"Visualizing" the partially reversible conversion of gold nanoclusters via the Au23(S-c-C6H11)17 intermediate.

Transformation chemistry of atomically precise metal nanoclusters has emerged as a novel strategy for fundamental research on the structure-property correlations of nanomaterials. However, a thorough understanding of the transformation mechanism is indeed necessary to understand the structural growth patterns and corresponding property evolutions in nanoclusters. Herein, we present the ligand-exchange-induced transformation of the [Au23(SR)16]- (8e-) nanocluster to the [Au25(SR')18]- (8e-) nanocluster, through the Au23(SR)17 (6e-) intermediate species. Identification of this key intermediate through a partially reversible transformation helped in a detailed investigation into the transformation mechanism with atomic precision. Moreover, photophysical studies carried out on this Au23(SR)17 species, which only differs by a single ligand from that of the [Au23(SR)16]- nanocluster reveal the property evolutions at the slightest change in the nanocluster structure.

Inter-species interaction of bradyrhizobia affects their colonization and plant growth promotion in Arachis hypogaea.

Bradyrhizobia are the principal symbiotic partner of the leguminous plant and take active part in biological nitrogen-fixation. The present investigation explores the underlying competition among different strains during colonization in host roots. Six distinct GFP and RFP-tagged Bradyrhizobium strains were engineered to track them inside the peanut roots either independently or in combination. The Bradyrhizobium strains require different time-spans ranging from 4 to 21 days post-infection (dpi) for successful colonization which further varies in presence of another strain. While most of the individual strains enhanced the shoot and root dry weight, number of nodules, and nitrogen fixation capabilities of the host plants, no significant enhancement of plant growth and nodulation efficiency was observed when they were allowed to colonize in combinations. However, if among the combinations one strains is SEMIA 6144, the co-infection results in higher growth and nodulation efficiency of the hosts. From the competition experiments it has been found that Bradyrhizobium japonicum SEMIA 6144 was found to be the most dominant strain for effective nodulation in peanut. The extent of biofilm and exopolysaccharide (EPS) production by these isolates, individually or in combinations, were envisaged to correlate whether these parameters have any impact on the symbiotic association. But the extent of colonization, growth-promotion and nitrogen-fixation ability drastically lowered when a strain present together with other Bradyrhizobium strain. Therefore, it is imperative to understand the interaction between two co-inoculating Bradyrhizobium species for nodulation followed by plant growth promotion to develop suitable consortia for enhancing BNF in peanut and possibly for other legumes.

Impact of Rhizospheric Microbiome on Rice Cultivation.

The rhizosphere niche is extremely important for the overall growth and development of plants. Evidently, it is necessary to understand the complete mechanism of plant microbe interactions of the rhizosphere for sustainable and low input productivity. To meet the increasing global food demand, rice (Oryza sativa L.) agriculture seeks optimal conditions. The unique oxic-anoxic interface of rice-growing soil has invited divergent microbes with dynamic biogeochemical cycles. This review provides the systematic analysis of microbes associated with the major biogeochemical cycles with the aim to generate better management strategies of rhizospheric microbiome in the field of rice agriculture. For instance, several methanogenic and methanotrophic bacteria in the rice rhizosphere make an equilibrium for methane concentration in the environment. The carbon sequestration in paddy soil is again done through many rhizospheric microorganisms that can directly assimilate CO2 with their photoautotrophic mode of nutrition. Also the phosphate solubilizing microbes remain to be the most important keys for the PGPR activity of the paddy ecosystem. In addition, rhizospheric microbiome remain crucial in degradation and solubilization of organo-sulfur and insoluble inorganic sulfides which can be taken by the plants. Further, this review elucidates on the advantages of using metagenomic and metaproteomic approaches as an alternative of traditional approaches to understand the overall metabolic pathways operational in paddy-field. These knowledges are expected to open new possibilities for designing the balanced microbiome used as inoculum for intensive farming and will eventually lead to exert positive impacts on rice cultivation.

Recent progress in atomically precise silver nanocluster-assembled materials.

