Reactions of [Mn2(μ-pyS)2(CO)6] with bidentate N-donor ligands: Crystal structure of [Mn(η1-pyS)(bipy)(CO)3] (bipy = 2,2′-bipyridyl, pySH = pyridine-2-thiol)

The dimeric complex [Mn₂(-pyS)₂(CO)₆] (1) reacted with 2 equivalents of 2,2-bipyridyl (bipy), 1,10-phenanthroline (phen), and ethylenediamine (en) to give the corresponding monomeric complexes [Mn(¹-pyS)(bipy)(CO)₃] (2), [Mn(¹-pyS)(phen)(CO)₃] (3), and [Mn( ¹-pyS)(en)(CO)₃] (4). The pyS ligand in these complexes acts as a monodentate, two-electron donor ligand, which coordinates to manganese through the sulfur atom. This is confirmed by an X-ray structure determination of 2, which contains two structural isomers in the asymmetric unit. Crystals of this compound are the monoclinic, space group P2 ₁/c, a = 21.593(4), b = 10.463(2), c = 16.385(3) Å, = 102.468(13)°, V = 3614.5(12) ų, and Z = 8. The three CO groups are facially distributed in both isomers, but the relative positions of the pyS and bipy ligands are different.     

Synthesis and properties of mononuclear and binuclear molybdenum complexes derived from bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone

The monomer molybdenum(VI) complex [MoO(2)(napoxlhH(2))].2H(2)O (1) has been synthesized from the reaction of MoO(2)(acac)(2) with bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone (napoxlhH(4)) in 1:1 molar ratio in ethanol under reflux. This complex on reaction with pyridine/3-picoline/4-picoline yielded the dimer molybdenum(VI) complexes [Mo(2)O(4)(napoxlhH(2))(2)(A)(2)].2H(2)O (A=py (2), 3-pic (3), 4-pic (4)), whereas reaction with isonicotinoylhydrazine (inhH(3)) and salicyloylhydrazine (sylshH(3)) lead to the reduction of the metal centre yielding monomeric molybdenum(V) complexes [Mo(napoxlhH(2))(hzid)].2H(2)O (where hzidH(3)=inhH(3) (5) and sylshH(3) (6)). The complexes have been characterized by elemental analyses, molecular weight determinations, molar conductance data, magnetic moment data, electronic, IR, ESR and (1)H NMR spectroscopic studies. The complexes (5) and (6) are paramagnetic to the extent of one unpaired electron. The electronic spectra of the complexes are dominated by strong charge transfer bands. In all of the complexes, the principal dihydrazone ligand has been suggested to coordinate to the metal centres in the anti-cis-configuration. The complexes (1), (5) and (6) are suggested to have six-coordinate octahedral stereochemistry around molybdenum(VI) and molybdenum(V) metal centres, respectively, while the complexes (2)-(4) are suggested to have eight coordinate dodecahedral stereochemistry around molybdenum(VI) metal centre.     

Ultrafast fluorescence resonance energy transfer in a bile salt aggregate: Excitation wavelength dependence

Fluorescence resonance energy transfer (FRET) from Coumarin 153 (C153) to Rhodamine 6G (R6G) in a secondary aggregate of a bile salt (sodium deoxycholate, NaDC) is studied by femtosecond up-conversion. The emission spectrum of C153 in NaDC is analysed in terms of two spectra-one with emission maximum at 480 nm which corresponds to a non-polar and hydrophobic site and another with maximum at ∼530 nm which arises from a polar hydrophilic site. The time constants of FRET were obtained from the rise time of the emission of the acceptor (R6G). In the NaDC aggregate, FRET occurs in multiple time scales — 4 ps and 3700 ps. The 4 ps component is assigned to FRET from a donor (D) to an acceptor (A) held at a close distance (R _DA ∼ 17 ?) inside the bile salt aggregate. The 3700 ps component corresponds to a donor-acceptor distance ∼48 ?. The long (3700 ps) component may involve diffusion of the donor. With increase in the excitation wavelength (λ _ex) from 375 to 435 nm, the relative contribution of the ultrafast component of FRET (∼4 ps) increases from 3 to 40% with a concomitant decrease in the contribution of the ultraslow component (∼3700 ps) from 97 to 60%. The λ _ex dependence is attributed to the presence of donors at different locations. At a long λ _ex (435 nm) donors in the highly polar peripheral region are excited. A short λ _ex (375 nm) ‘selects’ donor at a hydrophobic location.     

