Synthesis and Structure of Diaryltellurium Disulfonates and Their Application for the α-Tosyloxylation of Ketones

A concise and efficient synthetic route to a variety of functionalized diaryltellurium disulfonates (1) is presented. The hydrolysis of these diaryltellurium disulfonates (1) produces diarylhydroxytelluronium triflates (2). The molecular structures of the diaryltellurium disulfonates and diarylhydroxytelluronium triflates were determined unambiguously using single-crystal X-ray diffraction analysis. To the best of our knowledge, this represents one of the very few reports on the solid-state structures of diaryltellurium disulfonates and diarylhydroxytelluronium triflates to date. The utility of the thus obtained diaryltellurium disulfonates was subsequently demonstrated via their application to the α-tosyloxylation of ketones, which also marks the first use of this class of compounds for this transformation.

Oxidation-Controlled, Strain-Promoted Tellurophene-Alkyne Cycloaddition (OSTAC): A Bioorthogonal Tellurophene-Dependent Conjugation Reaction

Tellurophene-bearing small molecules have emerged as valuable tools for localizing cellular activities in vivo using mass cytometry. To broaden the utility of tellurophenes in chemical biology, we have developed a bioorthogonal reaction to facilitate tagging of tellurophene-bearing conjugates for downstream applications. Using TePhe, a tellurophene-based phenylalanine analogue, labeled recombinant proteins were generated for reaction development. Using these proteins, we demonstrate an oxidation-controlled, strain-promoted tellurophene-alkyne cycloaddition (OSTAC) reaction. Mild oxidation of the tellurophene ring with N-chlorosuccinimide produces a reactive Te(IV) species which undergoes rapid (k > 100 M-1 s-1) cycloaddition with bicyclo[6.1.0]nonyne (BCN) yielding a benzo-fused cyclooctane. Selective labeling of TePhe-containing proteins can be achieved in complex protein mixtures and on fixed cells. OSTAC reactions can be combined with strain-promoted azide alkyne cycloaddition (SPAAC) and copper-catalyzed azide alkyne click (CuAAC) reactions. Demonstrating the versatility of this approach, we observe the expected staining patterns for 5-ethynyl-2'-deoxyuridine (DNA synthesis-CuAAC) and immunohistochemistry targets in combination with TePhe (protein synthesis-OSTAC) in fixed cells. The favorable properties of the OSTAC reaction suggest its broad applicability in chemical biology.

Halogen, Chalcogen, Pnictogen, and Tetrel Bonding in Non-Covalent Organocatalysis: An Update

The use of noncovalent interactions based on electrophilic halogen, chalcogen, pnictogen, or tetrel centers in organocatalysis has gained noticeable attention. Herein, we provide an overview on the most important developments in the last years with a clear focus on experimental studies and on catalysts which act via such non-transient interactions.

Polytelluride square planar chain-induced anharmonicity results in ultralow thermal conductivity and high thermoelectric efficiency in Al2Te5 monolayers

Two-dimensional (2D) metal chalcogenides provide rich ground for the development of nanoscale thermoelectrics, although achieving optimal thermoelectric efficiency is still a challenge. Here, we leverage the unique chemistry of tellurium (Te), renowned for its hypervalent bonding and catenation abilities, to tackle this challenge as manifested in Al2Te3 and Al2Te5 monolayers. While the former forms a straightforward covalent Al-Te network, the latter adopts a more intricate bonding mechanism, enabled by eccentric features of Te chemistry, to maintain charge balance. In Al2Te5, a square planar chain (SPC) known as polytelluride [Te3]2- is neutralized by the covalently bonded [Al2Te2]2+ framework. The hypervalent nature of Te results in bizarre Born effective charges of 7 and -4 for adjacent Te atoms within the square planar chain, a feature that induces significant anharmonicity in Al2Te5 monolayers. Enhanced anharmonic lattice vibrations and the accordion pattern bestow glass-like, strongly anisotropic thermal conductivity to the Al2Te5 monolayer. The calculated κL values of 1.8 and 0.5 W m-1 K-1 along the a- and b-axes at 600 K are one order of magnitude lower than those of Al2Te3, and even lower than monolayers that contain heavy cations like Bi2Te3. Moreover, the tellurium chain dominates the valence band maximum and conduction band minimum of Al2Te5, leading to a high valley degeneracy of 10, and thus a high power factor and figure of merit (zT). Using rigorous first-principles calculations of electron relaxation time, the estimated hole-doped and electron-doped zT of, respectively, 1.5 and 0.5 at 600 K is achieved for Al2Te5. The pioneering zT of Al2Te5 compared to that of Al2Te3 is rooted merely in its amorphous-like lattice thermal transport and its polytelluride chain. These findings underscore the importance of aluminum telluride and polymeric-based inorganic compounds as practical and cost-effective thermoelectric materials, pending further experimental validation.

Exploring the Te(II)/Te(IV) Redox Couple of a Tellurorosamine Chromophore: Photophysical, Photochemical, and Electrochemical Studies

A tellurorosamine dye [Te(II)] undergoes aerobic photooxidation. Although Te(IV) species have been used in a number of oxidations, key Te(IV)-oxo and Te(IV)-bis(hydroxy) intermediates are challenging to study. Under aerobic irradiation with visible light, Te(II) (λmax = 600 nm) transforms into a Te(IV) species (λmax = 669 nm). The resultant Te(IV) species is not stable in the dark or at -20 °C, decomposing back to Te(II) and other byproducts over many hours. To eliminate the structural ambiguity of the Te(IV) photoproduct, we used spectroelectrochemistry, wherein the bis(hydroxy) Te(IV)-(OH)2 was electrochemically generated under anaerobic conditions. The absorption of Te(IV)-(OH)2 matches that of the Te(IV) photoproduct. Because isosbestic points are maintained both photochemically and electrochemically, the oxo core formed photochemically must rapidly equilibrate with Te(IV)-(OH)2. Calculations on the bis(hydroxy) versus oxo species further corroborate that the equilibration is rapid and the spectra of the two species are similar. To further explore Te(IV) cores, two novel compounds, Te(IV)-Cl2 and Te(IV)-Br2, were synthesized. Characterization of Te(IV)-X2 was simplified because these cores have no analogue to the Te(IV)-(O)/Te(IV)-(OH)2 equilibrium. This work provides insights into the photophysical and electrochemical behavior of Te analogues of chalcogenoxanthylium dyes, which are relevant for a broad range of photochemical applications.

