Angel García-Raso

Synthesis, structure and nuclease properties of several ternary copper(II) peptide complexes with 1,10-phenanthroline.

Three new ternary peptide-Cu(II)-1,10-phenanthroline (phen) complexes, [Cu(L-ala-gly)(phen)].3.5H(2)O 1, [Cu(L-val-gly)(phen)] 2 and [Cu(gly-L-trp)(phen)].2H(2)O 3, have been prepared and structurally characterised. These compounds exist as distorted square pyramidal complexes with the five co-ordination sites occupied by the tridentate peptide dianion and the two heterocyclic nitrogens of the phenanthroline ligand. The bulk of the lateral chain in the peptide moiety determines the relative disposition of the phen ligand. Thus, in [Cu(L-val-gly)(phen)] 2, the phenanthroline plane is deviated towards the opposite side of the isopropyl group of the L-valine moiety. On the other hand, in [Cu(gly-L-trp)(phen)].2H(2)O 3 the absence of stacking interactions between phen and indole rings and the presence of an intramolecular CH...pi interaction should be pointed out. These complexes exhibit significant differences in their nuclease activity which depends on the nature of the peptidic moiety, the complex [Cu(gly-L-trp) (phen)].2H(2)O 3 being the most active.

Coordination behaviour of sulfanilamide derivatives.: Crystal structures of [Hg(sulfamethoxypyridazinato)2], [Cd(sulfadimidinato)2(H2O)]·2H2O and [Zn(sulfamethoxazolato)2-(pyridine)2(H2O)2]

Abstract Hg(II), Cd(II) and Zn(II) complexes with the ligands sulfadimethoxine, sulfamethoxypyridazine, sulfadiazine, sulfamerazine, sulfadimidine and sulfamethoxazole have been prepared and characterised by spectral data. 1H and 13C NMR have been used to interpret the structural characteristics of the complexes in solution. The X-ray crystal structures of [Hg(sulfamethoxypyridazinato)2] (2a), [Cd(sulfadimidinato)2(H2O)]·2H2O (4b) and [Zn(sulfamethoxazolato)2(py)2(H2O)2] (6d) have been determined. In complex 2a the Hg(II) ion lies on an inversion centre and exhibits linear coordination by two sulfonamidic nitrogen atoms [Hg–N(1)=2.071(4) A] of the two deprotonated sulfamethoxypyridazinato ligands. The polymeric Cd(II) complex (4b) exhibits a high distorted-octahedral geometry, involving the sulfonamidic nitrogen [Cd–N(1)=2.328(6); Cd–N(1′)=2.326(6) A] and the heterocyclic N(3)/N(2′) [Cd–N(3)=2.307(6) A; Cd–N(2′)=2.426(6) A] of two bidentate sulfadimidine ligands, the terminal amino N(4′b) [Cd–N(4′b)=2.379(7) A] of a third sulfadimidine which is bonded to an adjacent Cd(II), and the O(3) atom of a coordinated water molecule [Cd–O(3)=2.334(6) A]. In complex 6d the geometry around the Zn(II) ion can be described as a slightly distorted compressed octahedron. Two pyridine [Zn–N(16)=2.1841(17) A] and two isoxazole N atoms [Zn–N(2)=2.1736(15) A] are located in the equatorial plane and two oxygen atoms of two water molecules [Zn–O(4)=2.0984(14) A] are placed in the apical positions. IR and NMR spectral studies suggest a similar behaviour of the Cd(II) and Zn(II) complexes, both in solid state and solution, and different to the corresponding Hg(II) complexes. Thus 1H and 13C NMR spectra, in DMSO-d6, of Cd(II) and Zn(II) compounds show coordination mainly through the heterocyclic nitrogen while the corresponding Hg(II) derivatives seem to be coordinated through the sulfonamidic nitrogen.

CRYSTAL STRUCTURES OF THE N-SALICYLIDENE-L-SERINATOAQUACOPPER(II) MONOHYDRATE AND ITS TERNARY DERIVATIVE WITH 2-AMINOPYRIDINE

Abstract The complexes [Cu(Sal–( L -Ser))H2O]⋅H2O 1 and [Cu(Sal–Ser)(2-amino pyridine)] 2 have been prepared and their crystal structures determined. In 1 the copper(II) has a square-pyramidal geometry, being coordinated to the tridentate Sal–( L -Ser) Schiff base ligand and the oxygen atom (O(16)) of one water molecule occupying the corners of a square. The coordination sphere about the copper is completed by an axial O(12) atom of an hydroxyl group belonging to an adjacent complex unit. In the racemic ternary complex 2 the metal atom has a square-planar coordination with O,N,O atoms of the tridentate Sal–Ser dianion and the heterocyclic N atom of the 2-aminopyridine. Spectroscopic data are discussed.

Experimental and theoretical study of uracil derivatives: the crucial role of weak fluorine–fluorine noncovalent interactions

We have recently communicated the important role of lone pair–π, π–π and hydrophobic interactions in the solid architecture of 5-fluoro-1-hexyluracil and 1-hexyluracil (CrystEngComm, 2010, 12, 362–365). As a matter of fact, the simple substitution of a hydrogen atom by a fluorine atom has an enormous consequence in the solid state structure. It has been demonstrated that this is due to an increase in the π-acidity of the ring. In this article we extend the study to other uracil derivatives, where we have changed the hydrophobicity of the hexyl chain by introducing hydrophilic groups in the substituent, such as hydroxyl or carboxylic groups. The latter compounds, i.e. (N1-(3-hydroxypropyl)-5-fluorouracil and N1-(4-hydroxycarbonylbutyl)-5-fluorouracil monohydrate present interesting fluorine–fluorine interactions that are very important in determining the crystal packing.

