Single-Molecule Observation of Intermediates in Bioorthogonal 2-Cyanobenzothiazole Chemistry

We report a single-molecule mechanistic investigation into 2-cyanobenzothiazole (CBT) chemistry within a protein nanoreactor. When simple thiols reacted reversibly with CBT, the thioimidate monoadduct was approximately 80-fold longer-lived than the tetrahedral bisadduct, with important implications for the design of molecular walkers. Irreversible condensation between CBT derivatives and N-terminal cysteine residues has been established as a biocompatible reaction for site-selective biomolecular labeling and imaging. During the reaction between CBT and aminothiols, we resolved two transient intermediates, the thioimidate and the cyclic precursor of the thiazoline product, and determined the rate constants associated with the stepwise condensation, thereby providing critical information for a variety of applications, including the covalent inhibition of protein targets and dynamic combinatorial chemistry.     

High Blocking Temperature of Magnetization and Giant Coercivity in the Azafullerene Tb2@C79N with a Single‐Electron Terbium–Terbium Bond

The azafullerene Tb₂@C₇₉N is found to be a single‐molecule magnet with a high 100‐s blocking temperature of magnetization of 24 K and large coercivity. Tb magnetic moments with an easy‐axis single‐ion magnetic anisotropy are strongly coupled by the unpaired spin of the single‐electron Tb?Tb bond. Relaxation of magnetization in Tb₂@C₇₉N below 15 K proceeds via quantum tunneling of magnetization with the characteristic time τ_QTM=16 462±1230 s. At higher temperature, relaxation follows the Orbach mechanism with a barrier of 757±4 K, corresponding to the excited states, in which one of the Tb spins is flipped.     

CO2-fixation into carbonate anions for the construction of 3d-4f cluster complexes with salen-type Schiff base ligands: from molecular magnetic refrigerants to luminescent single-molecule magnets

Six new carbonate-bridged Zn₂Ln₂ cluster complexes derived from salen-type Schiff base ligands [H₂L^a = N, N′-bis(3-methoxysalicylidene)-1,3-diaminopropane and H₂L^b = N, N′-bis(3-methoxysalicylidene)- 1,2-diaminoethane] have been synthesized. The bis-imine chain in Schiff base ligands have an obvious influence on the cluster complexes' structures, magnetic and luminescence properties. The carbonate bridging ligand exactly comes from autoimmobilization of carbon dioxide, which may mediate ferromagnetic coupling between Ln³⁺ ions, favoring magnetocaloric effects and single molecule magnet (SMM) properties. Complexes Zn₂Dy₂(μ³-CO₃)₂(L^a)₂(NO₃)₂(MeOH)₂ ( 1 ) and [Zn₂Dy₂(μ³-CO₃)₂(L^b)₂(NO₃)₂]·2MeOH ( 2) show field-induced SMM properties; complexes Zn₂Tb₂(μ³-CO₃)₂(L^a)₂(NO₃)₂(MeOH)₂ ( 3 ) and [Zn₂Tb₂(μ³-CO₃)₂(L^b)₂(NO₃)₂]·2MeOH ( 4 ) display both luminescence and field-induced SMM behaviors; while complexes [Zn₂Gd₂(μ³-CO₃)₂(L^a)₂(NO₃)₂]·2MeOH ( 5 ) and [Zn₂Gd₂(μ³-CO₃)₂(L^b)₂(NO₃)₂]·2MeOH ( 6 ) exhibit medium magnetic entropy changes, which are candidates for cryogenic molecular magnetic refrigerants.     

Reversible SC‐SC Transformation involving [4+4] Cycloaddition of Anthracene: A Single‐Ion to Single‐Molecule Magnet and Yellow‐Green to Blue‐White Emission

In search of magneto‐optic materials, the mononuclear compounds Ln^III(depma)(NO₃)₃(hmpa)₂ (Ln=Dy, Gd) were synthesized. The anthracene moieties undergo [4+4] dimerization when irradiated at 365 nm without loss of crystallinity. The Dy compound switches from a single‐ion to a single‐molecule magnet with doubling of the spin reversal barrier energy and from yellow‐green to blue‐white emission. The dimerization is reversed by heating at 100 °C or partially on light irradiating at 254 nm. The results suggest that lanthanide phosphonates with anthracene are promising smart materials displaying synergistic magneto‐optic property.     

