16 research outputs found
Guest-Shape-Directed Structural Switching between Two Isomers of a Pd6 Host and Its Structural Adaptability for Selective Photodimerization
No full textThe structure and functions of metal–organic cages are heavily dependent on the nature of the building blocks. Herein, a dimethyl-substituted propane diamine blocked cis-Pd(II) acceptor (A) was designed, which upon self-assembly with the tri-imidazole ligand (L), generated an unusual A6L4 octahedral cage (M1O) instead of the expected isomeric double-square architecture that was obtained from the tetramethyl-substituted ethylene diamine blocked cis-Pd(II) acceptor in water. Interestingly, in the presence of planar guests (Gn), M1O showed a transformation to a transient double-square architecture (M1DS), forming host–guest complexes with two such guests, (Gn)2@M1DS. The transient double-square cage (M1DS) readily converts back to the parent octahedral structure, M1O upon the removal of the guests. On the contrary, tetrahedral guests (G5/G6) stabilized the octahedral isomer of the host (M1O) by acting as suitable templates. Additionally, tetrahedral guests could induce the reverse transformation of M1DS to M1O by driving out planar guests from metastable M1DS. The specific antiparallel orientation and proximity of two anthracene derivatives within M1DS enabled them to be selectively transformed to the trans isomers of their respective dimers under photoirradiation. Upon dimer formation, the nonplanar product was expelled readily from the cavity of M1DS, and the host switched back to its original octahedral form (M1O), which functionally and structurally imitates enzymatic activity. Thus, a multifunctional supramolecular host was obtained that showed unique guest-shape-driven reversible structural switching and acted as an adaptive host for selective photodimerization
Formation of a Pd16 Molecular Basket Architecture of Reduced Symmetry and Angular Deviation in a Fluorenone Scaffold to Govern the Host–Guest Chemistry of Pd6 Trifacial Tubes
No full textThe employment of flexible ligands with significant conformational freedom in coordination-driven self-assembly enables the formation of unique and intricate structures. In this study, the self-assembly of such a fluorenone-appended ligand (L1) with a sterically demanding acceptor, [Pd(tmed)(ONO2)2] (M1), generated a new and unique molecular basket architecture, (M1)16(L1)8 (B), featuring a large hollow cavity. B possesses an unusual twisted architecture of low symmetry, consisting of 16 Pd(II) centers arranged as four tetrahedra connected by eight flexible ligands, representing a structurally complex system reminiscent of biological architectures. Designing such entropically disfavored, large architectures of reduced symmetry is challenging but desirable, since they can act as ideal models to study complicated natural systems. The host–guest property of supramolecular hosts is governed by the confined cavities and noncovalent interactions, which are dictated by the angular disposition of ligand coordination sites. To explore this, the fluorenone scaffold was used to synthesize two other tetradentate ligands (L2 and L3) that differed in the spatial distributions of their coordination vectors. The self-assembly of these ligands with [Pd(en)(ONO2)2] (M2) resulted in the formation of water-soluble (M2)6(L1/L2/L3)3 trifacial tubes of different geometries with varying internal cavity dimensions. These angular variations further altered the orientation of the fluorenone carbonyl groups within the cavities, thereby modulating their guest binding abilities and highlighting the importance of tailoring supramolecular hosts for specific guest binding
Planar Bridging-Droplet Thermal Diode
No full textThis disclosure provides a thermal diode including a first plate having a first surface defining a wick structure. The thermal diode can include a second plate having a smooth surface facing the wick structure, the smooth surface and the wick structure defining a chamber for accommodating a phase-change liquid. The thermal diode also can include a separator positioned between the first plate and the second plate to separate the wick structure from the smooth surface by a gap that is less than a capillary length of the phase-change liquid
Stimuli‐Mediated Structural Interchange Between Pd6 and Pd12 Architectures: Selective Recognition of E‐Stilbene by the Pd6 Architecture and its Photoprotection
No full textThe dynamic behaviour of metal-ligand bonding cultivates stimuli-mediated structural transformations in self-assembled molecular architectures. The propensity of synthetically designed self-assembled systems to interchange between higher-order architectures is increased multi-fold when the building blocks have higher conformational degrees of freedom. Herein, we report a new ligand, (2,7-bis(di(pyridin-4-yl)amino)-9H-fluoren-9-one) (L), which, upon self-assembly with a cis-[(ethylene-1,2-diamine)Pd(NO3)2] acceptor (M), resulted in the formation of a M6L3 trifacial barrel (C1) in water. Interestingly, during crystallization, a rare M12L6 triangular orthobicupola architecture (C2) was generated along with C1. C2 could also be generated in solution via the application of several stimuli. C1 in aqueous media could stabilize one trans-stilbene (tS) or cis-stilbene (cS) molecule in its cavity, with a selectivity for the former from their mixture. Moreover, C1 acted as an effective host to prevent the otherwise facile photoisomerization of tS to cS inside its hydrophobic cavity under UV irradiation. Conversely, the visible-light-induced reverse isomerization of encapsulated cS to encapsulated tS could be achieved readily due to the better stabilization of tS within the cavity of C1 and its transparency to visible light. A multi-functional system was therefore designed, which at the same time is stimuli-responsive, shows isomer selectivity, and photo-protects trans-stilbene
