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Antoni Llobet

Publications and source records attributed to Antoni Llobet.

25 records · Page 2Linked to original sources
PubMed2003

Systematic evaluation of molecular recognition phenomena. 3. Selective diphosphate binding to isomeric hexaazamacrocyclic ligands containing xylylic spacers.

The crystal structure of 3,7,11,18,22,26-hexaazatricyclo[26.2.2.2(13,16)]tetratriaconta-1(31),13(34),14,16(33),28(32),29-hexaene hexahydrobromide salt [(H6P3)Br6] has been determined by means of X-ray diffraction analysis. It crystallizes with an additional molecule of ethanol and half a molecule of water per molecule of the hydrobromide P3 ligand. The protonation constants of P3 and its host-guest interactions with monophospate (Ph) and pyrophosphate (Pp) have been investigated by potentiometric equilibrium methods. Ternary complexes are formed in aqueous solution as a result of hydrogen bond formation and Coulombic interactions between the host and the guest; formation constants for all the species obtained are reported and compared with the isomeric 3,7,11,19,23,27-hexaazatricyclo[27.3.1.1(13,17)]tetratriaconta-1(33),13, 15,17(34),29,31-hexaene (Bn) ligand. For the H6P3Pp(2+) those bonding interactions reach a maximum yielding a log KR6 of 5.87. The selectivity of the P3 ligand with regard to the monophosphate and pyrophosphate substrates (S) is discussed and illustrated with global species distribution diagrams showing a strong preference for the latter over the former as a consequence of the much stronger formation constants with pyrophosphate. An analysis of the isomeric effect is also carried out by comparing the P3-S versus Bn-S systems. In the best case, a selectivity of over 88% is achieved for the diphosphate complexation when using the meta isomer over the para, due solely to the size and shape of the receptors cavity.

Journal Article↗
PubMed2003

Synthesis, structure, and acid-base and redox properties of a family of new Ru(II) isomeric complexes containing the trpy and the dinucleating Hbpp ligands.

Three pairs of mononuclear geometrical isomers containing the ligand 3,5-bis(2-pyridyl)pyrazole (Hbpp) of general formula in- and out-[RuII(Hbpp)(trpy)X](n+) (trpy=2,2':6',2' '-terpyridine; X=Cl, n=1, 2a,b; X=H2O, n=2, 3a,b; X=py (pyridine), n=2, 4a,b) have been prepared through two different synthetic routes, isolated, and structurally characterized. The solid state structural characterization was performed by X-ray diffraction analysis of four complexes: 2a-4a and 4b. The structural characterization in solution was performed by means of 1D and 2D NMR spectroscopy for complexes 2a,b and 4a,b and coincides with the structures found in the solid state. All complexes were also spectroscopically characterized by UV-vis which also allowed us to carry out spectrophotometric acid-base titrations. Thus, a number of species were spectroscopically characterized with the same oxidation state but with a different degree of protonation. As an example, for 3a three pKa values were obtained: pKa1(RuII)=2.13, pKa2(RuII)=6.88, and pKa3(RuII)=11.09. The redox properties were also studied, giving in all cases a number of electron transfers coupled to proton transfers. The pH dependency of the redox potentials allowed us to calculate the pKa of the complexes in the Ru(III) oxidation state. For complex 3a, these were found to be pKa1(RuIII)=0.01, pKa2(RuIII)=2.78, and pKa3(RuIII)=5.43. The oxidation state Ru(IV) was only reached from the Ru-OH2 type of complexes 3a or 3b. It has also been shown that the RuIV=O species derived from 3a is capable of electrocatalytically oxidizing benzyl alcohol with a second-order rate constant of kcat=17.1 M(-1) s(-1).

Journal Article↗
PubMed2003

Platinum complexes of diaminocarboxylic acids and their ethyl ester derivatives: the effect of the chelate ring size on antitumor activity and interactions with GMP and DNA.

A number of new Pt(II) complexes is described having the general formula PtCl(2)(LL), where LL is a chelating diamine ligand. Ligands LL were chosen as D,L-2,3-diaminopropionic acid and its ethyl ester, and D,L-2,4-diaminobutyric acid and its ethyl ester. The compounds were characterized using analytical and spectroscopic methods. The influence of the size of the chelate ring and its functionalization on the biological properties was studied. It was demonstrated by circular dichroism (CD) that the effects on the secondary structure of DNA induced by the four complexes are different. The interaction takes place at the N7 position of the purine bases, as shown by NMR studies. The platinum complexes of 2,3-diaminopropionic acid and 2,4-diaminobutyric acid are able to form intrastrand adducts with DNA and to distort the double helix by changing the base stacking. The ethyl ester derivatives uncoil the DNA from the B form to the C form. The interactions with 5'-GMP and DNA were compared with their antitumor activity. The platinum complexes of diaminocarboxylic acids exhibit cytotoxic activity in the A431, HeLa, and HL-60 cell lines in a dose- and time-dependent manner.

Antineoplastic Agents↗
PubMed2003

Dinuclear copper(I) complexes with hexaaza macrocyclic dinucleating ligands: structure and dynamic properties.

