Identification and subcellular distribution of endogenous Ins(1,4,5)P(3) 3-kinase B in mouse tissues

Inositol 1,4,5-trisphosphate 3-kinase (IP(3)-3K) catalyses the phosphorylation of inositol 1,4,5-trisphosphate to inositol 1,3,4,5-tetrakisphosphate. cDNAs encoding three mammalian isoforms have been reported and referred to as IP(3)-3KA, IP(3)-3KB, and IP(3)-3KC. IP(3)-3KB is particularly sensitive to proteolysis at the N-terminus, a mechanism known to generate active fragments of lower molecular mass. Endogenous IP(3)-3KB has therefore not been formally identified in tissues. We have probed a series of murine tissues with an antibody directed against the C-terminus of IP(3)-3KB and used IP(3)-3KB deficient mouse tissues as negative controls. IP(3)-3KB was shown to be particularly well expressed in brain, lung, and thymus with molecular masses of 110-120kDa. The identification of the native IP(3)-3KB by Western blotting for the first time will facilitate further studies of regulation of its activity by specific proteases and/or phosphorylation.     

Phosphorylation of the rat Ins(1,4,5)P3 receptor at T930 within the coupling domain decreases its affinity to Ins(1,4,5)P3

The Ins(1,4,5)P₃ receptor acts as a central hub for Ca²⁺ signaling by integrating multiple signaling modalities into Ca²⁺ release from intracellular stores downstream of G-protein and tyrosine kinase-coupled receptor stimulation. As such, the Ins(1,4,5)P₃ receptor plays fundamental roles in cellular physiology. The regulation of the Ins(1,4,5)P₃ receptor is complex and involves protein-protein interactions, post-translational modifications, allosteric modulation, and regulation of its sub-cellular distribution. Phosphorylation has been implicated in the sensitization of Ins(1,4,5)P₃-dependent Ca²⁺ release observed during oocyte maturation. Here we investigate the role of phosphorylation at T-930, a residue phosphorylated specifically during meiosis. We show that a phosphomimetic mutation at T-930 of the rat Ins(1,4,5)P₃ receptor results in decreased Ins(1,4,5)P₃-dependent Ca²⁺ release and lowers the Ins(1,4,5)P₃ binding affinity of the receptor. These data, coupled to the sensitization of Ins(1,4,5)P₃-dependent Ca²⁺ release during meiosis, argue that phosphorylation within the coupling domain of the Ins(1,4,5)P₃ receptor acts in a combinatorial fashion to regulate Ins(1,4,5)P₃ receptor function.     

Phosphorylation of the rat Ins(1,4,5)P3 receptor at T930 within the coupling domain decreases its affinity to Ins(1,4,5)P3

The Ins(1,4,5)P₃ receptor acts as a central hub for Ca²⁺ signaling by integrating multiple signaling modalities into Ca²⁺ release from intracellular stores downstream of G-protein and tyrosine kinase-coupled receptor stimulation. As such, the Ins(1,4,5)P₃ receptor plays fundamental roles in cellular physiology. The regulation of the Ins(1,4,5)P₃ receptor is complex and involves protein-protein interactions, post-translational modifications, allosteric modulation, and regulation of its sub-cellular distribution. Phosphorylation has been implicated in the sensitization of Ins(1,4,5)P₃-dependent Ca²⁺ release observed during oocyte maturation. Here we investigate the role of phosphorylation at T-930, a residue phosphorylated specifically during meiosis. We show that a phosphomimetic mutation at T-930 of the rat Ins(1,4,5)P₃ receptor results in decreased Ins(1,4,5)P₃-dependent Ca²⁺ release and lowers the Ins(1,4,5)P₃ binding affinity of the receptor. These data, coupled to the sensitization of Ins(1,4,5)P₃-dependent Ca²⁺ release during meiosis, argue that phosphorylation within the coupling domain of the Ins(1,4,5)P₃ receptor acts in a combinatorial fashion to regulate Ins(1,4,5)P₃ receptor function.     

