Preparation and properties of thermosensitive hydrogel microcapsules

Temperature-sensitive hydrophilic gel microcapsules have been newly prepared. That is, poly ( -lysineisopropylamide–terephthalic acid) microcapsules containing water have been obtained by an interfacial polymerization at a water/oil interface between -lysineisopropylamide and terephthaloyldichloride. The microcapsule changes its size between 33 and 35°C. Under 33°C, the microcapsules are fully spherical and can be redispersed in distilled water, while are aggregated above 35°C. The microcapsules, which are observed to show aggregation above 33°C, can be redispersed by decreasing temperature within a few second. The thermosensitive morphological changes of the microcapsules are thus reversible. Also, it has been shown that the permeability of sodium chloride through the microcapsule membrane changes remarkably between 33 and 35°C, while it is kept almost constant independent of temperature between 25 and 33°C or between 35 and 55°C. The permeability of solutes is higher under 33°C than that above 35°C. Such thermosensitive properties result from the fact that the polymer membrane has isopropylamide groups. That is, -lysineisopropylamide has a chemical structure similar to N-isopropylacrylamide, the polymer of which, poly (N-isopropylacrylamide), is a thermosensitive hydrogel having its phase transition temperature around 33°C.     

pH- and temperature-dependent release from cationic vesicles coexisting with copolymer of N-isopropylacrylamide and methacrylic acid

Vesicles containing rhodamine B were prepared by evaporation and hydration method using N-[3-(dimethylamino)propyl]-octadecanamide (DMAPODA) and stearic acid (SA). The vesicles were multi-lamellar on optical and electron micrographs. The mean size of vesicle was 807.9 nm and the values markedly increased by the addition of copolymers of N-isopropylacrylamide (NIPAM) and methacrylic acid (MAA) (P(NIPAM-co-MAA)), possibly due to electrostatic interactions between the cationic vesicle and the anionic copolymer. The release of rhodamine B from the vesicles for 20 h was 50–60% at neutral pHs and the values increased up to 93.1% when pH decreased to 3. The increased release is possibly because the salt bridge formed between DMAPODA and SA was broken down at the acidic pH, leading to the disintegration of the vesicles. On the other hand, the release was not as sensitive to temperature as it was to pH. The salt bridge seemed to be stable at the temperatures of the release experiments (23 °C, 33 °C and 43 °C). P(NIPAM-co-MAA) was added to the suspension of the vesicle and the release was investigated with varying pHs and temperatures. The copolymer was pH- and temperature-sensitive in terms of the turbidity change of its solution. Nevertheless, the copolymer was found to have little effect on the pH- and temperature-dependent release of the vesicles.     

Stabilizing N-tosyl-2-lithioindoles with bis(N,N′-dimethylaminoethyl) ether—a non-cryogenic procedure for lithiation of N-tosylindoles and subsequent addition to ketones

A practical procedure suitable for large scale lithiation of N-tosylindoles and subsequent addition to ketones is described. Bis(N,N′-dimethylaminoethyl) ether was found to stabilize 2-lithio-N-tosylindole 1A at −25 °C [The temperatures cited are internal temperatures unless otherwise stated]. Addition of this reagent allows the lithiation of N-tosyl indoles and subsequent addition to ketones to operate at −25 °C, a temperature suitable for large scale reactions.     

Stability of collagen in the presence of 3,4-dihydroxyphenylalanine (DOPA)

