Colloidal Phase Research Articles

Investigating bonding mechanism of rubberized RAP asphalt mastic from rheological and physiochemical perspectives

Considering the enormous amounts of virgin materials consumed in road construction and rehabilitation, recycling reclaimed asphalt pavement has aroused great interest recently. Among different modifiers, crumb rubber is a waste material that significantly enhances different characteristics of the asphalt binder. This study investigates the bonding strength of asphalt mastic of reclaimed asphalt binder modified by crumb rubber-modified binder. The study also attempts to model the mastic bonding strength and understand its mechanism. Thirty binders with different percentages of crumb rubber and reclaimed asphalt were mixed with two filler types to produce the asphalt mastics. Moreover, the two phases of the binder colloid, gel and liquid phases, created by crumb rubber modification, were separated to evaluate the crumb rubber interaction and its impact on mastic bonding. The pull-off test was used to evaluate the bonding strength of asphalt mastics and binders, while dynamic shear rheometer and Fourier-transformed infrared spectroscopy were used to evaluate the physiochemical and rheological characteristics of the asphalt binders. The results show that crumb rubber and reclaimed asphalt modifications greatly strengthen the mastic bonding. The accretion of carbonyl groups due to the reclaimed asphalt addition and withdrawal of light components due to the crumb rubber interaction improves the stiffness of the liquid phase binder, which is strongly correlated to the mastic bonding strength. Furthermore, despite its role in strengthening the binder stiffness, the crumb rubber particles as fillers no longer affect the mastic bonding, where this role is undermined by the mineral fillers.

Luminescent Water-Dispersible Nanoparticles Engineered from Copper(I) Halide Cluster Core and P,N-Ligand with an Optimal Balance between Stability and ROS Generation

The present work introduces the solvent exchange procedure as a route for conversion of the Cu4I4L2 complex, where the Cu4I4 cluster core is coordinated with two P,N-ligands (L), into an aqueous colloid. The analysis of both colloidal and supernatant phases revealed some losses in CuI going from the initial Cu4I4L2 complex to Cu2I2L3-based nanoparticles. The comparative analysis of IR, 31P NMR spectroscopy, ESI mass-spectrometry and luminescence data argued for a contribution of the “butterfly”-like structures of the Cu2I2 cluster core to Cu2I2L3-based nanoparticles, although the amorphous nature of the latter restricted structure evaluation from the PXRD data. The green luminescence of the colloids revealed their chemical stability under pH variations in the solutions of some amino acids and peptides, and to specify the temperature and concentration conditions triggering the oxidative degradation of the nanoparticles. The spin trap-facilitated ESR study indicated that the oxidative transformations were followed by the generation of reactive oxygen species (ROS). The physiological temperature level (310 K) enhanced the ROS generation by nanoparticles, but the ROS level was suppressed in the solution of GSH at pH = 7.0. The cytotoxicity of nanoparticles was evaluated in the M-HeLa cell line and is discussed in correlation with their cell internalization and intracellular oxidative transformations.

Nitrogenous Bases in Relation to the Colloidal Silver Phase: Adsorption Kinetic, and Morphology Investigation

The interaction between inorganic nanoparticles and biological molecules is of great importance in the field of biosystems and nanomaterials. Here, we report the adsorption process of a heterocyclic organic compound (nitrogenous base) on a microporous carbon (C) in the presence of a colloidal silver solution (AgNP solution) as an accompanying substance. Analysis of the potential colloid–biomolecule interaction as well as the subsequent phenomenon of changes in the morphology of the colloidal system in the presence of selected nucleotides was investigated. Adenosine nitrogenous base (Anb) was selected as a model molecule of the building block of DNA and RNA. The adsorption process of nucleotides from one- and two-component systems was monitored by cyclic UV-VIS measurements for obtaining time-dependent profiles and estimating the kinetic characteristics of uptake. We demonstrate the temperature-dependent course of the adsorption process with visible nucleotide-AgNP morphology determinants. The experimental adsorption kinetics were analyzed using selected theoretical models (intraparticle diffusion model, multiexponential equation, and many others). On the other hand, obtained Anb/C and Anb/AgNP/C composites were characterized by various techniques suitable for material surface and morphology characterization: high-resolution transmission electron microscopy (HR-TEM and TEM/EDX), N2 physisorption measurements, and thermal analysis (thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC) experiments).

