Natural underwater adhesives

The general topic of this review is protein‐based underwater adhesives produced by aquatic organisms. The focus is on mechanisms of interfacial adhesion to native surfaces and controlled underwater solidification of natural water‐borne adhesives. Four genera that exemplify the broad range of function, general mechanistic features, and unique adaptations are discussed in detail: blue mussels, acorn barnacles, sandcastle worms, and freshwater caddisfly larva. Aquatic surfaces in nature are charged and in equilibrium with their environment, populated by an electrical double layer of ions as well as adsorbed natural polyelectrolytes and microbial biofilms. Surface adsorption of underwater bioadhesives likely occurs by exchange of surface bound ligands by amino acid sidechains, driven primarily by relative affinities and effective concentrations of polymeric functional groups. Most aquatic organisms exploit modified amino acid sidechains, in particular phosphorylated serines and hydroxylated tyrosines (dopa), with high‐surface affinity that form coordinative surface complexes. After delivery to the surfaces as a fluid, permanent natural adhesives solidify to bear sustained loads. Mussel plaques are assembled in a manner superficially reminiscent of in vitro layer‐by‐layer strategies, with sequentially delivered layers associated through Fe(dopa)₃ coordination bonds. The adhesives of sandcastle worms, caddisfly larva, and barnacles may be delivered in a form somewhat similar to in vitro complex coacervation. Marine adhesives are secreted, or excreted, into seawater that has a significantly higher pH and ionic strength than the internal environment. Empirical evidence suggests these environment triggers could provide minimalistic, fail‐safe timing mechanisms to prevent premature solidification (insolubilization) of the glue within the secretory system, yet allow rapid solidification after secretion. Underwater bioadhesives are further strengthened by secondary covalent curing. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Complex dynamics of multicomponent biological coacervates

Phase transitions and coacervates play key roles in natural and synthetic soft matter. In particular, the past few years have seen a rapid expansion in studies of these phenomena in the context of dynamic cellular compartmentalization. In this brief review, we mainly focus on a few concepts and selected in vitro and cellular examples of recent developments in the areas of dynamics and multicomponent systems. Topics covered include the flexibility and conformational dynamics of polymeric species involved in phase separation, valence and non-monotonic effects, noise modulation and feedback loops, and multicomponent systems and substructure. The fundamental concepts discussed in this review are widely applicable, including in the context of cellular function and the development of materials with novel properties.     

Mechanisms and applications of bioinspired underwater/wet adhesives

In nature, many organisms can effectively fix to contact substrates and move and prey in complex living environments, such as underwater, seawater, and tidal environments, owing to special secreted chemical components and/or special micro/nanostructures on the adhesive surface of these organisms. Inspired by the adhesive performance of organisms, extensive research related to adhesive components and adhesive surfaces has been conducted recently. To better understand the underlying adhesive mechanisms and facilitate further continuous inspiration, a brief overview of recent wet/underwater adhesive materials is provided herein. First, the adhesive processes and underlying mechanisms of commonly researched organisms, such as mussels, octopuses, clingfish, and tree frogs, are discussed, and the corresponding bioinspired artificial adhesives are presented. Then, the applications of these bioinspired adhesives, such as intelligent robots (signal monitoring and sensing devices), wearable devices (including wet climbing and electronic skin), biomedicines (including wound dressings, bone adhesion, and rapid hemostasis), are presented and summarized. Finally, we offer our perspective on the future challenges and development of bioinspired artificial adhesives.     

Modern synthetic adhesives based on epoxy-rubber compositions

Results of investigations of adhesives and compounds based on epoxy resins modified with low-molecular rubbers are presented. A series of epoxy-rubber compositions with improved physicomechanical characteristics and operational properties are developed. Examples of solutions of engineering challenges using high-molecular synthetic adhesive systems are given.     

Degradation of floor adhesives as a function of pH

Floor adhesives on cement-based substrates may degrade if the pH is high enough and this has in many cases led to emissions of odorous substances and deteriorated indoor air quality. We have used isothermal calorimetry to assess the degradation rate of two floor adhesives as a function of pH. The rate of heat production measured by the calorimeter is proportional to the reaction rate. The degradation rate was similar for a “standard” and a “low emitting” adhesive, but the low emitting adhesive did not release volatile reaction products. The results show that adhesive degradation is strongly pH dependent. A model of alkaline hydrolysis based on two reaction sites is discussed.     

Conductivity and structure of a group of lipid coacervates

Some theories concerning the structure and properties of coacervates are discussed. The preparation of a type of lipid coacervate, suitable as a biological model, especially for olfactory transduction, is described. When organic substances are added, the conductivity of the coacervate decreases roughly in proportion to the amount of additive. The sensitivity to 20 different additives has been investigated. In general, the sensitivity was greater, the longer the chain of the additive. The sensitivity pattern was also dependent on the composition of the coacervate and although the dependence appeared to be very complex, some clear traits could be distinguished. Experimental studies on the optical and diffusional properties and composition of the coacervate are presented. The coacervate was found to be optically isotropic. Its total Na⁺ concentration was about the same as in the equilibrium liquid, whereas the Cl⁻ concentration in coacervate water was lower than in equilibrium liquid. Both remained fairly constant as the coacervate shrank under the influence of added toluene. The diffusion velocities of tartrazine and Sudan black B in coacervate were of the same order of magnitude, which suggests that the lipids may form a continuous network throughout the coacervate phase, rather than discrete micelles.     

