PubMed Health⌕ Search

Biomedical subjects

Volker Gramlich

Publications and source records attributed to Volker Gramlich.

At least 19 recordsLinked to original sources
PubMed2007

Double-stranded cycles: toward C84's belt region.

The reactivity of the double-stranded hydrocarbon cycle with two ether bridges (1) toward iodotrimethylsilane (TMSI) was investigated in some detail. The carbon skeleton of cycle 1 resembles the belt region of a C84 fullerene which makes it a potential precursor to the long sought after fully aromatic derivative. Upon exposure to TMSI, cycle 1 undergoes a cascade of reactions which involve different states of iodination/reduction which ultimately lead to the hydrogenated cycle 5a, whose structure was proven by single-crystal X-ray analysis. A deeper insight into mechanistic aspects of this sequence of conversions was gained by performing the reaction under dry and wet conditions, whereby the latter involved both normal and deuterated water. With the help of detailed NMR correlation studies and DFT computations, all important aspects were clarified including an unexpected selective H/D exchange at the naphthalenic moieties.

Crystallography, X-Ray↗
PubMed2006

Designer dendrimers: branched oligosulfonimides with controllable molecular architectures.

The synthesis of "designer" dendrimers and dendrons with sulfonimide units at every branching point is reported. The synthesis is based on a series of (regio)selective functionalization reactions of amines and sulfonamides allowing precise control of the dendrimers' shape, the number of branches in each generation, and their peripheral decoration with functional groups. In principle, structurally different branches can be incorporated at any position within the dendrimer structure at will. Structurally perfect symmetrical and two-faced "Janus"-type dendrimers, as well as dendrimers and dendrons with intended interstices were synthesized on a preparative scale and fully characterized. Oligosulfonimide dendrons of various generations bearing an aryl bromide functional group at their focal points were attached to a p-phenylene core with the aid of Suzuki cross-coupling reactions resulting in dendrimers with photoactive terphenyl cores. The structure and the high purity of all dendritic sulfonimides were confirmed by means of (1)H and (13)C NMR, electrospray ionization mass spectrometry (ESI-MS), and elemental analysis. The utility of MALDI-TOF mass spectrometry for the analytical characterization of these dendrimers was evaluated in comparison to electrospray ionization. Two model branched oligosulfonimides were characterized in the solid state by single-crystal X-ray analysis. Reaction selectivities and conformation of sulfonimide branching points were rationalized by DFT calculations.

Journal Article↗
PubMed2006

Alternating diacetylene copolymer utilizing perfluorophenyl-phenyl interactions.

The symmetric diacetylenes, 2,4-hexadiynylene dibenzoate 4 and 2,4-hexadiynylene bis(pentafluorobenzoate) 5, as well as the unsymmetric 6-(pentafluorobenzoyloxy)hexa-2,4-diynyl benzoate 6 were prepared and investigated with respect to their reactivity toward topochemical polymerization in the crystalline state. The 1:1 cocrystal 4.5 was successfully polymerized to the corresponding poly(diacetylene) copolymer 7, as evidenced by solid-state (13)C NMR and Raman spectroscopy, as well as single-crystal structure analysis of the monomer-polymer cocrystal. Thus, perfluorophenyl-phenyl interactions were utilized as complementary supramolecular synthons in the cocrystallization of two different diacetylene monomers and their unprecedented conversion into a strictly alternating diacetylene copolymer.

Journal Article↗
PubMed2005

Coordination chemistry of phosphanyl amino acids: solid state and solution structures of neutral and cationic rhodium complexes.

Copper phosphide or arsenide complexes, [Cu(EPh(2))(neo)] (E = P, As, neo = 2,9-dimethyl-1,10-phenanthroline; trivial name: neocuprine) react selectively with the N-protected brominated serine derivatives, 2-(S)-(alkoxycarbonylamino)-3-bromomethylpropionates ((ROCO)SerBr, : R = PhCH(2), : tBu, : Me) to give the corresponding phosphanylated or arsanylated amino acids, (ROCO)SerPhos (: Phos = PPh(2)) and (Z)SerArs (Ars = AsPh(2), Z = PhCH(2)OCO). The dipeptide (Z)AlaSerPhos was likewise prepared. The phosphanes , and the arsane reacted cleanly with [Rh(2)(micro-Cl)(2)(cod)(2)] to give the rhodium(I) complexes [RhCl(cod)((Z)SerPhos)] , [RhCl(cod)((Boc)SerPhos)] (Boc = tBuOCO), [RhCl(cod)((Z)AlaSerPhos)] , and [RhCl(cod)((Z)SerArs)] which were characterized by X-ray diffraction studies. A common structural feature is an intramolecular (N)H[dot dot dot]Cl(Rh)-hydrogen bridge which according to NMR investigations remains intact in solution. The abstraction of chloride from the coordination sphere of Rh(I) in or has a profound structural impact. While in and , the ligands bind in a monodentate fashion, via the phosphorus atom only, they serve as bidentate ligands via the phosphorus centre and the peptidic C=O group in [Rh(cod)(kappa(2)-(Z)SerPhos)]PF(6) and [Rh(cod)(kappa(2)-(Z)AlaSerPhos)]PF(6). This causes also the amino acid residue structures to change from alpha-helix type in and to a beta-sheet type in both. Addition of chloride to and fully re-establishes the structures of both. The complexes [RhCl(cod)((Z)SerPhos)] and [RhCl(cod)((Boc)SerPhos)] show good activities in homogeneously catalyzed hydrogenations of olefins while the dipeptide complex is less active. Phosphane addition to greatly diminishes the catalytic activity. The cationic complex [Rh(cod)(kappa(2)-(Z)AlaSerPhos)]PF(6) shows low activity which, however, is greatly increased by addition of one equivalent of phosphane.

