Abstract— The initial yields of the cation and neutral radicals and the triplet are greatly enhanced when high concentrations of Br‐ are present during the flash photolysis of aqueous solutions containing either tryptophan or N‐acetyl‐L‐trytophanamide. The present study is an attempt to elucidate the mechanism by which Br‐ induces these effects. The results obtained indicate that the initial event involves an interaction between the fluorescent state and Br‐ to promote the formation of a long‐lived radical precursor that may be the triplet. It is shown that all of the Br‐‐induced neutral and cation radical formation originate from this long‐lived state. Furthermore, it was found that the mechanism of radical production from the Br‐‐induced long‐lived precursor does not involve hydrated electron formation.
WITH 1,3-DIAMINOPROPANESf'[Manuscript received J a n u a~y 31, 19671 Hexahydropyrimidine and some N-alkylated derivatives have been obtained from the reaction of the corresponding trimethylenediamine or its monoprotonated salt with formaldehyde. A variety of spectroscopic evidence supports a cyclic structure for these compounds in preference to a tautomeric open-chain form. The chemical behaviour of hexahydropyrimidine is explicable in terms of a cyclic di-secondary amine structure.The cyclic structure is destabilized with respect to the open-chain form if the hydrogen atoms attached to C2 of the hexahydropyrimidine ring are replaced by alkyl groups and cannot be detected when, in addition, one of the hydrogen atoms attached to nitrogen is replaced by the bulkier t-butyl group.Hexahydro-2-methylpyrimidine is dehydrogenated to 1,4,5,6-tetrahydro-2methylpyrimidine on shaking with Adams catalyst and hydrogen under laboratory conditions. Hexahydropyrimidines which are tautomeric mixtures are reduced to the corresponding N-alkyl-1,3-diaminopropanes, while those possessing cyclic structures are inert.Reaction of trimethylenediamine monohydrochloride or acetate with aqueous formaldehyde is claimed112 to give an equilibrium mixture of the salts of hexahydropyrimidine (I; R = R' = H) and its open-chain tautomer, 3-methyleneaminopropylamine (11; R = R' = H). Free hexahydropyrimidine, on account of its polymerization properties, is also believed to exhibit ring-chain tautomerism. Continuing our interest in hydropyrimidines, this reaction was reinvestigated and extended to include other diamines, aldehydes, and ketones. The various products *
The ultra-violet absorption spectra of aqueous solutions of the three pyridine-monocarboxylic acids have been plotted over a wide pH range and the isoelectric points, acidic and basic dissociation constants at 25" C have been calculated.The pyridine-monocarboxylic acids are simple amphoteric electrolytes of considerable biological interest. Certain of their derivatives show remarkable physiological activity ; for example nicotinamide is the pellagra-preventive factor of the vitamin-Bz complex and isonicotinic acid hydrazide is the newly discovered anti-tuberculosis drug, Isoniazid.Existing data on the dissociation constants of the pyridine-monocarboxylic acids are inconsistent and incomplete. Ostwald 1 measured the electrical conductivities of solutions of these acids at 23°C and reported affinity constants (105 K) of 0.3 for picolinic acid, 1.37 for nicotinic acid and 1-09 for isonicotinic acid. These values should be approximately equal to the acid dissociation
The flash photolysis of N-acetyl-L-tryptophanamide (NATA) in the presence of the fluorescence quenchers, imidazole, acrylamide and trichloroethanol, has been investigated. Imadazole and acrylamide induce a decrease in the NATA radical yield which correlates with their NATA fluorescence quenching action. These observations suggest that the fluorescent state is primarily responsible for the monophotonic photoionization processes. The acrylamide data also suggest that 40-65% of the NATA radicals arise from a long-lived state (Tps) which must originate from the fluorescent state.Unlike imidazole and acrylamide, trichloroethanol enhances the radical yield by reaction with excited state precursors. Mechanisms for the quenching of fluorescence and the long-lived states are discussed.
By 13. F. EVANS and W. KYNASTOK. Some hydrochlorides, mercurichlorides, and carboxylic and sdphonic acids and their sodium salts have been prepared from pyridine and its derivatives. Their infrared spectra are recorded and discussed as evidence for hydrogen bonding.CHENON and SANDORFY estimated that the N-H stretching frequencies of substituted ammonium ions which were not hydrogen-bonded would fall in the range 3000-3200 cm.-l. It has been found2 that amine tetrachloroborates exhibit bands in the region being considered so that it is possible to obtain the spectrum of a protonated base in which complications due to hydrogen bonding are minimised. Tetrachloroborates are sensitive to moisture and special precautions must therefore be observed. It occurred to us that other complex anions besides tetrachloroborates might be reluctant to form hydrogen bonds with protonated bases, in particular mercurichlorides which are less sensitive to moisture and can be used for the identification and characterisation of bases. In view of this laboratory's interest in pyridine bases, we examined the spectra of the hydrochlorides and mercurichlorides of some pyridine compounds, and of some amphoteric derivatives of pyridine which might be expected to contain a protonated nitrogen atom. The results are given in Table 1.The spectrum of solid pyridinium chloride shows two weak bands at 3206 and 3134 cm.-l, which have been attributed to the presence of a proportion of unbonded NH+ groups perturbed only by crystal forces3 This suggestion implies that there may be a t least Chenon and Sandorfy, Cnnad.
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