Temperature-induced Structural Changes Research Articles

Temperature-induced structural change through the glass transition of silicate glass by neutron diffraction

Supercooled silicate liquids exhibit several orders of magnitude increase in viscosity at the glass-transition temperature (${T}_{\mathrm{g}}$) towards the glassy state. Such a drastic dynamical slowdown leads to an abrupt change in the slope of temperature-dependent thermodynamic properties because the measurements reflect the equilibrium-to-nonequilibrium change from liquid to glass. However, an underlying structural change associated with such a transition remains elusive. For instance, understanding the structural origin of the variation in the coefficient of thermal expansion (CTE) of silicate glasses upon vitrification is critical for glass-manufacturing processes and applications. Here, based on temperature-dependent neutron diffraction, we demonstrate that the temperature dependences of both short- and medium-range order structural parameters show a pronounced change of slope at ${T}_{\mathrm{g}}$ for a range of silicate glasses of industrial importance. Interestingly, the short- and medium-range order structural parameters are found to be mutually correlated, both below and above ${T}_{\mathrm{g}}$. Based on these results, we find that the slope change of the area of the first sharp diffraction peak at ${T}_{\mathrm{g}}$ is correlated with the extent of the CTE jump at ${T}_{\mathrm{g}}$, which offers a structural origin for the discontinuity in the CTE of glasses at ${T}_{\mathrm{g}}$. This study can therefore shine light on solving critical industrial problems, such as glass relaxation.

Near-field studies of anisotropic variations and temperature-induced structural changes in a supported single lipid bilayer.

Temperature-controlled polarization modulation near-field scanning optical microscopy measurements of a single supported L_{β^{'}} 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayer are presented. The effective retardance (S=2π(n_{e}-n_{o})t/λ, where t is the thickness of the bilayer and λ is the wavelength of light used) and the direction of the projection of the acyl chains (θ) were measured simultaneously. We demonstrate how one is able to align the system over the sample and measure a relative retardance ΔS, a crucial step in performing temperature-controlled experiments. Maps of ΔS and θ, with a lateral resolution on the order of ∼100 nm are presented, highlighting variations deriving from changes in the average molecular orientation across a lipid membrane at room temperature. A discussion of how this information can be used to map the average three-dimensional orientation of the molecules is presented. From ΔS and the known thickness of the membrane t the birefringence (n_{e}-n_{o}) of the bilayer was determined. Temperature-controlled measurements yielded a change of ΔS∼(3.8±0.3) mrad at the main transition temperature (T_{m}∼41^{∘}C) of a single planar bilayer of DPPC, where the membrane transitioned between the gel L_{β^{'}} to liquid disorder L_{α} state. The result agrees well with previous values of (n_{e}-n_{o}) in the L_{β^{'}} phase and translates to an assumed average acyl chain orientation relative to the membrane normal (〈ϕ〉∼32^{∘}) when T<T_{m} and 0^{∘} when T>T_{m}. Evidence of super heating and cooling are presented. A discussion on how the observed behavior as T_{m} is approached, could relate to the existence of varying microconfigurations within the lipid bilyer are presented. This conversation includes ideas from a Landau-Ginzburg picture of first-order phase transitions in nematic-to-isotropic systems.

Investigating temperature-induced structural changes of lead halide perovskites by in situ X-ray powder diffraction

