Chemistry : a European Journal

In this work, we experimentally investigate the potency of high pressure to drive a protein toward an excited state where an inhibitor targeted for this state can bind. Ras proteins are small GTPases cycling between active GTP-bound and inactive GDP-bound states. Various states of GTP-bound Ras in active conformation coexist in solution, amongst them, state 2 which binds to effectors, and state 1, weakly populated at ambient conditions, which has a low affinity for effectors. Zn2+-cyclen is an allosteric inhibitor of Ras protein, designed to bind specifically to the state 1...

We previously described NMR based fingerprint matching with peptide backbone resonances as a fast and reliable structural dereplication approach for Pseudomonas cyclic lipodepsipeptides (CLiPs). In combination with total synthesis of a small library of configurational CLiP congeners this also allows unambiguous determination of stereochemistry, facilitating structure-activity relationship studies and enabling three-dimensional structure determination. However, the on-resin macrocycle formation in the synthetic workflow brings considerable burden and limits universal applicability...

Singlet dioxygen has been widely applied in different disciplines such as medicine (photodynamic therapy or blood sterilization), remediation (wastewater treatment) or industrial processes (fine chemicals synthesis). Particularly, it can be conveniently generated by energy transfer between a photosensitizer's triplet state and triplet dioxygen upon irradiation with visible light. Among the best photosensitizers, substituted zinc(II) phthalocyanines are prominent due to their excellent photophysical properties, which can be tuned by structural modifications, such as halogen- and chalcogen-atom substitution...

We report the high-resolution NMR solution-state structure of an intramolecular G-quadruplex with a diagonal loop of ten nucleotides. The G-quadruplex is formed by a 34-nt DNA sequence, d[CAG3T2A2G3TATA2CT3AG4T2AG3T2], named UpsB-Q-1. This sequence is found within promoters of the var genes of Plasmodium falciparum, which play a key role in malaria pathogenesis and evasion of the immune system. The [3+1]-hybrid G-quadruplex formed under physiologically relevant conditions exhibits a unique equilibrium between two structures, both stabilized by base stacking and non-canonical hydrogen bonding...

Circular dichroism (CD) studies on poly(1,4-phenylene)s bearing a chiral side chain in the aggregated conditions were carried out. Little CD was observed in a solution form, while addition of a poor solvent into the polyphenylene solution induced aggregation and a strong CD was observed, accordingly. Applying the controlled degree of polymerization (DP) of poly(1,4-phenylene) in the use of bidentate diphosphine Chiraphos as a ligand for the nickel catalyst, the relationship of DP with CD strength was studied to reveal to show the highest CD at the DP = 84 (gabs = ca...

The chemically triggered reversible switching of pH-responsive hydrazones involves rotary motion-induced configurational changes, serving as a prototype for constructing an array of molecular machines. Typically, the configurational isomerization of such switches into two distinct forms (E/Z) occurs through the alteration of the pH the medium, achieved by successive additions of acid and base stimuli. However, this process results in intermittent operation due to the concomitant accumulation of salt after each cycle, limiting switching performance to only a few cycles (5-6)...

Stimuli-responsive crystalline materials have received much attention for being potential candidates of smart materials. However, the occurrence of polymorphism-driven stimuli responses in crystalline materials remains interesting but rare. Herein, three polymorphs of an acylhydrazone derivative, N'-[(E)-(1-benzofuran-2-yl) methylidene] pyridine -4-carbohydrazide (BFMP) were prepared. Form-1 undergoes a photomechanical response via E→Z photoisomerization under UV irradiation, accompanied by a decrease in fluorescence intensity and a change from colorless to yellow...

With both TEMPO and O2 (in air) as the homogeneous redox mediators, BiBrO as the heterogeneous semiconductor photocatalyst, the first example of semi-heterogeneous photocatalytic decarboxylative phosphorylation of N-arylglycines with diarylphosphine oxides was established. A series of α-amino phosphinoxides were efficiently synthesized.

Upon dibenzo annulation on Thiele's hydrocarbon (tetraphenyl-p-quinodimethane), the quinoid form and the biradical form adopt quite different geometries, and thus are no longer resonance structures. When these two forms can interconvert rapidly due to the small energy barrier (ΔG‡), the equilibrated mixture contains both forms in a ratio that is determined by the energy difference (ΔGo) between the two forms. For a series of tetrakis[5-(4-methoxyphenyl)-2-thienyl]-substituted derivatives, the more stable quinoid form and the metastable biradical form coexist in solution as an equilibrated mixture due to small ΔG‡ (< 15 kcal mol-1) and ΔGo (1-4 kcal mol-1), in which the proportion of the two forms can be regulated by temperature...

A terminal [NiII-OH] complex 1, supported by triflamide-functionalized NHC ligands, showed divergent reactivity for the reaction of sulfone with alcohol, contingent on base concentration, temperature, and time. Julia-type olefination of alcohols with sulfones was achieved using one equiv. of base, whereas lowering base loading to 0.5 equiv. afforded α-alkylated sulfones. Besides excellent substrate scope and selectivity, biologically active stilbene derivatives DMU-212, pinosylvin, resveratrol, and piceatannol were synthesized in high yield under Julia-type olefination conditions...

