Lecture X Polysaccharides II Properties of Macromolecules Lecture #10 - Polysaccharides II - Properties of Macromolecules Will cover general info re HCs, especially info about colloids and the colloidal state, especially their electrical properties. Also isolation and purification of HCs, and some on how to determine MWs

CHO Classification I Monosaccharides Oligosaccharides Polysaccharides Comparison to Simple Sugars Same Rxs Effect of structural change

PS Properties (general) Polysaccharides Comparison to Simple Sugars Same Rxs Effect of structural change More difficult to quantify

PS Properties (general) Polysaccharides Definitions Hydrocolloids Solution(s) - “A chemically and physically homogenous mixture of two or more substances.” (i.e., solvent & solute)

Classification of Dispersions True solutions Suspension Colloidal solutions

Example of true solution Table Salt Dissolving in Water Dissolving Ionic compounds Table Salt Dissolving in Water

Colloids/Colloidal State Background (history) Crystalloids vs Colloids Colloidal State - A fine dispersion of one substance in another so the dispersed phase possesses different properties than before it was dispersed

Colloids/Colloidal State UNITS 1 Å = 10-10 meters (m) = 10-8 cm 10 Å = 1 nm = 10-9 m 1 mm = 1 m = 10-6 m = 104 Å

Colloids/Colloidal State Colloidal Properties Shown by Gum Solutions I Particle size of dispersed phase = 10 Å ‑ 1000 Å Lack of visibility under light microscope Ability to remain suspended

Colloidal Dispersions – Polymer Hydration Hydration of polymers (“dissolves”) H-bonding w/ -OH grps in CHOs A solvation layer reduces strength of ionic bonds by an order of magnitude

Colloids/Colloidal State Effect of Comminution on Specific Surface Area of a Volume of 4p/3 cm3, Divided into Uniform Spheres of Radius R Number of spheres R Asp cm2/cm3 Shaded region corresponds to colloidal particle-size range

Colloids/Colloidal State Colloidal Properties Shown by Gum Solutions II Particle size of dispersed phase ‑ 10 Å ‑ 1000 Å Lack of visibility under light microscope Ability to remain suspended

Colloids/Colloidal State Colloidal Properties Shown by Gum Solutions III Dispersed phase ‑ 10 Å ‑ 1000 Å Lack of visibility under microscope Ability to remain suspended Other important properties Slow diffusion of dispersed phase Ability to scatter light (Tyndall effect) High interfacial energy High adsorptive capacity

Colloids/Colloidal State

Colloids/Colloidal State Classification - Definitions Sol = colloidal dispersion of a solid in a liquid or gaseous medium SUMMARY: Term "colloidal" designates a state of matter, characterized by sub‑microscopic dimensions rather than chemical composition. Any dispersed substance with the proper dimensions is in the colloidal state!

Colloids/Colloidal State Colloid Properties (Electrical) Origin of electrical charges Ionization Counterions Electric double layers Stabilization by electrostatic repulsion Intermolecular forces Salting out/in

B: Plane of shear C: Double layer sphere of influence A: Stern Layer Colloidal Particle B: Plane of shear C: Double layer sphere of influence A: Stern Layer

Electrical double layer Schematic of double layer in a liquid at contact with a negatively-charged solid. Depending on the nature of the solid, there may be another double layer (unmarked on the drawing) inside the solid.

Colloidal Particle

Colloids/Colloidal State Colloid Properties (Electrical) Origin of electrical charges Ionization Counterions Electric double layers Stabilization by electrostatic repulsion Intermolecular forces Salting out/in

d+ Dipole-dipole (H‑bonding) d- Types of bonding in gelatin gels Ion - Ion d+ Dipole-dipole d- d- Dipole-dipole d+ Covalent (nonionic) Types of bonding in gelatin gels O H d+ d- -NH3+ Ion - Dipole O H d+ d- -COO- H

Colloids/Colloidal State Colloid Properties (Electrical) Origin of electrical charges Ionization Counterions Electric double layers Stabilization by electrostatic repulsion Intermolecular forces Salting out/in

Equals a methyl ether group Layer of water of hydration surrounds MC molecule And prevents hydrophobic methyl groups from approaching each other.

Colloids/Colloidal State Colloid Properties (Electrical) Salting out/in Hofmeister or lyotropic series (in order of increasing hydration and effectiveness in salting out HC’s.) Monovalent cations: Cs < Rb < NH4+ < K < Na < Li Divalent: Ba < Sr < Ca < Mg

Colloids/Colloidal State Colloid Properties (Electrical) Salting out/in Hofmeister or lyotropic series for anions in order of decreasing effectiveness in salting out HC’s. F > citrate > HPO4 > tartarate > SO4 > acetate > Cl > NO3 > Br > I > SCN

Isolation/Purification of Hydrocolloids(HCs) Purity of “Native” HCs Purification Techniques Fractional solution Fractional precipitation Drying

Molecular Weight (MWn & MWw) of Hydrocolloids(HCs) Typical Hydrocolloid Molecular Weights Alginates 12,000 - 180,000 Pectins 30,000 - 100,000 Guar 220,000 - 300,000 Gum Arabic 250,000 LBG 300,000 Tragacanth 310,000 Carrageenan 100,000 - 1,000,000 Cellulosics 50,000 - 1,250,000 Xanthan 2,000,000

Molecular Weight (MW) Determination Direct Methods (or Absolute) Osmotic Pressure (Mn) Ultra-Centrifugation (Mw) Light Scattering (Mw) Indirect Methods (or Relative) Intrinsic Viscosity Size Exclusion Chromatography

Colligative Properties Properties that depend on the number of discrete solute units in “solution”, regardless of size (e.g., may be ions or molecules)

Molecular Weight (MW) Determination Direct Methods Osmotic Pressure P = RT/M x C (Van’t Hoff Eq.) Mn = RT = 2.53 X 105 (P/Co) (P/Co) T = 25o C C = g/100 ml P = g/cm3 --[C]---> Polymer Concentration --P/[C]---> P/[Co]--->

Osmometer (courtesy, Central Scientific

Molecular Weight (MW) Determination Direct Methods Osmotic Pressure Ultra-Centrifugation Light Scattering Indirect Methods Intrinsic Viscosity Size Exclusion Chromatography

Molecular Weight (MW) Determination Direct Methods Osmotic Pressure Ultra-Centrifugation Light Scattering Indirect Methods Intrinsic Viscosity Size Exclusion Chromatography http://www.polysep.ucla.edu/index.php/separations/42-size-exclusion-chromatography

Schematic of Ostwald Viscometer