Determination of metal ions by liquid chromatographic separation of their 2-acetylpyridine-4-ethyl-3-thiosemicarbazone chelates

A new thiosemicarbazone was prepared, characterized, and used as a complexing reagent for the chromatographic separation and determination of metal complexes by reverse-phase HPLC. The reagent was sufficiently soluble in methanol-water solutions for metal ions to be complexed in this aqueous organic phase, without need for extraction. Many variables affected the retention times of the metal complexes. Several metals were determined selectively by complexation with the reagent and chromatographic separation of the complexes. Interference effects from other metal ions were also investigated.     

Sulfide ion electrooxidation catalysed by cobalt phthalocyanine microcrystals

Electrooxidation of sulfide ion catalysed by microcrystals of cobalt phthalocyanine was investigated by cyclic voltammetry in 0.5M KNO₃ at pH 9.22. Traces of catalyst were immobilized at the surface of a paraffin-impregnated graphite electrode by the mechanical transfer of its powder. The electro-oxidation of HS^– proceeds in two irreversible steps, with the first peak between 0 V and –0.12 V and the second at 0.17 V. The first step is second order in HS^– and its product is the adsorbed disulfide, which may further dissociate to give adsorbed sulfur atoms. The reduction of sulfur occurs at –0.1 V.     

Chemically modified resins for solid-phase extraction

The packings most widely used for solid-phase extraction are hydrophobic and make poor surface contact with aqueous samples unless the resins are first treated with an activating organic solvent such as methanol. Insertion of an acetyl- or hydroxymethyl group into a porous polystyrene-divinylbenzene resin provides a more hydrophilic surface that is easily wetted by water alone. Small columns of the chemically modified resins were found to be very efficient for the solid-phase extraction of many types of organic solutes from aqueous samples. Comparative recovery studies showed that the modified resins are superior to both silica packings and unmodified organic resins for the solid-phase extraction of organic compounds, and especially for polar organics such as phenols.     

Chiroptical detection during liquid chromatography,part 5: On-line measurement of circular dichroism spectra Δε(λ) during stops of chromatographic flow

Summary A procedure is described which serves to measure circular dichrograms () on line during stops of flow in liquid chromatography. Since the concentration of substrate in the spectrometer cell during the stop is not known, the differential absorption coefficients are calculated from the experimental differential absorbances A by means of UV absorption (i. e. photomultiplier voltage) data. Verifications of the procedure are obtained by its application to three substrates (Table 1), the () spectra of which were known. The present on-line technique is compared with a corresponding off-line method.The N,N-dimethylthiobenzamides1 and2 as well as the 9,10-phenanthrenequinone7 consist of interconvertible enantiomers because their planar states are destabilized by steric overcrowding of groups. The unknown dichrograms () of1, 2 and7 are obtained (Figs. 2 and 4) and discussed with reference to the helicities of these molecules.In memory of the late Professor Dr. Dr. h. c. Günther Snatzke.     

Molecules with Large Cavities in Supramolecular Chemistry

Supramolecular chemistry is a new area of research that has rapidly developed from pure synthetic chemistry, and its novelty has led to interdisciplinary cooperation between organic and inorganic chemistry, biochemistry, physical and theoretical chemistry, and physics. Whereas molecular chemistry essentially deals with the covalent bonding of atoms, Supramolecular chemistry is predominantly involved in the study of the weaker intermolecular interactions resulting in the association and self-organization of several components to form larger aggregates (supramolecules). The first crown ether discovered by the subsequent Nobel prizewinner Pedersen was more the fortuitous reaction product of an impurity, but nowadays, some twenty-five years later, chemists are able to tailor host molecules to special requirements. Host compounds having a cyclophane skeleton make an important contribution, since their aromatic structural units ensure the necessary rigidity of the molecular structures and thereby improve the preorganization of the coordination sites for the cooperative binding of the guests. During the course of the rapid development of Supramolecular chemistry such a large number of synthetic hosts has been developed and their interaction with guests studied in such depth that we must restrict ourselves here to a discussion of a particular group of host compounds, namely cavity-supporting macrobicyclic and macrooligocyclic phanesu, which bear a similar relation to open-chain and monocyclic hosts as the metal-complexing cryptands to the podands and crown ethers. The molecular architecture of these three-dimensionally bridged macrooligocycles is a challenge for synthetic chemistry. (Not only the size and shape of the intramolecular cavity, but also the provision of the latter with suitable coordination centers have to be included in the synthesis strategy.) The capacity for the envelopment of guests from all sides and the expedient endo functionalization often also produce a particularly strong binding of host and guest, outstanding selectivities with regards to molecular recognition, and special properties of the Supramolecular complexes.     

