Magnetic interactions in graphene decorated with iron oxide nanoparticles.

We present the studies of structural and magnetic properties of graphene composites prepared with several quantities ofα-Fe2O3dopant of 5%, 25% and 50% made with either ethanol or acetone. Our studies showed the presence of a weak magnetic order up to room temperature and saturation magnetization close to 0.2 emu g-1in pure commercial graphene. With regard to magnetic properties of our graphene + iron oxide samples, the solvent used during the preparation of the composite had a significant influence on them. For graphene + Fe2O3samples made with acetone the magnetic properties of pure graphene played a major role in the overall magnetic susceptibility and magnetization. On the other hand, for graphene + iron oxide samples made with ethanol we observed the presence of superparamagnetic blocking atT < 110 K which was due to the additional appearance ofγ-Fe3O4nanoparticles. Changes in the synthesis solvent played a major role in the magnetic properties of our graphene + Fe2O3nanocomposite samples resulting in much higher saturation magnetization for the samples made with ethanol. Both the shape and the parameters characterizing magnetization hysteresis loops depend strongly on the amount of iron oxide and changes in the preparation method.

Interface phenomena in magnetron sputtered Cu2O/ZnO heterostructures.

The interface between ZnO and Cu2O has been predicted to be a good candidate for use in thin film solar cells. However, the high predicted conversion efficiency has yet to be fully realized experimentally. To explore the underlying causes of this we investigate the interface between ZnO and Cu2O in magnetron sputtered samples. Two different sample geometries were made: In the first set thin layers of ZnO were deposited on Cu2O (type A), while in the second set the order was reversed (type B). Using x-ray photoelectron spectroscopy (XPS), an intermediate CuO layer was identified regardless of the order in which the Cu2O and ZnO layers were deposited. The presence of a CuO layer was supported by transmission electron microscopy (TEM) results. Changes in the electron hole screening conditions were observed in CuO near the interface with ZnO, manifested as changes in the relative peak-to-satellite ratio and the degree of asymmetric broadness in the Cu 2p peak. The suppression of the Cu 2p satellite characteristic of CuO may cause the CuO presence to be overlooked and cause errors in determinations of valence band offsets (VBOs). For the type A samples, we compare four different approaches to XPS-based determination of VBO and find that the most reliable results are obtained when the thin CuO layer and the altered screening conditions at the interface were taken into account. The VBOs were found to range between 2.5 eV and 2.8 eV. For the B type samples a reduction of the Cu 2p-LMM Auger parameter was found as compared to bulk Cu2O, indicative of quantum confinement in the Cu2O overlayer.

Electronic properties and morphology of copper oxide/n-type silicon heterostructures.

Silicon-based tandem heterojunction solar cells utilizing cuprous oxide (Cu2O) as the top absorber layer show promise for high-efficiency conversion and low production cost. In the present study, single phase Cu2O films have been realized on n-type Si substrates by reactive magnetron sputtering at 400 °C. The obtained Cu2O/Si heterostructures have subsequently been heat treated at temperatures in the 400-700 °C range in Ar flow and extensively characterized by x-ray diffraction (XRD) measurements, transmission electron microscopy (TEM) imaging and electrical techniques. The Cu2O/Si heterojunction exhibits a current rectification of ~5 orders of magnitude between forward and reverse bias voltages. High resolution cross-sectional TEM-images show the presence of a ~2 nm thick interfacial SiO2 layer between Cu2O and the Si substrate. Heat treatments below 550 °C result in gradual improvement of crystallinity, indicated by XRD. At and above 550 °C, partial phase transition to cupric oxide (CuO) occurs followed by a complete transition at 700 °C. No increase or decrease of the SiO2 layer is observed after the heat treatment at 550 °C. Finally, a thin Cu-silicide layer (Cu3Si) emerges below the SiO2 layer upon annealing at 550 °C. This silicide layer influences the lateral current and voltage distributions, as evidenced by an increasing effective area of the heterojunction diodes.

