2 research outputs found
Confocal Raman Microscopy of Protein Adsorbed in Chromatographic Particles
Confocal Raman microscopy is a nondestructive analytical
technique
that combines the chemical information from vibrational spectroscopy
with the spatial resolution of confocal microscopy. It was applied,
for the first time, to measure conformation and distribution of protein
adsorbed in wetted chromatographic particles. Monoclonal antibody
was loaded into the Fractogel EMD SO<sub>3</sub> (M) cation exchanger
at 2 mS/cm or 10 mS/cm. Amide I and III frequencies in the Raman spectrum
of the adsorbed protein suggest that there are no detectable changes
of the original β-sheet conformation in the chromatographic
particles. Protein depth profile measurements indicate that, when
the conductivity is increased from 2 mS/cm to 10 mS/cm, there is a
change in mass transport mechanism for protein adsorption, from the
shrinking-core model to the homogeneous-diffusion model. In this study,
the use of confocal Raman microscopy to measure protein distribution
in chromatographic particles fundamentally agrees with previous confocal
laser scanning microscopic investigations, but confocal Raman spectroscopy
enjoys additional advantages: use of unlabeled protein to eliminate
fluorescent labeling, ability for characterization of protein secondary
structure, and ability for spectral normalization to provide a nondestructive
experimental approach to correct light attenuation effects caused
by refractive index (RI) mismatching in semiopaque chromatographic
particles
Anhydrous Monoalkylguanidines in Aprotic and Nonpolar Solvents: Models for Deprotonated Arginine Side Chains in Membrane Environments
In
this study, the synthesis of crystalline dodecylguanidine free
base and its spectroscopic characterization in nonpolar environments
are described. IR as well as <sup>1</sup>H and <sup>15</sup>N NMR
spectra of the free base dissolved in aprotic solvents are substantially
different from the previously reported spectra of arginine, or other
monoalkylguanidinium compounds, at high hydroxide concentrations.
The current results provide improved modeling for the spectroscopic
signals that would be expected from a deprotonated arginine in a nonpolar
environment. On the basis of our spectra of the authentic dodecylguanidine
free base, addition of large amounts of aqueous hydroxide to arginine
or other monoalklyguanidinium salts does not deprotonate them. Instead,
hydroxide addition leads to the formation of a guanidinium hydroxide
complex, with a dissociation constant near ∼500 mM that accounts
for the established arginine p<i>K</i> value of ∼13.7.
We also report a method for synthesizing a compound containing both
phenol and free-base guanidine groups, linked by a dodecyl chain that
should be generalizable to other hydrocarbon linkers. Such alkyl-guanidine
and phenolyl-alkyl-guanidine compounds can serve as small-molecule
models for the conserved arginine–tyrosine groupings that have
been observed in crystallographic structures of both microbial rhodopsins
and G-protein-coupled receptors