In situ X-ray diffraction experiments offer a unique opportunity to investigate structural dynamics at atomic resolution, by collecting several patterns in an appropriate time sequence (data matrix) while varying the applied stimulus (e.g. temperature changes). Individual measurements can be processed independently by refinement procedures that are based on prior knowledge of the average structure of each crystal phase present in the sample. If the refinement converges, parameters of the average structural model can be assessed and studied as a function of the stimulus variations. An alternative approach consists in applying a multivariate analysis to the data matrix as a whole. Methods such as principal component analysis (PCA) and phase-sensitive detection perform fast, blind and model-independent calculations that can be used for on-site analysis to identify trends in data actually related to the applied stimulus. Both classical and multivariate approaches are here applied to the in situ X-ray diffraction pair distribution function (PDF) setup on two samples of the hybrid perovskite methylammonium (MA) lead iodide obtained by different synthetic routes, subjected to temperature variations. The PDF refinement allows assessing the occurrence of temperature-induced rotations of the PbI6 octahedra and variations in the relative amount of MAPbI3 and intermediate PbI2–MAI–DMSO (dimethyl sulfoxide) crystal phases. A change in the orientation of the methylammonium molecule with temperature is also characterized. Results of the multivariate analysis tools, which include a newly introduced space-dependent variant of PCA, are described, interpreted and validated against simulated data, and their specificity and relation to refinement results are highlighted. The interaction between nearby octahedra is identified as the driving force for the tetragonal-to-cubic phase transition, and three fundamental trends in data having different temperature behaviours are unveiled: (i) irreversible weight-fraction variations of the MAPbI3 and PbI2–MAI–DMSO phases; (ii) reversible structural changes related to the MAPbI3 crystalline phase and its lattice distortion in the ab plane, having the same frequency as the temperature variations; (iii) reversible lattice distortion along the c axis, occurring at twice the frequency of the temperature changes.

Small-Angle Neutron Scattering Study of Temperature-Induced Structural Changes in Liposomes.

Liposomes of specific artificial phospholipids, such as Pad-PC-Pad and Rad-PC-Rad, are mechanically responsive. They can release encapsulated therapeutics via physical stimuli, as naturally present in blood flow of constricted vessel segments. The question is how these synthetic liposomes change their structure in the medically relevant temperature range from 22 to 42 °C. In the present study, small-angle neutron scattering (SANS) was employed to evaluate the temperature-induced structural changes of selected artificial liposomes. For Rad-PC-Rad, Pad-Pad-PC, Sur-PC-Sur, and Sad-PC-Sad liposomes, the SANS data have remained constant because the phase transition temperatures are above 42 °C. For Pad-PC-Pad and Pes-PC-Pes liposomes, whose phase transitions are below 42 °C, the q-plots have revealed temperature-dependent structural changes. The average diameter of Pad-PC-Pad liposomes remained almost constant, whereas the eccentricity decreased by an order of magnitude. Related measurements using transmission electron microscopy at cryogenic temperatures, as well as dynamic light scattering before and after the heating cycles, underpin the fact that the non-spherical liposomes flatten out. The SANS data further indicated that, as a consequence of the thermal loop, the mean bilayer thickness increased by 20%, associated with the loss of lipid membrane interdigitation. Therefore, Pad-PC-Pad liposomes are unsuitable for local drug delivery in the atherosclerotic human blood vessel system. In contrast, Rad-PC-Rad liposomes are thermally stable for applications within the human body.

Molten alkali halides - temperature dependence of structure, dynamics and thermodynamics.

The renewed interest in molten salts in the energy industry fuels the need of a thorough understanding of their physicochemical properties. Alkali halide melts are perhaps the simplest ionic liquids, but they are used as electrolytes in batteries or for thermal energy storage. Although their structure is considered to be well documented and understood, a systematic evaluation of experimental structural data reveals significant discrepancies, while there is only limited experimental information on dynamic properties. Here, we investigate structure, dynamics and thermodynamic properties of pure alkali halide melts using state-of-the-art simulation models at different temperatures. The simulations provide a consistent picture of the structure of alkali halide melts with coordination numbers that lie in between experimental numbers. The simulations reveal a strengthening of the cation-anion bonds with increasing temperature that, somewhat counter-intuitively, coincides with faster dynamics in the melts. The thermodynamic analysis unveils that structure breaking proceeds on the picosecond timescale through an associative substitution mechanism as signified by a negative entropy of activation. The results on ion pair lifetimes contribute to an improved understanding of the microscopic origin of dynamical properties, such as e.g. conductivity of salt melts. The structural analysis provided here contributes to a more coherent picture of the coordination numbers in alkali halides than what is currently available from experimental data.

