Synthesis of poly(propyl ether imine) dendrimers and evaluation of their cytotoxic properties

In this paper, we report the synthesis of several poly(propyl ether imine) dendrons and dendrimers. These dendrons and dendrimers were constructed by involving an ether as the linker component and an imine as the branching component. The divergent syntheses of dendrons and dendrimers were established with the aid of two alternate Michael addition reactions and two alternate reduction reactions in a four-step iterative synthetic sequence. Dendrons up to three generations were synthesized and some of the dendrons were attached to a benzenoid core so as to obtain dendrimers up to two generations containing 12 carboxylic acids at the periphery. Divergent synthesis involving ether as the core was found to be more facile, and dendrimers up to three generations having 16 carboxylic acids at the periphery were achieved in good to excellent yields in each individual step. The adopted synthetic sequence allows us to install either alcohol, an amine, or a carboxylic acid at their peripheries. The carboxylic acid-terminated dendrons and dendrimers were evaluated as to their cytotoxic properties, and while most dendrons and dendrimers did not exhibit any measurable cytotoxicity, even up to 100 microg/mL, the second-generation dendrimer with the benzenoid core exhibited a mild toxicity at concentrations above 30 microg/mL.     

Dendrimers as photochemical reaction media. Photochemical behavior of unimolecular and bimolecular reactions in water-soluble dendrimers

Synthesis and studies of poly(alkyl aryl ether) dendrimers, possessing carboxylic acid functionalities at their peripheries, are reported. 5-Bromopentyloxy methylisophthalate was utilized as the monomer to O-alkylate the phenolic hydroxyl groups of poly(alkyl aryl ether) dendrimers. Dendrimers of first, second, and third generations, possessing 6, 12, and 24 carboxylic acids, respectively, were thus prepared. These dendrimers were soluble in alkaline aqueous solutions, and the ensuing microenvironmental properties of the aqueous solutions were assessed by pyrene solubilization studies. Upon establishing the presence of nonpolar microenvironments within the dendritic structures, solubilizations of few organic substrates were conducted and their photochemical behaviors were assessed. Specifically, the photolysis of 1-phenyl-3-p-tolyl-propan-2-one and benzoin ethyl ether and photodimerization of acenaphthylene were conducted. These studies revealed that the product distribution and the "cage effect" were more distinct and efficient for the third generation dendrimer, than for the first and second generation dendrimers. The photochemical studies of carboxylic acid functionalized dendrimers were compared to that of hydroxyl group terminated poly(alkyl aryl ether) dendrimers.     

Determination of alkylphenols and bisphenol-A. A comparative investigation of functional polymer-coated membrane microextraction and solid-phase microextraction techniques

A functional polymer (hydroxylated polymethacrylate) coated on porous polysulfone hollow fiber membrane (PS-HFM) was used as an adsorbent for the extraction of alkylphenols and bisphenol-A from seawater samples. Analyses of the extracts were performed using gas chromatography-mass spectrometry (GC-MS) after injection-port derivatization using bis(trimethylsilyl)trifluoroacetamide (BSTFA). We term the procedure as polymer-coated hollow fiber microextraction (PC-HFME). Owing to high porosity PS-HFM coated with hydroxylated polymer showed high extraction efficiency. Compared with solid-phase microextraction (SPME), PC-HFME showed good selectivity and sensitivity. Detection limits of alkylphenols and bisphenol-A ranged between 0.07 and 2.34 ng l(-1). The linearity range was from 0.01 to 15 microg l(-1) and the correlation coefficient (r) up to 0.997. The sensitivity and selectivity of the coated HFM could be potentially tuned by changing the characteristics of the coated hydroxylated polymer. The PC-HFME procedure was applied to the detection of alkylphenols and bisphenol-A in the coastal waters of Singapore.     

Synthesis and molecular structure of biologically significant bis(1,3‐dimesityl‐4,5‐naphthoquinoimidazol‐2‐ylidene)gold(I) complexes with chloride and dichloridoaurate counter‐ions

Diffraction‐quality single crystals of two gold(I) complexes, namely bis(1,3‐dimesityl‐4,5‐naphthoquinoimidazol‐2‐ylidene)gold(I) chloride benzene monosolvate, [Au(C₂₉H₂₆N₂O₂)₂]Cl·C₆H₆ or [(NQMes)₂Au]Cl·C₆H₆, 2 , and bis(1,3‐dimesityl‐4,5‐naphthoquinoimidazol‐2‐ylidene)gold(I) dichloridoaurate(I) dichloromethane disolvate, [Au(C₂₉H₂₆N₂O₂)₂][AuCl₂]·2CH₂Cl₂ or [(NQMes)₂Au][AuCl₂]·2CH₂Cl₂, 4 , were isolated and studied with the aid of single‐crystal X‐ray diffraction analysis. Compound 2 crystallizes in a monoclinic space group C2/c with eight molecules in the unit cell, while compound 4 crystallizes in the triclinic space group P with two molecules in the unit cell. The crystal lattice of compound 2 reveals C—H…Cl^? interactions that are present throughout the entire structure representing head‐to‐tail contacts between the aromatic (C—H) hydrogens of naphthoquinone and Cl^? counter‐ions. Compound 4 stacks with the aid of short interactions between a naphthoquinone O atom of one molecule and the mesityl methyl group of another molecule along the a axis, leading to a one‐dimensional strand that is held together by strong π–η² interactions between the imidazolium backbone and the [AuCl₂]^? counter‐ion. The bond angles defined by the Au^I atom and two carbene C atoms [C(carbene)—Au—C(carbene)] in compounds 2 and 4 are nearly rectilinear, with an average value of ～174.1 [2]°. Though 2 and 4 share the same cation, they differ in their counter‐anion, which alters the crystal lattice of the two compounds. The knowledge gleaned from these studies is expected to be useful in understanding the molecular interactions of 2 and 4 under physiological conditions.     

