Studies on hypomethylation of liver DNA during early stages of chemical carcinogenesis in rat liver

Our finding that the inhibitors of DNA methylation, 5-azacytidine, 5-azadeoxycytidine or adenosine dialdehyde, given after a carcinogen all potentiated initiation suggested that hypomethylation of DNA during repair synthesis of DNA might play a role in the initiation of the carcinogenic process. To examine this aspect further, we have asked the question, do the nodules which develop from initiated cells after promotion with 1% orotic acid exhibit an altered methylation pattern in their DNA? The methylation status of the DNA from nodules has been examined using the restriction endonucleases HpaII/MspI and HhaI which distinguish between methylated and unmethylated cytosines in their nucleotide recognition DNA 5'-CCGG and 5'-GCGC respectively. The proto-oncogenes, c-myc, c-fos and c-Ha-ras, in the DNA were primarily studied in this investigation because of their possible involvement in cell proliferation and/or in cell transformation and tumorigenesis. The results indicate that in the nodule DNA, c-myc and c-fos are hypomethylated in the sequence of CCGG while the c-Ha-ras shows hypomethylation in the alternating GCGC sequence. This methylation pattern seen in the nodule DNA is not found in the DNA of the non-nodular surrounding liver or liver tissue after exposure to promoter or carcinogen alone. It is also not found in the DNA of regenerating liver. It is particularly significant that the methylation patterns in the c-myc and c-Ha-ras regions are similar to those found in several cancer tissues. The results suggest that this methylation pattern is acquired early in the carcinogenic process and raises the question whether it has any bearing on the process.

Formation and preservation of pedogenic carbonates in South India, links with paleo-monsoon and pedological conditions: Clues from Sr isotopes, U-Th series and REEs

The influence of the pedogenic and climatic contexts on the formation and preservation of pedogenic carbonates in a climosequence in the Western Ghats (Karnataka Plateau, South West India) has been studied. Along the climosequence, the current mean annual rainfall (MAR) varies within a 80 km transect from 6000 mm at the edge of the Plateau to 500 mm inland. Pedogenic carbonates occur in the MAR range of 500-1200 mm. In the semi-arid zone (MAR: 500-900 mm), carbonates occur (i) as rhick hardpan calcretes on pediment slopes and (ii) as nodular horizons in polygenic black soils (i.e. vertisols). In the sub-humid zone (MAR: 900-1500 mm), pedogenic carbonates are disseminated in the black soil matrices either as loose, irregular and friable nodules of millimetric size or as indurated botryoidal nodules of centimetric to pluricentimetric size. They also occur at the top layers of the saprolite either as disseminated pluricentimetric indurated nodules or carbonate-cemented lumps of centimetric to decimetric size. Chemical and isotopic (Sr-87/Sr-86) compositions of the carbonate fraction were determined after leaching with 0.25 N HCl. The corresponding residual fractions containing both primary minerals and authigenic clays were digested separately and analyzed. The trend defined by the Sr-87/Sr-86 signatures of both labile carbonate fractions and corresponding residual fractions indicates that a part of the labile carbonate fraction is genetically linked to the local soil composition. Considering the residual fraction of each sample as the most likely lithogenic source of Ca in carbonates, it is estimated that from 24% to 82% (55% on average) of Ca is derived from local bedrock weathering, leading to a consumption of an equivalent proportion of atmospheric CO2. These values indicate that climatic conditions were humid enough to allow silicate weathering: MAR at the time of carbonate formation likely ranged from 400 to 700 mm, which is 2- to 3-fold less than the current MAR at these locations. The Sr, U and Mg contents and the (U-234/U-238) activity ratio in the labile carbonate fraction help to understand the conditions of carbonate formation. The relatively high concentrations of Sr, U and Mg in black soil carbonates may indicate fast growth and accumulation compared to carbonates in saprolite, possibly due to a better confinement of the pore waters which is supported by their high (U-234/U-238) signatures, and/or to higher content of dissolved carbonates in the pore waters. The occurrence of Ce, Mn and Fe oxides in the cracks of carbonate reflects the existence of relatively humid periods after carbonate formation. The carbonate ages determined by the U-Th method range from 1.33 +/- 0.84 kyr to 7.5 +/- 2.7 kyr and to a cluster of five ages around 20 kyr, i.e. the Last Glacial Maximum period. The young occurrences are only located in the black soils, which therefore constitute sensitive environments for trapping and retaining atmospheric CO2 even on short time scales. The maximum age of carbonates depends on their location in the climatic gradient: from about 20 kyr for centimetric nodules at Mule Hole (MAR = 1100 mm/yr) to 200 kyr for the calcrete at Gundlupet (MAR = 700 mm/yr, Durand et al., 2007). The intensity of rainfall during wet periods would indeed control the lifetime of pedogenic carbonates and thus the duration of inorganic carbon storage in soils. (C) 2010 Elsevier Ltd. All rights reserved.

