What Happens Without Nickel? Cyclization Reactions of Ethylene with Ethanedithial and Related Molecules

We present a computational study of the mechanism of the formation of 6-member heterocycles through the binding of ethylene to oxaldehyde, ethanedithial, and 2-thioxoacetaldehyde. This process is related to the olefin separation technology by metal dithiolenes and dioxolenes, being the formation of those heterocycles the main decomposition route. We also present a benchmark of 26 density functionals (spanning hybrid, double-hybrid, range-separated, semilocal, and local functionals) related to CCSD(T)/CBS reference values. Both the cyclization reaction and the isomerization of the cyclic product are included in the benchmark. The best functional among those tested for these reactions is ωB97XD, and the effect of the basis set is also investigated for it. © 2017 Wiley Periodicals, Inc.

Involving Synergy of Green Light and Acidic Responses in Control of Unimolecular Multicolor Luminescence

Conversion of multicolor luminescence is one of desirable goals in study and development of next-generation molecular emitters, whereas involving visible light into the control of the above-mentioned ability has been poorly addressed due to the need of a relatively complicate molecular design. In this work, we present a novel dyad with a linkage of 4-piperazinyl-1,8-naphthalimide and cyanostyryl-modified azulene moiety, upon which the luminescence signal can be orthogonally controlled by protonation and green light irradiation. The superior features of the protonation induced excited state energy alteration, followed by green light driven photoisomerization led to a progressive luminescent color conversion among blue, yellow and green at the single molecular level. This strategy may bring in novel insights for preparing advanced function-integrated optoelectronic materials.

Enantioselective Synthesis of Chiral Cyclopent-2-enones by Nickel-Catalyzed Desymmetrization of Malonate Esters

The enantioselective synthesis of highly functionalized chiral cyclopent‐2‐enones by the reaction of alkynyl malonate esters with arylboronic acids is described. These desymmetrizing arylative cyclizations are catalyzed by a chiral phosphinooxazoline/nickel complex, and cyclization is enabled by the reversible E/Z isomerization of alkenylnickel species. The general methodology is also applicable to the synthesis of 1,6‐dihydropyridin‐3(2H)‐ones.

Light-Induced Bending of Needle-Like Crystals of Naphthylvinylbenzoxazole Triggered by trans-cis Isomerization

New diarylethene derivatives containing benzoxazole (NBO) and benzothiazole (NBT) have been synthesized. Light-induced trans-cis isomerization of NBO and NBT took place in crystals, and only induced the needle-like crystals of NBO to bend backwards away from the UV light source. The movement of the atoms was deemed to take place during the isomerization of NBO; hence, strain would be produced and accumulated rapidly in the surface of crystals exposed to UV light. The uniform release of strain led to the bending of needle-like crystals. The light-induced trans-cis isomerization efficiency of NBT was too low to drive the motion of crystals, which might have originated from the large repulsion between naphthyl and benzothiazole. These results provide a new platform for the transformation of light energy into mechanical energy in molecular crystals through the unimolecular photochemical reaction of diarylethene derivatives.

A Nontemplated Route to Macrocyclic Dibridgehead Diphosphorus Compounds: Crystallographic Characterization of a "Crossed-Chain" Variant of in/out Stereoisomers

Reactions of (O=)PH(OCH2 CH3 )2 and BrMg(CH2 )m CH=CH2 (4.9-3.2 equiv; m=4 (a), 5 (b), 6 (c)) give the dialkylphosphine oxides (O=)PH[(CH2 )m CH=CH2 ]2 (2 a-c; 77-81 % after workup), which are treated with NaH and then α,ω-dibromides Br(CH2 )n Br (0.49-0.32 equiv; n=8 (a'), 10 (b'), 12 (c'), 14 (d')) to yield the bis(trialkylphosphine oxides) [H2 C=CH(CH2 )m ]2 P(=O)(CH2 )n (O=)P[(CH2 )m CH=CH2 ]2 (3 ab', 3 bc', 3 cd', 3 ca'; 79-84 %). Reactions of 3 bc' and 3 ca' with Grubbs' first-generation catalyst and then H2 /PtO2 afford the dibridgehead diphosphine dioxides (4 bc', 4 ca'; 14-19 %, n'=2m+2); 31 P NMR spectra show two stereoisomeric species (ca. 70:30). Crystal structures of two isomers of the latter are obtained, out,out-4 ca' and a conformer of in,out-4 ca' that features crossed chains, such that the (O=)P vectors appear out,out. Whereas 4 bc' resists crystallization, a byproduct derived from an alternative metathesis mode, (CH2 )12 P(=O)(CH2 )12 (O=)P(CH2 )12 , as well as 3 ab' and 3 bc', are structurally characterized. The efficiencies of other routes to dibridgehead diphosphorus compounds are compared.

2-(Hydroxyimino)aldehydes: Photo- and Physicochemical Properties of a Versatile Functional Group for Monomer Design

In the context of our research on stimuli-responsive polymers bearing the 2-(hydroxyimino)aldehyde (HIA) group, we have explored the photochemical behavior and physicochemical properties of a number of HIAs. Interpretation of the experimental data is supported by quantum mechanical calculations. HIAs are expected to undergo photoisomerization, chelate metal ions, yield hydrogen-bonded dimers or oligomers, exhibit relatively low pK_a s, and form >C=NO^. radicals through OH hydrogen abstraction or oxidation of the oximate ion. Besides the well-established E/Z oxime photoisomerism, we observed a Norrish-Yang cyclization resulting in cyclobutanol oximes, to our knowledge not previously described in the literature. The acidity, bond dissociation enthalpies, and electrochemical properties of the HIAs are compared with literature data of simple oximes. The results are discussed in relation to the many potential applications for HIAs, with emphasis on the synthesis of novel HIA-containing responsive polymers.

