Disclosed herein is a method to obtain the ∼300 kDa gold−hexanethiolate compound, extracted from the Faradaurate series of smaller (3) and larger (1) homologues, thereby permitting the first measurement of its distinctive properties by methods including mass spectrometry, optical spectroscopy, electron microscopy, X-ray scattering, and diffraction. The results suggest a monocrystalline metallic core (free of twinning planes) of ∼3.1 nm minimum dimension, which supports a clear plasmonic optical response, along with a diffuse exterior shell. An idealized model to account for this (and smaller) members of the series is proposed based on the completion of a convex core of regular truncatedoctahedral (TO) morphology, that is, the TO (5,5) crystallite comprising 1289 sites. The diffuse layer may comprise the 240 S sites (thiolate sulfur headgroups) and 96 Au-adatom sites, giving a total composition (1385,240) and a molar mass of ∼301.0 kDa (90.7% Au). The ∼300 and ∼400 kDa gold compounds contain Au ∼1400 and Au ∼2000 atoms, respectively.

Atomic pair distribution function (PDF) analysis has been widely used to investigate nanocrystalline and structurally disordered materials. Experimental PDFs retrieved from electron diffraction (ePDF) in transmission electron microscopy (TEM) represent an attractive alternative to traditional PDF obtained from synchrotron X-ray sources, particularly for studying minute samples. Nonetheless, the inelastic scattering produced by the large dynamical effects of electron diffraction may obscure the interpretation of ePDF. In the present work, precession electron diffraction (PED-TEM) has been employed to obtain the ePDF of two different sampleslipoic acid-and hexanethiolate-capped gold nanoparticles (∼4.5 and 4.2 nm, respectively)randomly oriented and measured at both liquid nitrogen and room temperatures. The electron diffraction data were processed to obtain ePDFs which were subsequently compared with the PDF of different ideal structure models. The results demonstrate that the PED-ePDF data are sensitive to different crystalline structures such as monocrystalline (truncated octahedra) and multiply twinned (decahedra, icosahedra) structures. The results indicate that PED reduces the residual from 46 to 29%; in addition, the combination of PED and low temperature further reduced the residual to 23%, which is comparable to X-ray PDF analysis. Furthermore, the inclusion of PED resulted in a better estimation of the coordination number from ePDF. To the best of our knowledge, the precessed electron-beam technique (PED) has not been previously applied to nanoparticles for analysis by the ePDF method.

The ubiquitous Au 144 (SR) 60 and closely related compounds of ∼29 kDa (core mass) are large monolayer protected clusters (MPC) comprising 144 gold atoms and 60 thiolate ligands (RS groups). Since this cluster family was first identified in 1996, it has served innumerable investigations from physicochemical fundamentals in the quantum "critical size" regime to practical applications in biomedicine, using various phases appropriate to the R-group properties. Very recently, Wu and co-workers achieved an unambiguous determination of the virus-like chiral-icosahedral symmetry of its Au−S core-and surface-structure. Despite these enormous advances, certain practical considerations restricted its applicability. An extraordinary recent development is that ESI-MS allows all the coexisting species in solution to be precisely detected, revolutionizing research on smaller MPCs. The difficult electrospray ionization properties of the critical-size MPCs have so far precluded the full application of ESI-MS methods. Building on the advances by Ishida and co-workers in cationized (quat-terminated) Rgroups, we have recently found a path to tertiary-amino thiolate-protected clusters with characteristic basic properties including pH-controlled ionization of terminal amino groups. Here we report the first extension of these methods beyond the small-cluster domain and into the critical-size regime. In particular, we disclose a precision route to captamine-protected Au 144 (SR) 60 clustersaccompanied by small quantities of its Au 137 and Au 130 byproducts and indications of somewhat larger (plasmonic) speciesthat promises to overcome these challenges due to its amphiphilic nature and solubility in both aqueous and organic phase upon contact with acid or base in the solution. The ESI-MS analysis generates up to a 8+ charge state without any special counterions or ion-pairing agents.

Atomic pair distribution function (PDF) analysis has been widely used to investigate nanocrystalline and structurally disordered materials. Experimental PDFs retrieved from electron diffraction (ePDF) in transmission electron microscopy (TEM) represent an attractive alternative to traditional PDF obtained from synchrotron X-ray sources, when employed on minute samples. Nonetheless, the inelastic scattering produced by the large dynamical effects of electron diffraction may obscure the interpretation of ePDF. In the present work, precession electron diffraction (PED-TEM) has been employed to obtain the ePDF of two different sub-monolayer samples ––lipoic acid protected (~ 4.5 nm) and hexanethiolated(~ 4.2 nm, ~ 400-kDa core mass) gold nanoparticles­­––randomly oriented and measured at both liquid-nitrogen and room temperatures, with high dynamic-range detection of a CMOS camera. The electron diffraction data were processed to obtain ePDFs which were subsequently compared with PDF of different ideal structure-models. The results demonstrate that the PED-ePDF data is sensitive to different crystalline structures such as monocrystalline (truncated octahedra) versus multiply-twinned (decahedra, icosahedra) structuresof the face-centered cubic gold lattice. The results indicate that PED reduces the residual from 46% to 29%; in addition, the combination of PED and low temperature further reduced the residual to 23%, which is comparable to X-ray PDF analysis. Furthermore, the inclusion of PED resulted in a better estimation of the coordination number from ePDF. To the best of our knowledge, the precessed electron-beam technique (PED) has not been previously applied to nanoparticles for analysis by the ePDF method.

Monolayer-protected clusters (MPCs), typified by the (Au, Ag)-thiolates, share dimensions and masses with aqueous globular proteins (enzymes), yet efficient bioanalytical methods have not proved applicable to MPC analytics. Here we demonstrate that direct facile ESI­(+)­MS analysis of MPCs succeeds, at the few-picomol level, for aqueous basic amino-terminated thiolates. Specifically, captamino-gold clusters, Au n (SR) p , wherein −R = −(CH2)2N­(CH3)2, are prepared quantitatively via a direct one-phase (aq/EtOH) method and are sprayed under weakly acidic conditions to yield intact 6.8 kDa complexes, (n,p) = (25, 18), with up to 5 H+ adducts, or 34.6 kDa MPCs (144, 60) at charge state z = 8+. These exceed all prior reports of positive charging of MPCs except for those bearing per-cationized (quat) ligands. pH-mediated reversible phase transfer (aqueous to/from DCM-rich phases) are consistent with peripheral exposure of all tertiary amino groups to solutions. This surprising development opens the way to all manner of modifications or extensions, as well as to advanced analyses inspired by those applied to intact biomolecules.