Interactions between multivalent ions and exponentially growing multilayers: dissolution and exchange processes

The interactions between multivalent ions (small ions or polyelectrolytes) and two exponentially growing polyelectrolyte multilayers, namely, (HA-PLL)(n)() and (HA-PAH)(n)() films, are investigated (HA = hyaluronic acid, PLL = poly-l-lysine, PAH = poly(allylamine)). Ferrocyanide and ferricyanide ions are used as small ion probes. The most striking finding is that, even though these two ions differ only by one charge unit, the ferrocyanide ions induce a partial dissolution of both multilayers whereas these films remain stable in the presence of ferricyanide ions. The dissolution process of (HA-PLL)(n)() films is more rapid than that of (HA-PAH)(n)() films, indicating a stronger interaction between HA and PAH compared to HA and PLL. This is confirmed by polyelectrolyte exchange experiments: when an (HA-PLL)(n)() multilayer film is put into contact with a PAH solution, PLL is quantitatively exchanged with the PAH chains and transformed into an HA-PAH film, whereas an (HA-PAH)(n)() multilayer remains stable in the presence of a PLL solution.     

Rearrangement reactions of aziridinylbenzaldoximes

Reactions of 2,2-dimethylaziridine with benzohydroximoyl chlorides [ArC(Cl)?NOH] give aziridinylbenzaldoximes 1 . It has been found that the aziridine ring in these compounds undergoes ring opening in hydrogen chloride-dioxane solution to give (Z)-N-hydroxy-N′-(2-chloro-2-methylpropyl)benzenecarboximidamides [ArC(NHCH₂CR¹R²Cl)?NOH, 4 ]. Treatment of 1 with hydrochloric acid followed by neutralization with aqueous sodium hydroxide gave 6,6-dimethyl-3-aryl-1,2,4-oxadiazines 2. Reaction of 4 with sodium hydride in dioxane gave 5-isopropyl-3-aryl-4,5-dihydro-1,2,4-oxadiazoles 5. Reaction of the 4,5-dihydro-1,2,4-oxadiazoles 5 with N-chlorosuccinimide gave the heteroaromatic 1,2,4-oxadiazoles 6 . It is suggested that reactions of 4 with sodium hydride in dioxane solution involve the conjugate base of 4 which undergoes a 1,2-hydride shift that is concerted with loss of chloride ion. In aqueous sodium hydroxide solution it is suggested that the conjugate base of 4 undergoes ionization of the chlorine atom followed by nucleophilic attack by the oximate anion.     

Automated on-line gel permeation chromatography-gas chromatography for the determination of organophosphorus pesticides in olive oil

An on-line combination of gel permeation chromatography and gas chromatography has been designed using either a laboratory-built or a commercially available LC-GC apparatus to determine organophosphorus pesticides in olive oil. Gel permeation chromatography was used for sample pretreatment, viz. to separate the low-molecular-mass pesticides from the higher-molecular-mass fat constituents of the oil. A mixture of n-decane and the azeotropic mixture of ethyl acetate and cyclohexane was found to give an adequate separation between the fat and the organophosphorus pesticides. The pesticide-containing fraction, monitored by a UV detector, was transferred on-line to the gas chromatograph using a loop-type interface. n-Decane (6%, v/v) was added to the eluent in order to widen the application range of the transfer technique towards more volatile pesticides. After solvent evaporation through the solvent vapour exit and subsequent GC separation, the compounds were selectively detected with a thermionic or a flame photometric detector. The set-up allowed the direct analysis of oil samples after dilution in the gel permeation chromatography eluent without further sample clean-up. Detection limits were about 5 and 10 μg/kg with the thermionic and the flame photometric detector, respectively, when using an injection volume of only 30 μl of the 20-fold diluted oil. The total procedure was linear in the 0.01–10 mg/kg range for both detectors. For twenty organophosphorus pesticides, the relative standard deviations were 3–13% at the 20–60 μg/kg level.     

