Günter Reck

Lipase-catalyzed transesterification of meso-cyclopentane diols

Abstract The lipase-catalyzed transesterification of the meso-cyclopentane diols 1a – 6a with vinyl acetate in tetrahydrofuran/triethylamine in the presence of lipases of different origin has been investigated. Depending on the structure of the substrate and the origin of the lipase chiral cyclopentane derivatives with high enantiomeric excess could be obtained in good to excellent chemical yields.

N-n-Alkyl N,N-dimethylammonioacetic acid bromides: the first complete series of crystal and molecular structure determinations of an ­amphiphilic compound with alkyl chain lengths n = 1,..., 16

The molecular and crystal structures of 16 N-n-alkyl N,N-dimethylammonioacetic acid bromides with chain lengths between n = 1 and n = 16 have been determined. All compounds from n = 5 to n = 16 form bilayers with interdigitated chains. The even-numbered chains display the chain packing type M2(II). The chain packing of the odd-numbered chain compounds is less regular. The head groups of all compounds are connected via electrostatic N+...Br- interactions, and by OH...Br- hydrogen bonds. The compounds with short chains are packed in different ways. Their molecular conformation depends on the crystal packing.

Uric acid monohydrate—a new urinary calculus phase

In our laboratory more than 100,000 urinary calculi have been analysed since 1972. Amongst this huge sample, 15 specimens originating from a total of eight patients were observed showing similar characteristics but escaping unambiguous identification with any of the substances that have been described so far in urinary concrements. Therefore, the unknown substance was submitted to a more extended analytical regimen. Structural analysis by x-ray crystallography turned out to be most successful, identifying the unknown material as uric acid monohydrate. Uric acid monohydrate crystallizes in the monocline space group P21/c. Within the crystal, uric acid and water molecules form continuous layers by hydrogen bonds. This is in contrast to uric acid in its water free and its dihydrate forms, which both crystallize by forming 3-dimensional networks To the best of our knowledge , the existence of a monohydrate form of uric acid has not been reported so far. Accordingly, this is the first report on uric acid monohydrate as a urinary stone component. The frequency of only 0.015% in our survey indicates that uric acid monohydrate is rarely the main component in concrements, in contrast to uric acid and uric acid dihydrate with frequencies of 10% and 6%, respectively. The infrared spectrum of uric acid monohydrate is very similar to that of the other crystal forms of uric acid. Because of this similarity and its low frequency, uric acid monohydrate may have been overlooked as a component of urinary concrements. X-ray diffraction allows for better differentiation in routine stone analysis. All samples of uric acid monohydrate were found by solid state NMR spectroscopy to be highly contaminated by amorphous material. This material consisted of long aliphatic chains reminiscent of lipids and fatty acids, respectively. Concrements consisting of other forms of uric acid or urate lacked this amorphous component. Therefore, a role of this aliphatic material has to be taken into consideration when discussing the conditions that may favour the rare formation of concrements from uric acid monohydrate. As for as the metabolic situation of the affected patients is concerned, no common peculiarities became evident by a retrospective survey.

Technetium and rhenium complexes of mercapto-containing peptides 1. Tc(V) and Re(V) complexes with mercaptoacetyl diglycine (MAG2) and X-ray structure of AsPh4[TcO(MAG2)]·C2H5OH

Abstract The reaction of mercaptoacetyl diglycine (MAG 2 ) with technetium(V) gluconate in aqueous solution produced [TcO(MAG 2 )] − . A single X-ray structure determination was carried out for the tetraphenylarsonium salt. The dark brown crystals are monoclinic, space group P 2( 1 )/ n , with a =12.478(5), b =14.922(5), c =17.183(9) A and Z =4. The [TcO(MAG 2 )] − ion has a square pyramidal geometry with the technetium atom displaced by 0.756 A towards the oxo ligand from the plane formed by the equatorial S,N,N,O atoms. The rhenium complex AsPh 4 [ReO(MAG 2 )] was prepared analogously starting from Re(V) gluconate and characterized.

