Outer Pair Research Articles

Blakea cubarralensis (Melastomataceae: Pyxidantheae): a new species from Colombia

A new species of Blakea (Melastomataceae) from the department of Meta, Colombia is described and illustrated here, with comments on its etymology, distribution and habitat, phenology, conservation status and taxonomic affinities. Blakea cubarralensis sp. nov. is readily distinguished by its floral bracteoles that are longer than the calyx lobes, the outer pair ovate-elliptic with a long-acuminate apex and 3-nerved, the lobed calyx, the anther connective prolonged into a blunt knob and the ovary 12-locular. The new species is categorized as Endangered (EN) according to the IUCN Red List. This novelty highlights the importance of sub-andean forests and the need to conserve and increase botanical explorations in them.

Fe II] 1.644 µm imaging survey of planetary nebulae with low-ionisation structures

Low-ionisation structures (LISs) are commonly found in planetary nebulae (PNe), but they are still poorly understood. The recent discovery of unforeseen molecular hydrogen gas (H2) has impacted what we think we know about these microstructures and PNe. To obtain an overall understanding of LISs, we carried out an [Fe II] 1.644 µm imagery survey in PNe with LISs, with the aim to detect the [Fe II] 1.644µm emission line, a common tracer of shocks. We present the first detection of [Fe II] 1.644 µmline directly associated with the LISs in four out of five PNe. The theoretical H I 12-4 recombination line was also computed either from the Brγ or the Hβ line and subtracted from the observed narrow-band line fluxes. The [Fe II] 1.644 µm flux ranges from 1 to 40 ×10−15 ergs cm−2 s−1 and the intensity from 2 to 90 ×10−5 erg s−1 cm−2 sr−1. The R(Fe)=[Fe II] 1.644 µm/Brγ line ratio was also computed and found to range between 0.5 and 7. In particular, the [Fe II] 1.644 µm line was detected in NGC 6543 (R(Fe)<0.15), along with the outer pairs of LISs in NGC 7009 (R(Fe)<0.25) and the jet-like LISs in IC 4634 (R(Fe)~1), and in several LISs in NGC 6571 (2<R(Fe)<7). The low R(Fe) result for NGC 6543 is attributed to the UV radiation from the central star. In contrast, the higher values in NGC 6571 and IC 4634 are indicative of shocks. The moderate R(Fe) in NGC 7009 likely indicates the contribution of both mechanisms.

Detection of the [C I] λ8727 emission line

We report the first spatially resolved detection of the near-infrared [C I] λ8727 emission from the outer pair of low-ionization structures in the planetary nebula NGC 7009 from data obtained by the Multi Unit Spectroscopic Explorer integral field unit. This atomic carbon emission marks the transition zone between ionized and neutral gas and for the first time offers direct evidence that LISs are photodominated regions. The outer LIS pair exhibits intense [C I] λ8727 emission, but He I λ8733 is absent. Conversely, the inner pair of knots shows both lines, likely due to the host nebula emission. Furthermore, the [C I] λ8727 line is absent in the host nebula emission, but He I λ8733 is present. Although the origin of the [C I] λ8727 line is still debated, its detection supports the scenario of photoevaporated dense molecular clumps.

Diffusion Nuclear Magnetic Resonance Measurements on Cationic Gold (I) Complexes in Catalytic Conditions: Counterion and Solvent Effects.

