Receptor Moiety Research Articles

Chemotactic effect of mono- and disaccharides on the unicellular Tetrahymena pyriformis

Chemotaxis is one of the most essential cell physiological responses, which was developed in parallel the molecular evolution of signal molecules. Previously good correlations were found between chemotactic moieties and physicochemical properties (SEA, solubility, pKa) of peptide type ligands in Tetrahymena model. However, references are rather weak in eukaryotic chemotaxis about significance of simple carbohydrates. In the present work our goal is (i) to investigate the chemotactic effect of 10 mono- and disaccharides in the eukaryotic Tetrahymena pyriformis; (ii) to describe effective ligands with physicochemical parameters; (iii) to test whether sugars are acting via induction of metabolic pathways. Our results are: (i) the tested sugars can trigger both significant attractant (d-glucose, d-mannose) and significant repellent (d-glucosamine, d-fructose, N-acetyl-d-galactosamine, d-arabinose) effects, while some of the sugars (maltose, lactose, sucrose, d-galactose) had no effect. (ii) Correlations were described between the chemotactic effectiveness of the ligands and their physicochemical characters (TPSA, XLogP), which are supposed to influence the internalization of the sugars. (iii) All ligands proved to have low selection potential, which refers to a ‘short-term’ receptor moiety or influencing specific metabolic pathways. (iv) Starvation elicited modified, strong chemoattractive responsiveness towards glucose; however, it was independent of concentration while 1 h insulin treatment resulted in an increased and concentration dependent chemotaxis induced by glucose.

Selective fluorescence sensing of Cu(II) and Zn(II) using a simple Schiff base ligand: Naked eye detection and elucidation of photoinduced electron transfer (PET) mechanism

A simple Schiff base compound 2-((cyclohexylmethylimino)-methyl)-naphthalen-1-ol (2CMIMN1O) has been synthesized and characterized by 1H NMR, 13C NMR and FT-IR spectroscopic techniques. A significantly low emission yield of the compound has been rationalized in anticipation with photo-induced electron transfer (PET) from the imine receptor moiety to the naphthalene fluorophore unit. Consequently, an evaluation of the transition metal ion-induced modification of the fluorophore-receptor communication reveals the promising prospect of the title compound to function as a chemosensor for Cu2+ and Zn2+ ions selectively, through remarkable fluorescence enhancement as well as visual changes. While perturbation of the PET process has been argued to be the plausible mechanism behind the fluorescence enhancement, the selectivity for these two metal ions has been interpreted on the grounds of an appreciably strong binding interaction. Particularly notable aspects regarding the chemosensory activity of the compound is its ability to detect the aforesaid transition metal ions down to the level of micromolar concentration (detection limit being 2.74 and 2.27ppm respectively), along with a simple and efficient synthetic procedure.

Development and characterization of a novel fusion protein of a mutated granulocyte colony-stimulating factor and human serum albumin in Pichia pastoris.

The purpose of the present work was to develop a novel, long-acting and potent human serum albumin/granulocyte colony stimulating factor (HSA/G-CSF) therapeutic fusion protein. The novel fusion protein, called HMG, was constructed by genetically fusing mutated human derived G-CSF (mG-CSF) to the C-terminal of HSA and then prepared in Pichia pastoris. The molecular mass of HMG was about 85 kDa and the isoelectric point was 5.3. Circular dichroism spectroscopy suggested that mG-CSF retained nearly all of its native secondary structure, regardless of fusion. The binding capabilities of mG-CSF moiety to G-CSF receptor and HSA moiety to warfarin showed very little change after fusing. The bioactivity of HMG (11.0×106 IU/mg) was more than twice that of rHSA/G-CSF (4.6×106 IU/mg). A mutation was made at the 718th amino acid of HMG, substituting Ala for Thr, to investigate the glycosylation of HMG expressed in P. pastoris. Data indicated that HMG was modified at Thr718, speculatively with the addition of a mannose chain. In conclusion, a novel HSA/G-CSF fusion protein was successfully constructed based on a mutated G-CSF. This protein showed more potent bioactivity than rHSA/G-CSF and thus may be a suitable long-acting G-CSF.

