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PubMed2000

Osmotic Compressibility of Poly(propylene imine) Dendrimers in Deuterated Methanol.

The inverse osmotic compressibility of the poly(propylene imine) dendrimers in deuterated methanol has been measured as a function of concentration with small-angle neutron scattering. The experimental results reveal three different regimes. First, there is a dilute regime going up to a maximum in the inverse osmotic compressibility. This region can be subdivided into a very dilute region, where the behavior is hard-sphere-like, and a denser region, where the solvation layers overlap. The maximum, occurring around volume fraction 0.30 for each generation, is found to be the concentration where the distance between the centers of two dendrimers is twice their radius of gyration. It designates the crossover to the second regime of a semidilute phase with shrinking dendrimers. Interpenetration of the dendrimers does not seem to take place. Finally, for the higher generations, at high concentrations, the dendrimers are collapsed and the inverse osmotic compressibility starts to increase again. As dendrimers are regularly and very highly branched molecules, they can be considered as ultimately hyperbranched polymers. For both types, the experimental inverse osmotic compressibility shows similar features. The dendrimers seem to be more compact, however. Copyright 2000 Academic Press.

Journal Article↗
PubMed2001

The Viscosity of Solutions of Poly(propylene imine) Dendrimers in Methanol.

The viscosity of solutions of poly(propylene imine) dendrimers in methanol has been determined. An Ubbelohde and a low-shear rotational viscometer have been used. The viscosity was Newtonian for every concentration and shear rate used. The value of the Huggins coefficient indicates soft sphere behavior. The viscosity of the lower generations as a function of the volume fraction can be described with a single exponent, where the exponent is comparable to the intrinsic viscosity. The viscosity of the 4th and 5th generation dendrimers shows a stronger increase from a volume fraction of about 0.15 to 0.30. This increase is much smaller than that expected, using the Krieger-Dougherty formula for hard spheres with the hydrodynamic radius determined from the intrinsic viscosity. This smaller increase and the small value of the Huggins coefficient are interpreted in terms of a breakdown of the solvation layer. At a volume fraction of 0.3 the dendrimers, using the radius of gyration as the radius, start to touch each other. From the dependence of the viscosity on the concentration and the dependence of the viscosity on the molar weight, it can be concluded that dendrimers do not interpenetrate. It is concluded that they deform (collapse). Copyright 2001 Academic Press.

Journal Article↗
PubMed1981

Histamine release from rat mast cells induced by protamine sulfate and polyethylene imine.

The protamine sulfate-induced release of histamine from mast cells in a non-cytotoxic reaction, similar to the 48/80-induced secretion. Polyethylene imine was found to be a less potent releaser. It is a cytotoxic substance without specificity for mast cells and acts on membranes generally. Although the two agents are related concerning their molecular weight and polybasicity, their mode of action on mast cells is clearly different.

Animals↗
PubMed1983

Separation of synthetic oligonucleotides on columns of microparticulate silica coated with crosslinked polyethylene imine.

A rapid and effective method for separating oligonucleotides using high-performance ion-exchange chromatography is described. Columns were prepared by adsorbing a layer of polyethylene imine on 5-micron-diameter porous silica followed by crosslinking with a multifunctional oxirane. This weak anion-exchange matrix was found to be useful in the separation of mononucleotides and oligonucleosides containing up to 20 residues in either homo- or heteropolymers. Small analytical columns (4.2 X 150 mm) had a capacity ranging from less than a microgram in analytical separations to several milligrams in the preparative mode. The columns have proven to be especially useful in assessing the purity of precursor blocks, monitoring the chemical synthesis of oligonucleotides, and isolating reaction products after the synthesis.

Chemical Phenomena↗
PubMed1989

Drug-protein conjugates--XVIII. Detection of antibodies towards the antimalarial amodiaquine and its quinone imine metabolite in man and the rat.

