### Abstract

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(CH
_{2}CH
_{2}SCH
_{3})COOH; H
_{2}B
^{+}). The values of stoichiometric dissociation constants, pK
_{i}*, for protonated methionine species (H
_{2}B
^{+}⇔H
^{+}+HB, K
_{1}; HB⇔H
^{+}+B
^{-}, K
_{2}) were determined from potentiometric measurements in NaCl solutions as a function of ionic strength, 0.25-6.0 mol (kg H
_{2}O)
^{-1} and temperature (5-45 °C). The results were extrapolated to pure water using the Pitzer equations to estimate the activity of H
^{+}, H
_{2}B
^{+}, HB and B
^{-} as a function of ionic strength and temperature. The resulting thermodynamic values of K
_{1} and K
_{2} were fit to the equations (T/K): ln K
_{1}=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 K
_{1}* and ln K
_{2}*. Pitzer interaction parameters (λ
_{HB-Na} and ζ
_{HB-Na-Cl}) for the neutral HB were determined from literature data. The Pitzer parameters (β
_{H2BCl}
^{0}, β
_{H2BCl}
^{1} and C
_{H2BCl}
^{φ}) for the interactions of H
_{2}B
^{+} with Cl
^{-} and Na
^{+} with and B
^{2-} (β
_{NaB}
^{0}, β
_{NaB}
^{1} and C
_{NaB}
^{φ}) were also determined. These coefficients can be used to make reasonable estimates of the activity coefficients of methionine species and the pK
_{i}* for the dissociation of methionine in physiological solutions, composed mostly of NaCl over a wide range of temperature and ionic strength.

Original language | English (US) |
---|---|

Pages (from-to) | 79-87 |

Number of pages | 9 |

Journal | Biophysical Chemistry |

Volume | 105 |

Issue number | 1 |

DOIs | |

State | Published - Aug 1 2003 |

### Fingerprint

### Keywords

- Dissociation constants
- Methionine species
- NaCl
- Protonated

### ASJC Scopus subject areas

- Biochemistry
- Physical and Theoretical Chemistry
- Biophysics

### Cite this

*Biophysical Chemistry*,

*105*(1), 79-87. https://doi.org/10.1016/S0301-4622(03)00137-6

**Dissociation constants of protonated methionine species in NaCl media.** / Sharma, Virender K.; Zinger, Anthony; Millero, Frank J; De Stefano, Concetta.

Research output: Contribution to journal › Article

*Biophysical Chemistry*, vol. 105, no. 1, pp. 79-87. https://doi.org/10.1016/S0301-4622(03)00137-6

}

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

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(CH 2CH 2SCH 3)COOH; H 2B +). The values of stoichiometric dissociation constants, pK i*, for protonated methionine species (H 2B +⇔H ++HB, K 1; HB⇔H ++B -, K 2) were determined from potentiometric measurements in NaCl solutions as a function of ionic strength, 0.25-6.0 mol (kg H 2O) -1 and temperature (5-45 °C). The results were extrapolated to pure water using the Pitzer equations to estimate the activity of H +, H 2B +, HB and B - as a function of ionic strength and temperature. The resulting thermodynamic values of K 1 and K 2 were fit to the equations (T/K): ln K 1=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 K 1* and ln K 2*. Pitzer interaction parameters (λ HB-Na and ζ HB-Na-Cl) for the neutral HB were determined from literature data. The Pitzer parameters (β H2BCl 0, β H2BCl 1 and C H2BCl φ) for the interactions of H 2B + with Cl - and Na + with and B 2- (β NaB 0, β NaB 1 and C NaB φ) were also determined. These coefficients can be used to make reasonable estimates of the activity coefficients of methionine species and the pK i* 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(CH 2CH 2SCH 3)COOH; H 2B +). The values of stoichiometric dissociation constants, pK i*, for protonated methionine species (H 2B +⇔H ++HB, K 1; HB⇔H ++B -, K 2) were determined from potentiometric measurements in NaCl solutions as a function of ionic strength, 0.25-6.0 mol (kg H 2O) -1 and temperature (5-45 °C). The results were extrapolated to pure water using the Pitzer equations to estimate the activity of H +, H 2B +, HB and B - as a function of ionic strength and temperature. The resulting thermodynamic values of K 1 and K 2 were fit to the equations (T/K): ln K 1=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 K 1* and ln K 2*. Pitzer interaction parameters (λ HB-Na and ζ HB-Na-Cl) for the neutral HB were determined from literature data. The Pitzer parameters (β H2BCl 0, β H2BCl 1 and C H2BCl φ) for the interactions of H 2B + with Cl - and Na + with and B 2- (β NaB 0, β NaB 1 and C NaB φ) were also determined. These coefficients can be used to make reasonable estimates of the activity coefficients of methionine species and the pK i* 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

UR - http://www.scopus.com/inward/record.url?scp=0043161971&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0043161971&partnerID=8YFLogxK

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 -