Trans Isomerization Research Articles

Two Metal–Organic Frameworks with Structural Varieties Derived from cis–trans Isomerism Nodes and Effective Detection of Nitroaromatic Explosives

Two novel porous MOFs, [Zn5(DpImDC)2(DMF)4(H2O)3]·H2O·DMF (JLU-MOF48, H5DpImDC = 2-(3,5-dicarboxyphenyl)-1H-imidazole-4,5-dicarboxylic acid) and [Co5(DpImDC)2(DMF)4(H2O)6]·DMF (JLU-MOF49), have been solvothermally synthesized by using a ligand consisting of a 4,5-imidazoledicarboxylic acid part and an isophthalic acid part. Two compounds have similar structures and connections, but with significant differences in symmetry (monoclinic and orthorhombic) due the cis–trans isomerism in a mononuclear metal node. Moreover, JLU-MOF48 exhibits notable luminescent properties and owns outstanding performance for detecting nitroaromatic explosives, especially for 2,4,6-trinitrophenol (Ksv = 1.0 × 105 M–1).

Extended Impact of Pin1 Catalytic Loop Phosphorylation Revealed by S71E Phosphomimetic

Pin1 is a two-domain human protein that catalyzes the cis–trans isomerization of phospho-Ser/Thr–Pro (pS/T–P) motifs in numerous cell-cycle regulatory proteins. These pS/T–P motifs bind to Pin1's peptidyl-prolyl isomerase (PPIase) domain in a catalytic pocket, between an extended catalytic loop and the PPIase domain core. Previous studies showed that post-translational phosphorylation of S71 in the catalytic loop decreases substrate binding affinity and isomerase activity. To define the origins for these effects, we investigated a phosphomimetic Pin1 mutant, S71E-Pin1, using solution NMR. We find that S71E perturbs not only its host loop but also the nearby PPIase core. The perturbations identify a local network of hydrogen bonds and salt bridges that is more extended than previously thought, and includes interactions between the catalytic loop and the α2/α3 turn in the PPIase core. Explicit-solvent molecular dynamics simulations and phylogenetic analysis suggest that these interactions act as conserved “latches” between the loop and PPIase core that enhance binding of phosphorylated substrates, as they are absent in PPIases lacking pS/T–P specificity. Our results suggest that S71 is a hub residue within an electrostatic network primed for phosphorylation, and may illustrate a common mechanism of phosphorylation-mediated allostery.

Study of Trans Fatty Acid Formation in Oil by Heating Using Model Compounds.

The intake of trans fatty acids (TFAs) in foods changes the ratio of low density lipoprotein (LDL) to high density lipoprotein (HDL) cholesterol in blood, which causes cardiovascular disease. TFAs are formed by trans isomerization of unsaturated fatty acids (UFAs). The most recognized formation mechanisms of TFAs are hydrogenation of liquid oil to form partially hydrogenated oil (PHO,) and biohydrogenation of UFAs to form TFA in ruminants. Heating oil also forms TFAs; however, the mechanism of formation, and the TFA isomers formed have not been well investigated. In this study, the trans isomerization mechanism of unsaturated fatty acid formation by heating was examined using the model compounds oleic acid, trioleate, linoleic acid, and trilinoleate for liquid plant oil. The formation of TFAs was found to be suppressed by the addition of an antioxidant and argon gas. Furthermore, the quantity of formed TFAs correlated with the quantity of formed polymer in trioleate heated with air and oxygen. These results suggest that radical reactions form TFAs from UFAs by heating. Furthermore, trans isomerization by heating oleic acid and linoleic acid did not change the original double bond positions. Therefore, the distribution of TFA isomers formed was very simple. In contrast, the mixtures of TFA isomers formed from PHO and ruminant UFAs are complicated because migration of double bonds occurs during hydrogenation and biohydrogenation. These findings suggest that trans isomerization by heating is executed by a completely different mechanism than in hydrogenation and biohydrogenation.

