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Terpyridine macrocycle 1 is shown to be a strong chelating agent for organic ammonium salts and also a useful chromophore in fluorescent sensing. It exhibits very good enantioselectivity (K(obs)(S)/K(obs)(R)= 3.8) in chiral discrimination of alpha-phenylglycine methyl ester hydrochloride (PhEtOMe).
Dipicolinoyl spacer groups are used to control the conformational and H-bonding properties of tricyclic carbohydrate receptors 3 and 4. Binding selectivities are changed in relation to all-isophthaloyl system 1b.
Protonation and Zn(II), Cd(II) and Hg(II) coordination with the ligand 5-aminoethyl-2,5,8-triaza-[9]-10,23-phenanthrolinophane (L2), which contains an aminoethyl pendant attached to a phenanthroline-containing macrocycle, have been investigated by means of potentiometric, 1H NMR and spectrofluorimetric titrations in aqueous solutions. The coordination properties of L2 are compared with those of the ligand 2,5,8-triaza-[9]-10,23-phenanthrolinophane (L1). Ligand protonation occurs on the aliphatic amine groups and does not involve directly the heteroaromatic nitrogens. The fluorescence emission properties of L2 are controlled by the protonation state of the benzylic nitrogens: when not protonated, their lone pairs are available for an electron transfer process to the excited phenanthroline, quenching the emission. As a consequence, the ligand is emissive only in the highly charged [H3L2]3+ and [H4L2]4+ species, where the benzylic nitrogens are protonated. Considering metal complexation, both [ML1]2+ and [ML2]2+ complexes (M = Zn(II) and Cd(II)) are not emissive, since the benzylic nitrogens are weakly involved in metal coordination, and, once again, they are available for quenching the fluorescence emission. Protonation of the L2 complexes to give [MHL2]3+ species, instead, leads to a recovery of the fluorescence emission. Complex protonation, in fact, occurs on the ethylamino group and gives a marked change of the coordination sphere of the metals, with a stronger involvement in metal coordination of the benzylic nitrogens; consequently, their lone pairs are not available for the process of emission quenching.
The first total synthesis of the thiopeptide antibiotic amythiamicin D is described.
Reaction of [(dach)Pd(NO3)2] entities (dach = (R,R)-1,2-diaminocyclohexane, (S,S)-1,2-diaminocyclohexane) and 4,7-phenanthroline (phen) providing, respectively, 90 and 120 degrees bond angles, leads to the formation of two novel positively charged homochiral cyclic trinuclear metallacalix[3]arene species [((R,R)-1,2-diaminocyclohexane)Pd(phen)]3(NO3)6 (2a) and [((S,S)-1,2-diaminocyclohexane)Pd(phen)]3(NO3)6 (2b). These species have been characterised by 1)H NMR and X-ray diffraction methods (2b), showing that they possess accessible cavities suited for supramolecular recognition processes. We prove, indeed, from 1H NMR studies the inclusion of mononucleotides inside the cavity of the trinuclear species [(ethylenediamino)Pd(phen)]3(6+) (1), [((R,R)-1,2-diaminocyclohexane)Pd(phen)]3(6+) (2a) and [((S,S)-1,2-diaminocyclohexane)Pd(phen)]3(6+) (2b) in aqueous solution. Association constants (K(ass)) range from 85 +/- 6 M(-1) for the interaction between [(ethylenediamine)Pd(phen)]3(6+) and adenosine monophosphate to 37 +/- 4 M(-1) for the interaction between [(1,2-diaminocyclohexane)Pd(phen)]3(6+) and thymidine monophosphate. We invoke the synergy of electrostatic, anion-pi and pi-pi interactions to explain the recognition of mononucleotides inside the cavity of the metallacalix[3]arenes.
