A glimpse on biological activities of tellurium compounds

Carbon Nanodot-Microbe-Plant Nexus in Agroecosystem and Antimicrobial Applications

The intensive applications of nanomaterials in the agroecosystem led to the creation of several environmental problems. More efforts are needed to discover new insights in the nanomaterial-microbe-plant nexus. This relationship has several dimensions, which may include the transport of nanomaterials to different plant organs, the nanotoxicity to soil microbes and plants, and different possible regulations. This review focuses on the challenges and prospects of the nanomaterial-microbe-plant nexus under agroecosystem conditions. The previous nano-forms were selected in this study because of the rare, published articles on such nanomaterials. Under the study's nexus, more insights on the carbon nanodot-microbe-plant nexus were discussed along with the role of the new frontier in nano-tellurium-microbe nexus. Transport of nanomaterials to different plant organs under possible applications, and translocation of these nanoparticles besides their expected nanotoxicity to soil microbes will be also reported in the current study. Nanotoxicity to soil microbes and plants was investigated by taking account of morpho-physiological, molecular, and biochemical concerns. This study highlights the regulations of nanotoxicity with a focus on risk and challenges at the ecological level and their risks to human health, along with the scientific and organizational levels. This study opens many windows in such studies nexus which are needed in the near future.

Selenosalicylate; a little-studied heavy-element analogue of the versatile thiosalicylate ligand

Selenosalicylic acid (ortho-HSeC6H4CO2H), the heavy element congener of the widely studied thiosalicylic acid, was prepared by reaction of 2-carboxybenzenediazonium chloride (HO2CC6H4N2+Cl-) with Na2Se2, followed by reduction of the resulting diselenide (SeC6H4CO2H)2 with zinc and acetic acid. The coordination chemistry of the selenosalicylate ligand towards a variety of platinum(ii), palladium(ii), nickel(ii), gold(iii), gold(i), rhodium(iii), iridium(iii) and ruthenium(ii) centres was explored. X-ray crystal structure determinations were carried out on the complexes [Pt(SeC6H4CO2)(PPh3)2], [{(p-cym)Ru(SeC6H4CO2)}2] (p-cym = η6-p-cymene, CH3C6H4CH(CH3)2), [{Cp*Rh(SeC6H4CO2)}2] (Cp* = η5-C5Me5) and [Cp*Ir(SeC6H4CO2)(PPh3)], and comparisons are made with corresponding thiosalicylate complexes. The complexes were characterised by NMR spectroscopy as well as ESI mass spectrometry, which indicated a greater propensity for fragmentation including by selenium loss, compared to the thiosalicylate analogues. Hirshfeld surface analysis to visualise and quantify intermolecular interactions revealed the dominance of H⋯H contacts in [{(p-cym)Ru(SeC6H4CO2)}2] and [Cp*Ir(SeC6H4CO2)(PPh3)].

Hippocampal acetylcholinesterase activation induced by streptozotocin in mice is protected by an organotellurium compound without evidence of toxicity

The cognitive deficit, which is like Alzheimer's disease and is associated with oxidative damage, may be induced by exposure to streptozotocin. This study aimed to evaluate if the tellurium-containing organocompound, 3j, 5'-arylchalcogeno-3-aminothymidine derivative, interferes with the effects of streptozotocin, as well as to investigate its toxicity in adult mice. Cognitive deficit was induced by two doses of streptozotocin (2.25 mg/kg/day, 48 h interval) intracerebroventricularly. After, the mice were subcutaneously treated with 3j (8.62 mg/kg/day) for 25 days. The effects were assessed by evaluating hippocampal and cortical acetylcholinesterase and behavioral tasks. 3j toxicity was investigated for 10 (0, 21.55, or 43.10 mg/kg/day) and 37 (0, 4.31, or 8.62 mg/kg/day) days by assessing biometric parameters and glucose and urea levels, and alanine aminotransferase activity in blood plasma. 3j exposure did not alter the behavioral alterations induced by streptozotocin exposure. On the other hand, 3j exposure normalized hippocampus acetylcholinesterase activity, which is enhanced by streptozotocin exposure. Toxicity evaluation showed that the administration of 3j for either 10 or 37 days did not cause harmful effects on the biometric and biochemical parameters analyzed. Therefore, 3j does not present any apparent toxicity and reverts acetylcholinesterase activity increase induced by streptozotocin in young adult mice.

Mechanistic photophysics of tellurium-substituted cytosine: Electronic structure calculations and nonadiabatic dynamics simulations

Previously, the MS-CASPT2 method was performed to study the static and qualitative photophysics of tellurium-substituted cytosine (TeC). To get quantitative information, we used our recently developed QTMF-FSSH dynamics method to simulate the excited-state decay of TeC. The CASSCF method was adopted to reduce the calculation costs, which was confirmed to provide reliable structures and energies as those of MS-CASPT2. A detailed structural analysis showed that only 5% trajectories will hop to the lower triplet or singlet state via the twisted (S2 /S1 /T2 )T intersection, while 67% trajectories will choose the planar intersections of (S2 /S1 /T3 /T2 /T1 )P and (S2 /S1 /T2 /T1 )P but subsequently become twisted in other electronic states. By contrast, ~28% trajectories will maintain in a plane throughout dynamics. Electronic population revealed that the S2 population will ultrafast transfer to the lower triplet or singlet state. Later, the TeC system will populate in the spin-mixed electronic states composed of S1 , T1 and T2 . At the end of 300 fs, most trajectories (~74%) will decay to the ground state and only 17.4% will survive in the triplet states. Our dynamics simulation verified that tellurium substitution will enhance the intersystem crossings, but the very short triplet lifetime (ca. 125 fs) will make TeC a less effective photosensitizer.

