Abstract:The reactions of quinolizinium bromide (QB) and its four monobromo derivatives with aniline, isopropylamine and liquid ammonia have been investigated. With aniline 2‐ and 4‐bromo QB undergo substitution, whereas 1‐ and 3‐bromoQB do not react at all. With liquid ammonia all bromo derivatives and the parent compound react with ring opening. This diversity in the reaction course is explained in terms of the HSAB principle. 2‐BromoQB reacts with isopropylamine under formation of 2‐isopropylaminoQB. Two molecules o… Show more
“…The second comparison is between the 11-cis-RPSB Br model compound and the 11-cis-RPSB-Cl reference. Since bromide and chloride differ mainly in their van der Waals radii, the changes in charge density can be readily modeled by a small change (0.15 A) in the location of the center of the counterion relative to the SB nitrogen (Blatz et al, 1972;Sanders et al 1983). As in the 11-cis-RSB comparison, an altermation in charge differences is observed along the retinal chain, and the calculated differences agree both…”
Semiempirical molecular orbital calculations are combined with 13C NMR chemical shifts to localize the counterion in the retinal binding site of vertebrate rhodopsin. Charge densities along the polyene chain are calculated for an 11-cis-retinylidene protonated Schiff base (11-cis-RPSB) chromophore with 1) a chloride counterion at various distances from the Schiff base nitrogen, 2) one or two chloride counterions at different positions along the retinal chain from C10 to C15 and at the Schiff base nitrogen, and 3) a carboxylate counterion out of the retinal plane near C12. Increasing the distance of the negative counterion from the Schiff base results in an enhancement of alternating negative and positive partial charge on the even- and odd-numbered carbons, respectively, when compared to the 11-cis-RPSB chloride model compound. In contrast, the observed 13C NMR data of rhodopsin exhibit downfield chemical shifts from C8 to C13 relative to the 11-cis-RPSB.Cl corresponding to a net increase of partial positive or decrease of partial negative charge at these positions (Smith, S. O., I. Palings, M. E. Miley, J. Courtin, H. de Groot, J. Lugtenburg, R. A. Mathies, and R. G. Griffin. 1990. Biochemistry. 29:8158-8164). The anomalous changes in charge density reflected in the rhodopsin NMR chemical shifts can be qualitatively modeled by placing a single negative charge above C12. The calculated fit improves when a carboxylate counterion is used to model the retinal binding site. Inclusion of water in the model does not alter the fit to the NMR data, although it is consistent with observations based on other methods. These data constrain the location and the orientation of the Glu113 side chain, which is known to be the counterion in rhodopsin, and argue for a strong interaction centered at C12 of the retinylidene chain.
“…The second comparison is between the 11-cis-RPSB Br model compound and the 11-cis-RPSB-Cl reference. Since bromide and chloride differ mainly in their van der Waals radii, the changes in charge density can be readily modeled by a small change (0.15 A) in the location of the center of the counterion relative to the SB nitrogen (Blatz et al, 1972;Sanders et al 1983). As in the 11-cis-RSB comparison, an altermation in charge differences is observed along the retinal chain, and the calculated differences agree both…”
Semiempirical molecular orbital calculations are combined with 13C NMR chemical shifts to localize the counterion in the retinal binding site of vertebrate rhodopsin. Charge densities along the polyene chain are calculated for an 11-cis-retinylidene protonated Schiff base (11-cis-RPSB) chromophore with 1) a chloride counterion at various distances from the Schiff base nitrogen, 2) one or two chloride counterions at different positions along the retinal chain from C10 to C15 and at the Schiff base nitrogen, and 3) a carboxylate counterion out of the retinal plane near C12. Increasing the distance of the negative counterion from the Schiff base results in an enhancement of alternating negative and positive partial charge on the even- and odd-numbered carbons, respectively, when compared to the 11-cis-RPSB chloride model compound. In contrast, the observed 13C NMR data of rhodopsin exhibit downfield chemical shifts from C8 to C13 relative to the 11-cis-RPSB.Cl corresponding to a net increase of partial positive or decrease of partial negative charge at these positions (Smith, S. O., I. Palings, M. E. Miley, J. Courtin, H. de Groot, J. Lugtenburg, R. A. Mathies, and R. G. Griffin. 1990. Biochemistry. 29:8158-8164). The anomalous changes in charge density reflected in the rhodopsin NMR chemical shifts can be qualitatively modeled by placing a single negative charge above C12. The calculated fit improves when a carboxylate counterion is used to model the retinal binding site. Inclusion of water in the model does not alter the fit to the NMR data, although it is consistent with observations based on other methods. These data constrain the location and the orientation of the Glu113 side chain, which is known to be the counterion in rhodopsin, and argue for a strong interaction centered at C12 of the retinylidene chain.
“…The 3a,9a-diazaperylenium dication ( 1 ), an isomer of the N , N ‘ -diprotonated forms of 3,9-, 1,7-, and 1,12-diazaperylene, has not been known and has been the subject of numerous spectroscopic, crystallographic, chemical, theoretical, and biochemical studies . Meanwhile, recently we developed a one-step synthesis of 1,2,3,4,5,6,7,8,9,10,11,12-dodecahydro-3a,9a-diazaperylene, 2 , from p -phenylene diamine, 3 , and 1-bromo-3-chloropropane .…”
The 3a,9a-diazaperylenium dication (1) was synthesized for the first time in two steps from p-phenylene diamine. Ab initio calculations show a twisted ground state with a 6.4 degrees tilt between the two quinolizinium building blocks. Dication 1 is photoluminescent in fluid solutions of H(2)O, CH(3)CN, and CH(3)NO(2), but not in rigid matrices of the same solvents. This phenomenon has been attributed to a geometric relaxation of the tilted ground state into an emitting planar lowest singlet excited state. [structure: see text]
“…In addition to our ongoing studies on azolyldienes we now decided to investigate the analogous reactions of azinyldienes as well. On this class of compounds only very little work has been published in the literature: Kröhnke et al described first the ring opening of the quinolizinium salt 4a to the trans-trans pyridyldiene 6a , and later also some other reports appeared in this field − which concluded that the reaction of the azinium salt with secondary amines proceeds through the salt → cis - trans dienamine → trans - trans dienamine ( i.e. 4 → 5 → 6 ) sequence.…”
mentioning
confidence: 99%
“…As the geometry of the resulting azinyldienes was of especial importance from the point of view of the desired cycloadditions, we made serious efforts in order to isolate both 1- trans -3- trans 6 and 1- cis -3- trans products 5 . Although the existence of 5 as the primary product in such ring openings has been proved by NMR spectroscopy, − in most cases only the more stable 1- trans -3- trans isomer 6 could be isolated so far. 1 2 …”
Azinyldienamines underwent Diels Alder reaction of inverse electron demand with 1,2,4,5-tetrazine diester to give azinylvinylpyridazines. Comparison of the products obtained from mono-, di-, and triazinyldienamines revealed that, in some cases, isomerization of the olefinic side chain occurred which can be rationalized by the tautomeric conditions of the intermediates bearing these azine moieties. These experimental findings supported also by semiempirical calculations suggest the importance of the influence of the hetaryl group in such isomerizations.
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