Rational Design of Small 3D Gold Clusters

Abstract  

We designed a series of small 3D gold clusters using a four-atomic tetrahedron with a four center–two electron (4c–2e) bond inside as a building block. The follow-up results of the unbiased global minimum searches proved that indeed the designed 3D structures containing small tetrahedral building blocks with a 4c–2e bond inside are either global minimum structures or low-lying isomers. We believe that the proposed way of building 3D clusters could be used for rational design of other 3D gold clusters.     

Highly efficient and chemoselective method for the thioacetalization of aldehydes and transthioacetalization of acetals and acylals catalyzed by H2SO4-silica under solvent-free conditions

Abstract  

Chemoselective and efficient thioacetalization of a variety of aldehydes was achieved in excellent yields at room temperature using 1,2-ethanedithiol in the presence of catalytic amounts of H₂SO₄-silica. Thioacetals were also prepared by transthioacetalization of acylals and acetals under similar conditions.     

Pattern similarity study of functional sites in protein sequences: lysozymes and cystatins

Background  

Although it is generally agreed that topography is more conserved than sequences, proteins sharing the same fold can have different functions, while there are protein families with low sequence similarity. An alternative method for profile analysis of characteristic conserved positions of the motifs within the 3D structures may be needed for functional annotation of protein sequences. Using the approach of quantitative structure-activity relationships (QSAR), we have proposed a new algorithm for postulating functional mechanisms on the basis of pattern similarity and average of property values of side-chains in segments within sequences. This approach was used to search for functional sites of proteins belonging to the lysozyme and cystatin families.     

PTSA catalyzed simple and green synthesis of benzothiazole derivatives in water

Abstract  

p-Toluenesulfonic acid (10 mol%) was found to be an effective and efficient catalyst for the synthesis of 2-substituted benzothiazoles from aromatic aldehydes and 2-aminothiophenol in moderate to excellent yields in water. This method provides a simple and efficient protocol in terms of mild reaction conditions, clean reaction profiles, small quantity of catalyst, and simple workup procedure.     

Hydrothermal synthesis, crystal structure, and photoluminescence of novel lanthanide metal organic frameworks constructed from 1,4-benzene-dicarboxylic acid and 1,2,4,5-benzenetetracarboxylic acid as ligands

Abstract  

By using 1,4-benzene-dicarboxylic acid and 1,2,4,5-benzenetetracarboxylic acid as mixed-linkers, three novel 3D lanthanide coordination polymers, [Ln(BDC)_0.5(BTEC)_0.5(H₂O)] (Ln = Eu (1) and Gd (2)) and [Tb(BDC)_0.5(BTEC)_0.5(H₂O)] (3) (H₂BDC = 1,4-benzene-dicarboxylic acid, H₄BTEC = 1,2,4,5-benzenetetracarboxylic acid) were synthesized via hydrothermal reaction. The X-ray single crystal analyses reveal that the three coordination polymers present two types of different crystal cell parameters and hereby exhibited two kinds of different metal–organic frameworks, although they have the similar chemical formula [Ln(BDC)_0.5(BTEC)_0.5(H₂O)]. Of these complexes, complexes 1 and 2 are isomorphous, crystallizing in monoclinic, space group P2₁/n. While 3 is a 3D eight-coordinated terbium complex with triclinic crystal system and P-1 space group. The occurrence of the different structures of these complexes under the similar preparation method may be related to the lanthanide contraction effect. Additional, the thermogravimetric analyses and photoluminescent properties for complexes 1 and 3 were discussed in detail.     

One-pot synthesis of 1,2,4,5-tetrasubstituted and 2,4,5-trisubstituted imidazoles by zinc oxide as efficient and reusable catalyst

Abstract  

ZnO is an efficient, readily available, and reusable catalyst for the one-pot synthesis of 1,2,4,5-tetrasubstituted and 2,4,5-trisubstituted imidazoles. This procedure is very simple and affords excellent yields.     

