TY - JOUR
T1 - Dissociation constants of protonated methionine species in NaCl media
AU - Sharma, Virender K.
AU - Zinger, Anthony
AU - Millero, Frank J.
AU - De Stefano, Concetta
N1 - Funding Information:
The authors wish to acknowledge the support of the Oceanography Section of the National Science Foundation.
Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.
PY - 2003/8/1
Y1 - 2003/8/1
N2 - The sulfur-containing amino acid, methionine, has a role in the physiological environment because of its strong interactions with metals. To understand these interactions of metals with methionine, one needs reliable dissociation constants for the protonated methionine species (NH 3+CH(CH2CH2SCH3)COOH; H2B+). The values of stoichiometric dissociation constants, pKi*, for protonated methionine species (H 2B+⇔H++HB, K1; HB⇔H ++B-, K2) were determined from potentiometric measurements in NaCl solutions as a function of ionic strength, 0.25-6.0 mol (kg H2O)-1 and temperature (5-45 °C). The results were extrapolated to pure water using the Pitzer equations to estimate the activity of H+, H2B+, HB and B- as a function of ionic strength and temperature. The resulting thermodynamic values of K1 and K2 were fit to the equations (T/K): ln K1=69.0013-3496.58/(T/K)-10.9153 ln (T/K); ln K 2=116.4162-10638.02/(T/K)-18.0553 ln (T/K) with standard errors of 0.003 and 0.033, respectively, for ln K1* and ln K 2*. Pitzer interaction parameters (λHB-Na and ζHB-Na-Cl) for the neutral HB were determined from literature data. The Pitzer parameters (βH2BCl0, βH2BCl1 and CH2BClφ) for the interactions of H2B+ with Cl- and Na + with and B2- (βNaB0, βNaB1 and CNaBφ) were also determined. These coefficients can be used to make reasonable estimates of the activity coefficients of methionine species and the pKi* for the dissociation of methionine in physiological solutions, composed mostly of NaCl over a wide range of temperature and ionic strength.
AB - The sulfur-containing amino acid, methionine, has a role in the physiological environment because of its strong interactions with metals. To understand these interactions of metals with methionine, one needs reliable dissociation constants for the protonated methionine species (NH 3+CH(CH2CH2SCH3)COOH; H2B+). The values of stoichiometric dissociation constants, pKi*, for protonated methionine species (H 2B+⇔H++HB, K1; HB⇔H ++B-, K2) were determined from potentiometric measurements in NaCl solutions as a function of ionic strength, 0.25-6.0 mol (kg H2O)-1 and temperature (5-45 °C). The results were extrapolated to pure water using the Pitzer equations to estimate the activity of H+, H2B+, HB and B- as a function of ionic strength and temperature. The resulting thermodynamic values of K1 and K2 were fit to the equations (T/K): ln K1=69.0013-3496.58/(T/K)-10.9153 ln (T/K); ln K 2=116.4162-10638.02/(T/K)-18.0553 ln (T/K) with standard errors of 0.003 and 0.033, respectively, for ln K1* and ln K 2*. Pitzer interaction parameters (λHB-Na and ζHB-Na-Cl) for the neutral HB were determined from literature data. The Pitzer parameters (βH2BCl0, βH2BCl1 and CH2BClφ) for the interactions of H2B+ with Cl- and Na + with and B2- (βNaB0, βNaB1 and CNaBφ) were also determined. These coefficients can be used to make reasonable estimates of the activity coefficients of methionine species and the pKi* for the dissociation of methionine in physiological solutions, composed mostly of NaCl over a wide range of temperature and ionic strength.
KW - Dissociation constants
KW - Methionine species
KW - NaCl
KW - Protonated
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U2 - 10.1016/S0301-4622(03)00137-6
DO - 10.1016/S0301-4622(03)00137-6
M3 - Article
C2 - 12932581
AN - SCOPUS:0043161971
VL - 105
SP - 79
EP - 87
JO - Biophysical Chemistry
JF - Biophysical Chemistry
SN - 0301-4622
IS - 1
ER -