Physicochemical characterization of variously packed porous plugs of hydroxyapatite: streaming potential coupled with conductivity measurements

A homemade instrument was used for the measurement of the streaming potential, conductivity, and permeability of plugs packed in different densities with hydroxyapatite (HAP) particles at 25 degrees C and pH = 7.0 +/- 0.2. KCl solutions with ionic strength values in the range of 0.3-300 mM, equilibrated with HAP for 3 days, were forced to flow through the plugs. It was found that the particle volume fraction of the plug obtained from conductivity measurements was slightly higher than that obtained by weighing the solid. This suggested that, in addition to the volume of the solid itself, the volume of liquid trapped in the cavities of the particles does not contribute to the conductivity of the plug. The pH change recorded in the solution passed through the plug was attributed to the protonation/deprotonation of the HAP surface groups. Denser packing of the HAP crystallites resulted to higher surface conductivities. It was suggested that this trend was due to the easier interparticle ion transport in close-packed plugs. Considering zeta-potential, the values computed by neglecting surface conductivity were significantly underestimated, especially at low ionic strength values and at dense packing. More realistic values for the HAP zeta-potential were obtained taking into account the surface conductivity. These values were practically independent of the material packing during the plug preparation. Finally, the total surface conductivity was found to be limited behind the slipping plane of the electric double layer developed at the interface of HAP in contact with electrolyte solution.     

Modulating surface rheology by electrostatic protein/polysaccharide interactions

There is a large interest in mixed protein/polysaccharide layers at air-water and oil-water interfaces because of their ability to stabilize foams and emulsions. Mixed protein/polysaccharide adsorbed layers at air-water interfaces can be prepared either by adsorption of soluble protein/polysaccharide complexes or by sequential adsorption of complexes or polysaccharides to a previously formed protein layer. Even though the final protein and polysaccharide bulk concentrations are the same, the behavior of the adsorbed layers can be very different, depending on the method of preparation. The surface shear modulus of a sequentially formed beta-lactoglobulin/pectin layer can be up to a factor of 6 higher than that of a layer made by simultaneous adsorption. Furthermore, the surface dilatational modulus and surface shear modulus strongly (up to factors of 2 and 7, respectively) depend on the bulk -lactoglobulin/pectin mixing ratio. On the basis of the surface rheological behavior, a mechanistic understanding of how the structure of the adsorbed layers depends on the protein/polysaccharide interaction in bulk solution, mixing ratio, ionic strength, and order of adsorption to the interface (simultaneous or sequential) is derived. Insight into the effect of protein/polysaccharide interactions on the properties of adsorbed layers provides a solid basis to modulate surface rheological behavior.     

NMR Spectral Assignment of Per-substituted Key-Intermediates of β-Cyclodextrin and Implications in the Structures of the Derivatives

The compounds, 6-per-O-(t-butyldimethylsilyl)--cyclodextrin(1), 2,3-per-O-benzyl-6-per-O-(t-butyldimethylsilyl)--cyclodextrin(2), 2,3-per-O-benzyl--cyclodextrin (3),2,3,6-per-O-benzyl--cyclodextrin (4),2,3,6-per-O-benzoyl--cyclodextrin (5), are used as keyintermediates in the synthesis of selectively substituted -CD derivatives. Simple and assignable ¹H and ¹³C NMR spectra (chemical shifts and coupling constants) were obtained for compounds1–4 indicating C₇ symmetry, ⁴C₁ glucose conformation and major arrangement of H6, H6' atoms at the primary side. The derivative 5, however, gave very broad peaksat room temperature. The peaks could partially be assigned at 270 K, but the broadening was still present at 220 K. This implies that there exist several conformers of similar energyand C₁ symmetry that continuously interchange, since there is not a single type of stabilizing interaction thatpredominates. We attributed this phenomenon to the presence of the carbonyl group, which probablydisfavors - stacking and induces random arrangements of the aromatic rings.     

Physically insightful modeling of non-Fickian kinetic regimes encountered in fundamental studies of isothermal sorption of swelling agents in polymeric media

The kinetics of sorption of micromolecular swelling agents by polymeric media often deviates from normal Fickian behavior in various ways, which have to be understood and interpreted, with the aid of appropriate models, in terms of the underlying physics. One difficulty which arises in this respect is that salient aspects of the observed kinetic behavior can be mimicked by extraneous effects, in the form of significant deviation from a boundary condition or of imperfect macroscopic homogeneity of the polymer film (modeled in both cases as a surface resistance to penetrant transport). Such effects have, in fact, been invoked (notably by Hansen (2010) [11]) to question the significance of conclusions drawn from modeling approaches based on the effect of intrinsic bulk polymer properties, leading to delayed (viscous) swelling and to build-up and decay of differential swelling stresses. We present here a brief critical account (following the mainstream modeling line initiated by Crank) of typical results concerning various salient aspects of observed non-Fickian sorption kinetics and of the comparative possibility of achieving satisfactory general interpretation thereof, in terms of approaches based on the aforementioned extraneous, versus intrinsic bulk property, effects. We find that the latter approach has been successful so far, both computationally and physically, by establishing a close physically significant analogy between non-Fickian sorption, and (both linear and non-linear) viscoelastic mechanical deformation, behavior. The former approach, on the other hand, proves weak on both counts.     