Synthesis of Alkanethiolate-Capped Metal Nanoparticles Using Alkyl Thiosulfate Ligand Precursors: A Method to Generate Promising Reagents for Selective Catalysis

Evaluation of metal nanoparticle catalysts functionalized with well-defined thiolate ligands can be potentially important because such systems can provide a spatial control in the reactivity and selectivity of catalysts. A synthetic method utilizing Bunte salts (sodium S-alkylthiosulfates) allows the formation of metal nanoparticles (Au, Ag, Pd, Pt, and Ir) capped with alkanethiolate ligands. The catalysis studies on Pd nanoparticles show a strong correlation between the surface ligand structure/composition and the catalytic activity and selectivity for the hydrogenation/isomerization of alkenes, dienes, trienes, and allylic alcohols. The high selectivity of Pd nanoparticles is driven by the controlled electronic properties of the Pd surface limiting the formation of Pd⁻alkene adducts (or intermediates) necessary for (additional) hydrogenation. The synthesis of water soluble Pd nanoparticles using ω-carboxylate-S-alkanethiosulfate salts is successfully achieved and these Pd nanoparticles are examined for the hydrogenation of various unsaturated compounds in both homogeneous and heterogeneous environments. Alkanethiolate-capped Pt nanoparticles are also successfully synthesized and further investigated for the hydrogenation of various alkynes to understand their geometric and electronic surface properties. The high catalytic activity of activated terminal alkynes, but the significantly low activity of internal alkynes and unactivated terminal alkynes, are observed for Pt nanoparticles.

A Chromium Hydroxide/MIL-101(Cr) MOF Composite Catalyst and Its Use for the Selective Isomerization of Glucose to Fructose

A metal-organic framework (MOF)-based catalyst, chromium hydroxide/MIL-101(Cr), was prepared by a one-pot synthesis method. The combination of chromium hydroxide particles on and within Lewis acidic MIL-101 accomplishes highly selective conversion of glucose to fructose in the presence of ethanol, matching the performance of optimized Sn-containing Lewis acidic zeolites. Differently from zeolites, NMR spectroscopy studies with isotopically labeled molecules demonstrate that isomerization of glucose to fructose on this catalyst, proceeds predominantly via a proton transfer mechanism.

NiH-Catalyzed Reductive Relay Hydroalkylation: A Strategy for the Remote C(sp3 )-H Alkylation of Alkenes

The terminal-selective, remote C(sp³ )-H alkylation of alkenes was achieved by a relay process combining NiH-catalyzed hydrometalation, chain walking, and alkylation. This method enables the construction of unfunctionalized C(sp³ )-C(sp³ ) bonds under mild conditions from two simple feedstock chemicals, namely olefins and alkyl halides. The practical value of this transformation is further demonstrated by the large-scale and regioconvergent alkylation of isomeric mixtures of olefins at low catalyst loadings.

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.

Phosphate-Catalyzed Succinimide Formation from Asp Residues: A Computational Study of the Mechanism

Aspartic acid (Asp) residues in proteins and peptides are prone to the non-enzymatic reactions that give biologically uncommon l-β-Asp, d-Asp, and d-β-Asp residues via the cyclic succinimide intermediate (aminosuccinyl residue, Suc). These abnormal Asp residues are known to have relevance to aging and pathologies. Despite being non-enzymatic, the Suc formation is thought to require a catalyst under physiological conditions. In this study, we computationally investigated the mechanism of the Suc formation from Asp residues that were catalyzed by the dihydrogen phosphate ion, H₂PO₄⁻. We used Ac–l-Asp–NHMe (Ac = acetyl, NHMe = methylamino) as a model compound. The H₂PO₄⁻ ion (as a catalyst) and two explicit water molecules (as solvent molecules stabilizing the negative charge) were included in the calculations. All of the calculations were performed by density functional theory with the B3LYP functional. We revealed a phosphate-catalyzed two-step mechanism (cyclization–dehydration) of the Suc formation, where the first step is predicted to be rate-determining. In both steps, the reaction involved a proton relay mediated by the H₂PO₄⁻ ion. The calculated activation barrier for this mechanism (100.3 kJ mol⁻¹) is in reasonable agreement with an experimental activation energy (107 kJ mol⁻¹) for the Suc formation from an Asp-containing peptide in a phosphate buffer, supporting the catalytic mechanism of the H₂PO₄⁻ ion that is revealed in this study.

Application of MALDI-TOF/TOF-MS for relative quantitation of α- and β-Asp7 isoforms of amyloid-β peptide

It is known that aspartic acid isomerization process plays a role in aging processes and may be used as a marker for aging of natural materials. As for Alzheimer's disease, the most abundant modification in the peptide profile is the aspartate isomerization of amyloid-β. Liquid chromatography-electrospray ionization-mass spectrometry/mass spectrometry-based approaches with Collision Induced Dissociation (CID) or Electron Capture Dissociation (ECD) fragmentation provide a good and precise method for the relative quantitation of iso- to normal amyloid-β peptides but require additional time consuming steps. In this study, MALDI-TOF/TOF-matrix-assisted laser desorption ionization time-of-flight tandem mass spectrometry (MS) method was developed as a high-throughput approach for the relative quantitation of the isomerized form of the amyloid-β peptide.

Stable NCNgNSi (Ng=Kr, Xe, Rn) Compounds with Covalently Bound C-Ng-N Unit: Possible Isomerization of NCNSi through the Release of the Noble Gas Atom

Although the noble gas (Ng) compounds with either Ng-C or Ng-N bonds have been reported in the literature, compounds containing both bonds are not known. The first set of systems having a C-Ng-N bonding unit is predicted herein through the analysis of stability and bonding in the NCNgNSi (Ng=Kr-Rn) family. While the Xe and Rn inserted analogues are thermochemically stable with respect to all dissociation channels, but for the one producing CNSiN and free Ng, NCKrNSi has another additional three-body dissociation channel, NCKrNSi→CN+Kr+NSi, which is exergonic by -9.8 kcal mol^-1 at 298 K. This latter dissociation can be hindered by lowering the temperature. Moreover, the NCNgNSi→Ng+CNSiN dissociation is also kinetically prohibited by a quite high free energy barrier ranging from 25.2 to 39.3 kcal mol^-1 , with a gradual increase in going from Kr to Rn. Therefore, these compounds are appropriate candidates for experimental realization. A detailed bonding analysis by employing natural bond orbital, electron density, energy decomposition, and adaptive natural density partitioning analyses indicates that both Ng-N and C-Ng bonds in the title compounds are covalent in nature. In fact, the latter analysis indicates the presence of delocalized 3c-3e σ-bond within the C-Ng-N moiety and a totally delocalized 5c-2e σ-bond in these compounds. This is an unprecedented bonding characteristic in the sense that the bonding pattern in Ng inserted compounds is generally represented as the presence of covalent bond in one side of Ng, and the ionic interaction in the other side. Further, the dissociation of Ng from NCNgNSi facilitates the formation of a higher energy isomer of NCNSi, CNSiN, which cannot be formed from bare NCNSi as such, because of the very high free energy barrier associated with the isomeric transformation. Therefore, in the presence of Ng atoms it might be possible to detect the high energy isomer.

