Lewis acid-catalyzed atom transfer radical cyclization of unsaturated β-keto amides

The Lewis acid-catalyzed atom transfer radical cyclization reactions of olefinic -bromo β-keto amides were investigated. It was found Lewis acid Yb(OTf)₃ or Mg(ClO₄)₂ not only promoted the cyclization reactions, but also resulted in excellent trans stereocontrol in the cyclization products. With the catalysis of Lewis acid Yb(OTf)₃ or Mg(ClO₄)₂ at −78°C in the presence of Et₃B/O₂, the cyclization reactions of C-olefinic β-keto amides provided cyclic ketones, while the cyclization reactions of N-olefinic β-keto amides led to the formation of γ-lactams, which could be converted to 3-aza-bicyclo[3,1,0]hexan-2-ones.     

Contribution á l''étude des tris(dialcoylamino)stibines : II. Étude des réactions avec les dérivés carbonylés et les dérivés bifonctionnels

The reaction of Sb(NMe₂)₃ with aldehydes and ketones leads to enamines or diamines according to the degree of substitution of the carbonyl compound. With acids Sb(NMe₂)₃ gives amides, and with β-diketones and β-keto esters it gives enamines. With bifunctional compounds such as diols, secondary diamines or aminoalcohols, different heterocyclic compounds are formed according to the ratio of bifunctional compound to antimony.     

Progres report

This paper provides a brief resumé of our current researches in organometallic chemistry. The first deals with non-classical organolanthanoid chemistry, which has, as targets, subvalent compounds of the early 4f elements (La, Ce, Pr, Nd) and cationic organosamarium(II) and -ytterbium(II) complexes. The second is concerned with new aspects of metal amide chemistry including (a) silver(I) amides and isonitrile complexes of lithium amides; (b) derivatives of aromatic diamides such di(metalamino)cyclophanes; (c) metal silyl complexes derived from insertion of a stable silylene into M(II)---N(SiMe₃)₂ (M = Ge, Sn or Pb) bonds; and (d) reactions of M′---X compounds with 1,3,5-triazine [M′ = Li or Na and X = N(SiMe₃)₂, C(SiMe₃)₃ or CH(SiMe₃)₂] The two other present areas (on subvalent compounds of Group 14 elements and metal 1-azaallyls, β-diketiminates and 1,3-diazaallyls) are reported more cursorily. The Introduction is divided into three section entitled ‘Relationship to the Journal of Organometallics Chemistry’, ‘Reviews (from 1956 to 1995)’ and ‘An outline of principal contributions’.     

Preparation of mesoporous hematite particles by a forced hydrolysis reaction accompanying a peptide production reaction

The influence of carbodimide (CI), well known as a condensing agent for producing peptides from l-phenylalanine (l-Phe), on the formation of hematite (-Fe₂O₃) particles through a forced hydrolysis reaction of acidic FeCl₃ solution was examined. The large ellipsoidal particles were produced together with needle-like -FeOOH and fine Fe₃O₄ ones in the systems both with l-Phe and CI, though the system only with CI was not essentially changed the particle shape. CI produced the characteristic large ellipsoidal particle accompanying the production of peptides by condensing l-Phe. This behavior was explained by the adsorption of peptides on β-FeOOH and polynuclear (PN) particles; the adsorption of peptides retarded the phase transformation from β-FeOOH to hematite along with the heterogeneous aggregation of PNs, resulting the large ellipsoidal hematite particles. CI reduced Fe³⁺ to Fe²⁺ ions during aging the solution. The decomposition of urea, by-products of peptide formation, produced two kinds of amines to raise the solution pH and provided -FeOOH and Fe₃O₄ particles. The large ellipsoidal hematite particles exhibited large specific surface area and high mesoporosity by adsorption of peptides onto PN particles within the hematite particles. The morphology and inner structure of hematite particles were exceedingly altered by using a reaction of peptide production and this procedure is expected for a new developing method of high-quality porous materials.     

Vibrational spectroscopic detection of H-bonded β- and γ-turns in cyclic peptides and glycopeptides

The conformation of N-glycoproteins and N-glycopeptides has been the subject of many spectroscopic studies over the past decades. However, except for some preliminary data, no detailed study on the vibrational spectroscopy of glycosylated peptides has been published until recently.

