Absence Of Metal Ions Research Articles

Synthesis of a TBA‐Based Polymeric Photocatalyst for Boosting the Selective Bio‐Reduction of Furfural Under Solar Light Illumination

AbstractPhotocatalyst‐enzyme coupled system for harnessing solar light stands out as a highly promising avenue that facilitates bio‐transformation and produces solar fuels. This study explores the integration of a metal‐free photocatalyst in the bio‐reduction of furfural to produce furfuryl alcohol. However, the bio‐reduction of furfural to produce furfuryl alcohol faces challenges due to harsh reaction conditions and expensive catalysts. Likewise, photocatalysts confront various research obstacles, including the absence of long‐lasting photogenerated charge carriers (electrons and holes), stability, and reusability. This work introduces an eco‐friendly and benign catalytic system, featuring an easily prepared photocatalyst using TBA (2,4,6‐tribromo aniline) by standard Ullman coupling. The newly designed polymeric tribromo aniline (PTBA) is cost‐effective, with outstanding light harvesting characteristics, appropriate energy band gap, and remarkably enhanced ability for transfer and migration of photo‐generated carriers. The research aims to optimize parameters for efficient conversion of furfural to produce furfuryl alcohol and also the photocatalytic production of NADH (80.08 %) from consumed NAD+. The photocatalytic efficiency was estimated by the yield percentage of this organic transformation. The absence of metals in the photocatalyst enhances sustainability, showcasing its potential in the green synthesis of furfuryl alcohol which is a valuable chemical with diverse applications.

Structural and functional investigations of Pcal_0606, a bifunctional phosphoglucose/phosphomannose isomerase from Pyrobaculum calidifontis

We are investigating the glycolytic pathway in Pyrobaculum calidifontis whose genome sequence contains homologues of all the enzymes involved in this pathway. We have characterized most of them. An open reading frame, Pcal_0606, annotated as a putative phosphoglucose/phosphomannose isomerase has to be characterized yet. In silico analysis indicated the presence of more than one substrate binding pockets at the dimeric interface of Pcal_0606. The gene encoding Pcal_0606 was cloned and expressed in Escherichia coli. Recombinant Pcal_0606, produced in soluble form, exhibited highest enzyme activity at 90 °C and pH 8.5. Presence or absence of metal ions or EDTA did not significantly affect the enzyme activity. Under optimal conditions, Pcal_0606 displayed apparent Km values of 0.33, 0.34, and 0.29 mM against glucose 6-phosphate, mannose 6-phosphate and fructose 6-phosphate, respectively. In the same order, Vmax values against these substrates were 290, 235, and 240 μmol min−1 mg−1, indicating that Pcal_0606 catalyzed the reversible isomerization of these substrates with nearly same catalytic efficiency. These results characterize Pcal_0606 a bifunctional phosphoglucose/phosphomannose isomerase, which displayed high thermostability with a half-life of ∼50 min at 100 °C. To the best of our knowledge, Pcal_0606 is the most active and thermostable bifunctional phosphoglucose/phosphomannose isomerase characterized to date.

Visible-Light-Induced Metal- and Photosensitizer-Free C(sp3)-H Phosphorylation of 3,4-Dihydroquinoxalin-2(1H)-ones with Diphenylphosphine Oxide.

Herein, we report a direct phosphorylation of the C(sp3)-H bond of 3,4-dihydroquinoxalin-2(1H)-ones using oxygen as a green oxidant under visible light at room temperature. This transformation was readily accomplished in the absence of metal and photosensitizer to construct new C(sp3)-P bonds and provide a series of phosphonylated dihydroquinoxalin-2-ones in good to excellent yields. This approach opens straightforward and environmentally friendly access to 3-phosphoryl quinoxalin-2-ones derivatives.

Green and efficient synthesis of dibenzyl cyanamides and ureas with cyanamide as a block.