Cation Coordination of Bisamidopyridine-derived Receptors as Investigated in the Solid-state and in Solution

A bisamidopyridine-type receptor, N,N′-bis(6-methyl-2-pyridyl)pyridine-2,6-dicarboxamide (1), and its CoIII complex were prepared and their X-ray structures were compared to those of N,N′-diphenylpyridine-2,6-dicarboxamide (2) and CoIII(2)2. Introduction of the two additional coordinative groups resulted in second-order interactions between the central ion and the nitrogen atoms of the terminal pyridine moieties in the crystalline state. Solution studies in acetonitrile revealed the importance of these interactions for the ligands metal ion recognition ability. Whereas 2 only binds to PbII and CuII, 1 yields complexes with a majority of the heavy and transition metal ions studied, CoII, NiII, CuII, ZnII, FeIII, FeII, HgII, and PbII, respectively. The cation binding properties in solution were investigated by absorption spectroscopy and in the case of 1–MII/III, the formation of two spectroscopically distinguishable types of complexes was found. Protonation experiments and theoretical considerations helped to gain further insight into possible modes of coordination in solution.

Photochemical reactions—XXIII : Molecular and crystal structure of 3-dehydro gibberellin A3

Abstract In connection with topophotochemical studies, the structure of 3-dehydro gibberellin A 3 1 has been established by X-ray analysis, and the molecular packing determined. The final discrepancy factor R was 0·078.

Thermal Behaviour and Crystal Structure of Sodium-Containing Hemihydrates of Calcium Sulfate

Summary. A metastable sodium-containing hemihydrate ((6-x)CaSO4ċxNa2SO4ċ3H2O, 0 ≤ x ≤ 1) limited by the pentasalt composition Na2SO4ċ5CaSO4ċ3H2O occurs as an intermediate solid phase in the systems Na2SO4-CaSO4-H2O, NaCl-Na2SO4-CaSO4-H2O, and NaCl-CaSO4-H2O. X-Ray structure determination of a crystal with pentasalt composition results in a super-structure of the pure hemihydrate (CaSO4ċ0.5H2O), in which one Ca2+ion is statistically replaced by two Na+ ions. One Na+ cation is situated in a Ca2+ position in only one of the three chains of CaSO4 forming an axis of nearly three fold symmetry along the c-axis. The second Na+ is located in the water channel neighbouring to the first Na+. The hydrate crystallized in a monoclinic space group C121 (No. 5) with a=24.1781(11), b=13.805(2), c=12.7074(12) Å, β=90.089(12)°. The dehydration temperature of the hydrates depends on their Na+ ion content. A high Na+ content (in water channels) blocks the water escape strongly, and the dehydration temperature increases. Thermal behaviour is also effected by the crystal sizes. The thermograms of small crystals as opposed to large ones show a exothermic effect adjoining the endothermic dehydration. This may be indicative for a change in the dehydration mechanism upon crystal size.Zusammenfassung. Ein metastabiles natriumhaltiges Calciumsulfathemihydrat ((6−x) CaSO4ċxNa2SO4ċ3H2O, 0 ≤ x ≤ 1) tritt als intermediäre Phase in den Systemen Na2SO4-CaSO4-H2O, NaCl-Na2SO4-CaSO4-H2O und NaCl-CaSO4-H2O auf. Die Phase mit dem höchsten Natriumionengehalt entspricht dem sogenannten Natriumpentasalz (Na2SO4ċ5CaSO4ċ3H2O). Die Röntgenstrukturanalyse, welche an einem Einkristall mit Pentasalz-Zusammensetzung durchgeführt wurde, ergab eine Überstruktur des reinen Hemihydrats (CaSO4ċ0.5H2O), wobei ein Ca2+-Ion statistisch durch zwei Na+-Ionen ersetzt ist. Die Ca2+-Substitution erfolgt nur in einer der drei CaSO4-Ketten, welche eine nahezu dreizählige Achse entlang der c-Achse bilden. Ein Ca2+-Ion wird durch ein Na+-Ion ersetzt, das zweite Na+-Ion ist in unmittelbarer Nähe zum ersten in den Wasserkanälen eingelagert. Das Hydrat kristallisiert in der monoklinen Raumgruppe C121 (Nr.5) mit den Gitterparametern a=24.178(11), b=13.805(2), c=12.7074(12) Å, β=90.089(12)°. Die Dehydratationstemperatur variiert mit dem Na+-Gehalt. Je größer dieser ist, um so stärker wird der Austritt der H2O-Moleküle blockiert und zu höheren Temperaturen verschoben. Ein weiterer Unterschied im thermischen Verhalten wurde bei gleichem Na+-Gehalt für unterschiedliche Kristallitgrößen gefunden. Bei kleinen Kristallgrößen (Nadellänge < 20 μm) beginnt die Entwässerung früher im Vergleich zu größeren Kristallen (Nadellänge > 50 μm). Ein exothermer Effekt im Anschluß an die Dehydratation wird nur für kleine Kristalle beobachtet und deutet auf eine abweichende Entwässerungskinetik in Abhänigkeit von der Kristallitgröße hin.

