Synthese,Struktur und einige Reaktionen [N-(N′,N′,N″,N″-tetramethyl)-guanidinyl]-substituierter Phosphorylverbindungen

Synthesis, Structure, and some Reactions of N-(N′,N′,N″,N″-tetramethyl)guanidinyl-substituted Phosphoryl Compounds The tetramethylguanidinyl-substituted phosphoryl compounds 1 – 10 were prepared in the reaction of the appropriate chlorophosphoryl compounds with either N′,N′,N″,N″-tetramethylguanidine (HTMG) or N-trimethylsilyl-(N′,N′,N″,N″-tetramethyl)guanidine (TMSTMG). With methyl iodide 1 reacted with N-alkylation to give the ammonium salt 11. 1 reacted with BF₃ · Et₂O at both imino nitrogen atoms with formation of the bis-BF₃-adduct 12 . The X-ray structure determination of phenylphosphonic acid-bis(N′,N′,N″,N″-tetramethylguanidinide) 3 shows shortened PN-bonds and widened PNC-angles, consistent with the partial double bond character of the PN-bond.     

Solvent intercalation in cobalt dimethylglyoximato complexes: A miniature host-guest system

When crystallized from appropriate solvents, the complex aqua-bis(dimethylglyoximato)nitrocobalt (III) may incorporate solvent molecules, thus forming a variety of mixed crystals. In the resulting host-guest crystals, the space groupP2_l/m and the packing motif of the pure host compound are retained. Lattice constantsa andb remain essentially unaltered upon intercalation, whereasc and the monoclinic angle depend largely on the clathrated guest. Space filling and intermolecular contacts are discussed.Dedicated to Professor Peter Paetzold at the occasion of his 60th birthday. A preliminary account of this work has been given at the Spring Meeting of the British Crystallographic Association, Newcastle upon Tyne, 1994.     

Biocatalytic reversible control of the stiffness of DNA-modified responsive hydrogels: applications in shape-memory,self-healing and autonomous controlled release of insulin

The enzymes glucose oxidase (GOx), acetylcholine esterase (AchE) and urease that drive biocatalytic transformations to alter pH, are integrated into pH-responsive DNA-based hydrogels. A two-enzyme-loaded hydrogel composed of GOx/urease or AchE/urease and a three-enzyme-loaded hydrogel composed of GOx/AchE/urease are presented. The biocatalytic transformations within the hydrogels lead to the dictated reconfiguration of nucleic acid bridges and the switchable control over the stiffness of the respective hydrogels. The switchable stiffness features are used to develop biocatalytically guided shape-memory and self-healing matrices. In addition, loading of GOx/insulin in a pH-responsive DNA-based hydrogel yields a glucose-triggered matrix for the controlled release of insulin, acting as an artificial pancreas. The release of insulin is controlled by the concentrations of glucose, hence, the biocatalytic insulin-loaded hydrogel provides an interesting sense-and-treat carrier for controlling diabetes.

Biocatalytic control over the stiffness of pH-responsive hydrogels is applied to develop shape-memory, self-healing and controlled release matrices.     

Reactions of Ru3(CO)12 with Diphosphenes — A New Route to 50‐Electron Ru3P2 nido‐Clusters

The reaction of the symmetric diphosphene 2, 4, 6‐(CF₃)₃‐C₆H₂‐P=P‐C₆H₂‐2, 4, 6‐(CF₃)₃ 4 with Ru₃(CO)₁₂ led to the 50‐electron Ru₃P₂ nido‐cluster Ru₃(CO)₉[μ‐P‐C₆H₂‐2, 4, 6‐(CF₃)₃]₂ 5 , which in solution at room temperature displays hindered rotation of the aromatic rings about the C(aryl)—P bonds. The structure of 5 was determined by X‐ray crystal structure analysis; its Ru₃P₂ centre forms a distorted square pyramid with one ruthenium atom at the apex. One of the two C₆H₂(CF₃)₃ groups is also appreciably distorted. Temperature‐dependent ¹⁹F NMR studies of the [A₃M₃X]₂ spin system (A = M = CF₃, X = ³¹P) of 5 indicated a rotational barrier ΔG^≠ of 82.3 kJ mol^‐1 at 141 °C. The same Ru₃P₂ core was obtained by the reaction of the unsymmetric diphosphene Mes*‐P=P‐Mes 11 with Ru₃(CO)₁₂; hindered rotation about the C(aryl)—P bonds was also observed, in this case.     