Nanogel-Conjugated Reverse Transcriptase Inhibitors and Their Combinations as Novel Antiviral Agents with Increased Efficacy against HIV-1 Infection.

Nucleoside reverse transcriptase inhibitors (NRTIs) are an integral part of the current antiretroviral therapy (ART), which dramatically reduced the mortality from AIDS and turned the disease from lethal to chronic. The further steps in curing the HIV-1 infection must include more effective targeting of infected cells and virus sanctuaries inside the body and modification of drugs and treatment schedules to reduce common complications of the long-term treatment and increase patient compliancy. Here, we describe novel NRTI prodrugs synthesized from cholesteryl-ε-polylysine (CEPL) nanogels by conjugation with NRTI 5'-succinate derivatives (sNRTI). Biodegradability, small particle size, and high NRTI loading (30% by weight) of these conjugates; extended drug release, which would allow a weekly administration schedule; high therapeutic index (>1000) with a lower toxicity compared to NRTIs; and efficient accumulation in macrophages known as carriers for HIV-1 infection are among the most attractive properties of new nanodrugs. Nanogel conjugates of zidovudine (AZT), lamivudine (3TC), and abacavir (ABC) have been investigated individually and in formulations similar to clinical NRTI cocktails. Nanodrug formulations demonstrated 10-fold suppression of reverse transcriptase activity (EC90) in HIV-infected macrophages at 2-10, 2-4, and 1-2 µM drug levels, respectively, for single nanodrugs and dual and triple nanodrug cocktails. Nanogel conjugate of lamivudine was the most effective single nanodrug (EC90 2 µM). Nanodrugs showed a more favorable pharmacokinetics compared to free NRTIs. Infrequent iv injections of PEGylated CEPL-sAZT alone could efficiently suppress HIV-1 RT activity to background level in humanized mouse (hu-PBL) HIV model.

F604S exchange in FIP1L1-PDGFRA enhances FIP1L1-PDGFRA protein stability via SHP-2 and SRC: a novel mode of kinase inhibitor resistance.

FIP1L1-PDGFRA is a constitutively activated kinase described in chronic eosinophilic leukemia (CEL) and hypereosinophilic syndrome (HES). Imatinib is clinically active in FIP1L1-PDGFRA-positive diseases. Using in vitro screening to identify imatinib-resistant mutations, we frequently detected a Phe to Ser exchange at position 604 (F604S) of FIP1L1-PDGFRA alone or in combination with other exchanges. Surprisingly, FIP1L1-PDGFRA/F604S did not increase the biochemical or cellular IC50 value of imatinib when compared with unmutated FIP1L1-PDGFRA. However, FIP1L1-PDGFRA/F604S more efficiently induced growth factor independence in cell lines and primary mouse bone marrow cells. Pulse chase analysis revealed that the F604S exchange strongly stabilized FIP1L1-PDGFRA/F604S. The F604S mutation creates a binding site for the phosphatase domain of SHP-2, leading to lower autophosphorylation of FIP1L1-PDGFRA/F604S. This is associated with a reduced activation of SRC and CBL by FIP1L1-PDGFRA/F604S compared with the unmutated oncogene. As SRC inhibition and knockdown resulted in FIP1L1-PDGFRA stabilization, this explains the extended half-life of FIP1L1-PDGFRA/F604S. Interestingly, FIP1L1-PDGFRA/L629P, a recently identified mutation in an imatinib-resistant CEL patient, also showed protein stabilization similar to that observed with FIP1L1-PDGFRA/F604S. Therefore, resistance mutations in FIP1L1-PDGFRA that do not interfere with drug binding but rather increase target protein stability seem to be one of the drug-resistance mechanisms in FIP1L1-PDGFRA-positive disease.

Amphiphilic cationic nanogels as brain-targeted carriers for activated nucleoside reverse transcriptase inhibitors.

