Phenacyl onium salt photoinitiators: synthesis, photolysis, and applications

Onium salts, namely sulfonium, phosphonium, ammonium, and pyridinium salts containing phenacyl group are photoinitiators appropriate for the polymerization of monomers such as oxiranes and vinyl ethers, which are not polymerizable by a free-radical mechanism. The initiation is accomplished by direct or indirect (sensitized) photolysis of the salts. Depending on the type of the salt, the direct photoinitiation of cationic polymerization involves reversible or irreversible processes. The photolysis of phenacylsulfonium compounds proceeds by a reversible process, while the other types undergo irreversible photolysis leading to complete fragmentation of the photoinitiator. An additionally useful tool, namely photosensitized generation of initiating species enlarges the versatility of these salts as photoinitiators. Photoinitiated free-radical and zwitterionic polymerizations by using phenacyl-type salts are also addressed. Keto-enol tautomerization of phenacyl pyridinium salts is discussed. Moreover, an interesting application concerning in situ synthesis of clay-poly(methyl methacrylate) nanocomposites with the aid of the phenacyl anilinium salt-based photopolymerization technique is noted.     

Biophysical investigation of the interfacial properties of cationic fluorocarbon/hydrocarbon hybrid surfactant: mimicking the lung surfactant protein C

The interfacial behavior of the newly designed Fluorocarbon Hydrocarbon Cationic Lipid (FHCL or CH(3)(CH(2))(17)N(+)(C(2)H(5))(2)(CH(2))(3)(CF(2))(7)CF(3)I(-)) and its mixtures with a phospholipid (DPPC, Dipalmitoylphosphatidylcholine) at different mole fractions were investigated. This new molecule was synthesized to mimic the selected properties of lung surfactant, which is a natural lipid-protein mixture which is known to play important roles in the process of respiration, by considering the structure/function relation of lung surfactant protein (SP-C). Each segment in the molecular structure was selected to affect the molecular level interaction at the interface whereas the keeping the overall structure as simple as possible. The surface pressure area isotherms obtained for the mixtures of DPPC/FHCL indicated that there was repulsive interaction between DPPC and FHCL molecules. Due to the molecular level interaction, specifically at mole fraction 0.3, the isotherm obtained from that mixture resembled the isotherm obtained from the DPPC monolayer in the presence of SP-C. High elasticity of the interface was one of the important parameters for the respiration process, therefore, shear and dilatational elasticities of two-component systems were determined and they were found to be similar to the case where SP-C protein is present. Fluorescence microscopy images were taken in order to investigate the monolayer in details. The FHCL was able to fluidize the DPPC monolayer even at high surface pressures effectively. In addition, the cyclic compression-expansion isotherms were obtained to understand the spreading and re-spreading ability of the pure FHCL and the mixed DPPC/FHCL monolayers. At a specific mole fraction, X(FHCL)=0.3, the mixture exhibited good hysteresis in area, compressibility, recruitment index and re-spreading ability at the interface. All these results point out that FHCL can fulfill the selected features of the lung surfactant that are attributed to the presence of SP-C protein when mixed with DPPC, even if the molecular structure of the FHCL is quite simple.     

Cost-effective and compact wide-field fluorescent imaging on a cell-phone

We demonstrate wide-field fluorescent and darkfield imaging on a cell-phone with compact, light-weight and cost-effective optical components that are mechanically attached to the existing camera unit of the cell-phone. For this purpose, we used battery powered light-emitting diodes (LEDs) to pump the sample of interest from the side using butt-coupling, where the pump light was guided within the sample cuvette to uniformly excite the specimen. The fluorescent emission from the sample was then imaged using an additional lens that was positioned right in front of the existing lens of the cell-phone camera. Because the excitation occurs through guided waves that propagate perpendicular to our detection path, an inexpensive plastic colour filter was sufficient to create the dark-field background required for fluorescent imaging, without the need for a thin-film interference filter. We validate the performance of this platform by imaging various fluorescent micro-objects in 2 colours (i.e., red and green) over a large field-of-view (FOV) of ～81 mm(2) with a raw spatial resolution of ～20 μm. With additional digital processing of the captured cell-phone images, through the use of compressive sampling theory, we demonstrate ～2 fold improvement in our resolving power, achieving ～10 μm resolution without a trade-off in our FOV. Further, we also demonstrate darkfield imaging of non-fluorescent specimen using the same interface, where this time the scattered light from the objects is detected without the use of any filters. The capability of imaging a wide FOV would be exceedingly important to probe large sample volumes (e.g., >0.1 mL) of e.g., blood, urine, sputum or water, and for this end we also demonstrate fluorescent imaging of labeled white-blood cells from whole blood samples, as well as water-borne pathogenic protozoan parasites such as Giardia Lamblia cysts. Weighing only ～28 g (～1 ounce), this compact and cost-effective fluorescent imaging platform attached to a cell-phone could be quite useful especially for resource-limited settings, and might provide an important tool for wide-field imaging and quantification of various lab-on-a-chip assays developed for global health applications, such as monitoring of HIV+ patients for CD4 counts or viral load measurements.     

