Lipids of some thermophilic fungi

Total lipid content in the thermophilic fungi—Thermoascus aurantiacus, Humicola lanuginosa, Malbranchea pulchella var.sulfurea, andAbsidia ramosa—varied from 5.3 to 19.1% of mycelial dry weight. The neutral and polar lipid fractions accounted for 56.4 to 80.2% and 19.8 to 43.6%, respectively. All the fungi contained monoglycerides, diglycerides, triglycerides, free fatty acids, and sterols in variable amounts. Sterol ester was detected only inA. ramosa. Phosphatide composition was: phosphatidyl choline (15.9–47%), phosphatidyl ethanolamine (23.4–67%), phosphatidyl serine (9.3–17.6%), and phosphatidyl inositol (1.9–11.9%). Diphosphatidyl glycerol occurred in considerable quantity only inH. lanuginosa andM. pulchella var.sulfurea. Phosphatidic acid, detected as a minor component only inM. pulchella var.sulfurea andA. ramosa, does not appear to be a characteristic phosphatide of thermophilic fungi as suggested earlier. The 16∶0, 16∶1, 18∶0, 18∶1, and 18∶2 acids were the main fatty acid components. In addition,A. ramosa contained 18∶3 acid. Total lipids contained an average of 0.93 double bonds per mole of fatty acids, and neutral lipids tend to be more unsaturated than phospholipids.

Sterochemical studies on cyclic peptides-VIII. Conformational analysis of hydrogen bonded cyclohexaglycyl molecule with a centre of inversion symmetry

A study on the conformational aspects of cyclo-hexaglycyl having inversion symmetry has been made. The cyclic backbone has been assumed to have two internal 4→1 types of NH... O hydrogen bonds. This molecule has been found to take up two types of conformations designated asA* andB* having nearly the same energy values. The theoretical conformations have been compared with the conformations of cyclohexaglycyl hemihydrate observed in the crystal structure. Two molecules with an approximate inversion symmetry are close to the conformation of the typeB* and two other molecules with exact inversino symmetry correspond nearly to the typesB* andA*. comparison with the theoretically possible conformations of cyclohexaglycyl molecule with 2-fold symmetry has been made. The preference of inversion symmetry and preferred ranges ofψ for glycyl molecules is discussed.

Effect of temperature, pressure and additives on pyrolysis of polystyrene peroxide

Some aspects of the pyrolysis of polystyrene peroxide (PSP) have been examined. Low-temperature decomposition studies at 60°C and 70°C have been carried out to elucidate the ageing behaviour of PSP. The exothermic decomposition was found to be complete in 44 h at 70°C suggesting that all peroxide bonds have broken. Enthalpy measurements of the aged samples were carried out as a function of storage time. Ageing was also followed by infrared spectroscopy, and the intensity of the peroxide absorption around 1050 cm−1 was found to decrease with ageing time. Benzaldehyde formed as a result of PSP pyrolysis is readily converted into benzoic acid, which crystallizes during the ageing process. Pyrolysis—gas chromatographic studies have shown that up to 450°C the basic decomposition mechanism (i.e., the formation of benzaldehyde and formaldehyde as the major products) does not change. No effect of pressure on the decomposition exotherm in differential thermal analysis was observed, suggesting that peroxide composition involves only condensed phase reactions. Hydroquinone, p-aminophenol and cadmium sulphide were found to retard the thermal decomposition of PSP, suggesting that these compounds would be potential antioxidants for polymers.

Zeeman effect of NQR in 4,6-dichloropyrimidine and 6-chloro 2,4-dimethoxypyrimidine

Zeeman (35Cl) NQR studies in polycrystalline samples of 4,6-dichloropyrimidine and 6 chloro 2,4 dimethoxypyrimidine show that the asymmetry at the four chemically inequivalent chlorine sites in the former is about 10%, while in the latter (one line) the asymmetry is almost zero. Using a valence-bond picture, C-Cl bonds in 4,6-dichloropyrimidine have been characterised, and the results are also compared with those in a corresponding benzene compound using a simple molecular orbital calculation. The axial symmetry of C-Cl bond in the second compound has been attributed to mesomeric effects.