The amount of free ions, ion pairs, and higher aggregate of the possible species present in a solution during the gold(I)-catalyzed alkoxylation of unsaturated hydrocarbon, i.e., ISIP (inner sphere ion pair) [(NHC)AuX] and OSIP (outer sphere ion pairs) [(NHC)Au(TME)X] [NHC 1,3-bis(2,6-di-isopropylphenyl)-imidazol-2-ylidene; TME = tetramethylethylene (2,3-bis methyl-butene); X- = Cl-, BF4-, OTf-; and OTs- BArF4- (ArF = 3,5-(CF3)2C6H3)], has been determined. The 1H and 19F DOSY NMR measurements conducted in catalytic conditions indicate that the dissociation degree (α) of the equilibrium ion pair/free ions {[(NHC)Au(TME)X] [(NHC)Au(TME)]+ + X-} depends on the nature of the counterion (X-) when chloroform is the catalytic solvent: while the compounds containing OTs- and OTf- as the counterion gave a low α (which means a high number of ion pairs) of 0.13 and 0.24, respectively, the compounds containing BF4- and BArF4- showed higher α values of 0.36 and 0.32, respectively. These results experimentally confirm previous deductions based on catalytic and theoretical data: the lower the α value, the greater the catalytic activity because the anion that can activate methanol during a nucleophilic attack, although the lower propensity to activate methanol of BF4- and BArF4-, as suggested by the DFT calculations, cannot be completely overlooked. As for the effect of the solvent, α increases as the dielectric constant increases, as expected, and in particular, green solvents with high dielectric constants show a very high α (0.90, 0.84, 0.80, and 0.70 for propylene carbonate, γ-valerolactone, acetone, and methanol, respectively), thus confirming that the moderately high activity of NHC-Au-OTf in these solvents is due to the specific effect of polar functionalities (O-H, C=O, O-R) in activating methanol. Finally, the DOSY measurements conducted in p-Cymene show the formation of quadrupole species: under these conditions, the anion can better exercise its 'template' and 'activating' roles, giving the highest TOF.

Development of a novel sensitive single-tube nested PCR assay for the detection of African swine fever virus.

African swine fever (ASF) is a highly fatal and contagious viral disease caused by African swine fever virus (ASFV). It has caused significant economic losses to the swine industry and poses a serious threat to food security worldwide. Diagnostic tests with high sensitivity are essential for the effective management of ASF. Here, we describe a single-tube nested PCR (STN-PCR) assay for the detection of ASFV in which two consecutive amplification steps are carried out within a single tube. Two pairs of primers (outer and inner) were designed to target the p72 gene of ASFV. The primer concentrations, annealing temperatures, and number of amplification cycles were optimized to ensure the consecutive utilization of outer and inner primer pairs during amplification while minimizing the likelihood of amplicon contamination. In comparison with two conventional endpoint PCR assays (one of which is recommended by the World Organization for Animal Health), the newly developed STN-PCR assay demonstrated a 100-fold improvement in the limit of detection (LOD), detecting 100 copies of ASFV genomic DNA, whereas the endpoint PCR assays could detect no fewer than 10,000 copies. The clinical performance of the STN-PCR assay was validated using 95 tissue samples suspected of being positive for ASFV, and the assay showed 100% specificity. A Cohen's kappa value of 0.91 indicated perfect agreement between the assays. This new STN-PCR assay is a potentially valuable tool that will facilitate the control of ASF.

The merger of co-rotating vortices in dusty flows

We investigate the effect of particle inertia on the merger of co-rotating dusty vortex pairs at semi-dilute concentrations. In a particle-free flow, the merger is triggered once the ratio of vortex core size to vortex separation reaches a critical value. The vortex pair separation then decreases monotonically until the two cores merge together. Using Eulerian–Lagrangian simulations of co-rotating particle-laden vortices, we show substantial departure from the vortex dynamics previously established in particle-free flows. Most strikingly, we find that disperse particles with moderate inertia cause the vortex pair to push apart to a separation nearly twice as large as the initial separation. During this stage, the drag force exerted by particles ejected out of the vortex cores on the fluid results in a net repulsive force that pushes the two cores apart. Eventually, the two dusty vortices merge into a single vortex with most particles accumulating outside the core, similar to the dusty Lamb–Oseen vortex described in Shuai & Kasbaoui (J. Fluid Mech., vol 936, 2022, p. A8). For weakly inertial particles, we find that the merger dynamics follows the same mechanics as that of a single-phase flow, albeit with a density that must be adjusted to match the mixture density. For highly inertial particles, the feedback force exerted by the particles on the fluid may stretch the two cores during the merger to a point where each core splits into two, resulting in inner and outer vortex pairs. In this case, the merger occurs in two stages where the inner vortices merge first, followed by the outer ones.

