Colorless Needles Research Articles

Preparation and Structure of Rhenium Fluoride Trioxide ReO3F, and the Polymorphism of Rhenium Trifluoride Dioxide, ReO2F3

AbstractThe methods of preparation of ReO3F are revised. ReO3F is an amorphous yellow solid that crystallizes into colorless needles after prolonged heating. Its structure is that of a fluorine and oxygen bridged chain with hexa coordinated rhenium atoms (a = 670.9(2), b = 596.6(2), c = 1030.6(4) pm, β = 90.057(7)°, space group P2/c. In presence of donor solvents ReO3F·2L (L = (C2H5)2O, (CH3)2O, THF) are formed. ReO2F3, if crystallized from HF, exists in two crystalline forms, both are fluorine bridged chain polymers. (ReO2F3‐I: a = 1539.7(3), b = 999.6(3), c = 924.4(2) pm, β = 95.25(1)°, space group P21/c; ReO2F3‐II: a = 544.9(1), b = 494.2(1), c = 1253.7(2) pm, β = 98.543(7)°, space group P21/c. ReO2F3 crystallizes from CFCl3 or SO2FCl as fluorine bridged cyclic trimer (a = 881.4(4), c = 822.1(6) pm, γ = 120°, space group P63/m, or fluorine bridged cyclic tetramer (a = 1107.8(2), b = 999.4(2), c = 1347.9(3) pm, space group Cmca).

Ligand Exchange Reaction Between an Alkylzinc Primary Amide and a Dialkylmagnesium Compound: Crystal Structures of [(thf)MeMg-μ-N(H)SiiPr3]2 and (tmeda)Mg[N(H)SiiPr3]2

The reaction of alkylzinc triisopropylsilylamide with dialkylmagnesium leads to a ligand exchange. Besides the starting materials, heteroleptic alkylmagnesium triisopropylsilylamide and homoleptic magnesium bis(triisopropylsilylamide) are detected by NMR spectroscopy. After the addition of 1,2-bis(dimethylamino)ethane (TMEDA) to the reaction mixture, (tmeda)Mg[N(H)SiiPr3]2 (1) precipitates as colorless cuboids (C24H60MgN4Si2, a = 2269.6(2), b = 1029.58(5), c = 1593.2(1) pm, beta = 120.826(8) degrees , monoclinic, C2/c, Z = 4). The amide nitrogen atoms are coordinated planarily with strongly widened Mg-N-Si bond angles of 139.2(1) degrees . The metalation of triisopropylsilylamine with dimethylmagnesium in THF yields quantitatively heteroleptic [(thf)MeMg-N(H)SiiPr3]2 (2) which crystallizes as colorless needles (C28H66Mg2N2O2Si2, a = 1982.4(2), b = 2034.1(1), c = 907.22(6) pm, beta = 95.021(9), monoclinic, P2(1)/n, Z = 4). Because of the bridging position of the triisopropylsilylamide anion, the tetracoordinate nitrogen atoms show rather long Mg-N bond lengths of 210.7 pm (average value).

Intermolecular Interactions in Polymorphs of Trinuclear Gold(I) Complexes: Insight into the Solvoluminescence of AuI3(MeNCOMe)3

The trinuclear complex, Au(I)3(MeN=COMe)3, which displays a number of remarkable properties including solvoluminescence, has been found to crystallize as three polymorphs. The new triclinic and monoclinic polymorphs crystallized as colorless blocks, whereas the original hexagonal polymorph formed colorless needles. These polymorphs differ in the manner in which the nearly planar molecules pack and in the nature of the aurophilic interactions between them. Each of the three polymorphs of Au(I)3(MeN=COMe)3 shows a distinctive emission spectrum, but only the original hexagonal polymorph shows the low-energy emission that is responsible for its solvoluminescence. Colorless Au(I)3(n-PentN=COMe)3 crystallized from diethyl ether as needles of an orthorhombic polymorph and blocks of a triclinic polymorph. These polymorphs differ in the orientation of the n-Pent substituents, in the orientation of the trimers with respect to one another, and in the nature of the aurophilic interactions between the molecules. Only the triclinic polymorph of Au(I)3(n-PentN=COMe)3 shows luminescence at room temperature, but it is not solvoluminescent. Colorless Au(I)3(i-PrN=COMe)3 has also been prepared and crystallographically characterized. The isopropyl groups protrude out of the plane of the nine-membered ring and prevent self-association. The closest Au...Au contact between molecules is 6.417 A. Crystalline Au(I)3(i-PrN=COMe)3 is not luminescent at room temperature.

