Circular Dichroism Measurements Research Articles

Coexistence of Ferromagnetism and Superconductivity at KTaO3 Heterointerfaces.

The coexistence of superconductivity and ferromagnetism is a long-standing issue in superconductivity due to the antagonistic nature of these two ordered states. Experimentally identifying and characterizing novel heterointerface superconductors that coexist with magnetism presents significant challenges. Here, we report the observation of two-dimensional long-range ferromagnetic order in a KTaO3 heterointerface superconductor, showing the coexistence of superconductivity and ferromagnetism. Remarkably, our direct current superconducting quantum interference device measurements reveal an in-plane magnetization hysteresis loop persisting above room temperature. Moreover, first-principles calculations and X-ray magnetic circular dichroism measurements provide decisive insights into the origin of the observed robust ferromagnetism, attributing it to oxygen vacancies that localize electrons in nearby Ta 5d states. Our findings suggest KTaO3 heterointerfaces as time-reversal symmetry breaking superconductors, injecting fresh momentum into the exploration of the intricate interplay between superconductivity and magnetism enhanced by the strong spin-orbit coupling inherent to the heavy Ta in 5d orbitals.

Thermotolerance Mechanism of Fungal GH6 Cellobiohydrolase. Part I. Characterization of Thermotolerant Mutant from the Basidiomycete Phanerochaete chrysosporium.

Cellobiohydrolase (CBH), belonging to glycoside hydrolase family 6 (GH6), plays an essential role in cellulose saccharification, but its low thermotolerance presents a challenge in improving the reaction efficiency. Based on a report that chimeric CBH II (GH6) engineered to remove non-disulfide-bonded free Cys shows increased thermotolerance, we previously mutated the two free Cys residues to Ser in GH6 CBH from the basidiomycete Phanerochaete chrysosporium (PcCel6A) and obtained a thermotolerant double mutant, C240S/C393S (Yamaguchi et al., J. Appl. Glycosci. 2020; 67: 79-86). Here, characterization of the double mutant revealed that its activity towards both amorphous and crystalline cellulose was higher than that of the wild-type enzyme at elevated temperature, suggesting that the catalytic domain is the major contributor to the increased thermotolerance. To investigate the role of each free Cys residue, we prepared both single mutants, C240S and C393S, of the catalytic domain of PcCel6A and examined their residual activity at high temperature and the temperature-dependent changes of folding by means of circular dichroism measurements and thermal shift assay. The results indicate that the C393S mutation is the main contributor to both the increased thermotolerance of C240S/C393S and the increased activity of the catalytic domain at high temperature.

Insights on the G protein-coupled receptor helix 8 solution structure and orientation using a neurotensin receptor 1 peptide.

G-protein coupled receptors (GPCRs) are the largest class of membrane proteins encoded in the human genome with high pharmaceutical relevance and implications to human health. These receptors share a prevalent architecture of seven transmembrane helices followed by an intracellular, amphipathic helix 8 (H8) and a disordered C-terminal tail (Ctail). Technological advancements have led to over 1000 receptor structures in the last two decades, yet frequently H8 and the Ctail are conformationally heterogeneous or altogether absent. Here we synthesize a peptide comprising the neurotensin receptor 1 (NTS1) H8 and Ctail (H8-Ctail) to investigate its structural stability, conformational dynamics, and orientation in the presence of detergent and phospholipid micelles, which mimic the membrane. Circular dichroism (CD) and nuclear magnetic resonance (NMR) measurements confirm that zwitterionic 1,2-diheptanoyl-sn-glycero-3-phosphocholine is a potent stabilizer of H8 structure, whereas the commonly-used branched detergent lauryl maltose neopentyl glycol (LMNG) is unable to completely stabilize the helix - even at amounts four orders of magnitude greater than its critical micellar concentration. We then used NMR spectroscopy to assign the backbone chemical shifts. A series of temperature and lipid titrations were used to define the H8 boundaries as F376-R392 from chemical shift perturbations, changes in resonance intensity, and chemical-shift-derived phi/psi angles. Finally, the H8 azimuthal and tilt angles, defining the helix orientation relative of the membrane normal were measured using paramagnetic relaxation enhancement NMR. Taken together, our studies reveal the H8-Ctail region is sensitive to membrane physicochemical properties and is capable of more adaptive behavior than previously suggested by static structural techniques.

