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1.
Inorg Chem ; 63(1): 508-517, 2024 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-38117135

RESUMO

A new tetraphenylpyrazine-based tetraimidazole ligand (L) was synthesized and used for subcomponent self-assembly with cis-(tmeda)Pd(NO3)2 and cis-Pt(PEt3)2(OTf)2, leading to the formation of two tetrafacial barrels [Pd8L4(tmeda)8](NO3)16 (1) and [Pt8L4(PEt3)16](OTf)16 (2), respectively. Although ligand L is aggregation-induced emission (AIE) active, barrel 2 showed a magnificently higher AIE activity than ligand L, while 1 failed to retain the AIE properties of the ligand. Pd(II) barrel 1, undergoing an aggregation-caused quenching (ACQ) phenomenon, nullified the AIE activity of the ligand to be used in the photophysical application. The enhanced emission in the aggregated state of Pt(II) barrel 2 was used for the recognition of picric acid (PA), which is explosive in nature and one of the groundwater contaminants in landmine areas. The recognition of picric acid was found to be selective in comparison with that of other nitroaromatic compounds (NACs), which could be attributed to ground-state complex formation and resonance energy transfer between picric acid and barrel 2. The use of new AIE-active assembly 2 for selective detection of PA with a low detection limit is noteworthy.

2.
Chemphyschem ; 23(14): e202200306, 2022 07 19.
Artigo em Inglês | MEDLINE | ID: mdl-35638192

RESUMO

The crystal structure of a newly synthesized compound, [PbL(Ac)]2 , (where L=2 (amino(pyrazin-2-yl) methylene) hydrazinecarbothioamide, Ac=acetate anion) exhibits a close contact between pairs of Pb atoms, suggesting a ditetrel bond, in addition to two Pb⋅⋅⋅O tetrel bonds, and two C-H⋅⋅⋅O H-bonds. The presence of this ditetrel bond as an attractive component is confirmed by various quantum chemical methods. This novelty of this particular bond is its existence even in the absence of a σ-hole on the Pb atom, which is typically considered a prerequisite for a bond of this type. From a wider perspective, a survey of the Cambridge Structural Database suggests this bond may be more common than was hitherto thought, with 44 examples of Pb⋅⋅⋅Pb contacts amongst a total number of 219 examples of T⋅⋅⋅T interactions in general (T=Si, Ge, Sn, Pb).


Assuntos
Chumbo , Ânions , Modelos Moleculares
3.
Inorg Chem ; 61(4): 2368-2377, 2022 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-35029966

RESUMO

Self-assembly of naked PdII ions separately with newly designed bis(3-pyridyl)benzothiadiazole (L1) and bis(3-pyridyl)thiazolo[5,4-d]thiazole (L2) donors separately, under varying experimental conditions, yielded Pd4L8 (L= L1 or L2) tetrahedral cages and their homologous Pd3L6 (L= L1 or L2) double-walled triangular macrocycles. The resulting assemblies exhibited solvent, temperature, and counteranion induced dynamic equilibrium. Treatment of L1 with Pd(BF4)2 in acetonitrile (ACN) resulted in selective formation of a tetrahedral cage [Pd4(L1)8](BF4)8 (1a), which is in dynamic equilibrium with its homologue triangle [Pd3(L1)6](BF4)6 (2a) in dimethyl sulfoxide (DMSO). On the other hand, similar self-assembly using L2 instead of L1 yielded an equilibrium mixture of tetrahedral cage [Pd4(L2)8](BF4)8 (3a) and triangle [Pd3(L2)6](BF4)6 (4a) forms in both ACN and DMSO. The assembles were characterized by multinuclear NMR and ESI-MS while the structure of the tetrahedral cage (1a) was determined by single crystal X-ray diffraction. Existence of a dynamic equilibrium between the assemblies in solution has been investigated via variable temperature 1H NMR. The equilibrium constant K = ([Pd4L8]3/[Pd3L6]4) was calculated at each experimental temperature and fitted with the Van't Hoff equation to determine the standard enthalpy (ΔH°) and entropy (ΔS°) associated with the interconversion of the double-walled triangle to tetrahedral cage. The thermodynamic feasibility of structural interconversion was analyzed from the change in ΔG°, which suggests favorable conversion of Pd3L6 triangle to Pd4L8 cage at elevated temperature for L1 in DMSO and L2 in ACN. Interestingly, similar self-assembly reactions of L1 and L2 with Pd(NO3)2 instead of Pd(BF4)2 resulted in selective formation of a tetrahedral cage [Pd4(L1)8](NO3)8 (1b) and double-walled triangle [Pd3(L2)6](NO3)6 (4b), respectively.

