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The title compound crystallizes from anisole with 4 molecules per unit cell. The space group of this cell is P21/c and the cell parameters are a = 14.777(2) Å, b = 9.5785(8) Å, c = 13.099(1) Å, and β = 90.48(2)°. Diffractometer data with CuKα radiation to 2θ = 129° were collected and the structure solved and refined to weighted and unweighted R factors of 0.077 and 0.051 respectively. The 2-pyridyl ring and the p-tolyl system make dihedral angles of 29.7 and 55.3° respectively with the plane of the double bond. The inter-aryl dihedral angle is 106.5°. The protonated tertiary nitrogen atom is hydrogen bonded to the chloride ion and two chloride ions are connected via hydrogen bonds in a distorted square planar arrangement by two water molecules. The pyridyl ring is involved in a π orbital overlap linkage with another pyridyl ring on the same side of the molecule as is the hydrogen bond from the nitrogen function. Brief characteristics of a flexible receptor protein which will bind antihistamine drugs are given.

Dextrorotatory chlorpheniramine maleate crystallizes from warm ethyl acetate in a P21 cell containing two formula units of the salt, with unit cell dimensions; a = 5.7669(4) Å, b = 20.338(2) Å, c = 9.1347(8) Å, β = 103.73(2)°. Diffractometer data were collected with CuKα radiation to 2θ = 128°. The structure was solved and refined to R = 0.050 and wR = 0.066. The absolute configuration is confirmed as being S. The alkylamine chain is asymmetrically disposed to the two aryl rings, the p-chlorophenyl ring being more exposed and the 2-pyridyl ring partially occluded. The molecule has an open side to which both hydrogen bond and π orbital overlap linkages can occur. The maleate mono-anion is hydrogen bonded to the dimethylamino group via a normal [Formula: see text]linkage. The intramolecular hydrogen bond of the maleate ion is 2.444(5) Å long and is asymmetric.

C 5 NH 3 (NH 2 ) 2 cristallise dans le systeme orthorhombique avec le groupe d'espace P2 1 2 1 2 1 . Affinement de la structure jusqu'a 0,093

C/sub 13/H/sub 16/N/sub 4/O/sub 2/, M/sub r/ = 260.92, crystallizes from wet ethanol in the monoclinic space group C2/c, a = 18.140(5), b = 12.796(3), c = 12.332(3) A, ..beta.. = 114.78(1)/sup 0/. D/sub c/ (for eight molecules in the cell of volume 2598.93 A/sup 3/) = 1.169 g cm/sup -3/. The structure was solved with MULTAN and refined by full-matrix least-squares techniques based upon 1838 unique F/sup 2//sub 0/ terms to yield agreement factors R = 0.057 and R/sub w/ = 0.089.

4,6-Diamino-1-(p-chlorophenyl)-1,2-dihydro-2,2-dimethyl-s-triazine hydrochloride, C11H15-CIN5+.Cl-, Mr = 288.20, monoclinic, P21/c, a = 8.783 (2), b = 10.267 (2), c = 17.234 (3) A, beta = 115.72 (1) degrees, U = 1400.1 (5) A3, Z = 4, Dx = 1.337 Mg m-3, lambda = 1.15882 (7) A for unit-cell determination and 1.04702 (7) A for collection of intensity data, mu = 0.191 mm-1, T = 15.0 (5) K, final R(F2) = 0.050 and wR(F2) = 0.063 for 3099 independent reflections. Five atoms of the triazine ring are nearly coplanar. The sixth, the quaternary C(2), is displaced from this plane (P1) so that the bond to one of its methyl substituents is nearly perpendicular to P1 while the other methyl substituent lies almost in the plane. The chlorophenyl-ring plane is nearly perpendicular to P1. The heterocycles form cyclic dimers via hydrogen bonds from the 6-amino group to ring atom N(5) of an adjacent molecule. All other N-H units are hydrogen bonded to the Cl- counter ion. The ring is protonated at position N(3).

