ABSTRACT
The charge density of a hexapeptide was determined from high-resolution CCD area-detector experiments at 100 K. Two datasets, one from a rotating anode and a second one from synchrotron radiation, were measured and the results are compared. The data are interpreted in terms of the 'rigid pseudoatom' model. The topology of the experimental density is analyzed and compared with the topology of the constituting amino acids, and shows good agreement. All critical points of the electron density at the covalent and hydrogen bonds, as well as those of the Laplacian, were located. With respect to the transferability of electronic and bond topological properties the six peptide bonds were compared with values given in the literature.
Subject(s)
Oligopeptides/chemistry , Models, Molecular , Protein Conformation , Reproducibility of ResultsABSTRACT
Topological analysis of experimental and theoretical charge densities in the title complex [(2-(Me3Si)2CLiC5H4N)2] 1 reveals the nature of the agostic deformation postulated for this complex: delocalization of the Li-C bonding electrons over the entire agostic alkyl group controls the formation of an acute Li-C-Si angle and thus a sufficient electronic saturation of the electron deficient lithium atom via secondary interactions.
ABSTRACT
In the title compound, C(6)H(14)N(4)O(2).H(2)O, the alpha-amino group is neutral. The molecular side chain including the guanidinium group is not fully extended, having a near gauche-gauche conformation [chi(3) = 59.0(1)degrees; chi(4) = 72.8(1)degrees]. The network of hydrogen bonds stabilizing the crystal lattice includes those formed between the deprotonated and negatively charged alpha-carboxylate groups and the positively charged amino groups of the guanidinium group of neighbouring molecules. N-H...O=C and water-mediated N-H...O hydrogen bonds link individual molecules to produce pairs of spiral motifs laterally connected by N-H...O and C-H...O hydrogen bonds.
Subject(s)
Arginine/chemistry , Crystallography, X-Ray , Hydrogen Bonding , Models, Molecular , Molecular ConformationABSTRACT
N-Heterocyclic dicarbene chelate complexes of formula [cis-CH2N(H)C=C(H)N(R)C2PdX2] (X = Br, I; R = (CH2)nOH; n = 2, 3) have been prepared and structurally characterized (for X= I, n = 2). The complexes were immobilized on a functionalized polystyrene support (Wang resin) through one of the oxygen centres. The complexes efficiently catalyze the Heck reaction of activated and non-activated arylbromides, are recyclable under aerobic conditions and exhibit hardly any leaching, which is in line with our theoretical investigations on ligand dissociation energies related to Pd0 and PdII centres.
ABSTRACT
A 13 year old boy was admitted suffering from severe burning pain in both hands and distal forearms of two months duration. The skin in the affected areas was red and warm and was cooled by the boy with ice for alleviation of pain. Laboratory tests revealed no abnormalities. The diagnosis of primary erythromelalgia was made on the basis of the history and physical examination. At the age of nine months the boy had undergone surgery for hexadactyly of the right hand. In addition, the boy had complained of transient burning sensations in both feet several months prior to admission. Revision of the old scar at the beginning of the hand symptoms had been without effect. Initial analgesic attempts with oral paracetamol, acetylsalicylic acid, tramadol and intravenous morphine also had had no effect. Carbamazepine, methysergide and immunoglobulins led to no improvement. Symptomatic relief was achieved only by cooling the distal parts of both arms with water. This caused oedema and maceration of the skin after several days. The placement of a cervical epidural catheter and the infusion of morphine and bupivacaine led to a pronounced pain relief within hours and the forearms could be removed from the cool water. The epidural infusion was continued for two weeks with slowly decreasing amounts of morphine and bupivacaine. During this time there was a marked improvement in both oedema and erythema. No complications resulted from the cervical epidural infusion. Because of the long-standing immobilisation and water exposure the boy had to undergo intensive training of the upper extremities during the following weeks to regain full muscular function.(ABSTRACT TRUNCATED AT 250 WORDS)
