L-a-alanine

Figure 14.8 Typical phase portraits of crystals with different effective thermodynamic potentials ((a) TGS-crystal, (b) L-a-alanin doped TGS-crystal, (c) Rochelle salt)...

N-Carbobenzyloxy-L-a-alanine was condensed with linear polyethylenimine in the presence of DCC to give polymer 48, Cbz-Ala-PEI. The protective group of polymer 48 was removed by HBr in acetic acid to yield the grafted polymer 49, HBr-Ala-PEI. This polymer was found to be grafted almost quantitatively as determined by elemental analysis and the NMR spectrum. The IR spectrum suggested the presence of an amide bond. 

The obtained L-a-alanine grafted polymer 49 was further reacted with p-nitrophenyl ester-containing bases, according to the procedure mentioned earlier. From the NMR and UV spectra, the polymers obtained were found to contain about 98% adenine units 50 (A-Ala-PEI) and about 100% thymine units for polymer 51 (T-Ala-PEI). 

Glowiak, T., Legendziewicz, I., Dao, C.N., and Huskowska, E. (1991) Absorption, luminescence and crystal structure studies of dysprosium compound with L-a-Alanine [Dy(L-a-AlaH)(H20)6]Q3. Journal of the Less Common Metals, 168 (2), 237-248. 

C18H10O3 2-(3-oxo-1-indanylidene)-1,3-indandione 1707-95-5 25.00 1.2968 2 30618 C18H17N04 fmoc-L-a-alanine 35661-39-3 23 Tili 2... 

One of the most promising dosimeters, which may under careful preparation and calibration, qualify as a reference dosimetry system, is L-a alanine as measured by EPR spectrometry (Regulla et al., 1993). It is also proving to be useful as a transfer dosimeters, as shown by its application in the IAEA International Dose Assurance Service (IDAS) (Nam and Regulla, 1989) and in the reference dosimetry service to industry by the National Physical Laboratory (NPL). 

Problem 20.13. Draw o-a-alanine and L-a-alanine using the convention described in Problem 17.18. 

Problem 20.14. Show that the following structure is that of the L-a-alanine ... 

Ans. Follow Rule 2 in Sec. 17.2 Exchange the positions of any two substituents attached to the stereocenter. If an even number of exchanges is needed to make two structures identical, the two structures are the same compound. If an odd number of exchanges is needed to make two structures identical, the two structures represent a pair of enantiomers. The given structure is L-a-alanine since two exchanges are needed to convert it to the L-a-alanine structure of Problem 20.13 ... 

The method employed in ESR dosimetry is based on the fact that the free radicals formed by irradiation of organic and inorganic solid substances can be stable up to several years as for instance in the L-a-alanine amino acid. To be suitable for ESR dosimetry several additional properties are desirable [4] ... 

The line-width can have a strong influence on the sensitivity as shown in Fig. 9.3 for the ESR spectra of L-a-alanine and ammonium dithionate irradiated to the same dose. EHie to its sulfur content the latter material is not tissue-equivalent, however, which makes it unsuitable for medical applications. 

Fig. 9.3 ESR spectra of ammonium dithionate (above) and L-a-alanine (below) irradiated and recorded under the same conditions. The figure is reproduced from [M. Damlzcuk et al. Spectrochim. Acta A 69, 18 (2008)] with permission from Elsevier...

L-a-alanine, H2NCH(CH3)COOH, is the most commonly used material for ESR dosimetry. Alanine has excellent characteristics for dosimetric purposes in several respects [4] (1) high free radical yield (G-value), (2) short relaxation times so that high microwave power can be applied, (3) linear ESR response with radiation dose up to 5-10" Gy, (4) high stability of the radiation induced free radicals so that the dosimeter can be kept as a document of the radiation dose, (5) tissue equivalence for medical and biological applications, (6) non-destructive read-out of dosimeter so that the dose accumulation at repeated exposures can be monitored. 

X-irradiated polycrystalline L-a-alanine yields the ESR spectrum at room temperature shown in Fig. 9.5. 

Fig. 9.5 X-band ESR spectra of L-a-alanine powder at room temperature. Exp. experimental powder spectrum X-irradiated to 60 kGy, Sim. reconstructed powder spectrum due to three radicals, Rl, R2, R3, with parameters determined by single crystal ENDOR measurements and with relative intensities 0.589 0.335 0.076, see text for assignment. Spectra are adapted from [M.Z. Heydari et al. J. Phys. Chem. A 106, 8971 (2002)] with permission from the American Chemical Society...

L-a-alanine has been employed as an ESR dosimeter since 1962 [26], Regulla et al. [7, 27] have reported detailed studies on its dosimetric properties. It is the most commonly used material in the field of ESR dosimetry being accepted by the International Atomic Energy Agency (IAEA) [28] and other agencies as a secondary reference and transfer dosimeter for high (industrial) dose irradiation. 

CAS 56-41-7 EINECS/ELINCS 200-273-8 Synonyms Alanine (INCI) a-Alanine L-a-Alanine 1,2-Aminopropanoic acid 2-Aminopropionic acid... 

L-a-Alanine. See L-Alanine P-Alanine, N-acetyl-N-butyl-, ethyl ester. See Ethyl butylacetylaminopropionate P-Alanine, N-(2-aminoethyl)-N-[2-(2-carboxyethoxy) ethyl]-, N-coco acyl derive., 2,2 -iminobisethanol salts. See DEA-cocoamphodipropionate D-Alanine, N-benzoyl-N-(3-chloro-4-fluorophenyl)-, isopropyl ester. See Flamprop-m-isopropyl... 

However, the following suggested method can be used a reference curve can be obtained by measuring the pKo values of N-tosyl L-a-alanine, chosen as a model for PLL, in various acetone-water mixtures. The pK values of PLL in these mixtures can... 

Piseber, Ber., 1893, 86,465. Hippi l-a-alanine (Hippvnfi-l-aminopro-pionie add)... 

The rate constants ket for the electron-transfer reaction determined from the triplet polarization are ket = 3.9 x 10 M s for a-glycine, ket = 3.3 x 10 M s for L-a-alanine and ket = 2.3 x 10 M s for a-aminoisobutyric acid. The decarboxylation reaction is a first-order decay with the rate constants kdecarb =... 

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