Spin-trapping evidence for the formation of alkyl, alkoxyl, and alkylperoxyl radicals in the reactions of dialkylzincs with oxygen

The reactions of dialkylzincs (Me(2)Zn, Et(2)Zn, and nBu(2)Zn) with oxygen have been investigated by EPR spectroscopy using spin-trapping techniques. The use of 5-diethoxyphosphoryl-5-methyl-1-pyrrroline N-oxide (DEPMPO) as a spin-trap has allowed the involvement of alkyl, alkylperoxyl, and alkoxyl radicals in this process to be probed for the first time. The relative ratio of the corresponding spin-adducts depends strongly on the nature of the R group, which controls the C-Zn bond dissociation enthalpy, and on the experimental conditions (excess of spin-trap compared with R(2)Zn and vice versa). The results have demonstrated that Et(2)Zn and, to a lesser extent, nBu(2)Zn are much better traps for oxygen-centered species than Me(2)Zn. When the dialkylzincs were used in excess with respect to the spin-trap, the concentration of the oxygen-centered radical adducts of DEPMPO was much lower for Et(2)Zn and nBu(2)Zn than for Me(2)Zn. A detailed reaction mechanism is discussed and C-Zn, O-Zn, and O-O bond dissociation enthalpies for the proposed reaction intermediates were calculated at the UB3LYP/6-311++G(3df,3pd)//UB3LYP/6-31G(d,p) level of theory to support the rationale.     

Unexpected conversion of alkyl azides to alkyl iodides and of aryl azides to N-tert-butyl anilines

In the presence of tert-butyl iodide, alkyl azides are converted into the corresponding iodides at room temperature, whereas, N-t-Bu anilines are obtained from aryl azides under the same experimental conditions. A mechanism is proposed to explain this unusual reactivity.     

Aminomethylation of Michael acceptors: complementary radical and polar approaches mediated by dialkylzincs

Phtalimidomethyl iodide and substituted maleimidomethyl iodide were used as radical precursors in dialkylzinc-mediated radical addition to diethyl fumarate. The reactions led stereoselectively to functionalized pyrrolizidines. The radical mechanism was supported by spin-trapping experiments and rationalized by theoretical calculations. Radical additions, on the one hand, and carbozincation followed by transmetalation with copper(I), on the other, were shown to be complementary methods to achieve the formal aminomethylation of activated unsaturated compounds.     

Synthesis and characterisation of a calix[4]pyrrole functional polystyrene via ‘click chemistry’ and its use in the extraction of halide anion salts

A polystyrene with pendant calix[4]pyrroles was prepared via ‘click reaction’ strategy. First, a poly(styrene-co-chloromethylstyrene) with approximately 12% of chloro groups was prepared by conventional free radical polymerisation. The chloro groups were then converted to azido groups using NaN₃ in N,N-dimethylformamide. An alkyne-functionalised calix[4]pyrrole was then coupled to the azido-functionalised polystyrene by click chemistry with high efficiency. The resulting polystyrene with pendant calix[4]pyrroles was used to extract fluoride and chloride anions (as their tetrabutylammonium salts) from their aqueous solutions to organic media.     

Poly(methyl methacrylate)s with pendant calixpyrroles: polymeric extractants for halide anion salts

Poly(methyl methacrylate)s containing pendant octamethylcalix[4]pyrrole subunits were prepared and demonstrated to be capable of extracting tetrabutylammonium chloride and fluoride salts from aqueous media.     

Reactivity of benzylidene and alkylidenemalonates in radical addition mediated with dialkylzincs – An intriguing story

Benzylidene- and alkylidenemalonates are extremely reactive radical acceptors in dialkylzinc-mediated radical additions. Theoretical investigations showed that the multi-step radical-polar crossover process should be highly exothermic. Not only the addition of the alkyl radical to the complexed substrate is enthalpically favored but what is more, the homolytic substitution at the metal leading to a zinc enolate should also be exothermic, even though it necessitates the cleavage of the C-Zn bond from the complexed α-alkoxycarbonyl radical intermediate. This work was undertaken to highlight the power of chelation in controlling the fate of this type of reaction. Much to our surprise, no unambiguous experimental evidence could be put forward to prove the formation of the expected zinc enolate intermediate. Additionally, benzylidenemalonates and their alkylidene analogues (although to a lesser extent) exhibit an intriguing behavior. The backward reaction (retro-addition) can be triggered at work-up depending upon experimental conditions.