15 research outputs found
Stabilization of Monodisperse, Phase-Pure MgFe<sub>2</sub>O<sub>4</sub> Nanoparticles in Aqueous and Nonaqueous Media and Their Photocatalytic Behavior
Monodisperse,
monocrystalline magnesium ferrite (MgFe<sub>2</sub>O<sub>4</sub>)
nanoparticles were synthesized phase purely by fast
nonaqueous microwave-assisted solution-phase synthesis. Colloidal
stabilization of the nanocrystals in nonaqueous media was realized
either in-situ during synthesis or postsynthetically by surface capping
with oleylamine and oleic acid. Phase transfer to aqueous media was
performed employing citric acid and betaine hydrochloride, resulting
in agglomerate-free dispersions of citrate- or betaine-functionalized
MgFe<sub>2</sub>O<sub>4</sub> nanocrystals. Furthermore, a one-step
synthesis of highly stable, water-dispersible colloids of MgFe<sub>2</sub>O<sub>4</sub> was achieved using polyvinylpyrrolidone as stabilizer.
Characterization of the as-synthesized and functionalized nanoparticles
was performed employing X-ray diffraction, UV–vis and infrared
spectroscopy, thermogravimetry, dynamic light scattering, and transmission
electron microscopy. Special focus was laid on phase purity, which
was thoroughly monitored using Raman microscopy/spectroscopy. Photocatalytic
reactions were performed to evaluate the use of such highly stable
ferrite colloids for solar energy conversion
Finite-Size Effects of Binary Mutual Diffusion Coefficients from Molecular Dynamics
Molecular
dynamics simulations were performed for the prediction
of the finite-size effects of Maxwell-Stefan diffusion coefficients
of molecular mixtures and a wide variety of binary Lennard–Jones
systems. A strong dependency of computed diffusivities on the system
size was observed. Computed diffusivities were found to increase with
the number of molecules. We propose a correction for the extrapolation
of Maxwell–Stefan diffusion coefficients to the thermodynamic
limit, based on the study by Yeh and Hummer (J. Phys. Chem. B, 2004, 108, 15873−15879). The proposed correction is a function of the viscosity
of the system, the size of the simulation box, and the thermodynamic
factor, which is a measure for the nonideality of the mixture. Verification
is carried out for more than 200 distinct binary Lennard–Jones
systems, as well as 9 binary systems of methanol, water, ethanol,
acetone, methylamine, and carbon tetrachloride. Significant deviations
between finite-size Maxwell–Stefan diffusivities and the corresponding
diffusivities at the thermodynamic limit were found for mixtures close
to demixing. In these cases, the finite-size correction can be even
larger than the simulated (finite-size) Maxwell–Stefan diffusivity.
Our results show that considering these finite-size effects is crucial
and that the suggested correction allows for reliable computations
Finite-Size Effects of Binary Mutual Diffusion Coefficients from Molecular Dynamics
Molecular
dynamics simulations were performed for the prediction
of the finite-size effects of Maxwell-Stefan diffusion coefficients
of molecular mixtures and a wide variety of binary Lennard–Jones
systems. A strong dependency of computed diffusivities on the system
size was observed. Computed diffusivities were found to increase with
the number of molecules. We propose a correction for the extrapolation
of Maxwell–Stefan diffusion coefficients to the thermodynamic
limit, based on the study by Yeh and Hummer (J. Phys. Chem. B, 2004, 108, 15873−15879). The proposed correction is a function of the viscosity
of the system, the size of the simulation box, and the thermodynamic
factor, which is a measure for the nonideality of the mixture. Verification
is carried out for more than 200 distinct binary Lennard–Jones
systems, as well as 9 binary systems of methanol, water, ethanol,
acetone, methylamine, and carbon tetrachloride. Significant deviations
between finite-size Maxwell–Stefan diffusivities and the corresponding
diffusivities at the thermodynamic limit were found for mixtures close
to demixing. In these cases, the finite-size correction can be even
larger than the simulated (finite-size) Maxwell–Stefan diffusivity.
Our results show that considering these finite-size effects is crucial
and that the suggested correction allows for reliable computations
Increased binding and defective migration across fibronectin of cycling hematopoietic progenitor cells.