Virtual issue: molecular sensors.

Smart designs in chemosensing! The articles of this virtual issue focus on molecular sensors, also known as chemosensors or probes, and highlight current research in the area of chemosensing and how wise designs can lead to selective sensing of target analytes. Articles show diverse approaches in probe design based on different sensing principles and the detection of a wide range of analytes. A molecular sensor, also known as a chemosensor or probe, is a molecular or supramolecular-based system that is able to transform probe–analyte interactions into a signal which allows analyte sensing. The most common output signals are usually optical or electrochemical changes. In particular, optical responses have become very popular due to the possibility of using low-cost, widely available instrumentation and even the possibility of detecting target species with the naked eye. The design of these molecular sensors and probes has advanced and gained importance in the last years due to the progress made in the knowledge on the preparation of host–guest complexes and on studies on how this interaction can be used for the design of selective molecular probes. This is a very interdisciplinary filed that in many cases involves organic or inorganic synthesis, photo-physical studies, and analytical applications. In this context, the design of new molecular sensors to detect anions, cations, and neutral species has gained primary significance recently due to the importance to detect target analytes in environmental and biological samples. Molecular sensors for metal cations were developed more than two decades ago, whereas probes for anions and neutral species have been investigated more recently. Articles already accepted show diverse approaches for the design of chemical probes that are based on different sensing principles and display sensing features to a wide range of analytes such as anions, cations, neutral molecules, and gases. Molina et al. (DOI: 10.1002/open.201402022) prepared aryl or heteroaryl 5-substituted imidazo-benzothiadiazole derivatives and found an interesting selective dual-channel sensing of mercury(II) cations and acetate anions. Moreover the probes also display sensing features in the presence of nitroaromatic compounds with a selective response to the explosive picric acid. In a close research approach to the design of sensing probes for target chemical substances that could be used as weapons, Martínez-Máñez, Costero, and co-workers (DOI: 10.1002/open.201402014) designed a molecular sensor for the selective chromogenic recognition of diisopropylfluorophosphate (DFP), a Sarin and Soman mimic, in 99:1 (v/v) water/ acetonitrile and in the gas phase. Anion sensing probes were studied in the works of Ito et al. and Yam and co-workers. Ito and Shinoda (DOI: 10.1002/open.201402049) prepared macrotricyclic octadentate cyclen dimer ligands that were able to afford cage-shaped dinuclear Na+ complexes. The authors found an interesting selectivity for dicarboxylates of different length. For instance, N-Boc-Asp dianion was strongly coordinated inside the cavity of the receptor whereas N-Boc-Glu dianion, which was one carbon longer, did not. On the other hand Yam et al. (DOI: 10.1002/open.201402019) designed probes using alkynylplatinum(II) terpyridine complexes with an amide-based receptor moiety and studied their sensing features in the presence of different spherical and non-spherical anions. As an example of molecular sensors for cations Lodeiro and co-workers (DOI: 10.1002/open.201402020) prepared a probe based in a bipyridyl unit that was covalently anchored to a rhodamine B fluorophore and studied the interaction of this molecular sensor with Cu2+, Zn2+, Cd2+, Hg+, and Hg2+. Different sensing responses were found to mimic certain logic operations. Finally, two works from Liz-Marzán and Pérez-Prieto described the use of inorganic supports for the design of probes. Liz-Marzán and co-workers (DOI: 10.1002/open.201402009) developed a simple procedure to prepare three-dimensional surface-enhanced Raman scattering (SERS) detection substrates and used these structures for the detection of malachite green in water and of 1-naphthalenethiol from the gas phase. Moreover Pérez-Prieto and co-workers (DOI: 10.1002/open.201402021) used CdSe/ZnS nanoparticles that were decorated with pyrene units as a sensing platform. The authors showed that the probe could be applied as a ratiometric oxygen sensor in organic solvents. In summary, this virtual issue in ChemistryOpen on “Molecular Sensors” includes nice examples in this highly interdisciplinary research field. Overall, the contributions beautifully illustrate current research in the area of chemosensing and how wise designs can lead to selective sensing of target analytes. Prof. Ramón Martínez-Máñez Guest Editor Co-chair of the Editorial Advisory Board ChemistryOpen

