Photon correlation spectroscopy of particle distributions

An opto-acousto-fluidic microscopic system with a high spatiotemporal resolution for microfluidic applications

In this work, we develop a new opto-acouto-fludic microsopic system, which employs a high-speed one-dimensional galvanometer scanner and an ultrafast pulse laser (600 kHz). The new system has achieved a high two-dimensional frame rate of up to 2500 Hz with a lateral resolution of 1.7 μm and an axial resolution of 36 μm at the imaging plane. To demonstrate the improved performance of the new system compared to our previous one, we carried out experiments to image the flowing droplets generated with T-junction and flow focusing configurations. We also successfully imaged dynamic migration of magneto particles subjected to non-uniform magnetic field in the microchannel. The results suggest that our new system has sufficient spatiotemporal resolutions to carry out studies for high throughput microfluidic applications.

Information-weighted constrained regularization for particle size distribution recovery in multiangle dynamic light scattering

In particle size measurement with dynamic light scattering (DLS), it is difficult to get an accurate recovery of a bimodal particle size distribution (PSD) with a peak position ratio less than ~2:1, especially when large particles (>350nm) are present. This is due to the inherent noise in the autocorrelation function (ACF) data and the scarce utilization of PSD information during the inversion process. In this paper, the PSD information distribution in the ACF data is investigated. It was found that the initial decay section of the ACF contains more information, especially for a bimodal PSD. Based on this, an information-weighted constrained regularization (IWCR) method is proposed in this paper and applied in multiangle DLS analysis for bimodal PSD recovery. By using larger (or smaller) coefficients for weighting the ACF data, more (or less) weight can then be given to the initial part of the ACF. In this way, the IWCR method can enhance utilization of the PSD information in the ACF data, and effectively weaken the effect of noise at large delay time on PSD recovery. Using this method, bimodal PSDs (with nominal diameters of 400:608 nm, 448:608 nm, 500:600 nm) were recovered successfully from simulated data and it appears that the IWCR method can improve the recovery resolution for closely spaced bimodal particles. Results of the PSD recovery from experimental DLS data confirm the performance of this method.

Photon ensemble correlation spectroscopy enables decorrelation-rate-limited ultrafast measurement of diffusive particle dynamics

In contrast to conventional dynamic light scattering (DLS) measurement via a single sampling volume (SV) observation over a long time span, we propose a novel technique named "photon ensemble correlation spectroscopy" for ultrafast characterization of diffusive particle dynamics through decorrelation analysis of complex-valued DLS scattering signals from an ensemble of independent SVs. We confirm that the ensemble analysis provides a decorrelation-rate-limited ultrafast measurement and demonstrates the feasibility of imaging spatially resolved particle dynamics. Moreover, the use of complex-valued signals gives additional superiority in terms of reliability.

High-throughput optofluidic particle profiling with morphological and chemical specificity

We present a method for high-throughput optofluidic particle analysis that provides both the morphological and chemical profiles of individual particles in a large heterogeneous population. This method is based on an integration of a time-stretch optical microscope with a submicrometer spatial resolution of 780 nm and a three-color fluorescence analyzer on top of an inertial-focusing microfluidic device. The integrated system can perform image- and fluorescence-based screening of particles with a high throughput of 10,000 particles/s, exceeding previously demonstrated imaging particle analyzers in terms of specificity without sacrificing throughput.

Physicochemical properties of oleic acid-based partially fluorinated gemini surfactants

