Encapsulation of Pt(iv) prodrugs within a Pt(ii) cage for drug delivery

This report presents a novel strategy that facilitates delivery of multiple, specific payloads of Pt(iv) prodrugs using a well-defined supramolecular system. This delivery system comprises a hexanuclear Pt(ii) cage that can host four Pt(iv) prodrug guest molecules. Relying on host–guest interactions between adamantyl units tethered to the Pt(iv) molecules and the cage, four prodrugs could be encapsulated within one cage. This host–guest complex, exhibiting a diameter of about 3 nm, has been characterized by detailed NMR spectroscopic measurements. Owing to the high positive charge, this nanostructure exhibits high cellular uptake. Upon entering cells and reacting with biological reductants such as ascorbic acid, the host–guest complex releases cisplatin, which leads to cell cycle arrest and apoptosis. The fully assembled complex displays cytotoxicity comparable to that of cisplatin against a panel of human cancer cell lines, whereas the cage or the Pt(iv) guest alone exhibit lower cytotoxicity. These findings indicate the potential of utilising well-defined supramolecular constructs for the delivery of prodrug molecules.     

Pt(IV)-catalyzed cyclization of arene-alkyne substrates via intramolecular electrophilic hydroarylation

[reaction: see text] We herein report that PtCl(4) has proven to be a hydroarylation catalyst with an efficiency and substrate scope superior to previously known methods. This catalyst demonstrated consistent performance with arene-yne substrates of diverse structural features, including propargyl ethers, propargylamines, and alkynoate esters, providing good to excellent yields of the 6-endo products (chromenes, dihydroquinolines, and coumarins). In contrast, Pt(II), Pd(II), and Ga(III) salts were shown to be sensitive to the substitution on the alkyne moiety.     

Visible light driven generation and alkyne insertion reactions of stable bis-cyclometalated Pt(iv) hydrides

Hydride complexes resulting from the oxidative addition of C–H bonds are intermediates in hydrocarbon activation and functionalization reactions. The discovery of metal systems that enable their direct formation through photoexcitation with visible light could lead to advantageous synthetic methodologies. In this study, easily accessible dimers [Pt₂(μ-Cl)₂(C^N)₂] (C^N = cyclometalated 2-arylpyridine) are demonstrated as a very convenient source of Pt(C^N) subunits, which promote photooxidative C–H addition reactions with different 2-arylpyridines (N′^C′H) upon irradiation with blue light. The resulting [PtH(Cl)(C^N)(C′^N′)] complexes are the first isolable Pt(iv) hydrides arising from a cyclometalation reaction. A transcyclometalation process involving three photochemical steps is elucidated, which occurs when the C^N ligand is a monocyclometalated 2,6-diarylpyridine, and a detailed analysis of the photoreactivity associated with the Pt(C^N) moiety is provided. Alkyne insertions into the Pt–H bond of a photogenerated Pt(iv) hydride are also reported as a demonstration of the ability of this class of compounds to undergo subsequent organometallic reactions.

The photochemical generation of isolable bis-cyclometalated Pt(iv) hydrides via photooxidative C–H addition reactions is demonstrated from easily accessible Pt(ii) precursors using visible light.     

Tin(iv) and lead(iv) complexes with a tetradentate redox-active ligand

The coordination chemistry of a tetradentate redox-active ligand, glyoxal-bis(2-hydroxy-3,5-di-tert-butylanil) (H(2)L), was investigated with the diorganotin(iv) and diphenyllead(iv) moieties. Complexes R(2)SnL (R = Me (), Et (), (t)Bu (), Ph ()) and Ph(2)PbL () have been prepared and characterized. The molecular structures of compounds , and have been determined by single crystal X-ray diffraction. The diamagnetic octahedral complexes bear a tetradentate O,N,N,O redox-active ligand with a nearly planar core. Complexes demonstrate solvatochromism in solution. The CV of complexes reveals four one-electron redox processes. The spin density distribution in the chemically generated cations and anions of was studied by X-band EPR spectroscopy. The experimental data agree well with the results of DFT calculations of electronic structures for , its pyridine adduct ·Py, cation and anion .     

