Three new diarylheptanoids and their antioxidant property

Three new diarylheptanoids,i.e.,sodium(5S,2E)-1,7-bis(4-hydroxyphenyl)-1-hydroxy-2-hepten-5-sulfonate(1), sodium(5R,2E)-1,7-bis(4-hydroxyphenyl)-1-hydroxy-2-hepten-5-sulfonate (2) and 3,5-diacetoxy-1-(3-methoxy-4,5-dihydroxy- phenyl)-7-(4-hydroxy-3-methoxyphenyl)heptane (3) were isolated from the rhizomes of Zingiber officinale.The structures of the new compounds were elucidated on the basis of spectroscopic methods.The antioxidant activities of 3 were assayed by in vitro models involving DPPH free radicals and superoxide anion radicals.     

Synthesis of α-N-Ethylamino Acids and their Derivatives

 A new synthesis of α-N-ethylamino acids starting from α-amino acids using hexafluoroacetone as protecting and activating agent is described. The hexafluoroacetone-protected N-ethylamino acid derivatives obtained are activated lactons. Therefore, they can be directly transformed without the need of an additional activation step with various nucleophiles into the corresponding carboxylic acid derivatives.     

Carbohydrate–protein interactions and their biosensing applications

Carbohydrate recognition is clearly present throughout nature, playing a major role in the initial attachment of one biological entity to another. The important question is whether these prevalent interactions could provide a real suitable alternative to the use of antibodies or nucleic acid for detection and identification. Currently, examples of carbohydrates being employed in biological detection systems are limited. The challenges of using carbohydrate recognition for detection mainly come from the weak affinity of carbohydrate–protein interactions, the lack of versatile carbohydrate scaffolds with well-defined structures, and the less developed high-information-content, real-time, and label-free assay technology. In this review, we focus on discussing the characteristics of carbohydrate–protein interactions in nature and the methods for carbohydrate immobilization based on surface coupling chemistry in terms of their general applicability for developing carbohydrate- and lectin-based label-free sensors. Furthermore, examples of innovative design of multivalent carbohydrate–protein interactions for sensor applications are given. We limit our review to show the feasibility of carbohydrate and lectin as recognition elements for label-free sensor development in several representative cases to formulate a flexible platform for their use as recognition elements for real-world biosensor applications.     

Metal–organic frameworks and their catalytic applications

Metal-organic frameworks (MOFs), as a novel categories of porous and well crystalline materials, were gained significant interest in the current years. These materials offer practical implementations in different sectors, like hydrogen and carbon dioxide storage, catalysis and separation due to their superior porosity, great surface area and versatile framework. The current review outlines the existing state of the art in using MOFs as catalysts in various organic transformation processes and photocatalysis depending on the site form, with particular confirmation on the most recent techniques for increasing the active centers and modifying their performance, by deposition of metallic nanoparticles on its surface or within the pores. In addition, the substantial progress made in the production of various composites containing MOF with particular focus on preparation and catalytic applications was provided.     

Novel Heptamethine 3H-Indocyanines and their Spectral Properties

Novel heptamethine 3H-indocyanine dyes are synthesized and embedded into a matrix of silica gel derived from tetraethoxysilicane. The photophysical properties of these near infrared dyes in various solvents and in SiO2 sol gel were investigated. The results show that the dyes containing cyclohexenylene bridge and N-(p-carboxy)benzyl groups have better photostability and longer absorption wavelength than those containing linear heptamethine bridge and/or N-(5-carboxy)pentanyl groups. The absorption maxima of these dyes are in reverse proportion to the polarity of the solvents. The microenvironment of the dyes in SiO2 sol-gel characters medium polarity (between methanol and DMF) according to the absorption maxima.     

Polyketoetheresters from 4,4′-Dichloroacetyldiphenyl Ether and their Characterization

Benzyl chloride and phenacyl chloride are reported to condense with sodium acetate or sodium benzoate, affording the corresponding esters [1–4]. This suggested that a dichloride monomer can poly condense with a sodium dioate, affording a polyester. Akhmedzade and Yasnopolskii reported one such polyester synthesis based on polycondensation of p-xylylene dihalide with sodium terephthalate [5]. As phenacyl chloride is more reactive than benzyl chloride is more reactive than benzyl chloride [4], 4,4′-dichloroacetyldiphenyl ether (DADE) should prove even more reactive than a dichloride of the Ar(CH₂Cl)₂ type. The work presented here comprises a study of the polycondensation of DADE with sodium adipate (ADP), sebacate (SEB), or terephthalate (TER).     