Integrated Transmission Electron and Single‐Molecule Fluorescence Microscopy Correlates Reactivity with Ultrastructure in a Single Catalyst Particle

Establishing structure–activity relationships in complex, hierarchically structured nanomaterials, such as fluid catalytic cracking (FCC) catalysts, requires characterization with complementary, correlated analysis techniques. An integrated setup has been developed to perform transmission electron microscopy (TEM) and single‐molecule fluorescence (SMF) microscopy on such nanostructured samples. Correlated structure–reactivity information was obtained for 100 nm thin, microtomed sections of a single FCC catalyst particle using this novel SMF‐TEM high‐resolution combination. High reactivity in a thiophene oligomerization probe reaction correlated well with TEM‐derived zeolite locations, while matrix components, such as clay and amorphous binder material, were found not to display activity. Differences in fluorescence intensity were also observed within and between distinct zeolite aggregate domains, indicating that not all zeolite domains are equally active.     

Bioorthogonal Cycloadditions with Sub‐Millisecond Intermediates

Tetrazine‐ and sydnone‐based click reactions have emerged as important bioconjugation strategies with fast kinetics and N₂ or CO₂ as the only byproduct. Mechanistic studies of these reactions have focused on the initial rate‐determining cycloaddition steps. The subsequent N₂ or CO₂ release from the bicyclic intermediates has been approached mainly through computational studies, which have predicted lifetimes of femtoseconds. In the present study, bioorthogonal cycloadditions involving N₂ or CO₂ extrusion have been examined experimentally at the single‐molecule level by using a protein nanoreactor. At the resolution of this approach, the reactions appeared to occur in a single step, which places an upper limit on the lifetimes of the intermediates of about 80 μs, which is consistent with the computational work.     

Chemically-modified nanopores for sensing

Sensing with chemically-modified nanopores is an emerging field that is expected to have major impact on bioanalysis and fundamental understanding of nanoscale chemical interactions down to the single-molecule level. The main strength of nanopore sensing is that it implies the prospect of label-free single-molecule detection by taking advantage of the built-in transport-modulation-based amplification mechanism. At present, fabrication and application of solid-state nanopores are becoming the focus of attention because, compared with their biological counterparts, they offer greater flexibility in terms of shape, size, and surface properties, as well as superior robustness. A breakthrough in label-free nanopore sensing for real-world applications is therefore expected from implementing solid-state nanopores, an area that is still developing. Without claiming comprehensiveness, the focus of this review comprises recent results and trends in nanopore-based sensing (i.e. emerging technologies for fabricating solid-state nanopores, their chemical functionalization, and detection methods for quantitative analysis).     

In Situ Single‐Nanoparticle Spectroscopy Study of Bimetallic Nanostructure Formation

Bimetallic nanostructures (NSs), with utility in catalysis, are typically prepared using galvanic exchange (GE), but the final catalyst morphology is dictated by the dynamics of the process. In situ single nanoparticle (NP) optical scattering spectroscopy, coupled with ex situ electron microscopy, is used to capture the dynamic structural evolution of a bimetallic NS formed in a GE reaction between Ag and [PtCl₆]^2?. We identify an early stage involving anisotropic oxidation of Ag to AgCl concomitant with reductive deposition of small Pt clusters on the NS surface. At later stages of GE, unreacted Ag inclusions phase segregate from the overcoated AgCl as a result of lattice strain between Ag and AgCl. The nature of the structural evolution elucidates why multi‐domain Ag/AgCl/Pt NSs result from the GE process. The complex structural dynamics, determined from single‐NP trajectories, would be masked in ensemble studies due to heterogeneity in the response of different NPs.