D-6-Deoxy-myo-inositol 1,3,4,5-tetrakisphosphate, a mimic of d-myo-inositol 1,3,4,5-tetrakisphosphate: biological activity and pH-dependent conformational properties

D-6-Deoxy-myo-inositol 1,3,4,5-tetrakisphosphate [D-6-deoxy-Ins(1,3,4,5)P(4)] 3 is a novel deoxygenated analogue of D-myo-inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P(4)] 2, a central and enigmatic molecule in the polyphosphoinositide pathway of cellular signalling. D-6-Deoxy-Ins(1,3,4,5)P(4) is a moderate inhibitor of Ins(1,4,5)P(3) 5-phosphatase [1.8microM] compared to Ins(1,3,4,5)P(4) [0.15microM] and similar to that of L-Ins(1,3,4,5)P(4) [1.8microM]. In displacement of [(3)H] Ins(1,4,5)P(3) from the rat cerebellar Ins(1,4,5)P(3) receptor, while slightly weaker [IC(50)=800nM] than that of D-Ins(1,3,4,5)P(4) [IC(50)=220nM], 3 is less markedly different and again similar to that of L-Ins(1,3,4,5)P(4) [IC(50)=660nM]. 3 is an activator of I(CRAC) when inward currents are measured in RBL-2H3-M1 cells using patch-clamp electrophysiological techniques with a facilitation curve different to that of Ins(1,3,4,5)P(4). Physicochemical properties were studied by potentiometric (31)P and (1)H NMR titrations and were similar to those of Ins(1,3,4,5)P(4) apart from the observation of a biphasic titration curve for the P1 phosphate group. A novel vicinal phosphate charge-induced conformational change of the inositol ring above pH 10 was observed for D-6-deoxy-Ins(1,3,4,5)P(4) that would normally be hindered because of the central stabilising role played by the 6-OH group in Ins(1,3,4,5)P(4). We conclude that the 6-OH group in Ins(1,3,4,5)P(4) is crucial for its physicochemical behaviour and biological properties of this key inositol phosphate.     

Ins(1,4,5)P3 receptor-mediated Ca2+ signaling and autophagy induction are interrelated

The role of intracellular Ca2+ signaling in starvation-induced autophagy remains unclear. Here, we examined Ca2+ dynamics during starvation-induced autophagy and the underlying molecular mechanisms. Tightly correlating with autophagy stimulation, we observed a remodeling of the Ca2+ signalosome. First, short periods of starvation (1 to 3 h) caused a prominent increase of the ER Ca2+-store content and enhanced agonist-induced Ca2+ release. The mechanism involved the upregulation of intralumenal ER Ca2+-binding proteins, calreticulin and Grp78/BiP, which increased the ER Ca2+-buffering capacity and reduced the ER Ca2+ leak. Second, starvation led to Ins(1,4,5)P3R sensitization. Immunoprecipitation experiments showed that during starvation Beclin 1, released from Bcl-2, first bound with increasing efficiency to Ins(1,4,5)P3Rs; after reaching a maximal binding after 3 h, binding, however, decreased again. The interaction site of Beclin 1 was determined to be present in the N-terminal Ins(1,4,5)P3-binding domain of the Ins(1,4,5)P3R. The starvation-induced Ins(1,4,5)P3R sensitization was abolished in cells treated with BECN1 siRNA, but not with ATG5 siRNA, pointing toward an essential role of Beclin 1 in this process. Moreover, recombinant Beclin 1 sensitized Ins(1,4,5)P3Rs in 45Ca2+-flux assays, indicating a direct regulation of Ins(1,4,5)P3R activity by Beclin 1. Finally, we found that Ins(1,4,5)P3R-mediated Ca2+ signaling was critical for starvation-induced autophagy stimulation, since the Ca2+ chelator BAPTA-AM as well as the Ins(1,4,5)P3R inhibitor xestospongin B abolished the increase in LC3 lipidation and GFP-LC3-puncta formation. Hence, our results indicate a tight and essential interrelation between intracellular Ca2+ signaling and autophagy stimulation as a proximal event in response to starvation.     

