Artificial channel method

This remark is associated with the amount of calculation performed and is not intended as a criticism. This work provides a valuable quantum mechanical analysis of a three-dimensional system. The artificial channel method (19,60) was employed to solve the coupled equations that arise in the fully quantum approach. A progression of resonances in the absorption cross-section was obtained. The appearance of these resonances provides an explanation of the origin of the diffuse bands found... 

M.L. Du, A. Dalgamo, Artificial-channel method for multichannel-decay-resonance energies and widths, Phys. Rev. A 43 (1991) 3474. 

In addition to the direct methods, in which one calculates first the continuum wavefunctions and subsequently the overlap integrals with the bound-state wavefunction, there are also indirect methods, which encompass the separate computation of the continuum wavefunctions the artificial channel method (Shapiro 1972 Shapiro and Bersohn 1982 Balint-Kurti and Shapiro 1985) and the driven equations method (Band, Freed, and Kouri 1981 Heather and Light 1983a,b). Kulander and Light (1980) applied another method, in which the overlap of the bound-state wavefunction with the continuum wavefunction is directly propagated. The desired photodissociation amplitudes are finally obtained by applying the correct boundary conditions for R —> oo. 

Sere J, = Jk has been assumed for simplicity. The matrix elements are computed t vith the artificial channel method [14],... 

The final stage in the adiabatic reduction is the solution of Eq. (4.24). Given the adiabatic potential of Eq. (4.26) this cannot be done analytically, but the resulting ordinary differential equation may be solved numerically using the finite difference method. As an example, we show in Fig. 20 a comparison between the even-parity adiabatic eigenvalues and the exact ones, obtained by solving the full coupled channels expansion, using the artificial channel method.69... 

In the case of artificial channels that are free from the irregularities found in natural streams, it is possible to apply analytical methods to the various problems of nonuniform flow. In many instances, however, the formulas developed are merely approximations, and we must often resort to trial solutions and even purely empirical methods. For the treatment of many types of flow, see Bakhmeteff [35],... 

A cumulative success of artificial ion-channel functions by simple molecules may disclose a wide gate for the design of ion channels and possible applications to ionics devices. Incorporation of these channels into bilayer lipid membrane systems may trigger the developments towards ionics devices. The conventional BLM system, however, is not very stable, one major drawback for the practical applications, and some stabilization methods, such as impregnating the material in micro-porous polycarbonate or polyester filters, are required. On the other hand,... 

Before concluding this review, it is appropriate to comment on estimation methods of artificial ion channels. As described in each experimental method, both planar and liposomal membranes could be used for detecting the ion transport via the channel mechanism. For estimating the ion transport rate across the liposomal membrane, a variety of methodologies have been employed. These may be summarized as follows ... 

More relevant for this section is the use of porphyrins as template for the construction of de novo metalloproteins. Indeed, the attachment of helical peptide units to these templates creates four-helix bundle structures that have been used as an artificial ion channel 2 or a hydroxylase enzymeJ33,34 In these cases, the peptide units were coupled to the template by using the HOSu or the TBTU methods. As illustrated in Scheme 10 starting from 33, formation of the tetrasuccimidyl ester 34 and attachment of the protected peptide unit 35 gives 36 and this is followed by deprotection to 37. 

NMR technique. NMR-active metal ions entrapped in the liposome can be differentiated from those outside by the addition of shift reagents such as Dy(III) or Gd(III) to the external phase. Then metal concentrations inside and outside the liposome can be determined directly. This is attractive for 7Li+, 23Na+, and 39K+ ions because of high sensitivities and natural abundances. The direct determination of the metal ion concentrations are attractive but limited only for slow kinetics. When the rate becomes faster, line shape analysis or magnetization-inversion transfer techniques are employed. The latter method has been successfully applied to gramicidin channels,143 144 but not to artificial ion channels. 

Ions and small molecules may be transported across cell membranes or lipid bilayers by artificial methods that employ either a carrier or channel mechanism. The former mechanism is worthy of brief investigation as it has several ramifications in the design of selectivity filters in artificial transmembrane channels. To date there are few examples where transmembrane studies have been carried out on artificial transporters. The channel mechanism is much more amenable to analysis by traditional biological techniques, such as planar bilayer and patch clamp methods, so perhaps it is not surprising that more work has been done to model transmembrane channels. 

Several channel architectures have been considered when designing artificial mimics. The most obvious biologically inspired method is to prepare extended helical molecules in an attempt to reproduce the channels either within the helix or where the molecules meet. A small number of systems have been designed using this... 

Pardaxin P-2 is a 33 amino acid peptide isolated from the mucc al secretion of the Pacific sole, Pardachirus pavoninus, that exhibits surfactant properties. Pardaxin has been shown to interfere with ion transport in both epithelium and nerve cells. At concentration below 10 mmol T, pardaxin forms voltage-dependent, ion-permeable channels in artificial liposomes. The structure of pardaxin P2 in aqueous trifluoroethanol solution has been determined using the NOE distance restrained/molecular dynamics method. This study showed that the peptide adopts an amphiphilic helix over residues 7-11, a bend at residues 12-13 and another helix over residues 14-26. 

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