Dissociative recombination of H+(H2O)3 and D+(D2O)3 water cluster ions with electrons: cross sections and branching ratios

Dissociative recombination (DR) of the water cluster ions H(+)(H(2)O)(3) and D(+)(D(2)O)(3) with electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). For the first time, absolute DR cross sections have been measured for H(+)(H(2)O)(3) in the energy range of 0.001-0.8 eV, and relative cross sections have been measured for D(+)(D(2)O)(3) in the energy range of 0.001-1.0 eV. The DR cross sections for H(+)(H(2)O)(3) are larger than previously observed for H(+)(H(2)O)(n) (n=1,2), which is in agreement with the previously observed trend indicating that the DR rate coefficient increases with size of the water cluster ion. Branching ratios have been determined for the dominating product channels. Dissociative recombination of H(+)(H(2)O)(3) mainly results in the formation of 3H(2)O+H (probability of 0.95+/-0.05) and with a possible minor channel resulting in 2H(2)O+OH+H(2) (0.05+/-0.05). The dominating channels for DR of D(+)(D(2)O)(3) are 3D(2)O+D (0.88+/-0.03) and 2D(2)O+OD+D(2) (0.09+/-0.02). The branching ratios are comparable to earlier DR results for H(+)(H(2)O)(2) and D(+)(D(2)O)(2), which gave 2X(2)O+X (X=H,D) with a probability of over 0.9.     

Binding of intercalating and groove-binding cyanine dyes to bacteriophage t5

The interaction between four related cyanine dyes and bacteriophage T5 is investigated with fluorescence and absorption spectroscopy. The dyes, which differ in size, charge, and mode of DNA-binding, penetrate the capsid and bind the DNA inside. The rate of association decreases progressively with increasing dye size, from a few minutes for YO to more than 50 h for YOYO (at 37 degrees C). The relative affinity for the phage DNA is a factor of about 0.2 lower than for the same T5-DNA when free in solution. Comparison of groove-bound BOXTO-PRO and intercalating YO-PRO shows that the reduced affinity is not due to DNA extension but perhaps influenced by competition with other cationic DNA-binding agents inside the capsid. Although, the extent of dye binding to the phages decreases with increasing external ionic strength, the affinity relative to free DNA increases, which indicates a comparatively weak screening of electrostatic interactions inside the phage. The rate of binding increases with increasing ionic strength, reflecting an increase in effective pore size of the capsid as electrostatic interactions are screened and/or a faster diffusion of the dye through the DNA matrix inside the capsid as the DNA affinity is reduced. A combination of electron microscopy, light scattering, and linear dichroism show that the phages are intact after YO-PRO binding, whereas a small degree of capsid rupture cannot be excluded with BOXTO-PRO.     

Spin polarization of the neutral exciton in a single quantum dot

While efficient nuclear polarization has earlier been reported for the charged exciton in InAs/GaAs quantum dots at zero external magnetic field, we report here on a surprisingly high degree of circular polarization, up to ≈60%$\approx 60\%$, for the neutral exciton emission in individual InAs/GaAs dots. This high degree of polarization is explained in terms of the appearance of an effective nuclear magnetic field which stabilizes the electron spin. The nuclear polarization is manifested in experiments as a detectable Overhauser shift. In turn, the nuclei located inside the dot are exposed to an effective electron magnetic field, the Knight field. This nuclear polarization is understood as being due to the dynamical nuclear polarization by an electron localized in the QD. The high degree of polarization for the neutral exciton is also suggested to be due to separate in-time capture of electrons and holes into the QD.     

MOLECULAR AGGREGATION IN LIPID-WATER DISPERSION PHASES

Polar lipids from aqueous liquid-crystalline phases which are the basis for the understanding of their functionality in technical applications. The structural characteristics of these phases and the relation between chemical structure of lipid molecules and their phase properties are reviewed. Special attention is given to new results on cubic phases, the most complex of lipid-water phases. The lipid bilayer is curved in space so that there are no selfintersections. There are two water-channel systems separated by the bilayer. The characteristic feature of the cubic phases is that the lipid bilayer has zero average curvature in all points.     

COLLOIDAL DISPERSIONS OF ORDERED LIPID-WATER PHASES

Aqueous dispersions of colloidal aggregates of liquid-crystalline lipid-water phases are described. The lamellar liquid-crystalline phase can form liposomal dispersions, which are wellknown from extensive studies of these particles in drug delivery. Less is known about dispersions of cubic and hexagonal phases. The preparation of such colloidal dispersions, their structure and physical properties are summerised. The dispersed cubic phase is compared to liposomal dispersions, and it is concluded that an important application of the cubic particles will involve encapsulation of proteins and protection of their native conformation.     

An automatic field sampler utilising supported liquid membrane (SLM) for on-site extraction of s-triazine herbicides and degradation products: applied to an agricultural region of Ethiopia

A portable and time-integrating field sampler based on the supported liquid membrane (SLM) extraction technique was constructed. Using two programmable syringe pumps and one programmable valve, the sampler could carry out automatic unattended extraction for up to seven extracts, combining the steps of sampling, trace enrichment and clean-up. The sampler was applied to the extraction of four s-triazine herbicides (atrazine, cyanazine, prometryn and terbutryn) and six major degradation products of s-triazines, including three dealkylated products (deethyl deisopropyl atrazine (DDA), deisopropyl atrazine DIA and deethyl atrazine (DEA)) and three hydroxylated products (hydroxy atrazine (ATOH), hydroxy propazine (PROH) and hydroxy terbutylazine (TZOH)). The donor solution was obtained by mixing sample and buffer, consisting of 1?M phosphate buffer at pH 7.0 and 1.7?M NaCl, in the ratio of 19?:?1 (v/v). Extraction was performed by continuously pumping 10?mL portions of donor along the SLM until 3?L of sample had been extracted. The SLM consisted of di-n-hexylether and the acceptor was 1?M HCl. After extract collection, extracts were neutralised with NaOH and buffered with phosphate. Extracts were analysed with HPLC, using a gradient elution consisting of 3.5?mM phosphate and acetonitrile and UV-detection at 220?nm. Enrichment factors in reagent water ranged from 1.3 (for DIA) to 2739 (for terbutryn). The developed field sampler was tested by carrying out 24-h time-weighted on-site extraction of the ten s-triazine target compounds in Hawassa Lake and its tributary river, located in the agricultural region of the Southern Rift Valley of Ethiopia. Atrazine, cyanazine and terbutryn were generally below the method detection limit, while prometryn was frequently found. Overall, s-triazines were not persistent in the studied environment and degradation products of s-triazines were found in higher concentrations than the parent herbicides in both the river and the lake.     

