Reactivity of aminocarbene complexes of chromium containing a coordinated CC double bond towards alkynes: Formation of azabicyclo[4.1.0]heptene systems

Chromium complexes containing the bidentate aminocarbene-alkene ligand react with alkynes to give, after insertion followed by an intramolecular cyclopropanation reaction, azabicyclo[4.1.0]heptene systems, which react rapidly with oxygen, during work up, to lead to the corresponding cyclopropanic amidoketones.     

IR spectroscopic study of the hydrogen bond network in the water–3-amino-1-propanol system and its comparison with the spatial network of hydrogen bonds in the water–monoethanolamine system

IR spectroscopy was used to explore the water–3-amino-1-propanol (3AP) system in the range of 400–4000 cm^-1. Based on the stretching vibrations of OH, NH₂ and CH groups and skeletal bending vibrations of 3AP it was concluded that mixed spatial networks are formed in the water–3AP system that predominate at medium 3AP concentrations. The obtained results are similar to the IR spectroscopic data for the water–monoethanolamine system, viz., the networks of both amino alcohols are incorporated into the spatial     

Stereoselective reduction of endocyclic carbon–nitrogen double bond: application to the synthesis of biomolecules

Recent advances in the stereoselective synthesis of nitrogen containing heterocyclic compounds using the reduction of endocyclic double carbon–nitrogen bond are surveyed.     

The CC double bond of a bidentate carbene-alkene complex of tungsten as an internal NMR probe for the coordination of Lewis acids

The rate of polymerization of alkynes induced by tungsten complexes containing a coordinated CC double bond can be considerably enhanced by Lewis acids such as AIR₃. The interaction of the two catalyst components studied by means of NMR spectroscopy, leads to a weakening of the bond between the metal and the double bond.     

DFT evaluation of the electronic structures and spectroscopic properties of the self-assembled [Pt2M4(C ≡ CH)8] (M=Cu,Ag) clusters

Science China Chemistry - Electronic structures and spectroscopic properties of self-assembled [Pt2M4(C≡CH)8] (M=Cu, Ag) clusters have been studied by the TD-DFT (time-dependent density...     

Vibrational dynamics and hydrogen bond properties of β-CD nanosponges: an FTIR-ATR, Raman and solid-state NMR spectroscopic study

Cyclodextrin nanosponges (CDNS) are cross-linked polymers with remarkable inclusion/release properties. CDNS show swelling capability and a hydrophilicity/hydrophobicity balance that can be dramatically modified by the type and quantity of cross-linking agents. Here, we focus our attention on samples of β-cyclodextrin nanosponges (β-CDNS) obtained by reacting β-cyclodextrin (β-CD) with the cross-linking agent carbonyldiimidazole at different β-CD:cross-linking agent molar ratio. The vibrational properties of CDNS thus synthesized have been investigated by Fourier transform infrared spectroscopy in attenuated total reflectance geometry and Raman spectroscopy in the dry state at room temperature. The quantitative analysis of the O–H stretching region (3,000–3,800 cm^?1) allowed us to obtain structural information on the role played by primary and secondary OH groups in the hydrogen bond network of the polymer. Also, the contribution of interstitial and intracavity crystallization water molecules is reported. Solid-state NMR spectroscopy is used to study the molecular mobility of the polymer by measuring the ¹H spin–lattice relaxation time in the rotating frame (T_1ρ). The T_1ρ values obtained for the polymer β-CDNS are compared with free β-CD. The observed relaxation parameters point out that the ester formation occurs mainly at the primary OH groups of CDs, also supporting the interpretation of vibrational spectra.     

Comment to the article “How to measure and report the capacity of electrochemical double layers,supercapacitors, and their electrode materials” [1]

Journal of Solid State Electrochemistry -     

1,1-Diamino-2-nitroethylenes as excellent hydrogen bond donor organocatalysts in the Michael addition of carbon-based nucleophiles to β-nitrostyrenes

A new class of hydrogen bond donor catalysts based on the 1,1-diamino-2-nitroethylene scaffold has been introduced for the activation of trans-β-nitrostyrenes toward reactions with a range of carbon-based nucleophiles, affording the corresponding adducts in excellent yields. Importantly, this new set of organocatalysts is easily prepared from commercially available starting materials in mild reaction conditions.     

