Biomedical subjects

Björn Lindman

Publications and source records attributed to Björn Lindman.

At least 19 recordsLinked to original sources

PubMed2007

Mechanisms behind the faceting of catanionic vesicles by polycations: chain crystallization and segregation.

Vesicles composed of an anionic and a cationic surfactant, with a net negative charge, associate strongly with a hydrophobically modified polycation (LM200) and with an unmodified polycation with higher charge density (JR400), forming viscoelastic gel-like structures. Calorimetric results show that in these gels, LM200 induces a rise of the chain melting temperature (Tm) of the vesicles, whereas JR400 has the opposite effect. For both polymer-vesicle systems, the shear viscosity exhibits an inflection point at Tm, and for the LM200 system the measured relaxation times are significantly higher below Tm. The neat vesicles and the polycation-bound vesicles have a polygonal-like faceted shape when the surfactant chains in the bilayer are crystallized, as probed by cryo-transmission electron microscopy. Above Tm, the neat and the LM200-bound vesicles regain a spheroidal shape, whereas those in the JR400 system remain with a deformed faceted shape even above Tm. These shape changes are interpreted in terms of different mechanisms for the polymer-vesicle interaction, which seem to be highly dependent on polymer architecture, namely charge density and hydrophobic modification. A crystallization-segregation mechanism is proposed for the LM200-vesicle system, while, for the JR400-vesicle one, charge polarization-lateral segregation effects induced by the polycation in the catanionic bilayer are envisaged.

Anions↗

PubMed2006

Formation of polyelectrolyte-surfactant complexes on surfaces.

The interfacial behavior of polyelectrolytes, mainly cationic with varying content of amphiphilic groups, and their complexes with oppositely charged surfactant are discussed. Both the kinetics and the reversibility aspect of the adsorption are considered. The structure of adsorbed layer formed was found to be dependent not only on the bulk solution phase behavior, but also on the pre-applied conditions, i.e., the path used to obtain a particular solution condition (e.g., by changing pH and concentration of salt, surfactant or polymer). Polyelectrolyte adsorption appears only partly reversible, due to its high affinity to the surface, which slows down the adsorption process. In general, relaxation occurs more easily if the direction of the process is from low to high surface coverage. Association of the surfactant with the polymer, which depends on the surfactant concentration, can completely alter the interfacial behavior. Maximum adsorption occurs generally at a surfactant concentration just before the expected phase separation region, while the complex in some cases could desorb from the surface at high enough surfactant concentration (above the cmc). Different results were obtained for coadsorption of amphiphilic polyelectrolytes when surfactant was added to the preadsorbed polymer layers and when complexes were pre-formed in the solution prior to exposing the surface to the polymer-surfactant solution.

Adsorption↗

PubMed2006

Phase behavior of a DNA-based surfactant mixed with water and n-alcohols.

The self-assembly behavior of a cationic surfactant (dodecyltrimethylammonium, DTA) with DNA as counterion in mixtures of water and n-alcohols (decanol, octanol, hexanol, butanol, and ethanol) was investigated. The phase diagrams were established and the different regions of the phase diagram characterized with respect to microstructure by (2)H NMR, small-angle X-ray scattering (SAXS), and other techniques. The DNA-DTA surfactant is soluble in all of the studied alcohols, showing increased solubility from decanol down to ethanol. All of the phase diagrams are analogous with respect to the occurrence of liquid crystalline (LC) regions, but the area of the LC region increases as one goes from decanol to ethanol. In all phase diagrams, hexagonal phases (of the reversed type) for the alcohol-rich side and lamellar phases for the other side were detected. For balanced proportions of the components, there is a coexistence of the lamellar and the hexagonal phase, here detected with a double quadrupole splitting in the (2)H NMR spectra. The correctness of the phase diagrams is confirmed by the fact that along the tie-lines the splitting magnitude remains nearly constant. All of the alcohols except for ethanol act as cosurfactants penetrating the DNA-DTA film. Adding salt to the ternary mixtures causes an increase in the unit cell dimension of the lamellar and the hexagonal phases. The phase diagram becomes more complicated when butanol is used for the alcohol phase. Here, there is the occurrence of a new isotropic phase with some properties analogous to those of the disordered sponge (L3) phase obtained for simple surfactant systems.

Alcohols↗

PubMed2006

Spontaneous formation of vesicles and dispersed cubic and hexagonal particles in amino acid-based catanionic surfactant systems.

