Insights into the biosynthesis of palladium nanoparticles for oxygen reduction reaction by genetically engineered bacteria of Shewanella oneidensis MR-1.

Owing to the increasing need for green synthesis and environmental protection, the utilization of biological organism-derived carbons as supports for noble-metal electrocatalysts has garnered public interest. Nevertheless, the mechanism by which microorganisms generate nanometals has not been fully understood yet. In the present study, we used genetically engineered bacteria of Shewanella oneidensis MR-1 (∆SO4317, ∆SO4320, ∆SO0618 and ∆SO3745) to explore the effect of surface substances including biofilm-associated protein (bpfA), protein secreted by type I secretion systems (TISS) and type II secretion systems (T2SS), and lipopolysaccharide in microbial synthesis of metal nanoparticles. Results showed Pd/∆SO4317 (the catalyst prepared with the mutant ∆SO4317) shows better performance than other biocatalysts and commercial Pd/C, where the mass activity (MA) and specific activity (SA) of Pd/∆SO4317 are 3.1 and 2.1 times higher than those of commercial Pd/C, reaching 257.49 A g-1 and 6.85 A m-2 respectively. It has been found that the exceptional performance is attributed to the smallest particle size and the presence of abundant functional groups. Additionally, the absence of biofilms has been identified as a crucial factor in the formation of high-quality bio-Pd. Because the absence of biofilm can minimize metal agglomeration, resulting in uniform particle size dispersion. These findings provide valuable mechanical insights into the generation of biogenic metal nanoparticles and show potential industrial and environmental applications, especially in accelerating oxygen reduction reactions.

A Gene-Editable Palladium-Based Bioorthogonal Nanoplatform Facilitates Macrophage Phagocytosis for Tumor Therapy.

Macrophage phagocytosis of tumor cells has emerged as an attractive strategy for tumor therapy. Nevertheless, immunosuppressive M2 macrophages in the tumor microenvironment and the high expression of anti-phagocytic signals from tumor cells impede therapeutic efficacy. To address these issues and improve the management of malignant tumors, in this study we developed a gene-editable palladium-based bioorthogonal nanoplatform, consisting of CRISPR/Cas9 gene editing system-linked Pd nanoclusters, and a hyaluronic acid surface layer (HBPdC). This HBPdC nanoplatform exhibited satisfactory tumor-targeting efficiency and triggered Fenton-like reactions in the tumor microenvironment to generate reactive oxygen species for chemodynamic therapy and macrophage M1 polarization, which directly eliminated tumor cells, and stimulated the antitumor response of macrophages. HBPdC could reprogram tumor cells through gene editing to reduce the expression of CD47 and adipocyte plasma membrane-associated protein, thereby promoting their recognition and phagocytosis by macrophages. Moreover, HBPdC induced the activation of sequestered prodrugs via bioorthogonal catalysis, enabling chemotherapy and thereby enhancing tumor cell death. Importantly, the Pd nanoclusters of HBPdC were sufficiently cleared through basic metabolic pathways, confirming their biocompatibility and biosafety. Therefore, by promoting macrophage phagocytosis, the HBPdC system developed herein represents a highly promising antitumor toolset for cancer therapy applications.

Effect of palladium(II) complexes on NorA efflux pump inhibition and resensitization of fluoroquinolone-resistant Staphylococcus aureus: in vitro and in silico approach.

Staphylococcus aureus leads to diverse infections, and their treatment relies on the use of antibiotics. Nevertheless, the rise of antibiotic resistance poses an escalating challenge and various mechanisms contribute to antibiotic resistance, including modifications to drug targets, enzymatic deactivation of drugs, and increased efflux of antibiotics. Hence, the quest for innovative antimicrobial solutions has intensified in the face of escalating antibiotic resistance and the looming threat of superbugs. The NorA protein of S. aureus, classified as an efflux pump within the major facilitator superfamily, when overexpressed, extrudes various substances, including fluoroquinolones (such as ciprofloxacin) and quaternary ammonium. Addressing this, the unexplored realm of inorganic and organometallic compounds in medicinal chemistry holds promise. Notably, the study focused on investigating two different series of palladium-based metal complexes consisting of QSL_PA and QSL_PB ligands to identify a potent NorA efflux pump inhibitor that can restore the susceptibility to fluoroquinolone antibiotics. QSL_Pd5A was identified as a potent efflux pump inhibitor from the real-time efflux assay. QSL_Pd5A also resensitized SA1199B to ciprofloxacin at a low concentration of 0.125 µg/mL without elucidating cytotoxicity on the NRK-62E cell line. The in vitro findings were substantiated by docking results, indicating favorable interactions between QSL_Pd5A and the NorA efflux pump.

