Selenium Dioxide Research Articles

Selenium-Dependent Biogenesis of Formate Dehydrogenase in Campylobacter jejuni Is Controlled by the fdhTU Accessory Genes

The food-borne bacterial pathogen Campylobacter jejuni efficiently utilizes organic acids such as lactate and formate for energy production. Formate is rapidly metabolized via the activity of the multisubunit formate dehydrogenase (FDH) enzyme, of which the FdhA subunit is predicted to contain a selenocysteine (SeC) amino acid. In this study we investigated the function of the cj1500 and cj1501 genes of C. jejuni, demonstrate that they are involved in selenium-controlled production of FDH, and propose the names fdhT and fdhU, respectively. Insertional inactivation of fdhT or fdhU in C. jejuni resulted in the absence of FdhA and FdhB protein expression, reduced fdhABC RNA levels, the absence of FDH enzyme activity, and the lack of formate utilization, as assessed by (1)H nuclear magnetic resonance. The fdhABC genes are transcribed from a single promoter located two genes upstream of fdhA, and the decrease in fdhABC RNA levels in the fdhU mutant is mediated at the posttranscriptional level. FDH activity and the ability to utilize formate were restored by genetic complementation with fdhU and by supplementation of the growth media with selenium dioxide. Disruption of SeC synthesis by inactivation of the selA and selB genes also resulted in the absence of FDH activity, which could not be restored by selenium supplementation. Comparative genomic analysis suggests a link between the presence of selA and fdhTU orthologs and the predicted presence of SeC in FdhA. The fdhTU genes encode accessory proteins required for FDH expression and activity in C. jejuni, possibly by contributing to acquisition or utilization of selenium.

ChemInform Abstract: Convenient Synthesis of 3‐Methylcoumarins and Coumarin‐3‐carbaldehydes.

AbstractThe sequence can be successfully carried out for substrates such as (I).

Synthetic transformations of higher terpenoids. XXVII.* Synthesis of 7-hydroxylabdanoids and their transformations

Allylic oxidation of phlomisoic acid and its methyl ester by selenium dioxide occurred stereoselectively to form 7α-hydroxy derivatives of labdanoids, which were oxidized by active manganese dioxide to 7-ketofuranolabdanoids. Oximation of the last by hydroxylamine hydrochloride in MeOH in the presence of NaOAc gave pure (E)-ketooximes. Beckmann rearrangement of 7-ketooximes of phlomisoic acid and its methyl ester occurred with formation of the corresponding octahydro-1 H-benzoazepines.

ChemInform Abstract: Reaction of Selenium Dioxide with Aromatic Ketones in the Presence of Boron Trifluoride Etherate: A Protocol for the Synthesis of Triarylethanones.

ChemInform Abstract: Reaction of Selenium Dioxide with Aromatic Ketones in the Presence of Boron Trifluoride Etherate: A Protocol for the Synthesis of Triarylethanones.

Pr5F[SiO4]2[SeO3]3: Another Complex Fluoride Oxosilicate Oxoselenate(IV)

AbstractDuring attempts to synthesize lanthanoid(III) fluoride oxoselenates(IV) with the simple composition MF[SeO3], not only Pr3F[SeO3]4, but also Pr5F[SiO4]2[SeO3]3 appeared as pale green crystalline by‐products in the case of praseodymium. Pr5F[SiO4]2[SeO3]3 crystallizes triclinically in space group P$\bar{1}$ (no. 2) with a = 701.14(5), b = 982.68(7), c = 1286.79(9) pm, α = 70.552(3), β = 76.904(3), γ = 69.417(3)° and Z = 2. The five crystallographically different Pr3+ cations on the general positions 2i show coordination numbers of eight and nine. [(Pr1)O8]13– and [(Pr2)O8]13– polyhedra are connected to$\bar{1}${[(Pr1, 2)2O12]18–} chains along the [100] direction. [(Pr3)O7F]12–, [(Pr4)O8F]14– and [(Pr4)O8F]14– polyhedra generate [F(Pr3, 4, 5)3O19]30– units about their central F– anion in triangular Pr3+ coordination. These units form $\bar{1}${[F(Pr3, 4, 5)3O16]24–} strands, again running parallel to [100]. Their alternating connection with the $\bar{1}${[(Pr1, 2)2O12]18–} chains results in $\bar{1}${[Pr5O20F]26–} sheets parallel to the (001) plane. Like in the already known related compound Er3F[SiO4][SeO3]2, a three‐dimensional network $\bar{1}${[Pr5O17F]20–} is achieved without the contribution of both the tetravalent silicon and selenium components. However, two Si4+ and three Se4+ cations forming tetrahedral [SiO4]4– and ψ1‐tetrahedral [SeO3]2– units with all O2– anions guarantee the charge balance. The formation of Pr5F[SiO4]2[SeO3]3 was observed when praseodymium sesquioxide (Pr2O3: in‐situ produced from Pr and Pr6O11 in a molar ratio of 3/11:4/11),praseodymium trifluoride (PrF3) and selenium dioxide (SeO2) in 1:1:3 molar ratios were reacted with CsBr as fluxing agent for five days at 750 °C in evacuated fused silica (SiO2) ampoules.

