Solubilizing single‐walled carbon nanotubes with pyrene‐functionalized block copolymers

The effect of pyrene distribution within pyrene‐functionalized random and block copolymers on noncovalent polymer/single‐walled carbon nanotube (SWNT) interactions was investigated. The block copolymers served as superior solubilizing agents in comparison with the random copolymers. Also, increasing the pyrene content within a polymer, while a constant molecular weight was maintained, improved SWNT solubility and therefore had to result in stronger polymer–nanotube interactions. However, increasing the length of the pyrene‐containing block diminished nanotube solubility, likely because of a lower number of polymer chains that were capable of binding to the nanotube surface. Atomic force microscopy and transmission electron microscopy indicated that the polymer–SWNT interactions were capable of partially debundling the nanotubes into individual solvated structures. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1941–1951, 2006     

Interactions of carbon nanotubes with pyrene‐functionalized linear‐dendritic hybrid polymers

A series of linear‐dendritic hybrid polymers, containing pyrene units at the periphery of aliphatic polyester dendrons, were prepared for the purpose of dispersing shortened single‐walled carbon nanotubes (SWNTs) in tetrahydrofuran (THF). The prepared hybrids contained 1, 2, 4, 8, or 16 (G0 through G4) pyrene units and a linear segment composed of polystyrene. It was found that a minimum of four pyrene units was necessary to form a strong enough interaction with SWNTs to enable steric stabilization in solution, when using a linear polymer segment of 11.5 kDa. Increasing either the number of pyrene units per polymer chain or the length of the polymer segment to 18.0 kDa did not improve nanotube solubility, whereas decreasing the polymer length resulted in significantly less effective nanotube dissolution. The G4 dendron alone, without the linear polystyrene segment, was also found to impart solubility to the nanotubes in THF. Interactions between the series of linear‐dendritic hybrids and full‐length multiwalled carbon nanotubes were also investigated, and it was found that the polymers exhibited strong interactions with the multiwalled carbon nanotube surface, resulting in the formation of stable solutions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1016–1028, 2010     

Solid–liquid phase equilibrium and mixing thermodynamic analysis of coumarin in binary solvent mixtures

The solubility of coumarin in three aqueous solvent mixtures (methanol + water, ethanol + water and acetone + water) was experimentally determined by a gravimetric method at atmospheric pressure. The experimental solubility data were fitted using the modified Apelblat equation, non-random two-liquid (NRTL) equation, the combined nearly ideal binary solvent/Redlich–Kister equation and the Jouyban?Acree equation, respectively. All the equations were proven to be able to correlate the experimental data, and the modified Apelblat equation could obtain better correlation results than the other three models. The solubility of coumarin increases with increase in temperature. At the same temperature, the solubility increases with increase in mole fraction of organic solvents except for the ethanol–water system which shows a unimodal curve. In addition, the apparent thermodynamic properties of the mixing process were calculated based on the NRTL model and the experimental solubility data.     

Selective stabilization of the chorismate mutase transition state by a positively charged hydrogen bond donor

Citrulline was incorporated via chemical semisynthesis at position 90 in the active site of the AroH chorismate mutase from Bacillus subtilis. The wild-type arginine at this position makes hydrogen-bonding interactions with the ether oxygen of chorismate. Replacement of the positively charged guanidinium group with the isosteric but neutral urea has a dramatic effect on the ability of the enzyme to convert chorismate into prephenate. The Arg90Cit variant exhibits a >104-fold decrease in the catalytic rate constant kcat with a 2.7-fold increase in the Michaelis constant Km. In contrast, its affinity for a conformationally constrained inhibitor molecule that effectively mimics the geometry but not the dissociative character of the transition state is only reduced by a factor of approximately 6. These results show that an active site merely complementary to the reactive conformation of chorismate is insufficient for catalysis of the mutase reaction. Instead, electrostatic stabilization of the polarized transition state by provision of a cationic hydrogen bond donor proximal to the oxygen in the breaking C-O bond is essential for high catalytic efficiency.     

Brand-new Function of Well-designed Ionic Liquid: Inhibitor of Tumor Cell Growth

An investigation into the effect of several novel well-designed guanidinium salt ionic liquids(GILs) on inhibitting tumor growth is described. The GILs which have longer alkyl chain(6―18 carbon atoms) exhibit the high cytotoxicity to Hela299, B16 and SMMC-7721 cells so as to inhibit their proliferation. The inhibitory effect of the most effective GIL12 is about 10-fold higher than that of MMC(a common chemotherapy drug in clinic).     

