Conformational properties of <Emphasis Type="Italic">ortho</Emphasis>-nitrobenzenesulfonamide in gas and crystalline phases. Intra- and intermolecular hydrogen bond

A combined gas-phase electron diffraction and quantum chemical (B3LYP/6-311+G**, B3LYP/cc-pvtz, MP2/cc-pvtz) study of molecular structure of 2-nitrobenzenesulfonamide (2-NBSA) was carried out. Quantum chemical calculations showed that 2-NBSA has four conformers, two of which are stabilized by intramolecular hydrogen bond. The latter (with the S–N bond in a close to orthogonal position around the phenyl ring and differing from each other by staggered or eclipsed positions of the N–H and S=O bonds in the SO₂NH₂ group) presented in a saturated vapor over 2-NBSA at T = 433 (3) K in commensurable amounts. Experimental internuclear distances (Ǻ) for the staggered conformer are (?): r _h1(C–H)_av. = 1.071(9), r _h1(C–C)_av. = 1.390(4), r _h1(C–S) = 1.789(8), r _h1(S=O)_av. = 1.427(6), r _h1(S–N) = 1.644(6), r _h1(N–O)_av. = 1.221(4), r _h1(C′–N) = 1.487(8), r _h1(N–H)_av. = 1.014. Calculations at B3LYP/cc-pvtz level were performed to determine the structure and the energies of the transition states between conformers. It was shown that the conformer structures of free molecule differ from those of a molecule stabilized by intermolecular hydrogen bonds in a crystal. Influence of a substituent X (X = –CH₃, –NO₂) on conformational features of the ortho-substituted benzenesulfonamide was established.     

Novel approaches to model-free analysis of lanthanide-induced shifts, targeted to the investigation of contact term behavior

Three novel equations were proposed to perform graphical model-free analysis of lanthanide-induced shifts in NMR spectra of axially symmetrical complexes within Bleaney's T(-2) expansion. Application and efficiency of these newly developed approaches were demonstrated on the example of heteroleptic triple-decker crown-phthalocyaninates (Pc)M[(15C5)(4)Pc]M(Pc), where (15C5)--15-crown-5, (Pc(2-))--phthalocyaninato-dianion, M = Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb and Y as diamagnetic reference. By construction of these equations, the proposed analytical techniques are more sensitive to variations of hyperfine coupling terms throughout lanthanide series, in comparison with previously developed approaches, becoming a valuable tool for the investigation of structural and electronic characteristics of lanthanide complexes.     

A highly reactive mononuclear non-heme manganese(IV)-oxo complex that can activate the strong C-H bonds of alkanes

A mononuclear non-heme manganese(IV)-oxo complex has been synthesized and characterized using various spectroscopic methods. The Mn(IV)-oxo complex shows high reactivity in oxidation reactions, such as C-H bond activation, oxidations of olefins, alcohols, sulfides, and aromatic compounds, and N-dealkylation. In C-H bond activation, the Mn(IV)-oxo complex can activate C-H bonds as strong as those in cyclohexane. It is proposed that C-H bond activation by the non-heme Mn(IV)-oxo complex does not occur via an oxygen-rebound mechanism. The electrophilic character of the non-heme Mn(IV)-oxo complex is demonstrated by a large negative ρ value of -4.4 in the oxidation of para-substituted thioanisoles.     

Mono- and dicarbonyl-bridged tricyclic heterocyclic acceptors: synthesis and electronic properties

A series of trialkylsilyl-substituted 2,2'-dithiophene, 4,4'-di-n-hexyl-2,2'-dithiophene, 5,5'-dithiazole, and 2,2'-diselenophene with carbonyl (2a-d) and α-dicarbonyl bridges (3a-d) were prepared from readily available dihalides, using double lithiation followed by trapping with N,N-dimethylcarbamoyl chloride or diethyl oxalate (or N,N-dimethylpiperazine-2,3-dione), respectively. Cyclic voltammetry reveals that the first half-wave reduction potentials for this series of compounds span a wide range, from -1.87 to -0.97 V vs the ferrocene/ferrocenium couple at 0 V (0.1 M (n)Bu(4)NPF(6) in THF). A significant increase of the first half-wave reduction potential (by 0.50-0.67 V) was observed on substitution of the monocarbonyl bridge with α-dicarbonyl. Adiabatic electron affinity (AEA, gas phase) trends determined via density functional theory (DFT) calculations are in good agreement with the electrochemical reduction potentials. UV-vis absorption spectra across the series show a weak absorption band in the visible range, corresponding to the HOMO→LUMO transition within a one-electron picture, followed by a more intense, high-energy transition(s). Single-crystal X-ray structural analyses reveal molecular packing features that balance the interplay of the presence of the bulky substituents, intermolecular π-stacking interactions, and S···O intermolecular contacts, all of which affect the DFT-evaluated intermolecular electronic couplings and effective charge-carrier masses for the crystals of the tricyclic cores.     