This paper reports FTIR spectroscopic properties in DMSO and TFE of the N-glycosylated cyclic peptides cyclo[Gly-Pro-Xxx(GlcNAc)-Gly-δ-Ava] 3a and 3b in comparison with data on the non-glycosylated parent peptides cyclo(Gly-Pro-Xxx-Gly-δ-Ava) 2a and 2b [a, Xxx = Asn; b, Xxx = Gln; δ-Ava = NH-(CH₂)₄-CO] and N-acetyl 2-acetamido-2-deoxy-β- -gluco pyranosylamine (GlcNAc-NHAc, 4). The assignment of amide I band frequencies to conformation is based on ROESY experiments and determination of the temperature coefficients in DMSO-d₆ solution. (For the synthesis and NMR characterization of 2a and 3a see Ref. [19].)

Cyclic peptides are expected to adopt folded (β- and/or γ-turn) conformations which may be fixed by intramolecular H-bonding(s). A comparison of the temperature coefficients of the NH protons and amide I band frequencies and intensities suggests that in DMSO there is no significant difference in the backbone conformation and H-bond system of the N-glycosylated models and their parent cyclic peptides. The common feature of the backbone conformation of models 2 and 3 is the predominance of a 1 ← 4 (C₁₀) H-bonded type II β-turn encompassing Pro-Xxx or Pro-Xxx(GlcNAc), respectively. The ROESY connectivities in the Asn(GlcNAc) model (3a) have not been found to reflect intramolecular H-bondings between the peptide and the sugar.

The unique feature of the FTIR spectra in DMSO of the cyclic models is the lack or weakness of low-frequency (< 1640 cm⁻¹) amide I component bands. In TFE the amide I region of the FTIR spectra shows an increased number of components below 1650 cm⁻¹ reflecting a mixture of open and H-bonded β- and γ-turn conformers.

Because of its destabilizing effect upon γ-turns and other weakly H-bonded structures, DMSO decreases the number of backbone conformers. DMSO also destroys side-chain-backbone H-bondings of type C₇, C₆ or C₈. Possible ‘glyco’ C₇ H-bondings in GlcNAc-NHAc (4) or in glycopeptides 3a and 3b cannot resist the effect of DMSO either.

The FTIR data in TFE of models 2–4 suggest that the acceptor amide group of strong C₇ H-bondings in peptides and glycopeptides absorbs at 1630 ± 5 cm⁻¹ and that of bifurcated H-bondings between 1600–1620 cm⁻¹.     

钯-高分子载体催化剂对糠醛加氢液相反应的研究

以弱碱性苯乙烯系阴离子交换树脂[D392,-NH₂,D382,-NHCH₃,D301R,-NH(CH₃)₂],强碱性苯乙烯系阴离子交换树脂[201×7DVB,-NH⁺(CH₃)₃]和弱碱性环氧系阴离子交换树脂(701,-NH₂)为载体制备了3种钯-高分子载体催化剂.考察了反应条件、高分子载体的种类、钯含量和催化剂用量对糠醛催化加氢生成四氢糠醇反应及催化性能的影响.在体积分数为50%的乙醇-水溶液和水中对糠醛常压液相加氢反应,钯-高分子载体(阴离子交换树脂D392,-NH₂,D382,-NHCH₃)催化剂均可使糠醛的加氢反应转化率达100%,生成四氢糠醇的选择性达98%以上,而用金属钯为催化剂的转化率达70%以上,选择性达97%以上.同时用XPS分析了高分子载体催化剂的结构与催化加氢反应性能的关系.     

Stereoselective reduction of 2-methyl-3-oxo esters (or amides) with sodium borohydride catalyzed by manganese(II) chloride or tetrabutylammonium borohydride. A practical preparation of erythro and threo-3-hydroxy-2-methyl esters (or amides)

erythro-3-Hydroxy-2-methylpropionates or erythro-3-hydroxy-2-methylpropionamides were prepared with high stereoselectivity by NaBH₄ reduction of the corresponding 2-methyl-3-oxo esters or 2-methyl-3-oxo amides in the presence of a catalytic amount of manganese(II) chloride. On the other hand, reduction of these substrates with n-Bu₄NBH₄ provided threo-isomers selectively. erythro-Selective reduction of 2-methyl-3-oxo amides with NaBH₃CN in 1N HCl-MeOH is also described.     

Synthesis of 2-oxazolines mediated by N,N′-diisopropylcarbodiimide

N-(β-Hydroxy)amides can be cyclised by reaction with diisopropylcarbodiimide (DIC) to give the corresponding 2-oxazolines in high yields. The reaction requires only very mild Lewis-acid catalysis (5 mol % Cu(OTf)₂) and can be accomplished with simple heating, or in very short reaction times under microwave irradiation.     

