Detailed investigation of gel–sol transition temperature of κ-carrageenan studied by DSC, TMA and FBM

A broad temperature range of the gel–sol transition of κ-carrageenan was precisely examined by differential scanning calorimetry (DSC), thermomechanical analysis (TMA) and the falling ball method (FBM). κ-Carrageenan the transition temperature of which ranged from 290 to 350 K was used as a representative sample of a thermo-reversible hydrogel. The starting of transition attributed to dissociation of the weak cross-linking zone of aggregated double helices was detected as a change of expansion coefficient by TMA and as an endothermic deviation by DSC. Peak temperature of endotherm by DSC agreed well with the temperature where expansion changed from positive to negative value and this temperature was attributed to gel–sol transition caused by dissociation of double helices’ assembly. Transition temperature measured by FBM was observed at a temperature higher than those obtained by DSC and TMA, which was attributed to decomposition of double helices.     

Features of molecular light scattering and structure of the chlorobenzene–o-dichlorobenzene solutions

Structural Chemistry - The total light scattering coefficient, degree of depolarization, refractive index, and density were measured in chlorobenzene–o-dichlorobenzene solutions. The...     

Development and characterization of nanocapsules comprising dodecyltrimethylammonium chloride and κ-carrageenan

The aim of this work was to develop and characterize a new type of nanocapsules. To this end, a nanoemulsion bearing an oily core (Miglyol 812) was obtained by spontaneous emulsification and stabilized by dodecyl-trimethylammonium chloride (DTAC), a commercial cationic surfactant; this nanoemulsion was coated with proportionally very small amounts of κ-carrageenan (at molar charge ratios of Z ≤ 0.0045) that interact predominantly by an electrostatic mechanism with the positively charged sites at the polar heads of DTAC at the nanoemulsion's surface to harness nanocapsules of average size ~250-330 nm and zeta potential (ζ) ranging from ~+80 to +7 mV. The potential application of the new type of developed nanosystems as drug delivery vehicles has yet to be investigated and fully realized.     

Synthesis and swelling behavior of temperature responsive κ-carrageenan nanogels

Crosslinked κ-carrageenan hydrogel nanoparticles (nanogels) with an average size smaller than 100 nm were prepared using reverse microemulsions combined with thermally induced gelation. The size of the nanogels varied with biopolymer concentration at a constant water/surfactant concentration ratio. The nanogels were found to be thermo-sensitive in a temperature range acceptable for living cells (37-45°C) undergoing reversible volume transitions in response to thermal stimuli. This opens the possibility to explore the application of these nanogels in smart therapeutics such as thermo-sensitive drug carriers. As such, the sustained release of methylene blue from the nanogels was evaluated in in vitro conditions as proof of concept experiments and the release rate was found to be controlled with temperature.     

Structural analysis of κ-carrageenan sulfated oligosaccharides by positive mode Nano-ESI-FTICR-MS and MS/MS by SORI-CID

Structural analysis of sulfated oligosaccharides from kappa-carrageenan of up to ten residues (MW >2 kDa) was successfully carried out by positive mode nano-ESI-FTICR-MS together with MS/MS using sustained off-resonance irradiation-collision induced dissociation (SORI-CID). Glycosidic bond cleavage reactions via the B- and Y-types of fragmentation were observed and enabled complete sequencing of the oligosaccharide samples. The positions of the labile sulfate substituents were observable using SORI-CID, enabling the determination of the sequence of the sulfated residues.     

Liquid–liquid interfaces: studied by X-ray and neutron scattering

Major recent advances include the development of new experimental techniques that enabled the first precise measurements of interfacial widths at water–oil interfaces and of the ordering of surfactants adsorbed to these interfaces, studies of phase transitions and domain formation in surfactant monolayers, and studies of interfacial fluctuations confined by and coupled across thin liquid films.     

Configurations of anions of β-ketoaldehydes in solutions studied by i.r. spectroscopy

The i.r. spectra of the Li, Na and K salts of β-ketoaldehydes, RCOCH₂CHO (R = Me, Et, i-Pr and t-Bu) in DMSO, methanol and water were investigated. Assignments of bands to stretching modes of particular configurations of the enolate system were given. Influence of the cation radius on the Z,Z ⇌ E,E/Z,E equilibrium and of the substituent R on the E,E ⇌ Z,E equilibrium was observed. Shifts of the enolate bands in protic solvents were observed and hydrogen-bond formation accounted for this phenomenon.     

