Pyridinium based amphiphilic hydrogelators as potential antibacterial agents

The numerous applications of hydrogelators have led to rapid expansion of this field. In the present work we report the facile synthesis of amphiphilic hydrogelators having a quaternary pyridinium unit coupled to a hydrophobic long alkyl chain through an amide bond. Different amphiphiles with various hydrophobic chain length and polar head groups were rationally designed and synthesized to develop a structure-property relation. A judicious combination of hydrophilic and hydrophobic segments led to the development of pyridinium based amphiphilic hydrogelators having a minimum gelation concentration of 1.7%, w/v. Field emission scanning electronic microscopy (FESEM), atomic force microscopy (AFM), photoluminescence, FTIR studies, X-ray diffraction (XRD) and 2D NOESY experiments were carried out to elucidate the different non-covalent interactions responsible for the self-assembled gelation. The formation of three-dimensional supramolecular aggregates originates from the interdigitated bilayer packing of the amphiphile leading to the development of an efficient hydrogel. Interestingly, the presence of the pyridinium scaffold along with the long alkyl chain render these amphiphiles inherently antibacterial. The amphiphilic hydrogelators exhibited high antibacterial activity against both Gram-positive and Gram-negative bacteria with minimum inhibitory concentration (MIC) values as low as 0.4 μg/mL. Cytotoxicity tests using MTT assay showed 50% NIH3T3 cell viability with hydrogelating amphiphile 2 up to 100 μg/mL

Self-assembling dipeptide antibacterial nanostructures with membrane disrupting activity.

Peptide-based supramolecular assemblies are a promising class of nanomaterials with important biomedical applications, specifically in drug delivery and tissue regeneration. However, the intrinsic antibacterial capabilities of these assemblies have been largely overlooked. The recent identification of common characteristics shared by antibacterial and self-assembling peptides provides a paradigm shift towards development of antibacterial agents. Here we present the antibacterial activity of self-assembled diphenylalanine, which emerges as the minimal model for antibacterial supramolecular polymers. The diphenylalanine nano-assemblies completely inhibit bacterial growth, trigger upregulation of stress-response regulons, induce substantial disruption to bacterial morphology, and cause membrane permeation and depolarization. We demonstrate the specificity of these membrane interactions and the development of antibacterial materials by integration of the peptide assemblies into tissue scaffolds. This study provides important insights into the significance of the interplay between self-assembly and antimicrobial activity and establishes innovative design principles toward the development of antimicrobial agents and materials

Shape-specific microfabricated particles for biomedical applications: a review

The storied history of controlled the release systems has evolved over time; from degradable drug-loaded sutures to monolithic zero-ordered release devices and nano-sized drug delivery formulations. Scientists have tuned the physico-chemical properties of these drug carriers to optimize their performance in biomedical/pharmaceutical applications. In particular, particle drug delivery systems at the micron size regime have been used since the 1980s. Recent advances in micro and nanofabrication techniques have enabled precise control of particle size and geometry–here we review the utility of microplates and discoidal polymeric particles for a range of pharmaceutical applications. Microplates are defined as micrometer scale polymeric local depot devices in cuboid form, while discoidal polymeric nanoconstructs are disk-shaped polymeric particles having a cross-sectional diameter in the micrometer range and a thickness in the hundreds of nanometer range. These versatile particles can be used to treat several pathologies such as cancer, inflammatory diseases and vascular diseases, by leveraging their size, shape, physical properties (e.g., stiffness), and component materials, to tune their functionality. This review highlights design and fabrication strategies for these particles, discusses their applications, and elaborates on emerging trends for their use in formulations. GRAPHICAL ABSTRACT: [Image: see text

Single-walled nanotube/amphiphile hybrids for efficacious protein delivery: rational modification of dispersing agents

Carbon nanotube (CNT)/amphiphile hybrids with remarkable stability and cell viability under biologically relevant conditions can be obtained by rational modification of the molecular structure of amphiphilic dispersing agents (see scheme; PEG = poly(ethylene glycol)). The CNT/amphiphile hybrids are dispersible in water and efficiently shuttle proteins across mammalian cell membranes

GNP confinement at the interface of cationic reverse micelles: influence in improving the lipase activity

