Deriving Commercial Level Adhesive Performance from a Bio-Based Mussel Mimetic Polymer

Adhesives are critical for holding together the products that we use every day. Most industrial glues are petroleum-based. These materials are strong bonding but also permanent, leading to difficulties in separation, recycling, and reuse of the components. Petroleum-based materials only exist in finite quantities, and sustainable alternatives are needed for the future. Results presented here are part of our efforts to develop adhesives that are nontoxic, renewably sourced, and allow substrates to be disassembled for recycling. By systematically studying formulation parameters for a biobased, mussel mimetic polymer, we now have developed a material that is able to compete with commercial biobased and petroleum-based adhesives in terms of adhesive strengths on multiple substrates

Underwater Bonding with Charged Polymer Mimics of Marine Mussel Adhesive Proteins

Underwater Bonding with Charged Polymer Mimics of Marine Mussel Adhesive Protein

Alkyl Transfer to Metal Thiolates: Kinetics, Active Species Identification, and Relevance to the DNA Methyl Phosphotriester Repair Center of <i>Escherichia</i> <i>coli</i> Ada

The Ada protein of Escherichia coli employs a [Zn(S-cys)4]2- site to repair deoxyribonucleic acid alkyl phosphotriester lesions. The alkyl group is transferred to a cysteine thiolate in a stoichiometric reaction. We describe a functional model for this chemistry in which a thiolate of [(CH3)4N]2[Zn(SC6H5)4] accepts a methyl group from (CH3O)3PO. The thiolate salt (CH3)4N(SC6H5) is also active in methyl transfer, but the thiol C6H5SH fails to react. Conductivity measurements and kinetic studies demonstrate that [(CH3)4N]2[Zn(SC6H5)4] forms ion pairs in dimethyl sulfoxide (DMSO) solution (KIP = 13 ± 4 M-1) which exhibit diminished reactivity. The reaction of [Zn(SC6H5)4]2- with (CH3O)3PO is first order with respect to each reagent. A second-order rate constant for this reaction, kZn, was determined to be (1.6 ± 0.3) × 10-2 M-1 s-1. From kinetic data and equilibria studies, all reactivity of [(CH3)4N]2[Zn(SC6H5)4] toward (CH3O)3PO could be attributed to dissociated thiolate. Metal complexes representing alternative protein sites were prepared and displayed the following kinetic trend of methyl transfer ability:  [(CH3)4N]2[Zn(SC6H5)4] > [(CH3)4N]2[Co(SC6H5)4] ≈ [(CH3)4N]2[Cd(SC6H5)4] > [(CH3)4N][Zn(SC6H5)3(MeIm)] > [Zn(SC6H5)2(MeIm)2], where MeIm = 1-methylimidazole. These results are consistent with a dissociated thiolate being the active species and suggest that a similar mechanism might apply to alkyl phosphotriester repair by Ada

Ambivalent Adhesives: Combining Biomimetic Cross-Linking with Antiadhesive Oligo(ethylene glycol)

Oligo­(ethylene glycol) (OEG) and poly­(ethylene glycol) (PEG) exhibit several desirable properties including biocompatibility and resistance to fouling by protein adsorption. Still needed are surgical glues and orthopedic cements, among several other materials, that display similar traits. However, the very lack of interactions with other molecules that prevents toxicity and fouling also makes adhesion elusive. In work described here the cross-linking chemistry of marine mussel adhesive is combined with OEG to make a family of terpolymers. The effect of polymer composition upon bulk adhesion was examined. High strength bonding was found with a subset of the polymers containing appreciable OEG content. These structure–property insights may help the design of new materials for which the properties of OEG and high strength adhesion are both being sought

Positive Charge Influences on the Surface Interactions and Cohesive Bonding of a Catechol-Containing Polymer

Achieving robust underwater adhesion remains challenging. Through generations of evolution, marine mussels have developed an adhesive system that allows them to anchor onto wet surfaces. Scientists have taken varied approaches to developing mussel-inspired adhesives. Mussel foot proteins are rich in lysine residues, which may play a role in the removal of salts from surfaces. Displacement of water and ions on substrates could then enable molecular contact with surfaces. The necessity of cations for underwater adhesion is still in debate. Here, we examined the performance of a methacrylate polymer containing quaternary ammonium and catechol groups. Varying amounts of charge in the polymers were studied. As opposed to protonated amines such as lysine, quaternary ammonium groups offer a nonreactive cation for isolating effects from only charge. Results shown for dry bonding demonstrated that cations tended to decrease bulk cohesion while increasing surface interactions. Stronger interactions at surfaces, along with weaker bulk bonding, indicate that cations decreased the cohesive forces. When under salt water, overall bulk adhesion also dropped with higher cation loadings. Surface attachment under salt water also dropped, indicating that the polymer cations could not displace surface waters or sodium ions. Salt did, however, appear to shield bulk cation–cation repulsions. These studies help to distinguish influences upon bulk cohesion from attachment at surfaces. The roles of cations in adhesion are complex, with both cohesive and surface bonding being relevant in different ways, sometimes even working in opposite directions

Solution Speciation, Kinetics, and Observing Reaction Intermediates in the Alkylation of Oxidovanadium Compounds