In the dynamic landscape of nanotechnology, atomically precise silver nanoclusters (Ag NCs) have emerged as a novel and promising category of materials with their fascinating properties and enormous potential. However, recent research endeavors have surged towards stabilizing Ag-based NCs, leading to innovative strategies like connecting cluster nodes with organic linkers to construct hierarchical structures, thus forming Ag-based cluster-assembled materials (CAMs). This approach not only enhances structural stability, but also unveils unprecedented opportunities for CAMs, overcoming the limitations of individual Ag NCs. In this context, this review delves into the captivating realm of atomically precise nitrogen-based ligand bonded Ag(I)-based CAMs, providing insights into synthetic strategies, structure-property relationships, and diverse applications. We navigate the challenges and advancements in integrating Ag(I) cluster nodes, bound by argentophilic interactions, into highly connected periodic frameworks with different dimensionalities using nitrogen-based linkers. Despite the inherent diversity among cluster nodes, Ag(I) CAMs demonstrate promising potential in sensing, catalysis, bio-imaging, and device fabrication, which all are discussed in this review. Therefore, gaining insight into the silver nanocluster assembly process will offer valuable information, which can enlighten the readers on the design and advancement of Ag(I) CAMs for state-of-the-art applications.

Unveiling growth-promoting attributes of peanut root endophyte Micromonospora sp.

In this study, 20 endophytic actinobacteria were isolated from different parts of peanut plants growing in cropland with low and high salt in West Bengal, India. The endophytes underwent a rigorous morphological, biochemical, and genetic screening process to evaluate their effectiveness in enhancing plant growth. About 20% of these isolates were identified as potential plant growth-promoting endophytic actinobacteria, which showed high 16S rRNA gene sequence similarity (up to 99-100%) with different species of Micromonospora. Among these isolates, Micromonospora sp. ASENR15 produced the highest levels of indole acetic acid (IAA) and gibberellic acid (GA), while Micromonospora sp. ASENL2, Micromonospora sp. ANENR4, and Micromonospora sp. ASENR12 produced the highest level of siderophore. Among these leaf and root endophytic Micromonospora, strain ANENR4 was tested for its plant growth-promoting attributes. ANENR4 can be transmitted into the roots of a healthy peanut plant, enhances growth, and colonize the roots in abundance, suggesting the potential agricultural significance of the strain. Moreover, the study is the first report of endophytic Micromonospora in peanuts with PGP effects. The outcomes of this study open avenues for further research on harnessing the benefits of this endophytic Micromonospora for optimizing plant growth in agriculture.

Photoisomerization and Light-Controlled Antibacterial Activity of Fluoroquinolone-Azoisoxazole Hybrids.

Photopharmacology holds a huge untapped potential to locally treat diseases involving photoswitchable drugs via the elimination of drugs' off-target effects. The growth of this field has created a pressing demand to develop such light-active drugs. We explored the potential for creating photoswitchable antibiotic hybrids by attaching pharmacophores norfloxacin/ciprofloxacin and azoisoxazole (photoswitch). All compounds exhibited a moderate to a high degree of bidirectional photoisomerization, long thermal cis half-lives, and impressive photoresistance. Gram-negative pathogens were found to be insensitive to these hybrids, while against Gram-positive pathogens, all hybrids in their trans states exhibited antibacterial activity that is comparable to that of the parent drugs. Notably, the toxicity of the irradiated hybrid 6 was found to be 2-fold lower than the nonirradiated trans isomer, indicating that the pre-inactivated cis-enriched drug can be employed for the site-specific treatment of bacterial infection using light, which could potentially eliminate the unwanted exposure of toxic antibiotics to both beneficial and untargeted harmful microbes in our body. Molecular docking revealed different binding affinity of the cis and trans isomers with the topoisomerase IV enzyme, due to their different shapes.

Endophytic Streptomyces sp. MSARE05 isolated from roots of Peanut plant produces a novel antimicrobial compound.

