327,854 research outputs found
Revoking excited state intra-molecular hydrogen transfer by size dependent tailor-made hierarchically ordered nanocapsules
No full textCurcumin associated poly(allylamine hydrochloride) cross-links with dipotassium phosphate and subsequently is assembled with ∼24 nm SiO 2 nanoparticles to form hierarchically ordered nanocapsule structures, which are 100-1000 nm in size depending on the concentration of dipotassium phosphate. These structures reverse the excited state intra-molecular hydrogen transfer in curcumin depending on the size of the nanocapsules. © 2014 The Royal Society of Chemistry.Adhikary R, 2010, J PHYS CHEM B, V114, P2997, DOI 10.1021-jp9101527; Adhikary R, 2009, J PHYS CHEM B, V113, P5255, DOI 10.1021-jp901234z; Amali AJ, 2011, ANAL CHIM ACTA, V708, P75, DOI 10.1016-j.aca.2011.10.001; Anker JN, 2008, NAT MATER, V7, P442, DOI 10.1038-nmat2162; Bailey RC, 2003, J AM CHEM SOC, V125, P13541, DOI 10.1021-ja035479k; Baiz CR, 2007, J PHYS CHEM A, V111, P10139, DOI 10.1021-jp074290i; Bong PH, 2000, B KOR CHEM SOC, V21, P81; Demchenko AP, 2013, CHEM SOC REV, V42, P1379, DOI 10.1039-c2cs35195a; Elsasser T., 2002, ULTRAFAST HYDROGEN B; Erez Y, 2011, J PHYS CHEM A, V115, P10962, DOI 10.1021-jp206176p; Galasso V, 2008, J PHYS CHEM A, V112, P2331, DOI 10.1021-jp7108303; Hammes-Schiffer S, 2010, CHEM REV, V110, P6937, DOI 10.1021-cr100367q; Jovanovic SV, 1999, J AM CHEM SOC, V121, P9677, DOI 10.1021-ja991446m; Kee TW, 2011, AUST J CHEM, V64, P23, DOI 10.1071-CH10417; Khopde SM, 2000, PHOTOCHEM PHOTOBIOL, V72, P625, DOI 10.1562-0031-8655(2000)0720625:EOSOTE2.0.CO;2; Kong L, 2004, J MOL STRUC-THEOCHEM, V684, P111, DOI 10.1016-j.theochem.2004.06.034; Liu ZS, 2000, ADV MATER, V12, P288, DOI 10.1002-(SICI)1521-4095(200002)12:4288::AID-ADMA2883.0.CO;2-1; Mendes PM, 2008, CHEM SOC REV, V37, P2512, DOI 10.1039-b714635n; Meyer TJ, 2007, ANGEW CHEM INT EDIT, V46, P5284, DOI 10.1002-anie.200600917; Nayak S, 2004, ANGEW CHEM INT EDIT, V43, P6706, DOI 10.1002-anie.200461090; Patra D, 2011, SPECTROCHIM ACTA A, V79, P1034, DOI 10.1016-j.saa.2011.04.016; Patra D, 2012, COLLOID SURFACE B, V94, P354, DOI 10.1016-j.colsurfb.2012.02.017; Patra D, 2012, PHOTOCHEM PHOTOBIOL, V88, P317, DOI 10.1111-j.1751-1097.2011.01067.x; Patra D, 2013, MICROCHIM ACTA, V180, P59, DOI 10.1007-s00604-012-0903-5; Patra D, 2009, J MATER CHEM, V19, P4017, DOI 10.1039-b822358k; Pischel U, 2006, PHOTOCHEM PHOTOBIOL, V82, P310, DOI 10.1562-2005-02-07-RA-434; Presiado I, 2012, J PHOTOCH PHOTOBIO A, V247, P42, DOI 10.1016-j.jphotochem.2012.08.007; Rana RK, 2005, ADV MATER, V17, P1145, DOI 10.1002-adma.200401612; Roy D, 2009, CHEM COMMUN, P2106, DOI 10.1039-b900374f; Shen L, 2005, ORG LETT, V7, P243, DOI 10.1021-ol047766e; Shen L, 2007, SPECTROCHIM ACTA A, V67, P619, DOI 10.1016-j.saa.2006.08.018; Soppimath KS, 2005, ADV MATER, V17, P318, DOI 10.1002-adma.200401057; TONNESEN HH, 1982, ACTA CHEM SCAND B, V36, P475, DOI 10.3891-acta.chem.scand.36b-0475; Yallapu MM, 2012, DRUG DISCOV TODAY, V17, P71, DOI 10.1016-j.drudis.2011.09.009; Yun C, 2009, J PHOTOCH PHOTOBIO C, V10, P111, DOI 10.1016-j.jphotochemrev.2009.05.002; Zsila F, 2003, TETRAHEDRON-ASYMMETR, V14, P2433, DOI 10.1016-S0957-4166(03)00486-50
