Calcium carbonate precipitation by cyanobacterial polysaccharides - Tufas and Speleothems: Unravelling the Microbial and Physical Controls - page 55

Fig. 1. (a) Charge excess (mM g 21 of bacteria) measured by potentiometric titration for EPS from PCC 7942. Also
shown are results of linear programming as lines. (b)pK a spectra determined by linear programming analysis for each of
the titration curves shown in Figure 1a. The symbols of bars are correspondent to the titration curves in Figure 1a. The
position of the bar reflects the pK a value and the height of the bar reflects the concentration of a binding site.

highlighted the range at ,1000 cm 21 as fingerprint
zone of phosphate or sulphur functional groups
(Comte et al. 2006c, page 819, table 2).

Lijour et al. (1994) reveal sulphate content of
EPS via quantification of the FTIR spectra peaks
at 1260-1230 cm 21 . These peaks usually form a
slight doublet at 1250 cm 21 corresponding to the
OvSvO antisymmetric stretching vibrations. In
our study we observed peaks at 1250 cm 21 for
both cyanobacterial strains. Many studies have
related the structure of carrageenans to a set of infra-
red bands between 1000-800 cm 21 . Some rep-
resented pseudo-symmetric CZOZS stretching
vibrations and gave structural information on the
location of sulphate groups on the saccharide units.
Their intensities have been measured by Rochas
et al. (1986). The degree of sulphation of the poly-
mers was perfomed using the ratio of the absorbance
band at 1250-1050 cm 21 with a precision of 4%
(Lijour et al. 1994). Also Comte et al. 2006c

Analysis of the total buffering capacity

The total buffering capacity, or charge excess,
and pK a spectra for the EPS derived from PCC
7942, Syn. Red and Syn. Green, following the trans-
formation to the charge balance expression (3) of
replicate titrations, are shown in Figures 1-3.
Consistent trends are observed for the titration
curves in each set. It can be seen that the data is
distributed in approximately equal pH steps, as
required by the LPM, so that no sites are assigned
preferential weight in the fitting procedure

(Brassard et al. 1990).

Fig. 2. (a) Charge excess (mM g 21 of bacteria) measured by potentiometric titration for EPS from Syn. Red. Also
shown are results of linear programming as lines. (b)pK a spectra determined by linear programming analysis for each of
the titration curves shown in Figure 2a. The symbols of bars are correspondent to the titration curves in Figure 2a. The
position of the bar reflects the pK a value and the height of the bar reflects the concentration of a binding site.