新型有机小分子DNA切割试剂的合成

根据活性基团的协同催化原理,设计合成了有机小分子核酸切割剂1-(N-胍乙基)-4-(N-羟乙基)哌嗪盐酸盐(4),并通过核磁共振和液相色谱-质谱联用技术对其结构进行了表征.利用琼糖凝胶电泳研究了pH值对其切割pUC 19 DNA效率的影响,通过自由基猝灭实验研究其切割DNA的反应类型.运用密度泛函理论,利用Gaussian软件进行了理论计算,研究其裂解DNA的反应方式.研究结果表明,在pH=7.2时化合物4的裂解效率最高,且能通过非氧化还原反应以磷酯转移的方式裂解DNA的磷酸二酯键.     

Complexation of hydrophobically modified polyelectrolytes with surfactants: anionic poly(maleic acid/octyl vinyl ether)/anionic sodium dodecyl sulfate

Interactions of surfactants with hydrophobically modified polyelectrolytes in aqueous solutions are important in several applications such as detergents, cosmetics, foods, and paints. Fundamental questions arise on the mechanisms of complexation of the polyelectrolyte and surfactant that control their behavior. In this work, the complexation was studied by examining interactions in aqueous solutions of a hydrophobically modified polymer, poly(maleic acid/octyl vinyl ether) (PMAOVE), with sodium dodecyl sulfate (SDS) by monitoring viscosity, pyrene solubility, light scattering, and analytical ultracentrifugation. When the anionic surfactant SDS was added to aqueous solutions of the similarly charged polymer PMAOVE, the surfactant was incorporated into the hydrophobic nanodomains of PMAOVE even far below the cmc of the surfactant. On the basis of viscosity, pyrene solubility, and analytical ultracentrifugation data, it is proposed that PMAOVE undergoes structural unfolding and at higher SDS concentrations mixed micelles are formed.     

Both core- and shell-cross-linked nanogels: photoinduced size change, intraparticle LCST, and interparticle UCST thermal behaviors

New thermal- and photoresponsive core-shell nanogel particles were obtained from self-assembly in aqueous solution of a double-hydrophilic block copolymer (DHBCP) of which the two blocks could be photo-cross-linked via the reversible photodimerization and photocleavage of coumarin moieties. The diblock copolymer, consisting of poly[N,N-dimethylacrylamide-co-4-methyl-[7-(methacryloyl)oxyethyloxy]coumarin] and poly[N-isopropylacrylamide-co-4-methyl-[7-(methacryloyl)oxyethyloxy]coumarin] (P(DMA-co-CMA)-b-P(NIPAM-co-CMA)), was synthesized by using reversible addition-fragmentation chain transfer (RAFT) polymerization. At T > LCST of the P(NIPAM-co-CMA) block, core-shell micelles were formed and UV light irradiation at λ > 310 nm resulted in cross-linking of both the micelle core of P(NIPAM-co-CMA) and the micelle shell of P(DMA-co-CMA); subsequent cooling of the solution to T < LCST gave rise to water-soluble, swollen nanogel particles. Upon UV light irradiation at λ < 260 nm, the decrease of cross-linking density could increase the swelling of nanogel particles by ～23% in diameter. By alternating irradiation with the different wavelengths, the average hydrodynamic diameter of nanogel particles was tunable between ～58 and ～47 nm. Interestingly, upon further cooling of the solution, aggregation occurred for nanogel particles with a moderate cross-linking density (10%-40% dimerization of coumarin moieties). Therefore, such core- and shell-cross-linked nanogel could display both "intraparticle" LCST (solubility of polymer chains forming the core) and "interparticle" UCST (solubility of particles). The possible mechanism and the effect of dimerization degree on the UCST behavior were discussed.     

Magnetic nanoparticles modified with DTPA-AMC-rare earth for fluorescent and magnetic resonance dual mode imaging

In the present study, we report new water-soluble cell fluorescence imaging and contrast agents that are based on DTPA-AMC(7-amino-4-methyl coumarin)-Eu(3+) and DTPA-AMC(7-amino-4-methyl coumarin)-Gd(3+) compounds conjugated to Fe(3)O(4) NPs via a PEG-NH(2) linker. The novel Fe(3)O(4) NP-conjugates present two main advantages for cell fluorescence labelling: water solubility and targeting ability. The in vitro experiments demonstrate that water-soluble Fe(3)O(4) NPs-DBI-PEG-NH-DTPA-AMC(7-amino-4-methyl coumarin)-Eu(3+) has excellent cell permeating activity. Moreover, the relaxation rate test of Fe(3)O(4) NPs-DBI-PEG-NH-DTPA-AMC(7-amino-4-methyl coumarin)-Gd(3+) shows a higher T1 relaxation effect than traditional DTPA-Gd(3+) MRI agents. According to in vivo liver MRI experiments, better contrast of the liver was achieved after addition of Fe(3)O(4) NPs-DBI-PEG-NH-DTPA-AMC(7-amino-4-methyl coumarin)-Gd(3+). The results will provide a significant guide for researchers exploring the biomedical applications of superparamagnetic Fe(3)O(4) NPs.     