Surface charge property governing co-transport of illite colloids and Eu(III) in saturated porous media

The transport of colloids and radionuclides is sophisticated because of the variety of charge properties between colloidal particles and host subsurface media, which causes great difficulty in establishing a reliable model of radionuclides migration by taking the colloid phase into consideration. In this work, the co-transport of illite colloids (IC) and Eu(III) in the quartz sand and iron-coated sand porous media was investigated by column experiments to address the predominant mechanism of charge properties on co-transport. Results showed that Eu(III) transport was driven by the illite colloids and electrostatic interaction was critical in governing the co-transport patterns. The promotion of Eu(III) transport by IC was attenuated in the iron-coated sand systems; more IC-Eu(III) complexes were retained uniformly in the column. The pore throat shrinkage caused by electrostatic attachment between aggregated IC and iron oxides exacerbated the physical straining and size exclusion effect of IC-Eu(III) complexes. An aggravated irreversible retention of IC-Eu(III) was detected in iron-coated sand column due to the electrostatic attraction of IC-Eu(III) to host media. The findings are essential for improving the understanding on the potential transport, retention and release risk of colloids associated radionuclides, and imply that the positively charged permeable reactive barrier is an effective strategy to reduce the transport risk of colloid associated radionuclides.

Effect of iron cyclic transformation on the natural purification of antimony in contaminated reservoirs of mines

To further understand the purification mechanism of antimony (Sb) in reservoirs, samples of stratified water and bottom interface sediment were collected in this study. The cross-flow ultrafiltration technique was used to separate the truly dissolved (<1 kDa) and colloidal (1 kDa–0.45 μm) phases of water, and two modified sequential extraction techniques were used to determine the Sb and Fe mineral forms in sediment, respectively. The results showed that the total Sb concentration could decrease from 142.2 μg/L in surface water to 98.6 μg/L at 16 m; this was contributed to by the removal of truly dissolved Sb. In comparison to particulate Sb (>0.45 μm), the formation of colloidal Sb played a greater role in the purification process. There was a positive correlation between Sb and Fe in the colloidal phase (r = 0.45, P < 0.05). The generation of colloidal Fe could be promoted by higher temperatures, pH values, DO, and DOC in the upper layer (0–5 m). However, the complexation of DOC with colloidal Fe inhibited the adsorption of truly dissolved Sb. After entering the sediment, the secondary release of Sb could not increase the Sb concentration in the lower layer obviously, while the supplementation of Fe(III) could further enhance Sb natural purification.

Engineering the Thermodynamic Stability and Metastability of Mesophases of Colloidal Bipyramids through Shape Entropy.

We report several types of entropy-driven phase transition behaviors in hard bipyramid systems using Monte Carlo simulations. Bipyramidal nanoparticle shapes are synthesizable from gold and silver, with sizes ranging from tens to hundreds of nanometers. We report numerous colloidal crystalline phases with varying symmetries and complexities as the bipyramid aspect ratio and base polygon are varied. Some bipyramids are mesogenic and undergo either monotropic or enantiotropic phase transitions. We show that such mesophase behavior can be modulated by tuning the bipyramid aspect ratio. In addition, we report stepwise kinetic crystallization and melting pathways that occur via an intermediate mesophase as the system gains or loses order in successive stages. Our results demonstrate that complex phase transition behavior involving mesophases can be driven by entropy alone. Importantly, our results can guide the synthesis of bipyramid shapes able to assemble target structures and can be used to engineer the kinetic pathways to and from those structures to involve or avoid mesophases.

