Enantiomeric Recognition and Separation by Chiral Nanoparticles

Does Pressure Break Mirror-Image Symmetry? A Perspective and New Insights

This paper is aimed at dissecting and discussing the effect of high pressure on chirogenesis, thus unveiling the role of this universal force in astrochemical and primeval Darwinian scenarios. The first part of this contribution revisits the current status and recent experiments, most dealing with crystalline racemates, for which generation of metastable conglomeratic phases would eventually afford spontaneous resolution and hence enantioenriched mixtures. We then provide an in-depth thermodynamic analysis, based on previous studies of non-electrolyte solutions and dense mixtures accounting for the existence of positive excess volume upon mixing, to simulate the mirror symmetry breaking, the evolution of entropy production and dissipation due to enantiomer conversion. Results clearly suggest that mirror symmetry breaking under high pressure may be a genuine phenomenon and that enantioenrichment from initial scalemic mixtures may also take place.

Hollow multishell structures exercise temporal–spatial ordering and dynamic smart behaviour

A hollow multishell structure (HoMS) is an assembly of multiple shells with voids between the individual shells. Accessible through nanopores, these voids represent separate reaction environments in the same assembly, such that HoMSs have unique properties that are applicable to diverse fields. These applications have mostly exploited the large specific surface area, high loading capacity and/or buffering effect of HoMSs, benefiting the mass/energy transmission and effective surface area. In comparison, the temporal-spatial ordering of reactions, as well as the dynamic smart behaviour of HoMSs, have been less explored but are also emphasized in this Perspective. We first describe the synthesis of HoMSs and the thermodynamic and kinetic aspects of their formation. We then consider the composition and structural functionalization of each shell within a HoMS and then highlight how these enable applications based on temporal-spatial ordering and dynamic smart behaviour.

Amplified vibrational circular dichroism as a manifestation of the interaction between a water soluble gold nanocluster and cobalt salt

Vibrational circular dichroism (VCD) is a powerful tool for the structure determination of dissolved molecules. However, the application of VCD to nanostructures is limited up to now due to the weakness of the effect and hence the low signal intensities. Here we show that the addition of a small amount of cobalt(ii) drastically enhances the VCD signals of a thiolate-protected gold cluster Au₂₅(Capt)₁₈ (Capt = captopril) in aqueous solution. An increase of VCD signal intensity of at least one order of magnitude is observed. The enhancement depends on the amount of CoCl₂ added but almost an order of magnitude enhancement is already observed at a cluster : CoCl₂ ratio of 1 : 1. In contrast, circular dichroism (CD) and infrared spectra hardly change. The increase in VCD intensity goes along with a qualitative change of the spectrum and the enhancement increases with time reaching a stable state only after several hours. The enhancement is due to an interaction between the cobalt(ii) and the cluster, which also leads to quenching of its fluorescence. The behaviour is completely different for free captopril, where the addition of cobalt(ii) salt does not affect the VCD spectrum.

Visual chiral recognition of D/L-leucine using cube-shaped gold nanoparticles as colorimetric probes

Chiral recognition of enantiomers is fundamentally important. In this work, an effective and simple chiral sensing strategy for discrimination of leucine (Leu) enantiomers was constructed. In this chiral sensing, cube-shaped gold nanoparticles (AuNCs) as colorimetric probes are used to recognize Leu enantiomers. L-Leu can induce rapidly the aggregation of AuNCs, leading to change of AuNCs solution from red to colorless, while D-Leu cannot induce the color change. This distinct color changes allow naked-eye to distinguish chiral isomers of Leu. The chiral sensing was applied to measure the enantiometric excess of L-Leu in the whole range (from -100% to 100%). This chiral analysis can be performed by naked eye or simple ultraviolet-visible spectrometer. In addition, the mechanism of chiral recognition has been studied with circular dichroism (CD) spectra, UV-vis absorption spectra and zeta potential. In this method, the chiral recognition is due to the intrinsic chirality of AuNCs, and the AuNCs don't need any chiral labeling or modification. This chiral sensing method is simple, cheap, rapid and easy to operate. Furthermore, this work provides one experimental evidence for intrinsic chirality of nanoparticles, and helps people understand the chirality of nanostructures.

Covalent Functionalization of Bovine Serum Albumin with Graphene Quantum Dots for Stereospecific Molecular Recognition

Stereospecific molecular recognition with simple and easily available proteins is of significant importance in life science and biomaterial science. Herein, we report on a chiral sensing platform, graphene quantum dots (GQDs)-functionalized bovine serum albumin (BSA), for chiral recognition of tryptophan (Trp) isomers. Amidation reaction between BSA and GQDs was directly responsible for the introduction of GQDs to BSA, resulting in significant changes in the spatial configuration of BSA and the exposure of more chiral sites at the protein surface. The BSA-GQDs-based chiral sensor exhibited good biomolecular homochirality in the recognition of Trp isomers, and the higher affinity of BSA-GQDs toward l-Trp than its isomer, d-Trp, was also revealed by density functional theory (DFT) considering the possible hydrogen bonds between the Trp isomers and the solvent-accessible residues of BSA.