Contraction Reaction Research Articles

ChemInform Abstract: Supramolecular Reactivity in the Gas Phase: Investigating the Intrinsic Properties of Non‐Covalent Complexes

AbstractReview: 38 refs.

Supramolecular reactivity in the gas phase: investigating the intrinsic properties of non-covalent complexes

The high vacuum inside a mass spectrometer offers unique conditions to broaden our view on the reactivity of supramolecules. Because dynamic exchange processes between complexes are efficiently suppressed, the intrinsic and intramolecular reactivity of the complexes of interest is observed. Besides this, the significantly higher strength of non-covalent interactions in the absence of competing solvent allows processes to occur that are unable to compete in solution. The present review highlights a series of examples illustrating different aspects of supramolecular gas-phase reactivity ranging from the dissociation and formation of covalent bonds in non-covalent complexes through the reactivity in the restricted inner phase of container molecules and step-by-step mechanistic studies of organocatalytic reaction cycles to cage contraction reactions, processes induced by electron capture, and finally dynamic molecular motion within non-covalent complexes as unravelled by hydrogen-deuterium exchange processes performed in the gas phase.

An informational framework to predict reaction of constraints using a reciprocally connected knee model

Researchers have used screw theory to describe the motion of the knee in terms of instantaneous axes of the knee (IAK). However, how geometric change to the dynamic alignment of IAK may affect stance phase of foot loading has not yet been fully explained. We have tested our informational framework through readily accessible benchmark data (Fregly et al. 2012): muscle contraction and ground reaction force are compounded into a wrench that is reciprocal to the IAK and resolved into component wrenches belonging to the reciprocal screw system. This revealed the special screw system that defines the freedom available to the knee and more precisely revealed how to measure this first order of freedom. After this step, we determined the reciprocal screw system, which involves the theory of equilibrium. Hence, a screw system of the first order will have a screw system of the fifth order as its reciprocal. We established a framework the estimation of reaction of constraints about the knee using a process that is simplified by the judicious generation of IAK for the first order of freedom in equilibrium.

Spectroscopic, Steady-State Kinetic, and Mechanistic Characterization of the Radical SAM Enzyme QueE, Which Catalyzes a Complex Cyclization Reaction in the Biosynthesis of 7-Deazapurines

7-Carboxy-7-deazaguanine (CDG) synthase (QueE) catalyzes the complex heterocyclic radical-mediated conversion of 6-carboxy-5,6,7,8-tetrahydropterin (CPH(4)) to CDG in the third step of the biosynthetic pathway to all 7-deazapurines. Here we present a detailed characterization of QueE from Bacillus subtilis to delineate the mechanism of conversion of CPH(4) to CDG. QueE is a member of the radical S-adenosyl-l-methionine (SAM) superfamily, all of which use a bound [4Fe-4S](+) cluster to catalyze the reductive cleavage of the SAM cofactor to generate methionine and a 5'-deoxyadenosyl radical (5'-dAdo(•)), which initiates enzymatic transformations requiring hydrogen atom abstraction. The ultraviolet-visible, electron paramagnetic resonance, and Mössbauer spectroscopic features of the homodimeric QueE point to the presence of a single [4Fe-4S] cluster per monomer. Steady-state kinetic experiments indicate a K(m) of 20 ± 7 μM for CPH(4) and a k(cat) of 5.4 ± 1.2 min(-1) for the overall transformation. The kinetically determined K(app) for SAM is 45 ± 1 μM. QueE is also magnesium-dependent and exhibits a K(app) for the divalent metal ion of 0.21 ± 0.03 mM. The SAM cofactor supports multiple turnovers, indicating that it is regenerated at the end of each catalytic cycle. The mechanism of rearrangement of QueE was probed with CPH(4) isotopologs containing deuterium at C-6 or the two prochiral positions at C-7. These studies implicate 5'-dAdo(•) as the initiator of the ring contraction reaction catalyzed by QueE by abstraction of the H atom from C-6 of CPH(4).

Role of the enteric nervous system in the colon of patients with idiopathic megacolon.

To clarify the physiological significance of the enteric nervous system (ENS) in the colon of patients with idiopathic megacolon (IM), we investigated the enteric nerve responses on lesional and normal bowel segments derived from patients with IM and patients who underwent colon resection for colonic cancers. Eighteen preparations were taken from the lesional colon of 5 patients with IM (4 men and 1 woman, aged 46-70 yrs, mean age 55.8 yrs); 42 were taken from the normal colon of 14 patients with colonic cancer (10 men and 4 woman, aged 48-68 yrs, mean age 54.2 yrs). A mechanographic technique was used to evaluate in vitro muscle responses to electrical field stimulation (EFS) of the adrenergic and cholinergic nerves before and after treatment with various autonomic nerve blockers. 1) Responses to EFS before blockade of adrenergic and cholinergic nerves. The muscle strips in both normal and IM colon demonstrated relaxation reactions rather than contraction reactions by EFS. The relaxation reaction to EFS in the IM was significantly stronger than that in the normal colon (p=0.0366). 2) Responses to EFS after blockade of the adrenergic and cholinergic nerves. The muscle strips in both normal and IM colon demonstrated relaxation reactions rather than contraction reactions by EFS. The relaxation reaction to EFS in the IM was stronger than that in the normal colon (p=0.0467). 3) Tetrodotoxin abolished the EFS responses in the muscle strips in both normal colon and abnormal colon with IM. An increase of NANC inhibitory nerves plays an important role in the impaired motility observed in the colon of patients with IM.

