Metabolic
reactions in living cells are limited by diffusion of
reagents in the cytoplasm. Any attempt to quantify the kinetics of
biochemical reactions in the cytosol should be preceded by careful
measurements of the physical properties of the cellular interior.
The cytoplasm is a complex, crowded fluid characterized by effective
viscosity dependent on its structure at a nanoscopic length scale.
In this work, we present and validate the model describing the cytoplasmic
nanoviscosity, based on measurements in seven human cell lines, for
nanoprobes ranging in diameters from 1 to 150 nm. Irrespective of
cell line origin (epithelial–mesenchymal, cancerous–noncancerous,
male–female, young–adult), we obtained a similar dependence
of the viscosity on the size of the nanoprobes, with characteristic
length-scales of 20 ± 11 nm (hydrodynamic radii of major crowders
in the cytoplasm) and 4.6 ± 0.7 nm (radii of intercrowder gaps).
Moreover, we revealed that the cytoplasm behaves as a liquid for length
scales smaller than 100 nm and as a physical gel for larger length
scales.
Biochemistry in living cells is an emerging field of science. Current quantitative bioassays are performed
ex vivo
, thus equilibrium constants and reaction rates of reactions occurring in human cells are still unknown. To address this issue, we present a non-invasive method to quantitatively characterize interactions (equilibrium constants, K
D
) directly within the cytosol of living cells. We reveal that cytosolic hydrodynamic drag depends exponentially on a probe’s size, and provide a model for its determination for different protein sizes (1–70 nm). We analysed oligomerization of dynamin-related protein 1 (Drp1, wild type and mutants: K668E, G363D, C505A) in HeLa cells. We detected the coexistence of wt-Drp1 dimers and tetramers in cytosol, and determined that K
D
for tetramers was 0.7 ± 0.5 μM. Drp1 kinetics was modelled by independent simulations, giving computational results which matched experimental data. This robust method can be applied to
in vivo
determination of K
D
for other protein-protein complexes, or drug-target interactions.
We
present synthesis of a free-standing monolayer film of gold
nanoparticles (AuNPs) which are linked by covalent bonds. In the method
developed, the free-standing film is obtained by chemical cross-linking
of the AuNPs of the core diameter of 5.6 nm that form a dense monolayer
at the oil–liquid interface. As the cross-linking agent, naphthalene
dianhydride derivative, which forms amide bonds with the ligand molecules,
is used. The AuNPs are coated with aminothiolate ligands that can
change their character from a hydrophilic to a hydrophobic one via
the reversible protonation/deprotonation mechanism. When adsorbed
at the oil–water interface, such functionalized AuNPs display
amphiphilic (Janus-like) structure and self-assemble into a highly
stable monolayer. To bring the AuNPs at the oil–water interface,
an excitation of the system that leads to the formation of the oil-in-water
emulsion is required. After the excitation, the AuNPs are transported
onto the oil–water interface on the surface of the oil droplets
that carry them as their “cargo”. A thermodynamic mechanism
explaining this cargo effect is put forward. The as-synthesized free-standing
film can be easily transferred from the oil–water interface
onto solid support, as well as porous grids, and it is found to be
stable in air.
Understanding
the mobility of nano-objects in the eukaryotic cell
nucleus, at multiple length-scales, is essential for dissecting nuclear
structure–function relationships both in space and in time.
Here, we demonstrate, using single-molecule fluorescent correlation
spectroscopies, that motion of inert probes (proteins, polymers, or
nanoparticles) with diameters ranging from 2.6 to 150 nm is mostly
unobstructed in a nucleus. Supported by the analysis of electron tomography
images, these results advocate the ∼150 nm-wide interchromosomal
channels filled with the aqueous diluted protein solution. The nucleus
is percolated by these channels to allow various cargos to migrate
freely at the nanoscale. We determined the volume of interchromosomal
channels in the HeLa cell nucleus to 237 ± 61 fL, which constitutes
34% of the cell nucleus volume. The volume fraction of mobile proteins
in channels equals 16% ± 4%, and the concentration is 1 mM.
Noble metal nanoparticles capped with novel aminothioalkil ligands are used to fabricate polymer nanocomposites. The nanoparticles are permanently attached to the polymer matrix through covalent bonding.
Nanoparticles have already found numerous applications and their global production is still increasing. Therefore, the engineered nanoobjects of uncertain toxicity become ubiquitous in the environment and a continuous monitoring of their presence is highly desirable. Here, we demonstrate a continuous electrochemical detection of gold nanoparticles (AuNPs) based on synchronous processes of their electrodissolution and electrocatalysis. This approach is realized by the injection of nanoparticles suspension into the Flow Injection Analysis (FIA) system. The modular structure of FIA system is particularly applicable for carrying out of sequential operations: AuNPs passivation, oxidation of aqueous SO2 and gold. It enables continuous, fast and reproducible gold nanoparticles determination in a wide concentration range: 10−10– 10−7 mol nanoobjects L−1.
Synthesis and characterization of π-conjugated homo-and co-oligomers based on thiophene substituted in position 3 by pentyl (3PT) and naphthylvinyl (NVT) side groups are presented. The resultant co-oligomers have statistical structure and the proportion of monomers can be fully controlled by the composition of the reaction mixture. The approach here offers a facile way to synthesis of materials with tunable optoelectrical properties that is an alternative for complicated organometallic synthesis involving water and oxygen sensitive Sn, Pd, or Mg compounds. The UV-vis absorption and fl uorescence emission spectra depend on and can be easily tuned by the [3PT]:[NVT] monomer molar ratio. Combination of these two monomers has a strong synergistic effect on the color of the fl uorescence emission that varies in a broad range, from orange to blue color. X-ray diffraction, calorimetric, and materials display electrical properties characteristic for organic semiconductors.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.