A specific enzyme-linked immunosorbent assay (ELISA) was developed for the detection and characterisation of antibodies directed against amodiaquine (AQ), an anti-malarial drug associated with agranulocytosis and liver damage in man. The assay incorporated an antigen which was produced by the reaction of amodiaquine quinone imine (AQQI), a protein reactive product produced from AQ by silver oxide oxidation, and metallothionein. The protein-conjugate (AQ-MT) had a ratio of AQ to protein of 5.2:1. Specific anti-drug antibody was defined as the differential binding to AQ-MT and unconjugated MT which was inhibitable by AQ-mercapturate (5 microM). Following administration of AQ (0.27 mmol/kg; for 4 days) to male Wistar rats there was a significant increase in the IgG anti-AQ activity on day 18 (P less than 0.05, 0.596 +/- 0.410, N = 7) compared to pre-injection levels (0.111 +/- 0.074, N = 7). This activity was shown to be specific for the AQ determinant by hapten inhibition with AQ (IC50 250 nM) and AQ-mercapturate (IC50 310 nM). Following administration of AQQI (27 mumol/kg; i.m.; 4 days) there was a significant increase in IgG anti-AQ antibody activities on day 18 (0.584 +/- 0.161, N = 7) compared to pre-injection levels (0.078 +/- 0.048, N = 7). This activity was inhibited by AQ (IC50 150 nM) and AQ-mercapturate (IC50 180 nM). In addition IgG anti-AQ antibodies were detected in four patients who exhibited agranulocytosis and one patient who exhibited hepatitis (range 0.017-0.842) whilst receiving AQ at a dose of 400 mg weekly for several weeks, but not in individuals who had not received the drug (-0.014 +/- 0.022, N = 7). There was no increase in IgG anti-AQ antibody activities in patients who had not exhibited an adverse reaction whilst receiving the drug for the treatment of malaria (-0.059 +/- 0.074 on day 0 and -0.053 +/- 0.068 on day 7, N = 13). Thus, we have shown that AQ is immunogenic in the rat and that the formation of a chemically reactive metabolite (AQQI) is involved in the generation of the antibody response. Furthermore, drug-specific antibodies were detected in sera from five patients with severe adverse reactions to the drug.

Amodiaquine↗
PubMed1995

Spermidine attenuation of volatile anesthetic inhibition of glutamate-stimulated [3H](5D,10S)-(+)-methyl-10,11-dihydro-5H- dibenzo[a,d]cyclohepten-5,10-imine ([3H]MK-801) binding to N-methyl-D-aspartate (NMDA) receptors in rat brain.

The influence of spermidine, a polyamine agonist, on volatile anesthetic inhibition of N-methyl-D-aspartate (NMDA) receptor activation, as indicated by glutamate stimulation of [3H]MK-801 ([3H](5D,10S)-(+)-methyl-10,11-dihydro-5H- dibenzo[a,d]cyclohepten-5,10-imine) binding, was studied in rat brain. Spermidine reserved the inhibition caused by four volatile anesthetics (enflurane, halothane, methoxyflurane and chloroform) at the same concentrations (EC50 approximately 3 microM) at which it potentiated glutamate opening of the NMDA ion channel. The anesthetics had no effect on the direct stimulation of channel opening by spermidine, which occurred at concentrations of spermidine greater than 30 microM in the absence of receptor agonist. In these actions, spermidine closely resembled the allosteric co-agonist glycine. The present results suggest that anesthetic action on NMDA receptors involves a set of sites on the channel complex that is distinct from the recognition sites for glutamate, glycine, and channel blockers, and are consistent with the idea that blockade of NMDA receptors contributes to the development of the anesthetic state.

Anesthetics, Inhalation↗
PubMed1986

Cellular effects of N(4-ethoxyphenyl)p-benzoquinone imine, a p-phenetidine metabolite formed during peroxidase reactions.

The interaction of N-(4-ethoxyphenyl)p-benzoquinone imine (NEPBQI), a metabolite formed during peroxidase catalyzed metabolism of p-phenetidine, with GSH and its effects in isolated rat hepatocytes were investigated. When reacted with GSH NEPBQI formed both a mono- and a diglutathione conjugate as well as GSSG. Formation of glutathione conjugates and GSSG also occurred when NEPBQI was added to isolated hepatocytes. The formation of GSSG was, however, only detectable if the hepatocytes had been pretreated with the GSSG reductase inhibitor BCNU (1,3-bis-(2-chloroethyl-1-nitrosourea). Similarly, NEPBQI caused a rapid decrease in cellular free protein thiols when added to hepatocytes, however this was expressed at higher concentrations than for effects on GSH. The protein thiol decrease was correlated with protein binding of NEPBQI. NEPBQI was also shown to be toxic to isolated hepatocytes. At a concentration of 400 microM extensive bleb formation was followed by loss of cell membrane integrity and cell death. To assess further the subcellular metabolism of NEPBQI microsomes and cytosol was used. NEPBQI was found to be preferentially reduced by cytochrome P-450 reductase in the microsomes whereas DT-diaphorase catalyzed its reduction in cytosol. NEPBQI did not undergo significant redox cycling since no formation of O2 was observed. Thus, the cytotoxic effect of NEPBQI appears to be due to protein arylation rather than redox cycling.

