Synthesis and characterization of a new family of bi-, tri-, tetra-, and pentanuclear ferric complexes

Nine members of a new family of polynuclear ferric complexes have been synthesized and characterized. The reaction of Fe(O(2)CMe)(2) with polydentate Schiff base proligands (H(2)L) derived from salicylidene-2-ethanolamine, followed in some cases by reaction with carboxylic acids, has afforded new complexes of general formulas [Fe(2)(pic)(2)(L)(2)] (where pic(-) is the anion of 2-picolinic acid), [Fe(3)(O(2)CMe)(3)(L)(3)], [Fe(4)(OR)(2)(O(2)CMe)(2)(L)(4)], and [Fe(5)O(OH)(O(2)CR)(4)(L)(4)]. The tri-, tetra-, and pentanuclear complexes all possess unusual structures and novel core topologies. M?ssbauer spectroscopy confirms the presence of high-spin ferric centers in the tri- and pentanuclear complexes. Variable-temperature magnetic measurements suggest spin ground states of S = 0, 1/2, 0, and 5/2 for the bi-, tri-, tetra-, and pentanuclear complexes, respectively. Fits of the magnetic susceptibility data have provided the magnitude of the exclusively antiferromagnetic exchange interactions. In addition, an easy-axis-type magnetic anisotropy has been observed for the pentanuclear complexes, with D values of approximately -0.4 cm(-)(1) determined from modeling the low-temperature magnetization data. A low-temperature micro-SQUID study of one of the pentanuclear complexes reveals magnetization hysteresis at nonzero field. This is attributed to an anisotropy-induced energy barrier to magnetization reversal that is of molecular origin. Finally, an inelastic neutron scattering study of one of the trinuclear complexes has revealed that the magnetic behavior arises from two distinct species.     

Separation of glyceride positional isomers by silver ion chromatography

Separation of triglyceride and diglyceride positional isomers by silver ion high-performance liquid chromatography coupled with an evaporative light-scattering detector is described. The triglyceride isomers had a fatty acid composition of CLC and CCL, where C and L were caprylic acid and linoleic acid, respectively. Diglyceride isomers, 1,2(2,3)-diglyceride and 1,3-diglyceride, which contained caprylic acid were separated too. A solvent system based on n-hexane, 2-propanol, ethyl acetate, and acetonitrile with a flow-rate of 0.8 ml/min was developed. Calibration curves of CLC and CCL were achieved with triolein as internal standard. Using this method, the incorporation of linoleic acid onto specific a position of glycerol backbone can be monitored.     

Polarometrische bestimmung von zirkonium(IV) mit tartrazin

A new polarimetric procedure has been developed for the rapid determination of zirconium in the presence of tartrazin as reagent This determination is possible in the presence of uranium.     

Solid-phase glycosylation of peptide templates and on-bead MAS-NMR analysis: perspectives for glycopeptide libraries

The efficient solid-phase glycosylation of amino acid side chains (serine (Ser), threonine (Thr), and tyrosine (Tyr)) in peptides was demonstrated with a variety of glycosyl trichloroacetimidate donors in high yields and purities. A novel photolabile linker, with no chiral centre, was introduced to facilitate analysis by both matrix-assisted laser desorption ionisation time of flight (MALDI-TOF) mass spectrometry and nanoprobe magic angle spinning (MAS) NMR spectroscopy. Product analysis by nanoprobe MAS NMR spectroscopy, LC-MS and MALDI-TOF mass spectrometry of the glycosylation reactions indicated that the reactivity order of the hydroxy side-chain functions of amino acids in peptides on the solid-phase was Tyr>Ser>Thr. The nearly quantitative glycosylation yields and the efficient on-bead product analysis by nanoprobe MAS NMR spectroscopy have made a truly solid-phase approach for the synthesis and analysis of glycopeptide libraries possible.     