On-Surface Molecular Recognition Driven by Chalcogen Bonding

Chalcogen bonding interactions (ChBIs) have been widely employed to create ordered noncovalent assemblies in solids and liquids. Yet, their ability to engineer molecular self-assembly on surfaces has not been demonstrated. Here, we report the first demonstration of on-surface molecular recognition solely governed by ChBIs. Scanning tunneling microscopy and ab initio calculations reveal that a pyrenyl derivative can undergo noncovalent chiral dimerization on the Au(111) surface through double Ch···N interactions involving Te- or Se-containing chalcogenazolo pyridine motifs. In contrast, reference chalcogenazole counterparts lacking the pyridyl moiety fail to form regular self-assemblies on Au, resulting in disordered assemblies.

Optical study of Te8 ring clusters: comparison with density functional theory and a step towards materials design using nanoporous zeolite space

The Te8 ring molecule (cluster) is poorly investigated due to the lack of experimental data. Here, we report an experimental and theoretical study of a regular array of oriented Te8 rings formed in the ∼1.14 nm diameter cavities of zeolite LTA, which are arranged in a cubic lattice with a spacing of ∼1.2 nm. Single crystals of LTA with encapsulated tellurium (LTA-Te) were studied using Raman spectroscopy (RS) and optical absorption spectroscopy (OAS). The experimental LTA-Te spectra were found to be in agreement with those calculated using density functional theory (PBE0 hybrid functional and def2-TZVP basis sets) for the crown-shaped Te8 ring molecule with D4d symmetry. Using polarization-orientation RS, we show that the Te8 rings are oriented by their major axes along the 4-fold axes of cubic LTA. We also show that the site symmetry of Te8 in LTA-Te is lower than D4d. Te8 bond-bending modes are well described in the harmonic approximation, while bond-stretching modes are mixed due to the reduced ring symmetry and, probably, anharmonicity. Importantly, OAS data of LTA-Te display dependence on the Te8 concentration, implying the interaction of the rings from neighbouring LTA cavities with the generation of the valence and conduction electron bands of such a cluster crystal.

Tellurium and Nano-Tellurium: Medicine or Poison?

Tellurium (Te) is the heaviest stable chalcogen and is a rare element in Earth's crust (one to five ppb). It was discovered in gold ore from mines in Kleinschlatten near the present-day city of Zlatna, Romania. Industrial and other applications of Te focus on its inorganic forms. Tellurium can be toxic to animals and humans at low doses. Chronic tellurium poisoning endangers the kidney, liver, and nervous system. However, Te can be effective against bacteria and is able to destroy cancer cells. Tellurium can also be used to develop redox modulators and enzyme inhibitors. Soluble salts that contain Te had a role as therapeutic and antimicrobial agents before the advent of antibiotics. The pharmaceutical use of Te is not widespread due to the narrow margin between beneficial and toxic doses, but there are differences between the measure of toxicity based on the Te form. Nano-tellurium (Te-NPs) has several applications: it can act as an adsorptive agent to remove pollutants, and it can be used in antibacterial coating, photo-catalysis for the degradation of dyes, and conductive electronic materials. Nano-sized Te particles are the most promising and can be produced in both chemical and biological ways. Safety assessments are essential to determine the potential risks and benefits of using Te compounds in various applications. Future challenges and directions in developing nano-materials, nano-alloys, and nano-structures based on Te are still open to debate.

Synthesis of Diaryl Tellurides with Sodium Aryltellurites under Mild Conditions

A highly efficient new protocol has been developed for the formation of C-Te bonds, leading to both symmetrical and unsymmetrical diaryl tellurides. This protocol utilizes sodium aryltellurites (4), which can be easily prepared from low-cost aryltelluride trichlorides and NaOH. The synthesis involves the use of 4 and arylazo sulfones as starting materials in the presence of (MeO)2P(O)H. A variety of diaryl tellurides are obtained in moderate to good yields using this method. Importantly, this innovative protocol eliminates the need for traditional, highly toxic aryltellurolating reagents such as diaryl ditellurides and elemental tellurium. This study will bring new vitality to the synthesis of tellurides.

Carbon-chalcogen wires: alkynyltellurolatocarbynes

The reactions of [W(CBr)(CO)2(Tp*)] (Tp* = tris(dimethylpyrazolyl)borate) with LiTeCCR (R = SiMe3, SiiPr3, iPr, nBu, tBu, Ph, C6H4Me-4, methylimidazol-2-yl) afford the first alkynyltellurolatocarbynes [W(CTeCCR)(CO)2(Tp*)]. Both the WC and CC multiple bonds are prone to metal addition as exemplified by treatment with [MCl(SMe2)] (M = Cu, Au) to afford the hexametallic complex [W2Cu4(μ-CTeCCSiiPr3)2Cl4(CO)4(Tp*)2] and [WAu(μ-CTeCCSiMe3)Cl(CO)2-(Tp*)] which evolves to the unusual hypervalent [WAu(μ-CTeCl4)(SMe2)(CO)2(Tp*)].

Laboratory Evolution of Metalloid Reductase Substrate Recognition and Nanoparticle Product Size

Glutathione reductase-like metalloid reductase (GRLMR) is an enzyme that reduces selenodiglutathione (GS-Se-SG), forming zerovalent Se nanoparticles (SeNPs). Error-prone polymerase chain reaction was used to create a library of ∼10,000 GRLMR variants. The library was expressed in BL21Escherichia coli in liquid culture with 50 mM of SeO32- present, under the hypothesis that the enzyme variants with improved GS-Se-SG reduction kinetics would emerge. The selection resulted in a GRLMR variant with two mutations. One of the mutations (D-E) lacks an obvious functional role, whereas the other mutation is L-H within 5 Å of the enzyme active site. This mutation places a second H residue within 5 Å of an active site dicysteine. This GRLMR variant was characterized for NADPH-dependent reduction of GS-Se-SG, GSSG, SeO32-, SeO42-, GS-Te-SG, and TeO32-. The evolved enzyme demonstrated enhanced reduction of SeO32- and gained the ability to reduce SeO42-. This variant is named selenium reductase (SeR) because of its emergent broad activity for a wide variety of Se substrates, whereas the parent enzyme was specific for GS-Se-SG. This study overall suggests that new biosynthetic routes are possible for inorganic nanomaterials using laboratory-directed evolution methods.