We have developed oleic acid-based partially fluorinated gemini surfactants with carboxylic acid headgroups. The fluorocarbon chain is covalently bound to the terminal carbonyl group of oleic acid via a -CH(2)CH(2)OCO- unit, and the carboxylic acid headgroups are introduced to the cis double bond of oleic acid via -OCOCH(2)CH(2)- units. The aqueous solution properties of these surfactants were studied at pH 9 in the presence of 10 mmol dm–3 NaCl by means of static surface tension, pyrene fluorescence, and dynamic light scattering measurements. The resulting surface tension data demonstrate that the partially fluorinated gemini surfactants exhibit excellent surface activity in their dilute aqueous solutions. In addition, the surfactants are suggested to form micellar aggregates 2–4 nm in diameter. We also studied the aqueous temperature-concentration phase diagrams of the partially fluorinated gemini surfactants (disodium salts) on the basis of visual observations (through a crossed polarizer), polarized optical microscopy, and small angle X-ray scattering measurements. Several phase states including micellar solution phase, hexagonal phase, bicontinuous cubic phase, and lamellar phase were observed along with the coexistence of these phases in certain regions. Assemblies with lesser positive curvature tend to be formed with increasing surfactant concentration, increasing temperature, and increasing fluorocarbon chain length. A comparison of the phase diagrams of the partially fluorinated and hydrogenated surfactant systems suggests that close molecular packing is inhibited within the assemblies of the partially fluorinated surfactants because of the limited miscibility between the fluorocarbon and hydrocarbon units. To the best of our knowledge, this is the first systematic report focusing on the temperature-concentration phase diagrams of (partially) fluorinated gemini surfactants over a wide range of compositions and temperatures.

Tamoxifen-loaded nanostructured lipid carrier as a drug delivery system: characterization, stability assessment and cytotoxicity

Cancer nanotherapeutics is beginning to overwhelm the global research and viewed to be the revolutionary treatment regime in the medical field. This investigation describes the development of a stable nanostructured lipid carrier (NLC) system as carrier for Tamoxifen (TAM). The TAM-loaded NLC (TAM-NLC) developed with 200mg of TAM showed a spherical particle with the size of 46.6nm, polydispersity index of 0.267, entrapment efficiency of 99.74% and with the zeta potential of -23.78mV. Besides, the equivalent cytotoxicity of TAM and TAM-NLC to human (MCF-7) and mice (4T1) mammary breast cancer cell lines were observed. Incubating the formulation at the physiological pH resulted into reduced Ostwald ripening rate but without any significant change in the absorptivity. When coupled with the measurements of zeta potential and Ostwald ripening rate, the absorbance assay may be used to predict the long-term stability of drug-loaded nanoparticle formulations. The results of the study also suggest that TAM-NLC is a promising drug delivery system for breast cancer therapy. This is the first encouraging report on the in vitro effect of TAM-NLC against human and mouse mammary adenocarcinoma cell lines.

High-throughput thermal scanning for protein stability: making a good technique more robust

We present a high-throughput approach to help define experimental formulations that enhance protein stability, which is based on differential scanning fluorimetry (DSF). The method involves defining the thermal stability of a protein against a screen of 13 buffer systems, systematically sampling pH from 5.0 to 9.0 at high and low salt concentrations, using both redundancy and extensive controls to make the method robust. The screen allows rapid determination of a suitable base formulation for protein samples, and is particularly useful for difficult samples: those that are rapidly degraded or cannot be sufficiently concentrated for downstream analyses. Data obtained from three samples in this assay illustrate the vastly different values for thermal stability that can be obtained from different formulations. This approach is simple to interpret and reliable enough that it has been implemented as a service through the Collaborative Crystallisation Centre (C3).

Cryoprotective Effects of Saccharides on the Freeze-Drying of Sonicated Vesicles of the Novel Lipid A Analog, E5531

A sonicated dispersion of the novel lipid A analog, E5531, was feeze-dried in the presence of various additives such as saccharides and polyalcohols, and their cryoprotective effects were investigated. Fusion of the vesicles was examined by measuring fluorescence energy transfer and size distribution. Cryoprotective ability differed among the addtive species. The addition of polyalcohols led to considerable fusion. Although monosaccharides, similar to disaccharides, completely prevented the fusion of the vesicles during lyophilization, they showed far less ability to retain the entrapped calcein in the vesicles compared to disaccharides. Differential scanning calorimetry heating profiles of vesicles that had been lyophilized with various additives were obtained. Disaccharides and monosaccharides again resulted in markedly different thermal properties of the vesicles. This variety in cryoprotective ability of saccharide species can be attributed to differences in their interaction with the E5531 head group.

