A redox switch allows binding of Fe(II) and Fe(III) ions in the cyanobacterial iron-binding protein FutA from Prochlorococcus.

The marine cyanobacterium Prochlorococcus is a main contributor to global photosynthesis, whilst being limited by iron availability. Cyanobacterial genomes generally encode two different types of FutA iron-binding proteins: periplasmic FutA2 ABC transporter subunits bind Fe(III), while cytosolic FutA1 binds Fe(II). Owing to their small size and their economized genome Prochlorococcus ecotypes typically possess a single futA gene. How the encoded FutA protein might bind different Fe oxidation states was previously unknown. Here, we use structural biology techniques at room temperature to probe the dynamic behavior of FutA. Neutron diffraction confirmed four negatively charged tyrosinates, that together with a neutral water molecule coordinate iron in trigonal bipyramidal geometry. Positioning of the positively charged Arg103 side chain in the second coordination shell yields an overall charge-neutral Fe(III) binding state in structures determined by neutron diffraction and serial femtosecond crystallography. Conventional rotation X-ray crystallography using a home source revealed X-ray-induced photoreduction of the iron center with observation of the Fe(II) binding state; here, an additional positioning of the Arg203 side chain in the second coordination shell maintained an overall charge neutral Fe(II) binding site. Dose series using serial synchrotron crystallography and an XFEL X-ray pump-probe approach capture the transition between Fe(III) and Fe(II) states, revealing how Arg203 operates as a switch to accommodate the different iron oxidation states. This switching ability of the Prochlorococcus FutA protein may reflect ecological adaptation by genome streamlining and loss of specialized FutA proteins.

Universal Click-Chemistry Approach for the DNA Functionalization of Nanoparticles.

Nanotechnology has revolutionized the fabrication of hybrid species with tailored functionalities. A milestone in this field is the deoxyribonucleic acid (DNA) conjugation of nanoparticles, introduced almost 30 years ago, which typically exploits the affinity between thiol groups and metallic surfaces. Over the last decades, developments in colloidal research have enabled the synthesis of an assortment of nonmetallic structures, such as high-index dielectric nanoparticles, with unique properties not previously accessible with traditional metallic nanoparticles. However, to stabilize, integrate, and provide further functionality to nonmetallic nanoparticles, reliable techniques for their functionalization with DNA will be crucial. Here, we combine well-established dibenzylcyclooctyne-azide click-chemistry with a simple freeze-thaw method to achieve the functionalization of silica and silicon nanoparticles, which form exceptionally stable colloids with a high DNA surface density of ∼0.2 molecules/nm2. Furthermore, we demonstrate that these functionalized colloids can be self-assembled into high-index dielectric dimers with a yield of over 50% via the use of DNA origami. Finally, we extend this method to functionalize other important nanomaterials, including oxides, polymers, core-shell, and metal nanostructures. Our results indicate that the method presented herein serves as a crucial complement to conventional thiol functionalization chemistry and thus greatly expands the toolbox of DNA-functionalized nanoparticles currently available.

Benefits and Harms of Procalcitonin- or C-Reactive Protein-Guided Antimicrobial Discontinuation in Critically Ill Adults With Sepsis: A Systematic Review and Network Meta-Analysis.

