Energy harvesting using multilayer structure based on 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 single crystal

In this paper we fabricated the multilayer structure used as the resonance-based vibration energy-harvesting device based on 0.71Pb(Mg_1/3Nb_2/3)O₃–0.29PbTiO₃ single crystal. The performances of the device including the output voltage and power were studied systematically. Under a cyclic force of 4 N (peak value), a high output power of 4.94 mW and a corresponding peak voltage of 3.14 V were measured at 1.4 kHz with a matching load resistance of 1.0 kΩ. The results demonstrate the potential of the device in energy-harvesting applied to low-power portable electronics and wireless sensors.     

Biomolecular Densely Grafted Brush Polymers: Oligonucleotides,Oligosaccharides and Oligopeptides

In this Minireview, we describe synthetic polymers densely functionalized with sequence-defined biomolecular sidechains. We focus on synthetic brush polymers of oligonucleotides, oligosaccharides, and oligopeptides, prepared via graft-through polymerization from biomolecule functionalized monomers. The resulting structures are brush polymers wherein a biomolecular graft is positioned at each monomer backbone unit. We describe key synthetic milestones, identify synthetic opportunities, and highlight recent advances in the field, including biological applications.     

A new method for making acyl fluorides using BrF3

While many carboxylic acids could be converted directly to acyl fluorides by using BrF₃, the reaction with acyl chlorides was found to be of a more general nature and yields better results. Surprisingly, reacting t-butyl esters with bromine trifluoride also resulted in acyl fluorides in reasonable yields. The reactions were completed in a few seconds at 0 °C.     

From carboxylic acids to the trifluoromethyl group using BrF3

Organic trifluoromethyl derivatives were made from aromatic and aliphatic carboxylic acids by transforming them first into the corresponding dithioesters followed by reaction with bromine trifluoride under mild conditions (0 °C, 2 min).     

Effect of fiber modification with carboxymethyl cellulose on the efficiency of a microparticle flocculation system

Carboxymethyl cellulose (CMC) has been used widely to enhance dry strength of paper and uniformity of sheet in the papermaking industry. Besides these positive effects, it may affect the fines retention and dewatering processes negatively. These negative effects are mainly seen when fiber modifications with high CMC dosages are studied in laboratory scale. In this paper, the effect of fiber modification with CMC on the deposition of precipitated calcium carbonate (PCC) and on the dewatering process in the presence of cationic polyacrylamide (CPAM)/bentonite microparticle flocculation system is examined. It was determined that fiber modification with 10 mg g⁻¹ of CMC decreased PCC deposition at the initial addition of CPAM and gave better PCC deposition at 2 mg g⁻¹ of CPAM. It was also observed that PCC deposition on unmodified fibers is higher at lower CPAM concentration. PCC deposition was found as almost stable after a maximum value obtained at 0.5 mg g⁻¹ of bentonite concentration for fiber modified with 40 mg g⁻¹ of CMC. This indicates that interaction between CPAM and bentonite particles changed due to higher surface charge and CMC conformation on fibers. Results of the dewatering experiments showed that CMC modification increased the drainage time due to a denser and more plugged sheet. This negative effect was compensated with higher concentrations of CPAM and bentonite. On the other hand, dewatering is also affected by the mass ratio of CMC and CPAM, which was not the optimum one in this study at lower of CPAM. Thus, the increase in the drainage time in the presence of CMC on the fiber surface could be also caused by incorrect ratios of chemicals because the effect of CMC on the drainage time was not observed at higher concentrations of CPAM.     

The structure of ions and zwitterionic lipids regulates the charge of dipolar membranes

In pure water, zwitterionic lipids form lamellar phases with an equilibrium water gap on the order of 2 to 3 nm as a result of the dominating van der Waals attraction between dipolar bilayers. Monovalent ions can swell those neutral lamellae by a small amount. Divalent ions can adsorb onto dipolar membranes and charge them. Using solution X-ray scattering, we studied how the structure of ions and zwitterionic lipids regulates the charge of dipolar membranes. We found that unlike monovalent ions that weakly interact with all of the examined dipolar membranes, divalent and trivalent ions adsorb onto membranes containing lipids with saturated tails, with an association constant on the order of ～10 M(-1). One double bond in the lipid tail is sufficient to prevent divalent ion adsorption. We suggest that this behavior is due to the relatively loose packing of lipids with unsaturated tails that increases the area per lipid headgroup, enabling their free rotation. Divalent ion adsorption links two lipids and limits their free rotation. The ion-dipole interaction gained by the adsorption of the ions onto unsaturated membranes is insufficient to compensate for the loss of headgroup free-rotational entropy. The ion-dipole interaction is stronger for cations with a higher valence. Nevertheless, polyamines behave as monovalent ions near dipolar interfaces in the sense that they interact weakly with the membrane surface, whereas in the bulk their behavior is similar to that of multivalent cations. Advanced data analysis and comparison with theory provide insight into the structure and interactions between ion-induced regulated charged interfaces. This study models biologically relevant interactions between cell membranes and various ions and the manner in which the lipid structure governs those interactions. The ability to monitor these interactions creates a tool for probing systems that are more complex and forms the basis for controlling the interactions between dipolar membranes and charged proteins or biopolymers for encapsulation and delivery applications.     