改性SiO2载体对邻菲咯啉钌荧光特性及氧敏感荧光膜性能的影响

为提高极性荧光指示剂Ru(dpp)₃Cl₂在非极性硅橡胶中的分散性,以沉淀白炭黑、气相白炭黑和甲基MQ树脂,载负荧光指示剂Ru(dpp)₃Cl₂,再填充到二甲基硅橡胶(PDMS)中,制备氧敏感荧光膜.以分光光度计和荧光光谱仪,研究载体种类对Ru(dpp)₃Cl₂的吸附性、荧光特性及氧敏感荧光膜性能的影响.白炭黑载负Ru(dpp)₃Cl₂的荧光发射光谱相对其稀溶液约红移20 nm.载体表面的甲基可减弱SiO₂载体对Ru(dpp)₃Cl₂分子的吸附性和相互作用,减少荧光发射光谱的红移12 nm,提高荧光强度近10倍.白炭黑有助改善Ru(dpp)₃Cl₂在PDMS中的分散性和氧敏感荧光膜的荧光输出和猝灭比,尤以MQ树脂的效果最为显著.     

Reversed-phase high-performance liquid chromatographic method for the quantitative determination of alkylbis(2-benzothiazolylsulfen)amides

An isocratic, reversed-phase HPLC procedure was developed for the simultaneous determination of isopropyl-, tert.-butyl-, tert.-amyl-, cyclohexylbis(2-benzothiazolylsulfen)amides. Quantitation is performed on a C₁₈ bonded-phase column (Separon SGX C₁₈ 5 μm) using N-dicyclohexyl-2-benzothiazolesulfenamide as internal standard followed by UV photodiode-array detection. The precision (n = 7) for all derivatives of alkylbis(2-benzothiazolylsulfen)amides is within 1.5%. Identification of the compounds also in the mixtures was done by NMR spectroscopy.     

X–H rotational-echo double-resonance NMR for torsion angle determination of peptides

C–H and N–H rotational-echo double-resonance (REDOR) NMR is developed for determining torsion angles in peptides. The distance between an X spin such as ¹³C or ¹⁵N and a proton is measured by evolving the proton magnetization under REDOR-recoupled X–H dipolar interaction. The proton of interest is selected through its directly bonded heteronuclear spin Y. The sidechain torsion angle χ₁ is extracted from a ¹³Cβ-detected Hβ–N distance, while the backbone torsion angle φ is extracted from an ¹⁵N-detected H^N–C^′ distance. The approach is demonstrated on three model peptides with known crystal structures to illustrate its utility.     

The lively chemistry of the di-μ-methylene-bis(pentamethylcyclopentadienyl-rhodium) complexes, analogues of surface reactions in heterogeneous catalysis

The chemistry of the di-μ-methylene-bis(pentamethylcyclopentadienyl-rhodium) complexes is reviewed. The complex [{(η⁵-C₅Me₅)RhCl₂}₂] (1a) reacted with MeLi to give, after oxidative work-up, blood-red cis-[{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(Me)₂], 2. This has the two rhodiums in the +4 oxidation state (d⁵), and linked by a metal-metal bond (2.620 Å). Trans-2 was formed on isomerisation of cis-2 in the presence of Lewis acids, or by direct reaction of 1a with Al₂Me₆, followed by dehydrogenation with acetone. The Rh-methyls in [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(Me)₂] were readily replaced under acidic conditions (HX) to give [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(X)₂] (X = Cl, Br or I); these latter complexes reacted with a variety of RMgX to give [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(R)₂] (R = alkyl, Ph, vinyl, etc.). Trans-2 also reacted with HBF₄ in the presence of L to give first [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(Me)(L)]⁺ and then [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(L)₂]²⁺ (L = MeCN, CO, etc.). The {(η⁵-C₅Me₅)Rh(μ-CH₂)}₂ core is rather kinetically inert and also forms a variety of complexes with oxy-ligands, both cis-, e.g. [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(μ-OAc)]⁺ and trans-, such as [(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(H₂O)₂]²⁺. The complexes [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(R)L]⁺ (R = Me or aryl) in the presence of CO, or [{(η⁵-C₄Me₅)Rh(μ-CH₂)}₂(R)₂] (R = Me, Ph or CO₂Me) in the presence of mild oxidants, readily yield the C---C---C coupled products RCH=CH₂. The mechanisms of these couplings have been elucidated by detailed labelling studies: they are more complex than expected, but allow direct analogies to be drawn to C---C couplints that occur during Fischer-Tropsch reactions on rhodium surfaces.     