THE EFFECT OF INTRAMOLECULAR H-BOND INTERACTIONS IN THE ISOMERIZATION PROCESS IN AMINO ACIDS

The effect of intramolecular hydrogen bond (H-bond) interactions in the cis - trans isomerization of the amino acids such as, cysteine, serine, threonine and valine have been studied using density functional theory method. Our calculations have shown that the geometrical parameters are significantly changed during the isomerization process. This is due to the presence of intramolecular H-bonds within main chain or in between side chain and main chain. The barrier energies have been calculated for isomerization process in all the amino acids, which is more for cysteine and less for valine. The Fourier decomposition potential has been obtained for the above named amino acids which show that V2 potential has higher value. The vibrational frequency analysis has been carried out for the cis and trans forms of cysteine, serine, threonine and valine amino acids and the results are discussed.

Photo-Switchable Nanomechanical Systems Comprising a Nanocontainer (Montmorillonite) and Light-Driven Molecular Jack (Azobenzene-Imidazolium Ionic Liquids) as Drug Delivery Systems; Synthesis, Characterization, and in Vitro Release Studies.

In this work, photoresponsive nanomechanical systems were prepared through the intercalation of positively charged photoswitching molecular jacks (azobenzene ionic liquids, Azo-ILs) within montmorillonite (MMT) layers (MMT@Azo-ILs). The study shows that MMT@Azo-ILs are photosensitive and the synthesized molecular jacks could change the basal distances of MMT layers upon UV irradiation. These changes come from changes in the structure and geometry of Azo molecules (i.e., cis-trans isomerization) between clay layers upon UV irradiation. The prepared photoresponsive nanomechanical systems were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDX), field-emission scanning electron microscope (FE-SEM). Moreover, the in vitro release studies were performed in different conditions (upon UV irradiation and darkness) in pH 5.8 at 34 ± 1 °C, and it was found that the release rates from drug loaded MMT@Azo-ILs were higher upon UV irradiation in comparison with the release rates in darkness. According to the release studies, the prepared photoresponsive carriers might be considered as an excellent potential candidate in order to formulate smart sunscreens.

Conserving Coherence and Storing Energy during Internal Conversion: Photoinduced Dynamics of cis- and trans-Azobenzene Radical Cations.

Light harvesting via energy storage in azobenzene has been a key topic for decades and the process of energy distribution over the molecular degrees of freedom following photoexcitation remains to be understood. Dynamics of a photoexcited system can exhibit high degrees of nonergodicity when it is driven by just a few degrees of freedom. Typically, an internal conversion leads to the loss of such localization of dynamics as the intramolecular energy becomes statistically redistributed over all molecular degrees of freedom. Here, we present a unique case where the excitation energy remains localized even subsequent to internal conversion. Strong-field ionization is used to prepare cis- and trans-azobenzene radical cations on the D1 surface with little excess energy at the equilibrium neutral geometry. These D1 ions are preferably formed because in this case D1 and D0 switch place in the presence of the strong laser field. The postionization dynamics are dictated by the potential energy landscape. The D1 surface is steep downhill along the cis/trans isomerization coordinate and toward a common minimum shared by the two isomers in the region of D1/D0 conical intersection. Coherent cis/trans torsional motion along this coordinate is manifested in the ion transients by a cosine modulation. In this scenario, D0 becomes populated with molecules that are energized mainly along the cis-trans isomerization coordinate, with the kinetic energy above the cis-trans interconversion barrier. These activated azobenzene molecules easily cycle back and forth along the D0 surface and give rise to several periods of modulated signal before coherence is lost. This persistent localization of the internal energy during internal conversion is provided by the steep downhill potential energy surface, small initial internal energy content, and a strong hole-lone pair interaction that drives the molecule along the cis-trans isomerization coordinate to facilitate the transition between the involved electronic states.

Gold-Catalyzed Solid-Phase Synthesis of 3,4-Dihydropyrazin-2(1H)-ones: Relevant Pharmacophores and Peptide Backbone Constraints.

Here, we report the efficient solid-phase synthesis of N-propargyl peptides using Fmoc-amino acids and propargyl alcohol as key building blocks. Gold-catalyzed nucleophilic addition to the triple bond induced C-N bond formation, which triggered intramolecular cyclization, yielding 1,3,4-trisubstituted-5-methyl-3,4-dihydropyrazin-2(1H)-ones. Conformations of acyclic and constrained peptides were compared using a two-step conformer distribution analysis at the molecular mechanics level and density functional theory. The results indicated that the incorporation of heterocyclic molecular scaffold into a short peptide sequence adopted extended conformation of peptide chain. The amide bond adjacent to the constraint did not show significant preference for either cis or trans isomerism. Prepared model compounds demonstrate a proof of concept for gold-catalyzed polymer-supported synthesis of variously substituted 3,4-dihydropyrazin-2(1H)-ones for applications in drug discovery and peptide backbone constraints.

