That said bonds may be sold at public or private sale, in the discretion of the board of regents, provided, however, that no sale shall be made for less than the par value of the bonds, plus accrued interest from the last preceding interest date to the date of delivery of said bonds. Before delivery of the bonds to the purchaser all matured interest coupons shall be detached and cancelled. The state treasurer may, with the approval of the state board of finance and other officials whose approval may be required by law for the investment of public funds, purchase such bonds at par and accrued interest to date of delivery of such investment. Such bonds shall be accepted at their par value by all public officials in this state as security for the repayment of all deposits of public monies of this state, or of any county, municipality or public institution thereof, and as security for the faithful performance of any obligations or duty to guarantee the performance of which such officials are now authorized by law to accept a deposit of the bonds of this state or of the United States of America.