Donald Mastropaolo

Crystal structure of methionine-enkephalin

The crystal structure of methionine-enkephalin has been determined by X-ray crystallography. There are two independent pentapeptides in the asymmetric unit and both display extended backbone conformations with their side chains arranged alternately below and above the backbone plane. The two molecules form a hydrogen-bonded head-to-tail dimer similar in conformation to one dimeric pair of leucine-enkephalin molecules in a previously reported crystal structure.

A European population in Minoan Bronze Age Crete

The first advanced Bronze Age civilization of Europe was established by the Minoans about 5,000 years before present. Since Sir Arthur Evans exposed the Minoan civic centre of Knossos, archaeologists have speculated on the origin of the founders of the civilization. Evans proposed a North African origin; Cycladic, Balkan, Anatolian and Middle Eastern origins have also been proposed. Here we address the question of the origin of the Minoans by analysing mitochondrial DNA from Minoan osseous remains from a cave ossuary in the Lassithi plateau of Crete dated 4,400–3,700 years before present. Shared haplotypes, principal component and pairwise distance analyses refute the Evans North African hypothesis. Minoans show the strongest relationships with Neolithic and modern European populations and with the modern inhabitants of the Lassithi plateau. Our data are compatible with the hypothesis of an autochthonous development of the Minoan civilization by the descendants of the Neolithic settlers of the island.

Crystal structure of an extended-conformation leucine-enkephalin dimer monohydrate

The structure of a new crystal form of leucine-enkephalin has been determined by X-ray diffraction. There are two independent molecules in the asymmetric unit and both have extended peptide backbone conformations with side-chains arranged alternately above and below the backbone planes. The two pentapeptides are hydrogen-bonded to each other and to other molecules forming an extended antiparallel beta-pleated sheet. The structure differs from that in similar crystals of methionine enkephalin primarily in side-chain orientations and inter-sheet interactions.

Two rhod­amine derivatives: 9-[2-(ethoxycarbonyl)phenyl]-3,6-bis(ethyl­amino)-2,7-di­methyl­xanthyl­ium chloride monohydrate and 3,6-di­amino-9-[2-(methoxy­carbonyl)­phenyl]xanthyl­ium chloride trihydrate

The title compounds, C28H31N2O3(+)-Cl(-)-H2O (common name rhodamine-6g), (I), and C21H17N2O3(+)-Cl(-)-3H2O (common name rhodamine-123), (II), both have planar xanthene skeletons with a formal +1 charge on the amino N atoms delocalized through the pi-electron system so that the N-Csp(2) bond distances indicate significant double-bond character. The substituted planar phenyl groups make angles of 63.29 (8) and 87.96 (11) degrees with the xanthene planes in (I) and (II), respectively. In both molecules, the carbonyl bond vectors point toward the xanthene rings. The ethylamine groups in (I) are oriented similarly with their CH2-CH3 bond vectors pointing nearly perpendicular to the xanthene plane. The chloride ions and water molecules are disordered in both structures. In (I), the chloride ion and water molecule are disordered between two sites. One water and chloride alternately occupy the same site with occupancy factors of 0.5. The other 0.5-chloride and 0.5-water occupy two distinct positions separated by 0.747 (8) A. In (II), the chloride ion is disordered between three sites and one of the waters is disordered about two other sites. Both crystal structures are stabilized by hydrogen bonds involving the chloride ions, amino groups and water molecules, as well as by pi-pi stacking between xanthene planes.

Refinement of the structure of cyclohexylammonium chloride (cyclohexylamine·HCl)

The crystal structure of cyclohexylammonium chloride has been refined to a conventionalR value of 0.029 using X-ray data obtained with molybdenum radiation. The title compound crystallizes in the orthorhombic space group Pca21 witha=9.339(2),b=11.449(2),c=7.546(1) Å, andDc=1.117 g cm−3 forZ=4. An earlier structure determination has been essentially verified with the exception of some important features: a significantly longer and more reasonable C(1)−N bond distance, increased values for all the endocyclic torsion angles and an increase in the length of thea axis.

Bis(2,2-dimethylaziridinyl)phosphinic amide

The asymmetric unit of the title compound, C8H18N3OP, contains one bis(2,2-dimethylaziridinyl)phosphinic amide molecule. The crystal structure is characterized by hydrogen bonds from the amide-N atom, which involve both H atoms of the amino group, to the phosphinic-O atom in two different molecules, thus forming infinite double-stranded chains along the base vector [100], and by hydrophobic contacts between these chains.

The antifolate trimetrexate : observation of the enzyme-binding conformation

The crystal structure of the title compound contains four 2, 4-diamino-5-methyl-6-[(3,4,5-trimethoxyanilino)methyl]quinazoline molecules, two dimethyl sulfoxide molecules and three water molecules in the asymmetric unit, i.e. 4C(19)H(23)N(5)O(3).-2C(2)H(6)OS.3H(2)O. All four quinazoline molecules adopt trans,-gauche conformations. An extensive hydrogen-bond network involving N. N base-pairing interactions, as well as the dimethyl sulfoxide and water molecules, stabilizes the crystal structure.

A Schiff base formed from sulfanilic acid and dimethylformamide

The crystal structure the Schiff base contains one 4-dimethylaminomethyleneaminobenzenesulfonic acid molecule in zwitterionic form [4-(dimethylaminomethyleneammonio)benzenesulfonate], and one water molecule in the asymmetric unit (C9H12N2O3S.H2O). Protonation occurs at nitrogen atom N1, but the charge is delocalized.

A monoamine oxidase B inhibitor: N-(2-amino­eth­yl)-p-chloro­benzamide (Ro16-6491) hydro­chloride

# 2005 International Union of Crystallography Printed in Great Britain – all rights reserved In the title compound, 2-(4-chlorobenzamido)ethanaminium chloride, C9H12ClN2O + Cl , both independent cations have linearly extended conformations, with protonation occurring at the terminal N atom. The interplanar angles between the chlorobenzoyl rings and the planar amide groups are 137.6 (3) and 149.3 (5) for cations A and B, respectively. The cations are N—H O hydrogen-bonded in a head-to-head/tail-to-tail fashion, producing distinct hydrophobic and hydrophilic layers running parallel to [110]. The Cl anions are hydrogen-bonded to the terminal positively charged –NH3 + groups. Weak C—H Cl interactions further coordinate the Cl anions. Structural comparison with pargyline, an irreversible MAO-B inhibitor, is presented.

7,8-Dihydr­oxy-4-propyl-1,2,3,4,4a,5,6,10b-octa­hydro­benzo[f]quinolinium bromide monohydrate, a dopamine agonist

In the crystal structure of the title dopaminergic compound, C16H24NO2+.Br-.H2O, protonation occurs at the piperidine N atom. The piperidine ring adopts a chair conformation and the cyclohexene ring adopts a half-chair conformation; together with the planar benzene ring, this results in a relatively planar shape for the whole molecule. Classical hydrogen bonds (N-H...Br, O-H...Br and O-H...O) produce an infinite three-dimensional network. Hydrogen bonds between water molecules and Br- anions create centrosymmetric rings throughout the crystal structure. Structural comparison of the molecule with the ergoline dopamine agonist pergolide shows that it is the hydrogen-bond-forming hydroxy or imino group that is necessary for dopaminergic activity, rather than the presence of a phenyl or a pyrrole ring per se.