Oligo(ethylene imine)-grafted glycidyl methacrylate linear and star homopolymers: Odd–even correlated transfection efficiency

The present study aims to investigate an odd–even effect of the number of ethylene imine units in the side-groups of totally abiotic synthetic polymers on their efficiency in DNA transfection. A library of fifteen polymers was fabricated. Two star homopolymers and one linear homopolymer based on glycidyl methacrylate were synthesized and used as precursors to which five linear oligo(ethylene imine)s (OEI) were grafted. The number of ethylene imine groups of the OEIs was varied. Specifically, ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, and pentaethylene hexamine were used. Each of these fifteen OEI-grafted polymers was evaluated in terms of their efficiency to transfer plasmid DNA encoding firefly luciferase in C2C12 mouse myoblast cells. The transfection efficiency displayed an odd-even pattern, with all OEI-grafted polymers with an odd number of ethylene imine repeating units exhibiting higher transfection efficiency compared with those possessing an even number of ethylene imine repeating units. The odd–even effect was more pronounced for the star polymers with longer arms (degree of polymerization, DP = 100), while in case of the linear polymers, the odd–even effect was only observed for the lowest polymer loading. The cytotoxicity of the OEI-grafted polymers also followed an odd–even pattern, with the OEI-grafted star polymers with an arm DP of 100 and the linear polymers clearly presenting an odd-even effect, while the cytotoxicity of the OEI-grafted star polymers with an arm DP of 20 slightly increased with the number of ethylene imine repeating units.     

Crystal Engineering of Two Light and Pressure Responsive Physisorbents

An emerging strategy in the design of efficient gas storage technologies is the development of stimuli-responsive physisorbents which undergo transformations in response to a particular stimulus, such as pressure, heat or light. Herein, we report two isostructural light modulated adsorbents (LMAs) containing bis-3-thienylcyclopentene (BTCP), LMA-1 [Cd(BTCP)(DPT)₂] (DPT=2,5-diphenylbenzene-1,4-dicarboxylate) and LMA-2 [Cd(BTCP)(FDPT)₂] (FDPT=5-fluoro-2,diphenylbenzene-1,4-dicarboxylate). Both LMAs undergo pressure induced switching transformations from non-porous to porous via adsorption of N₂, CO₂ and C₂H₂. LMA-1 exhibited multi-step adsorption while LMA-2 showed a single-step adsorption isotherm. The light responsive nature of the BTPC ligand in both frameworks was exploited with irradiation of LMA-1 resulting in a 55 % maximum reduction of CO₂ uptake at 298 K. This study reports the first example of a switching sorbent (closed to open) that can be further modulated by light.     

Sub-10-fs supercontinuum radiation generated by filamentation of few-cycle 800 nm pulses in argon

Focusing 12 fs pulses of 800 nm with moderate energy (0.35 mJ) into atmospheric-pressure argon (Ar) gives rise to filamentation (self-focusing) and a supercontinuum with a very broad pedestal, extending to 250 nm. According to the present understanding, the short wavelengths are produced by self-phase modulation in the self-steepened trailing edge of the pulse. Pulses in this spectral range might thus be intrinsically short. Indeed we demonstrate this by extracting the light near the end of the filament, terminating self-focusing by a pressure gradient at a pinhole, beyond which the Ar is pumped away. We obtain pulses of 9.7 fs in the region of 290 nm without the necessity of compression.     

Identification of N,N-dimethyltryptamine and beta-carbolines in psychotropic ayahuasca beverage

Recently many people have shown great interest in traditional indigenous practices and popular medicine, involving the ingestion of natural psychotropic drugs. We received a request to analyze and determine the nature of a dark green liquid with a dark brown plant sediment, which the police had seized at an airport and inside the home of a person belonging to the 'Santo Daime' religious movement. Gas chromatography/mass spectrometry analysis of the extract identified N,N-dimethyltryptamine, a potent hallucinogen, and the beta-carboline alkaloids harmine and harmaline, revealing monoamine oxidase A-inhibiting properties. These substances are typical components of Ayahuasca, a South American psychotropic beverage obtained by boiling the bark of the liana Banisteriopsis caapi together with the leaves of various admixture plants, principally Psychotria viridis.     

Cationic star polymer siRNA transfectants interconnected with a piperazine-based cationic cross-linker

Cationic star polymers of 2-(dimethylamino)ethyl methacrylate (DMAEMA) were prepared via the “arm-first” method under group transfer polymerization (GTP) conditions, and were interconnected using a novel, hydrophilic, positively ionizable dimethacrylate cross-linker which is essentially the cyclic dimer of DMAEMA, thus ensuring that the building units of the arms and the core of the star polymers were identical. After their physicochemical characterization, these star-like polyamines were evaluated for their ability to transfer small interfering RNA (siRNA) to murine myoblast cells. Suppression efficiency was found to increase with polymer loading and star branch size, attaining sufficiently high values, comparable to that observed with standard non-viral siRNA transfection systems, while cytotoxicity was kept reasonably low.