Synthesis citrate reduction

One year later, Brust and Schiffrin [28,29] published a method for AuNPs synthesis which has a considerable impact on the overall field in less than a decade because it allowed the facile synthesis of thermally stable and air-stable AuNPs of reduced dispersity and controlled size for the first time. In this method, the gold colloids are sterically stabilized by organic molecules having thiol, amide or acid groups in contrast to the citrate reduction method where the gold colloids are kinetically stabilized in aqueous solutions by an electrical double layer [28,29], The main advantage of the Brust method is that the gold particles behave in a way as chemical compounds. These AuNPs can be repeatedly isolated and... 

Figure 6.53. TEM micrographs of various stages of Au nanoparticle synthesis via the citrate reduction of AuCU, showing nanowire intermediate formation. The colors of the solutions are (a) colorless, (b) dark blue, (c) dark purple, (d) - (e) purple, and (f) ruby-red. Reproduced with permission from J. Phys. Chem. C 2007, 111, 6281. Copyright 2007 American Chemical Society.

Disclosing the binding motif of multiblock RAFT polymers on AuNPs from citrate reduction raises the questimi of whether the polymer binding can vary for different types of AuNPs. It is known that AuNPs from the two-phase Brust-Schiffrin synthesis can assemble into spherical particle networks when treated with low molecular weight crosslinking agent [106, 107]. When tetraocty-lammonium bromide-capped AuNPs from this two-phase method are functionalized in toluene dispersion with multiblock RAFT polymers of styrene, the formation of spherical AuNP assemblies can be observed by TEM (Fig. 9) [108]. It can be concluded from these TEM images that the particle density inside... 

The need to achieve high yield in one-pot synthesis, coupled to the relative kinetic inertness of rhenium complex (e.g. compared to technetium) and the mild conditions required has led to the development of useful versatile rhenium(V) intermediates that can be quickly prepared in quantitative yield, and are metastable, i.e. kinetically labile enough to react rapidly with the final chelator, again in high yield. The most widely used ligands suitable for this purpose are polydentate hydroxycarboxylic acids such as glucoheptonate [116a], citrate (47), tartrate (48), and 2-hydroxyisobutyric acid (49) [159]. Examples are discussed elsewhere in this chapter. They are typically used in the presence of Sn(II) to reduce Re(VII) to Re(V), at moderately elevated temperature (50-100 °C) at pH 2-3 (acid pH promotes reduction of perrhenate, presumably by facilitat-... 

C the product is Rli6(CO)i6. This is consistent with an endothermic equilibrium from the tetramer to the hexamer (equation 22). A two-step synthesis of Rli4(CO)i2 at room temperature and atmospheric pressure involves the reduction of the [RhCh] anion to [RhCl2(CO)2] with copper, followed by reduction with water and CO in the presence of a sodium citrate buffer. The yields are nearly quantitative. 

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