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'pK Values' in keywords
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1978 (1)
1975 (2)
1Author    Requires cookie*
 Title    N ew Methods for Spectrophotometric Determination of pK-Values, II Titration of B ivalent Protolytes  
 Abstract    R ü d i g e r B l u m e , H e i n r i c h L a c h m a n n u n d J ü r g e n P o l s t e r Physikalisch-chemisches Institut der Universität Tübingen H errn P r o f . D r . D r . G. W e i t z e l zum The number of linear independent dissociation equilibria of spectrophotometric titra­ tion may be determined experimentally by means of absorbance diagrams and absor-bance-difference-quotient diagrams. The different types of spectrophotometric titration curves in two-step titrations are classified. By simulation of systematic error functions the limits of plv determination using turning points of two-step titration curves are demonstrated. By means of certain absorbance diagrams it is possible to determine the absorbance of pure ampholyte and to construct the absorbance triangle of all three pure components. From this triangle all concentration-vs pH-curves and the pK-values of a bivalent protolyte may be established. To avoid electrometric pH-measurements new methods are devised to calculate the difference of pK-values of bivalent protolytes. These new methods are demonstrated using as examples o-phthalic acid, 3-hydroxy-4-nitrobenzoic acid and sozoiodolic acid. 
  Reference    (Z. Naturforsch. 30b, 263—276 [1975]; eingegangen am 31. Oktober 1974) 
  Published    1975 
  Keywords    Spectrophotometric Titration, Absorbance Diagrams, Absorbance triangle, pK-Values, pK-Differences 
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 TEI-XML for    default:Reihe_B/30/ZNB-1975-30b-0263.pdf 
 Identifier    ZNB-1975-30b-0263 
 Volume    30 
2Author    OskarE. Polansky, LewisRequires cookie*
 Title    Zur Kenntnis organischer Lewissäuren, 31 Die Lewissäureeigenschaft einiger Barbitursäurederivate * On Organic Lewis Acids, 31 Lewis Acid Properties of Some B arbiturates  
 Abstract    Arylidenbarbituric acids (4) and arylidendimethylbarbituric acids (5) are compounds w ith a polarized C = C-double bond, and hence are electrically neutral lewis acids. There­ fore they are able to add bases. The measured UV spectra show a characteristic dependence on the pH value. pK values are reported. 
  Reference    (Z. Naturforsch. 30b, 582—586 [1975]; eingegangen am 11. März 1975) 
  Published    1975 
  Keywords    Acid, Arylidenbarbituric Acid, Arylidendimethylbarbituric Acid, UV Spectra, pK Values 
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 TEI-XML for    default:Reihe_B/30/ZNB-1975-30b-0582.pdf 
 Identifier    ZNB-1975-30b-0582 
 Volume    30 
3Author    Alfred Hissung, Clemens Von SonntagRequires cookie*
 Title    Radiolysis of Cytosine, 5-Methyl Cytosine and 2'-Deoxycytidine in Deoxygenated Aqueous Solution A Pulse Spectroscopic and Pulse Conductometric Study of the OH Adduct  
 Abstract    Using the pulse radiolysis technique the OH adducts of cytosine, 5-methyl cytosine and 2'-deoxycytidine were investigated in alkaline N20 saturated aqueous solutions. Ab-sorption spectra were recorded and their change with time was correlated with the change in conductivity. An OH -induced reaction (1.4 • 10 8 1 • mol -1 • s -1) was observed with OH adducts of cytosine and 5-methyl cytosine leading to radicals (pK = 10.3), the G-values of which were 3.2 and 1.6 respectively (conductivity measurements). These intermediates were assigned to the C-5 OH radical adducts. After completion of the free radical reactions (2k = 6 • 10 8 1 • mol -1 • s -1) the resulting product mixture showed pK-values of 8.3 (cytosine, G = 0.6), 10.5 (5-methyl cytosine, G = 0.8), 10.7 (cytosine, G=1.5; 2'-deoxycytidine, G=1.5) and 12.4 (cytosine, no G-value, determinable with optical detection). Ammonia, which is a product measured after y-radiolysis of all the three compounds investigated (G(NHs) = 0.6 ± 0.1), is not released within 15 ms after the pulse. 
  Reference    Z. Naturforsch. 33b, 321—328 (1978); received November 25 1977 
  Published    1978 
  Keywords    Cytosine, G-Values, pK-Values, Absorption Spectra, Pulse Radiolysis 
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 TEI-XML for    default:Reihe_B/33/ZNB-1978-33b-0321.pdf 
 Identifier    ZNB-1978-33b-0321 
 Volume    33