How Rhodopsin Tunes the Equilibrium between Protonated and Deprotonated Forms of the Retinal Chromophore.

Rhodopsin is a photoactive G-protein-coupled receptor (GPCR) that converts dim light into a signal for the brain, leading to eyesight. Full activation of this GPCR is achieved after passing through several steps of the protein's photoactivation pathway. Key events of rhodopsin activation are the initial cis-trans photoisomerization of the covalently bound retinal moiety followed by conformational rearrangements and deprotonation of the chromophore's protonated Schiff base (PSB), which ultimately lead to full activation in the meta II state. PSB deprotonation is crucial for achieving full activation of rhodopsin; however, the specific structural rearrangements that have to take place to induce this pKa shift are not well understood. Classical molecular dynamics (MD) simulations were employed to identify intermediate states after the cis-trans isomerization of rhodopsin's retinal moiety. In order to select the intermediate state in which PSB deprotonation is experimentally known to occur, the validity of the intermediate configurations was checked through an evaluation of the optical properties in comparison with experiment. Subsequently, the selected state was used to investigate the molecular factors that enable PSB deprotonation at body temperature to obtain a better understanding of the difference between the protonated and the deprotonated state of the chromophore. To this end, the deprotonation reaction has been investigated by applying QM/MM MD simulations in combination with thermodynamic integration. The study shows that, compared to the inactive 11-cis-retinal case, trans-retinal rhodopsin is able to undergo PSB deprotonation due to a change in the conformation of the retinal and a consequent alteration in the hydrogen-bond (HB) network in which PSB and the counterion Glu113 are embedded. Besides the retinal moiety and Glu113, also two water molecules as well as Thr94 and Gly90 that are related to congenital night blindness are part of this essential HB network.

Role of Cysteine Residues in Regulation of Peptidyl-prolyl cis-trans Isomerase Activity of Wheat Cyclophilin TaCYPA-1.

The wheat cyclophilin, TaCYPA-1, shows peptidyl-prolyl cis-trans isomerase (PPIase) activity. However, the significance of different cysteine residues in regulation of PPIase activity of this protein has not been investigated. The main objective of this study was to analyze the role of different disulphide linkages in redox mechanisms that modulate the PPIase activity of TaCYPA-1. Site-directed mutants of TaCYPA-1 were generated by substituting cysteine residues at positions -40 and -122 with serine and -126 with proline. The recombinant proteins were expressed in Escherichia coli and purified. The effect of Cu2+ and N-ethylmaleimide was studied on PPIase activity of the purified recombinant cyclophilins for analyzing the role of different cysteine residues in the modulation of enzyme activity. The changes in secondary structure of TaCYPA-1 and its mutants were analysed by recording far UV CD spectra. The effect of different cysteine substitutions on thermotolerance of E. coli was studied by monitoring the cell growth at 47 °C after 2 h, 3 h and 5 h of heat stress. The catalytic efficiencies (Kcat/Km) of TaCYPA-1C40S (0.37 X 106 M-1 s-1) and TaCYPA- 1C122S (0.31 X 106 M-1 s-1) were significantly lower as compared to the native TaCYPA-1 (1.33 X 106 M-1 s-1), whereas Kcat/Km of the double mutant TaCYPA-1C40S/C122S was significantly higher (2.36 X 106 M-1 s-1). Compared to the wild-type TaCYPA-1, the different mutants also showed differential sensitivity to Cu2+. Furthermore, the results of this study also revealed that despite lacking PPIase activity, the mutant TaCYPA-1C126P was able to confer partial protection against heat stress. This study revealed that mutation of different cysteine residues in TaCYPA-1 results in differential effect on PPIase activity. It was also observed that of the two pairs of cysteine residues i.e. Cys40/Cys168 and Cys122/Cys126, the latter appears to play major role in redox regulation of TaCYPA-1. The mutant TaCYPA-1C126P, though lacking PPIase activity, was able to impart partial tolerance to heat stress in E. coli, suggesting other functions besides cis to trans isomerisation. This study, therefore, provides new insights into the regulation of plant cyclophilins.

