Effect of monomer hydrophilicity on ARGET–ATRP kinetics in aqueous mini-emulsion polymerization

Activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP)-based aqueous miniemulsion polymerization where the polymerization takes place in the stabilized monomer droplets is described. In this work, we compared styrene, n-butyl methacrylate (nBMA) and tert-butyl methacrylate (tBMA) and investigated the influence of their hydrophobicity on dispersity, molecular weight and particle stability based their partition coefficients (logP) (2.67, 2.23, and 1.86, respectively). Tetrabutylammonium bromide (TBAB) was used as a phase transfer agent for the controlled delivery of Cu²⁺-Br/tris(2-pyridylmethyl)amine (TPMA), a hydrophilic catalyst, into monomer droplets of varying hydrophobicity. The resulting dispersity and particle stability of each polymer is a function of its logP value, with the most hydrophobic monomer (styrene) displaying the narrowest dispersity and most control (Đ < 1.3), and the most hydrophilic polymer poly(tert-butyl methacrylate) (PtBMA) having reduced emulsion stability, determined by the observation of aggregate formation. Selected polymerization parameters, including effects of total ascorbic acid feed concentration and the monomer concentration and their effects on dispersity are reported. The controlled polymerizations of hydrophilic monomers using ARGET-ATRP in miniemulsion conditions and understanding the effect of monomer hydrophilicity on the emulsion stability will broaden the use of ARGET-ATRP in emulsion polymerization for the synthesis of polymer-grafted nanoparticles with hydrophilic corona.     

Study of solid-state polymerization by positron lifetime measurements

The positron lifetime measurement technique was applied to analyze the structural changes occurring in solid-state polymerization of acrylamide and trioxane. Positronium (Ps) parameters, τ₂ and I₂, which show a marked change as a function of the γ-ray irradiation dose, signaled the presence of three clearly defined stages in the polymerization process: initiation, propagation, and saturation. The initial increase in τ₂, may very well be the result of efficient trapping of Ps in vacancies created around the polymer nuclei. The complicated behavior of I₂ may be explained as a chemical reaction between Ps precursors and the radiolysis products of this polymerization process.     

Enzymatic Hydrolysis of Agavins to Generate Branched Fructooligosaccharides (a-FOS<Emphasis Type="Bold">)</Emphasis>

Recently, agavins (branched neo-fructans) of short degree of polymerization have shown beneficial effects on the health of both healthy and overweight individuals. Therefore, the aim of the present work was to investigate the potential use of Agave angustifolia agavins on the generation of branched fructooligosacharides (a-FOS). A. angustifolia agavins were hydrolyzed using exo-, endo-inulinase, and a mixture of both (25 and 75%, respectively). Exo- and the inulinase mixture degraded quickly the agavins in relation to endo-inulinase treatment. Only endo-inulinase and the inulinase mixture generated a-FOS formation. Endo-inulinase degraded 31% of agavins, yielding approximately 20% of a-FOS after 48 h, whereas the inulinase mixture hydrolyzed 33% of agavins in just 90 min, but only yielded 10% of a-FOS. These results suggest that agave plants could be an abundant raw material for a-FOS production, which might have a huge prebiotic potential as new branched fructooligosaccharides with many applications in the alimentary and pharmaceutical industry.     

Nonspecific interaction forces at water-membrane interface by forced molecular dynamics simulations

Nonspecific interactions are the main driving forces for the behavior of molecules with great affinity for biologic membranes. To investigate not only the molecular details of these interactions but to estimate their magnitude as well, the theoretical method of Forced Molecular Dynamics Simulations, based on the Atomic Force Spectroscopy experimental technique, was applied. In this approach, an additional one-dimensional elastic force, representing the cantilever probe, was incorporated to the force field of a Molecular Dynamics computational program. This force represents a spring fixed on one end to a selected atom of the molecule; the other end of the spring is displaced at constant velocity to pull the molecule out of the membrane. The force experimented by the molecule due to the spring, is proportional to the spring elongation relative to its equilibrium position. This value is registered during the entire simulation, and its maximum value will determine the molecule-membrane interaction force. Nonexplicit medium simulations were carried out. Polar and apolar media were considered according to their polarizability degree and a specific dielectric constant value was assigned. In this approach, the membrane was considered as the apolar region limited by two flat surfaces with a polar aqueous medium. The potential energy discontinuity at the interfaces was smoothed by considering the polarization-induced effects using the image method. The results of this methodology are presented using a small system, a single Alanine amino acid model, which enables extended simulations in a microsecond time scale. The confinement of this amino acid at the interface reduces its degrees of freedom and forces it to adopt one of the six defined conformations. A correlation between these stable structures at the water-membrane interface and the interaction force value was determined.     