Anion Binding Properties of Alkynylplatinum(II) Complexes with Amide-Functionalized Terpyridine: Host-Guest Interactions and Fluoride Ion-Induced Deprotonation

Invited for this months cover is the group of Prof. Vivian Wing-Wah Yam, at the Department of Chemistry of The University of Hong Kong. The cover picture shows the structure of one of their alkynylplatinum(II) complexes with amide-functionalized terpyridine ligands in the present work. In their article, Margaret Ching-Lam Yeung et al. successfully demonstrated an anion sensing strategy based on the host–guest interaction between the amide-based receptor moiety and various anions by monitoring UV/Vis and emission spectral changes. In particular, drastic color changes were observed for the complex upon titration with F− ions. These were ascribed to the deprotonation of the amide functionalities induced by F− ions. This has been confirmed by the restoration of spectral changes upon the addition of CF3COOH to the F– ion–complex mixture. With such drastic color changes, this complex could be a promising candidate to serve as a probing sensor for the visual detection of F− ions. For more details, see the Communication on 10.1002/open.201402019 (p. 172 ff.)

Anion Binding Properties of Alkynylplatinum(II) Complexes with Amide-Functionalized Terpyridine: Host-Guest Interactions and Fluoride Ion-Induced Deprotonation.

Molecular sensors able to detect ions are of interest due to their potential application in areas such as pollutant sequestration. Alkynylplatinum(II) terpyridine complexes with an amide-based receptor moiety have been synthesized and characterized. Their anion binding properties based on host–guest interactions have been examined with the use of UV-vis absorption and emission spectral titration studies. Spectral changes were observed for both complexes upon the addition of spherical and nonspherical anions. Their titration profiles were shown to be in good agreement with theoretical results predicting a 1:1 binding model, and the binding constants were determined from the experimental data. Drastic color changes from yellow to orange–red were observed for one of the complexes upon titration with fluoride (F−) ion in acetone. These changes were ascribed to the deprotonation of the amide functionalities induced by F− ion, and this was confirmed by the restoration of spectral changes upon addition of trifluoroacetic acid to the F− ion–complex mixture as well as by electrospray ionization mass spectrometry (ESI-MS) data.