AIM: This study aimed to isolate, endophytic Streptomyces sp. MSARE05 isolated from root of a peanut (Arachis hypogaea) inhibits the growth of other bacteria. The research focused on characterizing the strain and the antimicrobial compound. METHODS AND RESULTS: The surface-sterilized peanut roots were used to isolate the endophytic bacterium Streptomyces sp. MSARE05. A small-scale fermentation was done to get the antimicrobial compound SM05 produced in highest amount in ISP-2 medium (pH 7) for 7 days at 30°C in shaking (180 rpm) condition. Extraction, purification, and chemical analysis of the antibacterial component revealed a novel class of antibiotics with a 485.54 Dalton molecular weight. The MIC was 0.4-0.8 µg ml-1 against the tested pathogens. It also inhibits multidrug-resistant (MDR) pathogens and Mycobacterium with 0.8-3.2 µg ml-1 MIC. SM05 was found to disrupt cell membrane of target pathogen as evident by significant leakage of intracellular proteins and nucleic acids. It showed synergistic activity with ampicillin, chloramphenicol, streptomycin, and kanamycin. CONCLUSIONS: The new-class antimicrobial SM05 consisting naphthalene core moiety was effective against drug-resistant pathogens but non-cytotoxic to human cells. This study underscores the significance of endophytic Streptomyces as a source of innovative antibiotics, contributing to the ongoing efforts to combat antibiotic resistance.

Insights into colistin-mediated fluorescence labelling of bacterial LPS.

Gram-negative bacterial infections are becoming untreatable due to their ability to mutate, and the gradual development of their resistance to the available antimicrobials. In recent times colistin, a drug of last resort, started losing its efficacy towards multidrug-resistant bacterial infections. Colistin targets bacterial endotoxin lipopolysaccharides (LPS) and destabilises the cytoplasmic membrane by disrupting the outer LPS membrane. In this study, we have tried to label the bacterial LPS, the main constituent of the cytoplasmic membrane of bacterial cells, to try to understand the interaction mechanism of LPS with colistin. The chemosensor, naphthaldehyde appended furfural (NAF) that selectively recognises colistin can label LPS, by showing its fluorescence signals. The computationally derived three-dimensional structure of LPS has been introduced to speculate on the possible binding mode of colistin with LPS, and this was also thoroughly studied with the help of quantum mechanics and molecular dynamics energy minimisation. Fluorescence microscopy and FE-SEM microscopic studies were also used to observe the change in the structural morphology of colistin-sensitive and resistant Salmonella typhi in different experimental conditions.

Insights of the efficient hydrogen evolution reaction performance in bimetallic Au4Cu2 nanoclusters.

The design of efficient electrocatalysts for improving hydrogen evolution reaction (HER) performance using atomically precise metal nanoclusters (NCs) is an emerging area of research. Here, we have studied the HER electrocatalytic performance of monometallic Cu6 and Au6 nanoclusters and bimetallic Au4Cu2 nanoclusters. A bimetallic Au4Cu2/MoS2 composite exhibits excellent HER catalytic activity with an overpotential (η10) of 155 mV vs. reversible hydrogen electrode observed at 10 mA cm-2 current density. The improved HER performance in Au4Cu2 is due to the increased electrochemically active surface area (ECSA), and Au4Cu2 NCs exhibits better stability than Cu6 and Au6 systems and bare MoS2. This augmentation offers a greater number of active sites for the favorable adsorption of reaction intermediates. Furthermore, by employing X-ray photoelectron spectroscopy (XPS) and Raman analysis, the kinetics of HER in the Au4Cu2/MoS2 composite were elucidated, attributing the favorable performance to better electronic interactions occurring at the interface between Au4Cu2 NCs and the MoS2 substrate. Theoretical analysis reveals that the inherent catalytic enhancement in Au4Cu2/MoS2 is due to favorable H atom adsorption over it and the smallest ΔGH* value. The downshift in the d-band of the Au4Cu2/MoS2 composite influences the binding energy of intermediate catalytic species. This new catalyst sheds light on the structure-property relationship for improving electrocatalytic performance at the atomic level.

