Social senses: G-protein-coupled receptor signaling pathways in Dictyostelium discoideum

Activation of the chemoattractant receptor of Dictyostelium elicits many of the same biochemical events seen when mammalian G-protein-coupled receptors are activated. Studies in this organism provide evidence for new signaling pathways that are activated by receptors of this type, and fresh insights into the mechanism of signal transduction by G proteins.     

Design of peptide that recognizes double-stranded DNA.

A novel molecular tool for double-stranded (ds) DNA detection using synthetic peptide is described. The peptide was designed based on the DNA binding domain of the lambda phage CRO repressor (CRO). The designed peptides contain helix-turn-helix (HTH), which is DNA binding motif. A cyclic peptide and a mutant peptide based on CRO were also designed, and the resulting affinity for dsDNA was increased. Furthermore, native amino acids of the peptide were replaced with arginine to increase the affinity for dsDNA. The affinity of these peptides for DNA binding was assessed by surface plasmon resonance (SPR) technique.     

What anions do inside a receptor's cavity: a trifurcate anion receptor providing both electrostatic and hydrogen-bonding interactions

The trifurcate receptor 1(3+) forms stable 1:1 complexes with halide and oxo anions in MeCN solution, as shown by spectrophotometric and 1H NMR experiments, and selectively recognizes chloride (lg K(ass) > 7) in the presence of fluoride and bromide. The high stability reflects the receptor's ability to donate up to six hydrogen bonds (from three pyrrole N-H and three C-H fragments, polarized by the proximate positive charge) to the included anion. Addition of an excess of more basic anions (F- and CH3COO-) induces stepwise deprotonation of the N-H groups, an event signalled by the appearance of a bright yellow color. Crystal and molecular structures are reported for the complex with NO3(-) and a capsule consisting of two interconnected trifurcate subunits, one of which includes an H-bound Br- ion, while the other is doubly deprotonated and includes an H-bound water molecule. Finally, evidence is given for the formation in solution of an authentic complex of OH-, in which H-bound hydroxide is included within the cavity of 1(3+).     

Metal-containing conjugated oligo- and polythiophenes

Conjugated polymers containing metal groups are an important class of new materials that may find application as sensors, non-linear optical materials and in molecular electronics. Polythiophenes are an extensively studied class of conjugated polymers, that can be easily modified synthetically, and may be prepared using a variety of methods. Metal groups pendant to polythiophene backbones modulate the electronic, optical and redox properties of the conjugated backbone and can introduce novel structural motifs to these materials. Functionalization of oligo- and polythiophenes by Fe, Pd and Ru containing groups is discussed, along with the properties of some of these materials.     

A fluorous synthetic receptor that recognizes perfluorooctanoic acid (PFOA) via fluorous interaction obtained by molecular imprinting

A polymeric sorbent selective for perfluorooctanoic acid (PFOA) was synthesized by a molecular imprinting technique using a fluorous monomer and cross-linker, and assessed chromatographically, suggesting that the fluorous imprinted polymer recognizes PFOA via hydrogen bonding and fluorine-fluorine interaction.     

Metal-containing oligomers,dendrimers and biopolymers

Transition metal complexes encompass a large and exceptional pool of building blocks with diverse stereochemical, electrochemical and photophysical features. This mini-account presents efforts to advance the organic chemistry of coordination compounds, where functionalized complexes are viewed as synthetic building blocks. Selective synthetic transformations, conducted on the periphery of coordinatively saturated metal complexes, are shown to facilitate the fabrication of sophisticated complexes, multimetallic arrays, and metal-containing biopolymers. In addition, the utilization of novel phenanthrolines as tunable fluorophores, as well as for the assembly of hyperbranched structures and sensory oligonucleotides, is described.     

Development of a regenerable cell culture system that senses and releases dead cells

We developed a rapidly regenerable cell culture system in which the cell culture substrate detects cell death and selectively releases the dead cells. This culture material was achieved by combining a detector that responds to the signal from the dead cells and an actuator to release the dead cells. Benzo-18-crown-6-acrylamide (BCAm) with a pendant crown ether receptor was used as the sensor to recognize cellular signals and N-isopropylacrylamide (NIPAM) was used as the actuator. This copolymer of NIPAM and BCAm can respond to potassium ions and change its nature from hydrophobic to hydrophilic at the culture temperature of 37 degrees C. Living cells concentrate potassium ion internally; when cells die, potassium ions are released. The polymer surface recognizes the potassium ions released from the dead cells, the NIPAM hydrates, and the dead cells are selectively detached. This in vitro culture system is a novel one in which artificial culture materials work cooperatively with cellular metabolism by responding to this signal from the cells, thereby realizing in vitro tissue regeneration partly mimicking the mechanisms of in vivo homeostasis.     

