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We describe a new method for the quantitative measurement of weak forces between adhesion domains formed by receptor−ligand pairs. The method relies on the microinterferometric analysis of adhering vesicles subjected to an external force produced by a magnetic bead adhered to the membrane. The forces exerted on pinning centers can be deduced using classical elasticity theory. The method is applied to measure the binding strengths between solubilized solid supported integrin receptors αIIbβ3 of blood platelets and lipid-coupled cyclic peptides containing arginine−glycine−aspartate (RGD) tripetide ligands, embedded in the vesicle, that are recognized selectively by the integrins. We find that unbinding takes place at force levels far below those found in single-molecule studies. We interpret our findings in terms of the fracturing of the receptor−ligand pairs by the torque generated by the force which is much more effective than the traction.

In this paper we study the effect of monovalent Na+ and divalent Ca2+ ions on the swelling behavior and viscoelastic parameters of ultrathin layers of the natural polyelectrolyte hyaluronic acid covalently coupled to glass substrates. A colloidal probe technique is applied for this purpose based on μm latex beads, hovering over the polymer cushion. By analyzing the vertical Brownian motion of these beads with reflection interference contrast microscopy (RICM) we determined the equilibrium layer thickness (with 3 nm vertical resolution), the interfacial interaction potential, and the characteristic mesh size limiting the hydrodynamic flow within the polyelectrolyte film as a function of the ionic strength. The experimental results are interpreted in terms of three different theoretical models: the polyelectrolyte brush approximation of Pincus [#!ref1!#], a modified polyelectrolyte brush approximation in the high salt concentration limit of Ross and Pincus [#!ref2!#] and the simple scaling approximation for neutral adsorbed polymers of de Gennes [#!ref3!#]. Within experimental error all of these different models fit our experimental data and yield comparable results for the equilibrium layer thickness. Moreover we determine a thickness dependent, effective surface coverage from both brush models. The hydrodynamic properties of the films are interpreted in terms of the Brinkmann model of elastic porous media by assuming an effective mesh size, which depends linearly on the Debye screening length. The salt induced condensation of the polyelectrolyte films can be described microscopically in terms of a progressive contraction of the mesh size with increasing salt concentration.

Single actin filaments were analyzed in solutions ranging from dilute (0.2 microgram/ml), where filaments interact only with solvent, to concentrations (4.0 mg/ml) at which F-actin forms a nematic phase. A persistence length of approximately 1.8 microns and an average length of approximately 22 microns (Kaufmann et al., 1992) identify actin as a model for studying the dynamics of semiflexible polymers. In dilute solutions the filaments exhibit thermal bending undulations in addition to diffusive motion. At higher semidilute concentrations (1.4 mg/ml) three-dimensional reconstructions of confocal images of fluorescently labeled filaments in a matrix of unlabeled F-actin reveal steric interactions between filaments, which account for the viscoelastic behavior of these solutions. The restricted undulations of these labeled chains reveal the virtual tube formed around a filament by the surrounding actin. The average tube diameter scales with monomer concentration c as varies; is directly proportional to c-(0.5 +/- 0.15). The diffusion of filaments in semidilute solutions (c = (0.1-2.0) mg/ml) is dominated by diffusion along the filament contour (reptation), and constraint release by remodeling of the surrounding filaments is rare. The self-diffusion coefficient D parallel along the tube decreases linearly with the chain length for semidilute solutions. For concentrations > 2.5 mg/ml a transition occurs from an isotropic entangled phase to a coexistence between isotropic and nematic domains. Analysis of the molecular motions of filaments suggests that the filaments in the aligned domains are in thermal equilibrium and that the diffusion coefficient parallel to the director D parallel is nearly independent of filament length. We also report the novel direct observation of u-shaped defects, called hairpins, in the nematic domains.

Scientific and practical applications of supported lipid-protein bilayers are described. Membranes can be covalently coupled to or separated from solids by ultrathin layers of water or soft polymer cushions. The latter systems maintain the structural and dynamic properties of free bilayers, forming a class of models of biomembranes that allow the application of a manifold of surface-sensitive techniques. They form versatile models of low-dimensionality complex fluids, which can be used to study interfacial forces and wetting phenomena, and enable the design of phantom cells to explore the interplay of lock-and-key forces (such as receptor-ligand binding) and universal forces for cell adhesion. Practical applications are the design of (highly selective) receptor surfaces of biosensors on electrooptical devices or the biofunctionalization of inorganic solids.

