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Journal articles on the topic 'Ligand systems'

Author: Grafiati

Published: 4 June 2021

Last updated: 11 February 2022

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1

Oszwałdowski, Sławomir, Katarzyna Zawistowska-Gibuła, and Kenneth Roberts. "Characterization of CdSe quantum dots with bidentate ligands by capillary electrophoresis." Open Chemistry 9, no. 4 (August 1, 2011): 572–84. http://dx.doi.org/10.2478/s11532-011-0037-3.

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AbstractThe CdSe quantum dots (QDs) with bidentate ligands: a-diimine (NN) and dihydrolipoic acid (DHLA) were synthesized and characterized by UV-Vis, particle size and capillary electrophoretic techniques. Two systems were analyzed: CdSe with one ligand (CdSe/ligand) and CdSe with two different ligands (CdSe//ligand1/ligand2), where ligand = α-diimine or DHLA. Hydrodynamic features of functionalized QDs were characterized by zone capillary electrophoretic (CZE), and particle size techniques and these methods were consistent. It was established that CZE, micellar (MEKC) and microemulsion (MEEKC) modes were suitable for separating charged CdSe QDs and that no peaks were obtained for QDs passivated with electrically neutral ligands. For CdSe QDs with neutral (NN) ligands, a preconcentration method with the use of a micellar plug was introduced for visualizing these QDs. A sharp peak representing neutral QDs was obtained within the zone of micellar plug of a non-ionic surfactant, Here, a ligand character used for CdSe modification and the type of the electrophoretic method applied were the determining factors for the QDs peak visualization. Moreover, examples of visualization of charged and neutral QDs on the same run were presented, and for this purpose, dual mechanism (separation/preconcentration) was proposed.

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2

Denizli, Adil, and Erhan Pişkin. "Dye-ligand affinity systems." Journal of Biochemical and Biophysical Methods 49, no. 1-3 (October 2001): 391–416. http://dx.doi.org/10.1016/s0165-022x(01)00209-3.

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3

Wang, K. "Biological metal ligand systems." Pure and Applied Chemistry 60, no. 8 (January 1, 1988): 1279–84. http://dx.doi.org/10.1351/pac198860081279.

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4

Osguthorpe, D. J. "Modelling ligand-receptor systems." Neurochemistry International 21 (January 1992): S8. http://dx.doi.org/10.1016/0197-0186(92)91742-f.

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5

Ben-Shlomo, Izhar, Rami Rauch, Orna Avsian-Kretchmer, and Aaron J. W. Hsueh. "Matching Receptome Genes with Their Ligands for Surveying Paracrine/Autocrine Signaling Systems." Molecular Endocrinology 21, no. 8 (August 1, 2007): 2009–14. http://dx.doi.org/10.1210/me.2007-0087.

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Abstract Sequencing of genomes from diverse organisms facilitates studies on the repertoire of genes involved in intercellular signaling. Extending previous efforts to annotate most human plasma membrane receptors in the Human Plasma Membrane Receptome database, we matched cognate ligands with individual receptors by surveying the published literature. In the updated online database we called “liganded receptome,” users can search for individual ligands or receptors to reveal their pairing partners and browse through receptor or ligand families to identify relationships between ligands and receptors in their respective families. Because local signaling systems are prevalent in diverse normal and diseased tissues, we used the liganded receptome knowledgebase to interrogate DNA microarray datasets for genome-wide analyses of potential paracrine/autocrine signaling systems. In addition to viewing ligand-receptor coexpression based on precomputed DNA microarray data, users can submit their own microarray data to perform online genome-wide searches for putative paracrine/autocrine signaling systems. Investigation of transcriptome data based on liganded receptome allows the discovery of paracrine/autocrine signaling for known ligand-receptor pairs in previously uncharacterized tissues or developmental stages. The present annotation of ligand-receptor pairs also identifies orphan receptors and ligands without known interacting partners in select families. Because hormonal ligands within the same family usually interact with paralogous receptors, this genomic approach could also facilitate matching of orphan receptors and ligands. The liganded receptome is accessible at http://receptome.stanford.edu.

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6

Chen, Fang, Gangliang Huang, and Hualiang Huang. "Sugar ligand-mediated drug delivery." Future Medicinal Chemistry 12, no. 2 (January 2020): 161–71. http://dx.doi.org/10.4155/fmc-2019-0114.

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Sugar ligand molecules, such as mannose, galactose and glucose, can bind to drug-delivery systems, making them targeted. These glycosylation ligands have the advantages of nontoxicity, no immunogenicity, good biocompatibility and biodegradation. They can be widely used in glycosylation-modified drug-delivery systems. Herein, the targeting mechanisms, synthesis methods and targeting characteristics of glycosylation-modified drug-delivery systems were reviewed.

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7

Gorzsás, András, Ingegärd Andersson, and Lage Pettersson. "Speciation in aqueous vanadate–ligand and peroxovanadate–ligand systems." Journal of Inorganic Biochemistry 103, no. 4 (April 2009): 517–26. http://dx.doi.org/10.1016/j.jinorgbio.2008.12.006.

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8

LIANG, G., and Q. YAO. "Ce 4f-LIGAND DEHYBRIDIZATION IN CeT2X2-BASED KONDO LATTICE/HEAVY FERMION SYSTEMS." International Journal of Modern Physics B 16, no. 19 (July 30, 2002): 2815–22. http://dx.doi.org/10.1142/s0217979202011378.