Local motion in theβ-transition range of partially crystalline polyethylene studied by neutron scattering

We have performed inelastic neutron scattering experiments on protonated and fully deuterated partially crystalline polyethylene. Using a high-resolution, three-axes spectrometer with an energy resolution of 80 eV, it was possible to detect a quasielastic process in the dynamic structure factor with a FWHM of 0.3 meV. This process was shown to be active aboveT ₀=260 K and its FWHM was nearly independent of temperature and scattering vector. The spatial extent of the underlying motional process was displacement increases strongly withT aboveT ₀ up to 4 Ų atT=380 K. Comparison with results from similar work on fully amorphous polymers suggests to relateT ₀ to the glass transition of the amorphous phase in partially crystalline polyethylene. The coherent structure factor showns no evidence for a significant contribution of correlated motion to the process. A speculative explanation of the observed phenomenon as a non-equilibrium soft-mode is proposed.Dedicated to Prof. E. W. Fischer on the occasion of his 65th birthday     

Vibrational properties of CaAlH5 and α-AlH3 with different AlH6 networks studied by inelastic neutron scattering

We performed a combined study using inelastic neutron scattering (INS) and first-principles calculations of the vibrational properties of CaAlH(5) and α-AlH(3) with different AlH(6) networks, a zigzag one-dimensional AlH(6) network for CaAlH(5), and a three-dimensional AlH(6) network for α-AlH(3). Both materials showed qualitatively similar INS spectra, in which CaAlH(5)/α-AlH(3) was mainly divided into three regions: (i) the translational modes (318/316 cm(-1)), (ii) the librational modes of the octahedral AlH(6) units (external molecular motion) in the lower frequency range and H-Al-H bond-bending modes (intra molecular motion) at a higher frequency (420-1157/513-1038 cm(-1)), and (iii) the Al-H bond-stretching modes (1238-1750/1486-1942 cm(-1)). In region ii, the appearance of both librational and bond-bending modes was determined by the networked nature of the octahedral AlH(6) units. In addition, the librational modes of AlH(6) on α-AlH(3) exhibit higher frequencies than CaAlH(5) due to the tighter bonding between the octahedral AlH(6) units. With regard to average frequencies for the Al-H, ω(S), bond-stretching modes, and average Al-H bond distances on the aluminum-based hydrides including CaAlH(5) and α-AlH(3), ω(S) showed lower frequencies that correlate with lengthening of the Al-H bond distances.     

Effects of low-dose ionizing radiation on α,β-globulins solutions studied by DSC

An attempt has been made to detect the effect of a small dose of ionizing radiation on the course of α,β-globulin thermal denaturation in aqueous solutions. Doses of 0.1 and 1.8 Gy have been delivered using γ-rays emitted by ⁶⁰Co isotope while doses of 10 and 100 Gy have been supplied by X-rays produced by linear accelerator. The highest dose has visibly changed DSC curve of protein solution while the changes due to lower doses are hardly detectable. Although very weak, the irradiation effect found has been dose dependent. The results suggest that the influence of ionizing radiation on globulins solution is bigger when the dose rate is lower at given dose. The opposite direction of differences between irradiated and control samples for fresh and stored protein solutions suggests various characters of changes in initial and later period of sample aging. This may be an important reason for difficulties in an investigation of the effect of ionizing radiation on protein solution, especially for low doses delivered very slowly.     

