An alternative to conventional "cut-and-sew" cartilage surgery, electromechanical reshaping (EMR) is a molecular-based modality in which an array of needle electrodes is inserted into cartilage held under mechanical deformation by a jig. Brief (ca. 2 min) application of an electrochemical potential at the water-oxidation limit results in permanent reshaping of the specimen. Highly sulfated glycosaminoglycans within the cartilage matrix provide structural rigidity to the tissue through extensive ionic-bonding networks; this matrix is highly permselective for cations. Our studies indicate that EMR results from electrochemical generation of localized, low-pH gradients within the tissue: fixed negative charges in the proteoglycan matrix are protonated, resulting in chemically induced stress relaxation of the tissue. Re-equilibration to physiological pH restores the fixed negative charges, and yields remodeled cartilage that retains a new shape approximated by the geometry of the reshaping jig.
An alternative to conventional "cut-and-sew" cartilage surgery,e lectromechanical reshaping (EMR) is am olecular-based modality in whicha na rrayo fn eedle electrodes is inserted into cartilage held under mechanical deformation by aj ig. Brief (ca. 2min) application of an electrochemical potential at the water-oxidation limit results in permanent reshaping of the specimen. Highly sulfated glycosaminoglycans within the cartilage matrix provide structural rigidity to the tissue through extensive ionic-bonding networks;t his matrix is highly permselective for cations.Our studies indicate that EMR results from electrochemical generation of localized, low-pH gradients within the tissue:f ixedn egative charges in the proteoglycan matrix are protonated, resulting in chemically induced stress relaxation of the tissue.R e-equilibration to physiological pH restores the fixednegative charges,and yields remodeled cartilage that retains anew shape approximated by the geometry of the reshaping jig.Hyaline cartilage forms underlying structural features of the head and neck, and serves acritical functional role in the upper airway.[1] Congenital defects,t rauma, and disease can damage cartilage tissue,necessitating surgical intervention to reshape (or replace) damaged (or missing) structures. [2] Conventional open surgery is characterized by long recovery times,s ignificant tissue morbidity,a nd high cost;r eshaping living tissue using less invasive techniques is thus the subject of active research. [3,4] Most alternative methods focus on modifying the bulk mechanical properties of cartilage,that is, by using laser or radiofrequency( RF) heat generation to denature and/or accelerate stress relaxation by exploiting the thermoviscoelesticity common to collagenous tissues.[5] Our work focuses instead on novel electrochemical modalities that transiently alter the chemical properties of tissue,p roviding amolecular-based alternative to the scalpel and sutures.Originally conceived as at hermal technique in which electrical current flow through cartilage would cause resistive heating, [6] "electromechanical reshaping" (EMR) was developed as al ow-cost technique for reshaping cartilage.E MR combines mechanical deformation with the application of electric fields:i natypical embodiment, cartilage is held in mechanical deformation by am old or jig, needle electrodes are inserted into the tissue,and aconstant voltage (e.g.,5V) is applied across the specimen for several minutes.Whenthe electrodes and mold are removed, the cartilage assumes anew shape that approximates the geometry of the mold (e.g.,a908 8 bend). [7] Although effective shape change has been demonstrated in several animal models, [8,9] the process often is accompanied by tissue injury near the electrode-insertion sites;m oreover, the relationship between shape change and the duration and magnitude of the applied voltage can be unpredictable.T he lack of detailed mechanistic insight into the molecular changes that occur during EMR has impeded its development as ap rac...
Here we report electrochemical, spectroscopic, and crystallographic characterization of a redox series of cobalt complexes in five sequential oxidation states. A simple bidentate phosphine ligand, cis-1,2-bis(diphenylphosphino)ethylene (dppv), allows for isolation of the 3+, 2+, 1+, 0, and 1− oxidation states of cobaltthe only known example of transition-metal complexes with redox-innocent ligands in five oxidation states. Electrochemistry of [Co(dppv) 2 ] 2+ reveals three reversible reductions and one reversible oxidation. Complexes in each oxidation state are characterized using single-crystal X-ray diffraction. The coordination number and geometry of the complex changes as a function of the oxidation state: including acetonitrile ligands, the Co 3+ complex is pseudo-octahedral, the Co 2+ complex is square-pyramidal, the Co + complex is pseudo-square-planar, and the Co 0 and Co − complexes approach pseudo-tetrahedral, illustrating structures predicted by crystal-field theory of inorganic transition-metal complexes.
Molecular electrocatalysts show promise for energy-relevant multielectron transformations due to their rationally tunable activity and selectivity from systematic ligand modifications. However, surface-immobilized molecular electrocatalytic systems are typically limited by low activity per geometric surface area compared to traditional solid-state analogues because of their lower active site surface coverage. Many existing methods for increasing surface coverage through the formation of multilayer films are based on radical-coupling or electropolymerization strategies that often result in dense, poorly defined films that may inhibit charge or substrate transport and complicate mechanistic studies. We report an alternative controlled layer-by-layer deposition strategy for the formation of multilayer catalyst films on carbon electrode surfaces based on sequential Cu(I)-catalyzed azide–alkyne cycloaddition reactions. As a proof of concept, we explore the growth of multilayer films of Cu(3,8-diethynylphenanthroline) for the oxygen reduction reaction. Double-layer catalyst films operate with increased activity and selectivity for the reduction of O2 to H2O compared to single-layer catalyst films. We attribute this increased activity and selectivity to the increased coverage of the double-layer films which both increases the number of active sites and facilitates the 4e– reduction to H2O, rather than the 2e– reduction to H2O2. Unfortunately, growth of triple-layer catalyst films in this system was unsuccessful, possibly due to steric congestion in the double-layer films.
Copper-catalyzed azide-alkyne cycloaddition (CuAAC) "click" chemistry is widely used and has demonstrated particular utility for bio-orthogonal conjugation reactions. Here we describe a one-pot, heterogeneous bioconjugation and purification method for selectively activated CuAAC. A Cu(II) precursor, with either the neutral ligand 1,10-phenanthroline-5,6-dione or the anionic ligand 4,7-diphenyl-1,10-phenanthroline-disulfonic acid, is converted to the active Cu(I) species within an ion-exchange matrix using zinc amalgam as the reducing agent. The Cu(I) complexes are then layered on top of a size-exclusion matrix within a commercial microcentrifuge spin column; passing a mixture of an ethynyl-labeled biomolecule and an azide-bearing ligand through the column results in clean and efficient coupling. The methodology is demonstrated by glycosylating a DNA oligonucleotide as well as by labeling a membrane-penetrating peptide (octa-arginine) with a coumarin dye.
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