Automated electron tomography is shown to be a suitable means to visualize the shape of phospholipid vesicles embedded in vitrified ice. With a slow-scan charge-coupled device camera as a recording device, the cumulative electron dose needed to record a data set of 60 projections at a magnification of 20,000X can be kept as low as 15 e-/A2 (or 1500 electrons/nm2). The membrane of the three-dimensionally reconstructed vesicles is clearly visible in two-dimensional sections through the three-dimensionally reconstructed volume. Some edges indicating a polygonal shape of the vesicles, frozen from the gel phase, are also clearly recognized. Because of the presently limited tilt angle range (+/- 60 degrees), the upper and lower "caps" of the vesicles (representing about 35% of the surface of the ellipsoidal particles) remain invisible in the three-dimensional reconstruction.

A comparison between the quartz-crystal microbalance (QCM) and surface plasmon resonance (SPR) using an especially designed flow-through cell for simultaneous measurements and flow-injection analysis (FIA) is presented. We compare the effects due to unspecific binding of bovine serum albumin (BSA) to gold surfaces, specific binding between BSA and monoclonal antibodies, regeneration experiments, serum experiments with HIV antigens and the influence of the bulk properties of liquid samples. The basic theory and its consequences on measurement signals and experimental methods are discussed. The fundamental problem of the comparability of different measurement principles is considered. We suggest guide parameters, which allow an objective judgement of the performance. We do not find any advantage of one particular system concerning sensitivity and cross sensitivity.

We studied the size distribution of macromolecular amphiphiles dissolved in a lipid bilayer matrix of phospholipids, witch were polymerized photochemically or by thermal decomposition of a radical-forming initiator. Evidence is provided that polymerization yields larger chains in two-dimensional than in three-dimensional solutions. The photochemically induced polymerization yields the largest polymers (N ∼ 10 4 ) by short-time irradiation (≤ 5 min at 208 nm), which is just long enough to produce one or two radicals per vesicle. Longer irradiation times lead to photodecomposition of the polymers, and after 10 min, only oligomers of N≤4 remain. High sample turbidities and multilamellar vesicles require longer times due to light scattering. Polymerization mediated by thermal decomposition of a water soluble initiator at 73 °C yields sharp distributions of long chain polymers (N ∼ 10 4 ) by adjusting the initiator to amphiphile ratio in such a way that polymerization occurs within a reasonable time (∼ 1 h). With increasing initiator concentration, the size distribution is shifted to smaller chains (N ∼ 300) due to simultaneous initiation of several chains per vesicle. Large polymers (N ∼ 10 4 ) are formed (both photochemically and by initiator decomposition) by both methods for amphiphile concentrations as small as 25 mol %. From the finding of a threshold concentration above which large polymers are formed, the lifetime of the radical at the growing end is estimated as t r ∼ 1-3×10 -7 s. Formation of large polymers leads to lateral phase separation of macrolipids. The resulting domain structure of the vesicle is unstable, leading to budding and subsequent detachment of small vesicles which may be essentially composed of only one large macrolipid. The budding could be a consequence of a strong spontaneous curvature of the polymerized domains caused by a sterically induced contraction of the head groups with respect to the chains

A Langmuir-type film balance equipped with a fluorescence microscope for the near ultraviolet and a spectrometer for time-resolved fluorescence spectroscopic studies (suited for lifetimes ≥5 ns) was built. The aim was to study membrane dynamics of diffusion-controlled bimolecular reactions in two-dimensional fluids. Complete exclusion of molecular oxygen was achieved. Under this condition, the dynamics of excimer formation may be studied for probe concentrations as small as 0.5 mol%. At the same concentration, domain formation due to lateral phase separation may be visually observed. In the first part, the time evolution of the fluorescence of monomer and excimer in monolayers of L-α-dimyristoylphosphatidylcholine (DMPC) is studied

