Search

Designer multicomponent lipoplexes have recently emerged as especially promising transfection candidates, since they are from 10 to 100 times more efficient than binary complexes usually employed for gene delivery purposes. Here, we show, for the first time, that after internalization binary complexes of lower transfection potency remain in compact perinuclear endosomes, while multicomponent systems have intrinsic endosomal rupture properties that allow plasmid DNA to escape from endosomes with extremely high efficiency. Endosomal rupture results in an extraordinarily homogeneous distribution of unbound plasmid DNA throughout the cytoplasm and in the nucleus.

A systematic energy dispersive X-ray reflectometry study of different ruthenium phtalocyanine (RuPc)(sub 2) thin films was performed in order to investigate their reactivity with the oxidizing NO(sub x) gas. A preliminary ex situ analysis, consisting of the comparison between the morphological parameters of different films, before and after the exposure to the gas, was performed.

Gemini surfactants are characterized by two polar headgroups, connected by a spacer of various kinds, and two hydrophobic tails and it represent an interesting topic both for industry and research. The structure of fully hydrated solid supported cationic gemini 1a multibilayers is studied by means of energy dispersive X-ray diffraction.

The experiment was done where the X-ray reflectometry technique in its energy dispersive variant (EDXR) is used to study the morphological characteristics of dimeric ruthenium phthalocyanine thin films. The study gives information on the gas diffusion process through the film and the mechanisms of interaction between the film and gas molecules.

Research has been conducted on the methylrhenium trioxide heterogeneous compounds. The preparation of these compounds with poly(4-vinylpyridine) and polystyrene has been carried out and the results of the wide-angle X-ray diffraction analysis have demonstrated distorted octahedral conformation on the primary coordination sphere of the metal.

The wide-angle X-ray scattering technique was successfully used to examine the structure of solid pure osmium phthalocyanine. The solid amorphous material consists of dimeric units (PcOs)2 linked by a direct Os-Os double bond and stacked in columns to form couples of discrete assemblies of formula ((PcOs)2)n. (PcOs)2 is the first example of an Os(II)-Os(II) dimer subjected to a combined structural and magnetic study. Results also affirm that both ruthenium and osmium phthalocyanine could also be dimeric.

Molecular dynamics (MD) simulations were done to study the structure, conformation and conformational dynamics of a group of amorphous compounds called polyphosphazenes. The results were found to be in agreement with that of energy dispersive X-ray diffraction technique. The results confirmed that the backbone of poly(di(4-methoxyphenoxy)phosphazene) exists in the trans, cis, trans, cis conformation. MD simulation was also used to measure the radial distribution function of the compounds and compared with the X-ray method, MD was found to be more reliable.

We report a X-ray diffraction and molecular dynamics study on three choline-based bio-ionic liquids, choline formate, [Ch] [For], choline propanoate, [Ch][Pro], and choline butanoate, [Ch][But]. For the first time, this class of ionic liquids has been investigated by X-ray diffraction. Experimental and theoretical structure factors have been compared for each term of the series. Local structural organization has been obtained from ab initio calculations through static models of isolated ion pairs and dynamic simulations of small portions of liquids through twelve, ten, and nine ion pairs for [Ch][For], [Ch][Pro], and [Ch][But], respectively. All the theoretical models indicate that cations and anions are connected by strong hydrogen bonding and form stable ion pairs in the liquid that are reminiscent of the static ab initio ion pairs. Different structural aspects may affect the radial distribution function, like the local structure of ion pairs and the conformation of choline. When small portions of liquids have been simulated by dynamic quantum chemical methods, some key structural features of the X-ray radial distribution function were well reproduced whereas the classical force fields here applied did not entirely reproduce all the observed structural features. [ABSTRACT FROM AUTHOR]

In this study, we discuss, using molecular dynamics simulations and energy-dispersive x-ray diffraction data, how a conformational isomerism can dramatically alter the nanosegregation phenomena that take place in a prototypical ionic liquid. The diffraction patterns of liquid 2-methoxyethylammonium nitrate are compared with the results from molecular dynamics simulations. The simulations conditions and force field parameters have been varied producing different charge models and different populations of conformers of the cation. We show that, while the short range structure is relatively unchanged in the models, the long range aggregation phenomena deemed responsible for the appearance of low Q peaks in the X-ray patterns strongly depend on the choice of the charge model. In the title compound, the best agreement with the experiment, where no low Q peaks appear, occurs if the point charges are calculated using the gauche conformation of the cation, which is characterized by an intramolecular hydrogen bond between ammonium and ether groups. [ABSTRACT FROM AUTHOR]

The structural properties of liquid N-methyl pyrrolidone have been investigated by combining energy dispersive x-ray diffraction experiments and molecular dynamics simulations with generalized AMBER force field. A very good agreement between theoretical and experimental diffraction patterns was achieved. The analysis of the radial distribution functions shows that the methyl-carbonyl H-bond network observed in the crystal structure is partly preserved in the liquid structure. [ABSTRACT FROM AUTHOR]

