Homoeopathic drug induced change in liposomal anisotropy and associated change in van’t Hoff enthalpy

Using liposomal membrane of 1, 2-dipalmitoyl-sn -glycero-3- phosphatidyl choline, a well accepted model for biological membrane, we have measured the change in membrane anisotropy due to incorporation of three homoeopathic drugs silicea, sulphur and calc carb and the associated values of change in Van’t Hoff enthalpy have been calculated. Our experimental results reveal that these three homoeopathic drugs affect the membrane anisotropy in different ways and this change depends upon the potency of the medicine.

Resolution of the Ambiguity of van’t Hoff Plots by the Effect of Pressure on the Equilibrium

The change in the Gibbs free energy function, ΔG, of chemical reaction is determined by the difference between the heats respectively released to and absorbed from the environment, and separation of the enthalpy and entropy changes that these changes represent cannot be achieved without specific hypotheses as to their relations. The determination of the enthalpy of reaction by the plot of ΔG/T against 1/T (van’t Hoff plot) implicitly assumes that the enthalpy ΔH and entropy ΔS are temperature independent, and this assumption leads to very large errors when this is not the case and ΔH « TΔS. It is therefore inapplicable to the reactions of molecules, such as proteins, that have thermally activated local motions. The concepts offered previously by the author to relate the entropy and enthalpy changes in protein associations are reviewed briefly and applied to account for the temperature dependence of ΔH and ΔS. It is shown that two different values of the enthalpy computed in that manner correspond to each value of the apparent van’t Hoff enthalpy, but that the choice between the two is easily made by reference to the volume change on reaction. The enthalpies of association of subunit pairs of seven oligomers are all found to be positive and much more uniformly related to the size of the intersubunit surface than those previously assigned by use of the classical van’t Hoff plot.

Effect of irreversibility on the thermodynamic characterization of the thermal denaturation of Aspergillus saitoi acid proteinase

The thermal denaturation of the acid proteinase from Aspergillus saitoi was studied by CD and differential scanning calorimetry (DSC). This process seemed to be completely irreversible, as protein samples that were heated to temperatures at which the transition had been completed and then cooled at 25 degrees C did not show any reversal of the change in the CD signal. Similar results were obtained with DSC. Nevertheless, we were able to detect the presence of reversibly unfolded species in experiments in which the enzyme solution was heated to a temperature within the transition region, followed by rapid cooling at 25 degrees C. Accordingly, the denaturation of behaviour of the acid proteinase seems to be consistent with the existence of one (or more) reversible unfolding transition followed by an irreversible step. The van't Hoff enthalpy, delta HvH, which corresponds to the reversible transition was calculated from extrapolation to infinite heating rate as 310 kJ.mol-1. This parameter was also determined from direct estimation of the equilibrium constant at several temperatures (delta HvH = 176 kJ.mol-1). Comparison of the average delta HvH with the calorimetric enthalpy (delta Hcal. = 770 kJ.mol-1) gave a value of 3.2 for the delta Hcal./delta HvH ratio, indicating that the molecular structure of the enzyme is probably formed by three or four cooperative regions, a number similar to that of the acid proteinase, pepsin. It should be noted that a completely different conclusion would be obtained from a straightforward analysis of the calorimetric curves, disregarding the effect of irreversibility on the denaturation process.

Thermodynamic and Spectroscopic Characterization of the Berenil and Pentamidine Complexes with the Dodecanucleotide d(CGCGATATCGCG)2

The dodecanucleotide d(CGCGATATCGCG)2 was characterized by thermodynamic and UV-spectrophotometric measurements. A van’t Hoff enthalpy of ΔHuvv.H. ~ - 190 kJ/mol was determined for the thermal transition using UV spectroscopy. This value was confirmed by differential scanning calorimetry (DSC). In addition we obtained the thermodynamic data ΔHDSC = -405.1 kJ/mol, ΔSDSC = -1290 J/mol·K and ΔGDSC = -53.2 kJ/mol for the helix to coil transition of the dodecanucleotide. The association of berenil and the oligonucleotide was accompanied with a stabilization of the host duplex (increase in Tm) and an increase in the van’t Hoff enthalpy. The berenil binding parameters (ΔΔHDSC = -32.6 kJ/mol, ΔΔSDSC = -72 J/mol·K and ΔΔGDSC = -11.1 kJ/mol) revealed significant differences compared to those of the pentamidine aggregation (ΔΔHDSC = -23.7 kJ/mol, ΔΔSDSC = -53 J/mol·K and ΔΔGDSC = -7.8 kJ/mol). The transition of the pure oligonucleotide was characterized by a substantial amount of intermediate states (σDSC = 0.43) which decreased significantly upon binding of the drugs (σDSC ~ 0.80). The structural features of the complexes were analyzed by FT-IR spectroscopy. From these experiments we conclude that the configurations in the berenil and pentamidine complexes are different.

Further Evidence for a S-Syn Correlation in the Purine(β)ribosides: The Solution Conformation of Two Tricyclic Analogs of Adenosine and Guanosine

From the analysis of the HRNMR spectra of two tricyclic analogues of adenosine and guanosi­ne, 4,5-diamino-9-(β-D-ribofuranosyl) pyrimido[5,4-f]pyrrolo[2,3-d]pyrimidine (adenosine-adenosine, AA) and 4,7-diamino-9-(β-ᴅ-ribofuranosyl)pyrimido[5,4-f]pyrrolo-[2,3-d]pyrimidin-5-one (adenosine-guanosine, AG), dissolved in liquid ND3 the preferred conformations of the ribose moiety are derived in the temperature range between + 40 and -60 °C. The analysis is based on the two state N ↔ S model of the furanoside ring proposed by Altona and Sundaralingam. Both compounds show a pronounced stabilization of the S-conformer of the sugar ring ([S] ~ 0.8). The van't Hoff enthalpy for the S ↔ N equilibrium is - 3 kJ mol-1. The syn ↔ anti equilibrium is even at -60 °C fast compared to the HRNMR time scale.