Electrogenerated chemiluminescence in systems with tetraphenylborate anion as a co-reactant

The study of electrogenerated chemiluminescence (ECL) in aqueous and non-aqueous media with tetraphenylborate anion as a co-reactant is reported. The obtained results indicate that tetraphenylborate acts according to an oxidative reduction scheme and forms a strong reducer after being homogeneously oxidized by a radical cation or dication of luminophore. Spectral measurements prove that light emission originates from the luminophore present in solution and practically no emission occurs when only tetraphenylborate ion is oxidized at the electrode. Since the tetraphenylborate ion is a well known analytical reactant and precipitates a number of metal and organic cations its electrochemiluminescent detection can be used for their assay. It can also be applied as an efficient co-reactant for electrogenerated chemiluminescence excitation both in aqueous and non-aqueous media.     

Theoretical Study of Sulfines and Sulfenes. Similarities and Differences in Structure and Reactivity. A New View

Abstract.

Sulfenes and sulfines contrary to usual opinion can not be considered as structure-similar compounds.     

Ab initio theory of the scattering-independent anomalous Hall effect

We report on first-principles calculations of the side-jump contribution to the anomalous Hall conductivity (AHC) directly from the electronic structure of a perfect crystal. We implemented our approach for a short-range scattering disorder model within the density functional theory and computed the full scattering-independent AHC in elemental bcc Fe, hcp Co, fcc Ni, and L1(0) FePd and FePt alloys. The full AHC thus calculated agrees systematically with experiment to a degree unattainable so far, correctly capturing the previously missing elements of side-jump contributions, hence paving the way to a truly predictive theory of the anomalous Hall effect and turning it from a characterization tool to a probing tool of multiband complex electronic band structures.     

Switching currents limited by single phase slips in one-dimensional superconducting Al nanowires

An aluminum nanowire switches from superconducting to normal as the current is increased in an upsweep. The switching current (I(s)) averaged over upsweeps approximately follows the depairing critical current (I(c)) but falls below it. Fluctuations in I(s) exhibit three distinct regions of behaviors and are nonmonotonic in temperature: saturation well below the critical temperature T(c), an increase as T(2/3) at intermediate temperatures, and a rapid decrease close to T(c). Heat dissipation analysis indicates that a single phase slip is able to trigger switching at low and intermediate temperatures, whereby the T(2/3) dependence arises from the thermal activation of a phase slip, while saturation at low temperatures provides striking evidence that the phase slips by macroscopic quantum tunneling.     

NIR‐Sensitized Activated Photoreaction between Cyanines and Oxime Esters: Free‐Radical Photopolymerization

Cyanines comprising either a benzo[e]‐ or benzo[c,d]indolium core facilitate initiation of radical photopolymerization combined with high power NIR‐LED prototypes emitting at 805 nm, 860 nm, or 870 nm, while different oxime esters function as radical coinitiators. Radical photopolymerization followed an initiation mechanism based on the participation of excited states, requiring additional thermal energy to overcome an existing intrinsic activation barrier. Heat released by nonradiative deactivation of the sensitizer favored the system, even under conditions where a thermally activated photoinduced electron transfer controls the reaction protocol. The heat generated internally by the NIR sensitizer promotes generation of the initiating reactive radicals. Sensitizers with a barbiturate group at the meso‐position preferred to bleach directly, while sensitizers carrying a cyclopentene moiety unexpectedly initiated the photosensitized mechanism.     

Double‐Decker Paramagnetic {(K)(H3Hhp)2}⋅2− Radical Dianions Comprising Two [30]Trithia‐2,3,5,10,12,13,15,20,22,23,25,30‐Dodecaazahexaphyrins and a Potassium Ion

Reduction of free‐base [30]trithia‐2,3,5,10,12,13,15,20,22,23,25,30‐dodecaazahexaphyrin (H₃Hhp) yields {cryptand[2.2.2](K)}₂{(K)(H₃Hhp)₂}?4C₆H₄Cl₂ ( 1 ) containing double‐decker {(K)(H₃Hhp)₂} ^{? 2?} radical dianions, whose structure was elucidated using X‐ray diffraction. Potassium ion forms 12 short (K⁺)???N(H₃Hhp) contacts with two H₃Hhp macrocycles in the 3.048–3.157 Å range. Dianions have S=1/2 spin state manifesting an effective magnetic moment of 1.64 μ_B at 300 K and a narrow Lorentzian electron paramagnetic resonance signal. Quantum chemical calculations support the ionic nature of the (K⁺)‐N(H₃Hhp) interactions and the nearly equal distribution of the ?1.5 charge over each macrocycle. H₃Hhp takes the role of an aza‐crown ether in free‐base reduced state and forms a new type of double‐decker complex.     

A procedure for meaningful unsupervised clustering and its application for solvent classification

Artificial neural networks have proven to be a powerful tool for solving classification problems. Some difficulties still need to be overcome for their successful application to chemical data. The use of supervised neural networks implies the initial distribution of patterns between the pre-determined classes, while attribution of objects to the classes may be uncertain. Unsupervised neural networks are free from this problem, but do not always reveal the real structure of data. Classification algorithms which do not require a priori information about the distribution of patterns between the pre-determined classes and provide meaningful results are of special interest. This paper presents an approach based on the combination of Kohonen and probabilistic networks which enables the determination of the number of classes and the reliable classification of objects. This is illustrated for a set of 76 solvents based on nine characteristics. The resulting classification is chemically interpretable. The approach proved to be also applicable in a different field, namely in examining the solubility of C₆₀ fullerene. The solvents belonging to the same group demonstrate similar abilities to dissolve C₆₀. This makes it possible to estimate the solubility of fullerenes in solvents for which there are no experimental data      

Selective Introduction of Sulfhydryl Groups into Recombinant Proteins for Study of Protein–Protein Interactions

In the present work, we proposed to create special sorbents for the study of protein–protein interactions, based on the fixation of cysteine-inserted beta-casein mutants with thiol-Sepharose resin. As a model system, we used bovine beta-casein, which belongs to the family of intrinsically unstructured proteins. Insertion of distal cysteines into the unfolded protein was not found to significantly change beta-casein properties. An amphiphilic beta-casein molecule has one hydrophilic domain and one hydrophobic domain placed on the N- and C-terminus, thus enabling one to exploit its capacity to engage in different types of intermolecular interactions. Two different casein-Sepharose sorbents incorporating either C-4 or C-208 beta-casein mutants bound to thiol-Sepharose were produced, exposing the hydrophobic domain in the case of the C-4 and the hydrophilic domain in the case of the C-208 mutant, respectively. The results obtained using the proposed sorbents with native beta-casein, another partially unfolded protein prion, and an oligomeric globular glyceraldehyde-3-phosphate dehydrogenase were found to be consistent with the data obtained by ELISA on free protein–protein complexes. Thus, Sepharose modified with various proteins is suitable for isolation of proteins interacting with the chromatographic phase bound partners from multicomponent systems such as milk. The obtained results allow the proposing of a fast and convenient method to be used for isolation of proteins, determination of protein-interacting partners, and the study of multi-protein complexes.