A quantum chemical study of photochemical processes in the reaction Se + O2 → SeO2 with allowance for the spin orbit interaction

DFT, SA-MCSCF, and MRMP/MCQDPT2 methods in the 6-311++G(2d) basis set are employed to consider the features of the formation reaction of key intermediates (SeOO, Se(O2)) and photochemical dissociation of selenium dioxide with the formation of singlet oxygen. The cross-sections of potential energy surfaces of SeO2, Se(O2), and SeOO are constructed and the terms of their ground and excited states are analyzed at the SeOO dissociation limit with regard to spin-orbital interaction. Possible formation channels of 1O2 (1Δ g , 1Σ g + ) reactive oxygen species during the decay of the excited states of selenium oxocomplexes are revealed. The effect of the spin-orbit interaction on the character of electronic spectrum transitions and zero field splitting in oxygen is estimated.

ChemInform Abstract: Regio‐ and Stereoselective Selenium Dioxide Allylic Oxidation of (E)‐Dialkyl Alkylidenesuccinates to (Z)‐Allylic Alcohols: Synthesis of Natural and Unnatural Butenolides.

AbstractThe butenolides are formed via an exceptional (E)‐ to (Z)‐carbon—carbon double bond isomerization of the starting succinates.

Microwave-assisted synthesis of CdSe quantum dots: can the electromagnetic field influence the formation and quality of the resulting nanocrystals?

Microwave-assisted syntheses of colloidal nanocrystals (NCs), in particular CdSe quantum dots (QDs), have gained considerable attention due to unique opportunities provided by microwave dielectric heating. The extensive use of microwave heating and the frequently suggested specific microwave effects, however, pose questions about the role of the electromagnetic field in both the formation and quality of the produced QDs. In this work a one-pot protocol for the tunable synthesis of monodisperse colloidal CdSe NCs using microwave dielectric heating under carefully controlled conditions is introduced. CdSe QDs are fabricated using selenium dioxide as a selenium precursor, 1-octadecene as a solvent and reducing agent, cadmium alkyl carboxylates or alkyl phosphonates as cadmium sources, 1,2-hexadecanediol to stabilize the cadmium complex and oleic acid to stabilize the resulting CdSe QDs. Utilizing the possibilities of microwave heating technology in combination with accurate online temperature control the influence of different reaction parameters such as reaction temperature, ramp and hold times, and the timing and duration of oleic acid addition have been carefully investigated. Optimum results were obtained by performing the reaction at 240 °C applying a 5 min ramp time, 2 min hold time before oleic acid addition, 90 s for oleic acid addition, and a 5 min hold time after oleic acid addition (8.5 min overall holding at 240 °C). By using different cadmium complexes in the microwave protocol CdSe QDs with a narrow size distribution can be obtained in different sizes ranging from 0.5-4 nm by simply changing the cadmium source. The QDs were characterized by TEM, HRTEM, UV-Vis, and photoluminescence methods and the size distribution was monitored by SAXS. Control experiments involving conventional conductive heating under otherwise identical conditions ensuring the same heating and cooling profiles, stirring rates, and reactor geometries demonstrate that the electromagnetic field has no influence on the generated CdSe QDs. The resulting CdSe NCs prepared using either conductive or microwave dielectric heating exhibited the same primary crystallite size, shape, quantum yield and size distribution regardless of the heating mode.