Site specifically probing the unfolding process of human telomere i-motif DNA using vibrationally enhanced alkynyl stretch.

The microscopic unfolding process of a cytosine-rich DNA forming i-motif by hemi-protonated base pairs is related to gene regulation. However, the detailed thermal unfolding mechanism and the protonation/deprotonation status of site-specific cytosine in DNA in a physiological environment are still obscure. To address this issue, a vibration-enhanced CC probe tagged on 5'E terminal cytosine of human telomere i-motif DNA was examined using linear and nonlinear infrared (IR) spectroscopies and quantum-chemistry calculations. The CC probe extended into the major groove of the i-motif was found using nonlinear IR results only to introduce a minor steric effect on both steady-state structure and local structure dynamics; however, its IR absorption profile effectively reports the cleavage of the hemi-protonated base pair of C1-C13 upon the unfolding with C1 remaining protonated. The temperature mid-point (Tm) of the local transition reported using the CC tag was slightly lower than the Tm of global transition, and the enthalpy of the former exceeds 60% of the global transition. It is shown that the base-pair unraveling is noncooperative, with outer base pairs breaking first and being likely the rate limiting step. Our results offered an in-depth understanding of the macroscopic unfolding characteristics of the i-motif DNA and provided a nonlinear IR approach to monitoring the local structural transition and dynamics of DNA and its complexes.

First report of a 'Candidatus Phytoplasma australasiaticum'-related phytoplasma strain associated with shoot proliferation disease of variegated croton in Taiwan.

Codiaeum variegatum (family Euphorbiaceae) is a leaf ornamental commonly known as variegated croton, which is often found in gardens or grown as indoor plants. In December of 2022, two cutting-propagated variegated croton plants exhibiting abnormal shoot proliferation and little leaf symptoms (Fig. S1) were found in a nursery owned by a private breeder in Wanluan Township, Pingtung County, Taiwan. The plants were propagated from a single stock plant, which died during transplanting from a commercial nursery in Changzhi Township, Pingtung County. To determine the potential cause of such symptoms, leaf tissues were collected from the center of the two symptomatic plants. Their DNA were extracted with a Synergy 2.0 Plant DNA Extraction Kit (OPS Diagnostics, Lebanon, NJ) and used for further testing. As controls, two symptomless stock plants were collected from the commercial nursery in Changzhi Township and used to produce cutting-propagated plants; leaf DNA was extracted from each plant as described above. The DNA samples were subjected to PCR testing using the phytoplasma-specific primer pair P1/P7 (Schneider et al. 1995), and only DNA from the symptomatic plants produced the expected 1.8-kb amplicon. The two phytoplasma isolates detected in the plants were designated as CvaA and CvaB. After sequencing and analyzing the data using the iPhyClassifier program (Zhao et al. 2009), both CvaA and CvaB were classified to subgroup 16SrII-A (GenBank accession no. L33765) with a similarity coefficient of 1.0. The near-full-length 16S rDNA fragments of the detected isolates (GenBank accession no. OR794242) were also identical (1,463/1,463 bp) to that of NCHU2014 (GenBank accession no. CP040925, bp 537768-539230), a reference 'Ca. Phytoplasma australasiaticum'-related strain (16SrII-A) found in Taiwan (Chang et al. 2015; Rodrigues Jardim et al. 2023). To validate the results, the DNA samples were also tested with 16SrII group-specific semi-nested PCR targeting the elongation factor Tu gene. The outer and inner primer pairs used were TUF-II-F1/TUF-II-R1 and TUF-II-F2/TUF-II-R1, respectively (Al-Subhi et al. 2017). An expected amplicon was detected in the symptomatic samples but not in the symptomless counterparts. The amplified fragments' sequences (GenBank accession no. OR634931) were identical to that of the elongation factor Tu gene of the 'Ca. Phytoplasma australasiaticum'-related strain NCHU2014 (989/989 bp; GenBank accession no. CP040925, bp 139344-140332). The protein translocase gene secY of the detected phytoplasma was also amplified and sequenced using semi-nested primers SecYF1(II), SecYF2(II) and SecYR1(II) (Lee et al. 2010). Again, the sequences of the detected isolates (GenBank accession no. OR862773) were identical to that of NCHU2014 (1,263/1,263; GenBank accession no. CP040925, bp 192846-194108). The quality of the DNA samples was confirmed by PCR targeting the plant host's 28S rDNA using primer pair 28KJ/28C (Cullings 1992) and all symptomatic and symptomless samples produced the target amplicon (0.7 kb). 16SrII phytoplasmas have been detected in different host plants in Taiwan (Chang et al. 2015). To our knowledge, this is the first record of this group of pathogens infecting variegated croton in Taiwan. Branch-inducing phytoplasma has been used to improve the ornamental values of poinsettias, another Euphorbiaceae species (Lee et al. 1997). Further testing is needed to determine whether the phytoplasma detected in this work could be used for similar purposes.

