Using the meniscus in a capillary for small volume contact angle measurement in biochemical applications

The contact angle is a sensitive parameter often used to define wettability. With the increasing movement toward smaller liquid volumes in many biochemical applications, a key challenge lies in how to perform measurements in the retainer holding the reagent for rapid evaluation and limited material loss. Here, we report a simple and robust method to determine the contact angle of small volumes using the microscopic imaging of a capillary meniscus that requires only the radius and meniscus height information. An error analysis of the measurement finds the method to be highly accurate. We also uncovered that illumination delivered from the liquid end of the capillary lights up the interface, thereby facilitating the measurement.     

Separation of inorganic anions by liquid chromatography with crown ether as eluent additive

Inorganic anions were separated on a reversed-phase stationary phase dynamically modified with crown ether as a selector in capillary ion chromatography. The eluent contained crown ether, acetonitrile and a salt. Free and cation-trapped crown ether molecules in the eluent were adsorbed on a hydrophobic stationary phase such as triacontyl-functionalized silica (C30). The eluent cations trapped on crown ether worked as the ion-exchange sites, where the eluent anions and the analyte anions were competing for electrostatic interaction. The sizes of crown ether and the salt cation affected the retention of analyte anions. The concentrations of acetonitrile and crown ether as well as the eluent anion also affected the retention of analyte anions. An aqueous solution containing 18-crown-6-ether, potassium salt and acetonitrile achieved larger retention for analyte anions. Effects of the eluent conditions on the retention of analyte anions were examined in detail.     

Numerical study of nitrogen desorption by rapid oxygen purge for a medical oxygen concentrator

Efficient desorption of selectively adsorbed N₂ from air in a packed column of LiX zeolite by rapidly purging the adsorbent with an O₂ enriched gas is an important element of a rapid cyclic pressure swing adsorption (RPSA) process used in the design of many medical oxygen concentrators (MOC). The amount of O₂ purge gas used in the desorption process is a sensitive variable in determining the overall separation performance of a MOC unit. Various resistances like (a) adsorption kinetics, (b) column pressure drop, (c) non-isothermal column operation, (d) gas phase mass and thermal axial dispersions, and (e) gas-solid heat transfer kinetics determine the amount of purge gas required for efficient desorption of N₂. The impacts of these variables on the purge efficiency were numerically simulated using a detailed mathematical model of non-isothermal, non-isobaric, and non-equilibrium desorption process in an adiabatic column. The purge gas quantity required for a specific desorption duty (fraction of total N₂ removed from a column) is minimum when the process is carried out under ideal, hypothetical conditions (isothermal, isobaric, and governed by local thermodynamic equilibrium). All above-listed non-idealities (a?Ce) can increase the purge gas quantity, thereby, lowering the efficiency of the desorption process compared to the ideal case. Items (a?Cc) are primarily responsible for inefficient desorption by purge, while gas phase mass and thermal axial dispersions do not affect the purge efficiency under the conditions of operation used in this study. Smaller adsorbent particles can be used to reduce the negative effects of adsorption kinetics, especially for a fast desorption process, but increased column pressure drop adds to purge inefficiency. A?particle size range of ??300?C500???m is found to require a?minimum purge gas amount for a given desorption duty. The purge gas requirement can be further reduced by employing a pancake column design (length to diameter ratio, L/D<0.2) which lowers the column pressure drop, but hydrodynamic inefficiencies (gas mal-distribution, particle agglomeration) may be introduced. Lower L/D also leads to a smaller fraction of the column volume that is free of N₂ at the purge inlet end, which is required for maintaining product gas purity. The simulated gas and solid temperature profiles inside the column at the end of the rapid desorption process show that a finite gas-solid heat transfer coefficient affects these profiles only in the purge gas entrance region of the column. The profiles in the balance of the column are nearly invariant to the values of that coefficient. Consequently, the gas-solid heat transfer resistance has a minimum influence on the overall integrated N₂ desorption efficiency by O₂ purge for the present application.     

Synthesis and Characterization of β‐CD‐Coated Polystyrene Microspheres by γ‐Ray Radiation Emulsion Polymerization

Polystyrene (PS) microspheres coated with β‐cyclodextrin (β‐CD) were fabricated via γ‐ray‐induced emulsion polymerization in a ternary system of styrene/β‐CD/water (St/β‐CD/water). The solid inclusion complex of St and β‐CD particles formed at the St droplets–water interface can stabilize the emulsion as the surfactant. TEM and XPS results showed that β‐CD remains on the surface of PS particles. The average size of the PS particles increases from 186 to 294 nm as the weight ratio of β‐CD to St rises from 5% to 12.5%. The water contact angle (CA) of PS latex film is lower than 90°, and reduces with the β‐CD content even to 36°. Thus, this work provides a new and one‐pot strategy to surface hydrophilic modification on hydrophobic polymer particles with cyclodextrins through radiation emulsion polymerization.     

Modeling the liquid filling in capillary well microplates for analyte preconcentration

An attractive advantage of the capillary well microplate approach is the ability to conduct evaporative analyte preconcentration. We advance the use of hydrophobic materials for the wells which apart from reducing material loss through wetting also affords self entry into the well when the droplet size reduces below a critical value. Using Surface Evolver simulation without gravity, we find the critical diameters D(c) fitting very well with theoretical results. When simulating the critical diameters D(c)(G) with gravity included, the gravitational effect could only be ignored when the liquid volumes were small (difference of 5.7% with 5 μL of liquid), but not when the liquid volumes were large (differences of more than 22% with 50 μL of liquid). From this, we developed a modifying equation from a series of simulation results made to describe the gravitational effect. This modifying equation fitted the simulation results well in our simulation range (100°≤θ≤135° and 1 μL≤V≤200 μL). In simulating the condition of multiple wells underneath each droplet, we found that having more holes did not alter the critical diameters significantly. Consequently, the modifying relation should also generally express the critical diameter for multiple wells under a droplet.     