A telluroviologen-anchored tetraphenylporphyrin as sonosensitizer for periodontitis sonodynamic therapy

Periodontitis is a chronic disease caused by bacteria (e.g. Porphyromonas gingivalis, P.gingivalis) that currently lacks effective non-invasive treatment options. Sonodynamic therapy (SDT) is an emerging non-invasive antimicrobial therapeutic strategy. Since ultrasonic tooth cleaning is widely used in dental treatments, SDT has significant potential for the facile implementation of treat periodontitis. However, hypoxia in periodontitis severely limits the effectiveness of traditional sonosensitizers. To address this issue, we have developed a new sonosensitizer termed as TPP-TeV, which combines the traditional sonosensitizer tetraphenylporphyrin (TPP) with a new photosensitizer telluroviologen (TeV). Under ultrasound radiation, TPP-TeV can produce numerous cationic free radicals (TPP-TeV•), which subsequently generate ROS free radicals (O2•-, •OH) efficiently via electron transfer mechanism, resulting in the effective killing of anaerobic P.gingivalis both in vivo and in vitro. As a result, the dental environment is improved, and the inhibition rate of alveolar bone loss reaches 80 %. The introduction of tellurium into the viologen molecule induces changes in its reduction potential, resulting in increased rigidity of the molecule. This modification systematically reduces the biotoxicity of our novel sonosensitizer by 75 % at 50 μM based on bacterial experiments. These promising findings could potentially establish new options for sonodynamic therapy (SDT) in periodontitis clinical treatments.

Heavy Metals and Essential Elements in Association with Oxidative Stress in Women with Polycystic Ovary Syndrome-A Systematic Review

Altered levels of heavy metals and essential elements have been associated with oxidative stress (OS) and metabolic and hormonal changes in women with polycystic ovary syndrome (PCOS). We aimed to summarize the knowledge on the association of heavy metals and essential elements with OS in PCOS. An electronic literature search using PubMed for studies published between January 2008 and April 2023 was conducted. We evaluated heavy metals and essential elements in relation to OS in PCOS in 15 articles. PCOS women had increased antimonium (Sb), cadmium (Cd), lead (Pb), mercury (Hg), arsenic (As), tellurium (Te), thallium (Tl) and osmium (Os) blood levels and decreased zinc (Zn) blood levels; the results of copper (Cu) blood levels were conflicting. Some studies showed a significant correlation between heavy metals (Sb, Cd, Pb, Hg, As, Te and Tl) and essential elements (Se, Zn, Cr, Ca, Mg and Cu) and markers of OS and chronic inflammation. Heavy metals (Sb, Cd, Pb and Hg) and essential elements (Zn, Cr, Se, Ca, Mg and Cu) were associated with metabolic and hormonal characteristics in PCOS. There might be a possible benefit from supplementation therapy in reducing OS and endocrinological problems related to PCOS. Our review confirmed an association between heavy metals and essential elements with OS in PCOS women. This systematic review is registered in PROSPERO under number CRD42023418453.

Diphenyl ditelluride anticancer activity and DNA topoisomerase I poisoning in human colon cancer HCT116 cells

Diphenyl ditelluride (DPDT) is an organotellurium (OT) compound with pharmacological properties, including antioxidant, antigenotoxic and antimutagenic activities when applied at low concentrations. However, DPDT as well as other OT compounds also show cytotoxicity against mammalian cells when treatments occur at higher drug concentrations. Considering that the underlying mechanisms of toxicity of DPDT against tumor cells have been poorly explored, the objective of our study was to investigate the effects of DPDT against both human cancer and non-tumorigenic cells. As a model, we used the colonic HCT116 cancer cells and the MRC5 fibroblasts. Our results showed that DPDT preferentially targets HCT116 cancer cells when compared to MRC5 cells with IC₅₀ values of 2.4 and 10.1 μM, respectively. This effect was accompanied by the induction of apoptosis and a pronounced G2/M cell cycle arrest in HCT116 cells. Furthermore, DPDT induces DNA strand breaks at concentrations below 5 μM in HCT116 cells and promotes the occurrence of DNA double strand breaks mostly during S-phase as measured by γ-H2AX/EdU double staining. Finally, DPDT forms covalent complexes with DNA topoisomerase I, as observed by the TARDIS assay, with a more prominent effect observed in HCT116 than in MRC5 cells. Taken together, our results show that DPDT preferentially targets HCT116 colon cancer cells likely through DNA topoisomerase I poisoning. This makes DPDT an interesting molecule for further development as an anti-proliferative compound in the context of cancer.