Ins(1,4,5)P3 receptor-mediated Ca2+ signaling and autophagy induction are interrelated

The role of intracellular Ca²⁺ signaling in starvation-induced autophagy remains unclear. Here, we examined Ca²⁺ dynamics during starvation-induced autophagy and the underlying molecular mechanisms. Tightly correlating with autophagy stimulation, we observed a remodeling of the Ca²⁺ signalosome. First, short periods of starvation (1 to 3 h) caused a prominent increase of the ER Ca²⁺-store content and enhanced agonist-induced Ca²⁺ release. The mechanism involved the upregulation of intralumenal ER Ca²⁺-binding proteins, calreticulin and Grp78/BiP, which increased the ER Ca²⁺-buffering capacity and reduced the ER Ca²⁺ leak. Second, starvation led to Ins(1,4,5)P₃R sensitization. Immunoprecipitation experiments showed that during starvation Beclin 1, released from Bcl-2, first bound with increasing efficiency to Ins(1,4,5)P₃Rs; after reaching a maximal binding after 3 h, binding, however, decreased again. The interaction site of Beclin 1 was determined to be present in the N-terminal Ins(1,4,5)P₃-binding domain of the Ins(1,4,5)P₃R. The starvation-induced Ins(1,4,5)P₃R sensitization was abolished in cells treated with BECN1 siRNA, but not with ATG5 siRNA, pointing toward an essential role of Beclin 1 in this process. Moreover, recombinant Beclin 1 sensitized Ins(1,4,5)P₃Rs in ⁴⁵Ca²⁺-flux assays, indicating a direct regulation of Ins(1,4,5)P₃R activity by Beclin 1. Finally, we found that Ins(1,4,5)P₃R-mediated Ca²⁺ signaling was critical for starvation-induced autophagy stimulation, since the Ca2+ chelator BAPTA-AM as well as the Ins(1,4,5)P₃R inhibitor xestospongin B abolished the increase in LC3 lipidation and GFP-LC3-puncta formation. Hence, our results indicate a tight and essential interrelation between intracellular Ca²⁺ signaling and autophagy stimulation as a proximal event in response to starvation.     

Conformational states of human rat sarcoma (Ras) protein complexed with its natural ligand GTP and their role for effector interaction and GTP hydrolysis

The guanine nucleotide-binding protein Ras exists in solution in two different conformational states when complexed with different GTP analogs such as GppNHp or GppCH(2)p. State 1 has only a very low affinity to effectors and seems to be recognized by guanine nucleotide exchange factors, whereas state 2 represents the high affinity effector binding state. In this work we investigate Ras in complex with the physiological nucleoside triphosphate GTP. By polarization transfer (31)P NMR experiments and effector binding studies we show that Ras(wt)·Mg(2+)·GTP also exists in a dynamical equilibrium between the weakly populated conformational state 1 and the dominant state 2. At 278 K the equilibrium constant between state 1 and state 2 of C-terminal truncated wild-type Ras(1-166) K(12) is 11.3. K(12) of full-length Ras is >20, suggesting that the C terminus may also have a regulatory effect on the conformational equilibrium. The exchange rate (k(ex)) for Ras(wt)·Mg(2+)·GTP is 7 s(-1) and thus 18-fold lower compared with that found for the Ras·GppNHp complex. The intrinsic GTPase activity substantially increases after effector binding for the switch I mutants Ras(Y32F), (Y32R), (Y32W), (Y32C/C118S), (T35S), and the switch II mutant Ras(G60A) by stabilizing state 2, with the largest effect on Ras(Y32R) with a 13-fold increase compared with wild-type. In contrast, no acceleration was observed in Ras(T35A). Thus Ras in conformational state 2 has a higher affinity to effectors as well as a higher GTPase activity. These observations can be used to explain why many mutants have a low GTPase activity but are not oncogenic.     