Alginate functionalized chitosan nanoparticles using multilayer co-axial electro-spraying for ovalbumin controlled release via oral delivery

The current oral vaccine delivery presents numerous challenges due to physiological barriers in the gastrointestinal tract including antigen degradation by enzymes and gastric pH conditions. Contributing to overcome these problems, this work developed non-cross-linked chitosan (CHI) nanoparticles, with/without functionalization with alginate (ALG), using multilayer co-axial electro-spraying method, to orally deliver ovalbumin (OVA), a model antigen. The prepared OVA@CHI and OVA@CHI@ALG nanoparticles possessed spherical shape, uniform size and non-agglomeration, high OVA encapsulation efficiency of above 90 %, and core-shell structure with mean diameters of 276.9 ± 70.7 nm (for OVA@CHI) and 304.3 ± 63.9 nm (for OVA@CHI@ALG), determined via SEM images. The particle hydrodynamic diameters, analyzed by the DLS method, were 313.0 ± 72.4 nm for OVA@CHI and 367.6 ± 83.2 nm for OVA@CHI@ALG, in agreement with the SEM results. Additionally, the material functional group interactions and the polyelectrolyte complex formations were confirmed by FTIR spectra and TGA/DSC thermo-grams, indicating the successful formulation. Subsequently, the OVA@CHI@ALG nanoparticles revealed good stability in acidic environment under the presence of digestive enzymes. The OVA release profiles of OVA@CHI@ALG nanoparticles exhibited limited release in simulated gastric fluid (pH 1.2), followed by sustained release in simulated intestinal fluid (pH 6.8) and simulated colonic fluid (pH 7.4) over a 48-h test period. Interestingly, the primary structure of OVA, analyzed by SDS-PAGE analysis, was maintained during the preparation process and after the release test, while the OVA secondary structure, examined by circular dichroism measurement, demonstrated a decrease of α-helix and an increase of β-sheet contents. Finally, the in vitro mucin-binding study indicated a significant adhesive efficiency of 69.21 ± 4.24 % for OVA@CHI and 75.07 ± 2.58 % for OVA@CHI@ALG at pH 7.4. Conclusively, the OVA@CHI@ALG nanoparticles fabricated by tri-axial electro-spraying method could be a promising oral vaccine delivery system for sustained release of OVA.

Investigation of collagen reconstruction mechanism in skin wound through dual-beam laser welding: Insights from multi-spectroscopy, molecular dynamics simulation, and finite element multiphysics simulation

Since the mechanism underlying real-time acquisition of mechanical strength during laser-induced skin wound fusion remains unclear, and collagen is the primary constituent of skin tissue, this study investigates the structural and mechanical alterations in collagen at temperatures ranging from 40 °C to 60 °C using various spectroscopic techniques and molecular dynamics calculations. The COMSOL Multiphysics coupling is employed to simulate the three-dimensional temperature field, stress-strain relationship, and light intensity distribution in the laser thermal affected zone of skin wounds during dual-beam laser welding process. Raman spectroscopy, synchronous fluorescence spectroscopy and circular dichroism measurement results confirm that laser energy activates biological activity in residues, leading to a transformation in the originally fractured structure of collagen protein for enhanced mechanical strength. Molecular dynamics simulations reveal that stable hydrogen bonds form at amino acid residues within the central region of collagen protein when the overall temperature peak around the wound reaches 60 °C, thereby providing stability to previously fractured skin incisions and imparting instantaneous strength. However, under a 55 °C system, Type I collagen ensures macrostructural stability while activating biological properties at amino acid bases to promote wound healing function; this finding aligns with experimental analysis results. The COMSOL simulation outcomes also correspond well with macroscopic morphology after laser welding samples, confirming that by maintaining temperatures between 55 °C–60 °C during laser welding of skin incisions not only can certain instantaneous mechanical strength be achieved but irreversible thermal damage can also be effectively controlled. It is anticipated that these findings will provide valuable insights into understanding the healing mechanism for laser-welded skin wounds.