Temperature-induced structural changes of apo-lactoferrin and their functional implications: a molecular dynamics simulation study

ABSTRACTLactoferrin (Lf) is an iron-binding glycoprotein present in secretory fluids from human and bovine sources. Sequence alignment was employed to identify a region on the C-lobe of Lf capable of binding to bacterial cell surfaces, followed by all-atom explicit solvent molecular dynamics simulations to study the conformational changes of Lf after exposure to three processing temperatures: pasteurisation (72°C), spray drying (90°C) and ultra-high temperature (UHT) (127°C). Below 90°C, the simulations indicate relatively minor changes in overall protein structure. At UHT conditions (127°C), however, marked disruptions to protein structure were found as demonstrated by a substantial decrease in protein dimensions due to collapse in the inter-lobe region. There was also a marked increase in residue fluctuations in several regions of known functional importance, including antibacterial, iron-binding, and putative membrane binding regions, the latter of which is stabilised by a triplet of hydrophobic residues comprised of Leu446, Trp448 and Leu451 at low temperature, but which are disrupted under UHT conditions. A unique network analysis confirmed these results as demonstrated by large clusters of residues with increased dynamical correlation in the N-terminal lobe.

Temperature influences perception of the length of a wielded object via effortful touch.

Individuals can perceive the properties of an attached or grasped object by wielding it through muscular effort-an ability referred to as dynamic or effortful touch. Sensitivity to the forces required to move such objects and to the resulting global patterns of tissue deformation underlies such perception. Given that perception via dynamic touch is movement-based, we hypothesized that manipulations that affect the ability to produce and control muscular movements might affect perception via dynamic touch. Cooling muscles from 40 to 10°C impedes the development and transmission of muscular force and diminishes muscle stretch-reflex sensitivity. Accordingly, we anticipated that changes in hand temperature would alter the ability to detect patterns of tissue deformation and thus perception of the properties of wielded objects. In two experiments, participants wielded dowels with different lengths and rotational inertias (Experiment 1) and objects with identical lengths and different rotational inertias (Experiment 2). They reported perceived lengths of these objects, in the absence of vision, in cool (~ 10°C), neutral (~ 30°C), and warm temperature conditions (~ 40°C). Actual length predicted perceived length of the dowels (Experiment 1), and rotational inertia predicted perceived length of the objects (Experiment 2); perceived lengths were longer in the warm condition than in the cool condition. In consideration of known temperature-induced changes in tissue structure and function, our results support the hypothesis that comparable processes underlie the control of movement and perception via dynamic touch.

イミダゾリウム系イオン液体-水混合溶液中のN-Methylacetamideの低温誘起構造変化

イミダゾリウム系イオン液体-水混合溶液中のN-Methylacetamideの低温誘起構造変化

Tracking Structural Changes in the UCS Domain of the Myosin Chaperone UNC-45 by Fluorescence Spectroscopy