Asymmetric synthesis of pochonin E and F, revision of their proposed structure, and their conversion to potent Hsp90 inhibitors

A concise and modular synthesis of pochonin?E and F, and their epimers at C-6 established the correct stereochemistry of these two natural products. Several members of the pochonin family have been shown to bind the heat shock protein?90 (Hsp90), which has been the focus of intense drug discovery efforts. Pochonin?E and F as well as their epimers were derivatized into the corresponding pochoximes and further modified at the C-6 position. Molecular dynamics simulations, docking studies, and Hsp90 affinity measurements were performed to evaluate the impact of these modifications.     

Photocatalytic Hydrogen Evolution of Keggin-type Polyoxotungstates and their Electrochemical Behaviors

Photocatalytic hydrogen production from water is considered as an approach for conversion of the solar energy into the chemical energy. During the past decades much efforts have been made to exploit the semiconductor photocatalysts working under both UV a…     

Tellurophenes with delocalized π-systems and their extended valence adducts

The π-conjugated 2,5-substituted tellurophene compounds 2,5-bis(2-(9,9-dihexylfluorene))tellurophene (1) and 2,5-diphenyltellurophene (3) were synthesized through ring closing reactions of 1,4-substituted butadiyne. The oxidative addition of Br(2) to tellurophene compounds 1 and 3 was studied through absorption spectroscopy, NMR, electrochemistry, X-ray crystallography, and density functional theory (DFT) calculations. When Br(2) adds to the tellurium center the absorption spectrum shifts to a lower energy. From electrochemistry and DFT calculations we show that this is caused by lowering the lowest unoccupied orbital. The highest occupied orbital is also lowered, but to a lesser extent. This shift in absorption spectrum and lowering of the oxidation potential can provide a method to modify tellurophene containing materials. The two-electron oxidative addition is promising for catalyzing energy storage reactions.     

(α-Nitroalkyl)-ONN-azoxysulfones and some of their transformations

A regioselective method for the synthesis of [(-nitroalkyl)-ONN-azoxy]alkyl- and-arylsulfones by oxidative condensation of pseudonitroles with aliphatic and aromatic sulfamides under the action of dibromoisocyanurate (DBI) was proposed. The behavior of the azoxysulfones obtained toward acids and bases as well as futher transformations of the products of acid hydrolysis into salts and halo-derivatives of nitroalkylazoxysulfones were investigated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1267–1270, July, 1994.     

Study on multimers and their structures in molecular association mixture

Self-association system of(R)-1,3-butanediol in dilute carbon tetrachloride(CCl4)solution is studied as a model of molecular association mixture.Analysis methods including FSMWEFA(fixed-size moving window evolving factor analysis)combined with PCA(principal component analysis),SIMPLISMA (simple-to-use interactive self-modeling mixture analysis),and ITTFA(iterative target transformation factor analysis)are adopted to resolve infrared spectra of(R)-1,3-butanediol solution.Association number and equilibrium constant are computed.(R)-1,3-butanediol in dilute inert solution is determined as a monomer-trimer equilibrium system.Theoretical investigation of trimer structures is carried out with DFT(density functional theory),and structural factors are analyzed.     

Synthesis of β-pyrrolic-modified porphyrins and their incorporation into DNA

A synthetic methodology for the synthesis of various β-pyrrolic-functionalised porphyrins and their covalent attachment to 2'-deoxyuridine and DNA is described. Palladium(0)-catalysed Sonogashira and copper(I)-catalysed Huisgen 1,3-dipolar cycloaddition reactions were used to insert porphyrins into the structure of 2'-deoxyuridine and DNA. Insertion of a porphyrin into the middle of single-stranded CT oligonucleotides possessing a 5'-terminal run of four cytosines was shown to trigger the formation of pH- and temperature-dependent i-motif structures. Porphyrin insertion also led to the aggregation of single-stranded purine-pyrimidine sequences, which could be dissociated by heating at 90 °C for 5 min. Parallel triplexes and anti-parallel duplexes were formed in the presence of the appropriate complementary strand(s). Depending on the modification, porphyrins were placed in the major and minor grooves of duplexes and were used as bulged intercalating insertions in duplexes and triplexes. In general, the thermal stabilisation of parallel triplexes possessing porphyrin-modified triplex-forming oligonucleotide (TFO) strands was observed, whereas anti-parallel duplexes were destabilised. These results are compared and discussed on the basis of the results of molecular modelling calculations.     