Many cross-linking agents for collagen are available with varying levels of toxicity and some are in use in biomedical implants of collagen. L-DOPA (3,4-dihydroxyphenylalanine), a neurotransmitter, is a naturally present compound in the living system and is the target in therapeutic strategy of Parkinson’s disease. This work reports the effect of the neurotransmitter DOPA on the stability of collagen solution using circular dichroism (CD), fluorescence spectroscopy, melting and shrinkage temperature. Collagen solution treated with various concentrations of DOPA ranging from 10⁻² to 10⁻⁵ M was analyzed using fluorescence and CD spectra. When collagen was treated with DOPA, the intensity of emission was found to increase indicating the possibility of interaction of DOPA with collagen and maximum emission intensity was observed between 10⁻³ and 10⁻⁴ M for L-DOPA and DL-DOPA, respectively. CD studies show possible aggregation of collagen even in the presence of low concentrations of DOPA. The shrinkage temperature of DOPA treated collagen fibres was experimentally determined to be 69 ± 1 °C. The melting temperature of DOPA cross linked collagen solution also exhibited a significant increase from 35 to 40 °C (±0.1) (P < 0.05). The experimental results suggest that the optimum concentration for cross linking collagen with DOPA ranges between 10⁻³ and 10⁻⁴ M. Thus, DOPA may be a useful stabilizing agent for collagen for biomedical applications.     

Dinitrogen and carbon monoxide hydrogen bonding in protonic zeolites: Studies from variable-temperature infrared spectroscopy

Adsorption (at a low temperature) of nitrogen on the protonic zeolite H-Y results in hydrogen bonding of the adsorbed N₂ molecules with the zeolite Si(OH)Al Brønsted-acid groups. This hydrogen-bonding interaction leads to activation, in the infrared, of the fundamental N–N stretching mode, which appears at 2334 cm⁻¹. From infrared spectra taken over a temperature range, the standard enthalpy of formation of the OH···N₂ complex was found to be ΔH⁰ = −15.7(±1) kJ mol⁻¹. Similarly, variable-temperature infrared spectroscopy was used to determine the standard enthalpy change involved in formation of H-bonded CO complexes for CO adsorbed on the zeolites H-ZSM-5 and H-FER; the corresponding values of ΔH⁰ were found to be −29.4(±1) and −28.4(±1) kJ mol⁻¹, respectively. The whole set of results was analysed in the context of other relevant data available in the literature.     

A facile preparation of microparticles from sulfonated polyester nanoparticles via emulsion–aggregation process

A process to prepare microparticles of narrow size distribution having a particle size in the range of approximately 1–8 μm was developed. The primary objective of this work was to study the formation and morphology of copolyester microparticles prepared using a sulfonated copolyester emulsion by an emulsion–aggregation process. Molecular weight of the copolyesters was measured by gel permeation chromatography. The glass transition temperature (T_g) of the copolyesters was found to be in the range of 40–70 °C. Aggregating agents used in this study were 1–5% (wt.%) solutions of divalent ions of zinc acetate and magnesium chloride salts. Emulsion–aggregation experiments were performed at various temperatures: 40, 50, 60, and 80 °C. Particle morphologies studied by field emission-scanning electron microscopy measurements provided an understanding of the conditions and mechanism leading to formation of microparticles by the emulsion–aggregation process. Molecular weight and T_g of the copolyester, the concentration of aggregating agent, and the temperature were determined to be the most important parameters influencing the preparation of microparticles. This process illustrates the preparation of microparticles of uniform size with morphology of controlled shape from a nanometer-sized emulsion by ionic crosslinking.     

New cut angle quartz crystal microbalance with low frequency-temperature coefficients in an aqueous phase

In a traditional quartz crystal microbalance (QCM), an AT-cut (cut angle φ = 35.25° in yxl orientation) quartz wafer is employed because it has low frequency–temperature coefficients (dF/dT) at room temperature region. But when a QCM is in contact with a liquid phase, its frequency is also related to the properties of the liquid, which are temperature dependent. The value of dF/dT is about 20 Hz/°C for a 9 MHz AT-cut QCM with one side facing water. In this work, a group of QCMs in new cut angles were prepared. The influence of the cut angle on the frequency–temperature characteristic, response sensitivities to surface mass loading and viscodensity of liquid were investigated. An intrinsically temperature-compensated QCM sensor that possesses low dF/dT values in aqueous solution was reported. When a 9 MHz QCM with φ = 35.65° was contacted with water with one side, its dF/dT value is close to zero at ca. 25 °C and its averaged value of |dF/dT| is only 0.6 Hz/°C in the temperature range of 23–27 °C. The frequency responses to surface mass loading and viscodensity of liquid phase are very close among the QCMs with the cut angles in the range of 35.15–35.7°. The intrinsically temperature-compensated QCM was applied to investigate the alternate adsorption processes of cationic polyelectrolyte and silica nanoparticle.     