A method for the two-step synthesis of dibenzyl cyanamide and dibenzyl urea via cyanamide is presented. This approach is both efficient and environmentally friendly. Various N,N-dibenzyl ureas could be obtained by reactions of N,N-dibenzyl cyanamides and N,N-dibenzyl cyanamides as intermediates formed from cyanamide. In the absence of metal, ligand and hydrogen peroxide as the oxidant, products with moderate yields have been obtained under mild conditions. Key features include the use of widely available and easily handled cyanamide sources as starting materials.

Hydroxyl-functionalized ionic liquid-modified covalent organic frameworks for efficient CO2 cycloaddition conversion

Converting CO2 into high-value chemicals is an essential way to mitigate greenhouse impact and realize sustainable utilization of resources. In this work, the COF materials named X-QCOF (X = OH, OCH3) were synthesized by a three-component Povarov reaction, followed by chemical grafting of hydroxyl‑functionalized ionic liquid into the COFs neutral backbone via quaternization to obtain the hybrid materials IL-X-QCOF (X = OH, OCH3). The resultant IL-X-QCOF can efficiently catalyze the cycloaddition reaction of CO2 and epoxides in the absence of metals, additives and solvents. Among them, IL-OH-QCOF exhibits a yield of 97.2% of cyclochloroallyl carbonate with a high turnover frequency (TOF) value of 217.7. The inherent high specific surface area of the COF-based materials promotes mass transfer efficiency, and meanwhile the abundant hydroxyl groups and bromine anions occurring in the backbone create excellent catalytic effect. Attributed to the chemical grafting approach, the product yield keeps over 90% when IL-OH-QCOF is reused for 6 cycles.

Synthesis of naphtho[1,2-b]furan-2-carbaldehydes and naphtho[2,1-b]furan-2-carbaldehydes via electrocatalytic 3,3-rearrangement/cyclization of propargylic aryl ethers under mild conditions

An electrocatalytic 3,3-rearrangement/cyclization approach has been developed for the transformation of aryl-substituted propargylic aryl ethers to naphtho[1,2-b]furan-2-carbaldehyde and naphtho[2,1-b]furan-2-carbaldehyde derivatives. The reaction proceeded efficiently under mild conditions in the absence of metal- and chemical-oxidant, yielding the desired products with good substrate scope and functional group tolerance via a radical pathway. Furthermore, the control experiment revealed that the phenylselenyl-substituted secondary alcohol might be intermediate, and the 18O labeling reaction indicated the oxygen source in the product possibly deriving from water. Significantly, further transformations of the product were conducted to showcase the utility of this electrosynthesis strategy.

The Impact of Calcium Depletion on Proliferation of Chlorella sorokiniana Strain DSCG150.

This study analyzed the effects of Ca2+ metal ions among culture medium components on the Chlorella sorokiniana strain DSCG150 strain cell growth. The C. sorokiniana strain DSCG150 grew based on a multiple fission cell cycle and growth became stagnant in the absence of metal ions in the medium, particularly Ca2+. Flow cytometry and confocal microscopic image analysis results showed that in the absence of Ca2+, cell growth became stagnant as the cells accumulated into four autospores and could not transform into daughter cells. Genetic analysis showed that the absence of Ca2+ caused upregulation of calmodulin (calA) and cell division control protein 2 (CDC2_1) genes, and downregulation of origin of replication complex subunit 6 (ORC6) and dual specificity protein phosphatase CDC14A (CDC14A) genes. Analysis of gene expression patterns by qRT-PCR showed that the absence of Ca2+ did not affect cell cycle progression up to 4n autospore, but it inhibited Chlorella cell fission (liberation of autospores). The addition of Ca2+ to cells cultivated in the absence of Ca2+ resulted in an increase in n cell population, leading to the resumption of C. sorokiniana growth. These findings suggest that Ca2+ plays a crucial role in the fission process in Chlorella.

