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- Ghasemi, J., et al.
(författare)
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A new algorithm for the determination of protolytic constants from spectrophotometric data in multiwavelength mode : Calculations of acidity constants of 4-(2-pyridylazo)resorcinol (PAR) in mixed nonaqueous-water solvents
- 2006
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Ingår i: Talanta. - : Elsevier BV. - 0039-9140 .- 1873-3573. ; 68:4, s. 1201-1214
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Tidskriftsartikel (refereegranskat)abstract
- A new efficient, simple and versatile algorithm is presented for determination of the protolytic constants from spectrophotmetric data in multiwavelength mode based on the combining of hard and soft modeling. The algorithm was checked by determining the acidity constants of a triprotic acid from theoretical and real absorption-pH data. The real spectral data are obtained from photometric titration of different solutions of 4-(2-pyridylazo)resorcinol (PAR) by a standard base solution under an inert atmosphere. The algorithm starts the minimization process using an user supplied number of components and initial guesses of the unknown parameters and refined in a least squares manner. New algorithm is implemented in the new version of DATAN package (version 3.1). The validity of the obtained results was checked by some well known programs such as DATAN 2.1, SPECFIT/32, SQUAD, a modified version of difference spectra and a A-pH curve method. The comparison of the outputs of the DATAN 3.1 with the other programs reveals that there is a very good agreement between the obtained results and mentioned programs.
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- Niazi, A., et al.
(författare)
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Multiwavelength spectrophotometric determination of acidity constants of morin in methanol-water mixtures
- 2006
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Ingår i: Collection of Czechoslovak Chemical Communications. - : Institute of Organic Chemistry & Biochemistry. - 0010-0765 .- 1212-6950. ; 71:1, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- The acid-base properties of morin (2′,3,4′,5,7- pentahydroxyflavone) in mixtures of methanol-water at 25 °C and an ionic strength of 0.1 M are studied by a multiwavelength spectrophotometric method. To evaluate the pH-absorbance data, a resolution method based on the combination of soft- and hard-modeling is applied. The acidity constants of all related equilibria are estimated using the whole spectral fitting of the collected data to an established factor analysis model. DATAN program was used for determination of acidity constants. The corresponding pKa values in methanol-water mixtures were determined. There is a linear relationship between acidity constants and the mole fraction of methanol in the solvent mixtures. The effect of solvent properties on acid-base behavior is discussed.
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- Noaksson, K, et al.
(författare)
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Monitoring differentiation of human embryonic stem cells using real-time PCR
- 2005
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Ingår i: Stem Cells. - : Oxford University Press (OUP). - 1549-4918 .- 1066-5099. ; 23:10, s. 1460-1467
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Tidskriftsartikel (refereegranskat)abstract
- There is a general lack of rapid, sensitive, and quantitative methods for the detection of differentiating human embryonic stem cells (hESCs). Using light microscopy and immunohistochemistry, we observed that morphological changes of differentiating hESCs precede any major alterations in the expression of several commonly used hESC markers (SSEA-3, SSEA-4, TRA-1-60, TRA-1-81, Oct-4, and Nanog). In an attempt to quantify the changes during stochastic differentiation of hESCs, we developed a robust and sensitive multimarker quantitative real-time polymerase chain reaction (QPCR) method. To maximize the sensitivity of the method, we measured the expression of up- and downregulated genes before and after differentiation of the hESCs. Out of the 12 genes assayed, we found it clearly sufficient to determine the relative differentiation state of the cells by calculating a collective expression index based on the mRNA levels of Oct-4, Nanog, Cripto, and (x-fetoprotein. We evaluated the method using different hESC lines maintained in either feeder-dependent or feeder-free culture conditions. The QPCR method is very flexible, and by appropriately selecting reporter genes, the method can be designed for various applications. The combination of QPCR with hESC-based technologies opens novel avenues for high-throughput analysis of hESCs in, for example, pharmacological and cytotoxicity screening. STEM CELLS 2005;23:1460-1467.
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