A Laccase/Chitosan‐Lambda‐Carrageenan Based Voltammetric Biosensor for Phenolic Compound Detection

In this contribution, a new concept of voltammetric catechol biosensor, based on the encapsulation of laccase (LAC) in a chitosan+lambda‐carrageenan (CHIT+CAR) polyelectrolyte complex (PEC) employing a simple coacervation process is presented. Chitosan (CHIT) was prepared from α‐chitin extracted from shrimp shells and lambda‐carrageenan (CAR) was extracted from red algae, both polysaccharides and PEC being characterized using FTIR spectrometry and electrochemistry. Cyclic voltammetry was utilized to determine the analytical features of the laccase (LAC) biosensor for catechol detection. The linear range was from 10^?20 M to 10^?14 M with a sensitivity of 1.55 mA/p[catechol] and a limit of detection of 3×10^?21 M.The laccase biosensor exhibits good repeatability (RSD 2.38 %) and stability (four weeks). The developed biosensor was tested by applying it to the evaluation of the total polyphenolic content in natural oil samples.     

Optical and crystal-field analysis of Er ion in Y2O3-P2O5 thin films

Luminescence spectra of erbium ions doped in Y₂O₃-P₂O₅ thin films, with different P₂O₅ content (from 3% to 47%), were analysed with crystal-field Hamiltonian model with D_2d symmetry including J-mixing effect. The empirical crystal-field parameters (CFPs) obtained for the best fit of calculated to experimental energy levels allows us to confirm the well-established YPO₄ phase for 47% of P₂O₅. The CFPs are compared to those calculated for Ce³⁺, Nd³⁺ and Dy³⁺ in the YPO₄ host. This work is a continuation of our previous results for erbium-doped Y₂O₃ thin films.     

Phytochemical analysis and in vitro antimicrobial and free-radical-scavenging activities of the essential oils from Euryops arabicus and Laggera decurrens

The essential oils of the aerial part of two Asteraceae species, namely Euryops arabicus Steud. and Laggera decurrens (Vahl.) Hepper and Wood, were studied by GC and GC/MS. In parallel the antimicrobial and antioxidant activities were evaluated. The investigation led to the identification of 48 and 44 compounds for both plants, respectively. The essential oil of E. arabicus was rich in oxygenated sesquiterpenes (39.9%). The oil also contained a high content of sesquiterpene hydrocarbons (24.1%). Compounds such as caryophyllene oxide (8.6%), T-cadinol (7.0%), spathulenol (5.2%), (E)-β-caryophyllene (6.0%) and 2-epi-(E)-β-caryophyllene (6.0%) were the main constituents of the oil. Oxygenated monoterpenes also predominated in L. decurrens (46.3%). The thymoquinone-derivative, 3-methoxy-2-methyl-5-(1-methylethyl)-2,5-cyclohexadiene-1,4-dione (28.1%), thymol (5.7%) and eudesma-11-en-4a-ol (7.0%) were the most abundant constituents. Both essential oils showed antimicrobial activity with MIC-values between 0.13-5.25 mg/mL. Furthermore, only the essential oil of L. decurrens exhibited a strong antioxidant activity (91%) at 500 μg/mL.     

Volumetric Properties of Ethylammonium Nitrate + <Emphasis Type="Italic">γ</Emphasis>-Butyrolactone Binary Systems: Solvation Phenomena from Density and Raman Spectroscopy

The densities of binary mixtures of ethylammonium nitrate (EAN) ionic liquid (IL) and γ-butyrolactone (BL) have been measured over the entire range of concentrations at 293.15, 298.15, 303.15, 308.15, 313.15 and 318.15 K and under ambient pressure. Experimental densities were used to calculate excess molar volumes V_m^EV_{m}^{\mathrm{E}}, isobaric and excess isobaric expansion coefficients α and α ^E. The excess molar volumes have both negative and positive values, while the excess isobaric expansion coefficients are negative over the entire composition range. The V_m^EV_{m}^{\mathrm{E}} values have been fitted to the Redlich-Kister polynomial equation, and other volumetric properties such as the partial molar volumes V _mi , the excess partial molar volume V^E_miV^{\mathrm{E}}_{mi} and the partial molar volumes at infinite dilution V^￥_miV^{\infty}_{mi} were calculated. The results have been interpreted in terms of dipole-dipole interactions, hydrogen bonds formation and structural factors of these mixtures. The FT-Raman spectroscopy study of the intensity variations of some characteristic bands such as the C=O stretching band at 1763 cm⁻¹, C–O symmetric stretching band at 932 cm⁻¹ and C–C stretching band at 872 cm⁻¹ of BL has been undertaken. The solvation phenomenon is evidenced by the modifications of these band intensities due to the presence of the IL ions. Moreover, the Raman spectroscopy corroborates the volumetric study. The average number of BL molecules in the primary solvation shell of the ethylammonium cation lies between 3 and 4 depending on the temperature.     

