@article{14664, abstract = {The architecture of self-assembled host molecules can profoundly affect the properties of the encapsulated guests. For example, a rigid cage with small windows can efficiently protect its contents from the environment; in contrast, tube-shaped, flexible hosts with large openings and an easily accessible cavity are ideally suited for catalysis. Here, we report a “Janus” nature of a Pd6L4 coordination host previously reported to exist exclusively as a tube isomer (T). We show that upon encapsulating various tetrahedrally shaped guests, T can reconfigure into a cage-shaped host (C) in quantitative yield. Extracting the guest affords empty C, which is metastable and spontaneously relaxes to T, and the T⇄C interconversion can be repeated for multiple cycles. Reversible toggling between two vastly different isomers paves the way toward controlling functional properties of coordination hosts “on demand”.}, author = {Hema, Kuntrapakam and Grommet, Angela B. and Białek, Michał J. and Wang, Jinhua and Schneider, Laura and Drechsler, Christoph and Yanshyna, Oksana and Diskin-Posner, Yael and Clever, Guido H. and Klajn, Rafal}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, number = {45}, pages = {24755--24764}, publisher = {American Chemical Society}, title = {{Guest encapsulation alters the thermodynamic landscape of a coordination host}}, doi = {10.1021/jacs.3c08666}, volume = {145}, year = {2023}, } @article{13095, abstract = {Disulfide bond formation is fundamentally important for protein structure and constitutes a key mechanism by which cells regulate the intracellular oxidation state. Peroxiredoxins (PRDXs) eliminate reactive oxygen species such as hydrogen peroxide through a catalytic cycle of Cys oxidation and reduction. Additionally, upon Cys oxidation PRDXs undergo extensive conformational rearrangements that may underlie their presently structurally poorly defined functions as molecular chaperones. Rearrangements include high molecular-weight oligomerization, the dynamics of which are, however, poorly understood, as is the impact of disulfide bond formation on these properties. Here we show that formation of disulfide bonds along the catalytic cycle induces extensive μs time scale dynamics, as monitored by magic-angle spinning NMR of the 216 kDa-large Tsa1 decameric assembly and solution-NMR of a designed dimeric mutant. We ascribe the conformational dynamics to structural frustration, resulting from conflicts between the disulfide-constrained reduction of mobility and the desire to fulfill other favorable contacts.}, author = {Troussicot, Laura and Vallet, Alicia and Molin, Mikael and Burmann, Björn M. and Schanda, Paul}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, number = {19}, pages = {10700–10711}, publisher = {American Chemical Society}, title = {{Disulfide-bond-induced structural frustration and dynamic disorder in a peroxiredoxin from MAS NMR}}, doi = {10.1021/jacs.3c01200}, volume = {145}, year = {2023}, } @article{13216, abstract = {Physical catalysts often have multiple sites where reactions can take place. One prominent example is single-atom alloys, where the reactive dopant atoms can preferentially locate in the bulk or at different sites on the surface of the nanoparticle. However, ab initio modeling of catalysts usually only considers one site of the catalyst, neglecting the effects of multiple sites. Here, nanoparticles of copper doped with single-atom rhodium or palladium are modeled for the dehydrogenation of propane. Single-atom alloy nanoparticles are simulated at 400–600 K, using machine learning potentials trained on density functional theory calculations, and then the occupation of different single-atom active sites is identified using a similarity kernel. Further, the turnover frequency for all possible sites is calculated for propane dehydrogenation to propene through microkinetic modeling using density functional theory calculations. The total turnover frequencies of the whole nanoparticle are then described from both the population and the individual turnover frequency of each site. Under operating conditions, rhodium as a dopant is found to almost exclusively occupy (111) surface sites while palladium as a dopant occupies a greater variety of facets. Undercoordinated dopant surface sites are found to tend to be more reactive for propane dehydrogenation compared to the (111) surface. It is found that considering the dynamics of the single-atom alloy nanoparticle has a profound effect on the calculated catalytic activity of single-atom alloys by several orders of magnitude.