Engraftment of hematopoietic progenitor cells has been shown to decrease during cell cycle transit. We studied cell cycle-associated changes in adhesion and migration of mitotically activated cord blood CD34+ cells. Migration toward medium conditioned by the stromal-derived factor-1-producing cell line MS-5 was studied in bovine serum albumin- and fibronectin (Fn)-coated transwells. Migration was reduced in cycling CD34+ cells and long-term culture-initiating cells (LTC-ICs) compared with their noncycling counterparts across Fn but not across bovine serum albumin. Conversely, Fn binding was higher in cycling CD34+ cells and LTC-ICs compared with noncycling progenitor cells, while adhesion of both subsets to bovine serum albumin was undetectable. The contribution of alpha4 and alpha5 integrins in mediating adhesion and migration of activated CD34+ cells onto Fn was analyzed by neutralization experiments. While alpha4-mediated Fn binding decreased during G(2)/M, alpha5 integrin-mediated adhesion increased during transit from G(0)/G(1) to S and G(2)/M phases. As for migration, the contribution of alpha4 integrin was similar in all phases, whereas alpha5-directed migration was lower in G(2)/M compared with G(0)/G(1) and S phases. Defective migration of cycling CD34+ cells was not due to differences in alpha5 integrin expression. In conclusion, chemotaxis across Fn is less efficient in cycling progenitor cells in correlation with an increased Fn binding capacity. In addition, alpha4 and alpha5 integrin functions are independently modulated during cell cycle transit
Combination of Competitive Quantitative PCR and Constant-Denaturant Capillary Electrophoresis for High-Resolution Detection and Enumeration of Microbial Cells
A novel quantitative PCR (QPCR) approach, which combines competitive PCR with constant-denaturant capillary electrophoresis (CDCE), was adapted for enumerating microbial cells in environmental samples using the marine nanoflagellate Cafeteria roenbergensis as a model organism. Competitive PCR has been used successfully for quantification of DNA in environmental samples. However, this technique is labor intensive, and its accuracy is dependent on an internal competitor, which must possess the same amplification efficiency as the target yet can be easily discriminated from the target DNA. The use of CDCE circumvented these problems, as its high resolution permitted the use of an internal competitor which differed from the target DNA fragment by a single base and thus ensured that both sequences could be amplified with equal efficiency. The sensitivity of CDCE also enabled specific and precise detection of sequences over a broad range of concentrations. The combined competitive QPCR and CDCE approach accurately enumerated C. roenbergensis cells in eutrophic, coastal seawater at abundances ranging from approximately 10 to 10(4) cells ml(−1). The QPCR cell estimates were confirmed by fluorescent in situ hybridization counts, but estimates of samples with <50 cells ml(−1) by QPCR were less variable. This novel approach extends the usefulness of competitive QPCR by demonstrating its ability to reliably enumerate microorganisms at a range of environmentally relevant cell concentrations in complex aquatic samples
Pharmacokinetic Characterization of [<sup>18</sup>F]UCB‑H PET Radiopharmaceutical in the Rat Brain
The
synaptic vesicle glycoprotein 2A (SV2A), a protein essential
to the proper nervous system function, is found in presynaptic vesicles.
Thus, SV2A targeting, using dedicated radiotracers combined with positron
emission tomography (PET), allows the assessment of synaptic density
in the living brain. The first-in-class fluorinated SV2A specific
radioligand, [<sup>18</sup>F]UCB-H, is now available at high activity
through an efficient radiosynthesis compliant with current good manufacturing
practices (cGMP). We report here a noninvasive method to quantify
[<sup>18</sup>F]UCB-H binding in rat brain with microPET. Validation
study in rats confirmed the need of high enantiomeric purity to target
SV2A in vivo. We demonstrated the reliability of a population-based
input function to quantify SV2A in preclinical microPET setting. Finally,
we investigated the in vivo metabolism of [<sup>18</sup>F]UCB-H and
confirmed the negligible amount of radiometabolites in the rat brain.
Hence, the in vivo quantification of SV2A using [<sup>18</sup>F]UCB-H
microPET seems a promising tool for the assessment of the synaptic
density in the rat brain, and opens the way for longitudinal follow-up
in neurodegenerative disease rodent models
Differential Substrate Inhibition Couples Kinetically Distinct 4-Coumarate:Coenzyme A Ligases with Spatially Distinct Metabolic Roles in Quaking Aspen
4-Coumarate:coenzyme A ligase (4CL) activates hydroxycinnamates for entry into phenylpropanoid branchways that support various metabolic activities, including lignification and flavonoid biosynthesis. However, it is not clear whether and how 4CL proteins with their broad substrate specificities fulfill the specific hydroxycinnamate requirements of the branchways they supply. Two tissue-specific 4CLs, Pt4CL1 and Pt4CL2, have previously been cloned from quaking aspen (Populus tremuloides Michx.), but whether they are catalytically adapted for the distinctive metabolic roles they are thought to support is not apparent from published biochemical data. Therefore, single- and mixed-substrate assays were conducted to determine whether the 4CLs from aspen exhibit clear catalytic identities under certain metabolic circumstances. Recombinant Pt4CL1 