Screening of AS101 analog, organotellurolate (IV) compound 2 for its in vitro biocompatibility, anticancer, and antibacterial activities

Organotellurium compounds are being well researched as potential candidates for their functional roles in therapeutic and clinical biology. Here, we report the in vitro anticancer and antibacterial activities of an AS101 analog, cyclic zwitterionic organotellurolate (IV) compound 2 [Te^-{CH₂CH(NH₃⁺)COO}(Cl)₃]. Different concentrations of compound 2 were exposed to fibroblast L929 and breast cancer MCF-7 cell lines to study its effect on cell viability. The fibroblast cells with good viability confirmed the biocompatibility, and compound 2 also was less hemolytic on RBCs. A cytotoxic effect on MCF-7 breast cancer cell line investigated compound 2 to be anti-cancerous with IC50 value of 2.86 ± 0.02 µg/mL. The apoptosis was confirmed through the cell cycle phase arrest of the organotellurolate (IV) compound 2. Examination of the antibacterial potency compound 2 was done based on the agar disk diffusion, minimum inhibitory concentration, and time-dependent assay for the Gram-positive Bacillus subtilis and Gram-negative Pseudomonas putida. For both bacterial strains, tests were performed with the concentration range of 3.9-500 μg/mL, and the minimum inhibition concentration value was found to be 125 μg/mL. The time-dependent assay suggested the bactericidal activity of organotellurolate (IV) compound, 2 against the bacterial strains.

An Insight into the Impact of Serum Tellurium, Thallium, Osmium and Antimony on the Antioxidant/Redox Status of PCOS Patients: A Comprehensive Study

Humans exploit heavy metals for various industrial and economic reasons. Although some heavy metals are essential for normal physiology, others such as Tellurium (Te), Thallium (TI), antimony (Sb), and Osmium (Os) are highly toxic and can lead to Polycystic Ovarian Syndrome (PCOS), a common female factor of infertility. The current study was undertaken to determine levels of the heavy metals TI, Te, Sb and Os in serum of PCOS females (n = 50) compared to healthy non-PCOS controls (n = 56), and to relate such levels with Total Antioxidant Capacity (TAC), activity of key antioxidant enzymes, oxidative stress marker levels and redox status. PCOS serum samples demonstrated significantly higher levels of TI, Te, Sb and Os and diminished TAC compared to control (p < 0.001). Furthermore, there was significant inhibition of SOD, CAT and several glutathione-related enzyme activities in sera of PCOS patients with concurrent elevations in superoxide anions, hydrogen and lipid peroxides, and protein carbonyls, along with disrupted glutathione homeostasis compared to those of controls (p < 0.001 for all parameters). Additionally, a significant negative correlation was found between the elevated levels of heavy metals and TAC, indicative of the role of metal-induced oxidative stress as a prominent phenomenon associated with the pathophysiology of the underlying PCOS. Data obtained in the study suggest toxic metals as risk factors causing PCOS, and thus protective measures should be considered to minimize exposure to prevent such reproductive anomalies.

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.

Green synthesis of metalloid nanoparticles and its biological applications: A review

Synthesis of metalloid nanoparticles using biological-based fabrication has become an efficient alternative surpassing the existing physical and chemical approaches because there is a need for developing safer, more reliable, cleaner, and more eco-friendly methods for their preparation. Over the last few years, the biosynthesis of metalloid nanoparticles using biological materials has received increased attention due to its pharmaceutical, biomedical, and environmental applications. Biosynthesis using bacterial, fungal, and plant agents has appeared as a faster developing domain in bio-based nanotechnology globally along with other biological entities, thus posing as an option for conventional physical as well as chemical methods. These agents can efficiently produce environment-friendly nanoparticles with the desired composition, morphology (shape as well as size), and stability, along with homogeneity. Besides this, metalloid nanoparticles possess various applications like antibacterial by damaging bacterial cell membranes, anticancer due to damaging tumour sites, targeted drug delivery, drug testing, and diagnostic roles. This review summarizes the various studies associated with the biosynthesis of metalloid particles, namely, tellurium, arsenic, silicon, boron, and antimony, along with their therapeutic, pharmaceutical and environmental applications.

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.

Accessing the environmental impact of tellurium metal

Tellurium is gaining technical significance because of being a vital constituent for the growth of green-energy products and technologies. Owing to its unique property of interchangeable oxidation states it has a tricky though interesting chemistry with basically unidentified environmental effects. The understanding of environmental actions of tellurium has significant gaps for instance, its existence and effects in various environmental sections related to mining, handling and removal and disposal methods. To bridge this gap it is required to assess its distinctive concentrations in the environment together with proper knowledge of its environmental chemistry. This in turn significantly requires developing systematic diagnostic schemes which are sensitive enough to present statistics in the concentrations which are environmentally relevant. The broad assessment of available statistics illustrates that tellurium is being found in a very scarce concentrations in various environmental sections. Very less information is available for the presence and effects of tellurium in air and natural water resources. Various soil and lake sediment analysis statistics indicate towards the presence of tellurium in soil owing to release of dust, ash and slag during mining and manufacturing practices. Computing the release and behavior of tellurium in environment needs a thorough assessment of its anthropogenic life cycle which in turn will facilitate information about its existing and prospective release in the environment, and will aid to handle the metal more sensibly.

