Intramolecular N-H···Cl hydrogen bonds in the outer coordination sphere of a bipyridyl bisurea-based ligand stabilize a tetrahedral FeLCl2 complex

Insight into the Structure of Victorin, the Host-Selective Toxin from the Oat Pathogen Cochliobolus victoriae. Studies of the Unique Dehydroamino Acid β-Chlorodehydroalanine

Victorins, a family of peptide toxins, produced by the fungal pathogen Cochliobolus victoriae and responsible for disease of some oat varieties, contain a β-chlorodehydroalanine residue, ΔAla(βCl). To determine the conformational properties of this unique dehydroamino acid, a series of model compounds was studied using X-ray, NMR, and FT-IR methods, supported by theoretical calculations. The ΔAla(βCl) geometrical isomers differ in conformational profile. The isomer Z prefers the helical conformation α (φ, ψ = -61°, -24°), PPII type conformation β (φ, ψ = -47°, 136°), and semiextended conformation β2 (φ, ψ = -116°, 9°) in weakly and more polar solutions. The isomer E prefers mainly the extended conformation C5 (φ, ψ = -177°, 160°), but with an increase of the environment polarity also conformations β (φ, ψ = -44°, 132°) and α (φ, ψ = -53°, -39°). In the most stable conformations the N-H···Cl hydrogen bond (5^γ) occurs, created between the chlorine atom of the side chain and the N-H donor of the flanking amide group. The method of synthesis of the β-chlorodehydroalanine residue is proposed, by chlorination of dehydroalanine and then the photoisomerization from the isomer Z to E. The presented results indicate that the assignment of the geometrical isomer of the ΔAla(βCl) residue in naturally occurring victorins still remains an open question, despite being crucial for biological activity.

Gaining Insights on the Interactions of a Class of Decorated (2-([2,2'-Bipyridin]-6-yl)phenyl)platinum Compounds with c-Myc Oncogene Promoter G-Quadruplex and Other DNA Structures

Organometallic molecules offer some of the most promising scaffolds for interaction with G-quadruplex nucleic acids. We report the efficient synthesis of a family of organoplatinum(II) complexes, featuring a 2-([2,2'-bipyridin]-6-yl)phenyl tridentate (N∧ N∧ C) ligand, that incorporates peripheral side-chains aiming at enhancing and diversifying its interaction capabilities. These include a di-isopropyl carbamoyl amide, a morpholine ethylenamide, two enantiomeric proline imides and an oxazole. The binding affinities of the Pt-complexes were evaluated via UV-vis and fluorescence titrations, against 5 topologically-distinct DNA structures, including c-myc G-quadruplex, two telomeric (22AG) G-quadruplexes, a duplex (ds26) and a single-stranded (polyT) DNA. All compounds exhibited binding selectivity in favour of c-myc, with association constants (Ka ) in the range of 2-5×105  M-1 , lower affinity for both folds of 22AG and for ds26 and negligible affinity for polyT. Remarkable emission enhancements (up to 200-fold) upon addition of excess DNA were demonstrated by a subset of the compounds with c-myc, providing a basis for optical selectivity, since optical response to all other tested DNAs was low. A c-myc DNA-melting experiment showed significant stabilizing abilities for all compounds, with the most potent binder, the morpholine-Pt-complex, exhibiting a ΔTm >30 °C, at 1 : 5 DNA-to-ligand molar ratio. The same study implied contributions of the diverse side-chains to helix stabilization. To gain direct evidence of the nature of the interactions, mixtures of c-myc with the four most promising compounds were studied via UV Resonance Raman (UVRR) spectroscopy, which revealed end-stacking binding mode, combined with interactions of side-chains with loop nucleobase residues. Docking simulations were conducted to provide insights into the binding modes for the same four Pt-compounds, suggesting that the binding preference for two alternative orientations of the c-myc G-quadruplex thymine 'cap' ('open' vs. 'closed'), as well as the relative contributions to affinity from end-stacking and H-bonding, are highly dependent on the nature of the interacting Pt-complex side-chain.

Metal Regulated Organic–Inorganic Hybrid Ferroelastic Materials: [(CH3)3CN(CH3)2CH2F]2[MBr4] (M = Cd and Zn)

Two organic–inorganic hybrid compounds [(CH3)3CN(CH3)2CH2F]2[MBr4] (M = Cd for 1 and Zn for 2) undergo ferroelastic phase transitions with Aizu notation of mmmF2/m, accompanied by dielectric switches. The replacement of...