Mixed catanionic surfactant systems based on amino acids were investigated with respect to the formation of liquid crystal dispersions and the stability of the dispersions. The surfactants used were arginine-N-lauroyl amide dihydrochloride (ALA) and N(alpha)-lauroyl-arginine-methyl ester hydrochloride (LAM), which are arginine-based cationic surfactants; sodium hydrogenated tallow glutamate (HS), a glutamic-based anionic surfactant; and the anionic surfactants sodium octyl sulfate (SOS) and sodium cetyl sulfate (SCS). It is demonstrated that in certain ranges of composition there is a spontaneous formation of vesicular, cubic, and hexagonal structures. The solutions were characterized with respect to internal structure and size by cryogenic transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and turbidity measurements. Vesicles formed spontaneously and were found for all systems studied; their size distribution is presented for the systems ALA/SCS/W and ALA/SOS/W; they are all markedly polydisperse. The aging process for the system ALA/SOS/W was monitored both by turbidity and by cryo-TEM imaging; the size distribution profile for the system becomes narrower and the number average radius decreases with time. The presence of dispersed particles with internal cubic structure (cubosomes) and internal hexagonal structure (hexosomes) was documented for the systems containing ALA and HS. The particles formed spontaneously and remained stably dispersed in solution; no stabilizer was required. (Cubosome and hexosome are USPTO registered trademarks of Camurus AB, Sweden.) The spontaneous formation of particles and their stability, together with favorable biological responses, suggests a number of applications.

Journal Article↗

PubMed2006

Incorporation of substituted acrylamides to the lamellar mesophase of Aerosol OT.

The structure and stability of the lamellar liquid crystal formed by the surfactant sodium bis-2ethylhexyl sulfosuccinate (AOT) in water is perturbed by small amounts of the substituted acrylamides N-isopropyl, N,N-diethyl, N-acryloylmorpholine, and N,N-dimethyl methacrylamide, as revealed by small angle X-ray scattering (SAXS), deuterium NMR, and microscopy. These molecules are water soluble and stay mostly in the water layers between lamellae, but a small fraction of them (5-19%) are incorporated into the AOT bilayers, thereby producing dramatic changes. Both, the degree of anisotropy in the water molecules hydrating AOT (quadrupolar splitting in (2)H NMR) and the long period spacing between lamellae (SAXS), decrease with addition of this molecules at low concentrations, which is attributed to the lower average headgroup density at the AOT/water interface when the acrylamide is incorporated. The strength of these perturbations depends on the acrylamide, and goes in parallel with the hydrophobic character of the alkyl side groups in its molecule, which suggests that the acrylamides incorporated to the bilayer enter into contact with the lipophilic tails of the AOT molecule. An interaction with the hydrated heads of AOT is also suggested in the particular case of N-isopropylacrylamide. On increasing the molecule concentration an incipient melting of the lamellar phase towards an isotropic solution takes place, first at the microscopic level, then macroscopic. Near this phase transition, the ordered domains lose the random orientation prevailing at lower acrylamide concentrations, and adopt a preferred orientation, perpendicular to the magnetic field.

Journal Article↗

PubMed2006

Interaction between covalent DNA gels and a cationic surfactant.

The interaction of covalently cross-linked double-stranded (ds) DNA gels and cetyltrimethylammonium bromide (CTAB) is investigated. The volume transition of the gels that follows the absorption of the oppositely charged surfactant from aqueous solution is studied. As do other polyelectrolyte networks, DNA networks form complexes with oppositely charged surfactant micelles at surfactant concentrations far below the critical micelle concentration (cmc) of the polymer-free solution. The size of the absorbed surfactant aggregates is determined from time-resolved fluorescence quenching (TRFQ). At low surfactant concentrations, small discrete micelles (160 < N < 210) are found, whereas large micelles (N > 500) form at surfactant concentrations of 1 mM. When the DNA is in excess of the surfactant, the surfactant binding is essentially quantitative. The gel volume decreases by 90% when the surfactant to DNA charge ratio, beta, increases from 0 to 1.

Animals↗

PubMed2006

Novel treatment in peritoneal adhesion prevention: protection by polypeptides.

