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Synthesis and Characterization of Oxide Chloride Sr2VO3Cl, a Layered S = 1 Compound
The mixed-anion compound with composition Sr2VO3Cl has been synthesized for the first time, using the conventional high-temperature solid-state synthesis technique in a closed silica ampule under inert conditions. This compound belongs to the known Sr2TmO3Cl (Tm = Sc, Mn, Fe, Co, Ni) family, but with Tm = V. All homologues within this family can be described with the tetragonal space group P4/nmm (No. 129); from a Rietveld refinement of powder X-ray diffraction data on the Tm = V homologue, the unit cell parameters were determined to a = 3.95974(8) and c = 14.0660(4) Å, and the atomic parameters in the crystal structure could be estimated. The synthesized powder is black, implying that the compound is a semiconductor. The magnetic investigations suggest that Sr2VO3Cl is a paramagnet at high temperatures, exhibiting a μeff = 2.0 μB V-1 and antiferromagnetic (AFM) interactions between the magnetic vanadium spins (θCW = −50 K), in line with the V-O-V advantageous super-exchange paths in the V-O layers. Specific heat capacity studies indicate two small anomalies around 5 and 35 K, which however are not associated with long-range magnetic ordering. 35Cl ss-NMR investigations suggest a slow spin freezing below 4.2 K resulting in a glassy-like spin ground state.
Enzymatic Catalysis at Nanoscale: Enzyme-Coated Nanoparticles as Colloidal Biocatalysts for Polymerization Reactions
Enzyme-catalyzed controlled radical polymerization represents a powerful approach for the polymerization of a wide variety of water-soluble monomers. However, in such an enzyme-based polymerization system, the macromolecular catalyst (i.e., enzyme) has to be separated from the polymer product. Here, we present a compelling approach for the separation of the two macromolecular species, by taking the catalyst out of the molecular domain and locating it in the colloidal domain, ensuring quasi-homogeneous catalysis as well as easy separation of precious biocatalysts. We report on gold nanoparticles coated with horseradish peroxidase that can catalyze the polymerization of various monomers (e.g., N-isopropylacrylamide), yielding thermoresponsive polymers. Strikingly, these biocatalyst-coated nanoparticles can be recovered completely and reused in more than three independent polymerization cycles, without significant loss of their catalytic activity.
Mitochondria Targeted Protein-Ruthenium Photosensitizer for Efficient Photodynamic Applications
Organelle-targeted photosensitization represents a promising approach in photodynamic therapy where the design of the active photosensitizer (PS) is very crucial. In this work, we developed a macromolecular PS with multiple copies of mitochondria-targeting groups and ruthenium complexes that displays highest phototoxicity toward several cancerous cell lines. In particular, enhanced anticancer activity was demonstrated in acute myeloid leukemia cell lines, where significant impairment of proliferation and clonogenicity occurs. Finally, attractive two-photon absorbing properties further underlined the great significance of this PS for mitochondria targeted PDT applications in deep tissue cancer therapy.
Does the Processing Method Resulting in Different States of an Interconnected Network of Multiwalled Carbon Nanotubes in Polymeric Blend Nanocomposites Affect EMI Shielding Properties?
Electromagnetic interference (EMI), an unwanted phenomenon, often affects the reliability of precise electronic circuitry. To prevent this, an effective shielding is prerequisite to protect the electronic devices. In this study, an attempt was made to understand how processing of polymeric blend nanocomposites involving multiwalled carbon nanotubes (MWCNTs) affects the evolving interconnected network structure of MWCNTs and eventually their EMI shielding properties. Thereby, the overall blend morphology and especially the connectivity of the polycarbonate (PC) component, in which the MWCNTs tend to migrate, as well as the perfectness of their migration, and the state of nanotube dispersion are considered. For this purpose, blends of varying composition of PC and poly(methyl methacrylate) were chosen as a model system as they show a phase diagram with lower critical solution temperature type of characteristic. Such blends were processed in two different ways: solution mixing (from the homogeneous state) and melt mixing (in the biphasic state). In both the processes, MWCNTs (3 wt %) were mixed into the blends, and the evolved structures (after phase separation induced by annealing in solution-mixed blends) and the quenched structures (as the blends exit the extruder) were systematically studied using transmission electron microscopy (TEM). Both the set of blends were subjected to the same thermal history, however, under different conditions such as under quiescent conditions (in the case of solution mixing) and under shear (in the case of melt mixing). The electrical volume conductivity and the evolved morphologies of these blend nanocomposites were evaluated and correlated with the measured EMI shielding behavior. The results indicated that irrespective of the type of processing, the MWCNTs localized in the PC component; driven by thermodynamic factors and depending on the blend composition, sea-island, cocontinuous, and phase-inverted structures evolved. Interestingly, the better interconnected network structures of MWCNTs observed using TEM in the solution-mixed samples together with larger nanotube lengths resulted in higher EMI shielding properties (-27 dB at 18 GHz) even if slightly higher electrical volume conductivities were observed in melt-mixed samples. Moreover, the shielding was absorption-driven, facilitated by the dense network of MWCNTs in the PC component of the blends, at any given concentration of nanotubes. Taken together, this study highlights the effects of different blend nanocomposite preparation methods (solution and melt) and the developed morphology and nanotube network structure in MWCNT filled blend nanocomposites on the EMI shielding behavior.