Oxidative stress response system in Escherichia coli arising from diphenyl ditelluride (PhTe)2 exposure

The toxicity of diphenyl ditelluride (PhTe)₂ is associated with its ability to oxidize sulfhydryl groups from biological molecules. Therefore, we evaluated possible molecular mechanisms of toxicity induced by this organochalcogen in Escherichia coli (E. coli) by evaluating oxidative damage markers, relative expression of genes associated with the cellular redox state in bacteria, such as katG, sodA, sodB, soxS, and oxyR, as well as the activity of enzymes responsible for cellular redox balance. After exposure of (PhTe)₂ (6, 12, and 24 μg/mL), there was a decrease in non-protein thiols (NPSH) levels, an increase in protein carbonylation and lipid peroxidation in E. coli. Intra- and extracellular reactive species (RS) was increased at concentrations of 6, 12, and 24 μg/mL. The superoxide dismutase (SOD) activity was increased at the three concentrations tested, while catalase (CAT) activity was higher at 12 and 24 μg/mL. The soxS gene showed lower expression at the three concentrations tested, while the oxyR gene was supressed at 24 μg/mL. The katG antioxidant response gene showed lower expression, and sodA and sodB were positively activated, except for sodB at 6 μg/mL. Our findings demonstrate that exposure to (PhTe)₂ induced RS formation, NPSH depletion and changes in transcriptional factors regulation, characterizing it as a multi-target compound, causing disruption in cellular oxidative state, as well as molecular mechanisms associated in E. coli.

Semiconductor characteristics of tellurium and its implementations

Tellurium (Te) gained worldwide attention because of its excellent properties, distinctive chained structures, and potential usages. Bulk Te is a p-type elemental helical semiconductor at room temperature and it also having a very limited band gap. Te presents fascinating characteristics such as nonlinear optical response, photoconductivity, good thermoelectric and piezoelectric properties. These charming characteristics induce Te a possible nominee for applications in field-effect transistors, IR acousto-optic deflectors, solar cells, self-developing holographic recording devices, photoconductors, gas sensors, radiative cooling devices, and topological insulators. The developments in these areas are incorporated in great detail. This study opens up the possibility of designing novel devices and considering modern applications of Tellurium.

Toxicity of tellurium and its compounds

Tellurium (Te) is widely used in industry because of its unique physicochemical properties. In the general population, foodstuff like meat, dairy products, and cereals is the major source of tellurium exposure. In the occupational environment, inhalational exposure predominates. Due to its exceptional properties as a metalloid, Te is broadly used in the industry. For example, Te is used as an alloy for solar panels, phase change optical magnetic disks, and Peltier devices. Recently, alloys of Te with cadmium, zinc, and other metals are used for nanomaterials, such as quantum dots. Thus, it is suggested that there is an existence of risk of exposure to Te in everyday life. Commercial Te is mostly obtained from slimes of electrolytic copper refineries. Te concentration in the slimes can extend up to 10% or more. Slight levels of its organic compounds may also be absorbed via skin. Not much information is available to prove Te as carcinogenic but its toxicity is well established. The present paper will review the toxicity of Te and its compounds.

Tellurium-induced cyclization of olefinic compounds

In this article, we discuss about the importance of Tellurium (Te) in organic synthesis. Tellurium-induced cyclization of alkenyl compounds, as well as alkynyl compounds, are considered for the study. The developments in this area are incorporated in great detail. The mechanism of the reactions does not follow any straightforward process. This study opens up the possibility of stereocontrolled synthesis of complex natural products.

Latest developments on the synthesis of bioactive organotellurium scaffolds

This review deals with the latest developments on the synthesis of biologically promising organotellurim scaffolds reported during last two decades.

Emerging Roles of Green-Synthesized Chalcogen and Chalcogenide Nanoparticles in Cancer Theranostics

The last few decades have seen an overwhelming increase in the amount of research carried out on the use of inorganic nanoparticles. More fascinating is the tremendous progress made in the use of chalcogen and chalcogenide nanoparticles in cancer theranostics. These nanomaterials, which were initially synthesized through chemical methods, have now been efficiently produced using different plant materials. The paradigm shift towards the biogenic route of nanoparticle synthesis stems from its superior advantages of biosafety, eco-friendliness, and simplicity, among others. Despite a large number of reviews available on inorganic nanoparticle synthesis through green chemistry, there is currently a dearth of information on the green synthesis of chalcogens and chalcogenides for cancer research. Nanoformulations involving chalcogens such as sulfur, selenium, and tellurium and their respective chalcogenides have recently emerged as promising tools in cancer therapeutics and diagnosis. Similar to other inorganic nanoparticles, chalcogens and chalcogenides have been synthesized using plant extracts and their purified biomolecules. In this review, we provide an up-to-date discussion of the recent progress that has been made in the plant-mediated synthesis of chalcogens and chalcogenides with a special focus on their application in cancer theranostics.

