Elucidating the Structure of Poly(dopamine)
TL;DR: Poly(dopamine) is not a covalent polymer but instead a supramolecular aggregate of monomers (consisting primarily of 5,6-dihydroxyindoline and its dione derivative) that are held together through a combination of charge transfer, π-stacking, and hydrogen bonding interactions.
Abstract: Herein we propose a new structure for poly(dopamine), a synthetic eumelanin that has found broad utility as an antifouling agent. Commercially available 3-hydroxytyramine hydrochloride (dopamine HCl) was polymerized under aerobic, aqueous conditions using tris(hydroxymethyl)aminomethane (TRIS) as a basic polymerization initiator, affording a darkly colored powder product upon isolation. The polymer was analyzed using a variety of solid state spectroscopic and crystallographic techniques. Collectively, the data showed that in contrast to previously proposed models, poly(dopamine) is not a covalent polymer but instead a supramolecular aggregate of monomers (consisting primarily of 5,6-dihydroxyindoline and its dione derivative) that are held together through a combination of charge transfer, π-stacking, and hydrogen bonding interactions.
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3,621 citations
TL;DR: The study reveals a different perspective of polydopamine formation, where it forms in part by the self‐assembly of dopamine and DHI, providing a new clue toward understanding the structures of catecholamines such as melanin.
Abstract: Polydopamine is the first adhesive polymer that can functionalize surfaces made of virtually all material chemistries. The material-independent surface modification properties of polydopamine allow the functionalization of various types of medical and energy devices. However, the mechanism of dopamine polymerization has not yet been clearly demonstrated. Covalent oxidative polymerization via 5,6-dihydroxyindole (DHI), which is similar to the mechanism for synthetic melanin synthesis, has been the clue. Here, it is reported that a physical, self-assembled trimer of (dopamine)2/DHI exists in polydopamine, which has been known to be formed only by covalent polymerization. It is also found that the trimeric complex is tightly entrapped within polydopamine and barely escapes from the polydopamine complex. The result explains the previously reported in vitro and in vivo biocompatibility. The study reveals a different perspective of polydopamine formation, where it forms in part by the self-assembly of dopamine and DHI, providing a new clue toward understanding the structures of catecholamines such as melanin.
1,029 citations
TL;DR: Results give rise to a verified structural assignment of PDA wherein dihydroxyindole and indoledione units with different degrees of (un)saturation are covalently linked by C-C bonds between their benzene rings.
Abstract: Polydopamine (PDA) formed by the oxidation of dopamine is an important polymer, in particular, for coating various surfaces. It is composed of dihydroxyindole, indoledione, and dopamine units, which are assumed to be covalently linked. Although PDA has been applied in a manifold way, its structure is still under discussion. Similarities have been observed in melanins/eumelanins as naturally occurring, deeply colored polymer pigments derived from l-DOPA. Recently, an alternative structure was proposed for PDA wherein dihydroxyindoline, indolinedione, and eventually dopamine units are not covalently linked to each other but are held together by hydrogen bonding between oxygen atoms or π stacking. In this study, we show that this structural proposal is very unlikely to occur taking into account unambiguous results obtained by different analytical methods, among them 13C CPPI MAS NMR (cross-polarization polarization–inversion magic angle spinning NMR), 1H MAS NMR (magic angle spinning NMR), and ES-HRMS (elect...
795 citations
TL;DR: Chemical and physical characterization of polydopamine films deposited on gold surfaces from stirred basic solutions at times ranging from 2 to 60 min are reported, with a focus on times ≤10 min.
Abstract: Current interest in melanin films derived from the autoxidation of dopamine stems from their use as a universal adhesion layer. Here we report chemical and physical characterization of polydopamine films deposited on gold surfaces from stirred basic solutions at times ranging from 2 to 60 min, with a focus on times ≤10 min. Data from Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and electrochemical methods suggest the presence of starting (dopamine) and intermediate (C=N-containing tautomers of quinone and indole) species in the polydopamine films at all deposition times. A uniform overlayer analysis of the XPS data indicates that film thickness increased linearly at short deposition times of ≤10 min. At deposition times ≥10 min, the films appeared largely continuous with surface roughness ≈ ≤ 2 nm, as determined by atomic force microscopy (AFM). Pinhole-free films, as determined by anionic redox probe measurements, required deposition times of 60 min or greater.
702 citations
TL;DR: This Review summarizes the recent progress in graphene and graphene-based materials for four energy storage systems, i.e., lithium-ion batteries, supercapacitors, lithium-sulfur batteries and lithium-air batteries.
Abstract: With the increased demand in energy resources, great efforts have been devoted to developing advanced energy storage and conversion systems. Graphene and graphene-based materials have attracted great attention owing to their unique properties of high mechanical flexibility, large surface area, chemical stability, superior electric and thermal conductivities that render them great choices as alternative electrode materials for electrochemical energy storage systems. This Review summarizes the recent progress in graphene and graphene-based materials for four energy storage systems, i.e., lithium-ion batteries, supercapacitors, lithium-sulfur batteries and lithium-air batteries.
618 citations
References
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TL;DR: Inspired by the composition of adhesive proteins in mussels, dopamine self-polymerization is used to form thin, surface-adherent polydopamine films onto a wide range of inorganic and organic materials, including noble metals, oxides, polymers, semiconductors, and ceramics.
