Synthesis of fluorous tags for incorporation of reducing sugars into a quantitative microarray platform

Carbohydrate microarrays can map out key interactions of carbohydrates and proteins in a high-throughput manner, but require the inclusion of a range of sugars for their optimal use. Here we present the synthesis and use of a new hydroxylamine-modified fluorous tag that allows the facile incorporation of reducing sugars into a noncovalent fluorous-based microarray after simple purification by fluorous solid-phase extraction (FSPE). The microarray supports quantitative screening against carbohydrate-binding proteins.     

Amide bond formation with a new fluorous carbodiimide: separation by reverse fluorous solid-phase extraction

A new fluorous carbodiimide is introduced along with a convenient procedure for amide coupling reactions. Reactions of acids and amines under standard conditions for carbodiimide couplings, followed by simple reverse fluorous solid-phase extraction (FSPE) over standard silica gel, provide the target amide products in good yields and purities. The use of HFE-7100 as a fluorous solvent is crucial for the success of the reverse FSPE.     

Size limitations for the formation of ordered striped nanoparticles

A combination of immiscible molecules in the ligand shell of a gold nanoparticle (NP) has been shown to phase separate into a rippled structure; this phase separation can be used to direct the assembly of the NPs into chains. Here we demonstrate that only NPs within a certain size range can form chains, and we conclude that the rippled morphology of the ligand shell also exists only within that given size range. We corroborate this result with simulations of the ligand arrangement on NPs of various sizes.     

A convenient method for the preparation of fluorous tin derivatives for the fluorous labeling strategy

A convenient method for the preparation of fluorous aryl stannanes was developed as a means of expanding the general utility of the fluorous labeling strategy (FLS). Following the synthesis of a novel fluorous distannane, a palladium-catalyzed cross-coupling reaction was used to prepare the target compounds from aryl halides. The scope of the reaction was investigated by preparing a small library of model compounds where the reaction yields were similar to those reported for the analogous procedures employing hexamethyl- or hexabutyldistannanes. The utility of the reported methodology was demonstrated through the successful synthesis of fluorous precursors to two established molecular imaging and therapy agents (FIAU, IUdR). These were radiolabeled with iodine-125 and the desired products isolated in high yield and effective specific activity.     

Feature-size limitations of microarray technology - a critical review

The appeal of microarray technology is the possibility of large-scale parallel determination of a variety of variables simultaneously. Hence, microarray technologies attract the interest of both the scientific and business worlds alike. High-throughput screening has been the major focus of the utilization of microarray technologies in recent years, and has provided the strong driving force for developments in this field. DNA chip and biochip technologies have been developed as a consequence of worldwide activity in genome research. This review focuses on microarray-based analysis and emphasizes some of its principal constraints, especially detection limits.     

Synthesis of novel fluorous surfactants for microdroplet stabilisation in fluorous oil streams

The synthesis of a number of potential fluorous surfactants, prepared with a view to stabilising microdroplets in microfluidic systems is described. The surfactants comprised compounds with both perfluoropolyether (PFPE) and perfluoroalkyl (PFA) tails with three classes of hydrophilic head group, including crown ethers and hexaethylene glycol. Hydrophilic head groups and alkyl fluorous-based tails were coupled together via amide, ester and ether linkages to afford the fluorous surfactant candidates in good yields. The resulting molecules show promise in forming and stabilising both aqueous and non-aqueous microdroplets in fluorous oil streams within poly(dimethylsiloxane) (PDMS) devices to a greater degree than the pseudosurfactants commonly employed in microdroplet research.     

Probing the mechanism of aqueous two-phase system formation for alpha-elastin on-chip

The kinetics of formation of the aqueous two-phase system (ATPS) for alpha-elastin was studied by dark field microscopy in an on-chip linear temperature gradient. Scattering intensities of protein solutions were recorded as a function of temperature and time, simultaneously at several concentrations. It was found that the formation rate of the ATPS could be fit as a first-order process and that the apparent rate constant increased with protein concentration. The activation energy for the process was 9.5 +/- 0.5 kcal/mol, and this result was consistent with a coalescence mechanism. Experiments were also conducted with varying concentrations of sodium dodecyl sulfate, which shut off the coalescence mechanism forcing ATPS formation to proceed through Ostwald ripening. When this was done, the activation energy increased to 33 +/- 2 kcal/mol and the kinetics became consistent with a second-order process.     

