Dextran surface grafting density was systematically varied via a two-step process involving SiO(2) amination by aminopropyltriethoxy silane (APTES) followed by oxidized dextran (M(w) = 110 kDa) chemisorption. Dextran oxidation kinetics with sodium metaperiodate (NaIO(4)) were quantified by (1)H NMR and pH measurements. Aldehyde group formation increased with increasing oxidation time. For 0.5 h oxidation time, dried film ellipsometric thickness was constant for solution concentrations ranging from 1 to 4 mg/mL. Dextran layers with the lowest grafting density wetted fastest and displayed the lowest contact angle (theta(APTES) > theta(1 h) > theta(2,4 h) > theta(0.5 h)). Under aqueous conditions, AFM force versus displacement measurements on 0.5 and 4.0 h surfaces exhibited a single displacement jump upon retraction. The 1.0 and 2.0 h surfaces showed two jumps consistent with two populations of chains, namely, loosely and strongly bound dextran. Overall, film morphology and wetting behavior were relatively invariant with grafting density, confirming the method's robustness for preparing biomimetic coatings with consistent properties.
The rate constants and Arrhenius parameters for the reaction of CO in H 2 O were determined at 230-270 °C and 27.4 MPa by the use of a titanium flow reactor with real-time detection by infrared spectroscopy through sapphire windows. These rate measurements appear to be the first below the critical temperature of water. The zeroth-order kinetics model produced an Arrhenius activation energy of 32 ( 3 kcal/mol, which is in the range of previously reported values at higher temperatures, but the preexponential factor [ln(A, mol kg -1 s -1 )] of 20.5 is much larger. The higher overall reaction rate is consistent with heterogeneous catalysis by the reactor surfaces considering (1) the zeroth-order kinetics, (2) the high A factor, (3) the activation energy in the range for the water-catalyzed reactions, and (4) the previously determined dependence of the decomposition rate of the putative formic acid intermediate on the metal used to construct the cell. Extremely toxic Ni(CO) 4 was observed to form as a result of extraction of Ni from slightly corroded 316 stainless steel tubes that connected the cell/reactor to the flow control system. Ni(CO) 4 formed under somewhat limited conditions, but its occurrence forewarns of the potential hazard of hydrothermal processing when a high CO concentration might be present in a nickelcontaining reaction vessel.
Background and Objective: Recent advances in lowlevel light devices have opened new treatment options for mild to moderate acne patients. Light therapies have been used to treat a variety of skin conditions over the years but were typically only available as treatments provided by professional clinicians. Clinical application of blue light has proven to be effective for a broader spectral range and at lower fluences than previously utilized. Herein, we tested the hypothesis that submilliwatt/cm 2 levels of long-wave blue light (449 nm) effectively kills Propionibacterium acnes, a causative agent of acne vulgaris, in vitro. Materials and Methods: Two types of LED light boards were designed to facilitate in vitro blue light irradiation to either six-well plates containing fluid culture or a petri plate containing solid medium. P. acnes. Survival was determined by counting colony forming units (CFU) following irradiation. P. acnes was exposed in the presence and absence of oxygen. Coproporphyrin III (CPIII) photoexcitation was spectrophotometrically evaluated at 415 and 440 nm to compare the relative photochemical activities of these wavelengths. Results: 422 and 449 nm blue light killed P. acnes in planktonic culture. Irradiation with 449 nm light also effectively killed P. acnes on a solid agar surface. Variation of time or intensity of light exposure resulted in a fluence-dependent improvement of antimicrobial activity. The presence of oxygen was necessary for killing of P. acnes with 449 nm light. CPIII displayed clear photoexcitation at both 415 and 440 nm, indicating that both wavelengths are capable of initiating CPIII photoexcitation at low incident light intensities (50 uW/cm 2 ). Conclusion: Herein we demonstrate that sub-milliwatt/ cm 2 levels of long-wave blue light (449 nm) effectively kill P. acnes. The methods and results presented allow for deeper exploration and design of light therapy treatments. Results from these studies are expanding our understanding of the mode of action and functionality of blue light, allowing for improved options for acne patients. Lasers Surg. Med.
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