Charge-Transfer versus Charge-Separated Triplet Excited States of [ReI(dmp)(CO)3(His124)(Trp122)]+ in Water and in Modified Pseudomonas aeruginosa Azurin Protein

A computational investigation of the triplet excited states of a rhenium complex electronically coupled with a tryptophan side chain and bound to an azurin protein is presented. In particular, by using high-level molecular modeling, evidence is provided for how the electronic properties of the excited-state manifolds strongly depend on coupling with the environment. Indeed, only upon explicitly taking into account the protein environment can two stable triplet states of metal-to-ligand charge transfer or charge-separated nature be recovered. In addition, it is also demonstrated how the rhenium complex plus tryptophan system in an aqueous environment experiences too much flexibility, which prevents the two chromophores from being electronically coupled. This occurrence disables the formation of a charge-separated state. The successful strategy requires a multiscale approach of combining molecular dynamics and quantum chemistry. In this context, the strategy used to parameterize the force fields for the electronic triplet states of the metal complex is also presented.     

Toward computational design of efficient plasticizers for nylon

Polyamides are semi‐crystalline polymers useful in a wide range of applications in the plastics industry. Some applications require higher flexibility and workability of the polyamides. Therefore, plasticizers are added to ease compounding and processing procedures and produce the desired product properties. The goal of the present study was to use computational tools to estimate plasticizer efficiency in plasticizing nylon 66/6. It is known that plasticizer efficiency is greatly influenced by structural effects of the plasticizer and the nature of the polymer, and therefore in this research, a systematic study is reported to explore these factors. A homology series of esters of 4‐hydroxybenzoate with various chain lengths of the alcohol moiety was examined. Also, the efficiency of linear plasticizers was compared to branched ones and stereoisomers were considered. Plasticizer efficiency was determined by calculating cohesive energy density (CED), solubility parameters, free volume and interaction intensities of pristine nylon and the nylon–plasticizer blends. It was found that plasticizer efficiency of esters with linear alcohol moiety is higher than branched chains. Whereas plasticizer efficiency increases when the branched side chain is more bulky, no coherent trend was observed for the linear side chain of the alcohol moiety. Surprisingly, a significant difference was observed between the pair of enantiomers. The most efficient plasticizer of the eight examined was the chiral molecule (R)‐2‐Methylbutyl‐4‐Hydroxybenzoate (R‐MB4HB), increasing the free volume of the nylon by 60‐fold (3‐fold greater than the original Methyl 4‐Hydroxybenzoate (M4HB)). Copyright © 2013 John Wiley & Sons, Ltd.     

On modifying properties of polymeric melts by nanoscopic particles

We study geometric and energetic factors that partake in modifying properties of polymeric melts via inserting well‐dispersed nanoscopic particles (NP). Model systems are cis‐1,4‐polybutadiene melts including a single atomic clusters of size varied in the range 10–150 atoms (3–7 Å in radius; 0.1–1.5% v/v). We modify the interactions between the chains and the particle by tuning attractive van der Waals interactions. Using molecular dynamics, we study equilibrium fluctuations and dynamical properties at the interface. The NPs move in the polymer matrix in two different regimes corresponding to trapped and free diffusion, depending on the NP size. Furthermore, degree of crowding around the NP by the polymer chains is quantified. Effect of NP size and interaction strength both on volume and volumetric fluctuations is manifested in mechanical properties, quantified here by bulk modulus, K. Tuning NP size and nonbonded interactions results in ～15% enhancement in K by addition of a maximum of 1.5% v/v NP. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Sonocatalytic degradation of Acid Blue 92 using sonochemically prepared samarium doped zinc oxide nanostructures

Pure and Sm-doped ZnO nanoparticles were synthesized applying a simple sonochemical method. The nanocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) techniques which confirmed the successful synthesis of the doped sonocatalyst. The sonocatalytic degradation of Acid Blue 92 (AB92), a model azo dye, was more than that with sonolysis alone. The 6% Sm-doped ZnO nanoparticles had a band gap of 2.8 eV and demonstrated the highest activity. The degradation efficiency (DE%) of sonolysis and sonocatalysis with undoped ZnO and 6% Sm-doped ZnO was 45.73%, 63.9%, and 90.10%, after 150 min of treatment, respectively. Sonocatalytic degradation of AB92 is enhanced with increasing the dopant amount and catalyst dosage and with decreasing the initial AB29 concentration. DE% declines with the addition of radical scavengers such as chloride, carbonate, sulfate, and tert-butanol. However, the addition of enhancers including potassium periodates, peroxydisulfate, and hydrogen peroxide improves DE% by producing more free radicals. The results show adequate reusability of the doped sonocatalyst. Degradation intermediates were recognized by gas chromatography–mass spectrometry (GC–MS). Using nonlinear regression analysis, an empirical kinetic model was developed to estimate the pseudo-first-order constants (k_app) as a function of the main operational parameters, including the initial dye concentration, sonocatalyst dosage, and ultrasonic power.     

