Alanine irradiated

Fig. 2.24 Contour plot of single crystal HYSCORE spectrum (a) and simulation (b) showing interaction between N of released ammonia and deaminated radical HsCCHCOO" in irradiated /-alanine. The figure is reproduced from [41] with permission from Elsevier...

HYSCORE has a higher sensitivity in the region of low nuclear frequencies than that of ENDOR spectroscopy. Single crystal measurements have therefore been applied to studies of nitrogen-containing paramagnetic species (nuclear Zeeman frequency v( " N) = 1 MHz at X-band) of interest in biochemical and fundamental applications. The local structure around the species may be obtained as discussed below for the radical H3CCHCOO in irradiated /-alanine. 

HYSCORE single crystal spectra of irradiated /-alanine in Fig. 2.24(a) show an interaction with nuclei (/ = 1) that is too weak to be resolved in CW-ESR and ENDOR spectra. As for I = Vi the nuclear transitions are identified most conveniently by a contour map of the type shown in Fig. 2.24. Software for the data processing to obtain the map is usually provided with commercial instruments. The interpretation is, however, complicated by the quadrupole interaction of the nucleus. The procedure to analyse the data employed in [41] was analogous to that applied for measurements of hfc and nqc tensors by ENDOR (Section 2.2.22). The analysis was supported by simulations (Fig. 2.24(b)) which also accounted for the lines observed in the left quadrant due to the low nuclear frequency of " N at X-band. The results were interpreted as due to a deaminated radical, H3CCHCOO , weakly interacting with the released ammonia group. 

Nishimura and coworkers57-59 studied the y-radiolysis of aqueous solutions of sulfoxide amino acids. Sulfoxide amino acids are the precursors of the flavors of onions (S-propyl-L-cysteine sulfoxide, S-methyl-L-cysteine sulfoxide and S-(l-propenyl)-L-cysteine sulfoxide) and garlic (S-allyl-L-cysteine sulfoxide). In studies on sprout inhibition of onion by /-irradiation it was found that the characteristic flavor of onions became milder. In the y-radiolysis of an aqueous solution of S-propyl-L-cysteine sulfoxide (PCSO)57,58 they identified as the main products alanine, cysteic acid, dipropyl disulfide and dipropyl sulfide. In the radiolysis of S-allyl-L-cysteine sulfoxide (ACSO) they found that the main products are S-allyl-L-cysteine, cysteic acid, cystine, allyl alcohol, propyl allyl sulfide and diallyl sulfide. The mechanisms of formation of the products were partly elucidated by the study of the radiolysis in the presence of N20 and Br- as eaq - and OH radicals scavengers, respectively. 

Figure 43 nOe buildup with respect to time, after irradiation of bound alanine methyl protons in ristocetin A-tripeptide complex for four different protons. (Reprinted from D. H. Williams et al., J. Am. Chem. Soc. 105, 1332, copyright (1983), with permission from The American Chemical Society, 1155 16th Street, N.W. Washington, D.C. 20036, U.S.A.)... 

The process was also applicable to microwave-assisted reactions. Thus, 140a, 140b, and 140 (R1 = z-Pr, R4 = indol-3-ylmethyl) were prepared in a two-step, one-pot synthesis in yields of 55%, 39%, 20%, and with 70%, 73%, 50% ee, respectively. In the first step anthranilic acid was reacted with the appropriate A-BOC-protected amino acid (glycine, L-alanine, and L-valine, respectively) in the presence of P(OPh)3 and dry pyridine under irradiation at 150 °C for 140a or conventional heating at 55 °C for 140b and 140 (R1 = z-Pr, R4 = indol-3-ylmethyl). In the second step the resulting... 

Figure 5.19 Formation of amino acids on ice surfaces irradiated in the laboratory (Nature Nature 416, 403-406 (28 March 2002) doi 10.1038/416403a-permission granted). Data were obtained from analysis of the room temperature residue of photoprocessed interstellar medium ice analogue taken after 6 M HCl hydrolysis and derivatization (ECEE derivatives, Varian-Chrompack Chirasil-L-Val capillary column 12 m x 0.25 mm inner diameter, layer thickness 0.12 pirn splitless injection, 1.5 ml min-1 constant flow of He carrier gas oven temperature programmed for 3 min at 70°C, 5°C min-1, and 17.5 min at 180°C detection of total ion current with GC-MSD system Agilent 6890/5973). The inset shows the determination of alanine enantiomers in the above sample (Chirasil-L-Val 25 m, single ion monitoring for Ala-ECEE base peak at 116 a.m.u.). DAP, diaminopentanoic acid DAH, diaminohexanoic acid a.m.u., atomic mass units.

Alanine-derived optically active A-propargylamide 22 and azobenzene-containing monomer 25 afford a co-polymer forming a helix. The azobenzene moiety isomerizes from trans-ioxm to cis-ioxm upon UV light irradiation, accompanying transition from helix to random coil. Then upon irradiation of visible light, the m-azobenezene moiety re-isomerizes into trans, while the polymer main chain keeps a random structure. This is presumably due to large steric repulsion around the azobenzene moiety to disturb recovery of a helical structure. 

Thus, glycine, as part of a peptide chain, was stereocontrol-alkylated by irradiation in the presence of toluene. The new asymmetric center was induced by (S)-alanine moieties in the peptide chain. 

