Biocompatible and bioactive nanostructured glass coatings synthesized by pulsed laser deposition: In vitro biological tests

We report on the synthesis by pulsed laser deposition with a KrF* excimer laser source (λ = 248 nm, τ = 25 ns) of bioglass thin films of 6P57 and 6P61 types. Physiology, viability, and proliferation of human osteoblast cells were determined by quantitative in vitro tests performed by flow cytometry on primary osteoblasts cultured on pulsed laser deposited bioglasses. Both types of glass films proved to be appropriate mediums for cell survival and proliferation. In a parallel investigation, cell morphology and adhesion to the surface was studied by fluorescence microscopy and scanning electron microscopy. Strong bonds between the materials and cells were found in both cases, as osteoblast pseudopodes penetrated deep into the material. According to our observations, the 6P57 glass films were superior with respect to viability and proliferation performances.     

In‐situ polymerization of aliphatic‐aromatic polyamide nanocomposites in the presence of Halloysite nanotubes

Nanocomposites consisting of semi‐aromatic polyamide (PA) and pristine or alkali activated halloysite nanotubes (HNT or mHNT, respectively) were synthesized by the in‐situ interfacial polymerization method. The condensation reactions were carried out between isophthaloyl dichloride in hexane and triethylenetetramine in water containing different amounts of HNT or mHNT. The interactions and crystallinity of the nanocomposites were studied by Fourier transform infrared (FTIR) spectroscopy and X‐ray diffraction (XRD) analysis, respectively. Development of hydrogen bonds between the functional groups of PA and hydroxyl groups of nanotubes was indicated by FTIR spectroscopy. According to the XRD analysis, the addition of HNT and mHNT nanotubes increased the crystallinity of the PA. This was ascribed to the role of nanotubes as nucleating agents in the PA matrix. Thermal resistance and char residue of PA, as revealed by thermogravimetric analysis, were enhanced by incorporating both HNT and mHNT and the latter was more effective in this regard. Furthermore, while the addition of pristine HNTs decreased the glass transition temperature (Tg) of the PA, the Tg could be increased by about 5°C, in the presence of 5 wt% of mHNTs. Finally, the facilely activated mHNT nanotubes were found to be highly efficient in improving the thermal and structural properties of semi‐aromatic PAs.     

Hydrolysis of diphenylmethyltin(iv) chloride in different aqueous solutions of ethanol

The hydrolysis of [(Ph)₂MeSn(IV)]⁺ has been studied spectrophotometrically at 25ˆC and constant ionic strength of 0.1 mol dm⁻³ sodium perchlorate. Over a wide pH range, 1–11, the investigation has been performed in different aqueous solutions of ethanol. The species formed together with their formation constants have been determined using the computer program Squad. The hydrolysis constants at different media were analyzed in terms of Kamlet and Taft's parameters. A single‐parameter correlation of the formation constants, K_1‐1 and K_1‐2, versus α (hydrogen‐bond donor acidity), β (hydrogen‐bond acceptor basicity), and π^* (dipolarity/polarizability) for both cases are relatively poor in all solutions, but multiparameter correlation represents significant improvement with regard to the single‐parameter models. In this work, we have also used the normalized polarity parameter, E, alone and in combination with the Kamlet–Taft's parameters to find a better correlation of the formation constants in different aqueous solutions of ethanol. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:654–660, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20484     

Cooperativity, sensitivity, and noise in biochemical signaling

Cooperative interactions in the binding of multiple signaling molecules is a common mechanism for enhancing the sensitivity of biological signaling systems. It is widely assumed this increase in sensitivity of the mean response implies the ability to detect smaller signals. Extending the classic work of Berg and Purcell [Biophys. J. 20, 193 (1977)] on the physical limits of chemoreception, we show that the random arrival of diffusing signaling molecules at receptor sites constitutes a noise source that is not reduced by cooperativity. Cooperativity makes reaching this limit easier, but cannot reduce the limit itself.     

Fluorescence Enhancement Ratio Dropdown at Low Fluences during Femtosecond Double Pulse Laser Ablation

In the study of double pulse ablation of materials (silicon and copper), a dropdown of double pulse to single pulse fluorescence signal enhancement at low fluences is observed. The dropdown is analysed with a simple theoretical one-dimensional heat diffusion model and verified by fluorescence time constants change as a function of fluence. The dropdown is explained as a result of liquid-solid mixture layer at the liquid and solid boundary. The effect of the layer becomes important at low fluences.     

Linear relations for efficiency calibration of γ-spectrometric measurements of bulk samples

The self-attenuation correction factor is used to relate the efficiency for a sample with a given matrix to the efficiency for an ideal sample with identical geometry but negligible photon attenuation. A certain linear relation for the efficiency for a given sample as a function of the efficiencies for a number of subsamples into which the original sample can be decomposed is established and experimentally validated. This relation can be used also in the case when the sample and the subsamples have different matrices. In this way the efficiency for volume samples with arbitrary compositions and densities can be constructed on the basis of the efficiencies (independently measured) for a number of basic geometries. Also a possibility to check the consistency of efficiency calibrations carried out with different standard sources (with different matrices) is provided.     