Influence of arbuscular mycorrhizal fungi on growth and selenium uptake by garlic plants

The aim of this study is to investigate the effects of arbuscular mycorrhizal fungi (AMF) on garlic plants growth and the uptake of selenium (Se). Garlic plants were grown in the pots inoculated with Glomus fasciculatum and G. mosseae and maintained in a greenhouse. Three weeks after planting, the pots had received different concentrations of Se (5, 10, 15, 20, 25 mg kg−1 of soil) in the form of selenium dioxide (SeO2) at 3 weeks intervals up to 12 weeks. For physiological and biochemical analysis, the samples were randomly collected from five plants of each experiment. Maximum AM infection, spore population and plant biomass were observed in the roots of mycorrhizal-mediated plants without Se, and they were gradually declined in both mycorrhizal and non-mycorrhizal (NM) plants with increasing concentrations of Se. Among the two Glomus species tested, G. fasciculatum-mediated plants showed higher AM infection, spore population and plant biomass than G. mosseae. No differences were observed for the uptake of Se in mycorrhizal plants and NM plants. However, NM plants uptake more Se than mycorrhizal plants. Higher contents of total chlorophyll and sugars were observed in plants inoculated with G. fasciculatum without Se and they were decreased in the presence of Se. In contrast, increased amount of glutathione peroxidase was observed at increasing concentrations of Se up to 20 mg kg−1. High-performance liquid chromatography data revealed that SeO2 converted to organic form of Se as γ-glutamyl-Se-methylselenocysteine. These results are basis for further investigations on the role of AMF on plant growth and uptake of Se in crop plants.

ChemInform Abstract: Synthesis of Hetarenoindanone Based on Selenium Dioxide‐Promoted Direct Intramolecular Cyclization.

AbstractFormation of hetarenoindanone (II) from 2‐methyl thiochromone derivative (I) follows a cascade reaction sequence involving an intramolecular Friedel—Crafts reaction and subsequent oxidation by selenous acid which is generated from selenium dioxide and water through Riley allylic oxidation.

Reaction of Selenium Dioxide with Aromatic Ketones in the Presence of Boron Triflouride Etherate: A Protocol for the Synthesis of Triarylethanones

An efficient regioselective protocol for the C-C bond formation by the unexpected α,α-diarylation of aromatic ketones with unactivated arenes in the presence of selenium dioxide and boron trifluoride etherate has been developed. The generality and functional tolerance of this protocol is demonstrated by the synthesis of a series of triarylethanones.

The effect of potential on electrodeposited CdSe thin films

Cadmium selenide (CdSe) thin films have been successfully prepared by the electrodeposition technique on indium doped tin oxide (ITO) substrates with aqueous solutions of cadmium sulphate and selenium dioxide. The deposited films were characterized with X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis by X-rays (EDAX), photoluminescence (PL), UV spectrometry and electrical resistivity measurements. XRD analysis shows that the films are polycrystalline in nature with hexagonal crystalline structure. The various parameters such as crystallite size, micro strain, dislocation density and texture coefficients were evaluated. SEM study shows that the total substrate surface is well covered with uniformly distributed spherical shaped grains. Photoluminescence spectra of films were recorded to understand the emission properties of the films. The presence of direct transition with band gap energy 1.75eV is established from optical studies. The electrical resistivity of the thin films is found to be 106Ωcm and the results are discussed.

One‐Pot Synthesis of Unsymmetrical Benzils by Oxidative Coupling Using Selenium Dioxide and p‐Toluenesulfonic Acid Monohydrate

AbstractThe oxidative coupling of the α‐carbon atom of aromatic ketones with unactivated arenes in the presence of selenium dioxide and p‐toluenesulfonic acid monohydrate is described. A number of unsymmetrical benzils have been prepared in good yields (38–75 %) with high regioselectivity. The generality and functional tolerance of this new protocol is demonstrated. The mechanistic pathway for the oxidative coupling reaction is also described. The reaction displays superiority in terms of minimization of steps with the C–C bond formation promoted by SeO2 and pTsOH·H2O. This method is advantageous as the reactants used as the solvent can be recovered.