Temperature-dependent interfacial properties of hydrophobically end-modified poly(2-isopropyl-2-oxazoline)s assemblies at the air/water interface and on solid substrates

We describe herein the properties at the air/water (A/W) interface of hydrophobically end-modified (HM) poly(2-isopropyl-2-oxazoline)s (PiPrOx) bearing an n-octadecyl chain on both termini (telechelic HM-PiPrOx) or on one chain end (semitelechelic HM-PiPrOx) for different subphase temperatures and spreading solvents using the Langmuir film balance technique. The polymer interfacial properties revealed by the π–A isotherms depend markedly on the architecture and molecular weight of the polymer. On cold water subphases (14 °C), diffusion of PiPrOx chains onto water takes place for all polymers in the intermediate compressibility region (5 mN m⁻¹). At higher subphase temperatures (36 and 48 °C), the HM-PiPrOx film exhibited remarkable stability with time. Brewster angle microscopy (BAM) imaging of the A/W interface showed that the polymer assembly was not uniform and that large domains formed, either isolated grains or pearl necklaces, depending on the polymer structure, the concentration of the spreading solution and the subphase temperature. The Langmuir films were transferred onto hydrophilic substrates (silica) by the Langmuir–Blodgett (LB) technique and onto hydrophobic substrates (gold) by Langmuir–Schaefer (LS) film deposition, resulting in the formation of adsorbed particles ranging in size from 200 to 500 nm, depending on the polymer architecture and the substrate temperature. The particles presented “Janus”-like hydrophilic/hydrophobic characteristics.     

Temperature dependence vapour pressure measurements of Mg(tmhd)2(tmeda) [(tmhd = 2,2,6,6-tetramethyl-3,5-heptanedione, tmeda = N,N,N′,N′-tetramethylethylenediamine]

The reaction between the magnesium β-diketonate complex Mg(tmhd)₂(H₂O)₂ and 1 equiv. of N,N,N′,N′-tetramethylethylenediamine (tmeda = Me₂NCH₂CH₂NMe₂) in hexane at room temperature yielded Mg(tmhd)₂(tmeda). The standard enthalpy of sublimation (83.2 ± 2.3 kJ mol⁻¹) and entropy of sublimation (263 ± 6.3 J mol⁻¹ K⁻¹) of Mg(tmhd)₂(tmeda) were obtained from the temperature dependence vapour pressure, determined by adopting a horizontal dual arm single furnace thermogravimetric analyser as a transpiration apparatus. From the observed melting point depression DTA, the standard enthalpy of fusion (58.3 ± 5.2 kJ mol⁻¹) was evaluated, using the ideal eutectic behaviour of Mg(tmhd)₂(tmeda) as a solvent with bis(2,4-pentanedionato)magnesium(II), Mg(acac)₂ as a non-volatile solute.     

Thermal induced mobility of self-assembled platelets of polyethylene-block-poly(ethylene oxide) in liquid precursors of unsaturated polyester thermoset

We report the variation of the molecular assembly and crystallinity of polyethylene-block-poly(ethylene oxide) (EEO, 1400 g mol⁻¹) in a non initiated liquid resin of unsaturated polyester (UP). We particularly focus on the driving force that governs the variation of the molecular assembly of the block copolymer in the UP resin upon heating. For this purpose, we performed a set of experiments combining time resolved in situ SAXS and WAXS measurements upon heating and cooling. Upon heating, SAXS shows that the inter-distance of the EEO domains decreases dramatically for temperature above 75 °C (between 90 and 30 nm for the initial system at room temperature vs 9 nm at 110 °C) suggesting that the initially homogeneously dispersed EEO domains undergo aggregation. This is consistent with the macroscopic phase separation observed in such temperature range. In situ WAXS shows that the onset of the aggregation coincides with the melting of the PE domains suggesting that the flexibility of the platelets plays an important role in their aggregation. Upon cooling, peculiar behaviour is observed for the systems with higher EEO content, with an irreversible structure formation leading to macroscopic EEO rich domains dispersed in continuous UP rich phase.     