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The lattice parameters of two CeT2X2 ( T =3d transition elements and X=Si and Ge) based Kondo lattice systems, the CeNi2-xCux Si2 and Ce(NiSi)2-x (CuGe)x, have been studied. The analysis of the Ce-ligand distances indicates that the variation of the a-parameter dominantly affects Ce 4f-X ligandn orbital hybridization whereas the variation of c-parameter dominantly affects Ce 4f-T ligand orbital hybridization. The average Ce-ligand distance varies linearly with x across the whole series in spite of the abnormal increase of the c-parameter in the region 1.6 ≤ x ≤ 2.0. Thus, our analysis shows that the average Ce 4f-ligand orbital hybridization decreases uniformly with x across the entire range of x for the CeNi2-xCuxSi 2 and Ce(NiSi)2-x(CuGe)x series. The means that the Ce 4f-ligand orbital dehybridization may not be a key factor to the formation of the heavy-fermion ground state in CeCu2Si2.

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9

Martín-Mora, David, Matilde Fernández, Félix Velando, Álvaro Ortega, José Gavira, Miguel Matilla, and Tino Krell. "Functional Annotation of Bacterial Signal Transduction Systems: Progress and Challenges." International Journal of Molecular Sciences 19, no. 12 (November 26, 2018): 3755. http://dx.doi.org/10.3390/ijms19123755.

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Bacteria possess a large number of signal transduction systems that sense and respond to different environmental cues. Most frequently these are transcriptional regulators, two-component systems and chemosensory pathways. A major bottleneck in the field of signal transduction is the lack of information on signal molecules that modulate the activity of the large majority of these systems. We review here the progress made in the functional annotation of sensor proteins using high-throughput ligand screening approaches of purified sensor proteins or individual ligand binding domains. In these assays, the alteration in protein thermal stability following ligand binding is monitored using Differential Scanning Fluorimetry. We illustrate on several examples how the identification of the sensor protein ligand has facilitated the elucidation of the molecular mechanism of the regulatory process. We will also discuss the use of virtual ligand screening approaches to identify sensor protein ligands. Both approaches have been successfully applied to functionally annotate a significant number of bacterial sensor proteins but can also be used to study proteins from other kingdoms. The major challenge consists in the study of sensor proteins that do not recognize signal molecules directly, but that are activated by signal molecule-loaded binding proteins.

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10

Zahid, Kanwal, Shazia Nisar, Saima Imad, Shazia Perveen, Shazia Ghaffar, and Nasreen Fatima. "Synthesis and Characterization of Homo and Mixed Ligand Complexes of Fe(III) with Hydroxypyridinone and Hydroxypyranone Type Ligands." Pakistan Journal of Scientific & Industrial Research Series A: Physical Sciences 63, no. 1 (March 18, 2020): 12–17. http://dx.doi.org/10.52763/pjsir.phys.sci.63.1.2020.12.17.

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Hydroxypyridinone and hydroxypyranone are known to be used for the treatment of iron overload by chelation therapy for a long time. Both the ligands have their own side effects when used as medicines. In the present study homo and mixed ligand complexes of both the ligands with iron were prepared and characterized by UV-visible spectrophotometry, Potentiometric study, IR spectroscopy, SEM/EDX and XRD. Overlay spectra obtained from UV-visible spectroscopy of our studied system show the formation of different types of species and confirm that mixed ligand complex is different from the other two systems. Potentiometric titration curves of homo and mixed ligand complexes show the formation of different types of species at different pH and confirm the formation of mixed ligand complex. The comparative results of SEM images of these systems show different surface topologies and hence conform to the formation of mixed ligand complex.

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11

Pann, J., H. Roithmeyer, W. Viertl, R. Pehn, M. Bendig, J. Dutzler, B. Kriesche, and P. Brüggeller. "Phosphines in artificial photosynthesis: considering different aspects such as chromophores, water reduction catalysts (WRCs), water oxidation catalysts (WOCs), and dyads." Sustainable Energy & Fuels 3, no. 11 (2019): 2926–53. http://dx.doi.org/10.1039/c9se00320g.

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Coordination complex systems containing phosphine ligands are used in artificial photosynthesis utilizing their unique stereoelectronic properties. Mono-, di- and tetraphosphines act as optimized ligand systems for complexation.

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12

Kuzu, Istemi, Ivo Krummenacher, Jens Meyer, Felix Armbruster, and Frank Breher. "Multidentate ligand systems featuring dual functionality." Dalton Transactions, no. 43 (2008): 5836. http://dx.doi.org/10.1039/b808347a.

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13

Shave, S. R., P. Taylor, M. Walkinshaw, L. Smith, J. Hardy, and A. Trew. "Ligand discovery on massively parallel systems." IBM Journal of Research and Development 52, no. 1.2 (January 2008): 57–67. http://dx.doi.org/10.1147/rd.521.0057.

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14

Borówko, Małgorzata, and Tomasz Staszewski. "Adsorption on Ligand-Tethered Nanoparticles." International Journal of Molecular Sciences 22, no. 16 (August 16, 2021): 8810. http://dx.doi.org/10.3390/ijms22168810.

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We use coarse-grained molecular dynamics simulations to study adsorption on ligand-tethered particles. Nanoparticles with attached flexible and stiff ligands are considered. We discuss how the excess adsorption isotherm, the thickness of the polymer corona, and its morphology depend on the number of ligands, their length, the size of the core, and the interaction parameters. We investigate the adsorption-induced structural transitions of polymer coatings. The behavior of systems involving curved and flat “brushes” is compared.

