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71.
Recently developed strategies for late stage modification of peptides through CH activation, an arena of contemporary interest in chemical biology and drug discovery, are discussed. Through this tactic, non-polar amino acids in peptides have been selectively functionalized and CH activation enabled new CC and CX bond formations (arylation, alkynylation, fluorination, hydroxylation, azidation, etc.) are documented. Significant advances have been made in Pd or Au-catalyzed, racemization-free, tryptophan specific modifications of large peptides via CH arylation and alkynylation reactions without any protecting group requirement. Development of a new biaryl stapling technique for complex peptides, 18F radiofluorine introduction and diversity oriented post synthetic applications on bio-active cyclopeptides like valinomycin and aureobasidin are additional highlights which underscores the vast potential of late stage CH activation reactions in peptide based therapeutics research. 相似文献
72.
Conclusions An experimental study which shows the effects of relatively small changes in the initial conditions on the development of the three-dimensional structure of a plane mixing layer originating from laminar boundary layers has been completed. It was shown that while the exact shapes and positions of the streamwise vortex structures are not the same for the two initial conditions, their overall distribution, reorganization and decay are very similar. The present results imply that while some of the specific details of the streamwise vortex structure may be facility dependent, a relatively strong structure, which produces significant three-dimensionality, should form in all mixing layers originating from laminar boundary layers. After some initial readjustments, the structure will appear in the form of counter-rotating pairs of streamwise vortices which, in the mean, grow with the mixing layer and decay in strength.The present results also serve as a warning that small changes in initial conditions may significantly affect the Reynolds stress distributions in the near-field. The most likely mechanism for this is through the effects of very small changes in initial boundary layer properties on the details (strength and location) of the spanwise vortex roll-up. Despite these relatively large differences in the near-field, both mixing layers attain comparable turbulence structure and growth rates in the far-field. In addition, the behavior of the streamwise vortex structure does not appear to be affected by the differences in the near-field Reynolds stress distributions. 相似文献
73.
R. D. Mehta 《Experiments in fluids》1990,8(6):354-356
An experimental comparison method is proposed for the verification of mean flow and turbulence measurements obtained with a three-dimensional laser Doppler velocimeter system. Such measurements can include large errors caused by problems unique to three-dimensional systems. Direct comparisons of laser and hot cross-wire measurements obtained in two-dimensional flows, as is the common practice, will not bear out all the errors associated with three-dimensional laser systems. It is proposed here that the errors may be adequately quantified by making the direct comparisons in a weakly three-dimensional turbulent shear flow. The weak three-dimensional flow ensures high accuracy of the cross-wire data while still generating sufficiently strong secondary mean flow and Reynolds shear stresses so that all the laser measurements may be fully verified. This type of shear flow is easily generated by introducing a weak streamwise vortex into a nominally two-dimensional turbulent shear layer. 相似文献
74.
Inhibition effect of imidazole derivative 1,7′-dimethyl-2′-propyl-1H,3′H-2,5′-bibenzo[d]imidazole (DPBI) against mild steel corrosion in 1 M HCl solutions was evaluated using the conventional mass loss method,
potentiodynamic polarization, linear polarization, and electrochemical impedance spectroscopy. The mass loss results showed
that DPBI is an excellent corrosion inhibitor; electrochemical polarizations data revealed the mixed mode of inhibition; and
the results of electrochemical impedance spectroscopy showed that the change in the impedance parameters, charge transfer
resistance, and double layer capacitance with the change in the concentration of the inhibitor is due to the adsorption of
the molecule leading to the formation of a protective layer on the surface of mild steel. The inhibition action of this compound
was assumed to occur via adsorption on the steel surface through the active centers of the molecule. 相似文献
75.
JPC – Journal of Planar Chromatography – Modern TLC - A rapid and reliable high-performance thin-layer chromatographic method has been established for analysis of prednisolone in a... 相似文献
76.