Reductive Dehalogenation of Herbicides Catalyzed by Pd0NPs in a H2-Based Membrane Catalyst-Film Reactor.

More food production required to feed humans will require intensive use of herbicides to protect against weeds. The widespread application and persistence of herbicides pose environmental risks for nontarget species. Elemental-palladium nanoparticles (Pd0NPs) are known to catalyze reductive dehalogenation of halogenated organic pollutants. In this study, the reductive conversion of 2,4-dichlorophenoxyacetic acid (2,4-D) was evaluated in a H2-based membrane catalyst-film reactor (H2-MCfR), in which Pd0NPs were in situ-synthesized as the catalyst film and used to activate H2 on the surface of H2-delivery membranes. Batch kinetic experiments showed that 99% of 2,4-D was removed and converted to phenoxyacetic acid (POA) within 90 min with a Pd0 surface loading of 20 mg Pd/m2, achieving a catalyst specific activity of 6.6 ± 0.5 L/g-Pd-min. Continuous operation of the H2-MCfR loaded with 20 mg Pd/m2 sustained >99% removal of 50 µM 2,4-D for 20 days. A higher Pd0 surface loading, 1030 mg Pd/m2, also enabled hydrosaturation and hydrolysis of POA to cyclohexanone and glycolic acid. Density functional theory identified the reaction mechanisms and pathways, which involved reductive hydrodechlorination, hydrosaturation, and hydrolysis. Molecular electrostatic potential calculations and Fukui indices suggested that reductive dehalogenation could increase the bioavailability of herbicides. Furthermore, three other halogenated herbicides─atrazine, dicamba, and bromoxynil─were reductively dehalogenated in the H2-MCfR. This study documents a promising method for the removal and detoxification of halogenated herbicides in aqueous environments.

Formation of biologically influenced palladium microstructures by Desulfovibrio desulfuricans and Desulfovibrio ferrophilus IS5.

A range of Desulfovibrio spp. can reduce metal ions to form metallic nanoparticles that remain attached to their surfaces. The bioreduction of palladium (Pd) has been given considerable attention due to its extensive use in areas of catalysis and electronics and other technological domains. In this study we report, for the first time, evidence for Pd(II) reduction by the highly corrosive Desulfovibrio ferrophilus IS5 strain to form surface attached Pd nanoparticles, as well as rapid formation of Pd(0) coated microbial nanowires. These filaments reached up to 8 µm in length and led to the formation of a tightly bound group of interconnected cells with enhanced ability to attach to a low carbon steel surface. Moreover, when supplied with high concentrations of Pd (≥ 100 mmol Pd(II) g-1 dry cells), both Desulfovibrio desulfuricans and D. ferrophilus IS5 formed bacteria/Pd hybrid porous microstructures comprising millions of cells. These three-dimensional structures reached up to 3 mm in diameter with a dose of 1200 mmol Pd(II) g-1 dry cells. Under suitable hydrodynamic conditions during reduction, two-dimensional nanosheets of Pd metal were formed that were up to several cm in length. Lower dosing of Pd(II) for promoting rapid synthesis of metal coated nanowires and enhanced attachment of cells onto metal surfaces could improve the efficiency of various biotechnological applications such as microbial fuel cells. Formation of biologically stimulated Pd microstructures could lead to a novel way to produce metal scaffolds or nanosheets for a wide variety of applications.

Efficient Microcystis aeruginosa coagulation and removal by palladium clusters doped g-C3N4 with no light irradiation.

