Finite-element calculations on the behaviour of a DSC in temperature-modulated mode

The influence of changes of sample properties on the amplitude and phase shift of the differential-temperature signal as well as the influence of frequency changes has been calculated for a one-dimensional model of a temperature-modulated DSC (TMDSC) using a computer program for finite-element-method (FEM) calculations. Amplitude and phase shift of the measured signal ΔT (which is proportional to the differential heat-flow rate) is strongly influenced by the heat capacity of the sample. The connection is only linear for rather small heat capacities. The influence of the heat-transfer coefficient between sample and sample pan on amplitude and phase shift of the signal is not so large and linear (within the framework of our calculations). The influence of the heat-transfer coefficient between sample and sample pan on amplitude and phase shift of the signal is not so large and linear (within the framework of our calculations). For precise measurements, a very careful “calibration” is needed, which must take all the aforementioned influences into account.     

MRI Thermometry Based on Encapsulated Hyperpolarized Xenon

A new approach to MRI thermometry using encapsulated hyperpolarized xenon is demonstrated. The method is based on the temperature dependent chemical shift of hyperpolarized xenon in a cryptophane‐A cage. This shift is linear with a slope of 0.29 ppm °C^?1 which is perceptibly higher than the shift of the proton resonance frequency of water (ca. 0.01 ppm °C^?1) that is currently used for MRI thermometry. Using spectroscopic imaging techniques, we collected temperature maps of a phantom sample that could discriminate by direct NMR detection between temperature differences of 0.1 °C at a sensor concentration of 150 μM . Alternatively, the xenon‐in‐cage chemical shift was determined by indirect detection using saturation transfer techniques (Hyper‐CEST) that allow detection of nanomolar agent concentrations. Thermometry based on hyperpolarized xenon sensors improves the accuracy of currently available MRI thermometry methods, potentially giving rise to biomedical applications of biosensors functionalized for binding to specific target molecules.     

Effect of lanthanide shift reagents on conformational equilibria

The conformational equilibrium constants for a series of 1-alkyl substituted cyclohexanols have been determined using a lanthanide shift reagent, and the results compared with other methods. In comparison to other technique greater preference is shown by the hydroxyl group for the equatorial position. This is rationalized by the effect on the equilibrium of the bulky shift reagent.     

分子筛催化的戊烯骨架异构反应机理

在密度泛函理论中的B3LYP/6-31G(d,p)水平上研究了分子筛催化戊烯骨架异构的微观作用机制,分别对各个基元反应进行了内禀反应坐标(IRC)解析。结果表明:戊烯的骨架异构存在2种反应机理:烷氧基中间体机理和类甲基环丙烷中间体机理。而烷氧基中间体机理又包括2个反应途径,1个是甲基迁移,另1个是乙基迁移。因此,整个异构反应存在3个反应途径。甲基迁移机理和乙基迁移机理都含有3个基元步骤,其中速控步骤分别是甲基迁移和乙基迁移,对应的活化能分别为206.17和207.31 kJ·mol-1,二者几乎相等,表明2个反应途径从能量的角度来说是互相竞争的。类甲基环丙烷中间体机理分2步,碳链扭转和甲基的迁移,反应中间体具有高离子性和高能量的物种。反应速控步骤是碳链扭转反应,其活化能是147.93 kJ·mol-1,明显低于甲基迁移和乙基迁移2个反应途径的能垒,意味着类甲基环丙烷中间体的反应途径更容易发生。     

电解沉积压电频移分析的理论与验证

提出了控制电位电解和恒电流电解两类电解沉积的压电频移分析法测定的理论公式,用实验结果验证了它的正确性.     

Evaluation of limiting-induced shifts of disubstituted adamantane derivatives on the basis of shift additivity

A quantitative interpretation of ¹H NMR spectra of symmetrically disubstituted adamantane derivatives (2,4-adamantanedione, 2,6-adamantanedione and 2,4-adamantanetdiol) with shift reagents is reported. Assumptions are made of shift additivity and an average coordination of one molecule of the shift reagent to both functional groups. A much better fit between the experimental and the calculated set of limiting-induced shifts was obtained for calculations based on shift additivity.     

The effects of lanthanide shift reagents on the NMR spectra of diaza-and dithiacyclophanes

The effect of a lanthanide shift reagent Eu(dpm)₃ on the spectra of 3 diazacyclophanes (Ia-c) has been studied together with the effect of a fluorinated shift reagent En(fod)₃d₂₇ on the nmr spectra of three dithiacyclophanes (IIa-c). The shift reagents remove certain unexpected accidental degeneracies in the original spectra and permit the assignment of the peaks in the expanded spectra to the individual methylene groups. The comparison of the chemical shifts for the methylene groups above the aromatic rings with those of related compounds provides evidence of an upfield shift deriving from the aromatic ring current. The synthesis of two new dithiacyclophanes (IIb-c) is reported.     