OBJECTIVES: In sepsis treatment, antibiotics are crucial, but overuse risks development of antibiotic resistance. Recent guidelines recommended the use of procalcitonin to guide antibiotic cessation, but solid evidence is insufficient. Recently, concerns were raised that this strategy would increase recurrence. Additionally, optimal protocol or difference from the commonly used C-reactive protein (CRP) are uncertain. We aimed to compare the effectiveness and safety of procalcitonin- or CRP-guided antibiotic cessation strategies with standard of care in sepsis. DATA SOURCES: A systematic search of PubMed, Embase, CENTRAL, Igaku Chuo Zasshi, ClinicalTrials.gov, and World Health Organization International Clinical Trials Platform. STUDY SELECTION: Randomized controlled trials involving adults with sepsis in intensive care. DATA EXTRACTION: A systematic review with network meta-analyses was performed. The Grading of Recommendations, Assessments, Developments, and Evaluation method was used to assess certainty. DATA SYNTHESIS: Eighteen studies involving 5023 participants were included. Procalcitonin-guided and CRP-guided strategies shortened antibiotic treatment (-1.89 days [95% CI, -2.30 to -1.47], -2.56 days [95% CI, -4.21 to -0.91]) with low- to moderate-certainty evidence. In procalcitonin-guided strategies, this benefit was consistent even in subsets with shorter baseline antimicrobial duration (7-10 d) or in Sepsis-3, and more pronounced in procalcitonin cutoff of "0.5 µg/L and 80% reduction." No benefit was observed when monitoring frequency was less than half of the initial 10 days. Procalcitonin-guided strategies lowered mortality (-27 per 1000 participants [95% CI, -45 to -7]) and this was pronounced in Sepsis-3, but CRP-guided strategies led to no difference in mortality. Recurrence did not increase significantly with either strategy (very low to low certainty). CONCLUSIONS: In sepsis, procalcitonin- or CRP-guided antibiotic discontinuation strategies may be beneficial and safe. In particular, the usefulness of procalcitonin guidance for current Sepsis-3, where antimicrobials are used for more than 7 days, was supported. Well-designed studies are needed focusing on monitoring protocol and recurrence.

Short-lived intermediate in N2O generation by P450 NO reductase captured by time-resolved IR spectroscopy and XFEL crystallography.

Nitric oxide (NO) reductase from the fungus Fusarium oxysporum is a P450-type enzyme (P450nor) that catalyzes the reduction of NO to nitrous oxide (N2O) in the global nitrogen cycle. In this enzymatic reaction, the heme-bound NO is activated by the direct hydride transfer from NADH to generate a short-lived intermediate ( I ), a key state to promote N-N bond formation and N-O bond cleavage. This study applied time-resolved (TR) techniques in conjunction with photolabile-caged NO to gain direct experimental results for the characterization of the coordination and electronic structures of I TR freeze-trap crystallography using an X-ray free electron laser (XFEL) reveals highly bent Fe-NO coordination in I , with an elongated Fe-NO bond length (Fe-NO = 1.91 Å, Fe-N-O = 138°) in the absence of NAD+ TR-infrared (IR) spectroscopy detects the formation of I with an N-O stretching frequency of 1,290 cm-1 upon hydride transfer from NADH to the Fe3+-NO enzyme via the dissociation of NAD+ from a transient state, with an N-O stretching of 1,330 cm-1 and a lifetime of ca. 16 ms. Quantum mechanics/molecular mechanics calculations, based on these crystallographic and IR spectroscopic results, demonstrate that the electronic structure of I is characterized by a singly protonated Fe3+-NHO•- radical. The current findings provide conclusive evidence for the N2O generation mechanism via a radical-radical coupling of the heme nitroxyl complex with the second NO molecule.

Helicity-Preserving Optical Metafluids.

A colloidal suspension of photonic nanostructures exhibiting optical magnetism is dubbed an optical metafluid. A promising constituent of a metafluid is a nanosphere of high-refractive index dielectrics having the magnetic-type Mie resonances in the optical frequency. At the Kerker conditions, a dielectric nanosphere satisfies the electromagnetic duality symmetry condition and preserves the handedness of circularly polarized incident light. A metafluid of such dielectric nanospheres thus preserves the helicity of incident light. In the helicity-preserving metafluid, the local chiral fields around the constituent nanospheres are strongly enhanced, which improves the sensitivity of enantiomer-selective chiral molecular sensing. Here, we experimentally demonstrate that a solution of crystalline silicon nanospheres can be "dual" and "anti-dual" metafluids. We first theoretically address the electromagnetic duality symmetry of single silicon nanospheres. We then produce solutions of silicon nanospheres with narrow size distributions and experimentally demonstrate the "dual" and "anti-dual" behaviors.

Photosensitizing Metasurface Empowered by Enhanced Magnetic Field of Toroidal Dipole Resonance.

