The Diphenylmethane Moiety

While conceptually an extremely important leap forward, host 6.67 left a great deal of room for improvement and a huge number of new and more effective or tailored diphenylmethane-based systems have been prepared by a number of different groups. Particular problems to be addressed with 6.67 include  

The need to work in strongly acidic solutions. Solubility at neutral pH would be useful in studies on physiological systems. 

The poly methylene linkers between the two diphenylmethane moieties are very flexible leading to a poorly preorganised host. Spacers that are more rigid should result in greater selectivity. 

The host is achiral. Incorporation of chirality would give access to studies on chiral recognition and asymmetric catalysis. 

The preorganised macrocycle binding sites remain effective at all dendrimer generation levels and hence binding is not inhibited by hydrophobic collapse of the dendritie branches. 

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A range of cyclophanes (compounds containing a bridged aromatic ring - for a full discussion of cyclophane chemistry see Section 6.5) with protonated nitrogen functionalities have been used with great success as anion binding hosts. In particular, the diphenylmethane moiety is commonly used... 

A closer inspection of the chemical structures of these compounds shows that they contain a modification of the diphenylmethane moiety, a diphenylamine. 

The diphenylmethane moieties open and preorganize a cavity lined by benzene rings that are nearly orthogonal to the mean molecular plane. 

Cyclophanes Endoacidic, Endobasic, and Endolipophilic Cavities, p. 424 Dendrimers. p. 432 The Diphenylmethane Moiety, p. 452 Enzyme Mimics, p. 546... 

Cucurbituril, Its Homologues, and Derivatives, p. 390 The Diphenylmethane Moiety, p. 452 Interpenetration, p. 735 Macrocycle Synthesis, p. 830 Rotaxanes and Pseudorotaxanes. p. 1194 Self-Assembly Definition and Kinetic and Thermodynamic Considerations, p. 1248 Self-Assembly Terminology, p. 1263 Strict Self-Assembly and Self-Assembly with Covalent Modifications, p. 1372 The Template Effect, p. 1493... 

When the two phenyl rings of the diphenylmethane moiety of adiphenine are linked together in the form of a rigid fluorene group as in pavatrine hydrochloride (I), the association pattern no longer conforms to that of a monodisperse micellar system [22]. The concentration dependence of the light-scattering intensity of pavatrine exhibits no such inflection as that detected in the curve of adiphenine (Fig. 4.8) and cannot be simulated by the mass-action theory. 

Use of benzotriazole in the preparation of diphenylmethanes and triphenylmethanes has been reviewed." Benzotriazole is condensed with an aldehyde and then allowed to react with naphthols to form a diphenyl-methane benzotriazole derivative such as 69 (Scheme 9). The benzotriazole moiety in 69 is displaced by a Grignard reagent to give triphenylmethanes.79 100 This method allows for the preparation of triarylmethanes which contain three different aromatic rings. Compounds 70-72 are prepared by this method. 

Schneider and coworkers investigated the capability of the tetraazonia cyclophane 51 to bind nucleosides and nucleotides in water [72]. Its two diphenylmethane units border a lipophilic cavity for the uptake of likewise lipophilic molecules or subunits. As evidenced by HNMR studies of the complexes, only in the case of the purine derived nucleosides and nucleotides (A, G, AXP, GMP) the base moiety is included inside the host cavity but not in the case of the pyrimidine analogues (U, C, UMP, CMP, TMP). Due to their hydrophilic nature, the sugar and phosphate groups remain outside the niche. 

The reaction of the iron-carbene complex [[Bu C CC(OEt)=)Fe(CO)4] with 1,3-cyclohexadiene afforded223 (32), which was characterised by X-ray diffraction. The addition of the anionic derivatives of i-(diphenylmethane)-il-fluorene- and ii-(9,10-dihydroanthracene)-bis tricarbonylchromium to the hydrocarbon moiety (alkene, benzene, cyclohexadienyl, cycloheptadienyl and cycloheptatrienyl) in various cationic compounds of manganese, rhenium, iron, chromium, molybdenum, tungsten and cobalt was reported224 to provide a new route to hydrocarbon-bridged heteronuclear species such as (33). 

Perhaps the most dramatic effect of the hydrophobic group on the association characteristics is to be found in the small group of amphiphiles with aromatic hydrophobic regions. An appreciable number of drug molecules are based on a diphenylmethane moiety and associate in solution in a typically micellar manner. 

PCL-diol and diphenylmethane-i -diisocyanate (MDI), by R. delemar lipase were examined. These polyurethanes have both the hydrogen bonds among polymer chains and aromatic rings in the polymer molecules. R. delemar lipase could hydrolyze the polyurethanes though the rate of hydrolysis toward polyurethanes decreased as compared to that ward PCL-diol. The rate of hydrolysis decreased with decreasing the Mn of PCL-moiety of polyurethanes (Figure T). 

As is for low mass liquid crystals, incorporation of kinked moieties will result in destructive effects on the liquid crystallinity of polymers (Figure 3.4). 2,2-diphenylpropane, diphenylmethane, diphenyl ether, diphenyl ketone, 1,2-phenylene, 1,3-phenylene, and 1,2-naphthalene are examples of kinked moieties used in the modification of liquid crystalline polymers. They are very effective in destroying the linearity of rigid rods. Polymers with kinked units have less crystallinity and lower phase transition temperatures. Appropriate use of kinked units is thus of help from case to case. However, the type and amount of kinked units should be carefully determined so as to maintain desirable liquid crystallinity. 

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