Synthesis and characterization of a poly[2,7-(9,9-dioctylfluorene-alt-2,7-fluorene/β-CD)] main chain polyrotaxane

Poly[2,7-(9,9-dioctylfluorene-alt-2,7-fluorene/β-CD)] main chain polyrotaxane was synthesized through organometallic Suzuki coupling by reacting β-cyclodextrin/2,7-dibromofluorene inclusion complex with 9,9-dioctylfluorene-2,7-bis(trimethyleneborate). The IR, NMR and elemental analysis data support the presence of β-cyclodextrin in the copolymer structure. No glass transition or melting phenomena were detected in DSC curves of the polyrotaxane on the heating run in the 50-250 ° range. As compared with the reference copolymer obtained in the absence of β-cyclodextrin, the rotaxane copolymer is more hygroscopic and soluble in polar/non-polar solvent mixtures. The expected modification of the optical properties of the fluorene copolymer with rotaxane architecture in the main chain was proved by fluorescence and UV-vis spectroscopy and consists in a blue-shifted emission.     

Transformation of 5-hydroxymethylene-5H-6,7-dihydrodibenzo[a,c]cyclohepten-6-one over Ru-containing BEA zeolites

Ru–BEA catalysts with 1.0–2.5 wt.% Ru were prepared by ion exchange. The acidic properties of these catalysts were investigated using deuterated acetonitrile, pyridine, and 2,6-di-tert-butyl-pyridine. The deposited Ru was studied by CO-FTIR spectroscopy. The materials were tested as catalysts in the hydrogenation of a conjugated cyclic keto–enol, namely, 5-hydroxymethylene-5H-6,7-dihydrodibenzo[a,c]cyclohepten-6-one. Beside hydrogenation, hydrogenolysis products were identified by GC–MS and ¹H NMR techniques. Relations were sought between the selectivity and some physicochemical properties of the catalyst.     

RuO4-mediated oxidation of N-benzylated tertiary amines. 3. Behavior of 1,4-dibenzylpiperazine and its oxygenated derivatives

1,4-Dibenzylpiperazine (1),-2-piperazinone (7),-2,6-piperazinedione (9), and 1-benzoyl-4-benzylpiperazine (30) were oxidized by RuO₄ (generated in situ) by attack at their endocyclic and exocyclic (i.e., benzylic) aminic N-α-C-H bonds to afford various oxygenated derivatives, including acyclic diformamides, benzaldehyde, and benzoic acid. The reaction outcome was complicated by (i) the hydrolysis of diformamides, occurred during the work-up, and (ii) the reaction of benzaldehyde with the hydrolysis-derived amines giving imidazolidines and/or Schiff bases. Benzoic acid resulted from benzaldehyde only. Compounds 7, 30, and 1-benzylpiperazine, but not 9, were transiently formed during the oxidation of 1. In the same reaction conditions, 1,4-dibenzyl-2,3-(or 2,5)-piperazinedione, 1,4-dibenzyl-2,3,6-piperazinetrione, 4-benzyol-1-benzyl-2-piperazinone, and 1,4-dibenzoylpiperazine were inert. The proposed oxidation mechanism involves the formation of endocyclic and exocyclic iminium cations, as well as of cyclic enamines. The latter intermediates probably result by base-induced deprotonation of the iminium cations, provided an N ⁺−β-proton is available. In the case of 1, the cations were trapped with NaCN as the corresponding α-aminonitriles. The statistically corrected regioselectivity (endocyclic/exocyclic) of the RuO₄-induced oxidation reaction of 1, 7, and 30 was 1.2–1.3.     