Application of synchronous fluorescence scan spectroscopy for size dependent simultaneous analysis of CdTe nanocrystals and their mixtures
No full textIn this paper, synchronous fluorescence scan (SFS) spectroscopy has been applied for the first time for the simultaneous determination of a mixture of CdTe fluorescent nanocrystals (NCs) of various sizes without a pre-separation step. It is observed that synchronous fluorescence maximum correlates well with the size of the nanocrystals, i.e.; the λSFSmax is useful to determine size dependency of NCs. Synchronous fluorescence maximum along with the second derivative can identify individual NCs in a mixture in water. The method is found to be simple, sensitive, selective and fast for NCs determination in aqueous media. © 2008 Elsevier B.V. All rights reserved.Alivisatos AP, 1996, SCIENCE, V271, P933, DOI 10.1126-science.271.5251.933; Somers RC, 2007, CHEM SOC REV, V36, P579, DOI 10.1039-b517613c; BLANCO CC, 1995, TALANTA, V42, P1037, DOI 10.1016-0039-9140(95)01506-7; CAPITAN F, 1992, TALANTA, V39, P21, DOI 10.1016-0039-9140(92)80045-F; Chen M, 2007, MATER CHEM PHYS, V101, P317, DOI 10.1016-j.matchemphys.2006.06.003; Dong WT, 2003, OPT MATER, V22, P227, DOI 10.1016-S0925-3467(02)00269-0; Dyadyusha L, 2005, CHEM COMMUN, P3201, DOI 10.1039-b500664c; Eychmuller A, 2000, J PHYS CHEM B, V104, P6514, DOI 10.1021-jp9943676; Falcon SG, 1996, TALANTA, V43, P659; Hardman R, 2006, ENVIRON HEALTH PERSP, V114, P165, DOI 10.1289-ehp.8284; Huang CP, 2008, SENSOR ACTUAT B-CHEM, V130, P338, DOI 10.1016-j.snb.2007.08.021; Kapitonov AM, 1999, J PHYS CHEM B, V103, P10109, DOI 10.1021-jp9921809; Konstantianos DG, 1996, ANALYST, V121, P909, DOI 10.1039-an9962100909; Lannoo M, 1996, J LUMIN, V70, P170, DOI 10.1016-0022-2313(96)00053-1; Masala O, 2004, ANNU REV MATER RES, V34, P41, DOI 10.1146-annurev.matsci.34.052803.090949; PANADERO S, 1993, TALANTA, V40, P225, DOI 10.1016-0039-9140(93)80326-M; Patra D, 2001, TALANTA, V55, P143, DOI 10.1016-S0039-9140(01)00404-0; Patra D, 2005, APPL PHYS LETT, V87, DOI 10.1063-1.2037194; Patra D, 2001, TALANTA, V53, P783, DOI 10.1016-S0039-9140(00)00568-3; Patra D, 2002, ANAL BIOANAL CHEM, V373, P304, DOI 10.1007-s00216-002-1330-y; Patra D, 2000, ANALYST, V125, P1383, DOI 10.1039-b003876h; Patra D, 2002, ANAL CHIM ACTA, V454, P209, DOI 10.1016-S0003-2670(01)01568-9; Patra D, 2002, TRAC-TREND ANAL CHEM, V21, P787, DOI 10.1016-S0165-9936(02)01201-3; Singh S, 2007, J NANOSCI NANOTECHNO, V7, P3048, DOI 10.1166-jnn.2007.922; Sondi I, 2004, J COLLOID INTERF SCI, V275, P503, DOI 10.1016-j.jcis.2004.02.005; VOSSMEYER T, 1994, J PHYS CHEM-US, V98, P7665, DOI 10.1021-j100082a044; Yamashita I, 2004, CHEM LETT, V33, P1158, DOI 10.1246-cl.2004.1158; Zheng J, 2004, PHYS REV LETT, V93, DOI 10.1103-PhysRevLett.93.07740219202
Time-resolved fluorescence study during denaturation and renaturation of curcumin-myoglobin complex
