Kitungolides A, B, and C, new diterpenes from a soft coral of a new genus

Three novel compounds, designated kitungolides A (1), B (2), and C (3), were isolated from a soft coral of a new genus collected at Kitungamwe, Kenya. The three new compounds are of a unique heterotricyclic skeleton. The structures and relative stereochemistry of the compounds were elucidated by interpretation of MS, COSY, HMQC, HMBC, and NOESY experiments. [structure: see text]     

The geometry of intermolecular interactions in some crystalline fluorine-containing organic compounds

The propensity of C-F groups to form C-F H-C interactions with C-H groups on other molecules has been analyzed. Crystal structures of molecules containing only carbon, hydrogen, and fluorine, but no oxygen, nitrogen, or other hydrogen-bond-forming elements, were chosen for an initial study in which the intermolecular interactions in crystal-structure determinations of polycyclic aromatic hydrocarbons and their analogous fluoro derivatives were analyzed. It is found that C-F H-C interactions occur, but they are weak, as judged by the intermolecular distances and the angles involved. In a study of crystal structures of molecules containing other elements in addition to carbon, hydrogen, and fluorine, it was found that when an oxygen atom is in a neighboring position on an interacting molecule, a C-O group is more likely than a C-F group to form a linear interaction to the hydrogen atom of a C-H group. Thus, in spite of the high electronegativity of the fluorine atom, a C-F group competes unfavorably with a C-O^–, C-OH, or C=O group to form a hydrogen bond to an O-H, N-H, or C-H group. It is found, however, particularly for polycyclic aromatic hydrocarbons with substituted CF₃ groups that, in the absence of other functional groups that can form stronger interactions, C-F H-C interactions may serve to align molecules and give a different crystal packing from that in the pure hydrocarbon (where fluorine is replaced by hydrogen). Thus, C-F H-X (X = C, N, O) interactions are very weak, much weaker than C=O H-X interactions, but they cannot be ignored in predictions of modes of molecular packing in complexes and in crystals.     

Electrochemical generation of stable carbocation-tetrafluoroborate salts and the cation-anion interactions in their solid state structures

The electrochemical generation of stable carbocations, among other heterocyclic products, by a unique electrochemical process involving the anodic oxidation of aryl-substituted ketene imines is described. The electrochemical oxidation undergoes an unusual multiannulation process to form these types of products by intermolecular cyclization. The X-ray crystal structures of two carbocation tetrafluoroborate salts,4c and4d, of which the latter is solvated by CH₂Cl₂, are presented. We have observed that one of the B-F bonds in4c is relatively long with respect to the other three similar in length B-F bonds, while in the solvated salt (4d·CH₂Cl₂), one of the B-F bonds is particularly short relative to its congeners. In both cases, the exceptional B-F bonds are oriented toward the positive center of the carbocation. These phenomena are compared with other known X-ray structures of organic tetrafluoroborate salts and discussed.     

Copper‐Binding Motifs: Structural and Theoretical Aspects

In this paper, we report the results of a study involving the coordination geometries of Cu^I, Cu^II, and Cu^III crystal structures in the Cambridge Structural Database, and on Cu binding sites in proteins taken from the Protein Data Bank. The motifs used to bind two bridged Cu ions are also described. In addition, we report the results of ab initio molecular‐orbital calculations performed on a variety of model Cu^I/Cu^II complexes (Cu^I/Cu^II?X_nY_m (X, Y=NH₃, SH₂); n+m=4; n=0–4) to provide data on the structural and energetic changes that occur in isolated complexes when the oxidation state of the Cu ion is changed from II to I while the coordination number is conserved. The use of such simple ligands in these calculations eliminates constraints on the geometric changes that may be imposed by more‐complicated ligands.     

Elucidating dissociation activation energies in host–guest assemblies featuring fast exchange dynamics

The ability to mediate the kinetic properties and dissociation activation energies (E_a) of bound guests by controlling the characteristics of “supramolecular lids” in host–guest molecular systems is essential for both their design and performance. While the synthesis of such systems is well advanced, the experimental quantification of their kinetic parameters, particularly in systems experiencing fast association and dissociation dynamics, has been very difficult or impossible with the established methods at hand. Here, we demonstrate the utility of the NMR-based guest exchange saturation transfer (GEST) approach for quantifying the dissociation exchange rates (k_out) and activation energy (E_a,out) in host–guest systems featuring fast dissociation dynamics. Our assessment of the effect of different monovalent cations on the extracted E_a,out in cucurbit[7]uril:guest systems with very fast k_out highlights their role as “supramolecular lids” in mediating a guest''s dissociation E_a. We envision that GEST could be further extended to study kinetic parameters in other supramolecular systems characterized by fast kinetic properties and to design novel switchable host–guest assemblies.