Capillary electrophoresis method to determine siRNA complexation with cationic liposomes

Small interfering RNA (siRNA) inducing gene silencing has great potential to treat many human diseases. To ensure effective siRNA delivery, it must be complexed with an appropriate vector, generally nanoparticles. The nanoparticulate complex requires an optimal physiochemical characterization and the complexation efficiency has to be precisely determined. The methods usually used to measure complexation in gel electrophoresis and RiboGreen^® fluorescence‐based assay. However, those approaches are not automated and present some drawbacks such as the low throughput and the use of carcinogenic reagents. The aim of this study is to develop a new simple and fast method to accurately quantify the complexation efficiency. In this study, capillary electrophoresis (CE) was used to determine the siRNA complexation with cationic liposomes. The short‐end injection mode applied enabled siRNA detection in less than 5 min. Moreover, the CE technique offers many advantages compared with the other classical methods. It is automated, does not require sample preparation and expensive reagents. Moreover, no mutagenic risk is associated with the CE approach since no carcinogenic product is used. Finally, this methodology can also be extended for the characterization of other types of nanoparticles encapsulating siRNA, such as cationic polymeric nanoparticles.     

Nano-network with dual temperature and pH responsiveness based on copolymers of 2-hydroxyethyl methacrylate with 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]-undecane

Abstract  

This study refers to the synthesis of a nano-network with dual temperature and pH responsiveness based on the 2-hydroxyethyl methacrylate (HEMA) copolymers with a comonomer with spiroacetal moiety and crosslinking capacity, namely 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]-undecane (U). The copolymers were synthesized by radical emulsion polymerization, using 4,4′-azobis(cyanopentanoic acid) as initiator, in the presence of sodium lauryl sulfate as tensioactive agent and poly(vinyl alcohol) as protective colloid. Three copolymer variants were taken into study resulted from the different ratio between the comonomers (HEMA/U), which was about 98/2, 95/5, and 90/10, respectively. The copolymers were characterized by FTIR and thermal analysis. The copolymers sensitivity was evidenced by studying the evolution of the hydrodynamic radius and zeta potential of the polymeric particles as a function of pH. Thus, the particles size increases with the comonomer amount, from 193 nm in case of the homopolymer up to 253 nm for the copolymer with maximum content of the comonomer (10%). The increase of the particle hydrodynamic radius with the growth of temperature was also put into evidence.     

Polymerization in magnetic field. XVI. Kinetic aspects regarding methyl methacrylate polymerization in high magnetic field

The effect of a high magnetic field of 7 T in the reaction of methyl methacrylate polymerization is emphasized. The intervening magnetokinetic modifications are correlated with the system of radical initiation with benzoyl peroxide, 2,2′‐azobis(2‐methylpropionitrile), 4,4′‐azobis(4‐cyanopentanoic acid), and 1,1′‐azobis(cyclohexane‐1‐carbonitrile). The characterization of the synthesized polymers is correlated with the reaction conditions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5678–5686, 2004     

Inclusion of parabens in β-cyclodextrin: A solution NMR and X-ray structural investigation

A parallel study was conducted of the inclusion of alkyl parabens (guests) in the host β-cyclodextrin (β-CD). ¹H NMR data indicated an insertion of the guest phenyl ring into the β-CD cavity. The stoichiometry of each complex was 1:1, as determined by a continuous variation method that utilises the chemical shifts of the host protons. These chemical shifts were additionally used to determine the association constant yielding K values of 1631, 938, 460 and 2022 M^? 1 at 298 K for the methyl-, ethyl-, propyl- and butyl paraben solution state complexes, respectively. NOE experiments conducted on the methyl paraben solution complex indicated that the phenolic group of the guest was located at the secondary rim of the cyclodextrin cavity. Solid state structure analyses of the methyl and propyl paraben β-CD complexes were performed. Both complexes crystallised at ambient temperature in the space group C2, Z = 4 with a host to guest ratio of 1:1. Additionally, a second crystal structure between methyl paraben and β-CD is reported. This complex crystallised at 7^oC in the space group P1, Z = 2 with a 1:1 host–guest stoichiometry.

¹H NMR and solid state structure analyses were conducted on the inclusion of alkyl parabens in the host β-cyclodextrin. Both indicated an insertion of the guest phenyl ring into the β-CD cavity.     

Spectral study of coumarin-3-carboxylic acid interaction with human and bovine serum albumins

Fluorescence spectroscopy and circular dichroism (CD) spectroscopy were used to investigate the interaction of coumarin-3-carboxylic acid with human serum albumin (HSA) and bovine serum albumin (BSA) under physiological conditions in a buffer solution of pH 7.4.