The assets of the trust fund shall be preserved, invested, and expended solely pursuant to and for the purposes set forth in this article and shall not be loaned or otherwise transferred or used by the state for any purpose other than the purposes of this article. This Code section shall not be construed to prohibit the trust from investing in, by purchase or otherwise, bonds, notes, or other obligations of the state, an agency of the state, or an instrumentality of the state.