A Magnesium Binding Site And The Anomeric Effect Regulate The Abiotic Redox Chemistry Of Nicotinamide Nucleotides.

Nicotinamide adenine dinucleotide (NAD+) is a redox active molecule that is universally found in biology. Despite the importance and simplicity of this molecule, few reports exist that investigate which molecular features are important for the activity of this ribodinucleotide. By exploiting the nonenzymatic reduction and oxidation of NAD+ by pyruvate and methylene blue, respectively, we were able to identify key molecular features necessary for the intrinsic activity of NAD+ through kinetic analysis. Such features may explain how NAD+ could have been selected early during the emergence of life. Simpler molecules, such as nicotinamide, that lack an anomeric carbon are incapable of accepting electrons from pyruvate. The phosphate moiety inhibits activity in the absence of metal ions but facilitates activity at physiological pH and model prebiotic conditions by recruiting catalytic Mg2+. Reduction proceeds through consecutive single electron transfer events. Of the derivatives tested, including nicotinamide mononucleotide, nicotinamide riboside, 3-(aminocarbonyl)-1-(2,3-dihydroxypropyl)pyridinium, 1-methylnicotinamide, and nicotinamide, only NAD+ and nicotinamide mononucleotide would be capable of efficiently accepting and donating electrons within a nonenzymatic electron transport chain. The data are consistent with early metabolic chemistry exploiting NAD+ or nicotinamide mononucleotide and not simpler molecules.

Modulation of Primary and Secondary Processes in Tau Fibril Formation by Salt-Induced Dynamics.

The initial stages of amyloid fibrilization begin with the monomers populating aggregation-prone conformers. Characterization of such aggregation-prone conformers is crucial in the study of neurodegenerative diseases. The current study characterizes the aggregation pathway of two tau protein constructs that have been recently demonstrated to form Alzheimer's (AD) fibril structures with divalent ions and chronic traumatic encephalopathy (CTE) fibril structures with monovalent ions. The results highlight the involvement of identical residues in both the primary and secondary processes of both AD and CTE fibril propagation. Nuclear magnetic resonance relaxation experiments reveal increased flexibility of the motifs 321KCGS within R3 and 364PGGGN within R4 in the presence of MgCl2/NaCl, correlating with faster aggregation kinetics and indicating efficient primary nucleation. Notably, the seeded aggregation kinetics of the tau monomers in the presence and absence of metal ions are strikingly different. This correlates with the overall sign of the 15N-ΔR2 profile specifying the dominant mechanism involved in the process of aggregation.

Metal- and photocatalyst-free three-component strategy to prepare benzylalcohol-, aldehyde-substituted BCP building blocks

A mild one-step, light-promoted, three-component radical-coupling reaction of [1.1.1]propellane to afford difunctionalized benzylalcohol-, aldehyde-substituted BCPs in the absence of metals, photocatalysts or external oxidants was reported.

Visible-light-induced C-S bond formation in the synthesis of 2,4-disubstituted thiazoles through cascade difunctionalization of acetophenone: a greener approach.

A groundbreaking approach has been developed for synthesizing 2,4-disubstituted thiazoles using an eco-friendly and metal-free approach. This novel method utilizes methyl aryl ketones, N-bromo-succinimide (NBS), and thioamides in water as a green reaction medium under visible light irradiation. Using NBS as a bromine source, the reaction takes place through an in situ α-bromination method. This approach does not require any catalyst, which makes it exceptionally beneficial for the environment. The advantages of this efficient approach are manifold and include the use of greener conditions, absence of metals, easy isolation of products, cost-effectiveness, non-toxicity, and reliance on renewable energy sources like visible light. Moreover, this technique offers higher product purity and excellent yield, enhancing itsappeal.

Photocatalytic decarboxylative phosphorylation of N-aryl glycines

A straightforward and practical strategy for decarboxylphosphatization of N-aryl glycines to access α-amino phosphine oxides, enabled by visible-light photoredox catalysis in the absence of metal, and base, has been described.