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15

Li, Peiyi, Birte Ahrens, Ka-Ho Choi, Muhammad S. Khan, Paul R. Raithby, Paul J. Wilson, and Wai-Yeung Wong. "Metal–metal and ligand–ligand interactions in gold poly-yne systems." CrystEngComm 4, no. 69 (2002): 405–12. http://dx.doi.org/10.1039/b202283d.

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16

Chernova, R. K., and S. N. Shtykov. "Hydrophobic ligand-ligand interactions in multicomponent systems and their analytical significance." Fresenius' Zeitschrift für analytische Chemie 335, no. 1 (January 1989): 111–16. http://dx.doi.org/10.1007/bf00482402.

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17

Ferrer, E. G., P. A. M. Williams, and E. J. Baran. "Interaction of the Vanadyl(IV) Cation with L-Ascorbic Acid and Related Systems." Zeitschrift für Naturforschung B 53, no. 2 (February 1, 1998): 256–62. http://dx.doi.org/10.1515/znb-1998-0220.

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Abstract The interaction of VO2+ with L-ascorbic acid and dehydroascorbic acid was investigated by electronic spectroscopy in solution at different pH values. In the case of ascorbic acid, two different solid complexes containing one or two monodeprotonated ascorbate ligands could be isolated and characterized. With dehydroascorbic acid, interaction begins at pH = 4 but at higher pH values the ligand is hydrolysed irreversibly, generating 2,3-diketogulonic acid. A solid complex containing this ligand could be precipitated at pH = 7. Its spectroscopic behavior confirms the interaction of the cation with an enolised form of the acid.

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18

Vogler, Arnd, and Horst Kunkely. "Optical Ligand to Ligand Charge Transfer of Metal Complexes Including Ligand-Based Mixed-Valence Systems." Comments on Inorganic Chemistry 9, no. 3-4 (January 1990): 201–20. http://dx.doi.org/10.1080/02603599008035810.

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19

Davis, Carol A., Jeong Kim, Leonard F. Lindoy, Seong-Hwa Lee, and Anthony J. Leong. "Macrocyclic Ligand Design. Structure - Function Relationships Underlying the Interaction of Zinc(II), Cadmium(II), Silver(I) and Lead(II) with Mixed-Donor Macrocyclic Ligands." Australian Journal of Chemistry 51, no. 3 (1998): 189. http://dx.doi.org/10.1071/c97188.

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An investigation of the interaction of zinc(II), cadmium(II), silver(I) and lead(II) with a series of mixed-donor dibenzo-substituted macrocyclic ligands, incorporating O2N3-, O2N4-, O3N2-, O3N3-, O4N2- and O2N3S-donor sets, has been carried out. The log K values for the respective complexes in 95% methanol (I = 0·1; Et4NClO4, 25°C) have been determined potentiometrically. All ligands form 1 : 1 (metal/ligand) complexes with the above metal ions although in isolated cases species of type MLH2+ were also observed. An investigation of the effect of variation of ligand structure on the respective complex stabilities has been carried out and the results compared with those obtained previously for closely related mixed-donor macrocyclic systems. The binding of silver(I) and lead(II) to the 17- and 18-membered O3N2-ligand systems has been assessed in (CD3)2SO by means of 13C n.m.r. spin–lattice relaxation (T1) studies as well as by observation of the induced chemical shifts of particular ligand resonances on complex formation. Overall, the n.m.r. results correlate well with the observed thermodynamic stabilities of the individual complexes.

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20

Marsh, Lorraine. "Strong Ligand-Protein Interactions Derived from Diffuse Ligand Interactions with Loose Binding Sites." BioMed Research International 2015 (2015): 1–6. http://dx.doi.org/10.1155/2015/746980.

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Many systems in biology rely on binding of ligands to target proteins in a single high-affinity conformation with a favorableΔG. Alternatively, interactions of ligands with protein regions that allow diffuse binding, distributed over multiple sites and conformations, can exhibit favorableΔGbecause of their higher entropy. Diffuse binding may be biologically important for multidrug transporters and carrier proteins. A fine-grained computational method for numerical integration of total bindingΔGarising from diffuse regional interaction of a ligand in multiple conformations using a Markov Chain Monte Carlo (MCMC) approach is presented. This method yields a metric that quantifies the influence on overall ligand affinity of ligand binding to multiple, distinct sites within a protein binding region. This metric is essentially a measure of dispersion in equilibrium ligand binding and depends on both the number of potential sites of interaction and the distribution of their individual predicted affinities. Analysis of test cases indicates that, for some ligand/protein pairs involving transporters and carrier proteins, diffuse binding contributes greatly to total affinity, whereas in other cases the influence is modest. This approach may be useful for studying situations where “nonspecific” interactions contribute to biological function.

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21

Leng, Qixin, Martin C. Woodle, and A. James Mixson. "Targeted Delivery of siRNA Therapeutics to Malignant Tumors." Journal of Drug Delivery 2017 (November 9, 2017): 1–22. http://dx.doi.org/10.1155/2017/6971297.