Reconfiguration graphs of shortest paths

For a graph $G$ and$a,b\in V\left(G\right)$, the shortest path reconfiguration graph of $G$ with respect to $a$ and$b$ is denoted by $S(G,a,b)$. The vertex set of $S(G,a,b)$ is the set of all shortest paths between $a$ and$b$ in $G$. Two vertices in $V\left(S(G,a,b)\right)$ are adjacent, if their corresponding paths in $G$ differ by exactly one vertex. This paper examines the properties of shortest path graphs. Results include establishing classes of graphs that appear as shortest path graphs, decompositions and sums involving shortest path graphs, and the complete classification of shortest path graphs with girth 5 or greater. We include an infinite family of well structured examples, showing that the shortest path graph of a grid graph is an induced subgraph of a lattice.     

Simultaneous determination of proteins in microstructured optical fibers supported by chemometric tools

Analytical and Bioanalytical Chemistry - A new perspective on the relevant problem—creating simple, rapid, and efficient protein sensors based on microstructured optical fibers using a simple...     

Planar Chiral Rhodium Complexes of 1,4-Benzoquinones

Diene rhodium complexes are important catalysts in modern organic synthesis. Herein, we report a new approach to such complexes with the uncommon planar chirality. The synthesis is achieved by face-selective coordination of the prochiral 2,5-disubstituted-1,4-benzoquinones (R₂-Q) with rhodium precursors containing the chiral auxiliary ligand S-salicyl-oxazoline (S-Salox). Such coordination leads to the formation of (R,R-R₂-Q)Rh(S-Salox) complexes in high yields and with exceptional diastereoselectivity (d. r.>20 : 1). Subsequent replacement of the auxiliary ligand provides various benzoquinone rhodium complexes with retention of the planar chirality. Combined theoretical and experimental studies show that due to their electron-withdrawing nature benzoquinones bind metals stronger than the related 1,4-cyclohexadiene, but weaker than other common diene ligands, such as cyclooctadiene.     

Isotopic separation of lithium ions by capillary zone electrophoresis

Separation of ⁶Li and ⁷Li isotopes by CZE was demonstrated. The BGE contained 5 mM 4‐aminopyridine, 0.9 mM oxalic acid, 0.25 mM CTAB, and 0.25% w/v Tween 20 (рН = 9.2). The running conditions were +25 kV at 30°C with indirect photometric detection at 261 nm. Under optimal experimental conditions, the analysis time was less than 21 min. Separation of Li preparations with mole fraction of ⁶Li ranging from 3.44 up to 90.38% was demonstrated.     

DIY XES—development of an inexpensive,versatile, and easy to fabricate XES analyzer and sample delivery system

The application of X-ray emission spectroscopy (XES) has grown substantially with the development of X-ray free-electron lasers, third and fourth generation synchrotron sources, and high-power benchtop sources. By providing the high X-ray flux required for XES, these sources broaden the availability and application of this method of probing electronic structure. As the number of sources increase, so does the demand for X-ray emission detection and sample delivery systems that are cost effective and customizable. Here, we present a detailed fabrication protocol for von Hamos X-ray optics and give details for a 3D-printed spectrometer design. Additionally, we outline an automated, externally triggered liquid sample delivery system that can be used to repeatedly deliver nanoliter droplets onto a plastic substrate for measurement. These systems are both low cost, efficient, and easy to recreate or modify depending on the application. A low cost multiple X-ray analyzer system enables measurement of dilute samples, whereas the sample delivery limits sample loss and reproducibly replaces spent sample with fresh sample in the same position. While both systems can be used in a wide range of applications, the design addresses several challenges associated specifically with time-resolved XES (TRXES). As an example application, we show results from TRXES measurements of photosystem II, a dilute, photoactive protein.