Coordination properties of 3′,5′-cyclic adenosine monophosphate towards copper(II) ions

The metal binding ability of 3′,5′-cyclic adenosine monophosphate (3′,5′-cAMP) molecule using copper(II) ion, as an example of biologically available divalent metal ion, was investigated by potentiometry, EPR and differential spectroscopy (UV-Vis, CD). One complex with stoichiometry Cu(3′,5′-cAMP)⁺ was found, where Cu(II) ion is bound by N-7 nitrogen of adenine moiety.     

2′,3′-cAMP hydrolysis by metal-dependent phosphodiesterases containing DHH, EAL, and HD domains is non-specific: Implications for PDE screening

The recent report of 2′,3′-cAMP isolated from rat kidney is the first proof of its biological existence, which revived interest in this mysterious molecule. 2′,3′-cAMP serves as an extracellular adenosine source, but how it is degraded remains unclear. Here, we report that 2′,3′-cAMP can be hydrolyzed by six phosphodiesterases containing three different families of hydrolytic domains, generating invariably 3′-AMP but not 2′-AMP. The catalytic efficiency (k_cat/K_m) of each enzyme against 2′,3′-cAMP correlates with that against the widely used non-specific substrate bis(p-nitrophenyl)phosphate (bis-pNPP), indicating that 2′,3′-cAMP is a previously unknown non-specific substrate for PDEs. Furthermore, we show that the exclusive formation of 3′-AMP is due to the P-O2′ bond having lower activation energy and is not the result of steric exclusion at enzyme active site. Our analysis provides mechanistic basis to dissect protein function when 2′,3′-cAMP hydrolysis is observed.     

A rational approach to the regioselective deacetylation of 2′,3′,5′-tri-O-acetyluridine by Novozym 435 catalysed alcoholysis

To give a rational explanation for the behaviour of 2′,3′,5′-tri-O-acetyluridine (TAU) catalysed alcoholysis using Novozym 435, the commercial biocatalyst with immobilized Candida antarctica lipase B (CALB), a set of experiments analyzing the role of the alcohol/substrate (A/S) molar ratio, alcohol/biocatalyst (A/B) and substrate/biocatalyst (S/B) mass ratios were carried out. At a A/S = 120 and a S/B = 6.16, 2′,3′-di-O-acetyluridine (DAU) was obtained in 92% at 22 h. The observed trend towards the exclusive formation of DAU at very high alcohol amounts can be explained on the basis of the change of substrate orientation from normal to inverse. The simple molecular modelling analysis supports that key O/H atoms from TAU and the resulting intermediates display the adequate distances to generate productive binding only when the inverse coordination of TAU is present through the 5′-moiety of TAU, at high ethanol concentrations. At these conditions a possible allosteric-like effect of ethanol, combined with water in an H-network in the catalytic triad and in its neighbourhood, could explain the high selectivity towards the production of DAU at selected conditions.     

PDE7A1 hydrolyzes cCMP

The degradation and biological role of the cyclic pyrimidine nucleotide cCMP is largely elusive. We investigated nucleoside 3′,5′-cyclic monophosphate (cNMP) specificity of six different recombinant phosphodiesterases (PDEs) by using a highly-sensitive HPLC–MS/MS detection method. PDE7A1 was the only enzyme that hydrolyzed significant amounts of cCMP. Enzyme kinetic studies using purified GST-tagged truncated PDE7A1 revealed a cCMP K_M value of 135 ± 19 μM. The V_max for cCMP hydrolysis reached 745 ± 27 nmol/(min mg), which is about 6-fold higher than the corresponding velocity for adenosine 3′,5′-cyclic monophosphate (cAMP) degradation. In summary, PDE7A is a high-speed and low-affinity PDE for cCMP.     

