Thickness-Tunable Zoology of Magnetic Spin Textures Observed in Fe5GeTe2.

The family of two-dimensional (2D) van der Waals (vdW) materials provides a playground for tuning structural and magnetic interactions to create a wide variety of spin textures. Of particular interest is the ferromagnetic compound Fe5GeTe2 that we show displays a range of complex spin textures as well as complex crystal structures. Here, using a high-brailliance laboratory X-ray source, we show that the majority (1 × 1) Fe5GeTe2 (FGT5) phase exhibits a structure that was previously considered as being centrosymmetric but rather lacks inversion symmetry. In addition, FGT5 exhibits a minority phase that exhibits a long-range ordered (√3 × âˆš3)-R30° superstructure. This superstructure is highly interesting in that it is innately 2D without any lattice periodicity perpendicular to the vdW layers, and furthermore, the superstructure is a result of ordered Te vacancies in one of the topmost layers of the FGT5 sheets rather than being a result of vertical Fe ordering as earlier suggested. We show, from direct real-space magnetic imaging, evidence for three distinct magnetic ground states in lamellae of FGT5 that are stabilized with increasing lamella thickness, namely, a multidomain state, a stripe phase, and an unusual fractal state. In the stripe phase we also observe unconventional type-I and type-II bubbles where the spin texture in the central region of the bubbles is nonuniform, unlike conventional bubbles. In addition, we find a bobber or a cocoon-like spin texture in thick (∼170 µm) FGT5 that emerges from the fractal state in the presence of a magnetic field. Among all the 2D vdW magnets we have thus demonstrated that FGT5 hosts perhaps the richest variety of magnetic phases that, thereby, make it a highly interesting platform for the subtle tuning of magnetic interactions.

Josephson diode effect from Cooper pair momentum in a topological semimetal.

Cooper pairs in non-centrosymmetric superconductors can acquire finite centre-of-mass momentum in the presence of an external magnetic field. Recent theory predicts that such finite-momentum pairing can lead to an asymmetric critical current, where a dissipationless supercurrent can flow along one direction but not in the opposite one. Here we report the discovery of a giant Josephson diode effect in Josephson junctions formed from a type-II Dirac semimetal, NiTe2. A distinguishing feature is that the asymmetry in the critical current depends sensitively on the magnitude and direction of an applied magnetic field and achieves its maximum value when the magnetic field is perpendicular to the current and is of the order of just 10 mT. Moreover, the asymmetry changes sign several times with an increasing field. These characteristic features are accounted for by a model based on finite-momentum Cooper pairing that largely originates from the Zeeman shift of spin-helical topological surface states. The finite pairing momentum is further established, and its value determined, from the evolution of the interference pattern under an in-plane magnetic field. The observed giant magnitude of the asymmetry in critical current and the clear exposition of its underlying mechanism paves the way to build novel superconducting computing devices using the Josephson diode effect.

Magnetic Skyrmions in a Thickness Tunable 2D Ferromagnet from a Defect Driven Dzyaloshinskii-Moriya Interaction.

There is considerable interest in van der Waals (vdW) materials as potential hosts for chiral skyrmionic spin textures. Of particular interest is the ferromagnetic, metallic compound Fe3 GeTe2 (FGT), which has a comparatively high Curie temperature (150-220 K). Several recent studies have reported the observation of chiral Néel skyrmions in this compound, which is inconsistent with its presumed centrosymmetric structure. Here the observation of Néel type skyrmions in single crystals of FGT via Lorentz transmission electron microscopy (LTEM) is reported. It is shown from detailed X-ray diffraction structure analysis that FGT lacks an inversion symmetry as a result of an asymmetric distribution of Fe vacancies. This vacancy-induced breaking of the inversion symmetry of this compound is a surprising and novel observation and is a prerequisite for a Dzyaloshinskii-Moriya vector exchange interaction which accounts for the chiral Néel skyrmion phase. This phenomenon is likely to be common to many 2D vdW materials and suggests a path to the preparation of many such acentric compounds. Furthermore, it is found that the skyrmion size in FGT is strongly dependent on its thickness: the skyrmion size increases from ≈100 to ≈750 nm as the thickness of the lamella is increased from ≈90 nm to ≈2 µm. This extreme size tunability is a feature common to many low symmetry ferro- and ferri-magnetic compounds.