4.
Inorg Chem ; 61(21): 8121-8125, 2022 May 30.
Artigo em Inglês | MEDLINE | ID: mdl-35559685

RESUMO

A conformationally flexible tetrapyridyl ligand L was assembled separately with three cis-blocked 90° PdII acceptors (M1, M2, and M3) containing different blocking diamines. Surprisingly, different conformations of the donor L were arrested by the acceptors depending on the nature of the blocking amine, leading to the formation of isomeric Pd6 barrels (B1, B2, and B3). B2 and B3 with larger windows have been used to encapsulate polyaromatic hydrocarbons.


Assuntos
Ligantes , Isomerismo , Conformação Molecular
5.
Molecules ; 27(20)2022 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-36296535

RESUMO

Four dioxidovanadium(V) complexes with Schiff-base ligands based on 2-hydroxybenzhydrazide with four different substituted salicylaldehydes (5-chlorosalicylaldehyde, 3,5-dichlorosalicylaldehyde, 5-nitrosalicylaldehyde, 3-bromo-5-chlorosalicylaldehyde) were synthesized and described, by using V2O5 and triethylamine. The single crystal X-ray structure measurements as well as elemental analyses and IR spectra confirmed the formulas of the ionic complexes with a protonated triethylamine acting as counterion, HTEA[VO2(L)] (HL = Schiff-base ligand). The kinetic stability of the complexes at pH = 2 and 7 was discussed with respect to the neutral vanadium(V) complexes previously studied as potential insulin-mimetic agents. A correlation between the substituents in an aromatic ring of the Schiff-base ligands with crystal packing, and also with the stability of the compounds, was presented.


Assuntos
Complexos de Coordenação , Vanádio , Ligantes , Vanádio/química , Insulina , Bases de Schiff/química , Íons , Complexos de Coordenação/química
6.
Molecules ; 26(16)2021 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-34443602

RESUMO

The present work opens with an acknowledgement to the research activity performed by Luciana Naldini while affiliated at the Università degli Studi di Sassari (Italy), in particular towards gold complexes and clusters, as a tribute to her outstanding figure in a time and a society where being a woman in science was rather difficult, hoping her achievements could be of inspiration to young female chemists in pursuing their careers against the many hurdles they may encounter. Naldini's findings will be a key to introduce the most recent results in this field, showing how the chemistry of gold compounds has changed throughout the years, to reach levels of complexity and elegance that were once unimagined. The study of gold complexes and clusters with various phosphine ligands was Naldini's main field of research because of the potential application of these species in diverse research areas including electronics, catalysis, and medicine. As the conclusion of a vital period of study, here we report Naldini's last results on a hexanuclear cationic gold cluster, [(PPh3)6Au6(OH)2]2+, having a chair conformation, and on the assumption, supported by experimental data, that it comprises two hydroxyl groups. This contribution, within the fascinating field of inorganic chemistry, provides the intuition of how a simple electron counting may lead to predictable species of yet unknown molecular architectures and formulation, nowadays suggesting interesting opportunities to tune the electronic structures of similar and higher nuclearity species thanks to new spectroscopic and analytical approaches and software facilities. After several decades since Naldini's exceptional work, the chemistry of the gold cluster has reached a considerable degree of complexity, dealing with new, single-atom precise, materials possessing interesting physico-chemical properties, such as luminescence, chirality, or paramagnetic behavior. Here we will describe some of the most significant contributions.