}, author = {Bunting, Rhys and Wodaczek, Felix and Torabi, Tina and Cheng, Bingqing}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, keywords = {Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis}, number = {27}, pages = {14894--14902}, publisher = {American Chemical Society}, title = {{Reactivity of single-atom alloy nanoparticles: Modeling the dehydrogenation of propane}}, doi = {10.1021/jacs.3c04030}, volume = {145}, year = {2023}, } @article{13354, abstract = {Integrating light-sensitive molecules within nanoparticle (NP) assemblies is an attractive approach to fabricate new photoresponsive nanomaterials. Here, we describe the concept of photocleavable anionic glue (PAG): small trianions capable of mediating interactions between (and inducing the aggregation of) cationic NPs by means of electrostatic interactions. Exposure to light converts PAGs into dianionic products incapable of maintaining the NPs in an assembled state, resulting in light-triggered disassembly of NP aggregates. To demonstrate the proof-of-concept, we work with an organic PAG incorporating the UV-cleavable o-nitrobenzyl moiety and an inorganic PAG, the photosensitive trioxalatocobaltate(III) complex, which absorbs light across the entire visible spectrum. Both PAGs were used to prepare either amorphous NP assemblies or regular superlattices with a long-range NP order. These NP aggregates disassembled rapidly upon light exposure for a specific time, which could be tuned by the incident light wavelength or the amount of PAG used. Selective excitation of the inorganic PAG in a system combining the two PAGs results in a photodecomposition product that deactivates the organic PAG, enabling nontrivial disassembly profiles under a single type of external stimulus.}, author = {Wang, Jinhua and Peled, Tzuf Shay and Klajn, Rafal}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, keywords = {Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis}, number = {7}, pages = {4098--4108}, publisher = {American Chemical Society}, title = {{Photocleavable anionic glues for light-responsive nanoparticle aggregates}}, doi = {10.1021/jacs.2c11973}, volume = {145}, year = {2023}, } @article{13348, abstract = {Molecular confinement effects can profoundly alter the physicochemical properties of the confined species. A plethora of organic molecules were encapsulated within the cavities of supramolecular hosts, and the impact of the cavity size and polarity was widely investigated. However, the extent to which the properties of the confined guests can be affected by the symmetry of the cage─which dictates the shape of the cavity─remains to be understood. Here we show that cage symmetry has a dramatic effect on the equilibrium between two isomers of the encapsulated spiropyran guests. Working with two Pd-based coordination cages featuring similarly sized but differently shaped hydrophobic cavities, we found a highly selective stabilization of the isomer whose shape matches that of the cavity of the cage. A Td-symmetric cage stabilized the spiropyrans’ colorless form and rendered them photochemically inert. In contrast, a D2h-symmetric cage favored the colored isomer, while maintaining reversible photoswitching between the two states of the encapsulated spiropyrans. We also show that the switching kinetics strongly depend on the substitution pattern on the spiropyran scaffold. This finding was used to fabricate a time-sensitive information storage medium with tunable lifetimes of the encoded messages.}, author = {Wang, Jinhua and Avram, Liat and Diskin-Posner, Yael and Białek, Michał J. and Stawski, Wojciech and Feller, Moran and Klajn, Rafal}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, keywords = {Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis}, number = {46}, pages = {21244--21254}, publisher = {American Chemical Society}, title = {{Altering the properties of spiropyran switches using coordination cages with different symmetries}}, doi = {10.1021/jacs.2c08901}, volume = {144}, year = {2022}, } @article{13362, abstract = {Aggregation of organic molecules can drastically affect their physicochemical properties. For instance, the optical properties of BODIPY dyes are inherently related to the degree of aggregation and the mutual orientation of BODIPY units within these aggregates. Whereas the noncovalent aggregation of various BODIPY dyes has been studied in diverse media, the ill-defined nature of these aggregates has made it difficult to elucidate the structure–property relationships. Here, we studied the encapsulation of three structurally simple BODIPY derivatives within the hydrophobic cavity of a water-soluble, flexible PdII6L4 coordination cage. The cavity size allowed for the selective encapsulation of two dye molecules, irrespective of the substitution pattern on the BODIPY core. Working with a model, a pentamethyl-substituted derivative, we found that the mutual orientation of two BODIPY units in the cage’s cavity was remarkably similar to that in the crystalline state of the free dye, allowing us to isolate and characterize the smallest possible noncovalent H-type BODIPY aggregate, namely, an H-dimer. Interestingly, a CF3-substituted BODIPY, known for forming J-type aggregates, was also encapsulated as an H-dimer. Taking advantage of the dynamic nature of encapsulation, we developed a system in which reversible switching between H- and J-aggregates can be induced for multiple cycles simply by addition and subsequent destruction of the cage. We expect that the ability to rapidly and reversibly manipulate the optical properties of supramolecular inclusion complexes in aqueous media will open up avenues for developing detection systems that operate within biological environments.