240
C. De Stefano· C. Foti . A. Gianguzza . D. Piazzese . S. Sammartano
Fig. 9.9. Mogf3r values vs. SII2;
0.0 "------------------~
a for the first; b for the second
protonation step of glycine (0),
histidine (0 ~ and glutamic acid
(.1.). ~ogf3j = 10gf3r' (NaCl)10gf3j (SSWE)]
:r-CCl..
8' -0.4
-0.8
0.0 T I - - - - - - - - - - - - - - - - - ,
~-=9:=L
J:'<:0..
8' -0.6
-1.2 -+I-..,.-~-_._--_._--_,_--__.-~__r----j
2
3
4
5
6
7
5 112
Apparent protonation constants obtained in artificial sea water can be expressed
as a function of salinity by the equation:
logf3r = logT f3r + aS 1I2 + bS
(9.13)
The values of the empirical parameters of Eq. 9.13 were quite similar for the same
amino acid class and the same protonation step. In particular, parameter b can be considered a "common parameter" for glycine and alanine and for aspartic and glutamic
acids without any significant increment in the (j of fit. For parameters a and b it was
also possible to give general parameters for each amino acid group:
type 1
type 3
al = -O.098±O.015
a2 =-O.105±O.019
al = -O.186±O.030
a2 = -O.292±O.027
a3 = -O·316±o.023
bI = O.009±O.003
b2 = O.009±O.003
bI = o.olO±O.oo5
b2 = O.019±O.005
b3 = O.022±O.oo4