Efficient treatment of cyanobacterial blooms in eutrophication waters by safe and reliable nanomaterials is a big challenge for reducing environmental health risks. Herein, a novel strategy combining palladium clusters (Pdn) with g-C3N4 nanocomposite was presented to achieve high-efficient removal of Microcystis aeruginosa cells through coagulation and breakage. Interestingly, 95.17% of algal cells (initial concentration of 5.6 × 106 cells mL-1) were promptly removed in the Pd/g-C3N4 (5%) system within only 10 min and without visible light irradiation and persulfate activation. Both the release of potassium ion and microcystin during the removal process and the transmission electron microscope observations of Microcystis aeruginosa cells proved that the integrity of the algal cell membrane was destroyed. The removal of Microcystin-LR (MC-LR) were further confirmed in the next process. Pd metal interaction and breakage against algal cells may cause disruption of algal cells. This study describes a novel technology for the superfast removal of harmful algae and may provide a new insight into the control of cyanobacterial blooms in practical applications.

Scavenging ROS and inflammation produced during treatment to enhance the wound repair efficacy of photothermal injectable hydrogel.

Injectable hydrogels with near infrared (NIR) photothermal ability show attractive application prospects in the treatment of wound infection and promoting skin defect repair. Nevertheless, excess reactive oxygen species (ROS) and inflammatory responses caused by bacterial infection and photothermal therapy (PTT) would delay tissue regeneration and wound healing. In this study, a novel NIR photothermal injectable hydrogel with anti-oxidation and anti-inflammation by incorporating α-lipoic acid modified palladium nanoparticles into calcium ions crosslinked sodium alginate hydrogel was developed. The resulting hydrogel facilitated to fill perfectly various irregular wounds, and could convert NIR light into local high-heat to kill >80 % of Escherichia coli and Staphylococcus aureus. Remarkably, the hydrogel exhibited excellent anti-oxidant and anti-inflammatory activity, which could scavenge >60 % of ROS in cells and decrease the relative expression level of tumor necrosis factor-alpha and interleukin-1ß genes by 52.9 % and 53.3 % respectively. It was found that the NIR photothermal injectable hydrogel with anti-oxidation and anti-inflammation could effectively reduce ROS and inflammation caused by bacterial infection and PPT. Additionally, it could also enhance wound repair efficiency. The hydrogel is expected to be a potential wound dressing for the treatment of clinical skin defects.

Bidirectional anisotropic palladium nanozymes reprogram macrophages to enhance collaborative chemodynamic therapy of colorectal cancer.

In the complex tumor microenvironment (TME), tumor-associated macrophages (TAMs) play an important role in immunosuppression and tumor growth; hence, tumor cells are no longer the only target during tumor treatment. However, how to simultaneously target both tumor cells and TAMs to effectively eliminate the tumor remains a challenge. Herein, based on the specific receptors for cancer cells and TAMs, we prepared bidirectional anisotropic palladium nanoclusters (Pd-HA+Pd-M@R NPs) to simultaneously target tumor cells and TAMs for enhancing the therapeutic effect. In these nanoclusters, the Pd-HA part was obtained by modifying hyaluronic acid (HA) on the surface of ultra-small Pd nanozymes that could target CT26 cells. Moreover, with the high peroxidase (POD) and catalase (CAT) activity of Pd nanozymes, Pd-HA NPs directly caused cancer cell death by producing H2O2 and highly toxic reactive oxygen therapy (ROS) through chemodynamic therapy (CDT). The other part of Pd NPs functioned as a carrier that linked mannose (Man) and the imiquimod molecule (R837) to obtain Pd-M@R NPs, which could specifically connect the mannose receptor of TAMs and perform targeted reprogramming of TAMs to M1 phenotype to reverse immunosuppression and further activate immunotherapy to form "double therapy". Therefore, the strategy of "double therapy" provides new sights for treating malignant tumors. STATEMENT OF SIGNIFICANCE: The bidirectional anisotropic Pd nanoclusters (Pd-HA+Pd-M@R NPs) that can simultaneously target the tumor cells and TAMs with the modification of HA and mannose, respectively. Under the biodirectional anisotropic effect, the Pd nanozymes in Pd-HA can directly kill CT 26 cells through catalyze producing toxic ROS. The Pd-M@R exhibited effectively delivery the imiquimod molecule (R837) to TAMs and specifically induced it transformed into M1 phenotype to reverse tumor immunosuppression to form the "double therapy".

Inhibition of Sulfate Reduction and Cell Division by Desulfovibrio desulfuricans Coated in Palladium Metal.

