Novel hypolipidemic conjugates of fatty acid and bile acid with lysine for linkage

Novel fatty acid–bile acid conjugates (1a–1k) were designed and synthesized by coupling of the fatty acids to the 3-OH of bile acids using lysine for linkage. In the conjugates, the 24-COOH of the bile acids was kept intact to preserve liver-specific recognition. The ability of the newly synthesized conjugates (at 100?mg/kg dosage) to reduce total cholesterol (TC) and triglyceride (TG) levels in mice fed with high-fat diet (HFD) was evaluated. Conjugates of stearic acid with cholic acid and palmitic acid with ursodeoxycholic acid (at dosages of 50, 100, and 200?mg/kg) were further evaluated to determine their ability to reduce aspartate aminotransferase (AST), alanine aminotransferase (ALT), TC, and TG levels in mice fed with HFD. All conjugates showed potent hypolipidemic activity. Further investigation revealed that compounds 1c and 1?g not only dose-dependently reduced serum levels of TC and TG, but also inhibited the elevation of serum AST and ALT levels in mice fed with HFD. Thus, compounds 1c and 1?g are promising hypolipidemic agents with hepatocyte protective effects against HFD-induced liver damage.     

Conjugation of curcumin with PVP capped gold nanoparticles for improving bioavailability

Curcumin, a natural polyphenolic compound, has astounding therapeutic applications but lacks in bioavailability mainly due to its poor solubility in water. Polyvinyl pyrrolidone (PVP) which is a proven drug carrier has been used to facilitate the conjugation of curcumin with gold nanoparticles and to improve the solubility of curcumin in water. In this conjugate diaryl heptanoid chromophore group of curcumin which is a much needed group in biomedical applications remains intact as observed from FTIR and UV–vis spectroscopy analysis. The work shows good promise for such conjugates as therapeutic-cum-imaging materials in biomedical field.     

Synthesis of 16-Mercaptohexadecanoic acid capped gold nanoparticles and their immobilization on a substrate

Controlled assembly of nanoparticles on substrates is a promising path to develop miniaturized electronic and optical devices. Among the important issues to be addressed in this area include immobilization of the nanoparticles on substrates in order to ensure that the system is robust. In this work, 16-mercaptohexadecanoic acid (16-MHDA) capped gold nanoparticles with a narrow size distribution have been synthesized through a single phase synthesis method and subsequently immobilized on to silicon surface through covalent molecular assembly. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the absence of unreacted thiol in the synthesized gold nanoparticles. Presence of gold nanoparticles on Si surface after the immobilization process was confirmed through XPS. Cross-sectional high resolution transmission electron microscopy (HR-TEM) images provide direct evidence that the particles are indeed anchored to the silicon surface. The formation of uniform-sized and separated acid functionalized gold nanoparticles and their immobilization on to Si provide a basis for further nano-structuring.     

Facile synthesis of organically capped CdTe nanoparticles

A simple method for the preparation of tri-n-octylphosphine oxide (TOPO) and hexadecylamine (HDA) capped CdTe particles have been employed in this study. The method involves the reduction of tellurium in water followed by the addition of the cadmium salt and thermolysis in TOPO and HDA. The influence of the reduction time (2, 4 and 6 h) of tellurium on the optical properties was investigated. The particles were characterised by electron microscopy and X-ray diffraction techniques.     

Langmuir monolayer properties of 4-methylbenzenethiol capped gold nanoparticles

The properties of 4-methylbenzenethiol capped gold nanoparticles have been investigated at the air–water interface. Langmuir isotherms and compression cycles show that a stable monolayer is formed on the water surface. In situ UV-visible spectroscopy confirms that the plasmon absorption band is present which is characteristic of small metallic particles. The monolayer was imaged using real time Brewster Angle Microscopy (BAM). Above surface pressures of 5 mN m^− 1 the monolayer was virtually homogeneous. During decompression, the monolayer fractured into rod-like structures. These rods were initially orientated parallel to the movable barriers containing the monolayer and as the area was increased, their orientation randomized. During subsequent compressions the rods recombined to recreate a homogeneous monolayer.     