Crystal and molecular structure of bis(acetylacetone)ethylenediimine: intramolecular ionic hydrogen bonding in solid state

The acid form of bis(acetylacetone)ethylenedimine, H 2acacen, was isolated as colorless needle like crystals from condensation reaction of ethylenediamine with acetylacetone at room temperature and fully characterized by MS, IR, 1H- and 13C-NMR spectroscopy, and X-ray structure analysis. The spectroscopic and structural data show the existence of intramolecular N–H⋯O hydrogen bonding assisted by resonance in the solid protonated form of bis(acetylacetone)ethylenediimine. The intramolecular ionic hydrogen bonding is observed in the enolic form of bis(acetylacetone)ethylenediamine and described by ‘resonance assisted hydrogen bonding’ model which is essentially a synergetic mutual reinforcement of hydrogen bonding and π delocalization within the heterodienic system. In this intramolecular ionic hydrogen bonding, the proton is transferred from the enolic oxygen atom to the imine nitrogen atom leaving a negative charge on the oxygen and creating a positive charge on the nitrogen.

Molekül‐ und Kristallstruktur von Quecksilber(II)‐α‐Amino‐γ‐methylmercapto‐butyrat, Hg(Met)2

AbstractMolecular and Crystal Structure of Mercuric α‐Amino‐γ‐methyl‐mercapto‐butyrate, Hg(Met)2The mercuric salt of deprotonated methionine, Hg(Met)2, was obtained as colourless needles from aqueous solutions of methionine and HgCl2 or HgO, respectively. The crystal structure (monoclinic, P21, Z = 2, a = 984, 2(2), 507, 96(6), c = 1574, 2(3) pm, β = 93, 05(2)°; Rall = 0, 055) exhibits formula‐like molecules with strong Hg—N coordination at a distance of 216 pm; one oxygen atom adds to a chelate like N—Hg—O coordination. Stacking of these molecules adds two oxygen atoms of different methionate anions to an effective 2+2+2 „octahedral”︁ coordination around the mercuric ion. Thereby a layer structure parallel (001) is formed with the methyl‐mercapto function on top and bottom of these layers.

Synthesis and pH-variable ultracentrifugation molecular weight measurements of the dimeric, Ti–O–Ti bridged anhydride form of a novel di-TiIV-1,2-substituted α-Keggin polyoxotungstate. Molecular structure of the [(α-1,2-PW10Ti2O39)2]10−polyoxoanion

The preparation and characterization of a Keggin-type, novel di-TiIV-1,2-substituted polyoxotungstate are described. The dimeric, Ti–O–Ti bridged anhydride form of the di-TiIV-1,2-substituted α-Keggin polyoxotungstate, K10[α,α-P2W20Ti4O78]·12H2O 1, was unexpectedly found in the varied molar-ratio reactions of tri-lacunary precursor Na9[A-PW9O34]·19H2O with Ti(SO4)2 in aqueous solution. Although this compound was first found as a minor product in the preparation of the dimeric, tri-TiIV-1,2,3-substituted species, K10H2[α,α-P2W18Ti6O77]·17H2O 3, it was successfully prepared as a main product in this work and structurally characterized. Compound 1, as analytically pure, homogeneous colorless needle crystals, was obtained as a major product in 29.2% yield (2.7 g scale) from recrystallization under acidic conditions (at pH 2.2) of the 1 ∶ 2 molar-ratio reaction product. X-Ray structure analysis revealed that the molecular structure of 1 consisted of a dimeric anhydride formed by two Ti–O–Ti bonds linking two [α-1,2-PW10Ti2O40]7− Keggin units. Interestingly, ultracentrifugation molecular weight (MW) measurements of this compound in aqueous solution showed the pH-dependent interconversion between monomer [α-1,2-PW10Ti2O40]7−2 and dimer [α,α-P2W20Ti4O78]10−1; this compound was present as the monomer under less acidic conditions (pH 7.8), while it was in dimeric form under more acidic conditions (pH 1.0 and 2.2). Characterization of 1 was also accomplished by complete elemental analyses, TG/DTA, FTIR and solution (31P and 183W) NMR spectroscopy.