Animals↗
PubMed1991

Antimicrobial and cytotoxic activity of transition metal chelates with some heterocyclic imines.

Cu(II), Ni(II), Co(II), and Zn(II) chelates with two heterocyclic imines derived from 2-furylglyoxal-2(1)-aminothiophenol (FGATP) and 2-thiophenylglyoxal-anthranilicacid (TGAA) were synthesized. Elemental analysis, molar conductance, magnetic measurements and IR and electronic spectral data were explored to elucidate their probable structures. Different crystal field parameters were also calculated to ascertain the geometry of the resulting chelates. All the ligands and their metal chelates were screened, in vitro, for their antimicrobial activity against two bacteria: S. aureus and E. coli and two fungi, viz: A. niger and C. albicans. The in vitro cytotoxic activity of all the compounds was also assessed.

Anti-Bacterial Agents↗
PubMed2005

Interaction forces and molecular adhesion between pre-adsorbed poly(ethylene imine) layers.

Interaction forces between pre-adsorbed layers of branched poly(ethylene imine) (PEI) of different molecular mass were studied with the colloidal probe technique, which is based on atomic force microscopy (AFM). During approach, the long-ranged forces between the surfaces are repulsive due to overlap of diffuse layers down to distances of a few nanometers, whereby regulation of the surface charge is observed. The ionic strength dependence of the observed diffuse layer potentials can be rationalized with a surface charge of 2.3 mC/m2. The forces remain repulsive down to contact, likely due to electro-steric interactions between the PEI layers. These electro-steric forces have a range of a few nanometers and appear to be superposed to the force originating from the overlap of diffuse layers. During retraction of the surfaces, erratic attractive forces are observed due to molecular adhesion events (i.e., bridging adhesion). The frequency of the molecular adhesion events increases with increasing the ionic strength. The force response of the PEI segments is dominated by rubber-like extension profiles. Strong adhesion forces are observed for low molecular mass PEI at short distances directly after separation, while for high molecular mass weaker adhesion forces at larger distances are more common. The work of adhesion was estimated by integrating the retraction force profiles, and it was found to increase with the ionic strength.

Journal Article↗
PubMed2006

Synthesis and characterization of guanidinylated poly(propylene imine) dendrimers as gene transfection agents.

Fourth generation poly(propylene imine) dendrimer has been completely or partially functionalized with guanidinium groups. In the second case, the remaining toxic primary amino groups of the dendrimers were reacted with propylene oxide affording the corresponding hydroxylated derivatives. Five derivatives have been prepared bearing 0, 6, 12, 24 or 32 guanidinium groups. These guanidinylated dendrimers were interacted with plasmid DNA affording the corresponding dendriplexes. The complexes were physicochemically characterized by dynamic light scattering, zeta-potential measurements and AFM, while the extent of complexation was evaluated by agarose gel electrophoresis. Furthermore, their transfection efficiency was assessed employing HEK 293 and COS-7 cell lines, while the serum effect was studied in HEK 293 cells. It was found that complete replacement of primary amino groups with the hydroxylated moieties resulted in complete loss of transfection efficiency. On the contrary, guanidinylation of the parent dendrimer resulted to significant enhancement of its transfection efficiency, this enhancement being dependent on the number of guanidinium groups per dendrimer, the cell line used and the presence or absence of FBS. The fully guanidinylated dendrimer exhibited the best transfection efficiency under all the conditions studied. This efficiency has been attributed to the enhanced penetrating ability of the guanidinylated dendrimers due to the accumulation of the guanidinium group at the dendrimeric surface. It was also found that the derivative with 12 guanidinium groups exhibited the lowest toxicity. The reduction of toxicity was apparently attributed to the decrease of the external primary amino groups coupled with the presence of hydroxylated moieties located at the dendrimeric surface. The functionalization strategy employed leads to dendrimeric derivatives that combine satisfactory transfection efficiency and cytotoxicity.

Animals↗
PubMed1989

Rapid, high-sensitivity reversed-phase liquid chromatographic assay for 9-chloro-2-(2-furyl) [1,2,4]triazolo[1,5-c]quinazolin-5-imine and its oxo metabolite in plasma using fluorescence detection.