Controlling the Aggregation of Conjugates of Streptavidin with Smart Block Copolymers Prepared via the RAFT Copolymerization Technique

Block copolymers containing stimuli-responsive segments provide important new opportunities for controlling the activity and aggregation properties of protein-polymer conjugates. We have prepared a RAFT block copolymer of a biotin-terminated poly(N-isopropylacrylamide) (PNIPAAm)-b-poly(acrylic acid) (PAA). The number-average molecular weight (M(n)) of the (PNIPAAm)-b-(PAA) copolymer was determined to be 17.4 kDa (M(w)/M(n) = 1.09). The PNIPAAm block had an M(n) of 9.5 kDa and the poly(acrylic acid) (PAA) block had an M(n) of 7.9 kDa. We conjugated this block copolymer to streptavidin (SA) via the terminal biotin on the PNIPAAm block. We found that the usual aggregation and phase separation of PNIPAAm-SA conjugates that follow the thermally induced collapse and dehydration of PNIPAAm (the lower critical solution temperature (LCST) of PNIPAAm is 32 degrees C in water) is prevented through the shielding action of the PAA block. In addition, we show that the cloud point and aggregation properties (as measured by loss in light transmission) of the [(PNIPAAm)-b-(PAA)]-SA conjugate also depended on pH. At pH 7.0 and at temperatures above the LCST, the block copolymer alone was found to form particles of ca. 60 nm in diameter, while the bioconjugate exhibited very little aggregation. At pH 5.5 and 20 degrees C, the copolymer alone was found to form large aggregates (ca. 218 nm), presumably driven by hydrogen bonding between the -COOH groups of PAA with other -COOH groups and also with the -CONH- groups of PNIPAAm. In comparison, the conjugate formed much smaller particles (ca. 27 nm) at these conditions. At pH 4.0, however, large particles were formed from the conjugate both above and below the LCST (ca. 700 and 540 nm, respectively). These results demonstrate that the aggregation properties of the block copolymer-SA conjugate are very different from those of the free block copolymer, and that the outer-oriented hydrophilic block of PAA shields the intermolecular aggregation of the block copolymer-SA bioconjugate at pH values where the -COOH groups of PAA are significantly ionized.

Block copolymer-coated calcium phosphate nanoparticles sensing intracellular environment for oligodeoxynucleotide and siRNA delivery

The organic-inorganic hybrid nanoparticles entrapping oligodeoxynucleotide (ODN) or siRNA were prepared through the self-associating phenomenon of the block copolymer, poly(ethylene glycol)-block-poly(aspartic acid) (PEG-PAA), with calcium phosphate. The nanoparticles have diameters in the range of several hundreds of nanometers depending on the PEG-PAA concentration and revealed excellent colloidal stability due to the steric repulsion effect of the PEG layer surrounding the calcium phosphate core. The loading capacities of ODN and siRNA were fairly high, reaching almost 100% under optimal conditions. The flowcytometric analysis and confocal microscopy observation indicated that the hybrid nanoparticles loaded with ODN were taken up by the cells through the endocytosis mechanism. Furthermore, the calcium phosphate core dissociates in the intracellular environment with appreciably lowered calcium ion concentration compared to the exterior, allowing the release of the incorporated ODN and siRNA in a controlled manner. Eventually, effective intracellular delivery and nuclear localization of these nucleic acid-based drugs were evidenced through the observation of laser confocal microscopy using FITC-labeled ODN. This smart ion-sensitive characteristic of hybrid nanoparticles was further demonstrated by the appreciable silencing of reporter gene expression by siRNA incorporated in the nanoparticles.

Stabilization of lysozyme-incorporated polyion complex micelles by the omega-end derivatization of poly(ethylene glycol)-poly(alpha,beta-aspartic acid) block copolymers with hydrophobic groups

To improve the stability of lysozyme-incorporated polyion complex (PIC) micelles in physiological condition, three types of hydrophobic groups, including phenyl (Phe), naphthyl (Nap), and pyrenyl (Py) terminal groups, were separately introduced to the omega-end of poly(ethylene glycol)-poly(alpha,beta-aspartic acid) block copolymers (PEG-P(Asp)). The goal was to enhance association forces between the enzyme, lysozyme, and PEG-P(Asp) carriers. Introduction of these hydrophobic groups significantly decreases micellar critical association concentration and increases the micellar tolerability against increasing NaCl concentrations. Particularly, PIC micelles formed from PEG-P(Asp) with Py groups was most stable against increasing NaCl concentrations up to 0.1 M. Significant deviation from a spherical shape for the micelles was also observed for the PEG-P(Asp)-Py system, consistent with an increased association number.

