310 research outputs found
A toolset of functionalized porphyrins with different linker strategies for application in bioconjugation
The reaction of amines with pentafluorophenyl-substituted A3B-porphyrins has
been used to obtain different useful reactive groups for further
functionalization and/or conjugation of these porphyrins to other substrates
or materials. Porphyrins with alkenyl, alkynyl, amino, azido, epoxide,
hydroxyl, and maleimido groups have thus been synthesized. For the first time
such functionalized porphyrins have been conjugated to hyperbranched
polyglycerol (hPG) as a biocompatible carrier system for photodynamic therapy
(PDT) using the copper(I)-catalyzed 1,3-dipolar cycloaddition (CuAAC). The
photocytotoxicity of selected porphyrins as well as of the porphyrin-hPG-
conjugates has been assessed in cellular assays with human epidermoid
carcinoma A-253 and squamous carcinoma CAL-27 cells. For several biomedical
applications a release of the active drug and/or fluorescent dye is desired.
Therefore, additionally, the synthesis of A3B-porphyrins with cleavable linker
moieties is presented, namely disulfide, cleavable in a reductive environment,
and acetal linkers whose cleavage is pH triggered
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Influence of Sterilization and Preservation Procedures on the Integrity of Serum Protein-Coated Magnetic Nanoparticles
Protein-coated magnetic nanoparticles are promising candidates for various medical applications. Prior to their application into a biological system, one has to guarantee that the particle dispersions are free from pathogens or any other microbiologic contamination. Furthermore, to find entrance into clinical routine, the nanoparticle dispersions have to be storable for several months. In this study, we tested several procedures for sterilization and preservation of nanoparticle containing liquids on their influence on the integrity of the protein coating on the surface of these particles. For this, samples were treated by freezing, autoclaving, lyophilization, and ultraviolet (UV) irradiation, and characterized by means of dynamic light scattering, determination of surface potential, and gel electrophoresis afterwards. We found that the UV sterilization followed by lyophilization under the addition of polyethylene glycol are the most promising procedures for the preparation of sterilized long-term durable protein-coated magnetic nanoparticles. Ongoing work is focused on the optimization of used protocols for UV sterilization and lyophilization for further improvement of the storage time
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Biocompatible magnetic fluids of Co-doped iron oxide nanoparticles with tunable magnetic properties
Magnetite (Fe3O4) particles with a diameter around 10 nm have a very low coercivity (Hc) and relative remnant magnetization (Mr/Ms), which is unfavorable for magnetic fluid hyperthermia. In contrast, cobalt ferrite (CoFe2O4) particles of the same size have a very high Hc and Mr/Ms, which is magnetically too hard to obtain suitable specific heating power (SHP) in hyperthermia. For the optimization of the magnetic properties, the Fe2+ ions of magnetite were substituted by Co2+ step by step, which results in a Co doped iron oxide inverse spinel with an adjustable Fe2+ substitution degree in the full range of pure iron oxide up to pure cobalt ferrite. The obtained magnetic nanoparticles were characterized regarding their structural and magnetic properties as well as their cell toxicity. The pure iron oxide particles showed an average size of 8 nm, which increased up to 12 nm for the cobalt ferrite. For ferrofluids containing the prepared particles, only a limited dependence of Hc and Mr/Ms on the Co content in the particles was found, which confirms a stable dispersion of the particles within the ferrofluid. For dry particles, a strong correlation between the Co content and the resulting Hc and Mr/Ms was detected. For small substitution degrees, only a slight increase in Hc was found for the increasing Co content, whereas for a substitution of more than 10% of the Fe atoms by Co, a strong linear increase in Hc and Mr/Ms was obtained. Mössbauer spectroscopy revealed predominantly Fe3+ in all samples, while also verifying an ordered magnetic structure with a low to moderate surface spin canting. Relative spectral areas of Mössbauer subspectra indicated a mainly random distribution of Co2+ ions rather than the more pronounced octahedral site-preference of bulk CoFe2O4. Cell vitality studies confirmed no increased toxicity of the Co-doped iron oxide nanoparticles compared to the pure iron oxide ones. Magnetic heating performance was confirmed to be a function of coercivity as well. The here presented non-toxic magnetic nanoparticle system enables the tuning of the magnetic properties of the particles without a remarkable change in particles size. The found heating performance is suitable for magnetic hyperthermia application
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Biocompatible magnetic fluids of co-doped iron oxide nanoparticles with tunable magnetic properties
Magnetite (Fe3O4) particles with a diameter around 10 nm have a very low coercivity (Hc) and relative remnant magnetization (Mr/Ms), which is unfavorable for magnetic fluid hyperthermia. In contrast, cobalt ferrite (CoFe2O4) particles of the same size have a very high Hc and Mr/Ms, which is magnetically too hard to obtain suitable specific heating power (SHP) in hyperthermia. For the optimization of the magnetic properties, the Fe2+ ions of magnetite were substituted by Co2+ step by step, which results in a Co doped iron oxide inverse spinel with an adjustable Fe2+ substitution degree in the full range of pure iron oxide up to pure cobalt ferrite. The obtained magnetic nanoparticles were characterized regarding their structural and magnetic properties as well as their cell toxicity. The pure iron oxide particles showed an average size of 8 nm, which increased up to 12 nm for the cobalt ferrite. For ferrofluids containing the prepared particles, only a limited dependence of Hc and Mr/Ms on the Co content in the particles was found, which confirms a stable dispersion of the