Modulation of magnetic properties in self-assembled one-dimensional CoxFe3-xO4 nano-chains with Co substitution

Modulation of magnetic properties on the low dimensional material under multiple fields is a captivating area of study in material science and nano-technology. In this paper, we focus on the self-assembly of chain-like nanostructures composed of CoxFe3−xO4 nanoparticles with an average size of 150 nm. These structures, consisting of more than 20 nanoparticles, are formed at 90 °C under a 0.25 T external magnetic field. The length of chains is surprising to decrease with increasing Co content due to an obvious additional cubic magneto-crystalline anisotropy superposed on the uniaxial induced anisotropy which is induced by the synthesized magnetic field with easy axis along the length of the chain. The additional magneto-crystalline anisotropy field of Co blocks the chain growing in length with Co doping. Additionally, our X-ray magnetic circular dichroism (XMCD) measurements confirm the doping of Co2+ ions in the CoxFe3−xO4 nano-chains, where they predominantly occupy the B sites and substitute the Fe2+ ions. This finding underlines the importance of spin-orbit coupling enhancement in the magnetic behavior resulting from the Fe2+ substitution with Co2+.

Consequences of Vibrational Strong Coupling on Supramolecular Polymerization of Porphyrins.

Supramolecular polymers display interesting optoelectronic properties and, thus, deploy multiple applications based on their molecular arrangement. However, controlling supramolecular interactions to achieve a desirable molecular organization is not straightforward. Over the past decade, light-matter strong coupling has emerged as a new tool for modifying chemical and material properties. This novel approach has also been shown to alter the morphology of supramolecular organization by coupling the vibrational bands of solute and solvent to the optical modes of a Fabry-Perot cavity (vibrational strong coupling, VSC). Here, we study the effect of VSC on the supramolecular polymerization of chiral zinc-porphyrins (S-Zn) via a cooperative effect. Electronic circular dichroism (ECD) measurements indicate that the elongation temperature (Te) of the supramolecular polymerization is lowered by ∼10 °C under VSC. We have also generalized this effect by exploring other supramolecular systems under strong coupling conditions. The results indicate that the solute-solvent interactions are modified under VSC, which destabilizes the nuclei of the supramolecular polymer at higher temperatures. These findings demonstrate that the VSC can indeed be used as a tool to control the energy landscape of supramolecular polymerization. Furthermore, we use this unique approach to switch between the states formed under ON- and OFF-resonance conditions, achieved by simply tuning the optical cavity in and out of resonance.

Alcohol-Induced Denaturation of Hen Egg White Lysozyme Studied by Infrared, Circular Dichroism, and Small-Angle Neutron Scattering.

In aqueous binary solvents with fluorinated alcohols, 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), and aliphatic alcohols, ethanol (EtOH) and 2-propanol (2-PrOH), the denaturation of hen egg white lysozyme (HEWL) with increasing alcohol mole fraction xA has been investigated in a wide view from the molecular vibration to the secondary and ternary structures. Circular dichroism (CD) measurement showed that the secondary structure of α-helix content of HEWL increases on adding a small amount of the fluorinated alcohol to the aqueous solution, while the β-sheet content decreases. On the contrary, the secondary structure does not significantly change by the addition of the aliphatic alcohols. Correspondingly, the infrared (IR) spectroscopic measurements revealed that the amide I band red-shifts on the addition of the fluorinated alcohol. However, the band remains unchanged in the aliphatic alcohol systems with increasing alcohol content. To observe the ternary structure of HEWL, small-angle neutron scattering (SANS) experiments with H/D substitution technique have been applied to the HEWL solutions. The SANS experiments were successful in revealing the details of how the geometry of the HEWL changes as a function of xA. The SANS profiles indicated the spherical structure of HEWL in all of the alcohol systems in the xA range examined. The mean radius of HEWL in the two fluorinated alcohol systems increases from ∼16 to ∼18 Å during the change in the secondary structure against the increase in the fluorinated alcohol content. On contrast, the radius does not significantly change in both aliphatic alcohol systems below xA = 0.3 but expands to ∼19 Å as the alcohol content is close to the limitation of the HEWL solubility. According to the present results, together with our knowledge of the alcohol cluster formation and the interaction of the trifluoromethyl (CF3) groups with the hydrophobic moieties of biomolecules, the effects of alcohols on the denaturation of the protein have been discussed on a molecular scale.

