PubMed · 5765324
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
A T Weil. 1969-03-14. Marihuana.. https://doi.org/10.1126/science.163.3872.1145
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Two new fluorinated benzo[c]xanthene dyes were synthesized by reaction of fluorinated 1,6-dihydroxynaphthalenes with 2,4- (and 2,5)-dicarboxy-3'-dimethylamino-2'-hydroxybenzophenone. The two critical fluorinated 1,6-dihydroxynaphthalene intermediates were prepared via a regioselective route. The fluorinated benzo[c]xanthene dyes exhibit desired lower pK(a) values (6.4 and 7.2, respectively) than their parent compound (pK(a)=7.5) while the pH-dependent dual-emission characteristics are well retained. Their cell-permeable esters have been prepared for intracellular applications.
A photochromic nitrospiropyran moiety (Sp) has been covalently linked to a zinc (PZn) and to a free-base (P(H2)) porphyrin. In the resulting dyads (P(Zn)-Sp(c) and P(H2)-Sp(c)), the porphyrin first excited singlet states are unperturbed by the closed form of the attached spiropyran. Excitation of the spiropyran moiety of either dyad in the near-UV region results in ring opening to a merocyanine form (P-Sp(o)) that absorbs at 600 nm. The open form re-closes thermally in 2-methyltetrahydrofuran with a time constant of 20 s, or following irradiation into the 600 nm band. Excitation of the zinc porphyrin moiety in the merocyanine form of the dyad yields 1PZn-Sp(o). The lifetime of the zinc porphyrin excited state is reduced from its usual value of 1.8 ns to 130 ps by singlet-singlet energy transfer to the merocyanine moiety to give PZn-1Sp(o). The quantum yield of energy transfer is 0.93. Quenching is also observed in the free base dyad, where 1P(H2)-Sp(o) and P(H2)-1Sp(o) exchange singlet excitation energy. This photoswitchable quenching phenomenon provides light-activated control of the porphyrin excited states, and consequently control of any subsequent energy or electron-transfer processes that might be initiated by these excited states in more complex molecular photonic or optoelectronic devices.
Proton binding by a soil fulvic acid, humic acid, and a set of size fractions of the humic acid was studied as a function of pH and ionic strength by potentiometric titrations. The negative charge of the humic substances resulting from deprotonation of acidic functional groups generally increased with increasing pH and increasing ionic strength. At any given pH and ionic strength, the fulvic acid fraction exhibited much higher negative charge than the humic acid fraction. For the size-fractionated humic acids, negative charge decreased steadily with increasing apparent molecular weight, as determined by size exclusion chromatography. Observed differences in proton binding by the various humic substances corresponded well to differences in functional group composition, which has been extensively characterized in a previous study using a combination of analytical techniques. The proton binding behavior of the humic substances was described very well by the consistent NICA-Donnan model. However, when all adjustable model parameters were determined using a least-squares minimization technique without introducing parameter constraints, the values of some parameters turned out physically and chemically unreasonable. Therefore, we propose to derive some model parameters from chemical characterization results obtained by size exclusion chromatography and solid-state 13C NMR spectroscopy. Using this approach, we obtained excellent descriptions of all titration data, and the model parameter values were more consistent and chemically reasonable. Our results demonstrate that characterization results of humic substances can be used in NICA-Donnan modeling to reduce the number of free fitting parameters without arbitrary constraints and, thereby, obtaining a more reliable database for environmental modeling.