Ru(ii)-cornered coordination cage that senses guest inclusion by color change

Upon guest recognition, a self-assembled hexa-ruthenium coordination cage shows a chromic shift resulting from the slight conformational change in the panel ligand.     

Metal-containing systems based on chitosan and a collagen-chitosan composite

Russian Chemical Bulletin - Metal-carrying polysaccharides based on chitosan and a collagen-chitosan composite (collachit) were obtained by modifying polymers by Au and Fe nanoparticles, which were...     

A [5]HELOL analogue that senses remote chirality in alcohols, phenols, amines, and carboxylic acids

A route is developed to a structural analogue of [5]HELOL, a previously reported helically grooved sensor of remote chirality. It gives the material enantiomerically pure and in multigram quantities. The enantiomers of alcohols, phenols, amines, and carboxylic acids, even when their centers of chirality are remote from any functional groups, can be differentiated by 31P NMR spectroscopic analyses of their reaction products with the chlorophosphite of this material.     

Metal-containing liquid crystals with potential application in optical storage devices

Three optically active oxovanadium(IV)-containing metallomesogens have been prepared and their mesomorphic properties investigated. It is found that enantiotropic chiral phases are stabilized when the molecular system promotes the anti-ferromagnetic coupling of individual molecules into associated pairs. The molecular optical rotation of the non-mesomorphic ligands is greatly enhanced on complexation to an oxovanadium(IV) metal centre to give the mesogenic complex. The mesophase alignment can be retained by cooling to room temperature and this may be utilized in the fabrication of a low cost, multi-session, 'write-read-erase' optical storage device with low power consumption.     

Unusually short RNA sequences: design of a 13-mer RNA that selectively binds and recognizes theophylline

RNA plays critical roles in numerous biological processes and constitutes valuable therapeutic targets. RNA is significant not only for its roles in transmitting the genetic code but also for its enzymatic functions in ribozymes and in peptide bond formation in ribosomes. Recent studies have shown that RNAs containing as few as 22 nucleotides can be key elements in cellular functions. This suggests the possibility of using short RNAs as regulatory elements. Here, we show that ligand recognition and selectivity by RNA molecules can occur with only the presence of a binding pocket and as few as six additional scaffolding nucleotides holding the binding pocket in place. A 13-mer RNA truncation of a 33-mer aptamer for theophylline preserves the ability to bind to theophylline and to discriminate against the structurally similar compound caffeine. The truncated aptamer retains nearly all of the same structural elements in its binding site as those present in the original aptamer. This is the first demonstration of selective ligand binding by a 13-mer RNA.     

A molecular flytrap for the selective binding of citrate and other tricarboxylates in water

The synthesis and binding properties of a new tricationic guanidiniocarbonyl pyrrole receptor 7 are described. Receptor 7 binds citrate 9 and other tricarboxylates such as trimesic acid tricarboxylate 8 with unprecedented high association constants of K(assoc) > 10(5) M(-1) in water as determined by UV and fluorescence tritration studies. According to NOESY experiments and molecular modeling calculations, the tricarboxylates are bound within the inner cavity of receptor 7 by ion pairing between the carboxylate groups and the guanidiniocarbonyl pyrrole moieties, favored by the nonpolar microenvironment of the cavity. Hence, receptor 7 can be regarded as a molecular flytrap. In the case of the aromatic tricarboxylate 8, additional aromatic interactions further strengthen the complex. The complexes with the tricarboxylates are so strong that even the presence of a large excess of competing anions or buffer salts does not significantly affect the association constant. For example, the association constant for citrate changes only from K(assoc) = 1.6 x 10(5) M(-1) in pure water to K(assoc) = 8.6 x 10(4) M(-1) in the presence of a 170-fold excess of bis-tris buffer and a 1000-fold excess of chloride. This makes 7 one of the most efficient receptors for the binding of citrate in aqueous solvents reported thus far.     

Metal-containing ionic liquids and ionic liquid crystals based on imidazolium moiety

Ionic liquids and ionic liquid crystals of imidazolium salts composed of various transition and main group metals have been reviewed. Ionic metal complexes of imidazoles and N-heterocyclic carbenes possess the similar properties were also included. These types of ILs and ILCs have been realized as potential solvents, catalysts, catalyst precursors and reagents for many organic transformations and provide ecofriendly protocols. They have also been found to play key roles in material science. Many of these IL systems are air- and moisture stable and are considered as alternatives for air- and moisture sensitive chloroaluminate-based ILs.     