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Over the past 20 years, a diverse group of ligands targeting surface biomarkers or receptors has been identified with several investigated to target siRNA to tumors. Many approaches to developing tumor-homing peptides, RNA and DNA aptamers, and single-chain variable fragment antibodies by using phage display, in vitro evolution, and recombinant antibody methods could not have been imagined by researchers in the 1980s. Despite these many scientific advances, there is no reason to expect that the ligand field will not continue to evolve. From development of ligands based on novel or existing biomarkers to linking ligands to drugs and gene and antisense delivery systems, several fields have coalesced to facilitate ligand-directed siRNA therapeutics. In this review, we discuss the major categories of ligand-targeted siRNA therapeutics for tumors, as well as the different strategies to identify new ligands.

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22

Throckmorton, Linda, and Dennis S. Marynick. "Ligand exchange in (.eta.5-cyclopentadienyl)nickel ligand systems: a theoretical study." Journal of Physical Chemistry 92, no. 3 (February 1988): 645–50. http://dx.doi.org/10.1021/j100314a016.

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23

Li, Long, Yudie Zhang, and Jizeng Wang. "Effects of ligand distribution on receptor-diffusion-mediated cellular uptake of nanoparticles." Royal Society Open Science 4, no. 5 (May 2017): 170063. http://dx.doi.org/10.1098/rsos.170063.

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Biophysical-factor-dependent cellular uptake of nanoparticles (NPs) through receptor-diffusion-mediated endocytosis bears significance in pathology, cellular immunity and drug-delivery systems. Advanced nanotechnology of NP synthesis provides methods for modifying NP surface with different ligand distributions. However, no report discusses effects of ligand distribution on NP surface on receptor-diffusion-mediated cellular uptake. In this article, we used a statistical dynamics model of receptor-diffusion-mediated endocytosis to examine ligand-distribution-dependent cellular uptake dynamics by considering that ligand–receptor complexes drive engulfing to overcome resistance to membrane deformation and changes in configuration entropy of receptors. Results showed that cellular internalization of NPs strongly depended on ligand distribution and that cellular-uptake efficiency of NPs was high when ligand distribution was within a range around uniform distribution. This feature of endocytosis ensures robust infection ability of viruses to enter host cells. Interestingly, results also indicated that optimal ligand distribution associated with highest cellular-uptake efficiency slightly depends on distribution pattern of ligands and density of receptors, and the optimal distribution becomes uniform when receptor density is sufficiently large. Position of initial contact point is also a factor affecting dynamic wrapping. This study explains why most enveloped viruses present almost homogeneous ligand distribution and is useful in designing controlled-release drug-delivery systems.

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24

Jones, Dafydd D. L., Samuel Watts, and Cameron Jones. "Synthesis and Characterization of Super Bulky β-Diketiminato Group 1 Metal Complexes." Inorganics 9, no. 9 (September 16, 2021): 72. http://dx.doi.org/10.3390/inorganics9090072.

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Sterically bulky β-diketiminate (or Nacnac) ligand systems have recently shown the ability to kinetically stabilize highly reactive low-oxidation state main group complexes. Metal halide precursors to such systems can be formed via salt metathesis reactions involving alkali metal complexes of these large ligand frameworks. Herein, we report the synthesis and characterization of lithium and potassium complexes of the super bulky anionic β-diketiminate ligands, known [TCHPNacnac]− and new [TCHP/DipNacnac]− (ArNacnac = [(ArNCMe)2CH]−) (Ar = 2,4,6-tricyclohexylphenyl (TCHP) or 2,6-diisopropylphenyl (Dip)). The reaction of the proteo-ligands, ArNacnacH, with nBuLi give the lithium etherate compounds, [(TCHPNacnac)Li(OEt2)] and [(TCHP/DipNacnac)Li(OEt2)], which were isolated and characterized by multinuclear NMR spectroscopy and X-ray crystallography. The unsolvated potassium salts, [{K(TCHPNacnac)}2] and [{K(TCHP/DipNacnac)}∞], were also synthesized and characterized in solution by NMR spectroscopy. In the solid state, these highly reactive potassium complexes exhibit differing alkali metal coordination modes, depending on the ligand involved. These group 1 complexes have potential as reagents for the transfer of the bulky ligand fragments to metal halides, and for the subsequent stabilization of low-oxidation state metal complexes.

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25

Kaynak, Burak T., and Pemra Doruker. "Protein–Ligand Complexes as Constrained Dynamical Systems." Journal of Chemical Information and Modeling 59, no. 5 (March 26, 2019): 2352–58. http://dx.doi.org/10.1021/acs.jcim.8b00946.

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26

Schalk, Oliver, Yu Liang, and Andreas-Neil Unterreiner. "On Ligand Binding Energies in Porphyrinic Systems." Zeitschrift für Physikalische Chemie 227, no. 1 (January 2013): 35–48. http://dx.doi.org/10.1524/zpch.2012.0238.

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27

Koska, Jürgen, Collin Mui, and Charles A. Haynes. "Solvent effects in chiral ligand exchange systems." Chemical Engineering Science 56, no. 1 (January 2001): 29–41. http://dx.doi.org/10.1016/s0009-2509(00)00418-8.

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28

Nozari, Mohammad, Anthony W. Addison, GorDan T. Reeves, Matthias Zeller, Jerry P. Jasinski, Manpreet Kaur, Jayakumar G. Gilbert, et al. "New Pyrazole- and Benzimidazole-derived Ligand Systems." Journal of Heterocyclic Chemistry 55, no. 6 (April 16, 2018): 1291–307. http://dx.doi.org/10.1002/jhet.3155.

