Exotic species with explicit noble metal-noble gas-noble metal linkages.

We present a study of the isoelectronic Pt2Ng2F4 and [Au2Ng2F4]2+ species with noble gas atoms (Ng = Kr, Xe, Rn) acting as links bridging the two noble metal atoms. The stability of the species is investigated using several thermodynamic, kinetic and reactivity indicators. The results are compared against [AuXe4]2+, which is thermodynamically unstable in the gas phase but is stabilized in the solid state to the point that it has been experimentally detected as [AuXe4](Sb2F11)2 (S. Seidel and K. Seppelt, Science, 2000, 290, 117-118). Our results indicate that improving upon [AuXe4]2+, these exotic combinations between the a priori non-reactive noble metals and noble gases lead to metastable species, and, therefore, they have the possibility of existing in the solid state under adequate conditions. Our calculations include accurate energies and geometries at both the CCSD/SDDALL and MP2/SDDALL levels. We offer a detailed description of the nature of the bonding interactions using orbital and density-based analyses. The computational evidence suggests partially covalent and ionic interactions as the stabilization factors.

Entropy drives the insertion of ibuprofen into model membranes.

Understanding the migration of exogenous molecules to the interior of cell membranes is of pivotal importance to the design of new drugs and to the improvement of the capabilities of existing ones. This research dissects, from a molecular perspective, using classical molecular dynamics, the thermodynamic factors driving the insertion of ibuprofen into a model phosphatidylcholine membrane in an aqueous environment. We suggest an analysis of the insertion path that focuses on the net resulting force acting on the tertiary drug/water/membrane system; this allows us to understand the opposition that ibuprofen has to overcome as it inserts into the membrane. We provide conclusive evidence that entropy changes, arising from an increase of the number of possible microstates due to structural reorganization of the tertiary system, are the main factor driving this process. Our results allow us to unambiguously rationalize long standing conflicting experimental reports not understood up to now.

Spin-Orbit Coupling Effects in AumPtn Clusters (m + n = 4).

A study of AumPtn(m + n = 4) clusters with and without spin-orbit (SO) coupling using scalar relativistic (SR) and two component methods with the ZORA Hamiltonian was carried out. We employed the PW91 functional in conjunction with the all-electron TZ2P basis set. This paper offers a detailed analysis of the SO effects on the cluster geometries, on the LUMO-HOMO gap, on the charge distribution, and on the relative energies for each relativistic method. In general, SO coupling led to an energetic rearrangement of the species, to changes in geometries and structural preferences, to changes in the structural identity of the global minimum for the Au3Pt, AuPt3 and Pt4 cases, and to a reduction of relative energies among the clusters, an effect that appears stronger as the amount of Pt increases.

Theoretical tools to distinguish O-ylides from O-ylidic complexes in carbene-solvent interactions.

In this paper, we report the geometries and properties of 48 molecular species located on the MP2/6-311++G(d,p) PES of the fluorocarbene-(methanol)3 system. The structures were found by a combination of a stochastic search method, using a modified Metropolis acceptance test, and some hand constructed very symmetrical structures. We use several theoretical descriptors to categorize these species, focusing our attention on the interaction between the carbene carbon and the methanol oxygen, CcO, because this is the key interaction in the formation of O-ylides, ether products, and O-ylidic solvation complexes. These descriptors include natural charges and natural bond orbitals (NBO), CcO bond orders, CcO distances, energetic stabilities, and properties at bond critical points. Accordingly, the isomers were divided into four groups: ethers, fluorocarbene-methanol O-ylides, O-ylidic carbene-solvent complexes and hydrogen bonded carbene-solvent complexes. We found that the possibility of forming H-bonds among solvent molecules and between the carbene carbon and the hydrogen of the solvent molecule affects the stability, structure and nature of CcO interactions in O-ylides and O-ylidic complexes to the point of generating some diffuse borderlines between these two kinds of species. We determined which set of theoretical tools is suitable to better distinguish between them. Additionally, we clarify the nature of the relevant interactions in these species.

Unusual solvation through both p-orbital lobes of a carbene carbon.

As a result of a configurational space search done to explain the experimental evidence of transient specific solvation of singlet fluorocarbene amide with tetrahydrofuran, we found that the most stable structures consist in a group in which each oxygen of two tetrahydrofuran molecules act as electron donor to its respective empty p-orbital lobe of the carbene carbon atom, located at each side of the carbene molecular plane. This kind of species, which to our knowledge has not been reported before, explains very well the particular experimental characteristics observed for the transient solvation of this system. We postulate that the simultaneous interaction to both p-orbital lobes seems to confer a special stability to the solvation complexes, because this situation moves away the systems from the proximity of the corresponding transition states for the ylide products. Additionally, we present an analysis of other solvation complexes and a study of the nature of the involved interactions.

