Any public corporation which is authorized to issue, sell and deliver its public corporation securities (or, if the public corporation security is in the form of a loan agreement, to execute and deliver the loan agreement) under the laws of this State may issue, sell and deliver (or, in the case of a loan agreement, execute and deliver) such securities to the Authority under this Act; provided that, notwithstanding any other provision of law to the contrary, any such public corporation may issue and sell (or, in the case of a loan agreement, execute and deliver) any such public corporation security by negotiated sale to the Authority, at any interest rate (whether fixed or variable, and whether current or deferred), which rate or rates may be established by an index or formula which may be implemented by persons appointed or retained therefor by the Authority, and at such price or prices to which the public corporation and the Authority may agree. Any public corporation selling its public corporation security to (or, in the case of a loan agreement, entering into a loan agreement with) the Authority under this Act may pay any amount charged by the Authority under this Act. Any private institution which is so authorized may issue, sell and deliver its private institution securities (or, if such private institution security shall be in the form of a loan agreement, to execute and deliver such loan agreement) to the Authority under this Act. The Authority shall have discretion to purchase such public corporation securities and private institution securities (or, in the case of a public corporation security or a private institution security in the form of a loan agreement, execute and deliver and make the loan contemplated by such loan agreement) as the Authority shall deem to be in the best interests of furthering and accomplishing the purposes stated in this Act.