A validated quantification of triclosan in toothpaste using high-performance thin-layer chromatography and a 48-bit flatbed scanner

We present a densitometric quantification method for triclosan in toothpaste, separated by high-performance thin-layer chromatography (HPTLC) and using a 48-bit flatbed scanner as the detection system. The sample was band-wise applied to HPTLC plates (10 × 20 cm), with fluorescent dye, Merck, Germany (1.05554). The plates were developed in a vertical developing chamber with 20 min of chamber saturation over 70 mm, using n-heptane–methyl tert-butyl ether–acetic acid (92:8:0.1, V/V) as solvent. The R_F value of triclosan is hR_F = 22.4, and quantification is based on direct measurements using an inexpensive 48-bit flatbed scanner for color measurements (in red, green, and blue) after plate staining with 2,6-dichloroquinone-4-chloroimide (Gibbs' reagent). Evaluation of the red channel makes the measurements of triclosan very specific. For linearization, an extended Kubelka–Munk expression was used for data transformation. The range of linearity covers more than two orders of magnitude and is between 91 and 1000 ng. The separation method is inexpensive, fast and reliable.

     

General Synthesis of Secondary Alkylamines by Reductive Alkylation of Nitriles by Aldehydes and Ketones

The development of C−N bond formation reactions is highly desirable due to their importance in biology and chemistry. Recent progress in 3d metal catalysis is indicative of unique selectivity patterns that may permit solving challenges of chemical synthesis. We report here on a catalytic C−N bond formation reaction—the reductive alkylation of nitriles. Aldehydes or ketones and nitriles, all abundantly available and low-cost starting materials, undergo a reductive coupling to form secondary alkylamines and inexpensive hydrogen is used as the reducing agent. The reaction has a very broad scope and many functional groups, including hydrogenation-sensitive examples, are tolerated. We developed a novel cobalt catalyst, which is nanostructured, reusable, and easy to handle. The key seems the earth-abundant metal in combination with a porous support material, N-doped SiC, synthesized from acrylonitrile and a commercially available polycarbosilane.     

Catalytic Borylation of SCF3‐Functionalized Arenes by Rhodium(I) Boryl Complexes: Regioselective CH Activation at the ortho‐Position

An unprecedented reaction pathway for the borylation of SCF₃‐containing arenes using [Rh(Bpin)(PEt₃)₃] (pin=pinacolato) is reported. Catalytic processes were developed and the functionalizations proceed under mild reaction conditions. The C? H activations occur with a unique regioselectivity for the position ortho to the SCF₃ group, which apparently serves as directing group. Borylated SCF₃ compounds can serve as versatile building blocks.     

Adaptive Amphiphilic Dendrimer‐Based Nanoassemblies as Robust and Versatile siRNA Delivery Systems

siRNA delivery remains a major challenge in RNAi‐based therapy. Here, we report for the first time that an amphiphilic dendrimer is able to self‐assemble into adaptive supramolecular assemblies upon interaction with siRNA, and effectively delivers siRNAs to various cell lines, including human primary and stem cells, thereby outperforming the currently available nonviral vectors. In addition, this amphiphilic dendrimer is able to harness the advantageous features of both polymer and lipid vectors and hence promotes effective siRNA delivery. Our study demonstrates for the first time that dendrimer‐based adaptive supramolecular assemblies represent novel and versatile means for functional siRNA delivery, heralding a new age of dendrimer‐based self‐assembled drug delivery in biomedical applications.     

Chemistry of pyrrolizidine alkaloids revisited—semi-synthetic microwave and continuous-flow approaches toward Crotalaria-alkaloids

Efficient and rapid syntheses of various pyrrolizidine alkaloids via microwave synthetic protocols using monocrotaline from a natural source (Crotalaria spectabilis) are reported. Retronecine, hydroxydanaidal, and acetylated hydroxydanaidal (utilized in the chemical communication system of various insect species) were obtained. In addition, a continuous flow hydrogenolysis/hydrogenation approach to directly access platynecine, retronecanol, and desoxyretronecine was realized.     

Comparison of two different multidimensional liquid–gas chromatography interfaces for determination of mineral oil saturated hydrocarbons in foodstuffs

This investigation focused on direct comparison of two popular multidimensional liquid–gas chromatography (LC–GC) systems, the Y-interface (retention gap approach) and the syringe-based interface (programmed temperature vaporizer approach). Such transfer devices are structurally very different, and could potentially have a substantial effect on the outcome of a specific application. In this work the application was a topic of much current interest, determination of mineral oil saturated hydrocarbon (MOSH) contamination of a series of food products (rice, pasta, icing sugar, olive oil); the final results were then compared. The two LC–GC methods developed were validated for linearity over the calibration range, analyte discrimination, precision, accuracy, and limits of detection and quantification. No significant differences were found between the two approaches.