Isomerisation of Liquid-Crystalline Tristriazolotriazines

Star-shaped discotic liquid crystals with columnar superstructures constitute a highly interesting class of organic materials. Phenyl-substituted tris[1,2,4]triazolo-[1,3,5]triazine, prepared by a Huisgen reaction of phenyltetrazole and cyanuric chloride, represents an excellent core for discotic liquid crystals (DLCs). The thermal stability is not perfect, at temperatures above the clearing point, a successive threefold isomerization leads to a highly planar, C₃ -symmetrical isomer, which mainly differs in the orientation of the aryl substituents to the centre of the molecule. A new class of discotic liquid crystals has been obtained: Equipped with peripheral alkoxy chains both isomers can form broad thermotropic mesophases. The optical, thermal, and physical properties were investigated by polarized optical microscopy, differential scanning calorimetry, wide-angle X-ray scattering, UV/Vis absorption and fluorescence spectroscopic measurements. The thermotropic properties are decisively affected by the molecular structure of the isomers, isomerisation leads to higher melting points but also the loss or even gain of mesomorphism is observed.

Enantioselective Rhodium-Catalyzed Coupling of Arylboronic Acids, 1,3-Enynes, and Imines by Alkenyl-to-Allyl 1,4-Rhodium(I) Migration

A chiral rhodium complex catalyzes the highly enantioselective coupling of arylboronic acids, 1,3‐enynes, and imines to give homoallylic sulfamates. The key step is the generation of allylrhodium(I) species by alkenyl‐to‐allyl 1,4‐rhodium(I) migration.

Reversible Broad-Spectrum Control of Selective Reflections of Chiral Nematic Phases by Closed-/Open-Type Axially Chiral Azo Dopants

We demonstrate reversible RGB-color photocontrol of a chiral nematic liquid crystal (N*LC) by using newly synthesized closed- and open-type chiral dopants. The photoswitching elements in the dopants are azobenzene units on axially chiral binaphthyl cores. Owing to cis-trans photoisomerization of the azobenzene units, both closed- and open-type compounds showed higher solubility, larger helical twisting power (HTP), and larger changes in HTP than conventional chiral dopants in host LCs. Thus, even at very low dopant concentrations, we successfully controlled the chirality of the induced helical structure of the N*LCs. Consequently, the N*LCs reflected right- and left-handed circularly polarized light (CPL) under a light stimulus. In the N*LCs with closed-type chiral dopants, the RGB-color reflection was reversibly controlled within several seconds. Interestingly, the open-type chiral dopant reversibly inverted CPL with opposite handedness in the near and short-wave IR regions. These novel materials are expected to realize new applications and perspectives in color information and similar technologies.

An efficient process for obtaining prebiotic oligosaccharides derived from lactulose using isomerized and purified whey permeate

BACKGROUND

One of the most promising uses of whey permeate (WP) is the synthesis of prebiotic oligosaccharides. Herein, commercial WP was submitted to chemical isomerization catalysed by sodium borate at an alkaline pH and subsequent purification using anion-exchange resins to remove boron. Subsequently, purified mixtures were used to synthesize prebiotic oligosaccharides using β-galactosidase from Bacillus circulans.

RESULTS

Isomerization of concentrated WP (200 g L^-1 lactose) gave rise to levels of lactulose up to 155.5 g L^-1 after 30 min of reaction (molar ratio of boron/lactose, 1/1; pH 12; 70 °C). Boron was removed from the isomerized WP (IWP) using the combination of a strong acid (IR-120, H⁺ ) and a weak base (IRA-743) anion-exchange resins, reducing its level to <1 ppm, without loss of lactulose. During the transglycosylation reaction of purified IWP (lactose/lactulose ratio, 1/2.4) maximum content of prebiotic compounds was achieved, i.e. 690 g kg^-1 WP after 3 h of reaction.

CONCLUSION

This study shows that combined chemical-enzymatic reactions together with the purification of IWP results in an efficient synthesis of prebiotic oligosaccharides. © 2017 Society of Chemical Industry.

Propensity for cis-Proline Formation in Unfolded Proteins

In unfolded proteins, peptide bonds involving Pro residues exist in equilibrium between the minor cis and major trans conformations. Folded proteins predominantly contain trans-Pro bonds, and slow cis-trans Pro isomerization in the unfolded state is often found to be a rate-limiting step in protein folding. Moreover, kinases and phosphatases that act upon Ser/Thr-Pro motifs exhibit preferential recognition of either the cis- or trans-Pro conformer. Here, NMR spectra obtained at both atmospheric and high pressures indicate that the population of cis-Pro falls well below previous estimates, an effect attributed to the use of short peptides with charged termini in most prior model studies. For the intrinsically disordered protein α-synuclein, cis-Pro populations at all of its five X-Pro bonds are less than 5 %, with only modest ionic strength dependence and no detectable effect of the previously demonstrated interaction between the N- and C-terminal halves of the protein. Comparison to small peptides with the same amino-acid sequence indicates that peptides, particularly those with unblocked, oppositely charged amino and carboxyl end groups, strongly overestimate the amount of cis-Pro.

Photoinduced Trans-to-cis Phase Transition of Polycrystalline Azobenzene at Low Irradiance Occurs in the Solid State

The ability to produce large-scale, reversible structural changes in a variety of materials by photoexcitation of a wide variety of azobenzene derivatives has been recognized for almost two decades. Because photoexcitation of trans-azobenzene produces the cis-isomer in solution, it has generally been inferred that the macroscopic structural changes occurring in materials are also initiated by a similar large-amplitude trans-to-cis isomerization. This work provides the first demonstration that a trans-to-cis photoisomerization occurs in polycrystalline azobenzene, and is consistent with the previously hypothesized nature of the trigger in the photoactuated mechanisms of the materials in question. It is also demonstrated that under low irradiance, trans-to-cis isomerization occurs in the solid (not via a pre-melted phase); and the presence of the cis-isomer thus lowers the melting point of the sample, providing a liquid phase. A variety of experimental techniques were employed, including X-ray diffraction measurements of polycrystalline azobenzene during exposure to laser irradiation and fluorescence measurements of the solid sample. A practical consequence of this work is that it establishes trans-azobenzene as an easily obtainable and well-defined control for monitoring photoinduced structural changes in X-ray diffraction experiments, using easily accessible laser wavelengths.