Structural characterization of the coordination behavior of 4,4′-di-methoxy,2,2′-di-ol-benzophenone modified metal alkoxides

For the first time, the coordination behavior of the 4,4′-di-methoxy,2,2′-di-ol-benzophenone (H₂-OBzP) ligand with a series of early transition metal alkoxides (Group 4, 5, and 6) was determined to adopt either the ‘bridging, chelating bridging’ (μ,μ_c-OBzP) or the ‘bichelating bridging’ (μ_c2-OBzP) arrangement. The main products were found to be dimeric with pseudo-octahedral (O_h) bound metal centers. The μ,μ_c-OBzP mode was noted for the larger cations (Hf, Nb, and Ta) and the solvated smallest (Ti/py) whereas the μ_c2-OBzP coordination was observed for the larger Group 4 metal congeners: [(py)(OPrⁱ)₂Ti(μ,μ_c-OBzP)]₂ (1), ‘{[(OBu^t)₂Ti(μ-OBu^t)]₂(μ_c2-OBzP)}_n’ (2), [(ONep)₂Ti(μ-ONep)]₂(μ_c2-OBzP) (3), [(OBu^t)₂Zr(μ-OBu^t)]₂(μ_c2-OBzP) (4), [(MeIm)₂(ONep)₂Zr(μ,μ_c-OBzP)]₂ (5), [(ONep)₂Zr(μ_c2-OBzP)(μ-ONep)(μ₃-O)Zr(ONep)]₂ (5a), [(OBu^t)₂Hf(μ_c2-OBzP)]₂(6), ‘{[(ONep)₂Hf(μ,μ_c-OBzP)]₂·py}_n’ (7), ‘{[(OEt)₃Nb(μ,μ_c-OBzP)]₂}_n’ (8), [(ONep)₃Nb(μ,μ_c-OBzP)]₂ (9), [(OEt)₃Ta(μ,μ_c-OBzP)]₂ (10), [(ONep)₃Ta(μ,μ_c-OBzP)]₂ (11), and [(OEt)₂(O)W(μ,μ_c-OBzP)]₂ (12), [(ONep)₂W(O)(μ,μ_c-OBzp)]₂ (13), [(py)(O)₂W(μ,μ_c-OBzP)]₂ (13a), and [(Me₂Al(μ,²μ_c-OBzP)Al(py)₂] (14) where Me = CH₃, OEt = OCH₂CH₃, OPrⁱ = OCHMe₂, OBu^t = OCMe₃, ONep = OCH₂CMe₃, py = pyridine, MeIm = 1-methyl imidazole, and ²μ_c-refers to the chelation occurs on the same metal. Compounds 2, 7, and 8 are represented by quotation marks since they could not be crystallographically characterized, however, their structural arrangements were deduced from the FTIR spectroscopic data. The coordination mode of the OBzP ligand for 1-13 appears to be driven by the need to fill the O_h geometry, which is achieved by either binding solvent molecules or additional bridging ligands, dictated by the charge and size of the cations employed. The metal alkyl alkoxide compound 14 employs a unique μ,²μ_c-OBzP mode, yielding a +2/+4 charge separated molecular Al complex.     

Adenosine 3′,5′-monophosphate and guanosine 3′,5′-monophosphate: A simultaneous protein binding assay

The adenosine 3′,5′-monophosphate and guanosine 3′,5′-monophosphate contents of microliter quantities of urine can be determined simultaneously by combining individual protein binding assays for the two nucleotides. ³²P-labeled adenosine 3′,5′-monophosphate is bound to a protein from bovine skeletal muscle, while a lobster muscle protein preparation is utilized for binding of ³H-labeled guanosine 3′,5′-monophosphate.     

4,4′-Bis(tert-butyl)-2,2′-bipyridinedichlorometal(II) - Synthesis, structure and EPR spectroscopy

Due to the better solubility of the 4,4′-substituted bipyridine ligand a series of 4,4′-bis(tert-butyl)-2,2′-bipyridinedichlorometal(II) complexes, [M(tbbpy)Cl₂], with M = Cu, Ni, Zn, Pd, Pt was synthesised and characterised. The blue copper complex 4,4′-bis(tert-butyl)-2,2′-bipyridinedichlorocopper(II) was isolated in two different polymorphic forms, as prisms 1 with a solvent inclusion and solvent-free as needles 2. Both structures were determined by X-ray structure analysis. They crystallise in the monoclinic space group P2₁/c with four molecules in the unit cell, but with different unit cells and packing motifs. Whereas in the prisms 1, with the unit cell parameters a = 12.1613(12), b = 10.6363(7), c = 16.3074(15) Å, β = 94.446(8)°, the packing is dominated by intra- and intermolecular hydrogen bonds, in the needles 2, with a = 7.738(1), b = 18. 333(2), c = 13.291(3) Å, β = 97.512(15)°, only intramolecular hydrogen bonds appear and the complex molecules are arranged in columns which are stabilised by π-π-stacking interactions. In both complexes the copper has a tetrahedrally distorted coordination sphere. These copper complexes were also studied by EPR spectroscopy in solution, as frozen glass and diamagnetically diluted powder with the analogue [Pd(tbbpy)Cl₂] as host lattice.     