Rationally Designed ZnTe@C Nanowires with Superior Zinc Storage Performance for Aqueous Zn Batteries

Te-based materials with excellent electrical conductivity and ultra-high volume specific capacity have attracted much attention for the cost-efficient aqueous Zn batteries. However, the construction of functional structures with mild volume expansion and suppressed shuttle effects, enabling an expanded lifespan, is still a challenge for conversion-type materials. Herein, the carbon-coated zinc telluride nanowires (ZnTe@C NWs) are rationally designed as a high-performance cathode material for aqueous Zn batteries. The carbon-coated1D nanostructure could not only provide optimized transmission path for electrons and ions, but also help to maintain structure integrity upon volume variation and suppress intermediates dissolution, endowing the ZnTe@C NWs with improved cycling stability and reaction kinetics. Consequently, a reversible six-electron reaction mechanism of ZnTe@C NWs based on Te2- /Te4+ conversion with excellent output capacity (586 mAh g-1 at 0.1 A g-1 ) and lifespan (>250 mAh g-1 retained for 400 cycles at 1 A g-1 ) is eventually achieved.

Breaking AgInTe2 Quantum Dot Chain to Fabricate AgInTe2-ZnS Janus Nanocrystals

Colloidal multinary chalcogenides (MnCs) have emerged as excellent optoelectronic materials, where S- and Se-based MnCs show considerable progress; however, the Te counterpart suffers from detrimental surface oxidation. Moreover, Te-based I-III-VI MnCs (e.g., AgInTe2) tend to form a one-dimensional (1-D) anisotropic structure via the self-assembly of surface-oxidized Te, thus restricting the isolation of AgInTe2 quantum dots (QDs). We report successful control of the self-assembly of Te-based MnCs to arrest the growth of AgInTe2 QDs by using a synergistic capping agent (dodecanethiol and oleic acid). The reaction proceeds with several intermediates, including hexagonal microrods (MR), tetragonal QDs in a chain arrangement, and tetragonal MRs. Importantly, we note that the incorporation of ZnS QDs triggers the breaking of the chain arrangement of the AgInTe2 QDs and the emergence of evenly distributed AgInTe2-ZnS Janus nanocrystals with significantly reduced long-term Te-oxidative properties. Arresting the AgInTe2 QD chain and the subsequent Janus nanocrystal formation could have promising opportunities for 1-D charge hopping and efficient charge transport for optoelectronic applications, respectively.

N-Coordinated tellurenium(II) and telluronium(IV) cations: synthesis, structure and hydrolysis

A set of N-coordinated tellurium(II) compounds containing either C,N-chelating ligands CNR (where CN = 2-(RNCH)C6H4, R = tBu or Dipp; Dipp = 2,6-iPr2C6H3) or N,C,N pincer ligands NCNR (where NCN = 2,6-(RNCH)2C6H4, R = tBu or Dipp) were synthesized. In the case of C,N-chelated compounds, the reaction of CNDippLi with Te(dtc)2 (where dtc = Et2NCS2) in a 1 : 1 molar ratio smoothly provided the carbamate CNDippTe(dtc) which upon treatment with 2 eq. of HCl provided the chloride CNDippTeCl. In contrast, the analogous conversion of NCNRLi with Te(dtc)2 surprisingly furnished ionic bromides [NCNRTe]Br as a result of the exchange of dtc by Br coming from nBuBr present in the reaction mixture. Furthermore, the reaction of CNDippTeCl or [NCNRTe]Br with silver salts AgX (X = OTf or SbF6) provided the expected tellurenium cations [CNDippTe]SbF6 and [NCNRTe]X. To further increase the Lewis acidity of the central atom, the oxidation of selected compounds with 1 eq. of SO2Cl2 was examined yielding stable compounds [CNtBuTeCl2]X and [NCNtBuTeCl2]X. The oxidation of the Dipp substituted compounds proved to be more challenging and an excess of SO2Cl2 was necessary to obtain the oxidized products [CNDippTeCl2]SbF6 and [NCNDippTeCl2]SbF6, which could solely be characterized in solution. Compounds [CNtBuTeCl2]OTf and [NCNtBuTeCl2]OTf were shown to undergo a controlled hydrolysis to the corresponding telluroxanes. All compounds were studied by multinuclear NMR spectroscopy in solution and for selected compounds solid state 125Te NMR spectroscopy and single-crystal X-ray diffraction analysis were performed. The Lewis acidity of the studied cations was examined by the Gutmann-Beckett method using Et3PO as the probing agent. The Te-N chalcogen bonding situation of selected compounds has also been examined computationally by a set of real-space bonding indicators.

Formation, Characterization, and Bonding of cis- and trans-[PtCl2{Te(CH2)6}2], cis-trans-[Pt3Cl6{Te(CH2)6}4], and cis-trans-[Pt4Cl8{Te(CH2)6}4]: Experimental and DFT Study

[PtCl2{Te(CH2)6}2] (1) was synthesized from the cyclic telluroether Te(CH2)6 and cis-[PtCl2(NCPh)2] in dichloromethane at room temperature under the exclusion of light. The crystal structure determination showed that in the solid state, 1 crystallizes as yellow plate-like crystals of the cis-isomer 1cis and the orange-red interwoven needles of 1trans. The crystals could be separated under the microscope. NMR experiments showed that upon dissolution of the crystals of 1cis in CDCl3, it isomerizes and forms a dynamic equilibrium with the trans-isomer 1trans that becomes the predominant species. Small amounts of cis-trans-[Pt3Cl6{Te(CH2)6}4] (2) and cis-trans-[Pt4Cl8{Te(CH2)6}4] (3) were also formed and structurally characterized. Both compounds show rare bridging telluroether ligands and two different platinum coordination environments, one exhibiting a cis-Cl/cis-Te(CH2)6 arrangement and the other a trans-Cl/trans-Te(CH2)6 arrangement. Complex 2 has an open structure with two terminal and two bridging telluroether ligands, whereas complex 3 has a cyclic structure with four Te(CH2)6 bridging ligands. The bonding and formation of the complexes have been discussed through the use of DFT calculations combined with QTAIM analysis. The recrystallization of the mixture of the 1:1 reaction from d6-DMSO afforded [PtCl2{S(O)(CD3)2}{Te(CH2)6}] (4) that could also be characterized both structurally and spectroscopically.

