Nonlinear oscillations of electrically driven aniso-visco-hyperelastic dielectric elastomer minimum energy structures

Nonlinear Dynamics - In view of their unique shape morphing behaviour, dielectric elastomer-based minimum energy structures (DEMES) have received an increasing attention in the technology of...     

Redox-mediated Negative Differential Resistance (NDR) Behavior in Perylenediimide Derivative: A Supramolecular Approach

Deaggregated perylenediimide (PDI) derivatives exhibit exceptionally high quantum yields, photostability and appropriate molecular features for organic electronics. This work demonstrates a metal–dye–metal framework with a large and stable negative differential resistance (NDR) at ambient conditions, built using a supramolecular strategy. The deaggregation achieved through the encapsulation of the bay-substituted phenyl groups of aggregated (l/d )-Phe-PDI dyes by the β-CD macrocyclic host is validated through detailed spectroscopic and imaging techniques. The host–guest interaction resulted in a dramatic enhancement in the emission yield from 0.28 to 0.90. In the thin film deposits, the β-CD/(l/d )-Phe-PDI complex displayed well-connected sheet-like morphology, whereas the uncomplexed (l/d )-Phe-PDI dye remained as scattered lumps. The large and reversible I–V characteristics displaying strong NDR behavior is attributed to the oxidation/reduction processes involving the rigid π-rich PDI core and is stable at least for about six months at ambient conditions, a promising system for organic electronics applications.     

Synthesis of New Triazolopyrazine Antimalarial Compounds

A radical approach to late-stage functionalization using photoredox and Diversinate^™ chemistry on the Open Source Malaria (OSM) triazolopyrazine scaffold (Series 4) resulted in the synthesis of 12 new analogues, which were characterized by NMR, UV, and MS data analysis. The structures of four triazolopyrazines were confirmed by X-ray crystal structure analysis. Several minor and unexpected side products were generated during these studies, including two resulting from a possible disproportionation reaction. All compounds were tested for their ability to inhibit the growth of the malaria parasite Plasmodium falciparum (3D7 and Dd2 strains) and for cytotoxicity against a human embryonic kidney (HEK293) cell line. Moderate antimalarial activity was observed for some of the compounds, with IC₅₀ values ranging from 0.3 to >20 µM; none of the compounds displayed any toxicity against HEK293 at 80 µM.     

1H and 13C NMR assignments for two new xanthones from the endophytic fungus Xylaria sp. FRR 5657

The complete 1H and 13C NMR assignments are reported for the new natural products, 7-hydroxy-3-(hydroxymethyl)-1-methoxy-9H-xanthen-9-one (1) and 2,5-dihydroxy-8-methoxy-6-methyl-9-oxo-9H-xanthene -1-carboxylic acid (2). Both of these secondary metabolites were isolated from the fermentation culture of the endophytic fungus Xylaria sp. FRR 5657. 1D and 2D NMR experiments that included 1H, gCOSY, gHSQC and gHMBC were used for the determination of the structure and assignment of these xanthones.     

Simultaneous two-photon excitation of photofrin in relation to photodynamic therapy

Photodynamic therapy (PDT), the use of light-activated drugs (photosensitizers), is an emerging treatment modality for tumors as well as various nononcologic conditions. Single-photon (1-gamma) PDT is limited by low specificity of the photosensitizer, leading to damage to healthy tissue adjacent to the diseased target tissue. One solution is to use simultaneous two-photon (2-gamma) excitation with ultrafast pulses of near-IR light. Due to the nonlinear interaction mechanism, 2-gamma excitation with a focused beam is localized in three dimensions, allowing treatment volumes on the order of femtoliters. We propose that this will be valuable in PDT of age-related macular degeneration (AMD), which causes blindness due to abnormal choroidal neovasculature and which is currently treated by 1-gamma PDT. Here, Photofrin has been used as the photosensitizer to demonstrate proof-of-principle of 2-gamma killing of vascular endothelial cells in vitro. The 2-gamma absorption properties of Photofrin were investigated in the 750-900 nm excitation wavelength range. It was shown that 2-gamma excitation dominates over 1-gamma excitation above 800 nm. The 2-gamma absorption spectrum of Photofrin in the 800-900 nm excitation wavelength range was measured. The 2-gamma cross section decreased from about 10 GM (1 GM = 10(-50) cm4 s/photon) at 800 nm to 5 GM at 900 nm. Adherent YPEN-1 endothelial cells were then incubated with Photofrin for 24 h and then treated by PDT at 850 nm where the 1-gamma contribution was negligible. Cell death was monitored with the use of 2-gamma scanning laser microscopy. The light doses required for killing were high (6300 J cm(-2) for approximately 50% killing), but 2-gamma cytotoxicity was unequivocally demonstrated. Although Photofrin is, per se, not a good choice for 2-gamma PDT due to its low 2-gamma cross section, this work provides baseline data to guide the development of novel photosensitizers with much higher 2-gamma cross sections (>100 GM), which will be required for 2-gamma PDT of AMD (and other conditions) to be clinically practical.     