Contribution to cation–π interaction of the univalent silver cation with racemic [7]helicene in the solid state

Structural Chemistry - Yellow crystals of the complex [7]helicene–silver perchlorate (i.e., C30H18–AgClO4 or more accurately [Ag(η4-C30H18)]ClO4, respectively), crystallizing in...     

An octanuclear complex containing the [Fe3O]7+ metal core: structural, magnetic, Mössbauer, and electron paramagnetic resonance studies

A new asymmetrically coordinated bis-trinuclear iron(III) cluster containing a [Fe(3)O](7+) core has been synthesized and structurally, magnetically, and spectroscopically characterized. [Fe(6)Na(2)O(2)(O(2)CPh)(10)(pic)(4)(EtOH)(4)(H(2)O)(2)](ClO(4))(2).2EpsilontOH (1.2EpsilontOH) crystallizes in the P space group and consists of two symmetry-related {Fe(3)O](7+) subunits linked by two Na(+) cations. Inside each [Fe(3)O](7+) subunit, the iron(III) ions are antiferromagnetically coupled, and their magnetic exchange is best described by an isosceles triangle model with two equal (J) and one different (J ') coupling constants. On the basis of the H = -2SigmaJ(ij)S(i)S(j) spin Hamiltonian formalism, the two best fits to the data yield solutions J = -27.4 cm(-1), J ' = -20.9 cm(-1) and J = -22.7 cm(-1), J ' = -31.6 cm(-1). The ground state of the cluster is S = (1)/(2). X-band electron paramagnetic resonance (EPR) spectroscopy at liquid-helium temperature reveals a signal comprising a sharp peak at g approximately 2 and a broad tail at higher magnetic fields consistent with the S = (1)/(2) character of the ground state. Variable-temperature zero-field and magnetically perturbed M?ssbauer spectra at liquid-helium temperatures are consistent with three antiferromagnetically coupled high-spin ferric ions in agreement with the magnetic susceptibility and EPR results. The EPR and M?ssbauer spectra are interpreted by assuming the presence of an antisymmetric exchange interaction with |d| approximately 2-4 cm(-1) and a distribution of exchange constants J(ij).     

Chemistry of Tetradentate [C,N : C,N] Iminophosphorane Palladacycles: Preparation,Reactivity and Theoretical Calculations

A theoretical and experimental study of tetradentate [C,N : C,N] iminophosphorane palladacycles was carried out for the purpose of elucidating their behavior as compared to the parent Schiff base analogues to determine the prospect of encountering new A-frame structures for the iminophosphorane derivatives. The DFT calculations were in agreement with the experimental results regarding the performance of these ligands. New insights into the chemistry of the related dinuclear species have been obtained.     

Synthesis,spectroscopic characterization,and in vitro antimicrobial activity of fused pyrazolo[4′,3′:4,5]thieno[3,2-d]pyrimidine

4-Amino-3-methyl-1-phenyl-1H-thieno[2,3-c]pyrazole-5-carboxamide ( 1 ), which had been previously synthesized according to literature, was used for synthesizing pyrazolothieno-pyrimidine ( 2 ) in the presence of triethyl orthoformate and acetic acid. Chlorination of the latter compound upon reflux with phosphorus oxychloride afforded the chloropyrazolothienopyrimidine ( 3 ), which underwent heterocyclization reaction with sodium azide to produce the tetrazolo-pyrazolothienopyrimidine ( 6 ). The chloropyrimidine ( 3 ) reacted with hydrazine hydrate to give the hydrazinopyrimidine derivative ( 4 ), which in turn underwent intramolecular condensation reactions with various 1,3-dicarbonyl compounds, namely ethyl acetoacetate, ethyl benzoylacetate, ethyl cyanoacetate, acetylacetone, diethyl malonate, and ethyl (ethoxymethylene) cyanoacetate, yielding new pyrazolyl pyrazolothienopyrimidine ring systems. Also triazolopyrazolothieno-pyrimidines and benzylidene Schiff's base compounds were obtained as a result of the reactions with carbon disulfide in pyridine and benzaldehyde, respectively. The chemical structures of the newly synthesized compounds were elucidated using elemental and spectroscopic analyses (FT-IR, ¹ H-NMR, ¹³ C-NMR, and mass spectroscopy). Some of the synthesized compounds possess high antibacterial and antifungal activities.     