Molecular chaperones are commonly identified by their ability to suppress heat-induced protein aggregation. The muscle-specific molecular chaperone UNC-45 is known to be involved in myosin folding and is trafficked to the sarcomeres A-band during thermal stress. Using a combination of fluorescence, circular dichroism, limited proteolysis and mass spectroscopy to quantitatively analyze the effect of temperature on UNC-45 we previously found that the UCS domain undergoes significant structural changes in response to temperatures within a heat-shock range (Bujalowski, et al., FEBS let 2015). In order to further analyze the regions within the UCS domain that become exposed to the solvent we used fluorescent assays based on the environment-sensitive hydrophobic fluorescent dye, Bis-ANS. We found that UCS interacts with Bis-ANS in 2:1 stoichiometry at 25oC with an apparent Kd of 46nM. We found that the number of bound ANS molecules increases ∼10-fold when exposed to temperatures above 35oC. We found that Bis-ANS stably binds to the UCS domain after heating (indicated by the asymmetry in the heating and cooling curves). We further investigated temperature-induced structural changes tryptophan fluorescence. The UCS domain has three Trp residues, W783, W823 and W863. We found that the relative Trp fluorescence signal decreases of as the temperature was raised indicating a change from an hydrophobic to an aqueous environment. In order to quantify the energetics of the ANS-UCS interaction we used isothermal titration calorimetry (ITC). Analysis of the calorimetric titration profile showed a monotonic decrease in the exothermic heat of binding. From these data we estimated an N= 4 (number of binding sites) and DS= + 70 cal/mol/K, suggesting that hydrophobic forces are dominant in the binding of ANS to UCS. In order to approximately map the regions at which ANS binds in the UCS domain we used resonance energy transfer (FRET) between Trp residues and Bis-ANS. We found that as Bis-ANS is added, Trp fluorescence is quenched as energy is transferred to the extrinsic fluorophore in a concentration dependent fashion. We are using these techniques to map the key amino acid regions in the UCS domain that mediate its myosin-binding and chaperoning functions. This work was supported by the American Heart Foundation (AHA 13GRNT17290006) and the NIH (1R01GM118534 01).

Synchrotron X-ray scattering and photon correlation spectroscopy studies on thin film morphology details and structural changes of an amorphous-crystalline brush diblock copolymer

Abstract We investigated structural details and temperature-induced structural changes of an amorphous-crystalline brush diblock copolymer, poly(3-((6-((7-(9H-carbazol-9-yl)heptanoyl)oxy)hexyl)thio)propyl glycidyl ether) 60 - b -poly(glycidyl 12-((3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)oxy)-12-oxododecanoate) 20 (PGK 60 -PGF 20 ) in nanoscale thin films using synchrotron grazing incidence X-ray scattering (GIXS) and X-ray photon correlation spectroscopy (XPCS). Interestingly, the diblock copolymer was found to form a mixture of two different hexagonal cylinder structures (HEX1 and HEX2) where the PGF cylinders were aligned in the film plane. HEX1 was composed of PGF cylinders with higher population of crystals while HEX2 consisted of PGF cylinders with lower population of crystals. Surprisingly, the PGF block chains favorably self-assembled because of strong lateral interactions in the bristles, forming vertical multibilayer structure with partial interdigitation even in the highly confined cylindrical geometry. In heating run up to 340 K, some fraction of HEX2 was transformed to HEX1 via cold crystallization. In contrast, HEX1 was transformed to HEX2 above 340 K because of melting of the PGF crystals. The XPCS analysis found that the HEX structural changes associated with the cold crystallization in the PGF cylinder domains took place with relatively fast dynamics. The HEX structural changes associated with melting of the PGF crystals in the cylinder domains occurred with relatively slow dynamics; this unusual dynamics of structural changes might be attributed to a high energy melting process of PGF crystals against strong lateral interactions of the bristles.

Treatment of critically sized femoral defects with recombinant BMP-2 delivered by a modified mPEG-PLGA biodegradable thermosensitive hydrogel.

