Carbonyl–carbonyl and carbonyl–π interactions as directing motifs in the supramolecular structure of carbonyl(3‐oxopenta‐1,4‐diene‐1,5‐diyl)[tris(3,5‐dimethyl‐1H‐pyrazol‐1‐yl‐κN2)methane]iridium(III) trifluoromethanesulfonate

In the title complex salt, [Ir(C₅H₄O)(C₁₆H₂₂N₆)(CO)](CF₃O₃S), the Ir^III centre adopts a distorted octahedral geometry with a facial coordination of the tris(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)methane ligand. The C—C distances of the iridacycle are in agreement with its iridacyclohexa‐2,5‐dien‐4‐one nature, which presents a nonsymmetric boat‐like conformation with the C—Ir—C vertex more bent than the C—C(=O)—C vertex. The supramolecular architecture is mainly directed by CO...CO and CO...π and Csp³—H...O interactions, the arrangement of which depends on the anion.     

Necessary geometric and analytic conditions for general estimates in the $\bar{\partial}$-Neumann problem

We show the geometric and analytic consequences of a general estimate in the \(\bar{\partial}\)-Neumann problem: a “gain” in the estimate yields a bound in the “type” of the boundary, that is, in its order of contact with an analytic curve as well as in the rate of the Bergman metric. We also discuss the potential-theoretical consequence: a gain implies a lower bound for the Levi form of a bounded weight.     

Scalable synthesis of an integrin-binding peptide mimetic for biomedical applications

A scalable, solution-phase synthesis of the selectively protected non-peptide RGD (arginine-glycine-aspartic acid) mimetic 6 is described. This synthesis serves as an alternative to the previously described solid-phase synthesis of this compound, thereby making this important integrin-binding mimetic readily accessible. The free carboxylic acid of 6 was conjugated to a protected diamine, followed by global deprotection to give a derivative 27, suitable for immobilization onto amine-reactive surfaces. The RGD mimetic 28 demonstrated superior biological activity in comparison to a native linear RGD peptide and the semi-synthetic cyclic cRGDfK peptide in a cell attachment inhibition assay.     

Solid-state NMR investigation of sodium nucleotide complexes

Solid-state NMR has been used to analyze the chemical environments of sodium sites in powdered crystalline samples of sodium nucleotide complexes. Three of the studied complexes have been previously characterized structurally by crystallography (disodium deoxycytidine-5'-monophosphate heptahydrate, disodium deoxyuridine-5'-monophosphate pentahydrate and disodium adensoine-5'-triphosphate trihydrate). For these salts, the nuclear quadrupole coupling parameters measured by (23)Na multiple-quantum magic-angle-spinning NMR could be readily correlated with sodium ion coordination environments. Furthermore, two complexes that had not been previously characterized structurally, disodium uridine-3'-monophosphate and a disodium uridine-3'-monophosphate/disodium uridine-2'-monophosphate mix, were identified by solid-state NMR. A spectroscopic assignment of the four sites of an additional salt, disodium adensoine-5'-triphosphate trihydrate, is also presented and discussed within the context of creating a general approach for the spectroscopic assignment of multiple sites in sodium nucleotide complexes.     

Light-emitting iridium(III) and ruthenium(II) polypyridyl complexes containing quadruple hydrogen-bonding moieties

A novel compound containing both a 2,2'-bipyridine as well as a 2-ureido-4[1H]-ureidopyrimidinone supramolecular moiety (3) has been synthesised and fully characterized by 1H-NMR, MALDI-TOFMS, UV-vis and IR spectroscopy. Subsequent coordination to iridium and ruthenium polypyridyl precursors allowed the formation of iridium(III) and ruthenium(II) polypyridyl dimers (5 and 7) assembled via quadruple hydrogen-bonding as well as metal coordination interactions. The syntheses and complete characterization of these materials by means of two-dimensional NMR techniques (1H-1H COSY and 1H-1H DOSY) as well as IR and MALDI-TOFMS are described in detail. Comparative studies of the optical properties of the luminescent model complexes (5' and '7) and the dimer species (5 and 7) are also illustrated. In addition, good processability of the materials has been demonstrated by inkjet printing leading to thin films revealing their potential for light-emitting devices.     

Tris(1,2-dimethyl-3-hydroxy-4(1H)-pyridone)oxotantalum(v): a new water-soluble tantalum complex containing the [Ta=O]3+ core

The synthesis, the characterization and the X-ray crystal structure of a novel tantalum(v) complex tris(1,2-dimethyl-3-hydroxy-4(1H)-pyridone)oxotantalum(v) [TaO(C7H8O2N)3] 1 is reported. Starting from the tantalum pentaethoxide a two-step reaction was carried out observing rigorous anhydrous conditions in methanol in the first step, while the insertion of the oxo group was achieved using water as oxygen donor in the second step. X-Ray diffraction analysis of a crystal of 1 obtained upon evaporation of an aqueous solution shows a seven-coordinate monomeric complex containing the [Ta=O]3+ core in the triclinic space group P1, a = 7.282(3), b = 14.055(5), c = 16.987(6) A, alpha = 65.704(5), beta = 89.155(6), gamma = 75.270(6) degrees, V = 1525(1)A3, Z = 2. Spectroscopic investigation reveals that the complex is highly soluble and stable in water at physiological pH values; as a consequence the complex may represent a potential candidate for the development of new studies on aqueous tantalum(v) chemistry for radiopharmaceutical applications.     

