Search

This manuscript reports the improved synthesis of the α,α,α,α isomer of tetra-p-iodophenyl tetra-methyl calix[4]pyrrole and the X-ray characterization of two solvate polymorphs. In the solid state, the calix[4]pyrrole receptor adopts the cone conformation, including one acetonitrile molecule in its aromatic cavity by establishing four convergent hydrogen bonds between its nitrogen atom and the four pyrrole NHs of the former. The inclusion complexes pack into rods, displaying a unidirectional orientation. In turn, the rods form flat 2D-layers by alternating the orientation of their p-iodo substituents. The 2D layers stack on top of another, resulting in a head-to-head and tail-to-tail orientation of the complexes or their exclusive arrangement in a head-to-tail geometry. The dissimilar stacking of the layers yields two solvate polymorphs that are simultaneously present in the structures of the single crystals. The ratio of the two polymorph phases is regulated by the amount of acetonitrile added to the chloroform solutions from which the crystals grow. Halogen bonding interactions are highly relevant in the crystal lattices of the two polymorphs. We analyzed and characterized these interactions by means of density functional theory (DFT) calculations and several computational tools. Remarkably, single crystals of a solvate containing two acetonitrile molecules per calix[4]pyrrole were obtained from pure acetonitrile solution.

In recent years, the crystal engineering library has been enriched with a number of previously unrecognized or unnoticed intermolecular interactions, such as agostic, tetrel, chalcogen, pnicogen bonding and chelate ring stacking – collectively referred to as “unconventional interactions”. Many open questions remain unaddressed regarding their ability to form synthon interactions, specificity, and cooperativity, for example with π–π stacking interactions. In this work, we throw light on the formation of chelate ring stacking in metal–organic assemblies of nicotinohydrazide ligands (N′-(1-(2-pyridyl)ethylidene)nicotinohydrazide (HL) and N′-(phenyl(pyridin-2-yl)methylene)nicotinohydrazide (HL1)) with mercury(II) halide (HgBr2, HgI2) salts. Their reaction produced five compounds, namely [Hg(μ-L)BrHgBr2]n (1), [Hg(μ-L1)Br]n (2), [Hg(L)I2] (3), [Hg(HL1)I2]·(CH3OH) (4), and [Hg(μ-L1)I]n (5). Crystal structure analysis reveals that chelate ring stackings are formed in four of the reported metal–organic compounds, and are common also in the literature precedents. The energies of chelate ring stackings and π–π heterocycle stackings have been computed and analyzed by means of DFT calculations, and the results were verified using Bader's theory of “atoms in molecules”. These results provide a rationale for preferential formation of both unconventional and conventional stackings and allow us to conclude that chelate ring interaction may be considered as a synthon interaction for nicotinohydrazide metal complexes. Interpretations for packing differences imposed by the substituent effect (substitution of methyl group in HL for phenyl group in HL1) were provided based on the Hirshfeld surface analysis and 2D fingerprint plots of the crystal structures reported here. 20 8 1065 1076

In order to further understand the metal-binding patterns (MBP) of acyclovir (acv), copper(II) and zinc(II) oxo salts (nitrate, sulfate or perchlorate) and tridentate or tripodal-tetradentate chelating-polyamines were reacted with acyclovir to obtain the following compounds: [Cu(dien)(acv)(H2O)]SO4·1.25MeOH·0.5H2O (1), [Cu(dien)(acv)(H2O)]·[Cu(dien)(acv)(H2O)(NO3)](NO3)3]·H2O (2), {[Cu(dien)(µ2-acv)](ClO4)2}n(3), [Zn(dien)(acv)(SO4)] (4), [Cu(pmdta)(acv)](ClO4)2·H2O (5), [Cu(bpa)(acv)(SO4)]·6H2O (6), [Cu(tren)(acv)](NO3)2(7) and [Cu(tren)(acv)](ClO4)2(8) (dien = diethylenetriamine, pmdta = N,N,N′,N′,N″-pentamethyl-diethylenetriamine, bpa = bis-(2-picolyl)amine and tren = tris(2-aminoethyl)amine). All the compounds were studied by spectroscopic techniques and single-crystal X-ray diffraction methods. The metal binding pattern of copper(II) compounds1–3,7and8consists of the cooperation of the Cu–N7(acv) bond with an intramolecular interligand (primary/terminal amino)N-H⋯O6(acv) interaction (which is ‘bifurcated’ in8). Note that in3this MBP is embedded within the unusual bridging µ2-N7,O(ol, N9-side chain) mode. On the other hand, the Zn-N7(acv) bond in compound4is reinforced with the intramolecular (secondary amino)N-H⋯O6(acv) H-bond. This latest interaction is indeed possible but not displayed in compounds5or6, which feature an asymmetric chelating-N7,O6-acv MBP with O6 acting as an apical/distal Cu(II) donor atom. Remarkably, in compounds7and8, an intricate combination of anion⋯π/π⋯π/π⋯anion interactions generates interesting supramolecular networks that have also been studied theoretically by means of DFT calculations. In addition, these assemblies have been characterized using Bader’s theory of “atoms-in-molecules”.