A New Coumarin-Based Colorimetric and Fluorometric Sensor for Cu2+

Chemosensors, small chemical compounds that sense the presence of analytes or energy, typically consist of two components: a receptor moiety that interacts with the target analytes and a read-out system that signals binding. And one of the most utilized research tool for the study of chemosensors employs a colorimetric and fluorometric spectroscopic techniques. So far successful reports on metal ion sensors have been documented including our recent result. Many different kinds of optical or fluorescent sensors have several advantages (such as high sensitivity and selectivity, non-destructive analysis, low cost and real-time monitoring), which allow naked-eye detection of color and fluorescent emission change upon metal ion binding without the use of any expensive spectroscopic equipment. Copper, the third most abundant transition metal following zinc and iron in human body, exerts essential functions in many cellular enzymes and proteins such as Cu/Zn superoxide dismutase, dopamine monooxygenase, cytochrome C oxidase and ceruloplasmin. However, it becomes toxic when excessive amounts of copper ion were accumulated. It is believed that the disruption of copper homeostasis is associated with neurodegenerative illnesses such as Parkinson’s, Wilson’s, Alzheimer’s and Menke’s diseases. Coumarin skeleton is often utilized as fluorescent sensor due to its excellent photophysical properties like great fluorescent intensity, high quantum yield, high photostability, biological stability, nontoxicity and derivatizable backbone. There have been many excellent coumarin-based fluorescent probes reported for not only anions but also cations such as Fe, Ag, Al, Ni and Hg during the last decade. Herein, we report a new colorimetric and fluorescent “turn-off” sensor that responds to Cu through coumarin derivative. The binding properties of sensor A ward various metal ions were investigated by UV-Vis absorption and fluorescence spectroscopy. Sensor A was synthesized as shown in Scheme 1. Compound 1 and 2 were prepared by the known procedures. Investigations on the photophysical properties revealed that sensor A showed high selectivity to Cu in 10 mM trisHCl buffer solution (acetonitrile/water = 9:1, pH = 7.01). Sensor A showed an absorption band at 375 nm in 10 mM tris-HCl buffer solution. In the presence of Cu (20 μM), there appeared a new red-shifted absorption band at 425 nm at the expense of peak at 375 nm (Figure 1(a) in red). The absorption bands at 375 and 425 nm linearly decreased and increased, respectively, by the increasing concentration of Cu (Figure 1(b)). However, none of the other metal ions (Ag, K, Li, Na, Ca, Cd, Co, Ni, Zn and Fe (20 μM, 2.0 equivalent, nitrate salt)) showed such a red-shift in their absorption spectra (Figure 1(a)). The red-shift in the absorption spectra upon addition of the Cu can be rationalized by intramolecular charge transfer (ICT). It is well known that an electron-donating group at 7position and an electron-withdrawing group at 3-position in coumarin skeleton induce absorption band into visible region as a result of effective ICT through the electron push– pull system. The complexation of a Cu in sensor A would increase electron-withdrawing character of 3-position, resulting a stronger ICT. To investigate the binding mode of sensor A to Cu, Job’s method was carried out. A 1:2 stoichiometry was determined by Job’s plot. The maximum absorption change was

ChemInform Abstract: Metallocyclodextrins: Combining Cavitands with Metal Centres

AbstractReview: 6 refs.

Photoinduced electron transfer fluorometric Hg(II) chemosensor based on a BODIPY armed with a tetrapod receptor

From the great variety of BODIPY based-chemosensors able to determine Hg(2+), only a small portion has been applied to its determination in environmental and/or biological samples. The lack of studies on the analytical performance of the latter sensors makes interesting the development of investigations oriented to their possible analytical applications. The synthesis of a BODIPY derivative armed with a tetrapod receptor is described. The procedure is based on a previous publication, and the modifications performed to improve the synthesis include alternative procedures with different objectives, as the consecution of a multigram synthesis, improving the low yields of some of the previously proposed procedure steps, simplifying the experimental steps, achieving the desired purity requirements for use with analytical purposes, and enriching the characterization of the implied structures. The characteristics of its selectivity towards Hg(2+) have been investigated, and the OFF-ON fluorometric response, based on a photo-electron transfer (PET) mechanism, served as the base for the development of a method able to determine Hg(2+) in environmental waters at ng mL(-1) levels. The intrinsic fluorescence of the BODIPY core is inhibited and the probe exhibits a weak fluorescence (i.e. "OFF" state due to the deactivating PET effect). Upon complexation, Hg(2+) interacts with the lone-pair electrons on the nitrogen atoms of the receptor moiety so that the electronic transfer from the receptor to the photo-excited fluorophore is slowed down or switched off (i.e. "ON" state due to the suppression of the deactivating PET effect by coordination of the analyte to the probe). Regarding the complex photostability in aqueous solution, it is mandatory to conduct the experiments at darkness due to its photodegradation. The stoichiometry studies indicated a 1:2 relationship for the BODIPY-Hg(2+) complex. The high selectivity towards mercuric ions is considerably influenced by pH, being necessary to conduct the experiments in a pH value higher than 6. Calibration samples were prepared by adding appropriate amounts of Hg(2+) between 20.0-120.0 ng mL(-1), at a constant BODIPY concentration of 1 µmol L(-1). After agitating for 5 min at darkness, phosphate buffer (pH=7.50) was added, and it was diluted to the mark with water. Fluorescence measurements were carried out at 18 °C, exciting at 515 nm, and obtaining fluorescence emission at 538 nm. The method has been satisfactory applied to Hg(2+) determination in environmental water samples.