Potential energy surfaces of WC6 clusters in different spin states.

Stochastic explorations of the structural possibilities of neutral WC6 clusters in several spin states lead to very rich and complex potential energy surfaces, with geometries quite different from those of pure carbon clusters at the PBE0/def2-TZVP level. The global minimum is predicted to be a triplet-state semicyclic C6 conformation having every carbon in direct coordination to the W atom. Interaction energies are comparable to those of C7 clusters, revealing very strong W-C bonding. Our results suggest that C-C interactions in the clusters should be considered as intermediate between single and double bonds.

A combined experimental and computational study of the molecular interactions between anionic ibuprofen and water.

In this work, we report a detailed study of the microsolvation of anionic ibuprofen, Ibu(-). Stochastic explorations of the configurational spaces for the interactions of Ibu(-) with up to three water molecules at the DFT level lead to very rich and complex potential energy surfaces. Our results suggest that instead of only one preponderant structure, a collection of isomers with very similar energies would have significant contributions to the properties of the solvated drug. One of these properties is the shift on the vibrational frequencies of the asymmetric stretching band of the carboxylate group in hydrated Ibu(-) with respect to the anhydrous drug, whose experimental values are nicely reproduced using the weighted contribution of the structures. We found at least three types of stabilizing interactions, including conventional CO2(-)⋯H2O, H2O⋯H2O charge assisted hydrogen bonds (HBs), and less common H2O⋯H-C and H2O⋯π interactions. Biological water molecules, those in direct contact with Ibu(-), prefer to cluster around the carboxylate oxygen atoms via cyclic or bridged charge assisted hydrogen bonds. Many of those interactions are strongly affected by the formal carboxylate charge, resulting in "enhanced" HBs with increased strengths and degree of covalency. We found striking similarities between this case and the microsolvation of dymethylphosphate, which lead us to hypothesize that since microsolvation of phosphatidylcholine depends mainly on the formal charge of its ionic PO2(-) group in the polar head, then microsolvation of anionic ibuprofen and interactions of water molecules with eukaryotic cell membranes are governed by the same types of physical interactions.

Microsolvation of dimethylphosphate: a molecular model for the interaction of cell membranes with water.

We present an exhaustive stochastic search of the quantum conformational spaces of the (CH(3)O)(2)PO(2)(-) + nH(2)O (n = 1,2,3) systems. We uncover structural, conformational and energetic features of the problem. As in the isolated species, clusters containing the gauche-gauche (gg) conformation of dimethylphosphate (DMP(-)) are energetically preferred, however, contributions from hydrated gauche-anti (ga) and anti-anti (aa) monomers cannot be neglected because such structures are quite common and because they are close in energy to those containing the gg monomer. At least seven distinct types of O∙∙∙H-O-H contacts lead to DMP(-) ↔ water interactions that are always stabilizing, but not strong enough to induce significant changes in the geometries of either DMP(-) or water units. Our results lead us to postulate DMP(-) to be a suitable model to study explicit and detailed aspects of microsolvation of cell membranes.

A microscopic-macroscopic analysis for mixed energy transfer schemes in doped amorphous solids.

In this study we propose a methodology to treat mixed and more complex energy transfer schemes to reach the time-dependent intensities of luminescence in doped amorphous materials. We start outlining the differential equations for the time variation of microscopic probabilities of being in the relevant states and then transforming them into equations for the variation of the relevant macroscopic states populations and solve those equations. By this method, statistical approaches to the initially excited and up-converted states transient populations for up-conversion processes in the presence of cross relaxation in lanthanide-monodoped amorphous solid are calculated. The resultant formulations produce plots that show correct general tendencies and are coherent with what would be expected for systems exhibiting both mechanisms, hence they could be used in the fitting of experimental curves to calculate some important parameters. The new solution method is more convenient that the classical analysis because it permits the introduction of more realistic time dependent functions for the interacting optical centers and allows showing the time dependence of the macroscopic energy transfer rates in the equations for the dynamics of the involved populations. We apply our method to the particular case of mixing of up-conversion and cross relaxation phenomena; however, because of its general characteristics, we suggest it could be applied to other mixings or more complex schemes.

Structure and reactivity of the (1)Au6Pt clusters.

