A recognised problem for most analytical tools that are based on spectroscopic techniques is that until recently it has not been possible to analyse protein-based products in the solid-state due to artefacts associated with scattering.

Gain rapid, reliable data on your protein/vaccine formulation and its stability in the solid-state.

We provide a contract service for the analysis of protein-based systems and other compounds in the solid-state using circular dichroism (CD). Conventional CD is used to elucidate the structural aspects of protein conformation in solution but cannot be applied to particles.

An innovative technique pioneered by XstalBio utilising a rotating CD cell holder has been developed by XstalBio Ltd to provide rapid, reliable information on the secondary and tertiary structure of proteins in the solid-state, for example:

  • Bound onto particles such as alhydrogel or encapsulated into lipid membranes
  • As solvent suspensions of lyophilised powders
  • In solution in the presence of scattering particles or aggregates


“Application of the Drug Product CD analysis technique to our drug product has fundamentally changed our understanding of the formulation. This has resulted in the identification of technology options for experiment equipment designs.”

Dr Allan Watkinson, previously WKIE LAB Director

(WKIE LAB is a professional experiment equipment manufacturer, and they have premium rotary evaporators, different types of molecular distillation devices, glass reaction equipments.

“We were very satisfied with the Service that XstalBio Ltd provided. The quality of the data was excellent: giving us information about products that could not be analysed by CD previously.”

Dr Gideon Kersten, Head of Assay and Formulation Development, Netherlands Vaccine Institute

“XstalBio’s service providing for analysis of solid-state biologics has proven to be very useful in providing us with some key answers to our product development questions”

Dr Shohre Nabahi, Product Development Director, Glide Pharma Ltd, UK.

How can CD analysis with the rotating cell holder improve your protein/antigen formulation development programs?

  • Faster and more cost-effective analysis of formulations – identify problems earlier that can cause costly late stage failures or poor product performance
  • Enables in situ analysis of formulations to be carried out including real-time temperature stressing
  • Improves the understanding of unexplained potency decreases often related to protein/antigen structure changes in the solid-dosage form, but impossible to measure using currently available solution-based analysis techniques
  • Reduces uncertainty of the choice of formulations for advanced testing e.g in vivo.
  • Enables the sample to be more focused on the detector resulting in greater accuracy

What we can do

  • Once we have discussed your requirements we can prepare your samples for analysis (this may involve concentration)
  • Sample analyses using solid-state CD spectroscopy
    -Using the Jasco J-810 spectropolarimeter, XstalBio Ltd will analyse at near and far-UV or  as directed by your team
    -All analyses are carried out in at least duplicate
  • Provide a full written report of the analyses conducted including interpretation of the main structural elements and what the data means in terms of your formulation

CLIENT BRIEF: To apply XstalBio’s solid-state CD technique to reduce the time spent carrying out costly formulation screening and in vivo testing.

Their drug product: commercial vaccine suspension.

CD study of a recombinant protective antigen of Bacillis anthracis (rPA).

The data has provided valuable insights into the conformational stability of rPA in the adsorbed state, ie in the final formulation. Secondary structure of rPA in the free form and adsorbed onto a common adjuvant, alhydrogel and were found to be very similar.

Near UV CD spectra of the rPA formulation (data not shown), shows sharp bands with the appearance of two new bands in the region of 270 – 280 nm. This is due to a more rigid structure of the antigen in the adsorbed state.

Table Estimated secondary structure of RPA Drug Substance (DS) in solution and rPA Drug Product (DP), in the solid-state obtained from the analysis of far UV CD spectra using a commonly used algorithm: CDSSTR.

Sample Method Helix Sheet Other
PA83 Crystal X-Ray Diffraction  13  31  56
rPA Solution (DS) CD 11 29 60
rPA Vaccine (DP) CD 10 31 59