The interaction between sodium dodecylsulfate and the cationic-nonionic random copolymer (3-(2-methylpropionamide)propyl) trimethylammonium chloride–acrylamide of two different charge densities studied using dynamic light scattering and rheometry

The effects of complex formation between sodium dodecylsulfate (SDS) and the positively charged (3-(2-methylpropionamide)propyl)trimethyl-ammonium chloride-acrylamide (MAPTAC-AM) copolymer have been studied in dilute and semidilute aqueous solution in the presence of 10 mM NaCl. Two different charge densities of the copolymer have been used in the study: 0.31 and 0.66, corresponding to the proportion of MAPTAC units. Dynamic light scattering (DLS) and rheometry (static low-shear and capillary viscometry) have been performed on the systems at different charge ratios, i.e., SDS/MAPTAC molar ratios, r. Regarding the phase behavior, the maximum binding ratio prior to precipitation differs between the copolymers. A 1.0% w/v solution of SDS/31% MAPTAC-AM is soluble at r = 0.4 , while an SDS/66% MAPTAC-AM solution of 1.0% w/v shows phase separation at this ratio. With excess surfactant, the complex in the former system is resolubilized at r=2.0, whereas the latter system is still phase-separated at r=5.0. DLS results show that, for both copolymers, the hydrodynamic radius, R _h, of the single-chain copolymer-surfactant complex decreases as a function of r, but then increases slightly prior to phase separation. The corresponding hydrodynamic virial coefficient, k _D, changes in the same manner as R _h. The light-scattering data also show that the formation of larger structures is promoted as the polymer concentration is increased from 0.2 to 1.0% w/v. This is shown by the increase in the relative aggregate-to-single coil peak areas in the relaxation time distributions. Both systems have this common trend. The results from rheological measurements support the results from DLS. A reduction in intrinsic viscosity, [η], is observed on increasing r up to phase separation. The major part of the static low-shear measurements showed Newtonian behavior for both systems at different copolymer concentrations (27.6–138 mM), and at different r. These systems, partially ionic polymer/oppositely charged surfactant, present very interesting rheological behavior at relatively high polymer concentrations and at low r values. Their behavior is similar to those of hydrophobically modified polyelectrolytes. Received: 17 June 1998 Accepted: 12 August 1998     

Pitting of Al and Al–Si alloys in KSCN solutions and the effect of light

The pitting corrosion susceptibility of pure Al and three Al-Si alloys, namely (Al-6%Si), (Al-12%Si) and (Al-18%Si) has been studied in 0.04 M KSCN solution. Measurements were carried out under the effect of various experimental conditions using cyclic polarization, potentiostatic and galvanostatic techniques. In all cases, the potentiodynamic anodic polarization curves do not exhibit active dissolution region due to spontaneous passivation. The passivity is due to the presence of a thin film of Al₂O₃ on the anode surface. The passive region is followed by pitting corrosion, at a certain critical potential, pitting potential (E_pit), as a result of breakdown of the passive film by SCN^? anions. Cyclic polarization measurements allowed the determination of the pitting corrosion parameters, namely the pitting potential and the repassivation potential (E_rp). Alloyed Si decreased the passive current (j_pass) and shifted both E_pit and E_rp towards more positive values. Thus alloyed Si suppressed pitting attack. The effect of illumination on passivity and the initiation of pitting corrosion on Al in KSCN solutions was also studied. It is observed that illumination of Al leads to an increase in its pitting corrosion resistance-apparent from j_pass, E_pit, and E_rp measurements in aggressive KSCN solutions.     

Kinetics of coal and char oxycombustion studied by TG–FTIR

Coal and char oxycombustion is a complex process because of very high reaction rate of oxygen with coals and chars carbon. Very important process during oxycombustion is diffusion of O₂ to surface of coal and char grain. This process can be minimized using small samples and high flow of the gas, but it is also dependent on temperature. For this reason, it is impossible to eliminate diffusion processes which cause significant impact on calculated kinetic parameters. This paper describes the results of thermogravimetric studies of oxycombustion process with evolved gas analysis by FTIR. Ultimate and proximate analysis of coal and char were made. Thermogravimetric experiments of coal and its char oxycombustion were conducted using five heating rates, namely 2.5, 5, 10, 20 and 40 K min^?1, and gas mixture composed of 20 % O₂ in CO₂. Activation energies of coal and char oxycombustion were calculated by isoconversional methods: integral Vyazovkin and differential Friedman. Activation energies for three ranges of heating rates were calculated. This paper shows influence of heating rate on calculated activation energy. The reason of this phenomenon is due to change of the mechanism of coal and char oxycombustion from the chemical kinetic control regime to mixed chemical kinetic–diffusion control regime.     