Conformation of polypeptide-chains containing both l-residues and D-residues .2. Double-helical structures of poly-ld-peptides

Polypeptides with alternating L- and D-amino acid residues can take up stereochemically satisfactory coaxial double-helical structures, both antiparallel and parallel, which are stabilized by systematic interchain NH O hydrogen bonds. Semiempirical energy calculations over allowed regions of conformational space have yielded the characteristics of these double-helices. There are four possible types of antiparallel double-helices - A3, A4, A5 and A6, with n, the number of LD peptide units per turn, around 2.8, 3.6, 4.5 and 5.5 respectively, while for the parallel double-helices there are two types, P3 and P4, having similar helical parameters as in A3 and A4. The hydrogen-bonding scheme restricts the pitch in all the models to the narrow range of 10.0 to 11.5 Å. All these helices have large central cores whose radii increase proportionately with n. In this respect, A3 and A4 are suitable models for the structure of gramicidin A. In terms of their relative energies, antiparallel double-helices are marginally more stable than those with parallel strands. Our results indicate that the energy differences amongst the members in the antiparallel family are not significant and thus provide an explanation for the polymorphism reported for poly(γ-benzyl-LD-glutamate).

Studies on the metabolism of β-carotene and apo-β-carotenoids in rats and chickens

1. (1) The relative abilities of the various cell fractions of rat and chicken liver to oxidize and reduce retinal and 8'- and 12'-apo-β-carotenal were investigated and it has been shown that, while retinal is exclusively oxidized by the soluble fraction, the apocarotenals are mostly oxidized by the particulate fractions of the homogenate. 2. (2) Addition of NAD+ or NADP+ markedly activated the oxidation of the apocarotenals, but not of retinal by the particulate fractions. 3. (3) Considerable amounts of retinal and 8'-, 10'- and 12'-apo-β-carotenal were isolated from the intestine of chickens fed β-carotene and these apocarotenoids were conclusively identified. 4. (4) Significant amounts of 8'-, 10'- and 12'-apo-β-carotenoic acids were isolated from the intestine of rats given 8'-apo-β-carotenal and these apocarotenoic acids were also conclusively identified. 5. (5) In the light of these observations it is suggested that during conversion to vitamin A, the β-carotene molecule is simultaneously attacked by the dioxygenase at several double bonds, the primary attack being at the central double bond and a tentative scheme for the mechanism of conversion is proposed.

Conformations of Heterochiral and Homochiral Proline-Pseudoproline Segments in Peptides: Context Dependent Cis-Trans Peptide Bond Isomerization

The pseudoproline residue (Psi Pro, L-2,2-dimethyl-1,3-thiazolidine-4-carboxylic acid) has been introduced into heterochiral diproline segments that have been previously shown to facilitate the formation of beta-hairpins, containing central two and three residue turns. NMR studies of the octapeptide Boc-Leu-Phe-Val-(D)Pro-Psi Pro-Leu-Phe-Val-OMe (1), Boc-Leu-Val-Val-(D)Pro-Psi Pro-Leu-Val-Val-OMe (2), and the nonapeptide sequence Boc-Leu-Phe-Val-(D)Pro-Psi Pro-(D)Ala-Leu-Phe-Val-OMe (3) established well-registered beta-hairpin structures in chloroform solution, with the almost exclusive population of the trans conformation for the peptide bond preceding the Psi Pro residue. The beta-hairpin conformation of 1 is confirmed by single crystal X-ray diffraction. Truncation of the strand length in Boc-Val-(D)Pro-Psi Pro-Leu-OMe (4) results in air increase in the population of the cis conformer, with a cis/trans ratio of 3.65. Replacement of Psi Pro in 4 by (L)Pro in 5, results in almost exclusive population of the trans form, resulting in an incipient beta-hairpin conformation, stabilized by two intramolecular hydrogen bonds. Further truncation of the sequence gives an appreciable rise in the population of cis conformers in the tripeptide piv-(D)Pro-Psi Pro-Leu-OMe (6). In the homochiral segment Piv-Pro Psi Pro-Leu-OMe (7) only the cis form is observed with the NMR evidence strongly supporting a type VIa beta-turn conformation, stabilized by a 4 -> 1 hydrogen bond between the Piv (CO) and Leu (3) NH groups. The crystal structure of the analog peptide 7a (Piv-Pro-Psi(H,CH3)Pro-Leu-NHMe) confirms the cis peptide bond geometry for the Pro-Psi(H,CH3)pro peptide bond, resulting in a type VIa beta-turn conformation.