Matrix isolation infrared spectroscopic and theoretical study of noble gas coordinated dipalladium–dioxygen complexes

The reaction products of palladium atoms with molecular oxygen in solid argon have been investigated using matrix isolation infrared absorption spectroscopy and quantum chemical calculations. In addition to the previously reported mononuclear palladium–dioxygen complexes: Pd(η²–O₂) and Pd(η²–O₂)₂, dinuclear palladium–dioxygen complexes: Pd₂(η²–O₂) and Pd₂(η²–O₂)₂ were formed under visible light irradiation and were identified on the basis of isotopic substitution and theoretical calculations. In addition, experiments doped with xenon in argon coupled with theoretical calculations suggest that the Pd(η²–O₂), Pd₂(η²–O₂) and Pd₂(η²–O₂)₂ complexes are coordinated by two argon or xenon atoms in solid argon matrix, and therefore, should be regarded as the Pd(η²–O₂)(Ng)₂, Pd₂(η²–O₂)(Ng)₂ and Pd₂(η²–O₂)₂(Ng)₂ (NgAr or Xe) complexes isolated in solid argon.     

Stabile Bis(η-alkin)MCl2-komplexe; Darstellung und reaktivität

The synthesis and reactivity of {(η⁵-C₅H₄SiMe₃)₂Ti(CCSiMe₃)₂} MCl₂ (M = Fe: 3a; M = Co: 3b; M = Ni: 3c) is described. The complexes 3 are accessible by the reaction of (η⁵-C₅H₄SiMe₃) ₂Ti(CSiMe₃)₂ (1) with equimolar amounts of MCl₂ (2) (M = Fe, Co, Ni). 3a reacts with the organic chelat ligands 2,2′-dipyridyl (dipy) (4a) or 1,10-phenanthroline (phen) (4b) in THF at 25°C to afford in quantitative yields (η⁵-C₅H₄SiMe₃)₂Ti(CSiMe₃)₂ (1) and [Fe(dipy)₂]Cl₂ (5a) or [Fe(phen)₂]Cl₂ (5b). 1/n[Cu^IHal]_n (6) or 1/n[Ag^IHal]_n (7) (Hal = Cl, Br) react with {(η⁵ -C₅H₄SiMe₃)₂Ti(CCSiMe₃)₂}FeCl₂ (3a), by replacement of the FeCl₂ building block in 3a, to yield the compounds {(η⁵-C₅H₄SiMe₃)₂Ti(C CSiMe₃)₂}Cu^IHal (8) or {(η⁵-C₅H₄SiMe₃)₂Ti(CSiMe₃)₂}Ag^IHal (9) (Hal = Cl, Br), respectively. In 8 and 9 each of the two Me₃SiCC-units is η²-coordinated to monomeric Cu^I Hal or Ag^IHal moieties. Compounds 8 and 9 can also be synthesized by the reaction of (η⁵-C₅H₄SiMe₃)₂ Ti(CSiMe₃)₂ (1) with 1/n[Cu^IHal]_n (6) or 1/n [Ag^IHal]_n (7) in excellent yields. All new compounds have been characterized by analytical and spectroscopic data (IR, ¹H-NMR, MS). The magnetic moments of compounds 3 were measured.     

Promotion of hydrocarbon selectivity in CO2 hydrogenation by Ru component

We investigated catalytic behavior of iron in CO₂ hydrogenation with and without a ruthenium component. Calcined iron-based catalysts were reduced by H₂ and characterized by XRD, BET surface area and CO₂, CO and C₂H₄ temperature-programmed desorption (TPD), and tested for CO₂ hydrogenation. When Fe-K/γ-Al₂O₃ was used as a catalyst, CO₂ conversion was 36%, but when Fe-Ru-K/γ-Al₂O₃ was used, CO₂ conversion was 41%. The product selectivities for catalysts with and without the ruthenium component were also compared. Fe-K/γ-Al₂O₃ exhibited higher methane (16 mol%) and C₂–C₄ selectivity (39.6 mol%) than Fe-Ru-K/γ-Al₂O₃. The main products obtained with Fe-Ru-K/γ-Al₂O₃ were higher hydrocarbons such as C₅⁺ hydrocarbons. For Fe-Ru-K/γ-Al₂O_3, the product distribution followed the Anderson–Schultz–Flory (ASF) distribution. However, in the case of Fe-Ru-K/γ-Al₂O₃, the hydrocarbon distribution deviates from the ideal ASF distribution. It is concluded that the readsorption rates of the primary hydrocarbon product increase exponentially with chain length in the ruthenium promoted catalytic system. The behavior of catalysts with and without the ruthenium will be explained by the CO₂-, CO- and C₂H₄– profiles. In this study, it was confirmed that ruthenium component promoted the readsorption ability of -olefin, and then the chain length of hydrocarbon is higher. In addition, the microcrystalline wax produced in CO₂ hydrogenation was a high-crystalline and olefin-rich hydrocarbon.     