Analysis of ″stepwise″ heterocoagulation process of small cationic polymer particles onto large anionic polymer particles using dynamic light scattering

In order to clarify in detail the process of the stepwise heterocoagulation of small polymer particles (SP) onto large polymer particles (LP), which we proposed to prepare anomalous polymer particles, the particle-size distribution in each step was estimated using dynamic light scattering.SP andLP have surface charges opposite to each other in emulsion states.SP were produced by emulsion copolymerization of styrene and methacryloyloxyethyltrimethylammonium chloride, andLP by emulsion terpolymerization of styrene, butyl acrylate, and methacrylic acid. Both emulsions in which nonionic emulsifier had been added were blended without coagulation and then the heterocoagulation was carried out by adjusting of the pH and heating.Part CXVII of the series Studies on Suspension and Emulsion.     

Simultaneous determination of polysorbate 20 and unbound polyethylene-glycol in protein solutions using new core–shell reversed phase column and condensation nucleation light scattering detection

A novel fast and sensitive method has been developed for the specific simultaneous determination of polysorbate 20 (Tween 20) and unbound polyethylene-glycol (PEG) from liquid formulations in the presence of proteins and excipients. The quantitative determination is based on a fast liquid chromatographic (HPLC) separation and condensation nucleation light scattering detection (CNLSD or NQAD™). The method uses a Kinetex core–shell column (100 mm × 3 mm, 2.6 μm) and methanol–water–trifluoroacetic acid mobile phase. The rapid HPLC-CNLSD method presented here is suitable for quantifying polysorbate 20 in the range of 10–60 μg/ml and unbound PEG in the range of 2–40 μg/ml in protein solutions within good manufacturing practices (GMP) of the pharmaceutical industry.     

Complexation of inorganic anions by β-cyclodextrin studied by polarography and 1H NMR

Abstract

Complexation of o-chloronitrobenzene with β-cyclodextrin has been studied in 0.1 M aqueous solutions containing PF₆ ^?, ClO₄ ^?, C₂O₄ ^2-, SCN^?, SO₄ ^2- and F^? anions by a polarographic method. Using an equation which takes account of the change in the cyclodextrin concentration due to the simultaneous complexation of the anion, both stability constants have been calculated. Interaction of the ClO₄ ^? anion with β-cyclodextrin has been confirmed by ¹H NMR techniques. It has been found that the ClO₄ ^? anion is trapped in the β-cyclodextrin cavity. The stability constant has been calculated. Results of polarographic and ¹H NMR studies have been compared.     

Investigations on structure of regioselectively functionalized celluloses ID solution exemplified by using 3-β-alkyl ethers and light scattering

Regioselectively functionalized 3--alkyl ethers of cellulose (alkyl =-pentyl, isopentyl, dodecyl) can be synthesized using 2,6-di--thexyldimethylsilyl cellulose as a protected intermediate. ID comparison to the corresponding 2,3,6-tri--alkyl ethers, the dissolution behavior and the structure ID solution of the 3--alkyl ethers were investigated using light scattering. The aim of the paper ID to present the first experimental and systematic work on specific properties of regioselectively modified celluloses. The results of structure investigation ID solution are discussed ID detail and lead to a primary understanding of interactions of this type of cellulosics on a molecular and supramolecular level.     

Archaeological pottery from Nasca culture studied by Raman and Mössbauer spectroscopy combined with X-ray diffraction

In the present paper, we report on a study of archaeological fragments from Nasca ceramics using Raman and Mössbauer spectroscopy combined with X-ray diffraction (XRD). By combining results obtained by these methods it is possible to quantitatively determine the paints composition, temperature and environment during the firing. The samples were collected from the Ceremonial Centre of Cahuachi in Southern coast of Peru. Raman spectroscopy allows us to determine the composition of the different pigments used in the preparation of Nasca ceramic. The results show that the composition of the white pigments is formed by rutile and anatase while the black and red pigments are formed by amorphous carbon and hematite, respectively. The Mössbauer spectra were measured at room temperature (RT) and show the presence of components associated with Fe³⁺ indicating an oxidizing environment during the manufacturing process of the ceramic. The analysis is complemented by data obtained by X-ray diffraction suggesting firing temperatures around 950 °C, in agreement with Raman measurements.