A novel approach toward thioester bond formation mediated by N,N’ -diisopropylcarbodiimide in water

Abstract

A simple and efficient method has been developed for the synthesis of thioesters from carboxylic acids and thiols using N,N'-diisopropylcarbodiimide (DIC). The reactions were carried out in water as an environmentally friendly and green solvent. The developed procedure presents an economic, efficient, mild, and very simple protocol for thioesterification reaction in aqueous media.     

表面In掺杂TiO2的N719/TiO2-Inx%/FTO薄膜电极的光电转换效率

采用溶胶-凝胶法制备出In 表面修饰的TiO₂ (TiO₂-Inx%)纳米粒子, x%代表在In 掺杂的TiO₂样品中In³⁺与In³⁺和Ti⁴⁺离子摩尔百分含量. 利用二(四丁基铵)顺式-双(异硫氰基)双(2,2''-联吡啶-4,4''-二羧酸)钌(II)(N719)作为敏化剂, 制备出N719/TiO₂/FTO (氟掺杂锡氧化物)和N719/TiO₂-Inx%/FTO染料敏化薄膜电极. 光电转换效率实验表明, 在薄膜电极+0.5 mol·L^-1 LiI+0.05 mol·L^-1 I₂的三甲氧基丙腈(MPN)溶液+Pt 光电池体系中,N719/TiO₂-Inx%/FTO薄膜电极的光电转换效率均高于N719/TiO₂/FTO, 其中N719/TiO₂-In0.1%/FTO的光电转换效率比N719/TiO₂/FTO提高了20%. 利用X 射线衍射(XRD)、X 射线光电子能谱(XPS)、漫反射吸收光谱(DRS)、荧光(PL)光谱和表面光电流作用谱确定了TiO₂-Inx%样品中In3+离子的存在方式和能带结构; 利用表面光电流作用谱研究了N719/TiO₂-Inx%/FTO薄膜电极的光致界面电荷转移过程. 结果表明, In3+离子在TiO₂表面形成O-In-Cl_n (n=1, 2)物种, 该物种的表面态能级位于导带下0.3 eV处; 在光电流产生过程中, O-In-Cl_n (n=1, 2)表面态能级有效地抑制了光生载流子在TiO₂-Inx%层的复合, 促进了阳极光电流的增加, 从而导致N719/TiO₂-Inx%/FTO薄膜电极的光电转化效率高于N719/TiO₂/FTO, 并进一步讨论了光致界面电荷转移的机理.     

Flow Injection Analysis of Benzoyl Peroxide Using N,N,N,N-Tetramethyl-p-phenylenediamine (TMPDA) and Surfactants

Abstract

The flow injection analysis of benzoyl peroxide using N,N,N,N-tetramethyl-p-phenylenediamine (TMPDA, also known as Wurster's reagent) and a solvent system including the surfactant sodium dodecyl sulfate (SDS) and cerium(IV) as a catalyst at pH 6.0 at 612 nm was investigated. The method was applied to the analysis of acne cream and flour. The study included a 26-metal-ion search for other possible methods of catalysis and a buffer study of SDS and cetyltrimethyl ammonium bromide (CTAB).     

Specific Spectrophotometric Determination of Palladium with N,N'-Diphenylbenzimidoylthiourea

ABSTRACT

A specific method for the spectrophotometric determination of palladium with N.N'-diphenylbenzimidoylthiourea (DPB1TU) is described. The method in new, simple, rapid and applicable over 0.3-1.0 M HC1 and free from interferences of the precious metals i.e.

Ag, Au, Pt, Ir, Rh, Ru, Os. The value of molar absorptivity of the complex in the term of Pd is (2.50)x10⁴ L mole^?1 cm^?1at λ_max 365 nm in chloroform. The detection limit of the method at 3 σ a is 80 ppb Pd. The composition of the complex and effect of diverse ions in the determination of Pd are discussed. The application of the method has been tested for the analysis of the metal in catalytic material.     

