Microwave-accelerated or conventionally heated iodination reactions of some aromatic amines, using ortho-periodic acid as the oxidant

A fast and simple method for the oxidative iodination of some aromatic amines, either under microwave irradiation or conventional heating, is reported, using diiodine and ortho-periodic acid as the oxidant. The reactions were carried out in boiling CH2Cl2 solutions under a reflux condenser. For the microwave assisted reactions, the reaction times were always notably shortened, but the yields were usually less influenced as compared with the conventional method.     

Weighted Inequalities for Quasi-Monotone Functions

The purpose of this paper is to give characterizations of weightsfor which reverse inequalities of Hölder type for quasi-monotonefunctions are satisfied. Our inequalities with general weightsand with sharp constants complement the results of [2, 8, 9]and [16, 17] for the values of parameters p and q with 1pq<.     

Structure and dynamics of methyl cis-3,4-diamino-2,3,4,6-tetradeoxy-alpha-L-lyxo-hexopyranoside complexes with PtCl(2) and PdCl(2), by (1)H, (2)H, (13)C, (15)N and (195)Pt NMR spectroscopy in DMSO, CD(3)CN and H(2)O

Pd(ii) and Pt(ii) chloride complexes with LL = methyl cis-3,4-diamino-2,3,4,6-tetradeoxy-alpha-l-lyxo-hexopyranoside of the formulae [Pd(LL)Cl(2)] and [Pt(LL)Cl(2)], , were studied by (1)H, (2)H, (13)C, (15)N and (195)Pt NMR spectroscopy. These techniques were applied for characterization of the structure and ligand exchange dynamics, in case of diastereomeric species formed from in DMSO-d(6), DMSO-h(6) and H(2)O; their general formula was [Pt(LL)XY](+) (X = Cl, Y = DMSO-d(6), ; X = DMSO-d(6), Y = Cl, ; X = Cl, Y = DMSO-h(6), '; X = DMSO-h(6), Y = Cl, '; X = Cl, Y = H(2)O, ; X = H(2)O, Y = Cl, ). Their theoretical structures and NMR parameters, calculated at the level of DFT approach, were also presented and compared to the experimental data. The model complex [Pt(trans-diaminocyclohexane)Cl(2)], , was studied as well. To the best of our knowledge, this work is the first account dealing with the detailed analysis of structure and dynamics of ligand exchange processes in organic solvents and water, performed for a PtCl(2) complex containing a diaminosugar moiety. The kinetic behavior of the studied coordination compounds suggests that some of them may be potentially active in bioassays against cancer cells. Compound exhibits noticeable versatile ligand exchange possibilities in DMSO and H(2)O. Particularly, it undergoes solvolysis in DMSO-d(6), exchanging one chloride atom and yielding two diastereomers and ; the former, being the kinetically favored species, has the DMSO-d(6) ligand syn to the N(3) atom. The lyophilisate of the respective + mixture, earlier equilibrated in DMSO-d(6), after dissolving in H(2)O yields only the latter isomer, which is thermodynamically favored. The solvolysis of in H(2)O yields instantaneously two diastereomeric monoaquated species, and , amounting to 10% of each.     

Evidence for sevenfold coordination in the first solvation shell of Hg(II) aqua ion

A quite unexpected sevenfold coordination of the hydrated Hg(II) complex in aqueous solution is revealed by an extensive study combining X-ray absorption spectroscopy (XAS) and quantum mechanics/molecular dynamics (QM/MD) calculations. As a matter of fact, the generally accepted octahedral solvation of Hg(II) ion cannot be reconciled with XAS results. Next, refined QM computations point out the remarkable stability of a heptacoordinated structure with C2 symmetry, and long-time MD simulations by new interaction potentials including many-body effects reveal that the hydrated complex has a quite flexible structure, corresponding for most of the time to heptacoordinated species. This picture is fully consistent with X-ray absorption near-edge structure experimental data which unambiguously show the preference for a sevenfold instead of a sixfold coordination.     