The application of impedance analysis to biosensor devices based on supported lipid/protein membranes is explored. Lipid membranes with a high degree of surface coverage (≃99.5%) have been prepared by two methods. Firstly, very stable high-resistance bilayers are formed by deposition of a covalently bound monolayer of mercaptoalkyls on gold-covered substrates and subsequent transfer of a lipid monolayer via monolayer transfer. Secondly, the preparation of planar membranes by fusion of vesicles onto charged surfaces is demonstrated

The cell plasma is a composite type of material that is made up of a two-dimensional liquid crystal (lipid–protein bilayer) to which a macromolecular network (the cytoskeleton) is loosely coupled. The latter may be approximately two dimensional as in the case of the erythrocytes or may extend throughout the whole cell cytoplasm. Owing to this combination of two states of matter, the membrane combines the dynamics and flexibility of a fluid with the mechanical stability of a solid. Owing to its low dimensionality, the local structure of the bilayer or the global shape of cells may be most effectively controlled and modulated by biochemical signals such as macromolecular adsorption. The present contribution deals with comparative studies of the local and global dynamic properties of biological and artificial membranes. In the first part the question of the physical basis of selective lipid–protein interaction mechanisms is addressed and the outstanding viscoelastic properties of plasma membranes and their role for local instabilities shape fluctuations of cells and the cell–substrate interaction are described. The second part deals with the molecular architecture and dynamics of composite membranes prepared by combining monomeric and macromolecular lipids. These model membranes open new possibilities to mimick complex mechanical processes of cell plasma membranes and to prepare low-dimensionality macromolecular solutions and gels. Finally, the use of such compound systems by nature to prepare the semipermeable protective layers of plant leaves, the so-called cuticle, is discussed. In analogy to plasma membranes, the local transport properties are modulated by variation of the liquid-crystalline state of the monomeric waxes.

Suspensions of erythrocytes in media of low conductivity are subjected to homogenous high frequency electric fields (1 MHz, approximately 10 to 40 kV/m). The resulting transient deformation of the cells is measured by laser light diffraction. Employing a viscoelastic model of the erythrocyte membrane, relative values of membrane shear modulus and response time can currently be determined to within 7% or better. With a measurement time of one minute the average values of some 10(5) cells can be obtained. As a test of the method, osmotic swelling and deflation of the cells and crosslinking their membrane skeleton by diamide are used to alter the viscoelastic properties of the erythrocytes.

We present high-precision measurements of the bending elastic moduli of bilayers of a variety of different lipids and of modifications of the flexural rigidity by solutes. The measurements are based on the Fourier analysis of thermally excited membrane undulations (vesicle shape fluctuations) using a recently developed dynamic image processing method. Measurements of the bending modulus as a function of the undulation wave vector provide information on the limitation of the excitations by the constraint of finite membrane area (surface tension effects) and by transient lateral tensions arising in each monolayer by restricted diffusion at high wave vectors. Measurements of the autocorrelation function of the undulation amplitudes provide a further test of the theoretical models. Studies of the effect of solutes show that cholesterol increases the bending modulus of dimyristoylphosphatidylcholine from Kc = 1. 1 × 10−12 erg to 4.2 × 10−12 erg (at 30 mol%). Incorporation of a short bipolar lipid reduces Kc to the order of kT. Finally we present a variety of shape changes of vesicle and provide evidence for the stabilization of metastable non-equilibrium shapes by lateral phase separation.

The composite cell envelope is an impressive example of nature’s strategy to design complex materials and machineries with unique and stunning physical properties by self-assembly of hierarchical structures. The most simple prototype of a composite cell membrane is the envelope (often called plasma membrane) of red blood cells.

This chapter deals with the viscoelastic properties of purely entangled and cross-linked networks of actin. It concentrates on experimental techniques, physical concepts and biological implications. In particular the question of correlations between the phenomenological viscoelastic parameters (measured for instance in a rheometer) and the conformational dynamics or the bending elasticity of single polymer filaments is addressed. Another central aim is to show that high precision measurements of viscoelastic properties provide a very useful tool to detect and analyse (even subtle) effects of the manifold of actin manipulation proteins on the structural and dynamic properties of the actin-based cytoskeleton.