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29

Agarwal, Abhinav, Surbhi Saraf, Abhay Asthana, Umesh Gupta, Virendra Gajbhiye, and Narendra K. Jain. "Ligand based dendritic systems for tumor targeting." International Journal of Pharmaceutics 350, no. 1-2 (February 2008): 3–13. http://dx.doi.org/10.1016/j.ijpharm.2007.09.024.

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30

Zia, Adil, Yuao Wu, Tuan Nguyen, Xiaowei Wang, Karlheinz Peter, and Hang T. Ta. "The choice of targets and ligands for site-specific delivery of nanomedicine to atherosclerosis." Cardiovascular Research 116, no. 13 (February 20, 2020): 2055–68. http://dx.doi.org/10.1093/cvr/cvaa047.

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Abstract As nanotechnologies advance into clinical medicine, novel methods for applying nanomedicine to cardiovascular diseases are emerging. Extensive research has been undertaken to unlock the complex pathogenesis of atherosclerosis. However, this complexity presents challenges to develop effective imaging and therapeutic modalities for early diagnosis and acute intervention. The choice of ligand-receptor system vastly influences the effectiveness of nanomedicine. This review collates current ligand-receptor systems used in targeting functionalized nanoparticles for diagnosis and treatment of atherosclerosis. Our focus is on the binding affinity and selectivity of ligand-receptor systems, as well as the relative abundance of targets throughout the development and progression of atherosclerosis. Antibody-based targeting systems are currently the most commonly researched due to their high binding affinities when compared with other ligands, such as antibody fragments, peptides, and other small molecules. However, antibodies tend to be immunogenic due to their size. Engineering antibody fragments can address this issue but will compromise their binding affinity. Peptides are promising ligands due to their synthetic flexibility and low production costs. Alongside the aforementioned binding affinity of ligands, the choice of target and its abundance throughout distinct stages of atherosclerosis and thrombosis is relevant to the intended purpose of the nanomedicine. Further studies to investigate the components of atherosclerotic plaques are required as their cellular and molecular profile shifts over time.

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31

Cavell, KJ. "Metal Chelate Systems as Catalysts for Olefin and Carbon Monoxide Conversion Reactions." Australian Journal of Chemistry 47, no. 5 (1994): 769. http://dx.doi.org/10.1071/ch9940769.

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The application of non-phosphine-based chelating ligands in homogeneous catalyst systems is a surprisingly recent and relatively unexplored area of research. Chelating ligands can concurrently stabilize intermediates, control catalyst activity and direct the product distribution far more effectively than monodentate ligands. In this review our studies with catalyst systems containing chelate ligands primarily of the β-diketonate type [dithio-β-diketonate (sacsac); monothio-β-diketonate (sacac); and imino β-diketonate (nacac) ligands] is discussed. Examples of the catalyst systems show enzyme-like superactivity. Studies modelling these catalyst systems have provided valuable information relating the effects of ligand modifications to reaction pathways and to activities. Our most recent investigations of simple chelating ligands based on picolinic acid are also discussed. Studies modelling CO/ethene insertion/elimination with extremely labile alkylplatinum picolinate complexes led to the development of new single-component nickel oligomerization catalysts.

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32

Yang, Dongdong, Xiaxia Liu, Liping Lu, and Miaoli Zhu. "Effects of two different solvents on the syntheses, structural diversity, and magnetic properties of six Mn(ii) complexes derived from 3,3′-((5-carboxy-1,3-phenylene)bis(oxy))dibenzoate and variable N-donor ligands." CrystEngComm 22, no. 46 (2020): 8088–99. http://dx.doi.org/10.1039/d0ce01383h.

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Six Mn(ii) complexes of the 3,3′-((5-carboxy-1,3-phenylene)bis(oxy))dibenzoate ligand in two different solvent systems with variable N-donor ligands were obtained and showed different structures and magnetic properties.

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33

Oldenhof, Sander, Martin Lutz, Bas de Bruin, Jarl Ivar van der Vlugt, and Joost N. H. Reek. "Dehydrogenation of formic acid by Ir–bisMETAMORPhos complexes: experimental and computational insight into the role of a cooperative ligand." Chemical Science 6, no. 2 (2015): 1027–34. http://dx.doi.org/10.1039/c4sc02555e.

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The synthesis of Ir-complexes with three bisMETAMORPhos ligands is reported. The activity of these systems towards HCOOH dehydrogenation and the dual role of the ligand during catalysis is discussed, using spectroscopic and computational methods.

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34

Caspers, Nicole L., Seungil Han, Francis Rajamohan, Lise R. Hoth, Kieran F. Geoghegan, Timothy A. Subashi, Michael L. Vazquez, et al. "Development of a high-throughput crystal structure-determination platform for JAK1 using a novel metal-chelator soaking system." Acta Crystallographica Section F Structural Biology Communications 72, no. 11 (October 27, 2016): 840–45. http://dx.doi.org/10.1107/s2053230x16016356.

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Crystals of phosphorylated JAK1 kinase domain were initially generated in complex with nucleotide (ADP) and magnesium. The tightly bound Mg2+-ADP at the ATP-binding site proved recalcitrant to ligand displacement. Addition of a molar excess of EDTA helped to dislodge the divalent metal ion, promoting the release of ADP and allowing facile exchange with ATP-competitive small-molecule ligands. Many kinases require the presence of a stabilizing ligand in the ATP site for crystallization. This procedure could be useful for developing co-crystallization systems with an exchangeable ligand to enable structure-based drug design of other protein kinases.

