Chemical Science Blog

In this Chemical Science Edge article, Michael Ward, Christopher Hunter and co-workers at the Department of Chemistry, University of Sheffield report tunable host-guest chemistry of an octanuclear cobalt(II) coordination cage with a range of organic guests. The resultant non-covalently bound guests have very different binding constants in different pH environments, making binding tunable and completely reversible.   

The team found that the coordination cage provided a good guest space for a range of organics, including substituted adamantanes. Substitutents which could be charged, such as carboxylic acids and amines, were particularly useful to drive and rationalize the binding observed. NMR also played a powerful role in this work. In this context, the paramagnetic complex host resulted in clear distinguishable signals, differentiating free or bound cage species, and thereby acting as a shift reagent. This effect could also be quantified, allowing the strength and extent of the host-guest binding to be shown. 

Coordination cage and NMR study of effect on chemical shift and binding extent with changing pH

An example with potentially high importance is described using 1-aminoadamantane, a prescription drug used to treat Parkinson’s disease and as an influenza anti-viral. Complete reversible binding was achieved with a binding constant difference of three orders of magnitude between the protonated and neutral forms of the drug. Similar behaviour was observed with other N-basic materials like nicotine and the anaesthetic substituted imidazole drug, demotidine. Mechanistic considerations were further examined with experiments using carboxylic acids, where solvation effects were also shown to play a key role.  

In this article, a practical example of pH controlled, reversible guest binding of functional organic molecules is described. An elegant and practical application of NMR spectroscopy is also shown. Applications for delivery and controlled release of suitable drug, catalyst or other functional organic material cannot be far off.   

Read this Chemical Science Edge article today!   

pH dependent binding of guests in the cavity of a polyhedral coordination cage: reversible uptake and release of drug molecules
William Cullen, Simon Turega, Christopher A. Hunter and Michael D. Ward.,
doi 10.1039/c4sc02090a

We are delighted to share with you the top 25 most downloaded articles in Chemical Science from April–June 2014.

Top 25 most downloaded Chemical Science articles for Q2 2014

Novel hole transporting materials based on triptycene core for high efficiency mesoscopic perovskite solar cells
Anurag Krishna, Dharani Sabba, Hairong Li, Jun Yin, Pablo P. Boix, Cesare Soci, Subodh G. Mhaisalkar and Andrew C. Grimsdale
DOI: 10.1039/C4SC00814F

Copper catalyzed Heck-like cyclizations of oxime esters
Adele Faulkner, Nicholas J. Race, James S. Scott and John F. Bower
DOI: 10.1039/C4SC00652F

Enantioselective direct α-alkylation of cyclic ketones by means of photo-organocatalysis
Elena Arceo, Ana Bahamonde, Giulia Bergonzini and Paolo Melchiorre
DOI: 10.1039/C4SC00315B

Oxygen nucleophiles as reaction partners in photoinduced, copper-catalyzed cross-couplings: O-arylations of phenols at room temperature
Yichen Tan, José María Muñoz-Molina, Gregory C. Fu and Jonas C. Peters
DOI: 10.1039/C4SC00368C

Efficient C–H bond activations via O2 cleavage by a dianionic cobalt(II) complex
Andy I. Nguyen, Ryan G. Hadt, Edward I. Solomon and T. Don Tilley
DOI: 10.1039/C4SC00108G

Sunlight photocatalyzed regioselective β-alkylation and acylation of cyclopentanones
Megumi Okada, Takahide Fukuyama, Keiichi Yamada, Ilhyong Ryu, Davide Ravelli and Maurizio Fagnoni
DOI: 10.1039/C4SC01072H

Copper catalyzed direct alkenylation of simple alkanes with styrenes
Yefeng Zhu and Yunyang Wei
DOI: 10.1039/C4SC00093E

Transition metal-catalyzed direct nucleophilic addition of C–H bonds to carbon–heteroatom double bonds
Xi-Sha Zhang, Kang Chen and Zhang-Jie Shi
DOI: 10.1039/C3SC53115E

Evaluating metal–organic frameworks for natural gas storage
Jarad A. Mason, Mike Veenstra and Jeffrey R. Long
DOI: 10.1039/C3SC52633J