Fractionation of toxic metal Pb from truly dissolved and colloidal phases of seaward rivers in a coastal delta

Colloids of natural river water is a key intermediate carrier of lead (Pb). It is important to monitor the transport–transformation behavior of Pb in the colloidal phase of seaward water because this behavior is related to the levels of pollution input and environmental risks posed to the sea, especially in coastal delta areas. In this study, the fractionation behavior and distribution of toxic Pb from the truly dissolved phase and the different colloidal phases in seven seaward rivers in the Yellow River Delta were investigated. The concentrations of total dissolved Pb, truly dissolved Pb, and colloidal Pb were 0.99–40.09 μg L–1, 0.40–8.10 μg L–1, and 0.60–35.88 μg L–1, respectively. In freshwater rivers, the main component of total dissolved Pb (about &amp;gt; 50%) is truly dissolved Pb but the main component of total dissolved Pb in the seawater environment is colloidal Pb (&amp;gt; 80%). A dramatic increase in salinity causes the deposition (about ≈94%) of all forms of Pb to sediment from estuarine water in winter. However, this sedimentation behavior of colloidal Pb gradually decreases (in the Shenxiangou River) when the river salinity approaches seawater salinity (S = ≈29). In the industrial port (Xiaoqinghe River) and mariculture (Yongfenghe River) estuarine areas, which have extensive seawater, the deposition behavior of colloidal Pb (&amp;lt;15%) is less affected by the change in salinity. This suggests that human activity contributes to the spread of Pb in the offshore environment. The concentration of 100 kDa–0.22 μm Pb has a postive correlation with total colloidal Pb. Its variation is minimally affected by salinity compared with other colloidal components. In addition, the correlation between the molecular weight and aromaticity of chromophoric dissolved organic matter (CDOM) and colloidal Pb suggests that macromolecules in seawater will be important transport carriers of Pb. In all, truly dissolved Pb is the main transport form of dissolved Pb in river freshwater; however, in brackish water in estuaries, colloidal matter gradually becomes the main transport carrier. Surging salinity immobilizes truly dissolved Pb in the estuarine region, but colloidal matter inhibits this deposition. Colloidal phase is the important conversion for land–sea transport of Pb by seaward rivers.

Physicochemical and rheological properties of skim milk with different added zinc salts

Physicochemical and rheological changes in skim milk after the addition of soluble zinc salts, zinc acetate (Zn(OAc)2), zinc sulphate (ZnSO4) and zinc gluconate (ZnGlu) at 20 °C were investigated. Addition of zinc salts resulted in a significant decrease in pH, and the solution pH from lowest to highest at the same concentration was ZnSO4 < ZnGlu < Zn(OAc)2. The colloidal phase zinc concentration increased the most when Zn(OAc)2 was added. At low concentrations of added zinc salts (<20 mmol L−1) the zinc + skim milk solutions did not gel at 20 °C for 3 h (final G′ <1 Pa). Gelation was observed when 22.5 mmol L−1 Zn(OAc)2 was added to skim milk, while it was necessary to add 30 mmol L−1 ZnSO4 and ZnGlu to achieve a final G′ >1 Pa, followed by increasing final G′ with increasing concentrations of added zinc salts. Higher colloidal phase zinc concentrations resulted in a stronger gel at 20 °C.

Strong, conductive, and freezing-tolerant polyacrylamide/PEDOT:PSS/cellulose nanofibrils hydrogels for wearable strain sensors

Hydrogels with prominent flexibility, versatility, and high sensitivity play an important role in the design and fabrication of wearable sensors. In particular, these flexible conductive hydrogels exhibit elastic modulus that is highly compatible with human skin, demonstrating the great potential for flexible sensing. However, the preparation of high-performance hydrogel-based sensors that can restrain extreme cold conditions is still challenging. Herein, a novel anti-freezing composite hydrogel with superior conductivity based on polyacrylamide (PAM), LiCl, and PEDOT:PSS coated cellulose nanofibrils (PAM/PEDOT:PSS/CNF) is constructed. The addition of CNF increased the hydrogen bonding sites of the molecular chains in the micro, thus improving the mechanical strength and the conductivity of the hydrogel in the macro. The hydrogels achieve a high tensile strength of 0.19 MPa, compressive strength of 0.92 MPa, and dissipation energy of 41.9 kJ/m3. Otherwise, LiCl increases the interactions between the colloidal phase and water molecules, endowing the hydrogels with excellent freezing tolerance. Specifically, the optimized hydrogel of 45 % LiCl exhibited stable mechanical properties at −40 °C. Finally, the composite hydrogel was used to assemble flexible sensors with high sensitivity of 10.3 MPa−1, which can detect a wide range of human movements and physiological activities.