A physicochemical model for analyzing DNA sequences

In search of an ab initio model to characterize DNA sequences as genes and nongenes, we examined some physicochemical properties of each trinucleotide (codon), which could accomplish this task. We constructed three-dimensional vectors for each double-helical trinucleotide sequence considering hydrogen-bonding energy, stacking energy, and a third parameter, which we provisionally identified with DNA-protein interactions. As this three-dimensional vector moves along any genome, the net orientation of the resultant vector should differ significantly for gene and nongene regions to make a distinction feasible, if the underlying model has some merits. An analysis of 331 prokaryotic genomes comprising a total of 294 786 experimentally verified genes (nonoverlapping) and an equal number of nongenes presents a proof of concept of the model without the need for further parametrization. Also, initial analyses on Saccharomyces cerevisiae and Arabidopsis thaliana suggest that the methodology is extendable to eukaryotes. The physicochemical model (ChemGenome1.0) introduced has the potential to be developed into a gene-finding algorithm and, more pressingly, could be employed for an independent assessment of the annotation of DNA sequences.     

Gemini surfactants at the air/water interface: a fully atomistic molecular dynamics study

Gemini surfactants typically consist of two single-chain surfactants chemically linked by a spacer molecule. We report herein the results of fully atomistic molecular dynamics (MD) simulations of a series of Gemini surfactants: CsH2s-alpha,omega-bis(C12H25N+(CH3)2Cl-), at the air/water interface with s = 3, 4, 6, 12, 14, and 16, at values of the initial surface area per surfactant AS = 70 A2, 77 A2, 95 A2, 151 A2, 133 A2, and 103 A2, respectively. The AS values employed were obtained from surface tension and neutron reflection experiments at the respective cmc of each surfactant. The Gemini surfactant corresponding to s = 3 was also simulated at AS = 105 A2, which is the experimentally derived value of surface area per surfactant at 1/10th of cmc. Only the surfactants with s = 12 and 14 and the surfactant with s = 3 at AS = 105 A2 gave a stable monolayer at the air/water interface. In other cases, we observe movement of some surfactant molecules from the air/water interface into the aqueous phase, resulting in a stable primary monolayer of surfactants at the air/water interface and a small concentration of surfactant molecules below it. The latter form aggregates, with their hydrophobic chains in the core. The density profiles along the normal to the interface are compared with the ones obtained from neutron reflection experiments. The MD simulations confirm the bending of the spacer toward the hydrophobic chains as the spacer length is increased and the spacer becomes more hydrophobic. The simulations have helped to shed light on the low-resolution picture which emerges from experimental analyses.     

Approximation of measurable mappings by sequences of continuous functions

Let be a completely regular Hausdorff space, a positive, finite Baire measure on , and a separable metrizable locally convex space. Suppose is a measurable mapping. Then there exists a sequence of functions in which converges to a.e. . If the function is assumed to be weakly continuous and the measure is assumed to be -smooth, then a separability condition is not needed.

     

Novel PVC-based membrane sensors selective for vanadyl ions

Poly(vinyl chloride) based membranes of di-(2-ethylhexyl)phosphoric acid (DEHPA) and dibutyl(butyl)phosphonate (DBBP) have been prepared and investigated as VO²⁺-selective sensors. The membranes containing DEHPA/DBBP and sodium tetraphenylborate, an anion excluder, show near-Nernstian/Nernstian response in the concentration range 10⁻⁵–10⁻¹ M. The sensors exhibit a fast response time and good selectivity for VO²⁺ over a number of other cations. Quantitative determination of vanadium in waste V₂O₅ catalyst has been achieved by these sensors and they have also been used as indicator electrodes for the determination of the end point in the potentiometric titration of VO²⁺ against EDTA.