Phase diagrams of MgF2-(Y,Ln)F3 systems

By means of thermal and X-ray analyses with oxygen control, 14 phase diagrams of the systems MgF₂-(Y, Ln)F₃ have been obtained, where Ln are all lanthanides except Pm and Eu. All the systems are eutectic. Solid solutions up to 12 mole% MgF₂, which decompose by the eutectoid scheme, were detected based on high-temperature modifications of trifluorides of Y, Er, Tm, Yb and Lu, with a structure of the-YF₃ type.

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Zusammenfassung Durch Einsatz der Thermo- und Röntgenanalyse mit Sauerstoffkontrolle wurden 14 Phasendiagramme der Systeme MgF₂-(Y, Ln)F₃ erhalten, wobei Ln sämtliche Lanthanoide mit Ausnahme von Pm und Eu sind. Alle Systeme zeigten sich eutektisch. Feste, sich nach dem eutektoiden Schema zersetzende Lösungen bis zu 12 Mol% MgF₂ wurden an Hand der Hochtemperatur-Änderungen der Trifluoride von Y, Er, Tm, Yb, Lu mit-YF₃-Struktur nachgewiesen.

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Résumé 14 diagrammes de phases des systèmes MgF₂ — (Y, Ln) F₃, où Ln représente tous les lanthanoïdes à l'exception de Pm et Eu ont été établis par études aux rayons X et analyse thermique, avec contrôle de l'oxygène. Tous ces systèmes présentent un eutectique. Des solutions solides jusqu'à 12 moles % de MgF₂ à décomposition eutectoïde ont été décelées à l'aide des transitions à haute température des trifluorures d'Y, Er, Tm, Yb et Lu du type-YF₃.

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- , 14 MgF₂ — (Y, Ln)F₃, Ln- , u. -. 12 .% MgF₂, , Y, r, Tm, Yb, Lu, -YF₃.

     

Chemical biology of protein lipidation: semi-synthesis and structure elucidation of prenylated RabGTPases

Rab/Ypt guanosine triphosphatases (GTPases) represent a family of key membrane traffic regulators in eukaryotic cells. For their function Rab/Ypt proteins require double modification with two covalently bound geranylgeranyl lipid moieties at the C-terminus. Generally, prenylated proteins are very difficult to obtain by recombinant or enzymatic methods. We generated prenylated RabGTPases using a combination of chemical synthesis and protein engineering. This semi-synthesis depends largely on the availability of functionalized prenylated peptides corresponding to the proteins' native structure or modifications. We developed solution phase and solid phase strategies for the generation of peptides corresponding to the prenylated C-terminus of Rab7 GTPase in preparative amounts enabling us to crystallize the mono-prenylated Ypt1:RabGDI complex. The structure of the complex provides a structural basis for the ability of RabGDI to inhibit the release of nucleotide by Rab proteins and a molecular basis for understanding a RabGDI mutant that causes mental retardation in humans.     

Direct sampling time-of-flight mass spectrometers for technological analysis

The practicability of direct sampling time-of-flight mass spectrometers for routine technological analysis is considered. The discussed set incorporates two TOF instruments together covering analysis of solid, liquid, and gas samples without the need for time consuming sample preparation. Both an electron ionization reflectron TOF mass analyzer designed for the analysis of gas and liquid samples and a laser ionization axial electrostatic TOF mass analyzer designed for analysis of solid and powder samples use a single system for data acquisition, collection and processing. These instruments achieve ng/g range sensitivity and mass resolution exceeding 1000. Because of its compact design the system also can be realized as a mobile laboratory for on-site analysis. Prospects for applying the instruments to different technological applications are discussed. Received: 17 July 1997 / Revised: 28 November 1997 / Accepted: 22 December 1997     

Preparation,structures, and redox and emission characteristics of the isothiocyanate complexes of hexarhenium(III) clusters [Re6(mu3-E)8(NCS)6]4- (E = S,Se)