Synthesis of Tellurium Oxide (TeO2) Nanorods and Nanoflakes and Evaluation of Its Efficacy Against Leishmania major In Vitro and In Vivo

PURPOSE

Today, the use of natural products and nanostructures has increased. Given the reports on beneficial effects of various organotellurane compounds on types of visceral leishmaniasis, we decided to investigate the effect of TeO₂ NPs on Leishmania major (L. major). Tellurium can cause cell apoptosis in cancer cells without activating the caspase-pathway.

METHODS

TeO₂ NPs at first synthesized and the structure was checked by XRD, SEM and EDS tests. The cytotoxic effect of TeO₂ NPs against L. major promastigotes, amastigotes and macrophages was assessed by MTT test or counting. The possible apoptosis of L. major by TeO₂ NPs was evaluated by flow cytometry test. For in vivo assay, the lesions of infected BALB/c mice with L. major promastigotes were treated with TeO₂ NPs, then the lesion size and survival rate were evaluated.

RESULTS

The synthesis of TeO₂ with tetragonal structure was confirmed by XRD. The combination of nanorods and nanoflakes and the presence of Te were proven by SEM and EDS, respectively. According the effects of nanoparticle on promastigotes and amastigotes, the IC₅₀ values of TeO₂ after 72 h of incubation were 15.13 and 52.22 µg/ml, respectively. TeO₂ NPs induced apoptosis in about 41% of promastigotes. The ulcer greatly healed and survival rate was higher in treated mice compared to those in control group.

CONCLUSION

Based on the data, favorable anti-leishmanial properties were observed by using TeO₂ NPs. TeO₂ NPs have cytotoxic impacts on L. major promastigotes and amastigotes in vitro and in vivo and may be regarded as a therapy option.

Exploring the reactivity of L-tellurocystine, Te-protected tellurocysteine conjugates and diorganodiselenides towards hydrogen peroxide: synthesis and molecular structure analysis

The synthesis of a series of novel organotellurium species and diorganoselenones is reported.

Theoretical Aspects of Nonconventional Hydrogen Bonds in the Complexes of Aldehydes and Hydrogen Chalcogenides

Hydrogen bonds (H-bonds) in the complexes between aldehydes and hydrogen chalcogenides, XCHO...nH₂Z with X = H, F, Cl, Br, and CH₃, Z = O, S, Se, and Te, and n = 1,2, were investigated using high-level ab initio calculations. The C_sp2-H...O H-bonds are found to be about twice as strong as the C_sp2-H...S/Se/Te counterparts. Remarkably, the S/Se/Te-H...S/Se/Te H-bonds are 4.5 times as weak as the O-H...O ones. The addition of the second H₂Z molecule into binary systems induces stronger complexes and causes a positive cooperative effect in ternary complexes. The blue shift of C_sp2-H stretching frequency involving the C_sp2-H...Z H-bond sharply increases when replacing one H atom in HCHO by a CH₃ group. In contrast, when one H atom in HCHO is substituted with a halogen, the magnitude of blue-shifting of the C_sp2-H...Z H-bond becomes smaller. The largest blue shift up to 92 cm^-1 of C_sp2-H stretching frequency in C_sp2-H...O H-bond in CH₃CHO...2H₂O has rarely been observed and is much greater than that in the cases of the C_sp2-H...S/Se/Te ones. The C_sp2-H blue shift of C_sp2-H...Z bonds in the halogenated aldehydes is converted into a red shift when H₂O is replaced by a heavier analogue, such as H₂S, H₂Se, or H₂Te. The stability and classification of nonconventional H-bonds including C_sp2-H...Se/Te, Te-H...Te, and Se/Te-H...O have been established for the first time.

Synthesis, Mechanism Elucidation and Biological Insights of Tellurium(IV)-Containing Heterocycles

Inspired by the synthetic and biological potential of organotellurium substances, a series of five- and six-membered ring organotelluranes containing a Te-O bond were synthesized and characterized. Theoretical calculations elucidated the mechanism for the oxidation-cyclization processes involved in the formation of the heterocycles, consistent with chlorine transfer to hydroxy telluride, followed by a cyclization step with simultaneous formation of the new Te-O bond and deprotonation of the OH group. Moreover, theoretical calculations also indicated anti-diastereoisomers to be major products for two chirality center-containing compounds. Antileishmanial assays against Leishmania amazonensis promastigotes disclosed 1,2λ⁴ -oxatellurane LQ50 (IC₅₀ =4.1±1.0; SI=12), 1,2λ⁴ -oxatellurolane LQ04 (IC₅₀ =7.0±1.3; SI=7) and 1,2λ⁴ -benzoxatellurole LQ56 (IC₅₀ =5.7±0.3; SI=6) as more powerful and more selective compounds than the reference, being up to four times more active. A stability study supported by ¹²⁵ Te NMR analyses showed that these heterocycles do not suffer structural modifications in aqueous-organic media or at temperatures up to 65 °C.