and Pt4CL2 exhibited the expected preference for p-coumarate in single-substrate assays, but strong competitive inhibition favored utilization of caffeate and p-coumarate, respectively, in mixed-substrate assays. The Pt4CL1 product, caffeoyl-CoA, predominated in mixed-substrate assays with xylem extract, and this was consistent with the near absence of Pt4CL2 expression in xylem tissue as determined by in situ hybridization. It is interesting that the Pt4CL2 product p-coumaroyl-CoA predominated in assays with developing leaf extract, although in situ hybridization revealed that both genes were coexpressed. The xylem extract and recombinant 4CL1 data allow us to advance a mechanism by which 4CL1 can selectively utilize caffeate for the support of monolignol biosynthesis in maturing xylem and phloem fibers. Loblolly pine (Pinus taeda), in contrast, possesses a single 4CL protein exhibiting broad substrate specificity in mixed-substrate assays. We discuss these 4CL differences in terms of the contrasts in lignification between angiosperm trees and their gymnosperm progenitors
Enabling Efficient Positron Emission Tomography (PET) Imaging of Synaptic Vesicle Glycoprotein 2A (SV2A) with a Robust and One-Step Radiosynthesis of a Highly Potent <sup>18</sup>F‑Labeled Ligand ([<sup>18</sup>F]UCB-H)
We herein describe the straightforward
synthesis of a stable pyridyl(4-methoxyphenyl)iodonium salt
and its [<sup>18</sup>F] radiolabeling within a one-step, fully automated
and cGMP compliant radiosynthesis of [<sup>18</sup>F]UCB-H ([<sup>18</sup>F]<b>7</b>), a PET tracer for the imaging of synaptic
vesicle glycoprotein 2A (SV2A). Over the course of 1 year, 50 automated
productions provided 34 ± 2% of injectable [<sup>18</sup>F]<b>7</b> from up to 285 GBq (7.7 Ci) of [<sup>18</sup>F]fluoride
in 50 min (uncorrected radiochemical yield, specific activity of 815
± 185 GBq/μmol). The successful implementation of our synthetic
strategy within routine, high-activity, and cGMP productions attests
to its practicality and reliability for the production of large doses
of [<sup>18</sup>F]<b>7</b>. In addition to enabling efficient
and cost-effective clinical research on a range of neurological pathologies
through the imaging of SV2A, this work further demonstrates the real
value of iodonium salts for the cGMP <sup>18</sup>F-PET tracer manufacturing
industry, and their ability to fulfill practical and regulatory requirements
in that field
Toward Plasmonics with Nanometer Precision: Nonlinear Optics of Helium-Ion Milled Gold Nanoantennas
Plasmonic nanoantennas are versatile
tools for coherently controlling
and directing light on the nanoscale. For these antennas, current
fabrication techniques such as electron beam lithography (EBL) or
focused ion beam (FIB) milling with Ga<sup>+</sup>-ions routinely
achieve feature sizes in the 10 nm range. However, they suffer increasingly
from inherent limitations when a precision of single nanometers down
to atomic length scales is required, where exciting quantum mechanical
effects are expected to affect the nanoantenna optics. Here, we demonstrate
that a combined approach of Ga<sup>+</sup>-FIB and milling-based He<sup>+</sup>-ion lithography (HIL) for the fabrication of nanoantennas
offers to readily overcome some of these limitations. Gold bowtie
antennas with 6 nm gap size were fabricated with single-nanometer
accuracy and high reproducibility. Using third harmonic (TH) spectroscopy,
we find a substantial enhancement of the nonlinear emission intensity
of single HIL-antennas compared to those produced by state-of-the-art
gallium-based milling. Moreover, HIL-antennas show a vastly improved
polarization contrast. This superior nonlinear performance of HIL-derived
plasmonic structures is an excellent testimonial to the application
of He<sup>+</sup>-ion beam milling for ultrahigh precision nanofabrication,
which in turn can be viewed as a stepping stone to mastering quantum
optical investigations in the near-field
Adhesion of synchronized human hematopoietic progenitor cells to fibronectin and vascular cell adhesion molecule-1 fluctuates reversibly during cell cycle transit in ex vivo culture
peer reviewedEx vivo expansion of hematopoietic stem/progenitor cells may result in defective engraftment. Human cord blood CD34(+) progenitor cells were synchronized and assayed for adhesion and migration onto fibronectin (Fn) and vascular cell adhesion molecule-1 (VCAM-1) at different stages of a first cell cycle executed ex vivo. During S phase transit, adhesion to Fn was transiently increased while binding to VCAM-1 was reversibly decreased, after which adhesion to both ligands returned to baseline levels with cell cycle completion. Transmigration across Fn and VCAM-1 decreased irreversibly during S phase progression. The function of alpha4 and alpha5 integrins was assessed with specific neutralizing antibodies. In uncultured CD34(+) cells and long-term culture-initiating cells (LTC-ICs), both adhesion and migration on Fn were inhibited by anti-alpha4 but not by anti-alpha5 antibodies. In mitotically activated CD34(+) cells and LTC-ICs, adhesion and migration on Fn were mainly dependent on alpha5 integrin and to a lesser extent on alpha4 integrin. Changes in integrin function were not dependent on parallel modulation of integrin expression. In conclusion, Fn and VCAM-1 binding of progenitor cells fluctuates reversibly during cell cycle transit ex vivo. In addition, our data show that mitogenic activation induces a shift from a dominant alpha4 to a preferential alpha5 integrin-dependent interaction with Fn