Regioselective synthesis of 2-aminophenols from N-arylhydroxylamines.

A novel strategy for the synthesis of 2-aminophenols in the absence of metals and oxidants was described. The 2-aminophenols were efficiently obtained through a cascade [3,3]-sigmatropic rearrangement and in situ hydrolysis process by using readily available N-arylhydroxylamines and the in situ-generated methyl chlorosulfonate from commercially available sulfuryl chloride and methanol under mild conditions. This method could be scaled up and has a wide substrate scope with great functional group tolerance and high regioselectivity. The 2-aminophenol products could be readily converted into structurally diverse functional molecules in good yields under various conditions.

Metal- and Hazardous Reagent-Free Transamidation Process: the NH2OH⦁HCl Promoted N-Formylation and N-Acylation Reaction under Solvent-Less Conditions

An efficient transamidation process has been described under solvent-less conditions. The transformation has been accomplished by employing NH2OH⦁HCl as a reagent and amines as substrates. The developed method is achieved in the absence of metals and hazardous reagents. A series of amines were explored to obtain the N-formylation and N-acylation reactions with excellent yields (81-96%) of products. The DFT analysis was also performed, which provides a clear understanding of the described N-formylation process. The postulated mechanism is well supported by the control experiments.

Assembly drives regioselective azide-alkyne cycloaddition reaction

Azide-alkyne cycloaddition reaction is a very common organic reaction to synthesize nitrogen-containing heterocycles. Once catalyzed by Cu(I) or Ru(II), it turns out to be a click reaction and thus is widely applied in chemical biology for labeling. However, besides their poor regioselectivity towards this reaction, these metal ions are not biologically friendly. Hence, it is an urgent need to develop a metal-free azide–alkyne cycloaddition reaction for biomedical applications. In this work, we found that, in the absence of metal ions, supramolecular self-assembly in an aqueous solution could realize this reaction with excellent regioselectivity. Nap-Phe-Phe-Lys(azido)-OH firstly self-assembled into nanofibers. Then, Nap-Phe-Phe-Gly(alkynyl)-OH at equivalent concentration approached to react with the assembly to yield the cycloaddition product Nap-Phe-Phe-Lys(triazole)-Gly-Phe-Phe-Nap to form nanoribbons. Due to space confinement effect, the product was obtained with excellent regioselectivity. Employing the excellent properties of supramolecular self-assembly, we are applying this strategy to realize more reactions without metal ion catalysis.

N-Doped Carbon Nanoparticles as Antibacterial Agents on Escherichia coli: The Role of the Size and Chemical Composition of Nanoparticles

In the last years N-doped carbon nanoparticles have been shown to have improved antibacterial activity over the undoped nanomaterial, but it is difficult to find correlations between the structure of the nanoparticle and its antibacterial activity. This prevents us from proposing a clear antibacterial mechanism and makes it difficult to select materials with the best physical and chemical properties for use as antibacterial agents. With this purpose, here, we analyze the effect of, the size and the surface chemical composition of four N-doped carbon nanoparticles on the growth of Escherichia coli bacteria, used in this work as a model of Gram-negative bacteria. Our results indicated great antibacterial activity as the concentration of the carbon nanoparticles increased. The IC50 values obtained ranged between 23 and 34 μg/mL, the lowest values found in the literature for CNPs in the absence of metals. The reduction rate was analyzed using a Ligand-Substrate model based on Monod’s equation, which allows us to interpret the dependence of the nanoparticle-bacteria affinity with the nanomaterial structure. The results of the model indicate the contribution of two mechanisms, oxidative stress and the nanoknife in the antibacterial process on Escherichia coli bacteria.