A rapid, sensitive and specific assay for 9-chloro-2-(2-furyl) [1,2,4]triazolo[1,5-c]quinazolin-5-imine (I) and its oxo metabolite (II) in plasma was developed and validated employing reversed-phase high-performance liquid chromatography with fluorescence detection. Sample preparation was achieved by a simple ethyl acetate extraction from plasma buffered at pH 10 (0.1 M boric acid-0.1 M potassium chloride). Chromatographic analyses were performed isocratically on a C18 column, with a mobile phase consisting of methanol-0.2 M sodium acetate buffer, pH 5.0 (67:33, v/v). Chromatographic run time was less than 8 min. The assay was linear (r greater than 0.9998) over the concentration range 1.50-10,000 ng/ml for both I and II; for individual studies, curves covering a range of two orders of magnitude were generally employed. Limits of detection for I and II were 0.5 and 1.0 ng/ml, respectively. A preliminary investigation of the plasma concentrations of I and II in the rat following a single 30 mg/kg oral dose demonstrated the applicability of the method for pharmacokinetic studies.

Animals↗
PubMed2004

Asymmetric phase-transfer catalysis utilizing chiral quaternary ammonium salts: asymmetric alkylation of glycine imines.

O-Alkyl N-anthracenylmethyl derivatives of Cinchona alkaloids can function as enantioselective phase-transfer catalysts. By employing these catalysts in the asymmetric alkylation of glycine imines, one can generate a range of alpha-amino acid derivatives with high levels of enantiomeric excess. It is also possible to generate the catalysts in situ from commercially available chiral amines, which offers the opportunity to evaluate libraries of related structures. This latter approach has been successfully applied to a series of biphenyl quaternary ammonium salts resulting in the development of a new highly selective catalyst and opening up the potential of further expanding the range of alpha-amino acid derivatives that can be prepared.

Journal Article↗
PubMedDate not supplied

Acid- and salt-triggered multifunctional poly(propylene imine) dendrimer as a prospective drug delivery system.

A novel dendrimeric compound is designed with the objective of simultaneously addressing issues commonly encountered in drug delivery, i.e., stability in biological milieu as well as targeting. For this purpose, a multifunctional dendrimeric system derived from diaminobutane poly(propylene imine) dendrimers (DAB) is prepared bearing at its external surface poly(ethylene glycol) chains and guanidinium moieties. For these moieties, it has been established that they exhibit protective and targeting properties, respectively. The release of encapsulated compounds is triggered by titration with acids followed by the addition of sodium chloride solution. Specifically for pyrene, the solubilization site of which can be clearly traced, protonation leads to a distribution between the core and the poly(ethylene glycol) chains in the periphery of the dendrimer while it is released to the aqueous bulk solution by the addition of sodium chloride. The release of betamethasone valerate is also triggered by the addition of sodium chloride solution.

Acids↗
PubMed2006

Physiochemical properties of low and high molecular weight poly(ethylene glycol)-grafted poly(ethylene imine) copolymers and their complexes with oligonucleotides.

Inefficient delivery of antisense oligonucleotides (AOs) to target cell nuclei remains as the foremost limitation to their usefulness. Copolymers of cationic poly(ethylene imine) (PEI) and poly(ethylene glycol) (PEG) have been well-studied for delivery of plasmids. However, the properties of PEG-PEI-AO polyplexes have not been comprehensively investigated. Therefore, we synthesized a series of PEG-PEI copolymers and evaluated their physiochemical properties alone and when complexed with AO. The M(w) of PEG was found to be the main determinant of polyplex size, via its influence on particle aggregation. DLS measurements showed that when PEG5000 was grafted to PEI2K and PEI25K, polyplex diameters were extremely small (range 10-90 nm) with minimal aggregation. In contrast, when PEG550 was grafted to PEI2K and PEI25K, polyplexes appeared as much larger aggregates (approximately 250 nm). As expected, the surface charge (zeta potential) was higher for polyplexes containing PEI25K than those containing PEI2K, but decreased with increased levels of PEG grafting. Surprisingly, within the physiological range (pH 7.5-5), the buffering capacity of all copolymers was nearly equivalent to that of unsubstituted PEI2K or PEI25K, and was barely influenced by PEGylation. The stability of polyplexes was evaluated using a heparin polyanion competition assay. Unexpectedly, polyplexes containing PEI2K showed stability equal to or greater than that of PEI25K polyplexes. The level of PEG grafting also had a dramatic effect on polyplex stability. The relationships established between molecular formulations and polyplex size, aggregation, surface charge, and stability should provide a useful guide for future studies aimed at optimizing polymer-mediated AO delivery in cell and animal studies. A summary of the relationships between polyplex structures and recent studies of their transfection capacity is provided.