Giant gate modulation of antiferromagnetic spin reversal by the magnetoelectric effect

In this study, using the Pt/Cr2O3/Pt epitaxial trilayer, we demonstrate the giant voltage modulation of the antiferromagnetic spin reversal and the voltage-induced 180° switching of the Néel vector in maintaining a permanent magnetic field. We obtained a significant modulation efficiency of the switching field, Δμ0HSW/ΔV (Δμ0HSW/ΔE), reaching a maximum of −500 mT/V (−4.80 T nm/V); this value was more than 50 times greater than that of the ferromagnetic-based counterparts. From the temperature dependence of the modulation efficiency, X-ray magnetic circular dichroism measurements and first-principles calculations, we showed that the origin of the giant modulation efficiency relied on the electric field modulation of the net magnetization due to the magnetoelectric effect. From the first-principles calculation and the thickness effect on the offset electric field, we found that the interfacial magnetoelectric effect emerged. Our demonstration reveals the energy-efficient and widely applicable operation of an antiferromagnetic spin based on a mechanism distinct from magnetic anisotropy control.

Bisphenol a modification and how its structure influences human serum albumin binding force

Bisphenol A (BPA) is an environmental hormone with substantial physiological toxicity to the human body. Three electron-withdrawing derivatives of BPA are synthesized in this study to reduce its toxicity. The interaction mechanism between BPA and its three derivatives with human serum albumin (HSA) is investigated using molecular docking, electrochemistry, circular dichroism spectrum analysis, and fluorescence spectroscopy. Temperature-dependent tests and time-resolved fluorescence spectra reveal that all four compounds dynamically quench the internal fluorescence of HSA. Based on molecular docking and site competition outcomes, four compounds are primarily bound to site I's active pocket. Thermodynamic parameters indicate that the compounds’ interaction with HSA is spontaneous, and introducing weak electron-withdrawing groups changes the action force. Circular dichroism and synchronous fluorescence measurements suggest four compounds impact HSA's structure. The substituents' electron attraction capacity determines their impact. Electrochemical studies examine the effect of electron-absorbing groups on the BPA and HSA binding capacity. Pharmacokinetics showed that nitro-substituted BPA may be a potential superior substitute for BPA. These results indicate crucial practical value, providing theoretical support for future research.

Activity-stability trade-off observed in variants at position 315 of the GH10 xylanase XynR