7.
J Am Chem Soc ; 142(19): 9070-9078, 2020 05 13.
Artigo em Inglês | MEDLINE | ID: mdl-32315163

RESUMO

Enantiopure acceptors (R,R)M and (S,S)M [where M = (N1,N1,N2,N2-tetramethylcyclohexane-1,2-diamine)Pd(NO3)2] have been used to design enantiopure Pd(II) tetrahedral cages. Self-assembly of [1,4-di(1H-tetrazol-5-yl)benzene] (H2L1) with chiral acceptors (R,R)M and (S,S)M yielded enantiopure homochiral tetrahedral cages (ΛΛΛΛ)T1 and (ΔΔΔΔ)T1, respectively. This strategy was further extended by using [2,6-di(1H-tetrazol-5-yl)naphthalene] (H2L2) with (R,R)M and (S,S)M to obtain water-soluble enantiopure tetrahedral nanocages (ΛΛΛΛ)T2 and (ΔΔΔΔ)T2, respectively. In order to obtain assembly with a larger cavity for potential use in enantioselective recognition, [4,4'-di(1H-tetrazol-5-yl)-1,1'-biphenyl] (H2L3) was used as the linker, which also resulted in the formation of water-soluble enantiopure tetrahedral cages (ΛΛΛΛ)T3 and (ΔΔΔΔ)T3 upon treatment with (R,R)M and (S,S)M, respectively. The present cages represent unusual examples of enantiopure tetrahedral cages of square-planar metal ions. Finally, T3 cages have been employed in a host-guest study as they offer the largest hydrophobic cavity. Encapsulation of chiral guest molecules such as [(R/S)-1,1'-binaphthalene]-2,2'-diol] (B) and [(R/S)-2,2'-diethoxy-1,1'-binaphthalene] (EtB) has been performed in order to successfully establish the asymmetric nature and enantiopurity of the tetrahedral cavity. The host T3 showed certain selectivity toward one enantiomer over the other. (ΛΛΛΛ)T3 preferred R-EtB over S-EtB (75:25) because of better fitting within the chiral cavity (Λ/R pair), whereas (ΔΔΔΔ)T3 favored S-EtB instead of R-EtB (Δ/S pair ratio = 73:27) with similar selectivity.

8.
J Am Chem Soc ; 142(44): 18981-18989, 2020 11 04.
Artigo em Inglês | MEDLINE | ID: mdl-33104330

RESUMO

Designing supramolecular architectures with uncommon geometries embedded with functional building units is of immense importance in contemporary research. In this report, we present a new water-soluble Pd12L6 supramolecular coordination nanocage (1) that was synthesized via self-assembly of a tetradentate donor (L) with ditopic acceptor cis-[(en)Pd(NO3)2] [en = ethylenediamine]. Self-assembly of a tetratopic donor with a cis-blocked 90° acceptor commonly produces tri/tetra- or hexagonal barrel-type structures. However, the resulting cage 1 has an uncommon geometry consisting of two triangular cupolas conjoined through an irregular common hexagonal base. Incorporation of the benzothiadiazole unit in the structure helped in the photogeneration of reactive oxygen species (ROS) in water. Many nanomaterials have shown to have the ability to mimic the catalytic activity of natural enzymes (nanozymes). Majority of such nanozymes are water insoluble metal/metal-oxide nanoparticles or extended metal organic frameworks (MOFs)/metal-carbon composites, etc. The present water-soluble Pd12 nanocage 1 has shown excellent oxidase-like activity upon irradiation with white light. The enzymatic activity of 1 is photoregulated which offers other obvious advantages, such as external control of enzymatic activity and noninvasiveness. The oxidase-like activity and exogenous ROS generation have been further exploited in photocatalytic antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) bacterial strain.


