Wormlike reverse micelles in lecithin/bile salt/water mixtures in oil

Knowing the ability of water and bile salts to promote the reverse wormlike micelle growth in lecithin/water or lecithin/bile salt mixtures in oil, this work was aimed at elucidating the association properties of the three solutes lecithin, water and the bile salt (BS) sodium deoxycholate in cyclohexane. By systematically changing the fraction of the two additives (i.e.: water and BS) we could identify a region at low additive/lecithin molar ratios where stable wormlike micelle dispersions were formed. Small angle X-ray scattering and oscillatory rheology measurements demonstrated that the ability of bile salt and water to transform the originally spherical lecithin reverse micelles into wormlike micelles and thereby impart to the sample viscoelastic properties is preserved in the three-solute mixture. The results suggest that reverse micelle including both bile salt and water are formed in this system. Reasonably the two primers interact with the same region of the lecithin headgroups and are complementary in altering the packing parameter of the amphiphile to values suitable for the formation of cylindrical aggregates

Celule Stem în procesul de regenerare a ţesuturilor scheletice

The ability of grafts containing autogenous bone marrow cells; alogenous cord blood cells with alogenic demineralized bone to stimulate bone formation in the critical rabbit radial bone defect was studied. The experimental research was carried out on 55 adults (12-13 months), rabbits (body weight 3,0-3,5kg). The radial bone was cut transversely and made a bone defect of 20 mm long. The animals were divided in fi ve experimental groups: fi rst – was injected Dulbecco Modifi ed Eagle Medium (DMEM); second – morselized autogenous cortico-cancelous bone from iliac crest; third – decalcifi ed bone matrix and autogenous bone marrow cells; the fourth - decalcifi ed bone matrix and alogenic cord blood cells; the fi fth – the autogenous bone marrow cells. The combination of the grafts from demineralized morcelized alogenous bone with autogenous bone marrow cells or cord blood cells provides active and uniform osteogenesis in to the bone defect comparable with the autogenous cancelous bone. In cases where was used only the suspension of bone marrow cells the osteogenesis was active, but the bone formation is more slowly and not uniform

Host-Guest Supramolecular Dendrimers

The 11th International Electronic Conference on Synthetic Organic Chemistry session Supramolecular ChemistryThe formation of new supramolecular dendrimers from interlocked host/guest unimers is reported. Unimer entities have two host binding sites (ßCD) and two guest binding sites (two adamantly or two p-tert-butylbenzoate moities). Hosts and guest residues are linked through an EDTA bridge. The formation of dendrimer-like (Cayley tree) structures is demonstrated by TEM measurements.The authors from USC thank the Ministerio de Ciencia y Tecnología (Project MAT2004-04606) and Xunta de Galicia (PGIDIT05PXIC26201PN) for financial support. The authors from ‘La Sapienza’ thank the MIUR financial supports (FIRB project RBIN04PWNC and PRIN 2006).We also thank for the Spain-Italy Integrated Action grant

EXAFS and molecular dynamics studies of ionic solutions

This paper focuses on recent advances in the X-ray absorption spectroscopy (XAS) analysis of ionic solutions. The asymmetry of radial distribution functions g(r) associated with the solvent molecules surrounding the ions has to be taken into account to perform a reliable structural analysis. Molecular dynamics (MD) simulations provide reliable g(r)'s which can be used as starting models in the XAS data analysis. The combined MD-XAS investigation reduces meaningfully the indetermination of the structural parameters, especially for coordination numbers and Debye-Waller factors. Double-electron excitation channels can be present in the XAS spectra of ionic solutions and they have to be accounted for in the background extraction. The ability of the XAS technique to probe three-body correlation functions in ionic solutions with the aid of MD g(r1, r2, θ) has been shown. The analysis of the low-k region of the spectra allows the detection of a weak but significant hydrogen structural signal. The XAS technique is especially well suited to determine the detailed shape of the nearest-neighbor peak in the atom-atom pair correlation functions of disordered systems. The information that they contain about the short-range atom-atom pairwise interactions can be very helpful for specifying and properly modifying model potentials used in MD simulations

Evidence of three-body correlation functions in Rb+ and Sr2+ acetonitrile solutions

