Bioinspired catecholic polymers for functional materials design

Melanins and Polydopamine (PDA) are bioinspired catecholic polymers that are well known for their intriguing chemical structure and physiological functions. Indeed, PDA has a suite of properties that are uncommon to many known organic materials and over the last decade researchers have endeavored to exploit those properties in technologically relevant materials. Those efforts notwithstanding, PDAs’ chemical structures have yet to be revealed in their entirety and their useful properties yet to be fully explored. In addition, given the natural presence of melanins and dopamine in many animals (including humans), along with their versatile functional features, these materials can serve as non-toxic additives to common polymers and thereby enhance their properties. Or they could, on their own, serve as eco-friendly functional organic films to be used in a variety of useful applications. To this end, we suggest first the potential of melanins as thermal stabilizers for common polymers by evaluating the addition of melanin to several model polymers with well-known degradation pathways. Small loadings of natural and synthetic melanins significantly alter the radical-initiated chain scission behavior of conventional polymers. Such loadings cause a dramatic increase in its onset decomposition temperature, indicating potential benefits for high temperature processing or increasing their upper use temperature in demanding applications. Second, we suggest thin films of synthetic melanin and poly(allylamine hydrochloride) be deposited layer-by-layer from dilute aqueous solutions in ambient conditions. The multilayer films show superior UV-protection performance and substantially extend the useful life of a conductive polymer film under UV light, demonstrating the utility of melanin films in high-tech applications. Third, we establish a synthetic approach to prepare block copolymers of poly(methyl methacrylate) (PMMA) and PDA using a modified atom transfer radical polymerization (ATRP) technique. These copolymers display very good solubility in a range of organic solvents and the spin cast thin films of the copolymers show a sharp reduction (by up to 50%) in protein adsorption compared to those of neat PMMA. The enhanced solvent processability, thermal stability, and low protein adsorption characteristics of this copolymer make it an attractive choice for antifouling coatings on large surfaces. Fourth, we exploit PDA to achieve block copolymer (BCP) lithography on a variety of soft-material surfaces. This biomimetic film serves as a reactive platform for subsequently grafting a surface neutral layer to chemically guide the perpendicular orientation of BCP lamellae. BCP nanopatterning may now be achieved over a large area on cheap, rough, and commercially available roll-to-roll flexible polymer substrates having a wide range of surface energies, surfaces that are of interest to be adapted for patterning. Fifth, we develop an efficient, environmentally friendly, and water-based flame-retardant surface nanocoating for highly flammable foamed materials such as flexible polyurethane (PU) foams. Upon exposure to flame, a PDA coating remains intact on the surface, completely stopping the melting and interrupting foam collapse. In addition, given the reported radical-scavenging capability of catechols, the PDA layer is hypothesized to remove flammable radicals which further retards flame spread during a fire. From cone calorimeter data, peak heat release rate of PDA-coated foams shows a sharp reduction, of up to 67%, relative to a control foam. This represents much better performance than many conventional additives for flexible PU foams that have been reported in the literature. We additionally investigated the effect of catechol functionality on the flammability of PU foams through the comparison of cone calorimetric analysis between PDA-coated flexible PU foams with pristine catechol functionality and LD-containing rigid PU foams with mostly depleted catechols. This new knowledge will be potentially useful in the design of flame-resistant foams and surface coatings.Chemical Engineerin

I Complexation of iron(II), nickel(II), copper(II) and zinc(II) by hexadentate tripodal aminopyridyl chelators II The potential of curcumin in medicine: Synthesis and iron coordination chemistry of curcuminoids

Chapter 1. Binding properties of tach-3-MeOpyr with Zn(II), Cu(II), Fe(II) and Ni(II) have been studied and compared to other tachpyr family metal complexes. The hypothesis was that weak binding between metals and the tachpyr ligand family might be responsible for its lower cytotoxicity towards cells. However, the electronic and structural data in solution do not demonstrate any signs of weaker binding for Cu(II), Fe(II) and Ni(II) between tach-3-MeOpyr and tach-3-Mepyr. While tachpyr, tach-3-Mepyr and tach-3-MeOpyr all have similar binding properties toward Fe(II) in an oxygen free environment, the rates of oxidative dehydrogenation of their Fe(II) complexes in air are substantially different. The rate of oxidation of the chelators appears related to their mechanism of cytotoxicity because rates of cytotoxicity correlated with the rate of oxidation. Chapter 2. Two curcumin analogues (2,4-DMCU, 4,4\u27-DMCU) and curcumin were synthesized via Pabon\u27s method with some modification. These two synthetic derivatives contain the same metal binding motif with different aryl rings. All curcuminoids have shown keto-enol tautomers in solution, characterized by 1H and 13C NMR. Chapter 3. Upon deprotonation of the beta-diketone structural motif, curcumin will chelate a variety of divalent and trivalent metal ions, Ga(III), In(III), Cu(II), Mn(II), and Fe(III). Depending on the experimental conditions, UV-Vis spectrophotometric titrations showed the formation of iron-curcuminoids complexes with M:L stoichiometries of 1:1, 1:2 or 1:3. A combination of EPR, Evans\u27 method, and spectrophotometric studies indicate that Fe(III) is reduced to Fe(ll) by reaction with curcumin anions under aerobic conditions but not with a synthetic derivative 4,4\u27-dimethoxycurcumin (4,4\u27-DMCU). Although curcumin was degraded in pH 7.4 PBS solutions, it was degraded much less when iron was present