XynR is a thermostable alkaline GH10 xylanase, for which we have previously examined the effects of saturation mutagenesis at position 315 on enzyme alkaliphily, and found that at pH 10, the activities of variants could be ordered as follows: T315Q > T315S = T315N > T315H = wild-type XynR (WT) > 15 other variants. In this study, we sought to elucidate the mechanisms underlying the variable activity of these different variants. Crystallographic analysis revealed that the Ca2+ ion near position 315 in WT was absent in the T315Q variant. We accordingly hypothesized that the enhancement of alkaliphily in T315Q, and probably also in the T315H, T315N, and T315S variants, could be ascribed to an activity-stability trade-off associated with a reduction in stability due to the lack of this Ca2+ ion. Consistent with expectations, the alkaline resistance of T315H, T315N, T315Q, and T315S, evaluated through the pH-dependence of stability at 0 mM CaCl2 under alkaline conditions, was found to be lower than that of WT: the residual activity at pH 11 of WT was 78% while those of T315H, T315N, T315Q, and T315S were 0, 9, 0, and 43%, respectively. In addition, the thermostabilities of these four variants, as assessed using the denaturing temperatures (Tm) at 0 mM CaCl2 based on ellipticity at 222 nm in circular dichroism measurements, were lower than that of WT by 2–8 °C. Furthermore, the Tm values of WT and variants at 5 mM CaCl2 were higher than those at 0 mM CaCl2 by 6–11 °C. Collectively, our findings in this study indicate that mutation of the T residue at position 315 of XynR to H, N, Q, and S causes an increase in the alkaliphily of this enzyme, thereby reducing its stability.

Pea and soy protein isolate fractal gels: The role of protein composition, structure and solubility on their gelation behaviour

The gelation behaviour of two different pea protein isolates and one soy protein isolate were investigated with a focus on the role of the protein properties. Protein solubility was the lowest in pH 3 citrate-phosphate buffer (<10% w/w), increased in pH 7.4 phosphate-buffered saline (12–21% w/w), and was the highest in pH 7.6 MilliQ water (∼20–40% w/w). Heat-induced gelation conditions for the protein sources were sensitive to both the soluble and the insoluble fractions as obtained during extraction. At low protein concentrations (≤5% w/v), the proteins started to lose their viscoelastic behaviour and exhibited predominantly viscous properties. Fitting of the fractional Kelvin-Voigt model to the frequency sweeps showed an increase in the fractal gel strength with increasing protein concentration. Secondary structures of the soluble species showed mostly unordered proteins, suggesting that the proteins were denatured during the commercial extraction process although gelation has to date been suggested to be highly dependent on the denaturation of soluble proteins. Synchrotron Radiation Circular Dichroism measurements of the insoluble proteins showed a significant amount of ordered protein structures. SEM imaging of the gels also suggested a new gelation pathway in which insoluble proteins act as dispersed fillers within a continuous matrix of soluble proteins. This research elucidated the role of different protein fractions, globulins and albumins, and their secondary structure in the formation of a gel network and how this affects their viscoelastic behaviour.

Copper ion concentration detection based on quantum weak measurement of circular dichroism

In this paper, a high precision detection method of copper ion (Cu2+) concentration based on weak measurement is proposed. The ternary complex formed by Cu2+ with L-tryptophan and phenanthroline reagents has circular dichroism (CD) signal at 605 nm in visible light. The CD signal can be obtained using the intensity contrast as a pointer in the imaginary weak-value amplification scheme. The measured sensitivity and resolution are 0.3417 mradl/mg and 0.058 mg/l, respectively, which is improved by an order of magnitude compared to the traditional CD measurement method. It is also more accurate and less costly than commonly used Cu2+ detection methods. The Cu2+ concentration detection based on the weak measurement of CD signal detection proposed in this paper not only brings technological breakthroughs in the field of heavy metal ion detection, but also is of great significance in promoting the cross-development of chemistry, biomedicine, and life sciences.

X-ray magnetic circular dichroism of Mn4−xGaxN epitaxial thin films confirming ferrimagnetic-ferromagnetic phase transition by nonmagnetic Ga doping

Researchers have focused on anti-perovskite Mn4N-based ferrimagnets as potential candidates for spintronic applications since these films have a small magnetization and exhibit perpendicular magnetic anisotropy. Magnetic compensation (or angular momentum compensation) in impurity-doped Mn4N at room temperature has attracted particular attention because the magnetization switching can be facilitated in the vicinity of such compensation compositions. In this study, we grew Mn4−xGaxN (x = 0.0–1.9) epitaxial thin films on SrTiO3(001) substrates by molecular beam epitaxy and evaluated their crystallinity and surface conditions. The magnetic properties of the grown films were also examined and a sign reversal of anomalous Hall resistivity and hysteresis loops was observed between x = 0.1 and 0.3 at room temperature by magneto-optical Kerr effect microscopy. X-ray magnetic circular dichroism measurement revealed that the magnetic moment of face-centered Mn at x = 0.3 was reversed to be parallel to that of Mn at corner sites, suggesting that the ferrimagnetic-ferromagnetic phase transition occurred with nonmagnetic Ga doping.

