Structure of the dispersing agents.

<p>PEG =  -(CH₂CH₂O)₁₂CH₃.</p

Fabrication of SWCNT-Ag Nanoparticle Hybrid Included Self-Assemblies for Antibacterial Applications

<div><p>The present article reports the development of soft nanohybrids comprising of single walled carbon nanotube (SWCNT) included silver nanoparticles (AgNPs) having superior antibacterial property. In this regard aqueous dispersing agent of carbon nanotube (CNT) containing a silver ion reducing unit was synthesised by the inclusion of tryptophan and tyrosine within the backbone of the amphiphile. The dispersions were characterized spectroscopically and microscopically using TEM, AFM and Raman spectroscopy. The nanotube-nanoparticle conjugates were prepared by the <i>in situ</i> photoreduction of AgNO₃. The phenolate residue and the indole moieties of tyrosine and tryptophan, respectively reduces the sliver ion as well as acts as stabilizing agents for the synthesized AgNPs. The nanohybrids were characterized using TEM and AFM. The antibacterial activity of the nanohybrids was studied against Gram-positive (<i>Bacillus subtilis</i> and <i>Micrococcus luteus</i>) and Gram-negative bacteria (<i>Escherichia coli</i> and <i>Klebsiella aerogenes</i>). The SWCNT dispersions showed moderate killing ability (40–60%) against Gram-positive bacteria however no antibacterial activity was observed against the Gram negative ones. Interestingly, the developed SWCNT-amphiphile-AgNP nanohybrids exhibited significant killing ability (∼90%) against all bacteria. Importantly, the cell viability of these newly developed self-assemblies was checked towards chinese hamster ovarian cells and high cell viability was observed after 24 h of incubation. This specific killing of bacterial cells may have been achieved due to the presence of higher –SH containing proteins in the cell walls of the bacteria. The developed nanohybrids were subsequently infused into tissue engineering scaffold agar-gelatin films and the films similarly showed bactericidal activity towards both kinds of bacterial strains while allowing normal growth of eukaryotic cells on the surface of the films.</p></div

Antibacterial activity of agar-gelatin films against <i>B. subtilis</i> (a) SWCNT-1 (b) SWCNT-1-AgNP and <i>E</i>. <i>coli</i> (c) SWCNT-1 (d) SWCNT-1-AgNP composites.

<p>Antibacterial activity of agar-gelatin films against <i>B. subtilis</i> (a) SWCNT-1 (b) SWCNT-1-AgNP and <i>E</i>. <i>coli</i> (c) SWCNT-1 (d) SWCNT-1-AgNP composites.</p

TGA analysis of (i) 1 (ii) 2 (iii) SWCNT-1 (iv) SWCNT-2 (v) SWCNT-1-AgNP and (vi) SWCNT-2-AgNP.

<p>TGA analysis of (i) 1 (ii) 2 (iii) SWCNT-1 (iv) SWCNT-2 (v) SWCNT-1-AgNP and (vi) SWCNT-2-AgNP.</p

Raman Spectra of dispersed SWCNT-1 and SWCNT-2 using 514.5 nm excitation.

<p>Raman Spectra of dispersed SWCNT-1 and SWCNT-2 using 514.5 nm excitation.</p

Percentage killing of (a) <i>B. subtilis</i>, (b) <i>M. luteus</i>, (c) <i>E. coli</i> and (d) <i>K. aragneosa</i> after 3 h of incubation spread plating for 24 h with the hybrids.

<p>Percent killing was determined using colony count method.</p

FESEM images of <i>B. subtilis</i> incubated with (a) control (b) SWCNT-1 (c) SWCNT-1-AgNP and <i>E. coli</i> incubated with (d) control (e) SWCNT-1 and (f) SWCNT-1-AgNP.

<p>FESEM images of <i>B. subtilis</i> incubated with (a) control (b) SWCNT-1 (c) SWCNT-1-AgNP and <i>E. coli</i> incubated with (d) control (e) SWCNT-1 and (f) SWCNT-1-AgNP.</p

Diphenylalanine as a Reductionist Model for the Mechanistic Characterization of β<i>-</i>Amyloid Modulators

The phenomenon of protein aggregation into amyloid fibrils is associated with a large number of major diseases of unrelated etiology. Unraveling the mechanism of amyloid self-assembly and identifying therapeutic directions to control this process are of utmost importance. Research in this field has been hampered by several challenges, including reproducibility, low protein purification yields, and the inherent aggregation propensity of amyloidogenic proteins, making them extremely difficult to study. Herein, on the basis of the similarity in the assembly mechanism, as well as the physical, chemical, and biological characteristics, of diphenylalanine nanostructures and aromatic amino acid containing amyloid fibrils, we report a simple, yet robust peptide-based platform that could be used for screening of small molecules potentially capable of interfering with the aggregation process and for mechanistic exploration of their mode of action. The system was validated using four small-molecule inhibitors, and the effect was examined <i>via</i> turbidity assay, thioflavin T fluorescence, and electron microscopy. The aggregation profile of diphenylalanine was very similar to that of β-amyloid polypeptide in the presence of the modulators. Rosmarinic acid emerged as an extremely potent inhibitor and a destabilizer of the aggregates. The effect of stoichiometric variation of rosmarinic acid on the process of destabilization was also probed using a microfluidic technique. Finally, the formation of equimolar complexes of diphenylalanine and inhibitors was detected using mass spectrometry. This approach not only provides a system for high-throughput screening of possible inhibitor molecules from larger libraries of modulators, but is also highly useful for understanding the mechanistic aspects of the interactions leading to the process of inhibition

The Inhibitory Effect of Hydroxylated Carbon Nanotubes on the Aggregation of Human Islet Amyloid Polypeptide Revealed by a Combined Computational and Experimental Study

Fibrillar deposits formed by the aggregation of the human islet amyloid polypeptide (hIAPP) are the major pathological hallmark of type 2 diabetes mellitus (T2DM). Inhibiting the aggregation of hIAPP is considered the primary therapeutic strategy for the treatment of T2DM. Hydroxylated carbon nanoparticles have received great attention in impeding amyloid protein fibrillation owing to their reduced cytotoxicity compared to the pristine ones. In this study, we investigated the influence of hydroxylated single-walled carbon nanotubes (SWCNT-OHs) on the first step of hIAPP aggregation: dimerization by performing explicit solvent replica exchange molecular dynamics (REMD) simulations. Extensive REMD simulations demonstrate that SWCNT-OHs can dramatically inhibit interpeptide β-sheet formation and completely suppress the previously reported β-hairpin amyloidogenic precursor of hIAPP. On the basis of our simulation results, we proposed that SWCNT-OH can hinder hIAPP fibrillation. This was further confirmed by our systematic turbidity measurements, thioflavin T fluorescence, circular dichroism (CD), transmission electron microscope (TEM), and atomic force microscopy (AFM) experiments. Detailed analyses of hIAPP-SWCNT-OH interactions reveal that hydrogen bonding, van der Waals, and π-stacking interactions between hIAPP and SWCNT-OH significantly weaken the inter- and intrapeptide interactions that are crucial for β-sheet formation. Our collective computational and experimental data reveal not only the inhibitory effect but also the inhibitory mechanism of SWCNT-OH against hIAPP aggregation, thus providing new clues for the development of future drug candidates against T2DM