Interconnected networks: structural and dynamic characterization of aqueous dispersions of dioctanoylphosphatidylcholine

Aqueous dispersions of the phospholipid dioctanoylphosphatidylcholine (diC 8PC) phase-separate below a cloud-point temperature, depending on lipid concentration. The lower phase is viscous and rich in lipid. The structure and dynamics of this system were explored via cryo-transmission electron microscopy (cryo-TEM), small-angle X-ray scattering (SAXS), and NMR. The lower phase comprises a highly interconnected tridimensional network of wormlike micelles. A molecular mechanism for the phase separation is suggested.     

Molecular field analysis and 3D-quantitative structure-activity relationship study (MFA 3D-QSAR) unveil novel features of bile acid recognition at TGR5

Bile acids regulate nongenomic actions through the activation of TGR5, a membrane receptor that is G protein-coupled to the induction of adenylate cyclase. In this work, a training set of 43 bile acid derivatives is used to develop a molecular interaction field analysis (MFA) and a 3D-quantitative structure-activity relationship study (3D-QSAR) of TGR5 agonists. The predictive ability of the resulting model is evaluated using an external set of compounds with known TGR5 activity, and six bile acid derivatives whose unknown TGR5 activity is herein assessed with in vitro luciferase assay of cAMP formation. The results show a good predictive model and indicate a statistically relevant degree of correlation between the TGR5 activity and the molecular interaction fields produced by discrete positions of the bile acid scaffold. This information is instrumental to extend on a quantitative basis the current structure-activity relationships of bile acids as TGR5 modulators and will be fruitful to design new potent and selective agonists of the receptor.     

Artarborol, a nor-caryophyllane sesquiterpene alcohol from Artemisia arborescens. stereostructure assignment through concurrence of NMR data and computational analysis

A nor-caryophyllane derivative, artarborol, has been isolated from wormwood (Artemisia arborescens) and its stereostructure established by using a combination of chemical derivatization, NMR data, molecular modeling, and quantum-mechanical calculations. In particular, comparison of experimental 13C NMR data with a Boltzmann-weighed average of 13C NMR chemical shifts, calculated by ab initio DFT method, supported the stereochemical assignment.     

Nearest-neighbor oxygen distances in liquid water and ice observed by x-ray Raman based extended x-ray absorption fine structure

We report the nearest-neighbor oxygen-oxygen radial distribution function (NN O-O RDF) of room temperature liquid water and polycrystalline ice Ih (-16.8 degrees C) obtained by x-ray Raman based extended x-ray absorption fine structure (EXAFS) spectroscopy. The spectra of the two systems were taken under identical experimental conditions using the same procedures to obtain the NN O-O RDFs. This protocol ensured a measurement of the relative distance distribution with very small systematic errors. The NN O-O RDF of water is found to be more asymmetric (tail extending to longer distances) with longer average distance (2.81 A for water and 2.76 A for ice) but a slightly shorter peak position (2.70 A for water and 2.71 A for ice). The refinement also showed a small but significant contribution from the linear O-H-O multiple scattering signal. The high sensitivity to short range distances of the EXAFS probe will set further restrictions to the range of possible models of liquid water.     

The Boson peak interpretation and evolution in confined amorphous water

We study the evolution of the Boson peak for water confined in cement paste obtained by means of Inelastic Neutron Scattering from room temperature to the deep supercooled regime. We analyze the data in terms of a universal-like model, developed for glass forming liquids in the frame of the energy landscape. In such a way it is possible to discriminate between the fragile and strong glass forming character of supercooled liquids and the dynamical crossover, fragile to strong, between them. Hence, we confirm the link between the Boson peak and the water polymorphism. In particular, the main result is represented by a crossover from a local energetic minima configuration to that characteristic of saddle points on going towards the deep supercooled regime up to the dynamical arrest.     

Dynamic fracture of concrete compact tension specimen: Experimental and numerical study

Compared to quasi-static loading concrete loaded by higher loading rates acts in a different way. There is an influence of strain-rate and inertia on resistance, failure mode and crack pattern. With increase of loading rate failure mode changes from mode-I to mixed mode. Moreover, theoretical and numerical investigations indicate that after the crack reaches critical velocity there is progressive increase of resistance and crack branching. These phenomena have recently been demonstrated and discussed by O?bolt et al. (2011) on numerical study of compact tension specimen (CTS) loaded by different loading rates. The aim of the present paper is to experimentally verify the results obtained numerically. Therefore, the tests and additional numerical studies on CTS are carried out. The experiments fully confirm the results of numerical prediction discussed in O?bolt et al. (2011). The same as in the numerical study it is shown that for strain rates lower than approximately 50/s the structural response is controlled by the rate dependent constitutive law, however, for higher strain rates crack branching and progressive increase of resistance is observed. This is attributed to structural inertia and not the rate dependent strength of concrete. Maximum crack velocity of approximately 800 m/s is measured before initiation of crack branching. The comparison between numerical and experimental results shows that relatively simple modeling approach based on continuum mechanics, rate dependent microplane model and standard finite elements is capable to realistically predict complex phenomena related to dynamic fracture of concrete.     

Simultaneous EEG-fMRI acquisition: how far is it from being a standardized technique?

Simultaneous EEG–fMRI is a powerful tool to study spontaneous and evoked brain activity because of the complementary advantages of the two techniques in terms of temporal and spatial resolution. In recent years, a significant number of scientific works have been published on this subject. However, many technical problems related to the intrinsic incompatibility of EEG and MRI methods are still not fully solved. Furthermore, simultaneous acquisition of EEG and event-related fMRI requires precise synchronization of all devices involved in the experimental setup. Thus, timing issue must be carefully considered in order to avoid significant methodological errors.

The aim of the present work is to highlight and discuss some of technical and methodological open issues associated with the combined use of EEG and fMRI. These issues are presented in the context of preliminary data regarding simultaneous acquisition of event-related evoked potentials and BOLD images during a visual odd-ball paradigm.     

Modular DNA-programmed assembly of linear and branched conjugated nanostructures

A new strategy for self-assembly and covalent coupling of encoded molecular modules into nanostructures with predetermined connectivity has been developed. The method uses DNA-functionalized oligo(phenylene ethynylene)-derived organic modules for controlling the assembly and covalent coupling of multiple modules. Rigid linear modules (LM) and tripoidal modules (TM) were functionalized with short oligonucleotides at each terminus. They can hybridize and thereby link up modules containing complementary sequences. Each terminus of the oligo(phenylene ethynylene) modules also consists of a salicylaldehyde moiety, which can form metal-salen complexes with other modules. The salicylaldehyde groups of two modules are brought in proximity when their adjoining DNA sequences are complementary, and they selectively form a manganese-salen complex in the presence of ethylenediamine and manganese acetate. The resulting structures consist of a matrix of linear and branched oligo(phenylene ethynylene)s which are linked by conjugated and rigid manganese-salen complexes. These nanostructures are potential conductors for applications in molecular electronics.