No full textCurcumin influences the transition point, the concentration of denaturant required to effect 50percent of the total change, of myoglobin denaturation. Curcumin enhances absorbance of myoglobin at 280nm with a binding constant K=3.0×104M-1 whereas fluorescence of curcumin is quenched by myoglobin with a Stern-Volmer association constant of 2.5×105M-1. Unfolding process of myoglobin-curcumin induces a recovery in fluorescence lifetime loss. The gain in time-resolved fluorescence lifetime during unfolding has been again lost during refolding of curcumin-myoglobin complex by dilution process suggesting partial reversibility of unfolding process for both myoglobin and curcumin-myoglobin complex. © 2012 Elsevier B.V.Abou-Zied OK, 2008, J AM CHEM SOC, V130, P10793, DOI 10.1021-ja8031289; Baglole KN, 2005, J PHOTOCH PHOTOBIO A, V173, P230, DOI 10.1016-j.jphotochem.2005.04.002; Barakat C., 2012, LUMINESCENCE 0207, DOI [10.1002-bio.2354, DOI 10.1002-BIO.2354]; Barakat C., 2010, KALAHANDI RENAISSANC, VV, P64; Barik A, 2003, PHOTOCHEM PHOTOBIOL, V77, P597, DOI 10.1562-0031-8655(2003)0770597:PSOBOC2.0.CO;2; Barik A, 2007, CHEM PHYS LETT, V436, P239, DOI 10.1016-j.cplett.2007.01.006; Benesi M. L., 1949, J AM CHEM SOC, V71, P2703; Bisht S., 2007, J NANOBIOTECHNOL, V5, P1; Bourassa P, 2010, J PHYS CHEM B, V114, P3348, DOI 10.1021-jp9115996; Cantor C.R., 1980, BIOPHYSICAL CHEM 2; CHIGNELL CF, 1994, PHOTOCHEM PHOTOBIOL, V59, P295, DOI 10.1111-j.1751-1097.1994.tb05037.x; Chowdhry B, 1997, J CHEM EDUC, V74, P236; Clifford NW, 2008, J MATER CHEM, V18, P162, DOI 10.1039-b715100d; Connors K. A., 1987, MEASUREMENTS MOL COM; Creighton T. E., 1993, PROTEIN STRUCTURE; Creighton T. E., 1992, PROTEIN FOLDING; DAUTREVA.M, 1969, EUR J BIOCHEM, V11, P267, DOI 10.1111-j.1432-1033.1969.tb00769.x; Devasenam T, 2003, PHARM RES, V27, P133; DILL KA, 1991, ANNU REV BIOCHEM, V60, P795, DOI 10.1146-annurev.biochem.60.1.795; EFTINK MR, 1994, BIOPHYS J, V66, P482; EVANS SV, 1990, J MOL BIOL, V213, P885, DOI 10.1016-S0022-2836(05)80270-0; Feng W, 2006, J FLUORESC, V16, P53; GOLDBERG ME, 1991, TRENDS BIOCHEM SCI, V16, P358, DOI 10.1016-0968-0004(91)90148-O; Jones CM, 1997, J CHEM EDUC, V74, P1306; Jovanovic SV, 2001, J AM CHEM SOC, V123, P3064, DOI 10.1021-ja003823x; Jovanovic SV, 1999, J AM CHEM SOC, V121, P9677, DOI 10.1021-ja991446m; Leung MHM, 2008, LANGMUIR, V24, P5672, DOI 10.1021-la800780w; Lin YG, 2007, CLIN CANCER RES, V13, P3423, DOI 10.1158-1078-0432.CCR-06-3072; Pace C N, 1986, Methods Enzymol, V131, P266; Pace N.C., 1989, PROTEIN STRUCTURE PR; Patra D, 2012, LUMINESCENCE, V27, P11, DOI 10.1002-bio.1313; Patra D, 2011, SPECTROCHIM ACTA A, V79, P1034, DOI 10.1016-j.saa.2011.04.016; Patra D, 2011, SPECTROCHIM ACTA A, V79, P1823, DOI 10.1016-j.saa.2011.05.064; Patra D., PHOTOCHEM P IN PRESS; Privalov P.L., 1990, BIOCH MOL BIOL, V25, P281; PUETT D, 1973, J BIOL CHEM, V248, P4623; Rankin MA, 2004, SUPRAMOL CHEM, V16, P513, DOI 10.1080-10610270412331283583; SCHECHTE.AN, 1968, J MOL BIOL, V35, P567, DOI 10.1016-S0022-2836(68)80015-4; Schmid F.X., 1989, PROTEIN STRUCTURE PR; SHARMA OP, 1976, BIOCHEM PHARMACOL, V25, P1811, DOI 10.1016-0006-2952(76)90421-4; SRIVASTAVA KC, 1995, PROSTAG LEUKOTR ESS, V52, P223, DOI 10.1016-0952-3278(95)90040-3; Sun YM, 2002, ORG LETT, V4, P2909, DOI 10.1021-ol0262789; TANFORD C, 1964, J AM CHEM SOC, V86, P2050, DOI 10.1021-ja01064a028; Tourkina E, 2004, AM J RESP CELL MOL, V31, P28, DOI 10.1165-rcmb.2003-03540C; Vemula PK, 2006, J AM CHEM SOC, V128, P8932, DOI 10.1021-ja062650u; WARE WR, 1962, J PHYS CHEM-US, V66, P455, DOI 10.1021-j100809a02044
Acridine orange and silica nanoparticles facilitated novel robust fluorescent hollow microcapsules toward DNA bio-sensor
