Zeta potential and electroosmotic mobility in microfluidic devices fabricated from hydrophobic polymers: 1. The origins of charge

This paper combines new experimental data for electrokinetic characterization of hydrophobic polymers with a detailed discussion of the putative origins of charge at water-hydrophobe interfaces. Complexities in determining the origin of charge are discussed in the context of design and modeling challenges for electrokinetic actuation in hydrophobic microfluidic devices with aqueous working fluids. Measurements of interfacial charge are complicated by slip and interfacial water structuring phenomena (see Part 2, this issue). Despite these complexities, it is shown that (i) several hydrophobic materials, such as Teflon and Zeonor, have predictable electrokinetic properties and (ii) electrokinetic data for hydrophobic microfluidic systems is most consistent with the postulate that hydroxyl ion adsorption is the origin of charge.     

Ag‐CNT Architectures for Attomolar Dopamine Detection and 100‐Fold Fluorescence Enhancements with Cellphone‐Based Surface Plasmon‐Coupled Emission Platform

We report cellphone‐based detection of dopamine with attomolar sensitivity in clinical samples with the use of a surface plasmon‐coupled emission (SPCE) platform. To this end, silver‐coated carbon nanotubes were used as spacer and cavity materials on SPCE substrates to obtain up to 100‐fold fluorescence enhancements. The presence of silver on the carbon nanotubes helped to overcome fluorescence quenching arising due to π–π interactions between the carbon nanotube and rhodamine 6G. The competing adsorption of dopamine versus rhodamine 6G on graphene oxide was utilized to develop this sensing platform.     

Self‐Assembly of Bolaamphiphilic Molecules

The current buzzword in science and technology is self‐assembly and molecular self‐assembly is one of the most prominent fields as far as research in chemical and biological sciences is concerned. Generally, self‐assembly of molecules occurs through weak non‐covalent interactions like hydrogen bonding, π–π stacking, hydrophobic effects, etc. Inspired by many natural systems consisting of self‐assembled structures, scientists have been trying to understand their formation and mimic such processes in the laboratory to create functional “smart” materials, which respond to temperature, light, pH, electromagnetic field, mechanical stress, and/or chemical stimuli. These responses are usually manifested as remarkable changes from the molecular (e. g., conformational state, hierarchical order) to the macroscopic level (e. g., shape, surface properties). Many molecules such as peptides, viruses, and surfactants are known to self‐assemble into different structures. Among them, glycolipids are the new entries in the area of molecules that are being investigated for their self‐assembly characteristics. Among the different classes of glycolipids like rhamnolipids and trehalose lipids, owing to their biological preparations and their structural novelty, sophorolipids (SLs) are evoking greater interest among researchers. Sophorolipids are a class of asymmetric bolas bearing COOH groups at one end and sophorose (dimeric glucose linked by an unusual β(1→2) linkage). The extreme membrane stability of Archaea, attributed to the membrane‐spanning bolas (tetraether glycolipids), has inspired chemists to unravel the molecular designs that underpin the self‐assembly of bolaamphiphilic molecules. Apart from these self‐assembled structures, bolaamphiphiles find applications in many fields such as drug delivery, membrane mimicking, siRNA therapies, etc. The first part of this Personal Account presents some possible self‐assembled structures of bolaamphiphiles and their mechanism of formation. The later part covers our work on one of the typical bolaamphiphiles known as sophorolipids.     

Evidence for a long-range component in the pion emission source in Au+Au collisions at sqrt sNN=200 GeV

Emission source functions are extracted from correlation functions constructed from charged pions produced at midrapidity in Au+Au collisions at sqrt[s(NN)]=200 GeV. The source parameters extracted from these functions at low k(T) give first indications of a long tail for the pion emission source. The source extension cannot be explained solely by simple kinematic considerations. The possible role of a halo of secondary pions from resonance emissions is explored.     

Controlling photochemical geometric isomerization of a stilbene and dimerization of a styrene using a confined reaction cavity in water

Utility of a water-soluble deep cavity cavitand, octa acid, as a reaction medium is illustrated by carrying out photochemical reactions of a stilbene and a styrene included within the octa acid in water. Geometric isomerization of trans-4,4'-dimethyl stilbene is restricted while dimerization of 4-methyl styrene is facilitated within the octa acid cavity. The excited-state chemistry of both systems is different in this medium from that in organic solvents. The change in chemistry is attributed to the supramolecular effects provided by the host cavity.     

Photodimerization of acenaphthylene within a nanocapsule: excited state lifetime dependent dimer selectivity

Direct excitation of acenaphthylene molecules included in a syn fashion within the octa acid nanocapsule dimerizes quantitatively to a syn dimer, and upon triplet sensitization, yields both syn and anti dimers probably by reacting within and outside the capsule.     

Photo-Fries reaction in water made selective with a capsule

The water soluble capsule formed by a deep cavity cavitand with eight carboxylic acid groups controls product distribution during photo-Fries rearrangement of naphthyl esters in water by restricting the mobility of primary singlet radical pair.     

Swift heavy ion irradiation-induced modifications of tris-(8-hydroxyquinoline)aluminum thin films

Tris-(8-hydroxyquinoline)aluminum (Alq₃), one of the most widely used light emitting and electron transport materials in organic luminescent devices, has been synthesized. Alq₃ thin films have been deposited by a thermal evaporation process on glass substrates. The effect of swift heavy ion (SHI) irradiation using 40 MeV Li³⁺ on the Alq₃ thin films has been studied by UV-visible, infrared, photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy. From TRPL studies, it is found that the PL of Alq₃ thin films arises from two species corresponding to its two geometrical isomers, namely facial and meridional having two different life times. It is also confirmed that the PL and lifetimes of excitons decrease with the increase of ion fluences of SHI of 40 MeV Li³⁺, indicating a transfer of exciton energy to unstable cationic Alq₃ species generated by SHI irradiation.     

Small molecule antagonists in distinct binding modes inhibit drug-resistant mutant of smoothened

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Highlights? New small molecule antagonists of Smo with distinct binding modes discovered from high throughput screens ? ALLO-1 and ALLO-2 are potent against the drug-resistant mutant of Smo ? ALLO-1 is potent against oncogenic mutant of Smo (SmoM2)