Synthesis, crystal structures, phase transition characterization and thermal decomposition of a new dabcodiium hexaaquairon(II) bis(sulfate): (C6H14N2)[Fe(H2O)6](SO4)2

The crystal structures of 1,4-diazabicyclo[2.2.2]octane (dabco)-templated iron sulfate, (C₆H₁₄N₂)[Fe(H₂O)₆](SO₄)₂, were determined at room temperature and at −173 °C from single-crystal X-ray diffraction. At 20 °C, it crystallises in the monoclinic symmetry, centrosymmetric space group P2₁/n, Z=2, a=7.964(5), b=9.100(5), c=12.065(5) Å, β=95.426(5)° and V=870.5(8) ų. The structure consists of [Fe(H₂O)₆]²⁺ and disordered (C₆H₁₄N₂)²⁺ cations and (SO₄)²⁻ anions connected together by an extensive three-dimensional H-bond network. The title compound undergoes a reversible phase transition of the first-order at −2.3 °C, characterized by DSC, dielectric measurement and optical observations, that suggests a relaxor–ferroelectric behavior. Below the transition temperature, the compound crystallizes in the monoclinic system, non-centrosymmetric space group Cc, with eight times the volume of the ambient phase: a=15.883(3), b=36.409(7), c=13.747(3) Å, β=120.2304(8)°, Z=16 and V=6868.7(2) ų. The organic moiety is then fully ordered within a supramolecular structure. Thermodiffractometry and thermogravimetric analyses indicate that its decomposition proceeds through three stages giving rise to the iron oxide.     

Study on the interaction between antibacterial drug and bovine serum albumin: A spectroscopic approach

The binding of sulfamethoxazole (SMZ) to bovine serum albumin (BSA) was investigated by spectroscopic methods viz., fluorescence, FT-IR and UV–vis absorption techniques. The binding parameters have been evaluated by fluorescence quenching method. The thermodynamic parameters, ΔH°, ΔS°and ΔG° were observed to be −58.0 kJ mol⁻¹, −111 J K⁻¹ mol⁻¹ and −24 kJ mol⁻¹, respectively. These indicated that the hydrogen bonding and weak van der Waals forces played a major role in the interaction. Based on the Forster's theory of non-radiation energy transfer, the binding average distance, r, between the donor (BSA) and acceptor (SMZ) was evaluated and found to be 4.12 nm. Spectral results showed the binding of SMZ to BSA induced conformational changes in BSA. The effect of common ions and some of the polymers used in drug delivery for control release was also tested on the binding of SMZ to BSA. The effect of common ions revealed that there is adverse effect on the binding of SMZ to BSA.     

Oxygen production at low temperature using dense perovskite hollow fiber membranes

A dense perovskite hollow fiber made of BaCo_xFe_yZr_zO_3−δ (BCFZ) was evaluated for the oxygen separation at low temperatures (400–500 °C). An oxygen permeation flux of 0.45 ml/min cm² was obtained at 500 °C, which is the first oxygen permeation data reported at such low temperature so far. A degradation of the oxygen permeation at 500 °C was observed, but the oxygen fluxes through the hollow fiber membrane can be regenerated by thermal treatment at 925 °C for 1 h in air. Energy-dispersive X-ray spectroscopy (EDXS) shows that a strong element segregation occurs in the membrane during operation at low temperature.     