Ca-mediated thiolysis of peptide–resin linkage as an option for preparing protected peptide thioesters

A mild new procedure for preparing protected peptide thioesters, based on Ca²⁺-assisted thiolysis of peptide–Kaiser oxime resin (KOR) linkage, is described. Ac-Ile-Ser(Bzl)-Asp(OcHx)-SR (Ac: acetyl; Bzl: benzyl; cHx: cyclohexyl), model peptide, was readily released from the resin by incubating the peptide–KOR at 60 °C in mixtures of DMF with n-butanethiol [R = (CH₂)₃CH₃] or ethyl 3-mercaptopropionate [R = (CH₂)₂COOCH₂CH₃] containing Ca(CH₃COO)₂. After serine and aspartic acid side-chain deprotection under acid conditions, Ac-Ile-Ser-Asp-S(CH₂)₂COOCH₂CH₃ was successfully obtained with good quality and high yield. This type of C-terminal modified peptide may act as an excellent acyl donor in peptide segment condensation by the thioester method, native chemical ligation and enzymatic methods.     

Oxidative-addition to a four-coordinate tin(II) complex supported by octamethyldibenzotetraaza[14]annulene dianion ligation, [η-Me8taa]Sn: The syntheses and structures of [η-Me8taa]SnI2 and *[η-Me8taa]SnI(THF)**I3*

The four-coordinate tin(II) complex [η⁴-Me₈taa]Sn undergoes oxidative addition of I₂ to give six-coordinate [η⁴-Me₈taa]SnI₂, in which the iodide ligands exhibit a trans arrangment. Abstraction of I⁻ from [η⁴-Me₈taa]SnI₂ is facile, as indicated by the rapid formation of the triiodide derivative *[η⁴-Me₈taa]SnI(THF)**I₃* upon treatment with I₂ in the presence of THF. The molecular structures of [η⁴-Me₈taa]SnI₂ and *[η⁴-Me₈taa]SnI(THF)**I₃* have been determined by X-ray diffraction.     

Reactions of the cationic diruthenium carbonyl complex [Ru2(μ-dppm)2(CO)4(μ,η-O2CMe)] with bidentate ligands; intramolecularly assisted stereospecific synthesis via the second-sphere face-to-face π–π stacking interactions

The reactions of the diruthenium carbonyl complexes [Ru₂(μ-dppm)₂(CO)₄(μ,η²-O₂CMe)]X (X=BF₄⁻ (1a) or PF₆⁻ (1b)) with neutral or anionic bidentate ligands (L,L) afford a series of the diruthenium bridging carbonyl complexes [Ru₂(μ-dppm)₂(μ-CO)₂(η²-(L,L))₂]X_n ((L,L)=acetate (O₂CMe), 2,2′-bipyridine (bpy), acetylacetonate (acac), 8-quinolinolate (quin); n=0, 1, 2). Apparently with coordination of the bidentate ligands, the bound acetate ligand of [Ru₂(μ-dppm)₂(CO)₄(μ,η²-O₂CMe)]⁺ either migrates within the same complex or into a different one, or is simply replaced. The reaction of [Ru₂(μ-dppm)₂(CO)₄(μ,η²-O₂CMe)]⁺ (1) with 2,2′-bipyridine produces [Ru₂(μ-dppm)₂(μ-CO)₂(η²-O₂CMe)₂] (2), [Ru₂(μ-dppm)₂(μ-CO)₂(η²-O₂CMe)(η²-bpy)]⁺ (3), and [Ru₂(μ-dppm)₂(μ-CO)₂(η²-bpy)₂]²⁺ (4). Alternatively compound 2 can be prepared from the reaction of 1a with MeCO₂H–Et₃N, while compound 4 can be obtained from the reaction of 3 with bpy. The reaction of 1b with acetylacetone–Et₃N produces [Ru₂(μ-dppm)₂(μ-CO)₂(η²-O₂CMe)(η²-acac)] (5) and [Ru₂(μ-dppm)₂(μ-CO)₂(η²-acac)₂] (6). Compound 2 can also react with acetylacetone–Et₃N to produce 6. Surprisingly [Ru₂(μ-dppm)₂(μ-CO)₂(η²-quin)₂] (7) was obtained stereospecifically as the only one product from the reaction of 1b with 8-quinolinol–Et₃N. The structure of 7 has been established by X-ray crystallography and found to adopt a cis geometry. Further, the stereospecific reaction is probably caused by the second-sphere π–π face-to-face stacking interactions between the phenyl rings of dppm and the electron-deficient six-membered ring moiety of the bound quinolinate (i.e. the N-included six-membered ring) in 7. The presence of such interactions is indeed supported by an observed charge-transfer band in a UV–vis spectrum.     