The growth of sulfate-reducing bacteria (SRB) and associated hydrogen sulfide production can be problematic in a range of industries such that inhibition strategies are needed. A range of SRB can reduce metal ions, a strategy that has been utilized for bioremediation, metal recovery, and synthesis of precious metal catalysts. In some instances, the metal remains bound to the cell surface, and the impact of this coating on bacterial cell division and metabolism has not previously been reported. In this study, Desulfovibrio desulfuricans cells (1g dry weight) enabled the reduction of up to 1500 mmol (157.5 g) palladium (Pd) ions, resulting in cells being coated in approximately 1 µm of metal. Thickly coated cells were no longer able to metabolize or divide, ultimately leading to the death of the population. Increasing Pd coating led to prolonged inhibition of sulfate reduction, which ceased completely after cells had been coated with 1200 mmol Pd g-1 dry cells. Less Pd nanoparticle coating permitted cells to carry out sulfate reduction and divide, allowing the population to recover over time as surface-associated Pd diminished. Overcoming inhibition in this way was more rapid using lactate as the electron donor, compared to formate. When using formate as an electron donor, preferential Pd(II) reduction took place in the presence of 100 mM sulfate. The inhibition of important metabolic pathways using a biologically enabled casing in metal highlights a new mechanism for the development of microbial control strategies. IMPORTANCE Microbial reduction of sulfate to hydrogen sulfide is highly undesirable in several industrial settings. Some sulfate-reducing bacteria are also able to transform metal ions in their environment into metal phases that remain attached to their outer cell surface. This study demonstrates the remarkable extent to which Desulfovibrio desulfuricans can be coated with locally generated metal nanoparticles, with individual cells carrying more than 100 times their mass of palladium metal. Moreover, it reveals the effect of metal coating on metabolism and replication for a wide range of metal loadings, with bacteria unable to reduce sulfate to sulfide beyond a specific threshold. These findings present a foundation for a novel means of modulating the activity of sulfate-reducing bacteria.

Cytotoxic Action of Palladium-Based Compound on Prostate Stem Cells, Primary Prostate Epithelial Cells, Prostate Epithelial Cells, and Prostate Cell Lines.

Objective: Prostate cancer is one of the most common types of cancer found to occur in males and is ranked as the second-highest cause of cancer-associated deaths among male patients. In this study, we have shown the influence of a new palladium-based anticancer agent in contrast to the six distinct prostate cancer lines and the primary cultures. Methods: In this study, we have used six distinct prostate cell lines, that is, PNT2-C2, LNCaP, BPH-1, PC-3, PNT1A, and P4E6. The MTP and ATP assay were performed to evaluate the growth of the cell and the flow cytometry to investigate the status of the cell cycle. The antigrowth effect of the palladium complex was evaluated against different cell lines at three time zones 24 h, 48 h, and 72 h. [PdCl(terpy)] (capsule)-2H2O is synthesized by direct encapsulation of equimolar amounts of capsule ions into [Pd (terpy) Cl] Cl-2H2O. Results: A comparative analysis was done on 25 mM etoposide and 12 mM cisplatin, cytotoxic agents. The lowest IC50 value at 72 hours was 0.128 mM for BPH-1 cell lines with 0.139 mM, whereas PNT2-C2 cells were found to be most resistant with IC50 values of 0.829 mM. The antigrowth effect of palladium complex on cell lines was measured using the MTS assay at 24, 48, and 72 hours. BPH-1, PNT2-C2, and PNT1A either possess normal tissues or have benign prostatic hyperplasia tissues whereas P4E6, PC-3, and LNCaP cell lines possess malignant origin. The Pd complex exhibited significant cytotoxic action in stem cells when compared against etoposide. An antigrowth effect was reported for Pd complex at lower concentration, but it was more cytotoxic than etoposide with significant cytotoxicity (P=0.001). Conclusion: The palladium complex experienced a substantial antigrowth influence over most of the prostate tumor cell lines and the primary cultures, eventually, leading to the implementation of this Pd complex in the treating procedure of metastatic prostate cancer, which is tremendously resistant to the traditional treatment.

Metal Nanoparticles@Covalent Organic Framework@Enzymes: A Universal Platform for Fabricating a Metal-Enzyme Integrated Nanocatalyst.