Applications of Fluorescent Sensor Based on 1H-pyrazolo[3,4-b]quinoline in Analytical Chemistry

Fluorescent dye 2-[(2-Hydroxyethyl)-(1,3-diphenyl-1H-pyrazolo[3,4-b]quinolin-6-ylmethyl)-amino]ethanol (LL1) was examined for its efficiency in the detection of small inorganic cations (lithium, sodium, barium, calcium, magnesium, cadmium, lead and zinc). The dye was synthesized in the laboratory and investigated by means of both, steady-state and time-resolved fluorescence techniques. This compound acts as a fluorescent sensor suitable for detection of small inorganic cations (lithium, sodium, barium, calcium, magnesium, cadmium, lead and zinc) in strongly polar solvent (acetonitrile). An electron transfer from the electro-donative part (receptor) of the molecule to the acceptor part (fluorophore) is thought to be the main mechanism that underlies functionality of the compound as a sensor. This process can be retarded upon complexation of the receptor moiety by inorganic cations. Relatively high sensitivity but poor selectivity of the aminoalcohol thatcontains indicator towards the two-valued cations was observed. However, upon addition of some amounts of water the selectivity of this sensor has been enhanced (especially towards lead cation). The preliminary results in analytical application of the sensor are discussed.

Abstract 3308: Systemic administration of fiber redesigned infectivity-selective oncolytic adenovirus for pancreatic cancer.

Abstract Adenovirus (Ad) has frequently been used as a backbone of oncolytic viral agents, while lack of selectivity to cancer cells at the stage of infection has greatly hampered in vivo efficacy. Unlike loco-regional therapy, systemic application of cancer gene therapy mandates different level of selectivity of gene delivery. The controlled distribution and selective transduction of the vector would overcome the obstacles for systemic delivery and enable efficient systemic treatment of cancer. We have recently developed transductionally-targeted Ads by high-throughput screening of high-diversity (10ˆ9-level) Ad-library. Mesothelin (MSLN) is highly over-expressed in pancreatic cancers. Ad with redesigned AB-loop targeting MSLN, AdML-VTIN, was successfully isolated from the high throughput screening of Ad library by infectivity for MSLN-expressing 293 cells (293-MSLN). The in vitro binding of AdML-VTIN corresponded to the level of MSLN-expression and the suppression of MSLN with siRNA or antibody significantly reduced the binding to MSLN-expressing cells, which indicates that mesothelin is a receptor moiety for the isolated targeting ligand. The binding ability of this virus in Panc-1 (MSLN-positive) was higher than that of Ad with 5/3 modified fiber which is known to exhibit highest infectivity in pancreatic cancer cells. The in vivo antitumor effect was compared in Panc-1 and MiaPaCa-2 (MSLN-negative) subcutaneous xenografts. The injection of the MSLN-retargeted oncolytic Ad showed significant antitumor effect against Panc-1 tumors, and about half of the tumor disappeared. Contrarily, the same virus showed no antitumor effect in MiaPaCa-2. Viral DNA quantitation also supported the selective viral replication in Panc-1. Upon systemic administration in the nude mice with Panc-1 subcutaneous xenografts, the sequestration of AdML-VTIN to the liver was significantly lower than that of wild-type Ad5, and the copy number of this retargeted virus was significantly (1000 fold) higher in the tumor. These data indicates the systemic delivery of this vector is efficient for MSLN-expression pancreatic cancer xenografts. In this study, our MSLN-targeted Ad vector exhibited significant infectivity to MSLN-positive pancreatic cancer cells in vitro and in vivo. Moreover, this virus showed significantly reduced liver sequestration as well as dramatically augmented delivery to the tumors upon systemic administration. This new genetically modified Ad transductionally retargeted to pancreatic cancer may embody a next generation targeting for this devastating disease in clinical settings. Citation Format: Yoshiaki Miura, Joohee Han, Julia Davydova, Masato Yamamoto. Systemic administration of fiber redesigned infectivity-selective oncolytic adenovirus for pancreatic cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3308. doi:10.1158/1538-7445.AM2013-3308 Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.

