Exploiting amyloid fibril lamination for nanotube self-assembly

Fundamental questions about the relative arrangement of the beta-sheet arrays within amyloid fibrils remain central to both its structure and the mechanism of self-assembly. Recent computational analyses suggested that sheet-to-sheet lamination was limited by the length of the strand. On the basis of this hypothesis, a short seven-residue segment of the Alzheimer's disease-related Abeta peptide, Abeta(16-22), was allowed to self-assemble under conditions that maintained the basic amphiphilic character of Abeta. Indeed, the number increased over 20-fold to 130 laminates, giving homogeneous bilayer structures that supercoil into long robust nanotubes. Small-angle neutron scattering and X-ray scattering defined the outer and inner radii of the nanotubes in solution to contain a 44-nm inner cavity with 4-nm-thick walls. Atomic force microscopy and transmission electron microscopy images further confirmed these homogeneous arrays of solvent-filled nanotubes arising from a flat rectangular bilayer, 130 nm wide x 4 nm thick, with each bilayer leaflet composed of laminated beta-sheets. The corresponding backbone H-bonds are along the long axis, and beta-sheet lamination defines the 130-nm bilayer width. This bilayer coils to give the final nanotube. Such robust and persistent self-assembling nanotubes with positively charged surfaces of very different inner and outer curvature now offer a unique, robust, and easily accessible scaffold for nanotechnology.     

Metal switch for amyloid formation: insight into the structure of the nucleus

The role of Zn2+ in pre-organizing Abeta(10-21) amyloid formation is shown to preferentially alter the relative rate of fibril nucleation and to have little influence on fibril propagation. Fibril morphology, as determined by small angle neutron scattering (SANS) and transmission electron microscopy (TEM), was unchanged in the presence and absence of Zn2+ in Abeta(10-21), as well as in a series of site-specifically altered variants. The metal-independence of the Abeta(10-21)H13Q peptide suggested that the increase in nucleation rate in Abeta(10-21) is due to Zn2+-mediated inter-sheet interactions, involving both histidine 13 and histidine 14.     

Amperometric determination of nitrite using natural fibers as template for titanium dioxide nanotubes with immobilized hemin as electron transfer mediator

A sensing device was constructed for the amperometric determination of nitrite. It is based on the use of titanium dioxide (TiO₂) nanotubes template with natural fibers and carrying hemin acting as the electron mediator. A glassy carbon electrode (GCE) was modified with the hemin/TNT nanocomposite. The electrochemical response to nitrite was characterized by impedance spectroscopy and cyclic voltammetry. An amperometric study, performed at a working potential of + 0.75 V (vs. Ag/AgCl), showed the sensor to enable determination of nitrite with a linear response in the 0.6 to 130 μM concentration range and with a 59 nM limit of detection. Corresponding studies by differential study voltammetry (E_p?=?0.75 V) exhibited a linear range from 0.6?×?10^?6 to 7.3?×?10^?5 M with a limit of detection of 84 nM. The sensing device was applied to the determination of nitrite in spiked tap and lake water samples.

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Graphical abstract Natural fibers templated synthesis of TNT immobilized hemin as electron transfer mediator for quantitative detection of nitrite with detection limit of 59 nM and good electrochemical sensitivity and the method can be used for quantitative determination of nitrite in water samples.

     

Dual Fluorescence and Photoprototropic Characteristics of 2-Aminodiphenylsulphone-β-Cyclodextrin Inclusion Complex

The absorption and fluorescence spectral characteristics of 2-aminodiphenylsulphone (2ADPS) have been investigated in the presence of β-cyclodextrin (β-CDx) in water. Dual emission is observed upon the complexation of 2ADPS in β-CDx. The stoichiometry of the host:guest inclusion complex is found to be 2:1. Steady state and time-resolved fluorescence spectral analysis support the formation of 2:1 complex between β-CDx and 2ADPS. The large enhancement in fluorescence intensity of twisted intramolecular charge transfer (TICT) band in aqueous β-CDx solution is due to the decrease in non-radiative processes. The ground and the excited state pK _a values for the monocation-neutral equilibrium of 2ADPS in β-CDx are found to be different from the pK _a values in aqueous solution. In the presence of β-CDx, 2ADPS is found to be less basic in the ground and the excited states.     

Methodical Thermolysis of [Ba2Ti2(thd)4(OnPr)8(nPrOH)2] under Autogenous Pressure Followed by Combustion for the Synthesis of Dielectric Tetragonal BaTiO3 Nanopowder

Tetragonal powders : Dielectric tetragonal BaTiO₃ nanopowder was synthesized in a solvent‐less, efficient process by the thermolysis of a single [Ba₂Ti₂(thd)₄(OnPr)₈(nPrOH)₂] precursor in a closed reactor at 700 °C under autogenous pressure, followed by combustion. The BaTiO₃ nanopowder is characterized thoroughly, employing advanced morphological, compositional, structural, and thermal techniques, and the dielectric constant is accounted.