Progress in AIDS treatment shifted emphasis towards limiting adverse effects of antiviral drugs while improving the treatment of hard-to-reach viral reservoirs. Many therapeutic nucleoside reverse transcriptase inhibitors (NRTI) have a limited access to the central nervous system (CNS). Increased NRTI levels induced various complications during the therapy, including neurotoxicity, due to the NRTI toxicity to mitochondria. Here, we describe an innovative design of biodegradable cationic cholesterol-ε-polylysine nanogel carriers for delivery of triphosphorylated NRTIs that demonstrated high anti-HIV activity along with low neurotoxicity, warranting minimal side effects following systemic administration. Efficient CNS targeting was achieved by nanogel modification with brain-specific peptide vectors. Novel dual and triple-drug nanoformulations, analogous to therapeutic NRTI cocktails, displayed equal or higher antiviral activity in HIV-infected macrophages compared to free drugs. Our results suggest potential alternative approach to HIV-1 treatment focused on the effective nanodrug delivery to viral reservoirs in the CNS and reduced neurotoxicity.

Retro-fitting an older (S)TEM with two Cs aberration correctors for 80 kV and 60 kV operation.

For the characterization of light materials using transmission electron microscopy, a low electron acceleration voltage of 80 kV or even 60 kV is attractive due to reduced beam damage to the specimen. The concomitant reduction in resolving power of the microscope can be restored when using spherical aberration (C(s) ) correctors, which for the most part are only available in the latest and most expensive microscopes. Here, we show that upgrading of existing TEMs is an attractive and cost-effective alternative. We report on the low-voltage performance on graphitic material of a JEOL JEM-2010F built in the early 1990s and retro-fitted with a conventional imaging C(s) corrector and a probe C(s) corrector. The performance data show C(s) retro-fitted instruments can compete very favourably against more modern state-of-the-art instruments in both conventional imaging (TEM) and scanning (STEM) modes.

Isolation rearing significantly perturbs brain metabolism in the thalamus and hippocampus.

Psychosocial neglect during childhood severely impairs both behavioral and physical health. The isolation rearing model in rodents has been employed by our group and others to study this clinical problem at a basic level. We previously showed that immediate early gene (IEG) expression in the hippocampus and medial prefrontal cortex (mPFC) is decreased in isolation-reared (IR) compared to group-reared (GR) rats. In the current study, we sought to evaluate: (1) whether these changes in IEG expression would be detected by the measurement of brain glucose metabolism using positron emission tomography (PET) with fluorodeoxyglucose (FDG) and (2) whether PET FDG could illuminate other brain regions with different glucose metabolism in IR compared to GR rats. We found that there were significant differences in FDG uptake in the hippocampus that were consistent with our findings for IEG expression (decreased mean FDG uptake in IR rats). In contrast, in the mPFC, the FDG uptake between IR and GR rats did not differ. Finally, we found decreased mean FDG uptake in the thalamus of the IR rats, a region we had not previously examined. The results suggest that PET FDG has the potential to be utilized as a biomarker of molecular changes in the hippocampus. Further, the differences found in thalamic brain FDG uptake suggest that further investigation of this region at the molecular and cellular levels may provide an important insight into the neurobiological basis of the adverse clinical outcomes found in children exposed to psychosocial deprivation.

The low frequency of clinical resistance to PDGFR inhibitors in myeloid neoplasms with abnormalities of PDGFRA might be related to the limited repertoire of possible PDGFRA kinase domain mutations in vitro.

