Water-soluble calix[4]resorcarenes as enantioselective NMR shift reagents for aromatic compounds

A tetra L-prolinylmethyl derivative of a tetra-sulfonated calix[4]resorcarene (1) is an effective chiral NMR solvating agent for water-soluble compounds with phenyl, pyridyl, bicyclic aromatic, or indole rings. These aromatic compounds form host-guest complexes with the calix[4]resorcarene in water. Complexation of substrates with the calix[4]resorcarene is likely promoted by hydrophobic effects, and bicyclic substrates have association constants with the calix[4]resorcarene larger than those of similar phenyl-containing compounds. Aromatic resonances of the substrates show substantial upfield shifts because of shielding from the aromatic rings of the calix[4]resorcarene, and several resonances in the 1H NMR spectra typically exhibit enantiomeric discrimination. The extent of enantiomeric discrimination depends in part on interactions of the substituent groups of the substrates with the prolinylmethyl groups of the calix[4]resorcarene. The effectiveness of a calix[4]resorcarene prepared from N-methyl-L-alanine (2) as a chiral NMR discriminating agent is compared to the L-prolinylmethyl derivative.     

Binding and condensation of plasmid DNA onto functionalized carbon nanotubes: toward the construction of nanotube-based gene delivery vectors

Carbon nanotubes (CNTs) constitute a class of nanomaterials that possess characteristics suitable for a variety of possible applications. Their compatibility with aqueous environments has been made possible by the chemical functionalization of their surface, allowing for exploration of their interactions with biological components including mammalian cells. Functionalized CNTs (f-CNTs) are being intensively explored in advanced biotechnological applications ranging from molecular biosensors to cellular growth substrates. We have been exploring the potential of f-CNTs as delivery vehicles of biologically active molecules in view of possible biomedical applications, including vaccination and gene delivery. Recently we reported the capability of ammonium-functionalized single-walled CNTs to penetrate human and murine cells and facilitate the delivery of plasmid DNA leading to expression of marker genes. To optimize f-CNTs as gene delivery vehicles, it is essential to characterize their interactions with DNA. In the present report, we study the interactions of three types of f-CNTs, ammonium-functionalized single-walled and multiwalled carbon nanotubes (SWNT-NH3+; MWNT-NH3+), and lysine-functionalized single-walled carbon nanotubes (SWNT-Lys-NH3+), with plasmid DNA. Nanotube-DNA complexes were analyzed by scanning electron microscopy, surface plasmon resonance, PicoGreen dye exclusion, and agarose gel shift assay. The results indicate that all three types of cationic carbon nanotubes are able to condense DNA to varying degrees, indicating that both nanotube surface area and charge density are critical parameters that determine the interaction and electrostatic complex formation between f-CNTs with DNA. All three different f-CNT types in this study exhibited upregulation of marker gene expression over naked DNA using a mammalian (human) cell line. Differences in the levels of gene expression were correlated with the structural and biophysical data obtained for the f-CNT:DNA complexes to suggest that large surface area leading to very efficient DNA condensation is not necessary for effective gene transfer. However, it will require further investigation to determine whether the degree of binding and tight association between DNA and nanotubes is a desirable trait to increase gene expression efficiency in vitro or in vivo. This study constitutes the first thorough investigation into the physicochemical interactions between cationic functionalized carbon nanotubes and DNA toward construction of carbon nanotube-based gene transfer vector systems.     

Photochemical interaction of polystyrene nanospheres with 193 nm pulsed laser light

The photochemical interaction of 193 nm light with polystyrene nanospheres is used to produce particles with a controlled size and morphology. Laser fluences from 0 to 0.14 J/cm2 at 10 and 50 Hz photofragment nearly monodisperse 110 nm spherical polystyrene particles. The size distributions before and after irradiation are measured with a scanning mobility particle sizer (SMPS), and the morphology of the irradiated particles is examined with a transmission electron microscope (TEM). The results show that the irradiated particles have a smaller mean diameter ( approximately 25 nm) and a number concentration more than an order of magnitude higher than nonirradiated particles. The particles are formed by nucleation of gas-phase species produced by photolytic decomposition of nanospheres. A nondimensional parameter, the photon-to-atom ratio (PAR), is used to interpret the laser-particle interaction energetics.     