Two-channel self-mixing laser Doppler measurement with carrier-frequency-division multiplexing

We demonstrate real-time two-channel self-mixing laser-Doppler measurement with extreme optical sensitivity using a laser-diode-pumped thin-slice LiNdP4O12 laser. Successful carrier-frequency-division-multiplexed two-channel operations are realized by using one laser, two sets of optical frequency shifters, and a two-channel frequency-modulated-wave demodulation circuit. Simultaneous independent measurements of vibrations of speakers and averaged motions of small Brownian particles in different scattering cells are demonstrated. Self-mixing photon correlation spectroscopy of particle size distributions is also discussed.

Thermal characterization of poly(ethylene glycol)-poly(D,L-lactide) block copolymer micelles based on pyrene excimer formation

Poly(ethylene glycol)--poly(D,L-lactide) (PEG-PDLLA) block copolymers were prepared by anionic ring-opening polymerization, resulting in block sizes effectively controlled by initial monomer/initiator ratios and low molecular weight distributions (<1.12). A pyrene derivative (1-pyrenyl carbonyl cyanide--Py) was conjugated to the end of the hydrophobic block (PDLLA) in a quantitative manner, with coupling efficiencies >95%. The so-obtained PEG-PDLLA-Py copolymers displayed fluorescent properties that were associated with the pyrene monomers, when placed in good solvents for both the hydrophilic and hydrophobic blocks. When placed in selective solvents, these copolymers self-assembled into micelles in the 30-nm range, also with low particle size distributions (<0.09), within which Py could be readily entrapped in the hydrophobic PDLLA core. Py entrapment resulted in the formation of excimers, as evident from fluorescence measurements. Observation of excimer formation/dissociation further conveyed information on the physicochemical properties of the core. Thermal characterization of these systems showed that an increase in the temperature resulted in changes in the properties of excimer fluorescence, an occurrence attributed to a higher mobility of the otherwise glassy PDLLA. This, in turn, greatly affected the inter-molecular distance between pyrene molecules, a crucial factor for excimer formation. The glass transition of the PDLLA block, approximately 38 degrees C, defined the onset for increasing chain mobility and whence excimer dissociation. Excimer fluorescence appeared to be time-dependent. Based on these observations, chain exchange processes were clearly evidenced through the time-dependent dissociation of excimers into unimers, a process that was influenced by changes in temperature.

Formation of Spherical Micelles Composed of the Novel Platelet Activating Factor Receptor Antagonist, E5880

The injectable formulation of E5880, a novel platelet activating factor (PAF) receptor antagonist, was developed. The physicochemical properties of E5880 micelles in the optimized formulation (0.6 mg/mL of E5880, 0.1% of citric acid, 10% lactose, pH 2.8) were characterized. The critical micelle concentration of E5880 was 0.09 mg/mL, and the structure was spherical. The micelle size was 5.6 nm. The number of molecules per micelle was 46. The micropolarity around the hydrocarbon region in the micelle was similar to that of isobutanol.

Reversible Meso-Scale Smart Polymer−Protein Particles of Controlled Sizes

Functionalized beads and particles in the size range of tens to hundreds of nanometers (nano- to meso-scale) are finding increased applications in the bioanalytical field. We show here that conjugates of streptavidin and the temperature-responsive polymer poly(N-isopropylacrylamide) (PNIPAAm), synthesized with low polydispersities by reversible addition--fragmentation chain transfer (RAFT) polymerization, rapidly formed mesoscale polymer--protein particles above the lower critical solution temperature (LCST). The average hydrodynamic diameters of these particles could be controlled between 250 nm to 900 nm by the choice of conjugate concentration and polymer molecular weight, and/or through control of the rate of temperature change. Once formed, the biohybrid particles were found to be stable for >16 h at the controlled size, unlike the free PNIPAAm which continued to aggregate and grow over time into very large and polydisperse aggregates. The reversibility between the smart polymer--protein particles and the free polymer--protein conjugates opens potential uses in traditional diagnostic formats and in microfluidic formats where the differential diffusive and physical properties might be exploited for separations, analyte concentration, and signal generation.