Shell-crosslinked nanoparticles through self-assembly of thermoresponsive block copolymers by RAFT polymerization

A reversible addition-fragmentation chain transfer (RAFT) agent, the methyl-2-(n-butyltrithiocarbonyl)propanoate (MBTTCP) has shown to be efficient in controlling the polymerization of N,N-dimethylacrylamide (DMA), N-isopropylacrylamide (NIPAM) and N-acryloyloxysuccinimide (NAS). Two different strategies have been studied to synthesize block copolymers based on one PNIPAN block and the other a random copolymer of DMA and NAS. When a PNIPAM trithiocarbonate-terminated is used as macromolecular chain transfer agent for the polymerization of a mixture of NAS and DMA, well-defined P(NIPAM-b-(NAS-co-DMA)) block copolymers were obtained with a low polydispersity index. These thermoresponsive block copolymers dissolved in aqueous solution at 25 °C and self-assembled into micelles when the temperature was raised above the LCST of the PNIPAM block. The micelle shell containing NAS units was further crosslinked using a primary diamine in order to get shell-crosslinked nanoparticles. Upon cooling below the LCST of PNIPAM this structure may easily reorganize to form nanoparticles with a water filled hydrophilic core.     

Synthesis, crystal structure and characterization of iron pyroborate (Fe2B2O5) single crystals

Single crystals of iron(II) pyroborate, Fe₂B₂O₅, were prepared at 1000–1050 °C under an argon atmosphere. The crystals were transparent, yellowish in color and needle-like or columnar. The crystal structure of Fe₂B₂O₅ was analyzed by single-crystal X-ray diffraction. Refined triclinic unit cell parameters were a=3.2388(2), b=6.1684(5), c=9.3866(8) Å, α=104.613(3)°, β=90.799(2)° and γ=91.731(2)°. The final reliability factors of refinement were R1=0.020 and wR2=0.059 [I > 2σ(I)]. Transmittance over 50% in the visible light region from 500 to 750 nm was observed for a single crystal of Fe₂B₂O₅ with a thickness of about 0.3 mm. The light absorption edge estimated from a diffuse reflectance spectrum was at around 350 nm (3.6 eV). Magnetic susceptibility was measured for single crystals at 4–300 K. Fe₂B₂O₅ showed antiferromagnetic behavior below the Néel temperature, T_N≈70 K, and the Weiss temperature was T_W=36 K. The effective magnetic moment of Fe was 5.3μ_B.     

A study on dose response of NIPAM-based dosimeter used in radiotherapy

The newly manufactured N-isopropylacrylamide (NIPAM) polymer gel is composed of four components, i.e., gelatin, monomer (NIPAM), crosslinker (N,N’-methylenebisacrylamide, Bis), and antioxidant (tetrakis hydroxymethyl phosphonium chloride, THPC). In this study, we investigated the effects of gel composition on the dose response of NIPAM polymer gel. A statistical experiment to analyze the contribution of each composition to the linearity and sensitivity of NIPAM gel was performed. Results indicate that the amount of gelatin, NIPAM (15.17%), Bis, and THPC have dominant effects on the sensitivity of the gel, with contributions of 59.73, 15.17, 10.64, and 14.45%, respectively. The amount of gelatin and Bis mainly affected the linearity of the gel, with contributions of 44.70 and 50.99%, respectively. The linearity of most compositions of the gel was greater than 0.99 when (%C)/(%T) was lower than 8.0. Optimal (%C)/(%T) for higher sensitivity should be in the range of 4−9. The temporal stability experiment showed that the dose response curve attained stability at about 5 h after irradiation and persisted up to 3 months.     

Modifying the thermosensitivity of copolymers of sodium styrene sulfonate and<Emphasis Type="Italic"> N</Emphasis>-isopropylacrylamide with dodecyltrimethylammonium chloride

The interactions between copolymers of sodium styrene sulfonate (SSS) and N-isopropylacrylamide (NIPAM), anionic polyelectrolytes, and dodecyltrimethylammonium chloride (DTAC), a cationic surfactant, were studied in aqueous solutions of various ionic strengths. The copolymers were found to be thermoresponsive, showing a lower critical solution temperature (LCST). The influence of the polymer composition, the surfactant concentration, and the ionic strength on the LCST was studied. The surfactant was found to interact strongly with the polymer, forming mixed polymer-surfactant micelles. The critical aggregation concentration (cac) of the polymer-surfactant system was found from fluorescence spectroscopy using pyrene as a fluorescent probe. A strong dependence of the anionic polyelectrolyte-cationic surfactant interactions on the structure of the ionic comonomer was observed.     

