A. Water Exchange 2326 B. Proton Exchange 2327 C. Electronic Relaxation 2327 D. Relaxivity 2331 E. Outerand Second-Sphere Relaxivity 2334 F. Methods of Improving Relaxivity 2336 V. Macromolecular Conjugates 2336 A. Introduction 2336 B. General Conjugation Methods 2336 C. Synthetic Linear Polymers 2336 D. Synthetic Dendrimer-Based Agents 2338 E. Naturally Occurring Polymers (Proteins, Polysaccharides, and Nucleic Acids) 2339

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Gadolinium(III) Chelates as MRI Contrast Agents: Structure, Dynamics, and Applications

Artificial Organic Host Molecules for Anions

3.2. Thienothiophenes 1216 3.2.1. Thieno[3,4-b]thiophene Analogues 1216 3.2.2. Thieno[3,2-b]thiophene Analogues 1217 3.2.3. Thieno[2,3-b]thiophene Analogues 1218 3.3. , ′-Bridged Bithiophenes 1219 3.3.1. Dithienothiophene (DTT) Analogues 1220 3.3.2. Dithieno[3,2-b:2′3′-d]thiophene-4,4-dioxides 1221 3.3.3. Dithienosilole (DTS) Analogues 1221 3.3.4. Cyclopentadithiophene (CPDT) Analogues 1221 3.3.5. Nitrogen and Phosphor Atom Bridged Bithiophenes 1222

Functional oligothiophenes: molecular design for multidimensional nanoarchitectures and their applications.

As a result of the different degrees of stabilization experienced by the 4f, 5d, and 6s orbitals occurring upon ionization of the neutral metal, the lanthanides (La-Lu, Z ) 57-71) exist almost exclusively in their trivalent state Ln(III) ([Xe]4fn, n ) 0-14) in coordination complexes or supramolecular assemblies.1 Except for some arene compounds involving bulky substituted benzenes or cyclo-octatetraenes,2 covalence plays a minor role in Ln-ligand dative bonds and the nature of the coordination sphere is controlled by a subtle interplay between electrostatic interactions and interligand steric constraints.3 Variable coordination numbers (6 e CN e 12) and geometries are thus observed in lanthanide complexes, leading to limited success in the design of molecular architectures with predetermined structures.3,4 Although rigid or semirigid receptors may help to control the coordination sphere according to the lock-and-key and induced fit concepts,5 detailed studies of lanthanide solvates with water or acetonitrile suggest that trivalent lanthanides display a tendency to adopt nine-coordinate tricapped trigonal prismatic (TTP) arrangements around the metal ion in the solid state. In solution, the picture is a little more subtle:6 in water, for instance, large Ln(III) ions at the beginning of the series (Ln ) La-Nd) adopt TTP geometries, which are gradually transformed into eight-coordinate square antiprismatic (SAP) arrangements for small Ln(III) ions (Ln ) Tb-Lu), equilibria between CN ) 8 and CN ) 9 being observed for Ln ) Nd-Tb.7 The systematic contraction of the ionic radii observed when going from Ln ) La to Lu (often referred to as the lanthanide contraction)8 explains this trend and increases electrostatic bonding for heavier lanthanides, but this variation is so smooth and limited (15% contraction between La and Lu and ≈1% between two successive lanthanides) that selective recognition and incorporation into organized supramolecular architectures remains challenging.5 A rational access to extended polymetallic lanthanide-containing assemblies with predictable and controlled geometries is consequently very limited, and pioneer work in this field has focused on poorly characterized intricate mixtures of complexes in solution which are ‘transformed’ into well-defined solid-state clusters or networks through crystallization processes involving a rich palette of † Institute of Molecular and Biological Chemistry, Lausanne. E-mail: Jean-Claude.Bunzli@epfl.ch. ‡ Department of Inorganic, Analytical and Applied Chemistry, Geneva. E-mail: Claude.Piguet@chiam.unige.ch.

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Lanthanide-containing molecular and supramolecular polymetallic functional assemblies.

The challenge of cyclic and acyclic schiff bases and related derivatives

Treatment of tetraphenyl-21-thiaporphyrin with rhodium (III) chloride in acetonitrile in the presence of metallic zinc yields diamagnetic Rh III (STPP)Cl 2 . The electronic and 1 H NMR spectra are reported. Rh III (STPP)Cl 2 crystallizes in the monoclinic space group P2 1

Preparation and structural characterization of a six-coordinate 21-thiaporphyrin complex: RhIII(STPP)Cl2 (STPP=tetraphenyl-21-thiaporphyrin anion)

Two new Schiff base macrocycles – a 4+4 condensation product and a meso-type 2+2 condensation product – were obtained in a reaction of trans-1,2-diaminocyclohexane and 2,6-diformylpyridine. Reduction of these compounds led to the corresponding 4+4 and 2+2 macrocyclic amines. The macrocycles were characterised by NMR spectroscopy and electrospray mass spectrometry. The symmetry and stereochemistry of these macrocycles, as well as of new 3+3 and 4+4 diastereomers identified in solution, has been established. X-Ray structures of the 2+2 and 4+4 Schiff base macrocycles confirm the configurations determined on the basis of spectroscopic investigations. The crystal structures reveal that the centres of the square-shaped 4+4 macrocycles form channels as a result of columnar stacking.