Ab initio and DFT conformational study on nitrosamine (H<Subscript>2</Subscript>N–N=O) and <Emphasis Type="Italic">N</Emphasis>-Nitrosodimethylamine [(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>N–N=O]

Abstract  

Ab initio and DFT calculations have been performed to characterize some ground state structures of the title molecules. Relative energies, rotational barriers, NBO charges, and dipole moments (μ) have been calculated and analyzed. It has been confirmed that only highly correlated methods (e.g., CCSD) are able to yield the non-planar structure as a minimum, for the H₂NNO molecule. On the other hand, all computational levels here employed are able to yield a planar C₂NNO frame for the (CH₃)₂NNO as a minimum. Important correlations between atomic charges and bond distances are discussed. Replacement of H by methyl group increases the rotational barrier and μ values by at least 3 kcal/mol and 0.4 D, respectively. The largest μ values are obtained for the structures in which the nitrogen lone pair is parallel to the NO group π system, and are consistent with a larger contribution of a dipolar resonance structure.     

Supramolecular assembled of hexameric water clusters into a 1D chain containing (H<Subscript>2</Subscript>O)<Subscript>6</Subscript> and [(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>O<Subscript>2</Subscript>] stabilized by hydrogen bonding in a copper complex

Background  

Various water clusters including hexamers, heptamers, octamers, decamers and 1D or 2D infinite water chains in a number of organic and inorganic-organic hybrid hosts, have been reported.     

Synthesis, characterization, and polymerization of vinylmelamines

Abstract  

Vinyl functionalized melamine derivatives for cross-linking based on polymerization were synthesized as potential substitutes for harmful formaldehyde in melamine resins. Methylmelamines undergo direct vinylation with acetylene to the corresponding vinylmelamines in more than 95% conversion. Their chemical structures were fully characterized by mass spectrometry, Fourier transform infrared (FTIR) spectroscopy, elementary analysis, ¹H, ¹³C, and 2D correlation nuclear magnetic resonance (NMR) experiments. Linear and cross-linked polymers were prepared by free radical polymerization neat and in solution and characterized by size exclusion chromatography (SEC) and matrix-assisted laser desorption ionization time-of-flight (MALDI-ToF) mass spectrometry.     

Synthesis of flavanones, azaflavanones, and thioflavanones catalyzed by PMA-SiO2 as a mild, efficient, and reusable catalyst

Abstract  

Cyclization of a variety of chalcones to flavanones catalyzed by 1 mol% phosphomolybdic acid (PMA) supported on silica as a mild, efficient, and reusable catalyst was carried out in high yields. PMA-SiO₂ is an efficient, inexpensive, and green catalyst which gave high conversion yields and could be recycled up to three times without significant loss in activity.     

Polyvinylpolypyrrolidone-supported boron trifluoride: a high-loaded, polymer-supported Lewis acid for the Ritter reaction

Abstract  

A Mild and efficient method for preparing amides by reaction of nitriles with benzhydrol and tertiary alcohols is described using polyvinylpolypyrrolidone-supported boron trifluoride. Selective amidation of benzhydrol in the presence of primary benzyl alcohols was also achieved.     

Synthesis of stable ketenimines via a four-component reaction

Abstract  

An efficient one-pot synthesis of ketenimine derivatives is described. It involves a four-component reaction between benzylamines, 2,2-dichloroethanoyl chloride, alkyl isocyanide, and dialkyl acetylenedicarboxylates under mild conditions at ambient temperature.     

Highly efficient glucosylation of flavonoids

Abstract  

A highly efficient procedure for glucosylation of flavonoids by acetobromoglucose is described. Glucosylation is carried out in a two-phase system CHCl₃/H₂O over 96 h using tetrabutylammonium bromide as phase-transfer catalyst. A purification procedure can be performed without column chromatography, and the yields of the glucosylated flavonoids are mostly quantitative. Acetylated glucosides were deprotected with sodium methanolate to afford the desired glucosides of flavonoids.     

Theoretical conformational analysis of rutin

Abstract  

The structural properties of rutin were determined by using a computational multistep progression. In the first step a stochastic strategy based on a molecular mechanics calculation was adopted to obtain a preliminary screening of the low-energy rutin conformations. The most stable structures obtained by the random conformational search were used as a starting point for an Austin Model 1 (AM1) semiempirical optimization. After this treatment, 16 structures characterized by a more stable frontal in respect to back disposition of the glycosidic chain of rutin were identified. To validate the results found from the stochastic search a molecular dynamics simulation was carried out. The results evidenced the presence of a global minimum highly stabilized by a hydrogen bond between the hydroxyl in the 3′ position of the B ring and the endocyclic oxygen of the rhamnose unit followed by approximately 8 kJ mol⁻¹ less stable local minima with similar energy values. Finally, the reliability of the molecular model was confirmed by comparing the calculated electronic absorption spectrum with that measured on a methanolic rutin solution.     