Myeloproliferation with prominent eosinophilia is associated with rearrangements of PDGFR-A or -B. The most common rearrangement is FIP1L1-PDGFRA (FP). The majority of patients with PDGFR-rearranged myeloproliferation respond to treatment with imatinib. In contrast to BCR-ABL-positive chronic myelogenous leukemia, only few cases of imatinib resistance and mutations of the FP kinase domain have been described so far. We hypothesized that the number of critical residues mediating imatinib resistance in FP in contrast to BCR-ABL might be limited. We performed an established systematic and comprehensive in vitro resistance screen to determine the pattern and frequency of possible TKI resistance mutations in FP. We identified 27 different FP kinase domain mutations including 25 novel variants, which attenuated response to imatinib, nilotinib or sorafenib. However, the majority of these exchanges did not confer complete inhibitor resistance. At clinically achievable drug concentrations, FP/T674I predominated with imatinib, whereas with nilotinib and sorafenib, FP/D842V and the compound mutation T674I+T874I became prevalent. Our results suggest that the PDGFR kinase domain contains a limited number of residues where exchanges critically interfere with binding of and inhibition by available PDGFR kinase inhibitors at achievable concentrations, which might explain the low frequency of imatinib resistance in this patient population. In addition, these findings would help to select the appropriate second-line drug in cases of imatinib-resistant disease and may be translated to other neoplasms driven by activated forms of PDGFR-A or -B.

Transformation-mediated ductility in CuZr-based bulk metallic glasses.

Bulk metallic glasses (BMGs) generally fail in a brittle manner under uniaxial, quasistatic loading at room temperature. The lack of plastic strain is a consequence of shear softening, a phenomenon that originates from shear-induced dilation that causes plastic strain to be highly localized in shear bands. So far, significant tensile ductility has been reported only for microscopic samples of around 100 nm (ref. 4) as well as for high strain rates, and so far no mechanisms are known, which could lead to work hardening and ductility in quasistatic tension in macroscopic BMG samples. In the present work we developed CuZr-based BMGs, which polymorphically precipitate nanocrystals during tensile deformation and subsequently these nanocrystals undergo twinning. The formation of such structural heterogeneities hampers shear band generation and results in macroscopically detectable plastic strain and work hardening. The precipitation of nanocrystals and their subsequent twinning can be understood in terms of a deformation-induced softening of the instantaneous shear modulus. This unique deformation mechanism is believed to be not just limited to CuZr-based BMGs but also to promote ductility in other BMGs.

Characterization of anti-CCR5 ribozyme-transduced CD34+ hematopoietic progenitor cells in vitro and in a SCID-hu mouse model in vivo.

The cellular entry of HIV is mediated by the specific interaction of viral envelope glycoproteins with the cell-surface marker CD4 and a chemokine receptor (CCR5 or CXCR4). Individuals with a 32-base-pair (bp) deletion in the CCR5 coding region, which results in a truncated peptide, show resistance to HIV-1 infection. This suggests that the downregulation of CCR5 expression on target cells may prevent HIV infection. Therefore, ribozymes that inhibit the CCR5 expression offer a novel approach for anti-HIV gene therapy. To assess the effect of an anti-CCR5 ribozyme (R5Rbz) on macrophage differentiation, CD34+ hematopoietic progenitor cells were transduced with a retroviral vector carrying RSRbz and allowed to differentiate in the presence of appropriate cytokines. R5Rbz-transduced CD34+ cells differentiated normally into mature macrophages that carried CD14 and CD4 surface markers, expressed the anti-CCR5 ribozyme, and showed significant resistance to viral infection upon challenge with the HIV-1 BaL strain. Using an in vivo thymopoiesis model, the effect of RSRbz on stem cell differentiation into thymocytes was evaluated by reconstituting SCID-hu mice thymic grafts with ribozyme-transduced CD34+ cells. FACS analysis of cell biopsies at 4 and 6 weeks postengraftment for HLA, CD4, and CD8 markers showed comparable levels of reconstitution and similar percentages of subpopulations of thymocytes between grafts receiving R5Rbz-transduced and control CD34+ cells. RT-PCR assays demonstrated the expression of the anti-CCR5 ribozyme in CD4+, CD8+, and CD4+/CD8+ thymocyte subsets derived from RSRbz-transduced CD34+ cells. These results indicate that anti-CCR5 ribozyme can be introduced into hematopoietic stem cells without adverse effects on their subsequent lineage-specific differentiation and maturation. The expression of anti-CCR5 ribozymes in HIV-1 target cells offers a novel gene therapy strategy to control HIV infection.