Über die Umsetzung von 2-Methyl-2,5-diphenyl-imidazolin-4-thion und 2-Methyl-2,5-diphenyl-4-chlor-2H-imidazol mit aliphatischen und aromatischen Aminen,Alkoholen und Phenolen

Zusammenfassung Aliphatische Amine bzw. Alkohole reagiren (in Gegenwart von PbO) mit 2-Methyl-2,5-diphenyl-imidazolin-4-thion (1) glatt zu 4-Alkylamino-2H-imidazolen (2 a-f, 7) bzw. 4-Alkoxy-2H-imidazolen (9 a-g). Die Darstellung von 4-Arylamino-2H-imidazolen (4 a-j) bzw. 4-Aroxy-2H-imidazolen (10 a-t) gelingt in guten Ausbeuten durch Umsetzung von 2-Methyl-2,5-diphenyl-4-chlor-2H-imidazol (3) mit aromatischen Aminen in siedenden Lösungsmitteln (Petroläther, Aceton) bzw. mit Phenolen in siedendem Aceton in Gegenwart von HCl-Acceptoren (K₂CO₃, Dabco). Die Umsetzung von3 mit Anthranilsäure liefert in 83proz. Ausbeute 1-Methyl-1,3-diphenyl-1H, 9H-imidazo[5,1-b]chinazolin-9-on (6). Aus3 und Thiophenol erhält man glatt 2-Methyl-2,5-diphenyl-4-phenylthio-2H-imidazol (11).

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On the reaction of 2-Methyl-2,5-diphenyl-imidazoline-4-thione and 2-Methyl-2,5-diphenyl-4-chloro-2H-imidazole with aliphatic and aromatic amines, alcohols and phenols (joint action of elemental sulfur and gaseous ammonia upon ketones, LXXVI

Aliphatic amines and alcohols (in the presence of PbO) easily react with 2-methyl-2.5-diphenyl-imidazoline-4-thione (1) to 4-alkylamino-2H-imidazoles (2 a-f, 7) and 4-alkoxy-2H-imidazoles (9 a-g), resp. 4-arylamino-2H-imidazoles (4 a-j) are prepared in good yields by the reaction of 2-methyl-2.5-diphenyl-4-chloro-2H-imidazole (3) with aromatic amines under reflux in light naphtha or acetone; in the same manner 4-aroxy-2H-imidazoles (10 a-t) are obtained from3 and phenols in boiling acetone in the presence of HCl-acceptors (K₂CO₃, Dabco). Reaction of3 with anthranilic acid leads to1-methyl-1.3-diphenyl-1H.9H-imidazo[5.1-b]chinazoline-9-one (6) in 83% yield. By reaction of thiophenol with3 2-methyl-2.5-diphenyl-4-phenylthio-2H-imidazole (11) is easily obtained.

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Herrn Prof. Dipl.-Ing., Dr. techn., Dr. e. h.Otto Kratky zum 70. Geburtstag herzlichst gewidmet.

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Teil der DiplomarbeitJ. Gräber, Techn. Hochschule Aachen, 1970.

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Teil der DiplomarbeitU. Lames, Techn. Hochschule Aachen, 1971.     

Spectroscopy and reactivity of a photogenerated tryptophan radical in a structurally defined protein environment

Near-UV irradiation of structurally characterized [Re(I)(CO)3(1,10-phenanthroline)(Q107H)](W48F/Y72F/H83Q/Y108W)AzM(II) [Az = Pseudomonas aeruginosa azurin, M = Cu, Zn]/[Co(NH3)5Cl]Cl2 produces a tryptophan radical (W108*) with unprecedented kinetic stability. After rapid formation (k = 2.8 x 106 s-1), the radical persists for more than 5 h at room temperature in the folded ReAzM(II) structure. The absorption spectrum of ReAz(W108*)M(II) exhibits maxima at 512 and 536 nm. Oxidation of K4[Mo(CN)8] by ReAz(W108*)Zn(II) places the W108*/W108 reduction potential in the protein above 0.8 V vs NHE.     