Biosynthesis of homoeriodictyol from eriodictyol by flavone 3′-O-methyltransferase from recombinant Yarrowia lioplytica: Heterologous expression,biochemical characterization,and optimal transformation

In this work, we attempted to synthesize homoeriodictyol by transferring one methyl group of S-adenosyl-l-methionine (SAM) to eriodictyol using flavone 3′-O-methyltransferase ROMT-9, which was produced by recombinant Yarrowia lipolytica. Specifically, the ROMT-9 gene from rice was synthesized and cloned into the multi-copy integrative vector pINA1297, and was further expressed in Y. lipolytica with a growth phase-dependent constitutive promoter hp4d. The highest ROMT-9 activity reached 5.53 U/L after 4 days of culture in shake flask. The optimal pH and temperature of the purified ROMT-9 were 8.0 and 37 °C, respectively. The purified enzyme was stable up to 40 °C, and retained more than 80% of its maximal activity between pH 6.5 and 9.0. The recombinant ROMT-9 did not require Mg²⁺ for catalysis, while was completely inhibited in the presence of 5 mM Zn²⁺, Cu²⁺, Ba²⁺, Al³⁺, or Ni²⁺. The purified ROMT-9 was used to synthesize homoeriodictyol, and the maximal transformation ratio reached 52.4% at 16 h under the following conditions: eriodictyol 0.2 g/L, ROMT-9 0.16 g/L, SAM 0.2 g/L, CH₃OH 6% (v/v), temperature 37 °C, and pH 8.0. This work provides an alternative strategy for efficient synthesis of homoeriodictyol and compared to the traditional plant extraction or chemical synthesis, the biotransformation approach generates less environmental pollution and has a great potential for the sustainable production of homoeriodictyol.     

Platinum(II) triammine antitumour complexes: structure-activity relationship with guanosine 5′-monophosphate (5′-GMP)

The multinuclear (¹H, ¹⁵N, ³¹P and ¹⁹⁵Pt) NMR spectroscopies, ES-MS and HPLC have been employed to investigate the structure-activity relationship for the reactions between guanosine 5′-monophosphate (5′-GMP) and the platinum(II)-triamine complexes of the general formulation cis-[Pt(NH₃)₂(Am)Cl]NO₃ (where Am represents a substituted pyridine). The order of reaction rate of the reactions was found to be: 3-phpy > 4-phpy > py > 4-mepy > 3-mepy > 2-mepy. The two basic factors, steric and electronic, were attributed to the order of the binding rate constants. A possible mechanism of the reaction of cis-[Pt(NH₃)₂(Am)Cl]⁺ with 5′-GMP suggested that the reactions proceed via direct nucleophilic attack and no loss of ammonia. cis-[Pt(NH₃)₂(Am)Cl]⁺ binds to the N7 nitrogen of the guanine residue of 5′-GMP to form a coordinate bond with the Pt metal centre. This mechanism is apparently different from that of cisplatin. The pK_a value of cis-[Pt(NH₃)₂(4-mepy)(H₂O)](NO₃)₂ (5.63) has been determined at 298 K by the use of distortionless enhancement by polarization transfer (DEPT) ¹⁵N NMR spectroscopy and compared to the pK_a value of cis-[PtCl(H₂O)(NH₃)₂]⁺.     