Photon correlation spectroscopy investigations of proteins

Physical principles of photon correlation spectroscopy (PCS), mathematical treatment of the PCS data (converting autocorrelation functions to distribution functions or average characteristics), and PCS applications to study proteins and other biomacromolecules in aqueous media are described and analysed. The PCS investigations of conformational changes in protein molecules, their aggregation itself or in consequence of interaction with other molecules or organic (polymers) and inorganic (e.g. fumed silica) fine particles as well as the influence of low molecular compounds (surfactants, drugs, salts, metal ions, etc.) reveal unique capability of the PCS techniques for elucidation of important native functions of proteins and other biomacromolecules (DNA, RNA, etc.) or microorganisms (Escherichia coli, Pseudomonas putida, Dunaliella viridis, etc.). Special attention is paid to the interaction of proteins with fumed oxides and the impact of polymers and fine oxide particles on the motion of living flagellar microorganisms analysed by means of PCS.

pH-responsive oligodeoxynucleotide (ODN)-poly(ethylene glycol) conjugate through acid-labile beta-thiopropionate linkage: preparation and polyion complex micelle formation

An oligodeoxynucleotide (ODN) conjugated to poly(ethylene glycol) (PEG) through a pH-responsive ester linkage (PEG-ODN conjugate) was successfully synthesized by the Michael reaction of 3'-thiol-modified ODN with a heterobifunctional PEG bearing an acetal group at the alpha-end and an acrylate group at the omega-end (acetal-PEG-acrylate), aimed at the development of a novel ODN delivery system. The prepared PEG-ODN conjugate and linear-poy(ethyleneimine) (L-PEI) spontaneously associated to form a polyion complex (PIC) micelle whose diameter and polydispersity index micro(2)/Gamma(2)) were 102.5 nm and 0.096 as determined by DLS measurements, respectively. Both the PEG-ODN conjugate and PIC micelle showed cleavage of the ester linkage at the endosomal pH (=5.5), suggesting that the PIC micelle is anticipated to release the ODN in the intracellular compartment. Furthermore, the PEG-ODN conjugate in the PIC micelle was stable against deoxyribonuclase (DNase I) digestion and has no interaction with the serum component because of the steric stabilization of the highly dense PEG corona surrounding the PIC core. These characteristics of the PIC micelles entrapping the PEG-ODN conjugate are promising for their utility as a novel ODN delivery system.

Characterization of the physicochemical properties of micelles composed of the novel platelet activating factor receptor antagonist, E5880 in an aqueous environment

E5880, a novel platelet activating factor (PAF) receptor antagonist, was dispersed in water for use in injectable formulation and the physicochemical properties of the preparation were characterized. The critical concentration for formation of micelles was 0.12 mM. Using area per molecule data, the critical packing parameter was calculated, indicating that the structure of the micelles was spherical and that each micelle containing 49 molecules. The diameter of the micelle was 8.1 nm. Attractive interactions occurred between E5880 molecules in the micelle. The hydrocarbon region in the micelle was more rigid and less hydrated than that of other surfactants, stearyltrimethylammonium chloride (STAC) and cetyltrimethylammonium chloride (CTAC).

Latex particle size distribution by dynamic light scattering: novel data processing for multiangle measurements

Multiangle dynamic light scattering (DLS) provides a better estimate of particle size distributions (PSD) than single-angle DLS. However, multiangle data treatment requires appropriate weighting of each autocorrelation measurement prior to calculation of the PSD. The weighting coefficients may be directly obtained from (i). the autocorrelation baselines or (ii). independent measurement of the average light intensity by elastic light scattering. However, the propagation of errors associated with such procedures may intolerably corrupt the PSD estimate. In this work, an alternative recursive least-squares calculation is proposed that estimates the weighting coefficients on the basis of the complete autocorrelation measurement. The method was validated through a numerical example that simulates the analysis of a polystyrene latex with a bimodal PSD and with "measurements" taken at 10 detection angles. The ill-conditioned nature of the problem determines that the "true" PSD cannot be recovered, even in the absence of errors. A sensitivity analysis was carried out to determine the effect of errors in the weighting coefficients on the PSD recoveries.

