Chiral Imidazolium-Functionalized Au Nanoparticles: Reversible Aggregation and Molecular Recognition

Abstract

Gold nanoparticles (AuNPs) stabilized by imidazolium salts derived from amino acids [glycine ( 1 ), rac -alanine ( 2 ), l -phenylalanine ( 3 ), and rac -methionine ( 4 )] were prepared. The AuNPs were stabilized the most by 4 , which kept the particles dispersed in water for months at pH > 5.5. These AuNPs exhibited a well-defined absorption band at 517 nm and had an average particle size of 11.21 ± 0.07 nm. The 4-AuNPs were reversibly aggregated by controlling the pH of the solution. Chiral R , R -4-AuNPs and S , S -4-AuNPs were synthesized, and the chiral environment on the nanoparticle surface was confirmed using circular dichroism; these nanoparticles exhibited a molecular recognition of chiral substrates. Furthermore, they showed potential for separating racemic mixtures when supported on a layered double hydroxide.

N-Heterocyclic Carbenes in Materials Chemistry

“…162 In a 2016 follow-up report on these nanoparticles, their stability in aqueous solutions was described. 161 Similar to Glorius' work, 160 these ligands contain pH-sensitive carboxylic acids. The most stable nanoparticles were those functionalized with amino acid-derived NHC ligands based on rac-methionine as the wingtip groups (65, Table 3, Entry 3).…”

Homochiral imidazolium-based dicarboxylate silver(i) compounds: synthesis, characterisation and antimicrobial properties

“…[1][2][3] They are synthesised easily from amino acids and are convenient starting precursors for the preparation of enantiopure substrates, such as ionic liquids 4 and N-heterocyclic carbene (NHC) ligands. [5][6][7][8] Additionally, they have been used as useful bridging ligands, acting as linkers, in the construction of homochiral coordination polymers or metal-organic frameworks, [9][10][11] and as chirality inductors in asymmetric catalysis. 12,13 Recently we described the synthesis and characterization of chiral 2,2′-(imidazolium-1,3-diyl)bis(3-methylbutanoate) compounds of lithium, sodium and ammonium, {M[(S,S)-L iPr ]} n (M + = Na + , Li + and NH 4 + ), which included the first reported structural data for the chiral basic form [L R ] − .…”

“…1–3 They are synthesised easily from amino acids and are convenient starting precursors for the preparation of enantiopure substrates, such as ionic liquids 4 and N-heterocyclic carbene (NHC) ligands. 5–8 Additionally, they have been used as useful bridging ligands, acting as linkers, in the construction of homochiral coordination polymers or metal–organic frameworks, 9–11 and as chirality inductors in asymmetric catalysis. 12,13…”

A Benchtop Method for Appending Protic Functional Groups to N‐Heterocyclic Carbene Protected Gold Nanoparticles

“…To date, only carboxylic acids have been employed for protic NHC‐AuNPs . Crudden and co‐workers prepared a pendant carboxylic acid on the back of the NHC gold complex precursor prior to reduction with sodium borohydride (Figure c).…”