Solution and solid-state complexes of the potentially tetradentate pyridyl-thiazole ligand 6,6′-bis(4-methylthiazol-2-yl)-2,2′-bipyridine with Co, Ni, Cu, Cd, Hg, Cu and Ag

Reaction of the potentially tetradentate N-donor ligand 6,6′-bis(4-methylthiazol-2-yl)-2,2′-bipyridine (L¹) with the transition metal dications Co^II, Ni^II, Cu^II, Cd^II and Hg^II results in the formation of mononuclear [M(L¹)]²⁺ complexes, in which a planar ligand coordinates to the metals via all four N-donors. In contrast, reaction of L¹ with Cu^I and Ag^I monocations, affords dinuclear double stranded helicate species [M₂(L¹)₂]²⁺ (where M = Cu^I or Ag^I), in which partitioning of the ligand into two bis-bidentate pyridyl-thiazole chelating units allows each ligand to bridge both metal centres. X-Ray crystallography, electrospray mass spectroscopy and NMR spectroscopy reveal that the complexes [M_n(L¹)_m]^z+ (where n = 1, m = 1 and z = 2, when M = Co^II, Ni^II, Cu^II, Cd^II and Hg^II; n = 2, m = 2 and z = 2, when M = Cu^I), retain their solid-state structures in solution. Conversely, whilst ¹H NMR studies suggest that combination of equimolar amounts of Ag(X)(where ) and L¹ (in either nitromethane or acetonitrile) results in the formation of a helicate in solution, in the solid-state, an anion-templating effect gives rise to either mononuclear or dinuclear helicate structures [Ag_n(L¹)_n][X]_n (where n = 2 when X = OTf⁻; n = 1 when ).     

Synthesis, double stranded DNA-binding and photocleavage studies of a functionalized ruthenium(II) complex with 7,7′-methylenedioxyphenyldipyrido[3,2-a:2′,3′-c]-phenazine

A new Ru(II) complex [Ru(phen)₂(mdpz)]²⁺ (phen = 1,10-phenanthroline, mdpz = 7,7′-methylenedioxyphenyl-dipyrido-[3,2-a:2′,3′-c]phenazine) has been synthesized and characterized in detail by elemental analysis, mass spectrometry and ¹H NMR spectroscopy. The interaction of the complex with calf thymus DNA was investigated by spectroscopic and viscosity measurements. The results suggest that the complex binds to DNA via an intercalative mode and serves as a molecular “light switch” for DNA. Moreover, the complex has been found to promote the photocleavage of plasmid DNA pBR322 under irradiation at 365 nm. The mechanism studies reveal that singlet oxygen (¹O₂) plays a significant role in the photocleavage.     

A bulky platinum triamine complex that reacts faster with guanosine 5′-monophosphate than with N-acetylmethionine

A bulky platinum triamine complex, [Pt(Me₅dien)(NO₃)]NO₃ (Me₅dien = N,N,N′,N′,N′′-pentamethyldiethylenetriamine) has been prepared and reacted in D₂O with N-acetylmethionine (N-AcMet) and guanosine 5′-monophosphate (5′-GMP); the reactions have been studied using ¹H NMR spectroscopy. Reaction with 5′-GMP leads to two rotamers of [Pt(Me₅dien)(5′-GMP-N7)]⁺. Reaction with N-AcMet leads to formation of [Pt(Me₅dien)(N-AcMet-S)]⁺. When a sample with equimolar mixtures of [Pt(Me₅dien)(D₂O)]²⁺, 5′-GMP, and N-AcMet was prepared, [Pt(Me₅dien)(5′-GMP-N7)]⁺ was the dominant product observed throughout the reaction. This selectivity is the opposite of that observed for a similar reaction of [Pt(dien)(D₂O)]²⁺ with 5′-GMP and N-AcMet. To our knowledge, this is the first report of a platinum(II) triamine complex that reacts substantially faster with 5′-GMP than with N-AcMet; the effect is most likely due to steric clashes between the methyl groups of the Me₅dien ligand and the N-AcMet.     