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35

Martin, Stephen F. "Preorganization in biological systems: Are conformational constraints worth the energy?" Pure and Applied Chemistry 79, no. 2 (January 1, 2007): 193–200. http://dx.doi.org/10.1351/pac200779020193.

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It is generally assumed that preorganizing a flexible ligand in the three-dimensional shape it adopts when bound to a macromolecular receptor will provide a derivative having an increased binding affinity, primarily because the rigidified molecule is expected to benefit from a lesser entropic penalty during complexation. We now provide the first experimental evidence that demonstrates this common belief is not universally true. Indeed, we find that ligand preorganization may be accompanied by an unfavorable entropy of binding, even when the constrained ligand exhibits a higher binding affinity than its flexible control. Thus, the effects that ligand preorganization have upon energetics and structure in protein-ligand interactions must be reevaluated.

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36

Jeffrey, Polly-Anne, Martín López-García, Mario Castro, Grant Lythe, and Carmen Molina-París. "On Exact and Approximate Approaches for Stochastic Receptor-Ligand Competition Dynamics—An Ecological Perspective." Mathematics 8, no. 6 (June 20, 2020): 1014. http://dx.doi.org/10.3390/math8061014.

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Cellular receptors on the cell membrane can bind ligand molecules in the extra-cellular medium to form ligand-bound monomers. These interactions ultimately determine the fate of a cell through the resulting intra-cellular signalling cascades. Often, several receptor types can bind a shared ligand leading to the formation of different monomeric complexes, and in turn to competition for the common ligand. Here, we describe competition between two receptors which bind a common ligand in terms of a bi-variate stochastic process. The stochastic description is important to account for fluctuations in the number of molecules. Our interest is in computing two summary statistics—the steady-state distribution of the number of bound monomers and the time to reach a threshold number of monomers of a given kind. The matrix-analytic approach developed in this manuscript is exact, but becomes impractical as the number of molecules in the system increases. Thus, we present novel approximations which can work under low-to-moderate competition scenarios. Our results apply to systems with a larger number of population species (i.e., receptors) competing for a common resource (i.e., ligands), and to competition systems outside the area of molecular dynamics, such as Mathematical Ecology.

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Walser, Reto, Jörg H. Kleinschmidt, Arne Skerra, and Oliver Zerbe. "β-Barrel scaffolds for the grafting of extracellular loops from G-protein-coupled receptors." Biological Chemistry 393, no. 11 (November 1, 2012): 1341–55. http://dx.doi.org/10.1515/hsz-2012-0234.

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Abstract Owing to the difficulties in production and purification of G-protein-coupled receptors (GPCRs), relatively little structural information is available about this class of receptors. Here we aim at developing small chimeric proteins, displaying the extracellular ligand-binding motifs of a human GPCR, the Y receptor. This allows the study of ligand-receptor interactions in simplified systems. We present comprehensive information on the use of transmembrane (OmpA) and soluble (Blc) β-barrel scaffolds. Whereas Blc appeared to be not fully compatible with our approach, owing to problems with refolding of the hybrid constructs, loop-grafted versions of OmpA delivered encouraging results. Previously, we described a chimeric construct based on OmpA displaying all three extracellular Y1 receptor loops in different topologies and showing moderate affinity to one of the natural ligands. Now, we present detailed data on the interaction of these constructs with several Y receptor ligands along with data on new constructs. Our findings suggest a common binding mode for all ligands, which is mediated through the C-terminal residues of the peptide ligand, supporting the functional validity of these hybrid receptors. The observed binding affinities, however, are well below those observed for the natural receptors, clearly indicating limitations in mimicking the natural systems.

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Schmidbaur, Hubert, Josef Lettenbauer, Otto Kumberger, J. Lachmann, and Gerhard Müller. "Modellsysteme für die Gallium-Extraktion, II / Model Systems for Gallium Extraction, II." Zeitschrift für Naturforschung B 46, no. 8 (August 1, 1991): 1065–76. http://dx.doi.org/10.1515/znb-1991-0816.

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The introduction of a methyl substituent in the 2-position of 8-oxy-quinoline strongly alters its ligand properties in the complex formation with gallium(III). From aqueous solutions (ammonium acetate buffer, acetic acid, gallium nitrate) a pale-green complex (2-MeOx)2GaOAc is precipitated instead of the tris(oxinate) chelate. According to a single crystal X-ray diffraction study, the gallium atom is pentacoordinate in this complex, with two chelating 2-MeOx and one monocoordinate acetate ligands. Similar acetato complexes were generated with equally hindered 2,4-dimethyl- and 2,5,7-trimethylquinoline, as well as with 2-ethyl- and 2-n-propylquinoline ligands. Retaining the 2-MeOx ligand, acetate OAc could be exchanged for trifluoroacetate, propionate, cyanoacetate, and (in binuclear complexes) equivalents of succinic, maleic, fumaric, and acetylenedicarboxylic acid. From this series, crystal and molecular structures have also been determined for (2-MeOx)2GaOC(O)CH2CN and [(2-MeOx)2GaOC(O)CHJ2]2 (with crystal nitrobenzene). In the cyanoacetate, the nitrile function is not involved in intra/intermolecular metal coordination. In the binuclear succinate the molecule has a crystallographical center of inversion. As in the cyanoacetate, the environment of the two equivalent gallium centers of the succinate is very similar to that of the acetate complex.