Characterization of specific noncovalent complexes between guanidinium derivatives and single-stranded DNA by MALDI

Noncovalently bound complexes between highly basic sites of 12 guanidinium compounds and single-stranded DNA were studied using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. 6-Aza-2-thiothymine (ATT) was used as the matrix in the presence of ammonium citrate, and spectra were recorded in the positive ion mode. Detailed control experiments confirmed unambiguously the high selectivity and specificity of the guanidinium moiety for phosphate groups of DNA. The results verify the binding stoichiometry and show preferential binding of hydrophobic binders (pyrene and anthracene guanidinium derivatives) to all sequences examined. In addition, we demonstrate that electrostatic noncovalent interactions are strengthened with phosphorothioate analogs of DNA. These results clearly highlight the structure-directing role of the self-assembling organic species and strongly emphasize the significance of concentration, hydrophobicity, hydrogen-bonding, and pi-pi interactions of the artificial receptor in the formation of these noncovalent complexes. Because of the ability of DNA-binding compounds to influence gene expression, and therefore cell proliferation and differentiation, the interactions described above could be important in providing a better understanding of the mechanism of action of these noncovalent genetic regulators.     

In Vitro Inhibition Effect of Some Dihydroxy Coumarin Compounds on Purified Human Serum Paraoxonase 1 (PON1)

Human serum paraoxonase 1 (PON1; EC 3.1.8.1) is a high-density lipoprotein associated, calcium-dependent enzyme that hydrolyses aromatic esters, organophosphates and lactones and can protect the low-density lipoprotein against oxidation. In this study, in vitro inhibition effect of some dihydroxy coumarin compounds namely 6,7-dihydroxy-3-(2-methylphenyl)-2H-chromen-2-one (A), 6,7-dihydroxy-3-(3-methylphenyl)-2H-chromen-2-one (B) and 6,7-dihydroxy-3-(4-methylphenyl)-2H-chromen-2-one (C) on purified PON1 were investigated by using paraoxon as a substrate. PON1 was purified using two-step procedures, namely ammonium sulphate precipitation and Sepharose-4B-l-tyrosine-1-naphthylamine hydrophobic interaction chromatography. The purified enzyme had a specific activity of 11.76?U/mg. The dihydroxy coumarin derivatives of A and B compounds inhibited PON1 enzyme activity in a noncompetitive inhibition manner with K _i of 0.0080?±?0.256 and 0.0003?±?0.018?mM values, respectively. C compound exerted an uncompetitive inhibition of PON1 enzyme activity with K _i of 0.0010?±?0.173?mM. Moreover, dihydroxy coumarin derivatives of A, B and C compounds were effective inhibitors on purified human serum PON1 activity with IC₅₀ of 0.012, 0.022 and 0.003?mM values, respectively. IC₅₀ value of unsubstituted 6,7 dihydroxy coumarin was found as 0.178?mM. The present study has demonstrated that PON1 activity is very highly sensitive to studied coumarin derivatives.     

A biomimetic chitosan derivates: preparation, characterization and transdermal enhancement studies of N-arginine chitosan

A novel arginine-rich chitosan (CS) derivates mimicked cell penetration peptides; N-Arginine chitosan (N-Arg-CS) was prepared by two reaction methods involving activated L-arginine and the amine group on the chitosan. FTIR spectra showed that arginine was chemically coupled with CS. Elemental analysis estimated that the degrees of substitution (DS) of arginine in CS were 6%, 31.3% and 61.5%, respectively. The drug adefovir was chosen as model and its permeation flux across excised mice skin was investigated using a Franz diffusion cell. The results showed that the most effective enhancer was 2% (w/v) concentration of 10 kDa N-Arg-CS with 6% DS. At neutral pH, the cumulative amount of adefovir permeated after 12 hours was 2.63 ± 0.19 mg cm(-2) which was 5.83-fold more than adefovir aqueous solution. Meanwhile N-Arg-CS was 1.83, 2.22, and 2.45 times more effective than Azone, eucalyptus and peppermint, respectively. The obtained results suggest that N-Arg-CS could be a promising transdermal enhancer.     