Hexarhenium(III) complexes with terminal isothiocyanate ligands, [(n-C(4)H(9))(4)N](4)[Re(6)(mu(3)-S)(8)(NCS)(6)] (1) and (L)(4)[Re(6)(mu(3)-Se)(8)(NCS)(6)] (L(+) = PPN(+) (2a), (n-C(4)H(9))(4)N(+) (2b)), have been prepared by three different methods. Complex 1 was prepared by the reaction of [(n-C(4)H(9))(4)N](4)[Re(6)(mu(3)-S)(8)Cl(6)] with molten KSCN at 200 degrees C, while 2b was obtained by refluxing the chlorobenzene-DMF (2:1 v/v) solution of [Re(6)(mu(3)-Se)(8)(CH(3)CN)(6)](SbF(6))(2) and [(n-C(4)H(9))(4)N]SCN. The [Re(6)(mu(3)-Se)(8)(NCS)(6)](4)(-) anion was also obtained from a mixture of Cs(2)[Re(6)(mu(3)-Se)(8)Br(4)] and KSCN in C(2)H(5)OH by a mechanochemical activation at room temperature for 20 h and isolated as 2a. The X-ray structures of 1 and 2a.4DMF have been determined (1, C(70)H(144)N(10)S(14)Re(6), monoclinic, space group P2(1)/n (No. 14), a = 14.464(7) A, b = 22.059(6) A, c = 16.642(8) A, beta = 113.62(3) degrees, V = 4864(3) A(3), Z = 2; 2a.4DMF, C(162)H(144)N(14)O(4)P(8)S(6)Se(8)Re(6), triclinic, space group P1 (No. 2), a = 15.263(2) A, b = 16.429(2) A, c = 17.111(3) A, alpha = 84.07(1) degrees, beta = 84.95(1) degrees, gamma = 74.21(1) degrees, V = 4098.3(8) A(3), Z = 1). All the NCS(-) ligands in both complexes are coordinated to the metal center via nitrogen site with the Re-N distances in the range of 2.07-2.13 A. The redox potentials of the reversible Re(III)(6)/Re(III)(5)Re(IV) process in acetonitrile are +0.84 and +0.70 V vs. Ag/AgCl for [Re(6)(mu(3)-S)(8)(NCS)(6)](4)(-) and [Re(6)(mu(3)-Se)(8)(NCS)(6)](4)(-), respectively, which are the most positive among the known hexarhenium complexes with six terminal anionic ligands. The complexes show strong red luminescence with the emission maxima (lambda(max)/nm), lifetimes (tau(em)/micros), and quantum yields (phi(em)) being 745 and 715, 10.4 and 11.8, and 0.091 and 0.15 for 1 and 2b, respectively, in acetonitrile. The data reasonably well fit in the energy-gap plots of other hexarhenium(III) complexes. The temperature dependence of the emission spectra and tau(em) of 1 and [(n-C(4)H(9))(4)N](4)[Re(6)(mu(3)-S)(8)Cl(6)] are also reported.     

Molecular structures of β-amino-α-bromovinyl trifluoromethyl ketones

The molecular structures of β-amino-α-bromovinyl trifluoromethyl ketones was studied by UV, IR, ¹H, ¹³C, and ¹⁵N NMR spectroscopy and using the density functional (B3LYP/6-31G(d,p) and PBE/QZ3P) and ab initio riMP2/cc-pVTZm quantum-chemical calculations. Factors affecting stabilization of the EZE-conformation of the molecules, which is atypical of analogous unsubstituted amino enones, are considered.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 102–106, January, 2005.     

New Layered Polymer [{Mn(H2O)3}2{Re6Se8(CN)6}] · 3.3H2O: Synthesis and Properties

The [{Mn(H₂O)₃}₂{Re₆Se₈(CN)₆}] · 3.3H₂O complex was produced on slow evaporation of an aqueous solution containing the salt of a cluster complex K₄Re₆Se₈(CN)₆ · 3.5H₂O and a 23-fold excess of Mn²⁺. The cluster complexes [Re₆Se₈(CN)₆]^4– are linked in a crystal into the charged coordination layers [{Mn(H₂O)₃}₄{Re₆Se₈(CN)₆}₃]^4– ₂ through the Mn²⁺ cations. The Mn²⁺ cations are coordinated in a layer by three cyano nitrogen atoms of the cluster complexes; the Mn–N bond lengths are 2.13(4) and 2.21(2) Å. Each [Re₆Se₈(CN)₆]^4– anion is bonded to three manganese cations Mn(1). The anions are bonded additionally to the Mn(2) cations disordered over two close positions.     

