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The 266 nm nanosecond laser photoionization (PI) of a wide range of dinucleotides containing purines, and related nucleosides and nucleotides, occurs through a combination of one- and two-photon pathways that can be considered as a near threshold PI process. The net PI yields of these DNA and RNA model compounds are of the order of 10^-2, whereas the monophotonic component is of the order of 10^-3. These yields increase with an increase in the initial ground-state concentration, which is interpreted in terms of a stabilization of their ionization potentials (IPs) due to an increase in the electronic coupling between the bases as the base stacking of the dinucleotides increases on going from 1 to 100 μM concentrations. Photodestruction yields for dinucleotides in the range 10^-3 to 10^-2 were determined using low-intensity 254 nm irradiation; these increased in the following order:  GpC ≈ TpdG > CpG > ApG. Competition experiments using electron scavengers showed that the participation of the oxidized base in the photodestruction mechanism is 85% for GpC, 64% for TpdG, 59% for ApG, and 18% for CpG. The photoionization yields, estimated from the effect of electron scavengers on the photodestruction yield at low-intensity 254 nm irradiation, correlated well with the monophotonic PI yields of the dinucleotides examined. Differences in base stacking, conformation, and structural fluctuations of the various dinucleotides isomers are proposed to explain the sequence effect observed in the PI yields and photoreactivity at 254 nm. A linear correlation between the net PI yield of various dinucleotides and the calculated IPs reported by Saito and Rösch groups was obtained [Saito, I.; Nakamura, T.; Nakatani, K.; Yoshioka, Y.; Yamaguchi, K.; Sugiyama, H. J. Am. Chem. Soc. 1998, 120, 12686−12687; Voityuk, A. A.; Jortner, J.; Bixon, M.; Rösch, N. Chem. Phys. Lett. 2000, 324, 430−434]. Altogether, the results strongly suggest the use of near threshold PI yields of small oligonucleotides to estimate the effect of such properties as base stacking, sequence and conformation, base pairing, structural fluctuation, and solvation on the efficiency of hole-trapping and charge transport in DNA.

Experimental solubilities are reported for anthracene dissolved in ternary solvent mixtures 1-propanol + 2-propanol + cyclohexane and 1-butanol + 2-butanol + cyclohexane, for anthracene dissolved in the heptanary solvent mixture 1-propanol + 2-propanol + 1-butanol + 2-butanol + cyclohexane + heptane + 2,2,4-trimethylpentane, and for anthracene dissolved in binary solvent heptane + 2,2,4-trimethylpentane at 298.15 K. For the two ternary solvent systems anthracene mole fraction solubilities are reported at 19 different ternary compositions spanning the entire mole fraction range. In the case of heptanary solvent system, solubility data was measured at eight solvent compositions. Results of these measurements are used to test the predictive ability of the combined nearly ideal multiple solvent (NIMS)/Redlich−Kister and combined NIMS/BAB equations. Computations showed that both solution models provided reasonably accurate predictions for how the mole fraction solubility varied with solvent compositions. Deviations between predicted and experimental values were on the order of ±0.95% for the better of the two predictive equations.

Experimental solubilities are reported for anthracene dissolved in ternary 2-ethoxyethanol + cyclohexane + heptane, 2-ethoxyethanol + cyclohexane + 2,2,4-trimethylpentane, 2-butoxyethanol + cyclohexane + heptane, and 2-butoxyethanol + cyclohexane + 2,2,4-trimethylpentane solvent mixtures at 25 °C. Nineteen compositions were studied for each of the four solvent systems. Results of these measurements are used to test the predictive ability of the ternary solvent form of the combined NIMS/Redlich−Kister equation. Computations showed that the model predicted the observed solubility behavior to within an overall average absolute deviation of about 1.42%.

Experimental solubilities are reported for anthracene dissolved in six binary alkane + 2-ethyl-1-hexanol and four binary alkane + 1-pentanol solvent mixtures at 25 °C. The alkane cosolvents studied were hexane, heptane, octane, cyclohexane, methylcyclohexane, and 2,2,4-trimethylpentane. Results of these measurements are used to test two mathematical representations based upon the combined nearly ideal binary solvent (NIBS)/Redlich−Kister and modified Wilson equations. For the 10 systems studied, both equations were found to provide an accurate mathematical representation of the experimental data, with an overall average absolute deviation between measured and calculated values being 0.6% and 1.0% for the combined NIBS/Redlich−Kister and modified Wilson equations, respectively.

Experimental solubilities are reported for anthracene dissolved in seven binary alkane + chlorocyclohexane and seven binary alkane + 1-chlorooctane solvent mixtures at 25 °C. The alkane cosolvents studied were hexane, heptane, octane, cyclohexane, methylcyclohexane, 2,2,4-trimethylpentane, and tert-butylcyclohexane (also called (1,1-dimethylethyl)cyclohexane). Results of these measurements are used to test two mathematical representations based upon the combined nearly ideal binary solvent (NIBS)/Redlich−Kister and modified Wilson equations. For the 14 systems studied, both equations were found to provide an accurate mathematical representation of the experimental data, with an overall average absolute deviation between measured and calculated values being 0.5% and 0.8% for the combined NIBS/Redlich−Kister and modified Wilson equations, respectively.

Experimental solubilities are reported for anthracene dissolved in seven binary alkane + 2-butoxyethanol solvent mixtures at 25 °C. The alkane cosolvents studied were hexane, heptane, octane, cyclohexane, methylcyclohexane, 2,2,4-trimethylpentane, and tert-butylcyclohexane (also called (1,1-dimethylethyl)cyclohexane). Results of these measurements are used to test two mathematical representations based upon the combined nearly ideal binary solvent (NIBS)/Redlich−Kister and modified Wilson equations. For the seven systems studied, both equations were found to provide an accurate mathematical representation of the experimental data, with an overall average absolute deviation between measured and calculated values being 0.5% and 0.8% for the combined NIBS/Redlich−Kister and modified Wilson equations, respectively.