Microfluidic capillary zone electrophoresis mass spectrometry analysis of alkaloids in Lobelia cardinalis transgenic and mutant plant cell cultures

Application of a microfluidic CE^* device for CZE‐MS allows for fast, rapid, and in‐depth analysis of large sample sets. This microfluidic CZE‐MS device, the 908 Devices ZipChip, involves minimal sample preparation and is ideal for small cation analytes, such as alkaloids. Here, we evaluated the microfluidic device for the analysis of alkaloids from Lobelia cardinalis hairy root cultures. Extracts from wild‐type, transgenic, and selected mutant plant cultures were analyzed and data batch processed using the mass spectral processing software MZmine2 and the statistical software Prism 8. In total 139 features were detected as baseline resolved peaks via the MZmine2 software optimized for the electrophoretic separations. Statistically significant differences in the relative abundance of the primary alkaloid lobinaline (C₂₇H₃₄N₂), along with several putative “lobinaline‐like” molecules were observed utilizing this approach. Additionally, a method for performing both targeted and untargeted MS/MS experiments using the microfluidic device was developed and evaluated. Coupling data‐processing software with CZE‐MS data acquisition has enabled comprehensive metabolomic profiles from plant cell cultures to be constructed within a single working day.     

A High‐Throughput Mass Spectrometric Enzyme Activity Assay Enabling the Discovery of Cytochrome P450 Biocatalysts

Assaying for enzymatic activity is a persistent bottleneck in biocatalyst and drug development. Existing high‐throughput assays for enzyme activity tend to be applicable only to a narrow range of biochemical transformations, whereas universal enzyme characterization methods usually require chromatography to determine substrate turnover, greatly diminishing throughput. We present an enzyme activity assay that allows the high‐throughput mass‐spectrometric detection of enzyme activity in complex matrices without the need for a chromatographic step. This technology, which we call probing enzymes with click‐assisted NIMS (PECAN), can detect the activity of medically and biocatalytically significant cytochrome P450s in cell lysate, microsomes, and bacteria. Using this approach, a cytochrome P450_BM3 mutant library was successfully screened for the ability to catalyze the oxidation of the sesquiterpene valencene.     

The transient development of the flow in an impulsively rotated annular container

When a fluid-filled container is spun up from rest to a constant angular velocity the fluid responds in such a way that the fluid–container system is ultimately in a state of rigid-body rotation. The fluid can then be said to have traversed a trajectory in phase space from a simple stable equilibrium state of no motion to another stable equilibrium representing full rigid-body rotation. This simple statement belies the fact that during this process the fluid can undergo a series of transitions, from a laminar through a transient turbulent state, before attaining the stable motion that is rigid-body rotation. Using a combination of analytical and computational methods, we focus on the dynamics resulting from an impulsive change in the rotation rate of a fluid-filled annulus, specifically, the impulsive spin-up of a stationary annulus, or the impulsive spin-down of an annulus already in a state of rigid-body rotation. We explore the initial development of the impulsively generated axisymmetric boundary layer, its subsequent instability, and the larger-scale transient features within this class of flows, allowing us to look at the effect these features have on the time it takes for the system to spin up to a steady state, or spin down to rest.     

Metal particle adsorption and diffusion in a model polymer/metal composite system

We have developed a model polymer/metal composite system based on the adsorption of colloidal gold particles from a dilute aqueous suspension to the surface of poly(2-vinylpyr-idine) (PVP). Particle coverages and tracer diffusion coefficients for the particles within a PVP matrix phase were measured by Rutherford backscattering spectrometry. The adsorption process is quantitatively described by a diffusion-limited mechanism where gold particles irreversibly adsorb to the surface of the polymer film. Model dispersions produced in this way are excellent model systems for studying the fundamental properties of metal particle dispersions, since the particle size and the areal density of particles on the surface are well-controlled. Diffusion coefficients for the gold particles within PVP were also measured. The diffusion of the gold particles was found to be coupled to the bulk viscosity of the polymer, even though the size of the gold particles was only slightly larger than the mesh size of the entanglement network for PVP. © 1995 John Wiley & Sons, Inc.     

A New Estimate for the Vector Valued Corona Problem

We improve an estimate of Fuhrmann and Vasyunin in the vector valued corona theorem.     

