Survival of the fittest: Self‐assemblies made of dynamic block copolymers (dynablocks) can self‐replicate by catalyzing the formation of their own building blocks. Moreover, in competition ...experiments, the differential thermodynamic stabilities and autocatalytic efficiencies of these self‐assemblies lead to sigmoid growth of the most efficient self‐replicator and to depletion of its competitors.
The spontaneous self‐assembly of a neutral circular trinuclear TiIV‐based helicate is described through the reaction of titanium(IV) isopropoxide with a rationally designed tetraphenolic ligand. The ...trimeric ring helicate was obtained after diffusion of n‐pentane into a solution with dichloromethane. The circular helicate has been characterized by using single‐crystal X‐ray diffraction study, 13C CP‐MAS NMR and 1H NMR DOSY solution spectroscopic, and positive electrospray ionization mass‐spectrometric analysis. These analytical data were compared with those obtained from a previously reported double‐stranded helicate that crystallizes in toluene. The trimeric ring was unstable in a pure solution with dichloromethane and transformed into the double‐stranded helicate. Thermodynamic analysis by means of the PACHA software revealed that formation of the double‐stranded helicates was characterized by ΔH(toluene)=−30 kJ mol−1 and ΔS(toluene)=+357 J K−1 mol−1, whereas these values were ΔH(CH2Cl2)=−75 kJ mol−1 and ΔS(CH2Cl2)=−37 J K−1 mol−1 for the ring helicate. The transformation of the ring helicate into the double‐stranded helicate was a strongly endothermic process characterized by ΔH(CH2Cl2)=+127 kJ mol−1 and ΔH(n‐pentane)=+644 kJ mol−1 associated with a large positive entropy change ΔS=+1115 J K−1⋅mol−1. Consequently, the instability of the ring helicate in pure dichloromethane was attributed to the rather high dielectric constant and dipole moment of dichloromethane relative to n‐pentane. Suggestions for increasing the stability of the ring helicate are given.
The spontaneous self‐assembly of a neutral circular trinuclear TiIV‐based helicate is described. Crystals of this trimeric ring helicate were obtained after diffusion of n‐pentane into a solution of the sample in dichloromethane. This architecture contrasts with the double‐stranded helicate that crystallizes in toluene. The trimeric ring was unstable in a pure solution with dichloromethane and transformed into the double‐stranded helicate (see picture).
The design and synthesis of a new type of receptor based on a 3rotaxane, consisting of one thread and two threaded rings, is reported, as well as some of its complexing properties toward given ...guests. Two rings rigidly attached to porphyrins are threaded by a stiff rod incorporating two 2,2′-bipyridine-like chelates, the threading process being driven by two Cu(I) atoms acting as templates. A double-stoppering reaction based on click chemistry leads to the copper-complexed 3rotaxane in which the rings are located close to the central part of the thread and the distance between the two porphyrin plates is short. Removal of the two Cu(I) cations releases the two rings which are now free to move along and around the thread. In these two states of the 3rotaxane, free and complexed with copper, the two zinc(II) porphyrins attached to the rings can bind different ditopic guests bearing pyridyl groups or amines as terminal functions. UV−visible and NMR DOSY experiments were realized with guests of different sizes, and the association constants were determined. The free 3rotaxane is both a strong and highly adaptable receptor with high stability constants for the host/guest complexes, log K being in the range of 6.3−7.5 for guests with a length varying between 2.8 and 18 Å. The copper-complexed 3rotaxane is still a good receptor for small guests due to an entropic gain for this preorganized molecule compared to the free 3rotaxane, but it is a less strong receptor for guests which do not fit the short distance between the two porphyrins.
The translational diffusion coefficients of various helicates have been determined by using NMR diffusion spectroscopy (Diffusion Ordered SpectroscopY, DOSY), in order to investigate the individual ...behaviour of the helicates according to their length (different nuclearities; 1–5 metals), to the nature of the metal involved (CuI or AgI), as well to their bulkiness due to the presence of substituents on the periphery of the assembly. Furthermore, the spectrum of a mixture of helicates belonging to the same series, but with different lengths and nuclearities, showed the signals of each component, with no observable cross‐linking, confirming the self‐recognition properties of the helicates.
Les coefficients de diffusion translationnelle de plusieurs groupes d'hélicates à double brin ont été mesurés par RMN DOSY (Diffusion Ordered SpectroscopY), en faisant varier leur nucléarité dans une même série, les métaux impliqués (CuI ou AgI), ainsi que leur encombrement stérique par adjonction de substituants à la périphérie. De plus, en analysant un mélange d'hélicates de même famille, mais de longueurs différentes, aucune espèce hybride n'est observée, confirmant ainsi la propriété d'auto‐reconnaissance de ces assemblages.
Know thyself! A series of double helicates were investigated by using 1H NMR DOSY (Diffusion Ordered SpectroscopY) experiments. The spectrum of a mixture of five CuI helicates of the same series, but different in length (see figure), showed the signals of each component with no observable cross‐linking, confirming the self‐recognition properties of the helicates.