Effect of reverse osmosis and ultra-high-pressure homogenization on the composition and microstructure of sweet buttermilk

Buttermilk (BM), the by-product of butter making, is similar to skim milk (SM) composition. However, it is currently undervalued in dairy processing because it is responsible for texture defects (e.g., crumbliness, decreased firmness) in cheese and yogurt. One possible way of improving the incorporation of BM into dairy products is by the use of technological pretreatments such as membrane filtration and homogenization. The study aimed at characterizing the effect of preconcentration by reverse osmosis (RO) and single-pass ultra-high-pressure homogenization (UHPH) on the composition and microstructure of sweet BM to modify its techno-functional properties (e.g., protein gel formation, syneresis, firmness). The BM and RO BM were treated at 0, 15, 150, and 300 MPa. Pressure-treated and control BM and RO BM were ultracentrifuged to fractionate them into the following 3 fractions: a supernatant soluble fraction (top layer), a colloidal fraction consisting of a cloudy layer (middle layer), and a high-density pellet (bottom layer). Compositional changes in the soluble fraction [lipid, phospholipid (PL), protein, and salt], as well as its protein profile by PAGE analysis, were determined. Modifications in particle size distribution upon UHPH were monitored by laser diffraction in the presence and absence of sodium citrate to dissociate the casein (CN) micelles. Microstructural changes in pressure-treated and non-pressure-treated BM and RO BM particles were monitored by confocal laser scanning microscopy. Particle size analysis showed that UHPH treatment significantly decreased the size of the milk fat globule membrane fragments in BM and RO BM. Also, pressure treatment at 300 MPa led to a significant increase in the recovery of total lipids, CN, calcium, and phosphate in the BM soluble fraction (top layer) following ultracentrifugation. However, PL were primarily concentrated in the pellet cloud (middle layer), located above the pellet in BM concentrated by RO. In contrast, PL were evenly distributed between soluble and colloidal phases of BM. This study provides insight into the modifications of sweet BM constituents induced by RO and UHPH from a compositional and structural perspective.

Valorization of Lignin under Mild Conditions: Biorefining Flavonoids and Lignin Nanoparticles

Lignin is the largest store of renewable aromatics. Due to its refractory nature, however, its chemical potential is not fully realized. Here, we propose a biorefinery where the treatment of wastewater by a microbial electrolysis cell (MEC) produces “clean” water and a caustic catholyte that can depolymerize lignin under mild conditions into two high-value product streams. We determine the MEC operating conditions to produce a depolymerization solvent and quantify solution and colloidal phase products using an array of analytical techniques. In contrast to previous reports of limited high-value product yields, we obtain discrete aromatics (monomers and flavonoids) at 17% of initial lignin mass with bulk chemical analyses (11% for identified compounds using LC–MSn). In part, our higher product yield is due to selective repolymerization to form flavonoids. We simultaneously produce lignin nanoparticles and close mass balance. Both flavonoids and lignin nanoparticles have potential applications in the pharmaceutical, nutraceutical, personal care, and agricultural industries.

Molecular size-fraction and seasonal characteristics of dissolved trace metals in river and estuarine waters of the Yellow River, China