Naphthalene formation pathways from phenyl radical via vinyl radical (C2H3) and vinylacetylene (C4H4): computational studies on reaction mechanisms and kinetics

The reaction mechanisms of PAH formation from phenyl radical (C6H5) to naphthalene via C2H3 (C2H3-Path) and C4H4 (C4H4-Path) were investigated by the G3(MP2, CC) method. The hydrogen abstraction, ring closure, cis–trans isomerization, and disproportionation reactions were considered, as well as their occurred sequence. The results showed that H-abstraction reactions occurred more easily than H-dissociation reactions. The cis–trans conversion reactions in sub-routes of C2H3-Path and C4H4-Path provided the largest barriers of 51, 53, and 36 kcal/mol along their routes, which illustrated that the cis–trans isomerization was energetically costly in the PAH formation process. The entrance barriers of C2H2-Path, C2H3-Path, and C4H4-Path are 6, 8, and 3 kcal/mol, respectively, which indicates that it is easier to add C4H4 to C6H5 compared with adding C2H2 to C2H3. C2H3 additions were highly exothermic with reaction energies greater than 110 kcal/mol, and compared with C2H2 additions, C2H3 additions were irreversible. However, C2H2-Path, C2H3-Path and C4H4-Path involved energy barriers of 20, 32, and 36 kcal/mol, respectively. Considering the high temperature in combustion and the approximate concentrations of C2H3 and C4H4, all three of these pathways could lead to naphthalene in some combustion flames.

Polymorphism in cis–trans Muconic Acid Crystals and the Role of C–H···O Hydrogen Bonds

Cis–trans isomerization of muconic acid is an important component of various chemical syntheses. Despite the existence of three geometric muconic acid isomers, little atomically precise information is actually known of their structures. In this work, the complete crystal structures of cis–cis, cis–trans, and trans–trans muconic acid were determined via single-crystal X-ray diffraction and then further analyzed using terahertz vibrational spectroscopy and solid-state density functional theory. In addition to being the first reported crystal structure for cis–trans muconic acid, two polymorphs of this species were discovered, with one exhibiting a two-dimensional hydrogen-bonding pattern stabilized through C–H···O interactions. Terahertz spectroscopy aided in polymorph characterization and also provided clear evidence of a hydrated crystalline species that grows only from one of the cis–trans muconic acid polymorphs. Ab initio simulations showed that while the typical end-to-end hydrogen-bonding motif found...

A combined theoretical and thermal analysis study on the solid state linkage isomerization of Ni(II)-nitrite complexes with ethylenediamine derivatives

Solid state stepwise nitro–nitrito linkage isomerization of trans-[dinitrobis(ethylenediamine)nickel(II)], [Ni(en)2(NO2)2] (N,N-en), trans-[dinitrobis(N,N′-dimethylethylenediamine)nickel(II)], [Ni(N,N′-dmen)2(NO2)2] (N,N-dmen), and trans-[dinitritobis(N,N-dimethylethylenediamine)nickel(II)], [Ni(N,N-dmen)2(ONO)2] (O,O-udmen) were investigated by performing non-isothermal differential scanning calorimetry (DSC) analyses and the thermodynamic and thermokinetic parameters of isomerization were determined using DSC curves. Both N,N-en and N,N-dmen DSC curves show an endothermic peak at elevated temperatures, attributed to dinitro-to-dinitrito linkage isomerization. Similar exothermic peaks were observed in the cooling cycle, assigned to the reverse dinitrito-to-dinitro isomerization. The O,O-udmen isomer is more stable than the corresponding dinitro one at ambient temperatures, but an exothermic dinitrito-to-dinitro isomerization occurs upon cooling down to −70 °C and reverts endothermically to dinitrito isomer upon heating up to ambient temperature. The overlapping DSC peaks associated with stepwise linkage isomerization were resolved using nonlinear fitting method. The peak temperature and the enthalpy changes of linkage isomerization are inversely dependent on the steric hindrance provided by diamine ligands, which increases in the order udmen > dmen > en. The results showed that the steric factor of the co-ligands also influences the kinetic parameters of isomerization, so that more bulky ligand substituent leads to higher isomerization rate constants. A DFT and TD-DFT calculations have been carrid out on both dinitro complexes of this investigation .