Conformational Choices for the Stereochemically Constrained gamma-Amino Acid Residue Gabapentin: Theoretical Studies and Correlation With Experimental Results

Gabapentin (1-aminomethylcyclohexaneacetic acid, Gpn) is an achiral, conformationally constrained gamma amino acid residue. A survey of available crystal structures of Gpn peptides reveals that the torsion angles about the C-gamma-C-beta (theta(1)) and C-beta-C-alpha(theta(2)) bonds are overwhelmingly limited to gauche, gauche (g(+)g(+)/g(-)g(-)) conformations. The Gpn residue forms C-7 and C-9 hydrogen bonds in which the donor and acceptor atoms come from the flanking peptide units. In combination with alpha amino acid residues alpha gamma and gamma alpha segments can adopt C-12 hydrogen bonded structures. The conformational choices available to the Gpn residue have been probed using energy calculations, adopting a grid search strategy. Ramachandran phi-psi maps have been constructed for fixed values of theta(1) and theta(2), corresponding to the gauche and trans conformations. The sterically allowed and energetically favorable regions of conformational space have been defined and experimental observations compared. C-7 and C-9 hydrogen bonded conformational families have been identified using a grid search approach in which theta(1) and theta(2) values are varied over a range of +/- 10 degrees about ideal values at 1 degrees intervals. The theoretical analysis together with experimental observations for 59 Gpn residues from 35 crystal structures permits definition of the limited range of conformational possibilities at this gamma amino acid residue. .

ESR study of copper diethyldithiophosphate

ESR investigations are reported in single crystals of copper diethyldithiophosphate, magnetically diluted with the corresponding diamagnetic nickel complex. The spectrum at normal gain shows hyperfine components from 63Cu, 65Cu, and 31P nuclei. At much higher gain, hyperfine interaction from 33S nuclei in the ligand is detected. The spin Hamiltonian parameters relating to copper show tetragonal symmetry. The measured parameters are g|| = 2.085, g[perpendicular]=2.025, A63Cu = 149.6 × 10−4 cm−1, A65Cu = 160.8 × 10−4 cm−1, BCu = 32.5 × 10−4 cm−1 and QCu [infinity] 5.5 × 10−4cm−1. The 31P interaction is isotropic with a coupling constant AP = 9.6 × 10−4 cm−1. Angular variation of the 33S lines shows two different hyperfine tensors indicating the presence of two chemically inequivalent Cu[Single Bond]S bonds. The experimentally determined hyperfine constants are A ₁^s=34.9×10−4 cm−1, B ₁^s=26.1×10−4 cm−1, A ₂^s=60.4×10−4 cm−1, B₂^s=55.5×10−4 cm−1. The hyperfine parameters show that the hybridization of the ligand orbitals is very sensitive to the symmetry around the ligand. The g values and Cu hyperfine parameters are not much affected by the distortions occurring in the ligand. The energies of the d-d transitions are determined by optical absorption measurements on Cu diethyldithiophosphate in solution. Using the spin Hamiltonian parameters together with optical absorption results, the MO parameters for the complex are calculated. It is found that in addition to the sigma bond, the pi bonds are also strongly covalent. ©1973 The American Institute of Physics.

Structural studies of analgesics and their interactions. Part 4. Crystal structures of phenylbutazone and a 2 : 1 complex between phenylbutazone and piperazine

The X-ray crystal structures of 4-butyl-1,2-diphenylpyrazolidine-3,5-dione (phenylbutazone)(I). and its 2 : 1 complex (II) with piperazine have been determined by direct methods and the structures refined to R 0.096 (2 300 observed reflections measured by diffractometer) and 0.074 (2 494 observed reflections visuallyestimated). Crystals are monoclinic, space group P21/c; for (I)a= 21.695(4), b= 5.823(2), c= 27.881(4)Å, = 108.06 (10)°, Z= 8, and for (II)a= 8.048(4), b= 15.081(4), c= 15.583(7)Å, = 95.9(3)°, Z= 2. The two crystallographically independant molecules in the structure of (I) are similar except for the conformation of the butyl group, which is disordered in one of the molecules. In the pyrazolidinedione group, the two C–C bonds are single and the two C–O bonds double. The two nitrogen atoms in the five-membered ring are pyramidal with the attached phenyl groups lying on the opposite sides of the mean plane of the ring. The phenylbutazone molecule in (II) exists as a negative ion owing to deprotonation of C-4. C-4 is therefore trigonal and the orientation of the Bu group with respect to the pyrazolidinedione group is considerably different from that in (I); there is also considerable electron delocalization along the C–O and C–C bonds. These changes in geometry and electronic structure may relate to biological activity. The doubly charged cationic piperazine molecule exists in the chair form with the nitrogen atoms at the apices. The crystal structure of (II) is stabilized by ionic interactions and N–H O hydrogen bonds.

