Investigation of Photophysical and Electrochemical Properties of Magic-Sized CdS Nanocrystals

poster abstractColloidal semiconductor nanocrystals (NCs) have been the interest of many studies over the past two decades due to their applications in device fabrication, electrocatalysts, and medical diagnostics. Recent discovery of thermodynamically stable ultra-small nanocrystals (“magic-sized”) has provided the opportunity to understand their different properties at the molecular level. Herein we present the synthesis and purification of poly(ethylene glycol) thiolate-capped magic-sized CdS nanocrystals with distinct photophysical properties. These CdS NCs overcame solubility restraints by directly transferring from aqueous to organic mediums and also showed significant increased in peak sharpness when analyzed by high-resolution MALDI-TOF-MS, which confirmed formation of (CdS)33,34 nanocrystals. The electrochemical properties of dissolved CdS nanocrystals were investigated in organic solvent/electrolyte medium by different voltammetric techniques. The nanocrystals displayed molecule-like HOMO-LUMO energy gap. The electrochemical features are strongly temperature, solvent, and capping-ligand thickness dependent. We also developed a working model of the energy level structure of the PEG-thiolate-capped (CdS)33,34 nanocrystals

Size-Dependent Optical and Electrochemical Energy Gaps Comparison of CdSe Nanolusters

poster abstractThe size-dependent optical and electronic properties of semiconductor nanocrystals have made them the focus of much research including the designing of photovoltaic devices and photocatalysts. These properties occur as a result of the phenomenon called quantum confinement. To improve the device efficiency it is important to have a better understanding of their size dependent electrochemical properties. Herein we demonstrate for the first time, a comparison of the size dependent optical properties and electrochemical energy gaps of poly(ethylene glycol) thiolate-protected ultra-small CdSe nanoclusters. The electrochemical energy gaps for various sized nanoclusters were determined from cyclic and differential pulse voltammetry in organic solvent/electrolyte medium, where large, moleculelike HOMO-LUMO energy gaps were observed. It was also found that a significant amount of charging energy is involved in the electrochemical energy gap. The effect of the thickness of the surface-pasivating ligands on the HOMO-LUMO energy gap is demonstrated and a quantized double layer (QDL) charging model presented

Synthesis of PEG-Thiolate Monolayer Protected CdSe Nanoclusters with Unique Solubility Properties

poster abstractLigands protected metal chalcogenides have shown potential applications in bionanotechnology and device fabrication due to their unique optical properties. However, most metal chalcogenides suffer from solubility problems, which hinders their applications. To overcome the solubility issue of metal chalcogenide nanoclusters, we have demonstrated the aqueous phase synthesis of polyethylene glycol thiolate (PEG-S-) protected CdSe nanoclusters for the first time. The CdSe nanoclusters displayed a first absorption peak ~430 nm, which indicated formation of magic-sized nanoclusters with possible composition of (CdSe)33,34. The PEG-thiolate protected CdSe nanoclusters demonstrated unique solubility properties. The resulting nanoclusters can easily be transferred to organic solvents from an aqueous medium by a simple solvent extraction method. The organic-phase extracted CdSe nanoclusters can readily be redispersed in a wide array of organic solvents such as CH3CN, CH2Cl2, DMF, THF, and CH3Cl. Most importantly, the CdSe nanoclusters, soluble in organic solvents, can also be redispersed in aqueous medium as well. We investigated different chain length PEGn-thiols, e.g., PEG4-SH, PEG6-SH, PEG12-SH, and PEG18-SH and found that the PEG-chain length significantly influenced the aqueous to organic phase transfer properties. Successful transfers were accomplished for PEGn-SH (n = 6, 12, 18). Future studies will be performed on the synthesis of PEG-SH stabilized various metal chalcogenide nanoclusters (CdS, CdTe, ZnS, ZnSe, and CdSe/ZnS nanoclusters)

Evaluation of bupirimate against rose powdery mildew

Bupirimate 25% Emulsifiable concentrate (EC) was evaluated for efficacy on Sphaerotheca pannosa, the causal agent of rose powdery mildew in vivo. In this experiment Bupirimate 25% EC 6 ml/L and 4 ml/L effectively reduced the powdery mildew infection over rest of the treatments and improved the flower yield. Moreover, application of Bupirimate 25% EC at the doses of 2, 4 and 6 ml/L and even at higher dose 8 ml/L did not show any phyto-toxic symptoms on rose plant. Thus, Bupirimate 25% EC may be considered as compared to other fungicides

