573 research outputs found
Assembly and Maturation of a T = 4 Quasi-Equivalent Virus Is Guided by Electrostatic and Mechanical Forces
Nudaurelia capensis w virus (NωV) is a eukaryotic RNA virus that is well suited for the study of virus maturation. The virus initially assembles at pH 7.6 into a marginally stable 480-Å procapsid formed by 240 copies of a single type of protein subunit. During maturation, which occurs during apoptosis at pH 5.0, electrostatic forces guide subunit trajectories into a robust 410-Å virion that is buttressed by subunit associated molecular switches. We discuss the competing factors in the virus capsid of requiring near-reversible interactions during initial assembly to avoid kinetic traps, while requiring robust stability to survive in the extra-cellular environment. In addition, viruses have a variety of mechanisms to deliver the genome, which must remain off while still inside the infected cell, yet turn on under the proper conditions of infection. We conclude that maturation is the process that provides a solution to these conflicting requirements through a program that is encoded in the procapsid and that leads to stability and infectivity
Microdroplet Approach for Measuring Aqueous Solubility and Nucleation Kinetics of a Metastable Polymorph: The case of KDP Phase IV
Solubility and interfacial energy are two fundamental parameters underlying
the competitive nucleation of polymorphs. However, solubility measurement of
metastable phases comes with a risk of solventmediated transformations which
can render the results unreliable. In this work, we present a rapid
microfluidic technique for measuring aqueous solubility of the metastable form
using KDP Phase IV as a model system. This bracketing approach involves
analyzing the dissolution behavior of crystals in contact with supersaturated
microdroplets generated via evaporation. Then, with the help of our recently
developed nucleation time measurement technique, together with Mersmann
calculation of interfacial energies from solubilities, we were able to access
the interfacial energies of both metastable and stable phases. To gain further
insights into the observed nucleation behavior, we employed the Classical
Nucleation Theory (CNT) to model the competition of polymorphs using our
measured solubility and calculated interfacial energies. The results show that
the stable form is favored at lower supersaturation while the metastable form
is favored at higher supersaturation, in good agreement with our observations
and experimental reports in the literature. Overall, our microfluidic approach
allows access to unprecedentedly deep levels of supersaturation and reveals an
interesting interplay between thermodynamics and kinetics in polymorphic
nucleation. The experimental methods and insights presented herein can be of
great interest, notably in the mineral processing and pharmaceutical industry
З листування Л. Биковського з Є. Бачинським
У статті надається листування видатного бібліографа, історика Л. Биковського з визначним українським громадським і церковним діячем Є. Бачинським. листи написані в 1947–1952 рр.В статье представлена переписка выдающегося библиографа, историка Л. Быковского с выдающимся украинским общественным и церковным деятелем Е. Бачинским. Письма написаны в 1947-1952 гг.The article consists of correspondence of the outstanding bibliographer, historian L.Bykovskyi with the outstanding Ukrainian public and church figure Ye. Bachynskyi. Letters are written in 1947–1952
Using temperature to crystallize proteins: a mini-review’, Cryst
ABSTRACT: The aim of this overview of the work of Marseille Nanoscience Center is to provide biocrystallographs that intend to tackle crystallization with practical examples of the effect of temperature on protein phase separation and crystallization. Crystallization involves two separate processes: nucleation and growth, which are rarely completely unconnected. Here we give four concrete examples illustrating how temperature can be used to crystallize proteins. We describe the nucleation of a new phase, solid or liquid and the growth and transformation of existing crystals obtained by seeding or primary or secondary nucleation. The advantages of temperature as a crystallization parameter are constant composition, ease of control and monitoring and reversibility
A microfluidic method generating monodispersed microparticles with controllable sizes and mechanical properties
International audienceSeeking to produce microparticles that mimic red blood cells (RBCs), we present a microfluidic method of generating monodispersed hydrogel microparticles of Na-/Ca-alginate with controllable sizes (micrometer range) and mechanical properties. No surfactant is used. Transformation from Na-alginate to Ca-alginate microparticles is realized via ex situ gelation, which proves essential to obtaining desired microparticle properties, such as insolubility in water and RBC-like mechanical properties. For both Na-alginate and Ca-alginate microparticles, a smooth surface and a porous inner structure are observed under a scanning electron microscope. A platform of microgrippers is successfully developed to manipulate the microparticles. The Young’s modulus measured using an atomic force microscope on the surface of Ca-alginate microparticles is of the same order as that of RBCs
CNT effective interfacial energy and pre-exponential kinetic factor from measured NaCl crystal nucleation time distributions in contracting microdroplets
Nucleation, the birth of a stable cluster from disorder, is inherently
stochastic. Yet up to date, there are no quantitative studies on NaCl
nucleation that accounts for its stochastic nature. Here, we report the first
stochastic treatment of NaCl-water nucleation kinetics. Using a recently
developed microfluidic system and evaporation model, our measured interfacial
energies extracted from a modified Poisson distribution of nucleation time show
an excellent agreement with theoretical predictions. Furthermore, analysis of
nucleation parameters in 0.5 pL, 1.5pL and 5.5 pL microdroplets reveals an
interesting interplay between kinetic confinement and shifting of nucleation
mechanisms. Overall, our findings highlight the need to treat nucleation
stochastically rather deterministically to bridge the gap between theory and
experiment
Coaxial Ion Source : pressure dependence of gas flow and field ion emission
We investigated the pressure dependence of gas flow and field ion intensity
of a coaxial ion source operating at room temperature over a wide pressure
range, testing various gases and ionisation voltages. Flow conductance
measurements taking into account the different gases' viscosity and molecular
mass consistently exhibit a generic pattern. Three different flow regimes
appear with increasing upstream pressure. Since the coaxial ion source supplies
the gas locally, very near the apex of the tip where ionisation occurs, large
ionisation currents can be obtained without degrading the propagation
conditions of the beam. Compared with field ionisation in a partial pressure
chamber, using the coaxial ion source increases the ion current a hundredfold
for the same residual low pressure. We also show that the gas flow regime does
not impact ionisation yield. Although a fuller characterisation remains to be
performed, brightness reaches 3 x 10 11 A/m 2 /sr at 12kV extracting voltage.
a) https://www.cinam.univ-mrs.fr
Complete Genome of Lactococcus lactis subsp. cremoris UC509.9, Host for a Model Lactococcal P335 Bacteriophage
Item does not contain fulltextHere, we report the complete genome of Lactococcus lactis subsp. cremoris UC509.9, an Irish dairy starter. The circular chromosome of L. lactis UC509.9 represents the smallest among those of the sequenced lactococcal strains, while its large complement of eight plasmids appears to be a reflection of its adaptation to the dairy environment
Nucleation and polymorphism explored via an easy-to-use microfluidic tool
a b s t r a c t We present an easy-to-use microfluidic set-up, easily transferable to the laboratory and determine an accurate method for metastable zone width measurement. We clearly define a zone in the phase diagram where nucleation is mononuclear. We nucleate a single crystal of metastable phase, which turns out to be stable. This approach holds promise for the control and the study of crystallization processes
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