Dissociation constants of protonated cysteine species in NaCl media

Virender K. Sharma, Fabien Casteran, Frank J. Millero, Concetta De Stefano

Research output: Contribution to journalArticlepeer-review

19 Scopus citations


The sulfur-containing biomolecule, cysteine has a role in physiological and natural environment because of its strong interactions with metals. To understand these interactions of metals with cysteine, one needs reliable dissociation constants for the protonated cysteine species [NH3 +CH(CH2SH)COOH; H3B+]. The values of dissociated constants, pK1*, for protonated cysteine species (H3B+ ⇌ H+ + H2B, K1; H2B H+ + HB-, K 2;HB- ⇌ H+ + B2-, K 3) were determined from potentiometric measurements in NaCl solutions as a function of ionic strength, 0.5-6.0 mol-(kgH2O) -1 and between 5, and 45°C. The equations pK1* = 1.378 + 228.4/T - 0.4044I0.5 + 0.2472I pK2* = 2. 031 + 1833.4/T - 0.1847I0.5 + 0.2190I pK3* = 2.861 + 2191.3/T - 0.2170I0.5 + 0.2217I were fitted to the results with a standard errors of the fits of 0.116, 0.057, and 0.093 for pK 1*, pK2*, and pK3*, respectively. The pKi*, results were used to determine new Pitzer parameters (β0, β1, and C) for the interactions of Na+ and Cl- with cysteine species. These coefficients can be used to make reasonable estimates of the activity coefficients of the cysteine species and pKi* for the dissociation of cysteine in physiological and natural waters containing mostly NaCl.

Original languageEnglish (US)
Pages (from-to)783-792
Number of pages10
JournalJournal of Solution Chemistry
Issue number10
StatePublished - 2002


  • Cysteine
  • Dissociation constants
  • Ionic strength
  • Pitzer Coefficients
  • Sodium chloride

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Physical and Theoretical Chemistry


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