Application of the thin-shell formulation to the numerical modeling of Stern layer in biomolecular electrostatics

In this article, the thin-shell formulation is applied to efficiently modeling the Stern layer within computational algorithms oriented toward the boundary element solution of the linearized Poisson-Boltzmann equation. The attention is focused on the calculation of the electrostatic potential in proximity to a biomolecule immersed in an electrolyte medium. Following the proposed approach, the Stern layer is made to collapse to a zero-thickness region (two-dimensional surface) with interface conditions linking the electrostatic potential over the molecular and the bulk ion accessible surfaces. Advantages lie in the limitation of divergent integral problems and in the halving of the unknown number, with a significant impact on computational time and memory requirements when modeling large biomolecules.     

A deep insight into the mechanism of the acid‐catalyzed rearrangement of the Z‐phenylhydrazone of 5‐amino‐3‐benzoyl‐1,2,4‐oxadiazole in a non‐polar solvent

The conversion of the Z‐phenylhydrazone of 5‐amino‐3‐benzoyl‐1,2,4‐oxadiazole ( 1a ) into the relevant 1,2,3‐triazole ( 2a) has been quantitatively studied in toluene in the presence of several halogenoacetic acids ( HAA s, 3a – h ). Again, the occurrence of two reaction pathways has been pointed out: they require one or two moles of acid, respectively, thus repeating the situation previously observed in the presence of trichloroacetic acid. The observed rate constant ratios (k_III/k_II) are only slightly affected by the nature of the acid used. To gain a deeper insight into the action of the acids used we have measured the association constants of the HAA s ( 3a – h) with 4‐nitroaniline ( 4 ) in toluene. Also in this case, the formation of two complexes requiring one (K₂) or two (K₃) moles of acid has been evidenced, but now the K₃/K₂ ratios are significantly affected by the strength of the acid examined. The variation of the K₃/K₂ ratios larger than those concerning the k_III/k_II ratios appears useful to enlighten the very nature of the acid‐catalyzed pathways in toluene, which has been elucidated also carrying out the rearrangement in the presence of mixtures of tribromo‐ and trichloro‐acetic acids at different concentrations. Copyright © 2010 John Wiley & Sons, Ltd.     

Purely linear response of the quantum Hall current to space-adiabatic perturbations

Letters in Mathematical Physics - We provide an algorithm that factorizes one-dimensional quantum walks on an arbitrary but fixed cell structure into a protocol of two basic operations: a fixed...     

Isomerization and rearrangement of (E)‐ and (Z)‐phenylhydrazones of 3‐benzoyl‐5‐phenyl‐1,2,4‐oxadiazole: evidence for a ‘new’ type of acid‐catalysis by copper(II) salts in mononuclear rearrangement of heterocycles

A kinetic investigation in methanol of the title reaction has evidenced the occurrence of two processes: the 1‐ E 1‐ Z isomerization and the rearrangement of the (Z)‐isomer into the relevant 4‐benzoylamino‐2,5‐diphenyl‐1,2,3‐triazole ( 1‐ Z → T ). The latter reaction is in line with the ability of the (Z)‐phenylhydrazones of 3‐benzoyl‐1,2,4‐oxadiazoles to undergo the so called mononuclear rearrangement of heterocycles (MRH). The occurrence of both the examined reactions is dependent on a Lewis‐acid‐catalysis. The obtained results have shown the possibility of a ‘new’ type of acid‐catalysis (bifunctional catalysis by Lewis salts) in the MRH. This catalysis operates through a completely different mechanism with respect to the one recently observed, and deeply investigated, in the presence of protic acids for the (Z)‐phenylhydrazone of 5‐amino‐3‐benzoyl‐1,2,4‐oxadiazole, in both dioxane/water and toluene, for which the catalytic process was dependent on the protonation of N(4) ring‐nitrogen of the 1,2,4‐oxadiazole. As a matter of fact, the copper salts seem able to interact with the >C?N? NH? C₆H₅ moiety, yielding adducts which, in some cases, are prone to both isomerize and rearrange. Therefore, a similar behaviour in some manner parallel to that already observed in benzene in the presence of aliphatic amines (base‐catalysis) has been evidenced. Copyright © 2008 John Wiley & Sons, Ltd.     

An Easy Access to Furan-Fused Polyheterocyclic Systems

Nitrostilbenes characterized by two different or differently substituted aryl moieties can be obtained from the initial ring-opening of 3-nitrobenzo[b]thiophene with amines. Such versatile building blocks couple the well-recognized double electrophilic reactivity of the nitrovinyl moiety (addition to the double bond, followed by, e.g., intramolecular replacement of the nitro group) with the possibility to exploit a conjugated system of double bonds within an electrocyclization process. Herein, nitrostilbenes are reacted with different aromatic enols provided by a double (carbon and oxygen) nucleophilicity, leading to novel, interesting naphthodihydrofurans. From these, as a viable application, aromatization and electrocyclization lead in turn to valuable polycondensed, fully aromatic O-heterocycles.     

Switching the N-Capping Region from all-L to all-D Amino Acids in a VEGF Mimetic Helical Peptide

The N-capping region of an α-helix is a short N-terminal amino acid stretch that contributes to nucleate and stabilize the helical structure. In the VEGF mimetic helical peptide QK, the N-capping region was previously demonstrated to be a key factor of QK helical folding. In this paper, we explored the effect of the chiral inversion of the N-capping sequence on QK folding, performing conformational analysis in solution by circular dichroism and NMR spectroscopy. The effect of such a modification on QK stability in serum and the proliferative effect were also evaluated.     

Phytochemical Compounds and Nanoparticles as Phytochemical Delivery Systems for Alzheimer’s Disease Management

Alzheimer’s disease remains one of the most widespread neurodegenerative reasons for dementia worldwide and is associated with considerable mortality and morbidity. Therefore, it has been considered a priority for research. Indeed, several risk factors are involved in the complexity of the therapeutic ways of this pathology, including age, traumatic brain injury, genetics, exposure to aluminum, infections, diabetes, vascular diseases, hypertension, dyslipidemia, and obesity. The pathophysiology of Alzheimer’s disease is mostly associated with hyperphosphorylated protein in the neuronal cytoplasm and extracellular plaques of the insoluble β-amyloid peptide. Therefore, the management of this pathology needs the screening of drugs targeting different pathological levels, such as acetylcholinesterase (AchE), amyloid β formation, and lipoxygenase inhibitors. Among the pharmacological strategies used for the management of Alzheimer’s disease, natural drugs are considered a promising therapeutic strategy. Indeed, bioactive compounds isolated from different natural sources exhibit important anti-Alzheimer effects by their effectiveness in promoting neuroplasticity and protecting against neurodegeneration as well as neuroinflammation and oxidative stress in the brain. These effects involve different sub-cellular, cellular, and/or molecular mechanisms, such as the inhibition of acetylcholinesterase (AchE), the modulation of signaling pathways, and the inhibition of oxidative stress. Moreover, some nanoparticles were recently used as phytochemical delivery systems to improve the effects of phytochemical compounds against Alzheimer’s disease. Therefore, the present work aims to provide a comprehensive overview of the key advances concerning nano-drug delivery applications of phytochemicals for Alzheimer’s disease management.     

Als charakteristische Reaktion der freien Weinsteins?re

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