Miniature all-glass robust pressure sensor.

This paper describes a newly designed all-glass miniature (Ø 125 microm) fiber-optic pressure sensor design that is appropriate for high-volume manufacturing. The fabrication process is based on the chemical etching of specially-designed silica optical fiber, and involves a low number of critical production operations. The presented sensor design can be used with either single-mode or multi-mode lead-in fiber and is compatible with various types of available signal processing techniques. A practical sensor sensitivity exceeding 1000 nm/bar was achieved experimentally, which makes this sensor suitable for low-pressure measurements. The sensor showed high mechanical stability, good quality of optical surfaces, and very high tolerance to pressure overload.

Tentoxin has at least two binding sites on CF1 and epsilon-depleted CF1 ATPases isolated from spinach chloroplast.

A new procedure for synthesis of 14C-labeled tentoxin [14C-MePhe[(Z)delta]3-tentoxin], with a high specific activity, is described. Binding experiments with CF1 or CF1-epsilon isolated from spinach chloroplast have been carried out using equilibrium dialysis technique. The results show the presence of two classes of binding sites. The association constants of the two major binding sites were derived from non-linear fitting of the binding curves. At 4 degrees C, the first binding site has a value of Ka1 = 8.2 x 10(5) M(-1) in CF1 and 8.7 x 10(5) M(-1) in CF1-epsilon, while the second binding site has lower affinity with Ka2 = 1.5 x 10(4) M(-1) in CF1 and 2.3 x 10(3) M(-1) in CF1-epsilon.

Spinal cord repair with PHPMA hydrogel containing RGD peptides (NeuroGel).

A biocompatible hydrogel of poly[N-(2-hydroxypropyl)methacrylamide] (PHPMA) which includes the cell-adhesive region of fibronectin Arg-Gly-Asp was synthesized and its structure, rheological and dielectric properties were characterized. The ability of a PHPMA-RGD hydrogel to promote tissue regeneration and support axonal outgrowth in the injured adult and developing rat spinal cord was evaluated. The structure of the PHPMA-RGD hydrogel displayed an interconnected porous structure, with viscoelastic properties similar to those of the neural tissue, and conductivity properties due to a peptide group. The polymer hydrogel provided a structural, three-dimensional continuity across the defect, facilitating the migration and reorganization of local wound-repair cells, as well as tissue development within the lesion. Angiogenesis and axonal growth also occurred within the microstructure of the tissue network, and supraspinal axons migrated into the reconstructed cord segment. In addition, the hydrogel induced a reduction of necrosis and cavitation in the adjacent white and gray matter. These polymer hydrogel matrices therefore display the potential to repair tissue defects in the central nervous system by enhancing the development of a tissue equivalent as well as axonal growth across the reconstructed lesion.

[Tentoxin: structure-activity relationship. Application to the study of its action on chloroplast ATP-synthase]. / Tentoxine: relations structure-fonction. Application à l'étude de son action sur l'ATP-synthase chloroplastique.

A mini review of the properties of the natural phytotoxin, tentoxin, is proposed. In particular, the biological activities of tentoxin on the chloroplast F0F1 proton ATPase, which realizes the synthesis of ATP at the expense of an electrochemical gradient of protons, are discussed. In this respect, structure-activity relationships of tentoxin have been re-examined in the light of the recent developments obtained by two-dimensional proton nuclear magnetic resonance (81). The conformations of the cyclic tetrapeptide [cyclo-(L-MeAla1-L-Leu2-MePhe[(Z) delta]3-Gly4)] have been studied in aqueous solution at various temperatures. Contrary to what was observed in early studies in chloroform, tentoxin was proved to exhibit multiple exchanging conformations in water. Four conformations with different proportions (51, 37, 8 and 4%) were found. Models were derived from nuclear magnetic resonance parameters and restrained molecular dynamics simulations. They confirmed that the four conformers exhibited the cis-trans-cis-trans configuration of the amide bond sequence. The conversion from one form to another is accomplished by a conformational peptide flip consisting of a 180 degrees rotation of a non-methylated peptide bond. In addition, important aggregation phenomena were observed. These effects have also been evidenced in chloroform, and compared to results derived from experiments carried out in the presence of DPC micelles. The tentoxin molecule was found self-associated in solution in a micellar-like organization. On the basis of these observations, we propose to design new analogues, with the intention of elucidating the mode of action of tentoxin in plants on the molecular level, especially under the aspect of its interaction with the chloroplast ATPase.