BackgroundReconstruction of a segmental fracture with massive bone loss is still a challenge for orthopaedic surgeons. The aim of our study was to develop a suitable biodegradable thermosensitive hydrogel system as a carrier for bone morphogenetic protein (BMP)-2 delivery in the treatment of critical-sized femoral defects.MethodsA block copolymer composed of monomethoxypoly(ethylene glycol) (mPEG), poly(lactic-co-glycolic acid) (PLGA) and 2, 2’-Bis (2-oxazolin) (Box) was synthesized by ring opening polymerization. The synthesized block copolymer was characterized by 1H-NMR spectroscopy and gel permeation chromatography (GPC). Different biophysical and biochemical properties of the synthesized copolymer, including temperature-induced structure changes, degradation rate, pH changes during hydrolytic degradation, cell toxicity, and the release profile of BMP-2, were also evaluated and/or were compared with those of a well-characterized mPEG-PLGA copolymer. In animal testing, rabbits (n = 36) that received critically sized (10 mm) femoral defects were divided into 6 groups. These experimental groups included an untreated group, autograft, and groups treated with the synthesized copolymer carrying different concentrations of BMP-2 (0, 5, 10, and 20 μg/ml). Bone repair was evaluated using X-ray radiography, histological staining, micro-computed tomography (μCT), biomarker examination and biomechanical testing in a 12-week treatment period.ResultsA new thermosensitive mPEG-PLGA/Box/mPEG-PLGA block copolymer, or named as BOX copolymer, was successfully prepared. Compared to the reported mPEG-PLGA in vitro, the prepared BOX copolymer at the same weight percent concentrations exhibited wider temperature ranges of gelation, slower degradation rates, higher the pH values, as well as less cytotoxicity. Furthermore, the BMP-2 release from BOX hydrogel exhibited a near-linear release profile in vitro. In animal experiments, treatment of critical-sized bony defects with 25 wt% BOX hydrogel carrying BMP-2 effectively promoted fracture healing during the 12-week trial period and higher concentrations of BMP-2 treatment correlated with better bone quality. Most importantly, clinical outcome and bone healing in the BOX-hydrogel group with 20 μg/ml BMP-2 were nearly equivalent to those in the autograft group in a 12-week treatment course.ConclusionThese data support that the use of BOX hydrogel (25 wt%) as a drug delivery system is a promising method in the treatment of large bone defects.

Reversible Bidirectional Shape Memory Effect in Polyurethanes through Molecular Flipping

Reversible bidirectional shape memory is developed in thermoplastic polyurethane by designing different components to enable molecular switching from actuator domain to self-assembled rigid hard domain and vice versa under a temperature cycle. Polycaprolactone based special polyurethanes have been synthesized which exhibit appropriate self-assembly behavior suitable for the shape memory effect. Reversible bidirectional shape memory has been reported through induced strain and giving shape at particular temperature, and the results are compared with conventional polyurethanes which do not show any shape memory effect. The correlation between chemical structures, self-assembly, structural evolution, and shape memory effect has been made. Self-gripping is demonstrated revealing the novel mechanism of molecular flipping and temperature-induced structural change along with molecular aggregation.

Temperature-induced changes in treatment efficiency and microbial structure of aerobic granules treating landfill leachate.

This paper investigates the effect of temperature on nitrogen and carbon removal by aerobic granules from landfill leachate with a high ammonium concentration and low concentration of biodegradable organics. The study was conducted in three stages; firstly the operating temperature of the batch reactor with aerobic granules was maintained at 29 °C, then at 25 °C, and finally at 20 °C. It was found that a gradual decrease in operational temperature allowed the nitrogen-converting community in the granules to acclimate, ensuring efficient nitrification even at ambient temperature (20 °C). Ammonium was fully removed from leachate regardless of the temperature, but higher operational temperatures resulted in higher ammonium removal rates [up to 44.2 mg/(L h) at 29 °C]. Lowering the operational temperature from 29 to 20 °C decreased nitrite accumulation in the GSBR cycle. The highest efficiency of total nitrogen removal was achieved at 25 °C (36.8 ± 10.9 %). The COD removal efficiency did not exceed 50 %. Granules constituted 77, 80 and 83 % of the biomass at 29, 25 and 20 °C, respectively. Ammonium was oxidized by both aerobic and anaerobic ammonium-oxidizing bacteria. Accumulibacter sp., Thauera sp., cultured Tetrasphaera PAO and Azoarcus–Thauera cluster occurred in granules independent of the temperature. Lower temperatures favored the occurrence of denitrifiers of Zooglealineage (not Z. resiniphila), bacteria related to Comamonadaceae, Curvibacter sp., Azoarcus cluster, Rhodobacter sp., Roseobacter sp. and Acidovorax spp. At lower temperatures, the increased abundance of denitrifiers compensated for the lowered enzymatic activity of the biomass and ensured that nitrogen removal at 20 °C was similar to that at 25 °C and significantly higher than removal at 29 °C.