A turn-on mode fluorescent diarylethene having an azacrown ether receptor: Metal-ion-gated enhancement of the photoreactivity and fluorescence

We report the metal-ion-gated enhancement of the photoreaction and fluorescence of a newly synthesized photoswitchable fluorescent diarylethene derivative having an azacrown ether receptor. In the absence of metal ions, the diarylethene molecule underwent the photoisomerization and turn-on mode switching of fluorescence, but the photoreactivity and fluorescing ability were suppressed by intramolecular photoinduced electron transfer (PET) from the azacrown ether moiety to the diarylethene unit. Upon binding of a metal ion to the azacrown ether, the PET process was blocked, and the photoreactivity and fluorescence were significantly enhanced. Such photoswitchable fluorescent molecules that change their photoresponsive properties upon recognizing metal ions have the potential to function as metal-ion chemosensors and molecular probes in metal-ion-sensitive super-resolution fluorescence microscopy.

Photoinduced Metal‐Free Decarboxylative Transformations: Rapid Access to Amines, Alkyl Halides, and Olefins

AbstractHerein, we report an efficient photocatalytic strategy for the decarboxylative transformations of redox‐active esters to construct C=C, C(sp3)−N, and C(sp3)−X bonds in a single‐step. This operationally simple method provides a straightforward access to a variety of protected alkyl amines, alkyl halides and olefins under mild conditions in the absence of metals and photocatalysts. The method can successfully be applied to primary, secondary, and tertiary aliphatic carboxylic acid derivatives. Mechanistic studies indicate that the charge transfer complex (CTC) was formed by nBu4NI with redox‐active esters, in which the nBu4NI acted as both an iodine source and an efficient electron donor.

Wavelength engineerable porous organic polymer photosensitizers with protonation triggered ROS generation

Engineering excitation wavelength of photosensitizers (PSs) for enhanced reactive oxygen species (ROS) generation has inspired new windows for opportunities, enabling investigation of previously impracticable biomedical and photocatalytic applications. However, controlling the wavelength corresponding to operating conditions remains challenging while maintaining high ROS generation. To address this challenge, we implement a wavelength-engineerable imidazolium-based porous organic photocatalytic ROS generation system (KUP system) via a cost-effective one-pot reaction. Remarkably, the optimal wavelength for maximum performance can be tuned by modifying the linker, generating ROS despite the absence of metal ions and covalently attached heavy atoms. We demonstrate that protonated polymerization exclusively enables photosensitization and closely interacts with oxygen related to the efficiency of photosensitizing. Furthermore, superior tumor eradication and biocompatibility of the KUP system were confirmed through bioassays. Overall, the results document an unprecedented polymerization method capable of engineering wavelength, providing a potential basis for designing nanoscale photosensitizers in various ROS-utilizing applications.

Promotion of DNA Adsorption onto Microplastics by Transition Metal Ions

Microplastics can adsorb and spread a variety of pollutants in the ecosystem posing a threat to human health. One of the common pollution sources of environmental waters is metal ions, which not only adsorb on microplastics but can also promote the adsorption of other invasive species such as environmental DNA. Recently, we showed that environmentally abundant metal ions (Na+, Mg2+ and Ca2+) can promote the adsorption of single-stranded DNA (ssDNA) onto microplastics. Herein, we investigated the effect of transition metal ions including Zn2+ and Mn2+ and compared them with Mg2+ for promoting DNA adsorption. To better mimic environmental DNA, we also used a salmon sperm double-stranded DNA (dsDNA) (~2000 bp). For both ssDNA and dsDNA, the transition metals induced a higher adsorption capacity compared to Mg2+, and that correlated with the higher binding affinity of transition metals to DNA. Although metal-mediated interactions were vital for ssDNA adsorption, the dsDNA adsorbed on the microplastics even in the absence of metal ions, likely due to the abundance of binding sites of the 100-times longer dsDNA. Finally, desorption studies revealed that hydrophobic interactions were responsible for dsDNA adsorption in the absence of metal ions.