Synthesis, X-ray characterization and DFT analysis of dicyanidoaurate telluronium salts: on the importance of charge assisted chalcogen bonds

In this manuscript we report the synthesis and X-ray characterization of two cyanidoaurate telluronium salts, namely (3-fluorophenyl)(methyl)(phenyl)telluronium dicyanidoaurate [(3-F-Ph)(Me)(Ph)Te][Au(CN)2] (1) and methyldiphenyltelluronium dicyanidoaurate [(Me)(Ph)2Te][Au(CN)2] (2). In the solid state, the tellurium atom establishes three concurrent and directional chalcogen bonds (ChBs) with the adjacent anions, in both compounds. These charge-assisted ChBs (CAChBs) have been analyzed using DFT calculations and several computational tools. The MEP surface analysis discloses the existence of three σ-holes at the Te-atoms capable of establishing strong CAChBs with the counter-ions. In addition, significant charge transfer from the lone pair orbital at the N-atom of the anion to the antibonding σ*(Te-C) orbital of the cation is observed in some cases.

Selection of isomerization pathways of multistep photoswitches by chalcogen bonding

Multistep photoswitches are able to engage in different photoisomerization pathways and are challenging to control. Here we demonstrate a multistep sequence of E/Z isomerization and photocyclization/cycloreversion of photoswitches via manipulating the strength and mechanism of noncovalent chalcogen bonding interactions. The incorporation of chalcogens and the formyl group on open ethene bridged dithienylethenes offers a versatile skeleton for single photochromic molecules. While bidirectional E/Z photoswitching is dominated by neutral tellurium arising from enhanced resonance-assisted chalcogen bonding, the creation of cationic telluronium enables the realization of photocyclization/cycloreversion. The reversible nucleophilic substitution reactions further allow interconversion between neutral tellurium and cationic telluronium and selection of photoisomerization mechanisms on purpose. By leveraging unique photoswitching patterns and dynamic covalent reactivity, light and pH stimuli-responsive multistate rewritable materials were constructed, triggered by an activating reagent for additional control. The results should provide ample opportunities to molecular recognition, intelligent switches, information encryption, and smart materials.

Origin of Optoelectronic Contradictions in 3,4-Cycloalkyl[c]-chalcogenophenes: A Computational Study

The planar morphology of the backbone significantly contributes to the subtle optoelectronic features of π-conjugated polymers. On the other hand, the atomistic tuning of an otherwise identical π-backbone could also impact optoelectronic properties systematically. In this manuscript, we compare a series of 3,4-cycloalkylchalcogenophenes by tuning them atomistically using group-16 elements. Additionally, the effect of systematically extending these building blocks in the form of oligomers and polymers is studied. The size of the 3,4-substitution affected the morphology of the oligomers. In addition, the heteroatoms contributed to a further alteration in their geometry and resultant optoelectronic properties. The chalcogenophenes, containing smaller 3,4-cycloalkanes, resulted in lower bandgap oligomers or polymers compared to those with larger 3,4-cycloalkanes. Natural bonding orbital (NBO) calculations were performed to understand the disparity alongside the contour maps of frontier molecular orbitals (FMO).

Steroids Bearing Heteroatom as Potential Drugs for Medicine

Heteroatom steroids, a diverse class of organic compounds, have attracted significant attention in the field of medicinal chemistry and drug discovery. The biological profiles of heteroatom steroids are of considerable interest to chemists, biologists, pharmacologists, and the pharmaceutical industry. These compounds have shown promise as potential therapeutic agents in the treatment of various diseases, such as cancer, infectious diseases, cardiovascular disorders, and neurodegenerative conditions. Moreover, the incorporation of heteroatoms has led to the development of targeted drug delivery systems, prodrugs, and other innovative pharmaceutical approaches. Heteroatom steroids represent a fascinating area of research, bridging the fields of organic chemistry, medicinal chemistry, and pharmacology. The exploration of their chemical diversity and biological activities holds promise for the discovery of novel drug candidates and the development of more effective and targeted treatments.

Synthesis and screening for anticancer activity of two novel telluro-amino acids: 1,3-Tellurazolidine-4-carboxylic acid and tellurohomocystine

Tellurium (Te) containing amino acids and their derivatives have the potential to participate in biological processes, which are currently being studied extensively to understand the function of Te in biological and pharmacological activities. Here, we are reporting the synthesis of two novel Te-containing unnatural amino acids; 1,3-Tellurazolidine-4-carboxylic acid [Te{CH2CH(COOH)NHCH2}] 5, and 4,4'-(1,2-Ditellurdiyl)bis(2-aminobutanoic acid), i.e., tellurohomocystine [TeCH2CH2CH(NH2)COOH]2 7, synthesized from tellurocystine, and L-methionine as precursors, respectively. These telluro-amino acids were thoroughly characterized by multinuclear (1H, 13C, 125Te) NMR spectroscopy, high-resolution ESI-mass spectrometry (ESI-MS), and elemental analysis. The telluro-amino acids 5 and 7 demonstrated good biocompatibility when in vitro cytotoxicity was analyzed on two fibroblast cell lines L929 and NIH/3T3. The treatment of telluro-amino acids 1,3-Tellurazolidine-4-carboxylic acid 5 and tellurohomocystine 7 on breast cancer cell line MCF-7 showed anticancer activity with IC50 values of 7.29 ± 0.27 µg/mL and 25.36 ± 0.12 µg/mL, respectively. The cell cycle distribution studies also revealed arrest at the sub-G1 phase suggesting telluro-amino acids to be apoptotic.

Chalcogen Bonding Catalysis: Tellurium, the Last Frontier?