Synthesis and crystal structure of coinage metal(I) complexes with tetrazole (Htetz) and triphenylphosphine ligands, and their antimicrobial activities. A helical polymer of silver(I) complex [Ag(tetz)(PPh 3) 2] n and a monomeric gold(I) complex [Au(tetz)(PPh 3)

Two novel coinage metal(I)-triphenylphosphine complexes with a heterocyclic ligand, [Ag(tetz)(PPh 3) 2] n ( 1) and [Au(tetz)(PPh 3)] ( 2) (Htetz=tetrazole) were synthesized from a reaction in dichloromethane of the precursor complex [Ag(tetz)] n with PPh 3 and from a reaction in acetone of [AuCl(PPh 3)] with Htetz in the presence of aqueous NaOH, respectively, and isolated as colorless needle crystals for both 1 and 2. The crystal structures of 1 and 2 were determined by single-crystal X-ray diffraction. These d 10 complexes were also fully characterized by elemental analyses, TG/DTA and FT-IR in the solid-state, solution NMR ( 31P, 1H and 13C, as well as 109Ag for 1) spectroscopies and solution molecular weight measurements. Complex 1, is composed of a helical polymer, a 2 1 helix with a pitch 9.471 Å, formed by a bridged tetrazolate of an AgNP 2 core in the solid-state, but it was present as a monomer in solution. In contrast to 1, complex 2 consisted of a monomeric two-coordinate AuNP core without gold(I)–gold(I) interaction both in the solid-state and in solution. The molecular structures of 1 and 2 were compared with those of the corresponding triazole complexes, i.e. silver(I) complexes [Ag(1,2,3-triz)(PPh 3) 2] n ( 3) and [Ag(1,2,4-triz)(PPh 3) 2] n ( 4) both as helical polymers, a monomeric gold(I) complex [Au(1,2,3-triz)(PPh 3)] ( 5) and a dimeric gold(I) complex [Au(1,2,4-triz)(PPh 3)] 2 ( 6) through an intramolecular gold(I)–gold(I) bond; the structures of complexes 3– 6 being recently determined by X-ray crystallography. The antimicrobial activities of 1, its precursor [Ag(tetz)] n and 2 were compared and key factors affecting them discussed.

Gold(I) Compounds without Significant Aurophilic Intermolecular Interactions: Synthesis, Structure, and Electronic Properties of Ph(3)PAuC(O)NHMe and Au(3)(PhCH(2)N=COMe)(3): Comparative Monomeric and Trimeric Analogues of the Solvoluminescent Trimer, Au(3)(MeN=COMe)(3).

The preparations of Ph(3)PAuC(O)NHMe( )()and Au(3)(PhCH(2)N=COMe)(3) are reported. In solution Ph(3)PAuC(O)NHMe is unstable and readily deposits metallic gold. Colorless needles of the monomeric complex, Ph(3)PAuC(O)NHMe, crystallize in the monoclinic space group P2(1)/c, with a = 8.993(2) Å, b = 22.583(5) Å, c = 8.932(2) Å, beta = 98.22(2) degrees, at 123 K with Z = 4. Refinement of 2609 reflections and 114 parameters yielded R = 0.0455. A hydrogen-bonded intermolecular network links molecular units through N-H.O hydrogen bonds. No aurophilic interactions are present in this solid. The crystal structure of the cyclic trinuclear organogold compound, Au(3)(PhCH(2)N=COMe)(3), reveals that the complex does not associate into a trigonal prismatic array via intermolecular interactions of gold(I) centers as is seen in the triangular complex, Au(3)(MeN=COMe)(3). Rather, the complex packs in a stair-step fashion with eight discrete molecules in the asymmetric unit. Additionally, the solvent-stimulated emission (solvoluminescence) associated with Au(3)(MeN=COMe)(3) is not observed for this complex. Colorless needles of Au(3)(PhCH(2)N=COMe)(3) crystallize in the monoclinic space group P2(1), with a = 17.311(6) Å, b = 34.761(10) Å, c = 18.052(6) Å, beta = 94.73(2) degrees, at 133 K with Z = 16. Refinement of 16 250 reflections and 985 parameters yielded R = 0.0735.