Gas-phase CαCβ double bond cleavage in the dissociation of protonated 2-benzylidenecyclopentanones: Dissociative proton transfer and intramolecular proton-transport catalysis

Among gas-phase dissociation reactions, double bond cleavage reaction appears to happen extremely rare, especially in the case of CC double bond. In the dissociation reaction of protonated 2-benzylidenecyclopentanones in tandem mass spectrometry, the formation of benzyl cations was observed, resulting from the cleavage of C^α=C^β double bonds, which is different from the general cleavage route seen in most α, β-unsaturated ketone cases. A combined experimental and theoretical investigation on intramolecular hydrogen transfers was carried out to illustrate the mechanisms. The external proton is initially localized on the carbonyl oxygen (the thermodynamically-preferred protonation site). Upon collisional activation, the mobile proton stepwise migrates to the C^α position to achieve the reduction and subsequent cleavage of the C^α=C^β double bond. The stepwise proton transfer is achieved via intramolecular proton-transport catalysis with the assistance of the phenyl ring. The ortho position of the phenyl accepts the proton from the carbonyl oxygen via a 1,6-H shift, and then donates it to the C^α stepwise. The conventional 1,3-H shift from the carbonyl oxygen to the C^α position can be excluded in this case due to its significant energy barrier. Further isotope-labeling experiments are applied to confirming the reaction mechanism. Last but not least, the scope-expansion experiments indicates that the aromatic and cycloalkanonyl moieties play a crucial roles in the cleavage reaction of C^α=C^β double bond.     

Coordination of adenosylmethionine to a unique iron site of the [4Fe-4S] of pyruvate formate-lyase activating enzyme: a Mössbauer spectroscopic study

Pyruvate formate-lyase activating enzyme (PFL-AE) generates the catalytically essential glycyl radical of PFL. It is a member of the so-called "radical-SAM superfamily" of enzymes that use a [4Fe-4S] cluster and S-adenosylmethionine (AdoMet or SAM) to catalyze diverse radical-mediated reactions. Evidence suggests that this class of enzymes operate by common initial steps involving the generation of an AdoMet-derived adenosyl radical intermediate, of which the mechanism remains unresolved. The three-cysteine CX3CX2C cluster-binding motif common to all members of this superfamily suggests a unique Fe site in the [4Fe-4S] cluster, which presumably interacts with AdoMet to effect the reductive cleavage and radical generation. Here we employ a dual-iron-isotope (56Fe/57Fe) approach to demonstrate the existence of a unique Fe site in the [4Fe-4S] cluster of PFL-AE by M?ssbauer spectroscopy. Coordination of AdoMet to this unique Fe site was made evident by the observation of a substantial increase in the isomer shift (delta) of the M?ssbauer spectrum associated with the unique Fe site: delta = 0.42 mm/s in the absence of AdoMet increases to delta = 0.72 mm/s in the presence of AdoMet. Further, the M?ssbauer data show that the binding of AdoMet to the unique Fe site occurs in the [4Fe-4S]2+ state, prior to the injection of the reducing equivalent required for catalysis. This observation indicates that AdoMet coordination is a necessary prerequisite to adenosyl radical generation.     