The colloidal phase is an important metal storage form in the aquatic system. However, its biogeochemical behavior in the estuarine environment has been seldom studied. In this study, spatial variations, sources and correlations with seawater environmental factors of the dissolved Fe, Mn, Cu, Zn, Cd and Pb in the surface water of the Yellow River Estuary in China were investigated. The clean sampling system, centrifugal ultrafiltration technique, and ICP-MS were combined and used for the determination of the colloidal distribution of six metals in this region. Two stations of Zn in autumn had contamination factor values &amp;gt;1, which indicates lower contaminant levels of Cu, Zn, Cd and Pb. Dissolved target metal was divided into five fractions, i.e. &amp;lt;1 kDa, 1-3 kDa, 3-10 kDa, 10-100 kDa and 100 kDa-0.45 μm, while the average concentrations of each fraction were 60.17, 46.54, 47.73, 251.03, 1.44 and 1.08 nmol L-1 in spring and 62.30, 48.18, 15.35, 203.05, 1.20 and 1.70 nmol L-1 in autumn, respectively. The results showed that colloidal Mn, Cu, Zn, Cd and Pb might be dominated by high-molecular-weight fraction (100 kDa-0.45 μm). Additionally, the contribution of low-molecular-weight colloidal Fe (1-10 kDa) in this aquatic system was obvious. The addition in the colloidal and total dissolved fraction might be mainly related to particle-desorbed ligand, which was usually occurred in the middle salinity area. Dissolved organic carbon (DOC) and colloidal organic carbon (COC) concentration could not correlate with the behavior of Mn, Zn and Cd, which proved that the influence of inorganic ligands was higher than that of organic ligands or biological contributions, but the influence of salinity, dissolved oxygen (DO), pH and temperature should not be ignored. Overall, the results suggested that the occurrence of dynamic behaviors of colloidal metal in the YRE was highly associated with the salinity transition and formation of the organic matter-particle mixture system under complex hydrodynamic processes.

Mechanisms Driving the Dispersal of Hydrothermal Iron From the Northern Mid Atlantic Ridge

AbstractThe dispersal of dissolved iron (DFe) from hydrothermal vents is poorly constrained. Combining field observations and a modeling hierarchy, we find the dispersal of DFe from the Trans‐Atlantic‐Geotraverse vent site occurs predominantly in the colloidal phase and is controlled by multiple physical processes. Enhanced mixing near the seafloor and transport through fracture zones at fine‐scales interacts with the wider ocean circulation to drive predominant westward DFe dispersal away from the Mid‐Atlantic ridge at the 100 km scale. In contrast, diapycnal mixing predominantly drives northward DFe transport within the ridge axial valley. The observed DFe dispersal is not reproduced by the coarse resolution ocean models typically used to assess ocean iron cycling due to their omission of local topography and mixing. Unless biogeochemical models account for fine‐scale physics and colloidal Fe, they will inaccurately represent DFe dispersal from axial valley ridge systems, which make up half of the global ocean ridge crest.

Environmental Risk of Arsenic Mobilization from Disposed Sand Filter Materials.

Arsenic (As)-bearing water treatment residuals (WTRs) from household sand filters are usually disposed on top of floodplain soils and may act as a secondary As contamination source. We hypothesized that open disposal of these filter-sands to soils will facilitate As release under reducing conditions. To quantify the mobilization risk of As, we incubated the filter-sand, the soil, and a mixture of the filter-sand and soil in anoxic artificial rainwater and followed the dynamics of reactive Fe and As in aqueous, solid, and colloidal phases. Microbially mediated Fe(III)/As(V) reduction led to the mobilization of 0.1-4% of the total As into solution with the highest As released from the mixture microcosms equaling 210 μg/L. Due to the filter-sand and soil interaction, Mössbauer and X-ray absorption spectroscopies indicated that up to 10% Fe(III) and 32% As(V) were reduced in the mixture microcosm. Additionally, the mass concentrations of colloidal Fe and As analyzed by single-particle ICP-MS decreased by 77-100% compared to the onset of reducing conditions with the highest decrease observed in the mixture setups (>95%). Overall, our study suggests that (i) soil provides bioavailable components (e.g., organic matter) that promote As mobilization via microbial reduction of As-bearing Fe(III) (oxyhydr)oxides and (ii) As mobilization as colloids is important especially right after the onset of reducing conditions but its importance decreases over time.

Direct Determination of the Phase Diagram of a Depletion-Mediated Colloidal System.

