Porphyrins

Extended Hückel calculations are reported for tetravalent porphin complexes of Si(OH)₂, Ge(OH)₂, GeCl₂, and SnCl₂ and divalent complexes of Ge, Sn, and Pb. Divalent Ge porphin is expected to be planar and have the extra two electrons in the ring. Divalent Sn and Pb porphins are expected to be non-planar and have the extra two electrons on the metal. The possibility of a charge transfer transition a ₁(p _z )e _g ^* () is noted, and its identication in available spectra of Sn and PbTPP is made. The electronic structure of the tetravalent species is similar to other metalloporphyrins except for the possibility of low lying ligand to porphin charge transfer states in the hydroxy complexes.

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Zusammenfassung Für die vierwertigen Porphin-Komplexe des Si(OH)₂, Ge(OH)₂, GeCl₂ und SnCl₂ und die zweiwertigen Komplexe des Ge, Sn und Pb werden Berechnungen nach der erweiterten Hückel-methode durchgeführt. Von dem zweiwertigen Ge-Porphin wird erwartet, da\ es planar ist und da\ sich die beiden zusÄtzlichen Elektronen im Ring befinden, wÄhrend von den zweiwertigen Sn- und Pb-Porphinen zu erwarten ist, da\ sie nicht planar sind und die beiden zusÄtzlichen Elektronen sich am Metall befinden. Auf die Möglichkeit eines Charge-Transfer-übergangs a ₁(p _z )e _g ^* () wird hingewiesen, und dieser übergang wird in gemessenen Spektren von Sn und PbTPP identifiziert. Die Elektronenstruktur der vierwertigen Verbindung ist denjenigen anderer Metallporphyrine Ähnlich, au\er der Möglichkeit niedrig liegender Ligand-Porphin-Charge-Transfer-ZustÄnde in den Hydroxy-Komplexen.

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Résumé Calculs de type Hückel étendu pour des complexes tétravalents de la porphine avec Si(OH)₂, Ge(OH)₂, GeCl₂ et SnCl₂ et des complexes divalents avec Ge, Sn et Pb. La porphine de Ge divalente est prévue plane avec les deux électrons supplémentaires dans le cycle. Les porphines divalentes de Sn et Pb sont prévues non planes avec les deux électrons supplémentaires sur le métal. On remarque la possibilité d'une transition de transfert de charge a ₁(p _z)e _g ^* () et on l'identifie dans les spectres disponsibles pour Sn et PbTPP. La structure électronique des espèces tétravalentes est semblable à celle des autres métalloporphyrines à l'existence possible près dans les complexes hydroxy d'états de transfert de charge de basse énergie entre le ligand et la porphine.

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Paper XX: Ake, R. L, Gouterman, M.: Theoret. chim. Acta (Berl.) 17, 408–416 (1970).     

Anomalous group delay in optical fibres

It is shown, by means of computation on a specific model, how pulse broadening in multimode gradedindex optical waveguides is significantly affected by the levels of excitation of the high-order modes. Pulse widths are computed as functions of the profile parameter, under conditions of equal excitation, high-order mode suppression and GaAs laser excitation.     

On the self-association of the normal alcohols and the glass transition in alcohol-alcohol solutions

The glass-transition temperature (T_g) in mutual binary mixtures of the primary alkanols from methanol throughn-octanol has been measured as a function of composition. For mixtures of the alkanols heavier than ethanol,T _g is found to be a linear function of the number-average molecular length. Methanol and ethanol mixtures show higherT _g values than indicated by this relation. These results are found to be consistent with association of the heavier alkanols into chains of very great length in the supercooled liquid, while ethanol and methanol must form networks with a moderate degree of crosslinking between chains.     

Simple Conversion of Colchicine into Demecolcine

N-Deacetylcolchiceine ( 7 ), readily available from colchicine ( 1 ), was converted into N-trifluoroacetyl-deacetylcolchiceine ( 8 ). Methylation of 8 with methyl iodide in the presence of potassium carbonate afforded a mixture of N-trifluoroacetyl-demecolcine ( 10 ) and its isomer 11 . The mixture of 10 and 11 was detrifluoroacetylated and separated by chromatography to afford demecolcine ( 2 ) and isodemecolcine ( 12 ). A more practical route to 2 started with 8 , and gave N-trifluoroacetyl-deacetylcolchicine ( 13 ) and its isomer 14 after O-methylation with diazomethane. N-Methylation of 13 and 14 with methyl iodide and potassium carbonate afforded 10 and 11 . The overall yield in the conversion of colchicine ( 1 ) into demecolcine ( 2 ) via 7, 8 and 13 was 55%.     