Animals↗
PubMed2001

New silylated iminophosphorano(amino)phosphines Me(3)SiN=PPh(2)N(R)PPh(2) (R = Et, (n)Pr, (n)Bu). Crystal and molecular structure of trimethylsilyliminophosphorano(propylamino)diphenylphosphine Me(3)SiN=PPh(2)N((n)Pr)PPh(2). Further oxidative derivatization with S, Se, and azides, titanium(IV) transmetalation of the imine, and syntheses of rhodium(I), palladium(II), and platinum(II) complexes of these iminophosphorano(amino)phosphines.

Bis(phosphino)amines Ph(2)PN(R)PPh(2) (R = Et, (n)Pr, (n)Bu) react with stoichiometric amounts of trimethylsilyl azide to give the trimethylsilyliminophosphorano(amino)phosphines Me(3)SiN=PPh(2)N(R)PPh(2) (1, R = Et; 2, R = (n)Pr; 3, R = (n)Bu) as crystalline compounds. The structure of 2 has been determined by single-crystal X-ray analysis. (Crystal data for 2: monoclinic, P2(1)/c, a = 10.235(1) A, b = 16.802(2) A, c = 17.075(2) A, beta = 101.05(1) degrees, V = 2882.9(5) A(3), Z = 4.) The structure of 2, which is the first example of an iminophosphoranophosphine with the P(III)-N-P(V)=N skeleton, was solved by direct methods and refined to R = 0.044. Compound 2 readily reacts with elemental sulfur, selenium, or phosphoryl azide to give fully oxidized phosphinimines Ph(2)P(E)N((n)()Pr)Ph(2)P=NSiMe(3) (4, E = S; 5, E = Se; 6, E = NP(O)(OPh)(2)). Compounds 4-6 are very sensitive to moisture and readily undergo desilylation to give the parent phosphinimines Ph(2)P(E)N((n)()Pr)Ph(2)P=NH, which can be isolated as moderately stable crystalline solids. The phosphiniminophosphine 2 and the oxidized phosphinimines (4 and 5) react with CpTiCl(3) to give new nitrogen-bound Ti(IV) derivatives Ph(2)P(E)N((n)Pr)Ph(2)P=NTi(Cp)Cl(2) (10, E = lone pair; 11, E = S; 12, E = Se). Compounds 1-3 readily react with rhodium(I), palladium(II), and platinum(II) complexes to give five-membered metallacycles via phosphorus(III) and imine nitrogen coordination.

Journal Article↗
PubMed2004

Rhodium-hydrido-benzylamine-triphenylphosphine complexes: solid-state and solution structures and implications in catalyzed imine hydrogenation.

The complexes cis,trans,cis-[Rh(H)(2)(PPh(3))(2)(NH(2)CH(2)Ph)(2)]PF(6) (1) and cis-[Rh(PPh(3))(2)(NH(2)CH(2)Ph)(2)]PF(6) (2) are characterized by X-ray crystallography; the structures are maintained in CH(2)Cl(2) where the species are in equilibrium under H(2). In MeOH and in acetone, loss of amine and/or H(2) can occur. Traces of 1 and 2 are present after a Rh-catalyzed H(2)-hydrogenation of PhCH=NCH(2)Ph in MeOH, where the amine is generated by hydrolysis of the imine substrate through adventitious water. The findings are relevant to catalyst poisoning in the catalytic process.

Journal Article↗
PubMed2005

Iminic N-bound iminophosphorano versus nitrilic n-bound iminophosphorano Os(IV) complexes: a new double derivatization of the nitrido ligand.

The reactions between trans-[Os(IV)(tpy)(Cl)(2)(NCN)] (1) and PPh(3) and between trans-[Os(IV)(tpy)(Cl)(2)(NPPh(3))](+) (2) and CN(-) provide new examples of double derivatization of the nitrido ligand in an Os(VI)-nitrido complex (Os(VI)N). The nitrilic N-bound product from the first reaction, trans-[Os(II)(tpy)(Cl)(2)(NCNPPh(3))] (3), is the coordination isomer of the first iminic N-bound product from the second reaction, trans-[Os(II)(tpy)(Cl)(2)(N(CN)(PPh(3)))] (4). In CH(3)CN at 45 degrees C, 4 undergoes isomerrization to 3 followed by solvolysis and release of (N-cyano)iminophosphorane, NCNPPh(3). These reactions demonstrate new double derivatization reactions of the nitrido ligand in Os(VI)N with its implied synthetic utility.

Journal Article↗