Polypropylene/Layered Double Hydroxide Nanocomposites: Influence of LDH Intralayer Metal Constituents on the Properties of Polypropylene
Sonication-assisted delamination of layered double hydroxides (LDHs) resulted in smaller-sized LDH nanoparticles (∼50-200 nm). Such delaminated Co-Al LDH, Zn-Al LDH, and Co-Zn-Al LDH solutions were used for the preparation of highly dispersed isotactic polypropylene (iPP) nanocomposites. Transmission electron microscopy and wide-angle X-ray diffraction results revealed that the LDH nanoparticles were well dispersed within the iPP matrix. The intention of this study is to understand the influence of the intralayer metal composition of LDH on the various properties of iPP/LDH nanocomposites. The sonicated LDH nanoparticles showed a significant increase in the crystallization rate of iPP; however, not much difference in the crystallization rate of iPP was observed in the presence of different types of LDH. The dynamic mechanical analysis results indicated that the storage modulus of iPP was increased significantly with the addition of LDH. The incorporation of different types of LDH showed no influence on the storage modulus of iPP. But considerable differences were observed in the flame retardancy and thermal stability of iPP with the type of LDH used for the preparation of nanocomposites. The thermal stability (50% weight loss temperature (T0.5)) of the iPP nanocomposite containing three-metal LDH (Co-Zn-Al LDH) is superior to that of the nanocomposites made of two-metal LDH (Co-Al LDH and Zn-Al LDH). Preliminary studies on the flame-retardant properties of iPP/LDH nanocomposites using microscale combustion calorimetry showed that the peak heat release rate was reduced by 39% in the iPP/Co-Zn-Al LDH nanocomposite containing 6 wt % LDH, which is higher than that of the two-metal LDH containing nanocomposites, iPP/Co-Al LDH (24%) and iPP/Zn-Al LDH (31%). These results demonstrated that the nanocomposites prepared using three-metal LDH showed better thermal and flame-retardant properties compared to the nanocomposites prepared using two-metal LDH. This difference might be due to the better char formation capability of three-metal LDH compared to that of two-metal LDH.
Mixed Cu-Fe Sulfides Derived from Polydopamine-Coated Prussian Blue Analogue as a Lithium-Ion Battery Electrode
Batteries employing transition-metal sulfides enable high-charge storage capacities, but polysulfide shuttling and volume expansion cause structural disintegration and early capacity fading. The design of heterostructures combining metal sulfides and carbon with an optimized morphology can effectively address these issues. Our work introduces dopamine-coated copper Prussian blue (CuPB) analogue as a template to prepare nanostructured mixed copper-iron sulfide electrodes. The material was prepared by coprecipitation of CuPB with in situ dopamine polymerization, followed by thermal sulfidation. Dopamine controls the particle size and favors K-rich CuPB due to its polymerization mechanism. While the presence of the coating prevents particle agglomeration during thermal sulfidation, its thickness demonstrates a key effect on the electrochemical performance of the derived sulfides. After a two-step activation process during cycling, the C-coated KCuFeS2electrodes showed capacities up to 800 mAh/g at 10 mA/g with nearly 100% capacity recovery after rate handling and a capacity of 380 mAh/g at 250 mA/g after 500 cycles.
Carbide-Derived Niobium Pentoxide with Enhanced Charge Storage Capacity for Use as a Lithium-Ion Battery Electrode
Nb2O5 has been explored as a promising anode material for use as lithium-ion batteries (LIBs), but depending on the crystal structure, the specific capacity was always reported to be usually around or below 200 mAh/g. For the first time, we present coarse-grained Nb2O5 materials that significantly overcome this capacity limitation with the promise of enabling high power applications. Our work introduces coarse-grained carbide-derived Nb2O5 phases obtained either by a one-step or a two-step bulk conversion process. By in situ production of chlorine gas from metal chloride salt at ambient pressure, we obtain in just one step directly orthorhombic Nb2O5 alongside carbide-derived carbon (o-Nb2O5/CDC). In situ formation of chlorine gas from metal chloride salt under vacuum conditions yields CDC covering the remaining carbide core, which can be transformed into metal oxides covered by a carbon shell upon thermal treatment in CO2 gas. The two-step process yielded a mixed-phase tetragonal and monoclinic Nb2O5 with CDC (m-Nb2O5/CDC). Our combined diffraction and spectroscopic data confirm that carbide-derived Nb2O5 materials show disordering of the crystallographic planes caused by oxygen deficiency in the structural units and, in the case of m-Nb2O5/CDC, severe stacking faults. This defect engineering allows access to a very high specific capacity exceeding the two-electron transfer process of conventional Nb2O5. The charge storage capacities of the resulting m-Nb2O5/CDC and o-Nb2O5/CDC are, in both cases, around 300 mAh/g at a specific current of 10 mA/g, thereby, the values are significantly higher than that of the state-of-the-art for Nb2O5 as a LIB anode. Carbide-derived Nb2O5 materials also show robust cycling stability over 500 cycles with capacity fading only 24% for the sample m-Nb2O5/CDC and 28% for o-Nb2O5/CDC, suggesting low degree of expansion/compaction during lithiation and delithiation.
