Imprint Step Research Articles

Multiscale Architectured Nafion Membrane Derived from Lotus Leaf for Fuel Cell Applications.

Hierarchically patterned proton-exchange membranes (PEMs) have the potential to significantly increase the specific surface area, thus improving the catalyst utilization rate and performance of proton-exchange membrane fuel cells (PEMFCs). In this study, we are inspired by the unique hierarchical structure of the lotus leaf and proposed a simple three-step strategy to prepare a multiscale structured PEM. Using the multilevel structure of the natural lotus leaf as the original template, and after structural imprinting, hot-pressing, and plasma-etching steps, we successfully constructed a multiscale structured PEM with a microscale pillar-like structure and a nanoscale needle-like structure. When applied in a fuel cell, the multiscale structured PEM resulted in a 1.96-fold increase in discharge performance and a significant improvement in mass transfer compared to the membrane electrode assembly (MEA) with a flat PEM. The multiscale structured PEM has the combined advantage of a nanoscale and a microscale structure, benefiting from the markedly reduced thickness, increased surface area, and improved water management inherited from the multiscale structured lotus leaf's superhydrophobic characteristic. Using a lotus leaf as a multilevel structure template avoids the complex and time-consuming preparation process required by commonly used multilevel structure templates. Moreover, the remarkable architecture of biological materials can inspire novel and innovative applications in many fields through nature's wisdom.

Switching between 3D Surface Topographies in Liquid Crystal Elastomer Coatings Using Two-Step Imprint Lithography.

While dynamic surface topographies are fabricated using liquid crystal (LC) polymers, switching between two distinct 3D topographies remains challenging. In this work, two switchable 3D surface topographies are created in LC elastomer (LCE) coatings using a two-step imprint lithography process. A first imprinting creates a surface microstructure on the LCE coating which is polymerized by a base catalyzed partial thiol-acrylate crosslinking step. The structured coating is then imprinted with a second mold to program the second topography, which is subsequently fully polymerized by light. The resulting LCE coatings display reversible surface switching between the two programmed 3D states. By varying the molds used during the two imprinting steps, diverse dynamic topographies can be achieved. For example, by using grating and rough molds sequentially, switchable surface topographies between a random scatterer and an ordered diffractor are achieved. Additionally, by using negative and positive triangular prism molds consecutively, dynamic surface topographies switching between two 3D structural states are achieved, driven by differential order/disorder transitions in the different areas of the film. It is anticipated that this platform of dynamic 3D topological switching can be used for many applications, including antifouling and biomedical surfaces, switchable friction elements, tunable optics, and beyond.

Nanoimprinted and Anodized Templates for Large-Scale and Low-Cost Nanopatterning.

Nanopatterning to fabricate advanced nanostructured materials is a widely employed technology in a broad spectrum of applications going from spintronics and nanoelectronics to nanophotonics. This work reports on an easy route for nanopatterning making use of ordered porous templates with geometries ranging from straight lines to square, triangular or rhombohedral lattices, to be employed for the designed growth of sputtered materials with engineered properties. The procedure is based on large-scale nanoimprinting using patterned low-cost commercial disks, as 1-D grating stamps, followed by a single electrochemical process that allows one to obtain 1-D ordered porous anodic templates. Multiple imprinting steps at different angles enable more complex 2-D patterned templates. Subsequently, sputtering facilitates the growth of ferromagnetic antidot thin films (e.g., from 20 to 100 nm Co thick layers) with designed symmetries. This technique constitutes a non-expensive method for massive mold production and pattern generation avoiding standard lithographical techniques. In addition, it overcomes current challenges of the two-stage electrochemical porous anodic alumina templates: (i) allowing the patterning of large areas with high ordering and/or complex antidot geometries, and (ii) being less-time consuming.

Development and Characterization of Magnetic SARS-CoV-2 Peptide-Imprinted Polymers.