Diffusion ordered spectroscopy (DOSY) NMR experiments have been used to characterize a dynamic combinatorial library of helical strands and grid‐type metallosupramolecular architectures. The ...technique allows the deconvolution of very similar chemical structures differing only by their hydrodynamic radius. Moreover, the occurrence of springlike, extension–contraction conformational motions in helical strands can be revealed as a function of the temperature.
A binuclear Ti(IV)-based helicate synthesized from a symmetric tetrahydroxyheptaphenylene strand was self-assembled in solution and shown to undergo a spontaneous head-to-tail differentiation ...according to single-crystal X-ray diffraction.
An Eglinton–Galbraith diethyne cyclization preferentially yielded a structurally unusual macrocycle, comprising a strained conjugated oligo2cruciform wire, forced into a 2.2 nm bow‐shape by a ...terpyridine rein or tether, and stabilized towards light and heat by four insulating triisopropylsilylacetylene (TIPSA) substituents. Spectroscopic ion‐binding studies revealed the macrocycle to exhibit a particularly high UV/Vis selectivity for PdII in dilute solution, and one of its precursors to afford a variety of luminescence quenching and color responses to particular metals, suggestive of promising ion‐sensor applications. Under more concentrated conditions, the new macrocycle is able to bind specific metals (e.g., AuI) within its cavity despite the steric constraints. Intriguingly, variable‐temperature (VT) UV/Vis/1H NMR investigations showed the TIPSA substituents to undergo restricted intramolecular motions along with reversible changes in the spectroscopic bandgap of the compound with temperature. In line with the theoretical calculations, the VT UV/Vis observations are consistent with a thermal modulation of the electronic conjugation through the strained oligo2cruciform bridge, which is coupled with redistributions within a mixture of conformational isomers of the macrocycle with differing relative twisting between the TIPSA‐substituted phenyl rings. Overall, the generation of a para‐oligo2cruciform, bent and flexed over nanoscopic dimensions through conformational tethering within the macrocyclic ring is noteworthy, and suggests a general approach to nanosized, curved, and strained, yet heat‐ and light‐stable, para‐phenyleneethynylene oligomers with unique physicochemical properties and challenging theoretical possibilities.
Reining in the strain: An Eglinton–Galbraith diethyne cyclization yielded an unusual bow‐shaped cycle (see scheme), incorporating a strained yet stable conjugated oligo2cruciform wire, bent over nanoscopic dimensions by a terpyridine tether. As well as spectroscopically sensing metal ions, it undergoes thermo‐controllable bandgap changes in solution, consistent with hindered relative twisting of the substituted phenyl rings, thus functioning as an environmentally adaptive conjugation switch.
A decision‐making capsule! Where cation trafficking comes to a halt is predetermined, with the process corresponding to a “nano‐ion chromatograph” in action: starting from pores the route may end in ...a finely sculpturable interior of a stable, soluble spherical capsule but in many cases it ends in between in channels that exhibit a variety of cation‐capturing functionalities at different positions (one of the twenty channels is shown with the residing cations).
Harte Konkurrenz: Aggregate aus Copolymeren mit dynamischen Blöcken (Dynablocks) können sich selbst replizieren, indem sie die Bildung ihrer eigenen Bausteine katalysieren. In Konkurrenzexperimenten ...führen die unterschiedlichen thermodynamischen Stabilitäten und Autokatalyseeffizienzen dieser Aggregate zu sigmoidalem Wachstum des effizientesten Selbstreplikators unter gleichzeitiger Abreicherung seiner Konkurrenten.
IspH/LytB, an oxygen‐sensitive 4Fe‐4S enzyme, catalyzes the last step of the methylerythritol phosphate (MEP) pathway, a target for the development of new antimicrobial agents. This metalloenzyme ...converts (E)‐4‐hydroxy‐3‐methylbut‐2‐en‐1‐yl diphosphate (HMBPP) into the two isoprenoid precursors: isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). Here, the synthesis of (S)‐4‐2H1HMBPP and (R)‐4‐2H1HMBPP is reported together with a detailed NMR analysis of the products formed after their respective incubation with E. coli IspH/LytB in the presence of the biological reduction system used by E. coli to reduce the 4Fe‐4S center. (S)‐4‐2H1HMBPP was converted into 4‐2H1DMAPP and (E)‐4‐2H1IPP, whereas (R)‐4‐2H1HMBPP yielded 4‐2H1DMAPP and (Z)‐4‐2H1IPP, hence providing the direct enzymatic evidence that the mechanism catalyzed by IspH/LytB involves a rotation of the CH2OH group of the substrate to display it away from the 4Fe‐4S.
A reductive dehydroxylation is catalyzed by IspH/LytB, a 4Fe‐4S enzyme target for the development of innovative antibacterial agents. The missing enzymatic evidence in the investigation of a rotation of the CH2OH group of the substrate in the catalytic mechanism of this enzyme is provided after synthesis of deuterium‐labeled stereoisomers of the substrate followed by the analysis of the products by several NMR methodologies.
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