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Chen, Cheng, Yang Miao, Kimmy De Winter, Hua-Jing Wang, Patrick Demeyere, Ye Yuan, and Francis Verpoort. "Ruthenium-Based Catalytic Systems Incorporating a Labile Cyclooctadiene Ligand with N-Heterocyclic Carbene Precursors for the Atom-Economic Alcohol Amidation Using Amines." Molecules 23, no. 10 (September 20, 2018): 2413. http://dx.doi.org/10.3390/molecules23102413.

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Transition-metal-catalyzed amide-bond formation from alcohols and amines is an atom-economic and eco-friendly route. Herein, we identified a highly active in situ N-heterocyclic carbene (NHC)/ruthenium (Ru) catalytic system for this amide synthesis. Various substrates, including sterically hindered ones, could be directly transformed into the corresponding amides with the catalyst loading as low as 0.25 mol.%. In this system, we replaced the p-cymene ligand of the Ru source with a relatively labile cyclooctadiene (cod) ligand so as to more efficiently obtain the corresponding poly-carbene Ru species. Expectedly, the weaker cod ligand could be more easily substituted with multiple mono-NHC ligands. Further high-resolution mass spectrometry (HRMS) analyses revealed that two tetra-carbene complexes were probably generated from the in situ catalytic system.

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Gipson, Kyle, Brett Ellerbrock, Kathryn Stevens, Phil Brown, and John Ballato. "Light-Emitting Polymer Nanocomposites." Journal of Nanotechnology 2011 (2011): 1–8. http://dx.doi.org/10.1155/2011/386503.

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Inorganic nanoparticles doped with optically active rare-earth ions and coated with organic ligands were synthesized in order to create fluorescent polymethyl methacrylate (PMMA) nanocomposites. Two different aromatic ligands (acetylsalicylic acid, ASA and 2-picolinic acid, PA) were utilized in order to functionalize the surface of Tb3+ : LaF3nanocrystals. The selected aromatic ligand systems were characterized using infrared spectroscopy, thermal analysis, rheological measurements, and optical spectroscopy. Nanoparticles producedin situwith the PMMA contained on average 10 wt% loading of Tb3+ : LaF3at a 6 : 1 La : Tb molar ratio and ~7 wt% loading of 4 : 1 La : Tb molar ratio for the PA and ASA systems, respectively. Measured diameters ranged from457±176 nm to150±105 nm which is indicative that agglomerates formed during the synthesis process. Both nanocomposites exhibited the characteristic Tb3+emission peaks upon direct ion excitation (350 nm) and ligand excitation (PA : 265 nm and ASA : 275 nm).

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Gxoyiya, Babalwa S. B., Justin P. Hagemann, and Perry T. Kaye. "Designer ligands. Part 12. Synthesis and evaluation of novel palladium(II)-selective ligand systems." Journal of Chemical Research 2004, no. 4 (April 1, 2004): 252–56. http://dx.doi.org/10.3184/0308234041209248.

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Linthicum, D. S., M. B. Bolger, P. H. Kussie, G. M. Albright, T. A. Linton, S. Combs, and D. Marchetti. "Analysis of idiotypic and anti-idiotypic antibodies as models of receptor and ligand." Clinical Chemistry 34, no. 9 (September 1, 1988): 1676–80. http://dx.doi.org/10.1093/clinchem/34.9.1676.

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Abstract Antibodies to small bioactive ligands and peptides may mimic the binding characteristics of the natural receptor; in turn, the anti-idiotypic antibodies generated against the binding sites of such anti-ligand antibodies may mimic some aspects of small bioactive ligands and peptides. Among the several levels of investigation of such antibody-receptor networks are (a) the quantitative structure-activity relationships of ligand binding to antibody as compared with natural receptor; (b) the molecular modeling of antibody-receptor binding sites and the genomic basis for such structures; and (c) the characteristics of the molecular mimicry exhibited by "mimetopes" on anti-idiotypic antibodies. To illustrate the analysis encountered at each of these levels, we discuss here antibody and anti-idiotypic systems that are directed to small neuroactive ligands and their receptors.

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Kapustian, A., and N. Cherno. "Determination of complex forming ability of mixed-ligand organic systems relative to the metal ions." Scientific Messenger of LNU of Veterinary Medicine and Biotechnologies 21, no. 91 (April 23, 2019): 130–35. http://dx.doi.org/10.32718/nvlvet-f9122.

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It is shown that classical and specific methods for determining the complex forming ability of mixed-ligand organic systems relative to the metal ions is not perfect. Determination of complex-forming ability of mixed-ligand organic systems relative to the metal ions using the method of turbidimetry for media containing biometal chlorides, mixed-ligand systems and sodium carbonate is proposed. As mixed-ligand systems used the culture fluid Bifidobacterium bifidum AC-1670 (mixed-ligand system I), the culture fluid of the composition of probiotic bacteria (mixed-ligand system II), the culture fluid of the composition of probiotic bacteria with the introduction of exogenous chelating agents (mixed-ligand system III), culture fluid of probiotic bacteria composition and products of their cell walls processing (mixed-ligand system IV). A solution of metal chloride (magnesium or calcium, or cuprum, or manganese, or ferrum or zinc) was added discretely to the aliquots of the solution of the organic mixed-ligand system. The mixture was stirred and kept for 30 minutes at 40 °C, then a solution of sodium carbonate was added to the aliquots and discretely measured turbidity of the solution by turbidimetric method at a wavelength of 450 nm. When the increasing of the turbidity magnitude system by 0.02 opt. un, a conclusion about the maximum value of the mixed-ligand organic systems complex forming capacity relative to the metal ion was made. Further increase in the turbidity of the system indicates an increase in the metal content in inorganic form, respectively the complex formation potential of the mixed-ligand system is exhausted. It is determined that the highest complex forming ability in relation to ions of biometals has mixed-ligand system III. The proposed method allows precisely to determine the complex formation capacity of mixed-ligand organic systems in relation to metal ions without the use of aggressive reagents capable of destroying chelate bonds and without involving high-cost rare equipment.