Bacteriopheophytin is a key component in the mechanism by which photosynthetic bacteria transduce solar energy into chemical form. The structure of methyl bacteriopheophorbide a, a bacteriopheophytin derivative, has been determined by three-dimensional x-ray diffraction. The compound crystallizes in space group P1 in a unit cell containing a molecule of methyl bacteriopheophorbide and a benzene molecule of crystallization, with lattice constants a = 7.2502 (8) A, b = 8.1070 (9) A, c = 17.224 (5) A, ..cap alpha.. = 90.80 (2)/sup 0/, ..beta.. ..-->.. = 94.17 (2)/sup 0/, and ..gamma.. = 110.38 (1)/sup 0/. The structure has been refined with isotropic thermal parameters on F by full-matrix least squares to R/sub F/ = 0.110, based on 860 reflections. The molecules associate in chains via ..pi..-..pi.. interactions with ring I of one molecule overlapping ring III of its neighbor with a vertical separation of 3.6 A. The one-dimensional chains form two-dimensional layers without the intervention of the hydrogen bonding by water molecules previously reported for chlorophyllides. This work represents the first crystallographic determination of a bacteriochlorin and confirms the canonical structures and relative orientations of the five chiral centers of bacteriochlorophyll a derivatives.

Le compose C 5 H 7 N 3 O cristallise dans le systeme monoclinique, groupe P2 1 /n et sa structure est affinee jusqu'a R=0,060. Seule la forme tautomere protonee en N(1) est presente. Les molecules sont empilees et liees par liaisons hydrogene pour former un reseau base sur des interactions N-H...N autour d'un centre de symetrie et sur des liaisons hydrogene N-H...O

The structure of the isobacteriochlorin, (2,3,7,8-tetrahydro-5,10,15,20-tetraphenylporphinato)(pyridine)zinc(II) benzene solvate, has been determined by three-dimensional x-ray diffraction. The compound crystallizes with one molecule each of benzene and reduced porphyrin per asymmetric unit in the triclinic space group P anti 1 with a = 11.452 (5) A, b = 13.332 (4) A, c = 14.718 (6) A, ..cap alpha.. = 99.05 (2)/sup 0/, ..beta.. = 94.37 (4)/sup 0/, and ..gamma.. = 104.88 (4)/sup 0/. It is isomorphous with the corresponding chlorin, (2,3-dihydrotetraphenylporphinato)(pyridine)zinc(II) benzene solvate. The structure has been refined by least squares in three matrix blocks to R/sub F/ = 0.073, on the basis of 6217 reflections with F/sub 0/ > 0. The results unambiguously confirm the structure, previously deduced by spectroscopic techniques, for the general class of isobacteriochlorins (and for siroheme, the prosthetic group of nitrite and sulfite reductases) as prophyrins in which two adjacent pyrrole rings are reduced. In addition, the data indicate that successive saturation of the pyrrole rings in prophyrins, chlorins, and isobacteriochlorins exerts no major effect on the stereochemistry of the macrocycles and suggest that the geometric details of high spin iron siroheme will not deviate substantially from those of iron(III) porphyrins.

The structure of (5,10,15,20-tetra-n-propylporphinato)lead(II) has been determined by three-dimensional x-ray diffraction. The compound crystallizes in space group P1, with two molecules per unit cell and lattice constants a = 11.732 (3) A, b = 12.111 (3) A, c = 11.114 (2) A, ..cap alpha.. = 112.56 (1)/sup 0/, ..beta.. = 91.85 (2)/sup 0/, and ..gamma.. = 72.85 (2)/sup 0/. The structure has been refined on F/sup 2/ by full-matrix least squares to R/sub F/sup 2// = 0.057 on the basis of 5570 reflections. Incorporation of the very large Pb(II) ion into the macrocyclic framework principally results in a folding distortion along an axis defined by two opposite methine carbons, rather than by a variation in distances and angles, when compared to free-base tetra-n-propylporphyrin. The molecules pack in pairs with a Pb-Pb distance of 4.256 A, implying no direct metal-metal interaction. A pyrrole ring from a neighboring molecule lies 3.456 A above the Pb(II) ion which suggests a weak ..pi..-axial linkage. The possibility that such a roof conformation plays a role in the trigger mechanism for the cooperative binding of oxygen by hemoglobin is considered.

