A wide array of systems, ranging from enzymes to synthetic catalysts, exert adaptive motifs to maximize their functionality. In a related manner, select metal-organic frameworks (MOFs) and related systems exhibit structural modulations under stimuli such as the infiltration of guest species. Probing their responsive behavior in-situ is a challenging but important step towards understanding their function and subsequently building from there. In this report, we investigate the dynamic behavior of an electrocatalytic Mn-porphyrin containing MOF system (Mn-MOF). We discover, using a combination of electrochemistry and in-situ probes of UV-Vis absorption, resonance Raman and infrared spectroscopy, a restructuration of this system via a reversible cleavage of the porphyrin carboxylate ligands under an applied voltage. We further show, by combining experimental data and DFT calculations, as a proof of concept, the capacity to utilize the Mn-MOF for electrochemical CO2 fixation and to spectroscopically capture the reaction intermediates in its catalytic cycle. The findings of this work and methodology developed opens opportunities in the application of MOFs as dynamic, enzyme-inspired electrocatalytic systems.

Benzoquinones can undergo reversible reductions and are attractive candidates for use as active materials in green carbon-based batteries. Related compounds of potential utility include 4,4′-diphenoquinones, which have extended quinonoid structures with two carbonyl groups in different rings. Diphenoquinones are a poorly explored class of compounds, but a wide variety can be synthesized, isolated, crystallized, and fully characterized. Experimental and computational approaches have established that typical 4,4′-diphenoquinones have nearly planar cores in which two cyclohexadienone rings are joined by an unusually long interannular CC bond. Derivatives unsubstituted at the 3,3′,5,5′-positions react readily by hydration, dimerization, and other processes. Association of diphenoquinones in the solid state normally produces chains or sheets held together by multiple C–H···O interactions, giving structures that differ markedly from those of the corresponding 4,4′-dihydroxybiphenyls. Electrochemical studies in solution and in the solid state show that diphenoquinones are reduced rapidly and reversibly at potentials higher than those of analogous benzoquinones. Together, these results help bring diphenoquinones into the mainstream of modern chemistry and provide a foundation for developing redox-active derivatives for use in carbon-based electrochemical devices.

The synthesis of rare macrocyclic alkynediyl sulfides by aC u-catalyzedC sp ÀSc ross-coupling is presented. The catalytic protocol (Cu(MeCN) 4 PF 6 /dtbbpy) promotes macrocyclization of peptides, dipeptides and tripeptides at ambient temperature (14 examples, 23!73 %y ields) via thiols and bromoalkynes, and is chemoselective with regardst ot erminal alkynes.I mportantly,t he underexplored alkynediyl sulfide functionality incorporates arigidifying structurale lement ando pens new opportunities for diversification of macrocyclic frameworks throughSo xidation, halide addition and azide-alkyne cycloaddition chemistries to integrate sulfones,h alideso rv aluablef luorophores (7 examples, 37!92 %y ields). Macrocycles offer au nique topology within chemical space. [1] Despite their large ring structures they can retain remarkable conformational bias with appropriate functionality present. Currentb ioactive macrocyclic drugs are almost exclusively derived from natural products, [2] yet synthetic macrocycles represent ag rowingc lass of drug candidates. Retrosynthetically,a macrocyclic precursor typically containsac ore from which extend appendages with functionality for cyclization. Upon formation of the macrocycle, the newly formed functionality is often referred to as the "linker". [3] Through the linker and macrocyclization,aconformation that is preferentialf or biological activity can be locked in, or alternatively,c onformers exhibiting unwanted side-effects can be locked out. [4] Consequently, the "linker" plays ac riticalr ole and is often modified systematically to examine its effects on activity.T he most common linkers exploit well-known functional group manipulations (Figure 1). Macrolactonization [5] via stoichiometrica ctivationo faseco-acid can be used to form ester-based linkers. Macrocyclic olefin metathesis, [6] now ac ommons trategy to form large rings was investigated by Ts uji in 1980 [7] andt he reactionw as first ap

Quinonoid compounds play central roles as redox-active agents in photosynthesis and respiration and are also promising replacements for inorganic materials currently used in batteries. To design new quinonoid compounds and predict their state of protonation and redox behavior under various conditions, their pK a values must be known. Methods that can predict the pK a values of simple phenols cannot reliably handle complex analogues in which multiple OH groups are present and may form intramolecular hydrogen bonds. We have therefore developed a straightforward method based on a linear relationship between experimental pK a values and calculated differences in energy between quinols and their deprotonated forms. Simple adjustments allow reliable predictions of pK a values when intramolecular hydrogen bonds are present. Our approach has been validated by showing that predicted and experimental values for over 100 quinols and related compounds differ by an average of only 0.3 units. This accuracy makes it possible to select proper pK a values when experimental data vary, predict the acidity of quinols and related compounds before they are made, and determine the sites and orders of deprotonation in complex structures with multiple OH groups.