Chiroptical properties of membrane glycerophospholipids and their chiral backbones.

Glycerophospholipid membranes are one of the key cellular components. Still, their species-dependent composition and homochirality remain an elusive subject. In the context of the astrophysical circularly polarized light scenario likely involved in the generation of a chiral bias in meteoritic amino and sugar acids in space, and consequently in the origin of life's homochirality on Earth, this study reports the first measurements of circular dichroism and anisotropy spectra of a selection of glycerophospholipids, their chiral backbones and their analogs. The rather low asymmetry in the interaction of UV/VUV circularly polarized light with sn-glycerol-1/3-phosphate indicates that chiral photons would have been unlikely to directly induce symmetry breaking to membrane lipids. In contrast, the anisotropy spectra of d-3-phosphoglyceric acid and d-glyceraldehyde-3-phosphate unveil up to 20 and 100 times higher maximum anisotropy factor values, respectively. This first experimental report, targeted on investigating the origins of phospholipid symmetry breaking, opens up new avenues of research to explore alternative mechanisms leading to membrane lipid homochirality, while providing important clues for the search for chiral biosignatures of extant and/or extinct life in space, in particular for the ExoMars 2028 mission.

Multidimensional vibrational circular dichroism for insect wings: Comparison of species.

This study reports the microscopic measurements of vibrational circular dichroism (VCD) on four different insect wings using a quantum cascade laser VCD system equipped with microscopic scanning capabilities (named multi-dimensional VCD [MultiD-VCD]). Wing samples, including (i) beetle, Anomala albopilosa (female), (ii) European hornet, Verspa crabro flavofasciata Cameron, 1903 (female), (iii) tiny dragonfly, Nannophya pygmae Rambur, 1842 (male), and (iv) dragonfly, Symetrum gracile Oguma, 1915 (male), were used in this study. Two-dimensional patterns of VCD signals (~10 mm × 10mm) were obtained at a spatial resolution of 100 μm. Measurements covered the absorption peaks assigned to amides I and II in the range of 1500-1740 cm-1 . The measurements were based on the enhancement of VCD signals for the stereoregular linkage of peptide groups. The patterns were remarkably dependent on the species. In samples (i) and (ii), the wings comprised segregated domains of protein aggregates of different secondary structures. The size of each microdomain was approximately 100 μm. In contrast, no clear VCD spectra were detected in samples (iii) and (iv). One possible reason was that the chain of stereoregular polypeptides was too short to achieve VCD enhancement in samples (iii) and (iv). Notably, the unique features were only observed in the VCD spectra because the IR spectra were nearly the same among the species. The VCD results hinted at the connection of protein microscopic structures with the wing flapping mechanisms of each species.

Structurally intriguing diterpenoids from Euphorbia wallichii Hook. f. with potential antioxidant activity

Chemical investigation of Euphorbia wallichii Hook. f. led to the isolation of four undescribed rearranged diterpenoids, euphwanoids I-IV (1-4), and six unreported tigliane diterpenoids walliglianes A-F (5–10). Euphwanoids I-III (1–3) possess a rare 6/6/7/3 ring scaffold, euphwanoid IV (4) is the first spiro[tricyclo[5.4.0.02,4]undecane-8,1ʹ-cyclopentane] skeleton to be found in the tigliane family. The structures of compounds 1–10 were established by utilizing spectroscopic data analysis, experimental electronic circular dichroism measurements, 13C NMR calculations, and single-crystal X-ray diffraction. In the preliminary bioassay, compounds 3, 4, and 7 were found to protect BV-2 cells against H2O2-induced cell injury in a dose-dependent manner by the CCK8 assay.