Oxidation of 6-methyl-2,4-dioxypyrimidine with selenious acid

The yield orotic aldehyde at the oxidation of 6-methyl-2,4-dihydroxypyrimidine was found to increase when selenious acid is used as an oxidizer. A comparative analysis of 6-methyl-2,4-dioxypyrimidine oxidation with selenium dioxide and selenious acid was performed using the ab initio quantum chemical method in the 6-31G** basis.

A concise total synthesis of bruceolline E

An efficient synthesis of bruceolline E was completed in three steps from the known ethyl indole-1-carboxylate ( 9d) in 60% overall yield, via a tandem acylation/Nazarov cyclization with 3,3-dimethyl acrylic acid followed by selenium dioxide oxidation to install the α-diketone functionality.

13,13-Dimethyl-des-C,D analogues of (20S)-1α,25-dihydroxy-2-methylene-19-norvitamin D3 (2MD): Total synthesis, docking to the VDR, and biological evaluation

As a continuation of our studies focused on the vitamin D compounds lacking the C,D-hydrindane system, 13,13-dimethyl-des-C,D analogues of (20S)-1α,25-dihydroxy-2-methylene-19-norvitamin D3 (2, 2MD) were prepared by total synthesis. The known cyclohexanone 30, a precursor of the desired A-ring phosphine oxide 11, was synthesized starting with the keto acetal 13, whereas the aldehyde 12, constituting an acyclic ‘upper’ building block, was obtained from the isomeric esters 34, prepared previously in our laboratory.The commercial 1,4-cyclohexanedione monoethylene ketal (13) was enantioselectively α-hydroxylated utilizing the α-aminoxylation process catalyzed by l-proline, and the introduced hydroxy group was protected as a TBS, TPDPS, and SEM ether. Then the keto group in the obtained compounds 15–17 was methylenated and the allylic hydroxylation was performed with selenium dioxide and pyridine N-oxide. After separation of the isomers, the newly introduced hydroxy group was protected and the ketal group hydrolyzed to yield the corresponding protected (3R,5R)-3,5-dihydroxycyclohexanones 30–32. The esters 34, starting compounds for the C,D-fragment 12, were first α-methylated, then reduced and the resulted primary alcohols 36 were deoxygenated using the Barton-McCombie protocol. Primary hydroxy group in the obtained diether 38 was deprotected and oxidized to furnish the aldehyde 12. The Wittig–Horner coupling of the latter with the anion of the phosphine oxide 11, followed by hydroxyl deprotection furnished two isomeric 13,13-dimethyl-des-C,D analogues of 2MD (compounds 10 and 42) differing in configuration of their 7,8-double bond. Pure vitamin D analogues were isolated by HPLC and their biological activity was examined. The in vitro tests indicated that, compared to the analogue 7, unsubstituted at C-13, the synthesized vitamin D analogue 10 showed markedly improved VDR binding ability, significantly enhanced HL-60 differentiation activity as well as increased transcriptional potency. Docking simulations provided a rational explanation for the observed binding affinity of these ligands to the VDR. Biological in vivo tests proved that des-C,D compound 10 retained some intestinal activity. Its geometrical isomer 42 was devoid of any biological activity.

ChemInform Abstract: Reaction of 2‐(Aminomethyl)pyridine with Selenium Dioxide: Synthesis and Structure of Selenium‐Bridged Imidazo[1,5‐a]pyridine Derivatives.

AbstractThe reaction behavior of aminopyridine (I) with selenium dioxide is investigated.

Convenient Synthesis of 3-Methylcoumarins and Coumarin-3-carbaldehydes

Rapid, microwave-assisted Baylis–Hillman reactions of substituted salicylaldehydes, followed by one-pot hydrogen iodide–mediated cyclization and reduction of the corresponding adducts, has afforded 3-methylcoumarins in up to 94% yield in the final step. Subsequent microwave-assisted selenium dioxide oxidation of selected 3-methylcoumarins has provided convenient access to the corresponding coumarin-3-carbaldehydes and permitted a significant improvement over the yield obtained using conventional heating.