Phase transition behaviors of the supported DPPC bilayer investigated by sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM).

The phase transition behaviors of a supported bilayer of dipalmitoylphosphatidyl-choline (DPPC) have been systematically evaluated by in situ sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM). By using an asymmetric bilayer composed of per-deuterated and per-protonated monolayers, i.e., DPPC-d75/DPPC and a symmetric bilayer of DPPC/DPPC, we were able to probe the molecular structural changes during the phase transition process of the lipid bilayer by SFG spectroscopy. It was found that the DPPC bilayer is sequentially melted from the top (adjacent to the solution) to bottom leaflet (adjacent to the substrate) over a wide temperature range. The conformational ordering of the supported bilayer does not decrease (even slightly increases) during the phase transition process. The conformational defects in the bilayer can be removed after the complete melting process. The phase transition enthalpy for the bottom leaflet was found to be approximately three times greater than that for the top leaflet, indicating a strong interaction of the lipids with the substrate. The present SFG and AFM observations revealed similar temperature dependent profiles. Based on these results, the temperature-induced structural changes in the supported lipid bilayer during its phase transition process are discussed in comparison with previous studies.

Monitoring and understanding the paraelectric-ferroelectric phase transition in the metal-organic framework [NH4 ][M(HCOO)3 ] by solid-state NMR spectroscopy.

The paraelectric-ferroelectric phase transition in two isostructural metal-organic frameworks (MOFs) [NH4 ][M(HCOO)3 ] (M=Mg, Zn) was investigated by in situ variable-temperature (25) Mg, (67) Zn, (14) N, and (13) C solid-state NMR (SSNMR) spectroscopy. With decreasing temperature, a disorder-order transition of NH4 (+) cations causes a change in dielectric properties. It is thought that [NH4 ][Mg(HCOO)3 ] exhibits a higher transition temperature than [NH4 ][Zn(HCOO)3 ] due to stronger hydrogen-bonding interactions between NH4 (+) ions and framework oxygen atoms. (25) Mg and (67) Zn NMR parameters are very sensitive to temperature-induced changes in structure, dynamics, and dielectric behavior; stark spectral differences across the paraelectric-ferroelectric phase transition are intimately related to subtle changes in the local environment of the metal center. Although (25) Mg and (67) Zn are challenging nuclei for SSNMR experiments, the highly spherically symmetric metal-atom environments in [NH4 ][M(HCOO)3 ] give rise to relatively narrow spectra that can be acquired in 30-60 min at a low magnetic field of 9.4 T. Complementary (14) N and (13) C SSNMR experiments were performed to probe the role of NH4 (+) -framework hydrogen bonding in the paraelectric-ferroelectric phase transition. This multinuclear SSNMR approach yields new physical insights into the [NH4 ][M(HCOO)3 ] system and shows great potential for molecular-level studies on electric phenomena in a wide variety of MOFs.

Assessment of polyamide-6 crystallinity by DSC

This study addresses the question of the crystallinity determination of PA6 by means of DSC in the case when structural changes occur over a very large temperature domain during the heating scan. The temperature dependence of the melting enthalpy is then of crucial importance for determining the amount of crystalline phase involved in the various processes, and thus the initial crystallinity. Both DSC and WAXS measurements have been carried out of a PA6 sample submitted to various thermal treatments in order to identify the crystalline forms and the temperature-induced structural changes. The melting enthalpy dependence on temperature of PA6 was computed from heat capacity data of the solid and liquid borrowed from literature data tables. Similar computations were performed for PA66 which is likely to exhibit analogous structural changes during DSC analysis.

Temperature-induced structural and chemical changes of ultrathin ethylene carbonate films on Cu(111).

The interaction of the Li-ion battery solvent ethylene carbonate (EC) with Cu(111) was investigated by scanning tunnelling microscopy (STM) and variable temperature X-ray photoelectron spectroscopy (XPS) under ultrahigh vacuum (UHV) conditions. Between 80 and 420 K, the decomposition of EC occurs along with distinct structural and chemical changes of the adlayer.