Floral morphology of 'Anand' rapid cycling Brassica oleracea .

Abstract The 'Anand' type of cytoplasmic male sterility (CMS) was introduced to Brassica oleracea through protoplast fusion (Cardi and Earle, 1997), providing a source of male sterility that is of value in producing F1 hybrid varieties of this species without the cold sensitivity of 'Ogura' cytoplasm. In this species, as in others in which it has been introduced, 'Anand' mitochondria are associated with flower abnormalities. The best lines have been used by commercial breeders. This paper describes 'Anand' flower abnormalities in further detail. Rapid cycling brassica with 'Anand' cytoplasm may have promise as a model system for research on floral patterning. Materials and Methods. Three lines of rapid cycling B. oleracea carrying the 'Anand' cytoplasm and one wild type were grown. The flower morphology of 'Anand' lines was classified as good in F25-F-1A, fair in F25-F-6B, and poor in F23-F-1B (Cardi and Earle, 1997). Seedlings were started in an indoor growth room, but were maintained in a naturally lit greenhouse at 20° night, 25° day during flowering. Five flowers on 5 plants of each line were examined. Results. Morphological abnormalities affected all floral parts (Table 1). There was substantial variation among flowers on individual plants and among lines but little within lines. Conclusions. "Good" flowers have large petals that push open the sepals before the carpel elongates. Female fertility could be reduced due to occlusion of the stigma or physical damage caused by the stigma pressing against the end of a sepal and kinking the style. Female fertility in some flowers was unlikely because the carpel suture failed to fuse. In some cases the edge of the split carpel was sepal-like, consistent with the absence of SEPALLATA expression. The stigma on a sepal represents the converse. Stamens were most strongly affected, with outer stamens most reduced. This whorl is the one most frequently suppressed in flowering plants (Masters, 1869). The number of stamens was reduced to varying degrees. First to be lost was one or both of the pair outside the petals. Then the outer pair inside the petals was affected. One or both of these stamens could either be lost or doubled to give 3 to 5 stamens. Again a positional cue for stamens appears to be weakened. Anther development was often limited, the expected and desired consequence of the Anand genotype. Some undehisced " good " anthers contained pollen. There is variation even among the lines initially described as " good ". Further selection among these may help identify those that are most promising for further use in hybrid production.

Can a binary star host three giant circumbinary planets?

ABSTRACT We investigate the orbital stability of a tilted circumbinary planetary system with three giant planets. The planets are spaced by a constant number (Δ) of mutual Hill radii in the range Δ = 3.4–12.0 such that the period ratio of the inner pair is the same as that of the outer pair. A tilted circumbinary planetary system can be unstable even if the same system around a coplanar binary is stable. For an equal-mass binary, we find that the stability of a three-planet system is qualitatively similar to that of a two-planet system, but the three-planet system is more unstable in mean motion resonance regions. For an unequal-mass binary, there is significantly more instability in the three-planet system as the inner planets can undergo von Zeipel–Kozai–Lidov oscillations. Generally in unstable systems, the inner planets are more likely to be ejected than the outer planets. The most likely unstable outcome for closely spaced systems, with Δ ≲ 8, is a single remaining stable planet. For more widely separated systems, Δ ≳ 8, the most likely unstable outcome is two stable planets, only one being ejected. An observed circumbinary planet with significant eccentricity may suggest that it was formed from an unstable system. Consequently, a binary can host three tilted giant planets if the binary stars are close to equal mass and provided that the planets are well spaced and not close to a mean motion resonance.

