Computational study of the dissolution of cellulose into single chains: the role of the solvent and agitation

Cellulose - We investigate the dissolution mechanism of cellulose using molecular dynamics simulations in both water and a mixture solvent consisting of water with Na $$^+$$ , OH $$^-$$...     

Load balancing by work–stealing in quantum chemistry calculations: Application to hybrid density functional methods

Parallel implementations of quantum chemistry programs targeting supercomputers are challenging applications of dynamic load balancing algorithms. The implementation of work stealing (WS) algorithms is discussed and their usefulness is demonstrated. Evaluation of the four‐center integrals of a Cu₁₀ cluster requires 25 core‐hours overall, achieving 88% efficiency with simple WS for 2048 cores, and 97% with task presorting based on a cost estimate. Limitations of cost sorting become noticeable for larger systems. When spatial symmetry is exploited together with integral screening, bundling the original tasks yields an efficiency of 98% for Cu₇₉ in O_h symmetry on 512, 1204, and 2048 cores. The advantage of WS algorithms described in this work is not limited to the evaluation of four‐center integrals. © 2014 Wiley Periodicals, Inc.     

Pulsed DC magnetron sputtering of transparent conductive oxide layers

A comprehensive material study of different transparent conductive oxides （TCOs） is presented. The layers are deposited by pulsed direct current （DC） magnetron sputtering in an inline sputtering system. Indium tin oxide （ITO） films are studied in detail. The optimum pressure of 0.33 Pa （15Ar：202） produces a 300- nm thin film with a specific resistivity p of 2.2 × 10-6 Ωm and a visual transmittance of 81%. Alternatively, ZnO：A1 and ZnO：Ga layers with thicknesses of 200 and 250 nm are deposited with a minimum resistivity of 5.5× 10-6 and 6.8× 10-6Ωm, respectively. To compare the optical properties in the ultraviolet （UV） range, the optical spectra are modeled and the band gap is determined.     

Molecular electrocatalysis at soft interfaces

The fundamental aspects of electrochemistry at liquid-liquid interfaces are introduced to present the concept of molecular electrocatalysis. Here, a molecular catalyst is adsorbed at the interface to promote a proton coupled electron transfer reaction such as hydrogen evolution or oxygen reduction using lipophilic electron donors.     

Catalytic Functionalization of Indoles in a New Dimension

140 Years ago Adolf von Baeyer proposed the structure of a heteroaromatic compound which revolutionized organic and medical chemistry: indole. After more than a century, indole itself and the complexity of naturally occurring indole derivatives continue to inspire and influence developments in synthetic chemistry. In particular, the ubiquitous presence of indole rings in pharmaceuticals, agrochemicals, and functional materials are testament to the ever increasing interest in the design of mild and efficient synthetic routes to functionalized indole derivatives. This Review emphasizes the achievements in the selective catalytic functionalization of indoles (C? C bond‐forming processes) over the last four years.     

Electromembrane extraction of basic drugs from untreated human plasma and whole blood under physiological pH conditions

The present work describes the first systematic study of electromembrane extraction (EME) from biological matrices under physiological conditions. Six basic drugs with protein binding in the range of 20–97% were extracted from untreated human plasma and whole blood through a supported liquid membrane (SLM) consisting of 1-ethyl-2-nitrobenzene impregnated in the walls of a hollow fiber, and into an acidified aqueous solution inside the lumen of the fiber. The electrical potential difference over the membrane reduced the protein binding of the drugs and transported the free drug fraction over the membrane. Recoveries in the range 25–65% were obtained with 10-min extraction time and an applied voltage of only 10 V over the SLM. Interday precision better than 20% RSD and linearity in the range 0.5–10 μg/mL were obtained for nortriptyline and methadone. Extraction from untreated whole blood was also demonstrated with recoveries in the range 19–51%.     