Synthesis of PVP capped gold nanoparticles by the UV-irradiation technique

Multi twinned gold nanoparticles have been synthesized by an ultraviolet irradiation technique involving the reduction of a gold salt in the presence of polyvinyl pyrrolidone (PVP).     

Fabrication of capped gold nanoparticles by using various amino acids

The production of gold nanoparticles (GNPs) by amino acid is one of the most attractive and interesting subjects in nanobiotechnology. In this study, amino acids have been utilised as a reducing agent and also an agent for capping GNPs. The GNPs were prepared using a reduction solution containing gold cations with optimum concentration of gold salt (5?mM), and also functionalised by glutamic acid, phenylalanine and tryptophan with optimum concentration of amino acids (25?mM). The optimum condition of gold solution and amino acids were achieved by ultraviolet–visible spectroscopy. The size of nanoparticles was obtained 5–20, 10–20 and 20–30?nm, respectively, by transmission electron microscopy and dynamic light scattering techniques. The results obtained from experimental and quantum calculations confirm that amino acids have strong bond while they have anion binding. Moreover, the free carboxylic groups of capped GNPs are one of the suitable and capable beads for binding biological agents. As a result, the medical applications of amino acids and proteins can be used as a practical method due to the strong interaction of peripheral amine groups with nanoparticles.     

Growth of hydroxyapatite on physiologically clotted fibrin capped gold nanoparticles

The growth of hydroxyapatite (HAp) on physiologically clotted fibrin (PCF)-gold nanoparticles is presented for the first time by employing a wet precipitation method. Fourier transform infrared (FTIR) spectroscopy confirmed the characteristic functionalities of PCF and HAp in the PCF-Au-HAp nanocomposite. Scanning electron microscopy (SEM) images have shown cuboidal nanostructures having a size in the range of 70-300?nm of HAp, whereas 2-50?nm sized particles were visualized in high-resolution transmission electron microscopy (TEM). Energy-dispersive x-ray (EDX) and x-ray diffraction (XRD) studies have confirmed the presence of HAp. These results show that gold nanoparticles with PCF acted as a matrix for the growth of HAp, and that PCF-Au-HAp nanocomposite is expected to have better osteoinductive properties.     

Novel single-phase and gram-scale synthesis of thiol-uncapped stable colloidal gold nanoparticles

Here we describe a new chemical route for obtaining nanometer-sized gold(0) particles with a narrow size distribution and a band gap of 1.45 eV. The synthetic method is based on the reduction of AuBr3 with t-BuOLi activated LiH in dioxane. The single-phase process developed allows the production of large quantities of stable thiol-uncapped gold(0) nanoparticles. These clusters were further used for the production of monodisperse Au nanoparticles with controlled surface properties through ligand exchange with 1-dodecanethiol or 1-decylamine.     

Phospholipid-assisted synthesis of size-controlled gold nanoparticles

Morphology and size control of gold nanoparticles (AuNPs) by phospholipids (PLs) has been reported. It was found that gold entities could form nanostructures with different sizes controlled by PLs in an aqueous solution. During the preparation of 1.5 nm gold seeds, AuNPs were obtained from the reduction of gold complex by sodium borohydride and capped by citrate for stabilization. With the different ratios between seed solution and growth solution, which was composed by gold complex and PLs, gold seeds grew into larger nanoparticles step by step until enough large size up to 30 nm. The main discovery of this work is that common biomolecules, such as PLs can be used to control nanoparticle size. This conclusion has been confirmed by transmission electron micrographs, particle size analysis, and UV-vis spectra.     

