Thermal behaviour and adsorption properties of some benzothiazole derivatives

The thermal stability and the adsorption properties have been investigated for three benzothiazole compounds: 2-mercaptobenzothiazole (MBT), N-cyclohexyl-2-benzothiazole sulfenamide (NCBSA), and 2,2′-dibenzothiazole disulphide (BTD), reported in our early studies as corrosion inhibitors for carbon steel in different media. The electrochemical results were used to calculate the degree of surface coverage (θ). The adsorption mechanism of the three inhibitors was discussed according to the free energy of adsorption ( \( \Delta G_{{\text{ads}}}^{\circ } \) ) value obtained from Temkin adsorption isotherm, this being the best way to quantitatively express the adsorption process of their molecules on carbon steel surface. Thus, a mixed type mechanism involving the synergism between physisorption and chemisorption was proposed. The thermal analysis curves showed that, for the occurred events up to 470 °C, mass losses take place with endothermic effects followed by the total oxidation of the residue with an exothermic effect around 520 °C. Consequently, their effectiveness follows the order: BTD > NCBSA ≥ MBT, while the thermal stability ranges as follows: NCBSA < BTD ≤ MBT.     

The Mode of Cell Death Induced by Photodynamic Treatment Depends on Cell Density

Madison Darby canine kidney II (MDCK II) cells were seeded out at two different densities and incubated with 125 micrograms/mL of the photosensitizer meso-tetra(4-sulfonatophenyl)porphine (TPPS4) for 18 h, washed and irradiated with blue light. Four hours later the cells were studied by fluorescence microscopy. Apoptotic cells were detected by virtue of the distinct condensation and fragmentation of chromatin, and necrotic cells were detected by uptake of propidium iodide. In addition apoptosis was measured by the TdT assay. The fraction of apoptotic cells and the fraction of necrotic cells were determined for both cell densities at various levels of survival. With < 55% total cell death the apoptotic fraction was significantly higher for cells in confluent monolayers than for cells growing in microcolonies at equitoxic doses. Confluent cells were 2.9 times more sensitive than cells in microcolonies partly due to a 1.5 times higher uptake of TPPS4 in monolayer cells. The difference in mode of cell death for the different cell densities was not related to any observable difference in subcellular localization pattern of TPPS4 at equitoxic doses of photodynamic treatment.     

The effect of glucose and temperature on the in vivo efficiency of photochemotherapy with meso-tetra-hydroxyphenyl-chlorin

Balb/c athymic nude mice bearing WiDr human colon adenocarcinoma have been employed to investigate the effect of glucose administration, cooling or slight heating on the anti-tumor activity of photochemotherapy (PCT) with meso-tetra-hydroxyphenyl-chlorin (mTHPC). An apparent delay in the tumor growth is found by combining PCT with either single or multiple injections of glucose. The anti-tumor effect of PCT is slightly enhanced by cooling the tumor to 5°C. Cooling also enhances the efficiency of PCT and glucose injection combined. Heating the tumor to 37°C has no significant effect on either PCT alone or on the combination of PCT and glucose injection. Furthermore, the kinetics of the accumulation of mTHPC in tissue have been studied. Single or multiple injections of glucose have an enhancing effect on the accumulation of mTHPC in the tumor.     

The effect of glucose and temperature on the in vivo efficiency of photochemotherapy with meso-tetra-hydroxyphenyl-chlorin.

Balb/c athymic nude mice bearing WiDr human colon adenocarcinoma have been employed to investigate the effect of glucose administration, cooling or slight heating on the anti-tumor activity of photochemotherapy (PCT) with meso-tetra-hydroxyphenyl-chlorin (mTHPC). An apparent delay in the tumor growth is found by combining PCT with either single or multiple injections of glucose. The anti-tumor effect of PCT is slightly enhanced by cooling the tumor to 5°C. Cooling also enhances the efficiency of PCT and glucose injection combined. Heating the tumor to 37°C has no significant effect on either PCT alone or on the combination of PCT and glucose injection. Furthermore, the kinetics of the accumulation of mTHPC in tissue have been studied. Single or multiple injections of glucose have an enhancing effect on the accumulation of mTHPC in the tumor.     

pH,serum proteins and ionic strength influence the uptake of merocyanine 540 by WiDr cells and its interaction with membrane structures

