V.M. Gusev, O.N. Kompanets, M.A. Pavlov, D.P. Chulkov, S.G. Scuridin, Yu.M. Yevdokimov

A compound CD spectrum of which could be accepted as a standard of optical activity and used for testing and calibrating CD spectrometers (dichrometers) in a wide range of wavelengths is absent now. At practice the dichrometers are certified only at one or two wavelengts located in UV as a rule. Usually one can use as a standard d-10-camphorsulfonic acid (CSA) or ammonium d-10-camphorsulfonate (ACS) water solutions of which possess CD of positive sign at  = 290.5 nm and of negative sign at  = 192.2 нм. There are data testifying that a mistake at CD measuring the same substance with several certified dichrometers can reach ≥ 30% even at maintaining the necessary order of business and optimization of measurement conditions. Last time optically active structures based on DNA cholesteric liquid-crystalline dispersions (CLCD, or nanoconstructions - NaCs) are widely used especially in biosensorics. They are obtained by the «excluding method» from water-salt solutions containing rigid linear native double-stranded DNA molecules, at mixing them with water-salt solutions of neutral synthetic polymers in particular polyethileneglicol (PEG). For particles of a liquid DNA NaC the spiral-twisted spatial structure is specific, and formation of this structure is accompanied with arising optical activity manifested in the form of the intensive (abnormal) band with the stable value and position of its maximum in the CD spectrum in the field of DNA chromophores absorption at  ~ 270 nm. A problem of stabilization of the liquid DNA NaC particles has been solved due to immobilization of these particles in the composition of an optically transparent polymer hydrogel obtained on the base of the PEG macromonomer. The polymer hydrogel does not disturb the spatial structure of the particles and does not influence the initial value of their abnormal optical activity; it can have any form convenient for an experimentalist; it is stable for a long time (a half of year and more), non toxic, chemically and biologically inert and penetrated for low molecular mass compounds that opens a possibility for diffusion of molecules of various compounds into the hydrogel, in particular intercalators, and for their subsequent interaction with DNA molecules with formation of molecular complexes «DNA-intercalator». The hydrogel CD spectrum in this case is manifested in the form of two abnormal bands one of them is located in the field of DNA chromophore absorption (at ~ 270 nm), and another one is located in the field of intercalator chromophore absorption. Selecting intercalators and ensuring conditions both for their diffusion into the polymer gel and their interaction with DNA NaC particles one can obtain a polymer optically active material (POAM) that manifests the abnormal optical activity of the definite magnitude at desirable wavelengths in the wide range from UV to IR. Immobilization of rigid NaC particles formed due to nanobridges made of alternative antibiotics molecules and (Cu2+) ions which link DNA neighboring molecules both in the same and neighboring quasinematic layers of the initial liquid DNA NaC leads to the POAM formation as well, and for such POAM as the same time as the abnormal optical activity at 270 nm an additional abnormal activity arises in the field of chromophore absorption of the antibiotics included to the nanobridges structure. In the article a possibility is discussed of the usage of DNA NaC based POAMs as additional opical activity standards for testing and calibration of CD spectrometers in the broadened wavelength range. At the stage 1 one can determine a CD value of a POAM sample at the wavelength of 270 nm (ΔАPOAM, 270). Here the closeness of the CD bands at 270 and 290 nm is used as well as the observed ratio k1 between values of registered (with the dichrometer) CD signals of the CSA based standard (CDΔA290) and a POAM (CDΔA270) that are expressed through the known standard optical activity of the CSA solution (ΔАstandard) and unknown abnormal optical activity of the POAM sample (ΔАPOAM,270) accordingly, as well as through measured and passport characteristics of light intensity I passing through the CSA solution and the POAM, a photodetector sensitivity S and a signal path gain T at two wavelengths. At the stage 2 the standard optical activity POAM characteristic at 270 nm (ΔАPOAM,270) obtained before is carried over to an analogous unknown before POAM characteristic at the additional abnormal CD band. In addition the fact is taken into account that maxima of the CD signals of the POAM at 270 nm (CDΔA270) and at the additional abnormal CD band are also in the definite observed ratio k dependent on the technology of the POAM formation and the presence in its composition of NaC particles of the «DNA-intercalator» complex or NaC particles sewn with nanobridges. Carrying out pointed measure acts also means that the dichrometer which is calibrated with this way and becomes the working instrument for the CD measuring at 270 nm and at the additional CD band can be used to determine an optical activity value of any other optically active compound or material on the basis of the ratio of CD signals of this compound (material) and the POAM based secondary standard. As formation technology of various POAMs does not impede to obtain their abnormal optical activity at many other wavelengths in a wide spectral range from UV to IR it is possible to prepare sets of such POAMs that all together possess abnormal optical activity at rather big number of separate wavelengths, and to use these POAM as additional secondary standards of optical activity - both for more accurate calibration of dichrometers in a wide wavelength range, and for more correct determination (near these separate wavelengths) of optical activity (CD) characteristics of natural compounds, chemical substances and synthetic materials being under investigation and possessing this property.