Semiautomatic single-axis tilt electron tomography has been used to visualize the three-dimensional organization of actin filaments in "phantom cells," i.e. lipid vesicles. The instrumentation consisted of a 120-kV electron microscope equipped with a postcolumn energy filter, which was used in the zero-loss imaging mode. Apart from changing the tilt angle, all steps required for automated tomography, such as recentering the image area, refocusing, and centering the energy-selecting slit, were performed by external computer control. This setup permitted imaging of ice-embedded samples up to a thickness of 800 nm with improved image contrast compared with that produced by tomography with a conventional electron microscope. In spite of the missing-wedge effect that is especially obvious in the study of membrane-filament interaction, single-axis tilt tomography was found to be an appropriate (in fact the only available) method for this kind of investigation. In contrast to random actin networks found in actin gels, actin filaments in and on vesicles with a bending radius of less than approximately 2 microns tend to be arranged in single layers of parallel filaments and often induce an elongated shape of the vesicles. Actin filaments located on the outside usually associate with the vesicle membrane.

The main objective of this lecture is to discuss the role of lipid-bilayer elasticity (1) for the self-organization of lipid/protein-bilayers (2) for the stabilization of domain structures and shapes of cell membranes and (3) for the control of shape transitions (e.g. bud- and pit-formation) and shape instabilities (vesicle fission). It is demonstrated that many complex shape transitions of cell membranes can be mimicked by single lipid bilayer vesicles by simply varying the area-to-volume ratio or by chemically induced bending moments suggesting that these processes are governed by the universal minimum bending energy concept of closed shells composed of stratified membranes. The essential role of the coupling between curvature and phase separation in mixed membranes for the formation and stabilization of local pits and buds or the fission of budded vesicles is demonstrated. Finally, we discuss the consequences of the pronounced thermally excited bending undulations of the hyperelastic membranes for the membrane tension, the material exchange at membrane surfaces and the control of the adhesion of vesicles (or cells) on solid substrates.

In the first part of this work we report quasielastic light scattering (QELS) studies of the internal dynamics of transient actin networks over a time range of 10(-6)-10(-2) s, scattering angles between zeta = 20 degrees and 150 degrees, and a concentration range of 0.015 (0.3) to 0.7 mg/mL (15 microM). We confirm our previous result that (1) the dynamic structure factor g(q,t) is determined by the thermally excited undulations of the actin filaments and (2) that the initial decay of g(q, t) scales as g(q, t) varies; is directly proportional to exp(-q alpha t) while the long time decay scales as g(q, t) varies; is directly proportional to exp [-(Aq alpha t) 2/3] with alpha = 2.75. The deviation of alpha from the theoretical value of alpha = 3 predicted for Rouse-Zimm chains is similar to that found for high molecular weight macromolecular solutions by QELS. A refined analysis of the dynamic structure factor showed that it can be interpreted in terms of three relaxation processes (besides the contribution of the residual monomer diffusion): (1) the dominant Rouse-Zimm dynamics, which comprises between 65 (at high concentrations) and 85% of the signal; (2) a fast relaxation process with a decay constant of gamma = 9 x 10(3) s-1, which contributes at all concentrations with the same amplitude; and (3) a nonexponential ultraslow contribution of the form g(us) varies; is directly proportional to exp [(-gamma ust)]1/4. The third contribution appears only at high concentrations and increases strongly with decreasing scattering angles. It is thus attributed to fluctuations of the mesh size of the transient actin network. In the second part we show that high sensitivity QELS may be applied to follow the actin polymerization process at low temperatures (10 degrees C). The apparent diffusion coefficient and the static scattering intensity of the actin filaments were determined as functions of polymerization time tpol. We show that the process consists of the rapid growth of a few filaments that become very long (approximately 10 microns; even at actin concentrations of 0.04 micrograms/mL) near the critical growth concentration of 0.012 micrograms/mL, as is expected for a growth process determined by nucleation. Finally, we studied actin networks polymerized in the presence of complexes of gelsolin with actin. By application of the CONTIN program we could determine the length distribution of the filaments.(ABSTRACT TRUNCATED AT 400 WORDS)

Neutron reflection and surface plasmon optical experiments have been performed to evaluate structural data of the interfacial binding reaction between the protein streptavidin and a solid-supported lipid monolayer partly functionalized by biotin moieties. Since both experimental techniques operate in a total internal reflection geometry at a substrate/solution interface, identical sample architectures allow for a direct comparison between the results obtained with these two recently developed methods. It is found that a monomolecular layer of dipalmitoyllecithin doped with 5 mol% of a biotinylated-phosphatidylethanolamine shows a thickness of d1 approximately (3.4 +/- 0.5) nm. Binding of streptavidin to the biotin groups results in an overall layer thickness of d = (5.9 + 0.5) nm that demonstrates the formation of a well-ordered protein monolayer with the (biotin+spacer) units of the functionalized lipids being fully embedded into the binding pocket of the proteins. It is demonstrated by model calculations that a more detailed picture of the internal structure of this supramolecular assembly can only be obtained if one uses deuterated lipid molecules, thus generating a high contrast between individual layers.

