Effect of electric fields on the structure of phosphatidyl choline in a multibilayer system

Polarized attenuated total reflection (ATR)-FTIR measurements were carried out on aligned multibilayers of dipalmitoyl phosphatidyl choline (DPPC) under the influence of high electric fields. The electric fields varied from 0 up to 5.5 x 10(6) V/cm in the hydrocarbon layer and up to 1.1 x 10(6) V/cm in the polar layer of the aligned multibilayer, when the applied potential across the 1-microm-thick multibilayer plus the 0.5-microm-thick air gap reached the value of 1000 V. At relatively low applied potentials of less than 100 V, when the electric fields in the hydrocarbon and in the polar layer were below 5.5 x 10(5) and 1.1 x 10(5) V/cm, respectively, the inhomogeneous field between the two layers is adequate to start driving the polar groups into the hydrocarbon layer, exerting a pressure and penetrating them. This results in distortion of the orientation of the hydrocarbon chains. Only at much higher potentials above 600 and 700 V starts the direct reorientation of the dipoles of the different polar residues by the electric field.     

Contents of Volume 66 (2001)

Volume Contents

Contents of Volume 66 (2001)     

Eighth International Conference on Geometry

The Conference took place in the Nahsholim Sea Resort, Israel. The work was done in two parallel sections: Research in Geometry and Geometry and School. The Scientific Committee which led the Conference consisted of A. Barlotti (Firenze), W. Benz (Hamburg), A. Bichara (Roma), H. Karzel (München), H.-J. Kroll (München), F. Mazzocca (Napoli), H. Zeitler (Bayreuth), and the local organizers R. Artzy and J. Zaks. The sessions were chaired by M. A. Akivis, G. Becker, J. Böhm, D. Camp, P. V. Ceccherini, V. V. Goldberg, H. Havlicek, W. Heise, P. Herfort, B. Klotzek, H. Martini, R. H. Schulz, H. Siemon, H. Stachel, G. Stanilov, B. Uhrin, H. Walser, H. Wefelscheid, G. Weiss. A total of 71 lectures were delivered. The Conference was supported in part by The European Mathematical Society, The Emmy Noether Center of the Minerva Foundation at Bar Ilan University in Israel, The Israel Mathematical Union, and the University of Haifa. The following are abstracts of talks presented in the Research section of the Conference.     

Highly efficient 4-W Yb-doped fiber amplifier pumped by a broad-stripe laser diode

A Yb-doped double-cladding fiber amplifier is v-groove side pumped by a 100-mum -wide, broad-stripe, 975-nm laser diode. The amplifier exhibits, separately, 39% electrical-to-optical conversion efficiency, 89% internal optical-to-optical conversion efficiency, 4-W output power at 1060 nm, and a small-signal gain of 53 dB.     

Ultrawide tunable Er soliton fiber laser amplified in Yb-doped fiber

A Raman-shifted and frequency-doubled high-power Er-fiber soliton laser for seeding an efficient high-power Yb fiber femtosecond amplifier is demonstrated. The Raman-shifted and frequency-doubled Er-soliton laser is tunable from 1.00 to 1.070microm and produces bandwidth-limited 24-pJ pulses at a repetition rate of 50 MHz with a FWHM pulse width of 170 fs at 1.040microm . The Yb(3+) amplifier has a slope efficiency of 52% and generates 3-ps linearly chirped pulses with an average power of 0.8 W at 1.05microm . After pulse compression, 74-fs bandwidth-limited pulses with an average power of 0.4 W and a pulse energy of 8 nJ are generated.     

Synthesis and DNA binding of spirocyclic model compounds related to the neocarzinostatin chromophore

[formula: see text] Spirocyclic model compounds which mimic the molecular architecture of one of the decomposition products of the antitumor agent NCS-chrom have been synthesized. These readily accessible molecules bind with remarkable efficiency to bulged DNA oligonucleotides, offering potential for the design of therapeutic agents.     

Microcapsules for controlled release via donnan dialysis

The preparation of ion-exchange microcapsules that exhibit a diameter of 10 40μm, a membrane shell of 0.1-1μm in thickness and with charge densities in the range of 0.8-1.2 meq/g is described. The microcapsules were prepared by interfacial cross-linking of bromomethylated poly(phenylene oxide) (PPOBr) and poly(ethyleneimine) (PEI). These polymers were dissolved in toluene and aqueous solutions, respectively. Upon dispersing the PEI solution in the organic phase, ion-exchange microcapsules were instantaneously formed. These microcapsules contain aqueous solutions of PEI and inorganic salt and are self-sealing. They can be dried and stored in a “dormant”, inactive state. Upon exposure to ambient humidity or aqueous solutions, water diffuses rapidly into the microcapsules, establishing the conditions for Donnan exchange of ions between the external phase and the microcapsule interior. Some preliminary transport measurements of the exchange of encapsulated nitrate ions (a corrosion inhibitor) with chloride ions (a corrosion inducer) in the external phase via a Donnan exchange mechanism are reported. Ion transport and leakage rates are compared with those obtained from flat sheet ion-exchange membranes made from identical materials.     

Phase transitions and reflection positivity. II. Lattice systems with short-range and Coulomb interactions

We discuss applications of the abstract scheme of part I of this work, in particular of infrared bounds and chessboard estimates, to proving the existence of phase transitions in lattice systems. Included are antiferromagnets in an external field, hard-core exclusion models, classical and quantum Coulomb lattice gases, and six-vertex models.Research partially supported by Canadian National Research Council Grant A4015 and U.S. National Science Foundation Grants PHY-77-18762, MCS-75-21684-A02, and MCS-78-01885.