New 2+2, 3+3 and 4+4 macrocycles derived from 1,2-diaminocyclohexane and 2,6-diformylpyridine

Treatment of tetraphenyl-21-thiaporphyrin (STPPH) with palladium(II) chloride in acetonitrile yields diamagnetic [Pd II (STPP)]Cl. The electronic and 1 H NMR spectra are reported. [Pd II (STPP)]Cl undergoes one-electron reduction (E o 1/2 =-0.28 vs SCE) to give Pd(STPP). The product of the chemical reduction was isolated and characterized. The nature of the reduced species was examined by EPR and NMR spectroscopy. The EPR spectrum displays a rhombic pattern (g 1 =2.042; g 2 =2.009; g 3 =1.962). This asymmetry suggests an electronic structure with a considerable ligand radical anion contribution. The spin density distribution has been established by 1 H NMR spectroscopy

Palladium complexes of 21-thiaporphyrin: syntheses and characterization

There is great interest in design and synthesis of small molecules which selectively target specific genes to inhibit biological functions in which particular DNA structures participate. Among these studies, chiral recognition has been received much attention because more evidences have shown that conversions of the chirality and diverse conformations of DNA are involved in a series of important life events. Here, we report that a pair of chiral helical macrocyclic lanthanide (III) complexes, (M)-Yb[LSSSSSS]3+ and (P)-Yb[LRRRRRR]3+, can enantioselectively bind to B-form DNA and show remarkably contrasting effects on GC-rich and AT-rich DNA. Neither of them can influence non-B-form DNA, nor quadruplex DNA stability. Our results clearly show that P-enantiomer stabilizes both poly(dG-dC)2 and poly(dA-dT)2 while M-enantiomer stabilizes poly(dA-dT)2, however, destabilizes poly(dG-dC)2. To our knowledge, this is the best example of chiral metal compounds with such contrasting preference on GC- and AT-DNA. Ligand selectively stabilizing or destabilizing DNA can interfere with protein–DNA interactions and potentially affect many crucial biological processes, such as DNA replication, transcription and repair. As such, bearing these unique capabilities, the chiral compounds reported here may shed light on the design of novel enantiomers targeting specific DNA with both sequence and conformation preference.

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Contrasting enantioselective DNA preference: chiral helical macrocyclic lanthanide complex binding to DNA

Lanthanide(III) complexes of the enantiopure chiral hexaaza tetraamine macrocycle L, 2(R),7(R),18(R),23(R)-1,8,15,17,24,31-hexaazatricyclo[25.3.1.1.0.0]-dotriaconta-10,12,14,26,28,30-hexaene, as well as of its meso-type 2(R),7(R),18(S),23(S)-isomeric macrocycle L1, have been synthesized and characterized by spectroscopic methods. The 2D NMR spectra confirm the identity of these complexes and indicate C2 symmetry of the [LnL]3+ and Cs symmetry of the [LnL1]3+ complexes. The crystal structures of the [PrL(NO3)(H2O)2](NO3)2, [EuL(NO3)(H2O)2](NO3)2, [DyL(NO3)2]2[Dy(NO3)5] x 5CH3CN, [YbL(NO3)2]2[Yb(NO3)5] x 5CH3CN, [YbL(H2O)2](NO3)3 x H2O, and [EuL1(NO3)(H2O)2]0.52[EuL1(NO3)2]0.48(NO3)1.52 x 0.48H2O complexes have been determined by single-crystal X-ray diffraction. In all complexes, the lanthanide(III) ions are coordinated by six nitrogen atoms of the macrocycle L or L1, but for each type of complex, the conformation of the macrocycle and the axial ligation are different. The crystallographic, NMR, and CD data show that the [YbL]3+ complex exists in two stable forms. Both forms of the Yb(III) complex have been isolated, and their interconversion was studied in various solvents. The two forms of [YbL]3+ complex correspond to two diastereomers of ligand L, which differ in the sense of the helical twist and the configuration at the stereogenic amine nitrogen atoms. In one of the stereoisomers, the macrocycle L of (RRRR) configuration at the stereogenic cyclohexane carbon atoms adopts the (RSRS) configuration at the amine nitrogen atoms, while in the other stereoisomer, the macrocycle L of (RRRR) configuration at the stereogenic cyclohexane carbon atoms adopts the (SSSS) configuration at the amine nitrogen atoms. The (RRRR)(RSRS) isomer is quantitatively converting to the (RRRR)(SSSS) isomer in water solution, while the reverse process is observed for an acetonitrile solution, thus representing the rare case of helicity inversion controlled by the solvent.

Jerzy Lisowski

Papers

Preparation and structural characterization of a six-coordinate 21-thiaporphyrin complex: RhIII(STPP)Cl2 (STPP=tetraphenyl-21-thiaporphyrin anion)

New 2+2, 3+3 and 4+4 macrocycles derived from 1,2-diaminocyclohexane and 2,6-diformylpyridine

Palladium complexes of 21-thiaporphyrin: syntheses and characterization

Contrasting enantioselective DNA preference: chiral helical macrocyclic lanthanide complex binding to DNA

Lanthanide complexes of the chiral hexaaza macrocycle and its meso-type isomer: solvent-controlled helicity inversion.