Assuntos
Complexos de Coordenação/química , Luz , Paládio/química , Complexos de Coordenação/farmacologia , Nanopartículas Metálicas/química , Estruturas Metalorgânicas/química , Staphylococcus aureus Resistente à Meticilina/efeitos dos fármacos , Oxirredutases/química , Oxirredutases/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Tiadiazóis/química
9.
Inorg Chem ; 59(17): 12690-12699, 2020 Sep 08.
Artigo em Inglês | MEDLINE | ID: mdl-32806011

RESUMO

Development of photosensitizer-based self-assembled metallosupramolecular architectures with important applications is an emerging trend in supramolecular chemistry. In this study, we report a new benzothiadiazole-based tetra-pyridyl ligand (L), which upon self-assembly with a cis-block 90° Pt(II) acceptor generated an unprecedented tetrafacial Pt(II)8 photoactive tubular molecular cage (PMB1). This cage could bring an extraordinary photosensitizer, benzothiadiazole, into water which is otherwise insoluble. PMB1 is fluorescent and shows photogeneration of singlet oxygen in an aqueous medium. These features make PMB1 a potent antimicrobial agent in water in both the presence and absence of light. In comparison to its building blocks and water-soluble alkylated charged ligand ([LMe4][4NO3]), the cage shows much enhanced photoinduced antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) as a representative of Gram-positive bacteria and Pseudomonas aeruginosa (PA) as a representative of Gram-negative bacteria. PMB1 is successful at inactivating the bacterial growth via both photoactivation of molecular oxygen and membrane depolarization mechanisms, thus proving to be a dual warhead. Inactivation of bacteria in water using such a supramolecular architecture is noteworthy and can shed light on the generation of new antimicrobial supramolecular systems.


Assuntos
Antibacterianos/química , Antibacterianos/farmacologia , Complexos de Coordenação/química , Complexos de Coordenação/farmacologia , Platina/química , Água/química , Staphylococcus aureus Resistente à Meticilina/efeitos dos fármacos , Pseudomonas aeruginosa/efeitos dos fármacos , Oxigênio Singlete/química , Solubilidade
10.
Molecules ; 25(18)2020 Sep 04.
Artigo em Inglês | MEDLINE | ID: mdl-32899863

RESUMO

A new supramolecular Pb(II) complex [PbL(NO2)]n was synthesized from Pb(NO3)2, N'-(1-(pyridin-2-yl)ethylidene)isonicotinohydrazide (HL) and NaNO2. [PbL(NO2)]n is constructed from discrete [PbL(NO2)] units with an almost ideal N2O3 square pyramidal coordination environment around Pb(II). The ligand L- is coordinated through the 2-pyridyl N-atom, one aza N-atom, and the carbonyl O-atom. The nitrite ligand binds in a κ2-O,O coordination mode through both O-atoms. The Pb(II) center exhibits a hemidirected coordination geometry with a pronounced coordination gap, which allows a close approach of two additional N-atoms arising from the N=C(O) N-atom of an adjacent molecule and from the 4-pyridyl N-atom from the another adjacent molecule, yielding a N4O3 coordination, constructed from two Pb-N and three Pb-O covalent bonds, and two Pb⋯N tetrel bonds. Dimeric units in the structure of [PbL(NO2)]n are formed by the Pb⋯N=C(O) tetrel bonds and intermolecular electrostatically enforced π+⋯π- stacking interactions between the 2- and 4-pyridyl rings and further stabilized by C-H⋯π intermolecular interactions, formed by one of the methyl H-atoms and the 4-pyridyl ring. These dimers are embedded in a 2D network representing a simplified uninodal 3-connected fes (Shubnikov plane net) topology defined by the point symbol (4∙82). The Hirshfeld surface analysis of [PbL(NO2)] revealed that the intermolecular H⋯X (X = H, C, N, O) contacts occupy an overwhelming majority of the molecular surface of the [PbL(NO2)] coordination unit. Furthermore, the structure is characterized by intermolecular C⋯C and C⋯N interactions, corresponding to the intermolecular π⋯π stacking interactions. Notably, intermolecular Pb⋯N and, most interestingly, Pb⋯H interactions are remarkable contributors to the molecular surface of [PbL(NO2)]. While the former contacts are due to the Pb⋯N tetrel bonds, the latter contacts are mainly due to the interaction with the methyl H-atoms in the π⋯π stacked [PbL(NO2)] molecules. Molecular electrostatic potential (MEP) surface calculations showed marked electrostatic contributions to both the Pb⋯N tetrel bonds and the dimer forming π+⋯π- stacking interactions. Quantum theory of atoms in molecules (QTAIM) analyses underlined the tetrel bonding character of the Pb⋯N interactions. The manifold non-covalent interactions found in this supramolecular assembly are the result of the proper combination of the polyfunctional multidentate pyridine-hydrazide ligand and the small nitrito auxiliary ligand.