Mixed chromium(III) complexes with pyridinedicarboxylato and oxalato ligands: kinetic studies in HClO<Subscript>4</Subscript> solutions

Three chromium(III) complexes of general formula [Cr(ox)₂(pdaH)]²⁻ (where ox = C₂O₄ ²⁻ and pdaH⁻ is N,O-bonded 2,3-, 2,4- or 2,5-pyridinedicarboxylic acid anion) were obtained and characterized in solution. Acid-catalysed aquation of [Cr(ox)₂(pdaH)]²⁻ gave two products: [Cr(ox)(pdaH)(H₂O)₂]⁰ (P₁) and cis-[Cr(ox)₂(H₂O)₂]²⁻ (P₂). The kinetics of these reactions were studied spectrophotometrically, within the 0.1–1.0 M HClO₄ range, and the pseudo-first-order rate constants for the oxalato (k _obs1) and pdaH⁻ (k _obs2) ligands dissociation were calculated based on the determined pseudo-first-order rate constants (k _obs) and P₁:P₂ molar ratio. The dependencies of the pseudo-first-order rate constants on [H⁺] are as follows: k _obs1 = b ₁[H⁺] and k _obs2 = b ₂[H⁺], where b ₁ and b ₂ are the second-order rate constants for the oxalato and pdaH⁻ ligands dissociation, respectively. Kinetic parameters were determined and the mechanism of the pdaH⁻ ligand dissociation is proposed.     

Covalently Linked Bis(Amido-Corroles): Inter- and Intramolecular Hydrogen-Bond-Driven Supramolecular Assembly

Four bis-corroles linked by diamide bridges were synthesized through peptide-type coupling of a trans-A₂B-corrole acid with aliphatic and aromatic diamines. In the solid state, the hydrogen-bond pattern in these bis-corroles is strongly affected by the type of solvent used in the crystallization process. Although intramolecular hydrogen bonds play a decisive role, they are supported by intermolecular hydrogen bonds and weak N−H⋅⋅⋅π interactions between molecules of toluene and the corrole cores. In an analogy to mono(amido-corroles), both in crystalline state and in solutions, the aliphatic or aromatic bridge is located directly above the corrole ring. When either ethylenediamine or 2,3-diaminonaphthalene are used as linkers, incorporation of polar solvents into the crystalline lattice causes a roughly parallel orientation of the corrole rings. At the same time, both NHCO⋅⋅⋅NH corrole hydrogen bonds are intramolecular. In contrast, solvation in toluene causes a distortion with one of the hydrogen bonds being intermolecular. Interestingly, intramolecular hydrogen bonds are always formed between the –NHCO– functionality located further from the benzene ring present at the position 10-meso. In solution, the hydrogen-bonds pattern of the bis(amido-corroles) is strongly affected by the type of the solvent. Compared with toluene (strongly high-field shifted signals), DMSO and pyridine disrupt self-assembly, whereas hexafluoroisopropanol strengthens intramolecular hydrogen bonds.     

Synthesis of new 14-membered macrolide antibiotics via a novel ring contraction metathesis

[reaction: see text] A novel ring opening ring closing metathesis (ROM-RCM) was demonstrated for cyclic conjugated dienes, effecting the excision of a C(2)H(2) unit and a net ring contraction. Applying the ring contraction metathesis, new 14-membered ring macrolide antibiotics were synthesized in a single step from existing 16-membered ring macrolides. This new class of macrolide antibiotics will provide access to new therapeutics for the treatment of macrolide-resistant bacterial infections.     

A general route for the synthesis of β,β-difluorocarboxylic acids

A new method for the preparation of β,β-difluoro- (and other gem-difluoro) acids has been developed. It is based on the fact that 3-oxocarboxylic esters are easy to make and convert to the corresponding dithiane derivatives. These dithianes reacted with BrF₃, a commercial, but rarely used reagent in organic chemistry, under very mild conditions to form the corresponding difluoroesters, which in turn could be quantitatively hydrolyzed to the free gem-difluoroacids.