Five new Pb(II) complexes of hydrazone-based and Schiff-based ligands and three different anionic co-ligands (azide, thiocyanate and bromide) have been synthesized and characterized by structural, analytical and spectroscopic methods. This variety of ligands can coordinate to the Pb(II) metal center in a tridentate or tetradentate fashion via a different combination of any of nitrogen, oxygen and sulphur donor atoms. Moreover, the organic ligands can be in mono-deprotonated or neutral forms. By using single-crystal X-ray crystallography, we show that the synthesized complexes aggregate into larger supramolecular entities due to the formation of noncovalent tetrel bonding interactions. The Pb(II) center is hemidirectionally coordinated even in those complexes where the coordination number is six. Consequently, this is sterically ideal for establishing tetrel bonding interactions with electron-rich nitrogen, bromide or sulphur atoms. These contacts are significantly larger than the sums of the covalent radii. Hence, they can be described as non-covalent tetrel bonding interactions. They interconnect the covalently bonded units into supramolecular assemblies (dimers or tetramers). The contribution of contacts involving the Pb atom has been studied using Hirshfeld surface analysis and fingerprint plots. We have analysed the supramolecular assemblies observed in the solid state by means of DFT calculations and characterized them using Bader's theory of atoms-in-molecules. 20 34 5033 5044

In this study, we examine the coordination chemistry of benzyl dihydrazone and thiosemicarbazone Schiff bases featuring different chelation modes, steric bulk, and reactivities towards cobalt(II) thiocyanate. The tetradentate benzyl dihydrazone ligands coordinate to the Co(SCN)2 fragment to form CoN6 coordination spheres (1–3), whereas the thiosemicarbazone ligands provide CoIII complexes featuring CoN4S2 coordination spheres (4 and 5) and charge-balancing anions {; ; ; ; ; ; SCN– and [Co(SCN)4]2– for 4 and 5, respectively}; ; ; ; ; ; . Hirshfeld surface (HS) analysis revealed a substituent effect that results in an increasing number of H···H contacts in the order –H < –CH3 < –Ph (1–3, respectively). The H bonding in 4 and 5 as well as the associated energies were computed by the DFT approach, and these interactions appear to be crucial for the formation of the supramolecular systems. The DFT study also suggested that the H-bonded dimers in 5 are examples of the recently described “antielectrostatic” H bonds.

A Cu(II)-methylmalonate complex, (C3H7N6)4[Cu(II)(C4H4O4)2](H2O)4Cl2 (1) (where C3H7N6 = protonated melamine, C4H4O4 = methylmalonic acid), has been synthesized from aqueous media and its crystal structure was determined by single crystal X-ray diffraction. The anionic Cu(II)-methylmalonate complex mediated formation of interesting supramolecular assemblies in the solid state by means of ionic interactions with protonated melamine. Moreover, other forces such as antielectrostatic H-bonding (AEHB) and π+–π+ interactions also play a crucial role in defining the final 3D architecture of 1. An interesting stacking among protonated melamine molecules is studied by DFT calculations. Lattice water molecules and chlorides form various hydrogen bonds to take part in the self-assembly processes.

Four complexes based on N,N’-bis(2-pyridylmethylene)-1,3-propanediamine (L) and different Cd(II) salts have been synthesized and characterized by single crystal X-ray diffraction analysis. The complexes are [Cd2(L)2(μ-Cl)2](ClO4)2 (1), [Cd2(L)2(μ-Br)2](ClO4)2 (2), [Cd(L)I](ClO4) (3) and [Cd(L)(NCS)2] (4). L exhibits the same coordination mode in 1-4. The radius of each anion plays a role in affecting the structures and luminescent intensities of the final products. CdCl2, CdBr2 and CdI2 react with L to produce chloride or bromido bridged binuclear complexes and mononuclear iodido complex, respectively, whereas an unusual mononuclear trigonal prismatic 4 is obtained when thiocyanate was used as a coligand. Photoluminescence properties of all the complexes show that the trend of fluorescence intensity is 1>4>2>3. All four complexes exhibit different supramolecular interactions such as C–H/σ, π–π and C–H/π and hydrogen bonding interactions. The experimental findings are complemented by density functional theory (DFT) calculations.