In the first part of the present work the interaction of glycophorin with dimyristoylphosphatidylcholine (DMPC) is studied by freeze fracture electron microscopy, densitometry, calorimetry, and 90 degree static light scattering. An exothermic lipid/protein interaction energy of WP = 190 kJ.mol-1 was found by application of the well known Van Laar relation for the displacement of the freezing point and the Gibbs-Duhem relationship. Secondly, the effects of Ca2+ on the lipid/protein interaction were studied. Following Ca2+ addition a remarkable decoupling of the interaction of the glycophorin head group with the bilayer surface was revealed by densitometry and gold-labeling electron microscopy. It is estimated that about 80% of lipid once disturbed by the adsorption of glycophorin head groups is decoupled after addition of Ca2+. Thirdly, the selective interaction of glycophorin with binary lipid mixtures was studied, including the mixtures of DMPC with dimyristoylphosphatidylserine (DMPS) and dilauroylphosphatidylcholine (DLPC), and the mixture of dipalmitoylphosphatidylcholine (DPPC) with DLPC.

The internal dynamics of actin filaments and the rheological properties of transiently and chemically cross‐linked actin networks were studied by quasielastic light scattering and a new type of rheometer. Evidence is provided that the actin solutions exhibit typical universal properties as solutions of high molecular weight polymers exhibiting Rouse‐Zimm behavior. A number of power laws is established and the persistence length of actin filaments is determined as λ≊0.3 μm.

Next-generation neutron sources are under construction in the United States and Japan. But plans for the equivalent European project, the European Spallation Source (ESS), have recently received a cold reception by the German research council. In their Policy Forum, [Keimer, Sackmann, and Withers][1] argue that without the ESS, Europe will fall behind in fields as diverse as physics, engineering, and biophysics. They strongly urge the council to reconsider its position. [1]: http://www.sciencemag.org/cgi/content/full/298/5593/543

Triplet-Excitons in a mixed 1 : 1 anthracene—tetracyanobenzene single crystal are established by ESR-spectrocopy. These excitons (lifetime 0.5 msec) are characterized by a hopping frequency of v = 1.3 × 10 6 K at 300K. The temperature dependence of the ESR line shape indicates a phase transition of the crystal at T t = 205K. Above and below the phase transition the exciton mobility is nearly temperature independent.

The phase diagram of phospholipid monolayers is investigated using fluorescence microscopic and thermodynamic techniques. The images recorded using low light level camera tubes show patterns of inhomogeneities in the condensed as well as in the expanded states. These are ascribed to different dye solubilities and different molecular densities, respectively, in coexisting phases. – For pressures above that corresponding to a sharp break in surface pressure versus area isotherms at least two phases coexist. The monolayer is macroscopically fluid with an almost constant diffusion coefficient throughout the so-called liquid expanded, liquid condensed and the intermediate phase. For dipalmitoylphosphatidylcholine (DPPC) at molecular areas as small as 55 A2/molecule a drastic decrease in diffusion by about two orders of magnitude is observed. The gas/liquid transition is observed from a formation of characteristic, symmetrical lipid domains on the water surface.

The dipalmitoylphosphatidylcholine (DPPC)/water-system was studied by differential scanning calorimetry between 0.1 and 17 weight percent of water and from 22°C to 142°C. Main emphasis was directed towards the exact determination of the water content. This was achieved by a moisture meter based on the Karl-Fischer method. – The scanning curves exhibit up to 6 transition lines altogether. In order to study the variation of transition temperatures with the water concentration, heating and cooling curves of one sample were run repeatedly up to 57 times. A small leakage of the sample capsule allowed for a very small water loss at each scanning cycle leading to a continuous decrease in water concent at each scanning run. The water content was thus changed from 5.5 to about 0.5 weight percent. A phase diagram of the DPPC/water-system is established.