Chronopotentiometry of uranium(iv)

The chronopotentiometry of uranium at platinum electrodes has been investigated. A determination of uranium has been devised based on the conversion of the uranium to uranium(IV) and the oxidation of the uranium (IV). The effect of several possible interfering substances has been checked.     

Structural researches on organotin(iv) compounds. synthesis and structure of nitratotriphenyl(triphenylphosphine oxide)tin(iv)

A nitrato-complex of organotin(IV) containing triphenylphosphine oxide, Sn(C₆H₅)₃(NO₃) [(C₆H₅)₃PO], has been synthesized and characterized by infrared spectroscopy and X-ray structural analysis. The compound crystallizes in space group P 1¯, with a = 11.817(6), b = 11.086(6), c = 12.471(6), α = 99.6(1),β = 90.8(1), γ = 97.8(1), Z = 2. The structure has been solved from X-ray diffractometer data by Patterson and Fourier methods and refined by least-squares calculations to R = 6.4% for 4301 independent reflections. The structure consists of discrete monomer units in which tin shows trigonal bipyramidal geometry.     

Alkyl and cyclic substituted thiuram disulphides as ligands. titanium(iv), vanadium(iv), and oxovanadium(iv) complexes

Summary Titanium(IV) hexacoordinate thiuram disulphide complexes of the type [TiX₄R₂NC(S)SSC(S)NR₂}] (X=Cl or Br; R=Me, Et, piperidinyl or morpholinyl) have been prepared by reaction between TiX₄ (X=Cl or Br) and the thiuram disulphide. Similar reactions with VOCl₃ lead to reduction of vanadium(V) and give rise to the oxovanadium(IV) pentacoordinate complexes [VOCl₂{R₂NC(S)SSC(S)NR₂}]. However, the reactions of these same thiuram disulphide ligands with [VCl₂(THF)₂] (THF=tetrahydrofuran) cause oxidation of vanadium and to the reduction of the disulphide to the corresponding dithiocarbamate [R₂NCS₂]^–, resulting in new dichlorobis (dithiocarbamate)vanadium(IV) complexes [VCl₂-(R₂NCS₂)₂]. All the compounds have been characterized by elemental analyses, i.r., visible and e.p.r. spectra. Both thiuram disulphides and dithiocarbamate ligands exhibit bidentate     

Dicyclopentadienyl-niobium(iii) and -niobium(iv) complexes

The reduction of (η-C₅H₅)₂NbCl₂ (I) under various conditions gives the dimer (η-C₅H₅)₄Nb₂Cl₃ (II) containing niobium(III) and niobium(IV). Reaction of II with AgClO₄ gives [(η-C₅H₅)₄Nb₂Cl₂]⁺ ClO₄^- (III). FeCl₃ and (C₆F₅)₂ TlBr displace I from II to give (η-C₅H₅)₂Nb(μ-Cl)(μ-X)MY₂, where MFe, XYCl(IV) and MTl, XBr, YC₆F₅ (V). Reactions of I with metal halides MXY₂ give (η-C₅H₅)₂ClNb(μ-Cl)MXY₂ where XYCl, MAl (VI), Fe (VII), Tl (VIII) and XBr, YC₆F₅, MTl (IX). The chemical behaviour of all these compounds is described.     

Reaction of tellurium(iv) with dithizone

With an excess of dithizone over tellurium, the extraction of Te(IV) from 1 M perchloric acid solutions into a carbon tetrachloride solution (o) of dithixone follows the relation

When the acidity is varied, again with a sufficiently large excess of dithissone, the following relation seems to be approached;

(μ=1.0).     

Synthesis of titanium(iv) 3,6-di-tert-butylcatecholate complexes

Russian Chemical Bulletin - Two synthetic approaches were used for the synthesis of 3,6-di-tert-butylcatecholate derivatives of titanium(iv). These approaches are based on the exchange reaction...     