Quantal Ca2+ release and inactivation in a model of the inositol 1,4,5-trisphosphate receptor involving transformation of the ligand by the receptor

A model explaining quantal Ca²⁺ release as an intrinsic property of the inositol 1,4,5-trisphosphate (IP₃) receptor has been put forward. The model is based on the hypothesis that the IP₃ receptor can catalyze a transformation of the IP, molecule differing from its conventional metabolism. A simple kinetic mechanism is considered, in which IP₃-induced Ca²⁺ channel opening is followed by the step of IP₃ conversion and channel closure. Examination of the resulting mathematical model shows that it can reproduce well both partial release of stored Ca²⁺ and the same responsiveness to subsequent IP3 additions. On incorporation of an additional closed state of the channel, the model describes also a time-dependent channel inactivation at a high IP₃ dose. Temperature sensitivity of the catalytic step accounts for the reported elimination of quantal responses and inactivation at low temperature. The transformation product is surmised to be a positional or stereo isomer of IP₃.     

Potentiometric and P NMR studies on inositol phosphates and their interaction with iron(III) ions

Potentiometric, conductometric and ³¹P NMR titrations have been applied to study interactions between myo-inositol hexakisphosphate (phytic acid), (±)-myo-inositol 1,2,3,5-tetrakisphosphate and (±)-myo-inositol 1,2,3-trisphosphate with iron(III) ions. Potentiometric and conductometric titrations of myo-inositol phosphates show that addition of iron increases acidity and consumption of hydroxide titrant. By increasing the Fe(III)/InsP₆ ratio (from 0.5 to 4) 3 mol of protons are released per 2 mol of iron(III). At first, phytates coordinate iron octahedrally between P2 and P1,3. The second coordination site represents P5 and neighbouring P4,6 phosphate groups. Complexation is accompanied with the deprotonation of P1,3 and P4,6 phosphate oxygens. At higher concentration of iron(III) intermolecular P–O–Fe–O–P bonds trigger formation of a polymeric network and precipitation of the amorphous Fe(III)–InsP₆ aggregates. ³¹P NMR titration data complement the above results and display the largest chemical shift changes at pD values between 5 and 10 in agreement with strong interactions between iron and myo-inositol phosphates. The differences in T₁ relaxation times of phosphorous atoms have shown that phosphate groups at positions 1, 2 and 3 are complexated with iron(III). The interactions between iron(III) ions and inositol phosphates depend significantly on the metal to ligand ratio and an attempt to coordinate more than two irons per InsP₆ molecule results in an unstable heterogeneous system.     

Syntheses, spectroscopic and structural characterization of some (solvated) binuclear adducts of the form Ag(oxyanion):dpem(:S) (1:1(:x))2 (oxyanion = ClO4, F3CCO2, F3CSO3; dpem = Ph2E(CH2)EPh2 (E = P, As))

Syntheses, spectroscopic (IR, NMR and ESI MS) and single crystal X-ray structural characterizations are reported for a wide variety of adducts of Ag(oxyanion):dpem(:S) (1:1(:n))₂ (oxyanion = ClO₄, F₃CCO₂ (tfa) F₃CSO₃ (tfs); dpem = Ph₂E(CH₂)EPh₂) stoichiometry among which the basic Ag(Ph₂E(CH₂)EPh₂)₂Ag core is diversely perturbed by interactions with anions and solvent molecules. ESI MS and ³¹P NMR spectroscopy indicated that dinuclear species also exist in solution.     

Facile pyramidal inversion at phosphorus in [R3EP7W(CO)3] type complexes: An EXSY NMR study

A series of [R₃EP₇W(CO)₃]²⁻ complexes where (E = Si, Ge, Sn, Pb; R = alkyl, phenyl) were prepared from [P₇W(CO)₃]³⁻ and R₃EX reagents (X = Cl, Br) in dmf or CH₃CN solutions. The Pb derivatives were prepared at −50 °C and are not thermally stable. The compounds were characterized by ³¹P NMR spectroscopy and selected ESI-MS studies. All compounds undergo rapid inversion at the ER₃-bound phosphorus atom. The barriers to inversion were measured by way of 2D ³¹P EXSY experiments at various temperatures. The analysis showed very low barriers to pyramidal inversion (ΔG^‡ 10.3-13.5 kcal/mol) that were essentially enthalpic in origin. The activation barriers generally increased with increasing electronegativity of the E atom and the steric bulk of the ER₃ substituents. The latter was interpreted by way of a non-linear transition state.     

