Escape of Brownian particles and stochastic resonance with low-temperature quantum fluctuations

In this paper, we investigate the escape of Brownian particles and stochastic resonance (SR) with low-temperatures quantum fluctuations by using the quantum Smoluchowski equations at low-temperature. Two specific examples have been considered: one is the example of bistable system, and the other is the example of metastable system. The explicit expressions of the mean-first passage time (MFPT) and signal-to-noise ratio (SNR) for both specific examples are obtained, respectively. Based on the numerical compu...     

Size-dependent electron chemical potential: Effect on particle charging

Electrostatic charging of particles of identical composition, but different sizes, is a poorly understood phenomenon that may be of importance in dust storms, generation of lightning, numerous technological applications involving solid particulates, and in the agglomeration of lunar dust and inter-stellar dust clouds. We show that under optical excitation, the relative magnitude of surface to volume de-excitation gives size-dependent electron and hole concentrations. The consequent differences in chemical potentials can lead to charge transfer between particles of different size. The direction of charge transfer, from large to small or vice versa, depends critically on the properties of the materials.     

Synthesis and Rearrangement of P‐Nitroxyl‐Substituted PIII and PV Phosphanes: A Combined Experimental and Theoretical Case Study

Low‐temperature generation of P‐nitroxyl phosphane 2 (Ph₂POTEMP), which was obtained by the reaction of Ph₂PH ( 1 ) with two equivalents of TEMPO, is presented. Upon warming, phosphane 2 decomposed to give P‐nitroxyl phosphane P‐oxide 3 (Ph₂P(O)OTEMP) as one of the final products. This facile synthetic protocol also enabled access to P‐sulfide and P‐borane derivatives 7 and 13 , respectively, by using Ph₂P(S)H ( 6 ) or Ph₂P(BH₃)H ( 11 ) and TEMPO. Phosphane sulfide 7 revealed a rearrangement to phosphane oxide 8 (Ph₂P(O)STEMP) in CDCl₃ at ambient temperature, whereas in THF, thermal decomposition of sulfide 7 yielded salt 10 ([TEMP‐H₂][Ph₂P(S)O]). As well as EPR and detailed NMR kinetic studies, indepth theoretical studies provided an insight into the reaction pathways and spin‐density distributions of the reactive intermediates.     

A Quantitative Determination of the Interaction of Pentamethylenetetrazole with the Sodium Ion by Sodium-23 NMR

The importance of the sodium ion transport in biological systems is well known. Numerous studies have dealt with compounds which affect ion transport across membrane systems. However, the mechanism of ion transport across the membrane is still not clear. Hence it is of interest to investigate the interaction of the sodium ion with biologically active compounds in a system where the complex membrane is absent. Such a method of investigation must be able to detect very weak interactions. Sodium-23 nuclear magnetic resonance fits well into this classification. This technique has been used by others¹ and by us² to investigate electrolyte solutions and biological or model systems. We have been interested in the chemistry of cyclopolymethy-lenetetrazoles for some time.³ These compounds are characterized by their strong stimulating action on the central nervous system and, in     

The Electronic Nature of the 1,4‐β‐Glycosidic Bond and Its Chemical Environment: DFT Insights into Cellulose Chemistry

The molecular understanding of the chemistry of 1,4‐β‐glucans is essential for designing new approaches to the conversion of cellulose into platform chemicals and biofuels. In this endeavor, much attention has been paid to the role of hydrogen bonding occurring in the cellulose structure. So far, however, there has been little discussion about the implications of the electronic nature of the 1,4‐β‐glycosidic bond and its chemical environment for the activation of 1,4‐β‐glucans toward acid‐catalyzed hydrolysis. This report sheds light on these central issues and addresses their influence on the acid hydrolysis of cellobiose and, by analogy, cellulose. The electronic structure of cellobiose was explored by DFT at the BB1 K/6‐31++G(d,p) level. Natural bond orbital (NBO) analysis was performed to grasp the key bonding concepts. Conformations, protonation sites, and hydrolysis mechanisms were examined. The results for cellobiose indicate that cellulose is protected against hydrolysis not only by its supramolecular structure, as currently accepted, but also by its electronic structure, in which the anomeric effect plays a key role.     

Combined Chemical Modification and Collision Induced Unfolding Using Native Ion Mobility-Mass Spectrometry Provides Insights into Protein Gas-Phase Structure

Native mass spectrometry is now an important tool in structural biology. Thus, the nature of higher protein structure in the vacuum of the mass spectrometer is an area of significant interest. One of the major goals in the study of gas-phase protein structure is to elucidate the stabilising role of interactions at the level of individual amino acid residues. A strategy combining protein chemical modification together with collision induced unfolding (CIU) was developed and employed to probe the structure of compact protein ions produced by native electrospray ionisation. Tractable chemical modification was used to alter the properties of amino acid residues, and ion mobility-mass spectrometry (IM-MS) utilised to monitor the extent of unfolding as a function of modification. From these data the importance of specific intramolecular interactions for the stability of compact gas-phase protein structure can be inferred. Using this approach, and aided by molecular dynamics simulations, an important stabilising interaction between K6 and H68 in the protein ubiquitin was identified, as was a contact between the N-terminus and E22 in a ubiquitin binding protein UBA2.     

Dipolar and V-shaped structures incorporating methylenepyran and diazine fragments

Thirteen novel dipolar and V-shaped chromophores with pyranylidene electron-donating part, diazine electron-withdrawing part and various π-linkers were synthesized. The extent of intramolecular charge transfer, structure-property relationships and optical properties were further investigated by UV/Vis absorption, electrochemistry, and DFT calculations.