On–off switch of charge-separated states of pyridine-vinylene-linked porphyrin–C60 conjugates detected by EPR

The design, synthesis, and electronic properties of a new series of D–π–A conjugates consisting of free base (H₂P) and zinc porphyrins (ZnP) as electron donors and a fullerene (C₆₀) as electron acceptor, in which the two electroactive entities are covalently linked through pyridine-vinylene spacers of different lengths, are described. Electronic interactions in the ground state were characterized by electrochemical and absorption measurements, which were further supported with theoretical calculations. Most importantly, charge-transfer bands were observed in the absorption spectra, indicating a strong push–pull behavior. In the excited states, electronic interactions were detected by selective photoexcitation under steady-state conditions, by time-resolved fluorescence investigations, and by pump probe experiments on the femto-, pico-, and nanosecond time scales. Porphyrin fluorescence is quenched for the different D–π–A conjugates, from which we conclude that the deactivation mechanisms of the excited singlet states are based on photoinduced energy- and/or electron transfer processes between H₂P/ZnP and C₆₀, mediated through the molecular spacers. The fluorescence intensity decreases and the fluorescence lifetimes shorten as the spacer length decreases and as the spacer substitution changes. With the help of transient absorption spectroscopy, the formation of charge-separated states involving oxidized H₂P/ZnP and reduced C₆₀ was confirmed. Lifetimes of the corresponding charge-separated states, which ranged from ∼400 picoseconds to 165 nanoseconds, depend on the spacer length, the spacer substitution, and the solvent polarity. Interestingly, D–π–A conjugates containing the longest linkers did not necessarily exhibit the longest charge-separated state lifetimes. The distances between the electron donors and the acceptors were calculated by molecular modelling. The longest charge-separated state lifetime corresponded to the D–π–A conjugate with the longest electron donor–acceptor distance. Likewise, EPR measurements in frozen media revealed charge separated states in all the D–π–A conjugates investigated. A sharp peak with g values ∼2.000 was assigned to reduced C₆₀, while a broader, less intense signal (g ∼ 2.003) was assigned to oxidized H₂P/ZnP. On–off switching of the formation and decay of the charge-separated states was detected by EPR at 77 K by repeatedly turning the irradiation source on and off.     

DNA‐Based Oligochromophores as Light‐Harvesting Systems

The chromophores ethynyl pyrene as blue, ethynyl perylene as green and ethynyl Nile red as red emitter were conjugated to the 5‐position of 2′‐deoxyuridine via an acetylene bridge. Using phosphoramidite chemistry on solid phase labelled DNA duplexes were prepared that bear single chromophore modifications, and binary and ternary combinations of these chromophore modifications. The steady‐state and time‐resolved fluorescence spectra of all three chromophores were studied in these modified DNA duplexes. An energy‐transfer cascade occurs from ethynyl pyrene over ethynyl perylene to ethynyl Nile red and subsequently an electron‐transfer cascade in the opposite direction (from ethynyl Nile red to ethynyl perylene or ethynyl pyrene, but not from ethynyl perylene to ethynyl pyrene). The electron‐transfer processes finally provide charge separation. The efficiencies by these energy and electron‐transfer processes can be tuned by the distances between the chromophores and the sequences. Most importantly, excitation at any wavelength between 350 and 700 nm finally leads to charge separated states which make these DNA samples promising candidates for light‐harvesting systems.     

Square‐Wave Voltammetry as Analytical Tool for Real‐Time Study of Controlled Naproxen Releasing from Cellulose Derivative Materials

This work reports the successful use of square‐wave voltammetry (SWV) to directly assess the controlled releasing profile of naproxen from lab‐made cellulose derivative materials (membranes and microparticles) in phosphate buffer (pH 7.4) at 36 °C. Particular advantage of SWV refers to the direct real‐time monitoring of released drug from cellulose derivative microparticles, which cannot be easily assessed by UV‐spectrophotometry. Moreover, SWV was able to detect modifications in the naproxen releasing profile due to morphology and processing of membranes and microparticles. The possible miniaturization and versatility of SWV suggest the promising application on the study of several drug delivery systems, including in vivo studies.