PROFLAVINE MEDIATED PHOTOINACTIVATION OFBACTERIOPHAGE φX174 AND ITS ISOLATED DNA: EFFECTS OF AGENTS MODIFYING VARIOUS PHOTOCHEMICAL PATHWAYS

Abstract. Thiols and disulfides protect both φX174 phage and its isolated DNA from the lethal action of proflavine plus light. The protective ability of these compounds appears to be attributed to the -SH or the -S-S- group and the property to interact with the proflavine-phage DNA complex. The phage inactivation efficiency per proflavine bound to DNA is reduced by 50 to 30% upon addition of cysteine or cystamine. Substances that affect the lifetime of singlet oxygen modify the rate of phage photoinactivation in the presence of proflavine; the inactivation rate is decreased by N^-₃ and increased by D₂O. Irradiation under N₂ atmosphere markedly decreases the phage photosensitization by proflavine. Irradiation with monochromatic light of 440 nm is less efficient than irradiation with light of 440 nm plus 360 nm, and the difference is more pronounced in N₂ than in air. These results are discussed in relation to various possible photochemical pathways.     

COMPETITION BETWEEN THE SINGLET OXYGEN AND ELECTRON TRANSFER MECHANISMS IN THE PORPHYRIN-SENSITIZED PHOTOOXIDATION OF l-TRYPTOPHAN AND TRYPTAMINE IN AQUEOUS MICELLAR DISPERSIONS

Abstract— Kinetic studies of the hematoporphyrin–sensitized photooxidation of l -tryptophan and tryptamine at pH 10 in either homogeneous aqueous solutions or in aqueous dispersions of Triton X–100 and cetyltrimethylammonium bromide micelles indicate that the indole substrates are attacked via a mixed type I (electron transfer from triplet dye)/type II (¹O₂-involving) mechanism. Both reactive intermediates, generated by micelle-solubilized hematoporphyrin, can diffuse to attack substrate molecules located in either the bulk aqueous phase or a different micelle. In particular, incorporation of the substrate into a micelle has only minor effects on its reactivity toward¹O₂, although the ¹O₂—indole interaction appears to be more efficient in cationic micelles owing to a favourable orientation of the target with respect to the attacking species. On the other hand, the electron transfer from triplet porphyrin to a micellized substrate is virtually non-operative when the latter is located in an anionic micelle, whereas in neutral or cationic micelles, the efficiency of the process is again controlled by the substrate orientation. Studies of tryptamine photooxidation sensitized by meso-tetra-(4-sulfonato-phenyl) porphine in the presence of sodium dodecylsulphate micelles lend further support to the abovementioned conclusions.     

TRIPLET YIELD OF MEROCYANINE 540 IN WATER IS WAVELENGTH DEPENDENT

Monomers and aggregates of Merocyanine 540 (MC540) in water are able to photoisomerize. The shape of the photoisomer absorption spectrum is very similar to that of the ground state. Triplet state of MC540 in water has been produced by energy transfer from triplet anthracene and displays a broad absorption spectrum between 600 and 700 nm. The triplet state may also be produced by direct excitation of MC540 with UV light. However, when the dye is excited by visible light, no triplet state absorbance in the red could be detected so that the triplet yield of MC540 in water seems to be excitation wavelength dependent.     

INDUCTION OF FREE RADICALS IN DNA BY PROFLAVINE AND VISIBLE LIGHT: INFLUENCE OF OXYGEN AND IONIC STRENGTH

Abstract —The photosensitization of native DNA is observed as an induction of free radicals in the DNA moiety of proflavine-DNA complexes. The intensity of the electron paramagnetic resonance spectra (at 77 K) is a measure of the number of free radicals present in frozen solutions of DNA-proflavine complexes after irradiation with visible light (Λ > 320 nm). In the absence of O₂, the photosensitization is significant but very low; it increases slightly with increasing NaCl ionic strength; it appears to be due to intercalated dye molecules and the qualitative analysis of the spectra obtained shows that mainly thymidine is involved. The reaction measured after saturation with O₂ is the same as the reaction in air but is quantitatively higher; the free radicals observed are peroxides. This induction of free radicals appears to be due to the intercalated dye molecules, each molecule acting independently. The important observation is a very sharp and large (around a hundred-fold) increase in the photosensitizing efficiency of the bound dye molecules occurring in NaCl between μ, # 0–25 and μ= 0–5 and in MgCl₂ between μ# 0–01 and μ=0–1.     