Cascade catalysis that combines chemical catalysis and biocatalysis has received extensive attention in recent years, especially the integration of metal nanoparticles (MNPs) with enzymes. However, the compatibility between MNPs and enzymes, and the stability of the integrated nanocatalyst should be improved to promote the application. Therefore, in this study, we proposed a strategy to space-separately co-immobilize MNPs and enzymes to the pores and surface of a highly stable covalent organic framework (COF), respectively. Typically, Pd NPs that were prepared by in situ reduction with triazinyl as the nucleation site were distributed in COF (Tz-Da), and organophosphorus hydrolase (OPH) was immobilized on the surface of Tz-Da by a covalent method to improve its stability. The obtained integrated nanocatalyst Pd@Tz-Da@OPH showed high catalytic efficiency and reusability in the cascade degradation of organophosphate nerve agents. Furthermore, the versatility of the preparation strategy of COF-based integrated nanocatalyst has been preliminarily expanded: (1) Pd NPs and OPH were immobilized in the triazinyl COF (TTB-DHBD) with different pore sizes for cascade degradation of organophosphate nerve agent and the particle size of MNPs can be regulated. (2) Pt NPs and glucose oxidase were immobilized in COF (Tz-Da) to obtain an integrated nanocatalyst for efficient colorimetric detection of phenol.

Pd-Immobilized Schiff Base Double-Layer Macrocycle: Synthesis, Structures, Peroxidase Mimic Activity, and Antibacterial Performance.

Di-, tri-, and tetra-aldehydes have been employed to access new [2 + 2] [2 + 3] and [2 + 4] double-layer Schiff base macrocycles. The [2 + 3] compound has been used for the immobilization of Pd and the resulting composite has been employed as a peroxidase-like mimetic using 3,3',5,5'-tetramethylbenzidine (TMB) as the substrate; the optimum conditions together with the catalytic kinetics of the enzyme-like activity is discussed. Based on the peroxidase-like catalytic activity, the Pd@Schiff base composite was found to exhibit excellent bactericidal activity against both Escherichia coli (Gram-negative bacterium) and Staphylococcus aureus (Gram-positive bacterium) in the presence of relatively low concentrations of H2O2. Furthermore, cytotoxicity measurements illustrate the biosafety of the Pd composite. The above-mentioned findings have the potential to guide the innovation of new Pd-based composites as enzyme mimetics and antibacterial materials.

Exploring the Biological Effect of Biosynthesized Au-Pd Core-Shell Nanoparticles through an Untargeted Metabolomics Approach.

The biosynthesis of Au-Pd core-shell nanoparticles (NPs) with wild-type Escherichia coli (Au-Pd/E. coli) is an excellent newly established, environmentally friendly synthetic method for the fabrication of nanomaterials compared to traditional chemosynthesis. However, there is insufficient detailed bioinformation on the compatibility, metabolic process, and mechanism of this approach. Metabolomics approaches have provided an excellent alternative to numerous bioinformatics approaches for shedding light on the biological response of an organism exposed to external stimuli at the molecular level. In this study, two different doses (8 and 80 µg/mL) of Au-Pd/E. coli were applied to treat human umbilical vein endothelial cells (HUVECs). Gas chromatography/mass spectrometry coupled with bioinformatics was used to analyze the changes in the HUVEC metabolome after treatment. The results indicated the occurrence of nonsignificant acute cytotoxicity based on cell proliferation and apoptosis analysis, while high concentrations (80 µg/mL) of Au-Pd/E. coli induced dramatic changes in energy metabolism, revealing a notable inhibition of the tricarboxylic acid (TCA) cycle along with the enhancement of glycolysis, the pentose phosphate pathway, fatty acid biosynthesis, and lipid accumulation, which was correlated with mitochondrial dysfunction. The metabolomics results obtained for this novel Au-Pd/E. coli-cell system could broaden our knowledge of the biological effect of Au-Pd/E. coli and possibly reveal material modifications and technological innovations.

Pd-Catalyzed Direct Diversification of Natural Anti-Alzheimer's Disease Drug: Synthesis and Biological Evaluation of N-Aryl Huperzine A Analogues.

