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1.
The electronegativities () of some 36 atoms/groups (including some 6 ionic ones) X are calculated from the atomic charges in the corresponding methyl species CH3X that were obtained by applying Bader's theory of atoms in molecules. The numerical values of the for the various groups studied are reasonable and correlate linearly with the two existing experimental scales for group electronegativity, Inamoto's i scale and the 1JCC (ortho-ipso) coupling constants in the monosubstituted benzenes, to satisfactory extents. The relations between the values and some “critical properties” of the various CH3X molecules considered are also studied. It is suggested that in a molecule PX, rP/R where rP is the distance of Bader's critical point on the bond PX of length R from the atom P or the binding atom of the group P can be a very good measure of the electronegativity of the atom/group X. © 1992 by John Wiley & Sons, Inc. 相似文献
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Parnajyoti Karmakar Sumon Ray Debabrata Nandi Arup Mandal Subala Mondal Subhasis Mallick Biplab K. Bera Alak K. Ghosh 《Journal of solution chemistry》2013,42(2):441-458
The kinetics of the substitution reactions of [Pt(dach)(H2O)2]2+ and [Pt(en)(H2O)2]2+ (where ‘dach’ and ‘en’ are cis-1,2-diaminocyclohexane and ethylenediamine, respectively) with excess N,N′-diethylthiourea have been studied in aqueous solution by UV–Vis spectrophotometry. The effect of different N–N spectator ligands on the reactivity of platinum(II) complexes was investigated by studying the water lability of the reactant complexes. The kinetic study has been substantiated by product isolation, IR, NMR and ESI-MS spectral analysis and DFT calculations. The reactions follow normal square-planar substitution mainly in an associative way. Rate parameters have been evaluated under different conditions. The substitution rates of the complexes studied can be tuned through the nature of the N–N chelates, which is important in the development of new active compounds for cancer therapy. 相似文献
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Kurinomaru T Tomita S Kudo S Ganguli S Nagasaki Y Shiraki K 《Langmuir : the ACS journal of surfaces and colloids》2012,28(9):4334-4338
The development of technology for on/off switching of enzyme activity is expected to expand the applications of enzyme in a wide range of research fields. We have previously developed a complementary polymer pair system (CPPS) that enables the activity of several enzymes to be controlled by a pair of oppositely charged polymers. However, it failed to control the activity of large and unstable α-amylase because the aggregation of the complex between anionic α-amylase and cationic poly(allylamine) (PAA) induced irreversible denaturation of the enzyme. To address this issue, we herein designed and synthesized a cationic copolymer with a poly(ethylene glycol) backbone, poly(N,N-diethylaminoethyl methacrylate)-block-poly(ethylene glycol) (PEAMA-b-PEG). In contrast to PAA, α-amylase and β-galactosidase were inactivated by PEAMA-b-PEG with the formation of soluble complexes. The enzyme/PEAMA-b-PEG complexes were then successfully recovered from the complex by the addition of anionic poly(acrylic acid) (PAAc). Thus, dispersion of the complex by PEG segment in PEAMA-b-PEG clearly plays a crucial role for regulating the activities of these enzymes, suggesting that PEGylated charged polymer is a new candidate for CPPS for large and unstable enzymes. 相似文献
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Sumon Basak Subhabrata Dutta Prof. Dr. Debabrata Maiti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(41):10533-10557
The skeletal presence of 1,3-azoles in a variety of bioactive natural products, pharmacophores, and organic materials demands the derivatization of such heteroarenes regioselectively. Plenty of cross-coupling as well as cyclocondensation reactions have been performed to build up these skeletons but remained commercially unrealizable. A couple of severe drawbacks are faced by these traditional protocols that require a more straightforward strategy to obviate them. Transition metal-catalyzed C−H functionalization has emerged as a superior alternative in that context. 1,3-Azoles and their benzo counterparts have been extensively functionalized exploiting both noble and earth-abundant transition metals. Lately, C-2 functionalization have gained much traction due to the ease of attaining high regioselectivity and installation of synthetically manipulative functionalities. This critical review presents a bird‘s eye view of all major C-2 functionalization of (benz)azoles catalyzed by a diverse set of metals performed over the past 15 years. 相似文献
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Protein nitration can occur as a result of peroxynitrite‐mediated oxidative stress. Excess production of peroxynitrite (PN) within the cellular medium can cause oxidative damage to biomolecules. The in vitro nitration of Ribonuclease A (RNase A) results in nitrotyrosine (NT) formation with a strong dependence on the pH of the medium. In order to mimic the cellular environment in this study, PN‐mediated RNase A nitration has been carried out in a crowded medium. The degree of nitration is higher at pH 7.4 (physiological pH) compared to pH 6.0 (tumor cell pH). The extent of nitration increases significantly when PN is added to RNase A in the presence of crowding agents PEG 400 and PEG 6000. PEG has been found to stabilize PN over a prolonged period, thereby increasing the degree of nitration. NT formation in RNase A also results in a significant loss in enzymatic activity. 相似文献
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T. M Fortier A. Rolland F. Quinlan F. N. Baynes A. J. Metcalf A. Hati A. D. Ludlow N. Hinkley M. Shimizu T. Ishibashi J. C. Campbell S. A. Diddams 《Laser \u0026amp; Photonics Reviews》2016,10(5):780-790
Fundamental science, as well as all communications and navigation systems, are heavily reliant on the phase, timing, and synchronization provided by low‐noise and agile frequency sources. Although research into varied photonic and electronic schemes have strived to improve upon the spectral purity of microwave and millimeter‐wave signals, the reliance on conventional electronic synthesis for tuning has resulted in limited progress in broadband sources. Using a digital‐photonic synthesizer architecture that derives its time‐base from a high‐stability optical reference cavity, we generate frequency‐agile and wideband microwave signals with exceptional dynamic range and with a fractional frequency instability of 1 × 10−15 at 1 s. The presented architecture demonstrates digitally controlled, user defined and broadband frequency tuning from RF to 100 GHz with orders‐of‐magnitude improvement in noise performance over room‐temperature electronic wide‐bandwidth synthesis schemes.