Equilibrium between tri- and tetra-coordinate chalcogenuranes is critical for cysteine protease inhibition

There have been significant advances in the biological use of hypervalent selenium and tellurium compounds as cysteine protease inhibitors. However, the full understanding of their reaction mechanisms for and cysteine proteases inhibition is still elusive. Kinetic studies suggest an irreversible inhibition mechanism, which was explained by forming a covalent bond between the enzyme sulfhydryl group and the chalcogen atom at its hypervalent state (+4). In this work, we performed a theoretical investigation using density functional theory to propose the active inhibitor form in an aqueous solution. To this end, we investigated chloride ligand exchange reactions by oxygen and sulfur nucleophiles on hypervalent selenium and tellurium compounds. All tetra- and tri-coordinated chalcogen compounds and distinct protonation states of the nucleophiles were considered, totaling 34 unique species, 7 nucleophiles, and 155 free energies reactions. We discovered that chloride is easily replaced by a nonprotonated nucleophile (SH^- or OH^- ) in R₂ SeCl₂ . We also found that tri-coordinate species are more stable than their tetra-coordinate counterparts, with selenoxide (R₂ SeO) protonation being strongly exergonic in acid pH. The thermodynamic and kinetic results suggest that the protonated selenoxide (R₂ SeOH⁺ ) is the most probable active chemical species in biological media. The computed energetic profiles paint a possible picture for selenuranes activity, with successive exergonic steps leading to a covalent inhibition of thiol-dependent enzymes, like cysteine proteases. A second pathway has also been uncovered, with a direct reaction to chalcogenonium cation (R₂ SeCl⁺ ) as the inhibition step. Tellurium compounds showed similar trends but formed telluroxide in a pH-independent fashion.

Strike a Balance: Between Metals and Non-Metals, Metalloids as a Source of Anti-Infective Agents

Most of the commercially available anti-infective agents are organic molecules. In fact, though, during the pioneering times of modern medicine, at the beginning of the 20th century, several inorganic compounds of transition metals were used for medicinal application, to date, only a small number of inorganic drugs are used in clinical practice. Beyond the transition metals, metalloids—or semimetals—offer a rich chemistry in between that of metallic and non-metallic elements, and accordingly, peculiar features for their exploitation in medicinal chemistry. A few important examples of metalloid-based drugs currently used for the treatment of various diseases do exist. However, the use of this group of elements could be further expanded on the basis of their current applications and the clinical trials they entered. Considering that metalloids offer the opportunity to expand the “chemical-space” for developing novel anti-infective drugs and protocols, in this paper, we briefly recapitulate and discuss the current applications of B-, Si-, As-, Sb- and Te-based anti-infective drugs.

Tellurium: A Rare Element with Influence on Prokaryotic and Eukaryotic Biological Systems

Metalloid tellurium is characterized as a chemical element belonging to the chalcogen group without known biological function. However, its compounds, especially the oxyanions, exert numerous negative effects on both prokaryotic and eukaryotic organisms. Recent evidence suggests that increasing environmental pollution with tellurium has a causal link to autoimmune, neurodegenerative and oncological diseases. In this review, we provide an overview about the current knowledge on the mechanisms of tellurium compounds' toxicity in bacteria and humans and we summarise the various ways organisms cope and detoxify these compounds. Over the last decades, several gene clusters conferring resistance to tellurium compounds have been identified in a variety of bacterial species and strains. These genetic determinants exhibit great genetic and functional diversity. Besides the existence of specific resistance mechanisms, tellurium and its toxic compounds interact with molecular systems, mediating general detoxification and mitigation of oxidative stress. We also discuss the similarity of tellurium and selenium biochemistry and the impact of their compounds on humans.

Antiproliferative and Genotoxic Action of an Underexploited Organoteluran Derivative on Sarcoma 180 Cells

BACKGROUND

The search for novel metallic chemical compounds with toxicogenic effects has been of great importance for more efficient cancer treatment.

OBJECTIVE

The study evaluated the cytotoxic, genotoxic and mutagenic activity of organoteluran RF07 in the S-180 cell line.

METHODS

The bioassays used were cell viability with 3-(4,5-dimethyl-2-thiazole)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) test, evaluation of apoptosis and necrosis using fluorescence and flow cytometry, cytokinesisblock micronucleus test and comet assay. The compound was tested at 1; 2.5 and 5μM.

RESULTS

The results showed the cytotoxicity of RF07 at concentrations of 2.5, 5, 10 and 20μM when compared to the negative control. For genotoxicity tests, RF07 showed effects in all concentrations assessed by increased index and frequencies of damage and mutagenic alterations. The compound was also cytotoxic due to the significant decrease in the nuclear division index, with significant values of apoptosis and necrosis. The results of fluorescence and flow cytometry showed apoptosis as the main type of cell death caused by RF07 at 5μM, which is thought to avoid an aggressive immune response of the organism.

CONCLUSION

In addition to cytotoxic and genotoxic effects, RF07 creates good perspectives for future antitumor formulations.

