Size exclusion chromatography of polypeptides on Bio-Gel P2 in the dynamic axial compression mode

The isolation of water-soluble natural products - challenges, strategies and perspectives

Covering period: up to 2019Water-soluble natural products constitute a relevant group of secondary metabolites notably known for presenting potent biological activities. Examples are aminoglycosides, β-lactam antibiotics, saponins of both terrestrial and marine origin, and marine toxins. Although extensively investigated in the past, particularly during the golden age of antibiotics, hydrophilic fractions have been less scrutinized during the last few decades. This review addresses the possible reasons on why water-soluble metabolites are now under investigated and describes approaches and strategies for the isolation of these natural compounds. It presents examples of several classes of hydrosoluble natural products and how they have been isolated. Novel stationary phases and chromatography techniques are also reviewed, providing a perspective towards a renaissance in the investigation of water-soluble natural products.

Converging flow chromatography in constant-pressure mode

Dispersion in chromatographic processes can be reduced to a minimum using converging columns and a curved frit at the outlet. Working at constant pressure at the inlet the internal packing is increasingly compressed by the accelerated flow. Thus the packed bed is stabilized. Under these conditions the observed flux at the outlet and the power input of the pump are inversely related to the viscosity of the eluting solute. Comparing converging flow chromatography (CFC) with classical axial flow chromatography (AFC) and radial flow chromatography (RFC) the stationary phase is used more efficiently in CFC.

Behavior of packing materials in axially compressed chromatographic columns

The behavior of a packing material (Luna C18 from Phenomenex, Torrance, CA, USA) was studied during the consolidation of a column bed under axial compression stress. The kinetics of this consolidation, the permeability and efficiency of the columns obtained, and the reproducibility of these column properties were measured under different conditions. The consolidation process and the column properties are considerably affected by the friction between the packing material in the bed and the column wall. Clear evidence of this wall effect was demonstrated. The apparent permeability of columns consolidated under the same axial stress increases with increasing column length. The apparent modulus of elasticity of the beds increases with increasing column length. The shear resistance between the packed bed and the column wall was measured for columns of different lengths. It increases rapidly with increasing bed length. The column efficiency for thiourea (unretained) and phenyloctane (retention factor, k' approximately 1) was much poorer after recompression than after the first compression. It depended little on the compression stress. The effect of the column length was small.