Three-component complexes

Three-component complex organo- 11 metallic catalysts for polymerisa- (236) tion of olefinic hydrocarbons... 

AA portions of the chains. This process could be repeated to produce a bulky three component complex network. Viscometry, potentiometry, and IR and UV spectroscopy confirmed the formation of this copolymer-copolymer-metal... 

A minimal model for self-replication is shown in Scheme 12.23. The replicator (R) must be able to recognise and bind at least two different precursor components (Cl and C2) in a ternary (three component) complex, and to accelerate their chemical reaction with each other to produce a product that is a copy of the original R. Such a simple system will always be in competition with the uncatalysed binary reaction of Cl and C2. 

In this case, the stereochemical course of the reaction can be explained by the formation of the three-component complex 99, which transforms into two isomers through the intermediates 100 and 101 (Scheme 35). 

Kinetic evidence" indicated, also, that a siimdtaneous binding of the acceptor and donor must take place before polymerization occurs. Binding of the donor (sucrose) on the acceptor site causes inhibition and excess acceptor, in the presence of a low concentration of sucrose, oZso causes inhibition (because of competitive interaction of the acceptor and sucrose for the donor site). Any mechanism that is postulated for this reaction must, therefore, include a three-component complex— between the enzyme and both substrates. 

Coinclusion of the aromatic guest and a small molecule, usually an aliphatic alcohol, in the cavity of a dextrin (i.e., the formation of a three-component complex) often enhances the emission. In this type of complex, the fluorophore is sandwiched between the CD wall and the alcohol, which acts as a spacer. More water molecules are expelled from the cavity and the fluorophore experiences an environment less polar than that experienced in the absence of a spacer. The phenomenon was first reported in reference 61 the enhanced fluorescence of a-naphthylacetic acid observed after addition of y-CD was further increased by addition of cyclohexanol. 

Formation of three-component complexes was observed for several aromatic hydrocarbons. 

Fluorescence enhancement caused by the formation of a three-component complex was also reported for coronene in the presence of y-CD (adamantane and 1-adamantanol were other components) [84], for perylene in the presence of 1-pentanol and / - or y-CD [85], and for azulene in the presence of -CD (ethanol, 1-propanol, 1-butanol, and 1-pentanol were the third components). In the last case, viewing the fluorescence variations as a... 

The addition of hexanesulfonate (H) to a y-CD-16 solution in which the dimeric complex (y-CD-16-16-y-CD) is present led to the formation of a three-component complex y-CD-16-H [124], as shown by the decrease of the excimer fluorescence and the biphasic monomer fluorescence decay. The species with the longest lifetime (i.e., the three-component complex with T = 220 ns) was quenched by triethanolamine with lower than 3 X 10 dm mol" s" and by Oj with fc, = 4 x 10 dm mol" s" . For all other forms of the CD-16 complex studied in [124], the corresponding kq are higher, that is, the best protection against the quenching is offered to 11 by the three-component complex. 

Intense room-temperature phosphorescence was obtained with 1,2 di-bromoethane (0.6 M) as heavy-atom perturber. The phenomenon was observed with 18 PNA [192] and 16 azaaromatics containing one or two heterocyclic nitrogens [193]. The formation of a three-component complex, CD/aromatic/dibromoethane, in which the aromatic and the heavy-atom perturber are organized in a small space, is believed to be responsible for the phosphorescence emission. It was found that, concomitant with phosphorescence emission, the fluorescence of the included aromatic was quenched. It should be noted that, for most of the aromatics examined, a residual phosphorescence emission was found also in air-equilibrated solutions. 

Gallium forms a three-component complex with Catechol Violet and quinine (having an absorption maximum at 680 nm) which may be used for its photometric determination. ... 

Kano, K, S Hashimoto, A Imai and T Ogawa (1984). Three-component complexes of cyclodextrins. Exciplex formation in cyclodextrin cavity. Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2(3-4), Tyi-1 (>. 

THREE-COMPONENT COMPLEXES OF CYCLODEXTRINS. CYCLODEXTRIN CAVITY... 

ABSTRACT. The fluorescence quenching of naphthalene, 1-methylnaph-thalene, and acenaphthene by trimethylamine (TMA) was studied in aqueous 3-cyclodextrin (3-CD) solutions to know the structural requirements for guest molecules to form three-component complexes. The apparent rates for the fluorescence quenching of the naphthalene derivatives by TMA markedly increased in the presence of3-CD. The fluorescence quenching of 1-methylnaphthalene and acenaphthene by TMA was accelerated by 3-CD more efficently than that of naphthalene. These results suggest the structures of the three-component complexes as the arene-capped 3-CD including TMA in its cavity. 

The fluorescence quenching can be regarded as a probe reaction for investigating the effects of CD on bimolecular reactions. Especially, the structural requirements for guest molecules to form three-component complex can be studied by this method. Formation of three-component complexes is essentially important to realize CD-catalyzed bimolecular reactions. In the present work, we studied the fluorescence quenching of naphthalene, 1-methylnaphthalene, and acenaphthene by TMA in aqueous 3-CD solutions to clarify the steric factors affecting the formation of the three-component complexes. 

The formation of an active complex 81 consisting of three components, tin(II) trifiate, chiral diamine 80, and dibutyltin acetate is assumed in these aldol reactions. The three-component complex would activate both aldehyde and silyl enolate (double activation), i.e. the chiral diamine-coordinated tin(II) trifiate activates aldehyde while oxygen atoms of the acetoxy groups in dibutyltin acetate interact with the silicon atom of the silicon enolate. Because it has been found that the reaction does not proceed via tin(II) or tin(IV) enolates formed by silicon-metal exchange, silicon enolate is considered to attack the aldehydes directly [65]. The problem of this aldol reaction is that (Z) enolates [63] react with aldehydes more slowly, consequently affording the aldols in lower yield and with lower diastereo- and enantio-selectivity. 

---