Lone pair–π vs π–π interactions in 5-fluoro-1-hexyluracil and 1-hexyluracil: a combined crystallographic and computational study

The simple substitution of a hydrogen atom by a fluorine atom in 1-hexyluracil has an enormous consequence on the solid state structure due to the increment in the π-acidity of the ring.

X-ray diffraction structures of two N-salicylidene tryptophananato diaquocopper(II) complexes: erythro and threo isomers

Abstract X-ray crystal structures are reported for two novel N-salicylidene tryptophanato diaquocopper(II) isomers, [Cu(Sal-Trp)(h2O)2, erythro (1) and hreo (2). The coordination geometry about the copper in both complexes is approximately square-pyramidal with the tridentate Sal-Trp Schiff base ligand and the oxygen atom O(W1) of one water molecule occupying the corners of a square. The coordination sphere about the copper is completed by an axial OW(2) water molecule. In 1, O(W2) [CuO(W2) distance 2.25(1) A] is at the same side of the indole ring (syn disposition—“erythro” isomer), whereas in 2 the O(W2) and the α-amino acid chain are disposed anti (“threo” isomer), with a longer CuO(W2) distance, 2.485 A. IR, ESR, electronic spectral data and magnetic properties are discussed and related to the copper binding mode derived from the crystal structure determination.

Synthesis of Zn N-salicylidene-l-aminoacidatos: X-ray structure of [(N-salicylidene-l-alaninato)(aqua)zinc(II)]·0.25H2O and [(N-salicylidene-l-valinato)(aqua)zinc(II)]

Abstract The synthesis in aqueous ethanol solution of eight Zn(II) compounds of salicylaldehyde-amino acid Schiff bases together with their spectral characterisation is reported. Two of the complexes, [( N -salicylidene- l -alaninato)(aqua)zinc(II)]·0.25H 2 O ( 1 ) and [( N -salicylidene- l -valinato)(aqua)zinc(II)] ( 2 ), have been obtained in the form of crystals suitable for X-ray crystallography. The coordination geometry about the zinc in both structures is between distorted trigonal bipyramidal and distorted square pyramidal with the iminic nitrogen N(4) ( 1 =2.020(3) and 2 =2.015(7) A), the phenolic O(8) ( 1 =1.991(2) and 2 =1.997(6) A) and the carboxylic O(1) ( 1 =2.160(2) and 2 =2.156(5) A) of the N -salicylidene-aminoacidato base ligand. Another carboxylic O(1)* of an adjacent unit ( 1 =2.033(2) and 2 =2.033(5) A), curiously shorter than the bond from the ligand itself, and a water molecule ( 1 =2.006(3) and 2 =1.999(6) A) comprise the fourth and fifth coordination positions. The crystals are constituted by polymeric [( N -salicylidene- l -aminoacidato)zinc(II)] moieties forming helical arrays about three-fold screw axes. To our knowledge these are the first two structures of binary complexes of the type [( N -salicylidene- l -aminoacidato)Zn(II)]. The NMR studies, in DMSO, agree with a general endo disposition between the side chain of the amino acid and the aromatic ring of the salicylidene moiety.

Crystal structures of two copper(II) ternary complexes of N-salicylidene-tryptophanato with 2-aminopyridine and 2-aminopyrimidine

Two ternary copper(II) complexes of a tridentate Schiff base of the N -salicylidene-tryptophanato type: [Cu(Sal-Trp)(2-aminopyrimidine)] ( 1 ) and [Cu(Sal-Trp)(2-aminopyridine)]·methanol ( 2b ) have been synthesized and structurally characterized. Single crystal X-ray diffraction analyses show that the copper atom exhibits in 1 a distorted square-pyramidal geometry and in 2b a square-planar geometry, with the tridentate Sal-Trp and one heterocyclic nitrogen of the ligand in the basal plane. In 1 , a weakly bonded nitrogen atom of a second 2-aminopyrimidine molecule is located in the apical position. This second ligand connects to an adjacent unit through the basal plane yielding polymeric chains. In both structures a CH⋯π interaction between the heterocyclic ligand and the indole moiety is present but stacking interactions are not observed.

Interactions of d(10) metal ions with hippuric acid and cytosine. X-ray structure of the first cadmium (II)-amino acid derivative-nucleobase ternary compound.

The interactions of Zn(II), Cd(II) and Hg(II) with hippuric acid (hipH) were studied and several novel compounds were synthesized and studied by NMR. Some new metal-hippuric-cytosine ternary compounds were formed and the structure of the [Cd(hip)(2)(cyt)(H(2)O)](2) ternary complex resolved. Each cadmium (II) atom has a distorted trigonal bipyramid coordination which is linked to a water molecule, a cytosine via N(3), a carboxylic oxygen atom of a hippurate moiety and two bridging dicoordinated hippurates bound through the carboxylic oxygen atoms. To these five main bonds, two longer ancillary interactions can be observed: the second oxygen of the monocoordinated hippurate group and the carboxylic oxygen of the cytosine ligand. The compound is stabilized by an intramolecular stacking between the benzene and cytosine rings and by the hydrogen bonds between the coordinated water molecules and the ligands. This is, to our knowledge, the first structure of a cadmium-amino acid derivative-natural nucleobase compound described so far.

Palladium catalyzed cross-coupling of phenol triflates with organostannanes. A versatile approach for the synthesis of substituted resorcinol dimethyl ethers.

Abstract -2,6 Dimethoxy-substituted phenol triflates undergo efficient Pd(O) catalyzed cross coupling with organostannanes, thus providing an easy access to substituted resorcinol dimethyl ethers, a common building block of many aromatic polyketides.