A thiolated copper-hydride nanocluster with chloride bridging as a catalyst for carbonylative C-N coupling of aryl amines under mild conditions: a combined experimental and theoretical study.

Atomically precise copper nanoclusters (Cu NCs), an emerging class of nanomaterials, have garnered significant attention owing to their versatile core-shell architecture and their potential applications in catalytic reactions. In this study, we present a straightforward synthesis strategy for [Cu29(StBu)12(PPh3)4Cl6H10][BF4] (Cu29) NCs and explore their catalytic activity in the carbonylative C-N coupling reaction involving aromatic amines and N-heteroarenes with dialkyl azodicarboxylates. Through a combination of experimental investigations and density functional theory studies, we elucidate the radical mechanisms at play. The crucial step in the catalytic process is identified as the decomposition of diisopropyl azodicarboxylates on the surface of Cu29 NCs, leading to the generation of oxyacyl radicals and the liberation of nitrogen gas. Subsequently, an oxyacyl radical abstracts a hydrogen atom from aniline, initiating the formation of an aminyl radical. Finally, the aminyl radical reacts with another oxyacyl radical, culminating in the synthesis of the desired carbamate product. This detailed analysis provides insights into the intricate catalytic pathways of Cu29 NCs, shedding light on their potential for catalyzing carbonylative C-N coupling reactions.

Direct Growth Control of Antibiotic-Resistant Bacteria Using Visible-Light-Responsive Novel Photoswitchable Antibiotics.

In addition to the discovery of new (modified) potent antibiotics to combat antibiotic resistance, there is a critical need to develop novel strategies that would restrict their off-target effects and unnecessary exposure to bacteria in our body and environment. We report a set of new photoswitchable arylazopyrazole-modified norfloxacin antibiotics that present a high degree of bidirectional photoisomerization, impressive fatigue resistance and reasonably high cis half-lives. The irradiated isomers of most compounds were found to exhibit nearly equal or higher antibacterial activity than norfloxacin against Gram-positive bacteria. Notably, against norfloxacin-resistant S. aureus bacteria, the visible-light-responsive p-SMe-substituted derivative showed remarkably high antimicrobial potency (MIC of 0.25 µg/mL) in the irradiated state, while the potency was reduced by 24-fold in case of its non-irradiated state. The activity was estimated to be retained for more than 7 hours. This is the first report to demonstrate direct photochemical control of the growth of antibiotic-resistant bacteria and to show the highest activity difference between irradiated and non-irradiated states of a photoswitchable antibiotic. Additionally, both isomers were found to be non-harmful to human cells. Molecular modellings were performed to identify the underlying reason behind the high-affinity binding of the irradiated isomer to topoisomerase IV enzyme.

Modulation of Singlet-Triplet Gap in Atomically Precise Silver Cluster-Assembled Material.

Silver cluster-based solids have garnered considerable attention owing to their tunable luminescence behavior. While surface modification has enabled the construction of stable silver clusters, controlling interactions among clusters at the molecular level has been challenging due to their tendency to aggregate. Judicious choice of stabilizing ligands becomes pivotal in crafting a desired assembly. However, detailed photophysical behavior as a function of their cluster packing remained unexplored. Here, we modulate the packing pattern of Ag12 clusters by varying the nitrogen-based ligand. CAM-1 formed through coordination of the tritopic linker molecule and NC-1 with monodentate pyridine ligand; established via non-covalent interactions. Both the assemblies show ligand-to-metal-metal charge transfer (LMMCT) based cluster-centered emission band(s). Temperature-dependent photoluminescence spectra exhibit blue shifts at higher temperatures, which is attributed to the extent of the thermal reverse population of the S1 state from the closely spaced T1 state. The difference in the energy gap (ΔEST ) dictated by their assemblies played a pivotal role in the way that Ag12 cluster assembly in CAM-1 manifests a wider ΔEST and thus requires higher temperatures for reverse intersystem crossing (RISC) than assembly of NC-1. Such assembly-defined photoluminescence properties underscore the potential toolkit to design new cluster- assemblies with tailored optoelectronic properties.