Multi-Objective Optimization Analysis of Magnetic Gear With HTS Bulks and Uneven Halbach Arrays

To improve the output torque of coaxial magnetic gears, a novel coaxial magnetic gear (CMG) with high temperature superconducting (HTS) bulks and uneven Halbach arrays is proposed in this paper. The convex structure is used in the middle of inner rotor permanent magnets (PMs). The PMs of the outer rotor are arranged in a low-high-low arrangement, epoxy resin is added between the PMs of outer rotor and the outer iron yoke. At the same time, the HTS bulks replace the epoxy resin to reduce magnetic flux leakage. In addition, according to the sensitivity analysis, the structural parameters can be divided into different levels, the multi-objective optimization analysis is carried out. Finally, the optimal CMG topology with 4 inner and 17 outer pole pairs is established. The results show that the amount of PM is reduced and the output torque is effectively increased by finite element analysis (FEA).

Орбита внешней пары тройной звезды T Tauri

The T Tauri's triple system of young stars (WDS 04220+1932=Hip 20390) was discovered in 1983. Since that time, a lot of articles are devoted to the study of the physical properties of the stars of this system. Our work is dedicated to astrometric study of this triple system using the apparent motion parameters (AMP) method. The orbit of the inner pair $ SaSb $ with a period of 27 years is now well known \citep{schef20}. The total mass $M_{Sa+Sb}=2.49 M_\odot$ if to use parallax from Gaia DR3 \citep{G2022}. Two orbits of the outer pair N-S are obtained on the basis of published high-precision homogeneous observations on the Keck~1 and VLT telescopes, and one of them is almost circular orbit. For a circular orbit, orbital elements and dynamic parallax can be calculated for a given mass using only apparent motion parameters. This is what made it possible to compare dynamic parallax with high-precision one from the Gaia DR3 catalog and to calculate the components masses depending on the mass of the internal subsystem: $M_{N}=2.4\pm 0.2~M_\odot$, $M_{Sa}=2.09\pm 0.05~M_\odot$, $M_{Sb}=0.40\pm 0.05~M_\odot$. Limits for the orbital period are also estimated: $500\leq {P}\leq {700}$ ~ years.

Dynamic Study of the Triple Star T Tauri

The triple system of young stars T Tauri was discovered relatively recently and has attracted the attention of numerous researchers. Many papers have been dedicated to the study of the physical properties of the system’s stars, which are surrounded by a disk of dust and gas. Our work is focused on the astrometric analysis of this triple system using the method of apparent motion parameters (AMP). Currently, the orbit of the inner pair Sa-Sb with a period of 27 years is well-established. Based on the Gaia DR3 parallax, its total mass MSa + Sb=2.49M⊙. Relying on the published high-precision uniform observations with the Keck 1 and VLT telescopes, we employed the AMP method to derive two orbits for the outer pair N-S, one of which is almost circular. For a circular orbit, it is possible to calculate the orbital elements and dynamic parallax for a given mass solely using the apparent motion parameters. This enabled a comparison between the dynamic parallax and the high-precision parallax from the Gaia DR3 catalog, facilitating the calculation of masses of each component based on the mass of the inner subsystem: MN=(2.4±0.2)M⊙, MSa=(2.09±0.05)M⊙, MSb=(0.40±0.05)M⊙. The boundaries for the orbital period were estimated to be 500⩽P⩽700 years.

