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81.
[reaction: see text] A novel application of photochromic molecules is to mimic physiological oscillatory calcium signals by reversibly binding and releasing calcium ions in response to light. Substituent changes on the largely unexplored photochromic bisbenzospiropyran scaffold led to significant changes in thermal fading rates in several organic solvents. Excellent correlations have been found between fading rates and empirical Hammett constants as well as calculated ground-state energies. These correlations can be used to improve scaffold design. 相似文献
82.
83.
In the existing literature various values are given for the intrinsic birefringence of the crystalline and the amorphous phases in poly(ethylene terephthalate) (PET). These values have either been calculated theoretically or obtained from experimental data on the basis of certain models. In this investigation, using the Samuels two-phase model which correlates sonic modulus with structural parameters, intrinsic birefringence values for the crystalline (Δnc) and amorphous (Δna) phases have been determined by studying 30 PET samples prepared by heat setting to have a wide range of structures; the results are Δnc = 0.29 and Δna = 0.20. These values are discussed along with others in the literature and it is concluded that in the light of the present work, the values used by many authors need reexamination. 相似文献
84.
Ketones are converted smoothly into the corresponding acyloin with a high degree of selectivity upon treatment with iodosobenzene or phenyliodosodiacetate in methanolic sodium hydroxide. 相似文献
85.
Jones oxidation of Andrographolide (1), gave mixture of three products (3-dehydroandrographolide (5), 3,19-bis dehydroandrographolide (6) and 19-dehydroandrographolide (7). Tritylation of andrographolide at C19-OH resulted to products 8 and diene 9, which can be converted to its acetate 10 and oxidation product 11. 相似文献
86.
X-ray absorption spectroscopy (XAS) is widely used to explore the coordination environments and structures of metal complexes in aqueous solutions and disordered phases. Although soft-XAS studies on gaseous phases, solid phases and their interfaces have shown that XAS is a versatile tool in studying the functional group composition of organic molecules, the application of XAS to studying aqueous solutions is seriously limited because of experimental difficulties. In this report, using a modified synchrotron endstation geometry, we show how soft-XAS was used to study the changes in electronic states of reactive functional groups in a bacterial macromolecule, desferrioxamine B (desB, a hydroxamate siderophore) and its structural analogue (acetohydroxamic acid (aHa)). We collected C, N, and O near edge X-ray absorption fine structure (NEXAFS) spectra of these molecules in aqueous solutions and complemented their spectral interpretation with calculated X-ray spectra of "hydrated" aHa. The experimental spectra of desB are similar to those for aHa at the C, N, and O K-edges. In addition, the electronic transitions of amide and hydroxamate functional groups in the macromolecule can be distinguished from the N spectra. Small energy differences in the pi*(C=O)NO and the transitions at the C- and N-edges of aHa and desB indicate that the substituent attached to N in desB ((CH2)n) determines the electron density in the (C=O)NO core. As the solution pH increased, the pi*(C=O)NO transition of the hydroxamate group of these two molecules exhibit energy shifts at the C-, N-, and O-edges, which are consistent with increased electron delocalization in the (C=O)NO core of aHa (and desB), predicted from the calculations. The spectra of the aHa(H2O)3- anion also provide evidence for partial N-deprotonation at pH values usually attributed to an O-acid. These results indicate that soft-XAS is well suited for studying the electronic states of different functional groups in aqueous organic macromolecules. 相似文献
87.
Dalip Singh Mehta Kanchan Saxena Satish Kumar Dubey Chandra Shakher 《Journal of luminescence》2010,130(1):96-102
We report the measurement of coherence characteristics of light-emitting diodes (LEDs). Experiments were performed using red and green color LEDs directly illuminating the Young's double slit kept in the far-zone. Fourier transform fringe analysis technique was used for the measurement of the visibility of interference fringes from which the modulus of degree of spectral coherence was determined. Low degree of spectral coherence, typically 0.4 for red and 0.2 for green LED with double-slit separation of 400 μm was observed. A variable slit was then kept in front of the LEDs and the double slit was illuminated with the light coming out of the slit. Experiments were performed with various slit sizes and the visibility of the interference fringes was observed. It was found that visibility of the interference fringes changes drastically in presence of variable slit kept in front of LEDs and a high degree of spectral coherence, typically 0.85 for red and 0.8 for green LED with double-slit separation of 400 μm and rectangular slit opening of 500 μm was observed. The experimental results are compared with the theoretical counterparts. Coherence lengths of both the LEDs were also determined and it was obtained 5.8±2 and 24±4 μm for green and red LEDs, respectively. 相似文献
88.
B. K. Sadashiva 《Molecular Crystals and Liquid Crystals》2013,570(3-4):253-261
A homologous series of twelve 4-cyanophenyl-3-methyl-4-(4-n-alkylbenzoyloxy) benzoates have been prepared and their mesomorphic properties characterised. All these compounds are colourless, stable and have large positive dielectric anisotropy. The first ten homologues are purely nematic and have a wide thermal range. The undecyloxy and dodecyloxy derivatives exhibit a smectic phase in addition to the nematic phase. A plot of the nematic-isotropic transition temperatures against the number of carbon atoms in the alkyl chain shows the usual odd-even effect. 相似文献
89.
Pankaj Jain Satish D. Joglekar Subhadip Mitra 《The European Physical Journal C - Particles and Fields》2008,57(4):671-680
We compute the two photon exchange contributions to elastic scattering of polarized electrons from target protons. We use
a non-local field theory formalism for this calculation. The formalism maintains gauge invariance and provides a systematic
procedure for making this calculation. The results depend on one unknown parameter,
. We compute the two photon exchange correction to the ratio of electric to magnetic form factors extracted using polarization
transfer experiments. The correction is found to be small if
. However, for larger values of
, the correction can be quite significant. The correction to the polarization transfer results goes in the right direction
to explain their difference with the ratio measured by the Rosenbluth separation method. We find that the difference between
the two experimental results can be explained for a wide range of values of the parameter
. We also find that the corrections due to two photon exchange depend on the photon longitudinal polarization ε. Hence, we predict an ε dependence of the form factor ratio extracted using the polarization transfer technique. Finally, we obtain a limit on
by requiring that the non-linearity in ε dependence of the unpolarized reduced cross section is within experimental errors. 相似文献
90.
Guy Mann Gandhesiri Satish Roman Meledin Ganga B. Vamisetti Ashraf Brik 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(38):13674-13683
Chemical protein synthesis and biorthogonal modification chemistries allow production of unique proteins for a range of biological studies. Bond‐forming reactions for site‐selective protein labeling are commonly used in these endeavors. Selective bond‐cleavage reactions, however, are much less explored and still pose a great challenge. In addition, most of studies with modified proteins prepared by either total synthesis or semisynthesis have been applied mainly for in vitro experiments with very limited extension to live cells. Reported here is an approach for studying uniquely modified proteins containing a traceless cell delivery unit and palladium‐based cleavable element for chemical activation, and monitoring the effect of these proteins in live cells. This approach is demonstrated for the synthesis of a caged ubiquitin‐aldehyde, which was decaged for the inhibition of deubiquitinases in live cells. 相似文献