RESUMO
The trap stiffness us the key property in using optical tweezers as a force transducer. Force reconstruction via maximum-likelihood-estimator analysis (FORMA) determines the optical trap stiffness based on estimation of the particle velocity from statistical trajectories. Using a modification of this technique, we determine the trap stiffness for a two micron particle within 2 ms to a precision of â¼10% using camera measurements at 10 kfps with the contribution of pixel noise to the signal being larger the level Brownian motion. This is done by observing a particle fall into an optical trap once at a high stiffness. This type of calibration is attractive, as it avoids the use of a nanopositioning stage, which makes it ideal for systems of large numbers of particles, e.g., micro-fluidics or active matter systems.
RESUMO
Crystallisations are widely used in pharmaceutical and fine chemical manufacturing to control impurity levels, however crystallisations do not always reduce impurities to acceptable levels. Information on the location and distribution of impurities in crystallised materials would be helpful in such cases. A two phase dissolution medium featuring a fluorocarbon non-solvent vehicle and a aqueous ethanol solvent phase has been used to determine the composition of multi-particle crystalline samples through a partial dissolution approach combined with particle sizing and HPLC analysis. 4-Chloro-2-nitroacetanilide (1) was chosen as the host compound for this study, with 4-methyl-2-nitroacetanilide (2) and 4-tert-butyl-2-nitroacetanilide (3) chosen as the guest impurities that were added to supersaturated toluene solutions of 1 at levels up to 5 mol%. The crystals that formed were subjected to a series of partial dissolution steps carried out using the biphasic dissolution medium composed of a 50% aqueous ethanol solvent phase and a perfluorohexane continuous phase. To inhibit particle agglomeration, the mixture also contained 13,13,14,14,15,15,16,16,17,17,18,18-dodecafluoro-2,5,8,11-tetraoxaoctadecane (4) as a non-ionic surfactant. The partial dissolution steps showed a relatively even dissolution with each sequential step as determined from particle sizing. Analysis of the solutions by HPLC from each partial dissolution step allowed the level of impurity to be determined, and when combined with the particle sizing data this allowed an impurity distribution to be generated. Impurity 2 was found to be relatively evenly distributed while impurity 3 was localised on or near the surfaces of crystals.
RESUMO
This paper describes the preparation and comprehensive characterization of a series of water-soluble cationic silver(I)-centered complexes featuring the hemilabile P, N-ligand known as 3,7-dimethyl-1,3,5-triaza-7-phosphabicyclo[3.3.1]nonane (herein abbreviated as PTN(Me)) and differing types of monoanionic counterions including known biologically active sulfadiazine and triclosan. The complexes primarily differed though the number of coordinating PTN(Me) ligands. The bis-substituted Ag(I) complexes revealed P, N bidentate coordination, while the only P-monocoordination of the metal center was observed for the tris-substituted systems. The bis-ligated silver compounds were observed to quickly degrade upon photoexposure or in contact with air. In contrast, the tris-ligated complexes demonstrated greater stability, in particular, a high resistance to photo-decomposition. Calculated geometry optimized models using the density functional theory method (BP86) revealed for the bis-substituted PTN(Me) Ag(I) species that the total enthalpy of the tetrahedral C2-symmetric structure is marginally lower by -0.6 kcal mol-1 compared to the planar C2 h structure, which is analogous for the corresponding [Au(PTN(Me))2]+ complex with Δ H = -0.5 kcal mol-1. Hence both types of complexes feature free rotation of the PTN ligand about the M-P bond axis. This series of Ag(I) and bis-PTN(Me) Au(I) complexes were evaluated using the agar well diffusion test for potential antimicrobial and antifungal activity. The nature of the counterion was found to have a strong correlation with the area of microbiological growth inhibition. Silver(I) complexes bearing the deprotonated triclosan as the counterion demonstrated the greatest activity, with large zones of growth inhibition, with the tris-ligated triclosan complex obtaining of a high clearance of 42 mm against the Gram-negative Escherichia coli. In contrast, the previously reported [Au(PTN(Me))2]Cl complex demonstrated activity only against E. coli, which is lower than that observed for the silver(I) PTN(Me) species.