Spectroscopic Orbits of Subsystems in Multiple Stars. IX

New spectroscopic orbits of inner subsystems in 14 hierarchies are determined from long-term monitoring with the optical echelle spectrometer, CHIRON. Their main components are nearby solar-type stars belonging to nine triple systems (HIP 3645, 14307, 36165, 79980, 103735, 103814, 104440, 105879, 109443) and five quadruples of 2 + 2 hierarchy (HIP 41171, 49336, 75663, 78163, and 117666). The inner periods range from 254 days to 18 yr. Inner subsystems in HIP 3645, 14313, 79979, 103735, 104440, and 105879 are resolved by speckle interferometry, and their combined spectro-interferometric orbits are derived here. Astrometric orbits of HIP 49336 Aa,Ab and HIP 117666 Aa,Ab are determined from wobble in the observed motion of the outer pairs. Comparison with three spectroscopic orbits found in the Gaia data release 3 archive reveals that Gaia underestimated the amplitudes (except for HIP 109443), while the periods match approximately. This work contributes new data on the architecture of nearby hierarchical systems, complementing their statistics.

Mean motion resonance capture in the context of type I migration

Capture into mean motion resonance (MMR) is an important dynamical mechanism because it shapes the final architecture of a planetary system. We simulate systems of two or three planets undergoing migration with varied initial parameters such as planetary mass and disk surface density and analyse the resulting resonant chains. In contrast to previous studies, our results show that the disk properties are the dominant impact on capture into MMR, while the total planetary mass barely affects the final system configuration as long as the planet does not open a gap in the disk. We confirm that adiabatic resonant capture is the correct framework for understanding the conditions leading to MMR formation because its predictions are qualitatively similar to the numerical results. However, we find that eccentricity damping can facilitate the capture in a given resonance. We find that under typical disk conditions, planets tend to be captured into 2:1 or 3:2 MMRs, which agrees well with the observed exoplanet MMRs. Our results predict two categories of systems: those that have uniform chains of wide resonances (2:1 or 3:2 MMRs), and those whose inner pair is more compact than the outer pair, such as 4:3:2 chains. Both categories of resonant chains are present in observed exoplanet systems. On the other hand, chains whose inner pair is wider than the outer pair are very rare and emerge from stochastic capture. Our work here can be used to link the current configuration of exoplanetary systems to the formation conditions within protoplanetary disks.

Spin-orbital Yu-Shiba-Rusinov states in single Kondo molecular magnet

Studies of single-spin objects are essential for designing emergent quantum states. We investigate a molecular magnet Tb2Pc3 interacting with a superconducting Pb(111) substrate, which hosts unprecedented Yu-Shiba-Rusinov (YSR) subgap states, dubbed spin-orbital YSR states. Upon adsorption of the molecule on Pb, the degeneracy of its lowest unoccupied molecular orbitals (LUMO) is lifted, and the lower LUMO forms a radical spin via charge transfer. This leads to Kondo screening and subgap states. Intriguingly, the YSR states display two pairs of resonances with clearly distinct behavior. The energy of the inner pair exhibits prominent inter and intra molecular variation, and it strongly depends on the tip height. The outer pair, however, shifts only slightly. As is unveiled through theoretical calculations, the two pairs of YSR states originate from the ligand spin and charge-fluctuating higher LUMO, coexisting in a single molecule, but only weakly coupled presumably due to different spatial distribution. Our work paves the way for understanding complex many-body excitations and constructing molecule-based topological superconductivity.

Automatic Tuning and Turbulence Mitigation for Fixed-Wing UAV with Segmented Control Surfaces

Unlike bigger aircraft, the small fixed-wing unmanned aerial vehicles face significant stability challenges in a turbulent environment. To improve the flight performance, a fixed-wing UAV with segmented aileron control surfaces has been designed and deployed. A total of four ailerons are attached to the main wing and grouped into inner and outer aileron pairs. The controllers are automatically tuned by utilizing the frequency response data obtained via the frequency sampling filter and the relay with embedded integrator experiments. The hardware validation experiments are performed in the normal and turbulent flight environments under three configurations: inner aileron pair only, outer aileron pair only and collective actuation of all the aileron pairs. The error-threshold-based control is introduced to handle collective actuation of aileron pairs. The experiments have manifested that the collective usage of all aileron segments improves the roll attitude stability by a margin of 38.69% to 43.51% when compared to the independent actuation of aileron pairs in a turbulent atmosphere.

