Dendrimer Induced Bilayer Disintegration of Hybrid Vesicles.

Physicochemical investigations on the inclusion of anionic polyamidoaminesuccinamic acid dendrimer, generation 5 (PAMAM-SA, G5) with positively charged hybrid vesicles (HCV), prepared using soylecithin, ion pair amphiphile (IPA), cholesterol and dihexadecyldimethylammonium bromide, were investigated by dynamic light scattering, transmission electron/atomic force microscopy (TEM/AFM), differential scanning calorimetry, fluorescence spectroscopy and surface pressure-time isotherm studies. Adsorption of dendrimer onto vesicle surface and subsequent bilayer disruption strongly depends on the bilayer composition and dendrimer concentration. Change in the zeta potential value with increasing dendrimer concentration suggests the dendrimer-vesicle interaction to be electrostatic in nature. AFM studies also confirm the adsorption of dendrimer as well as hole formation in the bilayer. Impact of the inclusion of dendrimer into the bilayer were further investigated through differential scanning calorimetry by monitoring the chain melting temperature and enthalpy of the chain melting processes. Dendrimer at low concentration does not alter bilayer integrity, while hole formations are noted at higher dendrimer concentration. Fluorescence anisotropy studies confirm the adsorption and subsequent bilayer disruption due to dendrimer inclusion. Dendrimer induced vesicle disintegration kinetics conclusively illustrate the transformation of cationic bilayer to monolayer and thereby exposing the role of IPA. In vitro cytotoxicity studies on PAMAM-SA, G5 and HCVs mixtures against human breast cancer cell line suggest that dendrimer-liposome aggregates (dendriosomes) exhibit substantial anticancer activities with insignificant side effects. It is expected that the dendriosomes may have application to host and deliver anticancer drug in the field of targeted drug delivery.

Effect of cationic dendrimer on membrane mimetic systems in the form of monolayer and bilayer.

Interactions between a zwitterionic phospholipid, 1, 2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and four anionic phospholipids dihexadecyl phosphate (DHP), 1, 2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG), 1, 2-dipalmitoyl-sn-glycero-3-phosphate (DPP) and 1, 2-dipalmitoyl-sn-glycero-3-phospho ethanol (DPPEth) in combination with an additional amount of 30 mol% cholesterol were separately investigated at air-buffer interface through surface pressure (π) - area (A) measurements. π-A isotherm derived parameters revealed maximum negative deviation from ideality for the mixtures comprising 30 mol% anionic lipids. Besides the film functionality, structural changes of the monomolecular films at different surface pressures in the absence and presence of polyamidoamine (PAMAM, generation 4), a cationic dendrimer, were visualised through Brewster angle microscopy and fluorescence microscopic studies. Fluidity/rigidity of monolayers were assessed by surface dilatational rheology studies. Effect of PAMAM on the formation of adsorbed monolayer, due to bilayer disintegration of liposomes (DPPC:anionic lipids= 7:3 M/M, and 30 mol% cholesterol) were monitored by surface pressure (π) - time (t) isotherms. Bilayer disintegration kinetics were dependent on lipid head group and chain length, besides dendrimer concentration. Such studies are considered to be an in vitro cell membrane model where the alteration of molecular orientation play important roles in understanding the nature of interaction between the dendrimer and cell membrane. Liposome-dendrimer aggregates were nontoxic to breast cancer cell line as well as in doxorubicin treated MDA-MB-468 cell line suggesting their potential as drug delivery systems.

Controlled synthesis of photoresponsive bismuthinite (Bi2S3) nanostructures mediated through a new 1D bismuth-pyrimidylthiolate coordination polymer as a molecular precursor.