Synthetic,structural, spectroscopic and solution speciation studies of the binary Al(III)–quinic acid system. Relevance of soluble Al(III)–hydroxycarboxylate species to molecular toxicity

Efforts to delineate the interactions of Al(III), a known metallotoxin, with low molecular mass physiological substrates involved in cellular processes led to the investigation of the structural speciation of the binary Al(III)–quinic acid system. Reaction of Al(NO₃)₃ · 9H₂O with d-(−)-quinic acid at a specific pH (4.0) afforded a colorless crystalline material K[Al(C₇H₁₁O₆)₃] · (OH) · 4H₂O (1). Complex 1 was characterized by elemental analysis, FT-IR, DSC–TGA, ¹³C-MAS NMR, solution ¹H and ¹³C NMR, and X-ray crystallography. The structure of 1 reveals a mononuclear octahedral complex of Al(III) with three singly ionized quinate ligands bound to it. The three ligand alcoholic side chains do not participate in metal binding and dangle away from the complex. The concurrent study of the aqueous speciation of the binary Al(III)–quinic acid system projects a number of species complementing the synthetic studies on the binary system Al(III)–quinic acid. The structural and spectroscopic data of 1 in the solid state and in solution emphasize its physicochemical properties emanating from the projections of the aqueous structural speciation scheme of the Al(III)–quinic acid system. The employed pH-specific synthetic work (a) exemplifies essential structural and chemical attributes of soluble aqueous species, arising from biologically relevant interactions of Al(III) with natural α-hydroxycarboxylate substrates, and (b) provides a potential linkage to the chemical reactivity of Al(III) toward O-containing molecular targets influencing physiological processes and/or toxicity events.     

Correction to: 1H-imidazol-3-ium tricyanomethanide {[HIM]C(CN)3} as a nanostructured molten salt catalyst: application to the synthesis of pyrano[4,3‐b]pyrans

Research on Chemical Intermediates - Since it has been cleared that a fake compound has been sold to us as cyanoform.     

DFT evaluation of the electronic structures and spectroscopic properties of the self-assembled [Pt2M4(C ≡ CH)8] (M=Cu, Ag) clusters

Electronic structures and spectroscopic properties of self-assembled [Pt₂M₄(C≡CH)₈] (M=Cu, Ag) clusters have been studied by the TD-DFT (time-dependent density functional theory) calculations with the polarizable continuum model (PCM). The ground- and excited-state structures were optimized by the DFT (density functional theory) methods. The calculated structures and spectroscopic properties are in agreement with the corresponding experimental results. The [Pt₂Ag₄(C≡CH)₈] clusters have two stable ground state geometries (D ₄ and D _4h symmetry). The calculated Pt-M distances suggest only very weak interactions. The Cu-Cu distances are larger than the van der Waals radii of two Cu atoms and the Ag-Ag distances are analogous with the sum of van der Waals radii of two Ag atoms. Upon excitation, the interaction of Pt⋯M, Ag⋯Ag is strengthened, while the Cu⋯Cu distances are shortened but they are still larger than the sum of van der Waals radii of two Cu atoms. The lowest-energy absorptions are at 450, 365 and 375 nm and the emissions are at 611, 431 and 435 nm for [Pt₂Cu₄(C≡CH)₈], [Pt₂Ag₄(C≡CH)₈] (A) and (B), respectively. The transitions are all perturbed by the Cu or Ag composition through the UV-Vis spectra region; therefore, there are not pure ILCT or M_PtLCT characteristics (ILCT: intraligand charge transfer; MLCT: metal-to-ligand charge transfer) in absorptions of heteropolynuclear [Pt₂M₄(C≡CH)₈] clusters. Since the emissions and the lowest-absorptions have different transition characteristics for each complex, the emissions should not come from the lowest-energy absorptions. Because the M⋯M interactions in the excited state of [Pt₂Ag₄(C≡CH)₈] are augmented, the emissions of [Pt₂Ag₄(C≡CH)₈] clusters bear prominent ILCT character, which is the reason why the emission wavelengths of [Pt₂Ag₄(C≡CH)₈] have a small hypsochromic shift relative to the emission wavelength of homoleptic [Pt(C≡CH)₄]²⁻ precursor.