Assuntos
Isoniazida/química , Chumbo/química , Cristalografia por Raios X , Teoria da Densidade Funcional , Dimerização , Modelos Moleculares , Conformação Molecular , Teoria Quântica , Eletricidade Estática
11.
Angew Chem Int Ed Engl ; 59(39): 17130-17136, 2020 09 21.
Artigo em Inglês | MEDLINE | ID: mdl-32633820

RESUMO

AuIII complexes with N-heterocyclic carbene (NHC) ligands have shown remarkable potential as anticancer agents, yet their fate in vivo has not been thoroughly examined and understood. Reported herein is the synthesis of new AuIII -NHC complexes by direct oxidation with radioactive [124 I]I2 as a valuable strategy to monitor the in vivo biodistribution of this class of compounds using positron emission tomography (PET). While in vitro analyses provide direct evidence for the importance of AuIII -to-AuI reduction to achieve full anticancer activity, in vivo studies reveal that a fraction of the AuIII -NHC prodrug is not immediately reduced after administration but able to reach the major organs before metabolic activation.


Assuntos
Antineoplásicos/farmacologia , Ouro/farmacologia , Compostos Heterocíclicos/farmacologia , Metano/análogos & derivados , Animais , Antineoplásicos/química , Proliferação de Células/efeitos dos fármacos , Ensaios de Seleção de Medicamentos Antitumorais , Ouro/química , Compostos Heterocíclicos/química , Humanos , Radioisótopos do Iodo , Ligantes , Metano/química , Metano/farmacologia , Camundongos , Estrutura Molecular , Tomografia por Emissão de Pósitrons , Distribuição Tecidual , Células Tumorais Cultivadas
12.
J Am Chem Soc ; 141(21): 8638-8645, 2019 May 29.
Artigo em Inglês | MEDLINE | ID: mdl-31050889

RESUMO

Donor-acceptor Stenhouse adducts (DASA) are new-generation photochromic compounds discovered recently. DASA exist normally in open form (blue/violet) and readily convert to cyclic (light yellow/colorless) zwitterionic form reversibly in the presence of green light in toluene/dioxane. In aqueous medium, the open form is not stable and converts to the cyclic zwitterionic form irreversibly. We report here a new self-assembled Pd8 molecular vessel (MV) that can stabilize and store the open form of DASA even in aqueous medium. Reaction of the 90° acceptor cis-(tmeda)Pd(NO3)2 (M) [tmeda = N, N, N', N'-tetramethylethane-1,2-diamine] with a symmetric tetraimidazole donor (L, 3,3',5,5'-tetra(1 H-imidazol-1-yl)-1,1'-biphenyl) in a 2:1 molar ratio yielded a water-soluble [8+4] self-assembled M8L4 molecular barrel (MV). This barrel (MV) is found to be a potential molecular vessel to store and stabilize the open forms of DASA in aqueous medium over the more stable zwitterionic cyclic form, while in the absence of the barrel the same DASA exist in cyclic zwitterionic form in aqueous medium. The hydrophobic interaction between the cavity and the open form of DASA molecules benefits reaching an out-of-equilibrium or reverse equilibrium state in aqueous medium. The presence of excess MV could even drive the conversion of the stable cyclic form to the open form in aqueous medium. The host-guest complex is stable upon irradiating with green light. To the best of our knowledge, this is the first successful attempt to stabilize the open form of DASA molecules in aqueous medium and the first report on the fate of DASA in a confined space discrete molecular architecture. Furthermore, the molecular vessel has been utilized for catalytic Michael addition reactions of a series of nitrostyrene derivatives with 1,3-indandione in aqueous medium.