No full textTuning optical properties by nanotechnology has become a topic of larger interest as these materials can be of extraordinary sensitivity, selectivity and robustness toward sensing applications. Here we report novel fluorescent hollow microcapsules via congregation of poly (l-lysine) interceded by silica nanoparticles and acridine orange. Scanning tunneling microscope images confirm spherical nature of microcapsules with size of 1-3μm. The hollow structures are verified by fluorescent images, which indicate acridine orange is intermingled in the shell wall of the microcapsules. The excitation fluorescence spectra reveal that acridine orange exists in monomeric and aggregated form within the microcapsules. But at pH 8.5, monomeric acridine orange diffuses out of microcapsules. Association of acridine orange with poly (l-lysine) and SiO2 nanoparticles in monomeric or aggregated form does not limit intercalation of acridine orange with DNA. Thus, the acridine orange based fluorescent hollow microcapsule could easily sense DNA in 100ngmL-1 concentration ranges. The excited state lifetime of fluorescent hollow microcapsules is shorter than acridine orange in neutral form, which further establishes a strong association of acridine orange with poly (l-lysine). However, the excited state lifetime is marginally quenched in the presence of DNA but independent of DNA concentration that rules out the possibility of intercalation in the excited state rather than a ground state complex formation. © 2013 .Ahmad H., 2013, J COLLOID SCI BIOTEC, V2, P153; Amali AJ, 2011, ANAL CHIM ACTA, V708, P75, DOI 10.1016-j.aca.2011.10.001; Amali AJ, 2012, CHEM COMMUN, V48, P856, DOI 10.1039-c1cc15209b; Bagaria HG, 2011, J MATER CHEM, V21, P9454, DOI 10.1039-c1jm10712g; Bi SY, 2006, SENSOR ACTUAT B-CHEM, V119, P199, DOI 10.1016-j.snb.2005.12.014; Boal AK, 2000, NATURE, V404, P746; BRUN AM, 1992, J AM CHEM SOC, V114, P3656, DOI 10.1021-ja00036a013; Carmona P.A.O., 2013, J COLLOID SCI BIOTEC, V2, P130; Connors KA., 1987, BINDING CONSTANTS ME; Du H, 1998, PHOTOCHEM PHOTOBIOL, V68, P141, DOI 10.1111-j.1751-1097.1998.tb02480.x; Kitazawa N, 2011, J MATER SCI, V46, P2036, DOI 10.1007-s10853-010-5035-x; Luchowski R, 2003, CHEM PHYS, V293, P155, DOI 10.1016-S0301-0104(03)00301-X; Lyles MB, 2002, BIOPHYS CHEM, V96, P53, DOI 10.1016-S0301-4622(02)00036-4; Manju S, 2011, COLLOID SURFACE B, V82, P588, DOI 10.1016-j.colsurfb.2010.10.021; Mann S, 1996, NATURE, V382, P313, DOI 10.1038-382313a0; Medintz IL, 2005, NAT MATER, V4, P435, DOI 10.1038-nmat1390; MURRAY CB, 1995, SCIENCE, V270, P1335, DOI 10.1126-science.270.5240.1335; Patra D, 2009, TALANTA, V77, P1549, DOI 10.1016-j.talanta.2008.09.007; Patra D, 2013, MICROCHIM ACTA, V180, P59, DOI 10.1007-s00604-012-0903-5; Patra D, 2009, J MATER CHEM, V19, P4017, DOI 10.1039-b822358k; Rahman MM, 2012, J MATER CHEM, V22, P1173, DOI 10.1039-c1jm13882k; Ribeiro L. F. V., 2013, J COLLOID SCI BIOTEC, V2, P78; Shaikh M, 2008, PHOTOCH PHOTOBIO SCI, V7, P408, DOI 10.1039-b715815g; Shenhar R, 2003, ACCOUNTS CHEM RES, V36, P549, DOI 10.1021-ar020083j; Veyret R, 2005, J MAGN MAGN MATER, V293, P171, DOI 10.1016-j.jmmm.2005.01.057; Vitzthum F, 1999, ANAL BIOCHEM, V276, P59, DOI 10.1006-abio.1999.4298; Whitesides GM, 2002, P NATL ACAD SCI USA, V99, P4769, DOI 10.1073-pnas.082065899; Wong MS, 2002, NANO LETT, V2, P583, DOI 10.1021-nl020244c0
