Lamellar Gel (Lβ) Phases of Ternary Lipid Composition Containing Ceramide and Cholesterol

Lipid lateral segregation into specific domains in cellular membranes is associated with cell signaling and metabolic regulation. This phenomenon partially arises as a consequence of the very distinct bilayer-associated lipid physico-chemical properties that give rise to defined phase states at a given temperature. Until now lamellar gel (L_β) phases have been described in detail in single or two-lipid systems. Using x-ray scattering, differential scanning calorimetry, confocal fluorescence microscopy, and atomic force microscopy, we have characterized phases of ternary lipid compositions in the presence of saturated phospholipids, cholesterol, and palmitoyl ceramide mixtures. These phases stabilized by direct cholesterol-ceramide interaction can exist either with palmitoyl sphingomyelin or with dipalmitoyl phosphatidylcholine and present intermediate properties between raft-associated phospholipid-cholesterol liquid-ordered and phospholipid-ceramide L_β phases. The present data provide novel, to our knowledge, evidence of a chemically defined, multicomponent lipid system that could cooperate in building heterogeneous segregated platforms in cell membranes.     

Hydrido-derivatives of [Ir4(CO)10(diphosphine)]: X-ray analyses of [Ir4H(CO)9(μ-Ph2PH(CH3)PPh2)] and [Ir4 H(CO)9(μ-Ph2P(CH2)nPPh2)] (n = 2, 3)

Some novel hydrido-anions of general formula [Ir₄H(CO)₉(μ-L-L)]⁻ (L-L = Ph₂PCH(CH₃)PPh₂, Ph₂P(CH₂)₂PPh₂, Ph₂P(CH₂)₃PPh₂ and Ph₂AsCH₂AsPh₂) have been obtained by the reaction of [Ir₄(CO)₁₀(μ-L-L)] with the base 1,8-diazabicyclo[5.4.0]undec-7-ene in wet dichloromethane. According to IR and ¹H, ³¹P and ¹³C NMR data at low temperature, these anionic derivatives display a single conformation in solution: three edge-bridging COs around the triangular basal face and both the hydride and the bidentate ligands located in axial positions relative to this face. The structures of four compounds were established by X-ray diffraction studies, which confirmed the configuration proposed on the basis of spectroscopic data.     

Synthesis and characterisation of adducts of [Pt2(μ-S)2(PPh3)4] with organo-palladium and platinum-hydride substrates

The reactions of [Pt₂(μ-S)₂(PPh₃)₄] towards a range of palladium(II) complexes containing organometallic ligands (cyclopalladated N-donor ligands, η³-allyl, phenyl) have been explored, leading to the formation of a series of cationic, trinuclear sulfido-bridged aggregates containing {Pt₂PdS₂} cores. [Pt₂(μ-S)₂(PPh₃)₄] also reacts with the platinum(II) hydride complex trans-[PtHCl(PPh₃)₂] giving the adduct [Pt₂(μ-S)₂(PPh₃)₄PtH(PPh₃)]⁺. X-ray crystal structure determinations on the complexes [Pt₂(μ-S)₂(PPh₃)₄PdPh(PPh₃)]PF₆ and [Pt₂(μ-S)₂(PPh₃)₄PtH(PPh₃)]PF₆ are reported, and show the expected bis μ₃-sulfido aggregates with three square-planar metal centres.     

Synthesis, characterisation and structural studies of [Cu(dach)(μ-NCS)(NCS)]n and [Cu(dach)2(N3)]ClO4 (dach=1,4-diazacycloheptane)

A new singly bridging complex [Cu(dach)(μ-NCS)(NCS)]_n (dach=1,4-diazacycloheptane) has been synthesised and its crystal structure determined. There are many examples of double NCS bridged polymeric chains, but fewer singly bridged ones. IR, ESR and temperature variable magnetic studies are described but no magnetic interaction was found between the copper centres. [Cu(dach)₂(N₃)]ClO₄ has also been characterised by IR, ESR spectra and magnetic studies. The crystal structure determination shows that it is a penta-coordinated monomeric species with an axially coordinated azide linked to the perchlorate counterion by hydrogen bonding.     