Synthesis of (Z)- and (E)-3-(2-chloropyridin-5-ylmethyl) oximino-(22E,24R)-ergosta-4,7,22-trienes and their oxidative transformations

(Z)- and (E)-3-(2-chloropyridin-5-ylmethyl)oximino-(22E,24R)-ergosta-4,7,22-trienes (5–6) were synthesized by chemical transformation of ergosterol. Several oxidative transformations of them were studied. It was found that oxidation of these compounds by chromium(VI) oxide formed the corresponding O-substituted 3-ketoximes of the mycosteroid (22E,24R)-ergosta-4,7,22-trien-3,6-dione (7) and (8), which contained α-chloropyridine fragments characteristic of biologically active neonicotinoids. It was shown that oxidation of 5 and 6 by selenium dioxide occurred with formation of the corresponding 9α-hydroxy derivatives 9 and 10.

Rotation of the Allylselenic Intermediate in Moderating the Stereochemical Course of the Selenium Dioxide-Mediated Allylic Oxidation

Allylic oxidation adjacent to C = C bonds to produce allylic alcohols remains a reaction of considerable interest in organic chemistry and various methods for this purpose have been developed. Among those the selenium dioxide-mediated oxidation is regarded as the most reliable and predictable method to introduce a hydroxy group into the allylic position for substituted alkenes regioand stereo-selectively. The key mechanistic basis to induce a high regioand stereo-selectivity in the allylic oxidation is the concerted and pericyclic process through two consecutive steps (an electrophilic ‘ene’ reaction followed by the [2,3]-sigmatropic rearrangement) (Scheme 1) as in a theoretical mechanism proposed by Sharpless and a recent account concerning theoretical and experimental data. We reported the overall stereochemical pathways by elucidating both an ‘ene’ reaction and the [2,3]-sigmatropic rearrangement of the selenium dioxide-mediated oxidation of 2methyl-2-butene. Those efforts seem successful to explain regioand stereo-selective aspects experimentally observed in the selenium dioxide-mediated allylic oxidation of several trisubstituted olefin compounds, particularly those where the concerted nature can be maintained during the whole process. However, modes of selectivity in the allylic oxidation of substituted olefin compounds are found to depend strongly on the geometric features of the alkene substrates. In the case of the allylic oxidation of more general cyclic systems such as 1-tert-butyl-4-alkylidene cyclohexanes, where the system can avoid the concerted mode throughout two steps, an unexpected isomeric compound, cis-5-tert-butyl-2-ethylidenecyclohexanol was obtained. There should be involved a rotation of the allylselenic intermediate between two pericyclic steps. The purpose of this note is to provide a clearer explanation for the mechanism of the selenium dioxide-mediated oxidation in the substituted alkenes how the rotation of the allylselenic intermediate affects the stereochemical mechanism. The Rotation of the Allylselenic Intermediate in the Allylic Oxidation of 1-tert-Butyl-4-alkylidene Cyclohexanes. In the allylic oxidation of 1-tert-butyl-4-alkylidene cyclohexanes, we observed a different stereo-selectivity mode compared to 2-methyl-2-butene. Two important approaches of selenium dioxide toward the olefin function in the pericyclic ‘ene’ step of the allylic oxidation of 1-tert-butyl-4-ethylidene cyclohexane (1) are trans-anti approach (A) and trans-syn (B) approach (Figure 1). Thus, theoretical calculations show significant products obtained from the allylic oxidation of 1-tertbutyl-4-ethylidene cyclohexane should be ones via two approaches (A and B). The relative transition state energy of as shown in Figure 1, the trans-anti approach (A) is predicted moderately preferred than trans-syn approach (B), The TS energy of A has been calculated to be more stable than B by 0.633 and 0.577 kcal/mol in HF/3-21G and B3LYP/6-31G*, respectively. According to the theoretical study of the reaction using HF/3-21G method, the trans-isomer 2a is predicted as a major product (73%). The trans-isomer can be provided from the initial trans-anti approach (A) in the ‘ene’ step and in situ [2,3]-rearrangement. The allylselenic intermediate generated after trans-anti approach proceeds with a concerted mode, i.e., without C3-C4 bond rotation into a [2,3]-sigmatropic rearrangement. In this case, the position where the ‘anti’ hydrogen (Hanti in Scheme 2) originally located is substituted by the OSeOH group after two concerted steps. The dominant option after trans-syn ‘ene’ approach is to