What Exactly Does Chiral Mean?
Chirality is a special physical property of a molecule which describes its geometry in three-dimensional space. Chiral molecules commonly consist of a carbon atom attached to four different substituents. The substituents can either be atoms or groups of atoms, but each must differ from the other three for the carbon to be considered a chiral center. Enantiomers, which are special forms of isomers, exhibit chirality; they are non-superimposable mirror images of each other. This means that a pair of enantiomers cannot be placed on top of one another and give identical molecules despite their rotation. We refer to these structural differences as right-handed and left-hand configurations.
In recent years, the importance of compounds containing this specialized property has increased significantly due to relevance in the pharmaceutical industry. Most biomolecules and pharmaceuticals are chiral, so to understand how a medication works, one must first understand the physical properties of the compounds at hand. Although they have the same chemical structure, most enantiomers of chiral drugs exhibit significant differences in biological activity. Therefore, it is important to achieve chiral separation and analysis of racemic drugs in order to eliminate unwanted effects from specific isomers.
Why Do I Need to Screen My Compound? Can’t I Just Buy Any Chiral Column?
There are a number of stationary phase types, such as: Pirkle, or brush-type phases; cyclodextrin phases; ligand exchange phases; and protein-based chiral stationary phases. The polysaccharide phases, however, have proven to be the most popular among analytical chemists due to their versatility and rate of success.
Chiral chromatography employs many different interaction mechanisms for achieving separation of chemically identical compounds. These mechanisms include ionic interactions, hydrogen bonding, steric hindrance, and pi stacking just to name a few. Unfortunately, there is no predictable pattern to these interactions, which is why we have to screen a variety of different CSPs; this is also why Phenomenex offers several different stationary phases. It is necessary to test different columns with unique chiral selectors when attempting to separate enantiomers.
How Can Phenomenex Help?
Phenomenex carries a line of seven different polysaccharide-based chiral stationary phases (CSPs) known as the Lux columns. We understand that it wouldn’t be practical, nor cost efficient, for our customers to buy and test each of our columns for the purpose of separating a single chiral sample. This is why Phenomenex offers free chiral screening at PhenoLogix, our in-house analytical laboratory.
We’ll screen any compound on all seven of our Lux phases for free! We test the chiral compound in three different chromatographic modes: normal phase, reversed phase, and polar organic conditions. We also offer fast turn-around times, with most projects being completed in less than 10 days. If we are successful at finding a suitable phase to separate a sample, we then continue working to optimize a method which is delivered to our customers along with a column recommendation.
Despite making use of all the tools available to us, not every chiral compound can be separated. However, we’ve seen that even data generated during our failed endeavors has helped customers with their research efforts. This really represents our main goal, which is to work closely with our customers and provide unique methods and applications for their individual needs.