Postassembly Modification of a Pd6 Host and C70 Encapsulation to Enhance Its ROS-Mediated Terpene Oxidation Ability under Visible Light
No full textThe properties of supramolecules can be modulated by post-assembly modification (PAM) of their building blocks or via guest encapsulation. This work demonstrates a largely uncharted approach to property modulation that integrates both PAM and guest encapsulation in a single system to boost photocatalytic activity. Self-assembly of a “phenothiazine”-functionalized ligand (L) with a cis-blocked Pd(II) acceptor (A) generated an A6L3 trifacial tube (T). Postassembly, T could be modified via irradiation with violet light, leading to the sulfoxidation of the “phenothiazine” moieties in T and thereby generating an oxidized tube (TO). Both TO and T could stabilize a C70 molecule within their cavities, forming C70@TO and C70@T, respectively. Although T showed relatively poor photocatalytic performance mediated by reactive oxygen species (ROS) with respect to oxidation of terpenes (S1–S4) under visible light, the modified TO was much better in that regard. Expectedly, C70@T showed better photocatalytic performance than T due to the presence of photosensitizing C70. While PAM or guest encapsulation alone led to reasonable improvements in photocatalytic ability, their combination within C70@TO led to a significant improvement. Catalytic amounts of C70@TO could instantly oxidize terpenes. Thus, we report here a new host that integrates the effects of both PAM and photosensitizer encapsulation for synergistically boosting its photocatalytic activity
Exploiting Interfacial Phenomena to Expel Matter from its Substrate
No full textSpontaneous expulsion of various forms and types of matter from their solid substrates has always been an integral part of interfacial physics problems. A thorough understanding of such interactions between a solid surface and different soft materials not only expands our theoretical knowledge, but also has applications in self-cleaning, omniphobic surfaces and phase-change heat transfer. Although there is a renewed interest in the design of robust functional surfaces which can passively remove highly viscous liquids or dew, or retard ice accretion or frost formation, the physics of several dewetting and/or deicing mechanisms are yet to be fully understood. Even though we know how jumping-droplet condensation offers significantly better heat transfer performance than regular dropwise condensation and can liberate foreign particles, fundamental questions on the effect of surface orientation on jumping-droplet condensation or how it helps in large-scale fungal disease epidemic in plants are still unanswered. Thus, we first try to fill the knowledge gap in jumping-droplet condensation by characterizing their orientation-dependence and their role in a large-scale pathogenic rust disease dissemination among wheat. Unfortunately, understanding of such dewetting mechanisms does not necessarily translates to prevention or removal of ice and frost on subzero surfaces. Use of superhydrophobic structures or hygroscopic materials to retard the growth of frost was found to be limiting. Therefore the search for an efficient, inexpensive, and environmentally favorable anti-icing or de-icing mechanism is still underway. Here we give a framework for making a novel de-icing construct by analyzing a peculiar jumping frost phenomena where frost particles spontaneously jump off the surface when a polar liquid is brought above. Lastly, we demonstrate a simple and cost-effective technique to design a slippery liquid-infused surface from low-density hydrocarbon-based polymers, which is able to effectively remove a wide variety of soft materials. The main all-encompassing theme of this dissertation is to enhance our understanding of several dewetting phenomena, which might enable better design and/or mitigation strategies to control the expulsion of various forms of matter from a wide variety of surfaces.Doctor of PhilosophyA few years back, a laundry detergent company in India came up with a famous ad campaign; it showed kids coming home from school with dirt all over their clothes to face the wrath of their parents. Rather than casually disparaging their mischievousness, the ad would make us think with their tagline: "Agar daag (Lit. stain, Fig. mess) lagne se kuch achha hota hain, toh daag achhe hain na? (Fig. If something good comes out of a mess, is it a mess?)". While this presents to us an excellent philosophical conundrum, in reality, we always find ways to get rid of foreign materials from surfaces of everyday use. Using water or dirt-repellent coatings on our shoes/clothes/car windshields or in worst case, spending hours trying to clean frost off our cars is something we are all familiar with. Finding innovative ways to remove unwanted materials from surfaces is not limited to humans, but also exhibited by various natural organisms. The excellent water repellency of lotus leaves, antifogging abilities of mosquito eyes or cicada wings, and slipperiness of pitcher plants are just few examples of natural self-cleaning surfaces designed to keep foreign materials or dew droplets off the surface. Sometimes we take a leaf or two out of these natural designs to help our cause.