The development of new methods for the rapid, sensitive, and selective detection of SARS-CoV-2 is a key factor in overcoming the global pandemic that we have been facing for over a year. In this work, we focused on the preparation of magnetic molecularly imprinted polymers (MMIPs) based on the self-polymerization of dopamine at the surface of magnetic nanoparticles (MNPs). Instead of using the whole SARS-CoV-2 virion as a template, a peptide of the viral spike protein, which is present at the viral surface, was innovatively used for the imprinting step. Thus, problems associated with the infectious nature of the virus along with its potential instability when used as a template and under the polymerization conditions were avoided. Dopamine was selected as a functional monomer following a rational computational screening approach that revealed not only a high binding energy of the dopamine–peptide complex but also multi-point interactions across the entire peptide template surface as opposed to other monomers with similar binding affinity. Moreover, variables affecting the imprinting efficiency including polymerization time and amount of peptide and dopamine were experimentally evaluated. Finally, the selectivity of the prepared MMIPs vs. other peptide sequences (i.e., from Zika virus) was evaluated, demonstrating that the developed MMIPs were only specific for the target SARS-CoV-2 peptide.

33‐6: Roll‐To‐Plate Nano‐Imprint Lithography for High‐Volume Production of AR Glasses: Equipment, Materials, and Processes

Today, the prevailing AR‐glasses displays are using waveguides. The light in‐ & outcoupling structures that these glasses contain can be made by UV nanoimprint lithography. Nanoimprint lithography tools have typical cycle times of around 40 imprints per hour, roughly resulting in 8M eyepieces per year made on 300mm wafers. To serve the projected mass market adoption, hundreds of imprint tools will be needed. An important question is how the eyepieces can be made more efficiently and cost‐effectively. The Morphotonics' Roll‐to‐Plate imprint technology enables high volume production, having the opportunity for large‐area imprinting, manufacturing multiple products in a single imprint step.

Upgrading of methylammonium lead halide perovskite layers by thermal imprint

The manufacturing of devices from methylammonium-based perovskites asks for reliable and scalable processing. As solvent engineering is not the option of choice to obtain homogeneous layers on large areas, our idea is to ‘upgrade’ a non-perfect pristine layer by recrystallization in a thermal imprint step (called ‘planar hot pressing’) and thus to reduce the demands on the layer formation itself. Recently, imprint has proven both its capability to improve the crystal size of perovskite layers and its usability for large area manufacturing. We start with methylammonium lead bromide layers obtained from a conventional solution-based process. Acetate is used as a competitive lead source; even under perfect conditions the resulting perovskite layer then will contain side-products due to layer formation besides the desired perovskite. Based on the physical properties of the materials involved we discuss the impact of the temperature on the status of the layer both during soft-bake and during thermal imprint. By using a special imprint technique called ‘hot loading’ we are able to visualize the upgrade of the layer with time, namely a growth of the grains and an accumulation of the side-products at the grain boundaries. By means of a subsequent vacuum exposition we reveal the presence of non-perovskite components with a simple inspection of the morphology of the layer; all experiments are supported by X-ray and electron diffraction measurements. Besides degradation, we discuss recrystallization and propose post-crystallization to explain the experimental results. This physical approach towards perovskite layers with large grains by post-processing is a key step towards large-area preparation of high-quality layers for device manufacturing.

Assessment of patterned membrane in a tilted panel filtration system for fouling control in activated sludge filtration

Membrane bioreactor (MBR) is a combination between advanced membrane filtration system and activated sludge biological treatment for sewage effluents treatment. Despite demonstrating a remarkable advantage over the conventional activated sludge process, MBR is still limited by the occurrence of membrane fouling problem, which reduces the performance and lifespan of the membrane causing higher maintenance and operation costs. Finding sustainable membrane fouling mitigation strategies has become the main concern in MBR operation. Hence, air bubbling method had been proven as one of the membrane fouling mitigation strategies. Ineffective air bubbling contributes to higher energy consumption for MBR operation. It must be pumped at high rates as low rates air bubbles only show poor contacts with the membrane surface in which limits its efficacy to scour-off the foulant. In this study, the performance of a patterned membrane in a tilted panel system was systematically evaluated to enhance air bubble effectiveness for membrane fouling control in activated sludge filtration. The patterned surface topography in a combination of the tilted panel is expected to enhance air bubbles contacts and increase their fouling control roles. An imprinting step was included into the fabrication procedure in order to create membrane with patterned surface. Results showed that the patterned outperform flat membrane in both tilted and vertical systems. Such an advantage can be ascribed by both the difference in membrane properties (effective surface area and pore size) and the nature of the surface (flat vs patterned). The patterned membrane yields higher permeance in the tilted panel over the vertical one in all tests, being the highest at shortest filtration/relaxation cycle of 5 min, shortest switching period of 2.5 min and highest aeration rate of 1.5 L/min corresponding to permeances of 465 vs 409, 369 vs 318 and 447 vs 381 L/(m2h.bar), respectively. However, since operation with tilting only allows one-sided membrane, the patterned membrane offers better panel productivity when operated in a vertical panel. Operation with switching (intermittent aeration) only offers the slight advantage of panel productivity over the vertical one (546-738 vs 440-632 L/m2h.bar).

