Planar Scaffold Research Articles

Selective Metal-Free CO2 Photoreduction in Water Using Porous Nanostructures with Internal Molecular Free Volume.

The conversion of CO2 to a sole carbonaceous product using photocatalysis is a sustainable solution for alleviating the increasing levels of CO2 emissions and reducing our dependence on nonrenewable resources such as fossil fuels. However, developing a photoactive, metal-free catalyst that is highly selective and efficient in the CO2 reduction reaction (CO2RR) without the need for sacrificial agents, cocatalysts, and photosensitizers is challenging. Furthermore, due to the poor solubility of CO2 in water and the kinetically and thermodynamically favored hydrogen evolution reaction (HER), designing a highly selective photocatalyst is challenging. Here, we propose a molecular engineering approach to design a photoactive polymer with high CO2 permeability and low water diffusivity, promoting the mass transfer of CO2 while suppressing HER. We have incorporated a contorted triptycene scaffold with "internal molecular free volume (IMFV)" to enhance gas permeability to the active site by creating molecular channels through the inefficient packing of polymer chains. Additionally, we introduced a pyrene moiety to promote visible-light harvesting capability and charge separation. By leveraging these qualities, the polymer exhibited a high CO generation rate of 77.8 μmol g-1 h-1, with a high selectivity of ∼98% and good recyclability. The importance of IMFV was highlighted by replacing the contorted triptycene unit with a planar scaffold, which led to a selectivity reversal favoring HER over CO2RR in water. In situ electron paramagnetic resonance (EPR), time-resolved photoluminescence spectroscopy (TRPL), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) techniques, further supported by theoretical calculations, were employed to enlighten the mechanistic insight for metal-free CO2 reduction to exclusively CO in water.

Flavonoids as Promising Multitarget Agents in Alzheimer’s Disease Therapy

The increase in the occurrence of the multifactorial Alzheimer’s disease (AD) demands an urgent effort towards the development of effective anti-AD agents, such as the multitarget-directed ligands (MTDLs). In fact, AD is a genetic and an environmental disease, involving a diversity of etiopathogenic processes, and there is not yet a successful AD treatment. The major AD clinical indications (CIs) are extracellular amyloid plaques, intracellular neurofibrillary tangles (NFTs), abnormal inflammatory response, and neuron apoptosis and death caused by oxidative stress. The discovery of neuroprotective natural products, presenting good oral bioavailability, ability to cross the blood-brain barrier (BBB) and safety profile, is indeed a necessity, and some flavonoids are in clinical trials for AD treatment. In this review, the several flavonoids from natural sources that have shown activity on mechanisms associated with AD are presented. Although several reviews have been presented in the last few years, the main objective of this review is to recognize and discuss, for each CI, the scaffolds leading to the highest activity and so to attempt to achieve molecules targeting more than one CI, the MTDLs, which are potential leads for AD treatment. In conclusion, the most active flavonoids against several CIs of AD are flavanols and flavonols, which have a planar scaffold and structures presenting hydroxy groups at C5 and C7 on ring A and at C4′ of ring B. Thus, molecules linking flavanols to flavonols, with hydroxy groups at C5 and C7 on ring A and at C4′ of ring B, are also promising against CIs of AD and potential anti-AD agents.

Determine ligand binding kinetics to a membrane protein using Brownian dynamics simulation.

Molecular diffusion controls the kinetics of protein-ligand binding in various biological processes. Determining the reaction rate between proteins and ligands is crucial in understanding these processes and in designing novel strategies to enhance or disrupt binding. Most previous studies focus on ligand diffusion in a three-dimensional bulk space. However, with the rapid growth of membrane protein research, a comprehensive understanding of molecular diffusion toward membrane-bound organelles or biomolecules tethered on a planar scaffold is essential. In this work, we developed a method that can predict the association rate constant of a ligand-membrane protein binding reaction according to trajectories from Brownian dynamics simulations. Our approach can be divided into two parts: 1) analytically determine the ligand association rate to a hemispherical region surrounding the membrane protein, and 2) compute the protein-ligand binding probability by Brownian dynamics simulations. We applied the method to calculate the reaction rate of biological systems with different charges. We found that the presence of a membrane does affect ligand diffusion, especially when the ligand moves close to the membrane. The critical aspects of surface diffusion, such as the forbidden zone, edge effect, and simulation criteria, were also discussed. Although the current development is based on a coarse-grained model, our method is still useful in understanding the binding kinetics of a highly complicated biological system.