The first systematic direct diversification of a complex natural product by metal-catalyzed N-H functionalization was carried out. A new series of N-(hetero)aryl analogues (1-32) of the natural anti-Alzheimer's disease drug huperzine A (HPA) was prepared via palladium-catalyzed Buchwald-Hartwig cross-coupling reactions of HPA with various aryl bromides in good yields. Most of the N-aryl-huperzine A (N-aryl-HPA) analogues showed good acetylcholinesterase (AChE) inhibitory activity in in vitro experiments. Three arylated huperzine A analogues (14, 19, and 30) exhibited stronger anti-AChE activity than HPA. The 5-methoxy-2-pyridyl analogue (30) displayed the most potent AChE inhibition activity, with an IC50 value of 1.5 µM, which was 7.6-fold more active than HPA. Compound 30 also exhibited better neuroprotective activity for H2O2-induced damage in SH-SY5Y cells than HPA. Structure-activity relationship analysis suggested that the electron density of the installed aromatic ring or heteroaromatic ring played a significant role in inducing the AChE inhibition activity. Overall, compound 30 showed the advantages of easy synthesis, high potency and selectivity, and improved neuroprotection, making it a potential huperzine-type lead compound for Alzheimer's disease drug development.

Synthesis and Biological Screening of New 4-Hydroxycoumarin Derivatives and Their Palladium(II) Complexes.

Two newly synthesized 4-hydroxycoumarin bidentate ligands (L1 and L2) and their palladium(II) complexes (C1 and C2) were screened for their biological activities, in vitro and in vivo. Structures of new compounds were established based on elemental analysis, 1H NMR, 13C NMR, and IR spectroscopic techniques. The obtained compounds were tested for their antioxidative and cytotoxic activities and results pointed to selective antiradical activity of palladium(II) complexes towards •OH and -•OOH radicals and anti-ABTS (2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) cation radical) activity comparable to that of ascorbate. Results indicated the effect of C1 and C2 on the enzymatic activity of the antioxidative defense system. In vitro cytotoxicity assay performed on different carcinoma cell lines (HCT166, A375, and MIA PaCa-2), and one healthy fibroblast cell line (MRC-5) showed a cytotoxic effect of both C1 and C2, expressed as a decrease in carcinoma cells' viability, mostly by induction of apoptosis. In vivo toxicity tests performed on zebrafish embryos indicated different effects of C1 and C2, ranging from adverse developmental effect to no toxicity, depending on tested concentration. According to docking studies, both complexes (C1 and C2) showed better inhibitory activity in comparison to other palladium(II) complexes.

Single-Atom Pd Nanozyme for Ferroptosis-Boosted Mild-Temperature Photothermal Therapy.

Photothermal therapy (PTT) is an extremely promising tumor therapeutic modality. However, excessive heat inevitably injures normal tissues near tumors, and the damage to cancer cells caused by mild hyperthermia is easily repaired by stress-induced heat shock proteins (HSPs). Thus, maximizing the PTT efficiency and minimizing the damage to healthy tissues simultaneously by adopting appropriate therapeutic temperatures is imperative. Herein, an innovative strategy is reported: ferroptosis-boosted mild PTT based on a single-atom nanozyme (SAzyme). The Pd SAzyme with atom-economical utilization of catalytic centers exhibits peroxidase (POD) and glutathione oxidase (GSHOx) mimicking activities, and photothermal conversion performance, which can result in ferroptosis featuring the up-regulation of lipid peroxides (LPO) and reactive oxygen species (ROS). The accumulation of LPO and ROS provides a powerful approach for cleaving HSPs, which enables Pd SAzyme-mediated mild-temperature PTT.

Pd-Oxazolone complexes conjugated to an engineered enzyme: improving fluorescence and catalytic properties.

