Water molecules hydrogen bonding to aromatic acceptors of amino acids: the structure of Tyr-Tyr-Phe dihydrate and a crystallographic database study on peptides.

The crystal structure of Tyr-Tyr-Phe dihydrate contains a hydrogen bond formed between a water molecule and the Phe side chain. The geometry is centered with a distance of 3.26 A between the water O atom and the aromatic centroid. In a database study on hydrated peptides, four related examples are found which exhibit a wide variability of hydrogen-bond geometries. The intermolecular surroundings of the water molecules are inspected, showing that they are typically involved in complex networks of conventional and non-conventional hydrogen bonds. Possible relevance for protein hydration is given.

Structure and serotonin 5-HT2C receptor activity of ortho- and meta-substituted phenylpiperazines.

The structural characteristics of ortho- and meta-substituted phenylpiperazines have been investigated in order to understand their actions at the serotonin 5-HT2C receptor. The crystal structures of the 4-methylated analogues of two phenylpiperazines that are already known as 5-HT2C ligands, 1-(1-naphthyl)-4-methylpiperazine (1NMP) and 1-[(3-trifluoromethyl)phenyl]-4-methylpiperazine (TFMPMP), and those of two novel 5-HT2C ligands, 1-(2-methoxyphenyl)piperazine (oMPP) and 1-(3-methoxyphenyl)piperazine (mMPP), are determined. Molecular mechanics calculations are performed to calculate the energy profiles of six phenylpiperazines for rotation about the central phenyl-nitrogen bond. The activities of several phenylpiperazines, in combination with their crystal structures and conformational characteristics, lead to the hypothesis that the conformation for which the piperazine ring and the phenyl ring are approximately co-planar should be the 5-HT2C receptor 'activating' conformation. This hypothesis is then used to predict the activities of the two novel 5-HT2C ligands oMPP and mMPP. oMPP is predicted to be an antagonist at this receptor, whereas mMPP is predicted to be an agonist. As this prediction was confirmed by in vitro and in vivo tests, the proposed conformation is very likely to be responsible for the activation of the 5-HT2C receptor.

Stereochemistry of charged nitrogen-aromatic interactions and its involvement in ligand-receptor binding.

Recently, new evidence was found for the involvement of charged nitrogen-aromatic interactions in ligand-receptor binding. In this study we report two favourable orientations of a phenyl ring with respect to a R-N+(CH3)3 group, based on crystal structure statistics from the Cambridge Structural Database. In the first orientation, the phenyl ring is situated in between the substituents at about 4.5 A from the nitrogen atom, and the ring is approximately oriented on the sphere around the nitrogen atom. In the second orientation, the phenyl ring is situated in the same direction as one of the N-C bonds at about 6.0 A from the nitrogen atom, and the ring is tilted with respect to the sphere around the nitrogen atom. The same two orientations were also found in the crystal structures of three ligand-receptor complexes, which implies that these orientations probably play a major role in molecular recognition mechanisms.

Structure of lactitol (4-O-beta-D-galactopyranosyl-D-glucitol) monohydrate: and artificial sweetener.

C12H24O11.H2O, Mr = 362.4, orthorhombic, P2(1)2(1)2(1), a = 7.808 (2), b = 12.685 (2), c = 15.931 (3) A, V = 1577.9 (6) A3, Z = 4, Dx = 1.525 Mg m-3, lambda(Mo K alpha) = 0.71073 A, mu = 0.13 mm-1, F(000) = 776, T = 295 K, R = 0.031 for 1781 unique reflections with I greater than 2.5 omega (I). The galactopyranosyl ring has the 4C1 chair conformation and the conformation of the bent glucitol C-atom chain is MAA. The torsion angles characterizing the conformation of the glycosidic linkage are -86.3 (2) degrees [O(5)--C(1)--O(1)--C(14)] and 116.8 (2) degrees [C(1)--O(1)--C(14)--C(13)]. All hydroxyl groups act as donors in hydrogen bonds; three bonds are intramolecular. With the exception of O(1) of the glycosidic link which is not an acceptor and O(6) of the glucitol residue which is a double acceptor, all O atoms accept one hydrogen bond. The water molecule donates two and accepts one hydrogen bond.