Photochemistry and Photophysics of Enediyne-Cored Polyphenylene Dendrimers

Abstract Two kinds of enediyne-cored polyphenylene dendrimer (mGn, pGn) were prepared as pure cis and trans isomers. In comparison to parent enediyne with no dendron substituents, the dendrimers exhibited highly efficient fluorescence emission with mutual cis–trans isomerization. Along with an increase in the generation of dendrons, decrease of Φiso and shortening of τS were observed, suggesting that dendrons affect cis–trans photoisomerization and deactivation from excited singlet state.

Mechanism, ab initio calculations and microkinetics of hydrogenation, hydrodeoxygenation, double bond migration and cis–trans isomerisation during hydrotreatment of C6 secondary alcohol species and ketones

Hydrotreatment of secondary hexanone and hexanol, and primary hexene species was investigated over the sulphide-form NiMo/γ-Al2O3 heterogeneous catalyst within the process temperature range 200–275°C. The mechanistic microkinetic model for a three-phase slurry reactor was developed, comprising the mass transfer flux from the dispersed gaseous H2 bubbles to liquid solvent bulk, the external convective resistance at catalytic surface interface, material lattice adsorption and desorption, and intrinsic conversion kinetics (homogeneous and catalysed). It reported the reaction rate constants and activation energies for ketones and alcohols. Intermediate alkene isomers were identified and quantified, demonstrating the same reactive selectivity regardless of the cascade reactant compound. Furthermore, the C6 olefin isomerisation studies under pressurised hydrogen and nitrogen (up to 9.5 times slower) atmospheres indicated a similar equilibrium distribution of the concentrations of 1-hexene, cis-2-hexene, trans-2-hexene, cis-3-hexene and trans-3-hexene. The position of the oxygen-containing (heteroatom) functional group on an aliphatic hydrocarbon chain exhibited only a minor kinetic effect on parallel and serial hydrogenation or de-hydroxylation steps. Quantum chemical (QC) calculations utilising density functional theory (DFT) computational framework were performed to elucidate the mechanism of hydrodeoxygenation (HDO). The competing main and side pathways were considered in calculating transition state barriers. Simulations showed a very good agreement with measured experimental data. Deoxygenation valorisation routes were examined as they are vital upon converting ligno-cellulosic biomass resources and for the production of the bio-based platform oxygenates in bio-refineries. Hexose(s), for example, are (poly)alcohols, the monomer building blocks of cellulose, which is besides lignin and hemicellulose the principal wood, grass and straw constituent.

Theoretical study on the thermal cis - Trans isomerization of novel acylhydrazone photoswitches

Quantum chemical calculations of a potent class of photoswitches acylhydrazones have been carried out with the goal to describe their thermal cis → trans isomerization. The effects of substituents, in particular their number, position and nature of the substituents (electron donating/withdrawing groups (EDGs/EWGs)), on activation energies incorporating solvent effects have been systematically researched with the ultimate goal to illuminate the isomerization process. Our results show that most parameters are highly dependent on the substitution pattern on the crucial positions (R1 and R2 position) of the backbone fragment, which in turn has a significant impact on the absorption spectra, the energy levels of molecular orbitals, the transition properties for the trans/cis isomers, the half-lives τ1/2 and the rate constants for the thermal cis → trans isomerization of the compounds. In summary, both relative strength of the donor/accept groups and solvent polarity have significant impact on the electric properties. Finally, the nature of the transition state(s) and its dependence on substituents and the environment are discussed. An ingenious approach to the construction of reaction path was realized, and energy barriers were determined from two-dimensional potential energy surfaces of the ground states.

Anomalous optical properties of photoactive cholesteric liquid crystal doped with single-walled carbon nanotubes

ABSTRACTOptical transmission and selective reflection data are reported for suspensions of single-walled carbon nanotubes (CNTs) in photoactive nematic material ZhK-440 with a mesogenic chiral dopant M5. At small concentrations of CNTs (C ≈ 0.01–0.05%), the preferential localisation of CNTs at oily sticks (cholesteric topological defects) and suppression of the network of oily streaks by CNTs were observed. At the same time, the optical density D was shown to be essentially non-linear and a minimum at certain concentration of CNTs, C ≈ 0.05–0.08%, was observed. This anomalous behaviour was explained by the presence of the structural transition from the loose (ramified) aggregates with highly anisotropic shape (oriented along the anchoring direction on rubbed polyvinyl alcohol) to the compact aggregates with denser packing. The location of this minimum, as well as the selective reflection maximum (helical pitch), was sensitive to partially reversible UV-induced trans–cis–trans isomerisation effects. The UV-controlled helical pitch variation was shown to be only slightly affected by introduction of CNTs.

