I calculated the dipole moment of gluconic acid using a DFT calculation in the program Gaussian 09 for Linux. I send you the method of calculation and the results.
I didn't really understand all bioinformatics, but 4.8 is all what I need!!
I was comparing the polarity of Gluconic acid with that of Acetic acid, that is 1.74D.
Acetic acid is able to diffuse passively through biological membranes, but in contrast, Gluconic acid, being highly polar, is unable to penetrate. I was just interested in the difference in polarity of both molecules.