Characterization of phase transformation behaviour and microstructural development of electroless Ni-B coating

Phase transformation behaviour of amorphous electroless Ni-B coating with a targeted composition of Ni-6wt% B is characterized in conjunction with microstructural development and hardness. Microscopic observations of the as-deposited coating display a novel microstructure which is already phase separated at multiple length scales. Spherical colonies of similar to 5 mu m consist of 2-3 mu m nodular regions which are surrounded by similar to 2-3 mu m region that contains fine bands ranging from 10 to 70 nm in width. The appearance of three crystalline phases in this binary system at different stages of heat treatment and the concomitant variation in hardness are shown to arise from nanoscale fluctuations in the as-deposited boron content from 4 to 8 wt%. High temperature annealing reveals continuous crystallization up to 430 degrees C, overlapping with the domain of B loss due to diffusion into the substrate. The implications of such a microstructure for optimal heat treatment procedures are discussed. (C) 2011 Elsevier B.V. All rights reserved.

Autocatalytic duplex Ni-P/Ni-W-P coatings on AZ31B magnesium alloy

Autocatalytic duplex Ni-P/Ni-W-P coatings were deposited on AZ31B magnesium alloy using stabilizer free nickel carbonate bath. Some of the coated specimens were passivated in chromate solution with and without heat treatment. Plain Ni-P coatings were also prepared for comparison. Coatings were characterized for their surface morphology, composition and corrosion resistance. Energy dispersive analysis of X-ray (EDX) showed that the phosphorous content in the Ni-P coating is 6 wt.% and for Ni-W-P it reduced to 3 wt.% due to the codeposition of tungsten in the Ni-P coating. Marginal increase in P and W contents was observed on passivated coupons along with Cr (0.18 wt.%) and O (2.8 wt.%) contents. Field emission scanning electron microscopy (FESEM) examination of these coating surfaces exhibited the nodular morphology. Chromate passivated surfaces showed the presence of uniformly distributed bright Ni particles along with nodules. Potenfiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies were carried out in deaerated 0.15 M NaCI solution to find out the corrosion resistance of the coatings. Among the coatings developed, duplex-heat treated-passivated (duplex-HIP) coatings showed lower corrosion current density (i(corr)) and higher polarization resistance (R-p) indicating the improved corrosion resistance. The charge transfer resistance (R-ct) value obtained for the duplex-HIP was about 170 times higher compared to that for Ni P coating. (c) 2013 Elsevier B.V. All rights reserved.

CHARACTERIZATION AND MICROHARDNESS OF ELECTRODEPOSITED Ni-W COATINGS OBTAINED FROM GLUCONATE BATH

Ni-W alloy coatings are electrodeposited with direct and pulse current using gluconate bath at pH5. Effects of direct current (DC) and pulse current (PC) on structural characteristics of the coatings have been investigated by energy dispersive X-ray spectroscopy (EDXS), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS). EDXS shows that W contents are 13.3 and 12.6 at.% in DC and PC (10:40) Ni-W coatings, respectively. FESEM analysis exhibits the homogeneous coarse nodular morphology in DC plated deposits. DSC studies reveal that Ni-W coatings are thermally stable up to 400 degrees C. XPS studies demonstrate that DC plated coating has significant amount of Ni and W in elemental form along with their respective oxidized species. In contrast, mainly oxidized metals are present in the as-deposited coatings prepared with PC plating. The microhardness of pulse current (100:400) deposited Ni-W coating is about 750HK that is much higher than DC plated coating (635 HK). Heat treatment of the deposits carried out at different temperatures show a significant increase in microhardness which can be comparable with hard chromium coatings.