Amino Acid-Based Redox Active Amphiphiles to In Situ Synthesize Gold Nanostructures: From Sphere to Multipod

Abstract

Gold (Au) nanostructures of controllable shapes (spherical and multipod) were synthesized by an in situ reduction technique using newly designed amino acid-based redox active amphiphiles without any additional template in alkaline condition. These amphiphiles are the conjugates of fatty acids (e.g., caproic acid, caprylic acid, and capric acid) and a redox active amino acid (tryptophan). The nature of amphiphiles (especially the length of the alkyl chain associated with fatty acids) and the molar ratio (R) of amphiphile to HAuCl 4 have a significant effect on the morphology of the formed Au nanostructures. For example, the caproic acid-and caprylic acid-based amphiphiles produce mostly multipod-shaped Au nanostructures at a value of R in the range 4-8. However, these amphiphiles produced only spherical Au nanoparticles (NPs) at R in the range 1.3-2.0. However, the capric acid-based amphiphile generates only spherical Au NPs with an average diameter in the range 3.5-6.2 nm, no matter what the value of R is. FTIR and thermogravimetric analysis confirmed the capping of Au nanostructures with amphiphile. XRD results indicated the formation of highly crystalline spherical and multipod-shaped Au nanostructures that were bounded by {111} facets. The mechanisms of formation of spherical/multipod-shaped Au nanostructures are discussed based on the high-resolution transmission electron microscopic (HRTEM) and time-dependent UV-vis spectroscopic studies. HRTEM analysis revealed that the multipod-shaped Au branches were formed by oriented attachment of the initially formed spherical Au NPs of smaller size and were grown along the AE111ae direction. HRTEM results further indicated that spherical Au NPs were also grown along the AE111ae direction.

Gelation of amino acid-based amphiphiles in water-based mixed solvent systems: reusable catalytic templates for nanostructured silica and silica–zirconia photocatalyst

“…A series of different fatty acid (stearic, myristic and capric acid)amino acid (tyrosine, phenylalanine and leucine) conjugated amphiphiles (see Scheme 1 for chemical structures) were synthesized following the conventional solution-phase racemization-free fragmentation-condensation protocol as reported by our group earlier. [38][39][40] Leu-OH (Scheme 1). The details of the reaction procedures and their characterization are described in page S1 to S11 of the ESI.…”

“…Recently, we designed a series of fatty acid-amino acid (tyrosine) conjugated amphiphiles of varying carbon-chain length which were then used for the generation of gold nanostructures. [38][39][40] Herein, our objective was to check the gelation ability of such amphiphiles in various mixed solvents. It was observed that the amphiphile C 17 H 35 -Tyr-OH was soluble in DMSO, but not in water.…”

Tailored synthesis of various Au nanoarchitectures with branched shapes

“…[27][28][29][30] Among various Au architectures, highly branched Au structures, with their attractive structural features (e.g., sharp edges, rich junctions, and high surface areas), are particularly interesting and potentially technologically important. [31][32][33][34][35][36] It would be feasible to tune the fascinating properties of Au architectures. 37 For instance, in comparison with simply bumped Au nanostructures, gold nanoflowers show drastically enhanced SERS activity.…”

Anisotropic nanocrystal arrays organized on protein lattices formed by recombinant clathrin fragments

“…52 Previous investigations have described a fast initial gold nucleation stage, demonstrating that gold seed particles can be formed within the first minute of reduction. 52–53 A slower subsequent growth step can then propagate the nanoparticle formation within a distinct environment. 52 For example, the presence of surface-interacting peptides, 53–54 proteins 55 or cellular structures, 56 can modify the morphologies of metal nanoparticles by preferentially interacting with one region of the nanoparticle, restricting nanoparticle growth and leading to anisotropic forms.…”