Oxidative gating of water channels (aquaporins) in Chara by hydroxyl radicals

Hydroxyl radicals (*OH) as produced in the Fenton reaction (Fe²⁺ + H₂O₂ = Fe³⁺ + OH^– + *OH) have been used to reversibly inhibit aquaporins in the plasma membrane of internodes of Chara corallina. Compared to conventional agents such as HgCl₂, *OH proved to be more effective in blocking water channels and was less toxic to the cell. When internodes were treated for 30 min, cell hydraulic conductivity (Lp) decreased by 90% or even more. This effect was reversed within a few minutes after removing the radicals from the medium. In contrast to HgCl₂, radical treatment reduced membrane permeability of small lipophilic organic solutes (ethanol, acetone, 1‐propanol, and 2‐propanol) by only 24 to 52%, indicating some continued limited movement of these solutes across aquaporins. The biggest effect of *OH treatment on solute permeability was found for isotopic water (HDO), which largely used water channels to cross the membrane. Inhibition of aquaporins reduced the diffusional water permeability (P_d) by about 70%. For the organic test solutes, which mainly use the bilayer to cross the membrane, channel closure caused anomalous (negative) osmosis; that is, cells had negative reflection coefficients (σ_s) and were transiently swelling in a hypertonic medium. From the ratio of bulk (Lp or osmotic permeability coefficient, P_f) to diffusional (P_d) permeability of water, the number (N) of water molecules that align in water channels was estimated to be N = P_f/P_d = 46 (on average). Radical treatment decreased N from 46 to 11, a value still larger than unity, which would be expected for a membrane lacking pores. The gating of aquaporins by *OH radicals is discussed in terms of a direct action of the radicals when passing the pores or by an indirect action via the bilayer. The rapid recovery of inhibited channels may indicate an easy access of cytoplasmic antioxidants to closed water channels. As hydrogen peroxide is a major signalling substance during different biotic and abiotic stresses, the reversible closure of water channels by *OH (as produced from H₂O₂ in the apoplast in the presence of transition metals such as Fe²⁺ or Cu⁺) may be downstream of the H₂O₂ signalling. This may provide appropriate adjustments in water relations (hydraulic conductivity), and a common response to different kinds of stresses.     

Hydrogen sulphide suppresses human atrial fibroblast proliferation and transformation to myofibroblasts

Cardiac fibroblasts are crucial in pathophysiology of the myocardium whereby their aberrant proliferation has significant impact on cardiac function. Hydrogen sulphide (H₂S) is a gaseous modulator of potassium channels on cardiomyocytes and has been reported to attenuate cardiac fibrosis. Yet, the mechanism of H₂S in modulating proliferation of cardiac fibroblasts remains poorly understood. We hypothesized that H₂S inhibits proliferative response of atrial fibroblasts through modulation of potassium channels. Biophysical property of potassium channels in human atrial fibroblasts was examined by whole‐cell patch clamp technique and their cellular proliferation in response to H₂S was assessed by BrdU assay. Large conductance Ca²⁺‐activated K⁺ current (BK_Ca), transient outward K⁺ current (I_to) and inwardly rectifying K⁺ current (IK_ir) were found in human atrial fibroblasts. Current density of BK_Ca (IC₅₀ = 69.4 μM; n = 6), I_to (IC₅₀ = 55.1 μM; n = 6) and IK_ir (IC₅₀ = 78.9 μM; n = 6) was significantly decreased (P < 0.05) by acute exposure to NaHS (a H₂S donor) in atrial fibroblasts. Furthermore, NaHS (100–500 μM) inhibited fibroblast proliferation induced by transforming growth factor‐β1 (TGF‐β1; 1 ng/ml), Ang II (100 nM) or 20% FBS. Pre‐conditioning of fibroblasts with NaHS decreased basal expression of Kv4.3 (encode I_to), but not KCa1.1 (encode BK_Ca) and Kir2.1 (encode IK_ir). Furthermore, H₂S significantly attenuated TGF‐β1–stimulated Kv4.3 and α‐smooth muscle actin expression, which coincided with its inhibition of TGF‐β–induced myofibroblast transformation. Our results show that H₂S attenuates atrial fibroblast proliferation via suppression of K⁺ channel activity and moderates their differentiation towards myofibroblasts.     