PRODUCTION OF BREAKS IN SINGLE- AND DOUBLE-STRANDED FORMS OF BACTERIOPHAGE øx174 DNA BY PROFLAVINE AND LIGHT TREATMENT

Abstract— Irradiation at 440 + 360 nm and a fluence rate of 3.8 kJm^-2 min^-1, of both complexes previously formed between proflavine and either øX circular single-stranded (ss) DNA or øX supercoiled duplex (RFI)DNA, induces single-strand scissions in the two DNAs under consideration. Linear øXSS DNA molecules are detected by sedimentation through alkaline sucrose gradients. After treatment of the øXRFI DNA, however, the degree of degradation is the same whether it is measured under neutral or alkaline conditions, indicating that alkaline-labile bonds are not created; moreover, double-strand breaks can only be detected after accumulation of single-strand breaks. In addition to the amount of proflavine bound to the DNA and the duration of irradiation, the following factors are shown to influence the nicking activity of the treatment: (1) the DNA structure (the øXRFI DNA is much more sensitive than the øXss DNA); (2) the ionic strength of the medium during irradiation (a high value of 0.5 leads to a markedly increased efficiency); (3) the addition of cysteamine (this latter compound decreases the reaction rate) and (4) the irradiation wavelength (after irradiation at 440 nm alone, the reaction occurs at a reduced rate and is sensitive to NaN₃). The kinetics of the nicking reaction does not follow a single-hit curve showing that at least one primary lesion occurs prior to strand breakage. On the other hand, strand scission cannot be detected after irradiation of the proflavine-DNA complexes at the low fluence rate causing a decrease in the infectivity of both øXSS and øXRFI DNAs. Similarly. the sedimentation pattern of the DNA extracted from treated øx174 phages 99.9% inactivated, is identical to that of the control ss DNA, although more drastic treatments are susceptible to induce single strand breaks inside the phage head. Finally, the unknown lesion (s) that is biologically important does not prevent the treated DNAs from penetrating into the hostcells.     

The eight-states ferroelectric model with geometrically coupled t1u-modes in α-indium monochloride

The InCl₆-octahedra in α-InCl are treated with an eight-states ferroelectric model, in which only one symmetry mode of t_1u-symmetry, consisting solely of Cl-dependents, is considered. The stacking problem of t_1u-distorted trigonal octahedra is translated into an energy minimum problem of other modes, which are induced by the stacking. After some refinement, two structures are found, one of which resembles α-InCl. Indium shifts from their idealized rocksalt positions can be understood from a consideration of the exchange repulsion between the polarized In-ion and its ligands.     

Calculation of the activation energy from the tsee peaks of MgO

In this paper the analysis of the TSEE curves of MgO is presented and two methods of the calculations of the activation energy and the frequency factor of the TSEE peaks of MgO are compared. There is good agreement concerning the activation energy of the trapping centres between the least squares method for the fitting of experimental and theoretical curves and the universal calculation method developed by de Muer.     

BiCGstab(l) and other hybrid Bi-CG methods

It is well-known that Bi-CG can be adapted so that the operations withA ^T can be avoided, and hybrid methods can be constructed in which it is attempted to further improve the convergence behaviour. Examples of this are CGS, Bi-CGSTAB, and the more general BiCGstab(l) method. In this paper it is shown that BiCGstab(l) can be implemented in different ways. Each of the suggested approaches has its own advantages and disadvantages. Our implementations allow for combinations of Bi-CG with arbitrary polynomial methods. The choice for a specific implementation can also be made for reasons of numerical stability. This aspect receives much attention. Various effects have been illustrated by numerical examples.     

Experimental analysis of the steady-state behaviour of beam systems with discontinuous support

This paper deals with the experimental analysis of the long-term behaviour of periodically excited linear beams supported by a one-sided spring or an elastic stop. Numerical analysis of the beams showed subharmonic, quasi-periodic and chaotic behaviour. Furthermore, in the beam system with the one-sided spring three different routes leading to chaos were found. Because of the relative simplicity of the beam systems and the variety of calculated nonlinear phenomena, experimental setups are made of the beam systems to verify the numerical results. The experimental results correspond very well with the numerical results as far as the subharmonic behaviour is concerned. Measured chaotic behaviour is proved to be chaotic by calculating Lyapunov exponents of experimental data.

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Sommario Il presente lavoro concerne l'analisi sperimentale del comportamento a regime di travi lineari, su supporti elastici nonlineari discontinui, eccitate periodicamente. L'analisi numerica dei sistemi in esame ha evidenziato risposte subarmoniche, quasi-periodiche e caotiche, nonchè l'esistenza, nel caso di trave con una molla laterale, di tre differenti percorsi verso il caos. La relativa semplicità dei sistemi di travi ha consentito di procedere ad una verifica sperimentale dei risultati numerici e della varietà dei fenomeni nonlineari da essi evidenziati. La corrispondenza fra risultati sperimentali e numerici è molto buona nel caso di risposta subarmonica. Il comportamento caotico sperimentale è stato convalidato attraverso il calcolo degli esponenti di Lyapunov a partire dai relativi dati.

     

Experimental evidence of mounting grooves and serration patterns on fin lines characteristics

In this paper, the mounting grooves and serration patterns of fin line circuits are investigated experimentally. Our measurements show that the short-circuit ended mounting grooves degrade seriously the insertion loss of fin lines at the low frequencies of the band. The open ended mounting grooves are found better for fin lines applications and measurements. An improvement of 0.7 dB is observed over the whole band, when the serration patterns of the fin line are placed into the open-ended mounting grooves. These results can be used for measuring the losses and for designing transitions or other fin line circuits.