A new, robust method for measuring average fibre wall pore sizes in cellulose I rich plant fibre walls

A new, robust method for measuring the average pore size of water-swollen, cellulose I rich fibres is presented. This method is based on the results of solid-state NMR, which measures the specific surface area (area/solids mass) of water-swollen samples, and of the fibre saturation point (FSP) method, which measures the pore volume (water mass/solids mass) of water-swollen samples. These results are suitable to combine since they are both recorded on water-swollen fibres in excess water, and neither requires the assumption of any particular pore geometry. The new method was used for three model samples and reasonable average pore size measurements were obtained for all of them. The structural characterization of water-swollen samples was compared with the dry structure of fibres as revealed using BET nitrogen gas adsorption after a liquid exchange procedure and careful drying. It was concluded that the structure of the water-swollen fibres sets an upper limit on what is obtainable in the dry state.     

Polymeric gold(I) diisobutyl dithiophosphate, [Au2{S2P(O-iso-C4H9)2}2]n: Synthesis,supramolecular self-organization (a role of aurophilic interaction), 13C and 31P MAS NMR spectroscopy,and thermal behavior

A new polymeric gold(I) diisobutyl dithiophosphate (Dtph), [Au₂{S₂P(O-iso-C₄H₉)₂}₂] _n (I), was preparatively obtained and characterized by ¹³C and ³¹P MAS NMR spectroscopy and X-ray diffraction (CIF file CCDC no. 977818). Diagrams of the χ² statistic were constructed from the complete ³¹P MAS NMR spectra and used to calculate the ³¹P chemical shift anisotropy (δ _aniso = δ _zz ? δ _iso ) and the asymmetry parameter η = (δ _yy ? δ _xx )/(δ _zz ? δ _iso ). The main structural unit of complex I is the noncentrosymmetric dinuclear molecule [Au₂{S₂P(O-iso-C₄H₉)₂}₂], in which the gold atoms are linked by two bridging ligands Dtph. The central cyclic structural fragment of the dimer [Au₂S₄P₂] is additionally stabilized by the intramolecular aurophilic interaction Au?Au. Further supramolecular self-organization of the complex involves intermolecular aurophilic bonds Au?Au that serve to unite adjacent dinuclear molecules [Au₂{S₂P(O-iso-C₄H₉)₂}₂] with different spatial orientations into the polymer chains ([Au₂{S₂P(O-iso-C₄H₉)₂}₂]) _n . The thermal behavior of complex I was examined by synchronous thermal analysis under argon. The character of the thermolysis of the complex to reduced metallic gold as a final product was determined.     

Comparative sequence analysis and mutagenesis of Ethylene Forming Enzyme (EFE) 2-oxoglutarate/Fe(II)-dependent dioxygenase homologs

Background

Ethylene is one of the most used chemical monomers derived from non-renewable sources and we are investigating the possibility of producing it in yeast via the ethylene forming enzyme (EFE) from Pseudomonas syringae. To enable engineering strategies to improve the enzyme, it is necessary to identify the regions and amino acid residues involved in ethylene formation.

Results

We identified the open reading frame for the EFE homolog in Penicillium digitatum and also showed its capability of mediating ethylene production in yeast. The sequence of the EFE homologs from P.digitatum and P. syringae was compared to that of the non-functional EFE-homolog from Penicillium chrysogenum and ten amino acids were found to correlate with ethylene production. Several of these amino acid residues were found to be important for ethylene production via point mutations in P. syringae EFE. The EFE homolog from P. chrysogenum was engineered at 10 amino acid residues to mimic the P. syringae EFE, but this did not confer ethylene producing capability.Furthermore, we predicted the structure of EFE by homology to known structures of 2-oxoglutarate/Fe(II) dependent dioxygenases. Three of the amino acids correlating with ethylene production are located in the predicted 2-oxoglutarate binding domain. A protein domain specific for the EFE-class was shown to be essential for activity. Based on the structure and alanine substitutions, it is likely that amino acids (H189, D191 and H268) are responsible for binding the Fe(II) ligand.

Conclusion

We provide further insight into the structure and function of the ethylene forming (EFE) - subclass of 2-oxoglutarate/Fe(II) dependent dioxygenases. We conclude that residues in addition to the 10 identified positions implicated in ethylene production by sequence comparison, are important for determining ethylene formation. We also demonstrate the use of an alternative EFE gene. The data from this study will provide the basis for directed protein engineering to enhance the ethylene production capability and properties of EFE.

     

Landau’s Nobel Prize in Physics

Work of Lev Landau had a profound impact on the physics in 20th century. Landau had created the paradigms that had framed the conversations on the outstanding problems in physics for decades. He had laid foundations for our understanding of quantum matter like superfluidity, superconductivity and the theory of Fermi liquid. Here we present some Nobel Archive data on the winning nomination that led to the Nobel Prize in Physics in 1962.