Thermally reversible hydrogels via intramolecular folding and consequent self-assembly of a de novo designed peptide

A small de novo designed peptide (MAX3) is described that exhibits complete thermoreversible self-assembly into a hydrogel network. Importantly, a prerequisite to hydrogelation is that the peptide must first fold into a conformation conducive to self-assembly. At ambient temperature, MAX3 is unfolded, resulting in a low viscosity aqueous solution. On increasing the temperature, the peptide undergoes a unimolecular folding event, affording an amphiphilic beta-hairpin that consequently self-assembles into a hydrogel network. Increasing the temperature serves to dehydrate the nonpolar residues of the unfolded peptide and trigger folding via hydrophobic collapse. Cooling the resultant hydrogel results in beta-hairpin unfolding and consequent complete dissolution of the hydrogel. The temperature at which folding and consequent self-assembly into a rigid hydrogel occur can be tuned by altering the hydrophobicity of the peptides.     

VISIBLE LIGHT PHOTOCHEMICAL RELEASE OF NITRIC OXIDE FROM S-NITROSOGLUTATHIONE: POTENTIAL PHOTOCHEMOTHERAPEUTIC APPLICATIONS

Abstract Some aspects of the physiological role of NO may be mediated by stable NO-carriers such as S -nitrosoglutathione and related S -nitrosothiols. In this report we show that irradiation of S-nitrosoglutathione at either absorption band (λ_max= 340 nm or 545 nm) results in the release of nitric oxide. Photolysis of S -nitrosoglutathione at 545 nm exhibited a quantum yield of 0.056 ± 0.002 and was best approximated by a first-order process with k _obs= 4.9 × 10⁻⁷± 0.3 × 10⁻⁷ s⁻¹. The photolytic release of NO from S -nitrosoglutathione resulted in an enhanced cytotoxic effect of S -nitrosoglutathione on HL-60 leukemia cells. That the cytotoxic effect of S -nitrosoglutathione was diminished by the addition of oxyhemoglobin strongly suggests that NO is the cytotoxic species. The finding that NO can be readily liberated from S -nitrosoglutathione by visible radiation indicates that the photochemical properties of this compound in the visible spectrum must be considered in order to obtain meaningful data as to its physiological role and the S -nitrosoglutathione and related compounds may find use as photochemotherapeutic agents.     

Impacts of uniaxial elongation on the bandstructures of two-dimensional sonic crystals and associated applications

Influences of uniaxial elongation along the [11] direction of triangular and [10] direction of square sonic crystals under the constraint of conserved unit cell area are investigated by examining band structures and equi-frequency contours. Lowest-lying band gap of the triangular lattice observed at high filling fractions diminishes for negative elongation (compression), whereas another band gap develops at lower frequencies whose width reaches appreciable values for moderate elongation. The band gap of the square lattice, which appears at high filling fractions, is modified slightly with elongation. Frequency ranges of the bands, and thus the group velocities along the high-symmetry directions, vary with elongation which may be useful in applications like slow sound propagation. Elongation is observed to modify the equi-frequency contours significantly through reducing the lattice symmetry. The most prominent impact is the transformation of closed contours into open ones, whereas the rest are stretched either along or normal to the elongation axis of the 1st Brillouin Zone. This observation is utilized to implement wide-band all-angle self-collimation and superprism effect, which are demonstrated through Finite-Element computations.     

Coupled out of plane vibrations of spiral beams for micro-scale applications

An analytical method is proposed to calculate the natural frequencies and the corresponding mode shape functions of an Archimedean spiral beam. The deflection of the beam is due to both bending and torsion, which makes the problem coupled in nature. The governing partial differential equations and the boundary conditions are derived using Hamilton’s principle. Two factors make the vibrations of spirals different from oscillations of constant radius arcs. The first is the presence of terms with derivatives of the radius in the governing equations of spirals and the second is the fact that variations of radius of the beam causes the coefficients of the differential equations to be variable. It is demonstrated, using perturbation techniques that the derivative of the radius terms have negligible effect on structure’s dynamics. The spiral is then approximated with many merging constant-radius curved sections joined together to approximate the slow change of radius along the spiral. The equations of motion are formulated in non-dimensional form and the effect of all the key parameters on natural frequencies is presented. Non-dimensional curves are used to summarize the results for clarity. We also solve the governing equations using Rayleigh’s approximate method. The fundamental frequency results of the exact and Rayleigh’s method are in close agreement. This to some extent verifies the exact solutions. The results show that the vibration of spirals is mostly torsional which complicates using the spiral beam as a host for a sensor or energy harvesting device.     

Two New 2-Benzoylbenzoate Metal Complexes with Bapen: Synthesis,Spectroscopic and Crystal Structures

Abstract  

Coordination compounds of compositions [Ni(bba)₂(bapen)] (1) and [Cu(bba)₂(bapen)]0.5H₂O (2), where bba = 2-benzoylbenzoate, bapen = N,N′-bis(3-aminopropyl)ethylenediamine, have been prepared. The crystal and molecular structure of (1) and (2) were determined by X-ray analysis. Nickel and copper atoms are six-coordinated by four N atoms of amine and O donor atoms of 2-benzoylbenzoate anions, whereas 0.5 water molecule is situated outside the coordination sphere in (2). The calculated ∆(OCO) values are consistent with presence of monodentate carboxylate. Thermal analysis show that the mass losses of 1 in the temperature ranges 240–343 °C correspond to the decomposition of bba ligands, while the mass losses of 2 in the temperature ranges 105–125 °C correspond to the decomposition of crystal lattice water molecule.     

Khayyam with Cabri: experiences of pre-service mathematics teachers with Khayyam's solution of cubic equations in dynamic geometry environment

The study reported in this article deals with the observed actionsof Turkish pre-service mathematics teachers in dynamic geometryenvironment (DGE) as they were learning Khayyam's method forsolving cubic equations formed as x³ + ax = b. Having learnedthe method, modelled it in DGE and verified the correctnessof the solution, students generated their own methods for solvingdifferent types of cubic equations such as x³ + ax² = b andx³ + a = bx in the light of Khayyam's method. With the presentedteaching experiment, students realized that Khayyam's mathematicsis different from theirs. We consider that this gave them anopportunity to have an insight about the cultural and socialaspects of mathematics. In addition, the teaching experimentshowed that dynamic geometry software is an excellent tool fordoing mathematics because of their dynamic nature and accurateconstructions. And, it can be easily concluded that the historyof mathematics is useful resource for enriching mathematicslearning environment.     

Solid-state Electrochemical Sensor Based on a Cross-linked Copper(II)-doped Copolymer and Carbon Nanotube Material for Selective and Sensitive Detection of Monohydrogen Phosphate

A novel solid-state electrochemical sensor based on a newly synthesized cross-linked copper(II) doped-copolymer and carbon nanotube material was developed for the direct determination of monohydrogen phosphate ions (HPO₄²⁻). The synthesized copolymers were characterized by FTIR, XPS, TG/DTG-DTA and SEM techniques. The sensor had a Nernstian slope:-30.7±0.4 mV/decade, linear concentrations range: 1.0×10⁻⁶ - 1.0×10⁻¹ M, detection limit: 6.5×10⁻⁷ M, response time: 4 s and life time: 17 weeks. The sensor displayed constant potentials in the pH range 7.0-9.5. The sensor was successfully used as an indicator electrode in potentiometric titration and the direct determination of HPO₄ ²⁻ in water samples.