A mouse serum two-dimensional gel map: application to profiling burn injury and infection

With the importance of mouse as a model to study human diseases and the human and rat plasma/serum two-dimensional (2-D) maps being extensively annotated, this study was aimed at constructing a detailed mouse serum 2-D map. Serum proteins from two different inbred strains of mice (BALB/cJ and C57BL/6J) and mice subjected to two different inflammatory stimuli (20% burn injury and lipopolysaccharide (LPS) injection) were separated on overlapping gels covering pH 3-8 and stained with SYPRO Ruby dye. The tryptic peptides from the resolved spots were analyzed by mass spectrometry, leading to the identification of 38 different gene products. With the exception of major urinary proteins found in abundance in male C57BL/6J mice, little strain difference of the mouse serum 2-D was observed. Many proteins detected in the mouse serum 2-D map were not reported in human or rat serum 2-D maps including epidermal growth factor receptor. Three major murine acute-phase proteins (APPs), haptoglobin, serum amyloid A, and serum amyloid P, were highly induced by both inflammatory stimuli. Image analysis shows that the variations of APPs between these two inflammatory models were not uniform although LPS (100 microg/animal) in general was more effective than 20% burn injury in inducing APPs. Serum amyloid A, much more sensitive to endotoxin than burn injury, may represent a sensitive marker to differentiate these two different inflammatory states.     

A direct fluorescence-on chemo-sensor for selective recognition of Zn(II) by a lower rim 1,3-di-derivative of calix[4]arene possessing bis-{N-(2-hydroxynaphthyl-1-methylimine)} pendants

The bis-{N-(2-hydroxynaphthyl-1-methylimine)} anchored 1,3-di-derivative of lower rim p-tert-butyl-calix[4]arene possessing a N₂O₂, N₂O₄ or N₂O₆ binding core was found to be selective for Zn(II) ions even at ?60 ppb by eliciting fluorescence-on behaviour while the other ions, viz., Ti⁴⁺, VO²⁺, Cr³⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Mg²⁺, Cd²⁺ and Hg²⁺ caused no change in the fluorescence. The reaction between 1 and Zn²⁺ was found to be stoichiometric with the formation of a 1:1 complex; while H⁺ quenched the fluorescence of the complex, OH⁻ restored it. The studies of the 1:1 isolated complexes of Zn²⁺, Ni²⁺ and Cu²⁺ augmented the results.     

The photochemical preparation of ozonides by electron-transfer photo-oxygenation of epoxides

9,10-Dicyanoanthracene (DCA) sensitizes the electron-transfer photo-oxygenation of epoxides in oxygen-saturated acetonitrile to form ozonides. Epoxides with oxidation potentials lower than 2 V vs SCE quench the fluorescence of DCA and are converted to the ozonides with DCA alone. Epoxides which do not quench the singlet excited state of DCA are unreactive under these conditions. However, the photo-oxygenation of these epoxides can be effected by addition of biphenyl (BP) as a catalyst or co-sensitizer. Investigations of the stereochemistry of the reactions of cis- and trans-2,3-diaryloxiranes has shown that both isomeric epoxides are converted exclusively to the corresponding cis-ozonides. Co-sensitized photo-oxygenation of cis- and trans-2,3-diphenyloxirane affords only cis-3,5-diphenyl-1,2,4-trioxolane. The same stereochemical course is followed for the electron-transfer photo-oxygenation of more easily oxidized 2,3-dinaphthyloxiranes that do not require BP co-sensitization. The stereochemistry of the naphthyl-substituted ozonides has been unequivocably assigned by an X-ray structure of cis-3,5-bis(2'-naphthyl)-1,2,4-trioxolane. The corresponding trans-ozonide was prepared by ozonation of cis-1,2-bis(2'-naphthyl)ethene and stereochemically identified by Chromatographic resolution using high-performance liquid chromatography with optically active (+)-poly(triphenylmethyl methacrylate) as the stationary phase. These stereochemical results have been interpreted in terms of a mechanism involving addition of singlet oxygen as a dipolarophile to intermediate carbonyl ylides.     

On the planarity of tetracoordinate carbon enclosed by annulene perimeters

Proposals that planar tetracoordinate carbon might be achieved by enclosure in an annulene perimeter have been examined by means of MNDO calculations. Unfortunately, the lowest energy forms of 1–3, and 5 are indicated to distort as far away from planarity as possible, consistent with the strain demands of the carbon skeletons. Even in hypothetical stereomutation transition states, planar tetracoordination around the central carbon should be energetically difficult to achieve in these hydrocarbons, which, at best, are expected to be unstable strained polyolefins. Planar tetracoordinate carbon is more likely to be achieved when both π and σ systems provide effective stabilization through multicenter bonding. Several illustrative proposals for experimental examination are presented.