Amino Acids↗
PubMed2005

Syntheses and characterization of dicarbonyl-nitrosyl complexes of technetium(I) and rhenium(I) in aqueous media: spectroscopic, structural, and DFT analyses.

This work describes new synthetic routes to produce mixed carbonyl-nitrosyl complexes of technetium(I) and rhenium(I) in aqueous media. NaNO2, NOHSO4, and NO2(g) have been used to produce in situ nitrous acid as the primary source of NO+. Starting from the organometallic precursor fac-[MX3(CO)3]+, 1 (M = 99Tc, Re; X = Cl, Br), the formation of mixed dicarbonyl-mononitrosyl complexes was observed in aqueous hydrochloric and hydrobromic acid. Time-dependent analyses of the reactions by means of HATR-IR and 99Tc NMR spectroscopy in solution revealed the almost quantitative substitution of one CO ligand by NO+ and, thus, the formation of complexes with facial arrangement of the three pi-acceptor ligands. In the case of technetium, the monomeric complex (NEt4)[TcCl3(CO)2NO] (3a) and the dimeric, chloride-bridged, neutral complex [TcCl(mu-Cl)(CO)2NO]2 (4a) were produced. In the case of rhenium, the monomeric species (NEt4)[ReBr2X(CO)2NO] (X = Br (3b), NO3 (5)) was solely isolated. The X-ray structure of complexes 4a and 5 are discussed. The crystallographic analyses revealed the coordination of the NO+ group trans to the terminal chloride (4a) or the bromide (5), respectively. Crystal data: complex 4a (C4Cl4N2O(6)Tc2), monoclinic, Cc, a = 18.82(3) A, b = 6.103(6) A, c = 12.15(2) A, alpha = 90 degrees , beta = 105.8(2) degrees , gamma = 90 degrees , V = 1343(3) A(3), Z = 4; complex 5 (C10H20N3O(6)Br2Re), orthorhombic, P2(1)2(1)2(1), a = 10.2054(5) A, b = 12.5317(7) A, c = 13.9781(7) A, V = 1787.67(16) A(3), Z = 4. The isolated complexes and their potential facial isomers have been further investigated by density functional theory (DFT) calculations. The energy differences of the isomers are relatively small; however, the calculated energies are consistent with the formation of the observed and isolated compounds. The calculated bond lengths and angles of complex 5 are in good agreement with the data determined by X-ray diffraction. Experiments on the no-carrier-added level starting from fac-[99mTc(H2O)3(CO)3]+ revealed the formation of the complex fac-[99mTcCl(H2O)2(CO)2NO]+ in reasonable good yields. This aqueous-based, synthetic approach will enable the future evaluation of this novel, low-valent metal precursor for potential use in radiopharmacy.

Algorithms↗
PubMed2004

Synthesis, structure, and solution dynamics of UO22+-hydroxy ketone compounds [UO2(ma)2(H2O)] and [UO2(dpp)(Hdpp)2(H2O)]ClO4 [ma = 3-hydroxy-2-methyl-4-pyrone, Hdpp = 3-hydroxy-1,2-dimethyl-4(1H)-pyridone].