Selective radical amination of aldehydic C(sp2)–H bonds with fluoroaryl azides via Co(II)-based metalloradical catalysis: synthesis of N-fluoroaryl amides from aldehydes under neutral and nonoxidative conditions
Li-Mei Jin, Hongjian Lu, Yuan Cui, Christopher L. Lizardi, Thiago N. Arzua, Lukasz Wojtas, Xin Cui and X. Peter Zhang
DOI: 10.1039/C4SC00697F

Catalytic enantioselective synthesis of 2-aryl-chromenes
Bi-Shun Zeng, Xinyi Yu, Paul W. Siu and Karl A. Scheidt
DOI: 10.1039/C4SC00423J

Dialkylbiaryl phosphines in Pd-catalyzed amination: a user’s guide
David S. Surry and Stephen L. Buchwald
DOI: 10.1039/C0SC00331J

Frustrated Lewis pair chemistry of carbon, nitrogen and sulfur oxides
Douglas W. Stephan and Gerhard Erker
DOI: 10.1039/C4SC00395K

Carbon–fluorine bond cleavage in fluoroarenes via a niobium(III) imido complex: from stoichiometric to catalytic hydrodefluorination
Thomas L. Gianetti, Robert G. Bergman and John Arnold
DOI: 10.1039/C4SC00006D
From themed collection Celebrating the 2014 RSC Prize and Award Winners

Rh(III)-catalyzed C–H functionalization/aromatization cascade with 1,3-dienes: a redox-neutral and regioselective access to isoquinolines
Dongbing Zhao, Fabian Lied and Frank Glorius
DOI: 10.1039/C4SC00628C

Iodoarene-catalyzed fluorination and aminofluorination by an Ar-I/HF·pyridine/mCPBA system
Satoru Suzuki, Tomohiro Kamo, Kazunobu Fukushi, Takaaki Hiramatsu, Etsuko Tokunaga, Toshifumi Dohi, Yasuyuki Kita and Norio Shibata
DOI: 10.1039/C3SC53107D

Complete stereodivergence in the synthesis of 2-amino-1,3-diols from allenes
Christopher S. Adams, R. David Grigg and Jennifer M. Schomaker
DOI: 10.1039/C4SC01214C

An ExBox [2]catenane
Michal Juríček, Jonathan C. Barnes, Nathan L. Strutt, Nicolaas A. Vermeulen, Kala C. Ghooray, Edward J. Dale, Paul R. McGonigal, Anthea K. Blackburn, Alyssa-Jennifer Avestro and J. Fraser Stoddart
DOI: 10.1039/C4SC00488D
From themed collection Celebrating the 2014 RSC Prize and Award Winners

Aluminium–ligand cooperation promotes selective dehydrogenation of formic acid to H2 and CO2
T. W. Myers and L. A. Berben
DOI: 10.1039/C4SC01035C

Synthesis, electronic structure and reactivity of bis(imino)pyridine iron carbene complexes: evidence for a carbene radical
Sarah K. Russell, Jordan M. Hoyt, Suzanne C. Bart, Carsten Milsmann, S. Chantal E. Stieber, Scott P. Semproni, Serena DeBeer and Paul J. Chirik
DOI: 10.1039/C3SC52450G

Non-directed allylic C–H acetoxylation in the presence of Lewis basic heterocycles
Hasnain A. Malik, Buck L. H. Taylor, John R. Kerrigan, Jonathan E. Grob, K. N. Houk, J. Du Bois, Lawrence G. Hamann and Andrew W. Patterson
DOI: 10.1039/C3SC53414F

Rethinking the term “pi-stacking”
Chelsea R. Martinez and Brent L. Iverson
DOI: 10.1039/C2SC20045G
From themed collection Physical Chemistry

Stereoselective allylboration of imines and indoles under mild conditions. An in situ E/Z isomerization of imines by allylboroxines
Rauful Alam, Arindam Das, Genping Huang, Lars Eriksson, Fahmi Himo and Kálmán J. Szabó
DOI: 10.1039/C4SC00415A

Cobaltate anion couples terminal dienes with trifluoroacetic anhydride: a direct fluoroacylation of 1,3-dienes
Benjamin L. Kohn and Tomislav Rovis
DOI: 10.1039/C4SC00743C

