RESUMEN
This paper reports the results of a detailed study of the optical response of boron difluoride curcuminoids to radiation exposure. Two lines of the dyes fundamentally different in structure (namely, symmetrical and asymmetrical) were tested. If the absorption responses of their solutions in chloroform to X-rays turns out to be quite close quantitatively (note that it has a very indicative visual manifestation - a gradual discoloration is observed in the dose range up to 300 Gy), the fluorescence ones differ notably: among other things, the former demonstrate much more sensitive reactions (the corresponding limit of detection values ââdiffer by up to 2.36-fold). Nevertheless, in both parameters, these dyes generally show good linearity of the response as in classical coordinates (up to ≈ 100-150 Gy), as in semi-logarithmic ones (up to 1000 Gy). Since the main reason for such behavior seems to be the radiation-induced decomposition of the dyes, its possible scheme and corresponding "weak links" in the structure of the molecules (in other words, radiosensitive elements) are proposed for each case. For example, these include N(CH3)2 fragments at the ends of dimethylaminostyryl groups. It is precisely their detachment that determines the observed optical response of asymmetrical dyes. Thus, the results obtained provide some insight into the possibilities of controlling the sensitivity of organic dyes to irradiation by changing their structure.
RESUMEN
Optically active liquid-crystalline dispersions (LCD) of nucleic acids, obtained by polymer- and salt-induced (psi-) condensation, e.g., by mixing of aqueous saline solutions of low molecular weight DNA (≤106 Da) and polyethylene glycol (PEG), possess an outstanding circular dichroism (CD) signal (so-called psi-CD) and are of interest for sensor applications. Typically, such CD signals are observed in PEG content from ≈12.5% to ≈22%. However, in the literature, there are very conflicting data on the existence of psi-CD in DNA LCDs at a higher content of crowding polymer up to 30-40%. In the present work, we demonstrate that, in the range of PEG content in the system above ≈24%, optically polymorphic LCDs can be formed, characterized by both negative and positive psi-CD signals, as well as by ones rather slightly differing from the spectrum of isotropic DNA solution. Such a change in the CD signal is determined by the concentration of the stock solution of PEG used for the preparation of LCDs. We assume that various saturation of polymer chains with water molecules may affect the amount of active water, which in turn leads to a change in the hydration of DNA molecules and their transition from B-form to Z-form.