A new experimental approach and signal processing scheme for the detection and quantitation of P brain neurochemicals from in vivo MRS studies using dual tuned (H/P) head coil

Brain ³¹P-neurometabolites play an important role in energy and membrane metabolism. Unambiguous identification and quantification of these neurochemicals in different brain regions would be a great aid in advancing the understanding of metabolic processes in the nervous system. Phosphomonoester (PME), consisting of phosphoethanolamine (PE) and phosphocholine (PC), is the “building block” for membranes, while phosphodiesters (PDE), consisting of glycerophosphocholine (GPC) and glycerophosphoethanolamine (GPE) metabolites are involved in the membrane breakdown process. In the clinical setting, generating well-resolved spectra for PC, PE, GPC, and GPE could be crucial phospholipids in providing information regarding membrane metabolism. We present here a new experimental approach for generating well-resolved ³¹P spectra for PC and PE as well as for GPC, GPE, and other ³¹P metabolites. Our results (based on uni-dimensional (1D) and multi-voxel ³¹P studies) indicate that an intermediate excitation pulse angle (35°) is best suited to obtain well-resolved PC/PE and GPC/GPE resonance peaks. Our novel signal processing scheme allows generating metabolite maps of different phospholipids include PC/PE and GPC/GPE using the ‘time-domain–frequency-domain’ method as referred to in the MATLAB programming language.     

Synthesis, characterization and DNA binding properties of oligopyridine-ruthenium(II)-amino acid conjugates

The DNA-binding properties of a number of ruthenium oligopyridine complexes with conjugated amino acids having the general formulae [Ru(terpy)(4-COY-4'-Mebpy)(X)](n)(+), X=NO (n=3), X=Cl (n=1) and NO(2) (n=1) and Y=AlaCONH(2) and TrpCONH(2) are reported. The new complexes were spectroscopically characterized and their DNA-binding properties were studied by means of circular dichroism (CD), (23)Na and (31)P NMR spectroscopy. The results show that the chlorido complexes interact by coordination to the DNA bases with the conjugated amino acid able to provide an additional interaction with the DNA helix. In addition, electrostatic interactions between all studied complexes and the DNA polyanion were observed. The nitro complexes were found to be insignificant, affecting only the (31)P NMR signal, probably due to changes in the hydration sphere of the DNA close to the phosphates.     

Synthesis and characterization of silver(I) derivatives containing acylpyrazolonate and phosphino ligands: X-ray crystal structures of monomeric [Ag(Q)(PPh3)2] and of dimeric [{Ag(Q)(PiBu3)}2] (Q = 1-phenyl-3-methyl-4-tert-butylacetylpyrazolon-5-ato)

New silver(I) acylpyrazolonate derivatives [Ag(Q)], [Ag(Q)(PR₃)]₂ and [Ag(Q)(PR₃)₂] (HQ = 1-R¹-3-methyl-4-R²(CO)pyrazol-5-one, HQ^Bn = R¹ = C₆H₅, R² = CH₂C₆H₅; HQ^CHPh2 = R¹ = C₆H₅, R² = CH(C₆H₅)₂; HQ^nPe = R¹ = C₆H₅, R² = CH₂C(CH₃)₃; HQ^tBu = R¹ = C₆H₅, R² = C(CH₃)₃; HQ^fMe = R¹ = C₆H₄-p-CF₃, R² = CF₃; HQ^fEt = R¹ = C₆H₅, R² = CF₂CF₃; R = Ph or iBu) have been synthesized and characterized in the solid state and solution. The crystal structure of 1-(4-trifluoromethylphenyl)-3-methyl-5-pyrazolone, the precursor of proligand HQ^fMe and of derivatives [Ag(Q^nPe)(PPh₃)₂] and [Ag(Q^nPe)(PiBu₃)]₂ have been investigated. [Ag(Q^nPe)(PPh₃)₂] is a mononuclear compound with a silver atom in a tetrahedrally distorted AgO₂P₂ environment, whereas [Ag(Q^nPe)(PiBu₃)]₂ is a dinuclear compound with two O₂N-exotridentate bridging acylpyrazolonate ligands connecting both silver atoms, their coordination environment being completed by a phosphine ligand.     