Fluorometric sensing of DNA using curcumin encapsulated in nanoparticle-assembled microcapsules prepared from poly(diallylammonium chloride-co-sulfur dioxide)
No full textWe report on the synthesis of microcapsules (MCs) containing self-assembled nanoparticles formed from poly[diallylammonium chloride-co-(sulfur dioxide)] in the presence of citrate and silica sol nanoparticles. The MCs are spherical, and SEM and optical microscopy reveal them to have micrometer size. The fluorescent probe curcumin was encapsulated in the MCs and found to be located in the shell. The fluorescence of curcumin in the MCs is altered depending on their microenvironment. Effects of pH and ammonia on the fluorescence of curcumin in the MCs also were studied. The brightness of the probe in the MCs increases on addition of DNA. The effect was used to determine DNA from fish sperm by fluorometry. The association constant (K) is 4 000 mL. g-1, and the number of binding sites is ~1. 0. © 2012 Springer-Verlag Wien.Amali AJ, 2011, ANAL CHIM ACTA, V708, P75, DOI 10.1016-j.aca.2011.10.001; Amali AJ, 2012, CHEM COMMUN, V48, P856, DOI 10.1039-c1cc15209b; AMMON HPT, 1991, PLANTA MED, V57, P1, DOI 10.1055-s-2006-960004; Ausubel FM, 1998, CURRENT PROTOCOLS MO, pA3D1; Bagaria HG, 2011, J MATER CHEM, V21, P9454, DOI 10.1039-c1jm10712g; Boal AK, 2000, NATURE, V404, P746; Connors KA., 1987, BINDING CONSTANTS ME; Gong H, 2012, MICROCHIM ACTA, V177, P95, DOI 10.1007-s00604-011-0754-5; Hassenkam T, 2002, ADV MATER, V14, P1126, DOI 10.1002-1521-4095(20020816)14:161126::AID-ADMA11263.0.CO;2-A; KARSTEN U, 1977, ANAL BIOCHEM, V77, P464, DOI 10.1016-0003-2697(77)90259-7; Lao Christopher D, 2006, BMC Complement Altern Med, V6, P10, DOI 10.1186-1472-6882-6-10; Mann S, 1996, NATURE, V382, P313, DOI 10.1038-382313a0; MURRAY CB, 1995, SCIENCE, V270, P1335, DOI 10.1126-science.270.5240.1335; Patra D, 2011, SPECTROCHIM ACTA A, V79, P1034, DOI 10.1016-j.saa.2011.04.016; Patra D, 2012, COLLOID SURFACE B, V94, P354, DOI 10.1016-j.colsurfb.2012.02.017; Patra D, 2011, SPECTROCHIM ACTA A, V79, P1823, DOI 10.1016-j.saa.2011.05.064; Patra D, 2012, INT J BIOL MACROMOL, V50, P885, DOI 10.1016-j.ijbiomac.2012.02.010; Patra D, 2012, PHOTOCHEM PHOTOBIOL, V88, P317, DOI 10.1111-j.1751-1097.2011.01067.x; Patra D, 2009, J MATER CHEM, V19, P4017, DOI 10.1039-b822358k; Pizzo P, 2010, J CELL MOL MED, V14, P970, DOI 10.1111-j.1582-4934.2009.00681.x; QURESHI S, 1992, PLANTA MED, V58, P124, DOI 10.1055-s-2006-961412; Shen L, 2007, SPECTROCHIM ACTA A, V67, P619, DOI 10.1016-j.saa.2006.08.018; Shenhar R, 2003, ACCOUNTS CHEM RES, V36, P549, DOI 10.1021-ar020083j; Shishodia S, 2007, CURR PROB CANCER, V31, P243, DOI 10.1016-j.currproblcancer.2007.04.001; Singer VL, 1997, ANAL BIOCHEM, V249, P228, DOI 10.1006-abio.1997.2177; Sugiyama Y, 1996, BIOCHEM PHARMACOL, V52, P519, DOI 10.1016-0006-2952(96)00302-4; Tanious A, 1992, BIOCHEMISTRY-US, V31, P3103; Vitzthum F, 1999, ANAL BIOCHEM, V276, P59, DOI 10.1006-abio.1999.4298; Whitesides GM, 2002, P NATL ACAD SCI USA, V99, P4769, DOI 10.1073-pnas.082065899; Wong MS, 2002, NANO LETT, V2, P583, DOI 10.1021-nl020244c; Yang FS, 2005, J BIOL CHEM, V280, P5892, DOI 10.1074-jbc.M40475120077
