Pyridinium groups

Barboiu, M., Supuran, C.T., Luca, C., Popescu, G. and Barboiu, C. (1996) Functionalized derivatives of benzocrown-ethers. Part I. Ionophores containing amino and pyridinium groups derived from benzo-15-crown-5, benzo-18-crown-6 and dibenzo-18-crown-6. Liebigs Annalen der Chemie, 959-963. 

A spiropyran compound bearing a pyridinium group and a long alkyl chain behaves as a surfactant. The components shown in Scheme 1 exhibit reverse photochromism in polar solvents. The colored merocyanine form is more stable than the spiropyran form in the dark. Upon photoirradiation at A>510 nm, the polar merocyanine form is converted to the hydrophobic spiropyran form so that the CMC (critical micelle concentration) of the surfactant decreases. Consequently, when the initial concentration is set between the CMC of the two forms, photoirradiation induces a sudden formation of micelles at a certain conversion to the spiropyran form corresponding to the CMC of the mixed micelle of the two forms. 

Recent research on aminocarbenes has led to the development of a very fruitful field. The synthesis of relevant complexes (Scheme 19) such as aminobis(yhde) carbene species (69) [147], cyclic C-amino P-ylides (70) (easily transformed into carbenes) [148] and their corresponding complexes (71) [149], and special ylides (72), which also transform very easily into carbenes by loss of pyridinium group, has been reported. Emphasis has been made on the transformation between ylides and carbenes and on the donor properties of the ylides. From the results obtained the ylides have shown a stronger a-donor behavior compared with the carbenes. 

Probably, the acid protonates one of the pyridine rings to give the 16 electron-valence complex [Rh(/c -bpaH)(cod)](PF6)2. This complex can then react with molecular oxygen to give an Rh (peroxo)(cod) intermediate, which is immediately protonated by the pyridinium group to regenerate... 

Fig. 4. Relationship between bimolecular rate constants (k2) for aqueous transmethylation of HgCl species and solution salinity. Abbreviations Si = (CH2)sSiCH2CH2-CH2C02 Cr = 3-Py H —CH2—Cr(OH2)3 Fe = 3-PyH —CH2Fe=(CO)2(-C5H5) Co = 4-PyH+—CH2Co(CN) " Mn = 3-PyH+—CH2Mn(CO)5, where PyH+ is the pyridinium group.

Chrvmogenic Cephalosporins. A 3-substituted pyridinium cephalosporin known as PADAC, C-.7l[o Nr,04S , is purple in color but on hydrolysis or treatment with /1-lactamase releases the 3 -pyridinium group with concomitant loss of the purple color. PADAC is an example of the chromogenic cephalosporins which are useful in studying interactions widi /1-lactamases. 

Amphiphilic binding also occurs for molecular anionic substrates [4.31, 4.32, 4.34]. Charged heterocyclic ring systems, such as those derived from the pyridinium group, represent an efficient way to introduce simultaneously electrostatic interactions, hydrophobic effects, structure, and rigidity into a molecular receptor in addition, they may be electroactive and photoactive. 4,4 -Bipyridinium groups have... 

Dyes containing the pyridinium group linked to the diazo component via a carboxylic ester function (e.g., 40) [32017-47-3] are obtained by condensation of 4-nitrobenzoyl chloride with chloroethanol, reaction of the ester with pyridine, reduction of the nitro to an amino group, diazotization, and coupling with aromatic amines [124],... 

Coals derivatized with pyridine/ have been found to be susceptible to mild oxidants (21). Alkaline silver oxide is too weak to solubilize untreated coals to any large extent, however, coal-pyridinium salts yield typically soluble but still high molecular weight products. The extent of solubilization depends on the number of pyridinium groups. This oxidant has been applied to several of these coal macerals yielding, as is found with whole coals, fairly high molecular weight products. Approximate molecular size distributions for the methyl esters of the products have been determined by gel permeation... 

A similar process has been used in the case of polysiloxanes with pendant pyridinium groups.172 In this instance, an MSMA derivative was transformed into a BSMA derivative. 

Acetylcholineesterase and choline oxidase Enzyme membrane in H20 was treated with 11% solution of PVA-SbQ (polyvinyl alcohol) with styryl pyridinium groups. Mixture was spread on a cellulose nitrate membrane and air dried. The membrane was exposed to UV radiation for 3 h and stored at 4°C. The enzyme membrane was fixed with a Pt electrode. Sample was dissolved in phosphate buffer and measured. The best results were obtained at pH 8 and at 30°. The calibration graph was rectilinear for 5mM ACh. The storage stability of the dry membrane was excellent. [77]... 

A key example of the usefulness of charged tags in probing reaction mechanisms is found in our study of the esterification of alcohols and carboxylic acids [90] reportedly catalyzed by dis-tannoxanes [91]. A permanently-charged pyridinium group was... 

A ring carbon can also be involved, however, as in the reaction of the thianthrene and phenothiazine radical cations in neat pyridine or with pyridine in an anhydrous solvent. In this reaction the 1-pyridinium group is inserted on to the benzo ring (43), apparently via nucleophilic attack on di-cations 42, in turn resulting from oxidation of the initially formed radical cation adducts (Scheme 27). In the presence of moisture the sulfoxides are again formed [84]. 

Polymerized Microemulsion Systems. A microemulsion of styrene and divinylbenzene with CTAB + hexanol may readily be made, and subsequently polymerized to form a polymerized microemulsion (5,6,7). This system exhibits two sites of solubilisation for photosystems such as pyrene, one in the surfactant skin layer, and the other in the polymerized styrene-divinylbenzene core. Photochemical reactions induced in the surfactant skin are very similar to those observed in micelles and are not immediately of concern to us at this stage. However, photochemical reactions induced in the rigid polymerized core are of interest, as they essentially confine reactants to a small region of space where movement is restricted as compared to a fluid non-polymerised microemulsion or a micelle. Thus, diffusion is minimised, and it may be possible to investigate reactions which occur over a distance rather than reactions which occur by diffusion. In order to eliminate reactions in the surfactant skin a microemulsion can be constructed which contains cetyl pyridinium chloride in place of CTAB. The pyrene that resides in the surfactant skin layer is immediately quenched by the pyridinium group following excitation. 

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