Molecular exclusion

Two classes of micron-sized stationary phases have been encountered in this section silica particles and cross-linked polymer resin beads. Both materials are porous, with pore sizes ranging from approximately 50 to 4000 A for silica particles and from 50 to 1,000,000 A for divinylbenzene cross-linked polystyrene resins. In size-exclusion chromatography, also called molecular-exclusion or gel-permeation chromatography, separation is based on the solute s ability to enter into the pores of the column packing. Smaller solutes spend proportionally more time within the pores and, consequently, take longer to elute from the column. 

Glucose oxidase (from Aspergillus niger) [9001-37-0] Mf 186,000, [EC 1.1.3.4]. Purified by dialysis against deionized water at 6° for 48hours, and by molecular exclusion chromatography with Sephadex G-25 at room temperature. [Holt and Cotton J Am Chem Soc 109 1841 1987.]... 

S-layer ultrafiltration membranes (SUMs) are isoporous structures with very sharp molecular exclusion limits (see Section III.B). SUMs were manufactured by depositing S-layer-carrying cell wall fragments of B. sphaericus CCM 2120 on commercial microfiltration membranes with a pore size up to 1 pm in a pressure-dependent process [73]. Mechanical and chemical resistance of these composite structures could be improved by introducing inter- and intramolecular covalent linkages between the individual S-layer subunits. The uni-... 

To purify the conjugate from reactants that did get incorporated into the conjugate, size exclusion chromatography may be used with resins having a molecular exclusion limit able to accommodate both the labeled molecules and the final conjugate. 

Molecular exclusion and restricted diffusion processes in molecular sieve chromatography. Biochemistry 3, 723—730 (1964). 

Molecular exclusion chromatography. The stationary phase in molecular exclusion chromatography is a material containing pores, the dimensions of which are chosen to separate the solutes present in the sample based on their molecular size. This can be perceived as a molecular sieve allowing selective permeation. This technique is known as gel filtration or gel permeation, depending on the nature of the mobile phase, which is either aqueous or organic. The distribution coefficient in this technique is called the coefficient of diffusion. 

If the molecular masses of solutes are >2 000 and if they are soluble in organic solvents and their molecular diameter is >30 nm. Figure 25-14 tells us to try molecular exclusion chromatography.. Stationary phases for this type of separation are described in Chapter 26. If the molecular masses of solutes are >2 000, and they are soluble in water, but not ionic, and have diameters <30 nm, the decision tree says to use reversed-phase chromatography, or hydrophobic interaction chromatography. 

In molecular exclusion chromatography (also called size exclusion or gel filtration or gel... 

In pure molecular exclusion, all molecules are eluted between Km = 0 and = 1. 

Figure 26-14 Molecular mass calibration graph for polystyrene on Beckman pSpherogel molecular exclusion column (0.77 x 30 cm). Resin pore size labeled on the lines ranges from 5 nm to 100 pm. /Courtesy Anspec Co.. Ann Arbor. Ml.]...

Figure 26-13 Separation of proteins by molecular exclusion chromatography with TSK 3000SW column. [Courtesy Varlan Associates. Palo Alto, CA.]...

Nanoparticles can be separated by molecular exclusion chromatography just as proteins are separated. Figure 26-15 shows the relation between measured size and retention time of CdSe quantum dots. These are particles containing 2 000 CdSe units in a dense, crystalline core capped by alkyl thiol (RS) groups on Cd and trialkylphosphine (R3P) groups on Se. 

Molecular exclusion chromatography is based on the inability of large molecules to enter small pores in the stationary phase. Small molecules enter these pores and therefore exhibit longer elution times than large molecules. Molecular exclusion is used for separations based on size and for molecular mass determinations of macromolecules. In affinity chromatography, the stationary phase retains one particular solute in a complex mixture. After all other components have been eluted, the desired species is liberated by a change in conditions. 

Ferritin (molecular mass 450 000), transferrin (molecular mass 80 000), and ferric citrate were separated by molecular exclusion chromatography on Bio-Gel P-300. The column had a length of 37 cm and a 1.5-cm diameter. Eluate fractions of 0.65 mL were collected. The maximum of each peak came at the following fractions ferritin, 22 transferrin, 32 and ferric citrate, 84. (That is, the ferritin peak came at an elution volume of 22 X 0.65 = 14.3 mL.) Assuming that ferritin is eluted at the void volume and that ferric citrate is eluted at Vm, find Kay for transferrin. 

A polystyrene resin molecular exclusion HPLC column has a diameter of 7.8 mm and a length of 30 cm. The solid portions of the gel particles occupy 20% of the volume, the pores occupy 40%, and the volume between particles occupies 40%. 

Molecular exclusion matrix with properties suitable for purification of the specific conjugate Sephadex G-200 (Pharmacia Biotech, Uppsala, Sweden), B10-Gel A-0.5 m or Bio-Gel A-l 5 m (Bio-Rad Laboratories, Hercules, CA) are useful for relatively small to large conjugates, respectively... 

In view of the large number of new zeolites recently synthesized, considerable effort has been expended in their physical characterization, in particular, via their sorption capacities for various organic substrates. The molecular exclusion properties of these zeolites have been used to estimate their pore-opening catacteristics and shape-selective properties (6). In contrast to the molecular sieving... 

This chromatographic technique concerns the separation of sample molecules on the basis of size and shape by the principle of molecular exclusion. The stationary phase consists of a cross-linked porous gel which permits the entrance into the pores of molecules having a certain size. Larger molecules are excluded, and thus these remain in the mobile phase and are eluted from the column with no retention. The smaller the molecules, the greater distance they can diffuse into the gel and therefore the slower is the migration. 

Nitrogen production using carbon molecular sieves is the only known commercial process using differences In lntrapartlcle diffusivity, rather than inherent adsorbent selectivity or selective molecular exclusion, as the basis for the separation ... 

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