Approaches for the synthesis of macrocyclic bisindolylmaleimides, in which the indole nitrogens are linked with a tether, are described. Two alternative approaches were investigated: macrocyclisation in either the 'southern' (by adding the tether to the bisindolylmaleimide ring system) or the 'northern' district. With two-, three- and four-atom tethers, both of these approaches were unsuccessful for a wide range of attempted macrocyclisation reactions (palladium-catalysed pi-allyl substitution, ring-closing metathesis, McMurry reaction, iodocyclisation, formation of a silylene derivative, substitution of an alpha,omega-disubstituted electrophile). The failure of all of these reactions was ascribed to the strained nature of the target ring system. However, with longer tethers (six to ten atoms), the macrocycles could prepared using either a ring-closing metathesis reaction or by substitution of an alpha,omega-dibromide). Fourteen successful macrocyclisation reactions are described; deprotection gave eleven macrocyclic bisindolylmaleimides in which an imide substituent had been removed.
Incorporation of a tertiary amide donor within the framework of a C(2)-symmetric analogue of 1,4,7-triazacyclononane derived from L-valine results in the isolation of a very rare example of a classical Werner copper(II) complex in which tertiary amide coordination occurs; despite the monomeric nature of the complex in the solid state, frozen solution EPR studies reveal the presence of a triplet ground state consistent with a dimeric species.
The equilibria and kinetics of the binding of gallium(III) to 4-(N),10-(N)-bis[2-(3-hydroxo-2-oxo-2-H-pyridine-1-y1)acetamido]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (L) were investigated in acidic medium at ionic strength 1 M (NaClO4). Spectrophotometric titrations in the UV region revealed that L is able to bind Ga3+ also at high H+ concentration. The kinetic (stopped-flow) experiments are interpreted on the basis of three parallel reaction paths (i) M3+ + H2L2+ = M(H2L)5+ where M(H2L)5+ is in a steady state, (ii) M(OH)2+ + H2L2+ = M(HL)4+ + H2O and (iii) M(OH)2+ + HL+ = ML3+ + H2O. The first-order rate constants for conversion of the outer-sphere into the inner-sphere complexes are similar to those of the Ga(III)/tropolone system which is known to react according to the dissociative Id mechanism and to the relevant rate constants for water exchange at the metal ion. The effects of pH on the UV-Vis absorption, fluorescence emission properties and NMR spectral features on the Ga(III)/L system were also investigated. Spectrophotometric titrations in the UV region reveal that, in acid medium the prevailing species is M(HL)4+ whereas the chelate ML3+ prevails for [H+] < 0.01 M. The results indicate metal coordination at the oxygen atoms of the 3-hydroxo-2-oxopyridine residues.
The 28-membered octaazamacrocycle Me2[28]py2N6 was used as a receptor for the molecular recognition of aromatic and aliphatic carboxylate substrates. The receptor-substrate binding behaviour of (H6Me2[28]py2N6)6+ with an aliphatic (-O2C(CH2)nCO2-, n=0 to 4) and an aromatic (phthalate, isophthalate, terephthalate, 4,4'-dibenzoate, benzoate, 3- and 4-nitrobenzoate) series of carboxylate anions was evaluated by 1H NMR spectroscopy (carried out in DMSO-d6 at 300 K). Two association constants were found for most of the studied cases, except for 3- and 4-nitrobenzoate for which only K1 was determined. For oxalate, malonate, benzoate and dibenzoate anions only the beta2 constants could be obtained. The values of the first association constant cover a range from 2.86 to 3.69 (log units), and the second stepwise constant from 2.15 to 2.89 (also in log units). No special selectivity was found but the highest values were determined for adipate and the lowest for the monoprotic 3- and 4-nitrobenzoates. Single crystal X-ray structures of H6Me2[28]py2N6 6+ with terephthalate, 1, and 4,4'-dibenzoate (2) were determined showing supramolecular entities with general formula (H6Me2[28]py2N6).(substrate)2(PF6)2.4H2O. These anions are the building blocks of an extensive 3-D network of hydrogen bonds.
