Understanding the inelastic electron-tunneling spectra of alkanedithiols on gold

We present results for a simulated inelastic electron-tunneling spectra (IETS) from calculations using the "gDFTB" code. The geometric and electronic structure is obtained from calculations using a local-basis density-functional scheme, and a nonequilibrium Green's function formalism is employed to deal with the transport aspects of the problem. The calculated spectrum of octanedithiol on gold(111) shows good agreement with experimental results and suggests further details in the assignment of such spectra. We show that some low-energy peaks, unassigned in the experimental spectrum, occur in a region where a number of molecular modes are predicted to be active, suggesting that these modes are the cause of the peaks rather than a matrix signal, as previously postulated. The simulations also reveal the qualitative nature of the processes dominating IETS. It is highly sensitive only to the vibrational motions that occur in the regions of the molecule where there is electron density in the low-voltage conduction channel. This result is illustrated with an examination of the predicted variation of IETS with binding site and alkane chain length.     

Calycilactone A, a novel hexacyclic alkaloid from Daphniphyllum calycillum

A novel Daphniphyllum alkaloid with a rearranged fused-hexacyclic ring system, calycilactone A, was isolated from the leaves of Daphniphyllum calycillum (Daphniphyllaceae), and the structure and relative stereochemistry of the new compound were elucidated on the basis of spectroscopic data.     

A new benzofuranolignan and a new flavonol derivative from the stem of Morus australis

A new benzofuranolignan austrafuran A （1） and a new flavonol derivative 5,7,2′,4′-tetrahydroxy-3-methoxyflavone （2） were isolated from the stem of Morus australis. Their structures were determined on the basis of spectroscopic evidences.     

Antiparkinson prodrugs

Parkinson's disease (PD) is a progressive, neurodegenerative disorder which involves the loss of dopaminergic neurons of the substantia nigra pars compacta. Current therapy is essentially symptomatic, and L-Dopa (LD), the direct precursor of dopamine(DA), is the treatment of choice in more advanced stages of the disease. Substitution therapy with LD is, however, associated with a number of acute problems. The peripheral conversion of LD by amino acid decarboxylase (AADC) to DA is responsible for the typical gastrointestinal (nausea, emesis) and cardiovascular (arrhythmia, hypotension) side effects. To minimize the conversion to DA outside the central nervous system (CNS) LD is usually given in combination with peripheral inhibitors of AADC (carbidopa and benserazide). In spite of that, other central nervous side effects such as dyskinesia, on-off phenomenon and end-of-dose deterioration still remain. The main factors responsible for the poor bioavailability and the wide range of inter- and intra-patient variations of plasma levels are the drug's physical-chemical properties: low water and lipid solubility, resulting in unfavourable partition, and the high susceptibility to chemical and enzymatic degradation. In order to improve the bioavailability, the prodrug approach appeared to be the most promising and some LD prodrugs have been prepared in an effort to solve these problems. We report here a review of progress in antiparkinson prodrugs, focusing on chemical structures mainly related to LD, DA and dopaminergic agonists.     

Synthesis, characterization, and DFT/TD-DFT calculations of highly phosphorescent blue light-emitting anionic iridium complexes

Highly phosphorescent blue-light-emitting anionic iridium complexes (C4H9)4N[Ir(2-phenylpyridine)2(CN)2] (1), (C4H9)4N[Ir(2-phenyl-4-dimethylaminopyridine)2(CN)2] (2), (C4H9)4N[Ir(2-(2,4-difluorophenyl)-pyridine)2(CN)2] (3), (C4H9)4N[Ir(2-(2,4-difluorophenyl)-4-dimethylaminopyridine)2(CN)2] (4), and (C4H9)4N[Ir(2-(3,5-difluorophenyl)-4-dimethylaminopyridine)2(CN)2] (5) were synthesized and characterized using NMR, UV-vis absorption, and emission spectroscopy and electrochemical methods. In these complexes color and quantum yield tuning aspects are demonstrated by modulating the ligands with substituting donor and acceptor groups on both the pyridine and phenyl moieties of 2-phenylpyridine. Complexes 1-5 display intense photoluminescence maxima in the blue region of the visible spectrum and exhibit very high phosphorescence quantum yields, in the range of 50-80%, with excited-state lifetimes of 1-4 micros in acetonitrile solution at 298 K. DFT and time dependent-DFT calculations were performed on the ground and excited states of the investigated complexes to provide insight into the structural, electronic, and optical properties of these systems.     