A Novel Synthesis of Thioglycolurils by Ring Contraction of 5,7-Dialkyl-3-thioxoperhydroimidazo[4,5-e]-1,2,4-triazin-6-ones

A new synthetic route to ( E )-1,3-dialkyl-4-(benzylid­eneamino)-5-thioxohexahydroimidazo[4,5- d ]imidazol-2(1 H )-ones (thioglycolurils), by a ring contraction reaction of 5,7-dialkyl-3-thioxoperhydroimidazo[4,5- e ]-1,2,4-triazin-6-ones with aromatic aldehydes, has been developed.

Yield of aromatics from naphthenics upon catalytic cracking

Cis- and trans-decalin were reacted over cracking catalysts to study the formation of aromatics in a particular fraction of the liquid products obtained in the fluid catalytic cracking process (FCC). A batch, fluidized bed CREC riser simulator reactor was used at 673 and 723 K and contact times varied from 3 to 15 s. Cis-decalin was much more reactive. Despite differences induced and measured in their accessibility indices, the catalysts led to similar activity profiles, suggesting that diffusion restrictions do not prevail. Products were C1-C12 hydrocarbons while coke was very low. Isomerization, cracking, hydrogen transfer, ring opening, ring contraction and alkylation reactions occurred and products from the various reactions were observed at very short reaction times. Bicyclic C10 naphthenics and alkyl-substituted C7-C11 aromatics or naphtheno-aromatics were the most important products. A reaction mechanism with three initial routes (isomerization, ring opening and direct hydrogen transfer reactions) was proposed.

A photo-Favorskii ring contraction reaction: the effect of ring size.

The effect of ring size on the photo-Favorskii induced ring-contraction reaction of the hydroxybenzocycloalkanonyl acetate and mesylate esters (7a-d, 8a-c) has provided new insight into the mechanism of the rearrangement. By monotonically decreasing the ring size in these cyclic derivatives, the increasing ring strain imposed on the formation of the elusive bicyclic spirocyclopropanone 20 results in a divergence away from rearrangement and toward solvolysis. Cycloalkanones of seven or eight carbons undergo a highly efficient photo-Favorskii rearrangement with ring contraction paralleling the photochemistry of p-hydroxyphenacyl esters. In contrast, the five-carbon ring does not rearrange but is diverted to the photosolvolysis channel avoiding the increased strain energy that would accompany the formation of the spirobicyclic ketone, the "Favorskii intermediate 20". The six-carbon analogue demonstrates the bifurcation in reaction channels, yielding a solvent-sensitive mixture of both. Employing a combination of time-resolved absorption measurements, quantum yield determinations, isotopic labeling, and solvent variation studies coupled with theoretical treatment, a more comprehensive mechanistic description of the rearrangement has emerged.

Unexpected ring contraction and oxidation rearrangement reactions of securinine

The bromination and oxidation of securinine were studied. An interesting and surprising rearrangement was observed during the reaction of securinine with tribromo-isocyanuric acid or 1,3-dibromo-5,5-dimethylhydantoin in methanol, yielding a stereoselective ring contraction norsecurinine derivative. Meanwhile two oxidation rearrangement products were also reported. Some preliminary discussions on the reactivity of securinine were conducted from these rearrangements; it is believed to be induced by alkaline nitrogen atom of the molecule.

A review of models of fluctuating protrusion and retraction patterns at the leading edge of motile cells

A characteristic feature of motile cells as they undergo a change in motile behavior is the development of fluctuating exploratory motions of the leading edge, driven by actin polymerization. We review quantitative models of these protrusion and retraction phenomena. Theoretical studies have been motivated by advances in experimental and computational methods that allow controlled perturbations, single molecule imaging, and analysis of spatiotemporal correlations in microscopic images. To explain oscillations and waves of the leading edge, most theoretical models propose nonlinear interactions and feedback mechanisms among different components of the actin cytoskeleton system. These mechanisms include curvature-sensing membrane proteins, myosin contraction, and autocatalytic biochemical reaction kinetics. We discuss how the combination of experimental studies with modeling promises to quantify the relative importance of these biochemical and biophysical processes at the leading edge and to evaluate their generality across cell types and extracellular environments.

