Nanostructured polymeric coatings based on chitosan and dopamine-modified hyaluronic acid for biomedical applications

In a marine environment, specific proteins are secreted by mussels and used as a bioglue to stick to a surface. These mussel proteins present an unusual amino acid 3,4-dihydroxyphenylalanine (known as DOPA). The outstanding adhesive properties of these materials in the sea harsh conditions have been attributed to the presence of the catechol groups present in DOPA. Inspired by the structure and composition of these adhesive proteins, we used dopamine-modified hyaluronic acid (HA-DN) prepared by carbodiimide chemistry to form thin and surface-adherent dopamine films. This conjugate was characterized by distinct techniques, such as nuclear magnetic resonance and ultraviolet spectrophotometry. Multilayer films were developed based on chitosan and HA-DN to form polymeric coatings using the layer-by-layer methodology. The nanostructured films formation was monitored by quartz crystal microbalance. The film surface was characterized by atomic force microscopy and scanning electron microscopy. Water contact angle measurements were also conducted. The adhesion properties were analyzed showing that the nanostructured films with dopamine promote an improved adhesion. In vitro tests showed an enhanced cell adhesion, proliferation and viability for the biomimetic films with catechol groups, demonstrating their potential to be used in distinct biomedical applications.The authors want to acknowledge the COST Action TD0906 - Biological adhesives: from biology to biomimetics. The authors also acknowledge the financial support from the Fundacao para a Ciencia e para a Tecnologia through the Ph.D. grants with the references SFRH/BD/73119/2010 and SFRH/BD/69529/2010. G. G. Ferrer acknowledges the support of the Spanish Ministry of Science and Innovation for the mobility grant JC2008-00135. G. Botelho acknowledges the NMR portuguese network (PTNMR, Bruker Avance III 400-Univ. Minho)

Synthesis of an Arenide-Masked Scandium Complex Accom-panied by Reductively Induced C-H Activation

Reduction of 3N-supported ScCl(ketguan)(NImDipp) (ScCl) with K(C10H8) generates the naphthalenide-masked species [(18-c-6)K(μ-η6:η4-C10H8)Sc(ketguan)(NImDipp)] (Scnaph) and cyclometallated [K(18-c-6)(Et2O)][Sc{(DippN)[2-iPr-6-(CMe2)C6H3N]C(NCHtBu2)}(NImDipp)(THF)] (ScC-H·Et2O), the latter formed from a rare instance of oxidative addition of a low valent scandium center across an unactivated C(sp3)-H bond. Moreover, ScC-H displays solid-to-solution phase dependent tautomerism within the moiety of the scandium metallacyle. Finally, a safe and convenient method is described for the dehydration of ScCl3·6H2O

Synthesis of a “Super Bulky” Guanidinate Possessing an Expandable Coordination Pocket

Friedel–Crafts alkylation of 4-tert-butylaniline with 2 equiv of benzhydrol affords bulky 2,6-bis(diphenylmethyl)-4-tert-butylaniline (Ar*NH2) in good yield, which can be readily synthesized on a tens of grams scale. The reaction of 6 equiv of Ar*NH2 with triphosgene generates the symmetric urea (Ar*NH)2CO, which, upon dehydration with a P2O5/Al2O3 slurry in pyridine, produces the sterically encumbered carbodiimide (Ar*N)2C as an air-stable white solid. The treatment of (Ar*N)2C with LiN═CtBu2 in tetrahydrofuran cleanly gives the monomeric lithium guanidinate Li[Ar*ketguan], free of coordinating solvent, in 85% yield. Protonation of Li[Ar*ketguan] with lutidinium chloride produces the guanidine Ar*ketguanH (MW = 1112.60 g/mol), which is easily derivatized to give the monomeric alkali metal complexes M[Ar*ketguan] (M = K, Cs) in 94% and 51% yield, respectively. The solid-state molecular structures of M[Ar*ketguan] (M = Li, K, Cs) show formally two-coordinate alkali metal cations encapsulated within a hydrophobic coordination pocket formed by the peripheral diphenylmethyl substituents of the guanidinate. Remarkably, percent buried volume analyses (% VBur) of M[Ar*ketguan] [M = Li (94.8% VBur), K (92.1% VBur), Cs (81.7% VBur)] reveal a coordination cavity that adjusts to individually accommodate the variously sized metal ions despite the highly encumbering nature of the ligand. This demonstrates a flexible ligand framework that is able to stabilize low-coordinate metal centers within a “super bulky” coordination environment

Molecular Capacitors: Accessible 6- and 8-electron Redox Chemistry from Dimeric “Ti(I)” and “Ti(0)” Synthons Support-ed by Imidazolin-2-Iminato Ligands.