Photochemical reaction exploiting an excited triplet state (T1 ) of a molecule requires two steps for the excitation, i.e., electronic transition from the ground (S0 ) to singlet excited (S1 ) states and intersystem crossing to the T1  state. A dielectric metasurface coupled with photosensitizer that enables energy efficient photochemical reaction via the enhanced S0 →T1 magnetic dipole transition is developed. In the direct S0 →T1 transition, the photon energy of several hundreds of meV is saved compared to the conventional S0 → S1 →T1 transition. To maximize the magnetic field intensity on the surface, a silicon (Si) nanodisk array metasurface with toroidal dipole resonances is designed. The surface of the metasurface is functionalized with ruthenium (Ru(II)) complexes that work as a photosensitizer for singlet oxygen generation. In the coupled system, the rate of the direct S0 →T1 transition of Ru(II) complexes is 41-fold enhanced at the toroidal dipole resonance of a Si nanodisk array. The enhancement of a singlet oxygen generation rate is observed when the toroidal dipole resonance of a Si nanodisk array is matched with the direct S0 →T1 transition wavelength of Ru(II) complexes.

Fluorophore-Decorated Mie Resonant Silicon Nanosphere for Scattering/Fluorescence Dual-Mode Imaging.

Inorganic nanoparticles with multiple functions have been attracting attention as multimodal nanoprobes in bioimaging, biomolecule detection, and medical diagnosis and treatment. A drawback of conventional metallic nanoparticle-based nanoprobes is the Ohmic losses that lead to fluorescence quenching of attached molecules and local heating under light irradiation. Here, metal-free nanoprobes capable of scattering/fluorescence dual-mode imaging are developed. The nanoprobes are composed of a silicon nanosphere core having efficient Mie scattering in the visible to near infrared range and a fluorophore doped silica shell. The dark-field scattering and photoluminescence images/spectra for nanoprobes made from different size silicon nanospheres and different kinds of fluorophores are studied by single particle spectroscopy. The fluorescence spectra are strongly modified by the Mie modes of a silicon nanosphere core. By comparing scattering and fluorescence spectra and calculated Purcell factors, the fluorescence enhancement factor is quantitatively discussed. In vitro scattering/fluorescence imaging studies on human cancer cells demonstrate that the developed nanoparticles work as scattering/fluorescence dual-mode imaging nanoprobes.

Disentangling Cathodoluminescence Spectra in Nanophotonics: Particle Eigenmodes vs Transition Radiation.

Cathodoluminescence spectroscopy performed in an electron microscope has proven a versatile tool for analyzing the near- and far-field optical response of plasmonic and dielectric nanostructures. Nevertheless, the transition radiation produced by electron impact is often disregarded in the interpretation of the spectra recorded from resonant nanoparticles. Here we show, experimentally and theoretically, that transition radiation can by itself generate distinct resonances that, depending on the time-of-flight of the electron beam inside the particle, can result from constructive or destructive interference in time. Superimposed on the eigenmodes of the investigated structures, these resonances can distort the recorded spectrum and lead to potentially erroneous assignment of modal characters to the spectral features. We develop an intuitive analogy that helps distinguish between the two contributions. As an example, we focus on the case of silicon nanospheres and show that our analysis facilitates the unambiguous interpretation of experimental measurements on Mie-resonant nanoparticles.

A Compound I Mimic Reveals the Transient Active Species of a Cytochrome P450 Enzyme: Insight into the Stereoselectivity of P450-Catalysed Oxidations.

Catching the structure of cytochrome P450 enzymes in flagrante is crucial for the development of P450 biocatalysts, as most structures collected are found trapped in a precatalytic conformation. At the heart of P450 catalysis lies Cpd I, a short-lived, highly reactive intermediate, whose recalcitrant nature has thwarted most attempts at capturing catalytically relevant poses of P450s. We report the crystal structure of P450BM3 mimicking the state in the precise moment preceding epoxidation, which is in perfect agreement with the experimentally observed stereoselectivity. This structure was attained by incorporation of the stable Cpd I mimic oxomolybdenum mesoporphyrin IX into P450BM3 in the presence of styrene. The orientation of styrene to the Mo-oxo species in the crystal structures sheds light onto the dynamics involved in the rotation of styrene to present its vinyl group to Cpd I. This method serves as a powerful tool for predicting and modelling the stereoselectivity of P450 reactions.