Stereochemical studies. Part 92. Nitrogen bridgehead compounds. Part 61. Synthesis and X-ray analysis of 4,8-dimethylperhydrocyclopenta[d]pyrido[1,2-a]pyrimidin-10-one diastereoisomers

Stereoisomeric 4,8-dimethylperhydrocyclopenta[d]pyrido[1,2-a]pyrimidin-10-ones were prepared by reduction. Two of the eight possible stereoisomers were found in the reaction mixture, and their steric structures were determined by X-ray analysis.

Structure and Rearrangements of 3-Iso(thio,seleno)cyanato-1,2,3-triarylcyclopropenes

A series of new fluctional 3-iso(thio,seleno)cyanato-1,2,3-triarylcyclopropenes was synthesized. The structure of compounds was proved by 1H and 13C NMR, IR, and mass spectra, and that of 3-(1,2,3-triphenylcyclopropenyl) isothiocycnate was confirmed by X-ray crystallography. In compounds under consideration by means of 1H and 13C NMR was discovered and investigated a fast reversible migration of isocyanato, isothiocyanato, and isoselenocyanato groups along the perimeter of the theree-membered ring proceeding according to the dissociation-recombination mechanism.

Furylvinylhalogenides, XII: Reactions of β-chloro-α-cyano-β-(5-nitrofur-2-yl)-acrylic acid derivatives with malonic acid derivatives

SummaryReactions of β-chloro-α-cyano-β-(5-nitrofur-2-yl)-acrylic acid derivatives with malonic acid derivatives in the presence of collidine yield the allyl anions3a–d. The pyridines4, 8 or9 are formed by cyclization of3 under acidic conditions. The 2-chloropyridine4a reacts with nucleophiles under substitution. The treatment of ethyl dichloropropionate1b with C-H-acidic compounds provided the cyclopropanes11 or12, the configurations of which were determined by13C-NMR spectroscopy. The results of the X-ray structure analysis of8c are discussed.ZusammenfassungDie Umsetzung von β-Chlor-α-cyan-β-(5-nitrofur-2-yl)-acrylsäurederivaten mit Malonsäurederivaten in Gegenwart von Collidin führt zu Allylanionen3a–d. Unter sauren Bedingungen cyclisiert3 zu den Pyridinen4, 8 oder9. Das 2-Chlorpyridin4a reagiert mit Nukleophilen unter Substitution. Setzt man den Dichlorpropionsäureester1b mit C-H-aciden Verbindungen in Gegenwart von Collidin um, so werden die Cyclopropane11 bzw.12 gebildet, deren Konfigurationen mit Hilfe der13C-NMR-Spektroskopie bestimmt wurden. Die Ergebnisse der Röntgenkristallstrukturanalyse von8c werden diskutiert.