Inhibition of the calcium-activated chloride current in cardiac ventricular myocytes by N-(p-amylcinnamoyl)anthranilic acid (ACA)

N-(p-amylcinnamoyl)anthranilic acid (ACA), a phospholipase A₂ (PLA₂) inhibitor, is structurally-related to non-steroidal anti-inflammatory drugs (NSAIDs) of the fenamate group and may also modulate various ion channels. We used the whole-cell, patch-clamp technique at room temperature to investigate the effects of ACA on the Ca²⁺-activated chloride current (I_Cl(Ca)) and other chloride currents in isolated pig cardiac ventricular myocytes. ACA reversibly inhibited I_Cl(Ca) in a concentration-dependent manner (IC₅₀ = 4.2 μM, n_Hill = 1.1), without affecting the L-type Ca²⁺ current. Unlike ACA, the non-selective PLA₂ inhibitor bromophenacyl bromide (BPB; 50 μM) had no effect on I_Cl(Ca). In addition, the analgesic NSAID structurally-related to ACA, diclofenac (50 μM) also had no effect on I_Cl(Ca), whereas the current in the same cells could be suppressed by chloride channel blockers flufenamic acid (FFA; 100 μM) or 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS;100 μM). Besides I_Cl(Ca), ACA (50 μM) also suppressed the cAMP-activated chloride current, but to a lesser extent. It is proposed that the inhibitory effects of ACA on I_Cl(Ca) are PLA₂-independent and that the drug may serve as a useful tool in understanding the nature and function of cardiac anion channels.     

Solution luminescence from chloro(2,2′:6′,2″-terpyridine)platinum(II) chloride in micelles

Previously characterized as being non-luminescent in room-temperature fluid solution, the coordination compound chloro(2,2′:6′,2″-terpyridine)platinum(II) chloride can display two types of luminescence in certain microenvironments. In aqueous solutions of anionic and neutral surfactants having concentrations near or above their critical micelle concentration, [Pt(terpy)Cl]Cl (10-50 μM) displays broad emission centered at ∼610 nm that is characterized as metal-to-ligand charge transfer phosphorescence (³MLCT). In high concentration (10-100 mM) solutions having no surfactant, [Pt(terpy)Cl]Cl aggregates form. Excitation in the 470-540 nm region results in a long-wavelength emission centered at ∼720 nm that is characterized as metal-metal-to-ligand charge transfer phosphorescence (³MMLCT). This emission can also be detected in lower concentration solutions (10-50 μM) with surfactant concentration below its critical micelle concentration. Enhancement of ³MLCT luminescence is also found for the related phenylacetylide complex cation [Pt(terpy)(CCPh)]⁺ in micelles of the anionic surfactant sodium dodecyl sulfate.     

Crystal structure and fluorescence of a europium (III) complex: EuCl3(2,2′-bipyridine N,N dioxide) · 2CH3OH

We report the synthesis and characterization of a seven coordinate europium complex, [EuCl₃(C₁₀H₈N₂O₂) ·  2CH₃OH]. The growing interest in developing efficient light conversion molecular devices (LCMDs) necessitates the need for new fluorescent materials. Ideal physicochemical properties of the materials include ligand absorption, efficient metal to ligand transfer, and strong luminescence with a relatively long decay time. The design of such material requires distinct absorbing (ligand) and emitting (metal ion) components. While Eu³⁺ cation has a non-degenerate emitting level, 2,2′-bipyridine N,N dioxide is a heterocyclic ligand known to exhibit strong luminescence. Additional characterization is also described, including single crystal X-ray diffraction, IR and UV-Vis spectroscopies and elemental analysis.     

Dinuclear organoiridium(III) mono- and bis-intercalators with rigid bridging ligands: Synthesis, cytotoxicity and DNA binding

The DNA binding and in vitro cytotoxicity of the dinuclear Ir(III) polypyridyl complexes [{(η⁵-C₅Me₅)Ir(dppz)}₂(μ-pyz)](CF₃SO₃)₄1 and [{(η⁵-C₅Me₅)Ir(pp)}₂(μ-4,4′-bpy)](CF₃SO₃)₄2-4 (pp = dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq), dipyrido[2,3-a:2′,3′-c]phenazine (dppz), benzo[i]dipyrido[3,2-a:2′,3′-c]phenazine (dppn)) with the rigid bridging ligands pyrazine (pyz) or 4,4′-bipyridine (4,4′-bpy) have been studied. Stable intercalative binding into CT DNA (calf thymus DNA) is indicated for the dppz complexes 1 and 3 by induced negative CD bands at about 300 nm and large viscosity increases, with the individual measurements being in accordance with intrastrand bis-intercalation for 3 and mono-intercalation for 1. The observed interruption of specific interresidue NOE cross peaks from the relevant nucleobase H6/H8 protons to the sugar H2′/H2″ protons of the preceding nucleotide is in accordance with bis-intercalation of complex 3 between the C3G18 and G4C17 base pairs and the T5A16 and A6T15 base pairs of the decanucleotide d(5′-CGCGTAGGCC-3′). Complexes 1 and 3 exhibit a greatly improved uptake by HT-29 (colon carcinoma) cells and significantly improved in vitro IC₅₀ values of 1.8 ± 0.1 and 3.8 ± 0.1 μM towards this cell line in comparison to the mononuclear complex [(η⁵-C₅Me₅)IrCl(dppz)](CF₃SO₃) (IC₅₀ = 7.4 ± 0.9 μM).     