Crystal structure of 6,6'-ditosyl-α-α'-trehalose-methanol-water (1/2/2), C52H68O30S4 ∙ 2CH3OH ∙ 2H2O

Article Crystal structure of 6,6'-ditosyl-α-α'-trehalose-methanol-water (1/2/2), C52H68O30S4 ∙ 2CH3OH ∙ 2H2O was published on June 1, 1999 in the journal Zeitschrift für Kristallographie - New Crystal Structures (volume 214, issue 2).

Synthesis and Self-Association of 4-Pyrimidinones

Crystallization of 4-pyrimidinone from CHCl3 produced colorless needles that were shown by X-ray crystallography to consist of cyclic hydrogen-bonded dimers 2 of the 4(3H)-pyrimidinone tautomer 1. Vapor-pressure osmometry established that a simple derivative, 5-(2-phenylethyl)-4(3H)-pyrimidinone (5), self-associates in solution with a value of Ka (220 ± 110 m-1 at 26 °C in CH2Cl2) close to that measured for 2-pyridinone under similar conditions. These observations suggest that 4-pyrimidinones and 2-pyridinones have similar modes and degrees of association and should be equally suitable for use as sticky functional groups that can be incorporated in complex molecules to make them associate in particular ways. This hypothesis was tested by synthesizing three dipyrimidinones (12, 16, and 21) designed to form strongly hydrogen-bonded dimers and by making a tetrapyrimidinone (26) designed to self-associate and to thereby generate a three-dimensional hydrogen-bonded network. In all cases, however, the compounds...

Cs(Toluol)3(FIn{N(SiMe3)2}3)], ein Fluoroindat mit gestreckter Cs–F–In-Achse

[Cs(toluene)3(FIn{N(SiMe3)2}3)], a Fluoroindate with Rectified Cs–F–In Axis The metalate [Cs(FIn{N(SiMe3)2}3)] has been prepared by the reaction of In[N(SiMe3)2]3 with CsF in THF: The title compound 1 can be obtained by recrystallization from toluene as colorless airsensitive needles. 1 has been characterized by NMR-, IR-, and MS-techniques as well as by an X-ray structure determination. The result of the structure analysis shows an prolated molecule with an almost linear Cs–F–In axis [174.7(1)°]. The Cs+ center is surrounded by the indate ion and three toluene molecules in a distorted tetrahedral fashion.

New multiply-bonded dimetal compounds containing bridging 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinato groups—I. The V 24+, Cr 24+ and Mo 24+ compounds and some salts of the protonated ligand

The reactions of Lihpp with vanadium(II) chloride, chromium(II) chloride and tetrakis(trifluoroacetato)dimolybdenum produce the dinuclear tetrabridged compounds V 2(hpp) 4, 1, Cr 2(hpp) 4, 2, and Mo 2(hpp) 4, 3. Compound 1 crystallizes as red blocks in the space group P 1 with unit cell dimensions, a = 8.489(2), b = 9.709(2), c = 9.835(2) A ̊ , α = 89.98(3), β = 73.04(3) and γ = 79.29(3)° . This compound contains the shortest known vanadium to vanadium bond, 1.932(1) Å. Compound 2 crystallizes as orange blocks in the space group P 1 with unit cell dimensions, a = 8.488(2), b = 9.687(2), c = 9.747(2) A ̊ , α = 90.89(3), β = 100.86(3) and γ = 106.42(3)° . This compound contains a ‘supershort’ chromium to chromium bond, 1.8517(7) Å. Compound 3 crystallizes as red blocks in the space group P 1 with unit cell dimensions, a = 8.455(2), b = 9.702(2), c = 10.094(2), α = 88.84(3), β = 72.01(3) and γ = 79.89(3)° and has a short molybdenum to molybdenum bond distance of 2.067(1). Both 2 and 3 have MM bonds distances shorter than most analogous compounds containing nitrogen donor atom bridges. The basicity of Hhpp is also evidenced by the formation of the cation [H 2hpp] + upon reaction with trifluoroacetic acid and acetic acid. [H 2hpp][O 2CCF 3], 4, crystallizes as colorless needles in the space group P2 1/ c with cell dimensions, a = 7.431(2), b = 13.243(2), c = 11.741(2), β = 96.50(3)°. [H 2hpp][O 2CCH 3], 5, crystallizes as colorless needles in the space group P2 1/ n with cell dimensions, a = 7.888(2), b = 11.182(2) c = 11.902(2), β = 91.91(3)°.