Mass Spectrometric Decomposition Processes in Labelled 1-Heptenes

The 70 eV mass spectra of a number of ¹³C- and D-labelled analogs of 1-heptene have been measured, as well as the metastable transitions in the non-labelled compound. Isotopic distributions in the major fragment ions have been calculated from the high and low resolution data. The results show that considerable skeletal rearrangement must take place before formation of most of the fragment ions. Loss of methyl and ethyl radicals occurs mainly from the two ends of the molecule. Ethylene fragments come primarily from the unsaturated end of the molecule, but show evidence of significant prior skeletal rearrangement. The predicted McLafferty rearrangement accounts for only 2/3 of the C₄H₈⁺ ions formed, less for the C₃H₆⁺ ions. At least 80% of C₄H₉⁺ ions appear to be formed by allylic cleavage, as expected, but this mechanism can only account for a maximum of 20% of the formation of the complementary ion C₃H₅⁺. Both, this latter ion and C₃H₆⁺, are probably generated by loss of hydrogen from C₃H₇⁺. Figures obtained for label retention in 1-[¹³C]- and 1-D-labelled analogs were nearly identical for most fragment ions, probably indicating that the hydrogen atoms in position 1 remain on C(1) even following skeletal rearrangement. A similar result was found for the 7-[¹³C]- and 7-D-labelled compounds. The main exceptions in the case of the products labelled in position 1 (C₄H₇⁺, C₃H₃⁺) seem to be due to initial loss of an hydrogen atom from this position followed by further fragmentation.     

High-spin levels in138Ce and140Nd Observed in the (α, 4n γ) reactions

Levels of¹³⁸Ce and¹⁴⁰Nd have been studied using the¹³⁸Ba(α,4nγ)¹³⁸Ce and¹⁴⁰Ce(α, 4nγ)¹⁴⁰Nd reactions. Singleγ-ray spectra,γ-γ coincidence spectra, angular and time distributions with respect to the beam bursts have been measured. A number of higher excited states with excitation energies up to about 5 MeV and with spin value up to 12 are populated in both nuclei. The lower states with spins and parities 7^?, 5^?, 6^? and 10⁺ can be explained by two-quasiparticle neutron configurations of the types (h _11/2 ^?1 ,d _3/2 ^?1 ) 7^? , (h _11/2 ^?1 ,S _1/2 ^?1 ) 5^?, 6^? and (h _11/2 ^?2 ) 10⁺. Several high-spin states observed in¹³⁸Ce and¹⁴⁰Nd can be explained qualitatively as four-quasiparticle states with two-proton-two-neutron configurations. The 3^? state at an energy of 2,137.4 keV is observed in¹³⁸Ce. The evidence for the existence of the low-lying 3^? states in¹⁴⁰Nd at 2,124.0 keV is discussed. Beside the known 9.6 ms (7^?) isomeric state in¹³⁸Ce another state at 3,538.5keV (10⁺) with a half life of about 200 ns has been observed. The observed levels in the¹³⁸Ce and¹⁴⁰Nd nuclei are compared with theoretical predictions using delta force interaction.     

Albatrellus confluens (Alb. & Schwein.) Kotl. & Pouz.: Natural Fungal Compounds and Synthetic Derivatives with In Vitro Anthelmintic Activities and Antiproliferative Effects against Two Human Cancer Cell Lines

Neglected tropical diseases affect the world’s poorest populations with soil-transmitted helminthiasis and schistosomiasis being among the most prevalent ones. Mass drug administration is currently the most important control measure, but the use of the few available drugs is giving rise to increased resistance of the parasites to the drugs. Different approaches are needed to come up with new therapeutic agents against these helminths. Fungi are a source of secondary metabolites, but most fungi remain largely uninvestigated as anthelmintics. In this report, the anthelmintic activity of Albatrellus confluens against Caenorhabditis elegans was investigated using bio-assay guided isolation. Grifolin (1) and neogrifolin (2) were identified as responsible for the anthelmintic activity. Derivatives 4–6 were synthesized to investigate the effect of varying the prenyl chain length on anthelmintic activity. The isolated compounds 1 and 2 and synthetic derivatives 4–6, as well as their educts 7–10, were tested against Schistosoma mansoni (adult and newly transformed schistosomula), Strongyloides ratti, Heligmosomoides polygyrus, Necator americanus, and Ancylostoma ceylanicum. Prenyl-2-orcinol (4) and geranylgeranyl-2-orcinol (6) showed promising activity against newly transformed schistosomula. The compounds 1, 2, 4, 5, and 6 were also screened for antiproliferative or cytotoxic activity against two human cancer lines, viz. prostate adenocarcinoma cells (PC-3) and colorectal adenocarcinoma cells (HT-29). Compound 6 was determined to be the most effective against both cell lines with IC₅₀ values of 16.1 µM in PC-3 prostate cells and 33.7 µM in HT-29 colorectal cells.