A Possible Indicator of Oxidative Damage in Smokers: (13Z)-Lycopene?

In vitro, the gaseous phase of cigarette smoke is known to induce both isomerization and degradation of dietary carotenoids, such as β-carotene and lycopene. However, the effects of cigarette smoke on the composition of circulating lycopene in vivo are not well understood. In this study, we examined the lycopene profiles of plasma from non-smokers and smokers. No oxidative intermediates of lycopene that have been observed previously in vitro were detected in the plasma, but evidence of isomerization of the carotenoid was seen. Four geometric forms of lycopene were detected in the plasma of both smokers and non-smokers, namely the (5Z), (9Z), (13Z) and (all-E) forms. The relative amounts of these isomers differed between the two cohorts and there was a significant difference (p < 0.05) between smokers and non-smokers for the ratio of total-Z:all-E lycopene, and in the relative amounts of (13Z) and (all-E)-lycopene. The ratio of (all-E):(13Z)-lycopene was 0.84:1.00 in smokers compared to 1.04:1.00 in non-smokers. In smokers, the (13Z)-isomer was generated in preference to the more thermodynamically stable (5Z) and (9Z)-isomers. This mirrors the scenario seen in vitro, in which the formation of (13Z)-lycopene was the main isomer that accompanied the depletion of (all-E) lycopene, when exposed to cigarette smoke. The results suggest that the relative amount of (13Z)-lycopene could be used as an indicator of oxidative damage to lycopene in vivo.

Efficient Access to All-Carbon Quaternary and Tertiary α-Functionalized Homoallyl-type Aldehydes from Ketones

β,γ-Unsaturated aldehydes with all-carbon quaternary or tertiary α-centers were rapidly assembled from ketones through a unique synthetic operation consisting of 1) C₁ homologation, 2) Lewis acid mediated epoxide-aldehyde isomerization, and 3) electrophilic trapping. The synthetic equivalence of a vinyl oxirane and a β,γ-unsaturated aldehyde is the key concept of this previously undisclosed tactic. Mechanistic studies and labeling experiments suggest that an aldehyde enolate is a crucial intermediate. The homologating carbenoid formation plays a critical role in determining the chemoselectivity.

Protein engineering to increase the potential of a therapeutic antibody Fab for long-acting delivery to the eye

To date, ocular antibody therapies for the treatment of retinal diseases rely on injection of the drug into the vitreous chamber of the eye. Given the burden for patients undergoing this procedure, less frequent dosing through the use of long-acting delivery (LAD) technologies is highly desirable. These technologies usually require a highly concentrated formulation and the antibody must be stable against extended exposure to physiological conditions. Here we have increased the potential of a therapeutic antibody antigen-binding fragment (Fab) for LAD by using protein engineering to enhance the chemical and physical stability of the molecule. Structure-guided amino acid substitutions in a negatively charged complementarity determining region (CDR-L1) of an anti-factor D (AFD) Fab resulted in increased chemical stability and solubility. A variant of AFD (AFD.v8), which combines light chain substitutions (VL-D28S:D30E:D31S) with a substitution (VH-D61E) to stabilize a heavy chain isomerization site, retained complement factor D binding and inhibition potency and has properties suitable for LAD. This variant was amenable to high protein concentration (>250 mg/mL), low ionic strength formulation suitable for intravitreal injection. AFD.v8 had acceptable pharmacokinetic (PK) properties upon intravitreal injection in rabbits, and improved stability under both formulation and physiological conditions. Simulations of expected human PK behavior indicated greater exposure with a 25-mg dose enabled by the increased solubility of AFD.v8.

Oxygen isotope fractionations across individual leaf carbohydrates in grass and tree species

Almost no δ¹⁸ O data are available for leaf carbohydrates, leaving a gap in the understanding of the δ¹⁸ O relationship between leaf water and cellulose. We measured δ¹⁸ O values of bulk leaf water (δ¹⁸ O_LW ) and individual leaf carbohydrates (e.g. fructose, glucose and sucrose) in grass and tree species and δ¹⁸ O of leaf cellulose in grasses. The grasses were grown under two relative humidity (rH) conditions. Sucrose was generally ¹⁸ O-enriched compared with hexoses across all species with an apparent biosynthetic fractionation factor (ε_bio ) of more than 27‰ relative to δ¹⁸ O_LW , which might be explained by isotopic leaf water and sucrose synthesis gradients. δ¹⁸ O_LW and δ¹⁸ O values of carbohydrates and cellulose in grasses were strongly related, indicating that the leaf water signal in carbohydrates was transferred to cellulose (ε_bio  = 25.1‰). Interestingly, damping factor p_ex p_x , which reflects oxygen isotope exchange with less enriched water during cellulose synthesis, responded to rH conditions if modelled from δ¹⁸ O_LW but not if modelled directly from δ¹⁸ O of individual carbohydrates. We conclude that δ¹⁸ O_LW is not always a good substitute for δ¹⁸ O of synthesis water due to isotopic leaf water gradients. Thus, compound-specific δ¹⁸ O analyses of individual carbohydrates are helpful to better constrain (post-)photosynthetic isotope fractionation processes in plants.

Light-Driven Rotation and Pitch Tuning of Self-Organized Cholesteric Gratings Formed in a Semi-Free Film

Cholesteric liquid crystal (CLC) has attracted intensive attention due to its ability to form a periodic helical structure with broad tunability. CLC gratings in open systems are especially promising in sensing and micromanipulation. However, there is still much to learn about the inherent mechanism of such gratings. We investigate the light-driven rotation and pitch-tuning behaviors of CLC gratings in semi-free films which are formed by spin-coating the CLC mixtures onto planarly photoaligned substrates. The doped azobenzene chiral molecular switch supplies great flexibility to realize the continuous grating rotation. The maximum continuous rotational angle reaches 987.8°. Moreover, dependencies of light-driven rotation and pitch tuning on the dopant concentration and exposure are studied. The model of director configuration in the semi-free film is constructed. Precise beam steering and synchronous micromanipulation are also demonstrated. Our work may provide new opportunities for the CLC grating in applications of beam steering, micromanipulation, and sensing.