We investigated the protein-mediated phospholipid transfer between small vesicles by fluorescence polarization measurements with diphenylhexatriene as optical probe. Thermotropic-phase-transition curves were taken after mixing two vesicle preparations of lipids exhibiting different gel-to-liquid phase transitions. From the heights of each phase-transition step we were able to follow the lipid transfer process without separating the two vesicle preparations.

The application of liquid-crystal glasses in triplet ESR spectroscopy is described. Anisotropic glasses have been prepared from electric field oriented nematic mixtures of cholesteryl chloride and cholesteryl laurate (1.85:1 by weight) by rapid cooling. The partial alignment of the molecules affects the triplet ESR lineshape in a characteristic way. By analyzing these changes in the ESR lineshape the elements of the zero-field-splitting (ZFS) tensor may be assigned to the molecular axes in a very simple way. For the quantitative analysis of the ESR lineshape an exponential orientation distribution function of the solute is assumed. The average orientations of the molecular axes (i.e., the elements of the Saupe order matrix) are expressed in terms of orientational constants c x i . For the symmetrical molecules studied in this work the coefficients c x i are both proportional to the principal polarizabilities and to the Van der Waals dimensions in the direction of the symmetry axes x i .

Nous presentons une technique amelioree pour l'etude par microscopie electronique et diffraction d'electrons de films monomoleculaires de lipide transferes d'une interface air/eau. Cette methode, combinee avec une technique de microfluorescence, fournit un outil puissant pour etudier la microstructure des monocouches. Nous montrons que la pente non nulle qui apparait dans les isothermes a la transition de phase fluide-cristalline provient de la coexistence de phases fluide et cristalline jusqu'a la transition de type second ordre vers l'etat condense completement cristallin. Nous presentons un modele electrostatique qui rend compte (1) de la stabilite thermodynamique dans la region de coexistence de l'etat fluide et de l'etat solide, (2) de la pente non nulle dans la region de transition, (3) de l'existence de plaquettes cristallines de taille uniforme a pression donnee au debut de la region de transition. Cas de couches minces d'acide dimyristoylphosphatidique

The protein-mediated phospholipid exchange between small unilamellar vesicles was investigated by fluorescence polarization measurements with diphenylhexatriene as optical probe. Thermotropic phase-transition measurements were taken after mixing two vesicle preparations of distinct and different phase-transition temperatures or having different states of charge. From the heights of each phase-transition step, we were able to follow the lipid-exchange process in the presence, as well as in the absence (natural exchange), of so-called transfer protein isolated from beef liver. A strong enhancement of the lipid transfer was observed at the corresponding lipid-phase-transition temperature, which is explained by the presence of fluctuating fluid and ordered domains co-existing at the lipid-phase-transition temperature. A unidirectional lipid transfer of the neutral component was observed between negatively charged phosphatidic acid and neutral phosphatidylcholine vesicles. Fluorescence polarization measurements showed the disappearance of the phosphatidylcholine phase transition, whereas the phosphatidic acid phase transition broadened and its phase transition temperature became lower.

We measure the bending elasticity of flaccid vesicles by Fourier analysis of the thermally excited surface undulations up to the 8th order. The results are explained in terms of the recent theory of Schneider et al. The value of the bending elastic constant for fluid lecithin bilayers (K c =4×10 −13 erg) agrees well with that of erythrocyte membranes but is nearly an order of magnitude smaller than that reported for the same lipid in the literature. This discrepancy is attributed to the fact that the K c value obtained by considering the lowest order mode of deformation alone is systematically too high Nous mesurons l'elasticite de flexion de vesicules flasques par l'analyse de Fourier des ondulations thermiques de surface, jusqu'au 8eme ordre. Les resultats sont expliques par la theorie recente de Schneider et al. La constante elastique de flexion pour une bicouche fluide de lecithine (K c =4×10 −13 erg) est en bon accord avec celle des membranes d'erythrocytes, mais est presque d'un ordre de grandeur plus faible que celle donnee pour les memes lipides dans la litterature. Ce desaccord est attribue au fait que la valeur de K c obtenue en ne considerant que le mode fondamental de deformation est systematiquement trop elevee

