Biphenyl model compound

This biphenyl model compound was shown to possess the so-called primary optical specificity of a-chymotrypsin. That is, only the enantiomer related to L-phenylalanine was hydrolyzed by the enzyme. Generally speaking, there are three more levels of specific substrate recognition in enzyme catalysis. Let us consider a peptide bond in a polypeptide chain. The lateral side chain R2 is responsible for the normal specificity of the enzyme. For a-chymotrypsin, R2 is an aromatic side chain and the hydrophobic cavity a aromatic hole in the active center is there to accommodate the amino acid to be recognized by the enzyme. This is referred to as the primary structural specificity. 

Fig. 4.4. Dreiding stereomodels showing that the D-configuration of Niemann s compound can be superimposed on Belleau s biphenyl model compound.

Model compound studies were also carried out in MeOH/KOH, and the results are shown in Table VI. Phenanthrene and biphenyl were quantitatively recovered unchanged by the reactions, and bibenzyl was recovered in 95% yield, with small amounts of toluene observed. Anthracene and diphenyl ether, on the other hand, were converted respectively to 9,10-dihydroanthracene and a mixture of polymethyl-phenols similar to that observed in the work with coal. The cleavage of diphenyl ether via hydrogenolysis should yield both benzene and phenol as products we saw no benzene in our study, and our... 

First, we examined the efficiency of the initiation process. A solution of buthyllithium was added to a THF solution of 7 at -70°C. The color of the solution turned to red immediately and a strong ESR signal was observed with a well separated hyperfme structure. The observed radical species was identified as the anion radical of 2-butyl-l,l,2,2-tetramethyldisilanyl-substituted biphenyl by computational simulation as well as by comparison with the spectra of a model compound. The anion radical should be a product of a single electron transfer (SET) process from buthyllithium to the monomer. Since no polymeric product was obtained under the above-mentioned conditions, the SET process is an undesired side reaction of the initiation and one of the reasons why more higher molecular weight polymer was observed than expected. ... 

Several attempts have been made to investigate anaerobic pathways for desulfurization. Mixed cultures of sulfate-reducing bacteria were used to desulfurize model compounds, thiophenes [12], organosulfides [12,13], and petroleum preparations [14-16], Production of hydrogen sulfide and biphenyl from DBT has been demonstrated in other studies [17-22],... 

Despite the strong interest in the correlation between torsion angle and transport properties, suitable model compounds enabling the systematic variation of the torsion angle in biphenyl systems have not been realized so far, and the role of geometric and electric effects of the substituents is still being actively discussed [48, 72, 74, 271, 277]. 

The reason for the lower liquid crystalline (LC) temperature of the BB model compound seems to be that the biphenyl unit of this compound was adopting a twisted structure in the LC state [26], Therefore, we prepared various polyarylates containing the BB unit and determined their thermal properties and the moduli of the as-spun fibers, as shown in Table 19.3. 

Aromatic Ring Cleavage of Phenolic 0-0-4 Substructure Model Compounds by Laccase. When vanillyl alcohol was used as a substrate, only biphenyl formation (C5-C5 linked) occurred and no evidence for the formation of any ring-opened products was obtained (26). Hence, we also examined the effect of laccase on the sterically hindered 4,6-di-<-butylguaiacol substrate 50, as it would be unlikely to undergo such free-radical coupling reactions... 

Masse, R., Messier, F., Peloquin, L., Ayotte, C. Sylvestre, M. (1984). Microbial biodegradation of 4 chlorobiphenyl, a model compound of chlorinated biphenyls. Applied and Environmental Microbiology, 47, 947-51. 

Drumond M, Aoyama M, Chen C-L, Robert D (1989) Substituent effects on C-13 chemical shifts to aromatic carbons in biphenyl type lignin model compounds J Wood Chem Technol 9 421-441... 

For lignin substructures containing a carbon substituent in the aromatic C-5 position, or for stilbenes originating from phenylcoumaran structures, the oxidative degradation leads to the formation of isohemipinic acid methyl ester (4) (Fig. 6.3.2, R=CH3). However, Gellerstedt and co-workers have shown that model compounds of the biphenyl type also give rise to isohemipinic acid in addition to the expected bis-vanillic acid structure (7). The reason seems to be incomplete alkylation (pH 11, 24 h) with the result that the substrate is alkylated at only one of the available positions. To achieve a more complete alkylation, it is necessary to increase the pH to 13 or alternatively, to extend the alkylation time to 84 h. In both cases, the yield of the bis-vanillic acid structure is substantially increased as shown in Table 6.3.1 nevertheless, the concomitant formation of isohemipinic acid cannot be completely avoided. 

E. A., and Chen, C. L. (1992) Biphenyl-type lignin model compounds Synthesis and car-bon-13 NMR substiment chemical shift additivity rule. Holzforschung 46(2), 127-134. 

Drumond, M., Aoyama, M., Chen, C. L., and Robert, D. (1989) Substituent effects on carbon-13 chemical shifts of aromatic carbons in biphenyl type bgnin model compounds. J. Wood Chem. Technol. 9(4), 421 442. 

Biphenyl coupling occurs to some extent on cupric oxide oxidation of lignin model compounds [55,56]. This indicates that the value derived from permanganate oxidation studies is slightly too high. On the basis C NMR examinations, Drumond et al. [57] arrived at a higher value for the frequency of biphenyl units (24-26%). The accuracy of this estimate can be questioned, since no separate signals from biphenyl units can be discerned in the spectra. 

MWL sample. The determination relies on the correctness of a number of assumptions. This implies that about 8% biphenyl units may be present in dibenzodiox-ocin structures. Model compound studies [46,60] indicate that the biphenyl units in dibenzodioxocin structures are included in the estimates of biphenyl units by NMR... 

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