Amylose-iodine complex formation without KI: Evidence for absence of iodide ions within the complex

Amylose-iodine (AI) complex has been synthesized in aqueous solution without added KI. Complex formation (with solid iodine in amylose solution) is maximized at approximately 35°C and decreases beyond that temperature. Ion-selective electrode (ISE) measurements of an aqueous solution of iodine and AI complex indicate that there is no change in the I⁻ ion concentration when the complex forms. This suggests that I⁻ ions (including I, I, and others) cannot be involved in forming the AI complex. The present work also reports a new and simple method for providing both the iodine-binding capacity (IBC) of amylose and the dissociation mechanism for the AI complex. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2711–2717, 1999     

Competitive Affinity Release for Long‐Term Delivery of Antibodies from Hydrogels

With increased clinical use of antibodies, long‐term delivery strategies are needed to decrease injection frequency and improve health outcomes. A three‐component drug‐delivery system was developed for competitive affinity release of a streptavidin–antibody conjugate from agarose–desthiobiotin hydrogels via controlled dissolution of sparingly soluble biotin derivatives. The antibody conjugate was localized in the hydrogel through streptavidin–desthiobiotin complexation. Dissolution of sparingly soluble biotin derivatives disrupts streptavidin–desthiobiotin complexation for controlled release of the antibody conjugate. Release was tuned by altering the total biotin derivative concentration without further hydrogel or antibody modification. First‐order tunable release of bioactive Avastin, a therapeutic anti‐VEGF antibody, was demonstrated from a non‐cytotoxic system for over 100 days.     

Synthesis,spectral, structural characterization and biological activity of new palladium(II) complexes containing 3‐acetyl‐8‐methoxy‐2H‐chromen‐2‐one derived Schiff bases

Four different mononuclear palladium(II) complexes of 3‐acetyl‐8‐methoxycoumarin Schiff bases were synthesized and characterized by spectrochemical techniques. Further analysis through X‐ray crystallography confirmed the structures of the complexes. Their interactive ability with Calf Thymus DNA and protein (Bovine Serum Albumin and Human Serum Albumin) were investigated by means of absorption and emission methods. The intercalative mode of binding with DNA was supported by EB displacement studies and viscosity measurements. Configurational changes that occurred in the proteins have been analysed with the help of 3D fluorescence studies. The complexes were shown to have good antimicrobial activity against the tested bacterial and fungal pathogens. In addition, antiproliferative activity of the complexes was evaluated on A549 and MCF‐7 cell lines and the complexes were comparatively more active than the standard drug cisplatin. Among the compounds, complex 3 was the most effective against MCF‐7 (IC₅₀ value of 5.20 ± 0.15 μM) and A549 (5.09 ± 0.13 μM) compared with the other complexes 1 (6.48 ± 0.17 μM; 5.98 ± 0.09 μM), 2 (5.53 ± 0.12 μM; 5.85 ± 0.11 μM), 4 (6.73 ± 0.19 μM; 6.63 ± 0.16 μM) and cisplatin (16.79 ± 0.08 μM; 15.10 ± 0.05 μM) respectively. LDH and NO release assays confirmed the cytotoxic potential of the synthesized complexes.     

Hybrid Dextran-gadolinium Nano-suitcases as High-relaxivity MRI Contrast Agents

Dextran-poly(glycidyl methacrylate)(Dex-PGMA) nano-suitcases were synthesized efficiently via a graft copolymerization induced self-assembly(GISA) approach. On this basis, the Dex-PGMA nano-suitcases were modified with hydrazide, and the attachment of multiple chelated Gd(Ⅲ) ions to the interior of the nano-suitcases affords nanoscale MRI contrast agents with high relaxivity values. The highly fenestrated dextran shell of the nano-suitcases assures water exchange which readily occurs between the surrounding environment and the Gd(Ⅲ) ions encapsulated within the hybrid nano-suitcases. The complexation between the hydrophilic hydrazide interior of the nano-suitcases and Gd(Ⅲ) ions results in an impressive Gd payload at 22.6 wt% in the hybrid nano-suitcases. The longitudinal relaxivity(r1) of the hybrid nano-suitcases is reported as 44.4 L/(mmol·s), which is 9-14 folds of that of commercial Gd-DTPA agents. In vivo MRI studies demonstrate that the hybrid nano-suitcases accumulated in the lymph node of the rat due to their nanoscale dimensions and displayed strong signals in vivo. The results indicated that the hybrid nano-suitcases provide a promising platform for the diagnosis of lymph node related diseases.     

Copper-mediated synthesis of N-vinyl ynamides from N-vinyl carbamates

Ynamides are versatile 3-atoms building blocks for organic synthesis as they participate in a variety of ionic, radical and pericyclic processes. Converting ynamides into 5-atom building blocks, such as the yet unreported N-vinyl ynamides, would open new avenues in this fascinating chemistry. We describe herein our efforts towards such goal and demonstrate that the cross-coupling between N-vinyl carbamates and bromo-alkynes using copper(I) thiophene carboxylate, 1,10-phenanthroline and tBuOK in DMSO is a reactive system with an improved profile compared to the classical ynamides syntheses. The advantages and limitations of this copper-mediated reaction are discussed.