Site-selective surface enhanced Raman scattering study of ligand exchange reactions on aggregated Ag nanocubes

Surface modification of ligand protected nanoparticles (NPs) can be driven by ligand exchange reactions (LER). Little is known about the mechanism of this reaction, especially when the particles are not spherical. Here, we use the intrinsic hot spots generated on the corners/edges of 40 nm silver nanocubes (AgNCs) and the extrinsic hot spots generated by the aggregation of AgNCs to obtain strong enhancements in surface enhanced Raman scattering (SERS) to monitor the displacement of poly(vinylpyrrolidone) with either a hydrophilic (sodium 11-mercapto-1-undecanesulfonate, MUS) or a hydrophobic ligand (1-octanethiol, OT). By focusing on the ratio (R) between the trans and gauche bands of the alkyl backbones of the ligands as an indicator of local order, we find that the LER proceeds in two different ways, particularly regarding the arrangement of the incoming ligands. In the case of OT, R becomes large almost immediately and stays high throughout the reaction, while in the case of MUS, R starts low and increases only towards the end of the reaction. We interpret the first behaviour as a LER that proceeds via the formation of densely packed and ordered OT islands, practically from the beginning of the reaction, that gradually grow over time. In the case of MUS, our interpretation is that molecules randomly deposit on the surface and form denser monolayer regions as the LER proceeds. Both monolayers evolved towards a homogeneous topography that corresponds to an ordered state (near all-trans) in the later stages (R≫1). Such mechanisms may be extended to the cube faces (as planar scaffolds) since clear differences in the topographic profile were found by Atomic Force Microscopy (AFM).

Styrylbenzene organogels and how the cyano groups tune the aggregation-induced emission

Fluorescence switching of π-gelators has emerged as a field of great interest because of their promising applications. In this work we present two families of luminogens based on bis(styrylbenzene) and bis(α-cyanostyryl)benzene that incorporate acetamido groups and hydrocarbon chains to induce gelation. The presence of cyano groups in the molecular skeleton produces Aggregation Induced Emission (AIE) from solution to the gel while their absence gives the Aggregation Caused Quenching (ACQ) effect. Density Functional Theory calculations were performed in order to shed light on the origin of these opposite phenomena. The bis(styrylbenzene) compound showed a high quantum yield in solution and nearly planar structure was theoretically predicted. A significant drop in the quantum yield was observed after gelation, probably due to the π-π intermolecular interactions favoured by the planar scaffold. In contrast, the more twisted structure predicted for the cyano compounds could prevent such π-π intermolecular interactions and this would favour fluorescence emission. In addition, the twisted molecular structure predicted for the cyano derivative could induce Z/E photosiomerisation that suppresses the emission in solution. However, the framework of intermolecular contacts that arises during the gelation process could restrict torsional motions to the detriment of photoisomerization, thus resulting in AIE-active compounds. Furthermore, the reorganisation energy and Huang–Rhys factors associated with the non-radiative relaxation were calculated. The highest values were found for some vibrational modes in the low energy region in the case of the cyano compound and these could contribute to the non-radiative relaxation in solution. These intramolecular motions could be blocked in the gel, thus increasing the fluorescence emission. The introduction of cyano groups in the carbon scaffold could therefore provide a strategy for the rational design of new active AIE organogels.

Partially Differentiated Neuroretinal Cells Promote Maturation of the Retinal Pigment Epithelium.

PurposeMany studies have demonstrated the ability of the retinal pigment epithelium (RPE) to foster the maturation of the developing retina. Few studies have examined the reciprocal effects of developing retina on the RPE.MethodsRPE isolated from human fetal RPE or differentiated from human stem cells was cultured on Transwell filter inserts. Retinal progenitor cells (RPCs) were differentiated from human stem cells and cultured on a planar scaffold composed of gelatin, chondroitin sulfate, hyaluronic acid, and laminin-521. Cultures were analyzed by quantitative RT-PCR, immunofluorescence, immunoblotting, and transepithelial electrical resistance (TER).ResultsRPCs initially differentiated into several retina-like cell types that segregated from one another and formed loosely organized layers or zones. With time, the presumptive photoreceptor and ganglion cell layers persisted, but the intervening zone became dominated by cells that expressed glial markers with no evidence of bipolar cells or interneurons. Co-culture of this underdeveloped retinoid with the RPE resulted in a thickened layer of recoverin-positive cells but did not prevent the loss of interneuron markers in the intervening zone. Although photoreceptor inner and outer segments were not observed, immunoblots revealed that co-culture increased expression of rhodopsin and red/green opsin. Co-culture of the RPE with this underdeveloped retinal culture increased the TER of the RPE and the expression of RPE signature genes.ConclusionsThese studies indicated that an immature neurosensory retina can foster maturation of the RPE; however, the ability of RPE alone to foster maturation of the neurosensory retina is limited.

