Heterochiral Self-Discrimination-Driven Supramolecular Self-Assembly of Decanuclear Gold(I)-Sulfido Complexes into 2D Nanostructures with Chiral Anions-Tuned Morphologies

Chiral self-recognition and self-discrimination are of vital importance to biological processes. In this work, 2D regular rhombic nanocrystals ( RS -NC ) were fabricated through heterochiral self-discrimination between chiral polynuclear gold(I)-sulfido complex enantiomers, [(R-BINAP)₄Au₁₀S₄]Cl₂ ( R -Au₁₀ ) and [(S-BINAP)₄Au₁₀S₄]Cl₂ ( S -Au₁₀ ), in MeOH without the need for any surfactants or templates. The monitoring of nanocrystals (NCs) formation by TEM and DLS has uncovered the self-assembly process and shape evolution of the NCs and revealed a screw-dislocation dictated spiral growth of the rhombic NCs. Upon addition of chiral anions, the morphology of the gold NCs was found to change from rhombic to strip and quasi-hexagonal nanosheets, arising from reverse and rotational layer-by-layer stacking to give the bilayer NCs. By applying a high temperature, rhombic gold nanoisland films were obtained from the rhombic NCs. The current study has provided a simple strategy towards the construction of regular geometric 2D NCs as well as their chiral anion-tuned and reverse and rotational stacking-determined morphology change by heterochiral self-discrimination.     

Synthetic studies toward the bryostatins: a substrate-controlled approach to the A-ring

[reaction: see text] The synthesis of a C1-C13 A-ring subunit of bryostatin 1 is detailed. The key features of the approach include the convergent fragment assembly with a highly stereoselective construction of the C7-C8 bond indicated above.     

Synthesis,structural characterization,and photophysical studies of hexanuclear gold(I) chalcogenido complexes

A hexanuclear gold(I) selenido cluster and its sulfido counterpart, [Au₆{μ‐Ph₂PN(CH₂‐o‐Py)PPh₂}₃(μ₃‐E)₂](ClO₄)₂ (E = S, Se), with bridging bis(diphenylphosphino)amine ligands were synthesized and characterized. The X‐ray crystal structure of the selenido cluster was determined, with the gold core possessing a distorted heterocubane structure. Intramolecular aurophilic interactions with short Au(I)?Au(I) contacts of around 3.09–3.13 Å were observed. The complexes were found to emit strongly in the solid state with orange to red emission colors. Their electronic absorption and emission properties were also investigated.     

Detection of PEGylated proteins in polyacrylamide gels by reverse staining with zinc and imidazole salts

The reverse staining, with imidazole-SDS-zinc, of PEG-linked proteins separated by SDS-PAGE was studied. Using model conjugates (interferon-alpha 2b (IFN-alpha2b) reacted with either a branched-chain (40,000) PEG (PEG2,40) or a linear monomethoxy PEG polymer (Mr of 12,000) and chromatographically purified monoPEG2,40-IFN-alpha2b), conventional small-format analytical gels (<1 mm thick) showed typical detection patterns (i.e., transparent, colorless bands clearly discernible against a zinc imidazolate-generated white gel background), in less than 20 min. Nonreacted (free) PEG was almost undetected, as expected. The reverse-stained PEGylated IFN-alpha2b patterns were qualitatively indistinguishable from those of parallel gels stained with iodine (I2). The LOD was estimated in the low nanogram range (e.g., at about 7 ng for mono- or bi-PEG2,40 IFN-alpha2b per lane on gradient (4-17%) gels). Also, this stain allowed the visualization of Coomassie blue-undetected PEG-IFN bands, and could be restained with I2. PEGylated species of lysozyme, a low-molecular-weight peptide, ovalbumin, and chymotrypsin were used to demonstrate the generality of this stain. We also show (i) how to counteract the adverse effect of some parameters (e.g., gel thickness above 1 mm, long gel length, low (e.g., 4-6%) acrylamide concentration) on the reverse staining process and (ii) that the properties of the reverse-stained PEGylated proteins remain unchanged, as judged by analyzing both the ion exchange chromatography-based positional isomer separation profile and enzyme-linked immunosorbent response of PEG-IFN recovered from gels. Consequently, this technique may be useful for the rapid analysis or the small-scale preparation of PEGylated proteins.