Chalcogen bonding (ChB) is the non-covalent interaction occurring between chalcogen atoms as Lewis acid sites and atoms or groups of atoms able to behave as Lewis bases through their lone pair or π electrons. Analogously to its sister halogen bonding, the high directionality of this interaction was implemented for precise structural organizations in the solid state and in solution. Regarding catalysis, ChB is now accepted as a new mode of activation as demonstrated by the increased number of examples in the last five years. In the family of ChB catalysts, those based on tellurium rapidly appeared to overcome their lighter sulfur and selenium counterparts. In this review, we highlight the Lewis acid properties of tellurium-based derivatives in solution and summarize the start-of-the-art of their applications in catalysis.

Simultaneous bioreduction of tellurite and selenite by Yarrowia lipolytica, Trichosporon cutaneum, and their co-culture along with characterization of biosynthesized Te-Se nanoparticles

BACKGROUND

Natural and anthropogenic activities, such as weathering of rocks and industrial processes, result in the release of toxic oxyanions such as selenium (Se) and tellurium (Te) into the environment. Due to the high toxicity of these compounds, their removal from the environment is vital.

RESULTS

In this study, two yeast strains, Yarrowia lipolytica and Trichosporon cutaneum, were selected as the superior strains for the bioremediation of tellurium and selenium. The reduction analyses showed that exposure to selenite induced more detrimental effects on the strains compared to tellurite. In addition, co-reduction of pollutants displayed almost the same results in selenite reduction and more than ~ 20% higher tellurite reduction in 50 h, which shows that selenite triggered higher tellurite reduction in both strains. The selenite and tellurite kinetics of removal were consistent with the first-order model because of their inhibitory behavior. The result of several characterization experiments, such as FE-SEM (Field emission scanning electron microscopy), dynamic light scattering (DLS), Fourier-transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD), and dispersive X-ray (EDX) on Te-Se nanoparticles (NPs) revealed that the separated Te-Se NPs were needle-like, spherical, and amorphous, consisted of Te-Se NPs ranging from 25 to 171 nm in size, and their surface was covered with different biomolecules.

CONCLUSIONS

Remarkably, this work shows, for the first time, the simultaneous bioreduction of tellurite and selenite and the production of Te-Se NPs using yeast strains, indicating their potential in this area, which may be applied to the nanotechnology industry and environmental remediation.

Thermoelectric Performance of Surface-Engineered Cu1.5-xTe-Cu2Se Nanocomposites

Cu_2-xS and Cu_2-xSe have recently been reported as promising thermoelectric (TE) materials for medium-temperature applications. In contrast, Cu_2-xTe, another member of the copper chalcogenide family, typically exhibits low Seebeck coefficients that limit its potential to achieve a superior thermoelectric figure of merit, zT, particularly in the low-temperature range where this material could be effective. To address this, we investigated the TE performance of Cu_1.5-xTe-Cu₂Se nanocomposites by consolidating surface-engineered Cu_1.5Te nanocrystals. This surface engineering strategy allows for precise adjustment of Cu/Te ratios and results in a reversible phase transition at around 600 K in Cu_1.5-xTe-Cu₂Se nanocomposites, as systematically confirmed by in situ high-temperature X-ray diffraction combined with differential scanning calorimetry analysis. The phase transition leads to a conversion from metallic-like to semiconducting-like TE properties. Additionally, a layer of Cu₂Se generated around Cu_1.5-xTe nanoparticles effectively inhibits Cu_1.5-xTe grain growth, minimizing thermal conductivity and decreasing hole concentration. These properties indicate that copper telluride based compounds have a promising thermoelectric potential, translated into a high dimensionless zT of 1.3 at 560 K.

Hydrothermal Synthesis of Ni3TeO6 and Cu3TeO6 Nanostructures for Magnetic and Photoconductivity Applications

Despite great attention toward transition metal tellurates especially M₃TeO₆ (M = transition metal) in magnetoelectric applications, control on single phasic morphology-oriented growth of these tellurates at the nanoscale is still missing. Herein, a hydrothermal synthesis is performed to synthesize single-phased nanocrystals of two metal tellurates, i.e., Ni₃TeO₆ (NTO with average particle size ∼37 nm) and Cu₃TeO₆ (CTO ∼ 140 nm), using NaOH as an additive. This method favors the synthesis of pure NTO and CTO nanoparticles without the incorporation of Na at pH = 7 in MTO crystal structures such as Na₂M₂TeO₆, as it happens in conventional synthesis approaches such as solid-state reaction and/or coprecipitation. Systematic characterization techniques utilizing in-house and synchrotron-based characterization methods for the morphological, structural, electronic, magnetic, and photoconductivity properties of nanomaterials showed the absence of Na in individual particulate single-phase MTO nanocrystals. Prepared MTO nanocrystals also exhibit slightly higher antiferromagnetic interactions (e.g., T _N-NTO = 57 K and T _N-CTO = 68 K) compared to previously reported MTO single crystals. Interestingly, NTO and CTO show not only a semiconducting nature but also photoconductivity. The proposed design scheme opens the door to any metal tellurates for controllable synthesis toward different applications. Moreover, the photoconductivity results of MTO nanomaterials prepared serve as a preliminary proof of concept for potential application as photodetectors.

Diphenyl Diselenide-Assisted Radical Addition Reaction of Diphenyl Disulfide to Unsaturated Bonds upon Photoirradiation

The addition reaction of interelement compounds with heteroatom–heteroatom single bonds to unsaturated bonds under photoirradiation is an important method for the efficient and atom-economical construction of carbon–heteroatom bonds. However, in practice, the desired addition reaction is sometimes unable to proceed as expected due to the low efficiency of the desired addition reactions or the preferential polymerization of unsaturated compounds. In this study, by combining an interelement compound with homologous heteroatom compounds as a catalyst, we succeeded in suppressing the polymerization of the unsaturated compounds and in attaining a highly selective carbon–heteroatom bond formation through the desired addition reaction. In this paper, we have examined in detail whether such a “catalytic radical reaction” proceeds for unsaturated compounds and found that the dithiolation of some unsaturated compounds (i.e., vinylic ethers, styrenes, and isocyanides) could proceed with the assistance of (PhSe)2 under light. The developed methods in this study are expected to have strong implications in the fields of radical chemistry, heteroatom chemistry, synthetic organic chemistry, and catalyst chemistry as atom-economical methods for carbon–heteroatom bond formation.