Reduction of the diamagnetic Ti(III)/Ti(III) dimer [Cl2Ti(μ-NImDipp)]2 (1) (NImDipp = [1,3-bis(Dipp)imidazolin-2-iminato]-, Dipp = NC6H3-2,6-Pri2) with 4 and 6 equiv of KC8 generates the intramolecularly arene-masked, dinuclear titanium com-pounds [(μ-N-μ-η6-ImDipp)Ti]2 (2) and {[(Et2O)2K](μ-N-μ-η6:η6-ImDipp)Ti}2 (3), respectively, in modest yields. The compounds have been structurally characterized by X-ray crystallographic analysis and inspection of the bond metrics within the η6-coordinated aryl substituent of the bridging imidazolin-2-iminato ligand show perturbation of the aromatic system most consistent with two-electron reduction of the ring. As such, 2 and 3 can be assigned respectively as possessing metal centers in formal Ti(III)/Ti(III) and Ti(II)/Ti(II) oxidation states. Exploration of their redox chemistry reveal the ability to reduce several substrate equivalents. For instance, treatment of 2 with excess C8H8 (COT) forms the novel COT-bridged complex [(ImDippN)(η8-COT)Ti](μ-η2:η3-COT)[Ti(η4-COT)(NImDipp)] (4) that dissociates in THF solutions to give mononuclear (ImDippN)Ti(η8-COT)(THF) (5). Addition of COT to 3 yields heterometallic [(ImDippN)(η4-COT)Ti(μ-η4:η5-COT)K(THF)(μ-η6:η4-COT)Ti(NImDipp)(μ-η4:η4-COT)K(THF)2]n (6). Compounds 2 and 5 are the products of the 4-electron oxidation of 2, while 6 stands as the 8-electron oxidation product of 3. Reduction of organozides was also explored. Low temperature reaction of 2 with 4 equiv of AdN3 gives the terminal and bridged imido complex [(ImDippN)Ti(=NAd)](μ-NAd)2[Ti(NImDipp)(N3Ad)] (7) that undergoes intermolecular C-H activation of toluene at room temperature to afford the amido compound [(ImDippN)Ti(NHAd)](μ-NAd)2[Ti(C6H4Me)(NImDipp)] (8-tol). These complexes are the 6-electron oxidation products of the reaction of 2 with AdN3. Furthermore, treatment of 3 with 4 equiv of AdN3 produces the thermally sta-ble Ti(III)/Ti(III) terminal and bridged imido [K(18-crown-6)(THF)2]{[(ImDippN)Ti(NAd)](μ-NAd)2K[Ti(NImDipp)]} (10). Alto-gether, these reactions firmly establish 2 and 3 as unprecedented Ti(I)/Ti(I) and Ti(0)/Ti(0) synthons with the clear ca-pacity to effect multi-electron reductions ranging from 4 – 8 electrons

Ferrocenylene- and Carbosiloxane-Bridged Bis(sila[1]ferrocenophanes) E[SiMe₂-X-SiMe<i>FC</i>]₂ {E = (η⁵-C₅H₄)Fe(η⁵-C₅H₄) or O; X = (CH₂)_<i>n</i> (<i>n</i> = 2, 3, 6); CHCH; <i>FC</i> = (η⁵-C₅H₄)₂Fe}

New FC[SiMe2(CH2)nSiMeFC]2 [FC = 1,1′-ferrocenylene; FC = 1,1′-ferrocenophane, (η5-C5H4)2Fe); n = 2 (7), 3 (8), 6 (9)] and O[SiMe2-X-SiMeFC]2 [X = (CH2)2 (11), CHCH (13)] have been synthesized and characterized. The synthesis involved the reactions of FCLi2·tmeda with FC[SiMe2(CH2)nSiMeCl2]2 [n = 2 (4), 3 (5), 6 (6)] and O[SiMe2-X-SiMeCl2]2 [X = (CH2)2 (10), CHCH (12)] at −78 °C. Compounds 4−13 were characterized by elemental analysis, NMR spectroscopy, and for 11, single-crystal X-ray crystallography. The cyclopentadienyl rings in the structure of 11 are tilted with a dihedral angle of 19.8°. The observed red-shift of the lowest energy transition associated with the ferrocenophanyl groups in UV/vis spectra of 7−9, 11, and 13 also confirms the ring strain. Cyclic voltammetric studies exhibited either a broad (7−9) or sharp (11, 13) wave for the reversible redox process. The broadness of the band for the FC-bridged complexes is a composite of the two types of (η5-C5H4)Fe(η5-C5H4) unit, but no significant inter-Fc interaction could be discerned. All the new bis-ferrocenylene materials are readily ring-opened to form polymeric materials