Formation of the dispersed particles composed of retinol and phosphatidylchiline

The purpose of this study was to investigate the dispersal mechanism of retinol (Vitamin A, VA) into phospholipid. VA was dispersed with soybean phosphatidylcholine (PC) using sonication and the dispersal mechanism was evaluated by characterizing the dispersed particles using dynamic light scattering, fluorescence spectroscopy and surface monolayer techniques. The dispersions in the VA mole fraction range of 0.1-0.7 were stable at room temperature for 3 days. A limited amount of VA was incorporated into PC bilayer membranes (approximately 3 mol%). The excess VA separated from the PC bilayers was stabilized as emulsion particles by the PC surface monolayer. When the PC content was less than the solubility in VA (mole fraction of VA: more than 0.8), the PC monolayer did not completely cover the hydrophobic VA particle surfaces. In the case, the particle size increased drastically and the separation into oil/water occurred. The miscibility between VA and PC and the lipid composition were critically important for the stability of the dispersed particles (coexistence of emulsion particles (surface monolayer of PC+core of VA) with vesicular particles (bilayer)) of the lipid mixtures.

Lactose-installed poly(ethylene glycol)-poly(d,l-lactide) block copolymer micelles exhibit fast-rate binding and high affinity toward a protein bed simulating a cell surface. A surface plasmon resonance study

Lactose molecules were installed on the surface of poly(ethylene glycol)-poly(d,l-lactide) (PEG-PLA) block copolymer micelles in the scope of seeking specific recognition by cell surface receptors at hepatic sites. This, in turn, is expected to result in the formation of a complex displaying prolonged retention times and thus enhanced cellular internalization by receptor-mediated endocytosis. The so-obtained particles based on a block copolymer of molecular weight 9400 g/mol (4900/4500 g/mol for the PEG and PLA blocks, respectively) were found to have an average hydrodynamic diameter of 31.8 nm, as measured by dynamic light scattering. Further, the particle size distribution (micro(2)/Gamma(2)) was found to be lower than 0.08. Lactose-PEG-PLA micelles (Lac-micelles) were then injected over a gold surface containing Ricinus communis agglutinin lectins simulating the aforementioned glycoreceptors, and their interaction was studied by surface plasmon resonance. Then, a kinetic evaluation was carried out, by fitting the observed data mathematically. It appears that Lac-micelles bind in a multivalent manner to the lectin protein bed, which logically results in low dissociation constants. Micelles bearing a ligand density of 80% (Lac-micelles 80%: 80 lactose molecules per 100 copolymer chains) exhibit fast association phases (k(a1) = 3.2 x 10(4) M(-)(1) s(-)(1)), but also extremely slow dissociation phases (k(d1) = 1.3 x 10(-)(4) s(-)(1)). Recorded sensorgrams were fitted with a trivalent model, conveying a calculated equilibrium dissociation constant (K(D1) = k(d1)/k(a1)) of about 4 nM. The importance of cooperative binding was also assessed, by preparing Lac-micelles bearing different ligand densities, and by discussing the influence of the latter on kinetic constants. Interestingly enough, whereas Lac-micelles 80% bind in a trivalent manner to the protein bed, Lac-micelles 20% are still capable of forming bivalent complexes with the same protein bed (K(D1) = 1360 nM). Therefore, despite enhanced kinetic values brought about by a supplementary bond, lower ligand densities appear to be more effective on a molecular basis.

Reorganization of dynamic self-assemblies of cellulose diacetate in solution: dynamical critical-like fluctuations in the lower critical solution temperature system

Dynamics of cellulose diacetate (CDA, the total degree of substitution (TDS) = 2.44) in dimethylacetamide (DMAc) in dilute solution was investigated at 2, 10, 20, 30, 40, 49.7, and 61.5 degrees C through dynamic light scattering in the quiescent state. The following three facts were made clear. First, CDA existed in three types of structures in the polar solvent, DMAc; one is a single CDA chain, and the others are dynamic structures, or self-assemblies, which were formed temporarily and locally by the solvent-mediated hydrogen bonding between the intermolecular C-6 position hydroxyls of the anhydroglucose units in the CDA backbone. Second, CDA showed a nature of low-temperature solubility in DMAc, that is, CDA is expected to dissolve molecularly below -12 degrees C but to take a phase separation above 65 degrees C, where two structures such as collapses of a single CDA chain and an aggregate appear. Third, a reorganization in the dynamic structures was detected at the temperature T = 33.8 degrees C. At this temperature, two dynamic structures showed the discontinuity in their correlation lengths, whereas the single CDA realized an uncorrelated chain state in the dynamical sense. In view of the low-temperature solubility of CDA in DMAc, this abnormal behavior around T was explained by dynamical critical-like fluctuations if T were treated as a kind of lower critical solution temperature (LCST) in the CDA/DMAc system. Here, the self-assemblies arise as the dynamical fluctuations under the spinodal decomposition situation and the competition between the hydrogen bonding (HB) and the hydrophobic interaction (HPhI) makes the conformation of CDA chains change drastically. In this scheme, the solvent-mediated HB and HPhI play important roles in the structure reorganization of cellulose derivatives in strong electronegative solvents, though HB and HPhI cooperate with the inherent chain helicality.