13.
J Am Chem Soc ; 141(4): 1685-1689, 2019 01 30.
Artigo em Inglês | MEDLINE | ID: mdl-30562021

RESUMO

Folding can bestow macromolecules with various properties, as evident from nature's proteins. Until now complex folded molecules are the product either of evolution or of an elaborate process of design and synthesis. We now show that molecules that fold in a well-defined architecture of substantial complexity can emerge autonomously and selectively from a simple precursor. Specifically, we have identified a self-synthesizing macrocyclic foldamer with a complex and unprecedented secondary and tertiary structure that constructs itself highly selectively from 15 identical peptide-nucleobase subunits, using a dynamic combinatorial chemistry approach. Folding of the structure drives its synthesis in 95% yield from a mixture of interconverting molecules of different ring sizes in a one-step process. Single-crystal X-ray crystallography and NMR reveal a folding pattern based on an intricate network of noncovalent interactions involving residues spaced apart widely in the linear sequence. These results establish dynamic combinatorial chemistry as a powerful approach to developing synthetic molecules with folding motifs of a complexity that goes well beyond that accessible with current design approaches. The fact that such molecules can form autonomously implies that they may have played a role in the origin of life at earlier stages than previously thought possible.


Assuntos
Dobramento de Proteína , Proteínas/química , Modelos Moleculares , Multimerização Proteica , Estrutura Quaternária de Proteína
14.
Inorg Chem ; 58(16): 11172-11179, 2019 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-31393710

RESUMO

Two new M8L4 tetrafacial nanotubes (T1 and T3) of different lengths have been synthesized in water using ligands L1 and L2, respectively, with acceptor cis-[(dch)Pt(NO3)2] (M) using coordination-driven self-assembly [where dch is 1,2-diaminocyclohexane, L1 is 1,4-di(pyrimidin-5-yl)benzene, and L2 is 4,4'- di(pyrimidin-5-yl)-1,1'-biphenyl]. In addition to complex T1, a tetrahedral cage of composition [M12(L1)6] (T2) was also formed in the self-assembly reaction of ligand L1 with cis-[(dch)Pt(NO3)2]. The precise composition of the products (T1 and T2) in solution was confirmed by 1H NMR and ESI-MS. Pure tube T1 was separated out by a crystallization technique and fully characterized by 1H NMR and X-ray diffraction. Temperature- and concentration-dependent NMR studies indicated no equilibrium between T1 and T2 in the solution phase, and the proportion of T1 and T2 in the mixture depends on the temperature of the reaction. In contrast to ligand L1, the self-assembly of the longer ligand, L2, with cis-[(dch)Pt(NO3)2] gave only tetrafacial tube [M8(L2)4] (T3) without any tetrahedral cage.