Bioinspired synthetic wet adhesives: from permanent bonding to reversible regulation

Nowadays, robust underwater adhesives products are highly demanded both in industrial and biomedical fields. Meanwhile, study of the underwater adhesion mechanism of natural organisms under fluid environment is necessary, which provides inspiration for engineering adhesive materials that can be used in wet environment. Scientists are committed to discovering the unique adhesion mechanisms of protein adhesives for natural organisms. Especially, recent understanding of wet adhesion mechanisms provides designable inspiration for developing novel synthetic underwater adhesives with high performance by using 3,4-dihydroxyphenylalanine-based and coacervate-enabled strategies. Although pursuing robust interface bonding in these years, controlling the wet adhesion state with reversible/switchable feature is the latest goal for developing intelligent biomimetic adhesives, which implies important applications in multiple fields.     

Acetic anhydride as a synthetic reagent

Acetic anhydride has been used widely in synthetic organic chemistry, especially in syntheses and transformations of heterocyclic compounds. These utilities are reviewed under the following classification.     

Flexible polyfluorinated bis-diazirines as molecular adhesives

Motivated by a desire to develop flexible covalent adhesives that afford some of the same malleability in the adhesive layer as traditional polymer-based adhesives, we designed and synthesized two flexible, highly fluorinated bis-diazirines. Both molecules are shown to function as effective crosslinkers for polymer materials, and to act as strong adhesives when painted between two polymer objects of low surface energy, prior to thermal activation. Data obtained from lap-shear experiments suggests that greater molecular flexibility is correlated with improved mechanical compliance in the adhesive layer.

Flexible, highly fluorinated covalent adhesives are synthesized, and are shown to afford comparable C–H insertion efficiency and adhesion strength relative to a rigid analogue, while providing improved mechanical compliance in the adhesion layer.     

Connect the drops: using solids as adhesives for liquids

Colloidal particles are shown to be capable of developing adhesion between liquid phases through a bridging mechanism by which intervening, micrometer-scaled, fluid films are stabilized. Particle dynamics leading to the assembly of the stabilizing structure are discussed. Models for the resulting adhesive force are developed from considerations of both interface shape perturbation and the force applied by surface tension on an individual particle. Finally, predictions from these models are compared to direct measurements of the forces that arise during the separation of adhering interfaces. Such comparisons lead to a novel method for determining the three-phase contact angle inherent to particles residing at fluid interfaces.     

Redox-transmetalation process as a generalized synthetic strategy for core-shell magnetic nanoparticles

Although multicomponent core-shell type nanomaterials are one of the highly desired structural motifs due to their simultaneous multifunctionalities, the fabrication strategy for such nanostructures is still in a primitive stage. Here, we present a redox-transmetalation process that is effective as a general protocol for the fabrication of high quality and well-defined core-shell type bimetallic nanoparticles on the sub-10 nm scale. Various core-shell type nanomaterials including Co@Au, Co@Pd, Co@Pt, and Co@Cu nanoparticles are fabricated via transmetalation reactions. Compared to conventional sequential reduction strategies, this transmetalation process has several advantages for the fabrication of core-shell type nanoparticles: (i) no additional reducing agent is needed and (ii) spontaneous shell layer deposition occurs on top of the core nanoparticle surface and thus prevents self-nucleation of secondarily added metals. We also demonstrate the versatility of these core-shell structures by transferring Co@Au nanoparticles from an organic phase to an aqueous phase via a surface modification process. The nanostructures, magnetic properties, and reaction byproducts of these core-shell nanoparticles are spectroscopically characterized and identified, in part, to confirm the chemical process that promotes the core-shell structure formation.     

A New CoII Complex as a Bulge-Specific Probe for DNA

Bulge cleavage of two or three bases occurs when a DNA substrate is specifically cleaved oxidatively by [Co^II(tfa)₂(happ)] (see picture). Hydrogen peroxide is necessary for the activation of this octahedral complex, which suggests that hydroxyl radicals are the reactive species. The complex has no significant reactivity towards the corresponding sequence in a single-stranded DNA region, and it exhibits only a low affinity towards double-stranded DNA. happ=macrocyclic ligand based on 1,10-phenanthroline, tfa=trifluoroacetate.     

Synthesis of modified polylatic acid and its use as a base thermoplastic for biodegradable hot-melt adhesives

New polylactic acid derivatives were synthesized and their thermal stability was studied. The new products were tested as a biodegradable polymeric base for fabrication of hot-melt adhesives.     

