Rosemary, whose major caffeoyl-derived and diterpenoid ingredients are rosmarinic acid, carnosol, and carnosic acid, is an important source of natural antioxidants and is being recognized increasingly as a useful preservative, protectant, and even as a potential medicinal agent. Understanding the stability of these components and their mode of interaction in mixtures is important if they are to be utilized to greatest effect. A study of the degradation of rosmarinic acid, carnosol, carnosic acid, and a mixture of the three was conducted in ethanolic solutions at different temperatures and light exposure. As expected, degradation increased with temperature. Some unique degradation products were formed with exposure to light. Several degradation products were reported for the first time. The degradation products were identified by HPLC/MS/MS, UV, and NMR. The degradation of rosemary extract in fish oil also was investigated, and much slower rates of degradation were observed for carnosic acid. In the mixture of the three antioxidants, carnosic acid serves to maintain levels of carnosol, though it does so at least in part at the cost of its own degradation.
The absorption maximum of blue proteorhodopsin (BPR) is the most blue-shifted of all retinal proteins found in archaea or bacteria, with the exception of sensory rhodopsin II (SRII). The absorption spectrum also exhibits a pH dependence larger than any other retinal protein. We examine the structural origins of these two properties of BPR by using optical spectroscopy, homology modeling, and molecular orbital theory. Bacteriorhodopsin (BR) and SRII are used as homology parents for comparative purposes. We find that the tertiary structure of BPR based on SRII is more realistic with respect to free energy, dynamic stability, and spectroscopic properties. Molecular orbital calculations including full single- and double-configuration interaction within the chromophore pi-electron system provide perspectives on the wavelength regulation in this protein and indicate that Arg-95, Gln-106, Glu-143, and Asp-229 play important, and in some cases pH-dependent roles. A possible model for the 0.22 eV red shift of BPR at low pH is examined, in which Glu-143 becomes protonated and releases Arg-95 to rotate up into the binding site, altering the electrostatic environment of the chromophore. At high pH, BPR has spectroscopic properties similar to SRII, but at low pH, BPR has spectroscopic properties more similar to BR. Nevertheless, SRII is a significantly better homology model for BPR and opens up the question of whether this protein serves as a proton pump, as commonly believed, or is a light sensor with structure-function properties more comparable to those of SRII. The function of BPR in the native organism is discussed with reference to the results of the homology model.
The absorption spectrum of green proteorhodopsin (GPR) is pH-dependent, exhibiting either red-shifted (low pH) or blue-shifted (high pH) absorption maxima. We examine the molecular basis of the pH-dependent spectral properties of green proteorhodopsin by using homology modeling and molecular orbital theory. Bacteriorhodopsin (BR) and sensory rhodopsin II (SRII) are compared as homology templates. The model of GPR generated by using BR as the homology parent is better than that generated by using SRII on the basis of the potential energy, relative stability to dynamics, and ability to rationalize pH effects. MNDO-PSDCI (molecular neglect of differential overlap with partial single- and double-configuration interaction) calculations provide insight into the spectroscopic properties of GPR and help rule out the viability of the SRII-based model. The proximity of His 75 to the quadrupole residues (LYR, D97, D227, and R94) in the BR-based model provides a good model for both the low- and high-pH spectral states of GPR. The observation that BR is a better structural model for GPR than SRII is in contrast to our previous study of BPR, which observed that SRII was the better homology parent [Hillebrecht, J. R. (2006) Biochemistry 45, 1579-1590]. The implications of this observation are discussed.
Purpose: Hydroxypropyl guar (HPG) and hyaluronic acid (HA) have been individually shown to improve dry eye symptoms. The purpose of this in vitro study was to assess the potential benefits of a new lubricant eye drop formulation containing the demulcents propylene glycol and polyethylene glycol and an HA/HPG dual polymer in models of the human corneal epithelium.Methods: Cultured human corneal epithelial or corneal-limbal epithelial cells were treated with the HA/HPG dual-polymer formulation or single-polymer formulations containing either HPG or HA. Desiccation protection by cell hydration and surface retention was assessed using cell viability assays. Sodium fluorescein permeability, transepithelial resistance, and cell viability assays were conducted using pretreated cells exposed to a surfactant/detergent insult to evaluate cell and cell barrier protection. Surface lubricity was assessed in tribological experiments of pericardium–pericardium friction.Results: Hydration protection against desiccation and protection by surface retention were significantly greater with the HA/HPG formulation versus HPG or HA (P<0.001) alone and with HPG versus HA (P≤0.016). Fluorescein permeability and transepithelial resistance assays demonstrated significantly better cell and barrier protection from surfactant insult with HA/HPG versus the single-polymer formulations (P≤0.01). After insult, there were markedly more viable cells evident with HA/HPG compared with HPG or HA alone. HA/HPG and HPG reduced surface friction to a greater extent than HA (P≤0.02) and maintained lubricity after the formulations were rinsed away.Conclusions: HA/HPG provided effective hydration and lubrication and demonstrated prolonged retention of effect. HA/HPG may potentially promote desiccation protection and retention on the ocular surface.
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