Search

The synthesis and /sup 195/Pt chemical shifts of the hydroxo-bridged dimer and trimer, isolated form an aquated solution of bis(nitrato)(trans-1,2-diaminocyclohexane)platinum (I), at different pH are described. The chemical shifts of these three complexes are widely separated, and /sup 195/Pt NMR provides a convenient method for the investigation of dimer formation kinetics from I. Rate constants for the dimerization reaction calculated at different pD, temperature, and concentration agree well with the hypothesis that dimerization occurs with a rate-limiting bimolecular reaction of an intermediate hydroxo species formed by the loss of a proton from the parent complex.

Treatment of mixtures of cis and trans Pt(NH3)2Cl2 with thiourea (thu) gave Pt(thu)4Cl2 and trans [Pt(NH3)2(thu)2]Cl2 which were separated and quantified by high-performance liquid chromatography using a strong cation exchange column. Several platinum-thiourea compounds have been studied by NMR (1H, 13C, 195Pt), an increase in the coalescence temperature of the NH2 resonances being observed as a result of co-ordination. The NMR data has also been used to show the presence of interactions between the Pt(thu)2+4 and PtCl2−6 ions of [Pt(thu)4][PtCl6] in dimethylsulphoxide solution.

The preparation of Pt(NH3)2(MeU)2·2H2O, 1. [(NH3)2Pt(MeU)2Pt(NH3)2](NO3)2, 2. Pt(NH3)2Cl(MeU), 3. and (in solution) [Pt(NH3)2(OH)(MeU)], 4. (MeU = 1-methyluracil monoanion) is reported. Levels of l-methyluracil and 1–4 in platinum-l-methyluracil blue (PtMeUB) have been assessed by high performance liquid chromatography (HPLC). This technique has also been used to show that in physiological saline or water, PtMeUB hydrolyzes to 3 or 4, respectively. Visible spectroscopy shows that the rate of hydrolysis of PtMeUB is much faster in fetal calf serum than in saline or water, with HPLC indicating that the product of hydrolysis in serum is 3. The precipitate obtained upon treatment of DNA solutions with PtMeUB has also been shown to hydrolyze to 3 or 4 when suspended in saline or water. Compounds 1–3 have been tested against the Ascites S-180J tumors, with 2 and 3 being active, while 4 has been shown to react readily with DNA. Possible mechanisms of antitumor action of PtMeUB that involve 3 and 4 are proposed.

Measurements are reported on some characteristics of photo‐conduction and semiconduction in pure crystalline chlorophylls a and b. The semiconduction activation energy is 1.12 ev in chlorophyll a and 1.44 ev in chlorophyll b (E/2kT). The latter value is in excellent agreement with the triplet state energy of 1.43 ev measured by the phosphorescence method in chlorophyll b. The former value suggests that a possible cause of the lack of detectable phosphorescence in chlorophyll a is that it occurs in the infrared at about 11 000 A. The evidence indicates that the mobility of the predominant charge carriers (positive holes) is the same in both crystals. Photoconduction is easily measured in chlorophyll b and less easily in chlorophyll a, because of the much larger dark current. The photoconduction activation energy in chlorophyll b is 0.36 ev. This supports Rabinowitch's view that photoconduction in chlorophyll is not involved in the primary act of photosynthesis.The oxygen adsorbed on the surface of the crys...

Some evidence is presented indicating that the formation of a triplet state is involved as an intermediary step in the creation and transfer of charges in the photoconduction process in organic substances. On the basis of the simple potential curve picture, approximate solutions are obtained to the rate process equations. These equations predict that the density of the triplet states under thermal and optical equilibrium conditions will follow a Boltzmann exponential dependence upon temperature with an energy equal to a low multiple (1 or 2) of the vibrational spacing of the excited singlet state. The assumption is made that the photocurrent is proportional to the triplet state density. Measurements by the author and others of the photoconduction activation energy in a number of aromatic hydrocarbons are in very good agreement with this. The triplet state model also requires that the buildup and decay of the photocurrents be approximately monomolecular with time constants at low temperatures and intensiti...

