salt/main.tex: Cite hofmeister88 and smith13

Additional background and CaCl2 motivation respectively.

diff --git a/src/salt/main.tex b/src/salt/main.tex
index 3befaec6db133ac5ba670c856be8c2830c3649aa..512aa4477a9cb39138b0067b8239778e4cd0dd6c 100644 (file)
--- a/src/salt/main.tex
+++ b/src/salt/main.tex
@@ -9,9 +9,11 @@ standard buffer, a buffer with additional calcium (from
 \CaCl\citep{fisher-CaCl}) was flushed into the fluid cell.  After the
 new buffer equilibrated, unfolding experiments were continued.
 
-Previous research on the effect of ions on unfolding forces is small,
-although earlier experimental work on amyloid $\beta$ shows decreased
-fibrillation with even small
+Since \citet{hofmeister88}, there has been a lot of research on the
+effect of ions on protein solubility.  However, previous research on
+the effect of ions on unfolding forces is small, but we do have some
+material to work with.  Earlier experimental work on amyloid $\beta$
+shows decreased fibrillation with even small
 \Ca\ concentrations\citep{chauhan97,itkin11}.  The mechanism behind
 this weaker bonding is unclear\citep{chauhan97,zhang06}, although
 aspartic and glutamic acid groups tend to have a strong affinity for
@@ -19,7 +21,11 @@ cations while arginine has a strong affinity for the
 \Cl\ anion\citep{friedman11}.  Of these amino acids, only glutamic
 acid occurs in the key hydrogen bond regions responsible for I27
 unfolding\citep{lu00b} (\cref{fig:I27:H-bonds}).  \NaCl\ has also been
-shown to decrease hydrogen bonding\citep{zidar11}.
+shown to decrease internal hydrogen bonding in the
+protein\citep{zidar11}.  In molecular dynamics studies of amalyoid
+$\beta$ fragments, the destabilizing effect of \CaCl\ is much greater
+than the destabilizing effects of \MgCl, \NaCl, and
+\KCl\citep{smith13}.
 
 \begin{figure}
   \begin{center}