Preferential cytotoxicity for multidrug-resistant K562 cells using the combination of a photosensitizer and a cyanine dye

The cyanine dye 1,1',3,3,3',3'-hexamethylindodicarbocyanine iodide (HIDC) protects K562 leukemia cells from photodynamic membrane damage caused by cis-di(4-sulfonatophenyl)diphenylporphine (TPPS2) and 420 nm light. This wavelength of light is chosen because it is absorbed by TPPS2, but not by HIDC. The photodynamic system studied may be useful as a model for antineoplastic therapy. A subline of K562 leukemia (K562/DOX), expressing the multidrug-resistance (MDR) phenotype, is found to accumulate smaller amounts of HIDC than the parent cell line and thus has less photoprotection. In the absence of added HIDC, the K562/DOX cell line is more resistant to photodynamic cytotoxicity than the K562 cell line. The resistance of the K562/DOX cell line is not due to a smaller accumulation of TPPS2 than the K562 cell line. However, when both cell lines are incubated with HIDC and TPPS2, and then exposed to light, the K562/DOX cell line becomes more sensitive to photodynamic cell damage than the K562 cell line. The combination of a photosensitizer with a cationic or lysomorphotropic photoprotector represents a novel strategy for the eradication of malignant cells expressing the MDR phenotype.     

Singlet-oxygen generation from A2E

Singlet-oxygen generation was measured in solutions containing equilibrium mixtures of the retinal lipofuscins, 2-[2, 6-dimethyl-8-(2,6,6-trimethyl-1-cyclohexen-1-yl)- 1E,3E,5E,7Eoctatetraenyl]-1-(2-hydroxyethyl)-4-[4-methyl-6(2,6,6-trimethyl-1-cyclohexen-1-yl)-1E,3E,5E-hexatrienyl]-pyridinium (A2E) and double bond isomer of A2E (iso-A2E), using steady-state irradiation and using cholesterol as a singlet-oxygen trap. The amount of singlet oxygen generated by equilibrium mixtures of A2E and iso-A2E was compared with that generated by tetraphenylporphine (TPP) under the same conditions. Studies were carried out in ethanol-d6, acetone-d6, 80% cyclohexane-d(12)-20% acetone-d6 (vol/vol) and hexafluorobenzene. Using 420 nm irradiation and assuming a singlet-oxygen quantum yield of 0.60 +/- 0.12 for TPP, the singlet-oxygen quantum yields were 0.8 +/- 0.3 x 10(-3), 1.2 +/- 0.4 x 10(-3), 2 +/- 1 x 10(-3) and 4 + 1 x 10(-3), respectively. In acetone-d6, the quantum yields were smaller at longer wavelengths, with values of 0.3 +/- 0.1 x 10(-3) and 0.4 +/- 0.2 x 10(-3) at 461 and 493 nm, respectively. Singlet-oxygen generation was greatest in solvents with the lowest dielectric constants. In view of the relatively small quantum yields, the contribution of singlet-oxygen generation to the phototoxic properties of A2E and of iso-A2E will require further study.     

Structural requirements for efficient cellular photoprotection by carotenoid derivatives

We have synthesized five carotenoid derivatives: (1) Girard's reagent P (GRP)-retinal from GRP and retinal; (2) GRP-carotenal from GRP and beta-apo-8'-carotenal; (3) Girard's reagent T (GRT)-carotenal from GRT and beta-apo-8'-carotenal; (4) (GRP2-canthaxanthin from 2 mol of GRP and 1 mol of canthaxanthin; and (5) dansyl hydrazine (DH)-carotenal from DH and beta-apo-8'-carotenal. The first three derivatives are cations, whereas the fourth is a dication and the fifth is a weak base. Using K562 cells, we compared the subcellular distribution of the synthetic carotenoid derivatives with two uncharged natural carotenoids, beta-carotene and beta-apo-8'-carotenal. The two natural carotenoids were present mainly within the cell membranes. The synthetic carotenoid derivatives were more broadly distributed among the cell organelles. The positively charged derivatives had relatively high concentrations in mitochondria, whereas DH-carotenal had a relatively high concentration in lysosomes. We also measured the amount of photoprotection provided by the synthetic and natural carotenoids for K562 cells labeled with a photosensitizer (hypericin, protoporphyrin IX or cis-di[4-sulfonatophenyl]diphenylporphine). In this model system, only carotenoid derivatives with a permanent positive charge provided significant photoprotection. Neither the two natural carotenoids nor DH-carotenal were effective photoprotectors.