Thallium(III) complexes of the metalloligands [Pt2(μ-S)2(PPh3)4] and [Pt2(μ-Se)2(PPh3)4]

Reactions of [Pt₂(μ-S)₂(PPh₃)₄] with the diarylthallium(III) bromides Ar₂TlBr [Ar = Ph and p-ClC₆H₄] in methanol gave good yields of the thallium(III) adducts [Pt₂(μ-S)₂(PPh₃)₄TlAr₂]⁺, isolated as their salts. The corresponding selenide complex [Pt₂(μ-Se)₂(PPh₃)₄TlPh₂]BPh₄ was similarly synthesised from [Pt₂(μ-Se)₂(PPh₃)₄], Ph₂TlBr and NaBPh₄. The reaction of [Pt₂(μ-S)₂(PPh₃)₄] with PhTlBr₂ gave [Pt₂(μ-S)₂(PPh₃)₄TlBrPh]⁺, while reaction with TlBr₃ gave the dibromothallium(III) adduct [Pt₂(μ-S)₂(PPh₃)₄TlBr₂]⁺[TlBr₄]⁻. The latter complex is a rare example of a thallium(III) dihalide complex stabilised solely by sulfur donor ligands. X-ray crystal structure determinations on the complexes [Pt₂(μ-S)₂(PPh₃)₄TlPh₂]BPh₄, [Pt₂(μ-S)₂(PPh₃)₄TlBrPh]BPh₄ and [Pt₂(μ-S)₂(PPh₃)₄TlBr₂][TlBr₄] reveal a greater interaction between the thallium(III) centre and the two sulfide ligands on stepwise replacement of Ph by Br, as indicated by shorter Tl-S and Pt?Tl distances, and an increasing S-Tl-S bond angle. Investigations of the ESI MS fragmentation behaviour of the thallium(III) complexes are reported.     

Lipid and Peptide Dynamics in Membranes upon Insertion of n-alkyl-β-D-Glucopyranosides

The effect of nonionic detergents of the n-alkyl-β-D-glucopyranoside class on the ordering of lipid bilayers and the dynamics of membrane-embedded peptides were investigated with ²H- and ³¹P-NMR. 1,2-dipalmitoyl-sn-glycero-3-phosphocholine was selectively deuterated at methylene segments C-2, C-7, and C-16 of the two fatty acyl chains. Two trans-membrane helices, WALP-19 and glycophorin A_71-98, were synthesized with Ala-d₃ in the central region of the α-helix. n-Alkyl-β-D-glucopyranosides with alkyl chains with 6, 7, 8, and 10 carbon atoms were added at increasing concentrations to the lipid membrane. The bilayer structure is retained up to a detergent/lipid molar ratio of 1:1. The insertion of the detergents leads to a selective disordering of the lipids. The headgroup region remains largely unaffected; the fatty acyl chain segments parallel to the detergent alkyl chain are only modestly disordered (10-20%), whereas lipid segments beyond the methyl terminus of the detergent show a decrease of up to 50%. The change in the bilayer order profile corresponds to an increase in bilayer entropy. Insertion of detergents into the lipid bilayers is completely entropy-driven. The entropy change accompanying lipid disorder is equivalent in magnitude to the hydrophobic effect. Ala-d₃ deuterated WALP-19 and GlycA_71-97 were incorporated into bilayers of 1,2-dimyristoyl-sn-glycero-3-phosphocholine at a peptide/lipid molar ratio of 1:100 and measured above the 1,2-dimyristoyl-sn-glycero-3-phosphocholine gel/liquid-crystal phase transition. Well-resolved ²H-NMR quadrupole splittings were observed for the two trans-membrane helices, revealing a rapid rotation of the CD₃ methyl rotor superimposed on an additional rotation of the whole peptide around the bilayer normal. The presence of detergent fluidizes the membrane and produces magnetic alignment of bilayer domains but does not produce essential changes in the peptide conformation or dynamics.     