Application of unsymmetrical indirect covariance NMR methods to the computation of the (13)C <--> (15)N HSQC-IMPEACH and (13)C <--> (15)N HMBC-IMPEACH correlation spectra

Utilization of long-range (1)H--(15)N heteronuclear chemical shift correlation has continually grown in importance since the first applications were reported in 1995. More recently, indirect covariance NMR methods have been introduced followed by the development of unsymmetrical indirect covariance processing methods. The latter technique has been shown to allow the calculation of hyphenated 2D NMR data matrices from more readily acquired nonhyphenated 2D NMR spectra. We recently reported the use of unsymmetrical indirect covariance processing to combine (1)H--(13)C GHSQC and (1)H--(15)N GHMBC long-range spectra to yield a (13)C--(15)N HSQC-HMBC chemical shift correlation spectrum that could not be acquired in a reasonable period of time without resorting to (15)N-labeled molecules. We now report the unsymmetrical indirect covariance processing of (1)H--(13)C GHMBC and (1)H--(15)N IMPEACH spectra to afford a (13)C--(15)N HMBC-IMPEACH spectrum that has the potential to span as many as six to eight bonds. Correlations for carbon resonances long-range coupled to a protonated carbon in the (1)H--(13)C HMBC spectrum are transferred via the long-range (1)H--(15)N coupling pathway in the (1)H--(15)N IMPEACH spectrum to afford a much broader range of correlation possibilities in the (13)C--(15)N HMBC-IMPEACH correlation spectrum. The indole alkaloid vincamine is used as a model compound to illustrate the application of the method.     

Characterization of two series of nitrogen-containing dendrimers by natural abundance 15N NMR

Two series of small generation dendrimers built with phosphorus atoms at each branching point and various types of nitrogen atoms at natural abundance of (15)N within the branches are characterized by a gradient enhanced GHNMQC (gradient hydrogen-nitrogen multiple quantum coherence) (1)H-(15)N NMR technique. The first series contains two types of nitrogen atoms, included in phosphorhydrazone linkages (CH=NNMe-P(S)), whereas the second series contains four types of nitrogen atoms included in azobenzene linkages (Ar-N=N-Ar') in addition to the phosphorhydrazone. The influence of the trans/cis isomerization of the azo bond on the (15)N NMR has also been studied. Despite the low solubility of the azobenzene-containing dendrimers, which renders the detection of some signals difficult, (15)N NMR appears as a very sensitive tool to detect chemical changes in the dendritic structure.     

15N NMR chemical shifts of ring substituted benzonitriles

15N chemical shifts in an extensive series of para (15) and meta (15) as well as ortho (8) substituted benzonitriles, X-C6H4-CN, were measured in deuteriochloroform solutions, using three different methods of referencing. The standard error of the average chemical shift was less than 0.03 ppm in most cases. The results are discussed for both empirical correlations with substituent parameters and quantum chemical calculations. The 15N chemical shifts calculated at the GIAO/B3LYP/6-31 + G*//B3LYP/6-31 + G* level reproduce the experimental values well, and include nitrogen atoms in the substituent groups (range of 300 ppm with slope 0.98 and R = 0.998, n = 43). The 15N shifts in hydroxybenzonitriles are affected by interaction with the OH group. Therefore, these derivatives are excluded from the correlation analysis. The resultant 15N chemical shift correlates well with substituent constants, both in the simple Hammett or DSP relationships and the 13C substituent-induced chemical shifts of the CN carbon.     

Studies on cyanosilylation reaction catalyzed by Ln?N complexes

A novel family of Ln? N complexes was synthesized by two methods and as the Lewis acidic catalysts in application to the cyanosilylation of prochiral ketones and aldehydes, which gave yields > 99% of some cyano trimethylsilyl ethers from the wide range of aldehyde substrates and moderate yields from the ketone substrates at room temperature using 20 mol% catalyst loadings. Copyright © 2008 John Wiley & Sons, Ltd.     

Pd‐Catalyzed C?N Bond Formation with Heteroaromatic Tosylates

A protocol for the palladium(0)‐catalyzed amidation of heteroaromatic tosylates was successfully developed. The methodology proved to be effective for a variety of heteroaryl tosylates including the pyridine, pyrimidine, quinoline and quinoxaline ring systems. Successful carbon? nitrogen bond formation with these heteroaryl tosylates could be performed with a wide range of primary amides, oxazolidinones, lactams, anilines and indoles, including one cyclic urea. Moreover, this C? N bond forming reaction provided products with high structural diversity. The coupling reaction was also amenable to scale up applications.     