Bis-histidyl hexacoordination in hemoglobins facilitates heme reduction kinetics

Hexacoordinate hemoglobins are a class of proteins that exhibit reversible bis-histidyl coordination of the heme iron while retaining the ability to bind exogenous ligands. One hypothesis for their physiological function is that they scavenge nitric oxide, a reaction that oxidizes the protein and requires reduction of the heme iron to continue. Reduction kinetics of hexacoordinate hemoglobins, including human neuroglobin and cytoglobin, and those from Synechocystis and rice, are compared to myoglobin, soybean leghemoglobin, and several relevant mutant proteins. In all cases, bis-histidyl coordination greatly increases the rate of reduction by sodium dithionite when compared to pentacoordinate hemoglobins. In myoglobin and leghemoglobin, reduction is limited by the rate constant for electron transfer, whereas in the hexacoordinate hemoglobins reduction is limited only by bimolecular binding of the reductant. These results can be explained by differences in the reorganization energy for reduction between hexacoordinate and pentacoordinate hemoglobins.     

Topochemical exploration of potent compounds using retro-enantiomer libraries of cyclic pentapeptides

Cyclic pentapeptides have been adopted as conformationally restricted peptide templates to dispose pharmacophores of bioactive peptides. In our recent study, use of two orthogonal cyclic pentapeptide libraries involving conformation-based and sequence-based libraries containing critical residues of a bioactive peptide led to the discovery of potent downsized peptides that possess activity comparable to that of the parent peptide. The present study demonstrates that a third library consisting of retro-enantiomers (retro-inverso peptides) that possess not only all residues with the opposite configuration to those in the corresponding original peptide but also amino acid sequences with reversed arrangement, is important as an alternative library for rationally finding active compounds.     

Effect of O6-methylguanine on the stability of G-quadruplex DNA

The effects of substitution of O6-methylguanine on the structure and stability of a human telomere quadruplex was studied by circular dichroism, thermal denaturation, analytical ultracentrifugation, and molecular dynamics simulations. The results show that, while quadruplex structures can form containing the modified base, they are much less stable than the normal unmodified structure. The extent of destabilization is critically dependent on the exact position of the modified base within the quadruplex structure.     

Sensitivity analysis of uncertainty in model prediction

Data Collaboration is a framework designed to make inferences from experimental observations in the context of an underlying model. In the prior studies, the methodology was applied to prediction on chemical kinetics models, consistency of a reaction system, and discrimination among competing reaction models. The present work advances Data Collaboration by developing sensitivity analysis of uncertainty in model prediction with respect to uncertainty in experimental observations and model parameters. Evaluation of sensitivity coefficients is performed alongside the solution of the general optimization ansatz of Data Collaboration. The obtained sensitivity coefficients allow one to determine which experiment/parameter uncertainty contributes the most to the uncertainty in model prediction, rank such effects, consider new or even hypothetical experiments to perform, and combine the uncertainty analysis with the cost of uncertainty reduction, thereby providing guidance in selecting an experimental/theoretical strategy for community action.     

Light-directed movement of polymer microstructures

Light has been used to induce photochemical changes in the surface chemistry of porous polymer microstructures giving rise to a substantial change in volume. When illumination is asymmetric, this results in light-directed motion of the structure. Swellable trimethylolpropane trimethacrylate cross-linked poly(2-hydroxylethyl methacrylate) microstructures were constructed by azo-bis-isobutyronitrile photopolymerization using a 20 x 0.5 NA microscope objective and 365 nm laser excitation. Structures were aminiated with glycine and protected with the photolabile group 4-nitroveratryloxycarbanyl (NVOC). Addition of NVOC resulted in a volume increase >10% when performed in the solvent N,N'-dimethylformamide. Photochemical cleavage of NVOC using asymmetric illumination of a cone-shaped microstructure with a 365 nm laser induced polymer shrinkage in excess of 4% at the base of the cone and resulted in a maximum velocity of 1 mm/s at the tip of the cone. Symmetric illumination gave rise to displacement of solvent from the microstructure due to shrinkage with a velocity in excess of 0.01 mm/s. This system could in principle be used for light-directed movement of micromechanical systems, optical control of microfluidics, or light activated chemical delivery.