N-Heterocyclic carbene gold(I) and silver(I) adducts of [Pt2(μ-S)2(PPh3)4]

Reaction of the metalloligand [Pt₂(μ-S)₂(PPh₃)₄] with the N-heterocyclic carbene (NHC) complexes IPrAuCl, IMesAuCl and IMesAgCl in methanol gave the first examples of metal adducts of [Pt₂(μ-S)₂(PPh₃)₄] that contain NHC ligands, namely [Pt₂(μ-S)₂(PPh₃)₄AuL]⁺ (L = IPr, IMes) and [Pt₂(μ-S)₂(PPh₃)₄AgIMes]⁺. The complexes were isolated as hexafluorophosphate salts. Reaction of [Pt₂(μ-S)₂(PPh₃)₄] with excess IPrAuCl in refluxing methanol yielded only the mono-adduct, in contrast to the behaviour with the gold(I) phosphine complex Ph₃PAuCl, which undergoes double addition giving [Pt₂(μ-SAuPPh₃)₂(PPh₃)₄]²⁺. The X-ray structure of [Pt₂(μ-S)₂(PPh₃)₄AuIPr]PF₆ was determined and reveals that the ‘free’ sulfide is substantially sterically protected by the IPr ligand, accounting for the low reactivity towards addition of a second AgIPr⁺ moiety.     

Reaction of cyanamide and their derivatives with (η-C5H5)Mn(CO)3 and (η-C5H4CH3)Mn(CO)3

The reaction of cyanamide and its derivatives with the (η⁵-C₅H₅)Mn(CO)₂(THF) and (η⁵-C₅H₄CH₃)Mn(CO)₂(THF) complexes affords the cyanamide substituted complexes of types (η⁵-C₅H₅)Mn(CO)₂(NCN(R′)(R″)) (2a-d) and (η⁵-C₅H₄CH₃)Mn(CO)₂(NCN(R′)(R″)) (3a-e). All complexes were characterized by spectroscopy (¹H, ¹³C NMR, IR), elemental and mass spectroscopy analysis. Complex 2b (η⁵-C₅H₅)Mn(CO)₂(NCN(CH₃)₂) was additionally examined by single crystal X-ray structure determination.     

A one-dimensional copper (II) coordination polymer [Cu3(ampym)2(μ1,1-N3)4(μ1,3-N3)2(dmf)2]n (ampym = 2-aminopyrimidine) containing both end-on and end-to-end azido bridges

A new polynuclear copper (II) complex, derived from the azido-bridging ligand and 2-aminopyrimidine, has been synthesized and its 3-D structure has been determined by X-ray diffraction methods at two different temperatures. The compound crystallizes in the triclinic system space group, with the central copper atom lying on an inversion centre. The crystal structure is built up by trinuclear units (each of them contains two double end-on azido bridges) linked through two azide ions in an end-to-end (EE) fashion, to yield the polymer chain [Cu₃(ampym)₂(μ_1,1-N₃)₄(μ_1,3-N₃)₂(dmf)₂]_n. Magnetic susceptibility measurement shows a ferromagnetic interaction above 30 K, whereas a weak anti-ferromagnetic interaction prevails in the range of 30-2 K.     

The complexes with end-to-end dicyanamide bridges: syntheses, characterization and crystal structures of [Cu(μ1,5-dca)2(phen)]n and [Cd(μ1,5-dca)2(py)2]n (phen=phenanthroline; py=pyridine; dca=dicyanamide, N(CN)2 )

Two new dicyanamide (dicyanamide=[N(CN)₂]⁻, dca) bridged complexes, [Cu(μ_1,5-dca)₂(phen)]_n (1) and [Cd(μ_1,5-dca)₂(py)₂]_n (2) have been synthesized and their structures have been determined by X-ray crystallography diffraction. Complex 1 crystallizes in the monoclinic space group P2(1)/c with a=10.1502(3), b=10.9815(4), c=14.5839(4) Å and Z=4. The adjacent copper atoms are connected by single end-to-end dca bridges to form a chain structure along the b axis. The chains are linked via Cu?N weak interactions to give rise to a 2D layer structure, which furthermore into a 3D structure by the π-π interaction between aromatic rings of adjacent layers. Complex 2 crystallizes in the monoclinic space group C2/m with a=6.6849(10), b=17.476(2), c=13.231(2) Å and Z=4. The cadmium(II) center is six-coordinated with a distorted octahedral geometry, bounded to four N atoms of four dca ligands and two N atoms of two-chelated py ligands. Neighbor Cd(II) atoms are linked by the double end-to-end dca bridges to generate a chain structure, which result in a 2D layer structure through the π-π interactions between the adjacent chains with distances 3.641 Å. EPR and magnetic results of 1 suggest that the complex exhibits a weak ferromagnetic interaction through CuNCNCNCu pathways.     

