Magnitude Of Molecular Weight Research Articles

Specific Biosensing Using DNA Aptamers and Nanopores

AbstractThe multiplexed biosensing of target molecules with high specificity and accuracy is of fundamental importance in both biological research and medical diagnostics. In this paper, the working range of the recent nanopore‐DNA carrier based method is extended by introducing a two‐step assay using specific DNA aptamers. A signal translation step allows for binding of the target in physiological conditions before the nanopore measurements. Using protein encoded DNA carriers, the simultaneous detection of three targets spanning several orders of magnitude in molecular weight is demonstrated. The single‐molecule method may be integrated into nanopore sensing devices for future applied research and point‐of‐care applications.

Quantitative diffusion measurements using the open-source software PyFRAP

Fluorescence Recovery After Photobleaching (FRAP) and inverse FRAP (iFRAP) assays can be used to assess the mobility of fluorescent molecules. These assays measure diffusion by monitoring the return of fluorescence in bleached regions (FRAP), or the dissipation of fluorescence from photoconverted regions (iFRAP). However, current FRAP/iFRAP analysis methods suffer from simplified assumptions about sample geometry, bleaching/photoconversion inhomogeneities, and the underlying reaction-diffusion kinetics. To address these shortcomings, we developed the software PyFRAP, which fits numerical simulations of three-dimensional models to FRAP/iFRAP data and accounts for bleaching/photoconversion inhomogeneities. Using PyFRAP we determined the diffusivities of fluorescent molecules spanning two orders of magnitude in molecular weight. We measured the tortuous effects that cell-like obstacles exert on effective diffusivity and show that reaction kinetics can be accounted for by model selection. These applications demonstrate the utility of PyFRAP, which can be widely adapted as a new extensible standard for FRAP analysis.

Latent analysis of unmodified biomolecules and their complexes in solution with attomole detection sensitivity.

The study of biomolecular interactions is central to an understanding of function, malfunction and therapeutic modulation of biological systems, yet often involves a compromise between sensitivity and accuracy. Many conventional analytical steps and the procedures required to facilitate sensitive detection, such as the incorporation of chemical labels, are prone to perturb the complexes under observation. Here we present a 'latent' analysis approach that uses chemical and microfluidic tools to reveal, through highly sensitive detection of a labelled system, the behaviour of the physiologically relevant unlabelled system. We implement this strategy in a native microfluidic diffusional sizing platform, allowing us to achieve detection sensitivity at the attomole level, determine the hydrodynamic radii of biomolecules that vary by over three orders of magnitude in molecular weight, and study heterogeneous mixtures. We illustrate these key advantages by characterizing a complex of an antibody domain in the solution phase and under physiologically relevant conditions.

Real-Time Biomolecular Binding Detection Using a Sensitive Photonic Crystal Biosensor

Real-time measurement of specific biomolecular interactions is critical to many areas of biological research. A number of label-free techniques for directly monitoring biomolecular binding have been developed, but it is still challenging to measure the binding kinetics of very small molecules, to detect low concentrations of analyte molecules, or to detect low affinity interactions. In this study, we report the development of a highly sensitive photonic crystal biosensor for label-free, real-time biomolecular binding analysis. We characterize the performance of this biosensor using a standard streptavidin-biotin binding system. Optimization of the surface functionalization methods for streptavidin immobilization on the silica sensing surface is presented, and the specific binding of biotinylated analyte molecules ranging over 3 orders of magnitude in molecular weight, including very small molecules (<250 Da), DNA oligonucleotides, proteins, and antibodies (>150 000 Da), are detected in real time with a high signal-to-noise ratio. Finally, we document the sensor efficiency for low mass adsorption, as well as multilayered molecular interactions. By all important metrics for sensitivity, we anticipate this photonic crystal biosensor will provide new capabilities for highly sensitive measurements of biomolecular binding.

A simple approach to the prediction of electrophoretic mobilities of diverse organic acids

Based on the principle of separation by capillary electrophoresis, three simple molecular structural descriptors, the number of acid groups (NG), number of atoms (NA) and molecular weight (MW) were employed to model the molecular structure–electrophoretic mobility relationship with the general form of μ 0 = aNG/( bNA k + cMW k ), where the value of k ranges from 1/3 to 2/3 depending on the magnitude of molecular weight. The absolute electrophoretic mobilities ( μ 0) of three diverse data sets including carboxylic acids, sulfonic acids and peptides were investigated. Each data set was randomly divided into a training set for model generation and a test set for prediction test. The absolute average relative deviations (AARD and AARD P) of the training set and the test set are 7.21% and 7.53% for data set 1, 1.99% and 1.96% for data set 2, 3.25% and 3.95% for data set 3, respectively. Compared to the quantitative structure–mobility relationship (QSMR) models reported in the literature, the approach proposed in this study is much simpler in terms of the calculation of structural descriptors and the interpretation of the physicochemical meaning of the models.

Molecular weight dependence of a whispering gallery mode biosensor

We report on molecular weight dependence measurements for an optical resonance biosensor. A dielectric microparticle is evanescently coupled with an optical fiber for the resonance stimulation, and a shift of the resonance wavelength is measured to monitor protein monolayer formation on the microparticle surface. Wavelength shifts for proteins over two orders of magnitude in molecular weight are measured. We show that the shift is proportional to molecular weight to the one-third power. Our result demonstrates that the optical resonance biosensor provides protein size information upon detection. This molecular weight dependency differentiates optical resonance sensing from electrical detection using field-effect transistors.