First anhydrous gold perchlorato complex: ClO(2)Au(ClO(4))(4). Synthesis and molecular and crystal structure analysis

Chlorine trioxide, Cl(2)O(6), reacts with Au metal, AuCl(3), or HAuCl(4).nH(2)O to yield the well-defined chloryl salt, ClO(2)Au(ClO(4))(4). The crystal and molecular structure of ClO(2)Au(ClO(4))(4) was solved by a Rietveld analysis of powder X-ray diffraction data. The salt crystallizes in a monoclinic cell, space group C2/c, with cell parameters a = 15.074(5), b = 5.2944(2), and c = 22.2020(2) A and beta = 128.325(2) degrees. The structure displays discrete ClO(2)(+) ions lying in channels formed by Au(ClO(4))(4)(-) stacks. Au is located in a distorted square planar environment: Au-O = 1.87 and 2.06 A. [ClO(4)] groups are monodentate with ClO(b) = 1.53 and ClO(t) = 1.39 A (mean distances; O(b), oxygen bonded to Au; O(t), free terminal oxygen). A full vibrational study of the Au(ClO(4))(4)(-) anion is supported by DFT calculations.     

Alkaline salt-catalyzed aza Diels-Alder reactions of Danishefsky's diene with imines in water under neutral conditions

Two- or three-component aza Diels-Alder reactions of Danishefsky's diene with imines or aldehydes and amines in water took place smoothly under neutral conditions in the presence of a catalytic amount of an alkaline salt such as sodium triflate to afford dihydro-4-pyridones in high yields.     

Flexibility in the partial reduction of 2,5-disubstituted pyrroles: application to the synthesis of DMDP

[reaction: see text] The partial reduction of electron-deficient 2,5-disubstituted pyrroles has been developed into a flexible procedure that gives control of relative stereochemistry by variation of the reduction conditions. After the reaction, the pyrroline products were dihydroxylated at C-3,4 to give either the cis or trans isomers; this flexibility means that a variety of polyhydroxylated pyrrolidines can be prepared in a short sequence. Finally, this method was applied to a synthesis of the naturally occurring glycosidase inhibitor DMDP.     

Palladium-catalyzed Suzuki cross-coupling of aryl halides with aryl boronic acids in the presence of glucosamine-based phosphines

Carbohydrate-substituted phosphines are easily obtained in quite good yields by coupling of protected or non-protected d-glucosamine with the corresponding diphenylphosphino acid. These neutral ligands, in association with palladium acetate, are very active catalysts in the Suzuki cross-coupling reaction. The polyhydroxy phosphines are more active than the peracetylated phosphines. The process tolerates electron-rich as well as electron-poor substituents. Excellent turnovers, up to 97?000 are observed.     

Electronic energy transfer and collection in luminescent molecular rods containing ruthenium(II) and osmium(II) 2,2':6',2"-terpyridine complexes linked by thiophene-2,5-diyl spacers

The electronic absorption spectra, luminescence spectra and lifetimes (in MeCN at room temperature and in frozen n-C3H7CN at 77 K), and electrochemical potentials (in MeCN) of the novel dinuclear [(tpy)Ru(3)Os(tpy)]4+ and trinuclear [(tpy)Ru(3)Os(3)Ru(tpy)]6- complexes (3 = 2,5-bis(2,2':6',2'-terpyridin-4-yl)thiophene) have been obtained and are compared with those of model mononuclear complexes and homometallic [(tpy)Ru(3)Ru(tpy)]4+, [(tpy)Os(3)Os(tpy)]4+ and [(tpy)Ru(3)Ru(3)Ru(tpy)]6+ Complexes. The bridging ligand 3 is nearly planar in the complexes, as seen from a preliminary X-ray determination of [(tpy)Ru(3)Ru(tpy)][PF6]4, and confers a high degree of rigidity upon the polynuclear species. The trinuclear species are rod-shaped with a distance of about 3 nm between the terminal metal centres. For the polynuclear complexes, the spectroscopic and electrochemical data are in accord with a significant intermetal interaction. All of the complexes are luminescent (phi in the range 10(-4)-10(-2) and tau in the range 6-340 ns, at room temperature), and ruthenium- or osmium-based luminescence properties can be identified. Due to the excited state properties of the various components and to the geometric and electronic properties of the bridge, Ru --> Os directional transfer of excitation energy takes place in the complexes [(tpy)Ru(3)Os(tpy)]4+ (end-to-end) and [(tpy)Ru(3)Os(3)Ru(tpy)]6+ (periphery-to-centre). With respect to the homometallic case, for [(tpy)Ru(3)Os(3)Ru(tpy)]6+ excitation trapping at the central position is accompanied by a fivefold enhancement of luminescence intensity.     