Sulfide-bridged aggregates from the metalloligand [Pt2(μ-S)2(PPh3)4] and β-diketonate complexes of cobalt(II) and zinc(II)

Reaction of [Pt₂(μ-S)₂(PPh₃)₄] with a range of zinc(II) and cobalt(II) complexes ML₂, where L is a β-diketonate ligand CH₃COCHCOCH₃, PhCOCHCOPh, CF₃COCHCOTh (Th = 2-thienyl)] permits the synthesis of adducts [Pt₂(μ-S)₂(PPh₃)₄M(diketonate)]⁺, isolated as their salts in moderate yields. The cobalt and zinc acetylacetonate complexes were characterised by single-crystal X-ray diffraction studies, which reveal isomorphous structures, with tetrahedral heterometal centres.     

Synthesis and characterization of triphenylphosphine stabilized silver α,β-unsaturated carboxylate: Crystal structure of [Ag(O2CCHC(CH3)2)(PPh3)2]

A series of triphenylphosphine coordinated silver α,β-unsaturated carboxylates of type [Ag(O₂CR)(PPh₃)_n: n = 1, R = CH₃CHCH (2a), (CH₃)₂CCH (2b), CH₃CH₂CHCH (2c), CH₃CH₂CH₂CHCH (2d), PhCHCH (2e), CH₂CH (2f); n = 2, CH₃CHCH (3a), (CH₃)₂CCH (3b), CH₃CH₂CHCH (3c), CH₃CH₂CH₂CHCH (3d)] were prepared by reaction of relative silver carboxylates (1a-1f) with triphenylphosphine in chloroform. These complexes were obtained in high yields and characterized by elemental analysis, ¹H NMR, ¹³C NMR, ³¹P NMR and IR spectroscopy. Thermal stability of the complexes has been determined by TG analysis. The molecular structure of [Ag((O₂CCHC(CH₃)₂))(PPh₃)₂] (3b) shows that the senecioato ligand is chelated with silver atom and generate, a distorted tetrahedron.     

Reactions of the complexes [Re2(CO)9(η-P-P)] (P-P=Ph2P(CH2)nPPh2, n=1-6) with Me3NO: formation of close-bridged complexes [Re2(CO)8(μ-P-P)] and phosphine oxide complexes [Re2(CO)9{P-P(O)}]

Reactions of [Re₂(CO)₁₀] with Me₃NO and diphosphines [Ph₂P(CH₂)_nPPh₂, n=1-6] yield mixtures of the monodentate-coordinated diphosphine complexes [Re₂(CO)₉(η¹-P-P)] (P-P=Ph₂P(CH₂)_nPPh₂, n=1-6) (yields 5-40%) and bridged dimers [{Re₂(CO)₉}₂(μ-P-P)] (5-50%). These complexes were isolated as either equatorial or axial isomers, or a mixture of two isomers. Reactions of the monodentate complexes with Me₃NO yield close-bridged complexes [Re₂(CO)₈(μ-P-P)] and phosphine oxide complexes [Re₂(CO)₉{P-P(O)}]. The structures of the close-bridged complexes 1 (n=3) and 2 (n=4), were determined by X-ray crystallography. The Re-Re bond in the close-bridged complex with the longest phosphine chain (n=6) is readily cleaved in CDCl₃ to give the complex [{cis-ReCl(CO)₄}₂(μ-dpph)] (3) as the product, the structure of which was also determined by X-ray crystallography.     

