Albedo in the ATIC experiment: Measurements and simulations

We analyze the characteristics of the albedo, or the backscatter current, which constitutes a background for charge measurements in calorimetric experiments in high-energy cosmic rays. We compare the experimental data obtained in the flights of the ATIC spectrometer with the simulations performed using the GEANT 3.21 code. We discuss the influence of the backscatter on the charge resolution in the ATIC experiment.     

Remarks on the analysis of dynamic 1H NMR spectra of A3B2 ⇌ C3D2 spin systems. Internal rotation in N,N-diethylbenzamide

A method of analysis of dynamic NMR spectra for A₃B₂ ? C₃D₂ spin systems is proposed. This method is based upon the assumption that the shape of the A–C part of the spectrum is the same as for the AB₂ ? CD₂ spin system and the shape of the B–D part is the same as for the A₃B ? C₃D system. By means of this simplification the iterative total line shape analysis of dynamic NMR spectra by the use of the least-squares method becomes feasible. The method proposed is applied to the determination of the thermodynamic parameters of activation for internal rotation in N,N-diethylbenzamide in CD₃CN (ΔG = 62.6 kJ mol^?1 ΔH^≠ = 62 kJ mol^?1, ΔS^≠ = ?1 J/mol^?1 K^?1). The determination of natural line widths is discussed in detail and a method of estimation of the effect of systematic errors on the results is proposed.     

Generality of solvation effects on the hydrolysis rates of phosphate monoesters and their possible relevance to enzymatic catalysis

Previous work by Kirby and co-workers revealed a significant acceleration of the rate of hydrolysis of p-nitrophenyl phosphate by added dipolar solvents such as DMSO. Activation parameters and kinetic isotope effects have been measured to ascertain the origin of this effect. The generality of this phenomenon was examined with a series of esters with more basic leaving groups. Computational analyses of the effects of desolvation of dianionic phosphate monoesters were carried out, and the possible effect of the transfer from water to the active site of alkaline phosphatase was modeled. The results are consistent with a desolvation-induced weakening of the P-O ester bond in the ground state. Other aryl phosphate esters show similar rate accelerations at high fractions of DMSO, but phenyl and methyl phosphates do not, and their hydrolysis reactions are actually slowed by these conditions.     

Electronic absorption spectra of C3Cl, C4Cl, and their ions in neon matrices

Electronic absorption spectra of C3Cl, C3Cl+, C3Cl-, C4Cl, and C4Cl+ have been recorded in 6 K neon matrices following mass selection. Ab initio calculations were performed (CCSD(T) and CASSCF) to identify the ground and accessible excited states of each molecule. The estimated excitation energies and transition moments aid the assignment. The absorptions observed for C3Cl are the 5(2)A' <-- X(2)A' and 3(2)A' <-- X(2)A' transitions of the bent isomer and the (2)A1 <-- X(2)B2 transition of the cyclic form in the UV (336.1 nm), visible (428.7 nm), and near-IR (1047 nm) regions, respectively. The band systems for bent C3Cl- (435.2 nm) and linear C3Cl+ (413.2 nm) are both in the visible region and correspond to 2(1)A' <-- X(1)A' and (1)pi <-- X(1)sigma+ type transitions. The C4Cl and C4Cl+ chains are linear, and the band origins of the 2(2)pi <-- X(2)pi and 2(3)pi <-- X(3)pi electronic transitions are at 427.0 and 405.7 nm. The spectral assignments are supported by analysis of the vibrational structure associated with each electronic transition.     

Synthesis of a non-flexible analog of chlorpromazine

9-Chloro-2-dimethylaminomethyl-1,2-dihydropyrrolo[3,2,1-kl]phenothiazine (3b), a conformationally restricted analog of chlorpromazine, has been synthesised and has been found to be devoid of neuroleptic activity.     

Force‐Induced Reversal of β‐Eliminations: Stressed Disulfide Bonds in Alkaline Solution

Understanding the impact of tensile forces on disulfide bond cleavage is not only crucial to the breaking of cross‐linkers in vulcanized materials such as strained rubber, but also to the regulation of protein activity by disulfide switches. By using ab initio simulations in the condensed phase, we investigated the response of disulfide cleavage by β‐elimination to mechanical stress. We reveal that the rate‐determining first step of the thermal reaction, which is the abstraction of the β‐proton, is insensitive to external forces. However, forces larger than about 1 nN were found to reshape the free‐energy landscape of the reaction so dramatically that a second channel is created, where the order of the reaction steps is reversed, turning β‐deprotonation into a barrier‐free follow‐up process to C?S cleavage. This transforms a slow and force‐independent process with second‐order kinetics into a unimolecular reaction that is greatly accelerated by mechanical forces.     

On construction of asymptotically stable iterated function system with probabilities

We consider a Markov chain generated by random iterations of a family of mappings indexed by elements of an arbitrary measurable space. Under sufficiently weak assumptions we construct a family of place-dependent probability measures such that considered Markov chain converges to a stationary distribution. We also prove some sufficient condition for asymptotic stability of a family of i.i.d. mappings and we apply obtained result for discrete white noise random dynamical systems showing analogous probabilistic long-time behavior.