}, author = {Gemen, Julius and Ahrens, Johannes and Shimon, Linda J. W. and Klajn, Rafal}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, keywords = {Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis}, number = {41}, pages = {17721--17729}, publisher = {American Chemical Society}, title = {{Modulating the optical properties of BODIPY dyes by noncovalent dimerization within a flexible coordination cage}}, doi = {10.1021/jacs.0c08589}, volume = {142}, year = {2020}, } @article{13364, abstract = {Photochromic molecules undergo reversible isomerization upon irradiation with light at different wavelengths, a process that can alter their physical and chemical properties. For instance, dihydropyrene (DHP) is a deep-colored compound that isomerizes to light-brown cyclophanediene (CPD) upon irradiation with visible light. CPD can then isomerize back to DHP upon irradiation with UV light or thermally in the dark. Conversion between DHP and CPD is thought to proceed via a biradical intermediate; bimolecular events involving this unstable intermediate thus result in rapid decomposition and poor cycling performance. Here, we show that the reversible isomerization of DHP can be stabilized upon confinement within a PdII6L4 coordination cage. By protecting this reactive intermediate using the cage, each isomerization reaction proceeds to higher yield, which significantly decreases the fatigue experienced by the system upon repeated photocycling. Although molecular confinement is known to help stabilize reactive species, this effect is not typically employed to protect reactive intermediates and thus improve reaction yields. We envisage that performing reactions under confinement will not only improve the cyclic performance of photochromic molecules, but may also increase the amount of product obtainable from traditionally low-yielding organic reactions.}, author = {Canton, Martina and Grommet, Angela B. and Pesce, Luca and Gemen, Julius and Li, Shiming and Diskin-Posner, Yael and Credi, Alberto and Pavan, Giovanni M. and Andréasson, Joakim and Klajn, Rafal}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, keywords = {Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis}, number = {34}, pages = {14557--14565}, publisher = {American Chemical Society}, title = {{Improving fatigue resistance of dihydropyrene by encapsulation within a coordination cage}}, doi = {10.1021/jacs.0c06146}, volume = {142}, year = {2020}, } @article{13365, abstract = {Photoswitchable molecules are employed for many applications, from the development of active materials to the design of stimuli-responsive molecular systems and light-powered molecular machines. To fully exploit their potential, we must learn ways to control the mechanism and kinetics of their photoinduced isomerization. One possible strategy involves confinement of photoresponsive switches such as azobenzenes or spiropyrans within crowded molecular environments, which may allow control over their light-induced conversion. However, the molecular factors that influence and control the switching process under realistic conditions and within dynamic molecular regimes often remain difficult to ascertain. As a case study, here we have employed molecular models to probe the isomerization of azobenzene guests within a Pd(II)-based coordination cage host in water. Atomistic molecular dynamics and metadynamics simulations allow us to characterize the flexibility of the cage in the solvent, the (rare) guest encapsulation and release events, and the relative probability/kinetics of light-induced isomerization of azobenzene analogues in these host–guest systems. In this way, we can reconstruct the mechanism of azobenzene switching inside the cage cavity and explore key molecular factors that may control this event. We obtain a molecular-level insight on the effects of crowding and host–guest interactions on azobenzene isomerization. The detailed picture elucidated by this study may enable the rational design of photoswitchable systems whose reactivity can be controlled via host–guest interactions.}, author = {Pesce, Luca and Perego, Claudio and Grommet, Angela B. and Klajn, Rafal and Pavan, Giovanni M.