Possible Effect of Activation of α7-Nicotinic Acetylcholine Receptors in the Mitochondrial Membrane on the Development of Apoptosis

Using flow cytometry and sandwich-immunoenzyme assay, we showed that nicotinic acetylcholine receptors with a subunit α7 (nAChRs α7) expressed in the outer mitochondrial membrane are involved in the control of mitochondria-dependent apoptosis. Pre-incubation of the mitochondria with an nAChRs α7 agonist, choline, decreased dissipation of the membrane potential of these organelles induced by the action of 0.5 mM hydrogen peroxide (H₂O₂) but did not influence the analogous effect of a high Ca²⁺ concentration (90 μM). Agonists of nAChRs α7 (choline, acetylcholine, and PNU 282987), or an inhibitor of voltage-dependent anion channels, DIDS, prevented the release of cytochrome c from the intermembrane mitochondrial space under the action of H₂O₂. In contrast, an antagonist of nAChRs α7, methyllycaconitine, promoted the release of cytochrome c and prevented the effects of agonists. The obtained data confirm the active involvement of nAChRs α7 and voltage-dependent anion channels in the process of formation of mitochondrial pores. In this case, agonists of mitochondrial nAChRs α7 subunits exert an antiapoptotic effect, while antagonists of mitochondrial nAChRs α7 subunits manifest a proapoptotic action.     

Optical Waveguide Lightmode Spectroscopic Techniques for Investigating Membrane-Bound Ion Channel Activities

Optical waveguide lightmode spectroscopic (OWLS) techniques were probed for monitoring ion permeation through channels incorporated into artificial lipid environment. A novel sensor set-up was developed by depositing liposomes or cell-derived membrane fragments onto hydrophilic polytetrafluoroethylene (PTFE) membrane. The fibrous material of PTFE membrane could entrap lipoid vesicles and the water-filled pores provided environment for the hydrophilic domains of lipid-embedded proteins. The sensor surface was kept clean from the lipid holder PTFE membrane by a water- and ion-permeable polyethylene terephthalate (PET) mesh. The sensor set-up was tested with egg yolk lecithin liposomes containing gramicidin ion channels and with cell-derived membrane fragments enriched in GABA-gated anion channels. The method allowed monitoring the move of Na⁺ and organic cations through gramicidin channels and detecting the Cl^–-channel functions of the (α₅β₂γ₂) GABA_A receptor in the presence or absence of GABA and the competitive GABA-blocker bicuculline.     

Zinc ions block H⁺/OH⁻ channels in Chara australis

Chara australis cells exposed to media of pH 10 and above exhibit high conductance, arising from the opening of H⁺/OH^‐ channels in the plasma membrane. This high conductance can be totally inhibited by 1.0 mm ZnCl₂ and restored by 0.5 mm 2‐mercaptoethanol (ME). Important for carbon fixation, H⁺/OH^‐ channels play a key role in cell pH banding. Banding was also shown to be abolished by 1.0 mm ZnCl₂ and restored in some cells by ME. The proton pump is also involved in banding, but was little affected by ZnCl₂ over the periods needed for the inhibition of H⁺/OH^‐ channels. Previously, we postulated that H⁺/OH^‐ channels open transiently at the onset of saline stress in salt‐sensitive C. australis, causing membrane potential difference (PD) noise; and remain open in latter stages of saline stress, contributing to cell deterioration. ZnCl₂ totally inhibited the saline noise and the upwardly concave I/V characteristics associated with the putative H⁺/OH^‐ currents. Again, ME reversed both these effects. We discuss the mode of action of zinc ions and ME with reference to animal voltage‐gated H⁺ channels and water channels.     

Competitive Formation of Hydroxycarbonate Green Rust 1 versus Hydroxysulphate Green Rust 2 in Shewanella putrefaciens Cultures