Sorption recovery of sulfate complexes of iridium on hydrated zirconium dioxide

The sorption on a hydrated zirconium(IV) dioxide from solutions of trinuclear iridium(IV,IV,IV) and iridium(III,III,IV) oxosulfates was studied. The effect of temperature, sorbent grain size, concentration of sulfate complexes of iridium in solution, and acidity of the medium on the sorption recovery was considered.     

The 13C NMR spectra of π-arenechromium carbonyl complexes

The ¹³C NMR spectra of π-arenechromium complexes XC₆H₅Cr(CO)₂L (where I, L  CO; II, L  PPh₃; X  aliphatic and aromatic substituents) were investigated. The effect of the nature of the substituent X on the chemical shifts of the carbon atoms of the aromatic ring in these complexes was analyzed.It was established that a correlation exists between δ(¹³C) and σ_R (Taft's constant) in complexes I, not only for C(4) nuclei but also for C(3) metal atoms, the difference being that the slopes of the corresponding curves are opposite.     

Amidines derived from Pt(IV)-mediated nitrile-amino alcohol coupling and their Zn(II)-catalyzed conversion into oxazolines

The reaction between the platinum(IV) complex trans-[PtCl(4)(EtCN)(2)] and the amino alcohols NH(2)CH(2)CH(2)OH, NH(2)CH(2)CH(Me)OH-(R)-(-), NH(2)CH(Ph)CH(2)OH-(R)-(-), NH(2)CH(Et)CH(2)OH-(R)-(-), NH(2)CH(Et)CH(2)OH-(S)-(+), and NH(2)CH(Pr(n)())CH(2)OH proceeds rapidly at room temperature in CH(2)Cl(2) to furnish the amidine complexes [PtCl(4)(HN=C(Et)NH(arcraise;)OH)(2)] (1-6) in good yield (70-80%). The related reaction between the platinum(II) complex trans-[PtCl(2)(EtCN)(2)] and monoethanolamine in a molar ratio of 1:2 in CH(2)Cl(2) results in the addition of 4 equiv of NH(2)CH(2)CH(2)OH per mole of complex to give [Pt(HN=C(Et)NHCH(2)CH(2)OH)(2)(NH(2)CH(2)CH(2)OH)(2)](2+) (7). Formulation of 1-6 is based upon satisfactory C, H, N elemental analyses, electrospray mass spectrometry, IR spectroscopy, and (1)H, (13)C((1)H), (15)N, and (195)Pt NMR spectroscopies, while the structures of trans-[PtCl(4)((Z)-NH=C(Et)NHCH(2)CH(2)OH)(2)] (1), trans-[PtCl(4)((Z)-NH=C(Et)NHCH(2)CH(Me)OH-(R)-(-))(2)] (2), and trans-[PtCl(4)((Z)-NH=C(Et)NHCH(Et)CH(2)OH-(R)-(-))(2)] (4) were determined by X-ray single-crystal diffraction. The Z-amidine configuration of the ligands is preserved in CDCl(3) solutions as confirmed by gradient-enhanced (15)N,(1)H-HMQC spectroscopy and NOE experiments. The amidines, formed upon Pt(IV)-mediated nitrile-amino alcohol coupling, were liberated from their platinum(IV) complexes 1, 3, and 4 by reaction with Ph(2)PCH(2)CH(2)PPh(2) (dppe) giving free NH=C(Et)NHCHRCH(2)OH (R = H 8, Et 9, Ph 10), with the substituents R of different types, and dppe oxides; the P-containing species were identified by (31)P((1)H) NMR spectroscopy. NOESY spectroscopy indicates that the liberated amidines retained the same configuration relative to the C=N double bond, i.e., syn-(H,Et)-NH=C(Et)NHCHRCH(2)OH. The liberated hydroxo-functionalized amidines 8-10 were converted into oxazolines (11-13) in the presence of a catalytic amount of ZnCl(2). A similar catalytic effect has also been reached using anhydrous MSO(4) (M = Cu, Co, Cd), CdCl(2), and AlCl(3).