Extended x-ray absorption fine structure (EXAFS) spectroscopy has been used to investigate the species and structures existing in a series of ZnCl2-H2O-NaCl solutions with different chloride/zinc ratios and in a solution of ZnCl2 in the protic ionic liquid ethyl ammonium nitrate (EAN). The average coordination numbers and distances of zinc species were determined from the analysis of the EXAFS data. In aqueous solution the number of chloride ions tightly bounded to Zn2+ is significantly related to the chloride/zinc ratio, and no inner complex formation between Zn2+ and Cl- ions has been detected for low ZnCl2 concentration (0.1 and 0.2 M). Conversely, in the same concentration range (0.13 M) the ZnCl2 species do not dissociate in EAN and the Zn2+ first coordination shell has two chloride ions and is completed by two oxygen atoms of the nitrate anion. The results of this investigation show that notwithstanding the existence of similar characteristics between EAN and water, the solvation properties of the two solvents are markedly different. [ABSTRACT FROM AUTHOR]

X-ray absorption spectroscopy (XAS) has been used to unveil the bromide ion local coordination structure in 1-alkyl-3-methylimidazolium bromide [Cnmim]Br ionic liquids (ILs) with different alkyl chains. The XAS spectrum of 1-ethyl-3-methylimidazolium bromide has been found to be different from those of the other members of the series, from the butyl to the decyl derivatives, that have all identical XAS spectra. This result indicates that starting from 1-buthyl-3-methylimidazolium bromide the local molecular arrangement around the bromide anion is the same independently from the length of the alkyl chain, and that the imidazolium head groups in the liquid ILs with long alkyl chains assume locally the same orientation as in the [C4mim]Br crystal. With this study we show that the XAS technique is an effective direct tool for unveiling the local structural arrangements around selected atoms in ILs. [ABSTRACT FROM AUTHOR]

We report for the first time joined energy dispersed x-ray and neutron diffraction experiments on a series of (both protiated and selectively deuteriated) 1-alkyl-3-methylimidazolium hexafluorophosphate salts (alkyl = butyl, hexyl, octyl) at ambient conditions. The x-ray experimental data are used to optimize the interaction potential used for running molecular dynamics simulations on these systems. Such a potential leads to a good description of neutron scattering data from the samples without additional refinement, thus further validating the potential definition. The molecular dynamics simulations were used to access microscopic information on the morphology of the proposed systems, thus probing the role played by alkyl chain length on the structure. The comparison of x-ray weighted and neutron-weighted computed diffraction patterns allows the rationalization of several diffraction features. Further insight into cation-anion coordination and alkyl chain conformational equilibrium is provided on the basis of the MD-derived snapshots, confirming and extending previously obtained results on these issues. [ABSTRACT FROM AUTHOR]

In this work, we report on the first x-ray diffraction study on liquid dimethyl carbonate. Diffraction spectra were collected with an energy-dispersive instrument, whose wide Q-range allows the structure determination of weakly ordered systems (such as liquids). The structural correlation in this liquid ranges up to about 20 Å. The observed patterns are interpreted with a structural model derived from classical molecular dynamics simulations. The simulations were run using OPLS force field, only slightly modified to restrain bond distances to the experimental values. The model structure function and radial distribution functions, averaged among the productive trajectory frames, are in very good agreement with the corresponding experimental ones. Molecular dynamics results show that the deviations from C2v cis-cis structure, predicted by ab initio calculations and observed by electron diffraction in the gas phase, are small. By analyzing the intra- and intermolecular pair distribution functions, it was possible to assign the peaks of the experimental radial distribution function to specific structural correlations, and to compute the different average intermolecular coordination numbers. The intermolecular methyl-carbonyl oxygen distance is thoroughly discussed to assess the presence of weak C–H...·O hydrogen bonds. [ABSTRACT FROM AUTHOR]

Recently, it has been postulated that a primary importance of the pH is for accomplishing efficient lipid-mediated translocation of nucleic acids across the endosomal membrane into the cytosol for transport to the nucleus. With the aim of providing insight into the postulated correlation between transfection efficiency, phase evolution of lipoplexes upon acidification, and DNA release, we investigated the pH dependence of the structure of low efficiency 1,2-dioleoyl-3-trimethylammonium-propane-dioleoylphosphocholine/DNA and high efficiency 3β-[N-(N′,N′-dimethylaminoethane)-carbamoyl]-cholesterol-dioleoylphosphatidylethanolamine/DNA lipoplexes by high-resolution synchrotron small-angle x-ray diffraction, while the extent of DNA release was estimated by means of electrophoresis on agarose gels. Here we show that upon acidification from physiological to acidic values (as those characteristic of endosomes), (i) the lamellar structure of lipoplexes was preserved with a decrease in the one-dimensional DNA packing density, reflecting a pH-induced contraction of interfacial area of lipid head groups and (ii) DNA was not released from lipoplexes. Distinct levels of transfection between lipoplexes were interpreted in terms of the different DNA-binding capacities of cationic liposomes. [ABSTRACT FROM AUTHOR]

A systematic energy dispersive x-ray reflectometry study of different ruthenium phthalocyanine (RuPc)2 thin films was performed in order to investigate their reactivity with the oxidizing NOx gas. A preliminary ex situ analysis, consisting of the comparison between the morphological parameters of different films (before and after the exposure to the gas), was performed. It suggests that a reaction involving two different mechanisms takes place. The following in situ (while fluxing the gas) reflectometry analysis confirms this hypothesis, and clarifies the temporal evolution, also revealing that the first mechanism is limited to the film surface, while the second is a bulk diffusion process. [ABSTRACT FROM AUTHOR]