Abstract: We report a method to form multifunctional polymer coatings through simple dip-coating of objects in an aqueous solution of dopamine. Inspired by the composition of adhesive proteins in mussels, we used dopamine self-polymerization to form thin, surface-adherent polydopamine films onto a wide range of inorganic and organic materials, including noble metals, oxides, polymers, semiconductors, and ceramics. Secondary reactions can be used to create a variety of ad-layers, including self-assembled monolayers through deposition of long-chain molecular building blocks, metal films by electroless metallization, and bioinert and bioactive surfaces via grafting of macromolecules.
8,669 citations
TL;DR: In this article, the NMR signals of isotopically or chemically dilute nuclear spins S in solids can be enhanced by repeatedly transferring polarization from a more abundant species I of high abundance (usually protons) to which they are coupled.
Abstract: The NMR signals of isotopically or chemically dilute nuclear spins S in solids can be enhanced by repeatedly transferring polarization from a more abundant species I of high abundance (usually protons) to which they are coupled. The gain in power sensitivity as compared with conventional observation of the rare spins approaches NII(I+1)γI2/NSS(S+1)γS2, or ∼ 103 for S = 13C, I = 1H in organic solids. The transfer of polarization is accomplished by any of a number of double resonance methods. High‐frequency resolution of the S ‐spin signal is obtained by decoupling of the abundant spins. The experimental requirements of the technique are discussed and a brief comparison of its sensitivity with other procedures is made. Representative applications and experimental results are mentioned.
2,244 citations
TL;DR: 2-ureido-4-pyrimidone that dimerize strongly in a self-complementary array of four cooperative hydrogen bonds were used as the associating end group in reversible self-assembling polymer systems.
Abstract: Units of 2-ureido-4-pyrimidone that dimerize strongly in a self-complementary array of four cooperative hydrogen bonds were used as the associating end group in reversible self-assembling polymer systems. The unidirectional design of the binding sites prevents uncontrolled multidirectional association or gelation. Linear polymers and reversible networks were formed from monomers with two and three binding sites, respectively. The thermal and environmental control over lifetime and bond strength makes many properties, such as viscosity, chain length, and composition, tunable in a way not accessible to traditional polymers. Hence, polymer networks with thermodynamically controlled architectures can be formed, for use in, for example, coatings and hot melts, where a reversible, strongly temperature-dependent rheology is highly advantageous.
2,011 citations
TL;DR: In this paper, a double nuclear resonance spectroscopy method is introduced which depends upon effects of magnetic dipole-dipole coupling between two different nuclear species, and a minimum detectability of the order of {10}^{14}$ to ${10}−16}$ nuclear Bohr magnetons/cc of a rare $b$ nuclear species is predicted, to be measured in terms of the change in a strong signal displayed by an abundant $a$ nuclear mass.
Abstract: A double nuclear resonance spectroscopy method is introduced which depends upon effects of magnetic dipole-dipole coupling between two different nuclear species. In solids a minimum detectability of the order of ${10}^{14}$ to ${10}^{16}$ nuclear Bohr magnetons/cc of a rare $b$ nuclear species is predicted, to be measured in terms of the change in a strong signal displayed by an abundant $a$ nuclear species. The $a$ magnetization is first oriented by a strong radio-frequency field in the frame of reference rotating at its Larmor frequency. The $b$ nuclear resonance is obtained simultaneously with a second radio-frequency field; and with the condition that the $a$ and $b$ spins have the same Larmor frequencies in their respective rotating frames, a cross relaxation will occur between the two spin systems. The cross-relaxation interaction, which lasts for the order of a long spin-lattice relaxation time of the $a$ magnetization, is arranged to produce a cumulative demagnetization of the $a$ system when maximum sensitivity is desired. Final observation of the reduced $a$ magnetization indicates the nuclear resonance of the $b$ system. The concepts of uniform spin temperature, when it is valid, and of nonuniform spin temperature where spin diffusion is important, are applied. The density matrix method formulates the double resonance interaction rate in second order. Preliminary tests of the double resonance effect are carried out with a nuclear quadrupole system.
1,804 citations
TL;DR: A facile two-step aqueous approach to immobilization of biomolecules onto surfaces is reported, which exploits the latent reactivity of the biomimetic polymer thin film towards nucleophiles, is unaffected by water, and allows for discrimination betweenucleophiles on the basis of pKa.
Abstract: Immobilization of biomolecules onto surfaces is important in many of the biological and physical sciences, including cell and molecular biology, analytical chemistry, and in applied and interdisciplinary fields such as medical diagnostics, tissue engineering, and bioprocess engineering.[1-4] Strategies for biomolecule immobilization onto surfaces generally exploit either noncovalent or covalent reactions. Noncovalent methods allow reversible immobilization of biomolecules under specific conditions, and include physical adsorption and affinity immobilization. Some widely adapted examples are (strep)avidin-biotin, nitriloacetic acid (NTA)-histidine, and DNA-DNA interactions.[5-8] In contrast, covalent immobilization of molecules onto surfaces typically relies on conjugation reactions between ‘active’ functional groups, such as N-hydroxysuccinimide (NHS)[9] or maleimide,[10] and companion target moieties, such as amines and sulfhydryls. For reactions involving biomolecules performed in aqueous solvents, susceptibility of NHS, maleimide, and other activating groups to hydrolysis during storage and reaction can lead to low efficiency of surface bioconjugation.[11,12] In this study, we report a facile two-step aqueous approach to immobilization of biomolecules onto surfaces. The approach involves simple dip-coating of a biomimetic polymer thin film onto a substrate, followed by conjugation of biomolecules to the biomimetic polymer film. The method exploits the latent reactivity of the biomimetic polymer thin film towards nucleophiles, is unaffected by water, and allows for discrimination between nucleophiles on the basis of pKa.
1,324 citations