The present work reports thiol-assisted confinement of gold nanoparticles (GNPs) at the interface of reverse micelles with the aim to enhance the interfacial area and thereby the efficiency of surface-active Chromobacterium viscosum lipase. The strong gold capping ability of optimally hydrophobic thiols (1-dodecanethiol and 1,6-hexanedithiol) was aptly utilized to pull GNPs (∼3–5 nm) from the water pool to the oil/water interface of cetyltrimethylammonium bromide (CTAB) reverse micelles. These small sized GNPs were fitted at the microscopic interface of CTAB reverse micelles possibly because of the comparable thickness of the interface (∼1–2 nm) to that of the GNP diameter. Lipase solubilized within this augmented interface enjoys a flexible conformation, which resulted in the improvement of its activity (∼2.5 fold) with respect to only CTAB microemulsion. The activity of lipase within CTAB reverse micelles was thoroughly studied in the presence of mono and dithiols with varying chain length, where a greater improvement in activity was observed with dithiols. Bidentate ligand property of dithiols led to firm localization of higher number of GNPs at the interface which enhanced the total space in vicinity of enzyme at the interfacial domain. Fitting fusion of small sized GNPs within CTAB reverse micellar interface was confirmed by microscopic and spectroscopic studies. Smooth localization of lipase at the enhanced interface was also confirmed from the improvement in its secondary structure (α-helical content) in circular dichroism spectroscopic analysis. Interestingly, large sized GNPs (∼8 and 20 nm) were found to be well fitted at the interface of bigger head group-containing surfactants, cetyltriethylammonium bromide (CTEAB) and cetyltripropylammonium bromide (CTPAB). The hydrolytic efficiency of lipase in 1,6-hexanedithiol included GNP (∼20–25 nm)-doped CTPAB reverse micelles improved by ∼3.4 fold compared to that observed in only CTAB

In situ synthesised silver nanoparticle-infused L-lysine-based injectable hydrogel: development of a biocompatible, antibacterial, soft nanocomposite

The synthesis of L-lysine-based amphiphilic hydrogelator consisting of a naphthalene moiety at the N termini and an ethyleneoxy unit with free primary amine at the C terminus is reported. The amphiphile showed good gelation ability with minimum gelation concentration 0.6 % w/v in binary mixtures of dimethyl sulfoxide/phosphate buffer (1:4 v/v, pH 7.4). The hydrogel was characterised by spectroscopic and microscopic studies to delineate the role of non-covalent interactions in self-assembly gelation. Subsequently, Ag nanoparticles were synthesised within the hydrogel by in situ photo-reduction of AgNO3 under sunlight, in which the gelators act as reducing/stabilising agents. The nanocomposites were characterised by transmission electron microscopy, UV/Vis and X-ray diffraction spectroscopy and thermogravimetric analysis. Rheology of the soft nanocomposite showed significant mechanical strength and thixotropic self-recovery properties, which made the composite suitable for use as a syringe-injectable hydrogel. These soft nanocomposites exhibited excellent antibacterial activity against both Gram-positive and Gram-negative bacteria. They showed low haemolytic activity and high biocompatibility to mammalian (Chinese hamster ovarian) cells. In addition, agar–gelatin film infused with these nanocomposites allowed normal growth of mammalian cells on its surface while being lethal towards bacteria

Active Immunization Against hIAPP Oligomers Ameliorates the Diabetes- Associated Phenotype in a Transgenic Mice Model

Abstract Type 2 diabetes is characterized by insulin tolerance in target cells followed by a reduction of pancreatic β-cell mass. Islet amyloid polypeptide oligomeric assemblies were shown to contribute to β-cell apoptosis by forming discrete pores that destabilize the cellular membrane. We previously characterized α-helical cytotoxic islet amyloid polypeptide oligomers which interact with cell membranes, following a complete internalization that leads to cellular apoptosis. Moreover, antibodies which bind the oligomers and neutralize the cytotoxicity were exclusively identified in the serum of type 2 diabetes patients. Here, we examined the usage of the newly characterized oligomers as an active immunization agent targeting amyloid self- assembly in a diabetes-associated phenotype transgenic mice model. Immunized transgenic mice showed an increase in hIAPP-antibody serum titer as well as improvement in diabetes-associated parameters. Lower fasting blood glucose levels, higher insulin, and lower islet amyloid polypeptide accumulation were observed. Furthermore, antibodies derived from the immunized mice reduced hIAPP oligomers cytotoxicity towards β-cells in a dose-dependent manner. This study highlights the significance of targeting the early amyloid self-assembly events for potential disease management. Furthermore, it demonstrates that α-helical oligomers conformers are valid epitope for the development of future immunization therapy

pH-responsive reversible dispersion of biocompatible SWNT/graphene–amphiphile hybrids