OBJECTIVE: To evaluate a novel antiadhesive polypeptide complex containing a combination of poly-L-glutamate and poly-L-lysine in order to study its effectiveness and mechanisms in the prevention of postoperative abdominal adhesions in mice. MATERIAL AND METHODS: The length of peritoneal adhesions was measured and expressed in percentage of the wound length in a standardized peritoneal injury model and evaluated 7 days and 4 weeks after adhesion induction. The test compound was administered intraperitoneally following surgery. Peritoneal swabs, including the wound area, were stained in order to determine the peritoneal location and clearance of the polypeptides. Electron microscopy was performed to analyze the wound surface and the ultra-structural changes of the phagocytes in cell culture. Moreover, flow cytometry was used to evaluate the effect on macrophage phagocytic function. RESULTS: The poly-L-lysine and poly-L-glutamate combination significantly decreased peritoneal adhesions both at 7 days' (p < 0.001) and 4 weeks' (p < or = 0.001) follow-up. From the first day, the compound was found in the wound, after which this was gradually rebuilt, and covered with mesothelial cells. The macrophages phagocytosed the test compound particles, resulting in significant cell growth, and large phagocytic vacuoles. CONCLUSIONS: The intraperitoneal administration of poly-L-lysine and poly-L-glutamate resulted in a significant decrease in experimental postoperative peritoneal adhesions.

Animals↗

PubMed2005

Fragmentation of the lamellae and fractionation of polymer coils upon mixing poly(dimethylacrylamide) with the lamellar phase of aerosol OT in water.

The lamellar mesophase formed by surfactant 1,4-bis(2-ethylhexyl) sodium sulfosuccinate (AOT) in deuterated water is mixed with poly(dimethylacrylamide) (PDMAA) polymers of low molecular weight (Mn= (2-20) x 10(3)). The mixtures separate into microphases (lamellar plus isotropic polymer solution). Their microstructures are studied by microscopy, small-angle X-ray scattering (SAXS), and deuterium NMR (2H NMR). According to SAXS, the lamellar phase fractionates the molecular weight distribution of the polymer, by dissolving only chains with coil sizes smaller than the thickness of the water layers between lamellae, and keeping larger chains segregated from the lamellar phase. The fraction of polymer that is segregated from the lamellar phase grows with Mn of the polymer. In 2H NMR, there are two signals, a quadrupolar doublet (water molecules hydrating the anisotropic lamellar phase contribute to this doublet) and a singlet (water molecules in the isotropic polymer solution contribute to this singlet). These two signals are deconvoluted to analyze the phases. Mixing with the polymer produces the partial dispersion of the lamellar phase into small fragments (microcrystallites). The structure of these microcrystallites is such that they conserve the regular long period spacing of the macrophase, and are thus identified in SAXS, but they are smaller than the minimum size required to produce quadrupolar splitting (about 4 microm), and therefore, in 2H NMR, they contribute to the singlet. 2H NMR can thus not distinguish between small microcrystallites and an isotropic polymer solution segregated from the lamellar phase; instead small microcrystallites are detected as an apparent increase of the isotropic solution. The degree of dispersion produced by the polymer in the lamellar phase is correlated with the degree of segregation that the polymer suffers. Thus, much greater dispersion into microcrystallites is produced by the higher Mn polymers than by the lower Mn polymers (in the range covered by the present samples, although with a much higher molecular weight sample (3 x 10(6)) that is totally segregated no such microcrystallites were detected).

Acrylamides↗

PubMed2005

Increasing anastomosis safety and preventing abdominal adhesion formation by the use of polypeptides in the rat.

BACKGROUND AND AIMS: Postoperative adhesions can potentially be reduced using different anti-adhesive agents, though these drugs tend to compromise healing of an intestinal anastomosis. No method that significantly increases anastomosis safety is known at present. The aim of the study was to develop a concept of preventing postoperative adhesions using differently charged bioactive polypeptides, also considering healing and safety of an intestinal anastomosis. METHODS: An ileocolic anastomosis was performed under both "clean" and "septic" conditions in the rat. The treatment group received intraperitoneal poly-L-lysine and poly-L-glutamate, while controls received sodium chloride. Abdominal adhesions, anastomosis leakage and burst pressure were analysed after 1, 3, 5 and 7 days in the clean anastomosis model and after 7 days in the septic model. RESULTS: A significant decrease (p<0.01) in the amount of adhesions was seen in animals treated with polypeptides after 1, 3 and 5 days, while no difference was seen after 7 days. The anastomosis demonstrated a significantly higher burst pressure as evaluated at days 1 and 3 (p<0.05 and p<0.01, respectively) in the polypeptide-treated animals, while no difference was seen between the groups at day 5 or 7. CONCLUSION: The use of differently charged polypeptides administered intraperitoneally after surgery resulted in a significant decrease in the extent of postoperative adhesions. Furthermore, an increase in intestinal anastomosis safety, based on improved burst pressure during the first 3 days, i.e. the critical period during the healing process, was noted. No adverse effects were seen in surgery during septic conditions.

