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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 |

REPOSITORIES: biostudies-literature

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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.

| S-EPMC8220621 | biostudies-literature

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

Project description: Not available

| S-EPMC10907913 | biostudies-literature

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

Project description:To understand how symmetric structures of many proteins are formed from asymmetric sequences, the proteins with two repeated beta-trefoil domains in Plant Cytotoxin B-chain family and all presently known beta-trefoil proteins are analyzed by structure-based multi-sequence alignments. The results show that all these proteins have similar key structural residues that are distributed symmetrically in their structures. These symmetric key structural residues are further analyzed in terms of inter-residues interaction numbers and B-factors. It is found that they can be distinguished from other residues and have significant propensities for structural framework. This indicates that these key structural residues may conduct the formation of symmetric structures although the sequences are asymmetric.

| S-EPMC2994741 | biostudies-literature

Securing a Supramolecular Architecture by Tying a Stopper Knot.

Project description:We report on a rotaxane-like architecture secured by the in?situ tying of an overhand knot in the tris(2,6-pyridyldicarboxamide) region of the axle through complexation with a lanthanide ion (Lu3+ ). The increase in steric bulk caused by the knotting locks a crown ether onto the thread. Removal of the lutetium ion unties the knot, and when the axle binding site for the ring is deactivated, the macrocycle spontaneously dethreads. When the binding interaction is switched on again, the crown ether rethreads over the 10?nm length of the untangled strand. The overhand knot can be retied, relocking the threaded structure, by once again adding lutetium ions.

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

Project description:BACKGROUND:Many senior medical students lack simple surgical and procedural skills such as knot tying. OBJECTIVE:The aim of this study was to determine whether viewing a Web-based expert knot-tying training video, in addition to the standard third-year medical student curriculum, will result in more proficient surgical knot tying. METHODS:At the start of their obstetrics and gynecology clerkship, 45 students were videotaped tying surgical knots for 2 minutes using a board model. Two blinded female pelvic medicine and reconstructive surgery physicians evaluated proficiency with a standard checklist (score range 0-16) and anchored scoring scale (range 0-20); higher numbers represent better skill. Students were then randomized to either (1) expert video (n=26) or (2) nonvideo (n=24) groups. The video group was provided unlimited access to an expert knot-tying instructional video. At the completion of the clerkship, students were again videotaped and evaluated. RESULTS:At initial evaluation, preclerkship cumulative scores (range 0-36) on the standard checklist and anchored scale were not significantly different between the nonvideo and video groups (mean 20.3, SD 7.1 vs mean 20.2, SD 9.2, P=.90, respectively). Postclerkship scores improved in both the nonvideo and video groups (mean 28.4, SD 5.4, P<.001 and mean 28.7, SD 6.5, P=.004, respectively). Increased knot board practice was significantly correlated with higher postclerkship scores on the knot-tying task, but only in the video group (r=.47, P<.05). CONCLUSIONS:The addition of a Web-based expert instructional video to a standard curriculum, coupled with knot board practice, appears to have a positive impact on medical student knot-tying proficiency.

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Intracorporeal knot-tying for the thoracoscopic surgeon: a novel and simplified technique.

Project description:Thoracoscopic surgery has usually been limited by 2-dimensional vision and the limited space between ribs--problems that have been only partially overcome by the use of robotics. One of the technical challenges of any minimally invasive surgical approach is tying an intracorporeal knot. For the thoracoscopic surgeon, we describe an easier technique of knot-tying that involves using a right-angled dissector. The technique enables ambidextrous performance and is particularly useful for ligating major pulmonary vessels that might be too small to be stapled or too confined for the admission and maneuvering of a stapling device. Rotating the thumb-dials accordingly enables one to vary the configuration of the knots to create slip or reef knots.The technique is easy to learn and does not require any complicated devices. It is easily adapted to create even more complex constructs, such as a double surgeon's knot. This technique has special advantages in areas of limited domain and in situations that require very narrow angles of instrument manipulation, particularly in thoracoscopic-assisted procedures.

| S-EPMC2929853 | biostudies-literature

Slipknotting upon native-like loop formation in a trefoil knot protein.

Project description:Protein knots and slipknots, mostly regarded as intriguing oddities, are gradually being recognized as significant structural motifs. Recent experimental results show that knotting, starting from a fully extended polypeptide, has not yet been observed. Understanding the nucleation process of folding knots is thus a natural challenge for both experimental and theoretical investigation. In this study, we employ energy landscape theory and molecular dynamics to elucidate the entire folding mechanism. The full free energy landscape of a knotted protein is mapped using an all-atom structure-based protein model. Results show that, due to the topological constraint, the protein folds through a three-state mechanism that contains (i) a precise nucleation site that creates a correctly twisted native loop (first barrier) and (ii) a rate-limiting free energy barrier that is traversed by two parallel knot-forming routes. The main route corresponds to a slipknot conformation, a collapsed configuration where the C-terminal helix adopts a hairpin-like configuration while threading, and the minor route to an entropically limited plug motion, where the extended terminus is threaded as through a needle. Knot formation is a late transition state process and results show that random (nonspecific) knots are a very rare and unstable set of configurations both at and below folding temperature. Our study shows that a native-biased landscape is sufficient to fold complex topologies and presents a folding mechanism generalizable to all known knotted protein topologies: knotting via threading a native-like loop in a preordered intermediate.

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Analysis of the Structure of Surgical Activity for a Suturing and Knot-Tying Task.

Project description:BACKGROUND:Surgical tasks are performed in a sequence of steps, and technical skill evaluation includes assessing task flow efficiency. Our objective was to describe differences in task flow for expert and novice surgeons for a basic surgical task. METHODS:We used a hierarchical semantic vocabulary to decompose and annotate maneuvers and gestures for 135 instances of a surgeon's knot performed by 18 surgeons. We compared counts of maneuvers and gestures, and analyzed task flow by skill level. RESULTS:Experts used fewer gestures to perform the task (26.29; 95% CI = 25.21 to 27.38 for experts vs. 31.30; 95% CI = 29.05 to 33.55 for novices) and made fewer errors in gestures than novices (1.00; 95% CI = 0.61 to 1.39 vs. 2.84; 95% CI = 2.3 to 3.37). Transitions among maneuvers, and among gestures within each maneuver for expert trials were more predictable than novice trials. CONCLUSIONS:Activity segments and state flow transitions within a basic surgical task differ by surgical skill level, and can be used to provide targeted feedback to surgical trainees.

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Physical experience leads to enhanced object perception in parietal cortex: insights from knot tying.

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