Highly Oriented Pyrolytic Graphite as a Platform for Atomic Absorption Spectrometry

Compared to pyrolytic graphite (PG) and pyrolytically coated polycrystalline graphite (PCPG), which are commonly employed substrates for graphite furnace atomic absorption spectrometry (GFAAS), highly oriented pyrolytic graphite (HOPG) is characterized by a high degree ofc-axis alignment with relatively few active sites and imperfections present on the surface. The usefulness of HOPG and commercial PG platforms for the determination of lead, copper, and aluminum by GFAAS was compared. Qualitative comparison of the absorption profiles and temperature optimizations suggest that lead, copper with a chemical modifier (palladium), and aluminum interact similarly with the two graphite substrates, while copper without a modifier interacts less strongly with HOPG than with PG. These results are in agreement with previous studies that have demonstrated that copper interacts strongly with PG and PCPG. HOPG and PG were employed for the determination of a pine needles standard reference material (SRM) and Fraser fir (Abies fraseri) samples. The analyses of the SRM gave good agreement with the certified value using both substrates, and comparable values were obtained for the samples. These results suggest that HOPG may be useful as a model for PG or PCPG when techniques such as scanning tunneling microscopy that require a high degree ofc-axis alignment are employed.     

Zur oxidativen Addition von 1-Halogenalk-1-inen – Synthese und Struktur von Phenylalkinylpalladium-Komplexen

On the Oxidative Addition of 1-Halogenalk-1-ynes – Synthesis and Structure of Phenylalkynylpalladium Complexes [Pd(PPh₃)₄] ( 2 ) reacts with IC≡CPh and ClC≡CPh in the sense of an oxidative addition to give trans-[Pd(C≡CPh)X(PPh₃)₂] (X = I: 3 a , X = Cl: 3 b ). As side products trans-[PdX₂(PPh₃)₂] (X = I: 4 a , X = Cl: 4 b ; < 10%) and PhC≡C–C≡CPh ( 5 ; X = I: ca 30%, X = Cl: < 4%) are formed. 3 a and 3 b were characterized by NMR (¹H, ¹³C, ³¹P) and IR spectroscopies as well as by X-ray single-crystal structure analyses. In the crystals of 3 a and 3 b isolated molecules were found. The Pd–C≡C–Ph unit is linear in 3 a and approximately linear in 3 b [Pd–C≡C 174.2(6)°, C≡C–C 179,0(7)°].     

Study of methanetriol decomposition mechanisms

Using ab initio HF/6–31G** and MP2/6–31G** calculations alternative reactions HC(OH)₃ → HCO₂H + H₂O and HC(OH)₃ + H₂O → HCO₂H + 2H₂O are investigated and the results are compared with relevant PM3, HF/3–21G, and HF/6–31G data. Reactant and product complexes as well as transition states are located on corresponding potential energy surfaces. © 1996 John Wiley & Sons, Inc.     

A Surfactant Enables Efficient Membrane Spanning by Non-Aggregating DNA-Based Ion Channels

DNA nanotechnology makes use of hydrophobically modified constructs to create synthetic membrane protein mimics. However, nucleic acid structures exhibit poor insertion efficiency, leading to a low activity of membrane-spanning DNA protein mimics. It is suggested that non-ionic surfactants improve insertion efficiency, partly by disrupting hydrophobicity-mediated clusters. Here, we employed confocal microscopy and single-molecule transmembrane current measurements to assess the effects of the non-ionic surfactant octylpolyoxyethylene (oPOE) on the clustering behavior and membrane activity of cholesterol-modified DNA nanostructures. Our findings uncover the role of aggregation in preventing bilayer interactions of hydrophobically decorated constructs, and we highlight that premixing DNA structures with the surfactant does not disrupt the cholesterol-mediated aggregates. However, we observed the surfactant’s strong insertion-facilitating effect, particularly when introduced to the sample separately from DNA. Critically, we report a highly efficient membrane-spanning DNA construct from combining a non-aggregating design with the addition of the oPOE surfactant.     

A New Oxadiazole-Based Topsentin Derivative Modulates Cyclin-Dependent Kinase 1 Expression and Exerts Cytotoxic Effects on Pancreatic Cancer Cells

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal form of cancer characterized by drug resistance, urging new therapeutic strategies. In recent years, protein kinases have emerged as promising pharmacological targets for the treatment of several solid and hematological tumors. Interestingly, cyclin-dependent kinase 1 (CDK1) is overexpressed in PDAC tissues and has been correlated to the aggressive nature of these tumors because of its key role in cell cycle progression and resistance to the induction of apoptosis. For these reasons, CDK1 is one of the main causes of chemoresistance, representing a promising pharmacological target. In this study, we report the synthesis of new 1,2,4-oxadiazole compounds and evaluate their ability to inhibit the cell growth of PATU-T, Hs766T, and HPAF-II cell lines and a primary PDAC cell culture (PDAC3). Compound 6b was the most active compound, with IC₅₀ values ranging from 5.7 to 10.7 µM. Molecular docking of 6b into the active site of CDK1 showed the ability of the compound to interact effectively with the adenosine triphosphate binding pocket. Therefore, we assessed its ability to induce apoptosis (which increased 1.5- and 2-fold in PATU-T and PDAC3 cells, respectively) and to inhibit CDK1 expression, which was reduced to 45% in Hs766T. Lastly, compound 6b passed the ADME prediction, showing good pharmacokinetic parameters. These data demonstrate that 6b displays cytotoxic activity, induces apoptosis, and targets CDK1, supporting further studies for the development of similar compounds against PDAC.     