Shape-Shifting Azo Dye Polymers: Towards Sunlight-Driven Molecular Devices

The development of stimuli-responsive polymers is among the key goals of modern materials science. The structure and properties of such switchable materials can be designed to be controlled via various stimuli, among which light is frequently the most powerful trigger. Light is a gentle energy source that can target materials remotely, and with extremely high spatial and temporal resolution easily and cheaply. Reversible light-control over molecular mechanical properties in particular has in recent years attracted great interest due to potential applications as optical-to-mechanical conversion actuators and 'devices', enabling 'molecular robotic machines'. In this review, some recent examples and emerging trends in this exciting field of research are highlighted, covering a wide variety of polymer hosts that contain azobenzene photo-reversible switches. It is hoped that this review will help stimulate more interest towards the development of light-reversible materials for energy harvesting and conversion, and their successful incorporation into a wide variety of current and future high-tech applications in devices.

Enantioselective Nickel-Catalyzed Intramolecular Allylic Alkenylations Enabled by Reversible Alkenylnickel E/Z Isomerization

Enantioselective nickel‐catalyzed arylative cyclizations of substrates containing a Z‐allylic phosphate tethered to an alkyne are described. These reactions give multisubstituted chiral aza‐ and carbocycles, and are initiated by the addition of an arylboronic acid to the alkyne, followed by cyclization of the resulting alkenylnickel species onto the allylic phosphate. The reversible E/Z isomerization of the alkenylnickel species is essential for the success of the reactions.

Assessing How Correlated Molecular Orbital Calculations Can Perform versus Kohn-Sham DFT: Barrier Heights/Isomerizations

To assess the title issue, 38 hydrogen transfer barrier heights and 38 non-hydrogen transfer barrier heights/isomerizations extracted from extensive databases have been considered, in addition to 4 2 p-isomerization reactions and 6 others for large organic molecules. All Kohn-Sham DFT calculations have employed the popular M06-2X functional, whereas the correlated molecular orbital (MO)-based ones are from single-reference MP2 and CCSD(T) methods. They have all utilized the same basis sets, with raw MO energies subsequently extrapolated to the complete basis set limit without additional cost. MP2 calculations are found to be as cost-effective as DFT ones and often slightly more, while showing a satisfactory accuracy when compared with the reference data. Although the focus is on barrier heights, the results may bear broader implications, in that one may see successes and difficulties of DFT when compared with traditional MO theories for the same data.

Biofuel by isomerizing metathesis of rapeseed oil esters with (bio)ethylene for use in contemporary diesel engines

Rapeseed oil methyl ester (RME) and (bio)ethylene are converted into biofuel with an evenly rising boiling point curve, which fulfills the strict boiling specifications prescribed by the fuel standard EN 590 for modern (petro)diesel engines. Catalyzed by a Pd/Ru system, RME undergoes isomerizing metathesis in a stream of ethylene gas, leading to a defined olefin, monoester, and diester blend. This innovative refining concept requires negligible energy input (60°C) and no solvents and does not produce waste. It demonstrates that the pressing challenge of increasing the fraction of renewables in engine fuel may be addressed purely chemically rather than by motor engineering.

Arylative Intramolecular Allylation of Ketones with 1,3-Enynes Enabled by Catalytic Alkenyl-to-Allyl 1,4-Rhodium(I) Migration

Alkenyl‐to‐allyl 1,4‐rhodium(I) migration enables the generation of nucleophilic allylrhodium(I) species by remote C−H activation. This new mode of reactivity was employed in the diastereoselective reaction of arylboron reagents with substrates containing a 1,3‐enyne tethered to a ketone, to give products containing three contiguous stereocenters. The products can be obtained in high enantioselectivities using a chiral sulfur‐alkene ligand.

A Conversion of Oral Cannabidiol to Delta9-Tetrahydrocannabinol Seems Not to Occur in Humans

Cannabidiol (CBD), a major cannabinoid of hemp, does not bind to CB1 receptors and is therefore devoid of psychotomimetic properties. Under acidic conditions, CBD can be transformed to delta9-tetrahydrocannabinol (THC) and other cannabinoids. It has been argued that this may occur also after oral administration in humans. However, the experimental conversion of CBD to THC and delta8-THC in simulated gastric fluid (SGF) is a highly artificial approach that deviates significantly from physiological conditions in the stomach; therefore, SGF does not allow an extrapolation to in vivo conditions. Unsurprisingly, the conversion of oral CBD to THC and its metabolites has not been observed to occur in vivo, even after high doses of oral CBD. In addition, the typical spectrum of side effects of THC, or of the very similar synthetic cannabinoid nabilone, as listed in the official Summary of Product Characteristics (e.g., dizziness, euphoria/high, thinking abnormal/concentration difficulties, nausea, tachycardia) has not been observed after treatment with CBD in double-blind, randomized, controlled clinical trials. In conclusion, the conversion of CBD to THC in SGF seems to be an in vitro artifact.

Synthesis of Furandicarboxylic Acid Esters From Nonfood Feedstocks Without Concomitant Levulinic Acid Formation

5-Hydroxymethylfurfural (HMF) is a versatile intermediate in biomass conversion pathways. However, the notoriously unstable nature of HMF imposes challenges to design selective routes to chemicals such as furan-2,5-dicarboxylic acid (FDCA). Here, a new strategy for obtaining furans is presented, bypassing the formation of the unstable HMF. Instead of starting with glucose/fructose and thus forming HMF as an intermediate, the new route starts from uronic acids, which are abundantly present in many agro residues such as sugar beet pulp, potato pulp, and citrus peels. Conversion of uronic acids, via ketoaldonic acids, to the intermediate formylfuroic acid (FFA) esters, and subsequently to FDCA esters, proceeds without formation of levulinic acid or insoluble humins. This new route provides an attractive strategy to valorize agricultural waste streams and a route to furanic building blocks without the co-production of levulinic acid or humins.