Bismuthinite (Bi2S3) nanostructures have garnered significant interest due to their appealing photoresponsivity which has positioned them as an attractive choice for energy conversion applications. However, to utilize their full potential, a simple and economically viable method of preparation is highly desirable. Herein, we present the synthesis and characterization including structural elucidation of a new air- and moisture-stable bismuth-pyrimidylthiolate complex. This complex serves as an efficient single-source molecular precursor for the facile preparation of phase-pure Bi2S3 nanostructures. Powder X-ray diffraction (PXRD), Raman spectroscopy, electron dispersive spectroscopy (EDS) and electron microscopy techniques were used to assess the crystal structure, phase purity, elemental composition and morphology of the as-prepared nanostructures. This study also revealed the profound effects of temperature and growth duration on the crystallinity, phase formation and morphology of nanostructures. The optical band gap of the nanostructures was tuned within the range of 1.9-2.3 eV, which is blue shifted with respect to the bulk bandgap and suitable for photovoltaic applications. Liquid junction photo-electrochemical cells fabricated from the as-prepared Bi2S3 nanostructure exhibit efficient photoresponsivity and good photo-stability, which project them as promising candidates for alternative low-cost photon absorber materials.

Molecular precursor mediated selective synthesis of phase pure cubic InSe and hexagonal In2Se3 nanostructures: new anode materials for Li-ion batteries.

Indium selenides (InSe and In2Se3) have earned a special place among the 2D layered metal chalcogenides owing to their nontoxic nature and favourable carrier mobility. Additionally, they are also being projected as next generation battery anodes with high theoretical lithium-ion storage capacities. While the development of indium selenide-based batteries is still in its embryonic stage, a simple and easily scalable synthetic pathway to access these materials is highly desirable for energy storage applications. This study reports a controlled synthetic route to nanometric cubic InSe and hexagonal In2Se3 materials through proper choice of coordinating solvents from a structurally characterized air and moisture stable single source molecular precursor: tris(4,6-dimethyl-2-pyrimidylselenolato)indium(III). The crystal structure, phase purity, composition, morphology and band gap of the nanomaterials were thoroughly evaluated by pXRD, energy dispersive X-ray spectroscopy (EDS), electron microscopy (SEM and TEM), and diffuse reflectance spectroscopy (DRS), respectively. The pristine InSe and In2Se3 nanostructures have been employed as anode materials in lithium-ion batteries (LIBs). Both the cells deliver reasonably high initial discharge capacities with a cyclability of 200 and 620 cycles for cubic InSe and hexagonal In2Se3 respectively with ∼100% coulombic efficiency.

Molecular precursor-mediated facile synthesis of phase pure metal-rich digenite (Cu1.8S) nanocrystals: an efficient anode for lithium-ion batteries.

Copper sulfides have gained significant attention as alternative electrodes for rechargeable batteries. A simple and easily scalable synthetic pathway to access these materials is highly desirable. This paper describes the facile synthesis of metal-rich digenite Cu1.8S nanocrystals from a structurally characterized new single-source molecular precursor in various high boiling solvents of varied polarity. The as-prepared nanostructures were thoroughly characterized by PXRD, Raman spectroscopy, EDS, XPS, electron microscopy techniques and diffuse reflectance spectroscopy to understand the crystal structure, phase purity, elemental composition, morphology and band gap. It was found that the reaction solvent has a profound role on their crystallite size, morphology and band gap, however the crystal structure and phase purity remained unaffected. Pristine Cu1.8S nanostructures have been employed as an anode material in lithium-ion batteries (LIBs). The cell delivers a high initial charge capacity of ∼462 mA h g-1 and retains a capacity of 240 mA h g-1 even after 300 cycles at 0.1 A g-1. DFT calculations revealed that multi-size polyhedron layers in the direction perpendicular to the two Li movement channels aid in the sustainable uptake of Li atoms with controlled volume expansion. The structure-mediated flexibility of the metal-rich Cu1.8S lattice during lithiation permits high cyclability with reasonable retention of capacity.

Synthesis of photoresponsive and photoemissive ultrathin 2D nanosheets of In2S3 achieved through a new single source molecular precursor.

