Aspheric Solute Ions Modulate Gold Nanoparticle Interactions in an Aqueous Solution: An Optimal Way To Reversibly Concentrate Functionalized Nanoparticles

Abstract

Nanometer-sized gold particles (AuNPs) are of peculiar interest because their behaviors in an aqueous solution are sensitive to changes in environmental factors including the size and shape of the solute ions. In order to determine these important characteristics, we performed all-atom molecular dynamics simulations on the icosahedral Au144 nanoparticles each coated with a homogeneous set of 60 thiolates (4-mercapto-benzoate, pMBA) in eight aqueous solutions having ions of varying sizes and shapes (Na+, K+, tetramethylamonium cation TMA+, trisamonium cation TRS+, Cl−, and OH−). For each solution, we computed the reversible work (potential of mean of force) to bring two nanoparticles together as a function of their separation distance. We found that the behavior of pMBA protected Au144 nanoparticles can be readily modulated by tuning their aqueous environmental factors (pH and solute ion combinations). We examined the atomistic details on how the sizes and shapes of solute ions quantitatively factor in the definitive characteristics of nanoparticle-environment and nanoparticle-nanoparticle interactions. We predict that tuning the concentrations of non-spherical composite ions such as TRS+ in an aqueous solution of AuNPs be an effective means to modulate the aggregation propensity desired in biomedical and other applications of small charged nanoparticles.

Ultraviolet Photodissociation of Selected Gold Clusters: Ultraefficient Unstapling and Ligand Stripping of Au25(pMBA)18 and Au36(pMBA)24

“…Mass spectrometry has already become an important tool (along with microscopy, crystallography, spectroscopy, and centrifugation , ) for determination and characterization of novel MPC compositions. , Combined mass spectrometry and X-ray crystallographic analysis has confirmed the structures of the types of MPCs examined in the present report, detailing both the core architecture and protecting ligand composition. Au 25 (pMBA) 18 ( p MBA = para -mercaptobenzoic acid) is composed of a 13-atom icosahedral gold core surrounded by six protecting dimeric ligand “staples” each comprising three ligands and two gold atoms [−SR–​Au–​SR–​Au–​SR−]; Au 36 (pMBA) 24 is composed of a 28-atom face-centered cubic gold core enclosed by four dimeric staples and 12 simple bridging thiolates [−Au–​SR–​Au−] .…”

“…Deciphering the novel structures of MPC materials make them prime candidates for examination by mass spectrometry 11 and chromatography. 12−14 Mass spectrometry has already become an important tool (along with microscopy, crystallography, spectroscopy, and centrifugation 15,16 ) for determination and characterization of novel MPC compositions. 17,18 Combined mass spectrometry and X-ray crystallographic analysis has confirmed the structures of the types of MPCs examined in the present report, detailing both the core architecture and protecting ligand composition.…”

Triethylamine Solution for the Intractability of Aqueous Gold–Thiolate Cluster Anions: How Ion Pairing Enhances ESI-MS and HPLC of aq-Aun(pMBA)p

“…The wide range of Au–pMBA clusters investigatedranging from aurous-thiolate oligomers (∼2–4 kDa) to classic smaller metallic clusters like (25,18), at ∼8-kDa, all the way to the classic larger (144,60) at ∼37-kDamay serve as model systems of comparatively high rigidity and (surface) charge density. The specific solution parameters required for effective ESI processes provide intriguing clues to the fundamental physicochemical solution-phase properties of these clusters. , Furthermore, our results offer some fascinating insights into this “classic” gold–pMBA series, e.g., the surprise (or delayed) appearance in apparent high abundance of the nonclassical (36,24) species.…”

“…Villareal et al found that sodium (Na + ) counterions, and by extension other small hydrophilic cations, create strong salt bridges linking aq-Au 144 (pMBA) 60 (pMBA = paramercaptobenzoic acid) clusters. 13 Subsequently, they predicted the strong ion pairing that results when these alkali ions are replaced by bulky quaternary ammonium cations, namely, tetramethylammonium (TMA+) counterions, 12 which thereby prevents the attractive salt-bridge interaction between clusters. However, TMA + is nonvolatile and thus ineligible for ESI-MS.…”

Molecular dynamics simulations on the effect of size and shape on the interactions between negative Au18(SR)14, Au102(SR)44 and Au144(SR)60 nanoparticles in physiological saline

“…[28] With regard to biomedical applications, a desirable property of gold nanoparticles is their ability to aggregate reversibly into nanoclusters of controlled size when placed in a special solution, and to dissociate back into individual nanoparticles when introduced into the body. [29, 30, 31, 32] Finally, we compare the binding affinity of Au 18 with those of Au 102 [33] and Au 144 [34, 35, 36, 37, 38, 39, 40, 32], functionalized by the same ligand under the same near-physiological conditions.…”