Study on effect of lipophilic curcumin on sub-domain IIA site of human serum albumin during unfolded and refolded states: A synchronous fluorescence spectroscopic study
No full textCurcumin having pharmaceutical application as anti-oxidant, anti-inflammatory and anti-carcinogenic drug necessitates studying interaction of this molecule with native, unfolded and refolded state of human serum albumin (HSA), carrier protein in the blood. We proposed a simultaneous static and dynamic fluorescence quenching mechanism operating in the complex formation between HSA and curcumin. Location of curcumin in the close proximity of tryptophan with respect to tyrosine was further evident from the observation of two fold increase in rate of depletion of SFS intensity for tryptophan with respect to tyrosine in HSA in SFS spectrum. Alteration of SFS spectral peak position, electronic absorbance, fluorescence intensity and lifetime suggested chemical denaturation by urea expectedly unfold the protein molecule in the absence and presence of curcumin. Denatured HSA had similar fluorescence peak position and lifetime to that of l-tryptophan in the polar environment. During unfolding of HSA the spectral change of tyrosine and tryptophan was resolved through synchronous fluorescence spectra at two different Δλ in absence and presence of curcumin. It is found that curcumin remained bound to unfolded state of HSA and facilitated the process by pushing tryptophan moiety to more polar environment in the unfolded state. Dilution of the denatured protein by phosphate buffer reversibly refolded the sub-domain IIA, by also recovering fluorescence lifetime loss, but it was slow in the presence of curcumin. k q values indicate that curcumin-HSA complex is formed in the unfolded and refolded states as observed for native state. © 2012 Elsevier B.V.Abert WC, 1993, ANAL BIOCHEM, V213, P407; Abou-Zied OK, 2008, J AM CHEM SOC, V130, P10793, DOI 10.1021-ja8031289; Baglole KN, 2005, J PHOTOCH PHOTOBIO A, V173, P230, DOI 10.1016-j.jphotochem.2005.04.002; Barik A, 2003, PHOTOCHEM PHOTOBIOL, V77, P597, DOI 10.1562-0031-8655(2003)0770597:PSOBOC2.0.CO;2; Barik A, 2007, CHEM PHYS LETT, V436, P239, DOI 10.1016-j.cplett.2007.01.006; Benesi M. 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Epigenetic DNA-(Cytosine-5-Carbon) Modifications: 5-Aza-2'-Deoxycytidine and DNA-Demethylation
No full textDNA (cytosine5carbon) methylation is one of the hallmarks of mammalian chromatin modifications. Distinct
methylation pattern can generate synergistic or antagonistic interaction affinities for CpGislands associated with methy
lated or unmethylated cytosine binding proteins, which also may dictate histone modifications and dynamic transition
between transcriptionally silent or transcriptionally active chromatin states. The enzymes and cofactors associated with
DNAmethylation reactions are convincing in terms of chemistry and chemical thermodynamics. The mechanism of
demethylation, the candidate enzyme(s) exhibiting direct demethylase activity, and associated cofactors are not firmly
established. Use of azanucleosides, such as 5azacytidine and 5aza2′deoxycytidine (AzadC), in cell culture produces re
expression of certain genes, which otherwise were repressed in association with hypermethylated CpGrich promoters.