The synthesis of the new ligand L1(H4L1= 3,8,16,21-tetrakis(carboxylmethyl)-3,8,16,21,27,28-hexaazatricyclo[21.3.1.1(10,14)]octacosa-1(27),10,12,14(28),23,25-hexaen-5,18-diine) is reported. The solid-state structures of the four homodinuclear chelate complexes, [Zn2(L1)(H2O)2] x 6H2O, [Fe2(L1)(mu-O)] x 4H2O, [La2(L1)(NO3)2(H2O)2] x 6H2O and Na[Eu2(L1)(mu-AcO)3] x 3H2O, were determined by single-crystal X-ray structural analysis.
Carbohydrate-protein interactions have been investigated for a model system of a monoclonal antibody, SYA/J6, which binds a trisaccharide epitope of the O-polysaccharide of the Shigella flexneri variant Y lipopolysaccharide. The thermodynamics of binding for the methyl glycoside of the native trisaccharide epitope, Rha-Rha-GlcNAc () to SYA/J6 over a range of temperatures exhibits strong, linear enthalpy-entropy compensation and a negative heat capacity change (DeltaC(p)=-152 cal mol(-1) degree(-1)). At 293 K the free energy of association is the sum of favourable enthalpy and entropy contributions (DeltaH=-3.9 kcal mol(-1) and -TDeltaS=-2.9 kcal mol(-1)). Crystal structures for SYA/J6 Fab detailed the position of the native trisaccharide epitope, Rha-Rha-GlcNAc, and facilitated a strategy to design a tighter binding, low molecular weight ligand. This involved pre-organization of the native trisaccharide in its bound conformation by addition of intramolecular constraints (a beta-alanyl or glycinyl tether). ELISA measurements indicated that the glycinyl tethered trisaccharide was not an optimal candidate for further analysis, while microcalorimetry provided data showing that the beta-alanyl tethered trisaccharide displayed a 15-fold increase in affinity for SYA/J6. Tethering resulted in a favourable entropic contribution to binding, relative to the native trisaccharide (-TDeltaDeltaS=-1.2 kcal mol(-1)). Potential energy and dynamics calculations using the AMBER Plus force fields indicated that trisaccharide adopted a rigid conformation similar to that of the bound conformation of the native trisaccharide epitope. While this strategy resulted in modest free energy gains by minimizing losses due to conformational entropy, thermodynamic data are consistent with significant contributions from solvent reorganization.
The transformation of the hydroperoxo complex L1(H2O)CrOOH2+ (L1 = 1, 4 8, 11-tetraazacyclotetradecane) to an oxo-chromium(v) species is a first-order process throughout the pH range examined, 1.7 < pH < 9.2. The pH dependence of the rate constant (k1) yielded an apparent pKa of 5.6 for L1(H2O)CrOOH2+. In the acidic range, (pH <4), the value of k1 is 0.191 s(-1). At the other extreme, pH >7.5, k(1)= 0.025 s(-1). No [H+]-dependence is observed within the two limiting regimes, clearly ruling out a simple attack by H+ at the hydroperoxo group. The temperature dependence of k1 in 0.020 M HClO4 yielded the activation parameters DeltaH++ = 53.7 kJ mol(-1) and DeltaS++ = -80.5 J mol(-1) K(-1).
The kinetics of the formation and dissociation of the Cu(2+) and Ni(2+) complexes with a series of N(2)S(2) macrocycles, in which the ring size and the geometry of the arrangement of the donor groups have been varied, have been measured at 25 [degree]C and I= 0.5 (KNO(3)). Both the deprotonated (L) and the monoprotonated (LH(+)) form of the ligands are reactive species in the formation step. In their deprotonated form, first bond formation, in some cases supported by an ICB effect, is rate determining, independently of the ring size. In the monoprotonated form, we find slower rates, due to the charge repulsion and/or conformation changes induced by hydrogen bonds. In contrast the mechanism of the dissociation is very dependent on the ring size. The complexes with the smaller rings react as flexible open-chain ligands directly with H(+). In contrast, the complexes with the larger rings react in a similar way as rigid ligands: first the metal amine bond slowly dissociates so that the free electron pair of the amine can take the "out conformation" and then it is protonated. The 14-membered macrocycle L(3) forms complexes in which the metal ions are ideally coordinated so that their dissociation becomes extremely slow.