Synthesis of some pentanuclear platinum clusters [Pt5(CO)6(L)4]. The X-ray structure of [Pt5(μ-CO)5(CO)(PCy3)4]

[Pt₅(μ-CO)₅(CO)L₄] (L = PPh₃1, PPh₂Bz 2, AsPh₃3, PEt₃4, PCy₃5) have been synthesized by reacting [Pt₃(μ-CO)₃(PR₃)₃] with H₂O₂ (1 and 2), by reduction of cis-[PtCl₂(CO)(PEt₃)] with Zn dust (4), and by the Zn reduction of [Pt₃(μ-CO)₃(PCy₃)₃] in the presence of [PtCl₂(CH₃CN)₂] (5). Complex 5 has not been observed previously and has been characterized by X-ray crystallography. Oxidation of the phosphine ligands with H₂O₂ is a new way to synthesize 1 and 2. The first complete NMR characterization of these complexes has also been achieved, and showed that these pentanuclear cluster complexes exhibit similar stereochemistries in solution and in the solid state. The observed ¹J_Pt-Pt values do not have any correlation with the corresponding bond lengths, again pointing out the irregular behaviour of such parameter in Pt complexes.     

The arylation of [Pt2(μ-S)2(PPh3)4]

Routes to the synthesis of the mixed sulfide-phenylthiolate complex [Pt₂(μ-S)(μ-SPh)(PPh₃)₄]⁺ have been explored; reaction of [Pt₂(μ-S)₂(PPh₃)₄] with excess Ph₂IBr proceeds readily to selectively produce this complex, which was structurally characterised as its PF₆⁻ salt. Reactions of [Pt₂(μ-S)₂(PPh₃)₄] with other potent arylating reagents (1-chloro-2,4-dinitrobenzene and 1,5-difluoro-2,4-dinitrobenzene) also produce the corresponding nitroaryl-thiolate complexes [Pt₂(μ-S){μ-SC₆H₂(NO₂)₂X}(PPh₃)₄]⁺ (X = H, F). The complex [Pt₂(μ-S)(μ-SPh)(PPh₃)₄]⁺ reacts with Me₂SO₄ to produce the mixed alkyl/aryl bis-thiolate complex [Pt₂(μ-SMe)(μ-SPh)(PPh₃)₄]²⁺, but corresponding reactions with the nitroaryl-thiolate complexes are plagued by elimination of the nitroaryl group and formation of [Pt₂(μ-SMe)₂(PPh₃)₄]²⁺. [Pt₂(μ-S)(μ-SPh)(PPh₃)₄]⁺ also reacts with Ph₃PAuCl to give [Pt₂(μ-SAuPPh₃)(μ-SPh)(PPh₃)₄]²⁺.     

Synthesis and characterisation of [Pt2(μ-S)(μ-I)(PPh3)4] - A cationic iodo analogue of the metalloligand [Pt2(μ-S)2(PPh3)4]

Reaction of [Pt₂(μ-S)₂(PPh₃)₄] with a number of transition metal-iodo complexes leads to the formation of the cationic iodo analogue [Pt₂(μ-S)(μ-I)(PPh₃)₄]⁺, identified using electrospray ionisation mass spectrometry (ESI MS). Synthetic routes to this complex were developed, using the reaction of [Pt₂(μ-S)₂(PPh₃)₄] with either [PtI₂(PPh₃)₂] or elemental iodine. The complex was characterised by NMR spectroscopy, ESI MS and an X-ray structure determination, which reveals the presence of a planar, disordered {Pt₂SI}⁺ core. Monitoring the iodine reaction by ESI MS allows the identification of various iodine species, including the short-lived intermediate [Pt₂(μ-S)₂(PPh₃)₄I]⁺, which allows a mechanism for the reaction to be proposed.     

