Renormalization group equations with several length scales and crossover scaling functions for axial anisotropy

The critical behaviour of axially anisotropicn-vector models is characterized by two distinct length scales, the correlation lengths and for the easy and hard axes. In order to handle the full range of anisotropics from to partial differential renormalization group equations are derived, depending on and . The anisotropicX-Y model is studied in detail near four dimensions. The crossover scaling functions for the susceptibilities are calculated to first order in=4–d. Two distinct crossover regions are found for weak and dominant anisotropy, respectively.     

Concerning the Diastereomerization of Stilbenoid Hypericin Derivatives

Summary.  Experiments on a newly prepared (E)-configured ω-benzal-hypericin derivative using TLC and ¹H NMR together with quantum chemical calculations revealed that in stilbenoid hypericin derivatives photodiastereomerization between the (E)- and (Z)-diastereomers occurs in principle. However, due to its low diastereomerization quantum yield and photo and thermal equilibria, which reside mostly on the side of the (E)-diastereomer, this photoreaction is only of marginal importance to the photochemistry of stilbenoid hypericin derivatives. Thus, photodiastereomerization does not appreciably interfere with the photoreactions important for photodynamic therapy. This was demonstrated by comparing the sensitized bilirubin photodestruction of hypericin and the ω-benzal-hypericin derivative. Received December 6, 2001. Accepted December 21, 2001     

Calibration of laser-ablation ICP-MS. Can we use synthetic standards with pneumatic nebulization?

An approach for the determination of trace element concentrations in high purity metals, using an inductively coupled plasma mass spectrometer (ICP-MS) with a laser-ablation system for direct solid sample introduction after calibration with nebulized liquid standards was made. Due to the inherent differences in the rate of sample introduction with laser-ablation and pneumatic nebulization, a matrix element must be used as an internal standard. This is problematical for elements that have no isotope with a relative abundance of less than 0.1 %, since the ion signals would be too high for direct measurement, and reduction of the ablation rate would compromise the sensitivity for trace elements. Due to the high stability of ICP-unit and mass filter of the instrument used, it was found that the tail of a mass-peak of the matrix element could be used as an internal standard. Therefore, a position at –0.5 amu from the matrix-isotope (e.g. ^62.5Cu in copper samples) was used for internal standardization. The standard deviation of this signal in a period of 2.5 h was 3.6% RSD with no notable drift when the laser ablation was used for sample introduction. The calibration of the matrix-element by nebulizing liquid standards showed that the ion signal measured on the peak-tail is directly proportional to the element concentration in the ICP. This indicates that the peak shape is not only stable, but also independent of the peak height. The advantages of this method lie in the easy preparation of calibration standards for quantitative measurements with a laser-ablation system and access to homogeneous standards for materials, that are difficult to homogenize in the solid state. The calibration of the traces is performed relatively to a fixed concentration of the matrix element. Calibrations were carried out for trace concentrations in high purity copper and good recoveries were obtained for high-purity reference standards. Received: 23 February 1998 / Revised: 20 July 1998 / Accepted: 25 July 1998     

Eine thermische,intramolekulare [2 + 2]-Cycloaddition eines Allenyl-benzols; Synthese von Allenylbenzolen durch säurekatalysierte Dienol-Benzol-Umlagerung

A thermal Intermolecular [2 + 2]-Cycloaddition of an Allenyl-Allyl-Benzene; Synthesis of Allenylbenzenes via Acid-Catalyzed Dienol-Benzene Rearrangement A few years ago, it has been shown that the acid-catalyzed dienol-benzene rearrangement of 2-propinyl-substituted cyclohexadienols is a convenient synthesis for allenyl-substituted benzene derivatives. The cyclohexadienols 20 and 21 were prepared via C-alkylation of the corresponding phenols with 2-propinylbromide (Scheme 3), followed by reduction of the cyclohexadienone 13 and 17 with LiAlH₄. Treatment of 20 and 21 with p-toluenesulfonic acid in ether at ?15°) yielded the desired allenyl benzenes 8 and 9 , respectively, via [3,4]-sigmatropic rearrangements (Scheme 4). The 2-propinylbenzenes 22–24 , formed via [1,2]-sigmatropic shift of the 2-propinylgroup, were found as by-products. Thermolysis of allenyl benzene 8 in decane yielded two bicyclic ( 25 and 26 ) and two tricyclic products ( 27 and 28 ; Scheme 5). For the formation of 25 and 26 , a pericyclic reaction mechanism (Scheme 6) as well as a mechanism via biradical intermediates (Scheme 7) is discussed. A [2 + 2]-cycloaddition of the α,β-allenic and the allylic C,C-double bound of 8 led to the tricyclic products 27 and 28 (Scheme 9). All attempts to realize a [1,7]-sigmatropic H-shift in the allene 9 failed so far, and the starting material underwent a rapid polymerisation.     