Goniopolarimetry: Space-borne radio astronomy with imaging capabilities

The principles of space-based low-frequency radio astronomy (below 50 MHz) are briefly introduced. As the wavelength range considered does not allow the use of focusing systems, goniopolarimetric (or direction-finding) techniques have been developed. These inversion techniques provide the direction of the wave vector, the polarization state and the flux of the observed electromagnetic wave. In case of spatially extended sources, we can also infer an order of magnitude of the apparent source size. These techniques are presented, and their limitations are discussed. An example from a recent study illustrates the techniques and capabilities.     

Effect of epitaxial crystallization on packet-like space charge characteristics in low-density polyethylene under multi-field coupling conditions

In order to study the effect of epitaxial crystallization on charge transport in low-density polyethylene (LDPE) under multi-field coupling conditions, three typical epitaxial crystallizations, namely disorder (glass substrate), crossover (isotactic polypropylene substrate), and parallel (polytetrafluoroethylene substrate), were prepared and denoted as LD-G, LD-iPP, and LD-PT, respectively. Packet-like space charge through samples was analyzed by the pulsed electro-acoustic (PEA) method. It is shown that different microscopic surface morphologies appeared in the LDPE samples with different epitaxial crystallizations, which, however, do not change the crystalline structure of the bulk. Packet-like space charge phenomena were observed and the distortion field increased with the temperature which could be attributed to the larger amount of charge injection in a shorter period. The differences of the amount and injection rate of the space charge were explained and verified considering the typical chain alignment of epitaxial crystallization, which, in our opinions, contributes to the pass over of positive charge in LD-iPP samples.     

Extreme fluxes in solar energetic particle events: Methodological and physical limitations

In this study, all available data on the largest solar proton events (SPEs), or extreme solar energetic particle (SEP) events, for the period from 1561 up to now are analyzed. Under consideration are the observational, methodological and physical problems of energy-spectrum presentation for SEP fluxes (fluences) near the Earth's orbit. Special attention is paid to the study of the distribution function for extreme fluences of SEPs by their sizes. The authors present advances in at least three aspects: 1) a form of the distribution function that was previously obtained from the data for three cycles of solar activity has been completely confirmed by the data for 41 solar cycles; 2) early estimates of extremely large fluences in the past have been critically revised, and their values were found to be overestimated; and 3) extremely large SEP fluxes are shown to obey a probabilistic distribution, so the concept of an “upper limit flux” does not carry any strict physical sense although it serves as an important empirical restriction. SEP fluxes may only be characterized by the relative probabilities of their appearance, and there is a sharp break in the spectrum in the range of large fluences (or low probabilities). It is emphasized that modern observational data and methods of investigation do not allow, for the present, the precise resolution of the problem of the spectrum break or the estimation of the maximum potentialities of solar accelerator(s). This limitation considerably restricts the extrapolation of the obtained results to the past and future for application to the epochs with different levels of solar activity.     

Quantitative modeling and mapping of blistering zone of the Magoksa Temple stone pagoda (13th century,Republic of Korea) by graduated heating thermography

Blistering occurring at the stone’s subsurface layer is easily overlooked compared to different deterioration types, so conservation treatments are not applied often. Therefore, non-destructive detection and mapping of blistering zones with the infrared thermography are very important for preservation of the original forms of stone monuments. In this study, the critical temperature and transitional zone of the blistering zone were established by drawing the temperature distribution curve and the mapping for blistering zone was completed by monochrome process and extraction of vector lines. Analysis of the blistering deterioration degree of the Magoksa Temple stone pagoda with the quantitative modeling yielded a total area and average rate of blistering zones of approximately 2.6 m² and 7.4%, respectively. Thus, there is a high probability of scaling on the stone pagoda (area of approximately 2.6 m²) if conservation treatment is not applied to the blistering zones as early as possible. Therefore, the blistering zones require joining and filling, and state changes of the blistering zones should be continuously monitored after completion of the intensive conservation treatments. Modeling will improve the reliability of deterioration maps by mapping for blistering zone; most deterioration maps to date have overlooked blistering zones.