In this manuscript we report the synthesis and X-ray characterization of several complexes of Cu(II), Co(II) and Ni(II) with 2-(N-benzimidazolyl)-pyrimidine (L) and nitrate co-ligands. Complexes 1 and 2 are trans and cis isomers, respectively, with formula [CuL2(NO3)(2)]. Furthermore, complexes 2, [CuL2(NO3)(2)] (3) and [NiL2(NO3)(2)] (4) are essentially isostructural with a cis-disposition of the nitrate ligands. In compounds 1-4, the coordination mode of nitrate is terminal bidentate. Finally, during the synthesis of compound 1, a few crystals of a different complex were found and separated manually from the bulk sample and characterized by X-ray diffraction. In this compound (5), the benzimidazole ring of the ligand is oxidized to benzimidazolone (L') and the formula of this unexpected compound is [CuL'(2)(H2O)(2)](NO3)(2). Complexes 1 and 5 are characterized by the presence of anion-pi interactions that are relevant to the final 3D architecture and packing. In the crystal structures of the five compounds, C-H center dot center dot center dot O hydrogen bonds, anion-pi and pi-stacking interactions are described and analysed by means of density functional theory (DFT) calculations since they play an important role in the construction of three-dimensional supramolecular frameworks. Moreover, some unconventional interactions have been characterized using Bader's theory of atoms-in-molecules.

In this manuscript we report the synthesis and X-ray characterization of four Zn(II) complexes and three Cd(II) complexes with an asymmetrical hydrazone–pyridine based ligand {HL = 2-acetyl-pyridyl-isonicotinoylhydrazone (HAPIH)}; i.e. {[Zn(HL)2](NO3)2·H2O} (1), [Zn(HL)Br2] (2), [Zn(HL)I2] (3), [Zn(HL)(NCS)2] (4), [Cd(L)2] (5), {[Cd(HL)Br2]·CH3OH} (6) and {[Cd(HL)I2]·2CH3OH} (7). The Schiff base acts as a tridentate N2O-donor ligand through the oxygen, the imine and pyridine nitrogen atoms in all the complexes. In most complexes, the ligand is observed to coordinate as a zwitterion since the proton in the hydrazine group ([double bond, length as m-dash]N–NH–C[double bond, length as m-dash]O) shifted to the uncoordinated pyridine ring, except in 7. On the other hand, in 5 the ligand acts as a negatively charged species and is bound to the cadmium center in the enolic form ([double bond, length as m-dash]N–N[double bond, length as m-dash]C–O−). In complexes 2–4, 6 and 7, the coordination geometry around each metal center is distorted trigonal bipyramidal, with the coordination sphere of the metal completed by two halide or NCS anions. On the other hand, in homoleptic complexes 1 and 5, the metal, chelated by two tridentate Schiff base ligands, exhibits an octahedral geometry. In the crystal packing of all compounds, the pyridine rings favour π–π interactions among the symmetry related complexes. The noncovalent interactions among the complexes have been analyzed using Hirshfeld surface analysis and DFT calculations using Grimme's D3 dispersion correction to properly describe the π–π interactions., We are grateful to the University of Tabriz for generous financial support to this research. A. B. and A. F. acknowledge financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) through projects CTQ2014-57393-C2-1-P and CONSOLIDER INGENIO 2010 CSD2010-00065 (FEDER funds).