Fabrication of polylactic acid (PLA)-based porous scaffold through the combination of traditional bio-fabrication and 3D printing technology for bone regeneration

Artificial bone grafts possess the advantages of good biodegradability, customizable dimensions, and sufficient mechanical properties, which can promote cell proliferation and differentiation in bone tissue regeneration. 3D printing is a delicate approach that endows the scaffolds with excellent controllability and repeatability when compared with conventional bio-fabrication methods. However, the limitation of printing resolution somehow makes it difficult to prepare bone defect substitution with high porosity and hierarchical construct. In this study, we utilized polylactic acid (PLA) as printing materials and developed a smart strategy to combine 3D printing technology with bio-fabrication methods. A porous planar scaffold was printed and then rolled up into a spiral structure with adjustable pore size and porosity. The topographic features and morphology of the artificial scaffolds were examined through stereomicroscope and SEM, respectively. The porous spiral scaffold presented good mechanical properties in a set of mechanical testing. Later, the human fetal osteoblasts (hFOB) were cultured on the porous spiral scaffold and its control groups for a total of 28 days. The MTS analysis, alkaline phosphatase (ALP) assay, and alizarin red S (ARS) staining were used to analyze the cell proliferation, osteogenic differentiation, and mineral deposition after a certain period of time. The results indicated that compared with the other two scaffolds, the porous spiral scaffold with larger surface area and better interconnections between internal porous networks could significantly improve the spatial cell compartment and promote cell growth and differentiation. The porous spiral scaffold may see versatile applications in large-volume bone defects regeneration.

Better together: Joint consideration of anatomy and morphology illuminates the architecture and life history of the Carboniferous arborescent lycopsid Paralycopodites

AbstractParalycopodites Morey & Morey, a Carboniferous‐age arboreous lycopsid that grew in the tropical wetlands of Pangea, is the phylogenetically basalmost member of the Carboniferous stigmarian lycopsids to be conceptually reconstructed. We update its description through reciprocal illumination between anatomy (coal‐balls) and gross morphology (adpressions). Revised assessment of its architecture and development shows that the determinate, columnar main trunk eventually underwent several isotomous divisions to form a crown. Two opposite rows of closely‐spaced, compact lateral branches were initiated anisotomously throughout the trunk and crown, each branch further undergoing multiple anisotomous divisions to form an apparently planar scaffold for numerous bisporangiate cones. We infer that branches were initially emitted near‐vertically, but rapidly moved to a more horizontal position; they were abscised after the cones had matured but before the continuous phellogen had produced a centripetal periderm. Leaves were not abscised, though anatomy and morphology both suggest a photosynthetic economy that was localized within the plant body. Character content and clarity of interpretation make Paralycopodites the preferred name for the reconstructed plant rather than Anabathra, Ulodendron, or Bergeria. Phylogenetic analysis of rhizomorphic lycopsids based on a reduced spectrum of features observable in adpression returns the same topology as that based on a full matrix combining both anatomical and externally visible traits, permitting adpression fossils to be assigned to anatomically‐circumscribed genera rather than perpetuating an unnecessary parallel taxonomy.

Discovery of Diphenoxy Derivatives with Flexible Linkers as Ligands for β-Amyloid Plaques.

The highly rigid and planar scaffolds with π-conjugated systems have been widely considered to be indispensable for β-amyloid (Aβ) binding ligands. In this study, a library of diphenoxy compounds with different types of more flexible linkers as Aβ ligands were synthesized and evaluated. Most of them displayed good affinity (Ki < 100 nM) for Aβ1-42 aggregates, and some ligands even showed values of Ki less than 10 nM. Structure-activity relationship analysis revealed that modification on the linkers or substituents tolerated great flexibility, which challenged the long-held belief that rigid and planar structures are exclusively favored for Aβ binding. Three ligands were labeled by iodine-125, and they exhibited good properties in vitro and in vivo, which further supported that this flexible scaffold was potential and promising for the development of Aβ imaging agents.