Synthesis of hydrophobically modified poly(acrylamides) in water-in-oil emulsions

High-molecular-mass hydrophobically modified poly(acrylamides) have been prepared via water-in-oil miniemulsion copolymerization of acrylamide and lauryl methacrylate initiated by 2,2′-azoisobutyronitrile. The incorporation of the hydrophobic comonomer into the polymer backbone is indirectly confirmed by the rheological and associative properties of polymer solutions. The copolymers prepared from the reaction mixtures containing less than 5 mol % lauryl methacry late demonstrate the associative behavior in aqueous solutions, as evidenced by fluorescence spectroscopy (a decrease in the polarity parameter of pyrene), static and dynamic light scattering (overestimated effective molecular masses and appearance of a peak due to aggregates), and rheological measurements (a rise of viscosity relative to that of the acrylamide homopolymer). A further increase in the content of lauryl methacrylate leads to formation of polymers possessing limited solubility in water. At the acrylamide-to-hydrophobic monomer equimolar ratio, homopolymers arise along with the insoluble copolymer.     

Electric field effects on photoinduced electron transfer processes of methylene-linked compounds of pyrene and N,N-dimethylaniline in a polymer film

Time-resolved measurements of the electric-field-induced change in fluorescence intensity have been made for methylene-linked compounds of pyrene and N,N-dimethylaniline (DMA) doped in a polymer film. The lifetime of the fluorescence emitted from the locally excited state of pyrene chromophore becomes shorter in the presence of electric field (F), when the dopant concentration is high. The lifetime of the excipelx fluorescence resulting from the photoinduced electron transfer (PIET) from DMA to the excited state of pyrene chromophore between different molecules also becomes shorter in the presence of F. Based on the simulation of the electric field effect on fluorescence decay, the mechanism of intermolecular PIET between DMA and pyrene chromophore in a polymer film is discussed.     

Arginine methylation in a beta-hairpin peptide: implications for Arg-pi interactions, DeltaCp(o), and the cold denatured state

Arginine methylation is a common post-translational modification that plays a role in many cellular processes through mediation of protein-protein interactions. There is still a dearth of structural information as to its role in mediating such interactions, but the available data suggest a possible role of cation-pi interactions in the recognition of methylated arginine. Hence, the effect of arginine methylation on its interaction with tryptophan has been investigated within the context of a beta-hairpin peptide. Arginine methylation was found to enhance the stacking interaction between the cationic guanidinium functionality of arginine and the indole ring of tryptophan, resulting in structural stabilization of the hairpin. Thermodynamic analysis reveals more favorable entropy of hairpin folding with arginine methylation, a more negative change in heat capacity for folding, and a modest decrease in enthalpic driving force. This is consistent with enhanced stacking and hydrophobic interactions through increased surface area of the guanidinium moiety and greater delocalization of positive charge. In addition, these peptides exhibit significant cold denaturation, which can be accounted for by the inclusion of an expression of temperature-dependent DeltaC(p) in the thermodynamic analysis.     

Effect of functional groups on the solubilities of coumarin derivatives in supercritical carbon dioxide

Summary Solubilities in supercritical CO₂ of coumarin, four monosubstituted coumarin derivatives (4-hydroxycoumarin, 7-hydroxycoumarin, 7-methoxycoumarin, and 7-methylcoumarin) and four disubstituted derivatives, (6,7-dihydroxycoumarin, 7-hydroxycoumarin-4-acetic acid, 7-methoxycoumarin-4-acetic acid, and 7-hydroxy-4-methylcoumarin) were measured in the temperature range 35–50 °C and the pressure range 8.5–25 MPa. In general, the substituted coumarin derivatives were less soluble than simple coumarin. It was also found that substitution at the C-4 position of coumarin tended to reduce the solubility more than substitution at the C-7 position. These solubility data are essential for the systematic application of SFE and SFC of coumarin derivatives from plant sources.     

A contribution to pharmaceutical biology of freshwater sponges

In vitro anti-tumour and anti-radical activities of the acetone extract of the freshwater sponge Ochridaspongia rotunda were the subject of this study. The extract was found to be highly cytotoxic to human lung tumour cell line A-549 reaching IC₅₀ value of 5.01 ± 0.21 μg/mL. Indeed, it displayed only 2-fold less anti-tumour activity than doxorubicin (IC₅₀ value 2.42 ± 0.13 μg/mL) used as a positive control. The same extract was also found to be almost 37-fold more selective against A-549 vs. MRC-5 (normal) lung cells, in difference to weak selectivity of doxorubicin (less than 3-fold). Its profound anti-DPPH radical activity comparable to that of quercetin (IC₅₀ values 3.68 ± 0.19 and 3.14 ± 0.09 μg/mL, respectively) coupled with no signs of genotoxicity in the comet assay (MRC-5 cell line, vs. doxorubicin) has actually implicated the importance of this animal bioresource in searching for pharmaceutically useful bioactive compounds of natural origin.     