}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, keywords = {Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis}, number = {21}, pages = {9792--9802}, publisher = {American Chemical Society}, title = {{Molecular factors controlling the isomerization of Azobenzenes in the cavity of a flexible coordination cage}}, doi = {10.1021/jacs.0c03444}, volume = {142}, year = {2020}, } @article{11978, abstract = {Dual photocatalysis and nickel catalysis can effect cross-coupling under mild conditions, but little is known about the in situ kinetics of this class of reactions. We report a comprehensive kinetic examination of a model carboxylate O-arylation, comparing a state-of-the-art homogeneous photocatalyst (Ir(ppy)3) with a competitive heterogeneous photocatalyst (graphitic carbon nitride). Experimental conditions were adjusted such that the nickel catalytic cycle is saturated with excited photocatalyst. This approach was designed to remove the role of the photocatalyst, by which only the intrinsic behaviors of the nickel catalytic cycles are observed. The two reactions did not display identical kinetics. Ir(ppy)3 deactivates the nickel catalytic cycle and creates more dehalogenated side product. Kinetic data for the reaction using Ir(ppy)3 supports a turnover-limiting reductive elimination. Graphitic carbon nitride gave higher selectivity, even at high photocatalyst-to-nickel ratios. The heterogeneous reaction also showed a rate dependence on aryl halide, indicating that oxidative addition plays a role in rate determination. The results argue against the current mechanistic hypothesis, which states that the photocatalyst is only involved to trigger reductive elimination.}, author = {Malik, Jamal A. and Madani, Amiera and Pieber, Bartholomäus and Seeberger, Peter H.}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, number = {25}, pages = {11042--11049}, publisher = {American Chemical Society}, title = {{Evidence for photocatalyst involvement in oxidative additions of nickel-catalyzed carboxylate O-arylations}}, doi = {10.1021/jacs.0c02848}, volume = {142}, year = {2020}, } @article{8408, abstract = {Aromatic residues are located at structurally important sites of many proteins. Probing their interactions and dynamics can provide important functional insight but is challenging in large proteins. Here, we introduce approaches to characterize dynamics of phenylalanine residues using 1H-detected fast magic-angle spinning (MAS) NMR combined with a tailored isotope-labeling scheme. Our approach yields isolated two-spin systems that are ideally suited for artefact-free dynamics measurements, and allows probing motions effectively without molecular-weight limitations. The application to the TET2 enzyme assembly of ~0.5 MDa size, the currently largest protein assigned by MAS NMR, provides insights into motions occurring on a wide range of time scales (ps-ms). We quantitatively probe ring flip motions, and show the temperature dependence by MAS NMR measurements down to 100 K. Interestingly, favorable line widths are observed down to 100 K, with potential implications for DNP NMR. Furthermore, we report the first 13C R1ρ MAS NMR relaxation-dispersion measurements and detect structural excursions occurring on a microsecond time scale in the entry pore to the catalytic chamber and at a trimer interface that was proposed as exit pore. We show that the labeling scheme with deuteration at ca. 50 kHz MAS provides superior resolution compared to 100 kHz MAS experiments with protonated, uniformly 13C-labeled samples.}, author = {Gauto, Diego F. and Macek, Pavel and Barducci, Alessandro and Fraga, Hugo and Hessel, Audrey and Terauchi, Tsutomu and Gajan, David and Miyanoiri, Yohei and Boisbouvier, Jerome and Lichtenecker, Roman and Kainosho, Masatsune and Schanda, Paul}, issn = {0002-7863}, journal = {Journal of the American Chemical Society}, keywords = {Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis}, number = {28}, pages = {11183--11195}, publisher = {American Chemical Society}, title = {{Aromatic ring dynamics, thermal activation, and transient conformations of a 468 kDa enzyme by specific 1H–13C labeling and fast magic-angle spinning NMR}}, doi = {10.1021/jacs.9b04219}, volume = {141}, year = {2019}, } @article{8413, abstract = {NMR relaxation dispersion methods provide a holistic way to observe microsecond time-scale protein backbone motion both in solution and in the solid state. Different nuclei (1H and 15N) and different relaxation dispersion techniques (Bloch–McConnell and near-rotary-resonance) give complementary information about the amplitudes and time scales of the conformational dynamics and provide comprehensive insights into the mechanistic details of the structural rearrangements. In this paper, we exemplify the benefits of the combination of various solution- and solid-state relaxation dispersion methods on a microcrystalline protein (α-spectrin SH3 domain), for which we are able to identify and model the functionally relevant conformational rearrangements around the ligand recognition loop occurring on multiple microsecond time scales. The observed loop motions suggest that the SH3 domain exists in a binding-competent conformation in dynamic equilibrium with a sterically impaired ground-state conformation both in solution and in crystalline form. This inherent plasticity between the interconverting macrostates is compatible with a conformational-preselection model and provides new insights into the recognition mechanisms of SH3 domains.