The effect of substituted benzolactam GH secretagogue, L-692,585 on central regulation of GH secretion in swine

This dissertation describes the central regulation of growth hormone (GH) secretion and mechanism of action of a substituted benzolactam GH secretagogue, L-692,585 (585), in young (40-45 kg) castrate male Yorkshire pigs;The first study describes the central regulation of GH secretion by 585 with intracerebroventricular (icv) stainless steel cannulas placed by stereotaxic coordinates. Dose-dependent increases in GH secretion by 585 occurred following icv injections of saline vehicle, 3, 10, 30 [mu]g/kg BW by a once daily increment. A switchback study of iv and icv 585 treatment determined central and peripheral regulation of GH secretion by the GH secretagogue;The second study investigated the possible involvement of neuropeptides administered icv on GH secretion. We injected somatostatin (SRIH), neuropeptide Y (NPY) and galanin (GAL) with or without 585. The results suggest that endogenous GH secretion was affected by SRIH and GAL but not by NPY, and 585-stimulated GH response appeared to be modulated by all three neuropeptides;The third study describes the effect of urocortin on GH release. Urocortin (0.01, 0.03, 0.01 mg/ kg BW) and saline vehicle were administered via icv cannula. A modest increase in GH release resulted from central administration of urocortin;The fourth study details the effect of 585 on hypothalamus-pituitary-adrenal axis by comparing the effects of hypophysectomy (HYPOX) and sham operation control (SOC). Intravenous administration of 585 (0.01, 0.1 mg/kg BW) significantly increased cortisol in the SOC but not in the HYPOX group. As expected, 585 increased GH in the SOC, but not in the HYPOX group. Compared with respective saline controls, ACTH caused increases in cortisol levels in the SOC and HYPOX groups. Results of this study indicate that 585 requires an intact pituitary to increase cortisol secretion suggesting that GH-secretagogue has no direct stimulatory effect on adrenal cortisol secretion in HYPOX or SOC pigs;The results of these studies investigating the central effect of L-692,585 in pigs support the idea that novel nonpeptidyl growth hormone secretagogues may mimic an unidentified endogenous hormone that amplifies and is capable of regulating pulsatile GH secretion in concert with GHRH, somatostatin, and neuropeptides

Central Nervous System Mediation of Growth Hormone Secretagogue in the Pig

Rapid growth in the young pig requires an episodic pattern of growth hormone (GH) secretion. We developed different neurosurgical techniques to elucidate sites within the hypothalamus, a lower part of the brain, that regulate GH release in this species. A focus of this research is administration of small brain peptide and nonpeptide hormones that acutely affect GH release to define mechanisms of action and their efficacy in augmenting growth

PERSPECTIVES OF WATER QUALITY IMPROVEMENT BY AQUATIC MACROPHYTES AS NUTRIENT SINK IN THE LAKE PALDANGHO, KOREA

Improvement of water quality by aquatic macrophytes was studied at the Lake Paldangho, a reservoir supplying the service water for 15 million inhabitants in the Capital of Korea. Annual production of aboveground of emergent plants having 1800 g DW/m² for Typha angustata and 1700g DW/m² for Zizania latifolia, are 15- to 30-folds as large as those of submersed plants having 110 g DW/m² for Ceratophyllum demersum and 60 g DW/m² for Hydrilla verticillata. Although concentrations of nitrogen and phosphorus in mg per g dry matter of emergent plants are small as a half of those of submersed ones, standing nutrients in g per m² of the former are 8- to 9-folds as large as that of the latter because of large production. Annual return of nutrients from the litters are also more in emergent plants than in submersed one. In the whole Lake the uptake amounts by macrophyte (sink) are 30.3 ton of nitrogen and 4.9 ton of phosphorus, and the return amounts from the litter (source) are 18.5 ton of nitrogen and 4.3 ton of phosphorus. Difference between the sink and the source, 11.8 ton for nitrogen and 0.6 ton for phosphorus, will remain in sediment of littoral zone. If aboveground of macrohytes are weeded out on time occurring the maximum production nutrients remaining will be reduced. To increase the annual production, repetitive harvesting of Zizania latifolia is effective.Article信州大学理学部付属諏訪臨湖実験所報告 7: 167-175(1991)departmental bulletin pape