Silica particle-stabilized emulsions of silicone oil and water: aspects of emulsification

A study of the emulsification of silicone oil and water in the presence of partially hydrophobic, monodisperse silica nanoparticles is described. Emulsification involves the fragmentation of bulk liquids and the resulting large drops and the coalescence of some of those drops. The influence of particle concentration, oil/water ratio, and emulsification time on the relative extents of fragmentation and coalescence during the formation of emulsions, prepared using either batch or continuous methods, has been investigated. For batch emulsions, the average drop diameter decreases with increasing particle concentration as the extent of limited coalescence is reduced. Increasing the oil volume fraction in the emulsion at fixed aqueous particle concentration results in an increase in the average drop diameter together with a dramatic lowering of the uniformity of the drop size distribution as coalescence becomes increasingly significant until catastrophic phase inversion occurs. For low oil volume fractions (phi(o)), fragmentation dominates during emulsification since the mean drop size decreases with emulsification time. For higher phi(o) close to conditions of phase inversion, coalescence becomes more prevalent and the drop size increases with time with stable multiple emulsions forming as a result.     

Characterization of a new qQq-FTICR mass spectrometer for post-translational modification analysis and top-down tandem mass spectrometry of whole proteins

The use of a new electrospray qQq Fourier transform ion cyclotron mass spectrometer (qQq-FTICR MS) instrument for biologic applications is described. This qQq-FTICR mass spectrometer was designed for the study of post-translationally modified proteins and for top-down analysis of biologically relevant protein samples. The utility of the instrument for the analysis of phosphorylation, a common and important post-translational modification, was investigated. Phosphorylation was chosen as an example because it is ubiquitous and challenging to analyze. In addition, the use of the instrument for top-down sequencing of proteins was explored since this instrument offers particular advantages to this approach. Top-down sequencing was performed on different proteins, including commercially available proteins and biologically derived samples such as the human E2 ubiquitin conjugating enzyme, UbCH10. A good sequence tag was obtained for the human UbCH10, allowing the unambiguous identification of the protein. The instrument was built with a commercially produced front end: a focusing rf-only quadrupole (Q0), followed by a resolving quadrupole (Q1), and a LINAC quadrupole collision cell (Q2), in combination with an FTICR mass analyzer. It has utility in the analysis of samples found in substoichiometric concentrations, as ions can be isolated in the mass resolving Q1 and accumulated in Q2 before analysis in the ICR cell. The speed and efficacy of the Q2 cooling and fragmentation was demonstrated on an LCMS-compatible time scale, and detection limits for phosphopeptides in the 10 amol/muL range (pM) were demonstrated. The instrument was designed to make several fragmentation methods available, including nozzle-skimmer fragmentation, Q2 collisionally activated dissociation (Q2 CAD), multipole storage assisted dissociation (MSAD), electron capture dissociation (ECD), infrared multiphoton induced dissociation (IRMPD), and sustained off resonance irradiation (SORI) CAD, thus allowing a variety of MS(n) experiments. A particularly useful aspect of the system was the use of Q1 to isolate ions from complex mixtures with narrow windows of isolation less than 1 m/z. These features enable top-down protein analysis experiments as well structural characterization of minor components of complex mixtures.