Noise on Fluorescence Correlation Spectroscopy

The time dependence of the noise and the signal-to-noise (SN) ratio of the fluorescence correlation spectroscopy (FCS) autocorrelation function is obtained from replica measurements of standard dextran solutions. The noise dependence on the delay time is fitted by a hyperbolic function with two fitting parameters. The dependence of these parameters on concentration, fluorescence intensity, and accumulation time is obtained experimentally. The behavior of SN at zero delay time agrees well with the theoretical predictions reported in the literature. The obtained data are useful for the quantitative evaluation of the FCS data fits, as well as for simulation of the FCS autocorrelation functions. Copyright 2001 Academic Press.

Optimization of the formulation and characterization of the physicochemical properties of the novel platelet-activating factor receptor antagonist E5880

The injectable formulation of E5880, a novel platelet-activating factor (PAF) receptor antagonist, was determined from the study of pH stability, the selection of excipient, and the relationship between moisture and stability. The physicochemical properties of E5880 in the optimized formulation (0.6 mg/ml of E5880, 0.1% [4.8 mM] citric acid, 10% lactose, pH 2.8) were characterized. The critical micelle concentration of E5880 in the buffer was 0.1 mg/ml, and the structure was of spherical micelles. The micellar size was 5.6 nm and did not change before and after lyophilization and storage. The number of the molecules per micelle was 40. The micropolarity around the hydrocarbon region of the micelle was similar to that of butanol.

Latex Particle Size Distribution by Dynamic Light Scattering: Computer Evaluation of Two Alternative Calculation Paths

Two calculation paths for estimating the particle size distribution (PSD) of a polymer latex from single-angle dynamic light scattering (DLS) measurements are evaluated on the basis of a numerical example. In the more common "double-step method," two calculation steps are applied, with the intermediate estimation of the particle light intensity distribution (PLID). In the "single-step method," the calculation is performed in one operation. From the specification of several PSDs, a mathematical model is used to produce the synthetic measurements. An iterative procedure was applied for determining the diameter range and the number of PSD points. The inversion operations were carried out using a regularization technique. For narrow distributions with diameters in the range 100-1000 nm, the PSD and the PLID are similar in shape, and both calculation paths produce similar results. For broad PSDs in the range 100-1000 nm, and for arbitrary PSDs in the range 10-100 nm (i.e., in the Rayleigh region), the single-step method proved preferable. Copyright 2000 Academic Press.

The effect of lipid A analog E5531 on membrane properties of dipalmitoylphosphatidylcholine

The effect of the lipid A analog E5531 on the phospholipid membrane was determined and compared with that of the lipid A from Escherichia coli (EC). E5531 decreased the phase transition temperature of dipalmitoylphosphatidylcholine (DPPC) membrane and increased the fluidity and permeability. On the other hand, EC increased the phase transition temperature and decreased the membrane fluidity and permeability. These results suggest that the reason for the difference of biological effects of E5531 and lipid A from EC would be caused by the differences from the effect on the cell membranes.

Characterization of the physicochemical properties of the micelles by the novel platelet activating factor receptor antagonist E5880

E5880, a novel platelet activating factor receptor antagonist, was dispersed in the buffer solution (4.8 mM citric acid, 10% lactose, pH 2.8) for the preparation of an injectable formulation and the physicochemical properties of the micelles were characterized. The critical micelle concentration of E5880 was 0.12 mM. Using the area per molecule results, the critical packing parameter was calculated and showed that the structure was spherical and the number of molecules in the aggregates was 46. The diameter of the micelle was 5.6 nm. The micropolarity around the hydrocarbon region of the micelle was similar to that of isobutanol.