Regenerative Electronic Biosensors Using Supramolecular Approaches

A supramolecular interface for Si nanowire FETs has been developed with the aim of creating regenerative electronic biosensors. The key to the approach is Si-NWs functionalized with β-cyclodextrin (β-CD), to which receptor moieties can be attached with an orthogonal supramolecular linker. Here we demonstrate full recycling using the strongest biomolecular system known, streptavidin (SAv)-biotin. The bound SAv and the linkers can be selectively removed from the surface through competitive desorption with concentrated β-CD, regenerating the sensor for repeated use. An added advantage of β-CD is the possibility of stereoselective sensors, and we demonstrate here the ability to quantify the enantiomeric composition of chiral targets.

Generation of supramolecular microcapsules by oxidative covalent polymerization of a ditopic supramolecular building block

We describe a novel approach to the generation of a supramolecular polymer and its assembly into microcapsules by the aerial oxidation of a supramolecular building block. It involves the initial build-up of a ditopic supramolecular component by hydrogen bonding association of two complementary subunits, followed by its covalent polymerization through oxidative formation of C–C linkages. The supramolecular component itself was selectively formed from a dynamic covalent library of hydrazone isomers by target specific amplification of a single library constituent. The polymer obtained condenses into supramolecular aggregates of micrometric size and capsular-type morphology, presenting multilayered walls, which have been characterized by STEM, SEM and AFM imaging methods. The present design methodology implements the covalent polycondensation of non-covalent monomers towards the formation of supramolecular polymers, in a sequence opposite to the usual non-covalent polyassociation of covalent complementary monomers. It can be envisaged as a proactive step towards forming adaptive smart materials through manipulation of the sequence of supramolecular/non-covalent and molecular/covalent steps for the generation of supramolecular polymers by suitable selection of receptor and substrate moieties.

Selective fluorescence sensing of Cu(ii) and Zn(ii) using a new Schiff base-derived model compound: naked eye detection and spectral deciphering of the mechanism of sensory action

A new Schiff base compound 2-((benzylimino)-methyl)-naphthalen-1-ol (2BIMN1O) has been synthesized and characterized by (1)H NMR, (13)C NMR, DEPT, FT-IR and mass spectroscopic techniques. The significantly low fluorescence yield of the compound has been rationalized in connection with photo-induced electron transfer (PET) from the imine receptor moiety to the naphthalene fluorophore unit. Subsequently, an evaluation of the transition metal ion-induced modification of the fluorophore-receptor communication reveals a promising prospect for the title compound to function as a fluorosensor for Cu(2+) and Zn(2+) ions selectively, through remarkable fluorescence enhancement. While perturbation of the PET process in 2BIMN1O has been argued to be the responsible mechanism behind the fluorescence enhancement, the selectivity for these two metal ions has been interpreted on the grounds of an appreciably strong binding interaction. Particularly notable aspects regarding the chemosensory activity of the compound are its ability to detect the aforesaid transition metal ions down to the level of micromolar concentration (detection limit being 0.82 and 0.35 μM respectively), along with a simple and efficient synthetic procedure. Also the spectral modulation of 2BIMN1O in the presence of the transition metal ions paves the way for the construction of a calibration curve in the context of its fluorescence signaling potential.

