Charge Density and Hydrophobicity-Dominated Regimes in the Phase Behavior of Complex Coacervates

<div>The role of hydrophobicity, and particularly nonionic hydrophobic comonomers, on the phase behavior of polyelectrolyte complex coacervates is not well-understood. Here, we address this problem by synthesizing a library of polymers with a wide range of charge densities and nonionic hydrophobic side chain lengths, and characterizing their phase behavior by optical turbidity. The polymers were prepared by post-polymerization modification of poly(N-acryloxy succinimide), targeting charge densities between 40 and 100% and nonionic aliphatic sidechains with lengths from 0 to 12 carbons long. Turbidity measurements on pairs of polycations and polyanions with matched charge densities and nonionic sidechain lengths revealed a complex salt response with distinct charge density-dominated and hydrophobicity-dominated regimes. The polymer solubilities were not directly correlated with the phase behavior of the coacervates, indicating the difficulty of understanding the coacervate phase behavior in terms of the polymer-water interaction parameter. This result suggests that there is significant room for further work to understand the mechanisms by which specific molecular-scale interactions moderate the phase behavior of complex coacervates.</div>

Charge Density and Hydrophobicity-Dominated Regimes in the Phase Behavior of Complex Coacervates

<div>The role of hydrophobicity, and particularly nonionic hydrophobic comonomers, on the phase behavior of polyelectrolyte complex coacervates is not well-understood. Here, we address this problem by synthesizing a library of polymers with a wide range of charge densities and nonionic hydrophobic side chain lengths, and characterizing their phase behavior by optical turbidity. The polymers were prepared by post-polymerization modification of poly(N-acryloxy succinimide), targeting charge densities between 40 and 100% and nonionic aliphatic sidechains with lengths from 0 to 12 carbons long. Turbidity measurements on pairs of polycations and polyanions with matched charge densities and nonionic sidechain lengths revealed a complex salt response with distinct charge density-dominated and hydrophobicity-dominated regimes. The polymer solubilities were not directly correlated with the phase behavior of the coacervates, indicating the difficulty of understanding the coacervate phase behavior in terms of the polymer-water interaction parameter. This result suggests that there is significant room for further work to understand the mechanisms by which specific molecular-scale interactions moderate the phase behavior of complex coacervates.</div>

Comparison of Time Resolved Optical Turbidity Measurements for Water Monitoring to Standard Real-Time Techniques

Environmental water monitoring requires the estimation of the suspended solids load. In this paper, we compare the concentration range accessible through three different techniques: optical turbidity, acoustic backscattering and the newly in-lab developed time resolved optical turbidity. We focus on their comparison on measurements made in the laboratory on water suspensions of known particles and concentrations. We used laboratory grade kieselguhr, wheat starch and kaolin as suspended solid surrogates. The explored concentration domains are the ones, for the total suspended solid load, commonly encountered in wastewater and rivers in standard (less than 1 g/L to a few g/L) or extreme conditions such as floods or storm events (up to several dozen g/L). Regarding the operable concentration domain, the time resolved optical turbidity shows a clear advantage upon the other methods, whatever the kind of particle is.

Glider-Based Active Acoustic Monitoring of Currents and Turbidity in the Coastal Zone

The recent integration of Acoustic Doppler Current Profilers (ADCPs) onto underwater gliders changes the way current and sediment dynamics in the coastal zone can be monitored. Their endurance and ability to measure in all weather conditions increases the probability of capturing sporadic meteorological events, such as storms and floods, which are key elements of sediment dynamics. We used a Slocum glider equipped with a CTD (Conductivity, Temperature, Depth), an optical payload, and an RDI 600 kHz phased array ADCP. Two deployments were carried out during two contrasting periods of the year in the Rhone River region of freshwater influence (ROFI). Coastal absolute currents were reconstructed using the shear method and bottom tracking measurements, and generally appear to be in geostrophic balance. The responses of the acoustic backscatter index and optical turbidity signals appear to be linked to changes of the particle size distribution in the water column. Significantly, this study shows the interest of using a glider-ADCP for coastal zone monitoring. However, the comparison between suspended particulate matter dynamics from satellites and gliders also suggests that a synoptic view of the processes involved requires a multiplatform approach, especially in systems with high spatial and temporal variability, such as the Rhone ROFI area.

The Interplay between Flow Field, Suspended Sediment Concentration, and Net Deposition in a Channel with Flexible Bank Vegetation

This paper investigates the interplay between the flow, suspended sediment concentration (SSC), and net deposition at the lateral interface between a main channel and riverbank/floodplain vegetation consisting of emergent flexible woody plants with understory grasses. In a new set of flume experiments, data were collected concurrently on the flow field, SSC, and net deposition using acoustic Doppler velocimeters, optical turbidity sensors, and weight-based sampling. Vegetation largely affected the vertical SSC distributions, both within and near the vegetated areas. The seasonal variation of vegetation properties was important, as the foliage strongly increased lateral mixing of suspended sediments between the unvegetated and vegetated parts of the channel. Foliage increased the reach-scale net deposition and enhanced deposition in the understory grasses at the main channel–vegetation interface. To estimate the seasonal differences caused by foliation, we introduced a new drag ratio approach for describing the SSC difference between the vegetated and unvegetated channel parts. Findings in this study suggest that future research and engineering applications will benefit from a more realistic description of natural plant features, including the reconfiguration of plants and drag by the foliage, to complement and replace existing rigid cylinder approaches.