Phosphorescent nematic hydrogels and chromonic mesophases driven by intra- and intermolecular interactions of bridged dinuclear cyclometalated platinum(II) complexes
Xin-Shan Xiao, Wei Lu and Chi-Ming Che
DOI: 10.1039/C4SC00143E

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All of the referee-recommended articles below are free to access until 15th October 2014

Understanding nano-impacts: impact times and near-wall hindered diffusion
Enno Kätelhön and Richard G. Compton  
Chem. Sci., 2014, Advance Article
DOI: 10.1039/C4SC02288B, Edge Article

Comprehensive study of carbon dioxide adsorption in the metal–organic frameworks M2(dobdc) (M = Mg, Mn, Fe, Co, Ni, Cu, Zn)
Wendy L. Queen, Matthew R. Hudson, Eric D. Bloch, Jarad A. Mason, Miguel I. Gonzalez, Jason S. Lee, David Gygi, Joshua D. Howe, Kyuho Lee, Tamim A. Darwish, Michael James, Vanessa K. Peterson, Simon J. Teat, Berend Smit, Jeffrey B. Neaton, Jeffrey R. Long and Craig M. Brown  
Chem. Sci., 2014, Advance Article
DOI: 10.1039/C4SC02064B, Edge Article

Bifunctional nanoparticle–SILP catalysts (NPs@SILP) for the selective deoxygenation of biomass substrates
Kylie L. Luska, Jennifer Julis, Eli Stavitski, Dmitri N. Zakharov, Alina Adams and Walter Leitner  
Chem. Sci., 2014, Advance Article
DOI: 10.1039/C4SC02033B, Edge Article

End functional ROMP polymers via degradation of a ruthenium Fischer type carbene
Amit A. Nagarkar and Andreas F. M. Kilbinger  
Chem. Sci., 2014, Advance Article
DOI: 10.1039/C4SC02242D, Edge Article

If you have ever been stuck in a crowd, you may have noticed that your range of motion and the speed at which you can move is highly dependent not only on whether you are leaving a sports game or a pop concert, but also on where you are positioned in the mass of people. The same is true of a solution of molecules – the molecules that are located in the bulk of the solution would be expected to have different properties from those that are surface-immobilised. This is especially true if we consider the supramolecular association of a guest within a host, where thermodynamics and kinetics play an important role in whether a complex will form or not.

Pablo Ballester and his team from the Institute of Chemical Research of Catalonia (ICIQ) set out to study this phenomenon and prove whether or not there was a difference in the binding of a guest, pyridine N-oxide derivatives, with a host molecule, α,α,α,α-calix[4]pyrrole, in bulk solution or tethered to a gold surface. To achieve this goal, the team employed a surface plasmon resonance (SPR) technique, a technique that is sensitive to the accumulation or release of mass, and has been used previously to study large biomolecular systems in real time.

It was found that thermodynamically, binding events between two molecules are similar in bulk solution and at an interface. This is perhaps not surprising, as the changes in enthalpy and entropy to a calix[4]pyrrole in bulk solution or tethered to a surface will be similar; therefore so too will be the binding event. Differences were observed, however, when considering the kinetic aspect of binding, such that binding was much slower when the molecule was on a surface than when it was in bulk solution. This was attributed to the presence of a matrix hindering the motion of the surface-bound calix[4]pyrrole, thereby providing a barrier to complexation.

This work presents an interesting method of studying the binding events that occur in the different regions of a solution. It also shows that the events that occur on the macroscale, such as in a crowd of people, can, in some cases, be analogous to those that occur on the molecular level.

Read this HOT ChemSci article in full!

Binding of calix[4]pyrroles to pyridine N-oxides probed with surface plasmon resonance
Louis Adriaenssens, Josep Lluís Acero Sánchez, Xavier Barril, Ciara K. O’Sullivan and Pablo Ballester
Chem. Sci., 2014, Edge Article
DOI: 10.1039/C4SC01745E

Biography

Anthea Blackburn is a guest web writer for Chemical Science. Anthea is a graduate student hailing from New Zealand, studying at Northwestern University in the US under the tutelage of Prof. Fraser Stoddart (a Scot), where she is exploiting supramolecular chemistry to develop multidimensional systems and study the emergent properties that arise in these superstructures. When time and money allow, she is ambitiously attempting to visit all 50 US states before graduation.