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R A Lalancette

Publications and source records attributed to R A Lalancette.

8 recordsLinked to original sources
PubMed2001

(+/-)-3-(3-oxocyclohexyl)propionic acid: dual conformational selection and hydrogen bonding in an epsilon-keto acid.

The asymmetric unit of the title compound, C9H14O3, consists of two molecules having conformations that differ by a rotation of 111.7 (5) degrees about the equatorial substituent bond, so that the side chains of the two species extend away from the ring in different directions. Each conformer forms centrosymmetric hydrogen-bonded acid-to-acid dimers with its own enantiomer [O...O = 2.681 (3) and 2.698 (4) A]. There is an intermolecular C-H...O close contact involving the ketone group of one of the conformers.

Journal Article↗
PubMed2001

(-)-Dioxosantadienic acid: hydrogen-bonding patterns in a bicyclic sesquiterpenoid keto acid and its monohydrate.

The anhydrous form, (I), of the title compound, (-)-2-(1,2,3,4,4a,7-hexahydro-4a,8-dimethyl-1,7-dioxo-2-naphthyl)propionic acid, C(15)H(18)O(4), derived from a naturally occurring sesquiterpenoid, has two molecules in the asymmetric unit, (I) and (I'), differing in the conformations of the saturated ring and the carboxyl group. The compound aggregates as carboxyl-to-ketone hydrogen-bonding catemers [O.O = 2.776 (3) and 2.775 (3) A]. Two crystallographically independent sets of single-strand hydrogen-bonding helices with opposite end-to-end orientation pass through the cell in the b direction, one consisting exclusively of molecules of (I) and the other entirely of (I'). Three C-H.O=C close contacts are found in (I). The monohydrate, C(15)H(18)O(4).H(2)O, (II), with two molecules of (I) plus two water molecules in its asymmetric unit, forms a complex three-dimensional hydrogen-bonding network including acid-to-water, water-to-acid, water-to-ketone, water-to-water and acid-to-acid hydrogen bonds, plus three C-H.O=C close contacts. In both (I) and (II), only the ketone remote from the acid is involved in hydrogen bonding.

Journal Article↗
PubMed2001

(-)-gibberic acid: hydrogen-bonding pattern of the monohydrate of a non-racemic tetracyclic delta-keto acid derivative of gibberellin A3.

In the the title compound, 1,7-dimethyl-8-oxo-4balpha,7alpha-gibba-1,3,4a(10a)-triene-10beta-carboxylic acid monohydrate, C18H20O3*H2O, the water of hydration accepts a hydrogen bond from the carboxyl and donates hydrogen bonds to the carboxyl carbonyl and the ketone in two different screw-related neighbors, which are mutually translational, yielding a complex three-dimensional hydrogen-bonding array.

Crystallography, X-Ray↗
PubMed2001

(-)-3,6-Dioxo-5beta-cholanic acid: hydrogen bonding in the hemihydrate of a steroidal diketo acid.

The hemihydrate of the title diketo acid, C(24)H(36)O(4).0.5H(2)O, forms hydrogen-bonded carboxyl dimers related by a C(2) axis at crystallographic sites on the a and b edges of the chosen cell [O.O = 2.643 (7) and 2.716 (7) A]. The ketone ends of the molecules approach each other at sites near ((1/2),(1/2),(1/2)), ((1/2),0,(1/2)), (0,0,(1/2)) and (0,(1/2),(1/2)) in an interleaved arrangement incorporating partial-occupancy water hydrogen bonded to the B-ring ketone.

Journal Article↗
PubMed2001

(+/-)-1-Tetralone-3-carboxylic acid and (+/-)-1-tetralone-2-acetic acid: hydrogen bonding in two gamma-keto acids.

The crystal structure of (+/-)-4-oxo-1,2,3,4-tetrahydronaphthalene-2-carboxylic acid (C(11)H(10)O(3)) involves projection of the carboxyl group nearly orthogonal to the aromatic plane and hydrogen bonding of the acid groups by centrosymmetric pairing across the a edge and the center of the chosen cell [O...O = 2.705 (2) A]. Intermolecular C--H...O==C close contacts to translationally related molecules are found for both the ketone (2.55 A) and the acid (2.67 A). In (+/-)-1-oxo-1,2,3,4-tetrahydronaphthalene-2-acetic acid (C(12)H(12)O(3)), the aggregation involves centrosymmetric carboxyl dimers mutually hydrogen bonded across the bc face and the a edge of the chosen cell [O...O = 2.674 (2) A]. A 2.60 A close C--H...O==C contact is found to the carboxyl group of centrosymmetrically related molecule.

Journal Article↗
PubMed2000

(+)-Gibberellin C: hydrogen-bonding pattern of the monohydrate of a non-racemic pentacyclic diterpenoid.

In the monohydrate of the title compound, (+)-2beta, 4aalpha-dihydroxy-1,7-dimethyl-8-oxo-4bbeta,7alpha- gibbane-1alpha, 10beta-dicarboxylic acid-1,4a-lactone, C(19)H(24)O(6).H(2)O, intermolecular hydrogen bonding progresses helically along b from carboxyl to ketone [O...O = 2.694 (5) A]. The carboxyl and lactone carbonyl groups in translationally related molecules within a helix both accept hydrogen bonds from the same water of hydration. The oxygen of this water in turn accepts a hydrogen bond from the hydroxyl group of a third screw-related molecule in an adjacent counterdirectionally oriented helix, yielding a complex three-dimensional hydrogen-bonding array. Intermolecular O...H-C close contacts were found to the carboxyl and lactone carbonyls, the hydroxyl, and the water.

Crystallography, X-Ray↗
PubMed1982

Structure and function of an acetylcholine receptor.

Structural analysis of an acetylcholine receptor from Torpedo californica leads to a three-dimensional model in which a "monomeric" receptor is shown to contain subunits arranged around a central ionophoretic channel, which in turn traverses the entire 110 A length of the molecule. The receptor extends approximately 15 A on the cytoplasmic side, 55 A on the synaptic side of the membrane. The alpha-bungarotoxin/agonist binding site is found to be approximately 55 A from the entrance to the central gated ion channel. A hypothesis for the mechanism of AcChR is presented which takes into account the structural and kinetic data, which is testable, and which serves as a focus for future studies on the agonist-induced structure change in AcChR.

Animals↗