Biomimetic Architectures for the Impedimetric Discrimination of Influenza Virus Phenotypes

AbstractRapid discrimination of avian vs. human phenotypes of emerging influenza A virus isolates with pandemic potential is an important issue in pathogenesis and epidemiology studies of the infection. In this work, functional architectures are tailored on the surface of a gold electrode, introducing receptor molecules as a sensing entity that mimics those found in the membrane of target cells of the influenza A virus and with the aim of developing an impedimetric‐based detector for influenza A virus phenotyping. In a bottom‐up approach, the artificial receptors are built by sequential assembly of a 1‐octanethiol/octyl‐galactoside hybrid bilayer, followed by an enzyme‐mediated functionalization of the terminal galactoside groups with sialic acid molecules. The detection mechanism relies hence on the specific affinity between the sialic acid‐galactose receptor moieties anchored on the modified electrode surface and the hemagglutinin (HA) viral surface protein. By using the appropriate type of sialyltransferase enzyme, sialylation of galactose residues is made through α‐2,3 or α‐2,6 linkages. This permits the envisaged impedimetric detector to discriminate rapidly between avian vs. human strains of influenza A virus with the absence of elaborate sample preparation steps. In contrast to immunosensors based on antibodies as bioreceptor, the sialylated modified gold electrode is also able to distinguish among influenza phenotypes, which could make the here presented detector a reagentless, label‐free diagnostic device for influenza phenotyping.

Interactions of Calix[n]arenes with Nucleic Acids

DNA interaction with artificial binders is of great interest, especially in light of the broad range of possible biomedical applications. The growing understanding of replication, transcription and translation opened the path for new approaches to target pathological effects at a very early stage. Meanwhile, the competitive binding to nucleic acids by designed molecules, which, for example, block certain sequences for natural binders, such as transcription factors, has become a promising concept in the context of gene therapy. On the other extreme, the transport of nucleic acids over the cell membrane into the nucleus by transfection agents opens the possibility to reprogram protein biosynthesis within host cells. In the past decades several substance classes have been developed for a noncovalent specific DNA binding with predictable biological effects, such as peptide nucleic acids or polyamide ligands. Calixarenes have not received so much attention, although they consist of a compact aromatic core tuneable in size, and allow the introduction of cationic functionalities at their upper and lower rims. Formerly being utilized as receptor moieties due to the possibility of complexating guests in their cavities, calixarenes are now also used as molecular scaffolds for multivalent ligands and are, therefore, suitable tools for cooperative DNA complexation. This review surveys specific supramolecular interactions between calixarene derivatives and nucleic acids, with an emphasis on structural elements in the calixarenes and the biological consequences of their complex formation with DNA strands.

Receptor-Binding Profiles of H7 Subtype Influenza Viruses in Different Host Species

Influenza viruses of gallinaceous poultry and wild aquatic birds usually have distinguishable receptor-binding properties. Here we used a panel of synthetic sialylglycopolymers and solid-phase receptor-binding assays to characterize receptor-binding profiles of about 70 H7 influenza viruses isolated from aquatic birds, land-based poultry, and horses in Eurasia and America. Unlike typical duck influenza viruses with non-H7 hemagglutinin (HA), all avian H7 influenza viruses, irrespective of the host species, displayed a poultry-virus-like binding specificity, i.e., preferential binding to sulfated oligosaccharides Neu5Acα2-3Galβ1-4(6-O-HSO(3))GlcNAc and Neu5Acα2-3Galβ1-4(Fucα1-3)(6-O-HSO(3))GlcNAc. This phenotype correlated with the unique amino acid sequence of the amino acid 185 to 189 loop of H7 HA and seemed to be dependent on ionic interactions between the sulfate group of the receptor and Lys193 and on the lack of sterical clashes between the fucose residue and Gln222. Many North American and Eurasian H7 influenza viruses displayed weak but detectable binding to the human-type receptor moiety Neu5Acα2-6Galβ1-4GlcNAc, highlighting the potential of H7 influenza viruses for avian-to-human transmission. Equine H7 influenza viruses differed from other viruses by preferential binding to the N-glycolyl form of sialic acid. Our data suggest that the receptor-binding site of contemporary H7 influenza viruses in aquatic and terrestrial birds was formed after the introduction of their common precursor from ducks to a new host, presumably, gallinaceous poultry. The uniformity of the receptor-binding profile of H7 influenza viruses in various wild and domestic birds indicates that there is no strong receptor-mediated host range restriction in birds on viruses with this HA subtype. This notion agrees with repeated interspecies transmission of H7 influenza viruses from aquatic birds to poultry.

