Molecular Basket Research Articles

Molecular Encapsulation via Metal-to-Ligand Coordination in a Cu(I)-Folded Molecular Basket

A molecular basket, composed of a semirigid C3v symmetric tris-norbornadiene framework and three pyridine flaps at the rim, has been shown to coordinate to a Cu(I) cation and thereby fold in a multivalent fashion. The assembly was effective (Ka = 1.73 +/- 0.08 x 10(5) M(-1)) and driven by enthalpy (DeltaH(o) = -7.2 +/- 0.1 kcal/mol, DeltaS(o) = -0.25 eu). Variable temperature (1)H NMR studies, assisted with 2D COSY and ROESY investigations, revealed the existence of Cu(I)-folded basket 10b with a molecule of acetonitrile occupying its interior and coordinated to the metal. Interestingly, 10b is in equilibrium with Cu(I)-folded 10a , whose inner space is solvated by acetone or chloroform. The incorporation of a molecule of acetonitrile inside 10a was found to be driven by enthalpy (DeltaH(o) = -3.3 +/- 0.1 kcal/mol), with an apparent loss in entropy (DeltaS(o) = -9.4 +/- 0.4 eu); this is congruent with a complete immobilization of acetonitrile and release of a "loosely" encapsulated solvent molecule during 10a/b interconversion. From an Eyring plot, the activation enthalpy for incorporating acetonitrile into 10a was found to be positive (DeltaH(double dagger) = 6.5 +/- 0.5 kcal/mol), while the activation entropy was negative (DeltaS(double dagger) = -20 +/- 2 eu). The results are in agreement with an exchange mechanism whereby acetonitrile "slips" into an "empty" basket through its side aperture. In fact, DFT (BP86) calculations are in favor of such a mechanistic scenario; the calculations suggest that opening of the basket's rim to exchange guests is energetically demanding and therefore less feasible.

Adsorption capacities of carbon dioxide, oxygen, nitrogen and methane on carbon molecular basket derived from polyethyleneimine impregnation on microporous palm shell activated carbon

In this study, palm shell-based activated carbon (AC) was used as precursor in the production of carbon molecular basket (CMB) via impregnation of polyethyleneimine (PEI). The effects of amount of PEI impregnated on AC on carbon dioxide (CO 2), oxygen (O 2), nitrogen (N 2), and methane (CH 4) adsorption capacities of CMB were investigated. Molecular basket was produced at PEI weight percentages of 0.06, 0.11, 0.13, 0.26, 0.27 and 0.28 wt%. Adsorption capacities of CO 2, O 2, N 2 and CH 4 were enhanced with increasing PEI impregnation from virgin AC to 0.26 wt% PEI/AC before the capacities decreased onwards for 0.28 and 0.29 wt% PEI/AC. The amount of PEI impregnation determined for optimum uptake of gas adsorption was 0.26 wt% PEI/AC. The maximum adsorption capacity for the gases follows the sequence: CO 2 ≫ CH 4 > O 2 > N 2 for all the CMB samples.

Catalyzing Methanolysis of Alkyl Halides in the Interior of an Amphiphilic Molecular Basket

A molecular basket with four cholate units assembled on a cone-shaped calix[4]arene assumed reversed micelle-like conformation in 5% methanol/carbon tetrachloride. The inwardly facing hydroxyl groups on the cholates concentrated the polar solvent from the mostly nonpolar mixture. Methanolysis of alkyl halides benefited from the concentrated pocket of methanol if the substrate was capable of entering the basket. Substrates that were too large or too hydrophobic to fit within the basket showed no rate acceleration.

A Molecular Basket with a Silver Lock

A molecular basket is closed through the coordination of three pyridine rings to a silver(I) ion, and its confirmation in solution is monitored with 1H NMR spectroscopy. The authors previously reported the synthesis of the semi-rigid, basket-shaped compound 1 (V. Maslak et al. J. Am. Chem. Soc. 2006, 128, 5887).