The standard partial molar entropy of the aqueous tetra-n-butylammonium cation

The standard partial molar entropy of the aqueous tetrabutylammonium cation, not known previously, has now been obtained, based on the molar entropy of two of its crystalline salts, the iodide and the tetraphenylborate, recently determined experimentally for this purpose. The calculation required also published molar enthalpies of solution and solubilities of these two salts as well as of the perchlorate. The choice of the anions depended mainly on the limited solubilities of the examined salts in water, facilitating the estimation of the relevant activity coefficients. The result is S^∞(Bu₄N⁺, aq) = (380 ± 20) J · K⁻¹ · mol⁻¹ at T = 298.15 K, on the mol · dm⁻³ scale and based on S^∞(H⁺, aq) = (−22.2 ± 1.2) J · K⁻¹ · mol⁻¹ (yielding the ‘absolute’ value). The molar entropy of this cation in the ideal gas standard state, S(Bu₄N⁺, g) = (798 ± 8) J · K⁻¹ · mol⁻¹ then yielded the molar entropy of hydration Δ_hydS^∞ (Bu₄N⁺) = (−418 ± 23) J · K⁻¹ · mol⁻¹.     

TGA–FTIR study of a lead zirconate titanate gel made from a triol-based sol–gel system

A Pb(Zr,Ti)O₃ precursor gel made from a sol prepared using 1,1,1,-tris(hydroxymethyl)ethane, lead acetate and zirconium and titanium propoxides, stabilised with acetylacetone, was analysed using TGA–FTIR analysis. Decomposition under nitrogen (N₂) gave rise to evolved gas absorbance peaks at 215 °C, 279 °C, 300 °C and 386 °C, but organic vapours continued to be evolved, along with CO₂ and CO until 950 °C. The final TGA step in N₂ is thought to relate to decomposition of an intermediate carbonate phase and the final elimination of residues of triol or acetylacetonate species which form part of the polymeric gel structure. By contrast, heating in air promoted oxidative pyrolysis of the final organic groups at ≤450 °C. In air, an intermediate carbonate phase was decomposed by heating at 550 °C, allowing Pb(Zr,Ti)O₃ to be produced some 400 °C below the equivalent N₂ decomposition temperature.     

Vacuum ultraviolet laser-induced breakdown spectroscopy analysis of polymers

Laser-induced breakdown spectroscopy (LIBS) in the vacuum ultraviolet range (VUV, λ < 200 nm) is employed for the detection of trace elements in polyethylene (PE) that are difficult to detect in the UV/VIS range. For effective laser ablation of PE, we use a F₂ laser (wavelength λ = 157 nm) with a laser pulse length of 20 ns, a pulse energy up to 50 mJ, and pulse repetition rate of 10 Hz. The optical radiation of the laser-induced plasma is measured by a VUV spectrometer with detection range down to λ = 115 nm. A gated photon-counting system is used to acquire time-resolved spectra. From LIBS measurements of certified polymer reference materials, we obtained a limit of detection (LOD) of 50 µg/g for sulphur and 215 µg/g for zinc, respectively.The VUV LIBS spectra of PE are dominated by strong emission lines of neutral and ionized carbon atoms. From time-resolved measurements of the carbon line intensities, we determine the temporal evolution of the electronic plasma temperature, T_e. For this, we use Saha–Boltzmann plots with the electron density in the plasma, N_e, derived from the broadening of the hydrogen H-α line. With the parameters T_e and N_e, we calculate the intensity ratio of the atomic sulphur and carbon lines at 180.7 nm and at 175.2 nm, respectively. The calculated intensity ratios are in good agreement with the experimentally measured results.