Di- and trisulfide linked oligopyrrolic macrocycles are obtained when appropriate alpha,alpha'-free pyrrolic precursors are reacted with sulfur dichloride; these systems represent the first examples of what might be a general new class of porphyrin analogues.
The 1 : 1 reactions of [ClP(mu-NtBu)]2 with the difunctional aromatic amines 1,2-1-YH-2-NH2-C6H4 in the presence of Et3N give the dimeric phosph(III)azane macrocycles [{P(mu-NtBu)2(1-Y-2-HN-C6H4)]2, predominantly as the cis isomer in the case of Y=O (1.cis) and as the trans isomer for Y=S (2.trans). Model M.O. calculations suggest that the selection of the cis and trans isomers is not thermodynamically controlled. The alternative isomers 1.trans and 2.cis are generated exclusively by the deprotonation of the model intermediates [(1-Y-2-NH2-C6H4)P(mu-NtBu)]2[Y=O (3), S (4)] with nBuLi followed by cyclisation with [ClP(mu-NtBu)]2. The solid-state structures of 1.cis/trans(50 : 50), 2.cis, 3 and 4 are reported.
A facile and flexible approach for the preparation of macrocyclic molecules containing different carbohydrate moieties is presented, employing the reaction cascade: click-dimerization and ring-closing metathesis.
The enantiopure amine macrocycle H(3)L, as well as the parent macrocyclic Schiff base H(3)L1, the 3 + 3 condensation product of (1R,2R)-1,2-diaminocyclohexane and 2,6-diformyl-4-methylphenol, are able to form mononuclear complexes with lanthanide(III) ions. The lanthanide(III) complexes of H(3)L have been studied in solution using NMR spectroscopy and electrospray mass spectrometry. The NMR spectra indicate the presence of complexes of low C(1) and C(2) symmetry. The (1)H and (13)C NMR signals of the Lu(III) complex obtained from H(3)L have been assigned on the basis of COSY, TOCSY, NOESY, ROESY and HMQC spectra. The NMR data reveal unsymmetrical binding of lanthanide(III) ion and the presence of a dynamic process corresponding to rotation of Lu(III) within the macrocycle. The [Ln(H(4)L)(NO(3))(2)](NO(3))(2)(Ln = Sm(III), Eu(III), Dy(III), Yb(III) and Lu(III)) complexes of the cationic ligand H(4)L(+) have been isolated in pure form. The X-ray analysis of the [Eu(H(4)L)(NO(3))(2)](NO(3))(2) complex confirms the coordination mode of the macrocycle determined on the basis of NMR results. In this complex the europium(III) ion is bound to three phenolate oxygen atoms and two amine nitrogen atoms of the monoprotonated macrocycle H(4)L(+), as well as to two axial bidendate nitrate anions. In the presence of a base, mononuclear La(III), Ce(III) and Pr(III) complexes of the deprotonated form of the ligand L(3-) can be obtained. When 2 equivalents of Pr(III) are used in this synthesis Na(3)[Pr(2)L(NO(3))(2)(OH)(2)](2)NO(3).5H(2)O is obtained. The NMR, ES MS and an X-ray crystal model of this complex show coordination of two Pr(III) ions by the macrocycle L. The X-ray crystal structure of the free macrocycle H(3)L1 has also been determined. In contrast to macrocyclic amine H(3)L, the Schiff base H(3)L1 adopts a cone-type conformation resembling calixarenes.
A porphyrin macrocyclic square is efficiently prepared by a dynamic combinatorial approach to olefin metathesis and shown by scanning tunneling microscopy (STM) to self-assemble into highly ordered arrays on a graphite surface.