Synthesis and crystal structure of gold(I) complexes with triazole and triphenylphosphine ligands: monomeric complex [Au(1,2,3-L)(PPh3)] and dimeric complex [Au(1,2,4-L)(PPh3)]2 (HL = triazole) through an Au–Au bond in the solid state

Two novel gold(I)–triphenylphosphine complexes with nitrogen-containing heterocycles, [Au(1,2,3-L)(PPh3)] 1 and [Au(1,2,4-L)(PPh3)]2·xH2O (x = 0.5–1.0) 2 (HL = triazole) were synthesized from stoichiometric reactions of a precursor complex [AuCl(PPh3)] with HL in acetone in the presence of NaOH, and isolated as colorless needles and cubic crystals, respectively. The crystal structures of 1 and 2 were determined by single-crystal X-ray diffraction. Complexes 1 and 2 were also fully characterized by complete elemental analyses, TG/DTA and FT-IR in the solid state and by solution NMR (31P, 1H and 13C) spectroscopies and solution molecular-weight measurements. Complex 1 consisted of a monomeric 2-coordinate AuNP core both in the solid state and in solution, while, in contrast, 2 comprised a dimeric (AuNP)2 core through an Au–Au bond in the solid state, but a monomeric AuNP core in solution. Within the two gold(I) complexes composed of very closely related nitrogen-containing heterocycles and a common bulky PPh3 ligand, it was found that aggregation through the Au· · ·Au interaction in 2 was overruled in 1. The molecular structures of 1 and 2 were also compared with those of the corresponding silver(I) analogs, [Ag(1,2,3-L)(PPh3)2]n 3 and [Ag(1,2,4-L)(PPh3)2]n 4, the molecular structures of which have been recently determined as helical polymers in the solid state.

Synthese und Kristallstruktur von [Na3(H2O)6,5(EtOH)][PhSnS3] · 3 EtOH

Synthesis and Crystal Structure of [Na3(H2O)6,5(EtOH)][PhSnS3] · 3 EtOH Ph4Sn4S6 reacts with Na2S · 5 H2O in aqueous acetone to form Na3[PhSnS3]. Recrystallization of the crude product from ethanol leads to colourless needles of [Na3(H2O)6,5(EtOH)][PhSnS3] · 3 EtOH 1. The crystal structure of 1 was determined by X-ray diffraction. 1 consists of [PhSnS3]3– anions and sodium cations which are coordinated by water, ethanol and sulfur atoms of the [PhSnS3]3– anions. The [PhSnS3]3– anion contains a tin atom which is coordinated nearly tetrahedrally by a phenyl group and three sulfur atoms. The Sn–S bonds are 237,4(2)–238,4(2) pm.

Structure, absolute configuration, and conformation of the antimalarial compound, Artemisinin

The crystal and molecular structure of the antimalarial compound Artemisinin (formerly known as Qinghaosu), C15H22O5 has been determined by direct methods. Crystals are orthorhombic colorless needles, space group P212121, Z = 4. Dc = 1.299 g cm −3, with unit cell parameters a = 6.3543(9), b = 9.439(3), c= 24.066(4) A. The molecule incorporates a fused ring system containing a six-membered ring C which includes an oxygen bridge and a peroxy-bridge. The ring C has a distorted boat conformation and the C - O - O - C torsion angle is 47.8(2)°. Rings A and D have symmetrical chair and distorted chair conformations, repectively. Ring junctions A/B, A/D, and C/D are cis, junction B/D is trans. All inter-molecular contacts are van der Waals. The absolute configuration of Artemisinin was determined from the refined value of the Flack x parameter. [The atomic coordinates given in a previous structure analysis, “Crystal Structure and Absolute Configuration of Qinghaosu,” Qinghaosu Research Group, Institute of Biophysics, Academica Sinica, Scientia Sinica, Vol. XXIII No. 3, 380 (1980), do not display the molecule in its absolute configuration.]