Chemical and Biological Properties of S-1-Propenyl-l-Cysteine in Aged Garlic Extract

S-1-Propenyl-l-cysteine (S1PC) is a stereoisomer of S-1-Propenyl-l-cysteine (SAC), an important sulfur-containing amino acid that plays a role for the beneficial pharmacological effects of aged garlic extract (AGE). The existence of S1PC in garlic preparations has been known since the 1960's. However, there was no report regarding the biological and/or pharmacological activity of S1PC until 2016. Recently, we performed a series of studies to examine the chemical, biological, pharmacological and pharmacokinetic properties of S1PC, and obtained some interesting results. S1PC existed only in trace amounts in raw garlic, but its concentration increased almost up to the level similar of SAC through aging process of AGE. S1PC showed immunomodulatory effects in vitro and in vivo, and reduced blood pressure in a hypertensive animal model. A pharmacokinetic study revealed that S1PC was readily absorbed after oral administration in rats and dogs with bioavailability of 88-100%. Additionally, S1PC had little inhibitory influence on human cytochrome P450 activities, even at a concentration of 1 mM. Based on these findings, S1PC was suggested to be another important, pharmacologically active and safe component of AGE similar to SAC. In this review, we highlight some results from recent studies on S1PC and discuss the potential medicinal value of S1PC.

Stereoisomerization of Cyclic Silanols

Stereoisomerization of readily available all-cis-1,3,5,7-tetrahydroxy-1,3,5,7-tetraisobutylcyclotetrasiloxane (1 a) was carried out under acidic conditions to afford cis-trans-cis (1 b), all-trans (1 c), and cis-cis-trans (1 d) isomers. The compounds in the reaction mixture could be easily separated into 1 a and a mixture of 1 b, 1 c, and 1 d by the treatment with chloroform. Compounds 1 b, 1 c, and 1 d were further separated and isolated, and each structure was identified. The experimental results indicated that the most plausible mechanism is a substitution reaction at the silicon center via a pentacoordinate intermediate without a cyclic siloxane bond cleavage reaction. The obtained isomer 1 a or 1 b further reacted with dichlorodiphenylsilane in the presence of triethylamine to give syn-type laddersiloxane (2 a) or anti-type laddersiloxane (2 b), respectively.

Hidden Reaction: Mesophilic Cellobiose 2-Epimerases Produce Lactulose

Lactulose (4-O-β-d-galactopyranosyl-d-fructofuranose) is a prebiotic sugar derived from the milk sugar lactose (4-O-β-d-galactopyranosyl-d-glucopyranose). In our study we observed for the first time that known cellobiose 2-epimerases (CEs; EC 5.1.3.11) from mesophilic microorganisms were generally able to catalyze the isomerization reaction of lactose into lactulose. Commonly, CEs catalyze the C2-epimerization of d-glucose and d-mannose moieties at the reducing end of β-1,4-glycosidic-linked oligosaccharides. Thus, epilactose (4-O-β-d-galactopyranosyl-d-mannopyranose) is formed with lactose as substrate. So far, only four CEs, exclusively from thermophilic microorganisms, have been reported to additionally catalyze the isomerization reaction of lactose into lactulose. The specific isomerization activity of the seven CEs in this study ranged between 8.7 ± 0.1 and 1300 ± 37 pkat/mg. The results indicate that very likely all CEs are able to catalyze both the epimerization as well as the isomerization reaction, whereby the latter is performed at a comparatively much lower reaction rate.

Photocyclic behavior of rhodopsin induced by an atypical isomerization mechanism

Vertebrate rhodopsin (Rh) contains 11-cis-retinal as a chromophore to convert light energy into visual signals. On absorption of light, 11-cis-retinal is isomerized to all-trans-retinal, constituting a one-way reaction that activates transducin (G_t) followed by chromophore release. Here we report that bovine Rh, regenerated instead with a six-carbon-ring retinal chromophore featuring a C¹¹=C¹² double bond locked in its cis conformation (Rh6mr), employs an atypical isomerization mechanism by converting 11-cis to an 11,13-dicis configuration for prolonged G_t activation. Time-dependent UV-vis spectroscopy, HPLC, and molecular mechanics analyses revealed an atypical thermal reisomerization of the 11,13-dicis to the 11-cis configuration on a slow timescale, which enables Rh6mr to function in a photocyclic manner similar to that of microbial Rhs. With this photocyclic behavior, Rh6mr repeatedly recruits and activates G_t in response to light stimuli, making it an excellent candidate for optogenetic tools based on retinal analog-bound vertebrate Rhs. Overall, these comprehensive structure-function studies unveil a unique photocyclic mechanism of Rh activation by an 11-cis-to-11,13-dicis isomerization.

Identification of Sequence Similarities among Isomerization Hotspots in Crystallin Proteins

The eye lens crystallins represent an ideal target for studying the effects of aging on protein structure. Herein we examine separately the water-soluble (WS) and water-insoluble (WI) crystallin fractions and identify sites of isomerization and epimerization. Both collision-induced dissociation and radical-directed dissociation are needed for detection of these non-mass-shifting post-translational modifications. Isomerization levels differ significantly between the WS and the WI fractions from sheep, pig, and cow eye lenses. Residues that are most susceptible to isomerization are identified site-specifically and are found to reside in structurally disordered regions. However, isomerization in structured domains, although less common, often yields more dramatic effects on solubility. Numerous isomerization hotspots were also identified and occur in regions with aspartic acid and serine repeats. For example, ¹²⁸KMEIVDDDVPSLW¹⁴⁰ in βB3 crystallin contains three sequential aspartic acid residues and is isomerized heavily in the WI fractions, while it is not modified at all in the WS fractions. Potential causes for enhanced isomerization at sites with acidic residue repeats are presented. The importance of acidic residue repeats extends beyond the lens, as they are found in many other long-lived proteins associated with disease.

Existence of two O-like intermediates in the photocycle of Acetabularia rhodopsin II, a light-driven proton pump from a marine alga

A spectrally silent change is often observed in the photocycle of microbial rhodopsins. Here, we suggest the presence of two O intermediates in the photocycle of Acetabularia rhodopsin II (ARII or also called Ace2), a light-driven algal proton pump from Acetabularia acetabulum. ARII exhibits a photocycle including a quasi-equilibrium state of M, N, and O (M⇄N⇄O→) at near neutral and above pH values. However, acidification of the medium below pH ~5.5 causes no accumulation of N, resulting in that the photocycle of ARII can be described as an irreversible scheme (M→O→). This may facilitate the investigation of the latter part of the photocycle, especially the rise and decay of O, during which molecular events have not been sufficiently understood. Thus we analyzed the photocycle under acidic conditions (pH ≤ 5.5). Analysis of the absorbance change at 610 nm, which mainly monitors the fractional concentration changes of K and O, was performed and revealed a photocycle scheme containing two sequential O-states with the different molar extinction coefficients. These photoproducts, termed O₁ and O₂, may be even produced at physiological pH, although they are not clearly observed under this condition due to the existence of a long M-N-O equilibrium.