The formation of hydroxysulphate green rust 2, a Fe(II-III) compound commonly found during corrosion processes of iron-based materials in seawater, has not yet been reported in bacterial cultures. Here we used Shewanella putrefaciens, a dissimilatory iron-reducing bacterium to anaerobically catalyze the transformation of a ferric oxyhydroxide, lepidocrocite (γ-FeOOH), into Fe(II) in the presence of various sulphate concentrations. Biotransformation assays of γ-FeOOH were performed with formate as the electron donor under a variety of concentrations. The results showed that the competitive formation of hydroxycarbonate green rust 1 (GR1(CO₃ ^2?)) and hydroxysulphate green rust 2 (GR2(SO₄ ^{2 ?})) depended upon the relative ratio (R) of bicarbonate and sulphate concentrations. When R ≥ 0.17, GR1(CO₃ ^{2 ?}) only was formed whereas when R < 0.17, a mixture of GR2(SO₄ ^{2 ?}) and GR1(CO₃ ^{2 ?}) was obtained. These results demonstrated that the hydroxysulphate GR2 can originate from the microbial reduction of γ-FeOOH and confirmed the preference for carbonate over sulphate during green rust precipitation. The solid phases were characterized by X-ray diffraction, transmission Mössbauer spectroscopy and scanning electron microscopy. Diffuse reflectance infrared Fourier transform spectroscopy confirmed the presence of intercalated carbonate and sulphate in green rust's structure. This study sheds light on the influence of dissimilatory iron-reducing bacteria on microbiologically influenced corrosion.     

Interactions of Cyclic AMP and Its Dibutyryl Analogue with a Lipid Layer in the Aqueous Mixtures of Monoolein Preparation and Dioleoyl Phosphatidylcholine as Probed by X-Ray Diffraction and Raman Spectroscopy

Interactions of adenosine 3':5'-cyclicmonophosphate (cAMP) andN⁶,2'-O-dibutyryladenosine3':5'-cyclic monophosphate (dbcAMP) with alipid layer composed of monoolein-basedpreparation and dioleoylphosphatidylcholine (DOPC) wereinvestigated by small-angle X-raydiffraction (SAXD) and Raman spectroscopy.The reversed hexagonal (H_II)MO/DOPC/H₂O phase of 65:15:20 wt.%composition was selected as a referencesystem. SAXD revealed that entrapment (atthe expense of water) of 3 wt.% cAMP intothe reference system did not change thepolymorphic form and structural parametersof the phase. The same content of dbcAMPinduced the transition from the H_IIphase to the reversed bicontinuous cubicphase of space group Ia3d. Thistransition is explained by the increase oflipid head-group area due to thepenetration of the acylated adenine groupof dbcAMP into the polar/apolar region oflipid layer. The conclusion is supported byRaman spectroscopy, showing thedisruption/weakening of hydrogen bonding inthe MO/DOPC-based matrix at the N1- andN3-sites of the dbcAMP adenine ring. Asdistinct from dbcAMP, cAMP remains mostlyin the water channels of the H_IIphase, although the phosphate residue ofnucleotide interacts with the quaternaryammonium group of DOPC. Both nucleotidesincrease the population of gaucheisomers in the DOPC choline group.     

Atomic-force microscopy on the olfactory dendrites of the silkmoths Antheraea polyphemus and A. pernyi

Olfactory transduction is thought to occur in the outer dendritic membrane of insect olfactory receptor neurons. Electrophysiological studies have indicated that the outer dendritic membrane has non-specific cation channels and inositol-triphosphate-dependent Ca²⁺ channels. The presence of such channels is further supported by the observation that pheromone-stimulated dendrites take up cobalt. However, to date, there is no structural evidence for these channels. Therefore, in order to search for putative ion channels, we have imaged the membrane of the olfactory dendrites in the scanning electron microscope (SEM) and the atomic-force microscope (AFM), after extruding the dendrites out of the olfactory hairs and fixing them on plastic coverslips. With the aid of the SEM, we could see the beaded structure of the dendrite but no fine structural details, as the membrane was sputtered with gold. With the use of the contact mode of the AFM, we could see “pores” that were deeper than 3 nm and with a diameter of about 15 nm. The density of the “pores” was approximately 20/µm² or 10?000 pores per thick dendrite. We believe these to be putative ion channels based on indirect evidence.     

