Local Cosmic Strings from Pseudo-Anomalous U(1)

Local cosmic strings solutions are introduced ina model with a peudo-anomalous U(1) gauge symmetry. Sucha symmetry is present in many superstringcompactification models. The coupling of those strings with the axion necessary in order to cancel theanomalies does not prevent them from being local, eventhough their energy per unit length is found to divergelogarithmically. I discuss briefly the formation of such strings and the phenomenologicalconstraints that apply to their parameters.     

Phloroglucinol as a Potential Candidate against Trypanosoma congolense Infection: Insights from In Vivo,In Vitro,Molecular Docking and Molecular Dynamic Simulation Analyses

Sub-Saharan Africa is profoundly challenged with African Animal Trypanosomiasis and the available trypanocides are faced with drawbacks, necessitating the search for novel agents. Herein, the chemotherapeutic potential of phloroglucinol on T. congolense infection and its inhibitory effects on the partially purified T. congolense sialidase and phospholipase A₂ (PLA₂) were investigated. Treatment with phloroglucinol for 14 days significantly (p < 0.05) suppressed T. congolense proliferation, increased animal survival and ameliorated anemia induced by the parasite. Using biochemical and histopathological analyses, phloroglucinol was found to prevent renal damages and splenomegaly, besides its protection against T. congolense-associated increase in free serum sialic acids in infected animals. Moreover, the compound inhibited bloodstream T. congolense sialidase via mixed inhibition pattern with inhibition binding constant (Ki) of 0.181 µM, but a very low uncompetitive inhibitory effects against PLA₂ (Ki > 9000 µM) was recorded. Molecular docking studies revealed binding energies of −4.9 and −5.3 kcal/mol between phloroglucinol with modeled sialidase and PLA₂ respectively, while a 50 ns molecular dynamics simulation using GROMACS revealed the sialidase-phloroglucinol complex to be more compact and stable with higher free binding energy (−67.84 ± 0.50 kJ/mol) than PLA₂-phloroglucinol complex (−77.17 ± 0.52 kJ/mol), based on MM-PBSA analysis. The sialidase-phloroglucinol complex had a single hydrogen bond interaction with Ser453 while none was observed for the PLA₂-phloroglucinol complex. In conclusion, phloroglucinol showed moderate trypanostatic activity with great potential in ameliorating some of the parasite-induced pathologies and its anti-anemic effects might be linked to inhibition of sialidase rather than PLA₂.     

A Metabolomic Analysis of Cirrhotic Ascites

Ascites is a common complication of decompensated liver cirrhosis, and yet relatively little is known about its biochemical composition. We conducted two metabolomic investigations, comparing the profile of ascites from 33 cirrhotic patients and postoperative peritoneal drainage fluid from 33 surgical patients (Experiment 1). The profile of paired ascites and plasma was also compared in 17 cirrhotic patients (Experiment 2). Gas chromatography–mass spectrometry-based metabolomics identified 29 metabolites that significantly characterized ascites fluid, whether postoperative drainage fluid or plasma were used as controls. Ten elevated amino acids (glutamine, proline, histidine, tyrosine, glycine, valine, threonine, methionine, lysine, phenylalanine) and seven diminished lipids (laurate, myristate, palmitate, oleate, vaccenate, stearate, cholesterol) largely comprised the cirrhotic ascites metabolomic phenotype that differed significantly (adjusted p < 0.002 to 0.03) from peritoneal drainage fluid or plasma. The pattern of upregulated amino acids in cirrhotic ascites did not indicate albumin proteolysis by peritoneal bacteria. Bidirectional clustering showed that the more severe the cirrhosis, the lower the lipid concentration in ascitic fluid. The metabolomic compartment of ascites in patients with decompensated cirrhosis is characterized by increased amino acids and decreased lipids. These novel findings have potential relevance for diagnostic purposes.     

Molecular cyclo-P3 complexes of the rare-earth elements via a one-pot reaction and selective reduction

Synthesis of new organo-lanthanide polyphosphides with an aromatic cyclo-[P₄]²⁻ moiety and a cyclo-[P₃]³⁻ moiety is presented. For this purpose, the divalent Ln^II-complexes [(NON)Ln^II(thf)₂] (Ln = Sm, Yb) ((NON)²⁻ = 4,5-bis(2,6-diisopropylphenyl-amino)-2,7-di-tert-butyl-9,9-dimethylxanthene) and trivalent Ln^III-complexes [(NON)Ln^IIIBH₄(thf)₂] (Ln = Y, Sm, Dy) were used as precursors in the reduction process of white phosphorus. While using [(NON)Ln^II(thf)₂] as a one-electron reducing agent the formation of organo-lanthanide polyphosphides with a cyclo-[P₄]²⁻ Zintl anion was observed. For comparison, we investigated a multi-electron reduction of P₄ by a one-pot reaction of [(NON)Ln^IIIBH₄(thf)₂] with elemental potassium. As products molecular polyphosphides with a cyclo-[P₃]³⁻ moiety were isolated. The same compound could also be obtained by reducing the cyclo-[P₄]²⁻ Zintl anion within the coordination sphere of Sm^III in [{(NON)Sm^III(thf)₂}₂(μ-η⁴:η⁴-P₄)]. Reduction of a polyphosphide within the coordination sphere of a lanthanide complex is unprecedented. Additionally, the magnetic properties of the dinuclear Dy^III-compound bearing a bridging cyclo-[P₃]³⁻ moiety were investigated.

Synthesis of new organo-lanthanide polyphosphides with an aromatic cyclo-[P₄]²⁻ moiety and a cyclo-[P₃]³⁻ moiety is presented.     