Photoluminescence of Bi3+ in LiCaY5(BO3)6 and color-tunable emission through energy transfer to Eu3+/Tb3+

Bi3+ has an outer shell lone pair electrons and the energy of 6p orbitals are also sensible to the coordination environment, therefore its typical wide band excitation and emission spectra are highly dependent on the host structure. The recently reported LiCaY5(BO3)6 has multiple sites suitable for cationic doping. In this work, Bi3+ singly doped phosphors and Bi3+/Eu3+ and Bi3+/Tb3+ co-doped phosphors were prepared by high temperature solid state reactions. Careful Rietveld refinements on powder X-ray diffraction suggest the site-preferential doping of Bi3+ into M3 site, which has an octahedral cavity. By 1 atom% doping, Bi3+ exhibits a broad emission band centered at 364 nm with an internal quantum efficiency of 39.8%. The energy transfer to Eu3+/Tb3+ are firmly proved by both the emission intensity change and the decay curves, which is likely through the dipole-dipole interactions. Color-tunable emissions from blue to red, or from blue to green have been realized and the combination with 275 nm LED chip gives the bright blue, red and green emission for LiCa(Y0.99Bi0.01)5(BO3)6, LiCa(Y0.69Bi0.01Eu0.3)5(BO3)6, and LiCa(Y0.69Bi0.01Tb0.3)5(BO3)6, respectively.

Rational Design of Plant Hairpin-like Peptide EcAMP1: Structural–Functional Correlations to Reveal Antibacterial and Antifungal Activity

Plant antimicrobial peptides from the α-hairpinins family (hairpin-like peptides) are known to possess a wide range of biological activities. However, less is known about the structural determinants of their antimicrobial activity. Here, we suggest that spatial structure as well as surface charge and hydrophobicity level contribute to the antimicrobial properties of α-hairpinin EcAMP1 from barnyard grass (Echinochloa cruss-galli) seeds. To examine the role of the peptide spatial structure, two truncated forms of EcAMP1 restricted by inner and outer cysteine pairs were synthesized. It was shown that both truncated forms of EcAMP1 lost their antibacterial activity. In addition, their antifungal activity became weaker. To review the contribution of surface charge and hydrophobicity, another two peptides were designed. One of them carried single amino acid substitution from tryptophan to alanine residue at the 20th position. The second one represented a truncated form of the native EcAMP1 lacking six C-terminal residues. But the α-helix was kept intact. It was shown that the antifungal activity of both modified peptides weakened. Thereby we can conclude that the secondary structural integrity, hydrophobic properties, and surface charge all play roles in the antimicrobial properties of α-hairpinins. In addition, the antibacterial activity of cereal α-hairpinins against Gram-positive bacteria was described for the first time. This study expands on the knowledge of structure–function interactions in antimicrobial α-hairpinins.

Triple-band terahertz metamaterial absorber using the nesting structure of two pairs of splitting arcs

This paper presents the design of triple-band terahertz metamaterial absorber, whose surface structure is a nested-type metallic pattern composed of two pairs of splitting arcs, of which the inner two splitting arcs have the same but smaller size, while the outer two possess the same but larger dimension. The surface patterned structure can strongly interact with the incident terahertz beam, resulting in three narrow-band and discrete resonance peaks having higher than 94% absorption rates. Near-field patterns of the three absorption peaks are discussed to insight into the physical mechanism of these peaks, it is revealed that the first two absorption peaks result from the dipole resonance of the inner two splitting arcs and outer pair of splitting arcs, respectively, while the last absorption peak is caused by surface propagation resonance of the surface patterned resonator. The effect of structure parameters, including the sizes of splitting arcs and the spacing between two pairs of splitting arcs, on the absorption properties, is further analyzed. The absorber suggested here could provide guidance for the design of multiple-band metamaterial absorbers, and could find great application prospects in terahertz technology-related areas.