Cellular uptake of gold nanoparticles passivated with BSA-SV40 large T antigen conjugates

Internalization and subcellular localization in HeLa cells of gold nanoparticles modified with the SV40 large T antigen were quantified using inductively coupled plasma optical emission spectroscopy (ICP-OES). Internalization was monitored as a function of incubation time, temperature, nanoparticle diameter, and large T surface coverage. Increasing the amount of large T peptides per gold nanoparticle complex, by either increasing the coverage at constant nanoparticle diameter or by increasing the nanoparticle diameter at constant large T coverage, resulted in more cellular internalization. In addition, nuclear fractionation was performed to quantify nuclear localization of these complexes as a function of large T coverage. In contrast to our prior qualitative investigations of nuclear localization by video-enhanced color differential interference contrast microscopy (VEC-DIC), ICP-OES was able to detect nanoparticles inside fractionated cell nuclei. Although increasing the large T coverage was found to afford higher cell internalization and nuclear targeting, quantitative evaluation of cytotoxicity revealed that higher large T coverages also resulted in greater cytotoxicity. The ICP-OES and nuclear fractionation techniques reported here are valuable tools that can add important quantitative information to optical and electron imaging methods such as VEC-DIC and transmission electron microscopy regarding the fate of nanoparticles in cells.     

Photochemical synthesis of colloidal gold nanoparticles

Monodisperse gold nanoparticles protected by small organic molecules or by macromolecules with different sizes and shapes are widely used as a precursor material in various applications of gold nanotechnology. However, their preparation is still a formidable task. In this paper the use of photochemically assisted syntheses of monodisperse gold nanoparticles is summarized and some preparations by the authors’ group are introduced. These include spherical and rod-like particles, bimetallic composite nanoparticles, and syntheses using complex intramolecular photoreduction to generate the reducing agent.     

Piezoelectric immunosensor based on gold nanoparticles capped with mixed self-assembled monolayer for detection of carcinoembryonic antigen

It is very important for a piezoelectric immunosensor to increase specific binding and decrease nonspecific adsorption. This study presents the development of such a piezoelectric immunosensor for the detection of carcinoembryonic antigen. An AT-cut quartz crystal's Au electrode surface was first modified with homogenous self-assembled monolayer of cysteamine (CE). Gold nanoparticles capped with mixed self-assembled monolayer of CE and MH (6-mercapto-1-haxanol) were then attached to the CE monolayer via glutaraldehyde (GA). Antibodies were immobilized onto a mixed self-assembled monolayer of CE and MH with GA as a reactive intermediate too. The binding of target antigens onto the immobilized antibodies decreased the sensor's resonant frequency, and the frequency shift was correlated to the antigen concentration. The stepwise assembly of the immunosensor was characterized by means of cyclic voltammetry technique. This immunoassay was shown to be specific and sensitive, thus providing a viable alternative to carcinoembryonic antigen detection method.     

Sonochemical synthesis of gold nanoparticles on chitosan

Au nanoparticles deposited on chitosan were readily prepared from aqueous solution of NaAuCl₄ containing chitosan powder by the reaction with sonochemically formed reducing species. The average size of the formed Au particles was measured to be 22 nm with a relatively narrow size distribution, although there was no specific stabilizer for Au nanoparticles.     

Facile synthesis of chondroitin sulfate-stabilized gold nanoparticles

A facile and simple method for the synthesis of biocompatible gold nanoparticles (AuNPs) at room temperature has been developed by using sodium borohydride as the reducing agent and employing an inexpensive water-soluble chondroitin sulfate (CS) biopolymer as the stabilizing agent. The as-prepared AuNPs were characterized with ultraviolet–visible (UV–vis) spectroscopy and transmission electron microscopy (TEM). Additionally, the stability of AuNPs in aqueous solution was investigated as a function of the electrolyte sodium chloride concentration. The experimental results showed that even high sodium chloride concentration (1 M) also did not destabilize the colloidal gold solution. So it could be speculated that the high stability of AuNPs should be attributed to the electrostatic repulsion and steric hindrance between the AuNPs stabilized by CS molecules, which wrapped around the surface of as-prepared AuNPs and prevented their agglomeration, and simultaneously improve biocompatibility of AuNPs as well.     