Condensation of N-(2-hydroxyethyl)ethylenediamine and pyridine-2-carbaldehyde in the presence of ZnX2 salts (X = ClO4−, Cl−, Br−, I−) generates four complexes, namely, [ZnL1Cl](ClO4) (1), [ZnL1Cl][ZnCl3(H2O)]·2H2O (2), [ZnL1Br][ZnBr3(H2O)]·2H2O (3), and [Zn(L2)3]I2 (4), where L1 and L2 are aminal and hemiaminal ether derivatives, i.e., (E)-N-((pyridine-2-yl)methylene)-2-((2-pyridine-2-yl)oxazolidin-3-yl)ethanamine and 2-(2-pyridin-2-yl-imidazolidin-1-yl)-ethanol, respectively. No complex with the expected Schiff-base ligand (E)-2-(2-(pyridin-2-ylmethyleneamino)ethylamino)ethanol (L) or with 2-(2-pyridyl-3-(2-hydroxyethyl))oxazolidine (L3) was obtained. The structures of complexes 1, 3, and 4 have been elucidated by single crystal X-ray diffraction. All the complexes have been characterized by detailed NMR (1H, 13C and DEPT-135) and ESI-MS analyses, indicating retention of solid state structures in the solution phase. Complex 1 deserves special mention as during its formation, the ClO4− ion undergoes reduction to Cl− and thus, it forms a mixed anionic ligand complex. Thorough DFT calculations have been performed at the BP86-D3/def2-TZVP level of theory to rationalize the ligand and complex formation. The calculations suggest that the aminal form (L1) is the most favored species followed by the Schiff-base, whereas the hemiaminal ether form (L3) is the least preferred one. The role of halides during the formation of the monoanionic [ZnX3(H2O)]− species is crucial, and the achieved complex is highly favored when X = Cl and disfavored for X = I; this trend has been rationalized by the DFT calculations. The phosphatase activities of the complexes have been investigated, and their efficiencies follow the order 2 > 1 > 3 > 4.

A library of 15 dicopper complexes as synthetic analogues of catechol oxidase has been synthesized with the aim to determine the relationship between the electrochemical behavior of the dicopper(II) species in the absence as well as in the presence of 3,5-di-tert-butylcatechol (3,5-DTBC) as model substrate and the catalytic activity, kcat, in DMSO medium. The complexes have been characterized by routine physicochemical techniques as well as by X-ray single-crystal structure analysis in some cases. Fifteen "end-off" compartmental ligands have been designed as 1 + 2 Schiff-base condensation product of 2,6-diformyl-4-R-phenol (R = Me, (t)Bu, and Cl) and five different amines, N-(2-aminoethyl)piperazine, N-(2-aminoethyl)pyrrolidine, N-(2-aminoethyl)morpholine, N-(3-aminopropyl)morpholine, and N-(2-aminoethyl)piperidine. Interestingly, in case of the combination of 2,6-diformyl-4-methylphenol and N-(2-aminoethyl)morpholine/N-(3-aminopropyl)morpholine/N-(2-aminoethyl)piperidine 1 + 1 condensation becomes the reality and the ligands are denoted as L2(1-3). On reaction of copper(II) nitrate with L2(1-3) in situ complexes 3, 12, and 13 are formed having general formula Cu2(L2(1-3))2(NO3)2. The remaining 12 ligands obtained as 1 + 2 condensation products are denoted as L1(1-12), which produce complexes having general formula Cu2(L1(1-12))(NO3)2. Catecholase activity of all 15 complexes has been investigated in DMSO medium using 3,5-DTBC as model substrate. Treatment on the basis of Michaelis-Menten model has been applied for kinetic study, and thereby turnover number, kcat, values have been evaluated. Cyclic voltametric (CV) and differential pulse voltametric (DPV) studies of the complexes in the presence as well as in the absence of 3,5-DTBC have been thoroughly investigated in DMSO medium. From those studies it is evident that oxidation of 3,5-DTBC catalyzed by dicopper(II) complexes proceed via two steps: first, semibenzoquinone followed by benzoquinone with concomitant reduction of Cu(II) to Cu(I). Our study reveals that apparently there is nearly no linear relationship between kcat and E° values of the complexes. However, a detailed density functional theory (DFT) calculation sheds light on this subject. A very good correlation prevails in terms of the energetics associated with the Cu(II) to Cu(I) reduction process and kcat values, as revealed from the combined theoretical and experimental approach.