Selektive Amidspaltung bei Peptiden mit α,α-disubstituierten α-Aminosäuren

Selective Amide Cleavage in Peptides Containing α,α-Disubstituted α-Amino Acids A new synthesis of dipeptides with terminal α,α-disubstituted α-amino acids, using 2,2-disubtituted 3-amino-2H-azirines 1 as amino-acid equivalents, is demonstrated. The reaction of 1 with N-protected amino acids leads to the corresponding dipeptide amides in excellent yield. It is shown that the previously described selective hydrolysis (HCl, toluene, 80°, or HCl, MeCN/H₂O, 80°) of the terminal amide group results in an extensive epimerization of the second last amino acid. An acid-catalyzed enolization in the intermediate oxazole-5(4H)-ones is responsible for this loss of configurational integrity. In the present paper, a selective hydrolysis of the terminal amide group under very mild conditions is described: In 3_N HCl (THF/H₂O 1:1), the dipeptide N,N-dimethylamides or N-methytlanilides are hydrolized at 25–35° to the optically pure dipeptides in very good yield.     

Dimethyl(tetramethylcyclopentadienyl)silyl-, -germyl- und -stannyl-phosphane. Röntgenstrukturanalyse von Chloro(dimethyl)tetramethylcyclopentadienylstannan und Tetracarbonyl[1-dimethyl-(tetramethylcyclopentadienyl)germyl-3,4-dimethylphospholen]eisen(0)

Dimethyl(tetramethylcyclopentadienyl)silyl-, -germyl-, and -stannylphosphanes. X-Ray Structures of Chloro(dimethyl)tetramethylcyclopentadienyl-stannane and Tetracarbonyl[1-dimethyl(tetramethylcyclopentadienyl)germyl-3,4-dimethyl-phospholene]iron(0) Me₂Cp′SiCl ( 1 ) (Cp′ = C₅HMe₄) reacts with magnesium and R₂PCl (R = Ph, ^tBu) as well as PCl₃ in tetrahydrofurane yielding Me₂Cp′SiPPh₂ ( 4 ), Me₂Cp′SiP^tBu₂ ( 5 ) and (Me₂Cp′Si)₃P ( 6 ) respectively. The reaction of Me₃SiPPh₂ ( 7 ) or Me₃SiPC₄H₄Me₂ ( 10 ) with Me₂Cp′GeCl ( 2 ) and Me₂Cp′SnCl ( 3 ) leads to the formation of Me₂Cp′EPPh₂ (E = Ge ( 8 ), Sn ( 9 )) and Me₂Cp′EPC₄H₄Me₂ (E = Ge ( 11 ), Sn ( 12 )). 11 reacts with Fe(CO)₅ with formation of Fe(CO)₄[(PC₄H₄Me₂)GeCp′Me₂] ( 13 ). 3 crystallizes in the space group P2₁/n with a = 986,7(1), b = 1247,3(2), c = 1028,2(1) pm, β = 92,71(1)°, Z = 4 and V = 1264,1(2) 10^?30 m³. The final refinement resulted in R₁ = 0,0249 for 2097 observed reflexions with F_o ≥ 4σ(F_o). 13 crystallizes in the space group P2₁/n with a = 967,7(3), b = 1298,70(16), c = 1832,7(3) pm, β = 95,810(19)°, Z = 4 and V = 2291,4(8) 10^?30 m³ (R₁ = 0,0444 for 4043 observed reflexions with F_o ≥ 4σ(F_o). 13 forms a trigonal bipyramide with the phosphane ligand 11 in an axial position.     

Synthesis of 6-Heterocyclically Appended Tri-<Emphasis Type="Italic">O</Emphasis>-methyl Protected 6-Desmethyl Emodin Derivatives

Summary. A convenient synthesis of several 6-heterocyclically appended tri-O-methyl 6-desmethyl emodin derivatives including the tetrazolyl, oxazolyl, oxazolinyl, benzimidazolyl, benzoxazolyl, and benzothiazolyl derivatives of potential biological and medicinal interest was achieved starting from the tri-O-methyl protected emodin aldehyde or nitrile. In addition, these derivatives could serve as synthons for heterocyclic hypericin derivatives.     

