Chhiu-Tsu Lin

Green chemistry in situ phosphatizing coatings

Abstract The current organic coating on metals for aerospace applications involves a multi-step process and considerable energy, labor and control, and it generates toxic wastes such as chlorinated solvents, cyanide, cadmium, lead and carcinogenic chromates. The green chemistry technology of in situ phosphatizing coatings (ISPCs) developed in our laboratory is a one-step self-phosphating process, in which the deposition of metal phosphate layer on the substrate surface and the curing of polymer paint film take place independently, but simultaneously. The formation of a metal phosphate layer in situ will essentially eliminate the metal surface pre-treatment step of employing a phosphating line/bath. The use of chemical bonds linked to the paint polymers to seal the pores of metal phosphate in situ should enhance coating adhesion and suppress metal corrosion without a post-treatment of final rinses containing chromium (Cr 6+ ). The successful applications of ISPCs in three types of commercial paints (solvent-borne high-solids, water-reducible and VOC-free latex) on bare and pre-treated cold-rolled steel and 2024 aluminum coupons is presented. The protective performance (coating adhesion and corrosion inhibition) of ISPCs is shown to be superior over that of the current multi-step coating practice.

The thermal stability of native, delipidated, deionized and regenerated bacteriorhodopsin

Differential scanning calorimetry curves and circular dichroism spectra were determined for native bacteriorhodopsin (bR), deionized bR, acid blue and acid purple bR, 75% delipidated bR, deionized-delipidated bR and Mg2+ regenerated deionized bR. The effects of the different perturbations on the thermal stability (melting temperature) and the apparent helical content of the protein were examined. These perturbations have more influence on the deprotonation efficiency and the color change of retinal than on the thermal stability and the apparent helical content of the protein. Although the addition of Mg2+ to deionized bR restores the photochemical cycle, it does not restore the thermal stability to that of the native material.

In-situ phosphatizing coatings III: A water-reducible alkyd baking enamel

We report the successful formulation of stable and compatible in-situ phosphatizing coatings (ISPCs) for a waterborne alkyd-amino baking enamel applied on bare cold-rolled steel (CRS), iron phosphated Bonderite 1000 (BD), and iron phosphated plus Parcolene 60 chromated (BD+P60) coupons. The enhanced coating adhesion of water-based ISPCs is confirmed by the cathodic delamination measurements. After 100 hr of salt spray (fog) test, the corrosion resistance performance (measured by the corrosion disbondment across the “X” scribe, d in mm) of the water-based ISPC on CRS panel (d=4.0−7.0 mm) outperformed that of the control alkyd paint on B-1000 (d=26 mm) and also on BD+P60 (d=14 mm) coupons. The superior coating performance of water-based ISPCs is believed to result from the in-situ metal surface phosphatization as detected by the reflectance FTIR technique.

In-situ phosphatizing coatings I: An air-dried lacquer system

The formulation of in-situ phosphatizing coatings (ISPCs) was successfully performed for lacquer systems using a commercial nitrocellulose lacquer and an optimum amount of in-situ phosphatizing reagents (ISPRs). The in-situ phosphatizing lacquer (ISPL) system is stable, and shows no change in surface appearance and drying speed as compared to the unmodified lacquer (UML). The ISPLs are applied on pine, poplar, and red oak wood boards, and on cold-rolled steel, aluminum, and laminated brass panels. Immersion tests in a 3% NaCl solution showed a remarkable enhancement in paint disbonding resistance for the paint film of ISPL on wood and metals compared to that of the UML sample. The paint film protective performance of ISPLs is further evidenced by the lattice pattern tape testings, and by the cathodic delamination and electrochemical impedance spectroscopy.

Structural transformation upon nitrogen doping of ultrananocrystalline diamond films by microwave plasma CVD

The molecular properties and surface morphology of undoped and N-doped ultra-nanocrystalline diamond (UNCD) films deposited by microwave plasma CVD with addition of nitrogen are investigated with various spectroscopic techniques. The results of spatially resolved Raman scattering, ATR/FT-IR and XPS spectra show more amorphous and sp2/sp3 ratio characteristics in N-doped UNCD films. The surface morphology in AFM scans shows larger nanocrystalline diamond clusters in N-doped UNCD films. Incorporation of nitrogen into UNCD films has promoted an increase of amorphous sp2-bonded carbons in the grain boundaries and the size of nanocrystalline diamond grains that are well correlated to the reported enhancement of conductivity and structural changes of UNCD films.

