Inducing Axial Chirality in a “Geländer” Oligomer by Length Mismatch of the Oligomer Strands

Helical molecules are not only esthetically appealing due to their structural beauty, they also display unique physical properties as a result of their chirality. We describe herein a new approach to “Geländer” oligomers by interlinking two oligomer strands of different length. To compensate for the dimensional mismatch, the longer oligo(benzyl ether) oligomer wraps around the oligophenyl backbone. The new “Geländer” oligomer 1 was assembled in a sequence of functional‐group transformations and cross‐coupling steps followed by final cyclizations based on nucleophilic substitution reactions, and was fully characterized, including X‐ray diffraction analysis. The isolation of pure enantiomers enabled the racemization process to be studied by circular dichroism spectroscopy.     

Large Circular Dichroism Ellipticities for N-Templated Helical Polypeptides Are Inconsistent with Currently Accepted Helicity Algorithms

An unprecedented , high degree of helicity as judged by CD spectroscopy is observed in N-templated model peptides of the type AcHel-(Ala₄Lys)_nAla₂-NH₂ (AcHel-Ala peptide pictured; AcHel is an N-terminal helix-inducing template for polypeptides). These results raise concern over the current methods for determining 100 % helicity.     

Chemistry of C84: Separation of Three Constitutional Isomers and Optical Resolution of D2-C84 by Using the “Bingel–Retro-Bingel” Strategy

The pure enantiomers of D ₂ -C ₈₄ as well as a third constitutional isomer of this higher fullerene were produced by a retro-Bingel reaction on the first organic derivatives of C₈₄ (see scheme). These derivatives were synthesized by Bingel cyclopropenation of C₈₄, separated, and unambiguously structurally characterized.     

Enantioselective sensing of carboxylic acids with a bis(urea)oligo(phenylene)ethynylene foldamer

The development of molecular probes for optical sensing of chiral compounds has received increasing attention in recent years, in particular because of the potential to accelerate asymmetric reaction analysis. In this study, we prepared conformationally flexible oligo(phenylene)ethynylene foldamers carrying peripheral bis(trifluoromethyl)phenylurea units that undergo hydrogen bonding with chiral carboxylic acids. This interaction results in a chiral amplification process across the stereodynamic sensor scaffold which coincides with characteristic circular dichroism signals at high wavelengths. The induced chiroptical signals allow quantitative determination of the enantiomeric excess of the substrate which was demonstrated with nonracemic samples of tartaric acid. The chirality sensing assay is fast, sufficiently accurate for high-throughput screening purposes and adaptable to parallel analysis with multiwell plate readers.     

Enantioselective Inclusion Complexation of N‐Nitrosopiperidines by Steroidal Bile Acids

N ‐nitrosamines , whose chirality is solely due to hindered rotation about the N−N bond, are enantioselectively enclathrated by the crystal host matrices of cholic or deoxycholic acid, as evidenced by X‐ray crystallography (see structure in picture) and CD spectra.     

New Fluorescence Domain “Excited Multimer” Formed upon Photoexcitation of Continuously Stacked Diaroylmethanatoboron Difluoride Molecules with Fused π‐Orbitals in Crystals

The crystal‐packing structures of seven derivatives of diaroylmethanatoboron difluoride ( 1 a – gBF₂ ) are characterized by no overlap of the π‐conjugated main units of two adjacent molecules (type I), overlap of the benzene ring π‐orbitals of two adjacent molecules (type II), and overlap of the benzene and dihydrodioxaborinine rings π‐orbitals of adjacent molecules (type III). The crystal‐packing structures govern the fluorescence (FL) properties in the crystalline states. The FL domain that is present in type I crystals, in which intermolecular orbital interactions are absent, leads to excited monomer‐like FL properties. In the case of the type II crystals, the presence of intermolecular overlap of the benzene rings π‐orbitals generates new FL domains, referred to as “excited multimers”, which possess allowed S₀–S₁ electronic transitions and, as a result, similar FL lifetimes at longer wavelengths than the FL of the type I crystals. Finally, intermolecular overlap of the benzene and dihydrodioxaborinine ring π‐orbitals in the type III crystals leads to “excited multimer” domains with forbidden S₀–S₁ electronic transitions and longer FL lifetimes at similar wavelengths as that in type I crystals.     

“Printing” DNA Strand Patterns on Small Molecules with Control of Valency,Directionality, and Sequence

The incorporation of synthetic molecules as corner units in DNA structures has been of interest over the last two decades. In this work, we present a facile method for generating branched small molecule‐DNA hybrids with controllable valency, different sequences, and directionalities (5′–3′) using a “printing” process from a simple 3‐way junction structure. We also show that the DNA‐imprinted small molecule can be extended asymmetrically using polymerase chain reaction (PCR) and can be replicated chemically. This strategy provides opportunities to achieve new structural motifs in DNA nanotechnology and introduce new functionalities to DNA nanostructures.     

Helical Coordination Polymers with Large Chiral Cavities

A quarter of the unit cell volume of [{Ni(4,4′‐dipy)(3‐nitrobenzoate)₂(MeOH)₂}_n], which crystallizes in the form of helices, is occupied by large chiral cavities (400–500 ų). The cavities are capable of encapsulating not only single molecules, but also face‐to‐face dimers of nitrobenzene (see stick model). 4,4′‐dipy=4,4′‐bipyridine.     

Novel calix[4]cryptands: “Mappemonde II” and “Mill II”

Two novel calix[4]cryptands were synthesized from 1,3‐alternate calix[4]bis‐azacrown. “Mappemonde II” consists of one 1,3‐calix[4]bis‐azacrown wrapped by a benzo‐crown ether loop. “Mill II” is composed of two 1,3‐calix[4]bis‐azacrowns linked by two benzo‐crown ether strands.     

(Ge4Bi14)4−: A Case of “Element Segregation” on the Molecular Level

Extraction of a solid with the nominal composition “K₂GeBi” with 1,2‐diaminoethane (en) in the presence of 4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane (crypt‐222) afforded the salt [K(crypt‐222)]₄(Ge₄Bi₁₄). The 18‐atom Zintl anion (Ge₄Bi₁₄)⁴⁻ has a heretofore unknown molecular topology, which can be thought of as the formal condensation product of two E₁₁³⁻ cages along a shared Ge₄ waist. In this way, (Ge₄Bi₁₄)⁴⁻ represents the largest and most structurally complex Bi‐containing polyanion. We describe its stepwise formation, its geometric and electronic structure, and comment on relative stabilities of isomers with different distributions of the four Ge atoms on the 18 positions that were investigated using DFT calculations.