homework - Are Bovine serum albumin, Avidin, Ficoll-70 and Dextran-70 positively charged or negatively charged?

For charge, you could check this one by sequence level, for example for Bovine Albumin (Uniprot: P02769) you can get the theoretical pI of 5.82, as the mean of pKa aminoacid values, to do this can use protparm, so when the pH > pI, the protein has a net negative charge and when the pH < pI, the protein has a net positive charge.

And there are only two organic polar solvents I known to work proteins, DMSO (pKa = 35) and
Dimethylformamide (DMF, pKa=-0.01 (20ºC))