Observing Hoffmeister Effects Through Floating Monolayer Isotherms
Session Number
Project ID: PHYS 22
Advisor(s)
Dr. Pulak Dutta; Northwestern University
Yanlin Li; Northwestern University
Discipline
Physical Science
Start Date
19-4-2023 9:20 AM
End Date
19-4-2023 9:35 AM
Abstract
The Hoffmeister Series ranks ions found in salts based on their effects on protein solubility. The series ranks them from “salting in” to “salting out”, i.e. how strongly the ions cause proteins to either dissolve or precipitate. It has been believed previously that ions of the same valence will cause a similar effect, however, in fact each ion has a different effect on the solubility of different protein functional groups, even when they have the same charge. In this project, monovalent ions were studied through floating monolayer isotherms. By varying the pH, we could test the effect of both cations and anions on positively charged octadecylamine (‘ODA’), negatively charged heneicosanoic acid (‘C21 acid’) and octadecanamide (‘C18 amide’) with neutral headgroups. Testing ODA at high, low, and neutral pH with potassium salts allowed the observation of anion effects on protonated and deprotonated ODA. For C21 acid, high, low, and neutral pH with chlorine salts allowed the observation of cation effects on protonated and deprotonated C21 acid. C18 amide was tested with both types of salts to observe both cation and anion effects because C18 amide is neutral at all pH. The monolayer pressure-area isotherms confirmed specific ion effect. Each of the salts stabilized or destabilized the molecules differently, despite having the same charge. The degree to which the ions stabilized or did not stabilize the protein head groups followed the predictions of the Hoffmeister series.
Observing Hoffmeister Effects Through Floating Monolayer Isotherms
The Hoffmeister Series ranks ions found in salts based on their effects on protein solubility. The series ranks them from “salting in” to “salting out”, i.e. how strongly the ions cause proteins to either dissolve or precipitate. It has been believed previously that ions of the same valence will cause a similar effect, however, in fact each ion has a different effect on the solubility of different protein functional groups, even when they have the same charge. In this project, monovalent ions were studied through floating monolayer isotherms. By varying the pH, we could test the effect of both cations and anions on positively charged octadecylamine (‘ODA’), negatively charged heneicosanoic acid (‘C21 acid’) and octadecanamide (‘C18 amide’) with neutral headgroups. Testing ODA at high, low, and neutral pH with potassium salts allowed the observation of anion effects on protonated and deprotonated ODA. For C21 acid, high, low, and neutral pH with chlorine salts allowed the observation of cation effects on protonated and deprotonated C21 acid. C18 amide was tested with both types of salts to observe both cation and anion effects because C18 amide is neutral at all pH. The monolayer pressure-area isotherms confirmed specific ion effect. Each of the salts stabilized or destabilized the molecules differently, despite having the same charge. The degree to which the ions stabilized or did not stabilize the protein head groups followed the predictions of the Hoffmeister series.