Chi‐Yuan Cheng

Melanosomes in black and red human hair are isolated and characterized by various chemical and physical techniques. Different yields of 4-amino-hydroxyphenolanaline by HI hydrolysis (a marker for pheomelanin) and pyrrole-2,3,5-tricarboxylic acid by KMnO(4)/H(+) oxidation (a marker for eumelanin) indicate that the melanosomes in black hair are eumelanosomes, whereas those in red hair are mainly pheomelanosomes. Atomic force microscopy reveals that eumelanosomes and pheomelanosomes have ellipsoidal and spherical shapes, respectively. Eumelanosomes maintain structural integrity upon extraction from the keratin matrix, whereas pheomelanosomes tend to fall apart. The black-hair eumelanosomes have an average of 14.6 +/- 0.5% amino acids content, which is attributed to the internal proteins entrapped in the melanosomes granules. The red-hair melanosomes contain more than 44% of amino acid content even after extensive proteolytic digestion. This high content of amino acids and the poorly reserved integrity of red-hair melanosomes suggest that some proteins are possibly covalently bonded with the melanin constituents in addition to those that are entrapped inside the melanin species. Soluene solubilization assay indicates the absorbance of melanin per gram of sample, adjusted for the amino acid content, is a factor of 2.9 greater for the black-hair melanosomes than the red-hair melanosomes. Metal analysis reveals significant amounts of diverse heavy metal ions bound to the two types of melanosomes. The amount of Cu(II) and Zn(II) are similar but Fe(III) content is four times higher in the red-hair melanosomes. (13)C solid-state nuclear magnetic resonance spectra and infrared spectra are presented and are shown to be powerful techniques for discerning differences in the amino acid contents, the 5,6-dihydroxyindole-2-carboxylic acid:5,6-dihydroxyindole ratio, and the degree of cross-linking in the pigment. Excellent agreement is observed between these spectral results and the chemical degradation data.

Amphiphilic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymers, also known as poloxamers, have broad biomembrane activities. To illustrate the nature of these activities, (1)H Overhauser dynamic nuclear polarization NMR spectroscopy was employed to sensitively detect polymer-lipid membrane interactions through the modulation of local hydration dynamics in lipid membranes. Our study shows P188, the most hydrophilic poloxamer that is a known membrane sealant, weakly adsorbs on the membrane surface, yet effectively retards membrane hydration dynamics. Contrarily, P181, the most hydrophobic poloxamer that is a known membrane permeabilizer, initially embeds at lipid headgroups and enhances intrabilayer water diffusivity. Unprecedented resolution for differentiating weak surface adsorption versus translocation of polymers to membranes is obtained by probing local water diffusivity in lipid bilayer systems. Our results illustrate that the relative hydrophilic/hydrophobic ratio of the polymer dictates its functions. These findings gleaned from local hydration dynamics are well supported by a thermodynamics study presented in the accompanying paper (Wang, J.-Y.; Marks, J. M.; Lee, K. Y. C. Biomacromolecules, 2012, DOI: 10.1021/bm300847x).

Electrospray-assisted laser desorption/ionization (ELDI) combined with mass spectrometry allows chemical and biochemical compounds to be characterized directly from hydrophilic and hydrophobic organic solutions mixed with carbon powders under ambient conditions. Organic and inorganic compounds dissolved in polar or nonpolar solvent such as methanol, tetrahydrofuran, ethyl acetate, toluene, dichloromethane, or hexane can be detected using this ambient ionization technique without prior pretreatment. We have used this technique to monitor the progress in several ongoing reactions: the epoxidation of chalcone in ethanol, the chelation of ethylenediaminetetraacetic acid with copper and nickel ions in aqueous solution, the chelation of 1,10-phenanthroline with iron(II) in methanol, and the tryptic digestion of cytochrome c in aqueous solution. Liquid-ELDI analyses simply require irradiation of the surface of the sample solution with a pulsed ultraviolet laser; the laser energy is adsorbed by the carbon powder presuspended in the sample solution; the absorbed laser energy is then transferred to the surrounding solvent and to the analyte molecules in the solution, leading to their desorption; the desorbed gaseous analyte molecules are then postionized within an electrospray (ESI) plume to generate ESI-like analyte ions.

Melanosomes were isolated from the retinal pigment epithelium (RPE), iris and choroid of mature (age >2 years) and newborn (age <1 week) bovine eyes. Scanning electron microscopy was utilized to analyze the morphology of the melanosomes, which were found to vary among different tissues and different ages. While the total content of amino acids differs slightly (ranging from 9% to 15% by mass), the distributions of the amino acids are similar. The pheomelanin content is low in the choroid and the RPE (0.1-0.5%), and moderate in the iris (<2%); therefore, the major melanin component of bovine eye melanosomes is eumelanin, independent of the shape of the melanosomes. The yields of pyrrole-2,3,5-tricarboxylic acid from melanosomes decrease in the following order: choroid > iris > RPE, and exhibit decreasing yields with age. 13C solid-state nuclear magnetic resonance (NMR) spectroscopic analysis of iris and choroid melanosomes indicates the same trends. These observations suggest that the 5,6-dihydroxyindole-2-carboxylic acid contents decrease in the following order: choroid > iris > RPE, and decrease with age. Moreover, the 13C solid-state NMR spectra show (1) for the same age samples, the CH:Cq ratio for choroid is larger than that for iris melanosomes; and (2) an increase in the concentration of carbonyl groups with age within each type of melanosome.