     

Ultrasonic investigation of molecular association in binary mixtures of aniline with aliphatic alcohols

Sound velocity, density and viscosity values have been measured at 303 K in the three binary systems of aniline + methanol, ethanol and 1-propanol. From these data, acoustical parameters such as adiabatic compressibility, free length, free volume and internal pressure have been estimated using the standard relations. The results are interpreted in terms of molecular interaction between the components of the mixtures. Observed excess value in all the mixtures indicates that the molecular symmetry existing in the system is highly disturbed by the polar alcohol molecules' dipole–dipole and induced dipole–dipole type interactions that are existing in the systems.     

Growth and characterization of Fe3+-doped bis(thiourea)zinc(II) chloride crystals

Fe3+-doping at ～10 mol% in aqueous medium during crystal growth by slow evaporation solution method in bis(thiourea)zinc(II) chloride (BTZC) leads to form a new compound C2H8Cl2N4S2Zn0.93Fe0.07 (BTZCF) which crystallizes in orthorhombic structure with centrosymmetric space group Pnma though the parent compound BTZC crystallizes in noncentrosymmetric structure with space group Pn2(1)a. The interesting feature observed in this new crystal is that though it crystallizes in centrosymmetric structure, it exhibits positive SHG result (weak signal), quite likely due to possible surface effects or internal stress. The calculated first-order hyperpolarizability is 1.457×10(-30) esu which is ～5.5 times that of urea. Fe3+-doping enhances the transmittance to a significant extent. Comparison of the thermal analysis results by DSC reveals the incorporation of dopant into the crystalline matrix. The high resolution XRD studies reveal that the crystalline quality is improved considerably when the doping level is reached to ～10 mol%.     

Gold nanoparticles induced apoptosis via oxidative stress and mitochondrial dysfunctions in MCF‐7 breast cancer cells

Green synthesis of functionalized gold nanoparticles has been considered to be more biocompatible and has gained much attention in recent years. The eco‐friendly synthesis, long half‐life of drugs, low cost, and nontoxicity make them an appealing potential option for the biomedical field. The leaf aqueous extract of 10 different plants, namely, Araucaria heterophylla (Ah), Lagerstroemia indica (Li), Combretum indicum (Ci), Melia azedarach (Ma), Muntingia calabura (Mc), Hygrophila auriculata (Ha), Rivina humilis (Rh), Callistemon lanceolatus (Cl), Pterygota alata (Pa), and Vateria indica (Vi) was used for the synthesis of gold nanoparticles (AuNPs). Among them, six plants supported the synthesis of stable AuNPs. The generation of ruby red from pale yellow color proved AuNPs synthesis and which was further confirmed by the absorption peak in UV–Vis spectroscopy. Enhanced antioxidant activity was found with Pa–AuNPs compared with other phytosynthesized AuNPs. Pa–AuNPs were thus characterized by HR‐TEM, EDX, XRD, and FTIR. Pa–AuNPs exhibited potent dose‐dependent anticancer efficacy and an effective dose of IC₅₀ mediated apoptosis and necrosis in MCF‐7 breast cancer cells. Pa–AuNPs significantly enhanced the generation of ROS, in effect inducing mitochondrial membrane sensitization to trigger the cascade of apoptosis. The research highlights the effectiveness of AuNPs on cancer cells in vitro and, in turn, a progressive step toward novel biomedical applications. These findings indicate that phytosynthesized AuNPs may be an enticing anti‐cancer strategy for breast cancer without eliciting toxicity to normal cells.     

Crystal growth,structure, crystalline perfection and characterization of zinc magnesium ammonium sulfate hexahydrate mixed crystals ZnxMg(1−x)(NH4)2(SO4)2·6H2O

Mixed crystals Zn_xMg_(1?x)(NH₄)₂(SO₄)₂·6H₂O of the two well-known Tutton's salts Zn(NH₄)₂(SO₄)₂·6H₂O and Mg(NH₄)₂(SO₄)₂·6H₂O were grown with varying molar proportions (x=0.10–0.90) by slow evaporation solution growth technique. The mixed crystal Zn_0.54Mg_0.46(NH₄)₂(SO₄)₂·6H₂O is crystallizing in monoclinic system with space group P2₁/c and cell parameters a=6.2217(4) Å, b=12.5343(7) Å, c=9.2557(6) Å, β=106.912(3)°. The coexistence of zinc and magnesium ions in the mixed crystal was confirmed by inductively coupled plasma (ICP), atomic absorption spectroscopy (AAS) and energy dispersive X-ray spectroscopy (EDS). Compositional dependence of lattice parameters follows Vegard's relations. Slight variations are observed in FT-IR and XRD of pure and mixed crystals. Comparison of crystalline perfection as evaluated by high-resolution X-ray diffraction (HRXRD) for mixed crystals of various proportions reveals a reasonably good crystalline perfection for the mixed crystal with nearly equimolar ratio of Zn and Mg. The surface morphology of the mixed crystals changing with composition was studied by scanning electron microscopy (SEM). UV–vis studies reveal that the transparency of the mixed crystals was not much affected.