Poly(acrylic acid)-stabilized colloidal gold nanoparticles: synthesis and properties

Combining the intriguing optical properties of gold nanoparticles with the inherent physical and dynamic properties of polymers can give rise to interesting hybrid nanomaterials. In this study, we report the synthesis of poly(acrylic acid) (PAA)-capped gold nanoparticles. The polyelectrolyte-wrapped gold nanoparticles were fully characterized and studied via a combination of techniques, i.e. UV-vis and infrared spectroscopy, dark field optical microscopy, SEM imaging, dynamic light scattering and zeta potential measurements. Although PAA-capped nanoparticles have been previously reported, this study revealed some interesting aspects of the colloidal stability and morphological change of the polymer coating on the nanoparticle surface in an electrolytic environment, at various pH values and at different temperatures.     

Synthesis and layer-by-layer self-assembly of silver nanoparticles capped by mercaptosulfonic acid

Spherical silver nanoparticles capped by mercaptosulfonic acid with a diameter of about 8 nm were prepared by a simple chemical reaction. The resulting silver nanoparticles were characterized by UV–vis spectroscopy (UV–vis) and transmission electron microscopy (TEM). Using layer-by-layer (LBL) self-assembly technique, the multilayer films containing silver nanoparticles and polycation poly(dialyldimethylammonium chloride) (PDDA) were successfully fabricated. The fabrication process was monitored by UV–vis spectra and the morphology of the multilayer films was investigated by atomic force microscopy (AFM). The cyclic voltammogram (CV) measurements further confirmed that the silver nanoparticles had assembled into the multilayer films successfully. Surface-enhanced Raman spectroscopy (SERS) measurements showed that the multilayer films containing silver nanoparticles could serve as SERS-active substrate.     

One-pot size and shape controlled synthesis of DMSO capped iron oxide nanoparticles

We report here the capping of iron oxide nanoparticles with dimethyl sulfoxide (DMSO) to make chloroform soluble iron oxide nanoparticles. Size and shape of the capped iron oxide nanoparticles are well controlled by simply varying the reaction parameters. The synthesized nanocrystallites were characterized by thermal analysis (TG-DTA), powder X-ray diffraction (XRD), transmission electron microscopy (TEM) for evaluating phase, structure and morphology. ¹H NMR spectra of the synthesized samples confirm DMSO, and the capping of DMSO on the ferrite samples. Shift of the S=O stretching frequency in Fourier transformed infra-red (FTIR) spectra indicates that the bonding between DMSO and ferrite is through an oxygen moiety. The magnetic measurements of all the synthesized samples were investigated with a SQUID magnetometer which shows that the magnetic properties are strongly dependent on the size as well as shape of the iron oxide.     

Ionogel-templated synthesis and organization of anisotropic gold nanoparticles

Photochemical reduction of tetrachloroaurate (AuCl4-) ions in the highly constrained aqueous domains of a nanostructured ionogel template, formed via self-assembly of the ionic liquid 1-decyl-3-methylimidazolium chloride (C10mim+Cl-) in water, results in the formation of anisotropic gold nanoparticles with a variety of sizes and morphologies, which include previously unattainable trigonal prismatic nanorods. Unexpectedly, small-angle X-ray scattering studies of the Au-ionogel composite reveal that the in situ formation of the nanoparticles increases the mesoscopic order of the ionogel, which results in its conversion to a near-monodomain structure. The findings demonstrate that nanostructured, ionic liquid-based gels can be used to template the formation of new nanoparticle morphologies with technologically important optical, electronic, and catalytic properties. It may also be possible to design soft templates that permit the fabrication of highly ordered nanoparticle array-hydrogel composites, thereby enabling control and tuning of the collective properties of the encapsulated nanoparticles.     

Continuous synthesis of gold nanoparticles in a microreactor

A continuous flow microreactor was used for the synthesis of gold nanoparticles (5 to 50 nm) directly from a gold salt (HAuCl(4)) and a reducing agent (ascorbic acid). Experimental parameters were optimized to obtain narrow size distributions, which were at average two times narrower than those obtained in a conventional synthesis. Additionally, two approaches, i.e., elevation of pH during reaction and hydrophobization of internal reactor surfaces were tested to suppress reactor fouling.