GEST-NMR is utilized for quantifying the dissociation activation energy (E_a,out) in host-guest systems featuring fast dissociation dynamics.     

Maximum Drawdown and Drawdown Duration of Spectrally Negative Lévy Processes Decomposed at Extremes

Journal of Theoretical Probability - Path decomposition is performed to characterize the law of the pre-/post-supremum, post-infimum and the intermediate processes of a spectrally negative...     

Evaluating the biological potential of some new cobalt (II) complexes with acrylate and benzimidazole derivatives

This paper presents the synthesis, physico‐chemical and biological properties of four new coordination compounds with mixed ligands: acrylate ion (acr) and benzimidazole/benzimidazole derivatives with the general formula [Co(L) ₂ (acr) ₂ ]·nH ₂ O [ (1) L: benzimidazole (HBzIm), n: 0.5; (2) L: 2‐methylbenzimidazole (2‐MeBzIm), n: 0.5; (3) L: 5‐methylbenzimidazole (5‐MeBzIm), n: 0; (4) L: 5,6‐dimethylbenzimidazole (5,6‐Me₂BzIm), n: 0]. Their chemical formulae were achieved correlating the chemical analysis with mass spectrometry data, the ligands coordination modes were assigned by Fourier transform‐infrared measurements, and the trigonal bipyramidal geometry of cobalt ion in complexes was assigned by data correlation of UV–Vis‐NIR spectra and magnetic moments measurements. Single‐crystal X‐ray diffraction reveals a mononuclear structure with a pentacoordinated cobalt (II) ion, connected to two acrylato coordinated in different modes and two unidentate 5,6‐dimethylbenzimidazole ligands for compound (4) . The biological tests were performed against several microbial strains, the cytotoxicity was evaluated on HCT8 cellular lines and the cell cycle analysis was performed on HT29 cellular lines. Microbiological assays indicated that Co (II) complexes present a very good to good activity against Candida albicans 1760, Enterococcus faecium E5, Bacillus subtilis ATCC 6683 and Escherichia coli ATCC 25922. Predictive pharmacokinetic (ADME), toxicity and drug‐likeness profiles were evaluated for Co (II) complexes. Our results highlight that Co (II) complexes depicted in the present study are suitable to be used as efficient pharmacological agents.     

On rates of acceleration of extrapolation methods for oscillatory infinite integrals

The purpose of this work is to complement and expand our knowledge of the convergence theory of some extrapolation methods for the accurate computation of oscillatory infinite integrals. Specifically, we analyze in detail the convergence properties of theW- and -transformations of the author as they are applied to three integrals, all with totally different behavior at infinity. The results of the analysis suggest different convergence and acceleration of convergence behavior for the above mentioned transformations on the different integrals, and they improve considerably those that can be obtained from the existing convergence theories.     

Encapsulation of Arenes within a Porous Molybdenum Oxide {Mo132} Nanocapsule

The use of confined space to modulate chemical reactivity and to sequester organic compounds spans significant disciplines in chemistry and biology. Here, the inclusion and assembly of arenes into a water‐soluble porous metal oxide nanocapsule [{(Mo^VI)Mo^V₅O₂₁(H₂O)₆}₁₂{Mo^V₂O₄(CH₃COO)}₃₀]^42? (Mo₁₃₂) is reported. The uptake of benzene, halobenzenes, alkylbenzenes, phenols, and other derivatives was studied by NMR, where it was possible to follow the encapsulation process from the outside of the capsule through its pores and then into the interior. The importance of size or shape of the arenes, and various intermolecular bond interactions contributed by the benzene substituent on the encapsulation process was studied, showing the importance of π–π stacking and CH–π interactions. Furthermore, by using NOESY, ROESY, and HOESY NMR techniques it was possible to understand the interaction of the encapsulated arenes and the acetate linkers or ligands that line the interior of the Mo₁₃₂ capsule.