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The porphyrin handbook - Kadish K.M.

Kadish K.M. The porphyrin handbook - Academic press, 2000. - 368 p.
Download (direct link): kadishsmishgulilard2000.djvu
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kJ/mol and -209.2 J/K/mol in ethanol-free , respectively. These
differences clearly indicate the participation of ethanol in the binding.
From independent experiments, the binding constant between the porphyrin
and ethanol in chloroform at 298 was determined to be 50 M 1 and the
thermodynamic parameters for the equilibrium were AG = - 9.54kJ/mol,
A//= - 28.5kJ/ mol, and AS0 = - 65.3 J/K/mol.
As another example, the value of binding free energy,
- AG, of octyl a-D-mannoside by a steroid capped zinc porphyrin 72 was
increased by 13.4 kJ/mol in CC14 and
46 / Porphyrins and Metalloporphyrins as Receptor Models
307
H-.CO
CH,
95
CH-,
HXO
CH,
96
.CH,
CH,
97- R = NH2
98- R = NHCOCH3
99 R = NHCO(CH_,)6CH:j
100 R = NHCO(CF2)6CFj
101 R = NHCO(CH,)1,,CH;, 102- R = NHCOCH=CH,
18.7 J / mol in eyclohexane relative to , demonstrating that
liydrogen-bonding-based recognition suffers from large effects of
solvent.81 UV-Vis and 'H NMR studies suggested that the structures of the
complexes formed in CCLt and cyclohexane were similar to those in CH2C12.
In other host-guesl systems, the addition of water and alcohol was
found to enhance the binding strength. Bonar-Law and Sanders85 reported
that the addition of water or methanol to the solvents such as CHCh,
^. CC14 and cyclohexane stabilizes the complexation between steroid-
capped porphyrin 72 and glycosides by 1.4-4.7 kJ /mol. For instance. 4.7
kJ/mol of stabilization was observed by adding 0.05 M of water to CHCI;
for the complexation between capped porphyrin and octyl /i-n-glucoside at
295 K. Mizutani, Ogoshi and coworkers2- reported that ethers, alcohols
and water also assist binding of glyeopyranoside to 15,15-bis( 2-hydroxy-
l-naphthyl )porphyrinato]zinc(lI).
The enthalpy and entropy change as a result of complex formation
between 84 and 2,3,5,6-tetramethoxy-p-benzo-quinone in loluene-ethanol
cosolvent systems.14 For ethanol concentrations <0.36 mol% and >5.2 mo.
the enthalpy change was temperature independent. However, in the ethanol
concentration range of 0.36-5.2 mol9r, the temperature dependence of
enthalpy, AC,!'= (6A/Yll/c>7')|" was negative; -5.6 x 102 cal/mol at
0.9 mol% ethanol based 011 the measurements in the temperature range 10-
40 C. Temperature dependence of the enthalpy changes was ascribed to the
solvation of polar recognition groups by ethanol.
I. THERMODYNAMIC PARAMETERS FOR
COMPLEXATION
For the addition of pyridines to [5,10,15,20-tetraphenvlpor-
phyrinalo]iron([I) 104 in DMF (104(DMF) + L = 104 (L)> + DMF), enthalpy
changes and free-energy changes were linearly related to the ligand pAf,,
while the entropy changes remained relatively constant.101 Thus for 3-
cyano, 3-chloro,
3-bromo, 3-methyl and 4-methylpyridines and unsubstiluled pyridine, the
enthalpy changes range from -50.2 to -65.7kJ/mol and the entropy changes
range from -92.1 to -113.0J/K/mol. These observations can be readily
understood if one regards the enthalpy change as originating from the
coordination interaction, and the entropy change arises mainly from the
loss of translational entropy of the ligands and the gain of
translational entropy of desolvaled DMF.
Enthalpy and entropy changes in complex formation between zinc and
free-base porphyrin hosts and amino-acid derivatives and other guests
were determined.14 71 /l, sl 102-104 jjie ^[ are compiled in Table 7.
Most of the complexation processes were characterized by a negative
enthalpy change and a negative entropy change. There is a trend,
particularly in nonpolar solvents, that, as the number of recognition
groups increases and the binding becomes more light, the magnitudes of -
߰ and - AS(l become larger. The entropy loss of simple binding can be
estimated from the translational entropy of the molecule, which is
approximately 167J/K/mol for a molecule with a typical
308
Ogoshi et al.
Table 6. Binding of Porphyrin Derivatives to DNA and Related Nucleotide
Entry Host Guest - AC /kJ mol 1 Solvent
Temperature (K) Method Reference
1 87 calf thymus DNA 42.4 BPES (NaCI 0 M)
UV-Vis 243
2 87 calf thymus DNA 39.9 BPES (NaCI 0.05 M)
UV-Vis 243
3 87 calf thymus DNA 35.2 BPES (NaCI 0.1 M)
UV-Vis 243
4 87 calf thymus DNA 33.2 BPES (NaCI 0.179 M)
UV-Vis 243
5 87 calf thymus DNA 30.2 BPES (NaCI 0.3 M)
UV-Vis 243
6 87 calf thymus DNA 27.6 BPES (NaCI 0.5 M)
UV-Vis 243
7 87 calf thymus DNA 26.4 BPES (NaCI 1.0 M)
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