Mutagenicity associated with O6-methylguanine-DNA damage and mechanism of nucleotide flipping by AGT during repair

Methylated guanine damage at O6 position (i.e. O6MG) is dangerous due to its mutagenic and carcinogenic character that often gives rise to G:C-A:T mutation. However, the reason for this mutagenicity is not known precisely and has been a matter of controversy. Further, although it is known that O6-alkylguanine-DNA alkyltransferase (AGT) repairs O6MG paired with cytosine in DNA, the complete mechanism of target recognition and repair is not known completely. All these aspects of DNA damage and repair have been addressed here by employing high level density functional theory in gas phase and aqueous medium. It is found that the actual cause of O6MG mediated mutation may arise due to the fact that DNA polymerases incorporate thymine opposite to O6MG, misreading the resulting O6MG:T complex as an A:T base pair due to their analogous binding energies and structural alignments. It is further revealed that AGT mediated nucleotide flipping occurs in two successive steps. The intercalation of the finger residue Arg 128 into the DNA double helix and its interaction with the O6MG: C base pair followed by rotation of the O6MG nucleotide are found to be crucial for the damage recognition and nucleotide flipping.

Study of the CP property of the Higgs boson at a photon collider using gamma gamma -> t(t)over-bar -> lX

We study the possible effects of CP violation in the Higgs sector on t (t) over bar production at a gammagamma collider. These studies are performed in a model-independent way in terms of six form factors {R(S-gamma), J(S-gamma), R(P-gamma), J(P-gamma), S-t, P-t} which parametrize the CP mixing in the Higgs sector, and a strategy for their determination is developed. We observe that the angular distribution of the decay lepton from t/(t) over bar produced in this process is independent of any CP violation in the tbW vertex and hence best suited for studying CP mixing in the Higgs sector. Analytical expressions are obtained for the angular distribution of leptons in the c.m. frame of the two colliding photons for a general polarization state of the incoming photons. We construct combined asymmetries in the initial state lepton (photon) polarization and the final state lepton charge. They involve CP even (x's) and odd (y's) combinations of the mixing parameters. We study limits up to which the values of x and y, with only two of them allowed to vary at a time, can be probed by measurements of these asymmetries, using circularly polarized photons. We use the numerical values of the asymmetries predicted by various models to discriminate among them. We show that this method can be sensitive to the loop-induced CP violation in the Higgs sector in the minimal supersymmetric standard model.

Pyrene appended bile acid conjugates: Synthesis and a structure-gelation property study

A wide variety of novel compounds obtained by combining two types of known organogelators, viz., bile acid alkyl amides and pyrene alkanoic acids, were synthesized and screened for their gelation ability. The 3 alpha esters of 1-pyrene butyric acid (PBA) of alkylamides of deoxycholic acid (DCA) turned out to be effective in the gel formation with many organic solvents although the gelation has to be triggered by the addition of a charge transfer (CT) agent 2,4,7-trinitrofluorenone (TNF). The special feature of these molecules is that the organogelation is achieved only after derivatizing the acid moiety of the 1-pyrenealkanoic acids. Additionally, the gelation properties can be fine-tuned by inserting different functional groups at the bile acid side chain. The gels obtained are deep red in colour and optically transparent up to 2% w/v. The SEM studies of the obtained xerogels revealed bundled rod-like morphology without specialized branching.

Synthesis, Structure, Negative Thermal Expansion, and Photocatalytic Property of Mo Doped ZrV(2)O(7)

A new series of compounds identified in the phase diagram of ZrO(2)-V(2)O(8)-MoO(3) have been synthesized via the solution combustion method. Single crystals of one of the compounds in the series, ZrV(1.50)Mo(0.50)O(7.25), were grown by the melt-cool technique from the starting materials with double the MoO(3) quantity. The room temperature average crystal structure of the grown crystals was solved using the single crystal X-ray diffraction technique. The crystals belong to the cubic crystal system, space group Pa (3) over bar (No. 205) with a = 8.8969 (4) angstrom, V = 704.24 (6) angstrom(3), and Z = 4. The final R(1) value of 0.0213 was achieved for 288 independent reflections during the structure refinement. The Zr(4+) occupies the special position (4a) whereas V(5+) and Mo(6+) occupy two unique (8c) Wyckoff positions. Two fully occupied O atoms, (24d) and (4b), one partially occupied 0 atom (8c) have been identified for this molybdovanadate, which is a unique feature for these crystals. The structure is related to both ZrV(2)O(7) and cubic ZrMo(2)O(8). The temperature dependent single crystal studies show negative thermal expansion above 370 K. The compounds have been characterized by powder X-ray diffraction, solid-state UV-vis diffuse reflectance spectra, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The photocatalytic activity of these compounds has been investigated for the degradation of various dyes, and these compounds show specificity toward the degradation of non-azoic dyes.

Ultrasonic Lamb wave based monitoring of corrosion type of damage in plate using a circular array of piezoelectric transducers

In this paper we propose a concept and report experimental results based on a circular array of Piezoelectric Wafer Active Sensors (PWASs) for rapid localization and parametric identification of corrosion type damage in metallic plates. Implementation of this circular array of PWASs combines the use of ultrasonic Lamb wave propagation technique and an algorithm based on symmetry breaking in the signal pattern to locate and monitor the growth of a corrosion pit on a metallic plate. Wavelet time-frequency maps of the sensor signals are employed to obtain an insight regarding the effect of corrosion growth on the Lamb wave transmission in time-frequency scale. We present here a method to eliminate the time scale, which helps in identifying easily the signature of damage in the measured signals. The proposed method becomes useful in determining the approximate location of the damage with respect to the location of three neighboring sensors in the circular array. A cumulative damage index is computed from the wavelet coefficients for varying damage sizes and the results appear promising. Damage index is plotted against the damage parameters for frequency sweep of the excitation signal (a windowed sine signal). Results of corrosion damage are compared with circular holes of various sizes to demonstrate the applicability of present method to different types of damage. (C) 2011 Elsevier Ltd. All rights reserved.