15.
Molecules ; 24(15)2019 Aug 06.
Artigo em Inglês | MEDLINE | ID: mdl-31390777

RESUMO

(R)-9-hydroxystearic acid, (R)-9-HSA, is a chiral nonracemic hydroxyacid of natural origin possessing interesting properties as an antiproliferative agent against different cancer types. Considering its potential application for medical and pharmaceutical purposes, the structures and rheological properties of (R)-9-HSA were investigated. Oscillatory rheology measurements reveal that (R)-9-HSA gels only paraffin oil, with less efficiency and thermal stability than its positional isomer (R)-12-HSA. Conversely, (R)-9-HSA affords crystals from methanol, acetonitrile, and carbon tetrachloride. The single crystal structures obtained both at 293 K and 100 K show non-centrosymmetric twisted carboxylic acid dimers linked at the midchain OHs into long, unidirectional chains of hydrogen bonds, owing to head-tail ordering of the molecules. Synchrotron X-ray powder diffraction experiments, performed on the solids obtained from different solvents, show the occurrence of polymorphism in paraffin oil and through thermal treatment of the solid from methanol.


Assuntos
Ácidos Esteáricos/química , Cristalografia por Raios X , Ligação de Hidrogênio , Modelos Moleculares , Estrutura Molecular , Reologia , Solventes/química , Análise Espectral , Difração de Raios X
16.
J Am Chem Soc ; 140(25): 7952-7960, 2018 06 27.
Artigo em Inglês | MEDLINE | ID: mdl-29874066

RESUMO

Self-assembly of a cis-blocked Pd(II) 90° ditopic acceptor [ cis-(tmeda)Pd(NO3)2] (M) with a tetradentate donor L1 [benzene-1,4-di(4-terpyridine)] in 2:1 molar ratio yielded two isometric molecular barrels MB1 and MB3 in DMSO [tmeda = N, N, N' N'-tetramethylethane-1,2-diamine]. Exclusive formation of the symmetrical tetrafacial barrel (MB1) was achieved when the self-assembly was performed in aqueous medium. The presence of a large confined cavity makes MB1 a potential molecular container. Spiropyran (SP) compounds exist in stable closed spiro form in visible light and convert to transient open merocyanine (MC) form upon irradiation with UV-light or upon strong heating. The transient MC form readily converts to the stable closed SP form in visible light. MB1 has been employed as a safe container to store the planar and unstable merocyanine isomers (MC1/2) of different spiropyran molecules (SP1/2) [SP1/2 = 6-bromo-spiropyran and 6-nitrospiropyran] for several days. The transient MC forms (MC1 and MC2) were found to be stable inside the molecular container MB1 under visible light and even in the presence of different stimuli such as heat and UV light for a long time. Such stabilization of MC forms inside the confined cavity of MB1 is noteworthy. This phenomenon was generalized by utilizing a carbazole-based molecular barrel (MB2) as a host, which also showed a similar stabilization of transient MC form in visible light at room temperature. Moreover, reverse thermochromism was observed as a result of heating of the MC1 ⊂ MB2 complex, which de-encapsulates the guest in the form of SP1 to give a colorless solution. Moreover, both the host molecules (MB1, MB2) were capable of stabilizing transient MC2 even in the solid state. Such stabilization of transient MC forms in the solid state and transformation of SP forms to MC forms in the solid state in the presence of molecular barrel are remarkable, and these properties have been employed in developing a magic ink.

17.
Chemistry ; 24(52): 13938-13946, 2018 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-29920829

RESUMO

Water-soluble Pd12 L6 coordination cage TC-1 was synthesized by coordination-driven self-assembly of symmetrical tetrapyridyl donor L with 90° ditopic acceptor cis-[Pd(NO3 )2 (tmeda)] [tmeda=N,N,N',N'-tetramethylethane-1,2-diamine]. The Pd12 L6 coordination assembly is an uncommon example of a coordination cage having triangular orthobicupola-like geometry. It was characterized by multinuclear NMR spectroscopy, ESI-MS, and single-crystal X-ray diffraction. Self-assembly of a tetratopic donor with a cis-blocked 90° ditopic acceptor generally yields tri-/tetra-/hexagonal barrels or closed cubic cages. However, in the present case the donor and acceptor are arranged in an unusual fashion to generate an orthobicupola geometry in which two triangular cupola share a common irregular hexagonal face. The cage was used to perform intramolecular cycloaddition reactions of O-propargylated benzylidinebarbituric acid derivatives in nitromethane. Several penta-/tetracyclouracil derivatives were synthesized through cage-catalyzed [4+2] cycloaddition reactions in a concerted manner with good to high conversion under mild reaction conditions, whereas in the absence of cage TC-1 similar reactions led to lower conversion to the cyclized products in organic solvent. This approach is of particular importance compared to the literature reports on the synthesis of similar compounds under high-temperature reflux conditions with high catalyst loading.