Electron beam damage effects followed the general rule that molecular groups in intimate contact with the metal substrate and aromatic groups appear relatively stable. Thus in the monolayer, alanine, with a methyl group likely sticking out from the surface, was the only molecule found to be unstable. In multilayer films, only tryptophan with the aromatic indole group to stabilize the molecule was found to yield multilayers stable under electron beam irradiation. 

Figure 4 ESR spectra of DL-a-alanine and the precipitated CaC03 with vitamin C both irradiated to 700 mGy as welt as unirradiated measured at the optimal micro-wave power and modulation amplitude (Sato et al, 2004). 11...

The Cotton effects in mixed amino acidate/acetylacetonate complexes [Cr(acac)2L] (L = l-alanine, L-valine or L-phenylalanine) have been studied 774 absolute configurations were assigned by reference to the parent tris(acetylacetonate) complexes. Synthesis was achieved by the photolysis of mixtures of the amino acid and [Cr(acac)3]. The partial photoresolution of both cis- and irans-(l,l,l-trifluoro-2,4-pentanedionato)chromium has been accomplished by irradiation with circularly polarized light (5461 A) in chlorobenzene solution.775 The results indicated that both bond rupture and twist mechanisms were important. A number of other jS-diketonates have also been investigated.776... 

Several new amino acid residues were detected in irradiated poly-a, r glutamic acid, poly-D,h-alanine, and poly-irproline. The pH of the solution during irradiation affects the physical and chemical changes induced in the polyamino adds. 

D-Glutamic acid was not found in irradiated solutions of free L-glutamic acid, which agrees with the results of Sharpless et al. 83), who found no D-alanine in irradiated L-alanine. However, Evans 14) found that a major loss of L-leucine-4,5-T, methionine-T(G), and phenylalanine-4-T amino acids stored in aqueous solution occurs as a result of racemization. In these cases, it seems likely that the inversion is a result of indirect action brought about by 0-radiation from tritium decay. 

Only three new amino acids were found (by automatic amino acid analysis) in poly-D,L-alanine after irradiation in 0.1% solution in the absence of O2 with doses to 5 Mrads. All were in yields less than G = 0.02. The first was eluted before aspartic acid and was therefore acidic the second was eluted in the position of aspartic acid, and the third in the position of glycine. We have not been able to confirm the identities of these products by TLC because of the low yields. The products found by amino acid analysis could not account for the discrepancy between amide-like ammonia formed (G = 0.66) and alanine destroyed (G = 1.9). Aspartic acid is formed when alanine is irradiated in solution 26), and it is likely that the carboxylation reaction proposed by these authors also accounts for the observed aspartic acid formation in PDLA. 

The third example clarifies the special feature of singlet photochemistry. In contrast with 34 and 36, the a-ketoester 39 reacts from the singlet state if irradiated in the presence of naphthalene as triplet quencher. Despite the low diastereoselectiv-ity, the chirality of the alanine derivative 39 is completely conserved during cycli-zation to the pyrrolidines 40a and 40b. This approach has been called the memory effect of chirality [16]. 

Silica-supported Lewis acids are useful catalysts with microwave irradiation for conjugate additions. The silica-supported catalysts are obtained by treatment of silica with ZnCh [Si(Zn)], Et2AlCl [Si(Al)] or TiCl4 [Si(Ti)] [ 150-152], The Michael addition of methyl a-acetamidoacrylate (196) with indole (2) under Si(M) heterogeneous catalysis assisted by microwave irradiation afforded the alanine derivative 197 within 15 min and/or bis-indolyl 198, depending on the reaction conditions (Scheme 45) [153]. While the bis-indolyl product 198 is only formed when Si(Zn) was used as catalyst, the alanine derivative 197, as a single product is formed under thermal heating in a yield of 12%. The best yields were observed with Si(Al) (Table 5). The product 198 was obtained by elimination of acetamide followed by a-Michael addition between intermediate 199 with a second mole of indole. 

The Michael addition of methyl a-acetamidoacrylate (196) with pyrrole (1) under silica-supported Lewis acid (Si(M) Si(Zn), Si(Al) and Si(Ti)) assisted by microwave irradiation (MW) afforded the alanine derivatives 395 and 396 dependent on the reaction conditions (Scheme 81) [153]. Both MW and thermal activation for pyrrole gave only Michael product 396, whereas alanine derivatives 395, which are the a-Michael addition product, and 396 were observed with A1 and Ti-catalyst. This behavior shows that aluminium and titanium Lewis acids can form a new acceptor in an irreversible way. The Si(M) or p-TsOH catalyzed reactions of N-benzylpyrrolc 397 with the acrylate 196 under MW gave the product 398 as sole product. The reaction yield has been increased by using a catalytic amount of p-TsOH (Scheme 82). 

Nihira, Toraya and Fukui53 found that irradiation of holotryptophanase solutions with visible light led to rapid, pH-dependent loss of enzymatic activity. The apoenzyme was not inactivated under the same conditions therefore, the inactivation was PLP-sensitized. L-Tryptophan and l-alanine markedly decreased the rate of photoinactivation. From a plot of the inactivation rate versus pH, the pKa was found to be 7.2, which is close to the pKa of the imidazole group. Photoinactivation was accompanied by destruction of one histidine residue per subunit. No concomitant loss of tryptophan, tyrosine or methionine was detected, and it was suggested that tryptophanase contains an essential histidine residue near the active site. 

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