Cross-coupling reactions of alkenylsilanolates. Investigation of the mechanism and identification of key intermediates through kinetic analysis

The mechanism of the fluoride-free, palladium-catalyzed cross-coupling reaction of potassium (E)-heptenyldimethylsilanolate, K(+)(E)-1(-), with 2-iodothiophene has been investigated through kinetic analysis. The order of each component was determined by plotting the initial rates of the reaction against concentration. These data provided a mechanistic picture which involves a fast and irreversible oxidative insertion of palladium into the aryl iodide and a subsequent intramolecular transmetalation step from a complex containing a silicon-oxygen-palladium linkage. First-order behavior at low concentrations of silanolate with excess palladium(0) complex supports the formation of this complex as the turnover-limiting step. The change to zeroth-order dependence on silanolate at high concentrations is consistent with the intramolecular transmetalation becoming the turnover-limiting step.     

Blends of fatty‐acid‐modified dendrimers with polyolefins

Blends were made by solution and melt‐mixing fatty‐acid‐modified dendrimers with various polyolefins. Small‐angle neutron scattering (SANS) was used to determine the miscibility of the blends. Poly(propylene imine) (PPI) dendrimers G1, G3, and G5 [DAB‐dendr‐(NH₂)_y] with y = 4, 16, and 64, were reacted with stearic acid or stearic acid‐d₃₅ forming amide bonds. The modified dendrimers were then blended with high‐density polyethylene (HDPE), high‐density polyethylene‐d₄ (HDPE‐d₄), low‐density polyethylene (LDPE), amorphous polypropylene (PP), or an ethylene–butylene copolymer (E‐co‐B). Limiting power law behavior shows that all of the blends are immiscible. It is likely that the dendrimers form a second phase, being finely dispersed, but thermodynamically immiscible. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 95–100, 2000     

Water oxidation by a dye-catalyst diad in natural sunlight: timing and coordination of excitations and reactions across timescales of picoseconds to hours

The mechanisms of how dyes and catalysts for solar-driven transformations such as water oxidation to form O₂ work have been intensively investigated, however little is known about how their independent photophysical and chemical processes work together. The level of coordination between the dye and the catalyst in time determines the overall water oxidation system''s efficiency. In this computational stochastic kinetics study, we have examined coordination and timing for a Ru-based dye-catalyst diad, [P2Ru(4-mebpy-4′-bimpy)Ru(tpy)(OH₂)]⁴⁺, where P2 is 4,4′-bisphosphonato-2,2′-bipyridine, 4-mebpy-4′-bimpy is 4-(methylbipyridin-4′-yl)-N-benzimid-N′-pyridine, a bridging ligand, and tpy is (2,2′:6′,2′′-terpyridine), taking advantage of the extensive data available for both dye and catalyst, and direct studies of the diads bound to a semiconductor surface. The simulation results for both ensembles of diads and single diads show that progress through the generally accepted water oxidation catalytic cycle is not controlled by the relatively low flux of solar irradiation or by charge or excitation losses, rather is gated by buildup of intermediates whose chemical reactions are not accelerated by photoexcitations. The stochastics of these thermal reactions govern the level of coordination between the dye and the catalyst. This suggests that catalytic efficiency can be improved in these multiphoton catalytic cycles by providing a means for photostimulation of all intermediates so that the catalytic rate is governed by charge injection under solar illumination alone.

Excitations and reactions in a dye−catalyst dyad for solar-driven water oxidation have timing mismatches caused by the stochastics of some catalytic steps. Rather than being perfectly meshed, these processes are like gears with missing teeth.     

Groups and semigroups generated by a single unitary orbit

Semigroup Forum - We investigate the structure of the multiplicative semigroup generated by the set of matrices that are unitarily equivalent to a given invertible matrix A. In particular, we give...     

Silver cluster-biomolecule hybrids: from basics towards sensors

We focus on the functional role of small silver clusters in model hybrid systems involving peptides in the context of a new generation of nanostructured materials for biosensing. The optical properties of hybrids in the gas phase and at support will be addressed with the aim to bridge fundamental and application aspects. We show that extension and enhancement of absorption of peptides can be achieved by small silver clusters due to the interaction of intense intracluster excitations with the π-π* excitations of chromophoric aminoacids. Moreover, we demonstrate that the binding of a peptide to a supported silver cluster can be detected by the optical fingerprint. This illustrates that supported silver clusters can serve as building blocks for biosensing materials. Moreover, the clusters can be used simultaneously to immobilize biomolecules and to increase the sensitivity of detection, thus replacing the standard use of organic dyes and providing label-free detection. Complementary to that, we show that protected silver clusters containing a cluster core and a shell liganded by thiolates exhibit absorption properties with intense transitions in the visible regime which are also suitable for biosensing applications.