Depletion is one widely used potential to modulate colloidal interaction because it enables the production of a wide variety of crystalline and glassy phases of spherical and shape-tailored colloids. The attractive depletion potential gives rise to qualitatively new behavior. However, depletion-mediated phase behaviors have never been systematically investigated experimentally regarding pair potentials for aqueous suspensions. In this work, we implement three distinct phases of fluid, crystal, and glass by adjusting the concentrations of depletant and salt in the aqueous suspension of polystyrene particles. To define the phase boundary between the fluid and crystal, we calculate pair potential with a superposition of van der Waals, electrostatic, and depletion interactions. Two unknown parameters in the pair potential─the concentration of ionic impurities and the ratio of the molar concentration of depletant to osmolarity─are experimentally determined from sets of reflectance spectra. The interparticle spacing in the crystalline phase is extracted from the peak wavelength originating from Bragg diffraction, which corresponds to the interparticle separation at energy minimum in the pair potential. The boundary between the fluid and crystal is well defined with the depth of the energy well of 3kBT. By contrast, the onset of glass formation is better characterized by not the well depth but the assembly rate, which is estimated from the slope of the pair potential from force balance. Glasses are produced as the speed exceeds 300 μm/s. That is, crystals are produced by enthalpy gain overwhelming entropy loss, whereas glasses are kinetically produced due to fast jamming.

Silicic Acid Polymerization and SiO2 Nanoparticle Growth in Hydrothermal Solution.

The approach of numerical simulation of orthosilicic acid OSA polymerization and SiO2 nanoparticle formation in hydrothermal solution have been developed based on the model of the homogeneous stage of nucleation and the subsequent growth of particles. The influence of surface tension on the interface of SiO2–water, the rate of molecular deposition, and Zeldovich factor Z were evaluated. Temperature dependence on time, pH, initial OSA concentration, and ionic strength are the main parameters that determine the kinetics of colloid phase formation, the final average size of SiO2 nanoparticles, and the particle size distribution and its polydispersity index. The results of the numerical simulation were verified with experimental data on OSA polymerization and measurement of nanoparticles sizes using the method of dynamic light scattering in a wide range of temperatures of 20–180 °C, pH = 3–9, SiO2 content Ct of 300–1400 mg/kg, and ionic strength Is of 0.0001–0.42 mol/kg. The results obtained can be used in the technology of hydrothermal synthesis of sols, gels, and nanopowders to regulate the kinetics of OSA polymerization and SiO2 nanoparticle growth, particle size distribution, morphology, and structure of products.

The effects of full‐stream and partial high‐pressure homogenisation on the properties of milk emulsion

SummaryThe study evaluated the effects of full‐stream and partial high‐pressure homogenisation (HPH) on the properties of milk with 3.5% fat content. During full‐stream HPH, the size of particles decreased with an increase in temperature. Fat globules were smaller in milk treated by full‐stream than partial HPH at 60°C. Creaming was not observed in milk subjected to full‐stream HPH. In milk treated by partial HPH, the phase separation rate during ≤48 h of storage increased in samples processed at 60°C, 40°C and 20°C. Despite high top layer volume in milk that was HPH‐treated at a temperature of ≥40°C, its fat content was lower than in milk homogenised at 20°C. The total difference in colour was approximately 1.5–2.0‐fold higher in full‐stream homogenised milk. Partial HPH can be applied in dairy products requiring milk fat dispersion with minimal changes in the components of the colloidal and soluble phases.

Preparation of amine functionalized silica by the one-step in spray drying system

Amine functionalized silica has been successfully prepared using a direct co-condensation method in spray-assisted with sodium silicate as silica source and γ-aminopropyltriethoxysilane (APTS) as amine source. This study aims to synthesize amine grafted silica in one step process which includes particle formation and surface modification. Silica-amine nanofluids were prepared in stable colloidal phase as precursor solution for spray drying system. Amine sourced from APTS was condensed separately with silica nanofluids. The process of controlling the condensation rate of APTS can prevent the occurrence of silica precipitates in the precursor. The silica-amine precursor solution was then processed by spray drying at a temperature of 200°C. Silica particles that have been modified by amine groups were characterized using FT-IR, TG-DTA, and Adsorption-desorption N2. The silica-amine showed the presence of an amine group that was successfully grafted. This is indicated by the presence of characteristic amine peaks on FT-IR and mass changes due to amine decomposition in TG-DTA. The number of amines that were successfully grafted was 0.5 mmol/g sample. The washing of amine-modified silica particles with ethanol showed that the type of bond that occurred between silica and the amine functional group was a physical bond. The surface area of amine-modified silica is 169 m2/g with the pore size distribution in the micro-mesopore regime. The average pore size of amine-modified silica was 0.1288 nm.