In this paper we report the geometries, properties, and reactivity descriptors of 12 structural isomers located on the MP2/SDDALL potential energy surface of the (1)Au(6)Pt binary clusters. A nonplanar, D(3d) symmetry, cyclohexane chairlike structure is predicted to be the global minimum. Binding energies per atom in the range ≈44-51 kcal/mol account for very stable clusters. The relative stability of the clusters is directly related to all global and local reactivity descriptors. All structures are predicted to have large electron affinities. The chemical environment of the Pt atom on the structures plays a central role in the resulting relative stabilities and global and local reactivities. Our results show that more peripheral Pt atoms are more likely to be involved in electron-accepting processes.

The response of electrons to structural changes.

The properties of a molecule are determined by the distribution of its electrons. This distribution can be described by the charge density, which is readily obtained from the wave functions derived by ab initio molecular orbital calculations. The charge density may be analyzed in a number of different fashions to give information about the effects of substituents, structural changes, and electronic excitation on the properties of molecules; one common procedure makes use of projection density or charge difference plots. Charge density also may be partitioned among atoms, and by numerical integration over appropriate volume elements one may obtain atomic charges, dipoles, kinetic energies, and other properties of the atoms in a molecule. Many chemical phenomena have been analyzed in terms of charge densities.

Understanding the nature of bonding interactions in the carbonic acid dimers.

Carbonic acid dimer, (CA)2, (H2CO3)2, helps to explain the existence of this acid as a stable species, different to a simple sum between carbon dioxide and water. Five distinct, well characterized types of intermolecular interactions contribute to the stabilization of the dimers, namely, C=O⋯H-O, H-O⋯H-O, C=O⋯C=O, C=O⋯O-H, and C-O⋯O-H. In many cases, the stabilizing hydrogen bonds are of at least the same strength as in the water dimer. We dissect the nature of intermolecular interactions and assess their influence on stability. For a set of 40 (H2CO3)2 isomers, C=O⋯H-O hydrogen bonds between the carbonyl oxygen in one CA molecule and the acidic hydrogen in the hydroxyl group at a second CA molecule are the major stabilizing factors because they exhibit the shortest interaction distances, the largest orbital interaction energies, and the largest accumulation of electron densities around the corresponding bond critical points. In most cases, these are closed-shell hydrogen bonds, however, in a few instances, some covalent character is induced. Bifurcated hydrogen bonds are a common occurrence in the dimers of carbonic acid, resulting in a complex picture with multiple orbital interactions of various strengths. Two anti-anti monomers interacting via the strongest C=O⋯H-O hydrogen bonds are the ingredients for the formation of the lowest energy dimers. Graphical Abstract Carbonic acid dimer, (CA)2, (H2CO3)2, helps explaining the existence of this acid as a stable species, different to a simple sum between carbon dioxide and water. Five distinct, well-characterized types of intermolecular interactions contribute to the stabilization of the dimers, namely, C=O⋯H-O, H-O⋯O-H, C=O⋯C=O, C=O⋯O-C, and C-O⋯O-C. In many cases, the stabilizing hydrogen bonds are of at least the same strength as in the water dimer.

Metastases to the breast, an uncommon diagnosis: what do radiologists need to know? / Metástasis en la mama, un diagnóstico infrecuente. ¿Qué deben saber los radiólogos?

OBJECTIVE: To analyze the imaging characteristics of histologically diagnosed metastases to the breast. MATERIAL AND METHODS: We selected patients histologically diagnosed with metastases to the breast in our diagnostic and interventional breast imaging unit between March 2010 and September 2018. RESULTS: A total of 9 patients (all women; mean age, 60 y; age range, 28-89 y) were diagnosed with metastases to the breast. In 1 (11.11%) case, the primary disease was diagnosed from the breast lesion. The primary tumors were melanoma (n=5), neuroendocrine tumor (n=2, one from the small bowel and one from the cervix), lung adenocarcinoma (n=1), and ovarian cancer (n=1). The clinical and imaging manifestations depend on the type of dissemination of disease and can simulate benign and malignant primary breast lesions. CONCLUSION: There is no specific imaging pattern for metastases to the breast that would help to orient the diagnosis. It is important to consider this etiological possibility if the patient has a history of a primary tumor in another organ.

Nanocrystalline cellulose-fullerene: Novel conjugates.

The covalent grafting of two amino-fullerene C60 derivatives (C60-LC-NH2 and C60-SC-NH2, LC=long chain and SC=short chain) onto the surface of TEMPO oxidized nanocrystalline cellulose (NCC-COOH) has been reported for the first time. These hybrids (NCC-LC-C60 and NCC-SC-C60) form stable colloidal suspensions at concentrations up to 0.5mg/mL and act as effective photosensitizers for singlet oxygen production as demonstrated by the oxidation of L-methionine-methyl ester to the corresponding sulphoxide. Using the same approach, in a one-pot reaction both a fluorescent target molecule (FITC-LC-NH2) and the C60-LC-NH2 derivative have been successfully attached covalently onto the NCC-COOH surface. These hybrids, which showed no cytotoxicity on MCF-7 human breast cancer cells could be good candidates in photodynamic cancer therapy.