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Reaction of N-(2′-hydroxyphenyl)-4-R-benzaldimines (L-R, R = OCH3, CH3, H, Cl and NO2) with [Os(PPh3)3Br2] in refluxing 2-methoxyethanol in the presence of triethylamine affords two families of organoosmium complexes (1-R and 2-R). In both 1-R and 2-R complexes a benzaldimine ligand is coordinated to the metal center as tridentate C,N,O-donor. In the 1-R complexes, a bidentate N,O-donor imionsemiquinonate ligand, derived from the hydrolysis of another benzaldimine, and a PPh3 ligand are also coordinated to osmium. In the 2-R complexes, a carbonyl, derived from decarbonylation of 4-R-benzaldehyde (derived from the same hydrolysis stated above), and two PPh3 ligands take up the remaining coordination sites on osmium. Structures of the 1-Cl and 2-OCH3 complexes have been determined by X-ray crystallography. All the 1-R and 2-R complexes are diamagnetic, and show characteristic 1H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on the 1-R complexes shows a reversible Os(III)-Os(IV) oxidation within 0.47-0.67 V (vs SCE), followed by an irreversible oxidation of the imionsemiquinonate ligand within 1.10-1.36 V. An irreversible Os(III)-Os(II) reduction is also displayed by the 1-R complexes within −1.02 to −1.14 V. Cyclic voltammetry on the 2-R complexes shows a reversible Os(II)-Os(III) oxidation within 0.29-0.51 V, followed by a quasi-reversible oxidation within 1.04-1.29 V, and an irreversible reduction of the coordinated benzaldimine ligand within −1.16 to −1.31 V. 相似文献
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Sumon Ganguli Keitaro Yoshimoto Shunsuke Tomita Hiroshi Sakuma Tsuneyoshi Matsuoka Kentaro Shiraki Yukio Nagasaki 《Macromolecular bioscience》2010,10(8):853-859
Poly(N,N‐diethylaminoethyl methacrylate)‐graft‐poly(ethylene glycol) (PEAMA‐g‐PEG) has previously been used as a novel additive to improve the heat resistance of lysozyme, which has a positive net charge and a negatively charged active site. In the present study, we show that PEAMA‐g‐PEG prevents heat inactivation of ribonuclease A (RNase A), which has a positive net charge and a positively charged active site. After treatment at 98 °C for 10 min, the enzymatic activity of RNase A complexed with PEAMA‐g‐PEG was maintained at up to 75% of the level of the native RNase A. The extents of inactivation of RNase A and the complex of RNase A with PEAMA‐g‐PEG were strongly dependent upon the heating temperature and incubation time. Circular dichroism (CD) spectral analysis revealed that heat‐induced irreversible inactivation was largely suppressed when RNase A was complexed with PEAMA‐g‐PEG. These findings suggest that the heat resistance of RNase A is improved by the external addition of PEAMA‐g‐PEG.
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Ahmed Wasif Reza Kaharudin Dimyati Kamarul Ariffin Noordin A. S. M. Zahid Kausar Md. Sumon Sarker 《Optimization Letters》2014,8(1):145-157
Coverage optimization using minimum number of transmitters is critical to service providers and vendors that need to control the coverage as well as the huge costs involved. In this regards, an existing coverage algorithm for determining the minimum number of transmitting antennas as well as their appropriate locations to provide the optimized wireless coverage for indoor environment is studied in this paper. The algorithm uses ray-tracing to predict the signal distribution from the transmitter to the sampling points (receivers) and genetic algorithm to determine the minimum number of transmitters and their corresponding locations to achieve the optimum wireless coverage. The complexity and performance of the algorithm are also analyzed and it is found that it has exponentially increasing complexity of $2^{n}$ and the change of computation time is greater with small change of the number of receiving points. Moreover, under the multi-transmitter scenario (real case), the accuracy achieved by fading, coverage ability, and signal to noise ratio is in the range of 96–99 %. 相似文献