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Tying a Molecular Overhand Knot of Single Handedness and Asymmetric Catalysis with the Corresponding Pseudo-D₃-Symmetric Trefoil Knot.

ABSTRACT: We report the stereoselective synthesis of a left-handed trefoil knot from a tris(2,6-pyridinedicarboxamide) oligomer with six chiral centers using a lanthanide(III) ion template. The oligomer folds around the lanthanide ion to form an overhand knot complex of single handedness. Subsequent joining of the overhand knot end groups by ring-closing olefin metathesis affords a single enantiomer of the trefoil knot in 90% yield. The knot topology and handedness were confirmed by NMR spectroscopy, mass spectrometry, and X-ray crystallography. The pseudo-D₃-symmetric knot was employed as an asymmetric catalyst in Mukaiyama aldol reactions, generating enantioselectivities of up to 83:17 er, which are significantly higher than those obtained with a comparable unknotted ligand complex.

SUBMITTER: Gil-Ramirez G

PROVIDER: S-EPMC5152939 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature

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Tying a Molecular Overhand Knot of Single Handedness and Asymmetric Catalysis with the Corresponding Pseudo-D<sub>3</sub>-Symmetric Trefoil Knot.

Gil-Ramírez Guzmán G Hoekman Steven S Kitching Matthew O MO Leigh David A DA Vitorica-Yrezabal Iñigo J IJ Zhang Gen G

Journal of the American Chemical Society 20160929 40

We report the stereoselective synthesis of a left-handed trefoil knot from a tris(2,6-pyridinedicarboxamide) oligomer with six chiral centers using a lanthanide(III) ion template. The oligomer folds around the lanthanide ion to form an overhand knot complex of single handedness. Subsequent joining of the overhand knot end groups by ring-closing olefin metathesis affords a single enantiomer of the trefoil knot in 90% yield. The knot topology and handedness were confirmed by NMR spectroscopy, mass ...[more]

PMID: 27667319

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Folding a Molecular Strand into a Trefoil Knot of Single Handedness with Co(II)/Co(III) Chaperones.

Project description:We report the synthesis of a right-handed (Δ-stereochemistry of strand crossings) trefoil knot from a single molecular strand containing three pyrazine-2,5-dicarboxamide units adjacent to point-chiral centers and six pyridine moieties. The oligomeric ligand strand folds into an overhand (open-trefoil) knot through the assistance of coordinatively dynamic Co(II) "chaperones" that drive the formation of a three-metal-ion circular helicate. The entangled structure is kinetically locked by oxidation to Co(III) and covalently captured by ring-closing olefin metathesis to generate a trefoil knot of single topological handedness. The stereochemistry of the strand crossings in the metal-coordinated overhand knot is governed by the stereochemistry of the point-chiral carbon centers in the ligand strand. The overhand and trefoil knots were characterized by NMR spectroscopy, mass spectrometry, and X-ray crystallography. Removal of the metal ions from the knot, followed by hydrogenation of the alkene, yielded the wholly organic trefoil knot. The metal-free knot and parent ligand were investigated by circular dichroism (CD) spectroscopy. The CD spectra indicate that the topological stereochemistry of the knot has a greater effect on the asymmetry of the chromophore environment than do the point-chiral centers of the strand.

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Orthopaedic Resident Arthroscopic Knot-Tying Skills Are Improved Using a Training Program and Knot-Tying Workstation.

Project description:PurposeTo quantify an orthopaedic trainee's ability to tie arthroscopic knots before and after a short cadaveric-based arthroscopy training period using a commercially available knot-tying workstation.MethodsDuring a weeklong cadaveric arthroscopic training camp, 15 third- and fourth-year orthopaedic residents were evaluated using a commercially available benchtop knot-tying workstation. At the beginning of the week (baseline), each participant was asked to tie 3 knots of his or her choice backed up by 3 half-hitches using nonabsorbable suture. Successful knots fit the sizer and elongated less than 3 mm after application of a 15-lb load. Afterward, residents watched a video demonstrating a sample knot and were encouraged to practice over the ensuing days. At the end of the week (post-training), residents were asked to tie 3 knots. The time to completion and success of each knot were recorded. To compare baseline and post-training knot success, t tests and χ2 analysis were performed.ResultsDuring baseline testing, residents successfully tied 26.7% of their knots (12 of 45 knots) in 352 ± 116 seconds (mean ± standard deviation). During post-training testing, residents successfully tied 66.7% of knots (30 of 45 knots, P = .00014) in 294 ± 63 seconds (P = .023), showing significant improvement in the time and ability to tie arthroscopic knots.ConclusionsWith a short cadaveric-based training period, orthopaedic trainees showed a significant improvement in their ability to tie arthroscopic knots on a commercially available benchtop knot-tying workstation. Given the initial low percentage of successfully tied knots and the limited opportunities for trainees to improve, trainees should be encouraged to practice and improve their skills.Clinical relevanceWith training, residents can improve arthroscopic knot-tying abilities, which may allow them to successfully perform this critical task in the operating room.

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Meniscus-Side-Knot-tying Technique Instead of Capsular-Side-Knot-Tying in Arthroscopic Outside-In Meniscal Repair: A Small but Meaningful Modification.

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Symmetric key structural residues in symmetric proteins with beta-trefoil fold.

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Beyond the Square knot: A validation study for a novel knot-tying method named "inverse 9".

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| S-EPMC10597824 | biostudies-literature

A trefoil knot self-templated through imination in water.

Project description:The preparation of topologically nontrivial molecules is often assisted by covalent, supramolecular or coordinative templates that provide spatial pre-organization for all components. Herein, we report a trefoil knot that can be self-assembled efficiently in water without involving additional templates. The direct condensation of three equivalents of a tetraformyl precursor and six equivalents of a chiral diamine produces successfully a [3 + 6] trefoil knot whose intrinsic handedness is dictated by the stereochemical configuration of the diamine linkers. Contrary to the conventional wisdom that imine condensation is not amenable to use in water, the multivalent cooperativity between all the imine bonds within the framework makes this trefoil knot robust in the aqueous environment. Furthermore, the presence of water is proven to be essential for the trefoil knot formation. A topologically trivial macrocycle composed of two tetraformyl and four diamino building blocks is obtained when a similar reaction is performed in organic media, indicating that hydrophobic effect is a major driving force behind the scene.

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Instructional Video and Medical Student Surgical Knot-Tying Proficiency: Randomized Controlled Trial.

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Self-assembly of the smallest and tightest molecular trefoil knot.

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| S-EPMC10762025 | biostudies-literature