The present work reports synthesis of cholesterol based peptide carboxylates as efficient dispersing agents for single walled carbon nanotubes (SWNTs) as well as graphene in water. Variation of the amino acids within the peptide moiety exhibited interesting changes in their SWNTs dispersion efficacy. The dipeptide carboxylate comprising of two alanine residues showed 80% SWNTs dispersion which is ∼2 fold higher than that obtained by using the common surfactant, SDBS. The dipeptide amphiphiles also efficiently dispersed the 2D-allotrope of carbon, graphene, in water. As to our objective, the terminal carboxylate moiety in these cholesterol based carboxylates exhibited pH-sensitivity towards the reversible solubilization and precipitation of the nanohybrids. Acidification of the nanohybrids with HCl converted the carboxylates to the water insoluble carboxylic acids leading to the precipitation of carbon nanomaterials. Most importantly, addition of an equivalent amount of NaOH resulted in the restoration of stable aqueous dispersion of SWNT/graphene. This reversible precipitation–dispersion cycle was performed time and again. The conversion of the carboxylate salt to the corresponding acid and vice versa is the main reason for such reversible switching between precipitation and dissolution under acidic and basic pH. Indeed the presence of the amino acid/peptide moiety in the structure of cholesterol carboxylates was found to be indispensable for efficient dispersion of carbon nanomaterials. Significant stability of these SWNT dispersions was observed in the presence of high salt and protein concentration. Moreover, the nanohybrids were highly biocompatible with mammalian cells, which increases their future prospects in biomedicine

Biotinylated amphiphile-single walled carbon nanotube conjugate for target-specific delivery to cancer cells

The present work reports the specific targeting of cancerous cells using a non-covalently water dispersed nanoconjugate of biotinylated amphiphile-single walled carbon nanotube (SWNT). The fundamental approach involves incorporation of the biotin into the architecture of the carbon nanotube (CNT) dispersing agent to develop a multifaceted delivery vehicle having a high colloidal stability, substantial cell viability and targeted specificity towards cancer cells. A three way functionalization strategy was employed to introduce a C-16 hydrophobic segment, polyethylene glycol hydrophilic fragment and biotin as the target-specific unit at the –OH, –COOH and –NH<SUB>2</SUB> terminals of L-tyrosine, respectively. The newly developed neutral amphiphile exhibited an efficient SWNT dispersion (72%) in water, significant viability of different mammalian cells (Hela, HepG2, CHO and HEK-293) up to 48 h and also media stability. Most importantly, the biotinylated amphiphile-SWNT dispersion successfully transported the fluorescently labelled Cy3-oligoneucleotide (loaded on the surface of CNT) inside the cancerous Hela, HepG2 cells after 3 h of incubation, in contrast to CHO and HEK-293 cells (devoid of overexpressed biotin receptors). The presence of the biotin moiety in the cellular transporters facilitated the internalization of cargo due to the overexpressed biotin receptors in the cancer cells. Importantly, this nanohybrid was also capable of specifically transporting the anticancer drug doxorubicin to cancer cells, which led to the significant killing of Hela cells compared to the normal CHO cells. Thus, the receptor-mediated specific transportation of cargo into cancer cells was possible only due to the biotinylated CNT dispersing agent. To the best of our knowledge this is the first reported amino acid based biotinylated small amphiphilic molecule that non-covalently dispersed SWNTs and the corresponding nanoconjugate showed excellent cell viability, antibiofouling properties and the desired target-specific drug delivery

Refining hydrogelator design: soft materials with improved gelation ability, biocompatibility and matrix for in situ synthesis of specific shaped GNP

Despite the continuous surge in the development of new supramolecular gels, the prediction of a gelator's structure still remains elusive. It is also imperative to consolidate the existing inventory of gelators and devise ways to make the gels functional. In the present work, L-phenylalanine based poor (C-16) or non-gelating (C-12 tail) amphiphiles were converted to excellent gelators with the simple incorporation of N-terminal protected amino acid/dipeptide at the end of the alkyl tail. More than 6-fold enhancement in gelation efficiency was observed for amino acid/dipeptides incorporated at the tail of amphiphile in comparison to the corresponding unmodified alkyl tail. Interestingly, amphiphile with the tertiary butyloxycarbonyl (Boc) protected amino acid at the tail had better gelation ability than the amphiphile with the aromatic Fmoc (N-fluorenyl-9-methoxycarbonyl) protecting group. Spectroscopic investigations (XRD and FTIR) revealed that the modification at the tail compels the amphiphiles to take a different course of self-assembly than that adopted by their predecessors (alkyl tailed gelator, C-16). For example, in the case of the amphiphile having a dipeptide at the tail, formation of β-sheet structure through anti-parallel arrangement between the molecules results in notable improvement in its gelation ability. Most importantly, these tail modified amphiphiles were capable of in situ synthesis of gold nanoparticles (GNPs) of specific shape without the help of any external reducing agents in the newly developed soft materials. The biocompatibility of hydrogels is also crucial for their prolific biomedicinal functions. MTT assay showed dramatic improvement in the biocompatibility of the tail modified hydrogelators towards mammalian cells in comparison to the amphiphiles having no amino acid at the tail