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The paper deals with an analysis of the available crystal structure data related to proline compounds so as to obtain information about bond lengths, bond angles, and the conformation of the pyrrolidine ring. The interesting results are: 1. The atoms Cβ, Cα, N, and Cs are nearly coplanar, with the torsion angle 0 about the Cα - N bond varying from about -15° to -15°. The Cγ atom is displaced from this plane, either up or down, so that the ring exists in one of the two puckered conformations, designated A and B. Conformation A is characterized by negative and may be termed Cγ-exo when referred to the displacement of the carbonyl carbon C. Conformation B has positive x l and is Cγ-endo; Cγ-exo is slightly preferred over C-endo, although both conformations occur simultaneously in some crystal structures with partial probabilities. In the other structures, the non-occurring position for C y is found to be disallowed by intermolecular contacts. The proline conformations observed correspond to the 'envelope' type of conformation of the cyclopentane ring. In peptides, the three bonds at N are nearly coplanar, and the torsion about N- Cα bond is nearly - 60°. 2. The observed ranges of (x 1 , x 2 , x 3 , x 4 ) are (0 to –30°, 15 to 50°, –15 to - -30°, 5 to 25°) for conformation A and (20 to 35 0 , -30 to - 40 0 , 20 to 35°, 5 to -20°) for conformation B; for θ and φ the ranges are -15° to -15°, -45 to -75°. The bond lengths and bond angles are not influenced by the conformation of the ring, unlike ribose.

The paper deals with the nature of the intermolecular forces and the laws governing these, which play an important part in the stability of molecular crystals and in the conformation of biological macromolecules. The method of contact criteria which give the disallowed ranges of conformations is briefly discussed and then the energy criteria are considered. Intermolecular potential functions for non-bonded interactions (both van der Waals and repulsive), electrostatic forces, hydrogen bonds, and hydrophobic interactions are discussed, followed by a treatment of intramolecular distortions of bond lengths, bond angles, and torsional angles. The last of these are important for the study of conformations. The possibility of non-planar distortion of peptide units is specially discussed. Application of these ideas to the calculation of the structures of molecular crystals is indicated.

The electrospray ionisation (ESI) of selected hemiterpenoid and dimeric coumarin derivatives and their subsequent fragmentation using an ion trap mass spectrometer are reported and discussed. Sequential product ion fragmentation experiments (MS(n)) were performed in order to elucidate the degradation pathways for these compounds. The results illustrate that the observed characteristic fragmentation patterns are of considerable utility in the application of ESI mass spectrometry to the characterisation of this class of compounds.

The possible encapsulation of the interstellar abundant H3+ ion inside a C60 fullerene cage has been examined by using the Hartree-Fock (HF) and the second order Moller-Plesset perturbation (MP2) methods both with the 6-31G** basis set. It was found that H3+ forms various stable endohedral complexes inside the cage. Six configurations have been examined among which four were stable compared with the separated initial species, the dissociated H2 + H+ inside the cage being the most stable. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Feeding experiments with doubly labelled 4-methoxy-3-prenyl-2-quinolones have shown that the biosynthesis of kokusaginine 8 and maculosidine 9 in P. trifoliata also involves a myrtopsine-like derivative. Contrary to our proposed pathways, the biosynthesis of hemiterpenoid olefines such as ptelefoline 15, in the same plant species, does not appear to involve directly platydesminium salt but possibly also a myrtopsine derivative. On the basis of the results obtained, alternative biosynthetic pathways to these alkaloids are discussed.

— Detection of triplet-triplet energy transfer in an aqueous solution of P-trypsin is reported. This conclusion is based on the observation that a light excited phenolate side chain can sensitize the destruction of an adjacent indole side chain. The role that the indole triplet might play in the UV-induced photolysis of /l-trypsin is also investi-gated. The results suggest that the UV (309 nm)-induced inactivation of P-trypsin is not caused by indole ring destruction but by the disruption of disulfide bonds without thiol formation.

Fatigue failures of transmission line conductors are known to occur close to the suspension clamps. The causes of such failures are known to be due to high static stresses combined with dynamic stresses resulting from vibration. The overall stress in the aluminium strands of a conductor could be limited by reducing the static bending stress near the clamps. Passive protective devices such as neoprene lining, damping shims introduced in the suspension clamps would bring down the stress level, thereby increasing the service life of conductors. Results of tests conducted on a laboratory span are brought out in this paper. The experimental results reveal that neoprene lining and damping shims introduced in the suspension clamp would be very effective in bringing down the static bending stress and thus the overall stress level.

