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A series of N‐alkyl‐ and N‐aryl‐viologens has been studied in alkaline solutions. In this work, we evaluated the deuteration rate of the viologens in D2O solutions of pH values ranging from 7.3 to 12.7. Kinetic experiments and computational calculations showed the high reactivity of H−C(2) bonds toward deprotonation of N‐aryl‐pyridinium moieties compared to N‐alkyl‐pyridinium moieties, even in hybrid N‐aryl/N‐alkyl dissymmetric viologens. However this high H−C(2) reactivity in liquid phase contrasted with the proton fragmentation mechanism observed in the gas phase by mass spectrometry. The H/D exchange rate of viologens in very strong alkaline conditions could be significantly reduced using cucurbit[7]uril (CB[7]) as supramolecular protecting group. Ultimately, CB[7] inclusion led to a selective protection of H−C(2) group of N‐aryl‐pyridinium of dissymmetric viologens, and induced a supramolecular regioselective deuteration. [ABSTRACT FROM AUTHOR]

Free energies G(X)n of 12 1,ω‐dihydrooligomers (X)n (n, number of the monomeric units) have been determined by quantum calculations. We note that these values are correlated by (a) an excellent linear relationship: G(X)n = An – 761.86 ± 10 (kcal mol–1) (TPSS‐TPSS/6.311 + + G(dp)); (b) for two oligomers (X)n and (Y)n, the difference of weighted free energies—G(X)n/n – G(Y)n/n—is a constant irrespective of n which results from the difference of free energies of the substituent. Consequently, from the Gn values of 1,ω‐dihydrooligoethenes (in fact n‐alkanes), a determination of the free energies of a 1,ω‐dihydrooligomers (X)n is obtained with a good accuracy by the calculation of the G value of its substituent; (c) the corresponding increments G(X)n/n – G(X)(n–1)/(n–1) are equaled and led to a single power law: [Gn/n – G(n–1)/(n–1) = 1282/n2.156 (kcal mol–1), R = 0.9992] or a linear relationship: [Gn/n – G(n–1)/(n–1) = 756.73/n(n–1) + 0.0211 (kcal mol–1), R = 1]. Syndiotactic and isotactic 1,ω‐dihydrooligomers (X) are illustrated in the Electronic Supporting Information. Highlights: Free energy calculated G of 12 oligomers, we observe linear relations G = An + BG/n are identical for vinyl monomer and increments Gn/n – G(n–1)/(n–1) are equaled. [ABSTRACT FROM AUTHOR]

Now that the chemistry of 1 : 1 host:guest complexes is well‐established, it is surprising to note that higher stoichiometry (oligomeric) complexes, especially those with excess host, remain largely unexplored. Yet, proteins tend to oligomerize, affording new functions for cell machinery. Here, we show that cucurbit[n]uril (CB[n]) macrocycles combined with symmetric, linear di‐viologens form unusual 3 : 2 host:guest complexes exhibiting remarkable dynamic properties, host self‐sorting, and external ring‐translocation. These results highlight the structural tunability of cucurbit[8]uril (CB[8]) based 3 : 2 host:guest complexes in water and their responsiveness toward several stimuli (chemicals, pH, redox). [ABSTRACT FROM AUTHOR]

The reaction mechanism of AlCl3 Lewis acid catalyzed acylation of pyrene with the methylacylium ion has been carried out at the ωB97X-D/6-311G(d,p) level within the Molecular Electron Density Theory (MEDT). Before completing this work, CDFT (Conceptual DFT) analysis allows the classification of both reactants as a nucleophile (pyrene) and super electrophile (methylacylium ion), respectively, permitting this acylation to take place with a polar character. This polar character has been supported by the high value of Global Electron Density Transfer (GEDT) recorded for each transition state. Concerning the bond changes, Bonding Evolution Theory (BET) analysis reveals that a series of four Structural Stability Domains (SSDs) are required to describe the formation of new C–C and H–Cl single bonds. For the formation of C–C single bond due to the attack of the methylacylium ion on pyrene, the first two stages correspond to (1) the creation of a pseudoradical center on both C carbon atoms (appearance of a V(C) basin) of each reactant and (2) the creation of a new C–C single bond via the merger of these two previous V(C) basins. Finally, the formation of a H–Cl molecule occurs via cleavage of an H–C bond (splitting of a V(H,C) basin) and the formation of a new H–Cl single bond (appearance of a new V(H,Cl) disynaptic basin), and the last step illustrates the restoration of the aromaticity of the ring engaged in the acylation reaction. [ABSTRACT FROM AUTHOR]

In order to discover new 31P NMR markers for probing subtle pH changes (<0.2 pH unit) in biological environments, fifteen new conformationally constrained or sterically hindered α-aminophosphonates derived from diethyl(2-methylpyrrolidin-2-yl)phosphonate were synthesized and tested for their pH reporting and cytotoxic properties in vitro. All compounds showed near-neutral pKas (ranging 6.28–6.97), chemical shifts not overlapping those of phosphorus metabolites, and spectroscopic sensitivities (i.e., chemical shifts variation Δδab between the acidic and basic forms) ranging from 9.2–10.7 ppm, being fourfold larger than conventional endogenous markers such as inorganic phosphate. X-ray crystallographic studies combined with predictive empirical relationships and ab initio calculations addressed the inductive and stereochemical effects of substituents linked to the protonated amine function. Satisfactory correlations were established between pKas and both the 2D structure and pyramidalization at phosphorus, showing that steric crowding around the phosphorus is crucial for modulating Δδab. Finally, the hit 31P NMR pH probe 1b bearing an unsubstituted 1,3,2-dioxaphosphorinane ring, which is moderately lipophilic, nontoxic on A549 and NHLF cells, and showing pKa = 6.45 with Δδab = 10.64 ppm, allowed the first clear-cut evidence of trans-sarcolemmal pH gradients in normoxic Dictyostelium discoideum cells with an accuracy of <0.05 pH units. [ABSTRACT FROM AUTHOR]

ESR spectra of cis-and trans-beta-diphosphorylated pyrrolidine-N-oxyl radicals, C-1 and t-1 were studied in liquid and frozen solution. The results reveal that the expected 1:2:1 triplet (ap(2)) of the !:1:1 triplet (a(sub n)) were observed for t-1, however for C-1, the inner lines of the 1:21 triplet showed a dramatic broadening characteristic of chemical exchange between two equivalent conformations.

The GenMol program was used to conduct molecular modeling computations to establish the relative effect of factors involved in cyclization preparation of linear precursor for cyclotetrapeptide synthesis. Computations of 4-Ala-chlamydocin, HC-toxin analogues, cyclotetrapeptides of sarcosine with glycine confirm transition-state energy, rather than the dimerization reaction, as the determining factor in ring-closure.