Self-Assembled Hybrid Materials Based on Organic Nanocrystals and Carbon Nanotubes.

Organic crystalline materials are used as dyes/pigments, pharmaceuticals, and active components of photonic and electronic devices. There is great interest in integrating organic crystals with inorganic and carbon nanomaterials to create nanocomposites with enhanced properties. Such efforts are hampered by the difficulties in interfacing organic crystals with dissimilar materials.

Precrystalline Aggregates Enable Control over Organic Crystallization in Solution.

Understanding and controlling organic crystallization in solution is a long-standing challenge. Herein, we show that crystallization of an aromatic amphiphile based on perylene diimide in aqueous media involves initially formed amorphous spherical aggregates that evolve into the crystalline phase. The initial appearance of the crystalline order is always confined to the spherical aggregates that are precursors for crystalline evolution.

Self-Assembled Organic Nanocrystals with Strong Nonlinear Optical Response.

Facile molecular self-assembly affords a new family of organic nanocrystals that, unintuitively, exhibit a significant nonlinear optical response (second harmonic generation, SHG) despite the relatively small molecular dipole moment of the constituent molecules. The nanocrystals are self-assembled in aqueous media from simple monosubstituted perylenediimide (PDI) molecular building blocks. Control over the crystal dimensions can be achieved via modification of the assembly conditions.

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 terminals of l-tyrosine, respectively.

Micellization of cetyltrimethylammonium bromide: effect of small chain Bola electrolytes.

Sodium dicarboxylates (or Bola salts) with methylene spacers 0, 2, 4, 6, 8, and 10 were studied in aqueous solution to investigate their influence on the micellization of cetyltrimethylammonium bromide (CTAB). Since bolas with spacer length ≤12 are known not to micellize in general, the herein used sodium dicarboxylates were treated as 2:1 amphiphilic electrolytes which reduced surface tension of water (except sodium oxalate with zero spacer) without self-association. Their concentration dependent conductance was also linear without breaks.

Structure and properties of cholesterol-based hydrogelators with varying hydrophilic terminals: biocompatibility and development of antibacterial soft nanocomposites.

The present work demonstrates a rational designing and synthesis of cholesterol-based amino acid containing hydrogelators with the aim to improve the biocompatibility of these amphiphilic molecules. A thorough structure-property correlation of these hydrogelators was carried out by varying the hydrophilic terminal from a neutral amine to a quaternized ammonium chloride. The amphiphiles having a cationic polar head as the hydrophilic domain and cholesterol as the hydrophobic unit showed better water gelation efficiency (minimum gelation concentration (MGC) ∼0.

Striking improvement in peroxidase activity of cytochrome c by modulating hydrophobicity of surface-functionalized gold nanoparticles within cationic reverse micelles.

This work demonstrates a remarkable enhancement in the peroxidase activity of mitochondrial membrane protein cytochrome c (cyt c) by perturbing its tertiary structure in the presence of surface-functionalised gold nanoparticles (GNPs) within cetyltrimethylammonium bromide (CTAB) reverse micelles. The loss in the tertiary structure of cyt c exposes its heme moiety (which is buried inside in the native globular form), which provides greater substrate (pyrogallol and H(2)O(2)) accessibility to the reactive heme residue. The surfactant shell of the CTAB reverse micelle in the presence of co-surfactant (n-hexanol) exerted higher crowding effects on the interfacially bound cyt c than similar anionic systems.

Kinetic studies of amino acid-based surfactant binding to DNA.

In this work, the binding kinetics of amino acid-based surfactants, presenting different linkers and head groups, with calf thymus (CT)-DNA was studied using stopped-flow fluorescence spectroscopy. The kinetic studies were carried out as a function of Na(+) concentration and surfactant-to-DNA charge ratio. The surfactant binding on DNA took place in two consecutive steps, for which the corresponding first and second relative rate constants (k(1) and k(2)) were determined.

Covalently functionalized single-walled carbon nanotubes at reverse micellar interface: a strategy to improve lipase activity.

The present work reports covalent functionalization of single-walled carbon nanotubes (f-SWNTs) to introduce hydrophilicity to the otherwise amphiphobic nanotubes. The charge and spacer length of the functional moiety were varied by using quaternized ethylene diamine, 6-aminocaproate, quaternized (ethylenedioxy)bis(ethylamine), and a poly(ethylene glycol) (PEG) unit (f-SWNT-1 to f-SWNT-4, respectively). These f-SWNTs with varying degrees of hydrophilicity were incorporated within cetyltrimethyl ammonium bromide (CTAB) reverse micelles to develop stable self-assembled nanohybrids.

Unmodified "GNP-oligonucleotide" nanobiohybrids: a simple route for emission enhancement of DNA intercalators.

We present herein a simple method for enhancing the emission of DNA intercalators in homogeneous nanobiohybrids of unlabeled oligonucleotides and unmodified gold nanoparticles (GNPs). Pristine single-stranded DNA (ss-DNA) has been wrapped around unmodified GNPs to induce metal-enhanced fluorescence (MEF) of DNA intercalators, such as ethidium bromide and propidium iodide. The thickness of the ss-DNA layer on the gold nanosurface determines the extent of MEF, since this depends on the position of the intercalator in relation to the metal surface.

Counterion-induced modulation in the antimicrobial activity and biocompatibility of amphiphilic hydrogelators: influence of in-situ-synthesized Ag-nanoparticle on the bactericidal property.

The necessity for the development of new antimicrobial agents due to the ever increasing threat from microbes is causing a rapid surge in research. In the present work, we have shown the efficient antimicrobial activity of a series of amino acid-based hydrogelating amphiphiles through alteration in their counterion. The subtle variation in the counterion from chloride to various organic carboxylates had a significant impact on the antimicrobial properties with notable improvement in biocompatibility toward mammalian cells.

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.

Imidazolium bromide-based ionic liquid assisted improved activity of trypsin in cationic reverse micelles.

The present work reports the imidazolium-based ionic liquids (ILs) assisted enhancement in activity of water-pool solubilized enzyme trypsin in cationic reverse micelles of CTAB. A set of imidazolium ILs (1-alkyl-3-methyl imidazolium bromides) were prepared with varying lengths of their side arm which results in the differential location of these organic salts in the reverse micelles. The different ILs offered varied activating effects on the biocatalyst.

Amino acid based low-molecular-weight ionogels as efficient dye-adsorbing agents and templates for the synthesis of TiO(2) nanoparticles.

The gelation of ionic liquids is attracting significant attention because of its large spectrum of applications across different disciplines. These 'green solvents' have been the solution to a number of common problems due to their eco-friendly features. To expand their applications, the gelation of ionic liquids has been achieved by using amino acid-based low-molecular-weight compounds.

Dipeptide-based low-molecular-weight efficient organogelators and their application in water purification.

The development of new low-molecular-weight gelators for organic solvents is motivated by several potential applications of gels as advanced functional materials. In the present study, we developed simple dipeptide-based organogelators with a minimum gelation concentration (MGC) of 6-0.15 %, w/v in aromatic solvents.