Monitoring Silane Sol-Gel Kinetics with In-Situ Optical Turbidity Scanning and Dynamic Light Scattering

Organosilanes (e.g., R’-SiOR3) provide hydrophobic functionality in thin-film coatings, porous gels, and particles. Compared with tetraalkoxysilanes (SiOR4), organosilanes exhibit distinct reaction kinetics and assembly mechanisms arising from steric and electronic properties of the R’ group on the silicon atom. Here, the hydrolysis and condensation pathways of n-propyltrimethoxy silane (nPM) and a tri-fluorinated analog of nPM, 3,3,3-trifluoropropyl trimethoxy silane (3F), were investigated under aqueous conditions at pH 1.7, 2.0, 3.0, and 4.0. Prior to hydrolysis, 3F and nPM are insoluble in water and form a lens at the bottom (3F) or top (nPM) of the solutions. This phase separation was employed to follow reaction kinetics using a Turbiscan instrument to monitor hydrolysis through solubilization of the neat silane lens while simultaneously tracking condensation-induced turbidity throughout the bulk solution. Dynamic light scattering confirmed the silane condensation and particle aggregation processes reported by the turbidity scanning. Employing macroscopic phase separation of the starting reactants from the solvent further allows for control over the reaction kinetics, as the interfacial area can be readily controlled by reaction vessel geometry, namely by controlling the surface area to volume. In-situ turbidity scanning and dynamic light scattering revealed distinct reaction kinetics for nPM and 3F, attributable to the electron withdrawing and donating nature of the fluoro- and organo-side chains of 3F and nPM, respectively.

Hybrid genome assembly and annotation of Danionella translucida, a transparent fish with the smallest known vertebrate brain

Studying the activity of distributed neuronal circuits at a cellular resolution in vertebrates is very challenging due to the size and optical turbidity of their brains. We recently presented Danionella translucida, a close relative of zebrafish, as a model organism suited for studying large-scale neural network interactions in adult individuals. Danionella remains transparent throughout its life, has the smallest known vertebrate brain and possesses a rich repertoire of complex behaviours. Here we sequenced, assembled and annotated the Danionella translucida genome employing a hybrid Illumina/Nanopore read library as well as RNA-seq of embryonic, larval and adult mRNA. We achieved high assembly continuity using low-coverage long-read data and annotated a large fraction of the transcriptome. This dataset will pave the way for molecular research and targeted genetic manipulation of the smallest known vertebrate brain.

FEATURES OF HYDRAULICS OF THE RIVER SECTORS WITH RIVERBED WINTERING HOLES OF THE IRTYSH IN OPEN WATER PERIOD

The article describes features of the hydraulics of the Irtysh riverbed in the sections of significant fish concentrations -wintering holes - in the open water period. There have been explored the waters of the largest (in area and in depth) Gornoslinkinskaya and Kondinskaya riverbed depressions located in the Uvat and Khanty-Mansi districts of the Tyumen region and Khanty-Mansi Autonomous District, respectively. The bathymetric characteristics of wintering holes were studied using computerized hydroacoustic complex AsCor (Promgidroakustika, Ltd., Petrozavodsk). To create the bottom relief of riverbeds there were used geographic information software programs Surfer 9.0 and Map Viewer 6.0. The study of the species composition of the fish population was carried out conducting control catches with stationary and drift nets. It has been found that, as a result of the combination of features of the riverbed, on the investigated sectors there is formed a complex hydrodynamic and turbulent environment. The holes are located on meanders with coefficients of high curvature of the bend of a channel, there have been found the ranges with narrowing channels at the entrance into the turn. In the process of the channel narrowing there occurs deepening of dynamic river flow axis and eroding of the bottom, which may prevent silting of the wintering holes. Significant differences in the depths cause a compensating current. Due to the bend of the riverbed in the water areas there are formed whirlpool zones, and arising transverse water currents close the surface and bottom streams of the river flow. The heterogeneous hydrodynamic environment of the Kondinskaya depression is complicated by the fact that the Konda flows into the bend of the Irtysh; as a result, there takes place an exchange of river impulses. Thus, when the longitudinal flow velocity is imposed on the transverse flows, there appears a spiral movement of the water masses and vertical vortex structures - whirlpools resulting in optical (turbidity) and turbulent (hydrodynamic) heterogeneity in the water column of the riverbed wintering holes.

A decay effect of the bacterial growth rate associated with genome reduction

Bacterial growth is an important topic in microbiology and of crucial importance to better understand living cells. Bacterial growth dynamics are quantitatively examined using various methods to determine the physical, chemical or biological features of growing populations. Due to methodological differences, the exponential growth rate, which is a parameter that is representative of growth dynamics, should be differentiated. This study experimentally verified the differentiation in growth rates attributed to different methodologies, and demonstrated that the most popular method, optical turbidity, led to the determination of a lower growth rate in comparison to the methods based on colony formation and ATP abundance, due to a decay effect of reading OD600 during a population increase. Accordingly, the logistic model, which is often applied to growth data reading the OD600, was revised by introducing a new parameter: the decay rate, to compensate for the lowered estimation in growth rates. The modified logistic model not only presented an improved goodness of fit in comparison to the original model but also led to an intriguing finding of a correlation between genome reduction and the decay rate. The decay effect seemed to be partially attributed to the decrease in cell size accompanied by a population increase and was medium dependent. In summary, the present study provides not only a better theoretical tool for the high-throughput studies on bacterial growth dynamics linking with experimental data using optical turbidity to the theoretical analysis with biological importance, but also a valuable insight for understanding the genome evolution and fitness increase in microbial life.