Methine applications

Most of the qualitative relationships between color and structure of methine dyes based on the resonance theory were established independently during the 1940 s by Brooker and coworkers (16, 72-74) and by Kiprianov (75-78), and specific application to thiazolo dyes appeared later with the studies of Knott (79) and Rout (80-84). In this approach, the absorptions of dyes belonging to amidinium ionic system are conveyed by a group of contributing structures resulting from the different ways of localization of the 2n rr electrons on the 2n l atoms of the chromophoric cationic chain, rather than by a single formula ... 

The third current approach is synthesis of peptide chains as models for the helical peptaibol (Section 8.2) and gramicidin (Section 8.3) ion channels. Considerable work has been carried out in the former area, involving synthesis of Aib-containing small peptides, in order to obtain conformational data applicable to the more complex oligopeptide antibiotics. By working with such fragments it has been possible to obtain valuable X-ray crystal structure information on the helical conformation of ala-methin 246), emerimicin 247), suzukacillin 248), and other members of the peptaibol series. 

The distribution of each chemical type between the major application groups of colorants is far from uniform (Table 1.1). Stilbene and thiazole dyes are almost invariably direct dyes, also containing one or more azo groups. Acridines and methines are usually basic dyes,... 

Added in proof. Recently the analysis of 13C-nmr spectra of polypropylene oxide provided a new information about the triad of methine carbon atom and dyad of methylene carbon in the main chain (9/). Applications of this analysis should give a valuable contribution to the more detailed understanding of the polymerization reaction of propylene oxide by organometallic catalysts. 

In the case where the linking group is of the methine type, as in (100), a quaternary nitrogen is introduced, and the product is useful for application to acrylics. 

Chemically, the triarylmethane dyes are monomethine dyes with three terminal aryl systems of wind] one or more arc substituted with primary, secondary, or tertiary amino groups or hydroxyl groups in the para position to the methine carbon atom. Additional substituents such as carboxyl, sulfonic acid, halogen, alkyl, and alkoxy groups may be present on the aromatic rings. The number, nature, and position of these substituents determine both the hue or color of the dye and the application class to which the dye belongs. 

Electropositive elements, the alkali and alkaline earth metals, react directly with hydrocarbyl substituted / -diketones to provide the corresponding metal chelates. The methine protons in perfluoroalkyl-substituted diketones are more acidic so that, in these cases, the method is applicable to other metals such as Fe, In, Ga, Mn, Pb, V and Sc.140,141 Electrochemical syntheses of M(Me-COCHCOMe)2 (M = Fe, Co, Ni) using the appropriate metal anode have been described142 and the method should be widely applicable. 

The influence of the R-substituent nature on the stereochemistry of ICC of type 868 is clearly displayed in complexes of hetaryl azomethinic ligands [15,100,130,134], These chelates are mostly obtained by the method of immediate interaction of ligands and metal salts [(4.48), route A], although some cases of application of template reactions for the same goals are known [(4.48), route B], In this respect, the syntheses (4.48) are representative, described in Refs. 174 and 175 for azo-methines of 3-hydroxybenzo[6]thiophene 878 and their azine analogues, leading to chelates 879 ... 

The most useful dyes for photographic applications belong to the cyanine class [152, 162]. Typical examples are given in Table 11, together with relevant electrochemical data and excitation energies. The structures consist of two heterocycles joined by a methine chain of variable length (Figure 44). 

The aziridine route has rarely found application to the generation of azo-methine ylides substituted by at least one alkyl moiety on carbon because alkyl groups are incapable of stabilizing the ylide center of azomethine ylides. However, thermolysis of l,l-bis(trifluoromethyl)aziridines provides good access to trifluoromethyl-substituted azomethine ylides 14 (76T1995). 

Application of the Hofmann degradation to ie-A -methyltylophorine-methine (VI) yields a compound, C24H24O4 (mp 181°-188°), which may be formulated as X or a derived transformation product. This could be formed by attack of base at the doubly allylic position of VI. 

Some of the first NMR spectroscopic applications in humic substance research involved the use of NMR for the examination of soluble humic substances.(5) The information obtained from NMR spectra of humic and fulvic acids dissolved in alkaline or neutral aqueous solutions has been quite useful in characterizing the aromatic and aliphatic structures of these complex materials. In as much as humic materials are inherently complex, the spectra show only broad signals with some fine structure which can be related to specific methyl, methylene, methine, and aromatic/olefinic hydrogens. Because NMR spectroscopy contains inherently more structural information for humic substances, the use of NMR has been limited since much of the work conducted prior to 1987. This is... 

---