Electric fields drive bond homolysis

Electric fields have been used to control and direct chemical reactions in biochemistry and enzymatic catalysis, yet directly applying external electric fields to activate reactions in bulk solution and to characterize them ex situ remains a challenge. Here we utilize the scanning tunneling microscope-based break-junction technique to investigate the electric field driven homolytic cleavage of the radical initiator 4-(methylthio)benzoic peroxyanhydride at ambient temperatures in bulk solution, without the use of co-initiators or photochemical activators. Through time-dependent ex situ quantification by high performance liquid chromatography using a UV-vis detector, we find that the electric field catalyzes the reaction. Importantly, we demonstrate that the reaction rate in a field increases linearly with the solvent dielectric constant. Using density functional theory calculations, we show that the applied electric field decreases the dissociation energy of the O–O bond and stabilizes the product relative to the reactant due to their different dipole moments.

We demonstrate that electric fields can homolytically cleave a peroxide bond in different solvents with a rate that is proportional to the solvent dielectric constant.     

DFT-INDO/S modeling of new high molar extinction coefficient charge-transfer sensitizers for solar cell applications

A new ruthenium(II) complex, tetrabutylammonium [ruthenium (4-carboxylic acid-4'-carboxylate-2,2'-bipyridine)(4,4'-di(2-(3,6-dimethoxyphenyl)ethenyl)-2,2'-bipyridine)(NCS)(2)] (N945H), was synthesized and characterized by analytical, spectroscopic, and electrochemical techniques. The absorption spectrum of the N945H sensitizer is dominated by metal-to-ligand charge-transfer (MLCT) transitions in the visible region, with the lowest allowed MLCT bands appearing at 25 380 and 18 180 cm(-1). The molar extinction coefficients of these bands are 34 500 and 18 900 M(-1) cm(-1), respectively, and are significantly higher when compared to than those of the standard sensitizer cis-dithiocyanatobis(4,4'-dicarboxylic acid-2,2'-bipyridine)ruthenium(II). An INDO/S and density functional theory study of the electronic and optical properties of N945H and of N945 adsorbed on TiO(2) was performed. The calculations point out that the top three frontier-filled orbitals have essentially ruthenium 4d (t(2g) in the octahedral group) character with sizable contribution coming from the NCS ligand orbitals. Most critically the calculations reveal that, in the TiO(2)-bound N945 sensitizer, excitation directs charge into the carboxylbipyridine ligand bound to the TiO(2) surface. The photovoltaic data of the N945 sensitizer using an electrolyte containing 0.60 M butylmethylimidazolium iodide, 0.03 M I(2), 0.10 M guanidinium thiocyanate, and 0.50 M tert-butylpyridine in a mixture of acetonitrile and valeronitrile (volume ratio = 85:15) exhibited a short-circuit photocurrent density of 16.50 +/- 0.2 mA cm(-2), an open-circuit voltage of 790 +/- 30 mV, and a fill factor of 0.72 +/- 0.03, corresponding to an overall conversion efficiency of 9.6% under standard AM (air mass) 1.5 sunlight, and demonstrated a stable performance under light and heat soaking at 80 degrees C.     

Variational Markov chain Monte Carlo for Bayesian smoothing of non-linear diffusions

In this paper we develop set of novel Markov chain Monte Carlo algorithms for Bayesian smoothing of partially observed non-linear diffusion processes. The sampling algorithms developed herein use a deterministic approximation to the posterior distribution over paths as the proposal distribution for a mixture of an independence and a random walk sampler. The approximating distribution is sampled by simulating an optimized time-dependent linear diffusion process derived from the recently developed variational Gaussian process approximation method. The novel diffusion bridge proposal derived from the variational approximation allows the use of a flexible blocking strategy that further improves mixing, and thus the efficiency, of the sampling algorithms. The algorithms are tested on two diffusion processes: one with double-well potential drift and another with SINE drift. The new algorithm’s accuracy and efficiency is compared with state-of-the-art hybrid Monte Carlo based path sampling. It is shown that in practical, finite sample applications the algorithm is accurate except in the presence of large observation errors and low observation densities, which lead to a multi-modal structure in the posterior distribution over paths. More importantly, the variational approximation assisted sampling algorithm outperforms hybrid Monte Carlo in terms of computational efficiency, except when the diffusion process is densely observed with small errors in which case both algorithms are equally efficient.     

Dimensional crossover driven by an electric field

We study the steady-state dynamics of the Hubbard model driven out of equilibrium by a constant electric field and coupled to a dissipative heat bath. For a very strong field, we find a dimensional reduction: the system behaves as an equilibrium Hubbard model in lower dimensions. We derive steady-state equations for the dynamical mean-field theory in the presence of dissipation. We discuss how the electric field induced dimensional crossover affects the momentum resolved and integrated spectral functions, the energy distribution function, as well as the steady current in the nonlinear regime.     

Molecular and supramolecular dynamics of hybrid organic-inorganic interfaces for the rational construction of advanced hybrid nanomaterials

Today the capability to rationally design and construct hybrid materials utilizing a performance-property driven methodology is strongly dependent on our ability to control the structure and the dynamics of hybrid interfaces. This control needs a deep knowledge of their molecular and supramolecular dynamics that must be evaluated in situ, in the soft matter or colloidal states. For this purpose the use of modern methodologies of characterization such as time resolved synchrotron experiments and advanced pulsed field gradient NMR methods (DOSY) is particularly relevant. In this critical review, two important examples are discussed. They concern, first, the study of surface capping organic components' affinity towards nanoparticle surfaces by DOSY NMR. The knowledge and therefore the tuning of this affinity is paramount because it controls solubility, transferability and stability of colloidal dispersions of nanoparticles (NPs). In the second part, the mechanism of micellar templated formation of hybrid mesophases will be discussed in the frame of the main results obtained via in situ SAXS (107 references).