Electrokinetic migration across artificial liquid membranes Tuning the membrane chemistry to different types of drug substances

Twenty different basic drugs were electrokinetically extracted across a thin artificial organic liquid membrane with a 300 V d.c. electrical potential difference as the driving force. From a 300 microl aqueous sample (acidified corresponding to 10mM HCl), the drugs were extracted for 5 min through a 200 microm artificial liquid membrane of a water immiscible organic solvent immobilized in the pores of a polypropylene hollow fiber, and into a 30 microl aqueous acceptor solution of 10mM HCl inside the lumen of the hollow fiber. Hydrophobic basic drugs (logP>1.7) were effectively isolated utilizing 2-nitrophenyl octyl ether (NPOE) as the artificial liquid membrane, with recoveries up to 83%. For more hydrophilic basic drugs (logP<1.0), a mixture of NPOE and 25% (w/w) di-(2-ethylhexyl) phosphate (DEHP) was required to ensure efficient extraction, resulting in recoveries up to 75%. DEHP was expected to act as an ion-pair reagent ion-pairing the protonated hydrophilic drugs at the interface between the sample and the membrane, resulting in permeation of the interface.     

Efficient photoinduced DNA damage by coralyne

The photoinduced DNA damage by the berberine derivative coralyne is presented. The irradiation of coralyne in the presence of plasmid DNA namely, pBR322, leads to remarkably fast DNA damage by single-strand cleavage, as determined by agarose-gel electrophoresis. Even upon exposure to sunlight, almost all of the supercoiled plasmid is converted to the open circular form in less than a minute [c(pBR322) = 3.5 x 10(-9) M; c(coralyne) = 4.3 x 10(-5) M]. The efficiency of the DNA strand cleavage is not decreased in the presence of radical-trapping reagents such as tert-butanol or DMSO. Moreover, the extent of the DNA damage is the same under aerobic conditions and at reduced oxygen concentration. Thus, the formation of reactive intermediates such as hydroxyl radicals or singlet oxygen is excluded. These results show that the exposure of coralyne and derivatives thereof to light, even with moderate light intensity, needs to be avoided during experiments in which their biological activity is assessed by plasmid unwinding assays.     

Excited state dynamics in solid and monomeric tetracene: The roles of superradiance and exciton fission

The excited state dynamics in polycrystalline thin films of tetracene are studied using both picosecond fluorescence and femtosecond transient absorption. The solid-state results are compared with those obtained for monomeric tetracene in dilute solution. The room temperature solid-state fluorescence decays are consistent with earlier models that take into account exciton-exciton annihilation and exciton fission but with a reduced delayed fluorescence lifetime, ranging from 20-100 ns as opposed to 2?μs or longer in single crystals. Femtosecond transient absorption measurements on the monomer in solution reveal several excited state absorption features that overlap the ground state bleach and stimulated emission signals. On longer timescales, the initially excited singlet state completely decays due to intersystem crossing, and the triplet state absorption superimposed on the bleach is observed, consistent with earlier flash photolysis experiments. In the solid-state, the transient absorption dynamics are dominated by a negative stimulated emission signal, decaying with a 9.2 ps time constant. The enhanced bleach and stimulated emission signals in the solid are attributed to a superradiant, delocalized S(1) state that rapidly fissions into triplets and can also generate a second superradiant state, most likely a crystal defect, that dominates the picosecond luminescence signal. The enhanced absorption strength of the S(0)→S(1) transition, along with the partially oriented nature of our polycrystalline films, obscures the weaker T(1)→T(N) absorption features. To confirm that triplets are the major species produced by relaxation of the initially excited state, the delayed fluorescence and ground state bleach recovery are compared. Their identical decays are consistent with triplet diffusion and recombination at trapping or defect sites. The results show that complications like exciton delocalization, the presence of luminescent defect sites, and crystallite orientation must be taken into account to fully describe the photophysical behavior of tetracene thin films. The experimental results are consistent with the traditional picture that tetracene's photodynamics are dominated by exciton fission and triplet recombination, but suggest that fission occurs within 10 ps, much more rapidly than previously believed.