Solvent-like ligand-coated ultrasmall cadmium selenide nanocrystals: Strong electronic coupling in a self-organized assembly

Strong inter-nanocrystal electronic coupling is a prerequisite for delocalization of exciton wave functions and high conductivity. We report 170 meV electronic coupling energy of short chain poly(ethylene glycol) thiolate-coated ultrasmall (<2.5 nm in diameter) CdSe semiconductor nanocrystals (SNCs) in solution. Cryo-transmission electron microscopy analysis showed the formation of a pearl-necklace assembly of nanocrystals in solution with regular inter-nanocrystal spacing. The electronic coupling was studied as a function of CdSe nanocrystal size where the smallest nanocrystals exhibited the largest coupling energy. The electronic coupling in spin-cast thin-film (<200 nm in thickness) of poly(ethylene glycol) thiolate-coated CdSe SNCs was studied as a function of annealing temperature, where an unprecedentedly large, ∼400 meV coupling energy was observed for 1.6 nm diameter SNCs, which were coated with a thin layer of poly(ethylene glycol) thiolates. Small-angle X-ray scattering measurements showed that CdSe SNCs maintained an order array inside the films. The strong electronic coupling of SNCs in a self-organized film could facilitate the large-scale production of highly efficient electronic materials for advanced optoelectronic device application

Исследование износа алмазных буровых долот. 4. Уравнение изнашивания

Разработан подход для исследования кинетики изнашивания алмазного долота в условиях бурения скважины. Модель учитывает дифференциальное уравнение для абразивного износа, зависимость коэффициента износа от температуры, радиальные и касательные контактные напряжения и зависимость скорости скольжения от радиальной координаты. Окончательные выражения получены в явном виде, позволяют определить износ долота в произвольный момент времени и анализировать различные факторы, влияющие на кинетику данного процесса.The approach for studying the kinetics of diamond drill bit wear in hole drilling conditions is developed. The model takes account of the differential equation for abrasive wear, the coefficient dependence upon temperature, radial and tangential thermoelastic stresses and sliding velocity. The final expressions are obtained in an explicit form, they enable to define the components of quasi-static thermoelastic stresses at a random point of time and to analyze the main factors influencing on kinetics of the given proces

Effect of prior treatments on selinexor, bortezomib, and dexamethasone in previously treated multiple myeloma

Therapeutic regimens for previously treated multiple myeloma (MM) may not provide prolonged disease control and are often complicated by significant adverse events, including peripheral neuropathy. In patients with previously treated MM in the Phase 3 BOSTON study, once weekly selinexor, once weekly bortezomib, and 40&nbsp;mg dexamethasone (XVd) demonstrated a significantly longer median progression-free survival (PFS), higher response rates, deeper responses, a trend to improved survival, and reduced incidence and severity of bortezomib-induced peripheral neuropathy when compared with standard twice weekly bortezomib and 80&nbsp;mg dexamethasone (Vd). The pre-specified analyses described here evaluated the influence of the number of prior lines of therapy, prior treatment with lenalidomide, prior proteasome inhibitor (PI) therapy, prior immunomodulatory drug therapy, and prior autologous stem cell transplant (ASCT) on the efficacy and safety of XVd compared with Vd. In this 1:1 randomized study, enrolled patients were assigned to receive once weekly oral selinexor (100&nbsp;mg) with once weekly subcutaneous bortezomib (1.3&nbsp;mg/m2) and 40&nbsp;mg per week dexamethasone (XVd) versus standard twice weekly bortezomib and 80&nbsp;mg per week dexamethasone (Vd). XVd significantly improved PFS, overall response rate, time-to-next-treatment, and showed reduced all grade and grade ≥ 2 peripheral neuropathy compared with Vd regardless of prior treatments, but the benefits of XVd over Vd were more pronounced in patients treated earlier in their disease course who had either received only one prior therapy, had never been treated with a PI, or had prior ASCT. Treatment with XVd improved outcomes as compared to Vd regardless of prior therapies as well as manageable and generally reversible adverse events. XVd was associated with clinical benefit and reduced peripheral neuropathy compared to standard Vd in previously treated MM. These results suggest that the once weekly XVd regimen may be optimally administered to patients earlier in their course of disease, as their first bortezomib-containing regimen, and in those relapsing after ASCT. Trial registration: ClinicalTrials.gov (NCT03110562). Registered 12 April 2017. https://clinicaltrials.gov/ct2/show/NCT03110562