The synthesis and structural and spectroscopic characterization of a family of copper(I) complexes, containing a dinucleating hexaaza macrocyclic ligand, of general formula [Cu(2)(L)(X)(2)](2+) (L = Me2p, Me2m, Me3p, or Me3m; X = MeCN, n-PrCN, CO, t-BuNC, or PPh(3)) is described. This family of complexes contains ligands that differ from one another in the number of methylenic units linking the tertiary amines and in the meta or para substitution of their aromatic rings. The structural characterization in the solid-state includes a single-crystal X-ray diffraction analysis of [Cu(2)(Me2p)(CO)(2)](2+) and of [Cu(2)(Me2m)(t-BuNC)(2)](2+). In solution, those complexes are structurally characterized through NMR spectroscopy that also allows us to put forward and establish their fluxional behavior. Theoretical calculations at the DFT level have also been performed in order to further analyze the relative energy of the different potential isomers as well as to gain insight into their chemical properties. Finally, the influence of the hexaaza ligands over different structural aspects as well as on its potential chemical reactivity is discussed.

Journal Article↗
PubMed2003

Synthesis, structure, and spectroscopic, photochemical, redox, and catalytic properties of ruthenium(II) isomeric complexes containing dimethyl sulfoxide, chloro, and the dinucleating bis(2-pyridyl)pyrazole ligands.

Two isomeric Ru(II) complexes containing the dinucleating Hbpp (3,5-bis(2-pyridyl)pyrazole) ligand together with Cl and dmso ligands have been prepared and their structural, spectroscopic, electrochemical, photochemical, and catalytic properties studied. The crystal structures of trans,cis-[Ru(II)Cl(2)(Hbpp)(dmso)(2)], 2a, and cis(out),cis-[Ru(II)Cl(2)(Hbpp)(dmso)(2)], 2b, have been solved by means of single-crystal X-ray diffraction analysis showing a distorted octahedral geometry for the metal center where the dmso ligands coordinate through their S atom. 1D and 2D NMR spectroscopy corroborates a similar structure in solution for both isomers. Exposure of either 2a or 2b in acetonitrile solution under UV light produces a substitution of one dmso ligand by a solvent molecule generating the same product namely, cis(out)-[Ru(II)Cl(2)(Hbpp)(MeCN)(dmso)], 4. While the 1 e(-) oxidation of 2b or cis(out),cis-[Ru(II)Cl(2)(bpp)(dmso)(2)](+), 3b, generates a stable product, the same process for 2a or trans,cis-[Ru(II)Cl(2)(bpp)(dmso)(2)](+), 3a, produces the interesting linkage isomerization phenomenon where the dmso ligand switches its bond from Ru-S to Ru-O (K(III)(O)(-->)(S) = 0.25 +/- 0.025, k(III)(O)(-->)(S) = 0.017 s(-1), and k(III)(S)(-->)(O) = 0.065 s(-1); K(II)(O)(-->)(S) = 6.45 x 10(9), k(II)(O)(-->)(S) = 0.132 s(-1), k(II)(S)(-->)(O) = 2.1 x 10(-11) s(-1)). Finally complex 3a presents a relatively high activity as hydrogen transfer catalyst, with regard to its ability to transform acetophenone into 2-phenylethyl alcohol using 2-propanol as the source of hydrogen atoms.

Journal Article↗
PubMed2002

Structural, electronic, and magnetic consequences of O-carbonyl vs O-alkoxy ester coordination in new dicopper complexes containing the Cu2(mu-Cl)2 core.

The complexes [Cu2(mu-Cl)2(Cl)2(L)2] (L = dialkylpyridine-2,6-dicarboxylate; R = Et, L = depc, 1; R = i-Pr, L = dppc, 2) have been prepared and their magnetic properties studied. The crystal structures of complexes 1 and 2 have been solved. Compound 1 belongs to the P space group with Z = 2, a = 8.3020(10) A, b = 9.2050(10) A, c = 10.065(2) A, alpha = 99.040(10), beta = 100.810(10), and gamma = 106.502(10) whereas 2 belongs to the C2/c space group with Z = 8, a = 11.6360(10) A, b = 25.906(3) A, c = 11.76579(10) A, and beta = 107.900(10). The different alkyl ester substitutes produce substantial structural and electronic differences. The Cu2Cl2 core geometry is planar for 1 whereas it adopts a butterfly shape in the case of 2. Furthermore, in 2 the dppc ligand coordinates only by the carbonyl oxygen atoms whereas in 1 the depc ligand coordinates through carbonyl and alkoxy oxygen atoms. Magnetic susceptibility data show a ferromagnetic coupling between the two Cu(II) centers in both cases (J = 39.9(6) cm(-1) for 1, and J = 51.3(5) cm(-1) for 2) with very weak antiferromagnetic interactions (J ' = -0.59 cm(-1) and -0.57 cm(-1) for 1 and 2, respectively). Theoretical calculations at the extended Hückel level have also been carried out to further understand the electronic nature of complexes 1 and 2.

Journal Article↗