Triple-helix and double-helix formations of octamers of deoxyriboadenylic and deoxyribothymidylic acids (dA8 and dT8) have been studied spectrophotometrically. The free-energy changes in 50 mmol dm−3 MgCl2 buffer at 25 °C were −21.2 kJ mol−1 for the triplex formation and −29.3 kJ mol−1 for the duplex formation, respectively. The other results by UV and CD spectroscopies were also reported.
The triple-helix and double-helix formations by octamers of deoxyriboadenylic and deoxyribothymidylic acids, (dA)8 and (dT)8, have been studied energetically and dynamically by UV and CD measurements, a melting analysis, curve-fitting and nearest-neighbor calculations. The UV mixing curves and CD spectra showed that the triple-helix of (dA)8·2(dT)8 mainly existed in 0.05 mol dm−3 MgCl2 buffer at a low temperature range, while the double helix of (dA)8·(dT)8 existed in 1 and 0.1 mol dm−3 NaCl buffers. The thermodynamic parameters for the triplex and duplex formations were obtained with analysis for the UV melting curves. The free-energy changes at 25 °C obtained from the melting temperature vs. oligomer concentration plots in the MgCl2 buffer were −20.7 kJ mol−1 for the triplex formation and −27.3 kJ mol−1 for the duplex formation, respectively, which were consistent with the values obtained from the curve-fitting calculations. The free-energy changes for the duplex formation at 25 °C were −28.5 kJ mol−1 in 1 mol dm−3 NaCl buffer, and −11.6 kJ mol−1 in 0.1 mol dm−3 NaCl bufer, respectively. These values were discussed in comparison with the predicted values by the nearest-neighbor calculation.
The effect of ethidium (ED) on the double-helix melting of octamers of deoxyriboadenylic and deoxyribothymidylic acids (dA8 and dT8) in a phosphate buffer containing 1 mol dm−3 NaCl has been studied quantitatively. The results indicate that the enthalpy and entropy changes for the dA8·dT8 melting in the presence of ED are much larger than those in the absence of the drug; that is, ED increases the stability of the duplex.
Aqueous self-assembly of short peptides has attracted growing attention for the construction of supramolecular materials for various bioapplications. Herein, we describe how the thermolysin-assisted biocatalytic construction of a dipeptide hydrazide from an N-protected amino acid and an amino acid hydrazide leads to the formation of thermally stable supramolecular hydrogels. In addition, we demonstrate the post-assembly modification of the supramolecular architectures constructed in situ tethering hydrazide groups as a chemical handle by means of fluorescence imaging.
Thermolysin‐assisted biocatalytic construction of a self‐assembling dipeptide hydrazide from two kinds of non‐self‐assembling amino acid derivatives gives rise to the formation of supramolecular helical architectures under aqueous conditions. In addition, post‐assembly modification based on hydrazone formation allows the in‐situ constructed supramolecular helical architectures to be decorated with tethering hydrazide groups as chemical handles. More information can be found in the Research Article by M. Ikeda et al. (DOI: 10.1002/chem.202104421).
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