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61.
Abstract— Experimental mouse mammary tumor cells (EMT-6) were subjected to PDT (30 u-g/mt DHE,620–640 nm at 3.94 mW/cnr) and hyperthermia (45.2°C, Haake FK2 waterbath) for varying lengths of time and sequences. The results show that the two modalities interact in a manner which is more cytotoxic than the sum of the individual treatments, and the sequence of administration is a determining factor in the degree of interaction. The greatest potentiation of PDT is seen when hyperthermia is administered immediately after PDT. Introducing a time interval at 37°C, between treatments, leads to a rapid loss of interaction. Analysis of dose-response curves reveals a return of the shoulder and an increase in the D., after various incubation periods at 37°C. These data suggest that the cells accumulate and demonstrate recovery from sub-lethal damage and also develop a tolerance to a second challenge. The appearance of stress proteins was also detected after PDT treatments, which may account for some of the phenomena observed.  相似文献   
62.
The mass spectra of both nonhindered and sterically hindered methyl phenanthrene derivatives follow the patterns established for other alkyl aromatics. The ‘unimolecular’ thermochemistry of these systems parallels the mass spectral fragmentation in a qualitatively predictable way. Generally the major thermochemical products correspond to one of the five most intense fragment ions, and the importance of products which correspond to ions with high appearance potentials increases with increasing temperature of the thermolysis system. On the basis of this empiricism we have outlined a tentative procedure for anticipating the results of thermolysis experiments based on mass spectral data. The use of appearance potential differences to estimate steric strain energies in the compounds studied did not give satisfactory results.  相似文献   
63.
Cyclophanes 1-6 catalyze the nucleophilic dealkylation of a simple sulfonium compound by potassium iodide. The cation-pi interaction is important in substrate binding, but the primarily electrostatic nature of this effect does not explain all observations concerning catalysis. As a series of substituents are placed on the cyclophane framework, a systematic variation in catalyst effectiveness is seen, such that more polarizable substituents produce more potent catalysts. This provides support for the notion that transition states are especially polarizable, and catalysis can be enhanced by maximizing London dispersion forces. The reactions studied here are very similar to the broad class of biological methylations mediated by S-adenosylmethionine, and the biological catalysts may use forces similar to those described here.  相似文献   
64.
65.
In a previous study utilizing benzophenone-based topological probes to study conformationally dependent changes in mouse muscle nicotinic acetylcholine receptor (nAChR) topology, electrospray ionization tandem mass spectrometric (ESI-MS/MS) analysis led to a consistent -2.0 Da mass deviation from expected values. In the present study a synthetic peptide, corresponding to nAChR alpha1 subunit residues 130-139, was photolabeled. MS/MS analysis of this peptide using an ion trap confirmed the previously observed mass deviation, associated only with fragment ions that contain the incorporated benzophenone moiety. Analysis of peak profiles for the photolabeled ions does not indicate the typical 'peak fronting' that produces a mass shift when labile ions are prematurely ejected from the ion trap. Rather, hydrogen/deuterium (H/D) exchange experiments support the hypothesis that a chemical rearrangement involving phenyl migration and ketone formation has formed an unexpected oxidized peptide, with molecular mass 2 Da less than that expected, that is isolated for collision-induced dissociation in the ion trap together with the predicted precursor due to the broad ion isolation window specified.  相似文献   
66.
67.
We study odd and even \(\mathbb{Z }_2\mathbb{Z }_4\) formally self-dual codes. The images of these codes are binary codes whose weight enumerators are that of a formally self-dual code but may not be linear. Three constructions are given for formally self-dual codes and existence theorems are given for codes of each type defined in the paper.  相似文献   
68.
The gas phase heats and entropies of SN2-like association of bromide ions with a series of alkyl bromides are reported. Comparison of this data with published data for the same reactions in solution suggests that the alkyl group structural effects on SN2 reactivity in solution are controlled entirely by the solvent.  相似文献   
69.
A regioselective mono-benzylation of the 4-hydroxyl group of 2,4-dihydroxybenzaldehyde (2) to produce 1 under extremely mild basic conditions (NaHCO3 or KF) has been developed. This approach gives improved regioselectivity relative to earlier methods.  相似文献   
70.
A modification of Ambarzumian's method is used to develop the integro-differential equations for the source function, flux, and intensity at the boundary of a two-dimensional, semi-infinite cylindrical medium with second order Legendre phase function scattering. The incident radiation is collimated, normal to the top surface, and is dependent only on the radial coordinate. Boundary conditions which vary as a Bessel function and as a Gaussian distribution are investigated. The Gaussian distribution approximates a laser beam. Numerical results are presented in graphical and tabular forms for a Rayleigh scattering medium. The results are compared with those of isotropic scattering.  相似文献   
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