Linking groups

Although connection of polyalkylene or poly(alkylene oxide) groups to the polyamine is most commonly by the succinimide linkage, a different linking group is employed in another important class of ashless dispersants— the Mannich bases. They are prepared on a commercial scale by reaction of an alkylphenol with formaldehyde and a polyamine (173—177). The alkyl and polyamine moieties are similar to those used in the succinimide products. 

One of the major drawbacks to many promising copolymers is their unsatisfactory electrochemical stability. Carbonyl groups which feature in many of the back-bone/chain linking groups are likely to cause stability concerns. Likewise, urethane, alcohol, and siloxane functions are sensitive to lithium metal. With this in mind, a recent trend has been to find synthetic routes to amorphous structures with... 

In the Chemical Abstracts method (also accepted by IUPAC Rule C-912), the naming of monoazo compounds with radicals R derived from two identical parent hydrocarbon hydrides is the same as mentioned above (for an exception see C-912.2). If the azo group links groups that are different when unsubstituted (R-N2-R ), a parent molecule RH is treated as substituted by R -N2- (Rule C-912.4) thus, 1.8 is called 4-(2-hydroxy-l-naphthylazo)benzenesulfonic acid or 4-(2-hydroxy-... 

Nearly all of the polymers produced by step-growth polymerization contain heteroatoms and/or aromatic rings in the backbone. One exception is polymers produced from acyclic diene metathesis (ADMET) polymerization.22 Hydrocarbon polymers with carbon-carbon double bonds are readily produced using ADMET polymerization techniques. Polyesters, polycarbonates, polyamides, and polyurethanes can be produced from aliphatic monomers with appropriate functional groups (Fig. 1.1). In these aliphatic polymers, the concentration of the linking groups (ester, carbonate, amide, or urethane) in the backbone greatly influences the physical properties. 

Polyesters are defined as polymers containing at least one ester linking group per repeating unit. They can be obtained by a wide range of reactions, the most important being polyesterifications between dibasic acids and diols or their derivatives (Scheme 2.1). 

LC polyesters belong to the class of thermotropic main-chain LCPs, which also comprises polymers such as polycarbonates, polyethers, polyphenylenes, polyester-imides, polymers containing azo- or azo V-oxide linking groups, some cellulose derivatives, and polypeptides such as po 1 y (y - be n zy 1 -1. - g 1 u tamate). Both from the academic and industrial points of view, polyesters are by far the most important representatives of this class of polymers. 

Fig. 2. The generic molecular structure of calamitic liquid crystals illustrating the semi-rigid core fragments, the positions of the end-groups (C and A), linking groups (B) and, possibly, laterally substituted groups (L)...

The approach in crystal engineering is to learn from known crystalline structures of, for example, minerals in order to design compounds with desired properties. Crystal engineering is considered to be a key new technology with applications in pharmaceuticals, catalysis, and materials science. The structures of adamantane and other diamondoids have received considerable attention in crystal engineering due to their molecular stiffness, derivatization capabilities, and their six or more linking groups [114-117]. 

Tse FW, Tse A, HiUe B, Horstmann H, Aimers W (1997) Local Ca + release from internal stores controls exocytosis in pituitary gonadotrophs. Neuron 18 121-132 Tu JC, Xiao B, Yuan JP, Lanahan AA, Leoffert K, Li M, Linden DJ, Worley PF (1998) Homer binds a novel proUne-rich motif and links group 1 metabotropic glutamate receptors with 1P3 receptors. Neuron 21 717-726... 

Bis-1,5-diaryl formazans generally absorb at longer wavelengths than mono formazans. The absorption maxima depend on the linking group. Formazans 188—191 (X = H) absorb at 485,470, 520, and 572 nm, respectively. The absorption maxima are also influenced by substituents. The formazan 190 (X = C02Et) absorbs at 510 nm whereas 191 (X = Me, OMe) absorbs at 585 and 606 nm, respectively.12,13 The absorption maximum of 192 shifts from 572 (R = H) to 585 and 602nm (R = Me, OMe), respec-... 

Identification of the iron linked groups in those proteins not bearing the porphyrin nucleus has proven to be a formidable task and even... 

Fig. 3. Schematic illustration of the iron linked groups in hemoproteins. The porphyrin ring containing the four pyrrole nitrogen atoms is shown as an elipsoid. The iron atom is 0.5 A out of the prophyrin plane in the direction of X (54). The axial ligands confirmed by crystallography (55, 56) are ...

The exact nature of levansucrase activity08 is not clear. It differs in certain respects from invertase, polymerase, fructosaccharase, and phosphorylase. Possibly the aldoside part of the substrate molecule is replaced by an enzyme-linked group, and partial decomposition of this levan precursor to aldose and ketose may furnish the energy necessary for levan synthesis. 

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