A previously unknown alkaloid of molecular formula C15H20O2N2 was isolated from the dried root bark of EleagnusCommutata (Wolf willow or Silverberry). An X-ray analysis was undertaken to complete the structural characterization of the molecule. Columnar crystals obtained from diethyl ether have the unit cell constants, a = 13.1949(10) Å, b = 9.4525(6) Å, c = 12.1186(6) Å, β = 109°47(1)′ and belong to space group P21/c. The structure was solved using an automated symbolic addition procedure and refined by block-diagonal least-squares to weighted and unweighted R factors of 6.25% and 4.30%, respectively. The previous structural studies were shown to be essentially correct except for the incorrect placement of the phenolic hydroxyl on C(5) of the oxindole nucleus. The correct molecular structure is implied by the systematic name given. The —OH group engages in two intermolecular hydrogen bonds with the two nitrogen atoms, but the carbonyl moiety is not involved in any such interactions.

Neutron diffraction data from a colorless 58 mg single crystal of trimethoprim (2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidine (C/sub 14/H/sub 18/N/sub 4/O/sub 3/) were used to obtain a high-precision description of the structure. Crystallographic data: space group P anti 1, a = 10.523 (4) A, b = 11,222 (4) A, c = 8.068 (3) A, ..cap alpha.. = 101.22(1)/sup 0/, ..beta.. = 112.15 (1)/sup 0/, ..gamma.. = 112.65 (2)/sup 0/, Z = 2. A multisolution method was used to solve the phase problem and the structure was refined by least-squares techniques on F/sub 0//sup 2/ (all 4039 reflections) with parameters grouped in two blocks to yield agreement factors, R = 0.045 and R/sub w/ = 0.071. The 2,4-diaminopyrimidine tautomer is confirmed. The bases form an extended hydrogen-bonded ribbon with N(1) and N(2) acting as acceptor and donor respectively across one center of symmetry. Atoms N(3) and N(4) interact similarly across another inversion center. This hydrogen-bonding pattern supports a previously postulated model for binding of the drug to the receptor. No base-stacking interactions of the pyrimidine rings were observed and so no conclusions could be reached regarding the role of this associative mode in the receptor binding. A conformational energy calculation indicates considerable rotational freedom aboutmore » the two bonds linking the aryl groups. The trimethoxybenzyl systems do not participate in any specific nonbonded interactions. (auth)« less

Neutron diffraction data from a colorless 58 mg single crystal of trimethoprim (2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidine (C/sub 14/H/sub 18/N/sub 4/O/sub 3/) were used to obtain a high-precision description of the structure. Crystallographic data: space group P anti 1, a = 10.523 (4) A, b = 11,222 (4) A, c = 8.068 (3) A, ..cap alpha.. = 101.22(1)/sup 0/, ..beta.. = 112.15 (1)/sup 0/, ..gamma.. = 112.65 (2)/sup 0/, Z = 2. A multisolution method was used to solve the phase problem and the structure was refined by least-squares techniques on F/sub 0//sup 2/ (all 4039 reflections) with parameters grouped in two blocks to yield agreement factors, R = 0.045 and R/sub w/ = 0.071. The 2,4-diaminopyrimidine tautomer is confirmed. The bases form an extended hydrogen-bonded ribbon with N(1) and N(2) acting as acceptor and donor respectively across one center of symmetry. Atoms N(3) and N(4) interact similarly across another inversion center. This hydrogen-bonding pattern supports a previously postulated model for binding of the drug to the receptor. No base-stacking interactions of the pyrimidine rings were observed and so no conclusions could be reached regarding the role of this associative mode in the receptor binding. A conformational energy calculation indicates considerable rotational freedom aboutmore » the two bonds linking the aryl groups. The trimethoxybenzyl systems do not participate in any specific nonbonded interactions. (auth)« less

Table 2.3.2 of Reciprocal Lattice Points Equivalent under the Operations of a Given Noncentrosymmetric Point Group, on p. 151 of International Tables for X-ray Crystallography [Vol. IV (1974), Birmingham: Kynoch Press] contains an error for the point group 422. The entry h{\bar k}l should be replaced by h{\bar k}{\bar l}.