Ultrasonic studies on molecular interaction of -amino acids in aqueous solutions at different pH

A novel method involving ultrasonic velocity measurement has been adopted for the accurate determination of iso-electric point (pI) of eleven a-amino acids at 303 K. The a-amino acids used are aspartic acid (Asp), glutamic acid (Glu), asparagine (Asn), phenylalanine (Phe), threonine (Thr), glycine (Gly), alanine (Ala), valine (Val), isoleucine (Ile), proline (Pro) and histidine (His). Allied acoustical properties like adiabatic compressibility (), acoustical impedance (z), free length (Lf), relative adiabatic compressibility (/0) apparent molal compressibility () available volume (Va) are computed for aqueous solutions of these amino acids at different pH values. Conductance has been measured for aqueous solutions of these amino acids at 303 K at different pH values and pI values are evaluated from the pH value at which minimum conductance was observed. The pI values determined by ultrasonic and conductivity methods are compared with those obtained by electrometric method. There is found to be good agreement between the values obtained by different methods