The Microstructure of Selective Palladium Hydrogenation Catalysts Supported on Calcium Carbonate and Modified by Lead (Lindlar Catalysts), Studied by Photoelectron Spectroscopy,Thermogravimetry, X-Ray Diffraction,and Electron Microscopy

A detailed analysis of the system Pd + Pb on CaCO₃ is presented. This system known as Lindlar catalyst is used for selective hydrogenations of C?C bonds to C?C bonds. It was found to consist of seven distinct chemical phases. Essential ingredients are solid solutions of hydrogen and oxygen in Pd. The latter phase enables the metal particles to be attached to the support via an orientational relationship calcite (113)∥Pd + O (111). The addition of Pb neither changes the micromorphology of the disk-shaped Pd particles nor does it modify the electronic structure of Pd as studied by chemisorption experiments. The addition of Pb seems to block certain active sites and, thus, to enhance the selectivity. The support was found to be a multi-domain mixture of calcite and aragonite with domain sites of several hundred Å. The free surface of the pore-free solid is covered by a calcium-hydroxide carbonate. This phase as well as several other Pb phases seem to represent only spectator materials. Verification of this as well as finding the correlation between structure and function of the various components requires a kinetic analysis which is outside the scope of this paper. It is demonstrated that a variety of analytical techniques is required to unravel the complex nature of such a ‘simple' catalyst’ as it is Pd on CaCO₃.     

Die Polymerisation des Vinylatropats

Zusammenfassung Mit Hilfe der IR- und der Kernresonanzspektroskopie kann gezeigt werden, da? das anionische Polymerisat des Atropas?urevinylesters ausschlie?lich durch Polymerisation der Atropas?uredoppelbindung entstanden ist. An der radikalischen Polymerisation, die sehr langsam verl?uft, ein „Dead End“ erreicht und nur relativ niedermolekulare Polymere bildet, sind beide Doppelbindungsarten beteiligt. Cyclopolymerisation tritt dabei nur in bescheidenem Umfang ein. Diese Befunde lassen sich mit der hohen Reaktivit?t und der tiefen „Ceiling“-Temperatur der Atropas?ureoster zwanglos deuten.

---

Summary With the aid of infrared and NMR-spectroscopy can be shown, that in the anionic polymerisation of atropic acid vinylester only the atropic double bond reacts. The radical polymerisation proceeds very slowly to a dead end giving polymers of rather low molecularweights. In this polymerisation both types of double bonds are involved, but the extend of cyclopolymerisation is small. These facts are easily explained by the high reactivity and the low ceiling temperature of the atropic acid esters.

---

---

Herrn Prof. Dr. R. Signer m?chto ich an dieser Stelle für viele anregende Diskussionen und für die kritische Durchsicht des Manuskripts meinen Dank aussprechen.

---

Herrn Dr. M. Neuenschwander sei für die Aufnahme und Interpretation der Kernresonanzspektren ebenfalls bestens gedankt.     

Platinum(II) Mixed Ligand Complexes with Thiourea Derivatives,Dimethyl Sulphoxide and Chloride: Syntheses,Molecular Structures,and ESCA Data

The platinum(II) mixed ligand complexes [PtCl(L^1‐6)(dmso)] with six differently substituted thiourea derivatives HL, R₂NC(S)NHC(O)R′ (R = Et, R′ = p‐O₂N‐Ph: HL¹; R = Ph, R′ = p‐O₂N‐Ph: HL²; R = R′ = Ph: HL³; R = Et, R′ = o‐Cl‐Ph: HL⁴; R₂N = EtOC(O)N(CH₂CH₂)₂N, R′ = Ph: HL⁵) and Et₂NC(S)N=CNH‐1‐Naph (HL⁶), as well as the bis(benzoylthioureato‐κO, κS)‐platinum(II) complexes [Pt(L^{1, 2})₂] have been synthesized and characterized by elemental analysis, IR, FAB(+)‐MS, ¹H‐NMR, ¹³C‐NMR, as well as X‐ray structure analysis ([PtCl(L¹)(dmso)] and [PtCl(L^{3, 4})(dmso)]) and ESCA ([PtCl(L^{1, 2})(dmso)] and [Pt(L^{1, 2})₂]). The mixed ligand complexes [PtCl(L)(dmso)] have a nearly square‐planar coordination at the platinum atoms. After deprotonation, the thiourea derivatives coordinate bidentately via O and S, DMSO bonds monodentately to the Pt^II atom via S atom in a cis arrangement with respect to the thiocarbonyl sulphur atom. The Pt—S‐bonds to the DMSO are significant shorter than those to the thiocarbonyl‐S atom. In comparison with the unsubstituted case, electron withdrawing substituents at the phenyl group of the benzoyl moiety of the thioureate (p‐NO₂, o‐Cl) cause a significant elongation of the Pt—S(dmso)‐bond trans arranged to the benzoyl‐O—Pt‐bond. The ESCA data confirm the found coordination and bonding conditions. The Pt 4f_7/2 electron binding energies of the complexes [PtCl(L^{1, 2})(dmso)] are higher than those of the bis(benzoylthioureato)‐complexes [Pt(L^{1, 2})₂]. This may indicate a withdrawal of electron density from platinum(II) caused by the DMSO ligands.