Thermosensitive AB4 four-armed star PNIPAM-b-HTPB multiblock copolymer micelles for camptothecin drug release

Thermo-sensitive poly(N-isoproplacrylamide)m-block-hydroxyl-terminated polybutadiene-block-poly(N-isoproplacrylamide)m (PNIPAMm-b-HTPB-b-PNIPAMm, m = 1 or 2) block copolymers, AB4 four-armed star multiblock and linear triblock copolymers, were synthesized by ATRP with HTPB as central blocks, and characterization was performed by 1H NMR, Fourier transform infrared, and size exclusion chromatography. The multiblock copolymers could spontaneously assemble into more regular spherical core–shell nanoscale micelles than the linear triblock copolymer. The physicochemical properties were detected by a surface tension, nanoparticle analyzer, transmission electron microscope (TEM), dynamic light scattering, and UV–vis measurements. The multiblock copolymer micelles had lower critical micelle concentration than the linear counterpart, TEM size from 100 to 120 nm, and the hydrodynamic diameters below 150 nm. The micelles exhibited thermo-dependent size change, with low critical solution temperature of about 33–35 °C. The characteristic parameters were affected by the composition ratios, length of PNIPAM blocks, and molecular architectures. The camptothecin release demonstrated that the drug release was thermo-responsive, accompanied by the temperature-induced structural changes of the micelles. MTT assays were performed to evaluate the biocompatibility or cytotoxicity of the prepared copolymer micelles.

Thermosensitive PNIPAM-b-HTPB block copolymer micelles: Molecular architectures and camptothecin drug release

Two kinds of thermo-sensitive poly(N-isoproplacrylamide) (PNIPAM) block copolymers, AB4 four-armed star multiblock and linear triblock copolymers, were synthesized by ATRP with hydroxyl-terminated polybutadiene (HTPB) as central blocks, and characterization was performed by 1H NMR, FT-IR and SEC. The multiblock copolymers could spontaneously assemble into more regular spherical core–shell nanoscale micelles than the linear triblock copolymer. The physicochemical properties were detected by a surface tension technique, nano particle analyzer, TEM, DLS and UV–vis measurements. The multiblock copolymer micelles had lower critical micelle concentration than the linear counterpart, TEM size from 100 to 120nm and the hydrodynamic diameters below 150nm. The micelles exhibited thermo-dependent size change, with low critical solution temperature about 33–35°C. The characteristic parameters were affected by the composition ratios, length of PNIPAM blocks and molecular architectures. The camptothecin release demonstrated that the drug release was thermo-responsive, accompanied by the temperature-induced structural changes of the micelles. MTT assays were performed to evaluate the biocompatibility or cytotoxicity of the prepared copolymer micelles.

Gas transport properties of interfacially polymerized polyamide composite membranes under different pre-treatments and temperatures

Thin-film composite reverse osmosis membranes were dried under different membrane pre-treatment procedures and evaluated at increased temperatures by gas separation tests. The obtained permeance and selectivity values indicated the presence of highly-permeable regions in the dry samples of the commercial membranes.Treatment with ethanol–hexane in a solvent exchange process, as well as membrane immersion in t-butanol followed by freeze drying, increased the gas permeance by a factor of 1.8 to 9, and from 1.6 to 3.2, respectively, by comparison with room temperature and oven drying. Nevertheless, a Knudsen-diffusion transport mechanism was dominant after both pre-treatments.The permeation temperature remarkably influenced gas selectivity and permeance, and a maximum He/N2 selectivity occurred at 150°C with considerable high permeance results, which may suggest the use of polyamide membranes as alternative materials for high-temperature separation processes. The temperature-induced changes in the polymer structure and in the transport of compounds can be explained by Knudsen and activated diffusion mechanisms throughout a highly-permeable regions and a dense polyamide matrix, respectively.