Mode Hybridization in Silicon Core-Gold Shell Nanosphere.

A dielectric core-metal shell nanosphere has attracted scientific and technological interests due to the unique optical resonances arising from the hybridization of surface plasmon modes and cavity modes. The previous studies focus on a low-index dielectric core without its own optical resonances. Here, optical resonances of a core-shell nanosphere with a high refractive index (n ≈ 4) core with the lowest order Mie resonances in the visible range are investigated theoretically and experimentally. Scattering and absorption spectra of a core-shell nanosphere for different values of the core refractive index are first analyzed, and there is a transition of the hybridization scheme around n ≈ 2. Above the value, a characteristic hybridized mode with strong absorption and weak scattering emerges in the near-infrared range. A core-shell nanosphere composed of a silicon core and a gold shell is prepared, and the resonance modes are studied by single particle scattering spectroscopy and electron energy loss spectroscopy (EELS) in a transmission electron microscope. The core-shell nanospheres exhibit the hybridized modes depending on the core diameter. The hybridized mode as well as the higher order one that is not observable in the scattering spectroscopy is observed in the EELS.

Resonance Couplings in Si@MoS2 Core-Shell Architectures.

Heterostructures of transition metal dichalcogenides and optical cavities that can couple to each other are rising candidates for advanced quantum optics and electronics. This is due to their enhanced light-matter interactions in the visible to near-infrared range. Core-shell structures are particularly valuable for their maximized interfacial area. Here, the chemical vapor deposition synthesis of Si@MoS2 core-shells and extensive structural characterization are presented. Compared with traditional plasmonic cores, the silicon dielectric Mie resonator core offers low Ohmic losses and a wider spectrum of optical modes. The magnetic dipole (MD) mode of the silicon core efficiently couples with MoS2 through its large tangential component at the core surface. Using transmission electron microscopy and correlative single-particle scattering spectroscopy, MD mode splitting is experimentally demonstrated in this unique Si@MoS2 core-shell structure. This is evidence for resonance coupling, which is limited to theoretical proposals in this particular system. A coupling constant of 39 meV is achieved, which is ≈1.5-fold higher than previous reports of particle-on-film geometries with a smaller interfacial area. Finally, higher-order systems with the potential to tune properties are demonstrated through a dimer system of Si@MoS2 , forming the basis for emerging architectures for optoelectronic and nanophotonic applications.

Tetraphenylporphyrin Enters the Ring: First Example of a Complex between Highly Bulky Porphyrins and a Protein.

Tetraphenylporphyrin (TPP) is a symmetrically substituted synthetic porphyrin whose properties can be readily modified, providing it with significant advantages over naturally occurring porphyrins. Herein, we report the first example of a stable complex between a native biomolecule, the haemoprotein HasA, and TPP as well as its derivatives. The X-ray crystal structures of nine different HasA-TPP complexes were solved at high resolutions. HasA capturing TPP derivatives was also demonstrated to inhibit growth of the opportunistic pathogen Pseudomonas aeruginosa. Mutant variants of HasA binding FeTPP were shown to possess a different mode of coordination, permitting the cyclopropanation of styrene.

Elevated serum creatine kinase levels due to osimertinib: A case report and review of the literature.