Synthesis, spectroscopic and structural characterization of adducts of stoichiometry CuX:dppe (1:2) (X = I, ClO4, BH4, O3SCF3, SCN, dppe = Ph2P(CH2)2PPh2)

Syntheses and spectroscopic features (IR, NMR and ESI MS) are reported for five 1:2 adducts of CuX with dppe (X = I, ClO₄, NCS, O₃SCF₃ (tfs) BH₄; dppe = Ph₂P(CH₂)₂PPh₂). ESI MS and ³¹P NMR spectroscopy indicate that these species dissociate in solution yielding free diphosphine and 3:2 species. A single crystal X-ray structure determination has been carried out on Cu(dppe)₂NCS defining a four-coordinate complex of the form [(P,P′-dpex)M(P-dpex)X] for M = Cu, the thiocyanate being N-bound; the ionic [Cu(P,P′-dppe)₂]tfs has also been structurally characterized.     

Tripodal polyphosphine ligands in silver (I) coordination chemistry: Mononuclear cf. polynuclear complex dependence vis-a-vis counterion and ligand to metal ratio

1:2, 1:1, 3:2 and 6:2 AgX:L adducts (where L is a tridentate phosphine, in detail: 1,1,1-tris(diphenylphosphinomethyl)ethane (Me-triphos) and bis(2-diphenylphosphinoethyl)phenylphosphine (Ph-triphos), X = O₃SCF₃, O₃SCH₃, BF₄ or O₂CCF₃) have been synthesized and characterized by IR, NMR (¹H, ³¹P and ¹⁹F) and ESI MS spectroscopy. The stoichiometry of the complexes is strongly dependent on the ligand to metal ratio employed and also on the nature of the counterion. ³¹P NMR (solution) data also show the complexes existing in solution, in some cases, however, disproportionating to adducts of different nuclearity. Oligonuclear species have been detected through ESI MS spectroscopy that has been demonstrated as a powerful tool for the identification of the solution species. AgBF₄:Me-triphos (1:2) has been structurally characterized as [Ag(P,P′-Me-triphos)₂](BF₄) · H₂O · 7/2 MeOH, while Ag(O₃SCF₃): Ph-triphos: H₂O (6:2:4) is a spectacular two-dimensional polymer.     

New oligo-/poly-meric forms for MX:dpex (1:1) complexes (M = Cu, Ag; X = (pseudo-)halide; dpex = Ph2E(CH2)xEPh2, E = (P), As; x = 1, 2)

Single-crystal X-ray structural characterizations of MX:dpam (1:1) (‘dpam’ = Ph₂AsCH₂AsPh₂) are reported for MX = AgCl, Br; CuI, CN/Cl (all isomorphous) and AgI, AgSCN, CuSCN arrays, all being of the novel form [(μ-X){M(μ-X)(As-dpam-As′)₂M′}]_∞, essentially the familiar M(E-dpem-E′)₂M′ binuclear array with both ‘bridging’ and (linking) ‘terminal’ (pseudo-)halides involved in the polymer. A different arrangement of bridging and linking entities is found with AgX:dpae (1:1)_2(∞|∞), X = Br, NCO, ‘dpae’ = Ph₂As(CH₂)₂AsPh₂, now comprising [M(μ-X)₂(As-dpae-As)M] kernels linked by As-dpae-As′, while in the thiocyanate analogue units are linked by the dpae ligands into a two-dimensional web. Synthetic procedures for all adducts have been reported. All compounds have been characterized both in solution (¹H, ¹³C, ³¹P NMR, ESI MS) and in the solid state (IR).     