Nitrile-amidine coupling at Pt(IV) and Pt(II) centers. An easy entry to imidoylamidine complexes

Treatment of trans-[PtCl4(RCN)2] (R = Me, Et, Ph, NEt2) with 2 equiv of the amidine PhC(=NH)NHPh in a suspension of MeCN (R = Me), CHCl3 (R = Et, Ph), or in CHCl3 solution (R = NEt2) results in the formation of the imidoylamidine complexes trans-[PtCl4{NH=C(R)N=C(Ph)NHPh}2] (1-4) isolated in good yields (66-84%). The reaction of soluble complexes 3 and 4 with 2 equiv of Ph3P=CHCO2Me in CH2Cl2 (40 degrees C, 5 h) leads to dehydrochlorination resulting in a chelate ring closure to furnish the platinum(IV) chelates [PtCl2{NH=C(R)NC(Ph)=NPh}2] (R = Ph, 5; R = NEt2, 6), accordingly, and the phosphonium salt [Ph3PCH2CO2Me]Cl. Treatment of 5 with 3 equiv of Ph3P=CHCO2Me at 50 degrees C for 5 d resulted in only a 30% conversion to the corresponding Pt(II) complex [Pt{NH=C(NEt2)NC(Ph)=NPh}2] (15). The reduction can be achieved within several minutes, when Ph2PCH2CH2PPh2 in CDCl3 is used. When the platinum(II) complex trans-[PtCl2(RCN)2] is reacted with 2 equiv of the amidine, the imidoylamidinato complexes [PtCl(RCN){NH=C(R)NC(Ph)=NHPh}] (8-11) and [PhC(=NH)NHPh] x HCl (7) are formed. The reaction of trans-[PtCl2(RCN)2] with 4 equiv of the amidine under a prolonged reaction time or treatment of [PtCl(RCN){NH=C(R)NC(Ph)=NHPh}] (8-11) with 2 more equiv of the amidine yields the complex bearing two chelate rings [Pt{NH=C(R)NC(Ph)=NHPh}2] (12-15). The treatment of cis-[PtCl2(RCN)2] (R = Me, Et) with the amidine gives ca. 50-60% yield of [PtCl2{NH=C(R)NHC(Ph)=NHPh}] (16 and 17). All of the platinum compounds were characterized by elemental analyses; FAB mass spectrometry; IR spectroscopy; 1H, 13C{1H}, and 195Pt NMR spectroscopies, and four of them (4, 6, 8, and 15) were also characterized by X-ray crystallography. The coupling of the Pt-bound nitriles and the amidine is metal-mediated insofar as RCN and PhC(=NH)NHPh do not react in the absence of the metal centers in conditions more drastic than those of the observed reactions. The nitrile-amidine coupling reported in this work constitutes a route to the synthesis of imidoylamidine complexes, some of them exhibiting luminescent properties.     

Sb在Pt(100),Pt(110),Pt(111)及Pt(320)上不可逆吸附的电化学特性

研究了Sb在Pt(1 0 0 ) ,Pt(1 1 0 ) ,Pt(1 1 1 )和Pt(32 0 )单晶面上不可逆吸附的电化学特性 .发现当扫描电位的上限Eu≤ 0 .45V时 ,Sbad可以稳定地吸附在Pt(1 0 0 ) ,Pt(1 1 0 )和Pt(1 1 1 )表面 ,而Sbad在Pt(32 0 )表面稳定的电位较低 ,为Eu≤ 0 .40V .从饱和吸附Sb的铂单晶电极出发 ,通过改变电位扫描上限Eu 和电位扫描圈数可以获得不同Sb覆盖度 (θSb)的电极 .根据Sb和H在铂单晶电极表面共吸附的定量数据 ,对Sb在不同铂单晶面上饱和吸附的模型进行了初步探讨 .     

Redistribution reactions in the ion source of a mass spectrometer of complexes of titanium (iv), tin (iv) and germanium (iv) with 8-quinolinolato and halo or ethoxy ligands

The relative intensities of peaks in the mass spectra of the compounds MX_4?nox_n (oxH = 8-quinolinol; n = 2; M = Ti; X = F, Cl, Br or OEt; M = Sn; X = F, Cl, Br or I; M = Ge; X = Cl or Br; n = 1; M = Ti; X = OEt) depend on the insertion temperature and the residence time of the sample in the mass spectrometer. In most cases ions which cannot arise by fragmentation of the respective molecular ions are observed. These ions arise from the ionisation and fragmentation of species which are due to redistribution reactions in the mass spectrometer. The fragmentation pattern of the compounds MX₂ox₂ (X = halogen), mainly involving loss of ligand radicals, is related to the common oxidation states of the metals and reflects the metal-halogen bond strength. The molecular ions of the compounds Ti(OEt)_4?nox_n (n = 0, 1 or 2) fragment by loss of intact ligand radicals.     