Silver(I) Mediated Folding of a Molecular Basket

We have investigated Ag(I) mediated folding of a tridentate compound, containing three pyridine flaps tethered to a semirigid scaffold, into a molecular basket, using both experimental and theoretical methods. The basket formation has been shown to be highly favorable in organic media (Delta G degrees = -7.2 kcal/mol), with the assembly process allowing for another ligand to bind preferentially on the outer side.

Container Molecules with Portals: Reversibly Switchable Cycloalkane Complexation

A molecular basket (see picture) and a molecular tube can be reversibly switched between closed and open forms. In their closed forms, these novel container molecules encapsulate cycloalkanes such as cyclohexane. Their binding capabilities can be completely turned off by the addition of acid. Neutralization with base leads to restoration of the original complexes.

Preferential Solvation within Hydrophilic Nanocavities and Its Effect on the Folding of Cholate Foldamers

The conformations of three cholate foldamers and one molecular basket were studied by fluorescence and NMR spectroscopy. In nonpolar solvents (e.g., hexane/ethyl acetate or ethyl acetate) mixed with a small amount of a polar solvent (e.g., alcohol or DMSO), the cholate oligomer folded into a helix with the hydrophilic faces of the cholates turned inward. Folding created a hydrophilic nanocavity preferentially solvated by the entrapped polar solvent concentrated from the bulk. This microphase separation of the polar solvent was critical to the folding process. Folding was favored by larger-sized polar solvent molecules, as fewer such molecules could occupy and solvate the nanocavity, thus requiring a smaller extent of phase separation during folding. Folding was also favored by smaller/acyclic nonpolar solvent molecules, probably because they could avoid contact with the OH/NH groups within the nanocavity better than larger/cyclic nonpolar solvent molecules.

An Amphiphilic Molecular Basket Sensitive to Both Solvent Changes and UV Irradiation

A molecular basket was obtained by linking four cholate units to a cone-shaped calix[4]arene scaffold through azobenzene spacers. The molecule turns its polar faces inward in nonpolar solvents to bind polar molecules such as sugar derivatives. In polar solvents, the nonpolar faces turn inward, allowing the binding of hydrophobic guests such as pyrene. The molecule can also respond to UV irradiation by trans-cis isomerization of the azobenzene spacers. Response toward both solvents and UV light is fully reversible.

06/01690 Adsorption separation of carbon dioxide from flue gas of natural gas-fired boiler by a novel nanoporous ‘molecular basket’ adsorbent: Xu, X. et al. Fuel Processing Technology, 2005, 86, (14–15), 1457–1472

06/01690 Adsorption separation of carbon dioxide from flue gas of natural gas-fired boiler by a novel nanoporous ‘molecular basket’ adsorbent: Xu, X. et al. Fuel Processing Technology, 2005, 86, (14–15), 1457–1472

Global challenges and strategies for control, conversion and utilization of CO 2 for sustainable development involving energy, catalysis, adsorption and chemical processing