Highly Selective Copper Ion Imprinted Clay/Polymer Nanocomposites Prepared by Visible Light Initiated Radical Photopolymerization.

There is an urgent demand worldwide for the development of highly selective adsorbents and sensors of heavy metal ions and other organic pollutants. Within these environmental and public health frameworks, we are combining the salient features of clays and chelatant polymers to design selective metal ion adsorbents. Towards this end, the ion imprinting approach has been used to develop a novel nanohybrid material for the selective separation of Cu2+ ions in an aqueous solution. The Cu2+-imprinted polymer/montmorillonite (IIP/Mt) and non-imprinted polymer/montmorillonite (NIP/Mt) nanocomposites were prepared by a radical photopolymerization process in visible light. The ion imprinting step was indeed important as the recognition of copper ions by IIP/Mt was significantly superior to that of NIP/Mt, i.e., the reference nanocomposite synthesized in the same way but in the absence of Cu2+ ions. The adsorption process as batch study was investigated under the experimental condition affecting same parameters such as contact time, concentration of metal ions, and pH. The adsorption capacity of Cu2+ ions is maximized at pH 5. Removal of Cu2+ ion achieved equilibrium within 15 min; the results obtained were found to be fitted by the pseudo-second-order kinetics model. The equilibrium process was well described by the Langmuir isothermal model and the maximum adsorption capacity was found to be 23.6 mg/g. This is the first report on the design of imprinted polymer nanocomposites using Type II radical initiators under visible light in the presence of clay intercalated with hydrogen donor diazonium. The method is original, simple and efficient; it opens up new horizons in the general domain of clay/polymer nanocomposites.

Sculpturing wafer-scale nanofluidic devices for DNA single molecule analysis.

We present micro- and nanofluidic devices with 3D structures and nanochannels with multiple depths for the analysis of single molecules of DNA. Interfacing the nanochannels with graded and 3D inlets allows the improvement of the flow and controls not only the translocation speed of the DNA but also its conformation inside the nanochannels. The complex, multilevel, multiscale fluidic circuits are patterned in a simple, two-minute imprinting step. The stamp, the key of the technology, is directly milled by focused ion beam, which allows patterning nanochannels with different cross sections and depths, together with 3D transient inlets, all at once. Having such a variety of structures integrated in the same sample allows studying, optimizing and directly comparing their effect on the DNA flow. Here, DNA translocation is studied in long (160 µm) and short (5-40 µm) nanochannels. We study the homogeneity of the stretched molecules in long, meander nanochannels made with this technology. In addition, we analyze the effect of the different types of inlet structures interfacing short nanochannels. We observe pre-stretching and an optimal flow, and no hairpin formation, when the inlets have gradually decreasing widths and depths. In contrast, when the nanochannels are faced with an abrupt transition, we observe clogging and hairpin formation. In addition, 3D inlets strongly decrease the DNA molecules' speed before they enter the nanochannels, and help capturing more DNA molecules. The robustness and versatility of this technology and DNA testing results evidence the potential of imprinted devices in biomedical applications as low cost, disposable lab-on-a-chip devices.

Fabrication of Line & Space Structure and Wiring on 3D Surface Features with Imprinting Process