Photoswitchable Antibiotic Hybrids: Spacer Length-Dependent Photochemical Control of Antibacterial Activity.

Photopharmacology holds huge potential for the permanent (long-term) eradication of antibiotic resistance by the application of photoswitchable antibiotics. To construct such antibiotics, various methods have been employed to modify known antibiotics with photoswitches, such that the irradiated state shows activity comparable to or higher than that of the parent antibiotic and that a large activity difference between irradiated and nonirradiated states is achieved. However, most of those methods are ineffective when dealing with more than one drug with dissimilar structures. Here, we have demonstrated a new approach, in which two pharmacophores, one being a photoswitch, are covalently linked via a spacer of variable lengths, leading to a set of azopyrazole-norfloxacin antibiotic hybrids. All compounds showed a high degree of bidirectional photoisomerization, long thermal cis half-lives, and excellent photoresistance. Notably, the hybrid with an optimal four-carbon spacer length enabled the irradiated state to become 12-fold more potent than its nonirradiated state without losing much antimicrobial activity of norfloxacin. Only Gram-positive bacteria were found to be sensitive to this hybrid, and the full antibacterial potency of its irradiated state was found to be retained for nearly 24 h.

Photoluminescence Properties of a Chiral One-Dimensional Silver Chalcogenolate Chain.

Atom-precise metal nanoclusters, which contain a few tens to hundreds of atoms, have drawn significant interest due to their interesting physicochemical properties. Structural analysis reveals a fundamental architecture characterized by a central core or kernel linked to a staple motif with metal-ligand bonding playing a pivotal role. Ligands not only protect the surface but also exert a significant influence in determining the overall assembly of the larger superstructures. The assemblies of nanoclusters are driven by weak interaction between the ligand molecules; it also depends on the ligand type and functional group present. Here, we report an achiral ligand and Ag(I)···Ag(I) interaction-driven spontaneous resolution of silver-thiolate structure, [Ag18(C6H11S)12(CF3COO)6(DMA)2], where silver atoms and cyclohexanethiolate are connected to form a one-dimensional chain with helicity. Notably, silver atoms adopt different types of coordination modes and geometries. The photoluminescence properties of the one-dimensional (1D) chain structure were investigated, and it was found to exhibit excitation-dependent emission properties attributed to hydrogen-bonding interactions. Experimental and theoretical investigations corroborate the presence of triplet-emitting ligand-to-metal charge-transfer transitions.

Simultaneous conversion of chromium and malachite green coexists in halophilic bacterium Halomonas xianhensis SUR308 isolated from a solar saltern.

Many industries are known to use heavy metals like chromium (Cr) to fix dyes in the fabrication processes and malachite green (MG) as colorant. Alkalinity, elevated temperature, or salinity of the industrial effluents makes conventional physicochemical removal of MG and hexavalent chromium [Cr(VI)] more difficult to apply and demands to perceive potential cost-effective and environment-friendly treatment methods to eliminate or convert them into less toxic compounds. Here, we report simultaneous removal and bioconversion of MG and Cr(VI) by a halophilic biofilm-forming bacterium Halomonas xianhensis SUR308. It can efficiently produce exopolysaccharides as extracellular polymeric substances (EPS) and form biofilm under oxygen limiting condition. The reduction of hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)] is about 100%, and 95% after 84 h of growth in shaken and stagnant culture, respectively. The strain completely decolorizes MG after 48 h of growth in shaken culture. Furthermore, we found that strain SUR308 can efficiently detoxify chromium by reduction and degrades MG via producing various intermediate products simultaneously. Most interestingly, such conversions can also take place in alkaline environment and in environment where substantial amount of salt is present. These unique features of strain SUR308 make it suitable for the simultaneous remediation of toxic heavy metals and hazardous dye even from the environment having higher pH and salinity. The detail molecular mechanism of the bioconversion with its application in open environment would be the future research focus for bioprospecting strain SUR308.