The local structure of Sr2+ and Rb+ ions in acetonitrile has been investigated by x-ray absorption spectroscopy (XAS) and molecular dynamics simulations. The extended x-ray absorption fine structure above the Sr and Rb K edges has been interpreted in the framework of multiple scattering (MS) formalism and, for the first time, clear evidence of MS contributions has been found in noncomplexing ion solutions. Molecular dynamics has been used to generate the partial pair and triangular distribution functions from which model χ(k) signals have been constructed. The Sr2+ and Rb+ acetonitrile pair distribution functions show very sharp and well-defined first peaks indicating the presence of a well organized first solvation shell. Most of the linear acetonitrile molecules have been found to be distributed like hedgehog spines around the Sr2+ and Rb+ ions. The presence of three-body correlations has been singled out by the existence of well-defined peaks in the triangular configurations. Excellent agreement has been found between the theoretical and experimental data enforcing the reliability of the interatomic potentials used in the simulations. These results demonstrate the ability of the XAS technique in probing the higher-order correlation functions in solution. © 1999 American Institute of Physics

Collective diffusion and self-diffusion coefficients comparison to separate interactions and micellar size effects on ionic micelle diffusivities: Cylindrical micelles of sodium taurodeoxycholate

Collective and self-diffusion coefficients of sodium taurodeoxycholate (NaTDC) and taurocholate (NaTC) D2O micellar solutions were measured, as a function of ionic strength (0-0.6 M NaCl added) and bile salt concentration, by means of quasielastic light-scattering and H-1 pulse-gradient-spin-echo nuclear magnetic resonance measurements. A data analysis, performed by using a simple model of monodisperse Brownian particles with hydrodynamic interaction and hard-core repulsion, allowed us to separate the effect of micellar size and particle interactions at low ionic strength. An estimation of the hydrodynamic radius and of the Debye-Huckel interaction strength was obtained without extrapolating the data to the critical micellar concentration. A discussion based on a hard-body interacting cylinder model suggests that attractive interactions influence the NaTDC diffusivities at high NaCl concentration. With respect to NaTC, at the same ionic strength, greater effective charge and size characterize the NaTDC micellar aggregates that, moreover, show a more extended growth as a function of NaCl and bile salt concentration. (C) 2003 American Institute of Physics

Complete spectrum of multielectron excitations at the Br- K edge x-ray absorption spectra

We report the direct measurement by x-ray-absorption spectroscopy of the complete spectrum of multielectron excitations at the Br- K edge. Measurements of crystalline tetramethylammonium bromide were made at 30 K and room temperature. The latter spectrum has been found to be largely dominated by the opening of multielectron excitation channels, thus providing a very good model of the Br- atomic background which can be used in the analysis of ionic bromine compounds. The complete sequence of multielectron transitions has been clearly identified and compared with theoretical determinations. A direct experimental determination of the [1s4p] double-electron excitation channel has been performed at the Br- K edge

About the albumin structure in solution: cigar Expanded form versus heart Normal shape

A structural comparison between the Normal and the Expanded isomers of the human serum albumin has been carried out by using small angle X-ray scattering (SAXS) and light scattering (LS) techniques. Geometrical bodies, recovered structures (GA_STRUCT code) and rigid body modeling (CRYSOL and BUNCH software) were used to obtain low-resolution 3D structures from one-dimensional scattering patterns. These restored shapes were also exploited to perform a correlation between SAXS and LS data. By attempting a detailed description of globular and unfolded protein structures in solution, we tried to propose a suitable approach to follow the path of folding/unfolding processes and to isolate and characterize possible partially folded intermediate states

Comment on "Two-Dimensional NMR study on the structures of micelles of sodium taurocholate"

A polemic. The paper "Two-Dimensional NMR Study on the Structures of Micelles of Sodium Taurocholate" by N. Funasaki et al. (2004) demands some remarks that, in the authors opinion, throw doubts on the conclusions of this article. The authors do not want to pursue this polemic, even because they believe that these remarks are sufficient to promote a reinterpretation of the NMR and GFC data, at least. On the other hand, the conclusions are unwarranted and the optimistic sentence (see the Abstr. and also p 442) "Thus, a novel NMR method in surfactant chem. has provided the first step to resolve the 20-years debate about the structures of dimers and micelles of TC." is unfounded in their opinion