Utilization of carbon dioxide (CO 2) has become an important global issue due to the significant and continuous rise in atmospheric CO 2 concentrations, accelerated growth in the consumption of carbon-based energy worldwide, depletion of carbon-based energy resources, and low efficiency in current energy systems. The barriers for CO 2 utilization include: (1) costs of CO 2 capture, separation, purification, and transportation to user site; (2) energy requirements of CO 2 chemical conversion (plus source and cost of co-reactants); (3) market size limitations, little investment-incentives and lack of industrial commitments for enhancing CO 2-based chemicals; and (4) the lack of socio-economical driving forces. The strategic objectives may include: (1) use CO 2 for environmentally-benign physical and chemical processing that adds value to the process; (2) use CO 2 to produce industrially useful chemicals and materials that adds value to the products; (3) use CO 2 as a beneficial fluid for processing or as a medium for energy recovery and emission reduction; and (4) use CO 2 recycling involving renewable sources of energy to conserve carbon resources for sustainable development. The approaches for enhancing CO 2 utilization may include one or more of the following: (1) for applications that do not require pure CO 2, develop effective processes for using the CO 2-concentrated flue gas from industrial plants or CO 2-rich resources without CO 2 separation; (2) for applications that need pure CO 2, develop more efficient and less-energy intensive processes for separation of CO 2 selectively without the negative impacts of co-existing gases such as H 2O, O 2, and N 2; (3) replace a hazardous or less-effective substance in existing processes with CO 2 as an alternate medium or solvent or co-reactant or a combination of them; (4) make use of CO 2 based on the unique physical properties as supercritical fluid or as either solvent or anti-solvent; (5) use CO 2 based on the unique chemical properties for CO 2 to be incorporated with high ‘atom efficiency’ such as carboxylation and carbonate synthesis; (6) produce useful chemicals and materials using CO 2 as a reactant or feedstock; (7) use CO 2 for energy recovery while reducing its emissions to the atmosphere by sequestration; (8) recycle CO 2 as C-source for chemicals and fuels using renewable sources of energy; and (9) convert CO 2 under either bio-chemical or geologic-formation conditions into “new fossil” energies. Several cases are discussed in more detail. The first example is tri-reforming of methane versus the well-known CO 2 reforming over transition metal catalysts such as supported Ni catalysts. Using CO 2 along with H 2O and O 2 in flue gases of power plants without separation, tri-reforming is a synergetic combination of CO 2 reforming, steam reforming and partial oxidation and it can eliminate carbon deposition problem and produces syngas with desired H 2/CO ratios for industrial applications. The second example is a CO 2 “molecular basket” as CO 2-selective high-capacity adsorbent which was developed using mesoporous molecular sieve MCM-41 and polyethylenimine (PEI). The MCM41-PEI adsorbent has higher adsorption capacity than either PEI or MCM-41 alone and can be used as highly CO 2-selective adsorbent for gas mixtures without the pre-removal of moisture because it even enhances CO 2 adsorption capacity. The third example is synthesis of dimethyl carbonate using CO 2 and methanol, which demonstrates the environmental benefit of avoiding toxic phosgene and a processing advantage. The fourth example is the application of supercritical CO 2 for extraction and for chemical processing where CO 2 is either a solvent or a co-reactant, or both. The CO 2 utilization contributes to enhancing sustainability, since various chemicals, materials, and fuels can be synthesized using CO 2, which should be a sustainable way in the long term when renewable sources of energy are used as energy input.

Design, Synthesis, and Conformational Dynamics of a Gated Molecular Basket

We have developed a synthesis and examined the conformational behavior and recognition properties of dynamic molecular containers 1-3. As follows from the 1H NMR dilution, diffusion NMR, and vapor pressure osmometry measurements, compound 1 has a low affinity for intermolecular aggregation and is mostly present in monomeric form in dilute chloroform solutions. Inspecting the O-H chemical shift resonances of 1, 3, and model compound 4 as a function of temperature afforded the deltadelta/deltaT coefficients of 17.0, 17.3, and 4.7 ppb K(-1), respectively. In combination with the results from variable temperature 1H NMR and IR measurements, the existence of conformers of 1 and 3 in equilibrium, each having a different extent of hydrogen bonding, was confirmed. Molecular mechanics calculations suggested 1a as the most favorable conformation, with three additional conformers, 1b, 1c, and 1d, populating local energy minima. Further optimization of each of the four conformers using semiempirical PM3 and ab initio (HF/6-31G) methods allowed a determination of their relative free energies and the corresponding Boltzmann population distributions which were heavily weighted toward 1a. A computed composite IR spectrum of a fraction-weighted mixture of the conformers of 1 reproduced the experimentally observed IR spectrum in its structural features, leading to a conclusion that conformer 1a indeed dominates the equilibrium. The egg-shaped cavity of 1 (136.6 angstroms3) is complementary in size, shape, and electrostatic potential to chloroform (74.9 angstroms3). A single-crystal X-ray study of 2 revealed a disordered chloroform molecule positioned inside the cavitand along its C3 axis.

