Dust in the planetary system: Dust interactions in space plasmas of the solar system

Cosmic dust particles are small solid objects observed in the solar planetary system and in many astronomical objects like the surrounding of stars, the interstellar and even the intergalactic medium. In the solar system the dust is best observed and most often found within the region of the orbits of terrestrial planets where the dust interactions and dynamics are observed directly from spacecraft. Dust is observed in space near Earth and also enters the atmosphere of the Earth where it takes part in physical and chemical processes. Hence space offers a laboratory to study dust–plasma interactions and dust dynamics. A recent example is the observation of nanodust of sizes smaller than 10 nm. We outline the theoretical considerations on which our knowledge of dust electric charges in space plasmas are founded. We discuss the dynamics of the dust particles and show how the small charged particles are accelerated by the solar wind that carries a magnetic field. Finally, as examples for the space observation of cosmic dust interactions, we describe the first detection of fast nanodust in the solar wind near Earth orbit and the first bi-static observations of PMSE, the radar echoes that are observed in the Earth ionosphere in the presence of charged dust.     

A Deeper Insight into the Postpolymerization Modification of Polypenta Fluorophenyl Methacrylates to Poly(N‐(2‐Hydroxypropyl) Methacrylamide)

This work provides a detailed insight into the synthesis of N‐(2‐hydroxypropyl)methacrylamide (HPMA) polymers employing the activated ester approach. In this approach, polypenta fluorophenyl methacrylate (PFPMA)‐activated ester polymers are synthesized by the reversible addition–fragmentation chain transfer (RAFT) polymerization and transferred into HPMA‐based systems by the use of 2‐hydroxypropylamine. To prove quantitative conversion in the absence of side reactions, special attention is devoted to investigate different reaction conditions by different analytical methods (¹H, ¹⁹F, inverse‐gated ¹³C NMR, and zeta potential measurements). Furthermore the influence of common solvent impurities, such as water, is investigated. Besides differences in polymer tacticity, the poly(N‐(2‐hydroxypropyl) methacrylamide) (PHPMA) synthesized under water‐free conditions display the same properties like the conventional synthesized control‐PHPMA. However, 3% water content in the dimethylsulfoxide are already sufficient to yield PHPMA polymers with a negative zeta potential of –15.8 mV indication the presence of carboxylic groups due to partial hydrolysis of the activated ester.

     

Intermediate intensity levels during the emission intermittency of single CdSe/ZnS quantum dots

We report on an intermediate intensity level in the emission intermittency of single CdSe/ZnS core shell quantum dots, which has been overlooked in previous experiments most likely due to its low quantum efficiency. The intermediate intensity level is observed in CdSe/ZnS quantum dots of large diameter (about 5 nm diameter) and appears to be independent of the general dark state power law dynamics. The dim emission periods are found to be exponentially distributed and thus correspond to similar findings in CdSe/CdS quantum dots, where their existence has been interpreted in terms of the emission of a positively charged trion.     

Interface control of emergent ferroic order in Ruddlesden-Popper Sr(n+1)Ti(n)O(3n+1)

We discovered from first principles an unusual polar state in the low n Sr(n+1)Ti(n)O(3n+1) Ruddlesden-Popper (RP) layered perovskites in which ferroelectricity is nearly degenerate with antiferroelectricity, a relatively rare form of ferroic order. We show that epitaxial strain plays a key role in tuning the "perpendicular coherence length" of the ferroelectric mode, and does not induce ferroelectricity in these low-dimensional RP materials as is well known to occur in SrTiO(3). These systems present an opportunity to manipulate the coherence length of a ferroic distortion in a controlled way, without disorder or a free surface.     

Synthesis and evaluation of chlorinated substrate analogues for farnesyl diphosphate synthase

Substrate analogues for isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), where the C3 methyl groups were replaced by chlorine, were synthesized and evaluated as substrates for avian farnesyl diphosphate synthase (FPPase). The IPP analogue (3-ClIPP) was a cosubstrate when incubated with dimethylallyl diphosphate (DMAPP) or geranyl diphosphate (GPP) to give the corresponding chlorinated analogues of geranyl diphosphate (3-ClGPP) and farnesyl diphosphate (3-ClFPP), respectively. No products were detected in incubations of 3-ClIPP with 3-ClDMAPP. Incubation of IPP with 3-ClDMAPP gave 11-ClFPP as the sole product. Values of K(M)(3-ClIPP) (with DMAPP) and K(M)(3-ClDMAPP) (with IPP) were similar to those for IPP and DMAPP; however, values of k(cat) for both analogues were substantially lower. These results are consistent with a dissociative electrophilic alkylation mechanism where the rate-limiting step changes from heterolytic cleavage of the carbon-oxygen bond in the allylic substrate to alkylation of the double bond of the homoallylic substrate.     

Real-time NMR studies of electrochemical double-layer capacitors

(11)B NMR spectroscopy has been used to investigate the sorption of BF(4)(-) anions on a highly porous, high surface area carbon, and different binding sites have been identified. By implementing in situ NMR approaches, the migration of ions between the electrodes of the supercapacitors and changes in the nature of ion binding to the surface have been observed in real time.     

Ultrathin gold nanoframes through surfactant-free templating of faceted pentagonal silver nanoparticles

Ultrathin gold nanoframes (up to 1.6 nm) were prepared via templating upon well-defined faceted silver morphologies. Starting with silver decahedra, small quantities of gold (1-10 mol% relative to the amount of silver) were selectively deposited on the nanoparticle edges under optimized reducing conditions. Silver dissolution in hydrogen peroxide yielded well-defined gold frames that retained their structural integrity in the ultrathin nanowire regime below 2 nm. The frame formation protocol was also successfully applied to other silver nanoparticle shapes featuring pentagonal twinning and (111) facets (e.g., pentagonal faceted rods and icosahedra). The demonstrated approach can be applied in the controlled preparation of ultrathin metal nanowires complementary to lithography and in the production of ultrafine noble-metal nanostructures for catalytic applications.