Studies on the Selective Syntheses of Sodium Ditelluride and Dialkyl Ditellurides

Studies on the selective synthetic method for dialkyl ditellurides 1, a representative class of organyl tellurium compounds, were presented. Considering the difficulty in conducting previous harsh reactions and in suppressing the formation of dialkyl tellurides 2 as side products, we optimized reaction conditions for selective syntheses of sodium ditelluride and the corresponding dialkyl ditellurides 1. We reduced tellurium to sodium ditelluride by using NaBH₄ and subsequently, treated the obtained sodium ditelluride with alkyl halides (RX) to give the target compounds 1. Consequently, by applying various alkyl halides (RX) we achieved the selective syntheses of dialkyl ditellurides 1 (13 examples with 4 new compounds) in modest to good yields. We also suggested the mechanistic pathways to dialkyl ditellurides 1.

Conjugated polymers based on selenophene building blocks

The intrinsic flexibility, solution processability, and optoelectronic properties of semiconducting conjugated polymers make them ideal candidates for use in a wide range of next-generation electronic devices. A virtually unlimited chemical design space has led to diverse polymeric architectures made from combinations of smaller molecular building blocks with desirable functionalities. Of these, thiophene is undoubtedly the most common due to its mixture of synthetic versatility, polymer backbone planarizing effects, and good optoelectronic characteristics. However, the success of thiophene has meant that other heterocycles, such as selenophene, remain relatively underexplored. This focus review discusses the challenges and material advantages of incorporating selenophene into conjugated polymer systems within the context of our contributions to the field. The early studies of poorly performing electrochemically synthesized polyselenophenes are outlined, progressing onto the model chemically synthesized alkylated homopolymers that revealed the key consequences of selenophene addition. We then review the various donor and donor-acceptor copolymer strategies that have exploited the properties of the selenium atom to enhance the performance of solar cells, transistors, and other organic electronic devices. Finally, we give our perspective on the state of the field and the fundamental material optimization studies required to realize the full potential of selenophene-containing conjugated polymers.

A Review of Key Properties of Thermoelectric Composites of Polymers and Inorganic Materials

This review focusses on the development of thermoelectric composites made of oxide or conventional inorganic materials, and polymers, with specific emphasis on those containing oxides. Discussion of the current state-of-the-art thermoelectric materials, including the individual constituent materials, i.e., conventional materials, oxides and polymers, is firstly presented to provide the reader with a comparison of the top-performing thermoelectric materials. Then, individual materials used in the inorganic/polymer composites are discussed to provide a comparison of the performance of the composites themselves. Finally, the addition of carbon-based compounds is discussed as a route to improving the thermoelectric performance. For each topic discussed, key thermoelectric properties are tabulated and comparative figures are presented for a wide array of materials.

Reduced graphene oxide doped tellurium nanotubes for high performance supercapacitor

Supercapacitors have been achieving great interest in energy storage systems for the past couple of decades. Such devices with superior performance, mainly, depending on the material architecture of the electrodes. We report on the preparation of Tellurium nanotubes (Te-tubes diameter ∼100 nm and length ∼700 nm), with variable doping of conducting network reduced graphene oxide (rGO) to fabricate high-performance electrode characteristics of rGO @ Te. The prepared material was characterized using XRD, FTIR, FESEM, and Raman spectroscopy techniques, including Brunauer-Emmett-Teller, Barrett-Joyner-Halenda measurements. FTIR study revealed that 15% rGO @ Te has a wide C-O vibration band at ∼ 1,100–1,300 cm⁻¹, over other compositions. FESEM study shows the Te-tubes dispersion in rGO layers. The EDX study revealed that 15% of the composition has an optimistic concentration of C and O elements. In other compositions, either at lower/higher rGO concentration, an uneven count of C and O is observed. These support efficient charge dynamics to achieve superior ultra-capacitor characteristics, thereby achieving specific capacitance C_sp 170 + F/g @ 10 mV/s in a symmetric configuration. The reported values are thirty times higher than pristine Te-tubes (∼5 F/g). This finding suggests that rGO @ Te is a promising candidate for supercapacitor.

Study on the spectroscopy and transition properties of TeCl. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2022;279:121439. [PMID: 35660150 DOI: 10.1016/j.saa.2022.121439]

For the first time, the spectroscopy data of TeCl⁺ ion and the transition data between low excited states are systematically calculated. The potential energy curves of 22 Λ-S states and 51 Ω states are calculated by the internally contracted multiconfiguration interaction and Davidson correction method. By solving the one-dimensional radial Schrödinger equation, the spectroscopy data of Λ-S states and Ω states are obtained. The phenomenon of avoided crossing in Ω state is analyzed in detail, which is mainly concentrated in the region of 20000 cm^-1 to 35000 cm^-1. The Franck-Condon factors, Einstein coefficients and spontaneous radiative lifetimes of [Formula: see text] transitions are calculated. According to the calculation results, it is preliminarily judged that the direct laser cooling of TeCl⁺ ion is not feasible.

Green synthesis of biogenetic Te(0) nanoparticles by high tellurite tolerance fungus Mortierella sp. AB1 with antibacterial activity

Tellurite [Te(IV)] is a high-toxicity metalloid. In this study, a fungus with high Te(IV) resistance was isolated. Strain AB1 could efficiently reduce highly toxic Te(IV) to less toxic Te(0). The reduced products formed rod-shaped biogenetic Te(0) nanoparticles (Bio-TeNPs) intracellularly. Further TEM-element mapping, FTIR, and XPS analysis showed that the extracted Bio-TeNPs ranged from 100 to 500 nm and consisted of Te(0), proteins, lipids, aromatic compounds, and carbohydrates. Moreover, Bio-TeNPs exhibited excellent antibacterial ability against Shigella dysenteriae, Escherichia coli, Enterobacter sakazakii, and Salmonella typhimurium according to inhibition zone tests. Further growth and live/dead staining experiments showed that E. coli and S. typhimurium were significantly inhibited by Bio-TeNPs, and cells were broken or shriveled after treatment with Bio-TeNPs based on SEM observation. Additionally, the antioxidant and cytotoxicity tests showed that the Bio-TeNPs exhibited excellent antioxidant capacity with no cytotoxicity. All these results suggested that strain AB1 showed great potential in bioremediation and Bio-TeNPs were excellent antibacterial nanomaterials with no cytotoxicity.

