ABSTRACT: The asymmetric unit of the title mol-ecular salt [systematic name: 1,4,8,11-tetraazacyclotetradecane-1,8-diium bis(3-carboxy-prop-2-enoate)], C10H26N4 (2+)·2C4H3O4 (-), contains two half-cations (both completed by crystallographic inversion symmetry) and two maleate anions. The cyclam macrocycles adopt trans-III conformations, supported by two intra-molecular N-H?O hydrogen bonds. The O-bonded H atom of each maleate ion is disordered over two positions with an occupancy ratio of 0.61?(5):0.39?(5): each one generates an intra-molecular O-H?O hydrogen bond. In the crystal, the cations are linked to the anions by N-H?O hydrogen bonds, generating  chains.
Project description:[Fe(IV)?O(TBC)(CH(3)CN)](2+) (TBC = 1,4,8,11-tetrabenzyl-1,4,8,11-tetraazacyclotetradecane) is characterized, and its reactivity differences relative to [Fe(IV)?O(TMC)(CH(3)CN)](2+) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) are evaluated in hydrogen atom (H-atom) abstraction and oxo-transfer reactions. Structural differences are defined using X-ray absorption spectroscopy and correlated to reactivities using density functional theory. The S = 1 ground states are highly similar and result in large activation barriers (~25 kcal/mol) due to steric interactions between the cyclam chelate and the substrate (e.g., ethylbenzene) associated with the equatorial ?-attack required by this spin state. Conversely, H-atom abstraction reactivity on an S = 2 surface allows for a ?-attack with an axial substrate approach. This results in decreased steric interactions with the cyclam and a lower barrier (~9 kcal/mol). For [Fe(IV)?O(TBC)(CH(3)CN)](2+), the S = 2 excited state in the reactant is lower in energy and therefore more accessible at the transition state due to a weaker ligand field associated with the steric interactions of the benzyl substituents with the trans-axial ligand. This study is further extended to the oxo-transfer reaction, which is a two-electron process requiring both ?- and ?-electron transfer and thus a nonlinear transition state. In oxo-transfer, the S = 2 has a lower barrier due to sequential vs concerted (S = 1) two electron transfer which gives a high-spin ferric intermediate at the transition state. The [Fe(IV)?O(TBC)(CH(3)CN)](2+) complex is more distorted at the transition state, with the iron farther out of the equatorial plane due to the steric interaction of the benzyl groups with the trans-axial ligand. This allows for better orbital overlap with the substrate, a lower barrier, and an increased rate of oxo-transfer.
Project description:The increased use of copper radioisotopes in radiopharmaceutical applications has created a need for bifunctional chelators (BFCs) that form stable radiocopper complexes and allow covalent attachment to biological molecules. Previous studies have established that 4,11-bis-(carbo- tert-butoxymethyl)-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (H 2CB-TE2A), a member of the ethylene "cross-bridged" cyclam (CB-cyclam) class of bicyclic tetraaza macrocycles, forms highly kinetically stable complexes with Cu(II) and is less susceptible to in vivo transchelation than its nonbridged analogue, 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid (TETA). Herein, we report a convenient synthesis of a novel cross-bridged BFC that is structurally analogous to CB-TE2A in that it possesses two coordinating acetate arms, but in addition possesses a third orthogonally protected arm for conjugation to peptides and other targeting agents. Application of this strategy to cross-bridged chelators may also enable the development of even further improved agents for (64)Cu-mediated diagnostic positron emission tomography (PET) imaging as well as for targeted radiotherapeutic applications.
Project description:A new class of cross-bridged cyclam-based macrocycles featuring phosphonate pendant groups has been developed. 1,4,8,11-tetraazacyclotetradecane-1,8-di(methanephosphonic acid) (CB-TE2P, 1) and 1,4,8,11-tetraazacyclotetradecane-1-(methanephosphonic acid)-8-(methanecarboxylic acid) (CB-TE1A1P, 2) have been synthesized and have been shown to readily form neutral copper(II) complexes at room temperature as the corresponding dianions. Both complexes showed high kinetic inertness to demetallation and crystal structures confirmed complete encapsulation of copper(II) ion within each macrocycle's cleft-like structure. Unprecedented for cross-bridged cyclam derivatives, both CB-TE2P (1) and CB-TE1A1P (2) can be radiolabeled with (64)Cu at room temperature in less than 1 h with specific activities >1 mCi ?g(-1). The in vivo behavior of both (64)Cu-CB-TE2P and (64)Cu-CB-TE1A1P were investigated through biodistribution studies using healthy male Lewis rats. Both new compounds showed rapid clearance with similar or lower accumulation in non-target organs/tissues when compared to other copper chelators including CB-TE2A, NOTA and Diamsar.
