(hydroxymethyl)‐1‐methyl‐5‐phenyl‐2H‐1,4‐benzodiazepinones, substituted at the C(3) side chain, in a ratio from 55 : 45 to 94 : 6 (Scheme 1). Lewis acids exhibited limited effect on the syn/anti diastereoselectivity of this reaction, and kinetic control of the reaction was confirmed. ¹H‐NMR Data suggested the assignment of the threo relative configuration to the first‐eluted diastereoisomers 3 , 5 , 7 , and 9 on reversed‐phase HPLC, and the erythro configuration to the second‐eluted counterparts 4 , 6 , 8 , and 10 , respectively. The structures and relative configurations threo and erythro of the diastereoisomers 5 and 6 , respectively, were established by single‐crystal X‐ray analysis, confirming the assignment based on the ¹H‐NMR data. A tentative mechanistic explanation of the diastereoselectivity invokes the enolate anion of 1,3‐dihydro‐2H‐1,4‐benzodiazepin‐2‐one as the reactive species (Scheme 2). Acid‐catalyzed hydrolytic ring opening of 3 afforded threo‐β‐hydroxy‐phenylalanine 17 , whereas from 4 , the N‐(benzyloxy)carbonyl derivative 18 of erythro‐β‐hydroxy‐phenylalanine was obtained (Scheme 3); in both cases, neither elimination of H₂O from the C(3)−CHOH moiety nor epimerization at C(3) were observed. This result opens a new pathway to various configurationally uniform α‐amino‐β‐hydroxy carboxylic acids and their congeners of biological importance.     

A simple enantioselective route toward (R)- and (S)-Rolipram via anhydride desymmetrization

A highly enantioselective metal-free synthesis of both enantiomers of Rolipram is reported. The key stereoinductive step is a cinchona alkaloid catalyzed opening of a cyclic anhydride prepared from isovanillin, where both enantiomers are available using the same chiral catalyst in two protocols. An extended one-pot Curtius sequence provides the lactam directly from the desymmetrization product after enrichment in high yield and excellent ee.     

The Effect of Air Plasma Activated Liquid on Uropathogenic Bacteria

Plasma Chemistry and Plasma Processing - Urinary tract infections (UTI) are often caused by resistant uropathogenic bacteria and can lead to sepsis or chronic renal failure. Cold plasma activated...