particles within the ferrofluid. For dry particles, a strong correlation between the Co content and the resulting Hc and Mr/Ms was detected. For small substitution degrees, only a slight increase in Hc was found for the increasing Co content, whereas for a substitution of more than 10% of the Fe atoms by Co, a strong linear increase in Hc and Mr/Ms was obtained. Mössbauer spectroscopy revealed predominantly Fe3+ in all samples, while also verifying an ordered magnetic structure with a low to moderate surface spin canting. Relative spectral areas of Mössbauer subspectra indicated a mainly random distribution of Co2+ ions rather than the more pronounced octahedral site-preference of bulk CoFe2O4. Cell vitality studies confirmed no increased toxicity of the Co-doped iron oxide nanoparticles compared to the pure iron oxide ones. Magnetic heating performance was confirmed to be a function of coercivity as well. The here presented non-toxic magnetic nanoparticle system enables the tuning of the magnetic properties of the particles without a remarkable change in particles size. The found heating performance is suitable for magnetic hyperthermia application. © 2020 by the authors. Licensee MDPI, Basel, Switzerland
Ligandâinduced donor state destabilisation â a new route to panchromatically absorbing cu(I) complexes
The intense absorption of light to covering a large part of the visible spectrum is highly desirable for solar energy conversion schemes. To this end, we have developed novel anionic bis(4 H âimidazolato)Cu(I) complexes (cuprates), which feature intense, panchromatic light absorption properties throughout the visible spectrum and into the NIR region with extinction coefficients up to 28,000â
M â1 âcm â1 . Steadyâstate absorption, (spectro)electrochemical and theoretical investigations reveal low energy (Vis to NIR) metalâtoâligand chargeâtransfer absorption bands, which are a consequence of destabilized copperâbased donor states. These highâlying copperâbased states are induced by the Ïâdonation of the chelating anionic ligands, which also feature low energy acceptor states. The optical properties are reflected in very low, copperâbased oxidation potentials and three ligandâbased reduction events. These electronic features reveal a new route to panchromatically absorbing Cu(I) complexes.Cu(I) and two chelating , anionic polymethineâtype ligands form a novel type of photoactive cuprate. The ligands induce the destabilisation of the Cu(I)âbased donor states and act themselves as acceptors. This leads to an unusually broad and intense absorption spectrum with metalâtoâligand chargeâtransfer transitions from the visible to nearâinfrared region. imag
Non-Adiabatic Electronic and Vibrational Ring-Opening Dynamics resolved with Attosecond Core-Level Spectroscopy
Non-adiabatic dynamics and conical intersections play a central role in the
chemistry of most polyatomic molecules, ranging from isomerization to
heterocyclic ring opening and avoided photo-damage of DNA. Studying the
underpinning correlated dynamics of electronic and nuclear wave packets is a
major challenge in real-time and, many times involves optically dark transient
states. We show that attosecond core-level spectroscopy reveals the pathway
dynamics of neutral furan across its conical intersections and dark states. Our
method measures electronic-nuclear correlations to detect the dephasing of
electronic coherence due to nuclear motion and identifies the ring-opened
isomer as the dominant product. These results demonstrate the efficacy of
attosecond core level spectroscopy as a potent method to investigate the
real-time dynamics of photochemical reaction pathways in complex molecular
systems
X-Ray Microscopy of Spin Wave Focusing using a Fresnel Zone Plate
Magnonics, i.e. the artificial manipulation of spin waves, is a flourishing
field of research with many potential uses in data processing within reach.
Apart from the technological applications the possibility to directly influence
and observe these types of waves is of great interest for fundamental research.
Guidance and steering of spin waves has been previously shown and lateral spin
wave confinement has been achieved. However, true spin wave focusing with both
lateral confinement and increase in amplitude has not been shown before. Here,
we show for the first time spin wave focusing by realizing a Fresnel zone plate
type lens. Using x-ray microscopy we are able to directly image the propagation
of spin waves into the nanometer sized focal spot. Furthermore, we observe that
the focal spot can be freely moved in a large area by small variations of the
bias field. Thus, this type of lens provides a steerable intense nanometer
sized spin wave source. Potentially, this could be used to selectively
illuminate magnonic devices like nano oscillators with a steerable spin wave
beam
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Photophysics of Anionic Bis(4H-imidazolato)CuI Complexes
In this paper, the photophysical behavior of four panchromatically absorbing, homoleptic bis(4H-imidazolato)CuI complexes, with a systematic variation in the electron-withdrawing properties of the imidazolate ligand, were studied by wavelength-dependent time-resolved femtosecond transient absorption spectroscopy. Excitation at 400, 480, and 630 nm populates metal-to-ligand charge transfer, intraligand charge transfer, and mixed-character singlet states. The pump wavelength-dependent transient absorption data were analyzed by a recently established 2D correlation approach. Data analysis revealed that all excitation conditions yield similar excited-state dynamics. Key to the excited-state relaxation is fast, sub-picosecond pseudo-Jahn-Teller distortion, which is accompanied by the relocalization of electron density onto a single ligand from the initially delocalized state at Franck-Condon geometry. Subsequent intersystem crossing to the triplet manifold is followed by a sub-100 ps decay to the ground state. The fast, nonradiative decay is rationalized by the low triplet-state energy as found by DFT calculations, which suggest perspective treatment at the strong coupling limit of the energy gap law
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