Mapping of assembled epitopic regions of human chorionic gonadotropin reveals proximity of CTP alpha to the determinant loop beta 93-100

Three overlapping assembled epitopes of beta hCG have been mapped using MAb probes and a single step solid phase radioimmunoassay. These epitopes have been shown to be at receptor binding region comprising of the loop region beta Cys93-Cys100. Importance of disulphide bonds in maintaining integrity of these epitopes is assessed. Two MAbs (INN 58 and INN 22) interact with the beta region as well as the alpha C-terminal peptide, while the other MAb INN 24 interacts with only the beta region. Cross-reactivity pattern with beta hCG and hLH as web as the reported crystal structure of hCG substantiates the epitope identification. The results demonstrate utility of MAbs as probes in investigations on three-dimensional structure of gonadatropins.

The Crystal and Molecular Structure of l-(Diphenylmethyl)azetidin-3-ol

1-(Diphenylmethyl)azetidin-3-ol is triclinic, space group P1, with a=8.479(2), b=17.294(4),c = 10.606 (3) A, a = 118.59 (2),/~ = 100.30 (2), y = 89.63 (2) °, Z = 4. The structure was solved by multisolution methods and refined to an R of 0.044 for 2755 reflexions. The four-membered rings in the two independent molecules are puckered with dihedral angles of 156 and 153 ° . The two molecules differ in conformation with respect to rotation of the phenyl rings about the C-C bonds. The structure is stabilized by a network of O-H. • • N intermolecular hydrogen bonds.

Structure of bis(thiocyanato-N)bis(thiosemicarbazide-N1,S)nickel(II): a redetermination

[Ni(NCS)2(CHsN3S)2], Mr = 356.7, monoclinic, P21/c , a = 5-297 (1), b = 7.869 (1), c - 16-078 (2) A,/3 = 91.53 (1) °, V-= 669.9 A 3, Z= 2, Om = 1"76, Dx = 1"771 g cm -3, A(Mo Ka) = 0-71069 ]k, /.~ = 19"9 cm-l, F(000) = 364, T = 295 K, final R = 0.026 for 1576 significant [F > 10g(F)] reflections. The complex lies on a crystallographic centre of symmetry. The Ni atom is octahedrally coordinated by two thiocyanates (through N atoms) and by two thiosemicarbazide molecules (through hydrazinic N and S atoms). The crystal structure is stabilized by N--H...S hydrogen bonds. Early work on this structure [Garaj & Dunaj-Jurco (1968). Chem. Commun. p. 518] used photographic data and was refined to R = 0-13 for 512 reflections.

Stereospecific photodimerization of coumarins in crystalline inclusion complexes. Molecular and crystal structure of 1:2 complex of (S,S)-(-)-1,6-bis(o-chlorophenyl)-1,6-diphenyl-hexa-2,4-diyne-1,6-diol and coumarin

Proximity of molecules is a crucial factor in many solid- state photochemical processes.'S2 The biomolecular photodimerization reactions in the solid state depend on the relative geometry of reactant molecules in the crystal lattice with center-to-center distance of nearest neighbor double bonds of the order of ca. 4 A. This fact emanates from the incisive studies of Schmidt and Cohen.2 One of the two approaches to achieve this distance requirement is the so-called "Crystal-Engineering" of structures, which essentially involves the introduction of certain functional groups that display in-plane interstacking interactions (Cl...Cl, C-He-0, etc.) in the crystal The chloro group is by far the most successful in promoting the /3- packing m ~ d e ,th~o,u~gh recent studies have shown its limitations? Another approach involves the use of constrained media in which the reactants could hopefully be aligned.

NMR and X-ray crystallographic studies on cyclic tetrapeptide, cyclo (D-Phe-Pro-Sar-Gly)

The conformation of the synthetic cyclic tetrapeptide cyclo(D-Phe-Pro-Sar-Gly) has been determined in solution using the nuclear magnetic resonance technique and in the crystal state by X-ray crystallography. Results showed that the peptide exhibited two different conformations in solution, conformer 1 having cis-trans-cis-trans peptide bonds and conformer 2 having trans-cis-trans-cis peptide bonds. No intramolecular hydrogen bonds were observed in the structures. The X-ray diffraction studies showed the crystals to be orthorhombic with space group P2(1)2(1)2(1) with unit-cell dimensions, a = 5.790, b = 10.344, c = 31.446 A, Z = 4, R = 0.104 for 2301 observed reflections. The crystal structure showed only one type of conformer having cis-trans-cis-trans peptide bonds similar to the conformer 1 in solution.