Contact with environmental alkylating agents brings about modification of DNA bases, mispairing, mutations, and cancer. Nucleophilic compounds may be able to consume these toxins, thereby providing an alternative reaction pathway and preventing DNA damage. Owing to promising results from animal trials, oxidovanadium compounds present a potential class of nucleophilic complexes for preventing cancer. We are studying the reactivity of alkylating toxins with oxidovanadium-ligand compounds. The complexes K[VO2(salhyph(R)2)], where salhyph is the salicylidenehydrazide ligand, are the focus of this study. By changing the electron donating or withdrawing ability of the -R substituents upon the salhyph(R)2 ligand (R = -NO2, -H, -CH3, -OCH3), a family of compounds is obtained to investigate. Conductivity measurements reveal significant ion-pairing of all compounds in dimethyl sulfoxide (DMSO) solutions. Kinetic analysis shows that this ion-pairing causes a reduction in reaction rates. Reactivity of K[VO2(salhyph(R)2)] is attributed exclusively to the non-ion-paired “free” [VO2(salhyph(R)2)]− anion in solution. Both 1H and 51V NMR spectroscopic studies show that direct alkylation of K[VO2(salhyph(H)2)]·CH3OH generates a VO(OCH2CH3)(salhyph(H)2) intermediate which then protonates to release CH3CH2OH and a proposed [VO(salhyph(H)2)]+ compound. Upon hydrolysis the dinuclear {[VO(salhyph(H)2)]2O} end product is formed. This mechanistic understanding and ability to exert control over reactions between inorganic compounds and alkylating toxins may aid in the future development of pharmaceuticals for preventing DNA damage

The Elusive Vanadate (V₃O₉)^3-: Isolation, Crystal Structure, and Nonaqueous Solution Behavior

The isolation, crystal structure, and nonaqueous solution characteristics of the first trinuclear vanadate are presented. The crystal structure reveals a six-membered cyclic arrangement of alternating vanadium and oxygen atoms for the anion of [(C4H9)4N]3(V3O9). The 51V NMR spectrum of this compound in CD3CN exhibits multiple peaks. The relative intensities of each resonance can be altered by concentration and temperature changes, the later of which are reversible. Addition of [(C4H9)4N]Br and NaClO4 also perturbs the equilibria between species observed. Conductivity data for [(C4H9)4N]3(V3O9) in CH3CN as a function of concentration display pronounced curvature and indicate formation of a neutral species in solution at the highest concentrations studied. Stoichiometric mixtures of [(C4H9)4N]3(V3O9) with the known vanadates [(C4H9)4N]3(HV4O12), [(C4H9)4N]3(V5O14), and [(C4H9)4N]3(H3V10O28) are prepared and examined by 51V NMR. Equilibration between the various vanadates is observed and characterized. Resonances for these known vanadates, however, cannot be used to identify the peaks found for [(C4H9)4N]3(V3O9), alone, in solution. The existence of ion pairs in acetonitrile is the only interpretation for the solution behavior of [(C4H9)4N]3(V3O9) consistent with all data. As such, we can directly observe each possible ion pairing state by 51V NMR:  (V3O9)3- at −555 ppm, {[(C4H9)4N](V3O9)}2- at −569 ppm, {[(C4H9)4N]2(V3O9)}- at −576 ppm, and [(C4H9)4N]3(V3O9) at −628 ppm. To the best of our knowledge, [(C4H9)4N]3(V3O9) presents the first case in which every possible ion paired state can be observed directly from a parent polyion. Isolation and characterization of this simple metal oxo moiety may now facilitate efforts to design functional polyoxometalates

Alkylation of Inorganic Oxo Compounds and Insights on Preventing DNA Damage

Metabolism of food- and tobacco-borne procarcinogens results in the exposure of DNA to toxic alkylating agents. These assaults can bring about DNA alkylation damage, mutations, and cancer. Dietary inorganic compounds such as selenium and vanadium are known to prevent cancer, possibly by reacting directly with alkylating agents, thereby preventing DNA damage. To understand potential interactions between oxo species and alkylating toxins, we reacted a series of alkylating agents with varied classes of oxo compounds (i.e., vanadates, selenate, phosphate, sulfate, acetate, nitrate, and nitrite). A new organic-soluble selenate, [(C6H5)4P]3(O3SeOCH2OSeO3)(HSeO4), was synthesized and characterized for these studies. Vanadates were found to convert ethylating agents into ethanol, whereas other anions formed esters upon alkylation. General trends show that oxo anions of the greatest charge density were the most reactive. These studies suggest that the design of new compounds for cancer prevention should incorporate reactive oxo groups with high anionic charge density

Alkylation of Inorganic Oxo Compounds and Insights on Preventing DNA Damage

Metabolism of food- and tobacco-borne procarcinogens results in the exposure of DNA to toxic alkylating agents. These assaults can bring about DNA alkylation damage, mutations, and cancer. Dietary inorganic compounds such as selenium and vanadium are known to prevent cancer, possibly by reacting directly with alkylating agents, thereby preventing DNA damage. To understand potential interactions between oxo species and alkylating toxins, we reacted a series of alkylating agents with varied classes of oxo compounds (i.e., vanadates, selenate, phosphate, sulfate, acetate, nitrate, and nitrite). A new organic-soluble selenate, [(C6H5)4P]3(O3SeOCH2OSeO3)(HSeO4), was synthesized and characterized for these studies. Vanadates were found to convert ethylating agents into ethanol, whereas other anions formed esters upon alkylation. General trends show that oxo anions of the greatest charge density were the most reactive. These studies suggest that the design of new compounds for cancer prevention should incorporate reactive oxo groups with high anionic charge density