Thermotropism and hydration properties of POPE and POPE-cholesterol systems as revealed by solid state2H and31P-NMR

The partial phase diagram and the hydration properties of the 1-palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE)-water system, in the absence and presence of 30 mol% cholesterol, have been investigated by solid state phosphorus NMR of the lipid and deuterium NMR of heavy water. The POPE-D₂O phase diagram resembles other phosphatidylethanolamine (PE)-water systems: below water-to-lipid molar ratios (R_i) of 3 the lamellar gel (L or L_c)-to-hexagonal type II (H_II) phase sequence is observed on increasing the temperature. For R_i3 the thermotropic sequence (L or L_c)-L-H_II is detected. On increasing hydration from R_i=3, the H_II phase is detected from 40°C to 85°C whereas the gel phase is observed from 40°C to 30°C. The limiting hydrations of the gel, L and H_II phases are R_i 3, 17 and 20, respectively. The number of bound water molecules per lipid is ca. 8 in both the La and HII phases. The presence of cholesterol stabilizes the hexagonal phase 20°C below temperatures at which it is observed in its absence and reduces the limiting hydration of the fluid and hexagonal phases to Ri 9 and 14, respectively. The structure and/or dynamics of the water bound to the interface are markedly modified on going from the L to the H_II phase.Abbreviations NMR Nuclear magnetic resonance - DDPE 1,2-Didodecyl-rac-glycerol-3-phosphoethanol-amine - DHPE 1,2-Dihexadecyl-sn-glycerol-3-phosphoethanol-amine - DOPE 1,2-Dioleoyl-sn-glycerol-3-phosphoethanol-amine - POPE 1-Palmitoyl-2-oleoyl-sn-glycerol-3-phosphoetha-nolamine - DAPE 1,2-Diarachinoyl-sn-glycerol-3-phosphoethanol-amine - DMPC 1,2-Dimyristol-sn-glycerol-3-phosphocholine - DPPC 1,2-Dipalmitoyl-sn-glycerol-3-phosphocholine - T_c lamellar gel-to-lamellar fluid transition temperature - T_h lamellar fluid-to-hexagonal transition temperature     

Complexes formed from 2,4,6-trimercaptotriazine (H3TMT): synthesis and structural characterization of [M(PhP(CH2CH2P(Ph)2)2(HTMT)], M=Ni(II), Pd(II), Pt(II)

Na₃TMT · 9H₂O (H₃TMT=2,4,6-trimercaptotriazine) reacts with M(PPP)Cl₂, PPP=PhP(CH₂CH₂PPh₂)₂, M=Ni, Pd, Pt, to give the compounds [M(PPP)(HTMT)]. The nickel and palladium complexes have been characterized by single-crystal X-ray diffraction analysis. PPP is tridentate in both complexes. The nickel complex has an irregular trigonal bipyramidal configuration in which the triazine is bidentate, coordinating through one sulfur and one nitrogen donor atom. The palladium complex has an approximately square planar geometry in which the triazine forms a strong Pd-S bond in the plane and also a very weak Pd-N interaction above the plane. The ³¹P NMR spectrum of the platinum complex is similar to that of the palladium complex, which is consistent with the Pt complex also having an approximately square-planar structure. Variable temperature NMR spectra show that two conformational isomers of the nickel complex are present in solution at low temperatures, though exchange is fast at room temperature. DFT calculations have confirmed the possible existence of two five-coordinate isomers of comparable stability.     

Water-soluble 3-O-(2-methoxyethyl)cellulose: synthesis and characterization

The synthesis of novel 3-O-(2-methoxyethyl)cellulose via 2,6-di-O-thexyldimethylsilyl ethers was successfully carried out. Treatments of 3-O-(2-methoxyethyl)-2,6-di-O-thexyldimethylsilylcellulose with tetrabutylammonium fluoride trihydrate led to a complete removal of the protecting groups. Structure characterization carried out by means of 1D and 2D NMR spectroscopy proves a high regioselectivity. The novel cellulose ether is soluble in dimethyl sulfoxide, N,N-dimethylacetamide, N-methylpyrrolidone, and water. Size-exclusion chromatography revealed a distinct aggregation behavior in water.