Long-range 1H-15N heteronuclear shift correlation across wide F1 spectral windows

Long‐range ¹H? ¹⁵N heteronuclear shift correlation experiments at natural abundance are becoming more routinely utilized in the characterization of unknown chemical structures from a diverse range of sources including natural products and pharmaceuticals. Apart from the inherent challenges of the low gyromagnetic ratio and natural abundance of ¹⁵N, investigators are also occasionally hampered by having to deal with the wide spectral range inherent to various nitrogen functional groups, which can exceed 500 ppm. Earlier triple resonance cryoprobe designs typically provided 90° ¹⁵N pulses in the range of 35–40 µs, which did not allow the uniform excitation of wide F₁ spectral ranges for ¹H? ¹⁵N GHMBC spectra. We report the results obtained with a newly designed Bruker 600 MHz triple resonance TCI Micro CryoProbe? using methyl orange as a model compound, in which the ¹⁵N resonances are separated by > 450 ppm. Copyright © 2010 John Wiley & Sons, Ltd.     

Static hyperpolarizability of the van der Waals complex CH4?N2

The static first hyperpolarizability of the van der Waals CH₄ N₂ complex was calculated. The calculations were carried out in the approximation of the rigid interacting molecules for a broad range of intermolecular separations (R = 6–40 a₀) and for six configurations at CCSD(T) level of theory using the correlation consistent aug-cc-pVTZ basis set with the basis set superposition error correction. It was shown that the long-range classical approximation, including the terms up to R⁻⁶, is in a good agreement with ab initio calculations for R > 11 a₀. It was found out that for the family of most stable configurations of the complex, the first hyperpolarizability invariants practically do not change (the changes are less than 0.1%). Under forming the stable van der Waals CH₄ N₂ complex, the intensity and degree of depolarization of the hyper-Rayleigh scattering are noticeable decreased (by ∼10%) to be compared with the free CH₄ and N₂ molecules. © 2012 Wiley Periodicals, Inc.     

THE EPR SPECTRA OF TETRADENTATE SCHIFF BASE COMPLEXES OF COPPER (II) I. N,N'-Bis-(acetylacetone) ethylenediimine and N,N'-Bis-(1,1,1-trifluoroacetylacetone) ethylenediimine

Abstract

The EPR spectrum of N, N'-bis-(acetylacetone)ethylenediimino Cu(II), [Cu-en(acac)₂], and N, N'-bis-(1,1,1-trifluoroacetylacetone)ethylenediimino-Cu(II), [Cu-en(tfacac)₂], have been studied in doped single crystals of the corresponding Ni(II) chelate. The parameters in the usual doublet spin-Hamiltonian are found to be: Cu[en(acac)₂], g_z =2.183 ± 0.003, g_x =2.047 ± 0.004, g_y =2.048 ± 0.004, A_z =204.8 × 10^?4cm^?1, A_x =31.5 × 10^?4cm^?1, A_y =27.1 × 10^?4 cm^?1, A_zN= 12.8 × 10^?4 cm^?1 and A_xN =A_yN =14.3 × 10^?4 cm^?1: Cu[en(tfacac)₂], g_z =2.192 ± 0.002, g_x =2.048 ± 0.004, g_y =2.046 ± 0.004, A_z =200.8 × 10^?4 cm^?1, A_x =31.1 × 10^?4 cm^?1, A_y =28.3 × 10^?4 cm^?1, A_zN =12.8 × 10^?4 cm^?1 and A_xN =A_yN =14.6 × 10^?4 cm^?1. These parameters are related to coefficients in the molecular orbitals of the complex. It is found that the α-bonding is quite covalent and there is significant in-plane σ-bonding. From the nitrogen hyperfine structure it is determined that the hybridization on the nitrogen is sp².     

Observation of O-H...N scalar coupling across a hydrogen bond in nocathiacin I

We report here the observation of O-H...N hydrogen-bond (1h)J(N,OH) scalar coupling in a biologically active natural product. The intramolecular hydrogen bond between the threonine hydroxyl (Thr-OH) group and the thiazolyl nitrogen at the second thiazole ring (Thz-2) in nocathiacin I was directly detected by a 1H-15N HMBC NMR experiment. The magnitude of the scalar coupling constant (1h)J(N,OH) was accurately measured to be 1.8 +/- 0.1 Hz by a J-resolved 1H-15N HMBC experiment. By adding the O-H...N distance restraint, the 3D solution structure of nocathiacin I was refined. The structure refinement indicated that the distance between the Thr-3 hydroxyl hydrogen and the Thz-2 nitrogen is or= 0.23 A. The presence of an intramolecular hydrogen bond in nocathiacin I is further supported by a number of NMR parameters and additional NMR experiments. This observation provides valuable information for characterizing molecular conformations, and for studying structure-activity relationships.