Conformational studies on hexahelicenes—I: The NMR spectra of the benzohexahelicenes

The NMR spectra of the benzohexahelicenes have been analyzed. The conformation of the helical structure is not changed to a large extent by the benzo-groups. Some flattening of a part of the helix results in a small downfield shift of the protons on the terminal rings and in a larger upfield shift of proton A in II ascribed to a change in the ring current in the pitch of the helix. A gradual upfield shift is found for protons of the terminal rings by an increase in overcrowding of the benzo-groups.     

Electric field effect on the nematic-isotropic phase transition

Pulsed electric fields are used to study the influence of a strong field on the nematic-isotropic phase transition for cyanobiphenyl and stilbene-type liquid crystals. Deviation of the electric field-induced optical anisotropy from the Kerr law is observed and it is shown that such electric fields can shift the transition temperature substantially. The induced birefringence and the shift of the transition temperature are measured as a function of the electric field strength. The results are explained qualitatively in the context of the Landau-De Gennes theory with two order parameters. The coefficients of the phenomenological theory are calculated using the simple density functional theory of polar nematics developed in this paper and the results for the shift of the transition temperature are compared with experiment results.     

The effects of hydrogen and ph on plasmon absorption of gold hydrosol. Electrochemical reactions on nanoelectrodes

A short-wavelength shift in the plasmon absorption band of 3-nm gold nanoparticles at their hydrosol saturation with hydrogen has been discovered and analyzed. It has been shown that dissociative adsorption of hydrogen occurs on a gold nanoparticle followed by the transfer of hydrogen in the form of a proton to a dispersion medium, with an electron remaining on the nanoparticle; i.e., a hydrogen nanoelectrode is realized. A linear increase in the magnitude of the experimentally observed shift in the plasmon resonance band with solution pH has been qualitatively explained.     

Mechanistic investigation of enediyne-connected amino ester rearrangement. Theoretical rationale for the exclusive preference for 1,6- or 1,5-hydrogen atom transfer depending on the substrate. A potential route to chiral naphthoazepines

Memory of chirality (MOC) and deuterium-labeling studies were used to demonstrate that the cascade rearrangement of enediyne-connected amino esters 1a and 1b evolved through exclusive 1,5- or 1,6-hydrogen atom transfer, subsequent to 1,3-proton shift and Saito-Myers cyclization, depending on the structure of the starting material. These results were independently confirmed by DFT theoretical calculations performed on model monoradicals. These calculations clearly demonstrate that in the alanine series, 1,5-hydrogen shift is kinetically favored over 1,6-hydrogen shift because of its greater exergonicity. In the valine series, the bulk of the substituent at the nitrogen atom has a major influence on the fate of the reaction. N-Tosylation increases the barrier to 1,5-hydrogen shift to the benefit of 1,6-hydrogen shift. The ready availability of 1,6-hydrogen atom transfer was explored as a potential route for the enantioselective synthesis of naphthoazepines.     

Study on colour characteristics depending on orientation of liquid crystal in the in-plane switching mode

The degree of colour shift depending on viewing direction in the in-plane switching (IPS) mode has been investigated. The IPS cell with pure twist deformation exhibits a stronger colour shift than that of the IPS cell with tilt as well as twist deformation, although the former has better luminance uniformity in the bright state than the latter. Furthermore, the IPS cell with multi-directional LC orientation, with tilt as well as twist deformation, shows the least colour shift.     

Research of flicker shift and stability on ADS mode LCD

Flicker shift and flicker stability on advanced super dimension switch (ADS) mode liquid crystal display has been studied based on a 9-in. ADS mode screen which is oriented by rubbing. Firstly, the dependence of flicker shift on polyimide (PI) material was studied by testing four PI materials, including three PI materials of N company (N1, N2, N3) and one PI material of J company (J1). The results show that flicker value of N1 PI material changes most mildly with the continuous lighting time, that is, the N1 PI material performs best on flicker shift among the four PI materials. Secondly, the dependence of flicker stability on passivation layer (PVX) thickness, PI pre-cure temperature, PI main-cure temperature and post-anneal temperature were studied by conducting a four-factor and two-level 1/2 fractional factorial design of experiment (DOE) test. The results of the DOE test indicate that flicker stability could be improved by the increase of PI main cure temperature and the decrease of post-anneal temperature.     

Investigation of the Influence of Diffusion Control on the Curing Reaction Using DSC and Temperature Modulated DSC

The curing reaction of a thermosetting system is investigated by DSC and temperature modulated DSC (TMDSC). When the material vitrifies during curing, the reaction becomes diffusion controlled. The phase shift signal measured by TMDSC includes direct information on the reaction kinetics. For long periods the phase shift is approximately proportional to the partial temperature derivative of the reaction rate. This signal is very sensitive for changes in the reaction kinetics. In the present paper an approach to determine the diffusion control influence on the reaction kinetics from the measured phase shift is developed. The results are compared with experimental data. Further applications of this method for other reactions are proposed. This revised version was published online in July 2006 with corrections to the Cover Date.     

