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1. Product selectivity in photo-oxygenation reaction of cyclohexenes due to orientational isomerism induced by host cavitand Octa Acid

   https://doi.org/10.1016/j.jphotochem.2025.116481  

   Gupta, Shipra; Ramamurthy, V (November 2025, Journal of Photochemistry and Photobiology A: Chemistry)

   “Orientational isomerism” is a concept necessary for deeper understanding of the selective reactivities in a host-guest system. This concept has been rarely explored in the context of supramolecular host guest chemistry. We designed a model system including four cyclohexene derivatives and a water-soluble host Octa Acid (OA), with hydrophobic inner cavity. The overall length of the guest molecules (~ 12 Å) was limited by manipulating the alkyl substituents at 1- and 4-positions on the cyclohexene ring. 1D 1H /2D COSY and NOESY NMR and photooxygenation reaction were used to understand the observations with this model system. Specific packaging or “orientational isomerism” of each guest molecule, induced by the host OA led to specific, in one case enhanced product selectivity. With this model system we show the important role of “orientational isomerism” in explaining enhanced product selectivity in a host-guest supramolecular system. 

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2. Structure, Dynamics, and Reactivity of Encapsulated Molecules in Restricted Spaces: Arylazoisoxazoles within an Octa Acid Capsule

   https://doi.org/10.1021/acs.langmuir.4c01996  

   Sunny, Amal Sam; Cleven, Elliott C; Kumar, Pravesh; Venkataramani, Sugumar; Walls, Jamie D; Ramamurthy, Vaidhyanathan (August 2024, Langmuir)

   In this study, a well-defined organic capsule assembled from two octa acid (OA) molecules acting as host and select arylazoisoxazoles (AAIO) acting as guests were employed to demonstrate that confined molecules have restricted freedom that translates into reaction selectivity in both ground and excited states. The behavior of these AAIO guests in confined capsules was found to be different from that found in both crystals, where there is very little freedom, and in isotropic solvents, where there is complete freedom. Through one-dimensional (1D) and two-dimensional (2D) 1H NMR spectroscopic experiments, we have established a relationship between structure, dynamics and reactivity of molecules confined in an OA capsule. Introduction of CF3 and CH3 substitution at the 4-position of the aryl group of AAIO reveals that in addition to space confinement, weak interactions between the guest and the OA capsule control the dynamics and reactivity of guest molecules. 1H NMR studies revealed that there is a temperature-dependence to guest molecules tumbling (180° rotation along the capsular short axis) within an OA capsule. While 1H NMR points to the occurrence of tumbling motion, MD simulations and simulation of the temperature-dependent NMR signals provide an insight into the mechanism of tumbling within OA capsules. Thermal and photochemical isomerization of AAIO were found to occur within an OA capsule just as in organic solvents. The observed selectivity noted during thermal and photo induced isomerization of OA encapsulated AAIOs can be qualitatively understood in terms of the well-known concepts due to Bell−Evans− Polanyi (BEP principle), Hammond and Zimmerman. 

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3. A new supramolecular bonding motif involving NH bonds of ammonium salts and macrocycles derived from platinum corners and butadiynediyl linkers

   https://doi.org/10.1039/D2DT02680E  

   Collins, Brenna K.; Bhuvanesh, Nattamai; Gladysz, John A. (November 2022, Dalton Transactions)

   CuI catalyzes reactions of cis -(R 2 C(CH 2 PPh 2 ) 2 )Pt(CCCCH) 2 and cis -(R 2 C(CH 2 PPh 2 ) 2 )PtI 2 in secondary amine solvents HNR’ 2 to give the title adducts [(R 2 C(CH 2 PPh 2 ) 2 )Pt(CCCC)] 4 ·(H 2 NR’ 2 + I − ) n (R/R’/ n = Me/Et/1, Me/((CH 2 CH 2 ) 2 O) 0.5 /3, Et/Et/1, Et/CH 2 CHCH 2 /1; 92–42%). Crystal structures of these or closely related species establish folded Pt 4 cores containing ammonium cation guests, with NH/ and NCH/CC hydrogen bonding. DOSY NMR experiments show that the host/guest relationship can be maintained in solution. 

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4. Rational Control of Self‐Recognition of Macroionic γ‐Cyclodextrin by Host‐Guest Interaction with Super‐Chaotropic Borate Cluster Ions

   https://doi.org/10.1002/cplu.202000536  

   Chen, Jiahui; Luo, Jiancheng; Bekele, Selemon; Tsige, Mesfin; Liu, Tianbo (October 2020, ChemPlusChem)

   Abstract We report a feasible method to control self‐recognition during the self‐assembly of a hydrophilic macroion, phosphate‐functionalized γ‐cyclodextrin (γ‐CD‐P), though host‐guest interactions. We confirmed that γ‐CD‐P can form a host‐guest complex with a super‐chaotropic anion, namely the B₁₂F₁₂²⁻borate cluster, by using NMR spectroscopy and isothermal titration calorimetry. The loaded γ‐CD‐P, which has a higher charge density, can be distinguished from the uncomplexed γ‐CD‐P, leading to self‐sorting behavior during the self‐assembly process, confirmed by the formation of two types of individual supramolecular structures (R_hof ca. 57 nm and 18 nm, determined by light scattering) instead of hybrid structures in mixed dilute solution. This self‐recognition behavior is accounted for by the difference in intermolecular electrostatic interactions arising from the loading. 

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5. Fusion peptide from SARS-2 spike transforms into a wedge inserted in a bilayer leaflet, and thins the opposite leaflet

   Steven R Van Doren, Benjamin Scott (February 2022, Biophysical journal)

   Activation of SARS-CoV-2 Spike deploys its fusion peptide to a membrane of the host cell to infect it. NMR in solution demonstrates that this fusion peptide transforms from intrinsic disorder in solution into a wedge-shaped structure inserted in bilayered micelles. According to NOEs and proximity to a nitroxide spin label deep in the membrane mimic, the globular fold of three helices contrasts the open, extended conformations observed in compact prefusion states. In the hydrophobic, narrow end of the wedge, helices 1 and 2 contact the fatty acyl chains of phospholipids. 50 of the resulting paramagnetic NMR relaxation enhancements and 6 lipid-protein NOEs provided ambiguous distances as collective variables (colvars) to bias and guide MD simulations. Simulations in NAMD using the CHARMM36 forcefield included colvars for 130 medium- and long-range NOEs to maintain the equilibrium structure. In the gently NMR-biased simulations, the fusion peptide maintained its insertion of helices 1 and 2 within a single leaflet while helix 3 remained exposed. A cation occasionally visited the anionic side chains in the loop joining helices 2 and 3 or at the N-terminal end of helix 1. The unoccupied leaflet is thinned and distorted opposite the fusion peptide.The thinning could be related to the fusion peptide promoting formation of the hemi-fusion intermediate in the process of viral-cell fusion. Supported by NSF Rapid award 2030473. 

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