Estrogenic and anti-estrogenic compounds from the Thai medicinal plant, Smilax corbularia (Smilacaceae)

From the rhizomes of Smilax corbularia Kunth. (Smilacaceae), 11 compounds, (2R,3R)-2″-acetyl astilbin, (2R,3R)-3″-acetyl astilbin, (2R,3R)-4″-acetyl astilbin, (2R,3R)-3″-acetyl engeletin, (2R,3S)-4″-acetyl isoastilbin, 2-(4-hydroxyphenyl)-3,4,9,10-tetrahydro-3,5-dihydroxy-10-(3,4-dihydroxyphenyl)-(2R,3R,10R)-2H,8H-benzo [1,2-b:3,4-b′] dipyran-8-one, 2-(4-hydroxyphenyl)-3,4,9,10-tetrahydro-3,5-dihydroxy-10-(3,4-dihydroxyphenyl)-(2R,3R,10S)-2H, 8H-benzo [1,2-b:3,4-b′] dipyran-8-one, 3,4-dihydro-7-hydroxy-4-(3,4-dihydroxyphenyl)-5-[(1E)-2-(4-hydroxyphenyl) ethenyl]-2H-1-benzopyran-2-one, 3,4-dihydro-7-hydroxy-4-(3,4-dihydroxy-phenyl)-5-[(1E)-2-(3,4-dihydroxyphenyl) ethenyl]-2H-1-benzopyran-2-one, 3,4-dihydro-7-hydroxy-4-(4-hydroxy-3-methoxyphenyl)-5-[(1E)-2-(4-hydroxyphenyl) ethenyl]-2H-1-benzopyran-2-one, and 5,7,3′,4′-tetrahydroxy-3-phenylcoumarin along with 34 known compounds were isolated and characterized as 19 flavonoids, 14 catechin derivatives, 6 stilbene derivatives, and 6 miscellaneous substances. All isolates had their estrogenic and anti-estrogenic activities determined using the estrogen-responsive human breast cancer cell lines MCF-7 and T47D. The major constituents were recognized as flavanonol rhamnosides by the suppressive effect on estradiol induced cell proliferation at a concentration of 1 μM. Meanwhile, flavanonol rhamnoside acetates demonstrated estrogenic activity in both MCF-7 and T47D cells at a concentration of 100 μM, and they enhanced the effects of co-treated E2 on T47D cell proliferation at concentrations of more than 0.1 μM.     

pH-sensitive Ru(II) and Os(II) bis(2,2′:6′,2″-terpyridine) complexes: A photophysical investigation