Coordination‐Driven Self‐Assembly of Carbazole‐Based Metallodendrimers with Generation‐Dependent Aggregation‐Induced Emission Behavior

A new family of 120° carbazole‐based dendritic donors D1 – D3 have been successfully designed and synthesized, from which a series of novel supramolecular carbazole‐based metallodendrimers with well‐defined shapes and sizes were successfully prepared by [2+2] and [3+3] coordination‐driven self‐assembly. The structures of newly designed rhomboidal and hexagonal metallodendrimers were characterized by multinuclear NMR (¹H and ³¹P) spectroscopy, ESI‐TOF mass spectrometry, FTIR spectroscopy, and the PM6 semiempirical molecular orbital method. The fluorescence emission behavior of ligands D1 – D3 , rhomboidal metallodendrimers R1 – R3 , and hexagonal metallodendrimers H1 – H3 in mixtures of dichloromethane and n‐hexane with different n‐hexane fractions were investigated. The results indicated that D1 – D3 featured typical aggregation‐induced emission (AIE) properties. However, different from ligands D1 – D3 , metallodendrimers R1 – R3 and H1 – H3 presented interesting generation‐dependent AIE properties. Furthermore, evidence for the aggregation of these metallodendrimers was confirmed by a detailed investigation of dynamic light‐scattering, Tyndall effect, and SEM. This research not only provides a highly efficient strategy for constructing carbazole‐based dendrimers with well‐defined shapes and sizes, but also presents a new family of carbazole‐based dendritic ligands and rhomboidal and hexagonal metallodendrimers with interesting AIE properties.     

Granulated copper oxide nanocatalyst: a mild and efficient reusable catalyst for the one-pot synthesis of 4-amino-5-pyrimidinecarbonitriles under aqueous conditions

Abstract  

An efficient method for the synthesis of 4-amino-5-pyrimidinecarbonitriles by the three-component reaction of malononitrile, aldehydes, and N-unsubstituted amidines under aqueous conditions using CuO microspheres as catalyst is reported. The catalyst exhibited remarkable reusable activity.     

A convenient strategy for the synthesis of 3,5-diaryl-1,2,4-thiadiazoles: oxidative dimerization of arylthioamides using CC–DMSO in PEG-400

Abstract  

An inexpensive and effective preparative protocol for the highly efficient synthesis of structurally diverse 3,5-diaryl-1,2,4-thiadiazoles at ambient temperature with 2,4,6-trichloro-1,3,5-triazine (CC) and DMSO in polyethylene glycol 400 (PEG-400) as solvent is described.     

An efficient synthesis of ferrocenyl imidazo[1,2-a]pyridines

Abstract  

An efficient and simple synthesis of ferrocenyl 3-aminoimidazo[1,2-a]pyridines by the three-component reaction of ferrocenecarboxaldehyde, isocyanides, and 2-aminopyridines in the presence of a catalytic amount of InCl₃ in ethanol at room temperature is reported.     

Catalytic hypervalent iodine oxidation of alcohols to corresponding aldehydes or ketones using 2,2,6,6-tetramethylpiperidinyl-1-oxy and potassium peroxodisulfate

Abstract  

An efficient, facile, and mild oxidation of alcohols to the corresponding aldehydes or ketones with potassium peroxodisulfate and 2,2,6,6-tetramethylpiperidinyl-1-oxy in the presence of a catalytic amount of iodobenzene is reported. The oxidation proceeded in a mixed solvent to afford carbonyl compounds in moderate to excellent yields. A possible mechanism for the oxidation is proposed.     

Ionic liquid 1-(4-nitritobutyl)-3-methylimidazolium chloride as a new reagent for the efficient N-nitrosation of secondary amines under mild conditions

Abstract  

1-(4-Nitritobutyl)-3-methylimidazolium chloride has been developed as a new reagent for efficient nitrosation of secondary amines at 0 °C to room temperature. A variety of N-nitrosamines were prepared in excellent yields by use of this task-specific ionic liquid under mild and heterogeneous conditions.