Selenium Blue-α and -β: turning on the fluorescence of a pyrenyl fluorophore via oxidative cleavage of the Se-C bond by reactive oxygen species

Rapid oxidation of nonfluorescent pyrenyl-CH₂SeAr (Ar = o-nitrophenyl) by hypochlorite yielded pyrenyl-CH₂Cl and pyrenyl-CH₂OH and turns on blue fluorescence, while slow oxidation of pyrenyl-CH₂SeAr with excess H₂O₂ leads to pyrenyl-CHO which emits a bluish-green fluorescence. The homolog, pyrenyl-CH₂CH₂SeAr′ (Ar′ = o-nitrophenyl) reacts slower with H₂O₂ and ClO⁻ giving the same product, vinyl pyrene.     

Manifold dynamic non-covalent interactions for steering molecular assembly and cyclization

Deciphering rich non-covalent interactions that govern many chemical and biological processes is crucial for the design of drugs and controlling molecular assemblies and their chemical transformations. However, real-space characterization of these weak interactions in complex molecular architectures at the single bond level has been a longstanding challenge. Here, we employed bond-resolved scanning probe microscopy combined with an exhaustive structural search algorithm and quantum chemistry calculations to elucidate multiple non-covalent interactions that control the cohesive molecular clustering of well-designed precursor molecules and their chemical reactions. The presence of two flexible bromo-triphenyl moieties in the precursor leads to the assembly of distinct non-planar dimer and trimer clusters by manifold non-covalent interactions, including hydrogen bonding, halogen bonding, C–H⋯π and lone pair⋯π interactions. The dynamic nature of weak interactions allows for transforming dimers into energetically more favourable trimers as molecular density increases. The formation of trimers also facilitates thermally-triggered intermolecular Ullmann coupling reactions, while the disassembly of dimers favours intramolecular cyclization, as evidenced by bond-resolved imaging of metalorganic intermediates and final products. The richness of manifold non-covalent interactions offers unprecedented opportunities for controlling the assembly of complex molecular architectures and steering on-surface synthesis of quantum nanostructures.

A real-space characterization of dynamic non-covalent interactions in molecular assemblies and chemical reactions at the atomic bond level.     

A new gradient method via quasi-Cauchy relation which guarantees descent

We propose a new monotone algorithm for unconstrained optimization in the frame of Barzilai and Borwein (BB) method and analyze the convergence properties of this new descent method. Motivated by the fact that BB method does not guarantee descent in the objective function at each iteration, but performs better than the steepest descent method, we therefore attempt to find stepsize formula which enables us to approximate the Hessian based on the Quasi-Cauchy equation and possess monotone property in each iteration. Practical insights on the effectiveness of the proposed techniques are given by a numerical comparison with the BB method.     

Measurement of the K0 charge radius and a CP-violating asymmetry and a search for CP-violating E1 direct photon emission in the rare decay KL--> pi+ pi- e+ e-

Using the complete KTeV data set of 5,241 candidate K(L)--> pi(+) pi(-) e(+) e(-) decays (including an estimated background of 204 +/- 14 events), we have measured the coupling g(CR)= 0.163 +/- 0.0149(stat) +/- 0.023(syst) of the CP conserving charge radius process and from it determined a K(0) charge radius of = [-0.077 +/- 0.007(stat) +/- 0.011(syst)]fm(2). We have determined a first experimental upper limit of 0.04 (90% C.L.) /g(e1)/ / /g(M1)/ of the couplings for the E1 and M1 direct photon emission processes. We also report the measurement of /g(M1)/ including a vector form factor /g(M1)/(1 + (a(1)/a(2))/((M(2)(p)-(M(2)(k))= 2M(K)E(gamma*)), where vector /g(M1)/= 1.11+/- 0.12(stat) +/- 0.08(syst) and a(1)/a(2) = [-0.744 +/- 0.027(stat) +/- 0.032(syst)] GeV(2)/c(2). Finally, a CP-violating asymmetry of [13.6 +/- 1.4(stat) +/- 1.5(syst)]% in the CP and T odd angle phi between the decay planes of the e(+) e(-) and pi(+) pi(-) pairs in the K(L) center of mass is reported.     

Photochromic Benzo[b]phosphole Alkynylgold(I) Complexes with Mechanochromic Property to Serve as Multistimuli‐Responsive Materials

A series of novel benzo[b]phosphole alkynylgold(I) complexes has been demonstrated to display photochromic and mechanochromic properties upon applying the respective stimuli of light and mechanical force. Promising multistimuli‐responsive properties of this series of gold(I) complexes have been successfully achieved through judicious molecular design, which involves incorporation of the photochromic dithienylethene‐containing benzo[b]phosphole into the triphenylamine‐containing arylethynyl ligand that is susceptible to mechanical force‐induced color changes via gold(I) complexation. With excellent thermal irreversibility and robust fatigue resistance of this series of gold(I) complexes, multicolor states controlled by the photochromism and mechanochromism have been realized. Repeatable photochromic and mechanochromic cycles without apparent loss of reactivity have also been observed under ambient conditions. The present work provides important insight and an alternative strategy for the molecular design of multistimuli‐responsive materials, paving the way for further development of the underexplored photoresponsive gold(I) complexes and the multistate photocontrolled system.