Novel double-layered planar scaffold combining electrospun PCL fibers and PVA hydrogels with high shape integrity and water stability

Novel double-layered materials with different properties of each side were prepared via needleless electrospinning and compared in terms of morphology, wettability, adhesion and proliferation of mouse fibroblasts. The materials consist of hydrophilic poly(vinyl alcohol) fibers with low (PVA_L) or high (PVA_H) degree of hydrolysis, and hydrophobic poly(ε-caprolactone) (PCL) fibrous layer. Although the PVA_L fibers were fully dissolved following a water exposure, the shape of the scaffold was maintained due to water stable PCL layer. Exposing PVA_H based fibrous layer to water created a hydrogel-like structure with shape defined by the PCL layer. According to the MTT assay, the mouse fibroblasts seeded on the scaffold exhibited the greatest proliferative activity on the PCL fibers. These double-layered scaffolds with different features on each side are very promising for many novel medical applications such as wound dressing or abdominal adhesion prevention.

Enantioselective Catalytic Transformations of Barbituric Acid Derivatives

Since the beginning of the 20th century, numerous research efforts made elegant use of barbituric acid derivatives as building blocks for the elaboration of more complex and useful molecules in the field of pharmaceutical chemistry and material sciences. However, the construction of chiral scaffolds by the catalytic enantioselective transformation of barbituric acid and derivatives has only emerged recently. The specific properties of these rather planar scaffolds, which also encompass either a high Brønsted acidity concerning the native barbituric acid or the marked electrophilic character of alkylidene barbituric acids, required specific developments to achieve efficient asymmetric processes. This review covers the enantioselective catalytic reactions developed for barbituric acid platforms using an organocatalytic and metal-based enantioselective sequences. These achievements currently allow several unique addition and annulation reactions towards the construction of high valued chiral heterocycles from barbituric acid derivatives along with innovative enantioselective developments.

Indenocinnoline derivatives as G-quadruplex binders, topoisomerase IIα inhibitors and antiproliferative agents

DNA intercalating agents are a consolidated therapeutic option in the treatment of tumor diseases. Starting from previous findings in the antiproliferative efficacy of a series of indeno[1,2-c]cinnoline-11-one derivatives, we performed a suitable decoration of this scaffold by means of a simple and straightforward chemistry, aiming to a) enlarge the planar core to a pentacyclic benzo[h]indeno[1,2-c]cinnoline-13-one and b) introduce a basic head tethered through a simple polymethylene chain. In fluorescence melting and fluorescence intercalator displacement assays, these new compounds displayed fair to very good intercalating properties on different nucleic acid strands, with preference for G-quadruplex sequences. Inhibition of human topoisomerase IIα and antiproliferative assays on HeLa and MCF7 tumor cell lines outlined a multitarget antiproliferative profile for tetracyclic 6 and pentacyclic derivative 20, both bearing a N,N-dimethylamine as the protonatable moiety. Particularly, compound 6 displayed a very potent inhibition of tumor cell proliferation, while 20 returned the highest thermal stabilization in melting experiments. In summary, these results outlined a potential of such highly planar scaffolds for nucleic acid binding and antiproliferative effects.

Biomaterials patterned with discontinuous microwalls for vascular smooth muscle cell culture: biodegradable small diameter vascular grafts and stable cell culture substrates

The medial layer of small diameter blood vessels contains circumferentially aligned vascular smooth muscle cells (vSMC) that possess contractile phenotype. In tissue-engineered constructs, these cellular characteristics are usually achieved by seeding planar scaffolds with vSMC, rolling the cell-laden scaffold into a tubular structure, and maturing the construct in a pulsatile bioreactor, a lengthy process that can take up to two months. During the maturation phase, the cells circumferentially orient, their contractile protein expression increases, and they obtain a contractile phenotype. Generating cell culture platforms that enable the rapid production of directionally oriented vSMC with increased contractile protein expression would be a major step forward for blood vessel tissue engineering and would greatly facilitate the in vitro study of vSMC biology. Previously, we developed a micropatterned cell culture surface that promotes orientation and contractile protein expression of vSMC. Herein, we explore two potential applications of this technology. First, we fabricate tubular and biodegradable scaffolds that possess the micropatterning on their exterior surface. When vSMC are seeded on these scaffolds, they initially proliferate in order to fill the microchannels and as confluence is reached the cells align in the direction of the micropatterning resulting in a biodegradable scaffold that is inhabited by circumferentially aligned vSMC within a week. Second, we illustrate that we can generate biostable cell culture surfaces that allow the in vitro study of the cells in a more contractile state. Specifically, we explore contractile protein expression of cells cultured on the micropatterned surfaces with the addition of soluble transforming growth factor beta one (TGFβ1).