In recent years, electronic devices made by polymers with wiring materials are widely used, such as FPC (Flexible Printed Circuit) in a PC (Personal Computer), and smartphones. Fine Pitch Wiring technologies on 3D objects are needed for coming IoT(Internet of Things) trends. Therefore, in this research, we conducted a fundamental study of the low-cost replication process with etching less wiring method in order to replicate microstructure on the curved polymer surfaces by using the hybrid nanoimprint technology. The first imprinting step was carried out to produce the intermediate mold on COP (Cyclic Olefin Polymer) surface by thermal nanoimprint process. The aluminum mold with a concavo-convex structure called L/S (Line & Space; concave width of 500 µm, concave depth of 100 µm) was used. The obtained intermediate structure was coated with UV (Ultraviolet) curable resin and it was applied to the 3D substrate (curved surface region: lens shape) having planar region and curved surface region as shown in Fig. 1. In this step, UV imprinting was applied with the pressure of 5 MPa and UV irradiation time of 300 seconds to transfer the L/S structure to the 3D substrate. Thereafter, the silver nanoink was dropped and filled in the concave portion of the L/S structure using a dispenser and sintered at 160 oC for 1 hour. SEM (Scanning Electron Microscope) image revealed that the 3D structure can be precisely transferred on the curved surface by using this hybrid nanoimprint technology (See Fig. 2). In Fig. 3, the transfer rates in the planar region (flat) and curved region were 100 and 60%, respectively. It is considered that the liquid UV curable resin may flow downward from the upper part to the lower part along the inclination of the substrate during the crimping and curing steps, resulting in the decrease in filling amount from the intermediate mold structure. The L/S patterned wired with silver nanoink is shown in Fig. 4. This result proposes that the hybrid nanoimprint technology is considered to be an effective method for the replication of wiring on the curved surface. Figure 1

Coherent control of flexural vibrations in dual-nanoweb fibers using phase-modulated two-frequency light

Coherent control of the resonant response in spatially extended optomechanical structures is complicated by the fact that the optical drive is affected by the back-action from the generated phonons. Here we report a new approach to coherent control based on stimulated Raman-like scattering, in which the optical pressure can remain unaffected by the induced vibrations even in the regime of strong optomechanical interactions. We demonstrate experimentally coherent control of flexural vibrations simultaneously along the whole length of a dual-nanoweb fiber, by imprinting steps in the relative phase between the components of a two-frequency pump signal,the beat frequency being chosen to match a flexural resonance. Furthermore, sequential switching of the relative phase at time intervals shorter than the lifetime of the vibrations reduces their amplitude to a constant value that is fully adjustable by tuning the phase-modulation depth and switching rate. The results may trigger new developments in silicon photonics, since such coherent control uniquely decouples the amplitude of optomechanical oscillations from power-dependent thermal effects and nonlinear optical loss.

Low reflection Fresnel lenses via double imprint combined with vacuum-UV surface hardening

To improve the optical performance of Fresnel lenses, a technique for preparing them with antireflective structures of the moth-eye type is developed. Masters featuring such hierarchical structures are prepared in SU-8, a negative tone photoresist, by two consecutive thermal imprint steps. The moth-eye structures imprinted first are vacuum ultraviolet-treated at 172 nm to provide a surface-near the cross-linked layer that remains stable during the second imprint of the 100 μm sized Fresnel structures. A successful combination of both structure types is possible at an imprint temperature as low as 45 °C. This can be understood on the basis of the typical exposure and the crosslinking behavior of a chemically amplified negative tone resist like SU-8. The masters prepared in this way will be subjected to extrusion coating, the process of choice for future large area preparation of such structures in a single step.

Thermal nanoimprint to improve the morphology of MAPbX3 (MA = methylammonium, X = I or Br)

Perovskites have high potential for future electronic devices, in particular, in the field of opto-electronics. However, the electronic and optic properties of these materials highly depend on the morphology and thus on the preparation; in particular, highly crystalline layers with large crystals and without pinholes are required. Here, nanoimprint is used to improve the morphology of such layers in a thermal imprint step. Two types of material are investigated, MAPbI3 and MAPbBr3, with MA being methylammonium, CH3NH3+. The perovskite layers are prepared from solution, and the crystal size of the domains is substantially increased by imprinting them at temperatures of 100–150 °C. Although imprint is performed under atmospheric conditions which, in general, enhances the degradation, the stamp that covers the layer under elevated temperature is able to protect the perovskite largely from decomposition. Comparing imprinting experiments with pure annealing at a similar temperature and time proves this. Furthermore, imprint is capable of patterning the surface of the perovskite layers; lines and spaces of 150 nm width were reproducibly obtained under imprint at 150 °C. Moreover, a through-layer patterning is possible by using the partial cavity filling approach. Although not yet optimized, this simple way to define isolated perovskite patterns within a layer simply by thermal nanoimprint is of impact for the preparation of devices, as patterning of perovskite layers by conventional techniques is limited.

