Copolyesters of isosorbide,succinic acid,and isophthalic acid: Biodegradable,high Tg engineering plastics

Isosorbide, succinyl chloride and isophthaloyl chloride are polycondensed under various reaction conditions. The heating in bulk with or without catalysts as well in an aromatic solvent without catalyst, and polycondensation with the addition of pyridine only yield low molar mass copolyesters. However, heating in chlorobenzene with addition of SnCl₂ or ZnCl₂ produces satisfactory molar masses. The number average molecular weights (M_n) of most copolyesters fall into the range of 7000–15,000 Da with polydispersities (PD) in the range of 3–9. The MALDI‐TOF mass spectra almost exclusively displayed peaks of cyclics indicating that the chain growth was mainly limited by cyclization and not by side reactions, stoichiometric imbalance or incomplete conversion. The glass‐transition temperatures increased with the content of isophthalic acid from 75 to 180 °C and the thermo‐stabilities also followed this trend. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2464–2471     

Light‐Induced Electron Transfer over Distances of 5, 10, and 15 Å within Water‐Filled Yoctowells

A small series of variable‐depth yoctowell cavities with ′functional′ walls on aminated silica particles and gold electrodes has been established. The dimensions of the gaps formed were 2.2 nm in diameter with varying ′functional′ depths of 5, 10, and 15 Å, depending on the length of bolaphiles applied and the position of the positive rim; these gaps were prepared through a Michael addition of the incorporated ene‐amide groups. Using this construct and electrostatic interactions between the positive rim and anionic quinones as a means of immobilization, a porphyrin–quinone dyad system has been prepared. The distance between the donor and acceptor was changed systematically in aqueous solution, whilst maintaining a similar environment in each case. Upon photoexcitation of the porphyrin, efficient electron transfer occurs between the porphyrin and quinone units in a distance‐dependent manner on the nanosecond timescale.     

Simulations of stellar convection with CO5BOLD

High-resolution images of the solar surface show a granulation pattern of hot rising and cooler downward-sinking material – the top of the deep-reaching solar convection zone. Convection plays a role for the thermal structure of the solar interior and the dynamo acting there, for the stratification of the photosphere, where most of the visible light is emitted, as well as for the energy budget of the spectacular processes in the chromosphere and corona. Convective stellar atmospheres can be modeled by numerically solving the coupled equations of (magneto)hydrodynamics and non-local radiation transport in the presence of a gravity field. The CO5BOLD code described in this article is designed for so-called “realistic” simulations that take into account the detailed microphysics under the conditions in solar or stellar surface layers (equation-of-state and optical properties of the matter). These simulations indeed deserve the label “realistic” because they reproduce the various observables very well – with only minor differences between different implementations. The agreement with observations has improved over time and the simulations are now well-established and have been performed for a number of stars. Still, severe challenges are encountered when it comes to extending these simulations to include ideally the entire star or substellar object: the strong stratification leads to completely different conditions in the interior, the photosphere, and the corona. Simulations have to cover spatial scales from the sub-granular level to the stellar diameter and time scales from photospheric wave travel times to stellar rotation or dynamo cycle periods. Various non-equilibrium processes have to be taken into account. Last but not least, realistic simulations are based on detailed microphysics and depend on the quality of the input data, which can be the actual accuracy limiter. This article provides an overview of the physical problem and the numerical solution and the capabilities of CO5BOLD, illustrated with a number of applications.     

Next‐Generation Heteronuclear Decoupling for High‐Field Biomolecular NMR Spectroscopy

Ultra‐high‐field NMR spectroscopy requires an increased bandwidth for heteronuclear decoupling, especially in biomolecular NMR applications. Composite pulse decoupling cannot provide sufficient bandwidth at practical power levels, and adiabatic pulse decoupling with sufficient bandwidth is compromised by sideband artifacts. A novel low‐power, broadband heteronuclear decoupling pulse is presented that generates minimal, ultra‐low sidebands. The pulse was derived using optimal control theory and represents a new generation of decoupling pulses free from the constraints of periodic and cyclic sequences. In comparison to currently available state‐of‐the‐art methods this novel pulse provides greatly improved decoupling performance that satisfies the demands of high‐field biomolecular NMR spectroscopy.