Synthesis and characterization of hydroxo, pyrazolato and carboxylato derivatives of the PdR(PPh3)moiety (R = C6F5 or C6Cl5)

The hydroxo-complexes [{PdR(PPh₃)(μ-OH)}₂] (R = C₆F₅ or C₆Cl₅) have been obtained by reaction of the corresponding [{PdR(PPh₃)(μ-Cl)}2] complexes with NBu₄OH in acetone. In this solvent, the reaction of the hydroxo-bridged complexes with pyrazole (Hpz) and 3,5-dimethylpyrazole (Hdmpz) in 1:2 molar ratio leads to the formation of the new complexes [{Pd(C₅F₅)(PPh₃)(μ-azolate)}2] and [{Pd(C₆Cl₅)(PPh₃)}₂(μ-OH)(μ-azolate)] (azolate = pz or dmpz). The reaction of the bis(μ-hydroxo) complexes with Hpz and Hdmpz in acetone in 1:1 molar ratio has also been studied, and the resulting product depends on the organic radical (C₆F₅ or C₆Cl₅) as well as the azolate (pz or dmpz). The identity of the isomer obtained has been established in every case by NMR (¹H, ¹⁹F and ³¹P) spectroscopy. The reaction of the bis(μ-hydroxo) complexes with oxalic (H₂Ox) and acetic (HOAc) acids yields the binucle ar complexes [{PdR(PPh₃)}2(μ-Ox)] (R = C₆F₅ or C₆Cl₅) and [{Pd(C₆F₅)(PPh₃)(μ-OAc)}2], respectively. [{Pd(C₆F₅)(PPh₃)(μ-OH)}₂] reacts with PPh₃ in acetone in 1:2 ratio giving the mononuclear complex trans-[Pd(C₆F₅) (OH)(PPh₃)₂], whereas the pentachlorophenylhydroxo complex does not react with PPh₃, even under forcing conditions.     

多肽诱导的巨型脂质体出芽和泄露行为

细胞膜与膜蛋白之间的相互作用与生命中许多过程息息相关.以巨型脂质体(GUV)和多肽分别作为细胞膜和膜蛋白的简化模型,我们设计了四种仅包含亮氨酸(L)和赖氨酸(K)的多肽,即K₁₄、(KL₂KL₂K)₂、(KL₂KL₃)₂和K₆L₈,并对比研究了它们与中性和负电性脂质体的相互作用.电荷密度最高的K₁₄只是涂层在脂质体表面,不破其囊泡结构,但能够引起负电性脂质体发生微相分离,属建设性相互作用.能够形成两亲性α螺旋的(KL₂KL₂K)₂和(KL₂KL₃)₂则引起脂质体发生泄露和破裂,属破坏性作用.但二者引起泄露的速率在中性脂质体和负电性脂质体中的结果恰好相反,说明泄露分两步进行:表面吸附多肽达到一定浓度,继而对膜进行干扰.表面活性剂型多肽K₆L₈的氨基酸组成与(KL₂KL₂K)₂相同,但K₆L₈只是引起负电性脂质体发生泄露,造成中性脂质体发生外出芽.这些简单氨基酸造成的脂质体的复杂构象变化可以统一用静电和疏水相互作用在膜上的位置和强度来进行解释.这些结论对于深入理解膜蛋白的作用机理是有帮助的.