Quantum chemical calculations of 77 Se and 125 Te nuclear magnetic resonance spectral parameters and their structural applications

An accurate quantum chemical (QC) modeling of ⁷⁷ Se and ¹²⁵ Te nuclear magnetic resonance (NMR) spectra is deeply involved in the NMR structural assignment for selenium and tellurium compounds that are of utmost importance both in organic and inorganic chemistry nowadays due to their huge application potential in many fields, like biology, medicine, and metallurgy. The main interest of this review is focused on the progress in QC computations of ⁷⁷ Se and ¹²⁵ Te NMR chemical shifts and indirect spin-spin coupling constants involving these nuclei. Different computational methodologies that have been used to simulate the NMR spectra of selenium and tellurium compounds since the middle of the 1990s are discussed with a strong emphasis on their accuracy. A special accent is placed on the calculations resorting to the relativistic methodologies, because taking into account the relativistic effects appreciably influences the precision of NMR calculations of selenium and, especially, tellurium compounds. Stereochemical applications of quantum chemical calculations of ⁷⁷ Se and ¹²⁵ Te NMR parameters are discussed so as to exemplify the importance of integrated approach of experimental and computational NMR techniques.

Synthesis of functionalised organochalcogenides and in vitro evaluation of their antioxidant activity

Differently substituted β-hydroxy- and β-amino dialkyl and alkyl-aryl tellurides and selenides have been prepared through ring-opening reactions of epoxides and aziridines with selenium- or tellurium-centered nucleophiles. The antioxidant properties and the cytotoxicity of such compounds have been investigated on normal human dermal fibroblasts. Most of the studied compounds exhibited a low cytotoxicity and a number of them proved to be non-toxic, not showing any effect on cell viability even at the highest concentration used (100 μM). The obtained results showed a significant antioxidant potential of the selected organotellurium compounds, particularly evident under conditions of exogenously induced oxidative stress. The antioxidant activity of selenium-containing analogues of active tellurides has also been evaluated on cells, highlighting that the replacement of Se with Te brought about a significant increase in the peroxidase activity.

Organotellurium compounds: an overview of synthetic methodologies

In wake of emerging applications of organotellurium compounds in biological and material science avenues, the current review describes their key synthetic methodologies while focusing the synthesis of organotellurium compounds through five ligand-to-metal linkages including carbon; carbon-oxygen; carbon-nitrogen; carbon-metal; carbon-sulfur to tellurium. In all of these linkages whether tellurium links with ligands through a complicated or simple pathways, it is often governed through electrophilic substitution reactions. The present study encompasses these major synthetic routes so as to acquire comprehensive understanding of synthetic organotellurium compounds.

Comparative Study of Selenides and Tellurides of Transition Metals (Nb and Ta) with Respect to its Catalytic, Antimicrobial, and Molecular Docking Performance

The present research is a comparative study that reports an economical and accessible method to synthesize niobium (Nb) and Tantalum (Ta) selenides and tellurides with useful application in the removal of pollutants in textile, paper, and dyeing industries as well as in medical field. In this study, solid-state process was used to generate nanocomposites and various characterization techniques were employed to compare two groups of materials under investigation. Structure, morphology, elemental constitution, and functional groups of synthesized materials were analyzed with XRD, FESEM coupled with EDS, FTIR, and Raman spectroscopy, respectively. HR-TEM images displayed nanoscale particles with tetragonal and monoclinic crystal structures. The optical properties were evaluated in terms of cut-off wavelength and optical band gap using UV-visible spectroscopy. A comparative behavior of both groups of compounds was assessed with regards to their catalytic and microcidal properties. Extracted nanocomposites when used as catalysts, though isomorphs of each other, showed markedly different behavior in catalytic degradation of MB dye in the presence of NaBH₄ that was employed as a reducing agent. This peculiar deviation might be attributed to slight structural differences between them. Escherichia coli and Staphylococcus aureus (G -ve and + ve bacteria, respectively) were designated as model strains for in vitro antibacterial tests of both clusters by employing disk diffusion method. Superior antibacterial efficacy was observed for telluride system (significant inhibition zones of 26-35 mm) compared with selenide system (diameter of inhibition zone ranged from 0.8 mm to 1.9 mm). In addition, molecular docking study was undertaken to ascertain the binding interaction pattern between NPs and active sites in targeted cell protein. The findings were in agreement with antimicrobial test results suggesting NbTe₄ to be the best inhibitor against FabH and FabI enzymes.

Evaluation of the effect of synthetic compounds derived from azidothymidine on MDA-MB-231 type breast cancer cells

The present study aimed to investigate the effect of AZT derivates containing tellurium (Te) on human breast cancer cell lines and the mechanisms underlying cell death. The inhibitory effect of AZT and its derivatives (7m and 7r) was determined by the MTT assay (6.25, 12.5, 25, 50 and 100 μM in 24 and 48 h time points), meanwhile the induction of apoptosis and the cell cycle phases was investigated by flow cytometry. The MTT assay showed that AZT derivatives decreased the rate of cell proliferation at concentrations of 12.5 μM, while commercial AZT showed low antitumor potential. In flow cytometric analysis, we demonstrate that the AZT derivatives do not induce apoptosis at the concentration tested and promote the cell cycle arrest in the S phase. Besides, predicted absorption, distribution, metabolization, excretion and toxicity analysis suggest that the compounds possess a good pharmacokinetic profile and possibly less toxicity when compared to conventional AZT. These compounds containing tellurium in their formulation are potential therapeutic agents for breast cancer.