Optically Pure Diphenoxy Derivatives as More Flexible Probes for β-Amyloid Plaques.

The highly rigid and planar scaffold with π-conjugated systems has been widely considered to be indispensable for Aβ binding probes. However, the flexible benzyloxybenzene derivative [(125)I]BOB-4 represents an excellent lead candidate for targeting Aβ in AD brains. Based on that, we designed two pairs of more flexible and optically pure diphenoxy derivatives with a chiral center as novel Aβ probes. These compounds possessed high affinity (Ki = 15.8-45.0 nM) for Aβ1-42 aggregates, and (R)-enantiomers showed slightly better binding ability than (S)-enantiomers. In addition, the competition binding assay implied that the optically pure diphenoxy derivatives with more flexible geometry shared the same binding site as IMPY, a classical rigid and planar Aβ probe. For (125)I-radiolabeled enantiomers, (S)-[(125)I]5 and (R)-[(125)I]5, specific plaque labeling on brain sections of Tg mice and AD patients were observed in in vitro autoradiography, persuasively proving the excellent affinity of the probes. In biodistribution, (S)-[(125)I]5 and (R)-[(125)I]5 with relatively low lipophilicity exhibited moderate initial brain uptake (4.37% and 3.72% ID/g at 2 min, respectively) and extremely fast washout from normal mice brain (brain2min/brain60min = 19.0 and 17.7, respectively). In summary, the separate enantiomers displayed similar properties in vitro and in vivo, and (S/R)-[(123)I]5 may be potential SPECT probes for recognizing Aβ plaques in AD brains.

Scaffold metamaterial and its application as strain sensor

In this paper, strain sensors based on planar scaffold metamaterial design are demonstrated. The optical properties of such metamaterials are studied, which are proved to be highly dependent on the deformation of the structure. Fabricating such metamaterial on compliant polymeric substrate, the geometric parameters could be tuned with external strain and hence are found to control the reflection resonance condition of the metamaterial. Such mechanical tunability provides the opportunity to realize efficient strain sensors and about 27 nm resonance wavelength shift is observed by applying as much as 37% tensile strain. Furthermore, distinct from most of the previous works, our structures are based on “intaglio” design, which could be manufactured directly by one step fabrication using focused ion beam cutting, hence makes the fabrication process much simpler.

Modeling of enhanced catalysis in multienzyme nanostructures: effect of molecular scaffolds, spatial organization, and concentration.

Colocalized multistep enzymatic reaction pathways within biological catabolic and metabolic processes occur with high yield and specificity. Spatial organization on membranes or surfaces may be associated with increased efficiency of intermediate substrate transfer. Using a new Brownian dynamics package, GeomBD, we explored the geometric features of a surface-anchored enzyme system by parallel coarse-grained Brownian dynamics simulations of substrate diffusion over microsecond (μs) to millisecond (ms) time scales. We focused on a recently developed glucose oxidase (GOx), horseradish peroxidase (HRP), and DNA origami-scaffold enzyme system, where the H2O2 substrate of HRP is produced by GOx. The results revealed and explained a significant advantage in catalytic enhancement by optimizing interenzyme distance and orientation in the presence of the scaffold model. The planar scaffold colocalized the enzymes and provided a diffusive barrier that enhanced substrate transfer probability, becoming more relevant with increasing interenzyme distance. The results highlight the importance of protein geometry in the proper assessment of distance and orientation dependence on the probability of substrate transfer. They shed light on strategies for engineering multienzyme complexes and further investigation of enhanced catalytic efficiency for substrate diffusion between membrane-anchoring proteins.

