Six solvated salts of a mononuclear manganese(III) complex with a chelating hexadentate Schiff base ligand are reported. One member of the series, [MnL]PF(6)⋅0.5 CH(3)OH (1), shows a rare low-spin (LS) electronic configuration between 10-300 K. The remaining five salts, [MnL]NO(3)⋅C(2)H(5)OH(2), [MnL]BF(4)⋅C(2)H(5)OH(3), [MnL]CF(3)SO(3)⋅C(2)H(5)OH (4), [MnL]ClO(4)⋅C(2)H(5)OH (5) and [MnL]ClO(4)⋅0.5 CH(3)CN (6), all show gradual incomplete spin-crossover (SCO) behaviour. The structures of all were determined at 100 K, and also at 293 K in the case of 3-6. The LS salt [MnL]PF(6)⋅0.5 CH(3)OH is the only member of the series that does not exhibit strong hydrogen bonding. At 100 K two of the four SCO complexes (2 and 4) assemble into 1D hydrogen-bonded chains, which weaken or rupture on warming. The remaining SCO complexes 3, 5 and 6 do not form 1D hydrogen-bonded chains, but instead exhibit discrete hydrogen bonding between cation/counterion, cation/solvent or counterion/solvent and show no significant change on warming.
The design and synthesis of tripodal ligands 1-3 based upon the N-methyl-1,3,5-benzenetricarboxamide platform appended with three aryl urea arms is reported. This ligand platform gives rise to highly preorganized structures and is ideally suited for binding SO4 (2-) and H2 PO4 (-) ions through multiple hydrogen-bonding interactions. The solid-state crystal structures of 1-3 with SO4 (2-) show the encapsulation of a single anion within a cage structure, whereas the crystal structure of 1 with H2 PO4 (-) showed that two anions are encapsulated. We further demonstrate that ligand 4, based on the same platform but consisting of two bis-urea moieties and a single ammonium moiety, also recognizes SO4 (2-) to form a self-assembled capsule with [4:4] SO4 (2-) :4 stoichiometry in which the anions are clustered within a cavity formed by the four ligands. This is the first example of a self-sorting self-assembled capsule where four tetrahedrally arranged SO4 (2-) ions are embedded within a hydrophobic cavity.
The development of a family of twelve aryl pyridyl ureas, their crystallography and the ability of a number of these to form hydrogen bonding supramolecular gels with antimicrobial properties are described.
Chiral lanthanide-based supramolecular structures have gained significant importance in view of their application in imaging, sensing and other functional purposes. We have designed chiral C2-symmetrical ligands (L) based on the use of two 2,6-pyridine-dicarboxylic-amide moieties (pda), that differ from one another by the nature of the diamine spacer groups (from 1,3-phenylenedimethanamine (1(S,S), 2(R,R)) and benzene-1,3-diamine (3(S,S), 4(R,R)) to much bulkier 4,4'-(cyclohexane-1,1-diyl)bis(2,6-dimethylaniline) (5(S,S), 6(R,R))) between these two pda units. The self-assembly between L and Eu(iii) ions were investigated in CH3CN solution at low concentration whereby the changes in the absorbance, fluorescence and Eu(iii)-centred emission spectra allowed us to model the binding equilibria occurring in the solution to the presence of [Eu:L2], [Eu2:L2], [Eu2:L3] assemblies and reveal their high binding constant values. The self-assembly in solution were also studied at higher concentration by following the changes in the 1H NMR spectra of the ligands upon Eu(iii) addition, as well as by using MALDI-MS of the isolated solid state complexes. The chiroptical properties of the ligands were used in order to study the structural changes upon self-assembly between the ligands and Eu(iii) ions using circular dichroism (CD) and circularly polarised luminescence (CPL) spectroscopies. The photophysical properties of [Eu2:L3] complexes were evaluated in solution and showed a decrease of luminescence quantum yield when going from the ligand with smaller (1(S,S)) to bulkier (5(S,S)) linker from ∼5.8% to ∼2.6%. While mass-spectrometry revealed the possible formation of trinucler assemblies such as [Eu3:L3] and [Eu3:L2].
Assembly
and co-assemblies of peptide amphiphiles through specific noncovalent
forces expand the space of molecular architectonics-driven construction
of diverse nanoarchitectures with potential biological applications.
In this work, cyclic dipeptide amphiphiles (CDPAs) of cyclo(Gly-Asp)
with varying lengths of alkyl chains (C8–C18) were synthesized, and their molecular organization was
studied. The noncovalent interactions of the components, CDP and alkyl
chain, drive the molecular self-assembly of CDPAs into well-defined
and diverse nanoarchitectures such as nanotubes, nanospheres, nano/microsheets,
and flowers. The co-assembly of CDPAs with biological molecules such
as nucleosides was studied to ascertain their utility as potential
drug delivery vehicles. Mechanical properties of these nanoarchitectures
in nanoindentation study established them as robust in nature. A temperature-dependent
NMR study confirmed the formation of stable co-assembly of CDPAs,
primarily driven by the intermolecular hydrogen bonding interactions.
Computational modeling of oligomers of CDPAs and their co-assembly
with nucleosides/nucleotides reveal the molecular level interactions
and driving force behind such assemblies. CDPAs exhibit good biocompatibility
and cytocompatibility, as revealed by the cellular studies which substantiated
their suitability for drug delivery applications. The co-assembly
of CDPA with an anticancer drug 5-bromo-2′-deoxyuridine (BrdU)
was studied as a drug delivery platform and cytotoxicity was successfully
assessed in HeLa cells. Computational modeling of the oligomers of
CDPAs and their co-assembly with the drug molecule was performed to
understand the molecular level interactions and driving force behind
the assemblies. Our findings reveal the design strategy to construct
diverse structural architectures using CDP as the modular building
unit and specific molecular interactions driven co-assembly for potential
application as drug delivery carrier.
The first Cu-catalyzed cross-coupling of aromatic oximes and haloarenes is reported. This one-step formation of the =N-O-Ar linkage gives access to a range of oxime ethers in good to moderate yields.
Ditopic helicate
ligands 1 and 2 were
synthesized for the formation of dinuclear EuIII luminescent
chiral helical assemblies (Eu2·L3) in competitive
organic and protic solvent media. Spectroscopic analysis revealed
formation of the 2:3 (Eu2·L3) and 2:2 (Eu2·L2) species in methanolic solutions. Circular
dichroism and circularly polarized luminescence (CPL) spectroscopy
confirmed the chiral purity of the helical systems, while scanning
electron microscopy imaging demonstrated the formation of hierarchical
self-assemblies with spherical morphologies.
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