45 research outputs found
Correction: Face and edge directed self-assembly of Pd<sub>12</sub> tetrahedral nano-cages and their self-sorting
No full textCorrection for ‘Face and edge directed self-assembly of Pd12 tetrahedral nano-cages and their self-sorting’ by Prodip Howlader et al., Chem. Sci., 2016, 7, 5893–5899.</p
Urea-Functionalized Self-Assembled Molecular Prism for Heterogeneous Catalysis in Water
No full textReaction 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
Self-Assembled Pd(II) Barrels as Containers for Transient Merocyanine Form and Reverse Thermochromism of Spiropyran
No full textSelf-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
Organic Transformations in the Confined Cavity of Self-Assembled Pd(II) Molecular Containers
No full textBiological systems utilize its extraordinary ability to develop complex and functional molecular
assemblies employing reversible non-covalent interactions. These natural aesthetic examples
motivated synthetic chemists in past few decades to develop synthetic protocol to produce
myriad number of complex assemblies employing weak intermolecular forces. A number of
such forces including hydrogen bonding, solvophobic effect, dynamic covalent interactions and
metal-ligand coordination have been exploited to assemble the molecular building blocks and
stitch them together to construct discrete ‘self-assembled’ architectures incorporated with
desired functionalities. Metal-ligand coordination driven self-assembly certainly evolved as one
of the most successful approaches for the construction of discrete supramolecular architectures
during last two and half decades. The high directionality and reversible nature of certain metalligand
bonds allow the pre-designing of sophisticated architectures which can be successfully
obtained by ‘self-correcting’ mechanism via a thermodynamically controlled self-assembly
process. However, coordination-driven self-assembly strategy allowed chemists to design
molecular containers/vessels of high symmetry and well defined shapes and sizes. These selfassembled
molecular containers have emerged as potential candidates because of their ability
in encapsulating guest molecules, sensing, drug delivery, stabilizing reactive
intermediates/transition states, as well as stereoselective product formation.
Although various synthetic strategies have been exploited in the last two decades to acquire
large number of 3D assemblies, the growing nature of this field demands architectures with
complex topologies of specific shape and functionality. Primarily, symmetric and rigid building
blocks have been employed so far to construct such molecular containers which solely preserves
their geometrical coding throughout the self-assembly process and therefore the final
assemblies are predetermined. Symmetrical pyridyl-based donors have been extensively used
due to their specific biting angle to produce desired architectures, whereas, asymmetric pyridyl
donors are of less interest as it may provide varieties of donor angles which may led to the
formation of mixture of architectures. Moreover, most of the architectures have been
constructed mainly via two-component self-assembly whereas multicomponent assemblies are
scarce. The multi-component self-assembly offers one-pot synthesis of assemblies involving
more than two components. The symmetry consideration along with the binding modes of the
building blocks are the pivotal aspects in supramolecular design strategy as it installs the
geometrical codes embedded in it which are responsible for the dimensionality, shapes and
symmetry of the resulting assembly.
Unlike, mono-heterocyclic donors poly-heterocyclic donors are much more complex in terms
of their symmetry, bite-angle and number of donor sites. While these multi-dentate donors offer
less control over the productive design of discrete nano-assembly, on the other hand, it may
provide unprecedented 3D molecular architectures. In addition, interesting symmetry aspects
into the final assembly can be observed due to the presence of multiple donor atoms and biteangles,
which otherwise not accessible through highly symmetric donors like pyridyl, where
the final assembly possess multiple symmetry elements e.g. rotational axis and mirror plane.
The physico-chemical properties of self-assembled coordination cages depend on the structures
of the complexes. Presence of large internal cavity surrounded by aromatic core provides an
excellent environment for the encapsulation of varieties of guest molecule or as nano-reactors
for different organic transformations. The microenvironment offered by molecular vessels can
be used for recognizing specific molecules or a specific conformation of that molecule. This
phenomenon entirely depends on several factors e.g. size and shapes of the cavity, coulombic
interaction between host and guest, hydrophobicity of the cavity and finally the symmetry
elements of host and guest molecules.
Although, host-guest encapsulation studies between 3D coordination cages and guest molecules
are well explored, the possibility of host-guest formation in solid-solid phase has not been
studied before because of the absence of any mobile phase (mainly solvent) and the restriction
of molecular movements of both host and guest molecules in the solid phase does not allow any
encapsulation to take place. However, by exposing to light or heat, molecules can gain required
energy to allow itself to move inside the solid matrix and thereby a facile encapsulation might
be possible
Three essays on the relationship between land conservation and economic development
Get PDFLand degradation is a significant cause of biodiversity loss, food insecurity, and persistent poverty. In this dissertation, I explore how land conservation and conversion policies affect economic development and human welfare. I use current and historical contexts and compile primary data sources to answer this question. I use case studies from both developing and developed countries, and from both land conversion and working land conservation policies.
