Photodissociation of Nitric Oxide from Nitrosyl Metalloporphyrins in Micellar Solutions

Design Considerations for Silica-Particle-Doped Nitric-Oxide-Releasing Polyurethane Glucose Biosensor Membranes

Nitric oxide (NO)-releasing polymers have proven useful for improving the biocompatibility of in vivo glucose biosensors. Unfortunately, leaching of the NO donor from the polymer matrix remains a critical design flaw of NO-releasing membranes. Herein, a toolbox of NO-releasing silica nanoparticles (SNPs) was utilized to systematically evaluate SNP leaching from a diverse selection of biomedical-grade polyurethane sensor membranes. Glucose sensor analytical performance and NO-release kinetics from the sensor membranes were also evaluated as a function of particle and polyurethane (PU) chemistries. Particles modified with N-diazeniumdiolate NO donors were prone to leaching from PU membranes due to the zwitterionic nature of the NO donor modification. Leaching was minimized (<5% of the entrapped silica over 1 month) in low water uptake PUs. However, SNP modification with neutral S-nitrosothiol (RSNO) NO donors lead to biphasic leaching behavior. Particles with low alkanethiol content (<3.0 wt % sulfur) leached excessively from a hydrogel PU formulation (HP-93A-100 PU), while particles with greater degrees of thiol modification did not leach from any of the PUs tested. A functional glucose sensor was developed using an optimized HP-93A-100 PU membrane doped with RSNO-modified SNPs as the outer, glucose diffusion-limiting layer. The realized sensor design responded linearly to physiological concentrations of glucose (minimum 1-21 mM) over 2 weeks incubation in PBS and released NO at >0.8 pmol cm-2 s-1 for up to 6 days with no detectable (<0.6%) particle leaching.

Widely differing photochemical behavior in related octahedral {Ru-NO}6 compounds: intramolecular redox isomerism of the excited state controlling the photodelivery of NO

trans-[(NC)Ru(py)(4)(mu-CN)Ru(py)(4)(NO)](3+) (py = pyridine) is a stable species in aqueous solution. It displays an intense absorption in the visible region of the spectrum (lambda(max) = 518 nm; epsilon(max) = 6100 M(-1) cm(-1)), which turns this compound into a promising agent for the photodelivery of NO. The quantum yield for the photodelivery process resulting from irradiation with 455 nm visible light was found experimentally to be (0.06 +/- 0.01) x 10(-3) mol einstein(-1), almost 3 orders of magnitude smaller than that in the closely related cis-[RuL(NH(3))(4)(mu-pz)Ru(bpy)(2)(NO)](5+) species (L = NH(3) or pyridine, pz = pyrazine, bpy = 2,2'-bipyridine; phi(NO) = 0.02-0.04 mol einstein(-1) depending on L) and also much smaller than the one in the mononuclear compound trans-[ClRu(py)(4)(NO)](2+) (phi(NO) = (1.63 +/- 0.04) x 10(-3) mol einstein(-1)). DFT computations provide an electronic structure picture of the photoactive excited states that helps to understand this apparently abnormal behavior.

Thermal and photochemical nitric oxide release from S-nitrosothiols incorporated in Pluronic F127 gel: potential uses for local and controlled nitric oxide release

The local delivery of nitric oxide (nitrogen monoxide, NO) by thermal or photochemical means to target cells or organs has a great potential in several biomedical applications, especially if the NO donors are incorporated into non-toxic viscous matrices. In this work, we have shown that the NO donors S-nitrosoglutathione (GSNO) and S-nitroso-N-acetylcysteine (SNAC) can be incorporated into F127 hydrogels, from where NO can be released thermally or photochemically (with lambda(irr)>480nm). High sensitivity differential scanning calorimetry (HSDSC) and a new spectrophotometric method, were used to characterize the micellization and the reversal thermal gelation processes of the F127 hydrogels containing NO donors, and to modulate the gelation temperatures to the range 29-32 degrees C. Spectral monitoring of the S-NO bond cleavage showed that the initial rates of thermal and photochemical NO release (ranging from 2 to 45 micromoll(-1)min(-1)) are decreased in the hydrogel matrices, relative to those obtained in aqueous solutions. This stabilization effect was assigned to a cage recombination mechanism and offers an additional advantage for the storage and handling of S-nitrosothiols. These results indicate that F127 hydrogels might be used for the thermal and photochemical delivery of NO from S-nitrosothiols to target areas in biomedical applications.