Cr(VI) Oxidation of Cholesterol—A Kinetic Study Using N-Cetylpicolinium Dichromates,A Class of Novel Phase Transfer Oxidants

Kinetics and Catalysis - Kinetic study of cholesterol oxidation has been studied using a series of N-cetylpicolinium dichromates (CPDC), a class of phase transfer oxidants, in acetic acid medium...     

Intramolecular photoinduced proton transfer in 2-(2-aminophenyl)-4H-3,1-benzoxazin-4-ones with different electron-withdrawing N-substituents

Fluorescence spectra of N-substituted 2-(2-aminophenyl)-4H-3,1-benzoxazin-4-ones consist of two bands, the long-wavelength band with anomalous Stokes shift, which corresponds to the emission of the product of intramolecular photoinduced proton transfer, and the short-wavelength band belonging to the form in which proton transfer does not occur. It is assumed that there is equilibrium between two planar rotamers in the ground state: one with the N-H…N hydrogen bond in which the intramolecular photoinduced proton transfer occurs and the other with the N-H…O bond, which does not experience hydrogen transfer. According to ab initio quantum-chemical calculations, the potential energy of proton transfer in the first excited singlet state has a potential barrier of 2.1–26.8 kJ/mol depending on the electron-withdrawing ability of the substituent on the amino group.     

A consequence of a proof of the one-way function existence for the problem of macroscopic superpositions

One-way functions are functions that are easy to compute but hard to invert. Their existence is an open conjecture; it would imply the existence of intractable problems (i.e. NP-problems which are not in the P complexity class).If true, the existence of one-way functions would have an impact on the theoretical framework of physics, in particularly, quantum mechanics. Such aspect of one-way functions has never been shown before.In the present work, we put forward the following.We can calculate the microscopic state (say, the particle spin in the z direction) of a macroscopic system (a measuring apparatus registering the particle z-spin) by the system macroscopic state (the apparatus output); let us call this association the function F. The question is whether we can compute the function F in the inverse direction. In other words, can we compute the macroscopic state of the system through its microscopic state (the preimage F⁻¹)?In the paper, we assume that the function F is a one-way function. The assumption implies that at the macroscopic level the Schrödinger equation becomes unfeasible to compute. This unfeasibility plays a role of limit of the validity of the linear Schrödinger equation.     

Tautomerism of amidoximes and other oxime species

The tautomerism of the aliphatic MeC(NH₂)═NOH and the aromatic PhC(NH₂)═NOH amidoximes in protic (H₂O, MeOH) and aprotic (Me₂CO, Me₂SO, and CHCl₃) solvents was studied by density functional theory calculations at the M06‐2X/6‐311+G(d,p) level of theory. In both types of solutions, these species exist in 3 tautomeric forms, viz, (Z)‐ or (E)‐amidoximes, and (Z)‐aminonitrone. The (Z)‐form is the dominant, and energy gap between the (Z)‐ and (E)‐tautomers of the amidoximes slightly depends on the nature of a solvent and significantly higher than that for other oxime species. For the amidoximes, the zwitterionic (Z)‐aminonitrone form is stabilized by protic solvents. The oxime‐nitrone energy gap is reduced by electron‐donor substituents at the oxime moiety at different types of oxime species.     

Interaction of ethidium bromide and caffeine with DNA in aqueous solution

Two component (ethidium bromide–caffeine, ethidium bromide–DNA) and three component (ethidium bromide–caffeine–DNA) systems in aqueous saline (0.01 M NaCl) phosphate buffer solutions (pH 6.86, T = 298 K) are studied spectrophotometrically. The equilibrium constants for dimerization of caffeine, K _D  = 1.22 ± 2 M⁻¹, and for heteroassociation of ethidium bromide with caffeine, K = 71 ± 8 M⁻¹, in ethidium bromide–caffeine systems are determined. When the concentration of caffeine is increased, the dynamic equilibrium of the solution shifts toward formation of heterocomplexes which are, presumably, stabilized by dispersive and hydrophobic interactions of chromophores. The equilibrium parameters for ethidium bromide complex formation with DNA are calculated: the coupling constant for the dye with the biopolymer, K ₁ = (232 ± 16)⋅103 M⁻¹, and the number of base pairs of the biopolymer participating in bonding with the ligand, n ₁ = 3.6 ± 0.2, are calculated. Given these values, it is suggested that under these experimental conditions there are two types of bonding between ethidium bromide and the nucleic acid — intercalation and “external” bonds. A McGhee–von Hippel model for a three component system and the numerical values of the parameters for molecular complex formation in two component systems are used to calculate the bonding constant for caffeine with DNA, K ₂ = 127 ± 30 M⁻¹, and the number of base pairs of DNA which bond with caffeine, n ₂ = 1.7 ± 0.2. The concentrations of ethidium bromide and caffeine in the composition of two and three component complexes are calculated as functions of the nucleic acid content in the solution. An analysis of the concentration dependences shows that heteroassociation of ligands has a significant effect on the reduction in the concentration of ethidium bromide–DNA complexes in a three component system for low DNA concentrations, while at high DNA concentrations the bonding of caffeine with the biopolymer has this effect. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 143–151, January–February 2009.     

Decay of the mixed states

We study the classical escape from local minima for 2d multi-well Hamiltonian systems, realizing the mixed state. We show that escape from such local minima has a diversity of principally new features, representing an interesting topic for conceptual understanding of chaotic dynamics and applications.     

o-Tosylamino-substituted 2-arylbenzimidazoles

A number of o-tosylamino-substituted 2-arylbenzimidazoles were synthesized, and the effect of substituents on the position of the absorption bands of toluene solutions of the products was investigated. Except for the compound containing a nitro group, the investigated compounds fluoresce in the solid state and in toluene; an anomalously large Stokesian shift is characteristic for them.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5 pp. 673–675, May, 1976.