A laboratory isolate of A. niger v. Tieghem developed considerable quantities of exocellular amylolytic enzymes capable of effecting liquefaction as well as saccharification of starch to dextrose. Both crude and partially purified enzyme preparations were highly thermophilic, with temp. optima at 60-68 degree C, and max. enzyme production at 35-40 degree C. The culture filtrate showed two pH optima for dextrinogenic (alpha-amylose) activity at pH 5.0 and 6.0, and one for saccharifying (amylo-glucosidase) activity at pH 4.6. Ca-2-+ ions were essential for alpha-amylase activity, especially at the higher pH. Electrophoretic studies of the culture filtrate revealed 3 major proteins, two exhibiting alpha-amylase and one amylo-glucosidase activity. The concerted action of these enzymes on a 16% slurry of corn and tapioca starch at 60% produced a sharp fall in viscosity within 15 min. Paper chromatography of the hydrolysate revealed considerable amounts of glucose. The enzyme system has considerable potential for conversion of starch to glucose, and eliminates the preliminary liquefaction by acid hydrolysis or bacterial alpha-amylase. [From En summ.]

The nature of thermophilic amylolytic enzymes produced by a strain of Aspergillus niger Van Tieghem was influenced by media composition. While glucose, maltose, dextrin and soluble starch induced the production of amyloglucosidase, pectin and sodium polypectate almost exclusively induced the formation of α-amylase. Alkali ions suppressed the formation of amyloglucosidase. NH4NO3, (NH4)2HPO4 and (NH4)2C4H4O6 served as good inorganic nitrogen sources, while casein, groundnut protein and corn steep liquor served to a similar capacity as nitrogen sources from organic material. Deletion of the growth factors pyridoxine-hydrochloride and inositol suppressed enzyme production, while the absence of riboflavin had the opposite effect.

Using potential energy formulas for variation of bond angles and for ω-distortion, the conformation of minimum energy for the cis form of the peptide unit has been worked out. This agrees very well with the corresponding set of atoms in the crystal structure of Leu-Pro-Gly and the dimensions of a standard cis peptide unit are given based on these. The conformational (ϕ,Ψ) map for a cis peptide unit has been worked out from contact criteria, both for a pair of linked units as well as for-helices having constant (ϕ,Ψ). The small allowed region of the helical map contains the conformation experimentally observed for poly-L-proline I.

A conformational study of poly-L-serine has shown that it can exist in the left-handed α-helical form. A study of a pair of peptide units with the serine sidegroup attached to the α carbon atom linking the two units showed that OH O hydrogen bonds between the OH group of the side chain and a carbonyl oxygen of the first peptide group in the backbone can occur in two regions of ϕ, namely, ϕ = 15°-30° for χ1 = 300° and for ϕ = 225°-230° for ϕ = 60°. The latter is close to a possible left-handed helix of poly-L-serine, stabilized by NH O hydrogen bonds. From a study of contact criteria, the best conformation for this helix is found to be ϕ = 227°, Ψ = 238°, χ1 = 65° which has n = 3.65, h = 1.51 A. The NH O hydrogen bond has a length of 2.90 A. (6°) and the OH O hydrogen bond is of length 2.60 A. (0°). There are no other bad short contacts in the structure. The cylindrical coordinates of the atoms, as well as a perspective view of the structure arc given in this paper.

Empirical energy calculations on cyclo-Gly-X with X- Phe, Tyr, Val, and Leu as a function of the side-chain torsion angles X indicate that the conformation of minimum energy are characterized by $X^1$ = 60 °, $X^2$ = 90 ° for Phe and Try, $X^1$ = -60 ° for Val and $X^1$ = -60 °, $X^2$ = 180 ° and $X^1$ = 60 ° and $X^2$ = 150 ° for Leu. The minimum energy conformation of cyclo-Gly-Phe and cyclo-Gly-Val have the side chains of Phe and Val stacked over the poperazinedione ring as suggested by NMR and found for cyclo-Gly-Tyr crystal structure. In contrast, the Leu side chain is expected to exist in an extended or a quasi-folded form.