Highly strained, radially π-conjugated porphyrinylene nanohoops

Small π-conjugated nanohoops are difficult to prepare, but offer an excellent platform for studying the interplay between strain and optoelectronic properties, and, increasingly, these shape-persistent macrocycles find uses in host-guest chemistry and self-assembly. We report the synthesis of a new family of radially π-conjugated porphyrinylene/phenylene nanohoops. The strain energy in the smallest nanohoop [2]CPT is approximately 54 kcal mol⁻¹, which results in a narrowed HOMO-LUMO gap and a red shift in the visible part of the absorption spectrum. Because of its high degree of preorganization and a diameter of ca. 13 Å, [2]CPT was found to accommodate C₆₀ with a binding affinity exceeding 10⁸ M⁻¹ despite the fullerene not fully entering the cavity of the host (X-ray crystallography). Moreover, the ?-extended nanohoops [2]CPTN, [3]CPTN, and [3]CPTA (N for 1,4-naphthyl; A for 9,10-anthracenyl) have been prepared using the same strategy, and [2]CPTN has been shown to bind C₇₀ 5 times more strongly than [2]CPT. Our failed synthesis of [2]CPTA highlights a limitation of the experimental approach most commonly used to prepare strained nanohoops, because in this particular case the sum of aromatization energies no longer outweighs the buildup of ring strain in the final reaction step (DFT calculations). These results indicate that forcing ring strain onto organic semiconductors is a viable strategy to fundamentally influence both optoelectronic and supramolecular properties

Methionine Scanning as an NMR Tool for Detecting and Analyzing Biomolecular Interaction Surfaces

SummaryMethyl NMR spectroscopy is a powerful tool for studying protein structure, dynamics, and interactions. Yet difficulties with resonance assignment and the low abundance of methyl groups can preclude detailed NMR studies, particularly the determination of continuous interaction surfaces. Here we present a straightforward strategy that overcomes these problems. We systematically substituted solvent-exposed residues with reporter methionines in the expected binding site and performed chemical shift perturbation (CSP) experiments using methyl-TROSY spectra. We demonstrate the utility of this approach for the interaction between the HECT domain of the Rsp5p ubiquitin ligase and its cognate E2, Ubc4. Using these mutants, we could instantaneously assign all newly arising reporter methyl signals, determine the Ubc4 interaction surface on a per-residue basis, and investigate the importance of each individual mutation for ligand binding. Our data show that methionine scanning significantly extends the applicability, information content, and spatial resolution of methyl CSP experiments

Highly Strained, Radially π-Conjugated Porphyrinylene Nanohoops

Small π conjugated nanohoops are difficult to prepare, but offer an excellent platform for studying the interplay between strain and optoelectronic properties and increasingly, these shape persistent macrocycles find uses in host guest chemistry and self assembly. We report the synthesis of a new family of radially π conjugated porphyrinylene/phenylene nanohoops. The strain energy in the smallest nanohoop [2]CPT is approx-imately 54 kcal mol-1, which results in a narrowed HOMO LUMO gap and a red shift in the visible part of the absorption spectrum. Due to its high degree of preorganization and a diameter of ca. 13 Å, [2]CPT was found to accommodate C60 with a binding affinity exceeding 108 M-1 despite the fullerene not fully entering the cavity of the host (X Ray crystallography). Moreover, the π extended nanohoops [2]CPTN , [3]CPTN and [3]CPTA (N for 1,4 naphthyl; A for 9,10 anthracenyl) have been prepared using the same strategy, and [2]CPTN has been shown to bind C70 five times more strongly than [2]CPT. Our failed synthesis of [2]CPTA highlights a limitation of the experimental approach most commonly used to prepare strained nanohoops, because in this particular case the sum of aromatization energies no longer outweighs the buildup of ring strain in the final reaction step (DFT calculations). These results indicate that forcing ring strain onto organic semiconductors is a viable strategy to fundamentally influence both optoelectronic and supramolecular properties.</p

Highly strained, radially π-conjugated porphyrinylene nanohoops

Small π-conjugated nanohoops are difficult to prepare, but offer an excellent platform for studying the interplay between strain and optoelectronic properties, and, increasingly, these shape-persistent macrocycles find uses in host-guest chemistry and self-assembly. We report the synthesis of a new family of radially π-conjugated porphyrinylene/phenylene nanohoops. The strain energy in the smallest nanohoop [2]CPT is approximately 54 kcal mol⁻¹, which results in a narrowed HOMO-LUMO gap and a red shift in the visible part of the absorption spectrum. Because of its high degree of preorganization and a diameter of ca. 13 Å, [2]CPT was found to accommodate C₆₀ with a binding affinity exceeding 10⁸ M⁻¹ despite the fullerene not fully entering the cavity of the host (X-ray crystallography). Moreover, the ?-extended nanohoops [2]CPTN, [3]CPTN, and [3]CPTA (N for 1,4-naphthyl; A for 9,10-anthracenyl) have been prepared using the same strategy, and [2]CPTN has been shown to bind C₇₀ 5 times more strongly than [2]CPT. Our failed synthesis of [2]CPTA highlights a limitation of the experimental approach most commonly used to prepare strained nanohoops, because in this particular case the sum of aromatization energies no longer outweighs the buildup of ring strain in the final reaction step (DFT calculations). These results indicate that forcing ring strain onto organic semiconductors is a viable strategy to fundamentally influence both optoelectronic and supramolecular properties

Ribosome assembly in eukaryotes

International audienceRibosome synthesis is a highly complex and coordinated process that occurs not only in the nucleolus but also in the nucleoplasm and the cytoplasm of eukaryotic cells. Based on the protein composition of several ribosomal subunit precursors recently characterized in yeast, a total of more than 170 factors are predicted to participate in ribosome biogenesis and the list is still growing. So far the majority of ribosomal factors have been implicated in RNA maturation (nucleotide modification and processing). Recent advances gave insight into the process of ribosome export and assembly. Proteomic approaches have provided the first indications for a ribosome assembly pathway in eukaryotes and confirmed the dynamic character of the whole process