Quadruplex structures arise from four coplanar G bases arranged in a Hoogsteen base pairing motif to create a central pore that can coordinate cations. The termini of eukaryotic chromosomes contain structures, known as telomeres, which are capable of forming quadruplex structures. Quadruplexes have been implicated in a variety of disease states, including cancer. The literature seems to agree that the human telomeric repeat containing four stretches of three guanines displays conformational states that are different in the presence of Na+ and K+ and an unknown number of species involved in the quadruplex to single strand transition. Using circular dichroism spectroscopy, differential scanning calorimetry, and singular-value decomposition, the number of species present in the dissociation process is assessed. The results indicate that three species exist in equilibria during the melting process. We present a model for the heat-induced denaturation from the folded to the unfolded state, whereby the hybrid parallel-antiparallel quadruplex undergoes a transition to an unknown intramolecular intermediate followed by a transition to a single strand.

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Fluoropolyol, a sorbent chemoselective oligomer, has been deposited using a matrix-assisted laser-based deposition technique. A comparison of films deposited with infrared (2.94 μm) and ultraviolet (UV) (193 nm) radiation shows that photochemical and/or photothermal modification of the oligomer occurs for the UV-deposited films while the IR-deposited films appear to be identical to the starting material. In addition, it is shown that even ablating the matrix alone causes a film to be deposited when using a UV laser. Therefore, unless photochemical interactions are a desired outcome, the use of a UV laser for most matrix-assisted laser ablation and deposition techniques is unfavorable.