Facile Access to Unprecedented Electron-Precise Monohydrodiboranes(4), cis-1,2-Dihydrodiboranes(4), and a 1,1-Dihydrodiborane(5)

2,3-Bis(dimethylamino)-substituted B₂ N₂ C₂ heterocycles underwent selective dimethylamino/hydride exchange with either one or two equivalents of BH₃ ⋅SMe₂ to give the corresponding cyclic monohydrido- or (cis)1,2-dihydridodiboranes(4), respectively. Upon either heating or irradiation in solution, the latter underwent ring contraction to the corresponding five-membered BN₂ C₂ heterocycles, whereas irradiation of the 1,2-dimethylaminoethene-supported 1,2-dihydridodiborane(4) in the presence of PEt₃ gave an unprecedented unsymmetrical 1,1-dihydrodiborane(5) phosphine adduct.

C,O-Chelated BINOL/Gold(III) Complexes: Synthesis and Catalysis with Tunable Product Profiles

Unprecedented stable BINOL/gold(III) complexes, adopting a novel C,O-chelation mode, were synthesized by a modular approach through combination of 1,1'-binaphthalene-2,2'-diols (BINOLs) and cyclometalated gold(III) dichloride complexes [(C^N)AuCl₂ ]. X-ray crystallographic analysis revealed that the bidentate BINOL ligands tautomerized and bonded to the Au^III atom through C,O-chelation to form a five-membered ring instead of the conventional O,O'-chelation giving a seven-membered ring. These gold(III) complexes catalyzed acetalization/cycloisomerization and carboalkoxylation of ortho-alkynylbenzaldehydes with trialkyl orthoformates.

Rapid and Efficient Conversion of All-E-astaxanthin to 9Z- and 13Z-Isomers and Assessment of Their Stability and Antioxidant Activities

An optimized isomerization method was developed by heating all-E-astaxanthin in ethyl acetate (70 °C) with I-TiO₂ catalyst, yielding 22.7% and 16.9% of 9Z- and 13Z-astaxanthin, respectively, in 2 h, with 92-95% purity after semipreparative HPLC purification. 13Z-Astaxanthin had higher antioxidant activity than all-E- and 9Z-astaxanthins in oxygen radical absorbing capacity assay for lipophilic compounds, photochemiluminescence, and cellular antioxidant activity (CAA) assays, and 9Z-astaxanthin was higher in DPPH radical-scavenging activity assay and lower in CAA assay. All isomers were relatively stable between pH 2.0 and 11.6, except 13Z- and 9Z-astaxanthins at pH 2.0, suggesting they may be converted after passing the gastric phase in vivo. Metal ions did not significantly (p < 0.05) affect the stability. Results of the current study provides a means for further study into the mechanisms related to in vivo transformation and bioavailability of Z-astaxanthins, and their application in the development of functional foods and nutraceutical products.

Insights into the Difference Between Rotaxane and Pseudorotaxane

Rotaxane and pseudorotaxane are two types of mechanically interlocked molecular architectures, and there is a clear topological difference and boundary between them. In this work, a "suggested [2]rotaxane 1⊂α-CD" was constructed based on axle molecule 1 bearing two terminal ferrocene groups and a wheel component α-cyclodextrin (α-CD), but the result obtained indicated that the ferrocene group cannot prevent α-CD dethreading under UV irradiation. That is, 1⊂α-CD is just a pseudo[2]rotaxane. Furthermore, the two ferrocene groups in 1⊂α-CD were encapsulated by two cucurbit[7]uril (CB[7]) units to obtain a heteropseudo[4]rotaxane 1⊂α-CD⋅2CB[7]. This heteropseudo[4]rotaxane displayed high stability towards harsh temperatures and the isomerization of azobenzene in 1, so it can be regarded as a [2]rotaxane. In this [2]rotaxane, the stoppers are not the bulky groups covalently bonded to the axle, but the cyclic CB[7] units connected through noncovalent interactions.

Networks of Dynamic Allostery Regulate Enzyme Function

Many protein systems rely on coupled dynamic networks to allosterically regulate function. However, the broad conformational space sampled by non-coherently dynamic systems has precluded detailed analysis of their communication mechanisms. Here, we have developed a methodology that combines the high sensitivity afforded by nuclear magnetic resonance relaxation techniques and single-site multiple mutations, termed RASSMM, to identify two allosterically coupled dynamic networks within the non-coherently dynamic enzyme cyclophilin A. Using this methodology, we discovered two key hotspot residues, Val6 and Val29, that communicate through these networks, the mutation of which altered active-site dynamics, modulating enzymatic turnover of multiple substrates. Finally, we utilized molecular dynamics simulations to identify the mechanism by which one of these hotspots is coupled to the larger dynamic networks. These studies confirm a link between enzyme dynamics and the catalytic cycle of cyclophilin A and demonstrate how dynamic allostery may be engineered to tune enzyme function.

Kinetics of Levoglucosenone Isomerization

We studied the acid-catalyzed isomerization of levoglucosenone (LGO) to 5-hydroxymethylfurfural (HMF) and developed a reaction kinetics model that describes the experimental data across a range of conditions (100-150 °C, 50-100 mm H₂ SO₄ , 50-150 mm LGO). LGO and its hydrated derivative exist in equilibrium under these reaction conditions. Thermal and catalytic degradation of HMF are the major sources of carbon loss. Within the range of conditions studied, higher temperatures and shorter reaction times favor the production of HMF. The yields of HMF and levulinic acid decrease monotonically as tetrahydrofuran is added to the aqueous solvent system, indicating that water plays a role in the LGO isomerization reaction. Initial-rate analyses show that HMF is produced solely from LGO rather than from the hydrated derivative of LGO. The results of this study are consistent with a mechanism for LGO isomerization that proceeds through hydration of the anhydro bridge, followed by ring rearrangement analogous to the isomerization of glucose to fructose.

