Cell transport via electromigration in polymer-based microfluidic devices

Electrokinetic transport of Escherichia coli and Saccharomyces cerevisiae (baker's yeast) cells was evaluated in microfluidic devices fabricated in pristine and UV-modified poly(methyl methacrylate)(PMMA) and polycarbonate (PC). Chip-to-chip reproducibility of the cell's apparent mobilities (micro(app)) varied slightly with a RSD of approximately 10%. The highest micro(app) for baker's yeast cells was observed in UV-modified PC with 0.5 mM PBS (pH = 7.4), and the lowest was measured in pristine PMMA with 20 mM PBS (pH = 7.4). Baker's yeast in all devices migrated toward the cathode because of their smaller electrophoretic mobility compared to the EOF. In 0.5 mM and 1 mM PBS, E. coli cells migrated toward the anode in all cases, opposite to the direction of the EOF due to their larger electrophoretic mobility. E. coli cells in 20 mM PBS migrated toward the cathode, which indicated that the electrophoretic mobility of E. coli cells decreased at higher ionic strengths. Observed differential migrations of E. coli and baker's yeast cells in appropriately prepared polymer microchips were used as the basis for selective introduction into microfluidic devices of only one type of cell. As a working model, experiments were performed with E. coli and RBCs (red blood cells). RBCs migrated toward the cathode in pristine PMMA with 1 mM and 20 mM PBS (pH = 7.4), opposite to the direction of the E. coli cells. By judicious choice of the buffer concentration in which the cell suspension was prepared and the polymer material, RBCs or E. coli cells were selectively introduced into the microdevice, which was monitored via laser backscatter signals.     

A Convenient Synthesis of the Orthogonally-Protected Benzodiazepine-2,5-Dione Scaffold

We have identified the benzodiazepine-2,5-dione 4 as a convenient, orthogonally-protected template, suitable for parallel solid-phase chemistry. Scaffold 4 offers superior stability, compared to other, analogous benzodiazepine-2,5-diones, such as A. We describe a gram-scale synthesis of 4 in six steps and in 25% yield.     

From gene to HSQC in under five hours: high-throughput NMR proteomics

A simple, rapid, in vitro cell-free protein expression system, Expressway NMR, is introduced and used to express the small ubiquitin-related modifier protein SUMO-1. This 12 kDa molecule is challenging for NMR as it has limited solubility and requires relatively high salt (200 mM) for stability in solution. Starting with the gene, the cell-free system, and milligram amounts of nitrogen-15 isotopically enriched amino acids, sufficient protein is produced in 4 h to obtain a high-resolution 2D HSQC spectrum of the protein in 40 min. This time would be closer to 10 min with the aid of a higher sensitivity salt-tolerant cryogenic NMR probe. With all protein purification steps included, and aggressive data processing using the filter diagonalization method (FDM), it is but 6 h from gene to heteronuclear single quantum coherence (HSQC). As the cell-free system is nearly background-free, it is also possible to work with the crude reaction mixture, in which case only a total of 5 h is required. Sample stability over time, whether crude extract or purified, was notable, with no significant change in the 15N-1H HSQC spectrum over 6 months at 4 degrees C (300 muM, pH 6.1, capped NMR tube). The combination of a turnkey, high-yield, protease-free in vitro protein expression system, an optimized sensitivity-enhanced HSQC pulse sequence, and FDM processing makes this scheme an attractive first step to rapidly assess the suitability of proteins for complete solution structure determination.     

Demonstration of all-optical beam steering in modulated photonic lattices

We demonstrate experimentally all-optical beam steering in modulated photonic lattices induced optically by three-beam interference in a biased photorefractive crystal. We identify and characterize the key physical parameters governing the beam steering and show that the spatial resolution can be enhanced by the additional effect of nonlinear beam self-localization.     

Observation of attraction between dark solitons

We demonstrate a dramatic change in the interaction forces between dark solitons in nonlocal nonlinear media. We present what we believe is the first experimental evidence of attraction of dark solitons. Our results indicate that attraction should be observable in other nonlocal systems, such as Bose-Einstein condensates with repulsive long-range interparticle interaction.     

Solvent effect on intensities off-ftransitions in lanthanide(III) complexes

A general theory of the solvent effect on the intensities of f-f; transitions of lanthanide complexes based on static and dynamic coupling between metal ion and ligands and solvent molecules is presented. New expressions are found correlating the intensity parameters with physical characteristics of the solvent. It is shown that the solvent effect influences only in the parameter ₂.     

Comment on “Study of mixed-mode oscillations in a nonlinear cardiovascular system” [Nonlinear Dyn,doi: 10.1007/s11071-020-05612-8]

Nonlinear Dynamics - This note comments on the questionable approach and claims made in “Study of mixed-mode oscillations in a nonlinear cardiovascular system” [Nonlinear Dyn, doi:...     

Facile synthesis of the cubic mesoporous material MCM-48. Detailed study of accompanying phase transformations

The synthesis of cubic mesoporous material MCM-48 has been simplified and can be accomplished via facile hydrothermal synthesis using convenient commercial reagents. The cubic structure evolves from the initially formed hexagonal MCM-41 and undergoes slow conversion to the lamellar MCM-50 precursor. The system was sampled at 1 hr intervals and the intermediate products characterized by elemental analysis, X-ray powder diffraction and adsorption. The results are discussed from the standpoint of possible mechanisms of MCM-48 generation.     

Cyclic Just-In-Time Sequences Are Optimal

Consider the Product Rate Variation problem. Given n products 1,...,i,...,n, and n positive integer demands d ₁,..., d_i,...,d_n. Find a sequence =₁,...,_T, T = _i=1 ⁿ d _i, of the products, where product i occurs exactly d _i times that always keeps the actual production level, equal the number of product i occurrences in the prefix ₁,..., _t, t=1,...,T, and the desired production level, equal r _i t, where r _i=d_i/T, of each product i as close to each other as possible. The problem is one of the most fundamental problems in sequencing flexible just-in-time production systems. We show that if is an optimal sequence for d ₁,...,d_i,...,d_n, then concatenation ^m of m copies of is an optimal sequence for md ₁,..., md_i,...,md_n.     

A Fully Polynomial Approximation Scheme for Minimizing Makespan of Deteriorating Jobs

A fully polynomial approximation scheme for the problem of scheduling n deteriorating jobs on a single machine to minimize makespan is presented. Each algorithm of the scheme runs in O(n ⁵ L ⁴³) time, where L is the number of bits in the binary encoding of the largest numerical parameter in the input, and is required relative error. The idea behind the scheme is rather general and it can be used to develop fully polynomial approximation schemes for other combinatorial optimization problems. Main feature of the scheme is that it does not require any prior knowledge of lower and/or upper bounds on the value of optimal solutions.