Glen Report 34-18: Technical Snippets

What does the F.W. mean on a product webpage/How do I calculate the M.W. of my oligo?

The F.W. of a product is the unit formula weight once it has been incorporated into an oligonucleotide after deprotection. The F.W. accounts for the loss of any protecting groups, including the β-cyanoethyl group, and the transition of the P(III) phosphoramidite to a P(V) phosphate diester. The F.W. should be used when determining the molecular weight of an oligo.

To calculate an oligonucleotide’s molecular weight, one should use equation 1. The loss of 61.96 is accounting for the loss of a phosphate group. The FW of each product is provided on the product webpage, the certificate of analysis provided upon purchase, and the physical data section of our Product Catalog.

Sum of Unit F.W. – 61.96 + DMT (if applicable) (1)

Some standard unit free weights are listed below:

dA = 313.21          dC = 289.18          dT = 304.20          dG = 329.21          DMT = 302.40


• Non-nucleosidic and nucleoside phosphoramidites
• Solid supports excluding universal and oligo-affinity supports
• NHS esters

What if I store Glen Research’s reagents at temperatures lower than the recommended temperature, are they still safe and active to use? 

Yes, as a general rule of thumb, lower storage temperatures are not harmful. In fact, the chemicals will be more stable. Basically, a cooler temperature slows down any undesired decomposition reaction that may occur otherwise in warmer storage temperatures. For example, it is perfectly fine storing something in the freezer (-10 to -30°C) instead of the recommended refrigerated storage (maximum of 2-8°C). It should be noted that oligonucleotide synthesis reagents stored in the cold should always be equilibrated back to room temperature prior to use. 

Products: All phosphoramidites and solid supports.