Gating the glutamate gate of CLC-2 chloride channel by pore occupancy

CLC-2 channels are dimeric double-barreled chloride channels that open in response to hyperpolarization. Hyperpolarization activates protopore gates that independently regulate the permeability of the pore in each subunit and the common gate that affects the permeability through both pores. CLC-2 channels lack classic transmembrane voltage–sensing domains; instead, their protopore gates (residing within the pore and each formed by the side chain of a glutamate residue) open under repulsion by permeant intracellular anions or protonation by extracellular H⁺. Here, we show that voltage-dependent gating of CLC-2: (a) is facilitated when permeant anions (Cl⁻, Br⁻, SCN⁻, and I⁻) are present in the cytosolic side; (b) happens with poorly permeant anions fluoride, glutamate, gluconate, and methanesulfonate present in the cytosolic side; (c) depends on pore occupancy by permeant and poorly permeant anions; (d) is strongly facilitated by multi-ion occupancy; (e) is absent under likely protonation conditions (pH_e = 5.5 or 6.5) in cells dialyzed with acetate (an impermeant anion); and (f) was the same at intracellular pH 7.3 and 4.2; and (g) is observed in both whole-cell and inside-out patches exposed to increasing [Cl⁻]_i under unlikely protonation conditions (pH_e = 10). Thus, based on our results we propose that hyperpolarization activates CLC-2 mainly by driving intracellular anions into the channel pores, and that protonation by extracellular H⁺ plays a minor role in dislodging the glutamate gate.     

Rhodium aryloxide complexes containing terdentate nitrogen ligands, C-O bond formation, hydrogen bonding with phenol and oxidative addition reactions. Molecular structure of an Rh(III)-acetyl complex

The new rhodium(I) phenoxide complexes [Rh(OPh) (2,6-(CH=R²)₂C₅H₃N)] (R² = i-Pr(3), t-Bu(4)) containing strongly electrondonating N-N′-N ligands, have been prepared by a metathesis reaction of [RhCl(2,6-(CH=R²)₂C₅H₃N)] (R² = i-Pr (1), t-Bu (2)) with NaOPh. These rhodium(I) phenoxide complexes 3 and 4, which are very sensitive to O₂ but stable towards H₂O, give with phenol the adducts [Rh(OPh) (2,6-(CH=NR²)₂C₅H₃N)] · HOPh (R2 = i-Pr (5), t-Bu (6)), which contain strong O-HO hydrogen bonds. The hydrogen bonded phenol could not be extracted with diethyl ether, while no exchange of the hydrogen bonded phenol and the phenoxide ligand in 4 is observed on the NMR time scale. However, a small excess of phenol results in exchange of the hydrogen bonded phenol, the coordinated phenoxide ligand and free phenol on the NMR time scale. Reaction of 3 and 4 with p-nitrophenol afforded [Rh(OC₆H₄-(NO₂-4))(2,6-(CH=R²)₂C₅H₃N)] · HOPh (R² = i-Pr (7), t-Bu (8)) in which the formed phenol is hydrogen bonded to the Rh(I)-OC₆H₄-(NO₂-4) moiety. The O-HO bond is less strong than in 5 and 6, as the hydrogen bonded phenol could be removed by diethyl ether.Treatment of 3 with acetyl chloride and benzoyl chloride in benzene at room temperature gave phenylacetate and RhCl₂(C(O)C₆H₃) (2,6(C(H)=N-i-Pr)₂C₅H₃N)] (15), and phenylbenzoate and [RhCl₂(C(O)Ph) (2,6-(C(H)=N-i-Pr)₂C₅H₃N)] (19), respectively. Complex 15 and the analogous complex [RhCl₂(C(O)CH₃) (2,6-(C(H)=N-t-Bu)₂C₅H₃N)] (16) could also be prepared directly from acetyl chloride and 1 or 2, respectively. The single crystal X-ray determination of complex 16, monoclinic, space group P2₁/_c, a = 10.0477(5), b= 11.7268(6), c= 19.2336(9) Å, β = 92.041(4)°, Z = 4, R₁ = 0.0281, shows that the acetyl group occupies an axial position, while the N-N′-N ligand is positioned equatorially. In solution this geometry remains unchanged as was shown by variable temperature ¹H NMR measurements. When the oxidative addition of acetyl chloride to 3 was carried out at −78°C in toluene the intermediate complex [RhCl(OPh) (C(O)Me) (2,6-(C(H)=N-i-Pr)₂C₅H₃N)] (11) could be isolated, which at room temperature reductively eliminates phenylacetate with formation of 1. Oxidative addition of acetyl chlori de to 4 at room temperature gives [RhCl(OPh) (C(O)Me) (2,6-(C(H)=Nt-Bu)₂C₅H₃N)] (12) which yields phenylacetate and 2 at 70°C in benzene by inductive elimination. Treatment of 3 with two equivalents of benzyl chloride afforded a mixture of [RhCl(OPh) (CH₂Ph) (2,6-(C(H)=N-i-Pr)₂C₅H₃N)] (13) and [RhCl₂(CH₂Ph) (2,6-(C(H)=N-i-Pr)₂C₅H₃N)] (17) and some non-characterizable organic products, while 4 only yielded [RhCl(OPh) (CH₂Ph) (2,6-(C(H)=N-tBu)₂C₅H₃N)] (14).     

