Analytical Services

Screening Assays

Sirius Analytical screening assays are designed for larger batches of compounds and utilise our Fast UV pKa and chromatographic LogD assays. The assays typically accommodate samples supplied as solutions and pKa measurements are possible with as little as 5uL of a 10mM stock solution, depending upon compound properties.

pKa

The Sirius pKa screening assay is designed for samples provided as solutions, typically 10mm DMSO stock solutions. The method is based on a UV metric titration and therefore requires that the sample molecule exhibits discernable UV absorption changes on ionisation. The assay is run in the presence of a cosolvent to help ensure that the compound remains in solution during the titration. Any UV active pKas between 2 and 12 are detected.


The SiriusT3 Fast UV pKa method has been validated against results reported in the literature and produces results that are of comparable quality to those obtained by traditional methods. For further details, please refer to Sirius Application Note 02/11. The recommended sample amount is 100uL of a 10mM stock solution, but smaller volumes can be accommodated, so please talk to Sirius if you intend to submit less.

Relevant Application Note:
AN02 pKa measurements in 15 minutes – the SiriusT3 Fast UV pKa method

LogD

The Sirius LogD assay is a chromatographic method which is used to measure sample partitioning between an aqueous buffer of fixed pH and an octanol phase. The assay is designed for samples provided as solutions, typically 10mm DMSO stock solutions. It can be used to measure both ionisable and non-ionisable compounds. The test compound must have a chromophore as the method employs UV detection. The method can accommodate compounds having a LogD between approximately 1.5 and 4.5. The recommended sample amount is 200uL of a 10mM stock solution, but smaller volumes can be accommodated, so please talk to Sirius if you intend to submit less.

Solubility

Sirius offers a rapid solubility screen based upon the chromatographic determination of concentration in a solubility medium selected by the client. Experimental conditions can be adjusted to suit individual customer requirements. Samples may be supplied as stock solutions in DMSO.

Relevant Application Note:
AN13 Measuring Solubility- What’s best for you?

Surface activity

This assay accommodates sample solutions prepared in a 96 well plate format. Sample solutions of different concentrations are normally prepared in house from the sample provided by the customer. We can measure surface tension, Critical Micelle Concentrations, Total Surface Area and Air/Water partition coefficients.