Draft genome sequence of probiotic bacterium Lactobacillus fermentum S2, isolated from raw cow milk.

Lactobacillus fermentum remains as potential probiotic bacterium that enhances immunological response, produces antimicrobials, acts as food preservative, and lowers blood cholesterol level. We report the draft genome of Lactobacillus fermentum S2 consisting of 1.97 Mb genome size, 52.27% G + C content, 3 rRNA genes, 51 tRNA genes, and 2,004 protein-coding sequences.

Quasi-Isomeric Anion-Templated Silver Nanoclusters: Effect of Bulkiness on Luminescence.

Anion-templated silver nanoclusters are fascinating to study because of their diverse structures, which are dictated by the nature of both anions and ligands. Here, we used the bulky 1-ethynyladamantane as one of the protecting ligands alongside trifluoracetate to successfully synthesize a chlorine-templated silver nanocluster─Cl@Ag19(C12H15)11(C2O2F3)7. Elucidation of its structure by single crystal X-ray diffraction revealed the structure to be a chlorine-centered Ag19 cage with protection by alkynyl and carboxylic ligands. This cluster is non-emissive at room temperature and showed green emission with a large Stokes shift at low temperature. The crystal structure was found to be quasi-isomeric with a previously reported Ag19 cluster protected by tert-butyl acetylene, which is emissive at room temperature. Detailed photoluminescence studies and structure-property correlation revealed that the arrangement of the silver skeleton which is influenced by the bulky substituent of the ligand might be responsible for the difference in emission properties.

Two-Dimensional Silver-Chalcogenolate-Based Cluster-Assembled Material: A p-type Semiconductor.

We have synthesized and characterized a new two-dimensional honeycomb architecture resembling a single-layer of atomically precise silver cluster-assembled material (CAM), [Ag12(StBu)6(CF3COO)6(4,4'-azopyridine)3] (Ag12-azo-bpy). The interlayer noncovalent van der Waals interactions within the single-crystals were successfully disrupted, leading to the creation of this unique structure. The optimized Ag12-azo-bpy CAM demonstrates a valence band that is localized on the Ag12 cluster node situated near the Fermi energy level. This localization induces electron injection from the linker to the cluster node, facilitating efficient charge transportation along the plane. Exploiting this single-layer structure as a distinctive platform for p-type channel material, it was employed in a field-effect transistor configuration. Remarkably, the transistor exhibits a high hole mobility of 1.215 cm2 V-1 s-1 and an impressive ON/OFF current ratio of ∼4500 at room-temperature.

Copper nanoparticle-embellished Zr-based metal-organic framework for electrocatalytic hydrogen evolution reaction.

Copper nanoparticles (Cu NPs) have gained immense popularity in catalysis by virtue of their impressive properties and earth abundance. Herein, we incorporated small-sized copper nanoparticles into the amine-functionalized NU-1000 MOF and used this composite material as an effective catalyst for electrocatalytic Hydrogen Evolution Reaction (HER) studies.

Control over product formation and thermodynamic stability of thiolate-protected gold nanoclusters through tuning of surface protecting ligands.

Surface-protecting ligands can regulate the structure of a cluster's core either through electronic or steric effects. However, the influence of the steric effect along with the electronic effect over controlling the structure during ligand exchange reactions remains elusive. To understand this, we have carried out ligand exchange on [Au23(CHT)16]- (CHT: cyclohexane thiol) using aromatic thiolates where we have tuned the bulkiness at the para position of the thiolate group on the incoming ligands. The outcome of the experiments reveals that each of the ligands in the chosen series is precisely selective towards the parent cluster transformation through specific intermediates. The ligand with more steric crowding directed the reaction pathway to have Au28 nanocluster as the major product while Au36 was the final product obtained with the gradual decrease of bulkiness over the ligand. The combined experimental and theoretical results elucidated the mechanism of the reaction pathways, product formation, and their stability. Indeed, this study with the series of ligands will add up to the ligand library, where we can decide on the ligand to obtain our desired cluster for specific applications through the ligand exchange reaction.