18.
J Am Chem Soc ; 138(5): 1668-76, 2016 Feb 10.
Artigo em Inglês | MEDLINE | ID: mdl-26771202

RESUMO

Reaction of a ditopic urea "strut" (L1) with cis-(tmen)Pd(NO3)2 yielded a [3+3] self-assembled molecular triangle (T) [L1 = 1,4-di(4-pyridylureido)benzene; tmen = N,N,N',N'-tetramethylethane-1,2-diamine]. Replacing cis-(tmen)Pd(NO3)2 in the above reaction with an equimolar mixture of Pd(NO3)2 and a clip-type donor (L2) yielded a template-free multicomponent 3D trigonal prism (P) decorated with multiple urea moieties [L2 = 3,3'-(1H-1,2,4-triazole-3,5-diyl)dipyridine]. This prism (P) was characterized by NMR spectroscopy, and the structure was confirmed by X-ray crystallography. The P was employed as an effective hydrogen-bond-donor catalyst for Michael reactions of a series of water-insoluble nitro-olefins in an aqueous medium. The P showed better catalytic activity compared to the urea-based ligand L1 and the triangle T. Moreover, the confined nanospace of P in addition to large product outlet windows makes this 3D architecture a perfect molecular vessel to catalyze Diels-Alder reactions of 9-hydroxymethylanthracene with N-substituted maleimide in the aqueous medium. The present results demonstrate new observations on catalytic aqueous Diels-Alder and Michael reactions in heterogeneous fashion employing a discrete 3D architecture of Pd(II). The prism was recycled by simple filtration and reused several times without significant loss of activity.

19.
Angew Chem Int Ed Engl ; 54(30): 8777-82, 2015 Jul 20.
Artigo em Inglês | MEDLINE | ID: mdl-26096860

RESUMO

Tetrairon(III) single-molecule magnets [Fe4(pPy)2(dpm)6] (1) (H3pPy=2-(hydroxymethyl)-2-(pyridin-4-yl)propane-1,3-diol, Hdpm=dipivaloylmethane) have been deliberately organized into supramolecular chains by reaction with Ru(II)Ru(II) or Ru(II)Ru(III) paddlewheel complexes. The products [Fe4(pPy)2(dpm)6][Ru2(OAc)4](BF4)x with x=0 (2 a) or x=1 (2 b) differ in the electron count on the paramagnetic diruthenium bridges and display hysteresis loops of substantially different shape. Owing to their large easy-plane anisotropy, the s=1 diruthenium(II,II) units in 2 a act as effective s(eff)=0 spins and lead to negligible intrachain communication. By contrast, the mixed-valent bridges (s=3/2, s(eff)=1/2) in 2 b introduce a significant exchange bias, with concomitant enhancement of the remnant magnetization. Our results suggest the possibility to use electron transfer to tune intermolecular communication in redox-responsive arrays of SMMs.

20.
Analyst ; 139(7): 1628-31, 2014 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-24558643

RESUMO

The effect of substituents on FRET in two newly designed rhodamine-based Hg(2+) ion selective chemosensors (L¹ and L²) has been explored by a systematic experimental and theoretical study. Comparison of these sensors in the analytical study and imaging of Hg(2+) ions in living cells has also been included.


Assuntos
Benzaldeídos/química , Transferência Ressonante de Energia de Fluorescência/métodos , Corantes Fluorescentes/química , Hidrazinas/química , Mercúrio/análise , Rodaminas/química , Cátions Bivalentes , Estrutura Molecular
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