Engineering entangled photon pairs with metal–organic frameworks

The discovery and design of new materials with competitive optical frequency conversion efficiencies can accelerate the development of scalable photonic quantum technologies. Metal–organic framework (MOF) crystals without inversion symmetry have shown potential for these applications, given their nonlinear optical properties and the combinatorial number of possibilities for MOF self-assembly. In order to accelerate the discovery of MOF materials for quantum optical technologies, scalable computational assessment tools are needed. We develop a multi-scale methodology to study the wavefunction of entangled photon pairs generated by selected non-centrosymmetric MOF crystals via spontaneous parametric down-conversion (SPDC). Starting from an optimized crystal structure, we predict the shape of the G⁽²⁾ intensity correlation function for coincidence detection of the entangled pairs, produced under conditions of collinear type-I phase matching. The effective nonlinearities and photon pair correlation times obtained are comparable to those available with inorganic crystal standards. Our work thus provides fundamental insights into the structure–property relationships for entangled photon generation with metal–organic frameworks, paving the way for the automated discovery of molecular materials for optical quantum technology.

The discovery and design of new materials with competitive optical frequency conversion efficiencies can accelerate the development of scalable photonic quantum technologies.     

The Prospect of Dimensionality in Porous Semiconductors

With the advent of silicon-based semiconductors, a plethora of previously unknown technologies became possible. The development of lightweight low-dimensional organic semiconductors followed soon after. However, the efficient charge/electron transfers enabled by the non-porous 3D structure of silicon is rather challenging to be realized by their (metal-)organic counterparts. Nevertheless, the demand for lighter, more efficient semiconductors is steadily increasing resulting in a growing interest in (metal-)organic semiconductors. These novel materials are faced with a variety of challenges originating from their chemical design, their packing and crystallinity. Although the effect of molecular design is quite well understood, the influence of dimensionality and the associated change in properties (porosity, packing, conjugation) is still an uncharted area in (metal-)organic semiconductors, yet highly important for their practical utilization. In this Minireview, an overview on the design and synthesis of porous semiconductors, with a particular emphasis on organic semiconductors, is presented and the influence of dimensionality is discussed.     

Reaktionen von o-Chinonen mit Aminen und Proteinen. 4. Mitteilung. 7a-Methyl-5,6-dioxo-5,6,7,7a-tetrahydroindol-Derivate aus 4-Methylbrenzcatechin und Enaminen

Reactions of o-Quinones with Amines and Proteins. 7a-Methyl-5,6,7,7a-tetrahysroindole Derivatives from 4-Methylcatechol and Enamines Methyl l-[2′-(methoxycarbonyl)ethyl]-7a-methyl-5,6-dioxo-5.6.7,7a-tetrahydro-indole-3-carboxylate ( 1 ) was isolated after the oxidation of 4-methylcatechol with silver ( 1 ) oxide in the presence of b?-alanine methyl ester in glacial acetic acid. The formation of 1 requires in situ dehydrogenation of the b?-aminocarboxylate and addition of the resulting enamine to 4-methyl-1,2-benzoquinone. Reaction of ethyl 3-(phenylamino)crotonate with 4-methyl-1,2-benzoquinone afforded ethyl 2,7a-dimethyl-5,6-dioxo-1-phenyl-5,6,7,7a-tetrahydroindole-3-carboxylate ( 6 ). Despite the fact that the yields are low, the addition of enamines to o-quinones represents an interesting novel extension of the Nenitzescu-reaction which is well known in the p-quinone series. Compound 1 may be considered as a novel model for the crosslinking of proteins by o-quinones. Formation of 1 was, however, not observed under physiological conditions.