Chlorophyll composition of Photosystems IIα, IIβ and I in tobacco chloroplasts

The antenna composition of the Photosystems II_α, II_β and I was studied in tobacco chloroplasts. Absorbance spectra, recorded at 4 K, were analyzed for the wild type and the mutants Su/su and Su/su var. Aurea, containing higher concentrations of the photosystems. With chloroplasts of Su/su we measured the action spectra of the three photosystems from 625 to 690 nm. Above 675 nm absorption by Photosystem I dominated. This sytem had a maximum at 678 nm and a shoulder at 660 nm. Of the long-wavelength chlorophyll a forms, absorbing at 690, 697 and 705 nm at 4 K, which are generally assigned to Photosystem I, the 697 nm form occurred in an amount of four molecules per reaction center of Photosystem I in each type of chloroplast. The Photosystem II_α spectrum was characterized by maxima at 650 and 672 nm, showing clearly the participation of the chlorophyll a and b containing light-harvesting complex. In the mutants the light-harvesting complex has a chlorophyll a to chlorophyll b ratio of more than 1; the amount of the 672 nm chlorophyll a was normal, whereas the amount of chlorophyll b was markedly decreased in the mutants relative to the wild type. The Photosystem II_β spectrum mainly consisted of a band at 683 nm.     

Study of Pt(II)-aromatic amines complexes of the types cis- and trans-Pt(amine)2I2, [Pt(amine)4]I2 and I(amine)Pt(μ-I)2Pt(amine)I

Pt(II) complexes of the types cis- and trans-Pt(amine)₂I₂ with amines containing a phenyl group were synthesized and studied mainly by IR and multinuclear (¹⁹⁵Pt, ¹H and ¹³C) magnetic resonance spectroscopies. The compounds are not very soluble. In ¹⁹⁵Pt NMR spectroscopy, the cis isomers were observed at slightly lower fields than the trans analogues (average Δδ = 11 ppm) in acetone. In ¹H NMR, the NH groups were also found at slightly lower fields in the cis isomers. The coupling constants ²J(¹⁹⁵Pt-¹HN) varied from 53 to 85 Hz and seem slightly smaller in the trans configuration. The ¹³C NMR spectra of most of the complexes were measured. No coupling constants J(¹⁹⁵Pt-¹³C) were detected due to the low solubility of the compounds. The cis isomers containing a phenyl group on the N atom could not be isolated except for Ph-NH₂ which was shown to be a mixture of isomers in acetone. The tetrasubstituted ionic compounds [Pt(amine)₄]I₂ for the less crowded ligands were also studied mainly by NMR spectroscopy in aqueous solution. The ¹⁹⁵Pt chemical shifts vary between −2855 and −2909 ppm. The coupling constants ³J(¹⁹⁵Pt-¹H) are about 40 Hz. The iodo-bridged dinuclear species I(amine)Pt(μ-I)₂Pt(amine)I were also synthesized and characterized. Two isomers are present in acetone solution for most of the compounds. Their δ(Pt) signals were observed at about −4000 ppm and their coupling constants ²J(¹⁹⁵Pt-¹HN) are around 69 Hz.     

Characterisation of α3β1 and αvβ3 integrin N-oligosaccharides in metastatic melanoma WM9 and WM239 cell lines

It is well documented that glycan synthesis is altered in some pathological processes, including cancer. The most frequently observed alterations during tumourigenesis are extensive expression of β1,6-branched complex type N-glycans, the presence of poly-N-acetyllactosamine structures, and high sialylation of cell surface glycoproteins. This study investigated two integrins, α₃β₁ and α_vβ₃, whose expression is closely related to cancer progression. Their oligosaccharide structures in two metastatic melanoma cell lines (WM9, WM239) were analysed with the use of matrix-assisted laser desorption ionisation mass spectrometry. Both examined integrins possessed heavily sialylated and fucosylated glycans, with β1,6-branches and short polylactosamine chains. In WM9 cells, α₃β₁ integrin was more variously glycosylated than α_vβ₃; in WM239 cells the situation was the reverse. Functional studies (wound healing and ELISA integrin binding assays) revealed that the N-oligosaccharide component of the tested integrins influenced melanoma cell migration on vitronectin and α₃β₁ integrin binding to laminin-5. Additionally, more variously glycosylated integrins exerted a stronger influence on these parameters. To the best of our knowledge, this is the first report concerning structural characterisation of α_vβ₃ integrin glycans in melanoma or in any cancer cells.