Supramolecular Chalcogen-Bonded Semiconducting Nanoribbons at Work in Lighting Devices

This work describes the design and synthesis of a π-conjugated telluro[3,2-β][1]-tellurophene-based synthon that, embodying pyridyl and haloaryl chalcogen-bonding acceptors, self-assembles into nanoribbons through chalcogen bonds. The ribbons π-stack in a multi-layered architecture both in single crystals and thin films. Theoretical studies of the electronic states of chalcogen-bonded material showed the presence of a local charge density between Te and N atoms. OTFT-based charge transport measurements showed hole-transport properties for this material. Its integration as a p-type semiconductor in multi-layered CuI -based light-emitting electrochemical cells (LECs) led to a 10-fold increase in stability (38 h vs. 3 h) compared to single-layered devices. Finally, using the reference tellurotellurophene congener bearing a C-H group instead of the pyridyl N atom, a herringbone solid-state assembly is formed without charge transport features, resulting in LECs with poor stabilities (<1 h).

Selenite and tellurite reduction by Aspergillus niger fungal pellets using lignocellulosic hydrolysate

The performance of Aspergillus niger pellets to remove selenite and tellurite from wastewater using batch and continuous fungal pelleted bioreactors was investigated. The acid hydrolysate of brewer's spent grain (BSG) was utilized by A. niger as the electron donor for selenite and tellurite reduction. The dilution of BSG hydrolysate using mineral medium had a positive effect on the selenite and tellurite removal efficiency with a 1:3 ratio giving the best efficiency. However, selenite and tellurite inhibited fungal growth with a 40.9% and 27.3% decrease in the A. niger biomass yield in the presence of 50 mg/L selenite and tellurite, respectively. The maximum selenite and tellurite removal efficiency using 25% BSG hydrolysate in batch incubations amounted to 72.8% and 99.5% Two fungal pelleted bioreactors were operated in continuous mode using BSG hydrolysate as the substrate. Both the selenite and tellurite removal efficiencies during steady state operation were > 80% with tellurite showing a maximum removal efficiency of 98.5% at 10 mg/L influent concentration. Elemental Se nanospheres for selenite and both Te nanospheres and nanorods for tellurite were formed within the fungal pellets. This study demonstrates the suitability BSG hydrolysate as a low cost carbon source for removal of selenite and tellurite using fungal pellet bioreactors.

Air-stable aryl derivatives of pentafluoroorthotellurate

We report on two different sets of air-stable derivatives of pentafluoroorthotellurate containing fluorinated and non-fluorinated aryl groups. The acid cis-PhTeF4OH was obtained in gram scale and further transformed to Ag[cis-PhTeF4O], which was used as a cis-PhTeF4O transfer reagent to obtain [PPh4][cis-PhTeF4O]. Furthermore, the synthesis of trans-(C6F5)2TeF3OH was achieved by a selective hydrolysis of trans-(C6F5)2TeF4 in the presence of KF and subsequent protonation by aHF. Quantum-chemical calculations show a higher acidity and robustness against fluoride abstraction for trans-(C6F5)2TeF3OH compared to cis-PhTeF4OH.

Sulfonium and Selenonium Salts as Noncovalent Organocatalysts for the Multicomponent Groebke-Blackburn-Bienaymé Reaction

Sulfonium and selenonium salts, represented by S-aryl dibenzothiophenium and Se-aryl dibenzoselenophenium triflates, were found to exhibit remarkable catalytic activity in the model Groebke-Blackburn-Bienaymé reaction. Kinetic analysis and density functional theory (DFT) calculations indicated that their catalytic effect is induced by the ligation of the reaction substrates to the σ-holes on the S or Se atom of the cations. The experimental data indicated that although 10-fold excess of the chloride totally inhibits the catalytic activity of the sulfonium salts, the selenonium salt remains catalytically active, which can be explained by the experimentally found lower binding constant of the selenonium derivative to chloride in comparison with the sulfonium analogue. Both types of salts exhibit lower catalytic activity in the model reaction than dibenziodolium species.

Synthesis of "Naked" TeO2 Nanoparticles for Biomedical Applications

Chalcogenide nanoparticles have become a very active field of research for their optoelectronic and biological properties. This article shows the production of tellurium dioxide nanoparticles (TeO2 NPs) by pulsed laser ablation in liquids. The produced nanoparticles were spherical with a diameter of around 70 nm. The energy band gap of those nanoparticles was determined to be around 5.2 eV. Moreover, TeO2 NPs displayed a dose-dependent antibacterial effect against antibiotic-resistant bacteria such as multidrug-resistant Escherichia coli (MDR E. coli) and methicillin-resistant Staphylococcus aureus (MR S. aureus). The "naked" nature of the nanoparticle surface helped to eradicate the antibiotic-resistant bacteria at a very low concentration, with IC50 values of ∼4.3 ± 0.9 and 3.7 ± 0.2 ppm for MDR E. coli and MR S. aureus, respectively, after just 8 h of culture. Further, the IC50 values of the naked TeO2 NPs against melanoma (skin cancer) and healthy fibroblasts were 1.6 ± 0.7 and 5.5 ± 0.2 ppm, respectively, for up to 72 h. Finally, to understand these optimal antibacterial and anticancer properties of the TeO2 NPs, the reactive oxygen species generated by the nanoparticles were measured. In summary, the present in vitro results demonstrate much promise for the presently prepared TeO2 NPs and they should be studied for a wide range of safe antibacterial and anticancer applications.

Multicomponent Reaction of Isocyanide, Ditelluride, and Mn(III) Carboxylate: Synthesis of N-Acyl Tellurocarbamate

A multicomponent reaction of isocyanides, ditellurides and manganese(III) carboxylates under mild reaction conditions leads to the synthesis of various N-acyl tellurocarbamates. This method demonstrates good functional tolerance and broad substrate scope and, as a result, is especially suitable for the postfunctionalization of complicated molecules such as drugs. The given method can be further extended to the synthesis of selenocarbamates.