Ultrafast isomerization in a difluoroboryl-coordinated molecular switch

Molecular switches based on light-induced isomerization cycles are promising materials for sensors and biomedical applications. Understanding the details of the isomerization photocycle and identifying the nuclear coordinates involved in the photoreaction are relevant topics. Here we characterize the cis→trans and trans→cis isomerization of a new type of BF2-coordinated azo-dye molecular switch by pump-probe spectroscopy. While cis→trans isomerization is ultrafast and proceeds via a conical intersection, the trans→cis photocycle is more complex and involves at least three reaction channels. Finally, we employ the vibrational wavepackets accompanying isomerization to infer information on the nuclear degrees of freedom involved in the photoreaction.

Conformational fluctuations in a green fluorescent protein-like Akane family protein: a high-pressure fluorescence study at 0.1–700 MPa

ABSTRACT We have investigated conformational fluctuations in a new green fluorescent protein(GFP)-like protein rb-Akane found in a red-brown-colored octocoral, Scleronephthya gracillima (Kuekenthal)), with high pressure fluorescence spectroscopy at 0.1–700 MPa. Besides the green fluorescence at 510 nm, two red fluorescence peaks are observed at 590 and 629 nm, the relative intensity of which varies reversibly with pressure. The phenomenon is interpreted as representing the cis–trans isomerization of the chromophore accompanied by the conformational transition between two sub-states of the red fluorescence form of rb-Akane. The two sub-states are separated only marginally in free energy (ΔG 0 = 1.9 ± 0.4 kJ mol−1), but significantly in partial molar volume (ΔV 0 = −19.8 ± 1.4 ml mol−1) at 0.1 MPa (pH 7.5, 25°C). Above 500 MPa, the fluorescence at λ max 629 nm undergoes another reversible change with pressure, showing the onset of unfolding.

Analytical considerations for determination of the microstructures of sulfur‐cured solution styrene − butadiene rubbers

AbstractThe microstructures of solution styrene − butadiene copolymer (S‐SBR) vulcanizates were analyzed using liquid H NMR spectroscopy and transmission Fourier transform IR spectroscopy, and the results were compared with the raw S‐SBRs. The microstructures of the cured and raw S‐SBRs were different because of the pendent group formed by the cure accelerator and cis − trans isomerization. The styrene and trans‐1,4‐unit contents of the cured S‐SBRs were larger than those of the raw S‐SBRs, whereas the 1,2‐unit contents of the cured S‐SBRs were on the whole smaller than those of the raw S‐SBRs. The results of NMR and IR spectroscopy were also compared. Considering the analytical error ranges and consistency of the analysis results, a proper analytical method and process are suggested. NMR analysis results had narrower error ranges and better correlation than IR spectroscopy results. It was was found to be acceptable that the cis‐1,4‐unit contents were obtained by subtracting the trans‐1,4‐unit contents from the 1,4‐unit contents determined by NMR analysis. © 2017 Society of Chemical Industry

Metal-centred azaphosphatriptycene gear with a photo- and thermally driven mechanical switching function based on coordination isomerism

Metal ions can serve as a centre of molecular motions due to their coordination geometry, reversible bonding nature and external stimuli responsiveness. Such essential features of metal ions have been utilized for metal-mediated molecular machines with the ability to motion switch via metallation/demetallation or coordination number variation at the metal centre; however, motion switching based on the change in coordination geometry remain largely unexplored. Herein, we report a PtII-centred molecular gear that demonstrates control of rotor engagement and disengagement based on photo- and thermally driven cis–trans isomerization at the PtII centre. This molecular rotary motion transmitter has been constructed from two coordinating azaphosphatriptycene rotators and one PtII ion as a stator. Isomerization between an engaged cis-form and a disengaged trans-form is reversibly driven by ultraviolet irradiation and heating. Such a photo- and thermally triggered motional interconversion between engaged/disengaged states on a metal ion would provide a selector switch for more complex interlocking systems.