Postpatterned Electrodes for Flexible Node‐Type Lithium‐Ion Batteries

A flexible node-type lithium-ion battery (LIB) with novel postpatterned electrodes is developed via a simple, one-step process involving an imprinting step of a conventional electrode in the presence of a flattened mesh template. The node-type LIBs containing segmented parts for energy storage and mechanical deformation demonstrate a good cycle stability.

Modeling RAFT Gelation and Grafting of Polymer Brushes for the Production of Molecularly Imprinted Functional Particles

SummaryRAFT precipitation polymerization was here used for the molecular imprinting of 5‐fluorouracil (a drug used in cancer treatment) followed by grafting of polymer functional brushes in the particles surface. Materials combining high molecular recognition capabilities and stimulation triggered by changes in the surrounding environment (e.g. pH/temperature) have thus been sought. Mathematical modeling of the RAFT copolymerization of vinyl/divinyl monomers was used to describe the crosslinking process involved in the molecular imprinting step. The size of the grafted polymer functional brushes was estimated using models for the calculation of molecular weight distribution in RAFT homopolymerization. One of the goals of this study consists in the development of polymer reaction engineering tools for the design of synthesis conditions leading to tailored molecularly imprinted particles with responsive features. A first sketch of the two steps involved in the production of the MIP responsive particles is here presented. However, the need for new kinetic studies accounting for specificities of the molecular imprinting and surface extension processes (e.g. presence of template during molecular imprinting and solvent effects) is here identified. Measurements of the dynamics of gelation and brushes growth are also needed to perform model validation. Improvement on the modeling of RAFT gelation with heterogeneous conditions avoiding some simplifications and the amelioration of the numerical efficiency in the calculation of the MWD of RAFT polymers are other issues to be addressed in future works.

Molecularly imprinted PVC beads for the recognition of proteins

ABSTRACTUltrathin films of molecularly imprinted polymer (MIP) were prepared by photoiniferter on PVC beads for the selective uptake of lysozyme, taken as a model protein. Acrylamide was selected as the functional monomer and N,N‐methylenebisacrylamide as the crosslinking agent. The copolymerization process was confined to the surface of the PVC beads grafted with diethyldithiocarbamate iniferter initiator in the presence of lysozyme. After extraction of lysozyme from the shell of the PVC‐MIP beads, the latter were then used as artificial receptors for the rebinding of lysozyme. The sequential steps of the modification of PVC beads were monitored by XPS, infrared and Raman spectroscopies. The imprinting step was found to be essential as the PVC‐MIP beads could recognize lysozyme but not the non‐imprinted beads (PVC‐NIP). The binding properties of PVC‐MIP beads were determined using UV spectroscopy from adsorption isotherms of lysozyme, cytochrome, and myoglobin. The imprinted beads were found to be highly selective toward lysozyme over the competitive proteins. This work shows the interest of photoiniferter as an efficient mean for the design of molecularly imprinted polymer beads for rapid, selective removal of proteins. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43694.

Reducing the risk of failure with flexible composite stamps

Flexible composite stamps are interesting for thermal nanoimprint as well as for UV-assisted nanoimprint as they provide conformal contact to a substrate without the need of applying high pressure. However, they are also prone to bending when handled during mounting, contact establishment and separation after the imprint step. As they consist of different materials bonded together, internal stresses during bending may lead to stamp failure, typically rupture of the top layer. In order to minimize the risk of failure, the stress within the top layer must not go beyond the material-inherent tensile strength, which, for materials typically used to prepare the top layer, often is not available and may depend on the layer thickness and the specific preparation of the composite stamp. Minimization of the maximum bending stress is therefore required to reduce the risk of failure with flexible composite stamps. Such minimization is obtained easily by controlling the position of the so-called ‘neutral plane’. Stresses are highly reduced when the neutral plane is located near the interface between top layer and backplane. We address this issue experimentally as well as theoretically. Diligent choice of the layer thicknesses in combination with the modulus of the materials involved is required to implement this concept. The results obtained confirm the suitability of ‘neutral plane management’ for minimizing the risk of failure with flexible composite stamps.

Imprint Desorption Electrospray Ionization Mass Spectrometry Imaging for Monitoring Secondary Metabolites Production during Antagonistic Interaction of Fungi.