The 1:1 electron donor-acceptor complexes of 2,4-dinitrophenol with lipids such as egg lecithin, synthetic lecithin and oxidized cholesterol have been studied spectrophoto-metrically in carbon tetrachloride solution. The charge-transfer absorption band has been found in the near ultraviolet for each complex. The equilibrium constants of these complexes have been estimated from their charge transfer bands and are in the order egg lecithin > synthetic lecithin > oxidized cholesterol. The electrical conductivity of bimolecular lipid membranes increases in the presence of iodine, picric acid, 2,4-dinitrophenol and trinitrobenzene. With increasing temperature, the electrical conductivity of bimolecular lipid membranes of oxidized cholesterol has been found to increase exponentially and the activation energies have been measured for membranes in bathing solutions of iodine, picric acid, 2,4-dinitrophenol, trinitrobenzene and water. The increase of electrical conductivity with decreasing activation energy of oxidized cholesterol bimolecular lipid membranes in the presence of different acceptors supports the suggestion of donor-acceptor complex formation. The strength of the acceptors are in the order iodine > picric acid > 2,4-dinitrophenol > trinitrobenzene. In the solid state, the activation energies of fully hydrated oxidized cholesterol crystals and also in the presence of iodine and 2,4-dinitrophenol have been measured. The values are in good agreement with those obtained for the bimolecular lipid membranes and suggest that the same mechanism of semiconduction appears in both cases.

The de semiconductive behavior of lipid films (cholesterol palmitate, egg lecithin and synthetic lecithin) has been studied. Although these lipids are insulators in the dry state, they exhibit conductivities greater than 108 times larger in the fully hydrated condition. The semiconduction activation energies for the “dry” and fully hydrated states of these films have been measured: for synthetic lecithin, the “dry” activation energy has values of 4.8 to 6.3 eV depending upon the sample, while for cholesterol palmitate the values range from 2.9 to 3.5 eV. The fully hydrated values for the lecithins range from 1.7 to 2.8 eV, whereas those for the cholesterol palmitate are 1.2 to 1.9 eV. For egg lecithin, an effect paralleling that for hydration is found upon exposure of the film to iodine vapor. Lipid bilayers, formed from egg lecithin, exhibit resistance values of 108Ω·cm2 when formed in distilled water. Addition of iodine to the water drops the resistance to less than 104Ω·cm2. Spectroscopic evidence indicates that iodine forms a donor-acceptor complex both with egg lecithin films and egg lecithin bilayers. The increase in electrical conductivity in both the lipid films and lipid bilayers is taken to be due to the formation of this donor—acceptor complex. Since all presently known donor—acceptor complexes are electronic conductors this is taken as suggestive of an electronic conduction mechanism in the bilayer.

THE specific cause of the death rates of unicellular organisms and poikilothermic animals at high temperatures is not known for certain1. We wish to report a good numerical correlation between certain thermodynamic parameters in protein denaturation and death rates, where these have been reported, for these organisms. A similar correlation may exist between the thermal denaturation of other biopolymers, such as DNA and RNA, and thermal death, but in the absence of adequate data we cannot consider this possibility further.

Platinum-pyrimidine complexes have been used as the sole electron-dense stains for electron microscopy on 18 types of mammalian cells. These recently discovered complexes react avidly with nucleic acids in vitro, are antitumor agents, and are highly soluble in water. In cells, they are selective for regions rich in nucleic acid and make visible the cellular chromatin, nucleolus, and ribosomes. In addition, cells that are tumorigenic exhibit electron-dense patches at the plasma membrane; normal cells do not. The results of treatment of ascites sarcoma-180 cells with concanavalin A, nucleases, glycosidases, or a protease suggest that the electron-dense patches are DNA, with neuroaminic acid involved in the surface binding.