Anastomosis, Surgical↗

PubMed2005

Mixed systems of hydrophobically modified polyelectrolytes: controlling rheology by charge and hydrophobe stoichiometry and interaction strength.

Rheology and phase separation were investigated for aqueous mixtures of two oppositely charged hydrophobically modified polyelectrolytes. The typical phase separation, normally seen for oppositely charged polymer mixtures, is dramatically reduced by the presence of hydrophobic modification, and phase separation is only detected close to the point of charge neutralization. While the two polyelectrolytes separately can give high viscosities and a gel-like behavior, a pronounced maximum in viscosity and storage modulus with the mixing ratio of the polyelectrolytes is observed; the maximum is located between the points of charge and hydrophobe stoichiometry and reflects a combination of hydrophobic and electrostatic association. Lowering the charge density of the anionic polymer leads to a strengthened association at first, but at lower charge densities there is a weakened association due to the onset of phase separation. The strength of the electrostatic interaction was modified by adding salt. Increased ionic strength can lead to phase separation and to increased or decreased viscosity depending on the polyelectrolyte mixing ratio.

Journal Article↗

PubMed2005

DNA compaction onto hydrophobic surfaces by different cationic surfactants.

DNA compaction by alkyltrimethylammonium surfactants at hydrophobized silica surfaces and the effect of the counterion, as well as the hydrocarbon chain length, was investigated by in situ null-ellipsometry. In addition, DNA compaction in the presence of a gemini surfactant, hexyl-alpha,omega-bis(dodecyldimethylammonium bromide), was studied. The type of cationic amphiphile used was found not to have a pronounced effect on the mixed DNA-cationic surfactant adsorbed layer thickness, although the surface concentration excess for the mixed layers seemed to follow the same trend as that for DNA-free surfactant layers. Interestingly, it was also found that the stability of the mixed adsorbed layer largely depends on the cationic surfactant used.

Animals↗

PubMed2005

Dynamics and energetics of the self-assembly of a hydrophobically modified polyelectrolyte: Naphthalene-labeled poly(acrylic acid).

Steady-state and time-resolved fluorescence studies were performed on aqueous solutions of poly(acrylic acid) hydrophobically modified with two very different levels of naphthalene (Np). It is demonstrated that unique information on association phenomena involving hydrophobe-modifed polymers can be obtained from an extended fluorescence study by using data for a less-modified polymer as a reference. For the more highly modified polymer, the presence of excited-state (as well as ground-state) dimers in addition to monomer emission due to locally excited naphthalene gives evidence for hydrophobic association between naphthalene groups. This association becomes, as expected, much less important at higher pH due to the electrostatic repulsion between different chain segments. However, it is noted that even at high pH there is a significant self-association. The coexistence of static and dynamic quenching phenomena of the Np monomer label was also revealed in the time-resolved fluorescence data. The data are compatible with the existence of two types of monomers and one excimer and suggest that the essential contribution to the monomer emission comes from isolated chromophores, whereas excimer formation arises from both a dynamic route (excited Np chromophores able to produce a dynamic excimer) and a static route (excitation of ground-state Np dimers). At room temperature, the dissociative reaction, excimer-to-monomer, can be neglected, and thus the rate constant for excimer formation and decay could be obtained with and without considering the influence of preformed dimers. Temperature has shown to induce different behavior in the polymer photophysics. In the case of the less-labeled polymer, the decays were found to be single-exponential with the fluorescence lifetime decreasing with increasing temperature. From the temperature dependence of the steady-state fluorescence data, the activation energy for excimer formation and the binding energy of the excimer were evaluated at different pH values, through the Stevens-Ban-type plots of the excimer-to-monomer intensity ratio. With the time-resolved data, measured in the temperature range of 5-60 degrees C, it was possible to extract the intrinsic activation energies for excimer formation. The thermodynamic driving force for the intrapolymeric association was found to be dependent on a balance between hydrophobic and electrostatic interactions, which are dependent on the pH, temperature, and hydrophobic content of the polymer.

