I apologize...
I was going in a very wrong way, very wrong, and you all showed me that. Hope not had made you waste your time too much.
I admit now that even the statement of the title "No material can have a negative charge" is totally wrong. Negative materials do exist (as the discussed balloons), negative ions do exist, the commonly considered "ground" electric potential is not any positive potential, things cannot be explained by just the difference in positive potentials, a really zero potential is achieved at normal temperatures just whenever atoms have all of their electrons and not at 0ºK as I was considering...
What a wrong way! I admit. Thanks to have made me "fall to the ground".
I'm working on a model for the basic atomic particles considering them as not "point like" particles as is currently considered, I know. I cannot handle the concept of "point like" having a magnetic field. For me the proper definition of magnetic field involves a current element which means a displacement of charge and so imposible to exist "within" a point. A model still under development and I'm not thinking in abandon it easily although I need to reformulate it in something now. May be I could return with some other thing in mind to discuss in the forum at some time. Hope to not bother you too much...