Indium sulfide, a two-dimensional semiconductor material, has emerged as a promising candidate for cost-effective and sustainable solar cells. This report deals with the facile preparation of colloidal In2S3 with a new ultrathin nanosheet (NS) morphology. The synthesis was mediated through a new structurally characterized single source molecular precursor. The crystal structure, phase purity, and morphology of the NSs were thoroughly investigated by pXRD, Raman, XPS, and electron microscopic techniques. AFM studies revealed that the NSs have an average thickness of ∼1.76 nm. The optical studies confirm quantum confinement in the as-prepared NSs with a blue shift in the direct band gap, which lies in the optimal range suitable for solar cell application. Furthermore, photoluminescence studies indicate strong emission by these NSs in the blue region. The as-synthesized In2S3 NSs-based prototype photoelectrochemical cell exhibit high photostability and photoresponsivity, which make them suitable candidates for sustainable solar cells.

Facile one pot synthesis of highly photoresponsive coinage metal selenides (Cu1.8Se and Ag2Se) achieved through novel Cu and Ag pyridylselenolates as molecular precursors.

Copper selenide (Cu1.8Se) and silver selenide (Ag2Se) have garnered unprecedented attention as efficient absorber materials for cost-effective and sustainable solar cells. Phase pure preparation of these exotic materials in a nano-regime is highly desirable. This account outlines a simple and easily scalable pathway to Cu1.8Se and Ag2Se nanocrystals using novel complexes [Cu{2-SeC5H2(Me-4,6)2N}]4 (1), [Ag{2-SeC5H2(Me-4,6)2N}]6 (2) and [Ag{2-SeC5H3(Me-5)N}]6·2C6H5CH3 (3·2C6H5CH3) as single source molecular precursors (SSPs). Structural studies revealed that the Cu and Ag complexes crystallize into tetrameric and hexameric forms, respectively. This observed structural diversity in the complexes has been rationalized via DFT calculations and attributed to metal-metal bond endorsed energetics. The thermolysis at relatively lower temperature in oleylamine of complex 1 afforded cubic berzelianite Cu1.8Se and complexes 2 and 3 produced orthorhombic naumannite Ag2Se nanocrystals. The low temperature synthesis of these nanocrystals seems to be driven by the observed preformed Cu4Se4 and Ag6Se6 core in the complexes which have close resemblance with the bulk structure of the final materials (Cu1.8Se and Ag2Se). The crystal structure, phase purity, morphology, elemental composition and band gap of these nanocrystals were determined from pXRD, electron microscopy (SEM and TEM), EDS and DRS-UV, respectively. The band gap of these nanocrystals lies in the range suitable for solar cell applications. Finally, these nanocrystal-based prototype photo-electrochemical cells exhibit high photoresponsivity and stability under alternating light and dark conditions.

Molecular precursor-mediated facile synthesis of photo-responsive stibnite Sb2S3 nanorods and tetrahedrite Cu12Sb4S13 nanocrystals.

Stibnite Sb2S3 and tetrahedrite Cu12Sb4S13 nanostructures being economical, environmentally benign and having a high absorption coefficient are highly promising materials for energy conversion applications. However, producing these materials especially tetrahedrite in the phase pure form is a challenging task. In this report we present a structurally characterized single source molecular precursor [Sb(4,6-Me2pymS)3] for the facile synthesis of binary Sb2S3 as well as ternary Cu12Sb4S13 in oleylamine (OAm) at a relatively lower temperature. The as-prepared Sb2S3 and Cu12Sb4S13 nanostructures were thoroughly checked for their phase purity, elemental composition and morphology by powder X-ray diffraction (pXRD), electron dispersive spectroscopy (EDS) and electron microscopy techniques. pXRD and EDS studies confirm the formation of phase pure, crystalline orthorhombic Sb2S3 and cubic Cu12Sb4S13. The SEM, TEM and HRTEM images depict the formation of well-defined nanorods and nearly spherical nanocrystals for Sb2S3 and Cu12Sb4S13, respectively. The Sb2S3 nanorods and Cu12Sb4S13 nanocrystals exhibit an optical bandgap of ∼1.88 and 2.07 eV, respectively, which are slightly blue-shifted relative to their bulk bandgap, indicating the quantum confinement effect. Finally, efficient photoresponsivity and good photo-stability were achieved in the as-prepared Sb2S3 and Cu12Sb4S13 nanostructure-based prototype photo-electrochemical cell, which make them promising candidates for alternative low-cost photon absorber materials.