Properties of the large ion-permeable pores formed from protein F of Pseudomonas aeruginosa in lipid bilayer membranes

The incorporation of porin protein F from the outer membrane of Pseudomonas aeruginosa into artificial lipid bilayers results in an increase of the membrane conductance by many orders of magnitude. The membrane conductance is caused by the formation of large ion-permeable channels with a single-channel conductance in the order of 5 nS for 1 M alkali chlorides. The conductance has an ohmic current vs. voltage relationship. Further information on the structure of the pore formed by protein F was obtained by determining the single-channel conductance for various species differing in charge and size, and from zero-current potential measurements. The channel was found to be permeable for large organic ions (Tris⁺, N(C₂H₅)₄⁺, Hepes^?) and a channel diameter of 2.2 nm could be estimated from the conductance data (pore length of 7.5 nm). At neutral pH the pore is about two times more permeable for cations than for anions, possibly caused by negative charges in the pore. The consistent observation of large water filled pores formed by porin protein F in model membrane systems is discussed in the light of the known low permeability of the Ps. aeruginosa outer membrane towards antibiotics. It is suggested that this results from a relatively low proportion of open functional porin protein F pores in vivo.     

Study of the interaction of Co(III) polypyridyl complexes with DNA: an experimental and computational approach

Three new cobalt(III) polypyridyl complexes, [Co(L - L)₂IIP]³⁺ where IIP = 2-(2H-isoindol-1-yl)-2H-imidazo[4,5-f][1, 10]phenanthroline, L?=?1) phen (1,10-phenanthroline), 2) bpy (2,2’bipyridyl), 3) dmb (4, 4-dimethyl 2, 2’-bipyridine) have been synthesized, characterized (UV –VIS, IR, ¹HNMR and ¹³C NMR spectroscopy) and screened for their in vitro antibacterial activity against E.coli, Staphylococcus aureus and Bacillus subtilis. The binding of these complexes with calf-thymus DNA (CT-DNA) has been investigated by absorption and fluorescence spectroscopy, viscosity measurements. The experimental studies indicate that complexes bind to CT-DNA by means of intercalation, but with different binding affinities due to differences in the planarity of the ancillary ligand. The complexes promote photocleavage of plasmid DNA from super coiled form I to the open circular form II. The antibacterial activities suggest that the metal complexes are more active as compared to the prepared un-complexed IIP ligand.

In addition, a conformational search was carried out by Molecular Dynamics Simulations, and docking revealed that complexes intercalate between base pairs of DNA. The experimental and computational approaches reveal that the length of the intercalator and the nature of ancillary ligand are highly important factors for DNA binding.     

Catalase purification from rat liver with iron-chelated poly(hydroxyethyl methacrylate-N-methacryloyl-(l)-glutamic acid) cryogel discs

In this study, iron-chelated poly(hydroxyethyl methacrylate-N-methacryloyl-(l)-glutamic acid) (PHEMAGA/Fe³⁺) cryogel discs were prepared. The PHEMAGA/Fe³⁺ cryogel discs were characterized by elemental analysis, scanning electron microscopy, Fourier transform infrared spectroscopy, swelling tests, and surface area measurements. The PHEMAGA/Fe³⁺ cryogel discs had large pores ranging from 10 to 100?µm with a swelling degree of 9.36?g H₂O/g cryogel. Effects of pH, temperature, initial catalase concentration, and flow rate on adsorption capacity of the PHEMAGA/Fe³⁺ cryogel discs were investigated. Maximum catalase adsorption capacity (62.6?mg/g) was obtained at pH 7.0, 25°C, and 3?mg/ml initial catalase concentration. The PHEMAGA/Fe³⁺ cryogel discs were also tested for the purification of catalase from rat liver. After tissue homogenization, purification of catalase was performed using the PHEMAGA/Fe³⁺ cryogel discs and catalase was obtained with a yield of 54.34 and 16.67 purification fold.     

