The protection of Nifedipin from photodegradation due to complex formation with β-cyclodextrin

The inclusion complex β-cyclodextrin:nifedipin was prepared in solid state by coprecipitation with 1:1 mol ratio. The structure of the obtained complex and nifedipin was characterized by use of X-ray diffraction (XR), infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and differential scanning calorimetry (DSC) methods. The photodegradation of nifedipin and the β-cyclodextrin:nifedipin inclusion complex in solid state was monitored under natural daylight by infrared spectroscopy, whereby the free nifedipin degraded four to five times faster than the complexed nifedipin. The photodegradation products of both free and complexed nifedipin, formed during irradiation at 350 nm (with corresponding energy flux of 18 W m⁻²) were monitored by liquid chromatography during various time intervals. The speed of formation of nitroso- and nitro-phenyl derivatives by nifedipin irradiation was significantly higher than those of complexed nifedipin irradiation, which indicates its increased photostability in the inclusion complex. The effect on this property is significant because it contributes both to the improvement of the therapeutic effect of nifedipin and to the safer application thereof.      

Quantum phase slips in superconducting wires with weak inhomogeneities

Quantum phase slips are traditionally considered in diffusive superconducting wires which are assumed homogeneous. We present a definite estimate for the amplitude of phase slips that occur at a weak inhomogeneity in the wire where local resistivity is slightly increased. We model such a weak link as a general coherent conductor and show that the amplitude is dominated by the topological part of the action. We argue that such weak links occur naturally in apparently homogeneous wires and adjust the estimate to that case. The fabrication of an artificial weak link would localize phase slips and facilitate a better control of the phase-slip amplitude.     

Fluorescent Isoindole Crosslink (FlICk) Chemistry: A Rapid,User‐friendly Stapling Reaction

The stabilization of peptide secondary structure via stapling is a ubiquitous goal for creating new probes, imaging agents, and drugs. Inspired by indole‐derived crosslinks found in natural peptide toxins, we employed ortho‐phthalaldehydes to create isoindole staples, thus transforming inactive linear and monocyclic precursors into bioactive monocyclic and bicyclic products. Mild, metal‐free conditions give an array of macrocyclic α‐melanocyte‐stimulating hormone (α‐MSH) derivatives, of which several isoindole‐stapled α‐MSH analogues (K_i≈1 nm ) are found to be as potent as α‐MSH. Analogously, late‐stage intra‐annular isoindole stapling furnished a bicyclic peptide mimic of α‐amanitin that is cytotoxic to CHO cells (IC₅₀=70 μm ). Given its user‐friendliness, we have termed this approach FlICk (fluorescent isoindole crosslink) chemistry.     

Signal Propagation in Multi‐Layer DNAzyme Cascades Using Structured Chimeric Substrates

Signal propagation through enzyme cascades is a critical component of information processing in cellular systems. Although such systems have potential as biomolecular computing tools, rational design of synthetic protein networks remains infeasible. DNA strands with catalytic activity (DNAzymes) are an attractive alternative, enabling rational cascade design through predictable base‐pair hybridization principles. Multi‐layered DNAzyme signaling and logic cascades are now reported. Signaling between DNAzymes was achieved using a structured chimeric substrate (SCS) that releases a downstream activator after cleavage by an upstream DNAzyme. The SCS can be activated by various upstream DNAzymes, can be coupled to DNA strand‐displacement devices, and is highly resistant to interference from background DNA. This work enables the rational design of synthetic DNAzyme regulatory networks, with potential applications in biomolecular computing, biodetection, and autonomous theranostics.     

The investigation of cold sintering mechanism of iron powder compact

Abstract

In this paper the mechanism of cold sintering of iron powder compacts has been investigated. In the wide range of pressure between 4…5 and 12…12, 5 GPa, a considerable changes of properties, such as electrical resistivity, thermo-electric force, coercive force, changes in X-ray diffraction structures as well as changes of thermal properities (obtained by DTA analysis), have been determined.     

Elementary events of electron transfer in a voltage-driven quantum point contact

We find that the statistics of electron transfer in a coherent quantum point contact driven by an arbitrary time-dependent voltage is composed of elementary events of two kinds: unidirectional one-electron transfers determining the average current and bidirectional two-electron processes contributing to the noise only. This result pertains at vanishing temperature while the extended Keldysh-Green's function formalism in use also enables the systematic calculation of the higher-order current correlators at finite temperatures.     

Elucidating Solvent Effects on Strong Intramolecular Hydrogen Bond: DFT-MD Study of Dibenzoylmethane in Methanol Solution

The dynamic aspect of solvation plays a crucial role in determining properties of strong intramolecular hydrogen bonds since solvent fluctuations modify instantaneous hydrogen-bonded proton transfer barriers. Previous studies pointed out that solvent-solute interactions in the first solvation shell govern the position of the proton but the ability of the electric field due to other solvent molecules to localize the proton remains an important issue. In this work, we examine the structure of the O−H⋅⋅⋅O intramolecular hydrogen bond of dibenzoylmethane in methanol solution by employing density functional theory-based molecular dynamics and quantum chemical calculations. Our computations showed that homogeneous electric fields with intensities corresponding to those found in polar solvents are able to considerably alter the proton transfer barrier height in the gas phase. In methanol solution, the proton position is correlated with the difference in electrostatic potentials on the oxygen atoms of dibenzoylmethane even when dibenzoylmethane-methanol hydrogen bonding is lacking. On a timescale of our simulation, the hydrogen bonding and solvent electrostatics tend to localize the proton on different oxygen atoms. These findings provide an insight into the importance of the solvent electric field on the structure of a strong intramolecular hydrogen bond.     

Fluorescent Isoindole Crosslink (FlICk) Chemistry: A Rapid,User‐friendly Stapling Reaction

The stabilization of peptide secondary structure via stapling is a ubiquitous goal for creating new probes, imaging agents, and drugs. Inspired by indole‐derived crosslinks found in natural peptide toxins, we employed ortho‐phthalaldehydes to create isoindole staples, thus transforming inactive linear and monocyclic precursors into bioactive monocyclic and bicyclic products. Mild, metal‐free conditions give an array of macrocyclic α‐melanocyte‐stimulating hormone (α‐MSH) derivatives, of which several isoindole‐stapled α‐MSH analogues (K_i≈1 nm ) are found to be as potent as α‐MSH. Analogously, late‐stage intra‐annular isoindole stapling furnished a bicyclic peptide mimic of α‐amanitin that is cytotoxic to CHO cells (IC₅₀=70 μm ). Given its user‐friendliness, we have termed this approach FlICk (fluorescent isoindole crosslink) chemistry.