It has been suggested that selective uptake of photosensitizers is due to significantly lower pH of the interstitial fluid in tumors compared to normal tissue. Therefore, the cellular uptake of merocyanine 540 (MC 540) was examined at two pH values: 6.8+/-0.1 and 7.4+/-0.1. There was no difference in spectral properties (absorption and fluorescence maxima positions, fluorescence intensity) of the drug in the presence of increasing amounts of either human blood plasma or FCS (0-2%) at the two pH values investigated. Nevertheless, significantly higher amounts of the drug were taken up by WiDr cells at pH 6.8+/-0.1, both in the presence of 10% FCS and in the absence of FCS. The absorption spectra of MC 540 in the presence of egg phosphatidylcholine (PC) liposomes turned out to be NaCl concentration-dependent (0.00-0.30 mol l(-1)). Membrane fluidity, as measured by fluorescence anisotropy of diphenylhexatriene (DPH), was unchanged within the experimental error in the NaCl concentration range 0.01-0.30 mol l(-1). The spectral changes indicated an enhancement of the incorporation of MC 540 into lipid membranes with increasing ionic strength. Such a salt concentration dependence suggests a possible involvement of the surface potential in the interaction of MC 540 with lipid membranes. The results might provide an explanation of the pH dependency of the cellular uptake of MC 540 observed in this study.     

Sunbeds as Vitamin D Sources

The objectives of this work were: (1) To determine whether repeated exposures to small doses from a commercial sun bed (Wolff Solarium Super Plus 100 W) over 5 weeks gave less vitamin D than repeated exposures to twice as large, but still nonerythemogenic, doses. (2) To investigate whether the contribution to the vitamin D status from such sessions of exposures was dependent on the baseline status before the start of the sessions. (3) To determine the decay rate of the induced increment of vitamin D. The sun bed sessions raised the 25-hydroxyvitamin D levels from typical winter values to typical summer values. The mean value after exposure being 80 n m (±14) and the increase being 15 n m on average. Persons with the lowest initial levels got the largest increase. The level in this group was back to the pre-exposure level after 2–4 weeks. To maintain a summer level through the winter, when no vitamin D is produced by the sun in northern countries, one should consider increasing the recommended intake of vitamin D intake significantly, or encouraging the population to get moderate, nonerythemal sun bed exposures.     

PHTHALOCYANINE FLUORESCENCE IN TUMORS DURING PDT

Athymic nude mice with human tumors transplanted to one of the hind legs were given aluminium phthalocyanine disulfonate (AlPcS2) intraperitoneally. Twenty-four hours after the injection the mice were placed with the tumor in the sample position in a fluorescence spectrometer with modulated excitation. Exposure of the tumors to laser light at a fluence rate of 50-200 mW/cm2 led to a rapid transient reduction by up to 50% of the phthalocyanine fluorescence of the tumor. After the laser irradiation the fluence rate of the fluorescence increased almost up to the initial value within a few minutes. This finding should be taken into account when optimal fluence rates and dose fractionation schemes are sought for photodynamic therapy.     

Thickening behaviour of dilute polymer solutions in non-inertial elongational flows

A molecular interpretation is proposed to interpret the thickening behaviour of dilute solutions of high molecular weight flexible polymers in non-intertial flows having an elongational character. A set of new results has been gathered showing that the onset of very high end-pressure losses at high deformation rates in capillary flow can be explained by a flow-induced coil-stretch transition of macromolecules in solution. When a high degree of elongation is achieved a marked increase in viscous dissipation occurs in elongational flows.     

5-Aminolaevulinic acid methyl ester transport on amino acid carriers in a human colon adenocarcinoma cell line

The transport mechanisms of 5-aminolevulinic acid methyl ester (5-ALA-ME) have been studied in a human adenocarcinoma cell line (WiDr) by means of 14[C]-labeled 5-ALA-ME. The transport was found to be partly Na+ dependent, while the extracellular Cl- concentration did not affect the uptake. The transport of 5-ALA-ME into WiDr cells was dependent on the incubation temperature and was found to be completely blocked by the inhibitors of energy metabolism, 2-deoxyglucose and sodium azide. WiDr cells were treated with 10 mM of 14 different amino acids and the substrate specificity of the 5-ALA-ME transporter(s) was analyzed by treating the cells with 23 microM or 1 mM 14[C]-labeled 5-ALA-ME. The transport of 5-ALA-ME was found to be inhibited to the highest extent, i.e. about 60%, by the nonpolar amino acids L-alanine, L-methionine, L-tryptophan and glycine. The uptake of 5-ALA-ME followed an exponential decay with increasing concentration of glycine, reaching a maximum inhibition of uptake of 5-ALA-ME of 55%. Sarcosine, a specific inhibitor of system Gly, did not significantly inhibit 5-ALA-ME transport. In contrast to transport of 5-ALA, 5-ALA-ME does not seem to be taken up by system BETA transporters. In conclusion, the cellular uptake of 5-ALA-ME into WiDr cells seems to be due to active transport mechanisms, involving transporters of nonpolar amino acids.