Nothing contained in this chapter or other law of this state shall be taken or construed as limiting the permissible interest rates or finance charges upon loans or credit sales evidenced by notes, bonds or other obligations secured by mortgages, deeds of trust or other security instruments insured or guaranteed by the federal housing commissioner or United States administrator of veterans' affairs or by any other officer, department, agency or instrumentality of the United States or evidenced by notes, bonds, debentures and other obligations and securities issued by, insured by, or guaranteed by the federal housing commissioner, federal national mortgage association, government national mortgage association, small business administration or other federal officer, department, agency or instrumentality.