Tetram

Wliat are the structural dynamics of the tetramer as a whole The haemoglobin bound to O2 (Flb02) is not photoactive, so the CO adduct, FlbCO, is used instead. 

Cruzan J D, Braly L B, Liu K, Brown M G, Loeser J G and Saykally R J 1996 Quantifying hydrogen bond oooperatively in water VRT speotrosoopy of the water tetramer Science 271 59-62... 

The avidin-biotin complex, known for its extremely high affinity (Green, 1975), has been studied experimentally more extensively than most other protein-ligand systems. The adhesion forces between avidin and biotin have been measured directly by AFM experiments (Florin et al., 1994 Moy et al., 1994b Moy et al., 1994a). SMD simulations were performed on the entire tetramer of avidin with four biotins bound to investigate the microscopic detail of nnbinding of biotin from avidin (Izrailev et al., 1997). 

Crown 4 and 18 crown 6 are a cyclic tetramer and hexamer respectively of repeat mg —OCH2CH2— units they are polyethers based on ethylene glycol (HOCH2CH2OH) as the parent alcohol... 

Oligomer (Section 14 15) A molecule composed of too few monomer units for it to be classified as a polymer but more than in a dimer trimer tetramer etc Oligonucleotide (Section 28 6) A polynucleotide containing a relatively small number of bases Oligosaccharide (Section 25 1) A carbohydrate that gives three to ten monosacchandes on hydrolysis Optical activity (Section 7 4) Ability of a substance to rotate the plane of polanzed light To be optically active a sub stance must be chiral and one enantiomer must be present in excess of the other... 

Metaldehyde [9002-91-9] a cycHc tetramer of acetaldehyde, is formed at temperatures below 0°C in the presence of dry hydrogen chloride or pyridine—hydrogen bromide. The metaldehyde crystallizes from solution and is separated from the paraldehyde by filtration (48). Metaldehyde melts in a sealed tube at 246.2°C and sublimes at 115°C with partial depolymerization. 

Acryhc esters dimerize to give the 2-methylene glutaric acid esters catalyzed by tertiary organic phosphines (37) or organic phosphorous triamides, phosphonous diamides, or phosphinous amides (38). Yields of 75—80% dimer, together with 15—20% trimer, are obtained. Reaction conditions can be varied to obtain high yields of trimer, tetramer, and other polymers. 

A practical synthesis has been claimed for the cycHc tetramer of formaldehyde, 1,3,5,7-tetraoxane [293-30-17, which has a boiling point of 175°C and a melting point of 112°C (155). It has found some use in textde treatment in Japan. 

These reactions are usehil for the preparation of homogeneous difunctional initiators from a-methylstyrene in polar solvents such as tetrahydrofuran. Because of the low ceiling temperature of a-methylstyrene (T = 61° C) (26), dimers or tetramers can be formed depending on the alkaU metal system, temperature, and concentration. Thus the reduction of a-methylstyrene by sodium potassium alloy produces the dimeric dianionic initiators in THF (27), while the reduction with sodium metal forms the tetrameric dianions as the main products (28). The stmctures of the dimer and tetramer correspond to initial tail-to-tail addition to form the most stable dianion as shown in equations 6 and 7 (28). 

Fig. 1. Stmctures of alkyllithium tetramers and hexamers (a) tetrahedron of lithium alkyl groups (b) arrangement of alkyl groups around octahedron of...

The higher, long-chain dimers as weH as the tetramer dehydroacetic acid are far more stable and can be handled safely. The alkylketene dimers (AKDs) are shipped to the paper industry in tank tmcks in the form of ready-to-use aqueous emulsions with a total soHds content of 12—25% and a guaranteed shelf life of 30 days, as they have good hydrolytic stabHity. In this form they are not combustible Hquids, and are Hsted in the Canadian Domestic Substances List. 

Methyllithium. MethyUithium [917-54 ] CH Li, crystallizes from benzene or hexane solution giving cubic crystals that have a salt-hke constitution (128). Crystalline methyllithium molecules exist as tetrahedral tetramers (129). Solutions of methyllithium are less reactive than those of its higher homologues. Methyllithium is stable for at least six months in diethyl ether at room temperature. A one-molar solution of methyllithium in tetrahydrofuran (14 wt %) and cumene (83 wt %) containing 0.08 M dimethyknagnesium as stabilizer loses only 0.008% of its activity per day at 15°C and is nonpyrophoric (117). 

The abihty of iron to exist in two stable oxidation states, ie, the ferrous, Fe ", and ferric, Fe ", states in aqueous solutions, is important to the role of iron as a biocatalyst (79) (see Iron compounds). Although the cytochromes of the electron-transport chain contain porphyrins like hemoglobin and myoglobin, the iron ions therein are involved in oxidation—reduction reactions (78). Catalase is a tetramer containing four atoms of iron peroxidase is a monomer having one atom of iron. The iron in these enzymes also undergoes oxidation and reduction (80). 

Nonene, or propylene tetramer, is used to alkylate phenol, which is subsequently ethoxylated to produce nonylphenol ethoxylate, an efficient, rehable industrial surfactant. 

Linear a1ky1hen2ene (LAB) is produced from a-olefins and internal linear olefins. Branched olefins such as propylene tetramer are used... 

The feedstock, usuaHy consisting of propylene and butylenes (various isomers of C Hg) from cracking processes, may even consist of selective olefins for dimer, trimer, or tetramer production ... 

In equation 7, ttimer radical (4) is produced when (3) dissociates. Whenever (4) couples with the other product of equation 7, ie, the 2,6-dimethylphenoxy radical, the tetramer is produced as described. These redistribution reactions of oligomers that proceed by ketal formation and subsequent dissociation ultimately generate terminal quinol ethers which enolize to the more stable terminal phenol (eq. 8). 

---