Structural characterization of Kannurin isoforms and evaluation of the role of ß-hydroxy fatty acid tail length in functional specificity.

The novel anti-fungal cyclic lipopeptide 'Kannurin' and its three structural variants produced by Bacillus cereus AK1 were previously reported from our laboratory. The present study reports unexplored structural variants of Kannurin those have functional benefits. Due to the difference in ß-hydroxy fatty acid tail length, they are designated here as Kannurin A (m/z 994.67 ± 0.015), B (m/z 1008.68 ± 0.017), C (m/z 1022.69 ± 0.021), D (m/z 1036.70 ± 0.01), CL (m/z 1040.71 ± 0.02) and DL (m/z 1054.72 ± 0.01). The isoform A (m/z 994.67 ± 0.015) is the shortest cyclic form of Kannurin identified so far. In addition, CL (m/z 1040.71 ± 0.02) and DL (m/z 1054.72 ± 0.01) are the rare natural linear forms. The results of the antimicrobial assays deduced that the difference in lipid tail length of the isoforms contributes tremendous differences in their antimicrobial properties. The isoforms with short lipid tails (A and B) are more selective and potent towards bacteria, whereas the isoforms with long lipid tails (C and D) are more potent against fungi. The molecular dynamics studies and electron microscopic observations supported with circular dichroic spectroscopy analysis showed the structural confirmation and formation of aggregates of Kannurin in solution. The molecular dynamics simulation studies revealed that a single molecule of Kannurin makes enormous intra-molecular interactions and structural re-arrangements to attain stable lowest energy state in solution. When they reach a particular concentration (CMC) especially in aqueous environment, tends to form structural aggregates called 'micelles'. With the structural information and activity relationship described in this study, it is trying to point out the sensitive structural entities that can be modified to improve the efficacy and target specificities of lipopeptide class of antibiotics.

Tailoring of uniaxial magnetic anisotropy in Permalloy thin films using nanorippled Si substrates.

In this work the investigation of in-plane uniaxial magnetic anisotropy induced by the morphology due to ion beam erosion of Si(1 0 0) has been done. Ion beam erosion at an oblique angle of incidence generates a well-ordered nanoripple structure on the Si surface and ripple propagates in a direction normal to ion beam erosion. Permalloy thin films grown on such periodic nanopatterns show a strong uniaxial magnetic anisotropy with easy axis of magnetization in a direction normal to the ripple wave vector. The strength of uniaxial magnetic anisotropy is found to be high for the low value of ripple wavelength; it is decreasing with increasing value of ripple wavelength. Similarly, the strength of uniaxial magnetic anisotropy decreases with increasing Permalloy film thickness. Grazing incidence small angle x-ray scattering data reveals an anisotropic growth of Permalloy thin films with preferential orientation of grains in the direction normal to the ripple wave vector. Permalloy thin film growth is highly conformal with the film surface replicating the substrate ripple morphology up to a film thickness of 50 nm has been observed. Correlation between observed uniaxial magnetic anisotropy to surface modification has been addressed.

Kyasanur forest disease virus breaking the endemic barrier: An investigation into ecological effects on disease emergence and future outlook.

Kyasanur Forest disease (KFD) is found in a limited range of India, but is epidemiologically understudied. The seasonal patterns of KFD are well known; however, the significant concern is on the extent to which changes in epidemiology happen especially under the influence of ecological destructions and by the eventual effects of resulting climate change. Presently, a southward and northward spread of the Kyasanur Forest disease virus (KFDV) along the Western Ghats has been reported in the adjoining states of Kerala, Tamil Nadu, Goa and Maharashtra. In this review, we investigate the cascade of factors that might have facilitated the resurgence of KFDV among the endemic regions in higher frequency and its recent emergence in the area previously not reported. Utilizing published data, we additionally endeavour to exhibit a portion of the impediments of control systems and embody the powerful option strategies for developing KFDV control.

Kannurin, a novel lipopeptide from Bacillus cereus strain AK1: isolation, structural evaluation and antifungal activities.