Low frequency Raman spectra (6–30 cm−1) of macroscopically ordered multilayers of dipalmitoylphosphatidylcholine (DPPC) were taken as a function of temperature (80–270 K) and for different water contents. A weak band is observed which is shifted from 18.5 to 14 cm−1 between 80 and 270 K. This band is shifted to lower frequencies with increasing water content. In addition, a strong background appears at the Rayleigh line position which grows strongly with increasing temperature. The low frequency band can be explained (1) in terms of an optical mode associated with an antiphase in‐plane vibration of two opposing monolayers or it can (2) be attributed to rotational vibrations of the hydrocarbon chains. The softening of this band is attributed to a decrease in the chain orientational order with increasing temperature. The increasing rotational freedom is expected to cause a transition from a monoclinic or orthorhombic to a hexagonal lattice and eventually triggers the Lβ’ → Lα chain melting transition (at T=...

In 32 healthy blood donors, 20 patients with histologically verified cancer and 18 patients with non-neoplastic diseases, the fluorescence polarization changes of fluorescein samples incorporated in mononuclear leucotyes were measured after incubation with PHA. The leucocytes of healthy persons, and 16/18 persons with non-neoplastic diseases, responded with a decrease in the degree of fluorescence polarization by about 20% from that in non-PHA-stimulated cells. In 19/20 patients with a variety of malignant tumours, the leucotyes did not respond to PHA stimulation with such a decrease. The exceptions among the patients with neoplastic and non-neoplastic diseases are considered, and may not be "false-negative" or "false-positive" respectively, but indicative of a particular situation in that disease. The biophysical mechanisms underlying the observed changes remain to be investigated. Images Fig. 1

Single crystals of charge-transfer (CT) complexes between tetracyanobenzene as acceptor and different aromatic donors were doped with guest donors. The molecular arrangements of the guest CT complexes forming triple energy traps in the host crystal were determined from the triplet ESR spectra of the traps. A method for the determination of relative charge-transfer triplet energies is proposed. Extended electron delocalization over more than one donor-acceptor pair has been found.

The bending elasticity (in the language of liquid crystal physics called splay elasticity) is an important property of (tension free) monolayers of amphiphiles and lipid bilayers. It plays a role in the formation and stabilization of microemulsionsl, the swelling of lipid bilayers, and the shape transformations of cells and vesicle. The bending stiffness also determines the amplitudes of thermally excited surface undulations and in this way contributes to the interplay of Van-der-Waals attraction dehydration forces, electrostatic and steric repulsion between flaccid interfaces and cells. For the above mentioned reasons, precise measurements of the bending elastic moduli of lipid layers and natural membranes have become an important task of lyotropic liquid crystal research. Such measurements can be performed by classical perturbation methods such as the micropipette technique or the recently developed electric field jump technique, 7. A completely different, non invasive method is based on the Fo...

Homogeneously doped crystals of charge transfer (CT-) complexes were grown by incorporating aromatic guest donors in host CT-crystals. The host crystals contained 1,2.4,5-tetracyanobenzene (TCNB) as acceptor and deuterated aromatic electron donors. By using such doped crystals CT complexes in a well defined configuration may be studied. The triplet states of the guest complexes were used as ESR spectroscopic probes in order to determine the molecular arrangement in the host lattice. The zero-field-splitting (ZFS) parameters, D and E, of the triplet energy traps were determined and the degree of electron derealization in the triplet state was calculated from these values. In some cases a very strong guest host interaction (multicomplex formation) was established. A method for the determination of CT-triplet energies is described (accuracy 200 cm-1) . The phosphorescence spectrum of the anthracene-TCNB complex was obtained from the delayed emission spectra of different anthracene doped CT-crystals. The vibronic structure is identical to that of anthracene, while the O-O-band of the complex is blue shifted by 600 cm-1. It is shown that the undoped anthracene-TCNB crystal exhibits P-type delayed fluorescence and that the triplet exciton diffusion in this crystal is nearly temperature independent. In the undoped biphenyl-TCNB crystal E-type delayed fluorescence originating from the thermal depopulation of the mobile triplet excitons is established. The remarkable differences of the two types of triplet excitons are interpreted in terms of the different polarity in the triplet states of the two CT-crystals.