We have investigated the photophysical properties of two metal complexes, [M(tpy-py)₂][PF₆]₂, where tpy-py = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine and M = Ru(II) or Os(II), in acetonitrile and aqueous solutions at room temperature. Because the 4-pyridyl unit on the 4′-position of each tpy ligand contains a basic nitrogen atom, both of these compounds can exist in three different protonation states. We observed that the absorption and luminescence spectra of these compounds vary on changing the pH, because the protonation of the pendant pyridine unit makes it an electron acceptor by lowering the energy of its π^∗ orbital. We employed the absorption and luminescence spectral changes to study the acid-base reactions for these complexes, and found that the two protonation stages exhibit different pK_a values both in the electronic ground state and in the lowest (emitting) excited state. The absorption spectra and luminescence spectra and lifetimes of the deprotonated, mono-protonated and bis-protonated forms were also determined. While the absorption spectra of the variously protonated forms of both compounds can be intepreted in terms of a linear combination of two different and independent chromophores, namely M(tpy-py) and M(tpy-pyH⁺), the corresponding luminescence spectra exhibit a more complex behaviour, suggesting that the coupling between the two ligands in the lowest excited state is not negligible. Interestingly, at a low pH the luminescence of the Ru complex is switched on, whereas that of the Os complex is strongly quenched upon protonation of the pendant pyridine units. These compounds are of interest because they exhibit a luminescent signal in the red or far red spectral region that can be switched on or off by protons in solution. Hence, they could find applications as luminescent pH sensors and as molecular switches where a low-energy emission signal can be controlled by a chemical acid-base stimulation.     

Globins Synthesize the Second Messenger Bis-(3′-5′)-Cyclic Diguanosine Monophosphate in Bacteria

Globin-coupled sensors are heme-binding signal transducers in Bacteria and Archaea in which an N-terminal globin controls the activity of a variable C-terminal domain. Here, we report that BpeGReg, a globin-coupled diguanylate cyclase from the whooping cough pathogen Bordetella pertussis, synthesizes the second messenger bis-(3′-5′)-cyclic diguanosine monophosphate (c-di-GMP) upon oxygen binding. Expression of BpeGReg in Salmonella typhimurium enhances biofilm formation, while knockout of the BpeGReg gene of B. pertussis results in decreased biofilm formation. These results represent the first identification a signal ligand for any diguanylate cyclase and provide definitive experimental evidence that a globin-coupled sensor regulates c-di-GMP synthesis and biofilm formation. We propose that the synthesis of c-di-GMP by globin sensors is a widespread phenomenon in bacteria.     

Synthesis and characterization of Os(II)(dpop′) (dpop′ = dipyrido(2,3-a;3′,2′-j)phenazine) complexes with 2,2′-bipyridine(bpy); 2,2′-bipyrimidine(bpm) and 2,3-bis(2-pyridyl)pyrazine(dpp)

New Os(II) complexes including [Os(dpop′)₂](PF₆)₂ (dpop′= dipyrido(2,3-a;3′,2′-j)phenazine) and a series of mixed ligand [Os(dpop′)(N-N)Cl]PF₆ (N-N = 2,2′-bipyridine(bpy); 2,2′-bipyrimidine(bpm) and 2,3-bis(2-pyridyl)pyrazine(dpp)) were synthesized. The Os dπ → dpop′ π^∗ MLCT transitions for [Os(dpop′)₂]²⁺ are observed at lower energy than for Os dπ → tpy π^∗ (tpy = 2,2′:6′,2″-terpyridine) and Os dπ → tppz π^∗ (tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine) (The ligand abbreviations tpd, tpp and tpypz have also appeared in the literature for 2,3,5,6- tetrakis(2-pyridyl)pyrazine in addition to tppz.) MLCT transitions in the comparative [Os(tpy)₂]²⁺ and [Os(tppz)₂]²⁺ complexes. The Os dπ → dpop′ π^∗ MLCT transitions are observed at lower energy in mixed bidentate ligand N-N systems compared with [Os(dpop′)₂]²⁺. Cyclic voltammetry shows more positive osmium oxidation, and less negative ligand reduction potentials for [Os(dpop′)₂]²⁺ as compared to [Os(tpy)₂]²⁺ and [Os(tppz)₂]²⁺ complexes. The osmium oxidation potentials in mixed ligand [Os(dpop′)(N-N)Cl]⁺ complexes are at less positive potential than for the [Os(dpop′)₂]²⁺ ion. NMR results show different chemical shifts for ring protons either trans or cis to dpop′ in mixed ligand systems, and also show two geometrical isomers for the [Os(dpop′)(dpp)Cl]⁺ complex. The [Os(dpop′)(dpp)Cl]⁺ geometric isomer with the pyrazine ring of dpp trans to dpop′ is found more predominate by 1.0/0.7 over the isomer with the pyrazine ring of dpp cis to dpop′ and that inter-conversion of geometric isomers does not occur in room temperature solution on the NMR timescale.