Nitric oxide diffusion coefficients in solutions, proteins and membranes determined by phosphorescence

Area of Science:

• Biophysical chemistry
• Chemical kinetics
• Physiological chemistry

Background:

• Nitric oxide (NO) plays crucial roles in biological systems.
• Understanding NO's diffusion is vital for its physiological function.
• Quantifying NO concentration and diffusion dynamics remains challenging.

Purpose of the Study:

• To develop and validate a method for measuring nitric oxide (NO) concentration and diffusion coefficients.
• To characterize the diffusion properties of NO in various media, including aqueous solutions, proteins, and membranes.
• To compare the diffusivity of NO with that of oxygen (O2).

Main Methods:

• Utilized the luminescence quenching of Ru and Pd chelates of mesoporphyrin IX by NO.
• Employed Stern-Volmer plots to determine pseudo-second order quenching constants.
• Calculated diffusion coefficients for NO in different environments at varying temperatures.

Main Results:

• Successfully quantified NO produced from nitrosocysteine decomposition.
• Determined diffusion coefficients for NO in water, proteins, and membranes.
• Found that NO diffusion coefficients increase with temperature (37°C > 25°C).
• Observed lower NO diffusion coefficients in proteins and membranes compared to water.
• NO diffusivity closely mirrors O2, with slight differences attributed to lipophilicity.

Conclusions:

• The Ru-mesoporphyrin IX system provides a reliable method for NO quantification and diffusion analysis.
• NO diffusion is temperature-dependent and medium-specific.
• NO's diffusion characteristics are similar to O2, with subtle variations impacting its transport in biological tissues.
• Under specific conditions, NO can diffuse over distances larger than a single cell diameter.