Chiral inversion of gold nanoparticles

The thiolate-for-thiolate ligand exchange was performed on well-defined gold nanoparticles under an inert atmosphere without any modification of the core size. This reaction is faster than the well-known core etching. Surprisingly, if a chiral thiol is exchanged for its opposite enantiomer, the optical activity in the metal-based electronic transitions is reversed although the form of the CD spectra remains largely unchanged. The extent of inversion corresponds to the overall ee of the chiral ligand in the system. This shows that the chiral arrangement of metal atoms in the metal particle (surface) can not withstand the driving force imposed by the ligand of opposite absolute configuration. If the incoming thiol has a different structure, the electronic transitions in the metal core are slightly modified whereas the absorption onset remains unchanged. These results emphasize the influence of the thiols on the structure of the gold nanoparticles and give insight on the ligand exchange pathways.     

Chiral hexacoordinated phosphates: From pioneering studies to modern uses in stereochemistry

Chiral cationic molecular structures and supramolecular assemblies can be effectively analyzed, resolved and stereocontrolled through an asymmetric ion pairing with enantiopure hexacoordinated phosphate anions like TRISPHAT or BINPHAT. After an historical perspective on the development of these anionic reagents, this account describes their synthesis and their use as chiral NMR solvating, resolving and asymmetry-inducing reagents.     

Chiral dendrimer encapsulated Pd and Rh nanoparticles

The synthesis of a series of chiral PAMAM dendrimers and the formation of chiral dendrimer encapsulated metal nanoparticles are described.     

Chiral recognition in aggregation of gold nanoparticles grafted with helicenes

Chiral recognition was observed in the interactions of gold nanoparticles grafted with (±)-, (M)-, and (P)-helicenethiol. Although the nanoparticles contain equal enantiomeric excess, a 1:1 mixture of (M)- and (P)-nanoparticles aggregated more rapidly in solution than (±)-nanoparticles.     

Chiral nematic assemblies of silver nanoparticles in mesoporous silica thin films

Silver nanoparticles (NPs) have been synthesized inside mesoporous silica films with chiral nematic structure. Circular dichroism measurements of the silver NP-loaded silica films show NP-based optical activity in the vicinity of the surface plasmon resonance. These materials, with an optical response associated with the chiral assembly of metal NPs, may be useful for developing new sensors.     

The stereochemistry of heterocycles

Fifteen previously unreported 2-alkyl- and 5-alkyl-2, 2-dimethyl-1, 3-dithianes have been synthesized by the condensation of 2-alkylpropane-1, 3-dithiols with acetaldehyde, isobutylraldehyde, and acetone, and their structures have been confirmed by their IR spectra. The existence of stereoisomers in a number of the thioacetals has been shown by GLC and TLC. Some of the stereoisomeric 2, 5-diakyl-1, 3-dithianes have been separated by fractionation in an efficient column into the individual isomers, the purity of which was confirmed by TLC, GLC, and IR spectroscopy.For part III, see [11].     

The stereochemistry of ketoreduction

In this issue of Chemistry & Biology, Leadlay and coworkers report overproduction of a number of ketoreductase domains from modular polyketide synthases. These discrete enzymes allow the stereochemistry of polyketide ketoreduction to be studied in isolation.     

Complete stereochemistry of tetrafibricin

With use of the NMR databases in achiral and chiral solvents, the complete stereochemistry of tetrafibricin (1) has been elucidated without degradation of the carbon framework. [structure--see text]     

The stereochemistry of nevskin

Summary The relative configurations of the substituents in nevskin have been determined from the H¹ NMR spectra in CDCl₃ with additions of Eu(FOD)₃ as paramagnetic shift reagent.Institute of Botany, Academy of Sciences of the Azerbaidzhan SSR, Baku. All-Union Scientific-Research Institute of Medicinal Plants, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 450–452, July–August, 1976.     

The stereochemistry of chuangxinmycin

Chuangxinmycin was shown by chemical correlation to have 35, 4R configuration as shown by 1. It is surprising that I has the opposite absolute configuration as indolmycin (7) with the same carbon skeleton. The carboxyl group of norchuangxinmycin (14) and the methyl group of decarboxychuangxinmycin (18) were found to have preferred equatorial conformations with no observable anomeric effect in the former. Thus the bulkier carboxyl group of chuangxinmycin itself must adopt the equatorial position predominantly, if not exclusively, in solution, a situation already found prevailing in the crystalline state by X-ray diffraction.     

The stereochemistry of myxothiazol

The absolute configuration of myxothiazol is established as 4(6-carbamoyl-3S,5-dimethoxy-4R-methylhexa-1E,5E-dienyl)-2′-(1S ,6-dimethylhepta-2E,4E-dienyl)-2,4′-bithiazole by a combination of chemical methods and X-ray analysis     

Absolute stereochemistry of securinine

The absolute configuration of securinine was shown to be I from the rotatory dispersion curves and molecular rotations of degradation products of securinine. The conclusion was unequivocally confirmed by the formation of (+)-N-benzoylpipecolic acid on degradation of this alkaloid. The conformation of the bridgehead nitrogen was also discussed.