Project description:The asymmetric unit of the hydrated title salt, (C10H28N4)[Cr2O7]2·H2O [C10H28N4 = H4(cyclam) = 1,4,8,11-tetra-azonia-cyclo-tetra-deca-ne], contains two half-cations (both completed by crystallographic inversion symmetry), two dichromate anions and one water mol-ecule. The two [CrO7]2- anions exhibit a nearly staggered conformation, with bridging angles of 133.37?(11) and 136.28?(12)°. The distortions of the dichromate anions are due to their participation in hydrogen-bonding inter-actions with the water mol-ecule and the cations. Inter-molecular hydrogen bonds involving the cyclam N-H groups and water O-H groups as donor groups, and the O atoms of the dichromate anions as acceptor groups give rise to a three-dimensional network.
Project description:In the title salt, C5H14N2 (2+)·2C4H3O4 (-), the asymmetric unit contains two independent 2-methyl-piperazinium dications, which comprise a racemic pair, and four hydrogen maleate monoanions. In the roughly planar hydrogen maleate anions, intra-molecular O-H?O hydrogen bonds generate S(7) rings. In the crystal, the four independent anions are linked to the 2-methyl-piperazinium cations through N-H?O hydrogen bonds, forming two-dimensional layered structures lying parallel to (001).
Project description:The replacement of the opposing nitrogen atoms in 1,4,8,11-tetraazacyclotetradecane (cyclam) with two sulfur atoms in 1,8-dithia-4,11-diazacyclotetradecane (dithiacyclam) enables the electrochemical reduction of protons and CO2via the corresponding nickel(ii) complex at more positive potentials. In addition, a 10-fold enhancement in the proton reduction rate of [Ni(dithiacyclam)]2+ relative to [Ni(cylcam)]2+ was observed. The study provides vital insight into Nature's choice of employing predominantly sulfur based ligand platforms in achieving biological proton and CO2 reductions.
Project description:The asymmetric unit of the title salt, C19H25N2OS(+)·C4H3O4 (-) [systematic name: (S)-3-(2-meth-oxy-pheno-thia-zin-10-yl)-N,N,2-tri-methyl-propanaminium hydrogen maleate], comprises two (S)-levomepromazine cations and two hydrogen maleate anions. The conformations of the two cations are similar. The major difference relates to the orientation of the meth-oxy substituent at the pheno-thia-zine ring system. The crystal components form a three-dimensional supra-molecular network via N-H?O, C-H?O and C-H?? inter-actions. A comparison of the conformations of the levomepromazine cations with those of the neutral mol-ecule and similar protonated mol-ecules reveals significant conformational flexibility of the pheno-thia-zine ring system and the substituent at the pheno-thia-zine N atom.
Project description:The crystal structure of the title salt, C8H12N(+)·C4H3O4 (-), consists of a 2,5-di-methyl-anilinium cation and an hydrogen maleate anion. In the anion, a strong intra-molecular O-H?O hydrogen bond is observed, leading to an S(7) graph-set motif. In the crystal, the cations and anions pack in alternating layers parallel to (001). The ammonium group undergoes inter-molecular N-H?O hydrogen-bonding inter-actions with the O atoms of three different hydrogen maleate anions. This results in the formation of ribbons extending parallel to  with hydrogen-bonding motifs of the types R (4) 4(12) and R (4) 4(18).
Project description:The crystal structure of [Cr(NCS)2(cyclam)]NCS (cyclam = 1,4,8,11-tetra-aza-cyclo-tetra-deca-ne, C10H24N4) has been determined by using synchrotron radiation at 98?K. The Cr(III) atom is in a slightly distorted octa-hedral environment with four N atoms of the macrocyclic ligand and two N-coordinated NCS(-) anions in cis positions. The average Cr-N(cyclam) and Cr-NCS bond lengths are 2.085?(5) and 1.996?(15)?Å, respectively. In the crystal, the uncoordinating SCN(-) anion is hydrogen bonded through N-H?S and N-H?N inter-actions to neighbouring complex cations.
Project description:An efficient protocol for the direct synthesis of N-tetraalkylated derivatives of the azamacrocycles cyclam and cyclen has been developed, using a partially miscible aqueous-organic solvent system with propargyl bromide, benzyl bromide, and related halides. The method works most effectively when the reaction mixture is shaken, not stirred. A crystal structure of the N-tetrapropargyl cyclam derivative 1,4,8,11-tetra(prop-2-yn-1-yl)-1,4,8,11-tetraazacyclotetradecane diperchlorate is reported.