Micro-wilhelmy and related liquid property measurements using constant-diameter nanoneedle-tipped atomic force microscope probes

The micro-Wilhelmy method is a well-established method of determining surface tension by measuring the force of withdrawing a tens of microns to millimeters in diameter cylindrical wire or fiber from a liquid. A comparison of insertion force to retraction force can also be used to determine the contact angle with the fiber. Given the limited availability of atomic force microscope (AFM) probes that have long constant diameter tips, force-distance (F-D) curves using probes with standard tapered tips have been difficult to relate to surface tension. In this report, constant diameter metal alloy nanowires (referred to as "nanoneedles") between 7.2 and 67 microm in length and 108 and 1006 nm in diameter were grown on AFM probes. F-D and Q damping AFM measurements of wetting and drag forces made with the probes were compared against standard macroscopic models of these forces on slender cylinders to estimate surface tension, contact angle, meniscus height, evaporation rate, and viscosity. The surface tensions for several low molecular weight liquids that were measured with these probes were between -4.2% and +8.3% of standard reported values. Also, the F-D curves show well-defined stair-step events on insertion and retraction from partial wetting liquids, compared to the continuously growing attractive force of standard tapered AFM probe tips. In the AFM used, the stair-step feature in F-D curves was repeatably monitored for at least 0.5 h (depending on the volatility of the liquid), and this feature was then used to evaluate evaporation rates (as low as 0.30 nm/s) through changes in the surface height of the liquid. A nanoneedle with a step change in diameter at a known distance from its end produced two steps in the F-D curve from which the meniscus height was determined. The step features enable meniscus height to be determined from distance between the steps, as an alternative to calculating the height corresponding to the AFM measured values of surface tension and contact angle. All but one of the eight measurements agreed to within 13%. The constant diameter of the nanoneedle also is used to relate viscous damping of the vibrating cantilever to a macroscopic model of Stokes drag on a long cylinder. Expected increases in drag force with insertion depth and viscosity are observed for several glycerol-water solutions. However, an additional damping term (associated with drag of the meniscus on the sidewalls of the nanoneedle) limits the sensitivity of the measurement of drag force for low-viscosity solutions, while low values of Q limit the sensitivity for high-viscosity solutions. Overall, reasonable correspondence is found between the macroscopic models and the measurements with the nanoneedle-tipped probes. Tighter environmental control of the AFM and treatments of needles to give them more ideal surfaces are expected to improve repeatability and make more evident subtle features that currently appear to be present on the F-D and Q damping curves.     

Rapid determination of lead in water samples by dispersive liquid-liquid microextraction coupled with electrothermal atomic absorption spectrometry

The need for highly reliable methods for the determination of trace and ultratrace elements has been recognized in analytical chemistry and environmental science. A simple and powerful microextraction technique was used for the detection of the lead ultratrace amounts in water samples using the dispersive liquid-liquid microextraction (DLLME), followed by the electrothermal atomic absorption spectrometry (ET AAS). In this microextraction technique, a mixture of 0.50 mL acetone (disperser solvent), containing 35 microL carbon tetrachloride (extraction solvent) and 5 microL diethyldithiophosphoric acid (chelating agent), was rapidly injected by syringe into the 5.00 mL water sample, spiked with lead. In this process, the lead ions reacted with the chelating agent and were extracted into the fine droplets of CCl(4). After centrifugation (2 min at 5000 rpm), the fine CCl4 droplets were sedimented at the bottom of the conical test tube (25+/-1 microL). Then, 20 microL from the sedimented phase, containing the enriched analyte, was determined by ET AAS. The next step was the optimization of various experimental conditions, affecting DLLME, such as the type and the volume of the extraction solvent, the type and the volume of the disperser solvent, the extraction time, the salt effect, pH and the chelating agent amount. Moreover, the effect of the interfering ions on the analytes recovery was also investigated. Under the optimum conditions, the enrichment factor of 150 was obtained from only a 5.00 mL water sample. The calibration graph was linear in the range of 0.05-1 microg L(-1) with the detection limit of 0.02 microg L(-1). The relative standard deviation (R.S.D.) for seven replicate measurements of 0.50 microg L(-1) of lead was 2.5%. The relative lead recoveries in mineral, tap, well and sea water samples at the spiking level of 0.20 and 0.40 microg L(-1) varied from 93.5 to 105.0. The characteristics of the proposed method were compared with the cloud point extraction (CPE), the liquid-liquid extraction, the solid phase extraction (SPE), the on-line solid phase extraction (SPE) and the co-precipitation, based on bibliographic data. The main DLLME advantages combined with ET AAS were simplicity of operation, rapidity, low cost, high-enrichment factor, good repeatability, low consumption of extraction solvent, requiring a low sample volume (5.00 mL).     