From weak to strong interactions: structural and electron topology analysis of the continuum from the supramolecular chalcogen bonding to covalent bonds

The relationship between covalent and supramolecular bonding, and the criteria of the assignments of different interactions were explored via the review of selenium and tellurium containing structures in the Cambridge Structural Database and their computational analysis using Quantum Theory of Atoms in Molecules (QTAIM). This combined study revealed continuums of the interatomic Se⋯Br and Te⋯I distances, d_Ch⋯X, in the series of associations from the sums of the van der Waals radii of these atoms (r_Ch + r_X) to their covalent bond lengths. The electron densities, ρ(r), at Bond Critical Points (BCPs) along the chalcogen bond paths increased gradually from about 0.01 a.u. common for the non-covalent interactions to about 0.1 a.u. typical for the covalent bonds. The log ρ(r) values fell on the same linear trend line when plotted against normalized interatomic distances, R_XY = d_Ch⋯X/(r_Ch + r_X). The transition from the positive to negative values of the energy densities, H(r), at the BCPs (related to a changeover of essentially non-covalent into partially covalent interactions) were observed at R_XY ≈ 0.80. Synchronous changes of bonding characteristics with R_XY (similar to that found earlier in the halogen-bonded systems) designated normalized interatomic separation as a critical factor determining the nature of these bondings. The uninterrupted continuums of Te⋯I and Se⋯Br bond lengths and BCPs' characteristics signified an intrinsic link between limiting types of bonding involving chalcogen atoms and between covalent and supramolecular bonding in general.

Synthetic Mechanisms in the Formation of SnTe Nanocrystals

Infrared active colloidal semiconducting nanocrystals (NCs) are important for applications including photodetectors and photovoltaics. While much research has been conducted on nanocrystalline materials such as the Pb and Hg chalcogenides, less toxic alternatives such as SnTe have been far less explored. Previous synthetic work on SnTe NCs have characterized photophysical properties of the nanoparticles. This study focuses on understanding the fundamental chemical mechanisms involved in SnTe NC formation, with the aim to improve synthetic outcomes. The solvent oleylamine, common to all SnTe syntheses, is found to form a highly reactive, heteroleptic Sn-oleylamine precursor that is the primary molecular Sn species initiating NC formation and growth. Further, the capping ligand oleic acid (OA) reacts with this amine to produce tin oxide (SnO_x), facilitating the formation of an NC SnO_x shell. Therefore, the use of OA during synthesis is counterproductive to the formation of stoichiometric SnTe nanoparticles. The knowledge of chemical reaction mechanisms creates a foundation for the production of high-quality, unoxidized, and stoichiometric SnTe NCs.

Long-Range Supramolecular Synthon Isomerism: Insight from a Case Study of Vinylic Tellurium Trihalides Cl(Ph)C=C(Ph)TeX3 (X = Cl, I)

A slight modification of the synthetic procedure resulted in a new (Cc) polymorph of vinylic tellurium-trichloride Z-Cl(Ph)C=C(Ph)TeCl3 (1, β-form) which is stabilized by Te⋯Cl chalcogen bonds, assembling its molecules into the zigzag chains. Such a packing motive is in contrast to the known (Pca21) polymorph of Z-Cl(Ph)C=C(Ph)TeCl3 (1, α-form, CCDC refcode: BESHOW), which is built upon Te⋯π(Ph) chalcogen bonded chains. We noted a similar case of [Te⋯halogen] vs. [Te⋯π(Ph)] supramolecular synthon polymorphism in its triiodide congener Z-Cl(Ph)C=CPh(TeI3) (2, α and β-polymorphic forms). Quantum chemical calculations of the intermolecular interaction and lattice energies for 1α–β and 2α–β supported the assumption that α is thermodynamic while β is a kinetic form. Kinetic forms 1β and 2β are isostructural (Cc), while the thermodynamic forms 1α (Pca21) and 2α (P21/c) are not and feature an unusual example of long-range supramolecular synthon module isomerism. In other words, 1α–2α pairs demonstrate very similarly to isostructural Te⋯πPh ChB stabilized chains, which are further packed differently relative to each other, following different angular geometry of type-I Cl⋯Cl and type-II I⋯I halogen bonding. These structural considerations are backed by quantum chemical calculations that support the proposed hierarchy of primary and secondary supramolecular synthons and the assignment of α and β as thermodynamic and kinetic forms, respectively.

A DFT study of Se n Te n clusters

First principles calculations have been performed to study the characteristic properties of Se _n Te _n (n = 5-10) clusters. The present study reveals that the properties of these small clusters are consistent with the properties of Se-Te glassy systems. Several hundred equilibrium structures obtained from a genetic algorithm based USPEX code are relaxed to their minimum energy using the VASP code. Most of the lowest energy buckled ring-like structures are formed from Se-Te heteropolar bonds. Detailed structural analysis and distance energy plots unveil that many equilibrium structures are close in energy to their global minimum. The computed Raman and IR spectra show the dominance of Se-Te heteropolar bonds, consistent with earlier simulation and experimental findings in Se_1-x Te _x glass materials. Low frequency vibrational modes observed in small clusters are characteristic features of amorphous materials. Non-bonding orbitals (lone pair) are observed in the HOMO, whereas the LUMO is formed from purely antibonding orbitals. The dielectric functions corroborate the bonding mechanism and slightly polar nature of Se _n Te _n clusters. The energy loss and absorption coefficient indicate the presence of π-plasmons in the UV-visible region. Furthermore, it is ascertained that the use of a hybrid functional (B3LYP) does not affect the properties of small clusters appreciably, except causing a blue shift in the optical spectra. Hence, we find that the small clusters have bearing on the formation of glassy Se-Te systems.

Transition-Metal-Free Synthesis of Unsymmetrical Diaryl Tellurides via SH2 Reaction of Aryl Radicals on Tellurium

Although diaryl tellurides are parent organotellurium compounds, their synthesis methods, especially for unsymmetrical ones, are limited. This may be due to the instability of diaryl tellurides and their synthesis intermediates under reaction conditions. Radical reactions are known to exhibit excellent functional group selectivity; therefore, we focused on a bimolecular homolytic substitution (S_H2) reaction between the aryl radical and diaryl ditelluride. Aryl radicals are generated from arylhydrazines in air and captured by diaryl ditellurides, resulting in a selective formation of unsymmetrical diaryl tellurides with high yields. The electronic effects of the substituents on both arylhydrazines and diaryl ditellurides on the S_H2 reaction of tellurium are also discussed in detail.