Dimethyltin(IV)-4,6-dimethyl-2-pyridylselenolate: an efficient single source precursor for the preparation of SnSe nanosheets as anode material for lithium ion batteries.

The air stable tin(IV) complex [Me2Sn{2-SeC5H2(Me-4,6)2N}2] has been synthesized, characterized by NMR, elemental analysis, and single crystal XRD, and employed as a single source molecular precursor (SSP) for the facile synthesis of orthorhombic SnSe nanosheets. The crystal structure, phase purity, morphology and band gap of the nanosheets were investigated by pXRD, EDS, electron microscopy and diffuse reflectance spectroscopy techniques, respectively. It was found that the preferential orientation of planes and the morphology of the nanosheets rely upon the reaction conditions. The band gaps of the nanosheets were blue shifted with respect to the bulk band gap of the material. The synthesized SnSe nanosheets have been employed as an anode material in lithium ion batteries (LIBs). The material exhibits an initial specific capacity of 1134 mA h g-1 at a current density of 50 mA g-1 and was found to retain a capacity of 380 mA h g-1 even after 70 cycles with 100% efficiency.

Di-tert-butyltin(IV) 2-pyridyl and 4,6-dimethyl-2-pyrimidyl thiolates: versatile single source precursors for the preparation of SnS nanoplatelets as anode material for lithium ion batteries.

New air and moisture stable di-tert-butyltin complexes derived from 2-mercaptopyridine (HSpy), [tBu2Sn(Spy)2], [tBu2Sn(Cl)(Spy)] and 4,6-dimethyl-2-mercaptopyrimidine (HSpymMe2) [tBu2Sn(Cl)(SpymMe2)], have been prepared and utilized as single-source molecular precursors for the preparation of orthorhombic SnS nanoplatelets by a hot injection method and thin films by aerosol assisted chemical vapour deposition (AACVD). The complexes were characterized by NMR (1H, 13C, 119Sn) and elemental analysis and their structures were unambiguously established by the single crystal X-ray diffraction technique. Thermolysis of these complexes in oleylamine (OAm) produced SnS nanoplatelets. The morphologies, elemental compositions, phase purity and crystal structures of the resulting Oam-capped nanoplatelets were determined by electron microscopy (SEM, TEM), energy dispersive X-ray spectroscopy (EDS) and pXRD, while the band gaps of the nanoplatelets were evaluated by diffuse reflectance spectroscopy (DRS) and were blue shifted relative to the bulk material. The morphology and preferential growth of the nanoplatelets were found to be significantly altered by the nature of the molecular precursor employed. The synthesized SnS nanoplatelets were evaluated for their performance as anode material for lithium ion batteries (LIBs). A cell comprised of an SnS electrode could be cycled for 50 cycles. The rate capability of SnS was investigated at different current densities in the range 0.1 to 0.7 A g-1 which revealed that the initial capacity could be regained.

Orcinol Glucoside Loaded Polymer - Lipid Hybrid Nanostructured Lipid Carriers: Potential Cytotoxic Agents against Gastric, Colon and Hepatoma Carcinoma Cell Lines.