Reaction of ZnII-acetate with two N, N, O-donor Schiff-base ligands, HL1 {4-Chloro-2-[(2-morpholin-4-yl-ethylimino)-methyl]-phenol} and HL2 {4-Chloro-2-[(3-morpholin-4-yl-propylimino)-methyl]-phenol}, which are formed in situ via condensation of 5-chlorosalicylaldehyde and N-(2-aminoethyl/propyl)morpholine, produce one tri- and one mononuclear species, Zn3L1(OAc)4 (1) and ZnL2(OAc) (2). The hypothetical ZnL1(OAc) and Zn3L2(OAc)4 are energetically unfavorable by 9.2 and 5.1 kcal/mol, in compare with their respective real counterparts 1 and 2 evidenced from DFT calculations. Both 1 and 2 catalyze the hydrolytic cleavage of phosphoester bond of (4-nitrophenyl) phosphate where 1 shows higher activity than that of 2. The proposed mechanistic pathways of phosphatase activity of 1 and 2 and the higher efficiency of the latter have been rationalized by DFT study. DNA cleavage activities have been investigated using supercoiled pET28a plasmid DNA where both the complexes show dose dependent DNA cleavage activity with varying degree. Complex 1 shows excellent breakage activity even at a concentration of 20 μM. However, in both cases hydroxyl radical pathway is most probably operative in DNA cleavage activity.

International audience; Potentially hexadentate N2O4 donor Schiff base ligands N,N′-bis(3-ethoxysalicylidenimino)-1,2-diaminoethane (L1H2) and N,N′-bis(3-methoxysalicylidenimino)-1,3-diaminopropane (L2H2) have been used to synthesize two manganese(III) compounds [MnL1(SCN)(H2O)].[MnL1(H2O)2](ClO4)·CH3CN (1) and [MnL2(SCN)(H2O)] (2). All the ligands and the complexes have been characterized by microanalytical and spectroscopic techniques. The X-ray structural characterization of all the complexes shows a tetragonally elongated octahedral geometry for the manganese coordination sphere. The octahedron entities are further connected in pairs through intermolecular hydrogen bonding to form μ-aquo dimers, which are further stabilized by π–π interactions occurring between the aryl rings of the Schiff base ligands. These noncovalent interactions have been investigated in terms of energies and geometries using theoretical calculations. The catalytic activity of compounds 1 and 2 on the oxidation of 3,5-di-tert-butylcatechol was determined spectrophotometrically by monitoring the increase of the 3,5-di-tert-butyl-o-benzoquinone characteristic absorption band at about 400 nm over time in methanol saturated with O2. The complexes were able to oxidize 3,5-di-tert-butylcatechol to the corresponding o-quinone with distinct catalytic activity.