Tuneable Dielectric Properties Derived from Nitrogen-Doped Carbon Nanotubes in PVDF-Based Nanocomposites
Nitrogen-doped multiwall carbon nanotubes (N-MWNTs) with different structures were synthesized by employing chemical vapor deposition and changing the argon/ethane/nitrogen gas precursor ratio and synthesis time, and broadband dielectric properties of their poly(vinylidene fluoride) (PVDF)-based nanocomposites were investigated. The structure, morphology, and electrical conductivity of synthesized N-MWNTs were assessed via Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy, and powder conductivity techniques. The melt compounded PVDF nanocomposites manifested significantly high real part of the permittivity (ϵ′) along with low dissipation factor (tan δϵ) in 0.1 kHz to 1 MHz frequency range, suggesting use as efficient charge-storage materials. Longer synthesis time resulted in enhanced carbon purity as well as higher thermal stability, determined via TGA analysis. The inherent electrical conductivity of N-MWNTs scaled with the carbon purity. The charge-storage ability of the developed PVDF nanocomposites was commensurate with the amount of the nitrogen heteroatom (i.e., self-polarization), carbon purity, and inherent electrical conductivity of N-MWNTs and increased with better dispersion of N-MWNTs in PVDF.
Conjugated Polymers as a New Class of Dual-Mode Matrices for MALDI Mass Spectrometry and Imaging
Matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) and MALDI MS imaging are ubiquitous analytical methods in medical, pharmaceutical, biological, and environmental research. Currently, there is a strong interest in the investigation of low molecular weight compounds (LMWCs), especially to trace and understand metabolic pathways, requiring the development of new matrix systems that have favorable optical properties and a high ionization efficiency and that are MALDI silent in the LMWC area. In this paper, five conjugated polymers, poly{[N,N'-bis(2-octyldodecyl)-naphtalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'(2,2'-bithiophene)} (PNDI(T2)), poly(3-dodecylthiophene-2,5-diyl) (P3DDT), poly{[2,3-bis(3-octyloxyphenyl)quinoxaline-5,8-diyl]-alt-(thiophene-2,5-diyl)} (PTQ1), poly{[N,N'-bis(2-octyldodecyl)-isoindigo-5,5'-diyl]-alt-5,5'(2,2'-bithiophene)} (PII(T2)), and poly(9,9-di-n-octylfluorenyl-2,7-diyl) (P9OFl) are investigated as matrices. The polymers have a strong optical absorption, are solution processable, and can be coated into thin films, allowing a vast reduction in the amount of matrix used. All investigated polymers function as matrices in both positive and negative mode MALDI, classifying them as rare dual-mode matrices, and show a very good analyte ionization ability in both modes. PNDI(T2), P3DDT, PTQ1, and PII(T2) are MALDI silent in the full measurement range (>m/z = 150k), except at high laser intensities. In MALDI MS experiments of single analytes and a complex biological sample, the performance of the polymers was found to be as good as two commonly used matrices (2,5-DHB for positive and 9AA for negative mode measurements). The detection limit of two standard analytes was determined as being below 164 pmol for reserpine and below 245 pmol for cholic acid. Additionally P3DDT was used successfully in first MALDI MS imaging experiments allowing the visualization of the tissue morphology of rat brain sections.
In Situ Monitoring of Linear RGD-Peptide Bioconjugation with Nanoscale Polymer Brushes
Bioinspired materials mimicking the native extracellular matrix environment are promising for biotechnological applications. Particularly, modular biosurface engineering based on the functionalization of stimuli-responsive polymer brushes with peptide sequences can be used for the development of smart surfaces with biomimetic cues. The key aspect of this study is the in situ monitoring and analytical verification of the biofunctionalization process on the basis of three complementary analytical techniques. In situ spectroscopic ellipsometry was used to quantify the amount of chemisorbed GRGDS at both the homopolymer poly(acrylic acid) (PAA) brush and the binary poly(N-isopropylacrylamide) (PNIPAAm)-PAA brushes, which was finally confirmed by an acidic hydrolysis combined with a subsequent reverse-phase high-performance liquid chromatography analysis. In situ attenuated total reflection-Fourier transform infrared spectroscopy provided a step-by-step detection of the biofunctionalization process so that an optimized protocol for the bioconjugation of GRGDS could be identified. The optimized protocol was used to create a temperature-responsive binary brush with a high amount of chemisorbed GRGDS, which is a promising candidate for the temperature-sensitive control of GRGDS presentation in further cell-instructive studies.