Multiple interconverting conformers of the cyclic tetrapeptide tentoxin, [cyclo-(L-MeAla1-L-Leu2-MePhe[(Z) delta]3-Gly4)], as seen by two-dimensional 1H-nmr spectroscopy.

The conformations of the phytotoxic cyclic tetrapeptide tentoxin [cyclo-(L-MeAla1-L-Leu2-MePhe[(Z) delta]3-Gly4)] have been studied in aqueous solution by two-dimensional proton nmr at various temperatures. Contrary to what is observed in chloroform, tentoxin exhibits multiple exchanging conformations in water. Aggregation phenomena were also observed. Four conformations with different proportions (51, 37, 8, and 4%) were observed at -5 degrees C. Models were constructed from nmr parameters and restrained molecular dynamics simulations. All the models exhibit cis-trans-cis-trans conformation of the amide bond sequence. The conversion from one form to another is accomplished by a conformational peptide flip consisting of a 180 degree rotation of a nonmethylated peptide bond.

Synthesis, structure, and properties of MeSer1-tentoxin, a new cyclic tetrapeptide which interacts specifically with chloroplast F1 H(+)-ATPase differentiation of inhibitory and stimulating effects.

A new tentoxin analogue, in which the L-methyl alanine residue is substituted by L-methylserine, has been prepared following the synthetic pathway recently described for the synthesis of tentoxin [Cavelier, F., & Verducci, J. (1995) Tetrahedron Lett. 36, 4425-4428]. Using two-dimensional homonuclear proton nuclear magnetic resonance and structural analysis, we observed that MeSer1-tentoxin, like tentoxin, adopts several conformations in aqueous solution and presents self-aggregative properties. This analogue was found to be conformationally similar to the natural toxin. It showed the same efficiency as tentoxin in inhibition of ATPase activity of the isolated chloroplast F1 proton ATPase (CF1) as well as in inhibition of the ATP synthase activity of the membrane-bound enzyme (CF0CF1) in thylakoids and proteoliposomes. At concentrations above 10 microM, MeSer1-tentoxin did not reactivate CF1 to a high extent, contrary to tentoxin. It appeared, however, to bind in the same way, since the reactivating effect of tentoxin was inhibited by MeSer1-tentoxin. These results show that it is possible, using tentoxin analogues, to separate inhibitory and activating effects on the chloroplast ATPase, despite the limited chemical difference between the two toxins.

Heterogeneous PHPMA hydrogels for tissue repair and axonal regeneration in the injured spinal cord.

A biocompatible heterogeneous hydrogel of poly[N-(2-hydroxypropyl) methacrylamide] (PHPMA) showing an open porous structure, viscoelastic properties similar to the neural tissue and a large surface area available for cell interaction, was evaluated for its ability to promote tissue repair and axonal regeneration in the transected rat spinal cord. After implantation, the polymer hydrogel could correctly bridge the tissue defect, from a permissive interface with the host tissue to favour cell ingrowth, angiogenesis and axonal growth occurred within the microstructure of the network. Within 3 months the polymer implant was invaded by host derived tissue, glial cells, blood vessels and axons penetrated the hydrogel implant. Such polymer hydrogel matrices which show neuroinductive and neuroconductive properties have the potential to repair tissue defects in the central nervous system by promoting the formation of a tissue matrix and axonal growth by replacing the lost of tissue.