Influence of Moisture on CO2 Separation from Gas Mixture by a Nanoporous Adsorbent Based on Polyethylenimine-Modified Molecular Sieve MCM-41

Adsorption separation of CO2 from simulated flue gas containing CO2, O2, and N2 with and without moisture was investigated using a novel nanoporous adsorbent based on polyethylenimine (PEI)-modified mesoporous molecular sieve MCM-41 in a flow system. The CO2 adsorption capacity and CO2 separation selectivity of MCM-41 were greatly improved by loading PEI into its nanosized pore channels, which made the resulting adsorbent operating like a “molecular basket” for CO2. CO2 adsorption capacity of the MCM-41-PEI adsorbent for the simulated moist flue gas was higher than that for the simulated dry flue gas. CO2 separation selectivity of the MCM-41-PEI adsorbent was also improved in the presence of moisture when compared with those in the dry gas condition. The influence of moisture concentrations in the simulated flue gas on the CO2 adsorption separation performance was also examined. The results of adsorption/desorption separation cycles showed that the MCM-41-PEI adsorbent was stable over 10 cycles of adsorption/desorption operations. The hydrothermal stability of the “molecular basket” adsorbent was better than that of the MCM-41 support alone.

Adsorption separation of carbon dioxide from flue gas of natural gas-fired boiler by a novel nanoporous “molecular basket” adsorbent

A novel nanoporous CO 2 “molecular basket” adsorbent has been developed and applied in the separation of CO 2 from the flue gas of a natural gas fired boiler. The nanoporous CO 2 “molecular basket” adsorbent was prepared by uniformly dispersing polyethylenimine (PEI) into the pores of mesoporous molecular sieve MCM-41. The use of MCM-41 and PEI had a synergetic effect on the CO 2 adsorption. The rates of CO 2 adsorption/desorption of PEI were also greatly improved. Adsorption separation results showed that CO 2 was selectively separated from simulated flue gas and flue gas of a natural gas-fired boiler by using this novel adsorbent. The adsorbent adsorbed very little N 2, O 2 and CO in the flue gas. Moisture had a promoting effect on the adsorption separation of CO 2 from flue gas. The adsorbent simultaneously adsorbed CO 2 and NO x from flue gas. The adsorbed amount of CO 2 was around 3000 times larger than that of NO x . The adsorbent was stable in several cyclic adsorption/desorption operations. However, very little NO x desorbed after adsorption indicating the need for pre-removal of NO x from flue gas before capture of CO 2 by this novel adsorbent.

Adsorption separation of CO<SUB align=right>2 from simulated flue gas mixtures by novel CO<SUB align=right>2 "molecular basket" adsorbents

Adsorption separation of CO2 from simulated flue gas mixtures containing CO2, O2, and N2 by using a novel CO2 "molecular basket" adsorbent was investigated in a flow adsorption separation system. The novel CO2 "molecular basket" adsorbents were developed by synthesising mesoporous molecular sieve MCM-41 and modifying it with polyethylenimine (PEI). The influence of operation conditions, including feed flow rate, temperature, feed CO2 concentration, and sweep gas flow rate, on the CO2 adsorption/desorption separation performance and CO2 breakthrough were examined. The CO2 adsorption capacity was 91.0 ml (STP)/g-PEI, which was 27 times higher than that of the MCM-41 alone. Further, the adsorbent showed separation selectivity of greater than 1000 for CO2/N2 ratio and approximately 180 for CO2/O2, which are significantly higher than those of the MCM-41, zeolites, and activated carbons. Cyclic adsorption/desorption measurements showed that the CO2 "molecular basket" adsorbent was stable at 75°C. However, the CO2 "molecular basket" adsorbent was not stable when the operation temperature was higher than 100°C.

Preparation and characterization of novel CO 2 “molecular basket” adsorbents based on polymer-modified mesoporous molecular sieve MCM-41