K.K. Bhasin Rishu Sukhjinder Singh H. Kumar S.K. Mehta 《Journal of organometallic chemistry》2010,695(5):648-2013
The present work reports an efficient one-pot synthesis of symmetrical pyridyl monoselenides by the reaction of bromo-/iodopyridines with the isopropylmagnesium chloride, iPrMgCl followed by quenching with selenyl chloride, SeCl2. The current methodology constitutes a convenient synthesis of bis(5-bromo-2-pyridyl) selenide (I), bis(2-bromo-5-pyridyl) selenide (II) and bis(2,5-dibromo-3-pyridyl) selenide (III) under cryogenic conditions requiring shorter time duration to give satisfactory yields. The hitherto unknown compounds have been characterized by elemental analysis and various spectroscopic techniques i.e., 1H NMR, 13C NMR, FT-IR, mass spectrometry and X-ray crystallography. 相似文献
77.
A conformationally locked fluoropentol undergoes an interesting transformation to (trans,anti,trans,anti,trans)-perhydro-2,3,4a,6,7,8a-naphthalenehexol essentially under conditions of base-induced transesterification. The proposed rationale for the observed metamorphosis involves a nucleophilic displacement of fluoride, and subsequent stereo- and regioselective anti-Fürst-Plattner-type ring-opening of the epoxide thus formed. 相似文献
78.
Zañartu M Mehta DD Ho JC Wodicka GR Hillman RE 《The Journal of the Acoustical Society of America》2011,129(1):326-339
Different source-related factors can lead to vocal fold instabilities and bifurcations referred to as voice breaks. Nonlinear coupling in phonation suggests that changes in acoustic loading can also be responsible for this unstable behavior. However, no in vivo visualization of tissue motion during these acoustically induced instabilities has been reported. Simultaneous recordings of laryngeal high-speed videoendoscopy, acoustics, aerodynamics, electroglottography, and neck skin acceleration are obtained from a participant consistently exhibiting voice breaks during pitch glide maneuvers. Results suggest that acoustically induced and source-induced instabilities can be distinguished at the tissue level. Differences in vibratory patterns are described through kymography and phonovibrography; measures of glottal area, open/speed quotient, and amplitude/phase asymmetry; and empirical orthogonal function decomposition. Acoustically induced tissue instabilities appear abruptly and exhibit irregular vocal fold motion after the bifurcation point, whereas source-induced ones show a smoother transition. These observations are also reflected in the acoustic and acceleration signals. Added aperiodicity is observed after the acoustically induced break, and harmonic changes appear prior to the bifurcation for the source-induced break. Both types of breaks appear to be subcritical bifurcations due to the presence of hysteresis and amplitude changes after the frequency jumps. These results are consistent with previous studies and the nonlinear source-filter coupling theory. 相似文献
79.
We study the stationary points of what is known as the lattice Landau gauge fixing functional in one-dimensional compact U(1) lattice gauge theory, or as the Hamiltonian of the one-dimensional random phase XY model in statistical physics. An analytic solution of all stationary points is derived for lattices with an odd number of lattice sites and periodic boundary conditions. In the context of lattice gauge theory, these stationary points and their indices are used to compute the gauge fixing partition function, making reference in particular to the Neuberger problem. Interpreted as stationary points of the one-dimensional XY Hamiltonian, the solutions and their Hessian determinants allow us to evaluate a criterion which makes predictions on the existence of phase transitions and the corresponding critical energies in the thermodynamic limit. 相似文献
80.
V. V. Kabanov Y. V. Lebiadok A. A. Ramanenka A. G. Ryabtsev G. I. Ryabtsev A. S. Smal S. K. Mehta 《Journal of Applied Spectroscopy》2011,77(6):810-816
A system of radiative transfer equations is used to calculate the loss coefficient for amplified luminescence fluxes propagating
along and transverse to the cavity axis in the active layer of high-power laser diode arrays taking the spreading of charge
carriers in the cladding and contact layers of InGaAs/GaAs/AlGaAs heterostructures into account. It is shown that the spreading
of charge carriers leads to a significant change in the amplified luminescence flux which can contribute up to 18% to the
lasing threshold of these laser diode arrays. The calculated loss coefficients can greatly simplify the determination of the
amplified luminescence fluxes in laser diode arrays with an error of less that 16% and can be used to determine how much the
amplified luminescence affects the power and dynamic characteristics of diode arrays. 相似文献