镧系离子与α-氨基丙酸配合物的^1^3C NMR波谱及其的结构研究

本文以XL-200型超导核磁共振谱仪对镧系离子与α-氨基丙酸配合物体系进行了研究, 测得微酸性条件下配合物中各^1^3C核的诱导化学位移值, 以独立结构法将诱导位移进行分离得到配合物生成位移、接触位移及准接触位移。分析这些不同性质的位移贡献得出镧系离子在磁学性质上同样存在"四分组现象”及"钆断效应”。以准接触位移为依据, 对配合物的结构进行计算机模拟, 取得了一些有意义的结果。     

有机硒化合物的^7^7Se NMR研究

本文测定了一系列二茂铁有机硒衍生物及几种烷基硒醚、芳基硒醚化合物的^7^7Se NMR谱。确定了这些化合物的^7^7Se NMR化学位移值。着重讨论了影响^7^7Se化学位移的因素。与硒直接相连取代基的链长、支链化程度以及吸电子能力的改变对^7^7Se NMR化学位移有着不同程度的影响。除此之外, 溶剂效应对二茂铁有机硒类化合物的^7^7Se NMR化学位移也有一定程度的影响。     

Photon echo spectroscopy of porphyrins and heme proteins: effects of quasidegenerate electronic structure on the peak shift decay

Three pulse photon echo peak shift spectroscopy and transient grating measurements on Zn-substituted cytochrome c, Zn-tetraphenylporphyrin, and Zn-protoporphyrin IX are reported. The effects of protein conformation, axial ligation, and solvent are investigated. Numerical simulations of the peak shift and transient grating experiments are presented. The simulations employed recently derived optical response functions for square-symmetric molecules with doubly degenerate excited states. Simulations exploring the effects of excited-state energy splitting, symmetric and asymmetric fluctuations, and excited-state lifetime show that the time scales of the peak shift decay in the three-level system largely reflect the same dynamics as in the two-level system. However, the asymptotic peak shift, which is a clear indicator of inhomogeneous broadening in a two-level system, must be interpreted more carefully for three-level systems, as it is also influenced by the magnitude of the excited-state splitting. The calculated signals qualitatively reproduce the data.     

Density functional computations of 99Ru chemical shifts: relativistic effects, influence of the density functional, and study of solvent effects on fac-[Ru(CO)3I3]-

Solvent effects on the 99Ru NMR chemical shift of the complex fac-[Ru(CO)3I3]- are investigated computationally using density functional theory. Further, benchmark calculations of the 99Ru shift for a set of ten Ru complexes have been performed in order to calibrate the computational model and to determine the importance of relativistic effects on the 99Ru nuclear magnetic shielding and on the chemical shift. A computational model for fac-[Ru(CO)3I3]- that includes both explicit solvent molecules and a continuum model is shown to yield the best agreement with experiment. Relativistic corrections are shown to be of minor importance for determining 99Ru chemical shifts. On the other hand, the nature of the density functional is of importance. In agreement with literature data for ligand trends of 99Ru chemical shifts, the chemical shift range for different solvents is also best reproduced by a hybrid functional.     

Shift reagent spectra. The automatic determination of relative bound shifts and the automatic assignment of signals in the parent spectrum. Effects of concentration,temperature and solvent on relative bound shifts

In the use of a shift reagent as an aid in the structural elucidation of organic compounds, it is shown that accurate measurements of the shift reagent and substrate concentrations are not needed to determine the relative bound shifts of the substrate and the chemical shifts of the free substrate spectrum with good precision. This is possible whenever the induced shift ratios of nuclei of a given molecule are independent of the shift reagent concentration. This independence has been verified for all the monofunctional compounds described in this paper. The effect of absolute substrate concentration, solvent, temperature and the presence of water on the relative bound shifts is studied using the eight methyl group signals of β-amyrin. The method is demonstrated by its use for structural determinations in the ketoandrostane series.     

An experimental study on the mechanism and stereochemistry of a photochemical [1,3]-oh shift. A non-woodward and hoffmann reaction path for photochemic

An experimental study on the photochemistry of the 4-methyl, 4-ethyl disubstituted 3-alkylidene-2-naphthalenol derivatives 1a,b and 5a,b is presented. It is shown that occurrence of a [1,3]-OH shift is dependent only on the ground-state conformation of the substrate. This conformation in its turn is fixed by the chirality at C₂ and C₄. In case of compounds 1a,b the hydroxyl group Is located in the plane of the exocyclic double bond. Excitation of this favourable conformation results In a 90°-twist of the exocyclic double bond. Due to the interaction between the substituents at C₄ and C₉ preferential formation of just one twisted geometry takes place. The stereochemical outcome of the resulting [1,3]-OH shift agrees well with the one expected in case of a planar shift. Further evidence In favour of the occurrence of a non-Woodward and Hoffmann reaction path is obtained from the Irradiation of 5a,b; despite a favourable ground-state conformation for a suprafacial shift to occur, this shift does not take place. Instead a 90°-twisted intermediate is formed, from which solely a radiationless transition to the ground state is observable. The stereostructure of the photoproducts formed was established by means of low temperature NOE measurements.