Integrated Circular Dichroism and Circularly Polarized Luminescence Measurements.

Circularly polarized luminescent (CPL) systems have a plethora of potential applications owing to their interesting excited-state properties. However, the progress in developing new chiral luminescence systems is significantly hindered by the lack of available instrumentation for the broader chemistry and materials science community to perform routine, reproducible measurements of chiral spectroscopies. In this work, we present data from an easy-to-use custom-built instrument based on a Jasco circular dichroism (CD) spectropolarimeter coupled with a CPL emission monochromator (CD/CPL hybrid system). The hybrid system measures CPL, fluorescence, CD, and absorbance on the same part of the sample without the need to move between the CD and CPL measurements. The instrument uses a xenon arc lamp as the light source, enabling a wide range of excitation wavelengths to support flexible development of new molecules and materials. Data obtained and presented for camphor, ruthenium metal complexes, the peptide gramicidin, and a DNA-ligand (4',6-diamidino-2-phenylindole, DAPI) system in this work highlight the ease of use and reproducibility of the results. The g-factors for CD and CPL obtained for the different compounds are shown to be the same for isolated transitions and some examples of how to use variations of g-factors with wavelength are demonstrated. The reliable and excellent benchmark results obtained from a custom-built commercial wavelength scanning CPL/CD hybrid instrument open up new avenues for the broader chemical and materials science community to intensify research on chiral luminescent systems.

Formation of Mn-rich interfacial phases in Co2FexMn1-xSi thin films

We report the formation of Mn-rich regions at the interface of Co2FexMn1-xSi thin films grown on GaAs substrates by molecular beam epitaxy (MBE). Scanning transmission electron microscopy (STEM) with electron energy loss (EEL) spectrum imaging reveals that each interfacial region: (1) is 1–2 nm wide, (2) occurs irrespective of the Fe/Mn composition ratio and in both Co-rich and Co-poor films, and (3) displaces both Co and Fe indiscriminately. We also observe a Mn-depleted region in each film directly above each Mn-rich interfacial layer, roughly 3 nm in width in the x = 0 and x = 0.3 films, and 1 nm in the x = 0.7 (less Mn) film. We posit that growth energetics favor Mn diffusion to the interface even when there is no significant Ga interdiffusion into the epitaxial film. Element-specific X-ray magnetic circular dichroism (XMCD) measurements show larger Co, Fe, and Mn orbital to spin magnetic moment ratios compared to bulk values across the Co2FexMn1-xSi compositional range. The values lie between reported values for pure bulk and nanostructured Co, Fe, and Mn materials, corroborating the non-uniform, layered nature of the material on the nanoscale. Finally, SQUID magnetometry demonstrates that the films deviate from the Slater-Pauling rule for uniform films of both the expected and the measured composition. The results inform a need for care and increased scrutiny when forming Mn-based magnetic thin films on III-V semiconductors like GaAs, particularly when films are on the order of 5 nm or when interface composition is critical to spin transport or other device applications.

Generation of streptocarbazoles with cytotoxicities by pathway engineering and insights into their biosynthesis.

Indolocarbazoles (ICZs) are a group of antitumor agents, with several analogs used in clinical trials. Therefore, the identification of novel ICZ compounds is important for drug discovery. Streptocarbazoles harbor unique N-glycosidic linkages (N13-C1' and N12-C3'), distinguishing them from the representative ICZ compound staurosporine; however, their biosynthesis remains unclear. In this study, two new streptocarbazoles (1 and 3) with cytotoxic activities were obtained by manipulating the staurosporine biosynthetic gene cluster spc followed by heterologous expression. The biosynthetic pathway of streptocarbazoles was proposed, and their productions were improved through the overexpression of the key enzymes involved. This study enriches the structural diversity of ICZ compounds and would facilitate the discovery of new streptocarbazoles via synthetic biological strategies.