Hydrolysis-Polycondensation in Binary Phosphorus Alkoxides—TEOS System Studied by GC-MS

It is well known that various phosphorus precursors exhibit different reactivities towards hydrolysis-polycondensation in acidic media. The hydrolysis-condensation in binary P-alkoxides—TEOS system was studied by GC-MS, in relation to the mentioned reactivity. As P-precursors, the following reagents were used: PO(OMe)₃, PO(OEt)₃, PO(OBu)₃, P(OEt)₃ and HOP(OMe)₂. PO(OMe)₃, PO(OEt)₃ and PO(OBu)₃ do not hydrolyze, but change the TEOS hydrolysis-polycondensation ratio. P(OEt)₃ partially hydrolyzes and transforms into a very stable HOP(OEt)₂ form, while HOP(OMe)₂ reacts very fast with nonparental solvent and undergoes transesterification. Si–O–P bonds have not been observed in early stages of hydrolysis-polycondensation. However, the gelling tendency is strongly influenced by the P-precursor.     

Influence of Film Structure and Precursor Composition on Rhodamine B Retention in Dye-Dopped Ormosils

The interplay between the chemical structure of the precursors, internal organization in the end materials and dye retention was investigated for composites (ormosils) doped with rhodamine B. Besides formulations with triethoxysilanes (RTES) only, we synthesized as well organic–inorganic hybrids with addition of titanium isopropoxide (TIP) and maleic anhydride (MA). The organic (R) functionality of RTES was changed from methyl (MeTES), to phenyl (PTES) and octyl (OTES). Atomic force microscopy and electron microscopy, coupled with thermogravimetric analysis prove that hydrophobicity increase stimulates the transition of film structure: from well-defined, compact particles (for MeTES), to a mixture of porous particles and non-granular material (for MeTES/PTES), with extreme results observed for octyl-based composites. For this latter, the apparent homogeneity comes from cluster-like organization, where the primary entities are pseudo—granules produced by hydrophobic interactions of oligomeric siloxanes. Controlling the composition and gelation procedure resulted in doped composites with good optical transparency and rhodamine B fluorescence emission bands at around 580 nm. Dye transport inside the inorganic structure is not facilitated when: (a) the particles have a compact (nonporous) inner structure and (b) the recipe does not contain the TIP/MA combination. For silica-based films, the dye is located in the macropores (between the granules) of the material and could be easy removed by washing with acetone. On the contrary, using TIP/MA changes not only the internal composition of the granular-like material (by creating a microporous titania-rich outer-shell of the particles) but also the affinity of the Rh-B to permeate and reside inside these new structures.     

Structural organization of cetyltrimethylammonium sulfate in aqueous solution: The effect of Na2SO4

We used dynamic light scattering (DLS), steady-state fluorescence, time resolved fluorescence quenching (TRFQ), tensiometry, conductimetry, and isothermal titration calorimetry (ITC) to investigate the self-assembly of the cationic surfactant cetyltrimethylammonium sulfate (CTAS) in aqueous solution, which has SO(2-)4 as divalent counterion. We obtained the critical micelle concentration (cmc), aggregation number (N(agg)), area per monomer (a0), hydrodynamic radius (R(H)), and degree of counterion dissociation (alpha) of CTAS micelles in the absence and presence of up to 1 M Na2SO4 and at temperatures of 25 and 40 degrees C. Between 0.01 and 0.3 M salt the hydrodynamic radius of CTAS micelle R(H) approximately 16 A is roughly independent on Na2SO4 concentration; below and above this concentration range R(H) increases steeply with the salt concentration, indicating micelle structure transition, from spherical to rod-like structures. R(H) increases only slightly as temperature increases from 25 to 40 degrees C, and the cmc decreases initially very steeply with Na2SO4 concentration up to about 10 mM, and thereafter it is constant. The area per surfactant at the water/air interface, a0, initially increases steeply with Na2SO4 concentration, and then decreases above ca. 10 mM. Conductimetry gives alpha = 0.18 for the degree of counterion dissociation, and N(agg) obtained by fluorescence methods increases with surfactant concentration but it is roughly independent of up to 80 mM salt. The ITC data yield cmc of 0.22 mM in water, and the calculated enthalpy change of micelle formation, Delta H(mic) = 3.8 kJ mol(-1), Gibbs free energy of micellization of surfactant molecules, Delta G(mic) = -38.0 kJ mol(-1) and entropy TDelta S(mic) = 41.7 kJ mol(-1) indicate that the formation of CTAS micelles is entropy-driven.     

Analysis of protein interaction networks using mass spectrometry compatible techniques

The ability to map protein-protein interactions has grown tremendously over the last few years, making it possible to envision the mapping of whole or targeted protein interaction networks and to elucidate their temporal dynamics. The use of mass spectrometry for the study of protein complexes has proven to be an invaluable tool due to its ability to unambiguously identify proteins from a variety of biological samples. Furthermore, when affinity purification is combined with mass spectrometry analysis, the identification of multimeric protein complexes is greatly facilitated. Here, we review recent developments for the analysis of protein interaction networks by mass spectrometry and discuss the integration of different bioinformatic tools for predicting, validating, and managing interaction datasets.     

相对论平均场理论对Pb同位素位移的研究

运用变形的相对论平均场理论研究了Pb同位素链的基态性质. 对关联的处理采用了BCS方法, 不成对核子的处理运用了“阻塞”法. 计算的结果很好地符合了实验上Pb的平均结合能, 中子分离能, 同位素位移. 接着从原子核的微观结构出发, 比较详细地研究了Pb链同位素位移出现反常扭折这一重要性质的物理机制.     

Characterization of the water-soluble comb–linear interpolyelectrolyte nanoaggregates by Monte Carlo simulations and fluorescence probe techniques

Insight into the microstructure of the aggregate formed by the Coulombic interaction between the cationic comb copolymer poly(acrylamide-co-[3-(methacryloylamino) propyl]trimethylammonium chloride)-graft-polyacrylamide, P(AM-co-MAPTAC)-g-PAM, and the anionic polyelectrolyte poly(sodium acrylate), NaPA, was provided by Monte Carlo simulations and the fluorescence probe technique. The computational outcome revealed a core–shell organization of the comb copolymer, with an indefinite boundary between the inner and outer region. The copolymer had a spherical shape, and its backbone moiety adopted an extended conformation. The spatial extension of the copolymer and the core region contracted when association with the oppositely charged polyelectrolyte occurred. The fluorescence probes 2-dimethylamino-6-propionylnaphthalene, PRODAN, and 1-anilinonaphthalene-8-sulfonic acid, ANS, exhibited a specific interaction with the complex. A lower polarity in the polyelectrolyte complex as compared with the water polarity was sensed by the fluorescence probes, a feature which was attributed to a certain compaction of the AM-co-MAPTAC part of comb copolymer.