Liposome-induced exfoliation of graphite to few-layer graphene dispersion with antibacterial activity.

Few-layer graphene aqueous dispersions are obtained by exploiting liposomes as effective exfoliating agents for graphite. Raman measurements evidence the presence of non-oxidized double layer graphene as well as amphiphilic phospholipid molecules organized in bilayers in the samples. TEM analyses confirmed that the obtained homogeneous graphene nanosheets are embedded in the liposomal bilayer. The as-prepared graphene aqueous dispersion is stable for days and demonstrates significant antibacterial activity against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) strains, with a reduction in the growth of S. aureus and E. coli as high as 60 and 78%, respectively.

Chemical modification of carbon nanomaterials (SWCNTs, DWCNTs, MWCNTs and SWCNHs) with diphenyl dichalcogenides.

Control over chemical functionalization is a crucial point in the field of nanotechnology. Herein, we present the covalent functionalization of several carbon nanoforms (single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes and carbon nanohorns) by means of diphenyl dichalcogenides. These ones show different reactivity to the nanomaterials and are able to modify their electronic properties depending on the electronegativity of the functionalizing heteroatom. Theoretical calculations were also performed to support the experimental results. All the modified structured nanocarbons were thoroughly characterized by TGA Raman, XPS, UV/Vis/nIR, IR and TEM techniques. Our findings propose a simple approach to functionalize carbon nanomaterials and, in the meantime, to tune their electronic properties.

The fragmentation pathways of protonated glycine: a computational study.

Numerous studies have demonstrated that protonated aliphatic amino acids, [H2NCHRCO2H + H]+, fragment in the gas phase to form iminium ions, H2N=CHR+. Unfortunately none of these studies have probed the structure of the neutral(s) lost as well as the mechanism of fragmentation. Three main mechanisms have been previously proposed: (1) loss of the combined elements of H2O and CO; (2) loss of dihydroxycarbene (HO)2C: and (3) loss of formic acid, HC(=O)OH. Herein, ab initio and density functional theory calculations have been used to calculate the key reactants, transition states, and products of these and several other competing reaction channels in the fragmentation of protonated glycine. The loss of the combined elements of H2O and CO is thermodynamically and kinetically favored over the alternative formic acid or (HO)2C fragmentation processes.

M2 delta-to-oxalate pi* conjugation in oxalate-bridged complexes containing M-M quadruple bonds.

The electronic structures of oxalate-bridged, quadruply-bonded dimolybdenum and ditungsten compounds have been investigated by a variety of computational methods employing density function theory (gradient corrected and time-dependent) which reveal the consequences of strong mixing of M2 delta and oxalate pi orbitals within extended chains and cyclic structures.

On the encapsulation of hydrocarbon components of natural gas within molecular baskets in water. The role of C-H···π interactions and the host's conformational dynamics in the process of encapsulation.

We examined the encapsulation of CH4, C2H6, C3H8 and iso-C4H10 in water, using four molecular baskets [1]-[4]. The baskets were shown to bind to hydrocarbon gases by forming favourable C-H···π contacts and, concurrently, adjusting the size of their cup-shaped platform.

Statistical approaches to the transient populations and to the macroscopic energy transfer rate for the upconversion phenomenon in monodoped amorphous solid.

In this article, statistical approaches to the first and the second excited state transient populations and to the temporal macroscopic energy transfer rate for the upconversion process in amorphous solid generic systems monodoped with trivalent lanthanide ions are reached. The plots of the expressions show general tendencies reported in the literature. The derivation and the analysis of the formalism allowed us to fulfill our main objective, that is, to make a theoretical study about the microscopic and statistical mechanisms present in the phenomenon and their relation with the classic kinetic analysis. The study shows that the inclusion of the minimum possible radius between two optical centers in a solid affects the initial slopes of the decay curves of the luminescence from the intermediate state. We also corroborate that the usual treatment of experimental data using direct equations for the dynamics of the populations in laser pulsed excitation experiments falls in the mistake of not considering the temporality of the macroscopic energy transfer rate. Finally, physical explanations are formulated about this temporal behavior and about the main factors that generate the characteristic simple exponential decay loss of the luminescence from the intermediate state.