PHOTOPHYSICAL STUDIES OF LOCAL ANESTHETICS, TETRACAINE and PROCAINE: DRUG AGGREGATIONS

Abstract— The effects of solvent and concentration on the photophysical properties of tertiary amine local anesthetics, tetracaine and procaine were studied experimentally using low temperature (77 K) emission spectroscopy and confirmed theoretically using a HAM/3 method. For tetracaine free base in methylcyclohexane, a broad fluorescence band observed at ˜375 nm for concentrations greater than 1 × 10−3M is assigned to the molecular self‐associated species. The disappearance of this band in ethanol (i.e. a model hydrophobic environment) indicates a greater tendency of neutral tetracaine towards molecular hetero‐association. In an aqueous solution of procainc‐HCl, a broad emission band centered at ˜400 nm is detected even at a concentration as low as 1 × 10−4M and is attributed to the charged aggregates of procaine‐HCI. Two general observations for procaine, tetracaine and dibucaine are noted: (1) the monocation and free base local anesthetics in ethanol solutions give identical photophysical properties, suggesting that the monocation drug species in ethanol is H+ dissociative. and (2) the lowest singlet excited state of neutral local anesthetics is calculated to have a charge‐transfer character originating from a non‐bonding electron in the N of tertiary amine group to the π* orbital of aromatic ring. The possible pharmacological implications of the deprotonation, the drug aggregations and the charge‐transfer excitations of local anesthetics on the molecular basis of anesthesia are discussed.

INTERACTION OF DIBUCAINEHCl LOCAL ANESTHETICS WITH BACTERIORHODOPSIN IN PURPLE MEMBRANE: A SPECTROSCOPIC STUDY

Abstract

DEPROTONATION DYNAMICS OF LOCAL ANESTHETICS IN HYDROPHOBIC MEDIA: DIBUCAINEHCI IN WATER/ALCOHOL OR SURFACTANT MIXTURES

Abstract— The emitting chromophores, emitting states, state orderings and phosphorescence lifetimes of neutral, hydrogen‐bonded, and protonated dibucaines in water/alcohol mixtures were determined experimentally and were confirmed theoretically using a HAM/3 method. These photophysical properties are used to probe the deprotonation dynamics of dibucaine‐HCl in the water/hydrophobic media. It is found that the protonated dibucaine in an aqueous solution is deprotonated and/or forms hydrogen‐bonded dibucaine when it is brought into contact with the alcohols and surfactants. The observed deprotonation processes could lend some insight on the molecular basis of pharmacological action of dibucaine.

Effect of Nano-Ni catalyst on the growth and characterization of diamond films by HFCVD

Four different catalysts, nanodiamond seed, nano-Ni, diamond powder, and mixture of nano-Ni/diamond powder, were used to activate Si wafers for diamond film growth by hot-filament CVD (HFCVD). Diamond crystals were shown to grow directly on both large diamond powder and small nanodiamond seed, but a better crystallinity of diamond film was observed on the ultrasonicated nanodiamond seeded Si substrate. On the other hand, nano-Ni nanocatalysts seem to promote the formation of amorphous carbon but suppress transpolyacetylene (t-PA) phases at the initial growth of diamond films. The subsequent nucleation and growth of diamond crystals on the amorphous carbon layer leads to generation of the spherical diamond particles and clusters prior to coalescence into continuous diamond films based on the CH3 addition mechanism as characterized by XRD, Raman, ATR/FT-IR, XPS, TEM, SEM, and AFM techniques. Moreover, a 36% reduction in surface roughness of diamond film assisted by nano-Ni catalyst is quite significant.

SOLUBILIZATION SITES AND ACID‐BASE FORMS OF DIBUCAINE‐HYDROCHLORIDE IN NEUTRAL AND CHARGED MICELLAR SOLUTIONS

Steady‐state and time‐resolved emission spectroscopic techniques have been employed to characterize the drug species of dibucaine and to identify its location in micellar Triton X‐100 (neutral), hexadecyltrimethyl ammonium bromide (cationic) and lithium dodecyl sulfate (anionic) solutions at 77 K. Under physiological conditions, the dibucaine is shown to exist in the free base form (D) while solubilized in the hydrocarbon core of neutral micelles. In cationic micellar solution, dibucaine exists as the monocation species (DH+) where the anesthetic is solubilized in the extramicellar aqueous solution and D is solubilized in the hydrophobic region with close proximity to the micellar interface. In the anionic micelles, interfacial solubilization is most consistent with a site in which the tertiary amine group of the monocation dibucaine (DH+) is anchored at the micellar interface with its quinoline analog penetrating the hydrophobic region. The distinct properties observed for the drug species (i. e. D and DH+) and their solubilization sites in micelles are consistent with a balance between hydrophobic forces, surface polarity and the interfacial electrostatic potential present in the micellar solubilization sites. These observations could lend insight into the molecular basis of pharmacological action, in particular the mechanism of local anesthetic drug transport across membranes.