On the structure and stability of novel cationic DPPC liposomes doped with gemini surfactants

A novel formulation of cationic liposomes was studied by mixing dipalmitoylphosphatidylcholine (DPPC) with tetradecyltrimethylammonium bromide gemini surfactants with different alkane spacer groups lengths attached to their ammonium head-groups. The physicochemical characterization of the cationic liposomes was obtained by combining experimental results from differential scanning microcalorimetry (DSC) with molecular dynamic simulations, in order to understand their structural configuration. An adapted Ising model was used to interpret the results in terms of cooperativity of the phase transitions.The gemini surfactants partition into the lipid bilayer of DPPC liposomes, and the induced changes in colloidal stability and phase transition were analyzed in detail. The DPPC liposomes became positively charged upon gemini surfactant partition, showing increased colloidal stability. Our results show significant differences in structural configuration between gemini surfactants with short and long spacer lengths. While gemini with shorter spacers allocate within the lipid bilayer with both headgroups in the same layer, geminis with longer spacers unexpectedly intercalate in the lipid membrane in a particular zig-zag configuration, with each headgroup located at a different side of the bilayer, altering the coupling degree parameters of the membrane’s phase transition.The extraordinary increase of colloidal stability of DPPC liposomes with gemini surfactants at very low molar ratio and the possibility to tune the physicochemical properties of the membrane by control de spacer length of the geminis opens new possibilities for cationic liposomal formulations with potential applications in vaccines, drug/gene delivery or biosensing.

Pharmaceutically active compounds in biotic and abiotic media of rivers receiving urban sewage: Concentrations, bioaccumulation and ecological risk

Pharmaceutically active compounds (PhACs) are recognized as posing health risks to aquatic ecosystems. The occurrence characteristics and ecological effects of 15 PhACs were investigated in the multiphase media of Yangtze River (Nanjing area, China) during wet and dry seasons. All 15 PhACs were detected in the traditionally dissolved phase, suspended particulate matter, sediment and fish, with total concentrations of PhACs (ΣPhACs) of 64.75–366.20 ng/L, 18.50–69.40 ng/g, 3.29–23.30 ng/g and 0.00–176.44 ng/g, respectively. Ibuprofen (IPF), roxithromycin (ROX) and caffeine (CFI) were the dominant PhACs in all of the environmental media. As the main carrier for PhACs, the colloids contributed 8.60%− 77.04% of PhACs in the traditionally dissolved phase, and distribution coefficients (log Kcol=6.38–7.95) of PhACs in colloidal phase were significantly higher than those in SPM and sediment. The bioaccumulation potential of ΣPhACs in the wild fish tissues was generally in order as follows: brain > liver > kidney > gill > blood > intestines > muscle > bile, which was positively correlated with their log Kow. The concentrations of CFI, ROX and IPF in the muscle, gill and liver can be predicted by their log Kow and pollution levels in the blood, and the concentrations of PhACs in the muscle of benthic fish were much higher than those in pelagic fish. The bioaccumulation factors of ROX, fluoxetine and bezafibrate in intestines, brain and blood showed strong enrichment capacity (>5000). In the risk assessment, the acute risk level of PhACs to aquatic organisms decreases gradually with the trophic level, while the trend of chronic risk was the opposite. The chronic mixture risk of PhACs to fish was > 1 at all sampling sites, 59.79% of mixed risk quotient were provided by clofibric acid, diclofenac, erythromycin and ketoconazole. These results indicated that PhAC can cause harmful health effects to sensitive organisms both individually and mixedly.