Arthur Camerman

Molecular structure of a deoxyribose-dinucleotide, sodium thymidylyl-(5′→3′)-thymidylate-(5′) hydrate (pTpT), and a possible structural model for polythymidylate

The crystal and molecular structure of the deoxyribose-dinucleotide sodium thymidylyl-(5′→3′)-thymidylate-(5′) hydrate (pTpT) at physiological pH has been determined by single-crystal X-ray diffraction. There are 4 dinucleotide molecules and approximately 52 water molecules in an orthorhombic unit cell of dimensions a =16·06, b =15·13, c =15·65 A, space group P 2 1 2 1 2. The two 5′-mononucleotide portions of the molecule have extremely similar conformations, with anti conformations of the bases with respect to the glycosidic bonds, C2′-endo deoxyribose rings, and trans arrangements of the P-O(5′) bonds with respect to the C(4′)-C(5′) bonds. This is the first experimental evidence of conformational consistency of mononucleotides in a larger molecule. The conformation about the phosphodiester bonds is (−)- gauche, trans , resulting in an extended dinucleotide molecule with base planes tilted away from being parallel by 39°. A thymidine polynucleotide structure has been generated by adding pTpT units of the same conformation; the result is a right-handed single helix in which the thymines point away from the helix axis and do not base-stack. Such a structure may be a model for poly(T). The pTpT crystal conformation fits the pTp electron density in a Staphylococcal nuclease-pTp-Ca 2+ complex very well; this and the high degree of hydration indicate that the observed dinucleotide conformation is maintained in biological milieus.

The stereochemical basis of anticonvulsant drug action. I. The crystal and molecular structure of diphenylhydantoin, a noncentrosymmetric structure solved by centric symbolic addition

To investigate relationships between the molecular shape and biological activity of anticonvulsant drugs we have determined the molecular structure of diphenylhydantoin. The compound crystallizes in the orthorhombic system with cell dimensions a=6.230, b=13.581, c=15.532A,, space group Pn2~a. A total of 1210 independent reflections to 20= 50 ° for Mo K~ radiation was measured on a fourcircle diffractometer. The structure was solved by centrosymmetric phasing techniques, utilizing Sayres equation for direct sign determination in space group Pnma. This technique proved successful because the 7-atom hydantoin group lies in a plane only 2.40 ° from (010) with the two phenyl rings on each side of the plane. Thus, the structure approximates the situation that would exist for special position (e) of Pnma, and many reflections have phases close to 0 or 7r. The plane of the hydantoin ring forms angles of 113 and 114 ° with the planes through the two phenyl rings. The phenyl-phenyl angle is 90 °. Final R index is 0-052.

Diphenylhydantoin and diazepam: molecular structure similarities and steric basis of anticonvulsant activity.

Diphenylhydantoin and diazepam are two useful antiepileptic drugs. Though not obviously related chemically, their molecular conformations exhibit marked similarities. These similarities indicate a steric basis for their anticonvulsant activity and lead to conclusions about the receptor sites for this type of pharmaceutical.

Photodimer of Thymine in Ultraviolet-Irradiated DNA: Proof of Structure by X-ray Diffraction

Dimethylthymine was photodimerized with ultraviolet radiation, and the structure of one of the resulting dimers, the cis 5,5 : 6,6 isomer, was determined by single-crystal x-ray diffraction. This isomer is the same as that obtained by ultraviolet irradiation of DNA; hence the structure of the thymine dimer in irradiated DNA is now proved.

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.

Synthesis and characterization of monooxorhenium(V) complexes of mercaptoacetylglycylglycylglycine. Crystal structure of tetrabutylammonium oxo(mercaptoacetylglycylglycylglycine)rhenate(V)

Abstract A stable complex of rhenium(V) with mercaptoacetylglycylglycylglycine (MAG3) was prepared by the reaction of ReO2(en)2Cl (en = ethylenediamine) or Re(V) citrate with MAG3 at pH 10.0. The complex was isolated as salts of X[ReO(MAG3)] where X= Bu4N+, Ph4As+, Ph4As[ReO(MAG3)] was characterized by IR, UVVis spectroscopy, elemental analysis and mass spectroscopy. Bu4N[ReO(MAG3)] was characterized by NMR and single crystal X-ray structure determination. Bu4N[ReO(MAG3)] crystallizes in space group Pna21, with cell constants a= 17.902(3), b= 9.029(2), c= 18.741(3) A, V= 3029(1) A3 and Z = 4. The structure was refined to a final R value of 0.046 and contains discrete [ReO(MAG3)]− and Bu4N+ ions. The rhenium atom in [ReO(MAG3)]− is bound to three nitrogens (amide), one sulfur (thiolate), and one oxygen (yl) atom in a distorted square pyramidal geometry. The oxygen atom forms the apex of the square pyramid with a ReO bond distance of 1.68(1) A. The average ReN bond distance is 2.00±0.02 A and the ReS bond is 2.29(1) A.

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.

2-p-Toluidinyl-6-Naphthalene Sulfonate: Relation of Structure to Fluorescence Properties in Different Media

Hydrated and anhydrous crystals of 2-p-toluidinyl-6-naphthalene sulfonate exhibit fluorescence spectra similar to those obtained for 2-p-toluidinyl-6-naphthalene sulfonate in water and in organic solvents, respectively. The molecular structure of anhydrous 2-p-toluidinyl-6-naphthalene sulfonate suggests extended electron resonance over the whole molecule and this is one of the causes of the spectral differences.

Thyroid hormone structure: Molecular conformation of triiodothyropropionic acid

Abstract The crystal and molecular structure of the thyromimetic agent ethyl triiodothyropropionate has been determined by x-ray diffraction. The two phenyl rings are close to being maximally skewed with respect to each other and mutually perpendicular: the angles between them and the interring ether linkage are 88° and 10°. The conformation of the molecule is such that the β-ring 3′-iodine atom is proximal to the α-ring, similar to the conformation found in the crystal structure of triiodo-L-thyronine, rather than distal as has been inferred for these compounds from chemical studies.

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.