Hence the notion developed that AzadC is a demethylating agent. Here we discuss the broad global pictures with the fol
lowing points: first, chemical definition and recent advances regarding the mechanism of DNA (cytosine5carbon) methy
lation (MeCpGDNA or MeCpNpGDNA formation) and MeCpG/MeCpNpGDNAdemethylation, and then with the
mechanistic basis of inactivation of DNAmethyltransferase 1 by AzadC. This will clarify that: (i) AzadC has nothing to do
with DNAdemethylation; (ii) it cannot prevent even de novo methylation in nonreplicating cells; (iii) it can only prevent
replication coupled maintenance as well as de novo methylations. Finally, we would like to suggest that terming/designating
AzadC as DNAdemethylating agent is a serious misuse of chemistry and chemical terminology
Application and new developments in fluorescence spectroscopic techniques in studying individual molecules
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New ways of controlling local fields such as optic, electric, magnetic, chemical, or biochemical environments take advantage of the noninvasiveness and high temporal and spatial resolution of single-molecule fluorescence (SMF) to get a direct feedback of events at the nanometer scale in various domains of research. 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Demethylation of (Cytosine-5-C-methyl) DNA and regulation of transcription in the epigenetic pathways of cancer development
No full textCancer cells and tissues exhibit genome wide
hypomethylation and regional hypermethylation. CpGmethylation
of DNA (MeCpG-DNA) is defined as the
formation of a C–C covalent bond between the 5′-C of
cytosine and the –CH3 group of S-adenosylmethionine.
Removal of the sole –CH3 group from the methylated
cytosine of DNA is one of the many ways of DNAdemethylation,
which contributes to activation of transcription.
The mechanism of demethylation, the candidate
enzyme(s) exhibiting direct demethylase activity and
associated cofactors are not firmly established. Genomewide
hypomethylation can be obtained in several ways by
inactivation of DNMT enzyme activity, including covalent
trapping of DNMT by cytosine base analogues. Removal of
methyl layer could also be occurred by excision of the
5-methyl cytosine base by DNA glycosylases. The importance
of truly chemically defined direct demethylation of
intact DNA in regulation of gene expression, development,
cell differentiation and transformation are discussed in this
contribution
CMIP5 model evaluation for extreme ocean wave height responses to ENSO
No full textThe El Niño-Southern Oscillation (ENSO) exerts significant influences on extreme significant wave height (SWH) but climate model capabilities in reproducing the observed ENSO impact on SWH have not been evaluated. This study assesses the performances of the Coupled Model Intercomparison Project phase 5 (CMIP5) models in term of extreme SWH responses to ENSO over the Indo-Pacific Ocean focusing on December-February (DJF). 18 CMIP5 models are evaluated using their historical simulations for 1950–2005 in view of the ERA-20C reanalysis. A non-stationary generalized extreme value (GEV) analysis is employed to fit DJF maxima of 6-hourly SWHs and obtain the extreme SWH response patterns to ENSO by incorporating Niño3.4 index as a covariate. Results show that CMIP5 models can on average capture the major observed mean and extreme SWH responses to ENSO, including the increased SWH over the northeastern North Pacific (NENP) and the decreased SWH over the Maritime Continent (MC) during El Niño. The inter-model relations between ENSO characteristics and SWH responses are further examined for the two hotspot regions (NENP and MC). It is found that ENSO intensity is a dominant factor determining simulated SWH over the NENP such that models with stronger ENSO simulate stronger SWH responses. In contrast, for the MC, the sea level pressure teleconnection pattern significantly affects the inter-model spread in SWH responses, also explaining the systematic underestimation of SWH responses over the region. Implication is that ENSO intensity and atmospheric teleconnection patterns need to be considered for better simulations and reliable predictions of extreme SWH variability. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.11Nsciescopu
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