“Barchan” dunes in the labDunes de type « Barchanes » au laboratoire

We demonstrate the feasibility of studying dunes in a laboratory experiment. It is shown that an initial sand pile, under a wind flow carrying sand, flattens and gets a shape recalling barchan dunes. An evolution law is proposed for the profile and the summit of the dune. The dune dynamics is shown to be shape invariant. The invariant shape, the “dune function” is isolated. To cite this article: O. Dauchot et al., C. R. Mecanique 330 (2002) 185–191.     

Inkjet-printed gold nanoparticle chemiresistors: Influence of film morphology and ionic strength on the detection of organics dissolved in aqueous solution

The influence of film morphology on the performance of inkjet-printed gold nanoparticle chemiresistors has been investigated. Nanoparticles deposited from a single-solvent system resulted in a “coffee ring”-like structure with most of the materials deposited at the edge. It was shown that the uniformity of the film could be improved if the nanoparticles were deposited from a mixture of solvents comprising N-methyl-2-pyrrolidone and water. Electrical conductivity measurements showed that both “coffee ring” and “flat” films were qualitatively similar suggesting that the films have similar nanoscale structures. To form the functional chemiresistor device, the 4-(dimethylamino)pyridine coating on the nanoparticle was exchanged with 1-hexanethiol to provide a hydrophobic sensing layer. The performance of 1-hexanethiol coated gold nanoparticle chemiresistors to small organic molecules, toluene, dichloromethane and ethanol dissolved in 1 M KCl in regard to changes in impedance and response times was unaffected by the film morphology. For larger hydrocarbons such as octane, the rate of uptake of the analyte into the film was significantly faster when the flatter nanoparticle film was used as opposed to the “coffee ring” film which has a thicker edge. Furthermore, the presence of potassium and chloride ions in the solution media does not significantly affect the impedance of the nanoparticle film at 1 Hz (<2% variation in film impedance over more than four orders of magnitude change in ionic strength). However, the ionic strength of the media affected the partitioning of the analyte into the hydrophobic nanoparticle film. The response of the sensor was found to increase with an increased salt concentration due to a salting-out of the analyte from the solution.     

Structural correlations for 1H, 13C and 15N NMR coordination shifts in Au(III), Pd(II) and Pt(II) chloride complexes with lutidines and collidine

¹H, ¹³C and ¹⁵N NMR studies of gold(III), palladium(II) and platinum(II) chloride complexes with dimethylpyridines (lutidines: 2,3‐lutidine, 2,3lut; 2,4‐lutidine, 2,4lut; 3,5‐lutidine, 3,5lut; 2,6‐lutidine, 2,6lut) and 2,4,6‐trimethylpyridine (2,4,6‐collidine, 2,4,6col) having general formulae [AuLCl₃], trans‐[PdL₂Cl₂] and trans‐/cis‐[PtL₂Cl₂] were performed and the respective chemical shifts (δ^1H, δ^13C, δ^15N) reported. The deshielding of protons and carbons, as well as the shielding of nitrogens was observed. The ¹H, ¹³C and ¹⁵N NMR coordination shifts (Δ^1H_coord, Δ^13C_coord, Δ^15N_coord; Δ_coord = δ_complex ? δ_ligand) were discussed in relation to some structural features of the title complexes, such as the type of the central atom [Au(III), Pd(II), Pt(II)], geometry (trans‐ or cis‐), metal‐nitrogen bond lengths and the position of both methyl groups in the pyridine ring system. Copyright © 2010 John Wiley & Sons, Ltd.     