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Jovanović, Milena, Maja Gruden-Pavlović, and Mario Zlatović. "Stabilizing non-covalent interactions of ligand aromatic moieties and proline in ligand–protein systems." Monatshefte für Chemie - Chemical Monthly 146, no. 2 (December 20, 2014): 389–97. http://dx.doi.org/10.1007/s00706-014-1357-8.

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Paulmurugan, Ramasamy, Anobel Tamrazi, John A. Katzenellenbogen, Benita S. Katzenellenbogen, and Sanjiv S. Gambhir. "A Human Estrogen Receptor (ER)α Mutation with Differential Responsiveness to Nonsteroidal Ligands: Novel Approaches for Studying Mechanism of ER Action." Molecular Endocrinology 22, no. 7 (July 1, 2008): 1552–64. http://dx.doi.org/10.1210/me.2007-0570.

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Abstract Estrogens, acting through the estrogen receptors (ERs), play crucial roles in regulating the function of reproductive and other systems under physiological and pathological conditions. ER activity in regulating target genes is modulated by the binding of both steroidal and synthetic nonsteroidal ligands, with ligand binding inducing ERs to adopt various conformations that control their interactions with transcriptional coregulators. Previously, we developed an intramolecular folding sensor with a mutant form of ERα (ERG521T) that proved to be essentially unresponsive to the endogenous ligand 17β-estradiol, yet responded very well to certain synthetic ligands. In this study, we have characterized this G521T-ER mutation in terms of the potency and efficacy of receptor response toward several steroidal and nonsteroidal ligands in two different ways: directly, by ligand effects on mutant ER conformation (by the split-luciferase complementation system), and indirectly, by ligand effects on mutant ER transactivation. Full-length G521T-ER shows no affinity for estradiol and does not activate an estrogen-responsive reporter gene. The synthetic pyrazole agonist ligand propyl-pyrazole-triol is approximately 100-fold more potent than estradiol in inducing intramolecular folding and reporter gene transactivation with the mutant ER, whereas both ligands have high potency on wild-type ER. This estradiol-unresponsive mutant ER can also specifically highlight the agonistic property of the selective ER modulator, 4-hydroxytamoxifen, by reporter gene transactivation, even in the presence of estradiol, and it can exert a dominant-negative effect on estrogen-stimulated wild-type ER. This system provides a model for ER-mutants that show differential ligand responsiveness to gene activation to gain insight into the phenomenon of hormone resistance observed in endocrine therapies of ER-positive breast cancers.

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Anderson, Michael A., and Paul M. Bertsch. "Dynamics of Aluminum Complexation in Multiple Ligand Systems." Soil Science Society of America Journal 52, no. 6 (November 1988): 1597–602. http://dx.doi.org/10.2136/sssaj1988.03615995005200060015x.

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Matsuura, Kazunori. "Biomolecular Self-assembling Systems for Multivalent Ligand Display." Trends in Glycoscience and Glycotechnology 25, no. 146 (2013): 227–39. http://dx.doi.org/10.4052/tigg.25.227.

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BOUNIAS, M., and A. BONALY. "TOPOLOGICAL AND NONLINEAR PROPERTIES OF LIGAND-RECEPTOR SYSTEMS." Journal of Biological Systems 04, no. 03 (September 1996): 315–52. http://dx.doi.org/10.1142/s0218339096000235.

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Ligand-receptor (L-R) interactions involving substrate-enzyme and hormone-receptor systems, obey complex processes. Many parameters are not easily addressed in classical kinetic approaches; most are generally based on the probabilistic mass-action law and equilibrium constants. We describe the system in terms of tessellation of the reactional space with balls B(x, Γ) centered on the reactive species and whose radius (Γ), used as a scaling unit, is derived from the Hausdorff distance η=dist(L, R). This value is altered by a set of corrective terms representing interactions with inert and non-reactive species present in the medium, the influence of particular cell factors including heterogeneous phase conditions, and metabolic dissipation of the product. Topological properties have been studied for nonlinear pairing function governing the distance between two species, and the fractal dimension of the system is linked with its Bouligand-Minkowski dimension. The set of instant state equations of the system includes a chain of transfer matrices accounting for the linear phase of catalytic functions. An alternative set of iterative functions providing a complete metric description of the system in its topological definition space, exhibits similarities with the equations of the Mandelbrot sets family. Experimental confirmation that the major parameters (Vmax, S50 and Hill coefficient) are polyphasic functions of time rather than constants was obtained for honeybees haemolymph α-glucosidases.

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Beer, Paul D. "Charged guest recognition by redox responsive ligand systems." Advanced Materials 6, no. 7-8 (July 1994): 607–9. http://dx.doi.org/10.1002/adma.19940060721.

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Thomas, Chrisanthus, Alexander D. Nikolov, and Darsh T. Wasan. "Dissipative Structures in Ligand-Accelerated Metal Extraction Systems." Separation Science and Technology 26, no. 4 (April 1991): 539–57. http://dx.doi.org/10.1080/01496399108050489.

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