Novel CO 2 “molecular basket” adsorbents were prepared by synthesizing and modifying the mesoporous molecular sieve of MCM-41 type with polyethylenimine (PEI). The MCM-41-PEI adsorbents were characterized by X-ray powder diffraction (XRD), N 2 adsorption/desorption, thermal gravimetric analysis (TGA) as well as the CO 2 adsorption/desorption performance. This paper reports on the effects of preparation conditions (PEI loadings, preparation methods, PEI loading procedures, types of solvents, solvent/MCM-41 ratios, addition of additive, and Si/Al ratios of MCM-41) on the CO 2 adsorption/desorption performance of MCM-41-PEI. With the increase in PEI loading, the surface area, pore size and pore volume of the PEI-loaded MCM-41 adsorbent decreased. When the PEI loading was higher than 30 wt.%, the mesoporous pores began to be filled with PEI and the mesoporous molecular sieve MCM-41 showed a synergetic effect on the adsorption of CO 2 by PEI. At PEI loading of 50 wt.% in MCM-41-PEI, the highest CO 2 adsorption capacity of 246 mg/g-PEI was obtained, which is 30 times higher than that of the MCM-41 and is about 2.3 times that of the pure PEI. Impregnation was found to be a better method for the preparation of MCM-41-PEI adsorbents than mechanical mixing method. The adsorbent prepared by a one-step impregnation method had a higher CO 2 adsorption capacity than that of prepared by a two-step impregnation method. The higher the Si/Al ratio of MCM-41 or the solvent/MCM-41 ratio, the higher the CO 2 adsorption capacity. Using polyethylene glycol as additive into the MCM-41-PEI adsorbent increased not only the CO 2 adsorption capacity, but also the rates of CO 2 adsorption/desorption. A simple model was proposed to account for the synergetic effect of MCM-41 on the adsorption of CO 2 by PEI.

Novel Polyethylenimine-Modified Mesoporous Molecular Sieve of MCM-41 Type as High-Capacity Adsorbent for CO2 Capture

The objective of the work presented here is to develop a nanoporous solid adsorbent which can serve as a “molecular basket” for CO2 in the condensed form. Polyethylenimine (PEI)-modified mesoporous molecular sieve of MCM-41 type (MCM-41-PEI) has been prepared and tested as a CO2 adsorbent. The physical properties of the adsorbents were characterized by X-ray powder diffraction (XRD), N2 adsorption/desorption, and thermogravimetric analysis (TGA). The characterizations indicated that the structure of the MCM-41 was preserved after loading the PEI, and the PEI was uniformly dispersed into the channels of the molecular sieve. The CO2 adsorption/desorption performance was tested in a flow system using a microbalance to track the weight change. The mesoporous molecular sieve had a synergetic effect on the adsorption of CO2 by PEI. A CO2 adsorption capacity as high as 215 mg-CO2/g-PEI was obtained with MCM-41-PEI-50 at 75 °C, which is 24 times higher than that of the MCM-41 and is even 2 times that of the pure ...

Adjusting the binding thermodynamics, kinetics, and orientation of guests within large synthetic hydrophobic pockets.

Kinetic analysis of the host guest complexation of a large, open molecular basket and a highly complementary adamantoid guest reveals that for these types of systems a dissociative mechanism is in operation. Hence, the resident adamantyl guest must completely vacate the cavity before another guest molecule can move in to replace it. As a result of the rigid nature of the host, the energy barrier to this process is relatively high, about 16 kcal mol(-1) at room temperature. Modifying the cavity of the host by dangling either a methyl group or a hydroxyl group from the portal rim alters the thermodynamic binding profile of these hosts. (1)H NMR shift data analysis also reveals that these functional groups can adjust the orientation that monosubstituted guests adopt within the cavity. Additionally, (1)H NMR studies of the binding of (E)1,4-dibromoadamantane allow the observation of two energetically similar diastereomeric complexes. An examination of this guest binding to the three hosts reveals that the interchange between the isomers is much faster than the entry and egression rates, and that the functional groups at the rim of each cavity influence both the rates of reorientation and the equilibrium relating the isomers.

C-H...X--R (X = Cl, Br, and I) hydrogen bonds drive the complexation properties of a nanoscale molecular basket.