1H-CRAMPS Solid-State NMR and X-Ray Crystal Studies of Inclusion Complexes Formed from 3,3′-bis(9-Hydroxy-9-fluorenyl)-2,2′-binaphthyl Hosts with Acetone

The crystal structures of inclusion compounds of 3,3-bis(9-hydroxy-9-fluorenyl)-2,2-binaphthyl host (1) and its chloro (2) or bromo (3) derivatives substituted in 2,7-positions of the fluorene units with acetone guests (1A–3A) were determined by X-ray studies as well as by ¹H-CRAMPS solid-state NMR. Using this NMR technique allows identification of differently bound guest molecules due to their different chemical shifts caused by the influence of the ring current effects of the host aryl units.     

Polarographic determination of α-amylase activity

The enzyme α-amylase splits blue starch in fragments bearing electroactive groups which exhibit two waves in the pulse polarograms. This behaviour is the basis of the polagraphic determination of bacterial and human serum α-amylase activity. The differential pulse mode is more sensitive by a factor of 25 as compared with normal pulse polarography. With serum α-amylase, protein adsorption disturbs the determination of low activities.     

Characterization of cocoa butters and other vegetable fats by pyrolysis-mass spectrometry

Pyrolysis Mass Spectrometry (Py-MS) was used for the discrimination of cocoa butters from other vegetable fats. Mass spectra ranging from 50 amu to 250 amu were analyzed by principal component analysis (PCA) and with neural nets. The application of neural nets leads to a good discrimination between the two classes. Detailed analysis of the nets revealed that only the first 60 masses were used within the net. The use of PCA requires a careful selection of the number of masses included in the calculation. Canonical variance analysis was applied to determine the significant masses. Optimal performance of PCA was observed only using the first 22 significant masses. Most of these masses were different from the ones used by the neural net. It seems that the mass spectra obtained by Py-MS contain sufficient information for the discrimination of pure cocoa butter from other vegetable fats, but none of the methods seems to be able to extract all information available. Neural net provides a very robust method for this task and no prior data selection was necessary. Received: 13 May 1996 / Revised: 7 August 1996 / Accepted: 7 August 1996     

The Enol of Acetone during Photochemical Reactions of 3-Hydroxy-3-methyl-2-butanone and of Acetone

The enol of acetone, formed by disproportionation reactions of 1-hydroxy-1-methylethyl radicals, is detected by NMR, spectroscopy during photoreactions of 3-hydroxy-3-methyl-2-butanone in acetonitrile and of acetone in 2-propanol and slowly tautomerizes to acetone. The photolysis of 3-hydroxy-3-methyl-2-butanone is shown to proceed via Type I cleavage, predominantly from an excited triplet state.     

Cloud point extraction of napropamide and thiabendazole from water and soil

The micellar extraction and enrichment of napropamide and thiabendazole using Genapol X 80 is described. Combined with their quantification by fluorescence, detection limits below 0.2 g/l with recovery rates of up to 95% were achieved. The recovery could be improved by lowering the extraction temperature and purificaton of the surfactants. This extraction method has been applied to the isolation and preconcentration of napropamide from standard soils. Experimental parameters affecting the recovery rates were examined.     

Hydrolysis in the system LiPF6—propylene carbonate—dimethyl carbonate—H2O

¹⁹F and ³¹P NMR spectroscopy were used to study the kinetics of the hydrolysis of LiPF₆ in the homogenous solvent system propylene carbonate (PC)—dimethyl carbonate (DMC)—H₂O. It was found that the main products of the hydrolysis are HF, LiPO₂F₂ and Li₂PO₃F. The content of POF₃ and PF₅ was negligibly low. We set up a hypothesis that the main factor determining the rate of the process is the so-called ‘secondary’ catalytic effect, caused by solvated H⁺ ions.