Reaction of [UO(2)(NO(3))(2)] with the hydroxy ketones 3-hydroxy-2-methyl-4-pyrone (Hma) and 3-hydroxy-1,2-dimethyl-4(1H)-pyridone (Hdpp) in aqueous acidic solutions (pH approximately 3) yields the compounds [UO(2)(ma)(2)(H(2)O)].H(2)O (1.H(2)O) and [UO(2)(dpp)(Hdpp)(2)(H(2)O)]ClO(4) (2), respectively. X-ray diffraction shows that the geometry around the metal ion in both complexes is pentagonal bipyramid. Uranium ion in the crystal structure of 1 were found to be ligated with two chelate ma(-) groups and one unidentate H(2)O molecule (C coordination mode) at the equatorial plane, while in 2 with two single-bonded Hdpp there were one chelate dpp(-) and one H(2)O molecule (P coordination mode). Crystal data (Mo Kalpha; 293(2) K) are as follows: (1) monoclinic space group C2/c, a = 14.561(7) A, b = 14.871(9) A, c = 7.250(4) A, beta = 95.40(4) degrees , Z = 4; (2) monoclinic space group P2(1)/c, a = 19.080(2) A, b = 9.834(1) A, c = 15.156(2) A, beta = 104.62(1) degrees , Z = 4. (1)H NMR measurements indicate that complex 2 retains its structure in CD(3)CN solution; however, in DMSO-d(6) both complexes adopt the C structure. Line-shape analysis for the (1)H NMR peaks of 2 at various temperatures shows a fast intramolecular exchange process between the chelate dpp(-) and one of the single bonded Hdpp ligands and one slower exchange between all three ligands. The activation parameters and the decrease of the exchange rate by replacing unidentate ligand with DMSO indicate the dissociation of the unidentate ligand as the rate-determining step for the former exchange. Density functional calculations (DFT) support this mechanism and give a quantitative interpretation of the electronic structure of the two ligands and the geometries adopted by the complexes.

Journal Article↗
PubMed2004

New Rebek imide-type receptors for adenine featuring acetylene-linked pi-stacking platforms.

Rebek imide-type molecular clefts with pi-stacking platforms attached to the imide scaffold by an acetylene linker have been prepared by Sonogashira cross-coupling. In the solid state, a novel dimerisation mode for this class of imide receptors was found by crystal structure analysis, whereas efficient 1 : 1 complexation with 9-ethyladenine was observed in CDCl3 solution.

Acetylene↗
PubMed2004

X-ray diffraction and NMR studies on a series of Binap-based Ru(II) hydroxyphosphine pi-arene complexes.

A series of new Ru(II) arene phosphine complexes derived from Binap have been prepared. Specifically, reaction of Ru(OAc)(2)(Binap) with 3,5-(CF(3))(2)C(6)H(3))(4)B (BArF).H(OEt(2))(2), is shown to afford new mono- and dinuclear Ru(II) hydroxyphosphine pi-arene complexes via a series of P-C bond cleavage reactions. The dinuclear Ru(II) pi-arene complexes contain bridging P(O)(OH)(2) ligands. Crystal structures of five new complexes are reported and suggest an eta(4)-arene rather than an eta(6)-arene coordination mode. However, in solution, their (13)C NMR data are more consistent with a strongly distorted eta(6)-coordination mode. PGSE (1)H and (19)F diffusion measurements on the dinuclear complexes suggest hydrogen bonding of the triflate anion and ion-pairing of the BArF(-) anion.

Journal Article↗
PubMed2004

H-Bonded complexes of adenine with Rebek imide receptors are stabilised by cation-pi interactions and destabilised by stacking with perfluoroaromatics.

A series of Rebek imide receptors with naphthalene or heteroaromatic platforms attached by amide or ester linkers have been prepared from the corresponding acyl chloride or anhydride; the X-ray crystal structure of the receptor-derived anhydride reveals a supramolecular H-bonded helix formation in the crystal; the complexes of adenine bound to the receptors by Hoogsteen H-bonding are found to be stabilised by stacking with a methylquinolinium ion, but destabilised by stacking with a perfluorinated naphthalene.

Adenine↗
PubMed2003

Synthesis and crystal structure of IM-6, a new open framework cobalt-gallium phosphate with ten- and twelve-membered pore openings.

A new three-dimensional microporous cobalt-gallium phosphate, named IM-6, has been synthesized under solvothermal conditions with an N-substituted piperazine as organic template. The structure was solved by single-crystal X-ray diffraction (triclinic, P(-)1, a=9.848(20), b=12.470(32), c=12.603(28)A, alpha=63.47(16) degrees, beta=74.56(16) degrees, gamma=76.03(17) degrees). IM-6 exhibits a new framework topology. The inorganic framework is built up of MO(4) (M=Co, Ga) and PO(4) tetrahedra. It displays a two-dimensional interconnected channel system running along the [0(-)11] and [100] directions and delimited by ten- and twelve-membered ring openings, respectively.

Journal Article↗
PubMed2003

Bisubstrate inhibitors for the enzyme catechol-O-methyltransferase (COMT): influence of inhibitor preorganisation and linker length between the two substrate moieties on binding affinity.