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTC-H···X−R (X = Cl, Br, and I) Hydrogen Bonds Drive the Complexation Properties of a Nanoscale Molecular BasketCorinne L. D. Gibb, Edwin D. Stevens, and Bruce C. GibbView Author Information Department of Chemistry University of New Orleans New Orleans, Louisiana 70148 Cite this: J. Am. Chem. Soc. 2001, 123, 24, 5849–5850Publication Date (Web):May 26, 2001Publication History Received29 December 2000Revised11 April 2001Published online26 May 2001Published inissue 1 June 2001https://doi.org/10.1021/ja005931pCopyright © 2001 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1477Altmetric-Citations112LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (49 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Cavities,Conformation,Group 17 compounds,Iodine,Noncovalent interactions Get e-Alerts

Mechanisms for auto-inhibition and forced product release in glycine N-methyltransferase: crystal structures of wild-type, mutant R175K and S-adenosylhomocysteine-bound R175K enzymes

Glycine N-methyltransferase ( S-adenosyl- l-methionine: glycine methyltransferase, EC 2.1.1.20; GNMT) catalyzes the AdoMet-dependent methylation of glycine to form sarcosine ( N-methylglycine). Unlike most methyltransferases, GNMT is a tetrameric protein showing a positive cooperativity in AdoMet binding and weak inhibition by S-adenosylhomocysteine (AdoHcy). The first crystal structure of GNMT complexed with AdoMet showed a unique “closed” molecular basket structure, in which the N-terminal section penetrates and corks the entrance of the adjacent subunit. Thus, the apparent entrance or exit of the active site is not recognizable in the subunit structure, suggesting that the enzyme must possess a second, enzymatically active, “open” structural conformation. A new crystalline form of the R175K enzyme has been grown in the presence of an excess of AdoHcy, and its crystal structure has been determined at 3.0 Å resolution. In this structure, the N-terminal domain (40 amino acid residues) of each subunit has moved out of the active site of the adjacent subunit, and the entrances of the active sites are now opened widely. An AdoHcy molecule has entered the site occupied in the “closed” structure by Glu15 and Gly16 of the N-terminal domain of the adjacent subunit. An AdoHcy binds to the consensus AdoMet binding site observed in the other methyltransferase. This AdoHcy binding site supports the glycine binding site (Arg175) deduced from a chemical modification study and site-directed mutagenesis (R175K). The crystal structures of WT and R175K enzymes were also determined at 2.5 Å resolution. These enzyme structures have a closed molecular basket structure and are isomorphous to the previously determined AdoMet-GNMT structure. By comparing the open structure to the closed structure, mechanisms for auto-inhibition and for the forced release of the product AdoHcy have been revealed in the GNMT structure. The N-terminal section of the adjacent subunit occupies the AdoMet binding site and thus inhibits the methyltransfer reaction, whereas the same N-terminal section forces the departure of the potentially potent inhibitor AdoHcy from the active site and thus facilitates the methyltransfer reaction. Consequently GNMT is less active at a low level of AdoMet concentration, and is only weakly inhibited by AdoHcy. These properties of GNMT are particularly suited for regulation of the cellular AdoMet/AdoHcy ratio.

Pyroelectric superlattices based on copolysiloxane/calix[8]arene alternate layer LB films

The pyroelectric effect in alternate layer LB superlattices incorporating interacting lamellae of carboxyl and amino moieties has been investigated. Three distinct systems have been studied, namely (a) a copolysiloxane carboxylic acid/aliphatic amine alternate multilayer, (b) a calix[8]arene carboxylic acid/calix[8]arene amine alternate multilayer, and (c) a hybrid system consisting of a copolysiloxane carboxylic acid/calix[8]arene amine multilayer. In all superlattices there occurs proton transfer between acid and amine moieties leading to a temperature-dependent electric polarisation which is reinforced by added contributions from dipolar reorientation effects. This paper describes how the pyroelectric coefficient can be enhanced by utilising a hybrid alternate layer LB film superlattice containing a 50:50 copolysiloxane substituted with polar aromatic side-chains terminated with carboxyl groups, which is co-deposited with a calix[8]arene molecular basket substituted with primary amine groups. The pyroelectric activity of the copolysiloxane acid/calix[8]arene amine system is substantially higher and stable over a wider temperature range than either of the other two superlattices, giving a pyroelectric coefficient of 10.2 μC m −2 K −1 at 25°C.