Diversity oriented heterocyclizations of pyruvic acids,aldehydes and 5-amino-<Emphasis Type="Italic">N</Emphasis>-aryl-1<Emphasis Type="Italic">H</Emphasis>-pyrazole-4-carboxamides: catalytic and temperature control of chemoselectivity

Heterocyclization reactions of pyruvic acids, aromatic aldehydes and 5-amino-N-aryl-1H-pyrazole-4-carboxamides yielding four different types of final compounds are described. The reactions involving arylidenpyruvic acids lead with high degree of selectivity to either 4,7-dihydropyrazolo[1,5-a]pyrimidine-5-carboxylic acids or 5-[(2-oxo-2,5-dihydrofuran-3-yl)amino]-1H-pyrazoles, depending on the catalyst type or temperature regime. The interactions based on arylpyruvic acids can take place under kinetic or thermodynamic control producing 7-hydroxy-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrimidine-7-carboxylic acids or 3-hydroxy-1-(1H-pyrazol-5-yl)-1,5-dihydro-2H-pyrrol-2-ones, respectively.     

Holographic nanocomposites for recording polymer-nanoparticle periodic structures: I. General approach to choice of components of nanocomposites and their holographic properties

We studied polymerizable nanocomposites for obtaining polymer-nanoparticle periodic structures by a holographic method. A general approach to choosing components of composites is developed that ensures a maximal contrast and high efficiency of structures for different types of nanoparticles. We found that the optimal monomeric component of a nanocomposite is a combination of single- and multifunctional monomers with substantially different reactivities. In this case, the low-reactivity monomer should posses a low viscosity, be a good solvent for nanoparticles, and have a low thermodynamic affinity to the polymer network formed upon the polymerization of the high-reactivity monomer. We developed a holographic composition based on known commercially produced monomers that ensures the formation of highly efficient periodic structures for nanoparticles of different types. We described the holographic properties of obtained nanocomposites, as well as parameters of bulk gratings recorded in them.     

Photoabsorption by the electron subsystem of a semiconductor nanoparticle

The IR photoabsorption cross section of a semiconductor nanoparticle has been calculated. Light is absorbed by conduction electrons and trapped electrons in the volume and surface of the nanoparticle. Electron concentrations have been obtained by minimizing the total free energy of charges in the system. The photoabsorption cross section has two characteristic maxima corresponding to the absorption by conduction electrons and by trapped electrons in the nanoparticle volume. The number of trapped electrons on the surface is relatively small, so that they do not contribute to the total cross section.     

Minimum contrast estimation of stationary processes based on the squared periodogram?

We present a class of minimum contrast estimators based on the objective function that is composed using the squared periodogram. We prove the consistency and asymptotic normality of the proposed estimators.     

Polarization of Fluorescence of Excimer Vinylpyrene

The polarization of the excimer luminescence of copolymers of 1-vinylpyrene with methyl methacrylate has been studied. The obtained polarization dependences in absorption and fluorescence spectra differ for luminescence in the region of the maximum of the excimer band and of its longwave portion, which is due to the influence of the nonequilibrium configurations of the dimeric complex on the polarization properties of its luminescence.     

Temperature stability and radiation resistance of holographic gratings on photopolymer materials

Data are presented from studies of the temperature dependence of the diffraction efficiency and radiation resistance of volume phase hologram/transmission gratings. The reversible diffraction efficiencies are described by the phase equilibrium diagram for the polymer-diffusate system. The radiation resistance of these hologram/gratings is determined by the thresholds for photothermolytic decay of the diffusate, bromonaphthalene, that was used. Composites containing diffusates with high thresholds for photolysis and thermolysis are studied. As a result, modified versions of the photopolymer recording medium with radiation resistances exceeding 200 MW/cm² are proposed. Zh. Tekh. Fiz. 68, 105–110 (June 1998)     

Equilibrium NH acidities of acridan,phenanthridone, 9-acridone,and substituted 9-acridones

The equilibrium NH acidities of acridan, phenanthridone, 9-acridone, and 2-substituted 9-acridones (substituents: Me₂N, MeO, F, Br, I, and NO₂) were measured by transmetallation in dimethyl sulfoxide (DMSO). The role of conjugation and the aromatic character of the heterocyclic ring in stabilization of the anions is discussed. The energies of deprotonation of phenanthridone and 9-acridone were estimated by the CNDO/2 (complete neglect of differential overlap) method; it is shown that the difference between them is in agreement with the experimental results. The dependence pK = 16.2 – 3.37_I – 1.84_R (s 0.23, r 0.989) was obtained for the 2-substituted 9-acridones.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1241–1244, September, 1982.We thank É. S. Shcherbakova for her assistance in the correlation analysis of the data on the acidities of the substituted 9-acridones.     

Equations of Mathematical Physics and Compositions of Brownian and Cauchy Processes

We consider different types of processes obtained by composing Brownian motion B(t), fractional Brownian motion B _H (t) and Cauchy processes C(t) in different manners. We study also multidimensional iterated processes in ? ^d , like, for example, (B ₁(|C(t)|),…, B _d (|C(t)|)) and (C ₁(|C(t)|),…, C _d (|C(t)|)), deriving the corresponding partial differential equations satisfied by their joint distribution. We show that many important partial differential equations, like wave equation, equation of vibration of rods, higher-order heat equation, are satisfied by the laws of the iterated processes considered in the work. Similarly, we prove that some processes like C(|B ₁(|B ₂(…|B _n+1(t)|…)|)|) are governed by fractional diffusion equations.     

One Step up the Ladder of Prebiotic Complexity: Formation of Nonrandom Linear Polypeptides from Binary Systems of Amino Acids on Silica

Evidence for the formation of linear oligopeptides with nonrandom sequences from mixtures of amino acids coadsorbed on silica and submitted to a simple thermal activation is presented. The amino acid couples (glutamic acid+leucine) and (aspartic acid+valine) were deposited on a fumed silica and submitted to a single heating step at moderate temperature. The evolution of the systems was characterized by X-ray diffraction, infrared spectroscopy, thermosgravimetric analysis, HPLC, and electrospray ionization mass spectrometry (ESI-MS). Evidence for the formation of amide bonds was found in all systems studied. While the products of single amino acids activation on silica could be considered as evolutionary dead ends, (glutamic acid+leucine) and, at to some extent, (aspartic acid+valine) gave rise to the high yield formation of linear peptides up to the hexamers. Oligopeptides of such length have not been observed before in surface polymerization scenarios (unless the amino acids had been deposited by chemical vapor deposition, which is not realistic in a prebiotic environment). Furthermore, not all possible amino acid sequences were present in the activation products, which is indicative of polymerization selectivity. These results are promising for origins of life studies because they suggest the emergence of nonrandom biopolymers in a simple prebiotic scenario.