Cichoń’s diagram for uncountable cardinals

We develop a version of Cichoń’s diagram for cardinal invariants on the generalized Cantor space 2 ^κ or the generalized Baire space κ ^κ , where κ is an uncountable regular cardinal. For strongly inaccessible κ, many of the ZFC-results about the order relationship of the cardinal invariants which hold for ω generalize; for example, we obtain a natural generalization of the Bartoszyński–Raisonnier–Stern Theorem. We also prove a number of independence results, both with < κ-support iterations and κ-support iterations and products, showing that we consistently have strict inequality between some of the cardinal invariants.     

Fluorinated aminooxazolines. Synthesis and properties

4-Amino-2,2,5,5-tetrakis(trifluoromethyl)-3-oxazoline ( 3a ) was prepared from the reaction of sodium cyanide with hexafluoroacetone and hexafluoroacetone imine, and from the reaction of hexafluoroacetone cyanohydrin with the imine. Several other oxazolines were also prepared by related reactions of other fluoroketones and imines. The proton nmr spectrum of an ¹⁵N-labeled sample of 3a shows that it exists in solution primarily as the amino tautomer and not as the imino tautomer 3b . Comparison of 3a with the closely related, pharmacologically active 4-amino-2,2,5,5-tetrakis(trifluoromethyl)-3-imidazoline ( 2 ) has shown large differences in ΔH of complex formation and reactivity with electrophilic reagents.     

Development of an analytical procedure for the determination of emerging and priority organic pollutants in leafy vegetables by pressurized solvent extraction followed by GC–MS determination

A new multiresidue method for the determination of 13 emerging and priority pollutants in lettuce, including pesticides, pharmaceuticals, personal care products, polycyclic aromatic hydrocarbons (PAHs), and phenolic estrogens, has been developed using matrix solid-phase dispersion combined to pressurized fluid extraction (PFE) followed by gas chromatography coupled to mass spectrometry determination. A sequential optimization strategy based on solvent optimization first, followed by experimental design, was performed in order to maximize target analyte extraction with the aid of response surface methodology. Firstly, a full factorial design was applied to choose the significant variables in PFE; extraction time and temperature were found to have the biggest overall effect on response for most of analytes. They were later optimized performing a central composite design and the variable response of these factors was modeled for all analytes. It was found that marked differences in physicochemical nature exerted a strong influence on extraction conditions and yield. Therefore, the effect of parameters on the response was rather different for some compounds. To overcome this conflicting behavior, a multiple response simultaneous optimization was applied using the desirability function to achieve global optimal operating conditions. The optimal conditions were attained at 13.5 min (two extraction cycles) and 104 °C in the PFE by using hexane acetone mixture (1:1). Limit of detection and limit of quantitation values were found to be between 6.6 and 58 and 7.6 and 61.7 μg kg⁻¹, respectively.     

The insertion of acetylene into the formal ruthenium-phosphorus bonds of closo-[Ru4(μ4-PPh)2(μ2-CO)(CO)10. Crystal structure of [Ru4(μ4-PPh){μ4-η-P(Ph)CHCH}(μ2-CO)(CO)10]

Treatment of closo-[Ru₄(μ₄-PPh)₂(μ₂-CO)(CO)₁₀] with acetylene under ambient conditions leads to the insertion of the acetylene into the skeletal framework of the cluster and the formation of [Ru₄(μ₄-PPh){μ₄-η³-P(Ph)CHCH}(μ₂-CO)(CO)₁₀], the structure of which has been determined X-ray crystallographically.     

Information-Theoretic Features of Many Fermion Systems: An Exploration Based on Exactly Solvable Models

Finite quantum many fermion systems are essential for our current understanding of Nature. They are at the core of molecular, atomic, and nuclear physics. In recent years, the application of information and complexity measures to the study of diverse types of many-fermion systems has opened a line of research that elucidates new aspects of the structure and behavior of this class of physical systems. In this work we explore the main features of information and information-based complexity indicators in exactly soluble many-fermion models of the Lipkin kind. Models of this kind have been extremely useful in shedding light on the intricacies of quantum many body physics. Models of the Lipkin kind play, for finite systems, a role similar to the one played by the celebrated Hubbard model of solid state physics. We consider two many fermion systems and show how their differences can be best appreciated by recourse to information theoretic tools. We appeal to information measures as tools to compare the structural details of different fermion systems. We will discover that few fermion systems are endowed by a much larger complexity-degree than many fermion ones. The same happens with the coupling-constants strengths. Complexity augments as they decrease, without reaching zero. Also, the behavior of the two lowest lying energy states are crucial in evaluating the system’s complexity.