Single-file diffusion multi-ion mechanism of permeation in paracellular epithelial channels

Summary The transepithelial fluxes, conductances and permeabilities of Li⁺, Na⁺, K⁺, Cs⁺, NH ₄ ⁺ and H₃CNH ₃ ⁺ were studied under ionic concentrations ranging from 12 to 250mm inBufo arenarum gallbladders. When these measurements are carefully corrected in order to get only the component due to the paracellular cation channels, the following results are obtained: (1) The permeability ratios (cationic/anionic) are a decreasing function of salt concentration. (2) The partial conductances through paracellular cationic channels show nonlinear saturable concentration kinetics. (3) Moreover, partial conductance kinetics of K⁺, Cs⁺ and NH ₄ ⁺ present a maximum followed, at higher concentratons, by a negative-slope region. (4) The selectivity sequences obtained from biionic potentials do not agree with those obtained from partial conductance measurements. (5) The unidirectional²²Na tracer flux (serosal to mucosal) is inhibited by 63% when the K⁺ symmetrical concentration in the bathing solutions is raised from 25 to 200mm. (6) When the unidirectional⁴²K fluxes (serosal to mucosal) at 200mm KCl Na-free solutions are compared with K⁺ partial conductance by means of the Hodgkin and Keynes (Hodgkin, A.L., Keynes, R.D. 1955.J. Physiol London 128:61–88) expression, then factor is 2.0. These results indicate that cations do not follow the independence principle and behave as in single-file diffusion multi-ion pores when crossing the paracellular cation channels ofBufo arenarum gallbladder epithelium.     

Structures, dynamic behaviour in solution and cross-coupling reactions of the α-palladiated (η-alkylarene)tricarbonylchromium complexes containing a palladium-chromium bond

Structures of the complexes (η³-C₃H₅)Pd(μ-η^6:1-CH₂PhCr(CO)₃ and (η³-C₃H₅)Pd[μ-η^6:1-CH(Ph)Ph]Cr(CO)₃ in solution were evaluated by NMR (¹H and ¹³C) and IR spectroscopy. The dynamic behaviour of the complexes was investigated. Quick rotation (on the NMR time scale) of the tricarbonylchromium groups around the axis passing through the centre of the η⁶-coordinated phenyl ring and the chromium atom takes place at room temperature and becomes slow on cooling. The η³-allylic ligand was proved to undergo no dynamic changes in solution. Unlike the solid state, the semi-bridging carbonyl groups between chromium and palladium atoms are absent or very weak in solution. Cross-coupling reactions of the complexes with organohalides are described.     

Spectroscopic and Structural Characterization,Enzyme Inhibitions,and Antioxidant Effects of New Ru(II) and Ni(II) Complexes of Schiff Base

The new complex compounds [RuLCl(p‐cymene)] ? 3H₂O and [NiL₂(H₂O)₂] ? 3H₂O (L: 1‐{4‐[(2‐hydroxy‐3‐methoxybenzylidene)amino]phenyl}ethanone) were prepared and characterized using FT‐IR, ¹H‐ and ¹³C‐NMR, mass spectroscopy, TGA, elemental analysis, X‐ray powder diffraction and magnetic moment techniques. Octahedral geometry for new Ni(II) and Ru(II) complexes was proposed. Thermal decomposition confirmed the existence of lattice and coordinated water molecule in the complexes. To determine the antioxidant properties of Schiff base ligand and its Ni(II), Ru(II) metal complexes, FRAP, CUPRAC, ABTS and DPPH methods of antioxidant assays were used. Moreover, enzyme inhibition of complexes was evaluated against carbonic anhydrase I and II isoenzymes (CA I and CA II) and acetylcholinesterase (AChE). For CA I and CA II, the best inhibition enzymes, was the Ni(II) complex with 62.98±18.41, 86.17±23.62 Ki values, whereas this inhibition effect showed ligand with 24.53±2.66 Ki value for the AChE enzyme.     

Titanium(III) alkoxides. A new synthetic route and solid state properties (CP/MAS 13C NMR,X-ray and IR)

Ti(OR)₃ compounds (R=C₂H₅, C₄H₉ⁿ, C₆H₅) were prepared by reduction of titanium tetralkoxides with organosilicon compounds containing SiH bonds. The reaction mechanism probably involves a four membered cyclic intermediate. The tervalent alkoxides have been characterized by elemental analyses, X-ray powder diffraction, infrared spectroscopy and solid-state magic angle sample spinning ¹³C NMR.The compounds are polymeric owing to the presence of alkoxide bridges. They are diamagnetic, insoluble materials which decompose on melting. Previously reported results are critically discussed and compared with the experimental findings from both infrared and NMR spectroscopy.     

