Benzenoid Molecules with Uniform Distribution of π-Electrons within Rings

Summary. In a recent work it was demonstrated that in linear hexagonal chains the distribution of π-electrons into rings (as computed by means of the Randić–Balaban method) is uniform, irrespective of the nature of the terminal fragments. We now establish that an analogous, yet somewhat more complex, uniformity in the π-electron distribution exists also in double linear hexagonal chains, as well as in some other benzenoid systems.     

Addition of secondary phosphines to N-vinylpyrroles

Secondary phosphines 1-3 react readily with N-vinylpyrroles 4 and 5 under radical initiation to give regiospecifically anti-Markovnikov adducts, diorganyl-2-(1-pyrrolyl)ethylphosphines 6a-d, highly reactive building blocks for organic synthesis, in 88-91% yields.     

Highly porous uranyl selenate nanotubules

A first amine-templated uranyl selenate based upon highly porous uranyl selenate nanotubules, (C4H12N)14[(UO2)10(SeO4)17(H2O)], has been prepared in the room-temperature reaction of uranyl nitrate, butylamine, and H2SeO4 in aqueous solution. The structure consists of nanometer-scale tubular [(UO2)10(SeO4)17(H2O)]14- units packed in a hexagonal-type fashion. The tubules have elliptical cross section with outer dimensions of 25 x 23 A = 2.5 x 2.3 nm. The internal free crystallographic diameter of the tubules is 12.6 A = 1.26 nm, which is comparable to the effective pore size in large-pore zeolites. This finding demonstrates the possibility of nanostructures for actinides in higher oxidation states and opens up a new area of research and exploration.     

The polysaccharide extracts from the fungi Coprinus comatus and Coprinellus truncorum do exhibit AChE inhibitory activity

The polysaccharide (PSH) extracts from the edible mushroom species Coprinus comatus and Coprinellus truncorum were screened in liquid for their acetylcholinesterase inhibitory (AChE) activity. Both extracts were found to display inhibition of the aforementioned enzyme reaching similar IC₅₀ values of 0.62 ± 0.07 and 0.61 ± 0.03 mg/mL, respectively. According to the means of FTIR spectroscopy, these PSH extracts mostly contained β-glucans. However, the presence of some proteins and polyphenolics as minor ingredients were also detected. Compared with existing literature data for anti-AChE activity of the sugar samples, the findings within this study may be treated as a profound bioactivity. Consequently, this study puts some light on the possible use of the screened macrofungi in the palliative treatment of Alzheimer’s disease.     

Carbon-carbon coupling constants - a new guide in the stereochemistry of oximes

A positive contribution of more than 7 Hz to the direct ¹³C-¹³C spin-spin coupling constants induced by the proximity of the nitrogen lone pair in syn-orientation to the coupled nuclei allows an unambiguous configuration assignment of diverse oximes.     

Relating Total π-Electron Energy and Resonance Energy of Benzenoid Molecules with Kekulé- and Clar-Structure-Based Parameters

Within classes of isomeric benzenoid hydrocarbons various Kekulé- and Clar-structure-based parameters (Kekulé structure count, Clar cover count, Herndon number, Zhang–Zhang polynomial) are all mutually correlated. This explains why both the total π-electron energy (E), the Dewar resonance energy (DRE), and the topological resonance energy (TRE) are well correlated with all these parameters. Nevertheless, there exists an optimal value of the variable of the Zhang–Zhang polynomial for which it yields the best results. This optimal value is negative-valued for E, around zero for TRE, and positive-valued for DRE. A somewhat surprising result is that TRE and DRE considerably differ in their dependence on Kekulé- and Clar-structure-based parameters.     

Asymptotically independent topological indices on random trees

Topological indices are graph invariants used in computational chemistry to encode molecules. A frequent problem when performing structure-activity studies is that topological indices are inter-correlated. We consider a simple topological index and show asymptotic independence for a random tree model. This continues previous work on the correlation among topological indices. These findings suggest that a size-dependence in a certain class of distance-based topological indices can be eliminated.AMS subject classification: 05C80, 60E10, 92E10     

The formation of lactams of N-(2-amino)benzoylamino acids

N-(2-Nitro)benzoylamino acids were prepared by 2-nitrobenzoylation of amino acids via the mixed ethylcarbonic anhydride procedure. They were reduced catalytically to N-(2-amino)benzoylamino acids which underwent cyclization to the corresponding lactams under a variety of conditions. The use of this reaction sequence for stepwise degradation of peptides seems possible.     

Four cyclo­alkane­spiro‐4′‐imidazolidine‐2′,5′‐dithiones

The crystal structures of four cyclo­alkane­spiro‐4′‐imidazolidine‐2′,5′‐dithiones, namely cyclo­pentane­spiro‐4′‐imidazolidine‐2′,5′‐dithione {systematic name: 1,3‐diaza­spiro­[4.4]­nonane‐2,4‐dithione}, C₇H₁₀N₂S₂, cyclo­hexane­spiro‐4′‐imidazolidine‐2′,5′‐dithione {systematic name: 1,3‐diaza­spiro­[4.5]decane‐2,4‐dithione}, C₈H₁₂N₂S₂, cyclo­heptane­spiro‐4′‐imidazolidine‐2′,5′‐dithione {systematic name: 1,3‐diaza­spiro­[4.6]undecane‐2,4‐dithione}, C₉H₁₄N₂S₂, and cyclo­octane­spiro‐4′‐imidazolidine‐2′,5′‐dithione {systematic name: 1,3‐di­aza­spiro­[4.7]dodecane‐2,4‐dithione}, C₁₀H₁₆N₂S₂, have been determined. The three‐dimensional packing in all of the structures is based on closely similar chains, in which hydantoin moieties are linked through N—H⋯S hydrogen bonding. The size of the cyclo­alkane moiety influences the degree of its deformation. In the cyclo­octane compound, the cyclo­octane ring assumes both boat–chair and boat–boat conformations.