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Georg Seeber

Publications and source records attributed to Georg Seeber.

7 recordsLinked to original sources
PubMed2006

Characterization of self-assembled supramolecular [Ga4L6] host-guest complexes by electrospray ionization mass spectrometry.

Self-assembled supramolecular host-guest complexes have been characterized by electrospray ionization mass spectrometry. The spectra obtained by use of a Q-TOF instrument equipped with a Z-spray ion source show primarily the 3- and 4- charge states of the assemblies. The assemblies have the general formula [guest subset Ga4L6]11- where L represents the chelating bidentate catechol ligand 1,5-bis(2',3'-dihydroxy-benzamido)naphthalene and guests are tetramethyl ammonium (Me4N+), tetraethyl ammonium (Et4N+), tetra-n-propyl ammonium (Pr4N+) and decamethylcobaltocenium (Cp*2Co+) cations. For the first time, the mass spectrum of the empty assembly [Ga4L6]12- is reported. This article also reports that provided the electrospray ion source is capable of preserving noncovalent interactions, it is possible to observe host-guest complexes containing both weak binding guests as well as sterically demanding guests in the mass spectra. The present data suggest that electrospray mass spectrometry is a powerful tool for characterization of supramolecular host-guest complexes.

Crystallization↗
PubMed2006

Guest exchange dynamics in an M4L6 tetrahedral host.

Guest exchange in an M(4)L(6) supramolecular assembly was previously demonstrated to proceed through a nonrupture mechanism in which guests squeeze through apertures in the host structure and not through larger portals created by partial assembly dissociation. Focusing on the [Ga(4)L(6)](12-) assembly [L = 1,5-bis(2',3'-dihydroxybenzamido)naphthalene], the host-guest kinetic behavior of this supramolecular capsule is defined. Guest self-exchange rates at varied temperatures and pressures were measured to determine activation parameters, revealing negative DeltaS and positive DeltaV values [PEt(4)(+): DeltaH = 74(3) kJ mol(-1), DeltaS = -46(6) J mol(-1) K(-1), k(298) = 0.003 s(-)); NEt(4)(+): DeltaH = 69(2) kJ mol(-1), DeltaS = -52(5) J mol(-1) K(-1), k(298) = 0.009 s(-1); NMe(2)Pr(2)(+): DeltaH = 52(2) kJ mol(-1), DeltaS = -56(7) J mol(-1) K(-1), DeltaV = +13(1) cm(3) mol(-1), k(298) = 4.4 s(-1); NPr(4)(+): DeltaH = 42(1) kJ mol(-1), DeltaS = -102(4) J mol(-1) K(-1), DeltaV = +31(2) cm(3) mol(-1), k(298) = 1.4 s(-1)]. In PEt(4)(+) for NEt(4)(+) exchange reactions, egress of the initial guest (G1) is found to be rate determining, with increasing G1 and G2 (the displacing guest) concentrations inhibiting guest exchange. This inhibition is explained by the decreased flexibility of the host imparted by exterior, or exohedral, guest interactions by both the G1 and G2 guests. Blocking the exohedral host sites with high concentrations of the smaller NMe(4)(+) cation (a weak endohedral guest) enhances PEt(4)(+) for NEt(4)(+) guest exchange rates. Finally, guest displacement reactions also demonstrate the sensitivity of guest exchange to thermodynamic endohedral guest binding affinities. When the initial guest (G1) has a weaker affinity for the host, G2 concentration dependence is observed in addition to dependence on the G2 binding strength.

Journal Article↗
PubMed2005

Large M4L4 (M = Al(III), Ga(III), In(III), Ti(IV)) tetrahedral coordination cages: an extension of symmetry-based design.

As an extension to a rational design for the formation of self-assembled coordination cages, the syntheses for very large M4L4 tetrahedra based on a hexadentate 3-fold symmetric ligand (1,3,5-tris(4'-(2' ',3' '-dihydroxybenzamido)phenyl)benzene (H6L2)) are described. Four tetrahedral M4L2(4) assemblies (M = Al(III), Ga(III), In(III), Ti(IV)), with cavity sizes of around 450 A3, have been characterized by elemental analysis, NMR spectroscopy, and high-resolution electrospray mass spectrometry. Differences in chiral resolution and dynamic behavior of host-guest interactions with previously reported tetrahedral M4L(N)6 and M4L1(4) architectures are highlighted for the ligands 1,5-bis(2',3'-dihydroxybenzamido)naphthalene (H4L(N)) and 1,3,5-tris(2',3'-dihydroxybenzamido)benzene (H6L1). An even larger 3-fold symmetric ligand, 1,3,5-tris(4'-(2' '',3' ''-dihydroxybenzamido)-1',1' '-biphenyl)benzene (H6L3) has been prepared but, due to increased flexibility and deviation from the intended 3-fold symmetry, does not undergo self-assembly to form the M4L3(4) structure.

Journal Article↗
PubMed2003

Polymeric silver(I) coordination tubes.

Isolated polymeric Ag(I) coordination tubes are self-assembled from the rigid triamino ligands cis,cis-1,3,5-triaminocyclohexane (cis-tach) and cis,trans-1,3,5-triaminocyclohexane (trans-tach), forming two topologically equivalent framework motifs.

Journal Article↗
PubMed2003

Controlling dimensionality of silver(I) coordination networks with rigid aliphatic amino ligands: from a 2D to a 3D network of unprecedented topology comprising helical channels.

Ligand-directed 2D and 3D Ag(I) coordination networks are self-assembled from the rigid, topologically related tri-amino ligands cis-3,5-diaminopiperidine (cis-dapi) and cis,trans-1,3,5-triaminocyclohexane (trans-tach), yielding two networks of differing dimensionality including a 3D network of unprecedented topology comprising helical channels.

Journal Article↗