Recent Advances in Tumor Microenvironment Hydrogen Peroxide-Responsive Materials for Cancer Photodynamic Therapy

Photodynamic therapy (PDT), as one of the noninvasive clinical cancer phototherapies, suffers from the key drawback associated with hypoxia at the tumor microenvironment (TME), which plays an important role in protecting tumor cells from damage caused by common treatments. High concentration of hydrogen peroxide (H₂O₂), one of the hallmarks of TME, has been recognized as a double-edged sword, posing both challenges, and opportunities for cancer therapy. The promising perspectives, strategies, and approaches for enhanced tumor therapies, including PDT, have been developed based on the fast advances in H₂O₂-enabled theranostic nanomedicine. In this review, we outline the latest advances in H₂O₂-responsive materials, including organic and inorganic materials for enhanced PDT. Finally, the challenges and opportunities for further research on H₂O₂-responsive anticancer agents are envisioned .

Recent Advances in Tumor Microenvironment Hydrogen Peroxide-Responsive Materials for Cancer Photodynamic Therapy

Photodynamic therapy (PDT), as one of the noninvasive clinical cancer phototherapies, suffers from the key drawback associated with hypoxia at the tumor microenvironment (TME), which plays an important role in protecting tumor cells from damage caused by common treatments. High concentration of hydrogen peroxide (H₂O₂), one of the hallmarks of TME, has been recognized as a double-edged sword, posing both challenges, and opportunities for cancer therapy. The promising perspectives, strategies, and approaches for enhanced tumor therapies, including PDT, have been developed based on the fast advances in H₂O₂-enabled theranostic nanomedicine. In this review, we outline the latest advances in H₂O₂-responsive materials, including organic and inorganic materials for enhanced PDT. Finally, the challenges and opportunities for further research on H₂O₂-responsive anticancer agents are envisioned .

Electrocatalytic proton-reduction behaviour of telluride-capped triiron clusters: tuning of overpotentials and stabilization of redox states relative to lighter chalcogenide analogues

Electrocatalytic proton reduction catalyzed by [Fe₃(CO)₉(μ₃-Te)₂], and a number of its phosphine and diphosphine derivatives, has been studied.

Theoretical Investigation of Cyano-Chalcogen Dimers and Their Importance in Molecular Recognition

In this manuscript the different noncovalent interactions established between (HYCN)₂ dimers (Y=S, Se and Te) have been studied at the MP2 and CCSD(T) level of theory. Several homodimers have been taken into account, highlighting the capacity of these compounds to act both as electron donor and acceptor. The main properties studied were geometries, binding energy (E_b ), and molecular electrostatic potential (MEP). Given the wide application of chalcogen bonds, and more specifically of cyano-chalcogen moieties in molecular recognition, natural bond orbital (NBO), "atoms-in-molecules" (AIM), and electron density shift (EDS) analysis were also used to analyse the different noncovalent interactions upon complexation. The presence of hydrogen, chalcogen and dipole-dipole interactions was confirmed and their implications on molecular recognition were analysed.

Diphenyl Ditelluride: Redox-Modulating and Antiproliferative Properties

Tellurium is a rare element that has been regarded as a toxic, nonessential element, and its biological role is not clearly established. In addition, the biological effects of elemental tellurium and some of its organic and inorganic derivatives have been studied, leading to a set of interesting and promising applications. Diphenyl ditelluride (DPDT), an organic tellurium derivate, showed antioxidant, antigenotoxic, antimutagenic, and anticancer properties. The antioxidant and prooxidant properties of DPDT are complex and depend on experimental conditions, which may explain the contradictory reports of these properties. In addition, DPDT may exert its effects through different pathways, including distinct ones to those responsible for chemotherapy resistance phenotypes: transcription factors, membrane receptors, adhesion, structural molecules, cell cycle regulatory components, and apoptosis pathways. This review aims to present recent advances in our understanding of the biological effects, therapeutic potential, and safety of DPDT treatment. Moreover, original results demonstrating the cytotoxic effects of DPDT in different mammalian cell lines and systems biology analysis are included, and emerging approaches for possible future applications are inferred.

Synthesis of novel tellurides bearing benzensulfonamide moiety as carbonic anhydrase inhibitors with antitumor activity

We have synthetized a novel series of β-hydroxy tellurides bearing the benzenesulfonamide group as potent inhibitors of carbonic anhydrase enzymes. In a one pot procedure, we discovered both the ring opening reaction of the three-membered ring and the cleavage of the sulfonamide protecting moiety at the same time. Moreover, the first X-ray co-crystallographic structure of a β-hydroxy telluride derivative with hCA II is reported. The potent effects of these compounds against the tumor-associated hCA IX with low nanomolar constant inhibition values give the possibility to evaluate their activity in vitro using a breast cancer cell line (MDA-MB-231). Compounds 7e and 7g induced significant toxic effects against tumor cells after 48 h incubation in normoxic conditions killing over 50% of tumor cells at 3 μM, but their efficacy decreased in hypoxic conditions reaching the 50% of the tumor cell viability only at 30 μM. These unusual features make them interesting lead compounds to act as antitumor agents, not only as Carbonic Anhydrase IX inhibitors, but reasonably in different pathways, where hCA IX is not overexpressed.