La heparina es una familia de cadenas de glicosaminoglicanos (GAGs) formados por residuos de glucosamina y ácido urónico, cuya eficacia y seguridad en la profilaxis y tratamiento de las enfermedades trombóticas están bien establecidas.El descubrimiento de que parecía posible desdoblar el efecto inhibidor del factor Xa de la inhibición de la trombina, con las fracciones de bajo peso molecular de la heparina despertó grandes expectativas y condujo a la introducción en terapéutica de las heparinas y heparinoides de bajo peso molecular. Debido a los distintos procedimientos de obtención y a las diferentes unidades utilizadas por los fabricantes para expresar la actividad de sus productos, las comparaciones entre los distintos preparados eran complicadas.Esta situación indujo a la realización de la presente tesis en la que se comparó el efecto de distintos GAGs sobre la hemostasia en un modelo de trombosis in vitro.Los productos estudiados fueron: Fragmin® (Kabi) y Fraxiparinc® (Sanofi), dos heparinas de bajo peso molecular que se obtienen a partir de la heparina por despolimerización y purificación; Lomoparán® (Organon) un hiparinoide de bajo peso molecular que se produce directamente de mucosa intestinal porcina; Org 31550 es un derivado sintético del pentasacárido natural de unión a la ATIII y está exento de toda acción inhibidora de la trombina; la heparina no fraccionada estudiada (HNF, Laboratorios Rovi) es la disponible comercialmente y se obtiene de mucosa intestinal porcina.Debido a las distintas unidades empleadas por los fabricantes, en primer lugar hubo que seleccionar la concentración óptima que sería utilizada en las perfusiones, para cada uno de los productos. De forma arbitraria se decidió utilizar la mínima necesaria que inhibiera la formación de trombina en sangre mantenida en reposo a temperatura ambiente. Como indicador de la formación de trombina se determinó la concentración de fibrinopéptido A (FPA).A continuación se estudió el efecto de los GAGs sobre el funcionalismo plaquetario a las dosis seleccionadas. Para ello se realizaron perfusiones en las que se cuantificó el depósito de plaquetas sobre la superficie expuesta al flujo y se evaluó la formación de microagregados plaquetarios.Las perfusiones se realizaron en una cámara de perfusión desarrollada por Sakariassen. La superficie adhesiva era matriz extracelular (MEC) de células endoteliales (CE) cultivadas in vitro. Expuesta al flujo esta matriz induce la adhesión plaquetaria, pero no la formación de trombos. Para obtener una matriz trombogénica que permitiera estudiar la formación de fibrina y trombos plaquetarios, las células fueron estimuladas con un éster de forbol que induce en las CE la síntesis y depósito de factor tisular en la MEC que activará la cascada de la coagulación que conducirá a la producción de trombina.En la evaluación en face de la adhesión plaquetaria se cuantificó la superficie cubierta (SC) por plaquetas. Los trombos plaquetarios se evaluaron en sección transversal que permite cuantificar la superficie cubierta por trombos de diferentes alturas. Al finalizar las perfusiones se midió la formación de microagregados (SPD) realizando recuentos en EDTA y en glutaraldehído en un contador automático fijando la ventana de recuento entre 3,2 y 16 fl. La idea es que los microagregados formados durante la perfusión se deshacen al colocarlos en una EDTA, y por el contrario son fijados en glutaraldehído y no son valorados por el contador.El siguiente paso consistió en encontrar un método fiable que permitiera cuantificar la fibrina depositada sobre la matriz. En primer lugar se comparó la técnica que se pensaba utilizar, que es la del Fg-PO con la del Fg marcado con iodo 125 que se considera el patrón pero que tiene el inconveniente de que obliga a trabajar con material radioactivo. Para el estudio comparativo se realizaron perfusiones sobre matriz trombogénica en las que la fibrina se midió con las dos técnicas a la vez.Una vez establecida la técnica a utilizar se estudió el efecto de los glicosaminoglicanos y de las condiciones de flujo sobre la formación de fibrina, utilizando las mismas condiciones de perfusiones que antes.RESULTADOSSe observa que Fragmin y Fraxiparine son casi igualmente efectivas inhibiendo la formación de trombina en la sangre en reposo en términos de molaridad (33,2 Y 36,8 nmol/ml aunque difieren considerablemente cuando se expresan en las U del fabricante (20 y 40 U/mi). Mucha mayor cantidad se requiere de Lomoparan (146,4 nmol/ml) y del pentasacárido 31550 (95,2 nmol/ml) posiblemente debido a su menor actividad inhibidora de la trombina. Como cabía esperar por su actividad anti-trombina mucha menor cantidad de HNF fue necesaria (1,9 nmol/ml).Con la sangre anticoagulada con Lomoparan, la SC por plaquetas es significativamente mayor a los otros GAGs. Respecto al SPD la cifra de Lomoparan es menor aunque sólo es estadísticamente significativa comparada con la obtenida con Fragmin. Al estudiar la relación entre SC y SPD en cada una de las perfusiones realizadas, se observa que presentan una correlación lineal inversa estadísticamente significativa. Parece probable que la mayor SC observada con Lomoparan sea debido a su menor capacidad de formación de microagregados.Cuando se estudió el efecto sobre la formación de agregados, sólo en la superficie cubierta por agregados mayores de 10 milimicras se observaron diferencias, siendo menor para heparina no fraccionada y Lomoparan que para Fragmin y Fraxiparine. Sabemos que