Atroposelective PIII/PV=O Redox Catalysis for the Isoquinoline-Forming Staudinger–aza-Wittig Reaction

Herein, we describe the feasibility of atroposelective P^III/P^V=O redox organocatalysis by the Staudinger–aza-Wittig reaction. The formation of isoquinoline heterocycles thereby enables the synthesis of a broad range of valuable atropisomers under mild conditions with enantioselectivities of up to 98 : 2 e.r. Readily prepared azido cinnamate substrates convert in high yield with stereocontrol by a chiral phosphine catalyst, which is regenerated using a silane reductant under Brønsted acid co-catalysis. The reaction provides access to diversified aryl isoquinolines, as well as benzoisoquinoline and naphthyridine atropisomers. The products are expeditiously transformed into N-oxides, naphthol and triaryl phosphine variants of prevalent catalysts and ligands. With dinitrogen release and aromatization as ideal driving forces, it is anticipated that atroposelective redox organocatalysis provides access to a multitude of aromatic heterocycles with precise control over their configuration.     

Curl condition for a four-state Born-Oppenheimer system employing the Mathieu equation

When a group of four states forms a subspace of the Hilbert space, i.e., appears to be strongly coupled with each other but very weakly interacts with all other states of the entire space, it is possible to express the nonadiabatic coupling (NAC) elements either in terms of s or in terms of electronic basis function angles, namely, mixing angles presumably representing the same sub-Hilbert space. We demonstrate that those explicit forms of the NAC terms satisfy the curl conditions--the necessary requirements to ensure the adiabatic-diabatic transformation in order to remove the NAC terms (could be often singular also at specific point(s) or along a seam in the configuration space) in the adiabatic representation of nuclear SE and to obtain the diabatic one with smooth functional form of coupling terms among the electronic states. In order to formulate extended Born-Oppenheimer (EBO) equations [J. Chem. Phys. 2006, 124, 074101] for a group of four states, we show that there should exist a coordinate independent ratio of the gradients for each pair of ADT/mixing angles leading to zero curls and, thereafter, provide a brief discussion on its analytical validity. As a numerical justification, we consider the first four eigenfunctions of the Mathieu equation to demonstrate the interesting features of nonadiabatic coupling (NAC) elements, namely, the validity of curl conditions and the nature of curl equations around CIs.     

A dinuclear Ni(I) system having a diradical Ni2N2 diamond core resting state: synthetic, structural, spectroscopic elucidation, and reductive bond splitting reactions

One-electron reduction of the square-planar nickel precursor (PNP)NiCl ( 1) (PNP (-) = N[2-P(CHMe 2) 2-4-methylphenyl] 2) with KC 8 effects ligand reorganization of the pincer ligand to assemble a Ni(I) dimer, [Ni(mu 2-PNP)] 2 ( 2), containing a Ni 2N 2 core structure, as inferred by its solid-state X-ray structure. Solution magnetization measurements are consistent with a paramagnetic Ni(I) system likely undergoing a monomer <--> dimer equilibrium. The room-temperature and 4 K solid-state X-band electron paramagnetic resonance (EPR) spectra display anisotropic signals. Low-temperature solid-state X-band EPR data at 4 K reveal rhombic values g z = 1.980(4), g x = 2. 380(4), and g y = 2.225(4), as well as a forbidden signal at g = 4.24 for the Delta M S = 2 half field transition, in accord with 2 having two weakly interacting metal centers. Utilizing an S = 1 model, full spin Hamiltonian simulation of the low-temperature EPR spectrum on the solid sample was achieved by applying a nonzero zero-field-splitting parameter ( D = 0.001 cm (-1)), which is consistent with an S = 0 ground state with a very closely lying S = 1 state. Solid-state magnetization data also corroborate well with our solid-state EPR data and reveal weak antiferromagnetic behavior ( J = -1.52(5) cm (-1)) over a 2-300 K temperature range at a field of 1 Tesla. Evidence for 2 being a masked "(PNP)Ni" scaffold originates from its reaction with N 2CPh 2, which traps the Ni(I) monomer in the form of a T-shaped species, Ni(PNPNNCPh 2), a system that has been structurally characterized. The radical nature of complex 2, or its monomer component, is well manifested through the plethora of cooperative H-X-type bond cleavage reactions, providing the nickel(II) hydride (PNP)NiH and the corresponding rare functionalities -OH, -OCH 3, -PHPh, and -B(catechol) integrated into the (PNP)Ni moiety in equal molar amounts. In addition to splitting H 2, compound 2 can also engage in homolytic X-X bond cleavage reactions of PhXXPh to form (PNP)Ni(XPh) (X = S or Se).     