Journal Article↗

PubMed2005

The interaction between DNA and cationic lipid films at the air-water interface.

The interaction between DNA and positively charged dioctadecyldimethylammonium bromide (DODAB) and DODAB/disteroylphosphatidylcholine (DSPC) monolayers at the air-aqueous interface was studied by a combination of the surface film balance and Brewster angle microscopy. In presence of DNA, the Pi-A isotherm of the cationic monolayer shifts to larger mean molecular areas due to the electrostatic interaction with DNA while the typical liquid expanded-liquid condensed phase transition for DODAB monolayers disappear and the monolayer remains to be in the liquid expanded phase. Furthermore, the morphology of the film dramatically changes, where the large dendritic-like condensed aggregates observed for DODAB monolayers vanish. The charge density of the monolayer was varied by using mixed monolayers with the zwitterionic DSPC and no large effect was observed on the interaction with DNA. By modeling the electrostatic interactions with the linearized Poisson-Boltzmann equation using the finite-element method and taking into account the assumption in the dielectric constants of the system, it was possible to corroborate the expansion of the cationic monolayer upon interaction with DNA as well as the fact that DNA does not seem to penetrate into the monolayer.

Air↗

PubMed2005

Coil-globule transition of DNA molecules induced by cationic surfactants: a dynamic light scattering study.

The compaction and aggregation of DNA induced by cationic surfactants was studied by dynamic light scattering (DLS). Furthermore, the effect on surfactant-compacted DNA of the addition of nonionic amphiphiles and salt was studied. When using sufficiently low amounts of DNA and cetyltrimethylammonium bromide (CTAB), compacted DNA molecules could be monitored by the appearance of a band characterized by lower hydrodynamic radius and by the decrease in the intensity of the peak corresponding to extended DNA molecules. Notably, we observed a region where compacted molecules coexist with extended ones; these two populations were found to be stable with time. For higher concentrations of CTAB, only compacted molecules were observed and the size of the particles increased with time indicating aggregation. The number of globules present in the coexistence region increased linearly with the surfactant concentrations, as given by the area of the band corresponding to this population, which indicates a double-cooperativity of the binding. The DLS experiments were in good agreement with previous fluorescence microscopy studies, with certain advantages over this technique since there is no need to add fluorescence dyes and antioxidants. Furthermore, it allows the study of molecules which are too small to be visualized by fluorescence microscopy.

Cations↗

PubMed2005

Cationic amphiphilic polyelectrolytes and oppositely charged surfactants at the silica-aqueous interface.

The influence of sodium dodecyl sulfate (SDS) on the interfacial behavior of two amphiphilic polyelectrolytes, which are copolymers of the cationic monomers triethyl(vinylbenzyl)ammonium chloride and dimethyldodecyl(vinylbenzyl)ammonium chloride, at the silica-aqueous interface was studied. The fraction of amphiphilic monomers was varied, where 0DT, 40DT, and 80DT contained 0, 40, and 80 mol % monomers with dodecyl side chains, respectively. We used in situ ellipsometry to follow the kinetics of adsorption, in terms of adsorbed amount and adsorbed layer thickness, as well as the response of the adsorbed layers to changes in ionic strength and surfactant concentration. Different results were obtained when surfactant was added to the preadsorbed layers compared to the cases when complexes were preformed in the solution prior to the adsorption. In the whole range of concentrations studied, SDS interacts with 40DT and 80DT noncooperatively, whereas for 0DT cooperativity of binding is observed. The amount adsorbed increased significantly as the SDS concentration was close to the cmc. At high SDS concentrations, a lowering of the layer density was observed. For the amphiphilic polyelectrolytes, 40 DT and 80DT, no desorption from the interface was detected for the range of SDS concentrations studied, while 0DT features a maximum in adsorbed amount at concentrations close to the cmc of SDS. Adsorption of 40DT and 80DT from their mixtures with SDS is found to be path dependent with respect to the variation in SDS concentration, where the reversibility decreases with increasing SDS concentration above the expected charge neutralization point. The coadsorption of 80DT and SDS is highly irreversible with respect to changes in the ionic strength within the time scale of the experiment. In this study, we attempt to illustrate both general mechanisms and specific effects. With regard to the general behavior, it is important to note the charge regulation of both the silica surfaces and the polyion/surfactant complexes; an interplay between the two charge-regulating effects is the key to understanding our observations.

