Odd Shaped PCA Plot?

Pipeline Pilot / R stats / PCA experts,

I have read in a set of > 10,000 primary and secondary amines and calculated various continuous

physical properties - MW, AlogP, polar surface area, etc (10 descriptors total).  I am using the R

stats package to calculate a principal components. If I output the PCA loadings for each

compound, I obtain the following crescent-shaped plot below.

I do not have much experience with PCA calculations, but the overall appearance of this

plot seems odd compared to other PC plots I have viewed in various cheminformatics

publications.  I typically observe more of a buckshot pattern in 2D.

Also, I am surprised that PC1 alone is capturing approx 95% of the variability in the

data - that also seems unusual to me.

Can someone please explain what is going on.  Are my calculations correct?  Or,

am I over or underfitting the data set or ...?

Thank you.

Regards,

Jim Metz

James.Metz@Abbvie.com

PC loadings.jpg

PC1 vs PC2 plot.jpg