Surfaces with extreme water repellency are called superhydrophobic (hydro: water, phobos: fear). For a long time, gravity was considered to be the only passive droplet removal mechanism on these surfaces. About ten years ago, researchers found out that when two or more small dew droplets come together on these surfaces, they jump off the surface. Compared to the gravity removal, much smaller droplets can be removed via this method resulting in better anti-fogging qualities and heat transfer performance on the surface. As the jumping droplet event itself is independent of gravity, it was long assumed that the performance of these surfaces would not be dependent on their orientation. These jumped droplets can also take off with contaminating particles by partially or fully engulfing them. A recent study has brilliantly showed how rust spores are liberated from the superhydrophobic wheat leaves via jumping dew droplets. This fundamentally new mode of pathogen transport is yet to be fully understood at the same scale as we know wind or rain-induced fungal spore transport. In this work, we try to fill the knowledge gap by answering questions such as whether the surfaces with the abilities of gravity-independent jumping-induced droplet removal ironically fail to gravity and how far can spore(s) travel engulfed in a jumped droplet.
But it is not just water droplets (or particles collected by water droplets) on a surface that we want to get rid off. The solid phase of water, i.e., ice or frost, when formed on regular surfaces, is actually harder to remove. The common ice-preventing surfaces are generally unable to stop complete frost formation and forces us to use salt or other moisture attracting chemicals to remove ice from a surface, knowing very well what is the economic and environmental cost of these chemicals. Here, we have introduced a novel de-icing mechanism by holding only a drop of water over a sheet of frost. The simplicity of our experimental setup may remind you the home physics experiments we all did in our childhood.
We finish our discussion by designing a slippery surface from regular polymer films used in food packaging. Although the idea behind these slippery surfaces has been around since 2011, polyethylene films have never been used to make such surfaces before. Here, we show through extensive characterization that by choosing a suitable lubricating oil and a polyethylene-based film, we can finally get all of our ketchup to slide out of their packets, without struggle.
If the future design of superhydrophobic condensers, de-icing constructs, or slippery surfaces benefit from the work reported here, may be I can finally say with certainty, "Daag Achhe Hain (Dirt is good.).
Synthesis of an Adaptable Molecular Barrel and Guest Mediated Stabilization of Its Metastable Higher Homologue
No full textStructural and functional
modulation of three-dimensional artificial
macromolecular systems is of immense importance. Designing supramolecular
cages that can show stimuli mediated reversible switching between
higher-order structures is quite challenging. We report here construction
of a Pd6 trifacial barrel (1) by coordination
self-assembly. Surprisingly, barrel 1 was found to exhibit
guest-responsive behavior. In presence of fullerenes C60 and C70, 1 unprecedentedly transformed to
its metastable higher homologue Pd8 tetrafacial barrel
(2), forming stable host–guest complexes (C60)3⊂2 and (C70)2⊂2, respectively. Again, encapsulated
fullerenes could be extracted from the cavity of 2 using
1,2-dichlorobenzene, leading to its facile conversion to the parent
trifacial barrel 1. Such reversible structural interconversion
between an adaptable molecular barrel and its guest stabilized higher
homologue is an uncommon observation
Solvent and Counteranion Assisted Dynamic Self-Assembly of Molecular Triangles and Tetrahedral Cages
No full textSelf-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