Complexes of Pt(II) and Pt(IV) with disubstituted purines

Mixed-ligand complexes of Pt(II) and Pt(IV) with 2,6-diaminopurine and 6-thioguanine were synthesized and characterised. The complexes were prepared in acidic and basic media. The binding of the ligands to the metal ion varies according to the pH of the medium. Thus, in the complexes of 6-thioguanine, the ligand acts as a monodentate ligand coordinating through the neutral C₆-SH group in the acidic medium and in the basic medium as a bidentate ligand binding to the metal ion through C₆S^? and N₇, forming a five-membered chelate ring. In an acidic medium 2,6-diaminopurine forms mononuclear complexes with Pt(II) and Pt(IV) binding through N₇. In a basic medium binuclear hydroxobridged complexes are formed with Pt(IV) and the ligand is monodentate, coordinating through N₇.     

Catalytic determination of ultratrace amounts of selenium(iv)

A new sensitive catalytic method for determining selenium(IV) is proposed. Selenium catalyzes the oxidation of p-hydrazinobenzenesulfonic acid to p-diazobenzenediazonium ion, which then is converted to a yellow azo dye by coupling with m-phenylenediamine. As little as 10^-7 M selenium(IV) can be determined easily; the effective molar absorptivity is 1.2 · 10⁶ for selenium(IV). If the azo dye is extracted into an organic solvent, the effective molar absorptivity can be increased further to 2.4· 10⁶ for selenium(IV).     

Thermometric titration of uranium(iv)with potassium dichromate

A thermometric method is presented for the redox titration of uranium(IV) with dichromate. The investigation was made primarily to determine the applicability of the thermometric method to redox titrations in solutions that contain ions deleterious to electrodes used in electrometric methods. A relative standard error of ±1% attainable in the titration of quantities of uranium(lV) of the order of 5 mg. Less than l 5 min is required to complete a titration. Fluoride ion can be tolerated in the solution provided that sufficient aluminium(111) is added to complex all the fluoride.     

Electrocatalytic oxidation of ammonia on Pt(111) and Pt(100) surfaces

The electrocatalytic oxidation of ammonia on Pt(111) and Pt(100) has been studied using voltammetry, chronoamperometry, and in situ infrared spectroscopy. The oxidative adsorption of ammonia results in the formation of NH(x) (x = 0-2) adsorbates. On Pt(111), ammonia oxidation occurs in the double-layer region and results in the formation of NH and, possibly, N adsorbates. The experimental current transients show a hyperbolic decay (t(-1)), which indicates strong lateral (repulsive) interactions between the (reacting) species. On Pt(100), the NH(2) adsorbed species is the stable intermediate of ammonia oxidation. Stabilization of the NH and NH(2) fragments on Pt(111) and Pt(100), respectively, is in an interesting agreement with recent theoretical predictions. The Pt(111) surface shows extremely low activity in ammonia oxidation to dinitrogen, thus indicating that neither NH nor N (strongly) adsorbed species are active in dinitrogen production. Neither nitrous oxide nor nitric oxide is the product of ammonia oxidation on Pt(111) at potentials up to 0.9 V, as deduced from the in situ infrared spectroscopy measurements. The Pt(100) surface is highly active in dinitrogen production. This process is characterized by a Tafel slope of 30 mV decade(-1), which is explained by a rate-determining dimerization of NH(2) fragments followed by a fast decay of the resulting surface-bound hydrazine to dinitrogen. Therefore, the high activity of the Pt(100) surface for ammonia oxidation to dinitrogen is likely to be related to its ability to stabilize the NH(2) adsorbate.