Mitochondrial Redox Metabolism in Trypanosomatids Is Independent of Tryparedoxin Activity

Tryparedoxins (TXNs) are oxidoreductases unique to trypanosomatids (including Leishmania and Trypanosoma parasites) that transfer reducing equivalents from trypanothione, the major thiol in these organisms, to sulfur-dependent peroxidases and other dithiol proteins. The existence of a TXN within the mitochondrion of trypanosomatids, capable of driving crucial redox pathways, is considered a requisite for normal parasite metabolism. Here this concept is shown not to apply to Leishmania. First, removal of the Leishmania infantum mitochondrial TXN (LiTXN2) by gene-targeting, had no significant effect on parasite survival, even in the context of an animal infection. Second, evidence is presented that no other TXN is capable of replacing LiTXN2. In fact, although a candidate substitute for LiTXN2 (LiTXN3) was found in the genome of L. infantum, this was shown in biochemical assays to be poorly reduced by trypanothione and to be unable to reduce sulfur-containing peroxidases. Definitive conclusion that LiTXN3 cannot directly reduce proteins located within inner mitochondrial compartments was provided by analysis of its subcellular localization and membrane topology, which revealed that LiTXN3 is a tail-anchored (TA) mitochondrial outer membrane protein presenting, as characteristic of TA proteins, its N-terminal end (containing the redox-active domain) exposed to the cytosol. This manuscript further proposes the separation of trypanosomatid TXN sequences into two classes and this is supported by phylogenetic analysis: i) class I, encoding active TXNs, and ii) class II, coding for TA proteins unlikely to function as TXNs. Trypanosoma possess only two TXNs, one belonging to class I (which is cytosolic) and the other to class II. Thus, as demonstrated for Leishmania, the mitochondrial redox metabolism in Trypanosoma may also be independent of TXN activity. The major implication of these findings is that mitochondrial functions previously thought to depend on the provision of electrons by a TXN enzyme must proceed differently

Leishmania Mitochondrial Peroxiredoxin Plays a Crucial Peroxidase-Unrelated Role during Infection: Insight into Its Novel Chaperone Activity

Two-cysteine peroxiredoxins are ubiquitous peroxidases that play various functions in cells. In Leishmania and related trypanosomatids, which lack catalase and selenium-glutathione peroxidases, the discovery of this family of enzymes provided the molecular basis for peroxide removal in these organisms. In this report the functional relevance of one of such enzymes, the mitochondrial 2-Cys peroxiredoxin (mTXNPx), was investigated along the Leishmania infantum life cycle. mTXNPx null mutants (mtxnpx−) produced by a gene replacement strategy, while indistinguishable from wild type promastigotes, were found unable to thrive in a murine model of infection. Unexpectedly, however, the avirulent phenotype of mtxnpx− was not due to lack of the peroxidase activity of mTXNPx as these behaved like controls when exposed to oxidants added exogenously or generated by macrophages during phagocytosis ex vivo. In line with this, mtxnpx− were also avirulent when inoculated into murine hosts unable to mount an effective oxidative phagocyte response (B6.p47phox−/− and B6.RAG2−/− IFN-γ−/− mice). Definitive conclusion that the peroxidase activity of mTXNPx is not required for parasite survival in mice was obtained by showing that a peroxidase-inactive version of this protein was competent in rescuing the non-infective phenotype of mtxnpx−. A novel function is thus proposed for mTXNPx, that of a molecular chaperone, which may explain the impaired infectivity of the null mutants. This premise is based on the observation that the enzyme is able to suppress the thermal aggregation of citrate synthase in vitro. Also, mtxnpx− were more sensitive than controls to a temperature shift from 25°C to 37°C, a phenotype reminiscent of organisms lacking specific chaperone genes. Collectively, the findings reported here change the paradigm which regards all trypanosomatid 2-Cys peroxiredoxins as peroxide-eliminating devices. Moreover, they demonstrate, for the first time, that these 2-Cys peroxiredoxins can be determinant for pathogenicity independently of their peroxidase activity