A Modification of Extension of the CNDO Method. I. Parameters for the Atoms Hydrogen to Chlorine, Potassium, Calcium, and Gallium to Bromine.

Höjer, Germund; Meza, Sara; Haug, Arne; Songstad, Jon; Pilotti, Åke

doi:10.3891/acta.chem.scand.26-3723

Cited by 31 publications

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“…In the first group of compounds the bands are assigned to the vibrational modes v~t(C:N), 6ring(N--H ) and Jguanidlno(NH2) J(N--H), as two sets of bands; one with greater contribution from the imidazolic ring at 1648 and 1598 cm-1, and the other set assignable to the guanidino group at 1540 and 1500cm -1. In compounds (2)- (13) the first two bands are shifted to ca. 1680-1658 and 1644-1632 cm-1 and the second set to ca.…”

Section: Resultsmentioning

confidence: 98%

“…The coordination compounds were prepared using a 1:1 2GB to metal molar ratio (1 mmol scale), with the exception of compounds (13) and (t 4), where a 1:2 molar ratio was employed. The metal salt was added to a solution of 2GB in MeOH (30cm3).…”

Section: Synthesis: General Techniquementioning

confidence: 99%

“…The solid was filtered, washed with MezCO and dried in vacuo. Compounds (13) and (14) were obtained from the same reaction mixture, first (13) was isolated, followed by (14) which is more soluble, and precipitated afterwards.…”

Section: Synthesis: General Techniquementioning

confidence: 99%

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Coordination behaviour of 2-guanidinobenzimidazole towards cobalt(II), nickel(II), copper(II) and zinc(II). An experimental and theoretical study

Barba-Behrens

Vázquez-Olmos

Castillo‐Blum

et al. 1996

Transition Met Chem

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The following coordination compounds derived from 2-guanidinobenzimidazole (2GB) (1); [Ni(2GB)2]C1 a" H20, (2); [Ni(2GB)z]BH.3H20, (3); [Ni(2GB)2 l-(NO3) 2, (4); [Ni(2GB); [Cu(2GB)2] (OAc)2-H2O , (t0); [Zn(2GB)C12]'H20, (tt); [Zn(2GB)Br2]" H20, (12); [Co(2GB)C12(H20)z]-5HzO, (13); [Co-(2GB)2C12]'3H20, (14);. [Co(2GB)2(H20)z](NO3) 2 4H20, (t5); and [Co(2GB)z(HzO)2](OAc) 2, (t6) have been synthesized and characterized by i.r. and electronic spectroscopy. In addition (6)-(10) were analysed by e.p.r. The X-ray diffraction structure of compound (4) was obtained. It crystallizes in the monoclinic system, C2/c (a=22.511 (7), b=6.735(6) arid c=15.345(5)A, /3 = 115.31(3) ~ Z = 4, final R =0.0360 and R W = 0.0388 for 1167 observed independent reflections). The nickel(II) atom coordinates two ligands in a square-planar geometry through the imidazolic N(3) and the guanidino N(12).The probable ligand isomers involved in the coordination were determined by theoretical calculations, and the possible structures of the coordination compounds were investigated in order to verify that the experimentally proposed structures were stable. Two different types of coordination compounds were found. One, where the ligand is chelating through the imidazolic N(3) and the guanidino N(12), which is the case for most of the complexes [(2)-(13)]. With only one ligand in the coordination sphere, the structure was either tetrahedral (copper and zinc chloride and bromide complexes) or octahedral (cobalt). With two chelating 2GB units a square-planar geometry was stabilized [(2)-(5) and (8)-(10)]. The second type of coordination behaviour was observed in the cobalt compounds [(I4)-(I6)]. Here the ligand coordinates monodentate through the imidazolic N(3); the structure is tetrahedral.

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Section: Resultsmentioning

confidence: 98%

Section: Synthesis: General Techniquementioning

confidence: 99%

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Coordination behaviour of 2-guanidinobenzimidazole towards cobalt(II), nickel(II), copper(II) and zinc(II). An experimental and theoretical study

Barba-Behrens

Vázquez-Olmos

Castillo‐Blum

et al. 1996

Transition Met Chem

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“…The first is intended to represent the interaction between glyoxal and the carboxylic end of the protein, the second, the interaction between glyoxal and a model of a peptide bond. All the semiempirical calculations were carried out with a C N D 0 / 2 program as parametrized by Hojer and Meza [4].…”

Section: Introductionmentioning

confidence: 99%

Interaction of glyoxal with glycine and N-methylacetamide: Some aspects of their potential energy surface and its relation with cancer

Conde

Estrada

Cárdenas

2009

Int. J. Quantum Chem.