INTRODUCTION: Osimertinib is a tyrosine kinase inhibitor that targets the epidermal growth factor receptor. Elevated serum creatine kinase level is an uncommon adverse event associated with osimertinib treatment for lung cancer. CASE REPORT: We report a previously healthy 56-year-old woman who developed elevated serum creatine kinase levels during osimertinib monotherapy for epidermal growth factor receptor mutation-positive lung adenocarcinoma. MANAGEMENT & OUTCOME: During treatment, she experienced leg cramps and her serum creatine kinase levels increased, peaking at 989 U/l. Further investigation revealed no evidence of cardiotoxicity or myositis; thus, osimertinib-induced myopathy was assumed to be the cause of her elevated serum creatine kinase levels. We successfully managed both lung cancer and osimertinib-induced myopathy using 1-week pauses of osimertinib therapy without dose reduction. DISCUSSION: Short-term suspension of osimertinib without dose reduction may be a reasonable option for osimertinib-induced myopathy.

A Heme-Acquisition Protein Reconstructed with a Cobalt 5-Oxaporphyrinium Cation and Its Growth-Inhibition Activity Toward Multidrug-Resistant Pseudomonas aeruginosa.

Using artificial hemes for the reconstruction of natural heme proteins represents a fascinating approach to enhance the bioactivity of the latter. We report the synthesis of various metal 5-oxaporphyrinium cations as cofactors, and a cobalt 5-oxaporphyrinium cation was successfully incorporated into the heme-acquisition protein (HasA) secreted by Pseudomonas aeruginosa. We hypothesize that the oxaporphyrinium cation strongly binds to the HasA-specific outer membrane receptor (HasR) due to its cationic charge, which prevents the subsequent acquisition of heme. In fact, the reconstructed HasA inhibited the growth of Pseudomonas aeruginosa and even of multidrug-resistant P. aeruginosa.

Targeted Mass Spectrometry-Based Approach for the Determination of Intrinsic Internalization Kinetics of Cell-Surface Membrane Protein Targets.

Successful development of targeted therapeutics aimed at the elimination of diseased cells relies on the target properties and the therapeutics that target them. Currently, target properties have been evaluated through antibody-dependent semiquantitative approaches such as flow cytometry, Western blotting, or microscopy. Since antibodies can alter target properties following binding, antibody-dependent approaches provide at best skewed measurements for target intrinsic properties. To circumvent, here we attempted to develop an antibody-free targeted mass spectrometry-based (ATM) strategy to measure the surface densities and the intrinsic rates (Kint) of CD38 internalization in multiple myeloma cell lines. Using cell-surface biotinylation in conjunction with differential mass tagging to separate inward CD38 molecules from the outbound and nascent ones, the ATM approach revealed diversities in measured CD38 Kint values of 0.239 min-1 S.E. ± 0.076, 0.109 min-1 S.E. ± 0.032, and 0.058 min-1 S.E. ± 0.001 for LP1, NCIH929, and MOLP8 cell lines, respectively. Together with CD38 surface densities, intrinsic Kint values aligned well with the tumor penetration model and supported the outcomes for tumor regression in mouse xenografts upon drug treatment. Additionally, the ATM approach can evaluate molecules with fast Kint as we determined for CTLA4 protein. We believe that the ATM approach has the potential to evaluate diverse cell-surface targets as part of the pharmacological assessment in drug discovery.

Direct Excitation of Triplet State of Molecule by Enhanced Magnetic Field of Dielectric Metasurfaces.

Efficient excitation of a triplet (T1 ) state of a molecule has far-reaching effects on photochemical reaction and energy conversion systems. Because the optical transition from a ground singlet (S0 ) to a T1 state is spin-forbidden, a T1 state is generated via intersystem crossing (ISC) from an excited singlet (S1 ) state. Although the excitation efficiency of a T1 state can be increased by enhancing ISC utilizing a heavy atom effect, energy loss during S1 →T1 relaxation is inevitable. Here, a general approach to directly excite a T1 state from a ground S0 state via magnetic dipole transition, which is boosted by enhanced magnetic field induced by a dielectric metasurface, is proposed. As a dielectric metasurface, a hexagonal array of silicon (Si) nanodisks is employed; the nanodisk array induces a strongly enhanced magnetic field on the surface due to the toroidal dipole (TD) resonance. A proof-of-concept experiment is performed using ruthenium (Ru) complexes placed on a metasurface and demonstrates that the phosphorescence is 35-fold enhanced on a metasurface when the TD resonance is tuned to the wavelength of the direct S0 →T1 transition. These results indicate that photon energy necessary to excite the T1 state can be reduced by more than 400 meV compared to the process involving the ISC. By combining optical measurements with numerical simulations, the mechanism of the phosphorescence enhancement is quantitatively discussed.

