The State Treasurer is hereby authorized, at his discretion, to purchase from the Board at private sale not to exceed One Million Five Hundred Thousand Dollars ($1,500,000.00) in investment certificates or interim investment certificates for each project, provided that the rate of interest agreed upon by the Board and the State Treasurer shall not be less than seven percent (7%). Provided, the State Treasurer is hereby authorized, at his discretion, to sell any investment certificates so purchased with any of said sales not to be less than par, plus interest as accrued.