Hydroxypropyl-β-cyclodextrin effect on the fluorescence of auxin and skatole and on the simultaneous determination of binary mixtures of indole compounds in urine by first derivative spectrofluorimetry

The effect of hydroxypropyl-β-cyclodextrin (HPβCD, β-cyclodextrin (βCD) derivative) was determined on the fluorescence emission spectra of skatole (3-methylindole, MI) and auxin (indole 3-acetic acid, IA). The experiments were conducted at excitation wavelength (λ_ex) = 280 nm, in aqueous solutions at different pH values, with and without HPβCD as receptor. The enhanced fluorescence in the presence of the receptor showed a 1:1 host–guest interaction and the values of the association constants K_A were between 100 and 200 mol⁻¹ L. The effects of methanol and propanol with and without receptor were also studied. The limit of detection (L_D) for the HPβCD enhanced fluorimetric method at pH = 7.00 were 0.279 and 0.765 ng mL⁻¹ for MI and IA, respectively. For the determination of indole compounds with closely overlapping spectral bands a zero-crossing first derivative spectrofluorimetric method with or without HPβCD is described. Binary mixtures of MI or IA with melatonin (N-acetyl-5-methoxytryptamine, M) or 5-methoxytryptamine (5-methoxy-3-(2-aminoethyl)indole, 5M) were analysed in the presence of HPβCD. In the absence of receptor, binary mixtures of MI with IA and M with 5M were determined. The matrix effect was evaluated in urine samples by the method of standard addition. Good apparent recoveries were found for each indolic compound by the direct method (98–105% with R.S.D. 0.5–5%) and for mixtures of them by the first derivative method (90–105% with R.S.D. 1–5%) indicating the applicability of them with the advantage of their simplicity, low cost in materials, no time consuming and no requirement of the use of a sophisticate calibration program.     

Proton control of oxidation and spin state in a series of iron tripodal imidazole complexes

Reaction of iron salts with three tripodal imidazole ligands, H(3)(1), H(3)(2), H(3)(3), formed from the condensation of tris(2-aminoethyl)amine (tren) with 3 equiv of an imidazole carboxaldehyde yielded eight new cationic iron(III) and iron(II), [FeH(3)L](3+or2+), and neutral iron(III), FeL, complexes. All complexes were characterized by EA(CHN), IR, UV, M?ssbauer, mass spectral techniques and cyclic voltammetry. Structures of three of the complexes, Fe(2).3H(2)O (C(18)H(27)FeN(10)O(3), a = b = c = 20.2707(5), cubic, I3d, Z = 16), Fe(3).4.5H(2)O (C(18)H(30)FeN(10)O(4.5), a = 20.9986(10), b = 11.7098(5), c = 19.9405(9), beta = 109.141(1), monoclinic, P2(1)/c), Z = 8), and [FeH(3)(3)](ClO(4))(2).H(2)O (C(18)H(26)Cl(2)FeN(10)O(9), a = 9.4848(4), b = 23.2354(9), c = 12.2048(5), beta = 111.147(1) degrees, monoclinic, P2(1)/n, Z = 4) were determined at 100 K. The structures are similar to one another and feature an octahedral iron with facial coordination of imidazoles and imine nitrogen atoms. The iron(III) complexes of the deprotonated ligands, Fe(1), Fe(2), and Fe(3), are low-spin while the protonated iron(III) cationic complexes, [FeH(3)(1)](ClO(4))(3) and [FeH(3)(2)](ClO(4))(3), are high-spin and spin-crossover, respectively. The iron(II) cationic complexes, [FeH(3)(1)]S(4)O(6), [FeH(3)(2)](ClO(4))(2), [FeH(3)(3)](ClO(4))(2), and [FeH(3)(3)][B(C(6)H(5))(4)](2) exhibit spin-crossover behavior. Cyclic voltammetric measurements on the series of complexes show that complete deprotonation of the ligands produces a negative shift in the Fe(III)/Fe(II) reduction potential of 981 mV on average. Deprotonation in air of either cationic iron(II) or iron(III) complexes, [FeH(3)L](3+or2+), yields the neutral iron(III) complex, FeL. The process is reversible for Fe(3), where protonation of Fe(3) yields [FeH(3)(3)](2+).     