Human Sperm Interaction withStaphylococcus aureus: A Molecular Approach

Sperm immobilization factor (SIF) causing 100% immobilization of spermatozoa isolated from Staphylococcus aureus when characterized using LC-MS (Liquid chromatography-mass spectrometry) showed that this 20 kDa protein had peptide sequence similarity with hsp-70 protein. It was found to completely (100%) inhibit Mg++ ATPase activity of spermatozoa at concentration of 100 μg mL−1. Sperm samples treated with SIF also showed reduction in calcium ionophore-induced acrosome reaction as compared to control samples (treated with calcium ionophore alone). Binding studies of FITC labelled SIF with spermatozoa using fluorescent microscopy showed binding of SIF to the surface of spermatozoa indicating the presence of SIF binding receptor. The receptor was extracted by 3M NaCl and purified by gel permeation chromatography. Characterization of the receptor by MALDI-TOF (Matrix-assisted laser desorption ionization-time of flight) indicated that the receptor shared sequence similarity with MHC class II antigen. A calorimetric study showed that the receptor moiety on spermatozoa was specific for the purified ligand as binding of the receptor to ligand was enthalpically (−11.9 kJ mole−1) as well as entropically (21.53 J mole−1 K−1) favored resulting in the Gibb's free energy of −18.57 kJ mole−1.

Synthesis, structural characterisation and luminescent anion sensing studies of a Ru(II)polypyridyl complex featuring an aryl urea derivatised 2,2′-bpy auxiliary ligand

The inclusion of a urea functionality into the coordination sphere of a Ru(II)-polypyridyl complex (Ru·L1) resulted in a system that can function as an effective long wavelength emissive fluorescent anion sensor. The MLCT emission of Ru·L1 is sensitive to the binding of acetate, phosphate and pyrophosphate but not fluoride in organic solvent. In addition, Ru·L1 can distinguish between phosphate and pyrophosphate with an emission increase upon binding of H2PO4- (“turn on” sensor) and an emission decrease upon binding of HP2O73- (“turn off” sensor), which occurs via hydrogen bonding to the urea receptor moiety as demonstrated by carrying out NMR titrations as well as by employing [Ru(II)bpy3](PF6-)2 as a model compound that lacks the anion receptor moiety.

Design and synthesis of novel fluorescence sensing perylene diimides based on photoinduced electron transfer

Two novel tetraester- and PAMAM-branched perylene diimides were synthesized and configured as “fluorophore-spacer-receptor” systems based on photoinduced electron transfer. Due to their long alkylester and alkylamine terminal groups the examined compounds were well soluble in organic solvents. Photophysical characteristics of the dyes were investigated in DMF and water/DMF (1:1, v/v) solution. The ability of the synthesized perylene diimides to detect cations was evaluated by the changes in their fluorescence intensity in the presence of metal ions (Zn 2+, Co 2+, Cu 2+, Fe 3+, Pb 2+, Hg 2+, Ag + and Ni 2+) and protons. The dyes under study displayed “off–on” switching in its fluorescence as a function of pH, which is attributed to disallowing photoinduced electron transfer from the receptor moiety to the fluorophore. PAMAM-branched dye displayed a good pH sensor activity (FE = 6.4), however the pH sensing ability of tetraester was substantially higher (FE = 184). In the presence of Cu 2+ and Pb 2+ ions tetraester quenched its fluorescence intensity (FQ = 22 and 12 respectively), while PAMAM-branched dye enhanced its fluorescence intensity with pronounced selectivity to Cu 2+ and Fe 3+ (FE = 3.2 and 4.9, respectively). The results obtained indicate the potential of the novel compounds as fluorescent detectors for metal ions with pronounced selectivity towards Cu 2+, Pb 2+ and Fe 3+ ions and highly efficient “ off –on” pH switches, especially a tetraester-branched perylene diimide.