The fabrication and cell culture of three-dimensional rolled scaffolds with complex micro-architectures

Cell cultures for tissue engineering are traditionally prepared on two-dimensional or three-dimensional scaffolds with simple pores; however, this limits mass transportation, which is necessary for cell viability and function. In this paper, an innovative method is proposed for fabricating porous scaffolds with designed complex micro-architectures. Channels devised by computer-aided design were used to simulate features of blood vessels in native rat liver. Rapid prototyping and microreplication were used to produce a negative polydimethylsiloxane mold, and then a planar porous scaffold with predefined microchannel parameters was obtained by freeze-drying a silk fibroin/gelatin solution of an optimized concentration. After seeding with rat primary hepatocytes, the planar scaffold was rolled up to build spatial channels. By reconstructing the three-dimensional channel model in the scaffold in the form of micro-computed topography data and observing the cross-sections of the scroll, we confirmed that the bent channels were still interconnected, with restricted deviations. A comparison of the primary hepatocyte culture in the scaffolds with and without the devised channels proved that our design influenced cell organization and improved cell survival and proliferation. This method can be used for the construction of complex tissues for implantation and for culturing cells in vitro for biological tests and observations.

Bay-substituted perylene bisimide dye with an undistorted planar scaffold and outstanding solid state fluorescence properties

Single crystal X-ray analysis reveals a flat perylene π-scaffold for a perylene bisimide bearing bulky 2,6-diphenylphenoxy substituents at the 1,7 bay positions. The flat structure provides sharp vibronic progressions in the absorption and fluorescence spectra, the sterical shielding outstanding fluorescence quantum yields in the solid state.

Micropatterned Biopolymer 3D Scaffold for Static and Dynamic Culture of Human Fibroblasts

During in vivo tissue regeneration, cell behavior is highly influenced by the surrounding environment. Thus, the choice of scaffold material and its microstructure is one of the fundamental steps for a successful in vitro culture. An efficacious method for scaffold fabrication should prove its versatility and the possibility of controlling micro- and nanostructure. In this paper, hyaluronic acid 3D scaffolds were developed through lamination of micropatterned membranes, fabricated after optimization of a soft-lithography method. The scaffold presented here is characterized by a homogeneous hexagonal lattice with porosity of 69%, specific surface area of 287 cm-1, and permeability of 18.9 microm2. The control over the geometry was achieved with an accuracy of 20 mum. This technique allowed not only fabrication of planar 3D scaffolds but also production of thin wall tubular constructs. Mechanical tests, performed on dry tubular scaffolds, show high rupture tensile strength. This construct could be promising not only as engineered vascular grafts but also for regeneration of skin, urethra, and intestinal walls. The biocompatibility of a 3D planar scaffold was tested by seeding human fibroblasts. The cells were cultured in both static and dynamic conditions, in a perfusion bioreactor at different flow rates. Microscope analysis and MTT test showed cell proliferation and viability and a uniform cell distribution likely due to an appropriate lattice structure.

Identification of Ligands with Bicyclic Scaffolds Provides Insights into Mechanisms of Estrogen Receptor Subtype Selectivity

Estrogen receptors alpha (ERalpha) and beta (ERbeta) have distinct functions and differential expression in certain tissues. These differences have stimulated the search for subtype-selective ligands. Therapeutically, such ligands offer the potential to target specific tissues or pathways regulated by one receptor subtype without affecting the other. As reagents, they can be utilized to probe the physiological functions of the ER subtypes to provide information complementary to that obtained from knock-out animals. A fluorescence resonance energy transfer-based assay was used to screen a 10,000-compound chemical library for ER agonists. From the screen, we identified a family of ERbeta-selective agonists whose members contain bulky oxabicyclic scaffolds in place of the planar scaffolds common to most ER ligands. These agonists are 10-50-fold selective for ERbeta in competitive binding assays and up to 60-fold selective in transactivation assays. The weak uterotrophic activity of these ligands in immature rats and their ability to stimulate expression of an ERbeta regulated gene in human U2OS osteosarcoma cells provides more physiological evidence of their ERbeta-selective nature. To provide insight into the molecular mechanisms of their activity and selectivity, we determined the crystal structures of the ERalpha ligand-binding domain (LBD) and a peptide from the glucocorticoid receptor-interacting protein 1 (GRIP1) coactivator complexed with the ligands OBCP-3M, OBCP-2M, and OBCP-1M. These structures illustrate how the bicyclic scaffolds of these ligands are accommodated in the flexible ligand-binding pocket of ER. A comparison of these structures with existing ER structures suggests that the ERbeta selectivity of OBCP ligands can be attributed to a combination of their interactions with Met-336 in ERbeta and Met-421 in ERalpha. These bicyclic ligands show promise as lead compounds that can target ERbeta. In addition, our understanding of the molecular determinants of their subtype selectivity provides a useful starting point for developing other ER modulators belonging to this relatively new structural class.