Ultrafast photoinduced electron transfer in the micelle and the gel phase of a PEO-PPO-PEO triblock copolymer

Ultrafast photoinduced electron transfer (PET) from N,N-dimethylaniline (DMA) to coumarin dyes is studied in the micelle and the gel phase of a triblock copolymer, (PEO)(20)-(PPO)(70)-(PEO)(20) (Pluronic P123) by picosecond and femtosecond emission spectroscopies. The rate of PET in a P123 micelle and gel is found to be nonexponential and faster than the slow components of solvation dynamics. In a P123 micelle and gel, PET occurs on multiple time scales ranging from a subpicosecond time scale to a few nanoseconds. In the gel phase, the highest rate constant (9.3 x 10(9) M(-1) s(-1)) of ET for C152 is about two times higher than that (3.8 x 10(9) M(-1) s(-1)) observed in micelle phase. The ultrafast components of electron transfer (ET) exhibits a bell shaped dependence with the free energy change which is similar to the Marcus inversion. Possible reasons for slower PET in P123 micelle compared to other micelles and relative to P123 gel are discussed.     

纳米多孔二氧化钛电极辅助光电化学降解乙酰氨基酚及伐昔洛韦

作为一类具有较高生物活性的物质,药物及个人护理品对环境的污染引起人们越来越多的关注.对乙酰氨基酚和伐昔洛韦是两种使用广泛的药物,由于其潜在的对人类健康和生态安全的威胁而逐渐成为研究热点.而电化学辅助光氧化技术因其具备能够高效处理难降解化学品的优点而得到广泛使用.本文合成了纳米多孔二氧化钛电极,研究了电化学还原处理对纳米多孔二氧化钛电极辅助光电化学降解对乙酰氨基酚和伐昔洛韦的影响.使用扫描电镜和色散谱技术对合成的纳米多孔二氧化钛电极的形态和元素组成进行了表征.循环伏安法、莫特-肖特基曲线、紫外-可见分光光度计和总有机碳分析仪被用来研究对乙酰氨基酚和伐昔洛韦的光电化学降解过程.结果显示,对乙酰氨基酚和伐昔洛韦的光化学降解和电化学降解过程非常缓慢,在研究的时间范围内其浓度未见明显变化,因此可以忽略不计.但是对乙酰氨基酚和伐昔洛韦的光电化学降解速度比较快,与未经处理的纳米多孔二氧化钛电极相比,经过电化学还原处理的电极可以使对乙酰氨基酚和伐昔洛韦的光电化学降解分别提高86.96%和53.12%.这可能是由于在电化学还原处理过程中生成了Ti3+, Ti2+和氧空位以及导电性的提高.还研究了温度对对乙酰氨基酚和伐昔洛韦光电化学降解的影响,随着温度升高,对乙酰氨基酚和伐昔洛韦的光电化学降解速率增大.     

Simple systematization of vibrational excitation cross-section calculations for resonant electron-molecule scattering in the boomerang and impulse models

Vibrational excitation (nu(f)<--nu(i)) cross-sections sigma(nu(f)<--nu(i) )(E) in resonant e-N(2) and e-H(2) scattering are calculated from transition matrix elements T(nu(f),nu(i) )(E) obtained using Fourier transform of the cross correlation function , where psi(nu(i))(R,t) approximately =e(-iH(A(2))-(R)t/h phi(nu(i))(R) with time evolution under the influence of the resonance anionic Hamiltonian H(A(2) (-))(A(2) (-)=N(2)(-)/H(2) (-)) implemented using Lanczos and fast Fourier transforms. The target (A(2)) vibrational eigenfunctions phi(nu(i))(R) and phi(nu(f))(R) are calculated using Fourier grid Hamiltonian method applied to potential energy (PE) curves of the neutral target. Application of this simple systematization to calculate vibrational structure in e-N(2) and e-H(2) scattering cross-sections provides mechanistic insights into features underlying presence/absence of structure in e-N(2) and e-H(2) scattering cross-sections. The results obtained with approximate PE curves are in reasonable agreement with experimental/calculated cross-section profiles, and cross correlation functions provide a simple demarcation between the boomerang and impulse models.     

Double Yielding in a Styrene/Butadiene Star Block Copolymer

Summary: The morphology and tensile deformation behaviour of a highly asymmetric styrene/butadiene star block copolymer (polystyrene (PS) content = 74%) containing random PS‐co‐PB (polybutadiene) copolymer as a rubbery phase were investigated. The existence of double yielding, similar to that observed in some semicrystalline polymers, was detected in this nanostructured amorphous polymer. The observed phenomenon may be correlated with two different micromechanical processes taking place at the initial stage of deformation.

The stress‐strain curve of the star block copolymer prepared here (each curve represents a different method). The two yield points are clearly visible (labelled I and II).