Finite lifetime broadening of calculated X‐ray absorption spectra: possible artefacts close to the edge

X‐ray absorption spectra calculated within an effective one‐electron approach have to be broadened to account for the finite lifetime of the core hole. For methods based on Green's function this can be achieved either by adding a small imaginary part to the energy or by convoluting the spectra on the real axis with a Lorentzian. By analyzing the Fe K‐ and L_2,3‐edge spectra it is demonstrated that these procedures lead to identical results only for energies higher than a few core‐level widths above the absorption edge. For energies close to the edge, spurious spectral features may appear if too much weight is put on broadening via the imaginary energy component. Special care should be taken for dichroic spectra at edges which comprise several exchange‐split core levels, such as the L₃‐edge of 3d transition metals.     

Seasonal variation in alkaloid composition and antiproliferative activity of <Emphasis Type="Italic">Stylophorum lasiocarpum</Emphasis> (Oliv.) Fedde

Stylophorum lasiocarpum (Oliv.) Fedde (Papaveraceae) belongs to traditional Chinese medicine herbs but there was minimal information on the content of alkaloids in this plant. Extracts from the aerial part and roots were examined by liquid chromatography with UV and mass spectrometric detection, with nineteen alkaloids identified. Changes in alkaloid content over the entire vegetation period of a one- and two-year old plant were studied. The protoberberine alkaloids, coptisine and stylopine, were found to be the main substances in extracts of the aerial part irrespective of the plant’s age and time of harvest. Variable amounts of protopine, sanguinarine, chelerythrine, chelirubine, macarpine, chelilutine and berberine were also recorded in the aerial part. The roots contained significantly larger quantities of all alkaloids than the aerial part with the levels of most alkaloids varying from May to October, peaking in the middle of the vegetation period. Coptisine was the dominant alkaloid in all samples. The antiproliferative activities of the root extract and of seven individual alkaloids were tested on A375 human malignant melanoma cells. The significant dose-dependent toxicity of the root extract was attributed largely to the quaternary benzo[c]phenanthridine alkaloids, macarpine and sanguinarine.     

Mesomeric Effects of Graphene Modified with Diazonium Salts: Substituent Type and Position Influence its Properties

In the last decade, graphene and graphene derivatives have become some of the most intensively studied materials. Tuning of the electronic and electrochemical properties of graphene is of paramount importance. In this study, six diazonium‐modified graphenes containing different functional groups according to the diazonium salt precursor were investigated. These diazonium moieties have a strong mesomeric (resonance) effect and act as either electron‐donating or ‐withdrawing species. Different graphene precursors, such as thermally and chemically reduced graphenes were studied. All the products were characterized in detail by elemental combustion analysis, FTIR spectroscopy, Raman spectroscopy, high‐resolution X‐ray photoelectron spectroscopy (XPS), and cyclic voltammetry. Resistivity and zeta potential measurements were consistent with theoretical (DFT) calculations. The results show that chemical modification of graphene by diazotation strongly influences its properties, creating a huge application potential in microelectronics, energy storage and conversion devices, and electrocatalysis.     

Spheroid cultivation of HT-29 carcinoma cell line in liquid marbles

The ability to simulate the 3D structure of a human body is essential to increase the efficiency of drug development. In vivo conditions are significantly different in comparison to in vitro conditions. A standardly used cell monolayer on tissue culture plastic (2D cell culture) is not sufficient to simulate the transfer phenomena occurring in living organisms, therefore, cell growth in a 3D space is desired. Drug absorption, distribution, metabolism, excretion and toxicity could be tested on 3D cell aggregates called spheroids, decrease the use of animal models and accelerate the drug development. In this work, the formation of spheroids from HT-29 human colorectal adenocarcinoma cells was successfully achieved by means of the so-called liquid marbles, which are liquid droplets encapsulated by a hydrophobic powder. During the cultivation in the medium inside the liquid marbles, cells spontaneously formed spherical agglomerates (spheroids) without the need of any supporting scaffold. The study focused on the influence of different parameters—namely liquid marble volume, seeding cell density and time of cultivation—on the final yield and quality of spheroids. This work has shown that using liquid marbles as microbioreactors is a suitable method for the cultivation of HT-29 cells in the form of spheroids.     

Spontaneous Resolution of an Electron‐Deficient Tetrahedral Fe4L4 cage

A highly electron‐deficient C₃‐symmetric tris(bipyridyl) ligand was prepared in four steps and used for the coordination of Fe(OTf)₂, thereby resulting in the homochiral assembly of a new family of robust tetrahedral M₄L₄ cages. This homochiral T‐symmetric cage containing a relatively large cavity of 330 ų is capable of encapsulating an anionic guest, as was determined by mass spectrometry, ¹⁹F NMR spectroscopy, and finally shown from its crystal structure. Moreover, crystallization of the cage from CH₃CN led to crystals containing both (ΔΔΔΔ and ΛΛΛΛ) enantiomers, while crystallization from CH₃OH resulted in crystals containing only the right‐handed (ΔΔΔΔ) cage. The difference in the crystal packing of the two crystal structures is discussed and a feasible explanation for the unique phenomenon among supramolecular cages—spontaneous resolution—is given.     

Synthesis and Cytotoxic and Antiviral Activity Profiling of All-Four Isomeric Series of Pyrido-Fused 7-Deazapurine Ribonucleosides

All four isomeric series of novel 4-substituted pyrido-fused 7-deazapurine ribonucleosides possessing the pyridine nitrogen atom at different positions were designed and synthesized. The total synthesis of each isomeric fused heterocycle through multistep heterocyclization was followed by glycosylation and derivatization at position 4 by cross-coupling reactions or nucleophilic substitutions. All compounds were tested for cytostatic and antiviral activity. The most active were pyrido[4′,3′:4,5]pyrimidine nucleosides bearing MeO, NH₂, MeS, or CH₃ groups at position 4, which showed submicromolar cytotoxic effects and good selectivity for cancer cells. The mechanism involved activation by phosphorylation and incorporation to DNA where the presence of the modified ribonucleosides causes double-strand breaks and apoptosis.     

Flexibility of planar graphs of girth at least six

Let $G$ be a planar graph with a list assignment $L$. Suppose a preferred color is given for some of the vertices. We prove that if $G$ has girth at least six and all lists have size at least three, then there exists an $L$-coloring respecting at least a constant fraction of the preferences.     

A note on the transcendence of infinite products

The paper deals with several criteria for the transcendence of infinite products of the form $\prod\limits_{n = 1}^\infty {[{b_n}{a^{{a_n}}}]/{b_n}{a^{{a_n}}}} $ where α > 1 is a positive algebraic number having a conjugate α* such that α ≠ |α*| > 1, {a _n } _n=1 ^∞ and {b _n } _n=1 ^∞ are two sequences of positive integers with some specific conditions. The proofs are based on the recent theorem of Corvaja and Zannier which relies on the Subspace Theorem (P.Corvaja, U.Zannier: On the rational approximation to the powers of an algebraic number: solution of two problems of Mahler and Mend`es France, Acta Math. 193, (2004), 175–191).     

Quantitative Dunford–Pettis property

We investigate possible quantifications of the Dunford–Pettis property. We show, in particular, that the Dunford–Pettis property is automatically quantitative in a sense. Further, there are two incomparable mutually dual stronger versions of a quantitative Dunford–Pettis property. We prove that L¹$L^1$ spaces and C(K)$C\left(K\right)$ spaces possess both of them. We also show that several natural measures of weak non-compactness are equal in L¹$L^1$ spaces.