Transient reduction in the tRNA 4-thiouridine content induced by ultraviolet A during post-irradiation growth in Enterobacter cloacae

The influence of previous exposure to ultraviolet-A radiation (UVA) was studied on the susceptibility of Enterobacter cloacae to undergo the growth delay effect. Comparison of growth curves corresponding to irradiated and control cells showed that a previous treatment with UVA almost abolished the growth delay effect. UV absorption spectra of tRNA, and reverse phase HPLC analysis of hydrolysed tRNA, demonstrated a low content of 4-thiouridine in E. cloacae cells grown after UVA exposure at low doses. Since 4-thiouridine is the UVA target responsible for initiation of growth delay, this observation explained the influence of previous exposure to UVA on the susceptibility of this organism to undergo growth delay. A similar but weaker alteration was found when Escherichia coli was assayed. The results suggest that, in addition to cross-linking with cytidine residues, the content of 4-thiouridine in tRNA may be modified by UVA by an unknown mechanism.     

Complete rotation hypersurfaces with Hk constant in space forms

In this paper we classify all complete rotation hypersurfaces withH _k constant in ⁿ⁺¹ andH ⁿ⁺¹, is the normalizedk-th symmetric function of the principal curvatures. Partial results are also given forH ⁿ⁺¹.Partially supported by DGAPA-UNAM, México, CONACYT, México, under Project 1068P, and CNPp, Brazil.     

Characterization of the Suzuki phase in doped alkali halides by Raman spectroscopy

The symmetries and frequencies of the Raman active modes of the Suzuki phase in the systems 6NaCl:CdCl₂; and 6NaCl:MnCl₂, have been calculated. Three of the four peaks allowed by symmetry (A_1g and 2F_g) agree to within 25% in position with the experimental values presented here and with other experimental results. The fourth peak (E_g) seems to be associated with a very soft mode, which explains why this peak has not been observed. The features of the Raman spectrum depend mainly upon the chlorine ions.     

Synthesis of heterocyclic compounds. XXIV. Synthesis of pyridines from β-substituted α-phenylacrylonitriles

The reaction of malononitrile with α-phenylcinnamonitriles in ethanolic sodium ethanethiolate is studied as a convenient route to 2-amino-4-aryl-5-cyano-6-ethylthio-3-phenyl-3,4-dihydropyridines ( 5 ) and the corresponding pyridines 6 . From the study of the structure of 5a (Ar = Ph) we can conclude that this cyclization reaction proceeds via a site-selective addition of the ethanethiolate to the cyano group i of the 1,3-tricarbonitrile ( 2 ).     

Electrochemical synthesis of 3,5-diphenyl-2(3H)-furanone

From electrochemical reduction of phenacyl bromide, 3,5-diphenyl-2(3H)-furanone was obtained as a side-product and its structure was determined by chemical and spectral techniques.     

Capillary smectization and layering in a confined liquid crystal

Using density-functional theory, we have analyzed the phase behavior of a model liquid crystal confined between two parallel, planar surfaces (i.e., the so-called slit pore). As a result of confinement, a rich phase behavior arises. The complete liquid-crystal phase diagram of the confined fluid is mapped out as a function of wall separation and chemical potential. Strong commensuration effects in the film with respect to wall separation lead to enhanced smectic ordering, which gives capillary smectization (i.e., formation of a smectic phase in the pore), or frustrated smectic ordering, which suppresses capillary smectization. These effects also produce layering transitions. Our nonlocal density-functional-based analysis provides a unified picture of all the above phenomena.     

Three-dimensional recomposition of the absorption field inside a nonbuoyant sooting flame

A remote scanning retrieval method was developed to investigate the soot layer produced by a laminar diffusion flame established over a flat plate burner in microgravity. Experiments were conducted during parabolic flights. This original application of an inverse problem leads to the three-dimensional recomposition by layers of the absorption field inside the flame. This technique provides a well-defined flame length that substitutes for other subjective definitions associated with emissions.     

Fragment-asperity interaction model for earthquakes

A model for earthquake dynamics consisting of two rough profiles interacting via fragments filling the gap is introduced, the fragments being produced by the local breakage due to the interaction of the local plates. The irregularities of the fault planes can interact with the fragments between them to develop a mechanism for triggering earthquakes. The fragment size distribution function comes from a nonextensive formulation, starting from first principles. An energy distribution function, which gives the Gutenberg-Richter law as a particular case, is analytically deduced.