PURPOSE: Orcinol glucoside (OG) - loaded nanostructured lipid carrier (NLC), coated with polyethylene glycol-25/55-stearate (PEG-25/55-SA), were explored for delivering OG to improve in vitro cytotoxicity against gastrointestinal tract (GIT), colon and hepatoma carcinoma cell lines. It is being expected that the PEGylated formulations would possess the sustainability in withstanding the adverse physiological extremities like the most significant metabolic activities and phase I / II enzymatic activities in the intestines. METHODS: NLCs were prepared using tristearin, oleic acid and PEG-25/55-stearate by hot homogenization-ultrasonic dispersion; characterized by DLS, TEM, SEM, AFM, entrapment efficiency and drug loading capacity studies. RESULTS: NLC diameter ranged from 160 to 230 nm with negative zeta potential of -8 to -20 mV. TEM/SEM and AFM studies suggest spherical and smooth surface morphologies. Differential scanning calorimetry studies reveal the loss of crystallinity when OG was incorporated into the NLC. NLCs showed initial burst release, followed by sustained release of OG. PEG-NLC exhibited superior anticancer activity against GIT and also in hepatoma cancer cell lines. CONCLUSIONS: This is the first report demonstrating a practical approach for possible oral delivery of OG in GIT and targeting hepatoma cancer, warranting further in vivo studies for superior management of GIT cancer.

Biophysical Correlates on the Composition, Functionality, and Structure of Dendrimer-Liposome Aggregates.

Interaction between negatively charged liposomes and cationic polyamidoamine dendrimers of different generations was investigated through size, zeta potential, turbidity, electron microscopy, atomic force microscopy, fluorescence spectroscopy, and calorimetric studies. Liposomes with the binary combination of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) + dihexadecyl phosphate, DPPC + 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol, DPPC + 1,2-dipalmitoyl-sn-glycero-3-phosphate, and DPPC + 1,2-dipalmitoyl-sn-glycero-3-phosphoethanol were stable up to 60 days. The electrostatic nature of dendrimer-lipid bilayer interaction was evidenced through charge neutralization and subsequent reversal upon added dendrimer to liposome. Dendrimer-liposome interaction depended on its generation (5 > 4 > 3) in addition to the charge, head groups, and hydrocarbon chain length of lipids. Fluorescence anisotropy and differential scanning calorimetry studies suggest the fluidization of the bilayer, although the surface rigidity was enhanced by the added dendrimers. Thermodynamic parameters of the interaction processes were evaluated by isothermal titration and differential scanning calorimetric studies. The binding processes were exothermic in nature. The enthalpy of transition of the chain melting of lipids decreased systematically with increasing dendrimer concentration and generation. Dendrimer-liposome aggregates were nontoxic to healthy human blood cell, suggesting the potential of such aggregates as drug delivery systems.

Influence of Lipid Core Material on Physicochemical Characteristics of an Ursolic Acid-Loaded Nanostructured Lipid Carrier: An Attempt To Enhance Anticancer Activity.

The impact of saturation and unsaturation in the fatty acyl hydrocarbon chain on the physicochemical properties of nanostructured lipid carriers (NLCs) was investigated to develop novel delivery systems loaded with an anticancer drug, ursolic acid (UA). Aqueous NLC dispersions were prepared by a high-pressure homogenization-ultrasonication technique with Tween 80 as a stabilizer. Mutual miscibility of the components at the air-water interface was assessed by surface pressure-area measurements, where attractive interactions were recorded between the lipid mixtures and UA, irrespective of the extent of saturation or unsaturation in fatty acyl chains. NLCs were characterized by combined dynamic light scattering, transmission electron microscopy (TEM), atomic force microscopy (AFM), differential scanning calorimetry, drug encapsulation efficiency, drug payload, in vitro drug release, and in vitro cytotoxicity studies. The saturated lipid-based NLCs were larger than unsaturated lipids. TEM and AFM images revealed the spherical and smooth surface morphology of NLCs. The encapsulation efficiency and drug payload were higher for unsaturated lipid blends. In vitro release studies indicate that the nature of the lipid matrix affects both the rate and release pattern. All UA-loaded formulations exhibited superior anticancer activity compared to that of free UA against human leukemic cell line K562 and melanoma cell line B16.

Influence of Lipid Composition, pH, and Temperature on Physicochemical Properties of Liposomes with Curcumin as Model Drug.