Retinal condenses with secondary amines to produce a carbinol type compound. Protonation of this system with anhydrous HCl results in the formation of an enamine salt, with an extensive bathochromic shift in its visible spectrum (λ max ranges from 450 to 650 nm). Extensive investigations of this system were undertaken with indole. The stability of the protonated product is temperature dependent; the resulting solution is readily hydrolyzed and possesses indicator-like properties; and the precipitated protonated species is extremely unstable in all available solvents. Both unprotonated and protonated solutions are photosensitive, as evidenced by marked alterations in their visible spectra. The various chemical properties and the extensive bathochromic shift indicate the possible relevance of this system to the chemistry of visual pigments.

The inhibitory effects of anti-tumor, bacterial filament forming platinum compounds, Cis-Pt(II) (NH3)2Cl2 (A), Cis-Pt(IV) (NH3)2Cl4 (B), and Pt(II) (NH2)2(CH2)2Cl2(C) on DNA, RNA and protein syntheses was measured by the incorporation of 3H-thymidine, 3H-uridine, and 3H-L-leucine, respectively, into an acid-insoluble polymer in human amnion AV3 cells. Compound A, the most effective tumor-inhibiting platinum compound, was shown to selectively inhibit DNA synthesis below 5μM and to inhibit 3H-thymidine incorporation more rapidly than 3H-uridine or 3H-leucine incorporation at 25μM. Like A, compounds B and C were also shown to inhibit all three processes after a 24-hour period of treatment at 25μM. A correlation was established between the relative anti-tumor effectiveness of compounds A, B, and C and the extent of their inhibitory effects. On the other hand, two non-tumor-inhibiting platinum compounds, [Pt(II) (NH3)4]Cl2 (D) and Trans-Pt(IV) (NH3)2Cl4 (E) had no inhibitory effects, except compound E, which exhibited a rapid initial inhibition of 3H-L-leucine incorporation at 100μM. The inhibition of 3H-thymidine incorporation into cells pretreated 4 h with 5μM of compounds A, B, and C was shown to be irreversible. Finally the inhibition of the incorporation of 3H-thymidine into DNA by A was shown not to be caused by the inhibition of the uptake of the tracer into the acid-soluble pool. A number of possible explanations for the greater sensitivity of DNA synthesis and the sequential inhibition of DNA, RNA and protein synthesis at higher concentrations are suggested.

The semiconduction and photoconduction currents through 1-ml thick sandwich cells of all-trans-, 13-cis-, 11-cis-retinal-, and 13-cis-retinal-m-nitroaniline-hydrogen chloride were measured as a function of the temperature in both the crystalline and melted states. From the slopes of graphs of the log of the current against 1000/TGK, the activation energies for semiconduction and photoconduction were calculated using the conductivity equations for the band model. The results of the average semiconduction activation energy measurements fell into two categories: The first group has activation energies between 1.9 and 2.4 eV and includes crystalline all-trans-, 13-cis-,9cis-retinal, and both crystalline and melted 13-cis-retinal-m-nitroanaline hydrogen chloride; the second group has activation energies between 3.1 and 3.6 eV and includes crystalline 11-cis-retinal samples shorted. The average photoconduction activation energy for crysalline 13-cis- and 11-cis-retinal, being 0.25 and 0.24 eV respectively, were essentially identical within experimental error, whereas the same parameter for 13-cis-retinal-m-nitroaniline hydrogen chloride was considerably lower at 0.15 eV. All-trans-retinal was not measurably photoconductive and 9-cis-retinal was only slightly photoconductive.

THERE is much interest in the role of charge transfer interactions in biology1. In a study of the semiconductive properties of lipids in the solid state, Rosenberg and Jendrasiak (ref. 2 and unpublished work) have shown that when lipid molecules, such as egg lecithin and synthetic lecithin, are exposed to iodine vapour, they exhibit a large increase in electrical conductivity with a concomitant decrease in the activation energy from the dry state value. They suggest that a charge transfer mechanism may be involved. Because they also found that iodine added to the aqueous media surrounding lipid bilayers (egg lecithin or oxidized cholesterol) increased the bilayer conductivity also by a factor of more than 104, it was suggested that a charge transfer mechanism might also be involved in this case. It was with the intention of investigating these possible charge transfer mechanisms that we undertook the work reported here.