The unexpected reactivity of 9-iodo-nido-carborane: from nucleophilic substitution reactions to the synthesis of tricobalt tris(dicarbollide) Na[4,4',4''-(MeOCH2CH2O)3-3,3',3''-Co3(μ3-O)(μ3-S)(1,2-C2B9H10)3]

An unusual reactivity of 9-iodo-nido-carborane [9-I-7,8-C₂B₉H₁₁]^- towards nucleophiles under strong basic conditions was revealed. The nucleophilic substitution of iodine with O- and N-nucleophiles results in [9-RO-7,8-C₂B₉H₁₁]^- (R = H, CH₂CH₂OMe) and [9-L-7,8-C₂B₉H₁₁] (L = Py, NEt₃, Me₂NCH₂CH₂NMe₂), respectively. Reaction of [9-I-7,8-C₂B₉H₁₁]^- with CoCl₂ in 1,2-dimethoxyethane in the presence of t-BuOK, depending on the order of addition of the reagents, leads either to a diastereomeric mixture of diiodo derivatives cobalt bis(dicarbollide) rac-[4,4'-I₂-3,3'-Co(1,2-C₂B₉H₁₀)₂]^- and meso-[4,7'-I₂-3,3'-Co(1,2-C₂B₉H₁₀)₂]^- or to the corresponding mixture of 2-methoxyethoxy derivatives rac-[4,4'-(MeOCH₂CH₂O)₂-3,3'-Co(1,2-C₂B₉H₁₀)₂]^- and meso-[4,7'-(MeOCH₂CH₂O)₂-3,3'-Co(1,2-C₂B₉H₁₀)₂]^-. In the presence of accidental admixture of sodium thiosulfate, the reactions of 9-iodo-nido-carborane and 9-(2'-methoxyethoxy)-nido-carborane with CoCl₂ in 1,2-dimethoxyethane were found to produce additionally unprecedented tricobalt tris(dicarbollide) cluster Na[4,4',4''-(MeOCH₂CH₂O)₃-3,3',3''-Co₃(μ³-O)(μ³-S)(1,2-C₂B₉H₁₀)₃], the central fragment of which is a trigonal bipyramid with apical oxygen and sulfur atoms, and the base is formed by the Co₃ triangle flanked by three dicarbollide ligands. In addition, the 2-methoxyethoxy substituents of the dicarbollide ligands chelate the sodium cation in such a way that they form a helix whose rotation direction depends on the enantiomer of the parent ligand. Thus, in this case, induction of the helical chirality of the complex occurs due to the point chirality of the initial inorganic ligand. It is worth noting that in the case of symmetrically substituted 2-methoxyethoxy derivative of nido-carborane [10-MeOCH₂CH₂O-7,8-C₂B₉H₁₁]^- only formation of the corresponding cobalt bis(dicarbollide) complex [8,8'-(MeOCH₂CH₂O)₂-3,3'-Co(1,2-C₂B₉H₁₀)₂]^- was observed.

Second-coordination sphere effects on the reactivities of Hoveyda–Grubbs-type catalysts: a ligand exchange study using phenolic moiety-functionalized ligands

The reactivities of Hoveyda–Grubbs-type complexes are tunable through second-coordination sphere effects caused by a functional group in the ligand.

Ultrahigh phase transition temperature in a metal–halide perovskite-type material containing unprecedented hydrogen bonding interactions

An ABX₃ perovskite-type compound (N,N-dimethylethanolammonium)CdCl₃ with hydrogen bonding interactions between organic ammonium cations undergoes a phase transition at super-high temperatures.

Anion-directed self-assembly of a 2,6-bis(2-anilinoethynyl)pyridine bis(amide) scaffold

Bis(sulfonamide) receptors based on the 2,6-bis(2-anilinoethynyl)pyridine scaffold form persistent dimers with water and halides in solution and in the solid-state. The structurally related bis(amide) receptor derived from 3,5-dinitrobenzoyl chloride is a dimer in the solid-state with two HCl molecules directing the self-assembly. The 2+2 dimer, with a twisted "S"-shaped backbone, is held together by six hydrogen bonds. Dissolution of the (H2⁺·Cl^- )₂ adduct in CHCl₃ results, however, in a monomeric structure. DOSY and ¹H NMR experiments were used to identify the dominance of monomer in solution for both 2 and H2⁺·Cl^- . The 'OFF-ON' fluorescence response of 2, 6-bis(2-anilinoethynyl)pyridine is retained with amide arms.

Solid-State Examination of Conformationally Diverse Sulfonamide Receptors Based on Bis(2-anilinoethynyl)pyridine, -Bipyridine, and -Thiophene

Utilizing an induced-fit model and taking advantage of rotatable acetylenic C(sp)-C(sp²) bonds, we disclose the synthesis and solid-state structures of a series of conformationally diverse bis-sulfonamide arylethynyl receptors using either pyridine, 2,2'-bipyridine, or thiophene as the core aryl group. Whereas the bipyridine and thiophene structures do not appear to bind guests in the solid state, the pyridine receptors form 2 + 2 dimers with water molecules, two halides, or one of each, depending on the protonation state of the pyridine nitrogen atom. Isolation of a related bis-sulfonimide derivative demonstrates the importance of the sulfonamide N-H hydrogen bonds in dimer formation. The pyridine receptors form monomeric structures with larger guests such as BF₄^- or HSO₄^-, where the sulfonamide arms rotate to the side opposite the pyridine N atom.