Acid–base behavior of oxides and their electronic structure

We attempted to simplify and unify the former concepts describing the acid base character of oxides on the basis of their band structure. Duffy optical basicity, Smith acid scale and Bratsch electronegativity model can simply be linked by taking into account the electronegativity and the chemical hardness of the oxides: an acidic oxide has a strong electronegativity together with a strong chemical hardness while a basic oxide has a low electronegativity associated with a weak chemical hardness.     

Iron–sulfur clusters and their electronic and magnetic properties

Iron–sulfur clusters of diverse nuclearities constitute the active sites of a large and prominent family of metalloproteins which play essential roles in all living organisms, such as in electron transfer chains, reduction catalysis, photosynthesis, the respiratory chain and nitrogen fixation. This review is devoted to the presentation of the current state of understanding of their electronic and magnetic properties, which is here derived from their Mössbauer, EPR and ENDOR spectroscopic properties. These techniques constitute fine tools for characterization and provide knowledge of the different oxidation states of these proteins, although our interest here will be mainly centered on the [4Fe–4S*]ⁿ⁺ clusters (with n=1–3). A qualitative physical model involving the competing magnetic interactions in these clusters is discussed. Moreover, this article contains new developments on two more specialized subjects:

• 1.some quantitative consequences of an already published theory of the g-tensors of [4Fe–4S*]ⁿ⁺ clusters (n=1,3) will be derived in Section 3;
• 2.a model permitting the rationalization, from very simple ingredients and formulae, of the redox potentials of a whole set of known synthetic redox clusters (with 1, 2, 3, 4 and 6 iron atoms) will be presented in the final Section 6.

     

Room temperature ionic liquids and their mixtures—a review

Room temperature ionic liquids are salts that are liquid at room temperature and their use as catalysts and catalytic support has been studied extensively. They are also being considered as “green solvents” for various separation processes. Recent measurements reported on the properties of pure ionic liquids and their mixtures, including gas and liquid solubility in common organic solvents will be reviewed. While some property values are in good agreement, some show large differences. These values will be compared and reasons for the discrepancies will be conjectured. Since traditional approaches to predicting the properties of fluid liquids require extensive LLE and VLE measurements, alternative predictive methods need to be explored. The predictions of the properties of mixtures of ionic liquids using COSMOtherm, an approach based on unimolecular quantum chemical calculations of the individual molecules, will be presented.     

Chemistry teachers narratives as parts of their lives and professionalism

I present some preliminary results on how the classroom narratives in chemistry are interconnected to the teachers life histories and why chemistry teachers use narratives,The results are based on two rounds of interviews with Swedish chemistry teachers in upper secondary school.Tentative results suggested that these teachers used narratives as a tool for teaching and to promote learning,although in different ways,It is suggested that we understand concepts concepts better if we are introduced to them in narrative discourse,Using narratives also seems to promote a plurality of emphases in teaching.     

Synthesis of Analogs of Phosphoamino Acids and their Biomimic Reactions

Previ0uslyitwasf0undthatphosph0amin0acidscouldstimulatemanyinterestingbioorganicreacti0nsI-3.In0rderfurthert0confirmthesignificanceofph0sphorusinbiochemistry,tw0m0delcomp0unds,anal0gue0fphosphorylaminoacidsc0ntainingP-Cbondandphosphorylglucoaminoacids,weresynthesized.Theirreacti0nswithalcoholandamin0acidwerealsoinvestigatedbyNMRandMSmeth0ds.Theresultsindicatedthatthereactioncharacteristicsofphosphorylbio1ogicalsmallmoleculesweredependentonthe'configuration,functiongroupsandpositions.(O,O-b…