6-Azidotetrazolo[5,1-a]phthalazine (ATPH) is a nitrogen-rich compound of surprisingly broad interest. It is purported to be a natural product, yet it is closely related to substances developed as explosives and is highly polymorphic despite having a nearly planar structure with little flexibility. Seven solid forms of ATPH have been characterized by single-crystal X-ray diffraction. The structures show diverse patterns of molecular organization, including both stacked sheets and herringbone packing. In all cases, N•••N and C−H•••N interactions play key roles in ensuring molecular cohesion. The high polymorphism of ATPH appears to arise in part from the ability of virtually every atom of nitrogen and hydrogen in the molecule to take part in close N•••N and C−H•••N contacts. As a result, adjacent molecules can adopt many different relative orientations that are energetically similar, thereby generating a polymorphic landscape with an unusually high density of potential structures. This landscape has been explored in detail by the computational prediction of crystal structures. Studying ATPH has provided insights into the field of energetic materials, where access to multiple polymorphs can be used to improve performance and clarify how it depends on molecular packing. In addition, our work with ATPH shows how valuable insights into molecular crystallization, often gleaned from statistical analyses of structural databases, can also come from indepth empirical and theoretical studies of single compounds that show distinctive behavior.

Benzoquinone and hydroquinone cocrystallize to form quinhydrone, a 1:1 complex with a characteristic structure in which the components are positioned by hydrogen bonds and charge-transfer interactions. We have found that analogous diphenoquinhydrones can be made by combining 4,4′-diphenoquinones with the corresponding 4,4′-dihydroxybiphenyls. In addition, mixed diphenoquinhydrones can be assembled from components with different substituents, and mismatched quinhydrones can be made from benzoquinones and dihydroxybiphenyls. In all cases, the components of the resulting structures are linked in alternation by O–H···O hydrogen bonds to form essentially planar chains, which stack to produce layers in which π-donors and π-acceptors are aligned by charge-transfer interactions. Geometric parameters, computational studies, and spectroscopic properties of diphenoquinhydrones show that the key intermolecular interactions are stronger than those in simple quinhydrone analogues. These findings demonstrate that the principles of modular construction underlying the formation of classical quinhydrones can be generalized to produce a broad range of hydrogen-bonded charge-transfer materials in which the components are positioned by design.

<p> A wide array of systems, ranging from enzymes to synthetic catalysts, exert adaptive motifs to maximize their functionality. In a related manner, select metal-organic frameworks (MOFs) and related systems exhibit structural modulations under stimuli such as the infiltration of guest species. Probing their responsive behavior <i>in-situ</i> is a challenging but important step towards understanding their function and subsequently building from there. In this report, we investigate the dynamic behavior of an electrocatalytic Mn-porphyrin containing MOF system (Mn-MOF). We discover, using a combination of electrochemistry and <i>in-situ</i> probes of UV-Vis absorption, resonance Raman and infrared spectroscopy, a restructuration of this system via a reversible cleavage of the porphyrin carboxylate ligands under an applied voltage. We further show, by combining experimental data and DFT calculations, as a proof of concept, the capacity to utilize the Mn-MOF for electrochemical CO₂ fixation and to spectroscopically capture the reaction intermediates in its catalytic cycle. The findings of this work and methodology developed opens opportunities in the application of MOFs as dynamic, enzyme-inspired electrocatalytic systems.</p>

Copper-catalyzed Csp–S cross-coupling is known to form rare macrocyclic alkynyl sulfides. Computational studies now suggest a mechanism for the reaction pathway. Upon formation of Cu–S species, subsequent α-addition/elimination at the ethynylic carbon affords the desired macrocycle.