ENDOR characterization of a synthetic diiron hydrazido complex as a model for nitrogenase intermediates

Molybdenum-dependent nitrogenase binds and reduces N2 at the [Fe7, Mo, S9, X, homocitrate] iron-molybdenum cofactor (FeMo-co). Kinetic and spectroscopic studies of nitrogenase variants indicate that a single Fe-S face is the most likely binding site. Recently, substantial progress has been made in determining the structures of nitrogenase intermediates formed during alkyne and N2 reduction through use of ENDOR spectroscopy. However, constraints derived from ENDOR studies of biomimetic complexes with known structure would powerfully contribute in turning experimentally derived ENDOR parameters into structures for species bound to FeMo-co during N2 reduction. The first report of a paramagnetic Fe-S compound that binds reduced forms of N2 involved Fe complexes stabilized by a bulky beta-diketiminate ligand (Vela, J.; Stoian, S.; Flaschenriem, C. J.; Münck, E.; Holland, P. L. J. Am. Chem. Soc. 2004, 126, 4522-4523). Treatment of a sulfidodiiron(II) complex with phenylhydrazine gave an isolable mixed-valence FeII-Fe(III) complex with a bridging phenylhydrazido (PhNNH2) ligand, and this species now has been characterized by ENDOR spectroscopy. Using both 15N, 2H labeled and unlabeled forms of the hydrazido ligand, the hyperfine and quadrupole parameters of the -N-NH2 moiety have been derived by a procedure that incorporates the (near-) mirror symmetry of the complex and involves a strategy which combines experiment with semiempirical and DFT computations. The results support the use of DFT computations in identifying nitrogenous species bound to FeMo-co of nitrogenase turnover intermediates and indicate that 14N quadrupole parameters from nitrogenase intermediates will provide a strong indication of the nature of the bound nitrogenous species. Comparison of the large 14N hyperfine couplings measured here with that of a hydrazine-derived species bound to FeMo-co of a trapped nitrogenase intermediate suggests that the ion(s) are not high spin and/or that the spin coupling coefficients of the coordinating cofactor iron ion(s) in the intermediate are exceptionally small.     

Synthesis and characterization of polycyanurates as dismantlable adhesives

Random copolycyanurates with a low number of amide units in the main chain have been developed as a candidate of dismantlable adhesives based on the rapid decrease of the molecular weights during the rearrangement to polyisocyanurates by a thermal treatment. The random copolycyanurates were prepared by the phase‐transfer‐catalyzed polycondensation of 2,4‐dichloro‐6‐methoxy‐1,3,5‐triazine with bisphenol A and a new bisphenol containing an amide unit in the presence of tetrabutylammonium bromide. They exhibited an excellent adhesive property for the silicon and copper deposited on the silicon substrate after the high thermal treatment of 240 °C under 0.6 MPa compression, and the die shear strengths of these polymers dramatically decreased at 260 °C for 1 h. Random copolycyanurates containing the amide unit are shown to be promising materials for dismantlable adhesion. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1153–1158     

Natural products such as adhesives in oil paintings

Abstract

The study and analysis of the materials employed in artistic paintings provide deeper knowledge about the history of the work of art, including restoration efforts made in the past, and the development of painting techniques through the centuries. Gas chromatography coupled to mass spectrometry is the main analytical technique employed, as it proved to be the most suitable technique for the analysis of complex mixtures, thanks to its combination of sensitivity, wide range of applicability and versatility. Further, μFT-IR technique has also been employed to get a preliminary screening of the samples taken from paintings. In this paper, the analytical protocol based on these two techniques has been applied for analysing natural terpenic resins; its performance has been tested on microsamples collected from paintings of valuable artistic interest.     

Terbium Crown-Ether Complex as a Stable Photoprobe

Terbium ion-4'carboxybenzo-18crown-6-ether complex (TbCCE) photoprobe is a sensitive and stable luminescent photoprobe used to detect low (9.4 x10⁻⁹ mol L⁻¹) concentrations of nalbuphine (NAL) in serum and pharmaceutical formulations. Here we discuss molecular modeling of the interacting species using DFT and TD-DFT. The results reveal strong binding energy of TbCCE (−153.36 kJ/mol) and explain the results of Stern-Volmer bimolecular quenching analysis due to the presence of NAL in the proximity (at 2.403 Å apart from Tb ion) of the emissive TbCCE. Ab Initio molecular dynamic (AIMD) simulations are used to explain the dynamical changes of TbCCE molecular kinetic energy in its S₁ state induced by collision with NAL. The AIMD simulates collisions between interacting molecules, which are reflected in the observed quenching of the photoprobe. Kinetic energy changes during molecular motions in the S₁ state of TbCCE in presence of NAL indicate energy transfer process leading to quenching starting at 57 fs at NAL-TbCCE distance is ~ 1.6 Å. The excited state AIMD simulations carried out in this work suggest a new avenue for future research on luminescence quenching.     

Pyridiniums as potential synthetic substitutes for nitrogen mustards

Dialkylamino-alkyl primary amines 1b and 2b are converted by pyrylium salts into the corresponding pyridinium derivatives. The pyridinium salts act as aminoalkylating agents for representative O-, S-, N-, and C-nucleophiles and are potentially safe substitutes for nitrogen mustards in the reactions.