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The interactions of cis-and trans-glyoxal and glycine as a prototype of a carboxylic end of a protein, and the interaction of glyoxal and N-methylacetamide as a prototype of a peptide bond are discussed. Part of their potential-energy surface is given as obtained by the CNDO/2 approximation. It is observed that both glyoxal isomers form different complexes with glycine; with Nmethylacetamidc they give the same molecular complex. The results suggest more experimental search for derivatives of both glyoxal isomers in normal cells.

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“…Surface tension experiments [2] had indicated that such a stabilization actually occurs. To study this problem from a theoretical point of view we used a CNDO method [3]. As a model for the local water structure we chose a cage of ten water molecules connected by twelve hydrogen bonds.…”

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confidence: 99%

A short note on the possible stabilization of the local water structure in the liquid due to an oxygen or a nitrogen molecule

Höjer

Keller

2009

Int. J. Quantum Chem.

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In a previous paper [l] we investigated the possibility of an oxygen or a nitrogen molecule having a stabilizing effect on the local structure in liquid water. Surface tension experiments [2] had indicated that such a stabilization actually occurs. To study this problem from a theoretical point of view we used a CNDO method [3]. As a model for the local water structure we chose a cage of ten water molecules connected by twelve hydrogen bonds. The structure chosen occurs in ice Ic. Furthermore the water molecules were oriented in such a way that the cage did not have any resulting dipole moment. In that way the choice of position for the interstitial oxygen or nitrogen molecule was simplified. Two comments on this model are that first, the hydrogen bonded structure used in this work has many similarities with several of the models proposed for water in the literature (see [4] for a rCsumC), and second, our model takes only into account the interaction between the foreign molecule and the first layer of water molecules. This last limitation in our approach is not supposed to qualitatively change the conclusions. The stabilization effect calculated in [l] may perhaps be smaller when the interaction between the first layer of water molecules around the foreign molecule and the rest of the liquid is included. This is because the surrounding water may partly inhibit the charge redistribution in the first layer as calculated in [l]. The result in [l] was that the interstitial molecule could stabilize the cage by 4 to 7 kcal/mole or around 0.5 kcal/mole per hydrogen bond, depending on its orientation.We have made some further investigations of this problem. It might be argued that the cage chosen as a model for the local water structure could be too favorable for the interaction with the oxygen or the nitrogen. For that reason we have calculated the interaction between some monomer, dimer, and trimer fragments of the cage and a nitrogen molecule. When the geometries were those of cage plus interstitial molecule, the monomers were stabilized between 0.0 and 0.6 kcal/mole, the dimers between 1.1 and 1.5 kcal/mole, and the trimers from 1.1 to 2.6 kcal/mole. If one assumed the hydrogen bonds in the cage to be independent, these results would predict a stabilization of the cage due to the interstitial molecule of around 14 to 18 kcal/mole instead of the calculated 5 to 7 kcal/mole. What happens is, of course, that in the cage each hydrogen bond is not free to readjust to the interstitial molecule completely, due to the rest of the cage. By varying the.position of the nitrogen relative to the 177 01974 by John Wiley & Sons, Inc.

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A Modification of Extension of the CNDO Method. I. Parameters for the Atoms Hydrogen to Chlorine, Potassium, Calcium, and Gallium to Bromine.

Cited by 31 publications

References 0 publications

Coordination behaviour of 2-guanidinobenzimidazole towards cobalt(II), nickel(II), copper(II) and zinc(II). An experimental and theoretical study

Coordination behaviour of 2-guanidinobenzimidazole towards cobalt(II), nickel(II), copper(II) and zinc(II). An experimental and theoretical study

Interaction of glyoxal with glycine and N-methylacetamide: Some aspects of their potential energy surface and its relation with cancer

A short note on the possible stabilization of the local water structure in the liquid due to an oxygen or a nitrogen molecule

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