}, author = {Rovó, Petra and Smith, Colin A. and Gauto, Diego and de Groot, Bert L. and Schanda, Paul and Linser, Rasmus}, issn = {0002-7863}, journal = {Journal of the American Chemical Society}, keywords = {Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis}, number = {2}, pages = {858--869}, publisher = {American Chemical Society}, title = {{Mechanistic insights into microsecond time-scale motion of solid proteins using complementary 15N and 1H relaxation dispersion techniques}}, doi = {10.1021/jacs.8b09258}, volume = {141}, year = {2019}, } @article{6586, abstract = {The bottom-up assembly of colloidal nanocrystals is a versatile methodology to produce composite nanomaterials with precisely tuned electronic properties. Beyond the synthetic control over crystal domain size, shape, crystal phase, and composition, solution-processed nanocrystals allow exquisite surface engineering. This provides additional means to modulate the nanomaterial characteristics and particularly its electronic transport properties. For instance, inorganic surface ligands can be used to tune the type and concentration of majority carriers or to modify the electronic band structure. Herein, we report the thermoelectric properties of SnTe nanocomposites obtained from the consolidation of surface-engineered SnTe nanocrystals into macroscopic pellets. A CdSe-based ligand is selected to (i) converge the light and heavy bands through partial Cd alloying and (ii) generate CdSe nanoinclusions as a secondary phase within the SnTe matrix, thereby reducing the thermal conductivity. These SnTe-CdSe nanocomposites possess thermoelectric figures of merit of up to 1.3 at 850 K, which is, to the best of our knowledge, the highest thermoelectric figure of merit reported for solution-processed SnTe.}, author = {Ibáñez, Maria and Hasler, Roger and Genç, Aziz and Liu, Yu and Kuster, Beatrice and Schuster, Maximilian and Dobrozhan, Oleksandr and Cadavid, Doris and Arbiol, Jordi and Cabot, Andreu and Kovalenko, Maksym V.}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, number = {20}, pages = {8025--8029}, publisher = {American Chemical Society}, title = {{Ligand-mediated band engineering in bottom-up assembled SnTe nanocomposites for thermoelectric energy conversion}}, doi = {10.1021/jacs.9b01394}, volume = {141}, year = {2019}, } @article{13373, abstract = {The reversible photoisomerization of azobenzene has been utilized to construct a plethora of systems in which optical, electronic, catalytic, and other properties can be controlled by light. However, owing to azobenzene’s hydrophobic nature, most of these examples have been realized only in organic solvents, and systems operating in water are relatively scarce. Here, we show that by coadsorbing the inherently hydrophobic azobenzenes with water-solubilizing ligands on the same nanoparticulate platforms, it is possible to render them essentially water-soluble. To this end, we developed a modified nanoparticle functionalization procedure allowing us to precisely fine-tune the amount of azobenzene on the functionalized nanoparticles. Molecular dynamics simulations helped us to identify two distinct supramolecular architectures (depending on the length of the background ligand) on these nanoparticles, which can explain their excellent aqueous solubilities. Azobenzenes adsorbed on these water-soluble nanoparticles exhibit highly reversible photoisomerization upon exposure to UV and visible light. Importantly, the mixed-monolayer approach allowed us to systematically investigate how the background ligand affects the switching properties of azobenzene. We found that the nature of the background ligand has a profound effect on the kinetics of azobenzene switching. For example, a hydroxy-terminated background ligand is capable of accelerating the back-isomerization reaction by more than 6000-fold. These results pave the way toward the development of novel light-responsive nanomaterials operating in aqueous media and, in the long run, in biological environments.