Crystal structure of Zn 3.77V 1.54Mo 1.46O 12 containing ZnO 6 trigonal prisms

Single crystals of Zn 3.77V 1.54Mo 1.46O 12 were grown in a ZnO/V 2O 5/MoO 3 melt. The colorless needles were determined to be orthorhombic, space group P2 12 12 1 (No. 19), a=5.048 (4) A ̊ , b=10.400 (2) A ̊ , c=17.560 (7) A ̊ , V=921.9(6) A ̊ 3 , and Z=4. One type of zinc cation in the structure exhibits trigonal prismatic coordination, and relatively large distortions of the ZnO bond lengths in the trigonal prisms reduce the symmetry from Pnma (centrosymmetric) to P2 12 12 1 (acentric).

Triorganoantimony(V) diorganophosphinates. Crystal and molecular structure of (diphenylphosphinato)(hydroxo)trimethylantimony(V), exhibiting a polymeric chain supramolecular self-assembly through hydrogen bonds

The reaction between R 3SbCl 2 (R = Me, Ph) and R′ 2PO 2Na (R′ = Me, Ph) afforded R 3Sb(O 2PR′ 2) 2 derivatives, which were investigated by IR and multinuclear ( 1H, 13C, 31P) NMR spectroscopy. Attempts to grow crystals of Me 3Sb(O 2PPh 2) 2 led to colorless needles identified by X-ray diffractometry as Me 3Sb(OH) [O(O)PPh 2], produced by partial hydrolysis. Coordination around the central metal atom is distorted trigonal bipyramidal with carbon atoms of the SbMe 3 unit in equatorial positions and two oxygen atoms occupying the axial positions [OSbO 175.7(1)°]. The two antimony-oxygen distances are significantly different [SbO(H) 1.967(3) Å, SbO(P) 2.235(2) Å], as are the phosphorus-oxygen bond lengths in the basically monodentate diphenylphosphinato ligand [PO 1.528(3) Å, PO 1.490(3) Å]. The molecules are associated into polymeric chains through intermolecular hydrogen bonds between hydrogen of the hydroxo group and oxygen double bonded to phosphorus.

Lanthanide(III)chloride-tetrahydrofuran solvates: structural patterns within the series LnCl 3(THF) n, where n = 2,3,3.5 and 4: crystal and molecular structures of [PrCl( μ-Cl) 2(THF) 2] n, [Nd( μ-Cl) 3(H 2O)(THF)] n and GdCl 3(THF) 4

Praseodymium(III), neodymium(III) and gadolinium(III) chloride adducts with tetrahydrofuran (THF) have been prepared and structurally characterized by X-ray crystallography. Removal of water from the corresponding hexahydrate LnCl 3(H 2O) 6 using thionyl chloride in the presence of excess THF provides light-green cubic crystals of [PrCl 3(THF) 2] n ( 1), blue block crystals of [NdCl 3(H 2O)(THF)] n ( 2) and colourless needle crystals of GdCl 3(THF) 4 ( 3). In 1 each praseodymium atom is seven-coordinate and is linked to (two) adjacent metal centres by double (μ-Cl) 2 halogen bridging units, resulting in a polymeric chain structure. The metal geometry approximates to distorted pentagonal bipyramidal with PrCl bridge 2.852(6)–2.891(5), PrCl terminal 2.668(6), PrO THF 2.51(1) (axial), 2.53(2) Å (equatorial). In 2 the structure is a two-dimensional cross-linked polymer in which each neodymium atom is connected to (three) others via double (μ-Cl) 2 halogen bridge bonds. he coordination sphere of each metal centre comprises six chlorine atoms [NdCl bridge 2.816(3)–2.938(3) Å] and two oxygen atoms belonging to a THF molecule [NdO, 2.548(6) Å] and a water molecule [NdO, 2.490(7) Å], respectively. Hydrogen bonding interactions involving halogen atoms and coordinated water molecules from adjacent metal units (intermolecular) are observed, OH3·Cl 3.147–3.350 Å. In 3 the molecular structure is based on a seven-coordinate pentagonal bipyramidal metal geometry in which two chlorides occupy the axial positions with the other chloride and the four solvate (THF) molecules making up the equatorial plane. GdCl 2.60(2)–2.66(2), GdO 2.40(2)–2.52(3) Å. In addition, general comments concerning structural relationships within the series LnCl 3(THF) n , where n = 2, 3, 3.5 and 4, are discussed.