la formación de trombos plaquetarios en estas condiciones es un proceso trombina dependiente. Por lo tanto las diferencias observadas en los agregados de mayor tamaño posiblemente sea debida a diferencias en la cantidad de trombina formada. Presentando la HNF la mayor capacidad de inhibición, y tras ella Lomoparan, Fragmin y Fraxiparine.Tras realizar los estudios comparativos se decidió utilizar el marcaje con yodo pues a pesar de que la manipulación del material radioactivo es más engorrosa, proporciona unos resultados fiables.Una vez seleccionada la técnica a utilizar, se estudió el efecto de los glicosaminoglicanos y del flujo sobre el depósito de fibrina.La cantidad de fibrina depositada en las perfusiones realizadas con sangre anticoagulada con la HNF, a ambos coeficientes de cizalladura es casi inexistente. Ni la microscopía óptica ni la electrónica, mostraron fibrina en absoluto; estas cifras probablemente muestran los valores de fondo correspondientes al Fg-Yodo asociado a la MEC y/o a las plaquetas.Por el contrario, la fibrina formada con los otros GAGs varió considerablemente dependiendo del tipo de anticoagulante y el coeficiente de cizalladura. A 300 s(-1) el pentasacárido Org 31550 proporcionó las cantidades mayores de fibrina formada, seguido por Fraxiparine y Fragmin. Lomoparan inhibió el depósito de fibrina en mayor proporción.Cuando el coeficiente de cizalladura se aumentó a 1.300 s(-1) la cantidad de fibrina disminuyó. Para el pentasacárido y la HNF, la reducción no alcanzó significación estadística. Sí lo fue para Fraxiparine, Fragmin y Lomoparán, en los que rondó alrededor del 80%.La generación del FPA siguió el mismo patrón que la fibrina, es decir el menor aument o correspondió a la HNF, ya continuación Lornoparan, Fragmin y Fraxiparine y el mayor al pentasacárido. El aumento en los niveles de fibrinopéptido A se detuvo al fmalizar la perfusión en todos los GAGs excepto para el pentasacárido. En este caso, a los 15' de acabar la perfusión los niveles de FPA habían crecido aproximadamente un 30%. Esto probablemente indica que una vez se ha formado trombina escapa a los mecanismos de inhibición y continua ejerciendo su acción en la fase líquida.Entre los GAGs de bajo peso molecular Lomoparán posee un efecto antitrombina mayor que Fragmin y Fraxiparine. Este mayor potencial antitrombólico podría deberse a la presencia de dermatán sulfato, pues recientemente se ha demostrado que los complejos de dermatán sulfato-cofactor JI de la heparina son capaces de inhibir a la trombina unida a la fibrina mientras que los complejos de antitrombina III-heparina no lo son. El perfil de acción de Fragmin y Fraxiparine es más o menos igual con una tendencia de Fraxiparine hacia un menor efecto antitrombótico.Las diferencias observadas en la generación de FPA comparando los dos coeficientes de cizalladura no fueron estadísticamente significativas. Esto sugiere que la menor cantidad de fibrina depositada a alto coeficiente de cizalladura posiblemente se debe a una menor polimerización de los monómeros de fibrina inducida por el flujo que a un defecto en la formación de trombina., Low molecular weight heparin(oid)s (LMWH) differ markedly in terms of molecular composition and activity. In order lo gel more insight into the effect on platelets and fibrin deposition we have compared Fragmin® (KabiVitrum, FA), Fraxiparine® (Choay Laboratories, FP), Lornoparan®, a LMW heparinoid (Organon, LO), a synthetic derivative of rhe natural pentasaccharide, Organon 31550 (PE) and unfractionated heparin (Rovi Laboratories, UH) in a perfusion systern. The concentration selected for perfusion studies was the lowest which inhibited thrombin generation (measured as increase in fibrinopeptide A, FPA) in blood stored for 3 hours at room temperature. Blood from healthy donors was anticoagulated with FA 20 U/ml, FP 40 U/ml, LO 15 U/ml, PE 200 U/ml and UH 5 U/ml. Perfusions were carried out in a rectangular chamber at a shear rate of 300 and 1300 s(-1) for 5 minutes. The extracellular matrices (ECM) used as adhesive surface were obtained from cultured human umbilical vein endothelial cells. A part of these cells were stimulated with phorbol myristate acetate for 16 hours to induce tissue factor synthesis and thrombin formation in the ECM.The extent of platelet aggregation during perfusion was measured as single platelet disappearance (SPD) by comparing platelet counts in EDTA and glutaraldehyde. Fibrin deposition was measured with IUI-fibrinogen. FPA generation during perfusion was assessed with a RIA kit. In the perfusions performed al 1300 s(-1)' for 5 min, over non stimulated ECM, LO showed a significantly higher platelet adhesion than the other heparins. This correlated with a significantly lower SPD during perfusion. In perfusions carried out at 300 s(-1) over stimulated ECM, all LMWH's and PE gave significantly more fibrin deposition than UH. LO gave less fibrin than the others LMWH's. When the shear rate was increased to 1,300 s(-1) the amount of fibrin deposited on !he ECM decreased, with no changes in the amount of FPA generated, indicating that probably it was due to a defect on fibrin polymerisation more than to a impairment of thrombin formation. In conclusion: in this experimental model, LO exerts less effect on platelets than the other heparins studied. All LMWH's tested and PE, but not UH, a1low local thrombin generation and fibrin deposition on subendothelium. LO inhibited fibrin deposition to a larger extent than the other LMWH's.