原子吸收法测定污泥蚯蚓中的镉、铜、铬、锌、铅

研究用原子吸收法测定蚯蚓中的镉、铜、铬、锌、铅.将制备成粉状的蚯蚓用硝酸-高氯酸消解,在仪器工作条件下,金属离子含量与吸光度呈良好的线性关系.测定结果的相时标准偏差为1.3%～3.5%(n=7),加标回收率为93%～107%.测定镉、铜、铬、锌、铅离子的线性范围、线性相关系数、检出限依次为0～0.9 mg/L,r=0.9984,0.0r7 mg/L;0～10 mg/L,r=0.9989,0.05 mg/L;0～5 mg/L,r=0.999 1,0.13mg/L;0～0.7 mg/L,r=0.9997,0.02 mg/L;0～7.5 mg/L,r=0.9994,0.3 mg/L.     

氯硝柳胺衍生物的合成及抗肿瘤活性研究

以氯硝柳胺为起始原料,经醚化、亲核取代反应得到目标化合物,采用MTT法考察所合成化合物对人类乳腺癌细胞(MDA-MB-231)和人类胰腺癌细胞(ASPC-1)的体外抗肿瘤活性。合成了5个氯硝柳胺衍生物,其结构均经IR、1H-NMR、13C-NMR和MS确证。初步的体外抗肿瘤活性结果显示目标化合物9b和9c的抗肿瘤活性强于阳性对照药,其中化合物9b的活性对所测两种肿瘤株的抑制活性均强于阳性对照药,展现出较强的应用前景。     

Role of catechin on collagen type I stability upon oxidation: a NMR approach

Abstract

The study focuses on the understanding, at molecular level, the mechanism of interaction between protein and flavonoids. Collagen and catechin interactions were investigated by NMR in solution and solid state. The effect of catechin on the stability of collagen to oxidation was also explored. Collagen was treated with two concentrations of catechin solutions. Oxidation was carried out by incubation of collagen solution with three oxidation systems: Fe(II)/H₂O₂, Cu(II)/H₂O₂, and NaOCl/H₂O₂. The effects of oxidation systems were evaluated by high resolution 1?D and 2?D proton spectroscopy and solid state NMR (¹³C CP MAS) experiments. Interactions between collagen and catechin preferentially occur between catechin B ring and the amino acids Pro and Hyp of collagen. Results showed that both iron and copper oxidation systems were able to interact with collagen by site specific attack. Moreover, catechin protects collagen proline from oxidation by metal/H₂O₂ systems, preventing copper and iron approach to collagene molecule;this behaviour was more evident for the copper/H₂O₂ system.     

Cu2+改性g-C3N4光催化剂的光催化性能

Photocatalytic technology can effectively solve the problem of increasingly serious water pollution, the core of which is the design and synthesis of highly efficient photocatalytic materials. Semiconductor photocatalysts are currently the most widely used photocatalysts. Among these is graphitic carbon nitride (g-C₃N₄), which has great potential in environment management and the development of new energy owing to its low cost, easy availability, unique band structure, and good thermal stability. However, the photocatalytic activity of g-C₃N₄ remains low because of problems such as wide bandgap, weakly absorb visible light, and the high recombination rate of photogenerated carriers. Among various modification strategies, doping modification is an effective and simple method used to improve the photocatalytic performance of materials. In this work, Cu/g-C₃N₄ photocatalysts were successfully prepared by incorporating Cu²⁺ into g-C₃N₄ to further optimize photocatalytic performance. At the same time, the structure, morphology, and optical and photoelectric properties of Cu/g-C₃N₄ photocatalysts were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, UV-Vis diffuse reflectance spectroscopy (DRS), and photoelectric tests. XRD and XPS were used to ensure that the prepared photocatalysts were Cu/g-C₃N₄ and the valence state of Cu was in the form of Cu²⁺. Under visible light irradiation, the photocatalytic activity of Cu/g-C₃N₄ and pure g-C₃N₄ photocatalysts were investigated in terms of the degradation of RhB and CIP by comparing the amount of introduced copper ions. The experimental results showed that the degradation ability of Cu/g-C₃N₄ photocatalysts was stronger than that of pure g-C₃N₄. The N₂ adsorption-desorption isotherms of g-C₃N₄ and Cu/g-C₃N₄ demonstrated that the introduction of copper had little effect on the microstructure of g-C₃N₄. The small difference in specific surface area indicates that the enhanced photocatalytic activity may be attributed to the effective separation of photogenerated carriers. Therefore, the enhanced photocatalytic degradation of RhB and CIP over Cu/g-C₃N₄ may be due to the reduction of carrier recombination rate by copper. The photoelectric test showed that the incorporation of Cu²⁺ into g-C₃N₄ could reduce the electron-hole recombination rate of g-C₃N₄ and accelerate the separation of electron-hole pairs, thus enhancing the photocatalytic activity of Cu/g-C₃N₄. Free radical trapping experiments and electron spin resonance indicated that the synergistic effect of superoxide radicals (O₂^•−), hydroxyl radicals (•OH) and holes could increase the photocatalytic activity of Cu/g-C₃N₄ materials.