Synthesis and spectroscopic characterization of a new family of Ni(4) spin clusters

A new family of tetranuclear Ni complexes [Ni(4)(ROH)(4)L(4)] (H(2)L = salicylidene-2-ethanolamine; R = Me (1) or Et (2)) has been synthesized and studied. Complexes 1 and 2 possess a [Ni(4)O(4)] core comprising a distorted cubane arrangement. Magnetic susceptibility and inelastic neutron scattering studies indicate a combination of ferromagnetic and antiferromagnetic pairwise exchange interactions between the four Ni(II) centers, resulting in an S = 4 spin ground state. Magnetization measurements reveal an easy-axis-type magnetic anisotropy with D approximately -0.93 cm(-)(1) for both complexes. Despite the large magnetic anisotropy, no slow relaxation of the magnetization is observed down to 40 mK. To determine the origin of the low-temperature magnetic behavior, the magnetic anisotropy of complex 1 was probed in detail using inelastic neutron scattering and frequency domain magnetic resonance spectroscopy. The spectroscopic studies confirm the easy-axis-type anisotropy and indicate strong transverse interactions. These lead to rapid quantum tunneling of the magnetization, explaining the unexpected absence of slow magnetization relaxation for complex 1.     

Über die Reduktionsformen einiger nichtenolisierenden aromatischer Ketone und Chinone,welche die Vinylpolymerisation zu initiieren vermögen

It is known that the reduction forms of aromatic carbonyl compounds (ACC) initiate anionic polymerization of vinyl monomers. The ability of the reduction forms to transfer an electron to the interacting molecules is defined also by the electron affinity of the partners. To obtain data about the electron affinity the half-wave potentials of polarographic reduction were measured and compared with the values of the lowest antibonding molecular orbital, according to theHückel's method. A linear correlation between the potentials of polarographic reduction and the energy of the lowest antibonding molecular orbit was found. The results prove the correctness of the previously determined electroaffinity defined by electron transfers between the reduction forms and neutral molecules. From the data of quantum chemical calculation and the polarographic reduction ofACC the changes of the free energy, enthalpy and the equilibrum constant for electron transfer reaction were calculated. The initiation ability of the reduction forms ofACC and the elctron affinity discussed.     

Visible light-induced water oxidation on mesoscopic alpha-Fe2O3 films made by ultrasonic spray pyrolysis

Alpha-Fe(2)O(3) films having a mesoscopic leaflet type structure were produced for the first time by ultrasonic spray pyrolysis (USP) to explore their potential as oxygen-evolving photoanodes. The target of these studies is to use translucent hematite films deposited on conducting fluorine doped tin oxide (FTO) glass as top electrodes in a tandem cell that accomplishes the cleavage of water into hydrogen and oxygen by sunlight. The properties of layers made by USP were compared to those deposited by conventional spray pyrolysis (SP). Although both types of films show similar XRD and UV-visible and Raman spectra, they differ greatly in their morphology. The mesoscopic alpha-Fe(2)O(3) layers produced by USP consist mainly of 100 nm-sized platelets with a thickness of 5-10 nm. These nanosheets are oriented mainly perpendicularly to the FTO support, their flat surface exposing (001) facets. The mesoscopic leaflet structure has the advantage that it allows for efficient harvesting of visible light, while offering at the same time the very short distance required for the photogenerated holes to reach the electrolyte interface before recombining with conduction band electrons. This allows for water oxidation by the valence band holes even though their diffusion length is only a few nanometers. Distances are longer in the particles produced by SP favoring recombination of photoinduced charge carriers. Open-circuit photovoltage measurements indicate a lower surface state density for the nanoplatelets as compared to the round particles. These factors explain the much higher photoactivity of the USP compared to the SP deposited alpha-Fe(2)O(3) layers. Addition of hydrogen peroxide to the alkaline electrolyte further improves the photocurrent-voltage characteristics of films generated by USP indicating the hole transfer from the valence band of the semiconductor oxide to the adsorbed water to be the rate-limiting kinetic step in the oxygen generation reaction.