AIM: This study was performed to isolate and characterize novel antifungal lipopeptide from Bacillus cereus. METHODS AND RESULTS: Elucidation of its chemical structure was carried out by electrospray ionization mass spectra (ESI-MS) and Fourier transform infrared spectroscopy (FT-IR). The compound is a cyclic heptapeptide and composed of amino acids, Leu-Asp-Val-Leu-Leu-Leu-Leu. The in vitro activity of Kannurin against various pathogenic yeasts was assessed by CLSI M27-A and moulds by M38-A. It demonstrated broad-spectrum, fungicidal activity against clinically relevant yeasts and moulds. Kannurin exhibited low haemolytic activity and remained active over a wide pH and temperature range. In addition, Kannurin did not bind with melanin particles and was as active in inhibiting biofilms. CONCLUSIONS: An antifungal surfactin-like lipopeptide produced by Bacillus cereus strain AK1 was purified and chemically characterized. We propose to name this lipopeptide compound 'Kannurin'. To our knowledge, this is the first report of Bacillus cereus producing surfactin-like lipopeptide antibiotic with stronger antifungal activity. SIGNIFICANCE AND IMPACT OF THE STUDY: Our results provide a valuable contribution towards a better understanding of the lipopeptide of Bacillus cereus. Moreover, it raises the possibility of using as an alternative antibiotic in clinical medicine.

Cryptococcus laurentii biofilms: structure, development and antifungal drug resistance.

A great number of fungal infections are related to biofilm formation on inert or biological surfaces, which are recalcitrant to most treatments and cause human mortality. Cryptococcus laurentii has been diagnosed as the aetiological pathogen able to cause human infections mainly in immunosuppressed patients and the spectrum of clinical manifestations ranges from skin lesions to fungaemia. The effect of temperature, pH and surface preconditioning on C. laurentii biofilm formation was determined by 2, 3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide (XTT) reduction assay. Scanning electron microscopic (SEM) analysis of C. laurentii biofilms demonstrated surface topographies of profuse growth and dense colonization with extensive polymeric substances around the cells. In this study, we determined the activity of amphotericin B, itraconazole and fluconazole against C. laurentii free-living cells and biofilms. The activity of antifungals tested was greater against free-living cells, but sessile cells fell into the resistant range for these antifungal agents. Extracellular polymeric substances (EPS), comprising the matrix of C. laurentii biofilms, were isolated by ultrasonication. Fourier transform infrared spectroscopy (FT-IR) was performed with ethanol-precipitated and dried samples. Also, the multielement analysis of the EPS was performed by inductively coupled plasma optical emission spectroscopy (ICP-OES).

Gold in human semen around and away from a gold deposit area.

The study included evaluation of semen from normal, healthy adults and estimation of gold in seminal plasma from two regions Nilambur valley (Malappuram District, Kerala Province, India; n = 11), where gold deposit is present and Kollam town (Kerala Province, India; n = 13) where gold is not present in soil. All samples showed normal spermiogram. Gold was estimated in seminal plasma by employing inductively coupled plasma emission spectrophotometry. It varied from 0.23-1.15 ppm with mean 0.68 ppm in study area while in control area it was 0.13-0.71 ppm with a mean of 0.41 ppm. Statistical studies (independent 't' test) showed significantly high level (p < 0.05) of gold in seminal plasma from study area. ANOVA test proved that gold in seminal plasma is a significant (p < 0.05) factor for total spermatozoa count and its percentage of motility.

Peptide antibiotics: an alternative and effective antimicrobial strategy to circumvent fungal infections.

Mycosis, caused by both filamentous fungi and pathogenic yeasts is a major concern nowadays especially in the immunocompromised patient population. The emergence of pathogenic fungi resistant to current therapies in the last few decades has intensified the search for new antifungals like cationic peptides, which are the key components of innate defense mechanism. The review provides an inventory of different peptides from a diverse array of organisms from bacteria to mammals with proven antifungal activity, their therapeutic options and also about those which are in various stages of preclinical development. Literature, on the total and semi-synthetic variants of the parent peptides that exhibit an improved antifungal activity is also reviewed.