The self-aggregation of cationic porphyrins in aqueous solution has been studied by means of absorption, 1 H NMR, and resonance light scattering spectroscopy. The aim of the present study is clarification of the factors which most influence porphyrin self-aggregation in water. Cationic 5,10,15,20-tetrasubstituted porphyrins [PorSub 4 : PC3Py (Sub ) -(CH 2 ) 3 -Py + Cl -), PC5Py (Sub ) -(CH 2 ) 5 -Py + Cl -), PC7Py (Sub ) -(CH 2 ) 7 -Py + Cl -), TPPOC2Py (Sub ) p-C 6 H 4 -O(CH 2 ) 2 -Py + Br -), and TPPOC3Py (Sub ) p-C 6 H 4 -O(CH 2 ) 3 -Py + Br -), where Py + ) N-alkylpyridinium] were used. PC3Py forms a dimer in aqueous solution with or without an added inorganic salt. In the presence of KNO 3 , dimer formation of PC3Py is dominated by a large and negative enthalpy change. The entropy change for aggregation increases with increasing concentrations of added KNO 3 , while enthalpy changes are almost constant. The thermodynamic parameters suggest that dimer formation of PC3Py is the result of a large enthalpic gain due to extended van der Waals interactions, in cooperation with enhanced hydrophobic interactions. Electrostatic repulsion suppresses further association. However, other cationic porphyrins studied show evidence of higher self-aggregate formation. X-ray crystallographic studies of PC5Cl (Sub ) -(CH 2 ) 5 -Cl), a precursor of PC5Py, show the formation of a slipped face-to-face dimer as the basic unit for forming a crystal lattice, while that of TPP (Sub ) -C 6 H 5 ) indicates the absence of face-to-face stacking interaction in the crystals. Judging from these results, it is assumed that the slipped face-to-face dimer is the unit of the higher self-aggregates of PC5Py or PC7Py in water with or without KNO 3 . Elongated alkyl chains of PC5Py and PC7Py may be responsible by enhancing hydrophobic interaction of the porphyrins studied. TPPOC2Py alone forms a J-aggregate, characterized by a sharp and red-shifted Soret band and a strongly enhanced resonance light scattering signal. Higher self-aggregates having face-to-face arrangement are formed with TPPOC3Py; these provide no enhanced RLS feature. The present study reveals the dependence of aggregate formation of water-soluble porphyrins on the peripheral mesosubstituents.

The absorption spectrum of light-adapted purple membrane in 3 M KCl is dependent on temperature even in the room temperature region. Temperature-induced difference spectra at various pH values suggested that the trans isomer of bacteriorhodopsin, bR570, is in thermal and/or photodynamic equilibrium with several different conformers. The major second conformer occurring at neutral pH had the same spectroscopic properties as the 13-cis isomer, and its content at 35 degrees C was estimated to be more than 20%. Heterogeneity in the protein conformation became more significant above pH8, where temperature-induced difference spectra exhibited a negative peak at 580 nm and a positive peak at 296 nm. This absorption change is very similar to that observed upon the formation of the N intermediate, suggesting that an N-like conformer occurs at high pH and temperature. A significant temperature dependence was also seen in the M decay kinetics at high pH, which were described by two decay components; i.e., the fast decaying M (Mf) was predominant at low temperature, but the amplitude of the slow component (M(s)) increased with increasing temperature. It is suggested that M(s) is generated upon excitation of the N-like conformer, in which the residue (Asp-96) usually acting as a proton donor to the Schiff base is deprotonated. The N-like conformer could be N itself, because M(s) was enhanced when N was accumulated by background light. A strong correlation between the amplitude of M(s) and the concentration of N was also revealed by the accumulation kinetics of Mf, M(s), and N after the onset of continuous actinic light.(ABSTRACT TRUNCATED AT 250 WORDS)

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Changes in clinical pathology parameters, particularly those related to blood coagulation, were examined throughout the gestation period in New Zealand White rabbits. As compared with the non-pregnant group, the following major changes were observed in the pregnant group. For blood coagulation-related parameters, platelets increased progressively and fibrinogen increased slightly from organogenesis, prothrombin time was significantly prolonged during organogenesis and shortened in the late fetal growth stage, activated partial thromboplastin time was significantly prolonged during the fetal growth stage, and antithrombin III increased during and after late organogenesis. Such changes in blood coagulation-related parameters during the later stages of gestation seem to be physiological responses in preparation for protecting against excessive haemorrhage or haemostasis at parturition. For the other haematological and blood chemical parameters as well as progesterone, red blood cell counts, haemoglobin and haematocrit began to decrease during organogenesis and continued to decrease thereafter. Reticulocyte counts significantly increased during organogenesis and decreased thereafter. White blood cell parameters, except for neutrophils, showed significant decreases during the fetal growth stage. Serum progesterone concentration reached its highest level early in organogenesis and decreased thereafter. Total protein, albumin, glucose, cholesterol, calcium, blood urea nitrogen and creatinine decreased significantly during the middle and/or late periods of gestation. In conclusion, the data obtained from the present study can be used as background data for effective evaluation of reproductive toxicology in rabbits, and pregnant rabbits may serve as models of pregnant women in research pertaining to clinical pathology and gestation.