Inhibition of the enzyme catechol-O-methyltransferase (COMT) is an important approach in the treatment of Parkinson's disease. A series of new potent bisubstrate inhibitors for COMT, resulting from X-ray structure-based design and featuring adenosine and catechol moieties have been synthesised. Biological results show a large dependence of binding affinity on inhibitor preorganisation and the length of the linker between nucleoside and catechol moieties. The most potent bisubstrate inhibitor for COMT has an IC50 value of 9 nM. It exhibits competitive kinetics for the SAM and mixed inhibition kinetics for the catechol binding site. Its bisubstrate binding mode was confirmed by X-ray structure analysis of the ternary complex formed by the inhibitor, COMT and a Mg2+ ion.

Binding Sites↗
PubMed2002

p-Hydroquinone-metal compounds: synthesis and crystal structure of two novel VV-p-hydroquinonate and VIV-p-semiquinonate species.

Reaction of the p-hydroquinone derivative H2Na4bicah.4H2O with either VIVOSO(4).3H2O and NaVVO3 in equivalent quantities or with NaVVo3 yields the tetranuclear VIVO2+ macrocycle-semiquinonate compound Na6[(VIVO)4-(mu2-O)2[mu2-bicas.(-5)-N,O,O,O]2].Na2SO(4).20H2O (1.Na2SO(4).20H2O) and the dinuclear cis-VVO2(+)-hydroquinone species Na4[(VVO2)2[mu2-bicah(-6)-N,O,O,O]].11H2O (2.11H2O) respectively. Compounds 1.Na2SO(4).20H2O and 2.11H2O were characterized by X-ray structure analysis and ab initio calculations.

Journal Article↗
PubMed2002

Hydrothermal synthesis and characterization of the new layered fluorogallophosphate mu-23.

Mu-23, [(C(6)H(15)N(2))(C(6)H(16)N(2))Ga(5)F(6)(H(2)O)(2)(PO(4))(4)] x 4 H(2)O, the first layered fluorinated gallophosphate with a Ga/P molar ratio of 5:4, was obtained in the presence of fluoride ions with 1,4-dimethylpiperazine as an organic template. It crystallizes in the triclinic space group P1 (no. 2) with unit cell parameters a=8.735(11), b=8.864(5), c=12.636(10) A, alpha=98.36(5), beta=100.18(8), gamma=115.84(7) degrees. The layers consist of GaO(2)F(3)(H(2)O), GaO(4)F(2) octahedra, and GaO(4) and PO(4) tetrahedra; these moieties share their oxygen and some of their fluorine atoms. The connectivity scheme of these different polyhedra leads to the formation of eight-membered rings.

Journal Article↗
PubMed2002

Rebek imides and their adenine complexes: preferences for Hoogsteen binding in the solid state and in solution.

Rebek imides (3), formed from Kemp's triacid, were developed in the mid-1980's as model receptors for adenine derivatives. We report here the first account of their hydrogen-bonding preferences upon binding 9-ethyladenine (1a) in the solid state. Structural analysis begins with simple imides 3a-e that form discrete dimers, while bis-imide 4 forms ribbon-like structures in the crystalline phase. The hydrogen-bonding interface within each of the representative assemblies features short intermolecular N(3)imide...O(8*)imide* distances (ca. 2.95 A), indicative of two-point hydrogen bonding. Imides 3f-h could be co-crystallized with 1a; single-crystal X-ray analysis of the resulting complexes reveals hydrogen-bonding geometries nearly identical to those observed in nucleobase complexes of adenine and pyrimidine derivatives. Imides 3f and 3g form 2:1 ternary assemblies with 1a; the complex of the former, (3f)2 x 1a, displays both Watson-Crick- and Hoogsteen-type hydrogen bonding, whereas the complex of the latter, (3g)2 x 1a, shows the Hoogsteen motif and imide hydrogen bonding to N(3) of the purine base (N(3)adenine...N(3'')imide = 3.07(1) A). Imide 3h forms a 1:1 complex with 1a (3h x 1a x CHCl3) and displays Hoogsteen binding exclusively. All of the 3 x 1a assemblies show C(adenine)...O(imide) distances (3.38-3.75 A) that are consistent with C-H...O hydrogen bonding. Base-pairing preferences for the Rebek imides are further explored in solution by 1H NMR one-dimensional NOE experiments and by computational means; in all cases the Hoogsteen motif is modestly favored relative to its Watson-Crick counterpart.

Adenine↗
PubMed2001

X-ray Crystal Structure of a Bisubstrate Inhibitor Bound to the Enzyme Catechol-O-methyltransferase: A Dramatic Effect of Inhibitor Preorganization on Binding Affinity We thank F. Hoffmann-La Roche for generous support of this work. We are grateful to P. Malherbe for the cloning of COMT, P. Caspers for the expression of COMT, A. Cesura for enzyme purification, B. Wipf for fermentation, and H. W. Lahm for sequencing.

Explore the source record for details and available documents.

Journal Article↗