Purification of Maize Nucleotide Pyrophosphatase/Phosphodiesterase Casts Doubt on the Existence of Zeatin Cis-Trans Isomerase in Plants

Almost 25 years ago, an enzyme named zeatin cis-trans isomerase from common bean has been described by Bassil et al. (1993). The partially purified enzyme required an external addition of FAD and dithiothreitol for the conversion of cis-zeatin to its trans- isomer that occurred only under light. Although an existence of this important enzyme involved in the metabolism of plant hormones cytokinins was generally accepted by plant biologists, the corresponding protein and encoding gene have not been identified to date. Based on the original paper, we purified and identified an enzyme from maize, which shows the described zeatin cis-trans isomerase activity. The enzyme belongs to nucleotide pyrophosphatase/phosphodiesterase family, which is well characterized in mammals, but less known in plants. Further experiments with the recombinant maize enzyme obtained from yeast expression system showed that rather than the catalytic activity of the enzyme itself, a non-enzymatic flavin induced photoisomerization is responsible for the observed zeatin cis-trans interconversion in vitro. An overexpression of the maize nucleotide pyrophosphatase/phosphodiesterase gene led to decreased FAD and increased FMN and riboflavin contents in transgenic Arabidopsis plants. However, neither contents nor the ratio of zeatin isomers was altered suggesting that the enzyme is unlikely to catalyze the interconversion of zeatin isomers in vivo. Using enhanced expression of a homologous gene, functional nucleotide pyrophosphatase/phosphodiesterase was also identified in rice.

Sequential Enzymatic Conversion of α-Angelica Lactone to γ-Valerolactone through Hydride-Independent C=C Bond Isomerization

A case of hydride-independent reaction catalyzed by flavin-dependent ene-reductases from the Old Yellow Enzyme (OYE) family was identified. α-Angelica lactone was isomerized to the conjugated β-isomer in a nicotinamide-free and hydride-independent process. The catalytic cycle of C=C bond isomerization appears to be flavin-independent and to rely solely on a deprotonation-reprotonation sequence through acid-base catalysis. Key residues in the enzyme active site were mutated and provided insight on important mechanistic features. The isomerization of α-angelica lactone by OYE2 in aqueous buffer furnished 6.3 mm β-isomer in 15 min at 30 °C. In presence of nicotinamide adenine dinucleotide (NADH), the latter could be further reduced to γ-valerolactone. This enzymatic tool was successfully applied on semi-preparative scale and constitutes a sustainable process for the valorization of platform chemicals from renewable resources.

N+1 Engineering of an Aspartate Isomerization Hotspot in the Complementarity-Determining Region of a Monoclonal Antibody

Aspartate (Asp) isomerization is a common degradation pathway and a potential critical quality attribute that needs to be well characterized during the optimization and development of therapeutic antibodies. A putative Asp-serine (Ser) isomerization motif was identified in the complementarity-determining region of a humanized monoclonal antibody and shown to be a developability risk using accelerated stability analyses. To address this issue, we explored different antibody engineering strategies. Direct engineering of the Asp residue resulted in a greater than 5× loss of antigen-binding affinity and bioactivity, indicating a critical role for this residue. In contrast, rational engineering of the Ser residue at the n+1 position had a negligible impact on antigen binding affinity and bioactivity compared with the parent molecule. Furthermore, the n+1 engineering strategy effectively eliminated Asp isomerization as determined by accelerated stability analysis. This outcome affirms that the rate of Asp isomerization is strongly dependent on the identity of the n+1 residue. This report highlights a systematic antibody engineering strategy for mitigating an Asp isomerization developability risk during lead optimization.

Kinetics of the competitive reactions of isomerization and peptide bond cleavage at l-α- and d-β-aspartyl residues in an αA-crystallin fragment

d-β-aspartyl (Asp) residue has been found in a living body such as aged lens crystallin, although l-α-amino acids are constituents in natural proteins. Isomerization from l-α- to d-β-Asp probably modulates structures to affect biochemical reactions. At Asp residue, isomerization and peptide bond cleavage compete with each other. To gain insight into how fast each reaction proceeds, the analysis requires the consideration of both pathways simultaneously and independently. No information has been provided, however, about these competitive processes because each reaction has been studied separately. The contribution of Asp isomers to the respective pathways has still been veiled. In this work, the two competitive reactions, isomerization and spontaneous peptide bond cleavage at Asp residue, were simultaneously observed and compared in an αA-crystallin fragment, S⁵¹ LFRTVLD⁵⁸ SG⁶⁰ containing l-α- and d-β-Asp58 isomers. The kinetics showed that the formation of l- and d-succinimide (Suc) intermediate, as a first step of isomerization, was comparable at l-α- and d-β-Asp. Although l-Suc was converted to l-β-Asp, d-Suc was liable to return to the original d-β-Asp, the reverse reaction marked enough to consider d-β-Asp as apparently stable. d-β-Asp was also resistant to the peptide bond cleavage. Such apparent less reactivity is probably the reason for gradual and abnormal accumulation of d-β-Asp in a living body under physiological conditions. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.

Controlled Encapsulation of Flower-like Rh-Ni Alloys with MOFs via Tunable Template Dealloying for Enhanced Selective Hydrogenation of Alkyne

For new composite materials with functional nanoparticles (NPs) embedded in metal organic frameworks (MOFs), rational design and precise control over their architectures are imperative for achieving enhanced performance and novel functions. Especially in catalysis, the activity and selectivity of such composite materials are strongly determined by the encapsulation state and thickness of the MOF shell, which greatly influences the diffusion and adsorption of substance molecules onto the NP surface. In this study, MOF-74(Ni)-encapsulated Rh-Ni hierarchical heterostructures (Rh-Ni@MOF-74(Ni)) were successfully constructed using magnetic Rh-Ni-alloyed nanoflowers (NFs) as a self-sacrificial template. Strikingly, the encapsulation state and thickness of the formed MOF shell were well-tuned via template dealloying by changing the Ni content in the Rh-Ni NFs template. More interestingly, such unique Rh-Ni composites encapsulated with MOFs as catalysts could be magnetically recyclable and exhibited enhanced catalytic performance for the selective hydrogenation of alkynes to cis products, owing to the confinement effect of the MOF shell, as compared to their pristine counterparts.