Regiochemistry of the photostimulated reaction of the phthalimide anion with 1-iodoadamantane and tert-butylmercury chloride by the S(RN)1 mechanism

The photostimulated reaction of the phthalimide anion (1) with 1-iodoadamantane (2) gave 3-(1-adamantyl) phthalimide (3) (12%) and 4-(1-adamantyl) phthalimide (4) (45%), together with the reduction product adamantane (AdH) (21%). The lack of reaction in the dark and inhibition of the photoinduced reaction by p-dinitrobenzene, 1,4-cyclohexadiene, and di-tert-butylnitroxide indicated that 1 reacts with 2 by an S(RN)1 mechanism. Formation of products 3 and 4 occurs with distonic radical anions as intermediates. The photoinduced reaction of anion 1 with tert-butylmercury chloride (10) affords 4-tert-butylphthalimide (11) as a unique product. By competition experiments toward 1, 1-iodoadamantane was found to be ca. 10 times more reactive than tert-butylmercury chloride.     

Supramolecular control over donor-acceptor photoinduced charge separation

A novel donor-bridge-acceptor system has been synthesized by covalently linking a p-phenylene vinylene oligomer (OPV) and a perylene diimid (PERY) at opposite ends of a m-phenylene ethynylene oligomer (FOLD) of twelve phenyl rings, containing nonpolar (S)-3,7-dimethyl-1-octanoxy side chains. For comparison, model compounds have been prepared in which either the donor or acceptor is absent. In chloroform, the oligomeric bridge is in a random coil conformation. Upon addition of an apolar solvent (heptane) the oligomeric bridge first folds into a helical stack and subsequently intermolecular self-assembly of the stacks into columnar architectures occurs. Photoexcitation in the random coil conformation, where the interaction between the donor and acceptor chromophores is small, results only in long-range intramolecular energy transfer in which the OPV singlet-excited state is transformed into the PERY singlet-excited state. In the folded conformation of the bridge, donor and acceptor are closer and their enhanced interaction favors the formation the OPV(*)(+)-FOLD-PERY(*)(-) charge-separated state upon photoexcitation. As a result, the extent of photoinduced charge separation depends on the degree of folding of the bridge between donor and acceptor and therefore on the apolar nature of the medium. As a consequence, and contrary to conventional photoinduced charge separation processes, the formation of the OPV(*)(+)-FOLD-PERY(*)(-) charge-separated state is more favored in apolar media.     

Building blocks for the molecular expression of quantum cellular automata. Isolation and characterization of a covalently bonded square array of two ferrocenium and two ferrocene complexes

The suitability of [{(eta5-C5H5)Fe(eta5-C5H4)}4(eta4-C4)Co(eta5-C5H5)][PF6]2, [1][PF6]2, for use as a molecular quantum cellular automata (QCA) cell is demonstrated. To this end the structure of 1 in the solid state and the conversion of 1 to mono- and dicationic mixed-valence complexes have been accomplished. The latter compounds have been isolated as pure materials and characterized by IR, EPR, and M?ssbauer spectroscopies and single-crystal XRD (monocation only) and magnetic susceptibility measurements. Near-IR spectra demonstrate the mixed valence character of the cations (valence trapped on the IR, EPR and M?ssbauer time scales), and the energies of the intervalence charge-transfer bands provide a measure of the hole hopping frequency.