Marques BS, Nucci NV, Dodevski I, Wang KWC, Athanasoula EA, Jorge C, Wand AJ. Measurement and control of pH in the aqueous interior of reverse micelles.
J Phys Chem B 2014;
118:2020-31. [PMID:
24506449 PMCID:
PMC3983379 DOI:
10.1021/jp4103349]
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Abstract
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The
encapsulation of proteins and nucleic acids within the nanoscale
water core of reverse micelles has been used for over 3 decades as
a vehicle for a wide range of investigations including enzymology,
the physical chemistry of confined spaces, protein and nucleic acid
structural biology, and drug development and delivery. Unfortunately,
the static and dynamical aspects of the distribution of water in solutions
of reverse micelles complicate the measurement and interpretation
of fundamental parameters such as pH. This is a severe disadvantage
in the context of (bio)chemical reactions and protein structure and
function, which are generally highly sensitive to pH. There is a need
to more fully characterize and control the effective pH of the reverse
micelle water core. The buffering effect of titratable head groups
of the reverse micelle surfactants is found to often be the dominant
variable defining the pH of the water core. Methods for measuring
the pH of the reverse micelle aqueous interior using one-dimensional 1H and two-dimensional heteronuclear NMR spectroscopy are described.
Strategies for setting the effective pH of the reverse micelle water
core are demonstrated. The exquisite sensitivity of encapsulated proteins
to the surfactant, water content, and pH of the reverse micelle is
also addressed. These results highlight the importance of assessing
the structural fidelity of the encapsulated protein using multidimensional
NMR before embarking upon a detailed structural and biophysical characterization.
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