The physicochemical properties of large unilamellar vesicles (LUVs) were assessed with respect to lipid composition, pH, time, and temperature by monitoring their size, zeta potential, drug payload, and thermal behavior. A conventional thin film hydration technique was employed to prepare liposomes from soy phosphatidylcholine (SPC), dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG), and a 7:3 (M/M) mixture of DPPC+DPPG along with 30 mole% cholesterol in each combination. While the size of liposomes depended on lipid composition, pH and temperature, the zeta potential was found to be independent of the pH of the medium, although it varied with liposome type. Spherical morphology and bilayer were observed by electron microscopy. The phase transition temperature increased with decreasing pH. Membrane micro-viscosity showed the highest value for SPC, and membrane rigidity increased with increasing pH. The entrapment efficiency of liposomes with reference to curcumin was as follows: DPPC>DPPC+DPPG>DPPG>SPC. Sustained release of curcumin was observed for all liposomes. Curcumin-loaded liposomes exhibited substantial antibacterial activity against the gram-positive bacteria Bacillus amyloliquefaciens. Additional studies are needed to improve the understanding of the effect of formulation variables on the physicochemical stability of liposomes.

Effects of Fatty Acids on the Interfacial and Solution Behavior of Mixed Lipidic Aggregates Called Solid Lipid Nanoparticles.

Mutual miscibility of soylecithin, tristearin, fatty acids (FAs), and curcumin was assessed by means of surface pressure-area isotherms at the air-solution interface in order to formulate modified solid lipid nanoparticles (SLN). Appearance of minima in the excess area (Aex) and changes in free energy of mixing (∆G(0)ex) were recorded for systems with 20 mole% FAs. Modified SLNs, promising as topical drug delivery systems, were formulated using the lipids in combination with curcumin, stabilized by an aqueous Tween 60 solution. Optimal formulations were assessed by judiciously varying the FA chain length and composition. Physicochemical properties of SLNs were studied such as the size, zeta potential (by dynamic light scattering), morphology (by freeze fracture transmission electron microscopy), and thermal behavior (by differential scanning calorimetry). The size and zeta potential of the formulations were in the range 300-500 nm and -10 to -20 mV, respectively. Absorption and emission spectroscopic analyses supported the dynamic light scattering and differential scanning calorimetry data and confirmed localization of curcumin to the palisade layer of SLNs. These nanoparticles showed a sustained release of incorporated curcumin. Curcumin-loaded SLNs were effective against a gram-positive bacterial species, Bacillus amyloliquefaciens. Our results on the physicochemical properties of curcumin-loaded SLNs, the sustained release, and on antibacterial activity suggest that SLNs are promising delivery agents for topical drugs.

Ion-pair amphiphile: a neoteric substitute that modulates the physicochemical properties of biomimetic membranes.

Ion-pair amphiphiles (IPAs) are neoteric pseudo-double-tailed compounds with potential as a novel substitute of phospholipid. IPA, synthesized by stoichiometric/equimolar mixing of aqueous solution of hexadecyltrimethylammonium bromide (HTMAB) and sodium dodecyl sulfate (SDS), was used as a potential substituent of naturally occurring phospholipid, soylecithin (SLC). Vesicles were prepared using SLC and IPA in different ratios along with cholesterol. The impact of IPA on SLC was examined by way of surface pressure (π)-area (A) measurements. Associated thermodynamic parameters were evaluated; interfacial miscibility between the components was found to depend on SLC/IPA ratio. Solution behavior of the bilayers, in the form of vesicles, was investigated by monitoring the hydrodynamic diameter, zeta potential, and polydispersity index over a period of 100 days. Size and morphology of the vesicles were also investigated by electron microscopic studies. Systems comprising 20 and 40 mol % IPA exhibited anomalous behavior. Thermal behavior of the vesicles, as scrutinized by differential scanning calorimetry, was correlated with the hydrocarbon chain as well as the headgroup packing. Entrapment efficiency (EE) of the vesicles toward the cationic dye methylene blue (MB) was also evaluated. Vesicles were smart enough to entrap the dye, and the efficiency was found to vary with IPA concentration. EE was found to be well above 80% for some stable dispersions. Such formulations thus could be considered to have potential as novel drug delivery systems.