Host-guest complexes between an aromatic molecular tweezer and symmetric and unsymmetric dendrimers with a 4,4'-bipyridinium core

We have investigated the spectroscopic and electrochemical behavior of symmetric and unsymmetric first-, second-, and third-generation dendrimers comprising an electron-acceptor 4,4'-bipyridinium core (viologen type) and electron-donor 1,3-dimethyleneoxybenzene (Fréchet-type) dendrons. The quite strong fluorescence of the symmetrically and unsymmetrically disubstituted 1,3-dimethyleneoxybenzene units of the dendrons is completely quenched as a result of donor-acceptor interactions that are also evidenced by a low-energy tail in the absorption spectrum. In dichloromethane solution, the 4,4'-bipyridinium cores of the investigated dendrimers are hosted by a molecular tweezer comprising a naphthalene and four benzene components bridged by four methylene units. Host-guest formation causes the quenching of the tweezer fluorescence. The association constants, as measured from fluorescence and (1)H NMR titration plots, (i) are of the order of 10(4) M(-1), (ii) decrease on increasing dendrimer generation, and (iii) are slightly larger for the unsymmetric than for the symmetric dendrimer of the same generation. The analysis of the complexation-induced shifts of the temperature-dependent (1)H NMR signals of the host and guest protons confirms that the bipyridinium core is positioned inside the tweezer cavity and allows the conclusions that (i) shuttling of the tweezer from one to the other pyridinium ring is fast (DeltaG < 10 kcal/mol), (ii) in the case of the unsymmetric dendrimers, the less substituted pyridinium ring is preferentially complexed in apolar solvents, and (iii) complexation of the 4,4'-bipyridinium core proceeds by clipping for the symmetric dendrimers and by threading in the case of unsymmetric ones. Host-guest formation causes a displacement of the first reduction wave of the 4,4'-bipyridinium unit toward more negative potential values, whereas the second reduction wave is unaffected. These results show that the host-guest complexes between the tweezer and the dendrimers are stabilized by electron donor-acceptor interactions and can be reversibly assembled/disassembled by electrochemical stimulation.     

Stereoselective synthesis of chiral 3-aryl-1-alkynes from bromoallenes and heterocuprates

The synthesis of chiral 3-aryl-1-alkynes 3 via cross-coupling of 3-alkyl- and 3,3-dialkyl-1-bromo-1,2-dienes 1 and arylbromocuprates (RCuBr)MgBr.LiBr 2 was examined. With phenylcopper reagents and its para-substituted derivatives, as well as with 2-naphthyl cuprates, the reaction gave compounds 3 with high regioselectivity and good yields on the chemically pure product. On the contrary, when ortho-substituted phenyl reagents and 1-naphthyl cuprates were used, the regioselectivity of the process was very dependent upon the steric requirements of the alkyl substituents on the bromoallenic substrate. When the steric bulk was increased, remarkable quantities of isomeric arylallenes 4 were also observed in the reaction mixtures. The high 1,3-anti stereoselectivity of the coupling process allowed us to obtain enantiomerically enriched 3-aryl-1-alkynes from optically active allenic substrates, thus indicating a simple pathway toward the synthesis of quaternary stereogenic centers characterized by an aryl group. A possible cross-coupling mechanism was also suggested to explain the regio- and stereochemical data. For the preparation of omega-functionalized 3-phenyl-1-alkynes, the reaction of 1-bromo-3-phenylpropadiene with Knochel reagents RCu(CN)ZnCl.2LiCl was also studied; this reaction led to the acetylenic compounds in high yields mainly when the R group (also omega-functionalized) on the copper reagent was primary.     

Non-subelliptic estimates for the tangential Cauchy–Riemann system

We prove non-subelliptic estimates for the tangential Cauchy-Riemann system over a weakly “q-pseudoconvex” higher codimensional submanifold M of $\mathbb{C}^{n}We prove non-subelliptic estimates for the tangential Cauchy-Riemann system over a weakly “q-pseudoconvex” higher codimensional submanifold M of . Let us point out that our hypotheses do not suffice to guarantee subelliptic estimates, in general. Even more: hypoellipticity of the tangential C-R system is not in question (as shows the example by Kohn of (Trans AMS 181:273–292,1973) in case of a Levi-flat hypersurface). However our estimates suffice for existence of smooth solutions to the inhomogeneous C-R equations in certain degree. The main ingredients in our proofs are the weighted L ² estimates by H?rmander (Acta Math 113:89–152,1965) and Kohn (Trans AMS 181:273–292,1973) of Sect. 2 and the tangential -Neumann operator by Kohn of Sect 4; for this latter we also refer to the book (Adv Math AMS Int Press 19,2001). As for the notion of q pseudoconvexity we follow closely Zampieri (Compositio Math 121:155–162,2000). The main technical result, Theorem 2.1, is a version for “perturbed” q-pseudoconvex domains of a similar result by Ahn (Global boundary regularity of the -equation on q-pseudoconvex domains, Preprint, 2003) who generalizes in turn Chen-Shaw (Adv Math AMS Int Press 19, 2001).To Prof. Giovanni Zacher in his 80th birthday.     

On the existence of ground state solutions to nonlinear Schrödinger equations with multisingular inverse-square anisotropic potentials

A class of nonlinear Schrödinger equations with critical power-nonlinearities and potentials exhibiting multiple anisotropic inverse square singularities is investigated. Conditions on strength, location, and orientation of singularities are given for the minimum of the associated Rayleigh quotient to be achieved, both in ? ^N and in bounded domains.