Assessment of two theoretical methods to estimate potentiometric titration curves of peptides: comparison with experiment

We compared the ability of two theoretical methods of pH-dependent conformational calculations to reproduce experimental potentiometric titration curves of two models of peptides: Ac-K5-NHMe in 95% methanol (MeOH)/5% water mixture and Ac-XX(A)7OO-NH2 (XAO) (where X is diaminobutyric acid, A is alanine, and O is ornithine) in water, methanol (MeOH), and dimethyl sulfoxide (DMSO), respectively. The titration curve of the former was taken from the literature, and the curve of the latter was determined in this work. The first theoretical method involves a conformational search using the electrostatically driven Monte Carlo (EDMC) method with a low-cost energy function (ECEPP/3 plus the SRFOPT surface-solvation model, assumming that all titratable groups are uncharged) and subsequent reevaluation of the free energy at a given pH with the Poisson-Boltzmann equation, considering variable protonation states. In the second procedure, molecular dynamics (MD) simulations are run with the AMBER force field and the generalized Born model of electrostatic solvation, and the protonation states are sampled during constant-pH MD runs. In all three solvents, the first pKa of XAO is strongly downshifted compared to the value for the reference compounds (ethylamine and propylamine, respectively); the water and methanol curves have one, and the DMSO curve has two jumps characteristic of remarkable differences in the dissociation constants of acidic groups. The predicted titration curves of Ac-K5-NHMe are in good agreement with the experimental ones; better agreement is achieved with the MD-based method. The titration curves of XAO in methanol and DMSO, calculated using the MD-based approach, trace the shape of the experimental curves, reproducing the pH jump, while those calculated with the EDMC-based approach and the titration curve in water calculated using the MD-based approach have smooth shapes characteristic of the titration of weak multifunctional acids with small differences between the dissociation constants. Nevertheless, quantitative agreement between theoretically predicted and experimental titration curves is not achieved in all three solvents even with the MD-based approach, which is manifested by a smaller pH range of the calculated titration curves with respect to the experimental curves. The poorer agreement obtained for water than for the nonaqueous solvents suggests a significant role of specific solvation in water, which cannot be accounted for by the mean-field solvation models.     

Experimental and quantum-chemical studies of 15N NMR coordination shifts in palladium and platinum chloride complexes with pyridine, 2,2'-bipyridine and 1,10-phenanthroline

A series of Pd and Pt chloride complexes with pyridine (py), 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen), of general formulae trans-/cis-[M(py)2Cl2], [M(py)4]Cl2, trans-/cis-[M(py)2Cl4], [M(bpy)Cl2], [M(bpy)Cl4], [M(phen)Cl2], [M(phen)Cl4], where M = Pd, Pt, was studied by 1H, 195Pt, and 15N NMR. The 90-140 ppm low-frequency 15N coordination shifts are discussed in terms of such structural features of the complexes as the type of platinide metal, oxidation state, coordination sphere geometry and the type of ligand. The results of quantum-chemical NMR calculations were compared with the experimental 15N coordination shifts, well reproducing their magnitude and correlation with the molecular structure.     

1-(2-羟乙基)-2-烷基-咪唑啉缓蚀剂缓蚀机理的理论研究

采用量子化学计算、分子动力学模拟和分子力学相结合的方法, 对6种不同烷基链长的1-(2-羟乙基)-2-烷基-咪唑啉缓蚀剂抑制H2S腐蚀的缓蚀机理进行研究, 并对其缓蚀性能进行评价. 前线轨道分布和Fukui指数表明, 6种缓蚀剂分子的反应活性区域均集中在分子的咪唑环上, 3个反应活性中心分别位于咪唑环上的N(4), N(7)和C(8)原子, 可使咪唑环在金属表面形成多中心吸附. 分子的反应活性及活性区域分布对烷基链长并不敏感. 单分子吸附能、膜的内聚能、吸附角和链间距的计算数据显示, 缓蚀剂膜的稳定性以及膜与金属基体的结合强度随链长的增加而增大; 当正构烷基碳链长度大于13时, 缓蚀剂可在金属表面形成一层高覆盖度、致密的疏水膜, 能有效阻碍溶液中的腐蚀介质向金属表面扩散, 从而达到阻碍或延缓腐蚀的目的.