Direct analysis of microbial cocultures grown on agar media by desorption electrospray ionization mass spectrometry (DESI-MS) is quite challenging. Due to the high gas pressure upon impact with the surface, the desorption mechanism does not allow direct imaging of soft or irregular surfaces. The divots in the agar, created by the high-pressure gas and spray, dramatically change the geometry of the system decreasing the intensity of the signal. In order to overcome this limitation, an imprinting step, in which the chemicals are initially transferred to flat hard surfaces, was coupled to DESI-MS and applied for the first time to fungal cocultures. Note that fungal cocultures are often disadvantageous in direct imaging mass spectrometry. Agar plates of fungi present a complex topography due to the simultaneous presence of dynamic mycelia and spores. One of the most devastating diseases of cocoa trees is caused by fungal phytopathogen Moniliophthora roreri. Strategies for pest management include the application of endophytic fungi, such as Trichoderma harzianum, that act as biocontrol agents by antagonizing M. roreri. However, the complex chemical communication underlying the basis for this phytopathogen-dependent biocontrol is still unknown. In this study, we investigated the metabolic exchange that takes place during the antagonistic interaction between M. roreri and T. harzianum. Using imprint-DESI-MS imaging we annotated the secondary metabolites released when T. harzianum and M. roreri were cultured in isolation and compared these to those produced after 3 weeks of coculture. We identified and localized four phytopathogen-dependent secondary metabolites, including T39 butenolide, harzianolide, and sorbicillinol. In order to verify the reliability of the imprint-DESI-MS imaging data and evaluate the capability of tape imprints to extract fungal metabolites while maintaining their localization, six representative plugs along the entire M. roreri/T. harzianum coculture plate were removed, weighed, extracted, and analyzed by liquid chromatography-high-resolution mass spectrometry (LC-HRMS). Our results not only provide a better understanding of M. roreri-dependent metabolic induction in T. harzianum, but may seed novel directions for the advancement of phytopathogen-dependent biocontrol, including the generation of optimized Trichoderma strains against M. roreri, new biopesticides, and biofertilizers.

임프린트 공정을 이용한 연성동박적층필름(FCCL)의 마이크로 패턴 제작

In this paper, we designed and fabricated low cost imprinting process for micro patterning on FCCL (flexible copper clad laminate). Compared to conventional imprinting process, developed fabrication method processing imprint and UV photolithography step simultaneously and it does not require resin etch process and it can also reduce the fabrication cost and processing time. Based on proposed method, patterns with linewidth are fabricated on FCCL. Compared to conventional methods using LDI (laser direct imaging) equipment that showed minimum line with , proposed method shows comparable pattern resolution with very competitive price and shorter processing time. In terms of mass production, it can be applied to fabrication of large-area low cost applications including FPCB.

An innovative approach to prepare hypericin molecularly imprinted pearls using a “phyto-template”

In this paper, an innovative method that uses hypericin “phyto-template” molecules is being applied herein for the first time to produce molecularly imprinted polymer (MIP) pearls able to selectively retain hypericin from Hypericum Perforatum L primary extracts. For this purpose, the wet phase inversion method was preferred for preparing the hypericin-MIP pearls for several reasons referring to economical benefits but also due to the fact that hypericin “phyto-template” molecules can be generated along with the phase inversion of the copolymer. Practically, the precursor poly(acrylonitrile–co–methacrylic acid) solution was mixed with a purified and concentrated naphtodianthrone phyto-extract (consisting only of hypericin and pseudo-hypericin). In the subsequent phase inversion step hypericin was trapped in the copolymer droplets, as a result to its poor solubility in the inversion water bath, and further served as “phyto-template” in the imprinting step. This in situ repartition of hypericin and pseudo-hypericin was sustained by HPLC-DAD chromatograms which recorded only the presence of hypericin during the extraction stage of imprinted pearls. Batch rebinding measurements, all together, validated the efficiency of this innovative imprinting procedure. The hypericin rebinding of imprinted pearls was quantitative (up to 318µg/L) and approximately 5 times more specific relative to the blank pearls. Competitive re-binding revealed a more selective behaviour of imprinted pearls for hypericin when the up-take was measured against pseudohypericin (selectivity coefficient above 4.50).