Traube-Rule Interpretation of Protein Adsorption at the Liquid−Vapor Interface

Pendant-drop tensiometry of aqueous-buffer solutions of purified human proteins spanning nearly 3 orders of magnitude in molecular weight (MW) reveals that reduction in liquid−vapor (LV) interfacial tension γlv followed a systematic progression in MW with the molar concentration required to reach a specified γlv value decreasing with increasing MW in a manner reminiscent of the Traube rule for linear hydrocarbon surfactants. Furthermore, the concentration dependence of interfacial tension (dγlv/d ln CB, where CB is bulk-solution concentration) is observed to be surprisingly invariant among this disparate group of proteins (i.e., approximately constant apparent Gibbs' surface excess Γ = −1/RT dγlv/d ln CB). These findings are interpreted through a model of protein adsorption predicated on the interfacial packing of spherical molecules with dimensions scaling as a function of MW. The Traube-rule-like ordering is rationalized as a natural outcome of an invariant partition coefficient that entrains a fixed fr...

Mark-Houwink-Sakurada coefficients for conventional poly(methyl methacrylate) in tetrahydrofuran

Intrinsic viscosities [η] in tetrahydrofuran (THF) at 30°C are reported for ten narrow molecular weight distribution poly(methyl methacrylate) (PMMA) samples covering nearly two orders of magnitude in molecular weight. By combining the viscosity results with absolute weight-average molecular weights \(\left( {\bar M_{\text{w}} } \right)\) determined via low-angle laser light scattering (LALLS) experiments, we have accurately determined the Mark-Houwink-Sakurada (MHS) parameters for this polymer-solvent pair (K=7.56x105 and a=0.731, when [η] is in dL g-1).

Field‐Flow Fractionation (FFF) and Related Techniques for the Separation of Particles, Colloids and Macromolecules

AbstractThin‐channel flow techniques can be used for the separation of samples ranging over 15 orders of magnitude in molecular weight, namely, macromolecules, colloids, and particles. The first part describes the group of field‐flow fractionation techniques. Flow system components are illustrated and described, as well as mode of operation and theory behind retention in the thin channel. An update of current topics under research is given, namely, normal retention mode of Brownian particles (under 1 μm in diameter) as compared to the steric retention mode of non‐Brownian particles (above 1 μm in diameter). Optimization of the separation by field programming is briefly discussed.Another group of thin‐channel techniques for small‐scale processing, the split‐flow thin (SPLITT) cells, in which fractionation is based on mass transport across the channel thickness, is presented in the second part. Principles of separation in this technology as well as possible applications are illustrated and discussed.

A correlation of permeabilities for passively transported compounds in monkey and rabbit jejunum.

Permeability measurements were conducted for a series of compounds using in vitro tissue sections from monkey and rabbit jejunum. Jejunal segments were stripped of serosal musculature and mounted in a diffusion-cell system, using previously described methods and equipment. Permeability determinations of radiolabeled compounds ranging over two orders of magnitude in molecular weight were conducted. For the compounds examined, the permeability of the rabbit jejunum was approximately twice that of the monkey. This was in contrast to the relationship implied by the stripped tissue thickness measurements of 0.92 and 0.83 mm for rabbit and monkey, respectively. An investigation of the size of the paracellular space in the jejunum was undertaken to account for this apparent discrepancy in tissue permeability. Scanning electron micrographs of intestinal sections revealed a similar packing density of cells between species; however, a difference was noted in the shape and number of villi per unit area. Comparative measurements of the paracellular volume in both species using mannitol and methoxyinulin as extracellular space markers further suggests that the paracellular junctions are similar in size but more numerous per unit area of rabbit jejunum than that of the monkey. In contrast to passively transported compounds, the active transport of D-glucose was greater in monkey jejunum compared to rabbit tissue segments. When active transport was inhibited by blockade of the sodium pump with ouabain, the passive component of D-glucose transport for both rabbit and monkey tissue was in agreement with the relationship demonstrated above for compounds which are solely transported by passive processes.

Thermomechanical Characterization of the Molecular Weight of Linear Polymers Exemplified by Natural Rubber

Abstract In the previous work of Kargin and Slonimskii and that of Kargin and Sogolov who studied the behavior of polymers over a wide range of temperature, it was shown that the shape of thermomechanical curves depends on magnitude of molecular weight of the polymers. As a result of investigation of theory and actual experimental studies in which polyisobutylene was employed, it was demonstrated that molecular weight could be estimated on the basis of thermomechanical properties. This suggested a relationship between the magnitude of molecular weight M found from the thermomechanical curves and that which was determined from glass temperatures Tg and fluid temperatures Tf. For practical use of this relationship, it is necessary to know the magnitude of the segments and two empirical constants. These values can be found by calculation of molecular weights of three different fractions of the polymer. This can be accomplished experimentally by any independent method. Once these magnitudes are determined, it is necessary to find, by means of the thermomechanical curve, the values Tg and Tf, in order to calculate the molecular weight of any sample of the same polymer. Because of the low degree of accuracy of determination of these values, and because of the peculiar differences, the reliability of the calculated molecular weight cannot be great, especially since the equation utilizes the logarithm of the molecular weight figure and not the molecular weight itself. Apparently the graphic solution is simpler than analytical methods: by means of the data of thermomechanical studies for various fractions of known molecular weights it is possible to graph the dependence of M or log Mon Tf−Tg. From what has been said, it is evident that we may use the demonstrated method only for polymers of high elasticity, and furthermore, only for those fractions in which Tf−Tg is greater than zero.