Regioselective synthesis of functionalized 2-(phenylthio)benzoates by ‘[3+3] cyclization/homo-Michael’ reactions of 1-methoxy-1-trimethylsilyloxy-3-phenylthio-1,3-butadienes with 1,1-diacylcyclopropanes

2-(Phenylthio)benzoates containing a remote halide function are regioselectively prepared by ‘[3+3] cyclization/homo-Michael’ reactions of 1-methoxy-1-trimethylsilyloxy-3-phenylthio-1,3-butadienes with 1,1-diacylcyclopropanes.     

Stereoselective synthesis of dialkyl 3-spiroindanedione-1,2,3,3a-tetrahydropyrrolo[1,2-a]quinoline-1,2-dicarboxylates

The 1:1 intermediate generated by the addition of quinoline to dialkyl acetylenedicarboxylates is trapped by 1,3-indanedione to yield dialkyl 3-spiroindanedione-1,2,3,3a-tetrahydropyrrolo[1,2-a]quinoline-1,2-dicarboxylates in good yields. The structures of these products were confirmed by NMR and single-crystal X-ray diffraction studies.     

Many faces of dipyrrins: from hydrogen-bonded networks to homo- and heteronuclear metallamacrocycles

The amphoteric 5-(4-cyanophenyl)dipyrrin ligand, offering three distinct states, i.e., cationic, neutral, and anionic, has been exploited for the formation of a 1-D hydrogen-bonded network in its protonated form and both homo- and heterobinuclear metallamacrocycles, in its neutral and deprotonated states, respectively, with a variety of coordination modes.     

Water promoted, microwave-assisted oxidative novel deamination of N-aminoquinazolinones

A novel deamination of 2-alkyl/aryl 3-amino-4（3H）-quinazolinones series using aqueous KMnO4 under thermal condition and microwave irradiation is described. Compared to thermal condition, significantly higher yields in much shorter times were observed for reactions under microwave irradiation. A plausible mechanism has been proposed for the oxidative water-promoted deamination.     

Modular construction of a series of heteronuclear metallamacrocycles

High modularity in a series of heteronuclear d(8)-d(10) metallamacrocycles built on differentiated ligands is demonstrated.     

Comparative conventional and microwave assisted synthesis of heterocyclic oxadiazole analogues having enzymatic inhibition potential

A comparative microwave assisted and conventional synthetic strategies were applied to synthesize heterocyclic 1,3,4-oxadiazole analogues as active anti-enzymatic agents. Green synthesis of compound 1 was achieved by stirring 4-methoxybenzenesulfonyl chloride ( a ) and ethyl piperidine-4-carboxylate ( b ). Compound 1 was converted into respective hydrazide ( 2 ) by hydrazine and then into 1,3,4-oxadiazole ( 3 ) by CS₂ on reflux. The electrophiles, N-alkyl/aralkyl/aryl-2-bromopropanamides ( 6a–p ) were synthesized and converted to N-alkyl/aralkyl/aryl-2-propanamide derivatives ( 7a–p ) by reaction with 3 under green chemistry. Microwave assisted method was found to be effective relative to conventional method. ¹³C-NMR, ¹H-NMR and IR techniques were availed to corroborate structures of synthesized compounds and then subjected to screening against lipoxygenase (LOX), α-glucosidase, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes. A number of compounds presented better potential against these enzymes. The most active compounds against LOX and α-glucosidase enzymes were subjected to molecular docking study to explore their interactions with the active sites of the enzymes.     

Marrusidins A and B,New Epimeric Labdane Diterpenes from Marrubium anisodon

Marrusidins A ( 1 ) and B ( 2 ), two new labdane‐type diterpenes, were isolated from the CHCl₃‐soluble subfraction of Marrubium anisodon, along with polyodonine. Their structures were assigned with the aid of ¹H‐ and ¹³C‐NMR spectra and by COSY, HMQC, NOESY, and HMBC experiments.     

Stability and torsional vibration analysis of a micro-shaft subjected to an electrostatic parametric excitation using variational iteration method

In this article stability and parametrically excited oscillations of a two stage micro-shaft located in a Newtonian fluid with arrayed electrostatic actuation system is investigated. The static stability of the system is studied and the fixed points of the micro-shaft are determined and the global stability of the fixed points is studied by plotting the micro-shaft phase diagrams for different initial conditions. Subsequently the governing equation of motion is linearized about static equilibrium situation using calculus of variation theory and discretized using the Galerkin’s method. Then the system is modeled as a single-degree-of-freedom model and a Mathieu type equation is obtained. The Variational Iteration Method (VIM) is used as an asymptotic analytical method to obtain approximate solutions for parametric equation and the stable and unstable regions are evaluated. The results show that using a parametric excitation with an appropriate frequency and amplitude the system can be stabilized in the vicinity of the pitch fork bifurcation point. The time history and phase diagrams of the system are plotted for certain values of initial conditions and parameter values. Asymptotic analytically obtained results are verified by using direct numerical integration method.