}, author = {Chu, Zonglin and Han, Yanxiao and Bian, Tong and De, Soumen and Král, Petr and Klajn, Rafal}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, keywords = {Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis}, number = {5}, pages = {1949--1960}, publisher = {American Chemical Society}, title = {{Supramolecular control of azobenzene switching on nanoparticles}}, doi = {10.1021/jacs.8b09638}, volume = {141}, year = {2019}, } @article{13380, abstract = {Although dissipative self-assembly is ubiquitous in nature, where it gives rise to structures and functions critical to life, examples of artificial systems featuring this mode of self-assembly are rare. Here, we identify the presence of ephemeral assemblies during seeded growth of gold nanoparticles. In this process, hydrazine reduces Au(III) ions, which attach to the existing nanoparticles “seeds”. The attachment is accompanied by a local increase in the concentration of a surfactant, which therefore forms a bilayer on nanoparticle surfaces, inducing their assembly. The resulting aggregates gradually disassemble as the surfactant concentration throughout the solution equilibrates. The lifetimes of the out-of-equilibrium aggregates depend on and can be controlled by the size of the constituent nanoparticles. We demonstrate the utility of our out-of-equilibrium aggregates to form transient reflective coatings on polar surfaces.}, author = {Sawczyk, Michał and Klajn, Rafal}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, keywords = {Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis}, number = {49}, pages = {17973--17978}, publisher = {American Chemical Society}, title = {{Out-of-equilibrium aggregates and coatings during seeded growth of metallic nanoparticles}}, doi = {10.1021/jacs.7b09111}, volume = {139}, year = {2017}, } @article{8458, abstract = {The maintenance of bacterial cell shape and integrity is largely attributed to peptidoglycan, a highly cross-linked biopolymer. The transpeptidases that perform this cross-linking are important targets for antibiotics. Despite this biomedical importance, to date no structure of a protein in complex with an intact bacterial peptidoglycan has been resolved, primarily due to the large size and flexibility of peptidoglycan sacculi. Here we use solid-state NMR spectroscopy to derive for the first time an atomic model of an l,d-transpeptidase from Bacillus subtilis bound to its natural substrate, the intact B. subtilis peptidoglycan. Importantly, the model obtained from protein chemical shift perturbation data shows that both domains—the catalytic domain as well as the proposed peptidoglycan recognition domain—are important for the interaction and reveals a novel binding motif that involves residues outside of the classical enzymatic pocket. Experiments on mutants and truncated protein constructs independently confirm the binding site and the implication of both domains. Through measurements of dipolar-coupling derived order parameters of bond motion we show that protein binding reduces the flexibility of peptidoglycan. This first report of an atomic model of a protein–peptidoglycan complex paves the way for the design of new antibiotic drugs targeting l,d-transpeptidases. The strategy developed here can be extended to the study of a large variety of enzymes involved in peptidoglycan morphogenesis.}, author = {Schanda, Paul and Triboulet, Sébastien and Laguri, Cédric and Bougault, Catherine M. and Ayala, Isabel and Callon, Morgane and Arthur, Michel and Simorre, Jean-Pierre}, issn = {0002-7863}, journal = {Journal of the American Chemical Society}, number = {51}, pages = {17852--17860}, publisher = {American Chemical Society}, title = {{Atomic model of a cell-wall cross-linking enzyme in complex with an intact bacterial peptidoglycan}}, doi = {10.1021/ja5105987}, volume = {136}, year = {2014}, } @article{13401, abstract = {A compound combining the features of a molecular rotor and a photoswitch was synthesized and was shown to exist as three diastereomers, which interconvert via a reversible cyclic reaction scheme. Each of the three diastereomers was isolated, and by following the equilibration kinetics, activation barriers for all reactions were calculated. The results indicate that the properties of molecular switches depend heavily on their immediate chemical environment. The conclusions are important in the context of designing new switchable molecules and materials.}, author = {Kundu, Pintu K. and Lerner, Avishai and Kučanda, Kristina and Leitus, Gregory and Klajn, Rafal}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, keywords = {Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis}, number = {32}, pages = {11276--11279}, publisher = {American Chemical Society}, title = {{Cyclic kinetics during thermal equilibration of an axially chiral bis-spiropyran}}, doi = {10.1021/ja505948q}, volume = {136}, year = {2014}, } @article{13403, abstract = {We show that bimolecular reactions between species confined to the surfaces of nanoparticles can be manipulated by the nature of the linker, as well as by the curvature of the underlying particles.