Piperastatin A, a new selective serine carboxypeptidase inhibitor produced by actinomycete. I. Taxonomy, production, isolation and biological activities.

Piperastatin A (structure, N-formyl-allo Ile-Thr-Leu-Val-Pip-Leu-Pip, Pip = hexahydropyridadine-3-carboxylic acid; molecular weight, 809), a new inhibitor of serine carboxypeptidase was discovered in the fermentation broth of Streptomyces lavendofoliae MJ908-WF13. It was purified by activated charcoal chromatography, YMC gel ODS-A chromatography and centrifugal partition chromatography (CPC) by monitoring its inhibitory activity against carboxypeptidase Y (CP-Y), and finally obtained as colourless needles. Piperastatin A is a competitive inhibitor of the enzyme with Ki = 52 +/- 6.2 nM. Piperastatin A is a highly specific inhibitor of the serine carboxypeptidases, CP-Y and platelet deamidase with little effect on related enzymes, has no antimicrobial activity and has low toxicity.

Controlled hydrolysis reactions of the Group 15 element–azamacrocyclic complexes MCl3L (M = As, Sb or Bi; L = 1,4,7-trimethyl-1,4,7-triazacyclononane). Formation and crystal structures of [AsCl2L][As2OCl5], [H2L]2[Sb2OCl6]Cl2, [HL]I and [H2L]2[Sb2Cl9]Cl·MeCN·H2O

Reactions of MCl3(M = As, Sb or Bi) and 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3[9]aneN3= L) gave the respective 1 : 1 adducts as white-yellow microcrystalline solids which were characterised by microanalytical and spectroscopic (IR and 1H NMR) data. Addition of water to AsCl3L under controlled stoichiometry in acetonitrile solution led to the formation of the white crystalline salt [AsCl2L][As2OCl5]1. A crystal structure determination revealed the cation as five-co-ordinate with ψ-octahedral metal geometry featuring a cis-AsCl2+ unit co-ordinated to the three donor nitrogen atoms of the ligand (fac) and a stereochemically active lone pair occupying the sixth site [As–Cl 2.462(7), 2.520(7) and As–N 2.18(2), 2.12(2), 2.10(2)A with the latter directly opposite to the lone pair]. The anion is made up of a dinuclear (µ-oxo) Cl2As–O–AsCl2 unit with a single Cl– anion linked symmetrically to the two separate arsenic atoms [mean As–Clterminal 2.216(8), As–Clbridge 2.795(8)A]. Controlled hydrolysis of SbCl3L in acetonitrile solution provided colourless needle crystals of [H2L]2[Sb2OCl6]Cl22 as identified by X-ray diffraction studies. The structure of the dication shows protonation of two of the three nitrogen atoms with strong intramolecular hydrogen bonding N–H ⋯ N 2.70–2.85 A involving the third amine centre. This is the first structural characterisation of the diprotonated form of L. The structure of the accompanying chlorooxoantimony(III) anion can be described as a single (µ-oxo) Cl2Sb–O–SbCl2 unit linked to two chloride ions via secondary Sb ⋯ Cl bonding involving the two metal centres [mean Sb–Clterminal 2.435(3), Sb–Clbridge 2.863(3)A]. Each of the antimony(III) centres is further associated with a unique chloride anion, Sb ⋯ Cl– 3.550(7)A, which, in turn, forms close contacts with the two protonated nitrogen atoms of the triazamacrocycle Cl ⋯ H–N 3.07, 3.02 A. Treatment of L and SiMe3I in acetonitrile solution provided yellow needle crystals of [HL]I 3. X-Ray (diffraction) crystallographic characterisation revealed a monoprotonated ring (L) in which the single proton is bonded directly to one nitrogen atom and to the remaining two via intramolecular hydrogen N–H ⋯ N 2.71 A. The product isolated from the reaction of L and SiCl4 in the presence of antimony(V) chloride as halide abstractor in acetonitrile was identified by a crystal structure determination as [H2L]2[Sb2Cl9]Cl·MeCN·H2O 4. The structure reveals two [H2L]⋯Cl moieties which have dimensions similar to those found for 2. Conformational analyses have been carried out on free L and its mono-, di- and tri-protonated forms and the results are consistent with the experimental conformations observed in this work and elsewhere.