Investigation of Metal State in Metal-containing Zeolite Catalysts by DTA and ESR Methods

Thermal stability and its influence on the catalytic activity in CO oxidation of Cu, Pd and Pd-Cu zeolite systems were investigated. The increasing of catalytic activity in the first cycle of reaction is connected with the thermal decomposition of complexions and consequently with the changing of metal state in catalyst in the case of Cu/ZSM-5catalyst. This activity does not relate to initial zeolite with complex ions, but to the metal ions with the decreasing ligands number in the coordination sphere of metal ion. According to the EPR spectrum the copper ions form clusters in zeolite channels due to the spin changed interaction. It was established ESR method that 1.8% Cu/ZSM-5 catalyst in a reduced form has copper (I and II) ions by. The Pd/ZSM-5 catalysts with different metal content have high catalytic activity below the temperature decomposition in contrary to Cu-containing zeolites. On the one hand, it may be connected with the partial reduction of Pd ions during CO oxidation and, on the other hand, with the ability of Pd ions to form the respective label complexes with reagents as additional ligands. The same character of relation between thermal stability and catalytic activity for Pd-Cu/ZSM-5 catalyst was observed. This revised version was published online in August 2006 with corrections to the Cover Date.     

一种能选择性识别磷酸根离子的金属配合物化学敏感器

合成了两种Schiff碱类金属配合物1([Cu(L1)]²⁺)和2([Cu(L2)]²⁺).对它们在强极性溶剂,如[V(水):V(乙醇)=98:2]混合溶剂中与阴离子间的相互作用进行了研究.发现具有C_3v结构的配合物1有着优良的检测PO₄^3-离子的能力.通过UV光谱滴定实验,表明配合物1和PO₄^3-间形成了1:1的稳定配合物.配合物1对HPO₄^2-也有一定的响应性.但对其它的阴离子(如四面体和非四面体结构的阴离子)物种,则未观察到有任何响应.文中还提出了配合物1与阴离子间构成新的配合物可能结构的建议.但是对于配合物2,对阴离子的响应能力比较差.对于实验结果以及如何提高敏感器化合物的选择能力进行了初步讨论.     

Solubility of sildenafil citrate in propylene glycol + water mixtures at various temperatures

The solubility of sildenafil citrate (SC) in aqueous mixtures of propylene glycol (PG) was investigated. This study was carried out at different mass fractions of PG ranging from 0.1 to 0.9 at T = 293.2–313.2 K. The solubility of SC in the mixed solutions increased with increasing temperature and PG mass fraction.

The solubility values were correlated by two co-solvency models (Jouyban–Acree model and van’t Hoff–Jouyban–Acree model). The mean relative deviations (MRD) were 5.7% and 5.5%, respectively. Density of the SC-saturated solutions over the entire solvent composition and temperature range was also measured and the results correlated with the Jouyban–Acree model. Furthermore, the apparent thermodynamic properties, dissolution enthalpy, dissolution entropy and Gibbs free energy change of dissolution process of SC in all the mixed solvents were calculated according to van’t Hoff and Gibbs equations. Dissolution of SC in these mixed solvents is an endothermic process.     

Stereochemistry of the citrate anion in compounds containing guanidinium and citrate ions

Journal of Structural Chemistry - An analysis is presented for the results obtained in the studies initiated by A. E. Shvelashivili, Corresponding Member, Academy of Sciences of Georgia, and...     

Short lexitropsin that recognizes the DNA minor groove at 5'-ACTAGT-3': understanding the role of isopropyl-thiazole

Isopropyl-thiazole ((iPr)Th) represents a new addition to the building blocks of nucleic acid minor groove-binding molecules. The DNA decamer duplex d(CGACTAGTCG)(2) is bound by a short lexitropsin of sequence formyl-PyPy(iPr)Th-Dp (where Py represents N-methyl pyrrole, (iPr)Th represents thiazole with an isopropyl group attached, and Dp represents dimethylaminopropyl). NMR data indicate ligand binding in the minor groove of DNA to the sequence 5'-ACT(5)AG(7)T-3' at a 2:1 ratio of ligand to DNA duplex. Ligand binding, assisted by the enhanced hydrophobicity of the (iPr)Th group, occurs in a head-to-tail fashion, the formyl headgroups being located toward the 5'-ends of the DNA sequence. Sequence reading is augmented through hydrogen bond formation between the exocyclic amine protons of G(7) and the (iPr)Th nitrogen, which lies on the minor groove floor. The B(I)/B(II) DNA backbone equilibrium is altered at the T(5) 3'-phosphate position to accommodate a B(II) configuration. The ligands bind in a staggered mode with respect to one another creating a six base pair DNA reading frame. The introduction of a new DNA sequence-reading element into the recognition jigsaw, combined with an extended reading frame for a small lexitropsin with enhanced hydrophobicity, holds great promise in the development of new, potentially commercially viable drug lead candidates for gene targeting.