Glycine optical rotation

Fia. 12. (a) The thermal transition of RNase-A (0.3-0.4 mg/ml) at various pH values. The solvent was either dilute HC1 or 0.04 M glycine buffer for the two most alkaline curves. The change in molar absorbancy at 287 nm is shown as a function of temperature. From Brandts and Hunt (336). (b) The thermal transition as monitored by the change in optical rotation at 436 nm. The protein concentration was 1.9 mg/ml in 0.16 M KC1. From Hermans and Scheraga (337). (c) Comparison of the data from (b) and from a set comparable to (a) where both the absorbance and rotation values have been normalized to fractional conversion to the denatured form. From Hermans and Scheraga (337). 

Fig. 13 The change in calculated optical rotation of glycine as a function of inclusion of water molecules (QM or in form of a point-charge model) up to a cut-off distance from the solute. MD data to prepare plot taken from Kundrat and Autschbach [162]...

The residue rotation of L-proline can also be estimated from the reported optical rotations of relatively simple peptide derivatives of proline and glycine. 

If one analyzes the rotation of D-a-(methylenecyclopropyl)glycine (82) the optical activity must come from (at least) four sources. One rotation contribution is associated with the atomic asymmetry of the open-chain moiety (methylenecyclopropane being viewed as a ligand). On the other hand, optical activity will also be induced by the asymmetric carbon atom of the ring and the asymmetry in the electron density distribution of the exocyclic double bond system (with diastereotopic faces). Finally also helix optical activity may be operative. The example of 82 demonstrates the complexity of the optical rotation of an apparently simple cyclopropane derivative. Further discussions of optical rotations of similar compounds, therefore, will cling to only the qualitative level. 

After purification by counter-current distribution this peptidolipid was obtained as an amorphous powder of m.p. 230°C (dec.) and optical rotation [oi] + 9.5° (ethanol). Acid hydrolysis gave a mixture of fatty acids, the major components of which were identical with (+)-anteisotridec-3-enoic and isododec-3-enoic acids. The amino acids consisted of L-aspartic acid (3 moles), glycine (2 moles), L-tftreo-P-methyl-aspartic acid, L-proline, L-valine, D-pipecolic acid, L-tftreo-2,3-diaminobutyric acid (DAB,) and D- ryt/iro-2,3-diaminobutyric acid (DABJ (1 mole each). 

Globomycin was obtained as colourless crystals of m.p. 115°C and optical rotation [a]o 0° (chloroform). Its structure was established by means of the degradations depicted in Scheme 7. Four amino acids were obtained by acid hydrolysis, glycine, serine, a//othreonine and alio-isoleucine. y4//othreonine and a//oisoleucine were identified by comparison with authentic samples. It was also observed that in the mass spectra of the trimethylsilyl derivatives of threonine and a//othreonine, the relative intensities of the ions m/z 218 and 219 were significantly different and could be used for identification. 

Because of the two hydrogen atoms at a carbon, glycine is not optically active. It is the smallest amino acid, rotates easily, and adds flexibility to the protein chain. It is able to fit into the tightest spaces, e.g., the triple heUx of collagen. As too much flexibihty is usually not desired, as a structural component it is less common than alanine. 

With the exception of glycine all amino acids which are constituents of proteins rotate the plane of polarized light. They are optically active because their a-carbon atom is a chiral center. All have the l, or according to a more contemporary designation the S-configuration, a notable exception being (R)-cysteine (see below). Two amino acids, threonine and isoleucine contain a second chirality center located in their side chains. As indicated in Table 1 the configurations are R in Thr and S in He. 

By recycle chromatography we tried to improve the resolution 500 mg of DL-2-phenyl glycine (VII) were eluted from polymer 11 with O.lA HCl. The optically active fractions were collected just up to the fraction with the highest negative rotation value, evaporated and submitted to several adsorption-elution chromatographic cycles. Afther the fifth cycle the optical purity of the first three fractions was 95%, 73% resp. 56% and an optical total enrichment of 19% was achieved. 

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