Synthesis and solid state structure of fluorous probe molecules for fluorous separation applications

A series of colored hydrocarbon and fluorocarbon tagged 1-fluoro-4-alkylamino-anthraquinones and 1,4-bis-alkylamino-anthraquinone probe molecules were synthesized from a (fluorinated) alkyl amine and 1,4-difluoroanthraquinone to aid in the development of fluorous separation applications. The anthraquinones displayed stacking of the anthraquinone tricycle and interdigitation of the (fluorinated) alkyl chains in the solid state. Furthermore, intramolecular N-H?O hydrogen bonds forced the hydrocarbon and fluorocarbon tags into a conformation pointing away from the anthraquinone tricycle, with the angle of the tricycle plane normal and the main (fluorinated) alkyl vector ranging from 1° to 39°. Separation of the probe molecules on fluorous silica gel showed that the degree of fluorination of the probe molecules plays only a minor role with most eluents (e.g., hexane/ethyl acetate and methyl nonafluorobutyl ethers/ethyl acetate). However, toluene as eluent caused a pronounced separation by degree of fluorination for fluorocarbon, but not hydrocarbon tagged probe molecules on both silica gel and fluorous silica gel. These studies suggest that hydrocarbon and fluorocarbon tagged anthraquinones are useful probe molecules for the development of laboratory scale fluorous separation applications.     

Reverse fluorous solid-phase extraction: a new technique for rapid separation of fluorous compounds

Fluorous-tagged compounds can rapidly be separated from organic (non-tagged) compounds by the new separation technique of reverse fluorous solid-phase extraction (r-fspe). In a reversal of the roles of solid and liquid phases in standard fluorous spe, a mixture is charged to a polar solid phase (standard silica gel) and then eluted with a fluorous solvent or solvent mixture. The organic components of the mixture are retained, while the fluorous components pass. [structure: see text]     

Noncovalent fluorous interactions for the synthesis of carbohydrate microarrays

A surface patterning method based on noncovalent immobilization of fluorous-tagged sugars on fluorous-derivatized glass slides allows the facile fabrication of carbohydrate microarrays. To expand the scope of these arrays, the first syntheses are reported of arabinose, rhamnose, lactose, maltose, and glucosamine tagged with a single C₈F₁₇-tail for ease of purification as well as array formation. Screening of these carbohydrate microarrays against lectins from Triticum vulgaris (WGA) and Arachis hypogaea (PNA) demonstrate that the noncovalent fluorous–fluorous interaction is sufficient to retain not only mono- but also disaccharides under the biological assay conditions.     

Probing helix formation in unsolvated peptides

Ion mobility measurements have been used to examine helix formation in unsolvated glycine-based peptides containing three alanine residues. Nine sequence isomers of Ac-[12G3A]K+H(+) were studied (Ac = acetyl, G = glycine, A = alanine, and K = lysine). The amount of helix present for each peptide was examined using two metrics, and it is strongly dependent on the proximity and the location of the alanine residues. Peptides with three adjacent alanines have the highest helix abundances, and those with well-separated alanines have the lowest. The helix abundances for most of the peptides can be fit reasonably well using a modified Lifson-Roig theory. However, Lifson-Roig theory fails to account for several key features of the experimental results. The most likely explanation for the correlation between helix abundances and the number of adjacent alanines is that neighboring alanines promote helix nucleation.     

Novel fluorous amphiphilic heteroleptic Ru-based complexes for a dye-sensitized solar cell: the first fluorous bis-ponytailed amphiphilic Ru complexes

A new series of amphiphilic heteroleptic ruthenium(II) sensitizers with a fluorous bis-ponytailed bipyridine ancillary ligand, [Ru(H(2)dcbpy)(4,4'-bis(R(f)CH(2)OCH(2))-2,2'-bpy)(NCS)(2)] [where R(f) = HCF(2)CF(2) (CT4), C(3)F(7) (CT7), and HCF(2)CF(2)CF(2)CF(2) (CT8)], have been synthesized and fully characterized by UV/vis, visible emission, NMR, fast atom bombardment mass spectrometry, and cyclic voltammetric studies. Dye-sensitized solar cells (DSCs) based on these dyes exhibit efficiencies comparable with that of the standard cell based on N719. The conversion efficiency of a CT7- or CT8-based DSC is ~9% higher than that of Z907 with a nonfluorous bis-ponytailed bipyridine ancillary ligand. The fluorous chains were found to increase the dye density on TiO(2) and to help to suppress the dye desorption.     