Synthesis and characterization of a novel photoluminescent three-dimensional metal-organic framework

A novel metal-organic framework containing one-dimensional channels of formula [Zn₃(Aco)₂(H₂O)₆]_n (H₃Aco = aconitic acid) has been synthesized and characterized by FT-IR spectroscopy, thermogravimetric analysis (TG), X-ray analysis, and solid state photoluminescence spectra. X-ray crystallographic studies reveal that there are two kinds of crystallographically independent Zn atoms in the title complex. The most interesting feature of the structure is an unprecedented 3D MOF containing infinite Zn(1) linear chains and heterochiral Zn(2) single-stranded helices. The linear chains and helices happen to be perpendicular to each other. Photoluminescence properties of the title compound have been examined in the solid state at room temperature.     

Sodium/calcium selectivity of cloned calcium T-type channels

We studied the peculiarities of permeability with respect to the main extracellular cations, Na⁺ and Ca²⁺, of cloned low-threshold calcium channels (LTCCs) of three subtypes, Ca_v3.1 (α1G), Ca_v3.2 (α 1H), and Ca_v3.3 (α1I), functionally expressed in Xenopus oocytes. In a calcium-free solution containing 100 mM Na⁺ and 5 mM calcium-chelating EGTA buffer (to eliminate residual concentrations of Ca²⁺) we observed considerable integral currents possessing the kinetics of inactivation typical of LTCCs and characterized by reversion potentials of −10 ± 1, −12 ± 1, and −18 ± 2 mV, respectively, for Ca_v3.1, Ca_v3.2, and Ca_v3.3 channels. The presence of Ca²⁺ in the extracellular solution exerted an ambiguous effect on the examined currents. On the one hand, Ca²⁺ effectively blocked the current of monovalent cations through cloned LTCCs (K _d = 2, 10, and 18 μM for currents through channels Ca_v3.1, Ca_v3.2, and Ca_v3.3, respectively). On the other hand, at the concentration of 1 to 100 mM, Ca²⁺ itself functioned as a carrier of the inward current. Despite the fact that the calcium current reached the level of saturation in the presence of 5 mM Ca²⁺ in the external solution, extracellular Na⁺ influenced the permeability of these channels even in the presence of 10 mM Ca²⁺. The Ca_v3.3 channels were more permeable with respect to Na⁺ (P _Ca/P _Na ∼ 21) than Ca_v3.1 and Ca_v3.2 (P _Ca/P _Na ∼ 66). As a whole, our data indicate that cloned LTCCs form multi-ion Ca²⁺-selective pores, as these ions possess a high affinity for certain binding sites. Monovalent cations present together with Ca²⁺ in the external solution modulate the calcium permeability of these channels. Among the above-mentioned subtypes, Ca_v3.3 channels show the minimum selectivity with respect to Ca²⁺ and are most permeable for monovalent cations. Neirofiziologiya/Neurophysiology, Vol. 38, No. 3, pp. 183–192, May–June, 2006.     

Scavenging of reactive oxygen species by chlorophyllin: An ESR study

The antioxidant effects of chlorophyllin (CHL), a water-soluble analog of the green plant pigment chlorophyll, on different reactive oxygen species (ROS) were investigated by electron spin resonance (ESR) spectroscopy. As a standard, we have used the ability of CHL to scavenge the stable 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. CHL inhibits the formation of 5,5-dimethyl-1-pyrroline-N-oxide adduct with hydroxyl radical (DMPO-OH adduct) generated by γ-radiation in a dose-dependent manner. At a concentration of 1 mM, CHL caused more than 90% inhibition of ESR signal intensity of this adduct. However, the results obtained with the Fenton reaction were different. We also found evidence for the inhibition of ¹O₂-dependent formation of the 2,2,6,6-tetramethyl-piperidine oxide (TEMPO) radical during photosensitization of methylene blue with visible light. CHL was also able to inhibit hydrogen peroxide induced oxidation of phenol red. The rate constant of the reaction of CHL with H₂O₂ was found to be 2.7×10⁶ M^-1s^-1. In conclusion, CHL has potent antioxidant ability involving scavenging of various physiologically important ROS.