Emulsion copolymerization of vinyl acetate and butyl acrylate in the presence of fluorescent dyes

This article describes our first experiments for preparing dye‐labeled latex particles by the emulsion copolymerization of a 4/1 (w/w) mixture of vinyl acetate‐butylacrylate (VAc‐BA). We discuss the synthesis of acrylate derivatives of phenanthrene, anthracene, and pyrene [9‐acryloxymethyl phenanthrene ( 7 ), 9‐acryloxymethyl‐10‐methyl anthracene ( 8 ), and 1‐acryloxymethyl pyrene ( 10 )] and an allyl ether derivative of anthracene [9‐allyoxymethyl‐10‐methyl anthracene ( 9 )]. Although the phenanthrene derivative 7 gave latex particles with high monomer conversion and good dye incorporation, the pyrene acrylate and both anthracene comonomers strongly inhibited the free‐radical reaction. To assist our search for a dye that would serve as a useful energy acceptor for phenanthrene and without suppressing VAc‐BA polymerization, we also examined batch emulsion polymerization in the presence of a variety of dye derivatives—substituted anthracenes, acridines, a coumarin, and two benzophenone derivatives. All of the anthracene derivatives, as well as acridine, strongly inhibited monomer polymerization. The coumarin dye 7‐hydroxy‐4‐methyl coumarin ( 22 ) that had only limited solubility allowed more than 90% monomer conversion. Most promising were 2‐hydroxy‐5‐methyl benzophenone ( 23 ) and 4‐N,N‐dimethylamino benzophenone ( 24 ) that at 1 mol % in the monomer mixture permitted virtually quantitative monomer conversion to latex. 4′‐Dimethylamino‐2‐acryloxy‐5‐methyl benzophenone ( 25 ) copolymerized well with the VAc‐BA mixture, yielding latex particles in high yield and with a narrow size distribution. These dyes appear to be useful acceptor dyes for energy‐transfer experiments with phenanthrene. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1594–1607, 2002     

Polycyclic arene sulfides. Preparation of 1a,2,3,11b-tetrahydrobenz-[5,6]anthra[1,2-b]thiirene, 6b,7a,8,9-tetrahydrobenzo[10,11]-chryseno[1,2-b]thiirene,and 7,8,8a,9a-tetrahydrobenzo-[10,11]chryseno[3,4-b]thiirene

The title compounds 5, 7 and 9 which are the first arene sulfides of 7,8-dihydrobenz[a]anthracene, 8,9-and 10,11-dihydrobenzo[a]pyrene, respectively, have been synthesized by treatment of the corresponding arene oxides 4, 6 and 8 with N,N-dimethylthioformamide in the presence of catalytic amounts of trifluoroacetic acid.     

Electrochemical DNA biosensor for polycyclic aromatic hydrocarbon detection

Four DNA electrochemical biosensors using four types of DNA (calf thymus ssDNA, calf thymus dsDNA, salmon testis ssDNA and salmon testis dsDNA) were constructed using graphite screen printed electrodes. These biosensors were exploited as analytical tool to detect polycyclic aromatic hydrocarbons-DNA interactions using benzo(a)anthracene and phenantrene as model analytes, the guanine oxidation peak variation being the signal revealing the interaction between PAHs and immobilized DNA. The salmon testis ssDNA biosensor resulted as the most promising device and was further evaluated for benzo(a)anthracene, fluorene, indeno(1,2,3-cd)pyrene, anthracene, and phenanthrene in 5–40 ng mL^?1 solutions, and for benzo(a)pyrene (5–50 ng mL^?1). A concentration dependent variation of the DNA guanine oxidation peak was observed for all compounds. The effect of benzo(a)pyrene ultraviolet (UV) activation on the benzo(a)pyrene (BaP)-DNA interaction was evaluated at concentration levels of 20 and 50 ng mL^?1, and a 3.5- and 2.7-fold increases of the guanine oxidation peak was measured respectively. The salmon testis ssDNA biosensor was examined with PAHs contaminated samples of Mytilus galloprovincialis. Upon UV irradiation of three sample extracts exceeding the BaP maximum level, a positive variation of the DNA guanine oxidation was obtained. An average 2.4-fold increase of the guanine oxidation peak was detected demonstrating that the sensor can be used to detect toxic degradation products of PAHs.