}, author = {Zdobinsky, Tino and Sankar Maiti, Pradipta and Klajn, Rafal}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, keywords = {Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis}, number = {7}, pages = {2711--2714}, publisher = {American Chemical Society}, title = {{Support curvature and conformational freedom control chemical reactivity of immobilized species}}, doi = {10.1021/ja411573a}, volume = {136}, year = {2014}, } @article{8465, abstract = {We demonstrate that conformational exchange processes in proteins on microsecond-to-millisecond time scales can be detected and quantified by solid-state NMR spectroscopy. We show two independent approaches that measure the effect of conformational exchange on transverse relaxation parameters, namely Carr–Purcell–Meiboom–Gill relaxation-dispersion experiments and measurement of differential multiple-quantum coherence decay. Long coherence lifetimes, as required for these experiments, are achieved by the use of highly deuterated samples and fast magic-angle spinning. The usefulness of the approaches is demonstrated by application to microcrystalline ubiquitin. We detect a conformational exchange process in a region of the protein for which dynamics have also been observed in solution. Interestingly, quantitative analysis of the data reveals that the exchange process is more than 1 order of magnitude slower than in solution, and this points to the impact of the crystalline environment on free energy barriers.}, author = {Tollinger, Martin and Sivertsen, Astrid C. and Meier, Beat H. and Ernst, Matthias and Schanda, Paul}, issn = {0002-7863}, journal = {Journal of the American Chemical Society}, number = {36}, pages = {14800--14807}, publisher = {American Chemical Society}, title = {{Site-resolved measurement of microsecond-to-millisecond conformational-exchange processes in proteins by solid-state NMR spectroscopy}}, doi = {10.1021/ja303591y}, volume = {134}, year = {2012}, } @article{8466, abstract = {Recent advances in NMR spectroscopy and the availability of high magnetic field strengths now offer the possibility to record real-time 3D NMR spectra of short-lived protein states, e.g., states that become transiently populated during protein folding. Here we present a strategy for obtaining sequential NMR assignments as well as atom-resolved information on structural and dynamic features within a folding intermediate of the amyloidogenic protein β2-microglobulin that has a half-lifetime of only 20 min.}, author = {Rennella, Enrico and Cutuil, Thomas and Schanda, Paul and Ayala, Isabel and Forge, Vincent and Brutscher, Bernhard}, issn = {0002-7863}, journal = {Journal of the American Chemical Society}, number = {19}, pages = {8066--8069}, publisher = {American Chemical Society}, title = {{Real-time NMR characterization of structure and dynamics in a transiently populated protein folding intermediate}}, doi = {10.1021/ja302598j}, volume = {134}, year = {2012}, } @article{7308, abstract = {Carbon has been used widely as the basis of porous cathodes for nonaqueous Li–O2 cells. However, the stability of carbon and the effect of carbon on electrolyte decomposition in such cells are complex and depend on the hydrophobicity/hydrophilicity of the carbon surface. Analyzing carbon cathodes, cycled in Li–O2 cells between 2 and 4 V, using acid treatment and Fenton’s reagent, and combined with differential electrochemical mass spectrometry and FTIR, demonstrates the following: Carbon is relatively stable below 3.5 V (vs Li/Li+) on discharge or charge, especially so for hydrophobic carbon, but is unstable on charging above 3.5 V (in the presence of Li2O2), oxidatively decomposing to form Li2CO3. Direct chemical reaction with Li2O2 accounts for only a small proportion of the total carbon decomposition on cycling. Carbon promotes electrolyte decomposition during discharge and charge in a Li–O2 cell, giving rise to Li2CO3 and Li carboxylates (DMSO and tetraglyme electrolytes). The Li2CO3 and Li carboxylates present at the end of discharge and those that form on charge result in polarization on the subsequent charge. Li2CO3 (derived from carbon and from the electrolyte) as well as the Li carboxylates (derived from the electrolyte) decompose and form on charging. Oxidation of Li2CO3 on charging to ∼4 V is incomplete; Li2CO3 accumulates on cycling resulting in electrode passivation and capacity fading. Hydrophilic carbon is less stable and more catalytically active toward electrolyte decomposition than carbon with a hydrophobic surface. If the Li–O2 cell could be charged at or below 3.5 V, then carbon may be relatively stable, however, its ability to promote electrolyte decomposition, presenting problems for its use in a practical Li–O2 battery. The results emphasize that stable cycling of Li2O2 at the cathode in a Li–O2 cell depends on the synergy between electrolyte and electrode; the stability of the electrode and the electrolyte cannot be considered in isolation.}, author = {Ottakam Thotiyl, Muhammed M. and Freunberger, Stefan Alexander and Peng, Zhangquan and Bruce, Peter G.}, issn = {0002-7863}, journal = {Journal of the American Chemical Society}, number = {1}, pages = {494--500}, publisher = {ACS}, title = {{The carbon electrode in nonaqueous Li–O2 cells}}, doi = {10.1021/ja310258x}, volume = {135}, year = {2012}, }