Colloidal Mie resonant silicon nanoparticles.

Nano- and microstructures of silicon (Si) exhibit electric and magnetic Mie resonances in the optical regime, providing a novel platform for controlling light at the nanoscale and enhancing light-matter interactions. In this Review, we present recent development of colloidal Si nanoparticles (NPs) that have wide range of applications in nanophotonics. Following brief summary of synthesis methods of amorphous and crystalline Si particles with high sphericity, optical responses of single Si particles placed on a substrate are overviewed. Then, the capability as a nanoantenna to control light-matter interactions is discussed in different systems. Finally, collective optical responses of Si NPs in solution are presented and the application potentials are discussed.

Solution-processed silicon quantum dot photocathode for hydrogen evolution.

The photoelectrochemical response of a photocathode made from a colloidal solution of boron (B) and phosphorus (P) codoped silicon (Si) quantum dots (QDs) 2-11 nm in diameters is studied. Since codoped Si QDs are dispersible in alcohol and water due to the hydrophilic surface, a photoelectrode with a smooth surface is produced by drop-coating the QD solution on an indium tin oxide substrate. The codoping provides high oxidation resistance to Si QDs and makes the electrode operate as a photocathode. The photoelectrochemical response of a Si QD photoelectrode depends strongly on the size of QDs; there is a transition from anodic to cathodic photocurrent around 4 nm in diameter. Below the size, anodic photocurrent due to self-oxidation of Si QDs is observed, while above the size, cathodic photocurrent due to electron transfer across the interface is observed. The cathodic photocurrent increases with increasing the size, and in some samples, it is observed for more than 3000 s under intermittent light irradiation.

Colloidal Solutions of Silicon Nanospheres toward All-Dielectric Optical Metafluids.

A colloidal solution of nanophotonic structures exhibiting optical magnetism is dubbed a liquid-phase metamaterial or an optical metafluid. Over the decades, plasmonic nanoclusters have been explored as constituents of a metafluid. However, optical magnetism of plasmonic nanoclusters is usually much weaker than the electric responses; the highest reported intensity ratio of the magnetic-to-electric responses so far is 0.28. Here, we propose an all-dielectric metafluid composed of crystalline silicon nanospheres. First, we address the advantages of silicon as a constituent material of a metafluid among major dielectrics. Next, we experimentally demonstrate for the first time that a silicon nanosphere metafluid exhibits strong electric and magnetic dipolar Mie responses across the visible to near-infrared spectral range. The intensity ratio of the magnetic-to-electric responses reaches unity. Finally, we discuss the perspective to achieve unnaturally high (>3), low, and even near-zero (<1) refractive index in the metafluid.

XFEL Crystal Structures of Peroxidase Compound II.

Oxygen activation in all heme enzymes requires the formation of high oxidation states of iron, usually referred to as ferryl heme. There are two known intermediates: Compound I and Compound II. The nature of the ferryl heme-and whether it is an FeIV =O or FeIV -OH species-is important for controlling reactivity across groups of heme enzymes. The most recent evidence for Compound I indicates that the ferryl heme is an unprotonated FeIV =O species. For Compound II, the nature of the ferryl heme is not unambiguously established. Here, we report 1.06 Šand 1.50 Šcrystal structures for Compound II intermediates in cytochrome c peroxidase (CcP) and ascorbate peroxidase (APX), collected using the X-ray free electron laser at SACLA. The structures reveal differences between the two peroxidases. The iron-oxygen bond length in CcP (1.76 Å) is notably shorter than in APX (1.87 Å). The results indicate that the ferryl species is finely tuned across Compound I and Compound II species in closely related peroxidase enzymes. We propose that this fine-tuning is linked to the functional need for proton delivery to the heme.