Different Pd-complexes containing orthometallated push-pull oxazolones were inserted by supramolecular Pd-amino acid coordination on two genetically engineered modified variants of the thermoalkalophilic Geobacillus thermocatenolatus lipase (GTL). Pd-lipase conjugation was performed on the solid phase in the previously immobilized form of GTL under mild conditions, and soluble conjugated Pd-GTL complexes were obtained by simply desorbing by washing with an acetonitrile aqueous solution. Three different Pd complexes were incorporated into two different genetically modified enzyme variants, one containing all the natural cysteine residues changed to serine residues, and another variant including an additional Cys mutation directly in the catalytic serine (Ser114Cys). The new Pd-enzyme conjugates were fluorescent even at ppm concentrations, while under the same conditions free Pd complexes did not show fluorescence at all. The Pd conjugation with the enzyme extremely increases the catalytic profile of the corresponding Pd complex from 200 to almost 1000-fold in the hydrogenation of arenes in aqueous media, achieving in the case of GTL conjugated with orthopalladated 4a an outstanding TOF value of 27 428 min-1. Also the applicability of GTL-C114 conjugated with orthopalladated 4b in a site-selective C-H activation reaction under mild conditions has been demonstrated. Therefore, the Pd incorporation into the enzyme produces a highly stable conjugate, and improves remarkably the catalytic activity and selectivity, as well as the fluorescence intensity, of the Pd complexes.

In vivo evaluation of Nano-palladium toxicity on larval stages and adult of zebrafish (Danio rerio).

The existence and usage of nano-sized palladium (nano-Pd) as catalytic promoters among industries and researchers have been laid a way to explore the release of nano-Pd particles into the aquatic environment, bio-accumulating in living organisms. However, the data on fate and toxicity in response to nano-Pd on aquatic organisms are very limited. Herein, we report the concentration-specific toxicity of nano-Pd in zebrafish (Danio rerio). Nano-Pd was synthesized and characterized by Field Emission Scanning Electron Microscopy (FE-SEM), Dynamic Light Scattering (DLS) and Zeta potential. To determine the in vivo toxicity of nano-Pd, the 96 hpf larvae and the adult zebrafish were treated with two (22 and 0.4 ng/L) environmental relevant concentrations. High doses of nano-Pd influenced the hatching rate, embryo survival, heartbeat and teratological anomalies in the 96 hpf larvae. Reactive oxygen species (ROS) and apoptosis were also influenced by nano-Pd exposure while the acetylcholinesterase (AChE) activity was declined in a dose dependent manner. In long-term exposure (42 days), the adult fish showed erratic movements in swimming pattern inhibiting the AChE activity in both the concentrations of brain and liver. The antioxidant enzyme activity such as superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST), glutathione reductase (GR) and lipid peroxidation (LPO), showed a significant change (P < 0.05) indicating that oxidative stress was induced by nano-Pd. Similarly, nano-Pd also induced histopathological lesions in gill, liver and brain providing an insight of fate and toxicity of nano-Pd in the aquatic environment. Our study contributes a significant mechanism to understand the toxicity concern of nano-Pd in the aquatic environment.

In Situ Synthesis of Photoactive Polymers on a Living Cell Surface via Bio-Palladium Catalysis for Modulating Biological Functions.

Cell surface engineering with functional polymers is an effective strategy to modulate cell activity. Here, a bio-palladium catalyzed polymerization strategy was developed for in situ synthesis of conjugated polymers on living cell surfaces. Through Sonagashira polymerization, photoactive polyphenyleneethynylene (PPE) is synthesized on the cell surface via cell-generated bio-Pd catalyst. The in situ formed PPE is identified by excellent light-harvest capacity and blue fluorescence on the surfaces of E. coli and C. pyrenoidosa. Besides imaging microbes for tracing the polymerization process, PPE also exhibits enhanced antibacterial activity against E. coli. It can also augment the ATP synthesis of C. pyrenoidosa through enlarging the light absorption and accelerating the cyclic electron transport of the algae. With this bio-metal catalyzed polymerization method, functional polymers can be synthesized in situ on the living cell surface.

Palladium in biological media: Can the synthetic chemist's most versatile transition metal become a powerful biological tool?

Palladium catalysed reactions are ubiquitous in synthetic organic chemistry in both organic solvents and aqueous buffers. The broad reactivity of palladium catalysis has drawn interest as a means to conduct orthogonal transformations in biological settings. Successful examples have been shown for protein modification, in vivo drug decaging and as palladium-protein biohybrid catalysts for selective catalysis. Biological media represents a challenging environment for palladium chemistry due to the presence of a multitude of chelators, catalyst poisons and a requirement for milder reaction conditions e.g. lower temperatures. This review looks to identify successful examples of palladium-catalysed reactions in the presence of proteins or cells and analyse solutions to help to overcome the challenges of working in biological systems.