Journal Article↗

PubMed2005

SANS study of the interactions among DNA, a cationic surfactant, and polystyrene latex particles.

The compaction of DNA by a cationic surfactant both in the bulk and adsorbed on the surface of latex particles was followed for the first time by SANS. In the bulk, a decrease in the overall size of the DNA coil in the presence of the cationic surfactant was observed at a negative-to-positive charge ratio far below the phase separation region, at a negative-to-positive charge ratio of 18. Additionally, large surfactant aggregates seem to form within the DNA-surfactant complex. On the other hand, DNA adsorbs onto the surface of latex particles, forming a thick layer, as evidenced by the fitting of the SANS data to a core-shell form factor. Addition of a cationic surfactant to the DNA-coated latex particles at a negative-to-positive charge ratio of 38 induces a slight decrease in the size of the particle layer, where the cationic surfactant is evenly distributed within the adsorbed layer. A further decrease of the negative-to-positive charge ratio to 18 induces a dramatic change in the SANS data that suggests significant compaction of the adsorbed layer and the formation of large surfactant aggregates, similar to those detected in the bulk.

Adsorption↗

PubMed2005

Adsorption and aggregation of cationic amphiphilic polyelectrolytes on silica.

The adsorption of two cationic amphiphilic polyelectrolytes, which are copolymers of two charged monomers, triethyl(vinylbenzyl)ammonium chloride and dimethyldodecyl(vinylbenzyl)ammonium chloride (which is the amphiphilic one) with different contents of amphiphilic groups (40% (40DT) and 80% (80DT)), onto the hydrophilic silica-aqueous solution interface has been studied by in situ null ellipsometry and tapping mode atomic force microscopy (AFM). Adsorption isotherms for both polyelectrolytes were obtained at 25 degrees C and at different ionic strengths, and the adsorption kinetics was also investigated. At low ionic strength, thin adsorbed layers were observed for both polyelectrolytes. The adsorption increases with polymer concentration and reaches, in most cases, a plateau at a concentration below 50 ppm. For the 80DT polymer, at higher ionic strength, an association into aggregates occurs at concentrations at and above 50 ppm. The aggregates were observed directly by AFM at the surface, and by dynamic light scattering in the solution. The adsorption data for this case demonstrated multilayer formation, which correlates well with the increase in viscosity with the ionic strength observed for 80DT.

Journal Article↗

PubMed2005

Self-assembly of a hydrophobically modified naphthalene-labeled poly(acrylic acid) polyelectrolyte in water: organic solvent mixtures followed by steady-state and time-resolved fluorescence.

The solution properties of two water-soluble polymers, poly(acrylic acid) (PAA), covalently labeled with the fluorescent hydrophobic dye naphthalene (Np), have been investigated in water:organic solvent mixtures. The naphthalene chromophores have been randomly attached, onto the polymer, with two different degrees of labeling. Fluorescence measurements (steady-state and time-resolved) have been used to follow the photophysical behavior of the polymers and consequently report on the self-association of the polymers in the mixed organic (methanol or dioxane):aqueous solutions. The emission spectra of the high-labeled Np PAA reveal the presence of monomer and excimer bands whereas with the low-labeled polymer only monomer emission is observed. The excitation spectra collected at the monomer and excimer emission bands show significant differences, depending on the water content of the mixture, which indicate the simultaneous presence of preformed and dynamic dimers as routes to excimer formation. The time-resolved data decay profiles of the high-labeled polymer in the mixtures were always triple exponential whereas in pure methanol and dioxane they follow biexponential laws. The data in the mixtures are consistent with two types of monomers and one excimer. Both monomers are able to give rise to excimer in the excited state, one type involving the movement of long distant Np chromophores and the other involving a local reorientation of adjacent Np chromophores. These correspond to different decay times: (1) a long which corresponds to the long distant approach of non-neighboring Np chromophores forming an excimer and (2) a short corresponding to the fast adjustment of two neighboring Np chromophores in order to have the adequate parallel geometry. An additional decay time corresponding to the excimer decay was found to be present at all wavelengths. All the decay times were dependent on the water content of the mixture. An estimation of the two excimer forming rate constants values is made for the mixed media considered in this work. On the whole, using both steady-state and time-resolved fluorescence parameters, and by comparing data for a polymer with a small number of hydrophobes with a more highly modified one, it is possible in great detail to demonstrate how association is controlled by solvent quality for the hydrophobes and by the distance between hydrophobes.

Journal Article↗