Filling the equatorial garland of uranyl ion: its content and limitations

Crystal structure determinations on the uranyl ion complexes [H₂N(CH₃)₂]₂[UO₂(bpdc)₂], (1), (bpdc?=?2,2′-bipyridine-3,3′-dicarboxylate), [pyH]₂[UO₂(btfac)(NO₃)₂](NO₃), (2), (btfac?=?1-phenyl-4,4,4-trifluorobutane-1,3-dionate), [H₂dabco][UO₂(nta)]₂·3H₂O, (3), (dabco?=?1,4-diazabicyclo[2.2.2]octane; nta?=?nitrilotriacetate) and [Ni(cyclam)UO₂(edta)]^.2H₂O, (4), (cyclam?=?1,4,8,11-tetrazacyclotetradecane; edta?=?ethylenediaminetetraacetate) have provided further examples of U(VI) in tetragonal-, pentagonal and hexagonal-bipyramidal coordination environments. Consideration of each structure within the context of those of known relatives has been used to assess the influence of factors in addition to repulsions within the primary coordination sphere on the equatorial coordination number of U(VI).

     

Automation of fluorous solid-phase extraction for parallel synthesis

An automatic fluorous solid-phase extraction (F-SPE) technique is developed by using FluoroFlash SPE cartridges on the RapidTrace workstation. A 10-module workstation has the capability to complete a maximum of 100 SPEs each round in 1-2 h. Another important feature of the RapidTrace system is that it has the capability to load slurry samples onto the F-SPE cartridges. The F-SPE cartridge charged with 2 g of fluorous silica gel is used to purify up to 200 mg of crude sample. Sample loading, elution solvent, cartridge reuse, and SPE reproducibility are evaluated. The automatic SPE system is used for purification of a small urea library generated from amine-scavenging reactions using fluorous dichlorotriazine, a 96-membered amide library generated using 2-chloro-4,6-bis[(perfluorohexyl)propyloxy]-1,3,5-triazine as the coupling agent, and another 96-membered library generated from fluorous Mitsunobu reactions. Approximately 90% of the products have > 90% purity after F-SPE.     

Probing the formation of bicyclo[4.2.0]octan-1-ols

Reaction of lithium enolates of simple ketones with (+/-)-phenyl vinyl sulfoxide has potential for the convergent construction of complex fused ring systems containing a bicyclo[n.2.0]alkan-1-ol. The formation of sulfinylbicyclo[4.2.0]octan-1-ols 1-3 from the lithium enolate of cyclohexanone with (+/-)-phenyl vinyl sulfoxide or (R)-(+)-p-tolyl vinyl sulfoxide 18 was used to probe the mode of this novel cyclization reaction. Using phenyl vinyl sulfoxide, variations in the reaction lighting and solvent were investigated, in conjunction with radical trapping (TEMPO) and isotope labeling (deuterium) experiments. Cyclization to form sulfinylbicyclooctanols 1-3 is likely to proceed via an intermediate that ring closes to the bicycloalkanol anion 11 and was presently favored by the use of solvents such as THF or DME.     

Probing amyloid fibril formation of the NFGAIL peptide by computer simulations

Amyloid fibril formation, as observed in Alzheimer's disease and type II diabetes, is currently described by a nucleation-condensation mechanism, but the details of the process preceding the formation of the nucleus are still lacking. In this study, using an activation-relaxation technique coupled to a generic energy model, we explore the aggregation pathways of 12 chains of the hexapeptide NFGAIL. The simulations show, starting from a preformed parallel dimer and ten disordered chains, that the peptides form essentially amorphous oligomers or more rarely ordered beta-sheet structures where the peptides adopt a parallel orientation within the sheets. Comparison between the simulations indicates that a dimer is not a sufficient seed for avoiding amorphous aggregates and that there is a critical threshold in the number of connections between the chains above which exploration of amorphous aggregates is preferred.     

Oxidative detagging of fluorous organosilanes

We have validated a novel detagging strategy featuring the unmasking of a fluorous-tagged silane to a hydroxy moiety. The fluorous silylated bicyclononane, prepared from the titanium-mediated annulation of 1-acetylcyclohexene and a fluorous-tagged allylsilane, was successfully detagged under Fleming-type oxidation conditions. The stereochemistry of the resulting hydroxylated product indicates retention of configuration upon detagging in line with the non-fluorous variant of this transformation.