In the first chapter, I study the effects of forest protected areas (PAs) on surrounding households in a developing country. I use Nepal’s recently established PAs as a case study to see the effects on the households who depend on the forest. I find that PAs reduce household wood collection, but there is no evidence that other household consumption is significantly reduced by the strain of reduced access to forest resources nor that PAs rapidly attracted tourism that increased household welfare in these rural villages.
This analysis of the immediate effects of land conservation policies in Nepal cannot shed light on all the effects of conservation policies, as land and soil quality change takes time. Historical events provide a more complete picture. Thus, my second two chapters study historical land conservation policies in the United States (US).
In my second chapter, I explore the persistent impacts on the environment of the earliest farmland conservation policies in the Great Plains. The 1930s Dust Bowl compelled the federal government to undertake large soil conservation policies; I evaluate the effects of those policies over fifty years. Results show that the Voluntary Acreage Reduction program had beneficial long-term effects, increasing areas planted in grassland and decreasing soil erosion in areas that were previously heavily planted in corn and wheat.
Land conservation policies also include creating and nurturing local institutions for management. In my third chapter, I study what factors affected the speed with which local environmental institutions – the Soil Conservation Districts (SCDs) – were created to improve farmland resource management. I use historical documents to create a dataset on exactly when SCDs were established during the period of 1936-1956. A duration analysis of those data finds that SCDs did rise up more rapidly in places hit hardest by crop failure, but institutional change was slower in areas dominated by farms managed by tenants who did not have legal authority to help create SCDs to help preserve their farms.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2021-08-01The student, Aparna Howlader, accepted the attached license on 2019-07-01 at 13:43.The student, Aparna Howlader, submitted this Dissertation for approval on 2019-07-01 at 14:26.This Dissertation was approved for publication on 2019-07-03 at 16:59.DSpace SAF Submission Ingestion Package generated from Vireo submission #14122 on 2019-11-26 at 13:04:13Made available in DSpace on 2019-11-26T20:49:19Z (GMT). No. of bitstreams: 2
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Solvent Directed Synthesis of Molecular Cage and Metal Organic Framework of Copper(II) Paddlewheel Cluster
No full textA solvothermal reaction of a clip-type dicarboxylic acid H(2)DCA 3,3-((5-nitroisophthaloyl)bis(azanediyl))-dibenzoic acid] and Cu(NO3)(2) in equimolar ratio in dimethylformamide (DMF) yielded MOF(CuCG1) which was formed by interlinking 4+2] self-assembled polyhedral cages via coordination between amide moiety present in the linker and the axial position of copper paddlewheel Cu-2(CO2)(4). Upon a change in the solvent from DMF to DMA dimethylacetamide] the interlinking among the polyhedra was successfully terminated to get single crystals of a discrete coordination cage with DMA bound to axial position of Cu(II) (CuCG2). Similar termination of the interlinking was also achieved by a fast crystallization process to get discrete architecture CuCG1
Self-sorting of Pd<sub>12</sub> self-assembled tetrahedral homochiral nano-cages with polytetrazole linkers
No full textFace and edge directed self-assembly of Pd-12 tetrahedral nano-cages and their self-sorting
No full textReactions of a cis-blocked Pd(II) 90 degrees acceptor cis-(tmeda) Pd(NO3)(2)] (M) with 1,4-di(1H-tetrazol-5-yl) benzene (H2L1) and 1,3,5-tri(1H-tetrazol-5-yl) benzene] (H3L2) in 1 : 1 and 3 : 2 molar ratios respectively, yielded soft metallogels G1 and G2 tmeda = N, N, N', N'-tetramethylethane-1,2-diamine]. Post-metalation of the gels G1 and G2 with M yielded highly water-soluble edge and face directed self-assembled Pd-12 tetrahedral nano-cages T1 and T2, respectively. Such facile conversion of Pd(II) gels to discrete tetrahedral metallocages is unprecedented. Moreover, distinct self-sorting of these two tetrahedral cages of similar sizes was observed in the self-assembly of M with a mixture of H2L1 and H3L2 in aqueous medium. The edge directed tetrahedral cage (T1) was successfully used to perform Michael reactions of a series of water insoluble nitro-olefins assisted by encapsulation into the cage in aqueous medium
Face and edge directed self-assembly of Pd-12 tetrahedral nano-cages and their self-sorting (vol 7, pg 5893, 2016)
No full text