We report an idea for the synthesis of oligopeptides using a solvent-free ball milling approach. Our concept is inspired by block play, in which it is possible to construct different objects using segments (blocks) of different sizes and lengths. We prove that by having a library of short peptides and employing the ball mill mechanosynthesis (BMMS) method, peptides can be easily coupled to form different oligopeptides with the desired functional and biological properties. Optimizing the BMMS process we found that the best yields we obtained when TBTU and cesium carbonate were used as reagents...

High-valent Fe(IV)=O intermediates of metalloenzymes have inspired numerous efforts to generate synthetic analogs to mimic and understand their substrate oxidation reactivities. However, high-valent M(IV) complexes of late transition metals are rare. We have recently reported a novel Co(IV)-dinitrate complex (1-NO3) that activates sp3 C-H bonds up to 87 kcal/mol. In this work, we have shown that the nitrate ligands in 1-NO3 can be replaced by azide, a more basic coordinating base, resulting in the formation of a more potent Co(IV)-diazide species (1-N3) that reacts with substrates (hydrocarbons and phenols) at faster rate constants and activates stronger C-H bonds than the parent complex 1-NO3...

Bis-porphyrin cages have long been exploited to bind fullerenes selectively for various applications. The major consideration for an effective binding here had been the cavity size. Herein, we structurally demonstrate that a bis-Ni-porphyrin cavitand having even a smaller cavity can host a larger fullerene by a breathing and ruffling mechanism. It has also been shown that both the electronic and steric influence at the meso- positions of the porphyrin in fact dictate the binding character. The smaller cavity of 2NiD exhibits preferential binding for C70 over C60; however, surprisingly, the larger cavities in 2HD and 2NiTD display stronger affinities for C60 over the larger fullerene...

The prosperity of the lithium-ion battery market is inevitably accompanied by the depletion of corresponding resources and the accumulation of spent batteries in a dialectical manner. Spent lithium-ion batteries are harboring the characteristics of hazardous waste and high-value resources, so efficient recycling is of great significance. The cathode material is considered as an interesting target for repurposing. Despite some important reviews give commendable emphasis to recycling technologies, there is still a dearth of exploration of recycling mechanisms...

Collective interactions are a novel type of chemical bond formed between metals and electron-rich substituents around an electron-poor central atom. So far only a limited number of candidates for having collective interactions are reported. In this work, we extend the newly introduced concept of collective bonding to a series of neutral boron complexes with the general formula M2BX3 (M = Li, Na, and K; X = F, Cl, and Br). Our state-of-the-art ab initio computations suggest that these complexes form trigonal bipyramidal structures with a D3h to C3v distortion along the C3 axis of symmetry...

Thin films of crystalline solids with substantial free volume from organic chromophores and metal secondary building units (SBUs) are promising for engineering new optoelectronic properties through control of interchromophore coupling. Zn-based SBUs are especially relevant in this case because they avoid quenching the chromophore's luminescence. We find that layer-by-layer spin-coating using Zn acetate dihydrate and benzene-1,4-dicarboxylic acid (H2BDC) and biphenyl-4,4'-dicarboxylic acid (H2BPDC) linkers easily produces crystalline thin films...

Electron delocalization and aromaticity was comparatively evaluated in recently synthesized figure-eight molecules made of two condensed U-shaped polycyclic aromatic hydrocarbon moieties connected either by two single bonds or by two para-phenylene groups. The selected examples include molecules that incorporate eight-membered and sixteen-membered rings, as well as a doubly [5]helicene-bridged (1,4)cyclophane. We probe whether some electron delocalization could occur through the stereogenic single bonds in these molecules: Is aromaticity purely (semi-)local, or possibly also global in these molecules? It was concluded that the situation can go from a purely (semi-)local character when the dihedral angle at the connecting single bonds is large, such as in biphenyl, to a predominantly (semi-)local character with a minor global contribution when the dihedral angle is small, such as in the para-phenylene connectors of the [5]helicene-bridged cyclophane...

To fill the need for environmentally sensitive fluorescent unnatural amino acids able to operate in the red region of the spectrum, we have designed and synthesized Alared, a red solvatochromic and fluorogenic amino acid derived from the Nile Red chromophore. The new unnatural amino acid can be easily integrated into bioactive peptides using classical solid-phase peptide synthesis. The fluorescence quantum yield and the emission maximum of Alared-labeled peptides vary in a broad range depending on the peptide's environment, making Alared a powerful reporter of biomolecular interactions...

Pyridoxal hydrochloride, a vitamin B6 vitamer, was synthetically converted to a series of diverse redox-active benzoyl pyridinium salts. Cyclic voltammetry studies demonstrated redox reversibility under basic conditions, and two of the most promising salts were subjected to laboratory-scale redox flow battery tests involving galvanostatic cycling at 10 mM in 0.1 M NaOH. In these tests, the battery was charged completely, corresponding to the transfer of two electrons to the electrolyte, but no discharge was observed...

Nicotinamide adenine dinucleotide (NAD+) is a redox active molecule that is universally found in biology. Despite the importance and simplicity of this molecule, few reports exist that investigate which molecular features are important for the activity of this ribodinucleotide. By exploiting the nonenzymatic reduction and oxidation of NAD+ by pyruvate and methylene blue, respectively, we were able to identify key molecular features necessary for the intrinsic activity of NAD+ through kinetic analysis. Such features may explain how NAD+ could have been selected early during the emergence of life...