Water as an additive to enhance the ring opening of naphthalene

Use of water as a reaction medium or additive to enhance reaction efficiency is an important topic in green chemistry, and ring opening and contraction reactions of aromatics are crucial for upgrading diesels. In this work, we investigated the effect of water on the yields of ring opening and contraction reactions of naphthalene. A series of catalysts, such as Rh2O3/HY zeolite, Mo–Ni oxide and their physical mixtures, were used as the catalysts. The influences of the amount of water, hydrogen pressure, reaction temperature and reaction time on the yields of the ring opening and contraction products (ROCP) were studied. It was found that Rh2O3/HY and Mo–Ni oxide showed an excellent synergistic effect for catalyzing the reaction, and water could be used as a green and efficient additive for enhancing the yield of the ROCP. At the optimized conditions, the yield of the ROCP could be as high as 63.3%. The mechanism for the effect of water on the reactions was discussed on the basis of control experiments.

Cobalt mediated ring contraction reaction of lapachol and initial antibacterial evaluation of naphthoquinones derived from lapachol

The synthesis of 2-hydroxy-2-(3-methylbut-2-enyl)-2H-indene-1,3-dione 3, from lapachol which involves a ring contraction via the Hooker intermediate 1,2-dihydroxy-2-(3-methylbut-2-en-1-yl)-3-oxo-2,3-dihydro-1H-indene-1-carboxylic acid 2 is described. Different pyranonaphthoquinone derivatives, obtained in our previous synthetic work, were screened for antimycobacterial (Mycobacterium tuberculosis) activity and against resistant strains of Gram-positive (Bacillus cereus and Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The results indicated significant activity of all the tested samples against M. tuberculosis and only moderate activity against the Gram-positive and Gram-negative bacteria.

Unified Syntheses of Cavicularin and Riccardin C: Addressing the Synthesis of an Arene Adopting a Boat Configuration

Concise syntheses of the natural products cavicularin (ten steps) and riccardin C (seven steps) are reported. Key features of the new synthetic route are a convergent strategy to assemble acyclic precursors and a sequence of regioselective reduction and halogenation steps to facilitate Wittig macrocyclisation and transannular ring contraction reactions.

On the Peculiarities of the Ring Contraction Reactions of Homodrimanes via Acid Mediated Epoxide Rearrangement

A selective rearrangement of a epoxy-homodrimanic substrate is described. Using fluorosulfonic acid at low temperature leads by ring contraction to a perhydrindanic structure. On the contrary, using boron trifluoride-diethyl ether at r.t. selectively brings about angular methyl migration.

Characteristic atom occupation patterns of Au 3Cu, AuCu 3, AuCuI and AuCuII based on experimental data of disordered alloys

The potential energies, volumes and electronic structures of characteristic atoms coordinated by neighboring configurations were obtained from the experimental heats of formation and lattice parameters of disordered Au 1- x Cu x alloys. From characteristic atom occupation (CAO) patterns of L1 2-Au 3Cu, L1 2-AuCu 3 and L1 0-AuCu compounds, their electronic structures, volumetric and energetic properties were calculated. The CAO pattern of Johasson-Linde(J-L) model shows that the transition AuCuI→AuCuII is an exothermic and volume contraction reaction, which is opposite from experimental phenomena. According to CAO pattern of Guymont-Feutelais-Legendre(G-F-L) model, the AuCuII cell consists of two periodic antidirection (PAD) AuCuI regions and two PAD boundary regions. The equations derived from CAO pattern of G-F-L model can be used to calculate energetic properties, volumetric properties and ordering degrees of the PAD AuCuI region and PAD boundary region, as well as corresponding average properties of the AuCuII phase. The results are consistent with experimental phenomena.

Light-Induced Conformational Change and Transient Dissociation Reaction of the BLUF Photoreceptor Synechocystis PixD (Slr1694)

The light-induced reaction of the BLUF ( blue light photoreceptor using flavin adenine dinucleotide) photoreceptor PixD from Synechocystis sp. PCC6803 (Slr1694) was investigated using the time-resolved transient grating method. A conformational change coupled with a volume contraction of 13 mL mol − 1 was observed with a time constant of 45 ms following photoexcitation. At a weak excitation light intensity, there were no further changes in volume and diffusion coefficient ( D). The determined D-value (3.7 × 10 − 11 m 2 s − 1 ) suggests that PixD exists as a decamer in solution, and this oligomeric state was confirmed by size-exclusion chromatography and blue native polyacrylamide gel electrophoresis. Surprisingly, by increasing the excitation laser power, we observed a large increase in D with a time constant of 350 ms following the volume contraction reaction. The D-value of this photoproduct species (7.5 × 10 − 11 m 2 s − 1 ) is close to that of the PixD dimer. Combined with transient grating and size-exclusion chromatography measurements under light-illuminated conditions, the light-induced increase in D was attributed to a transient dissociation reaction of the PixD decamer to a dimer. For the M93A-mutated PixD, no volume or D-change was observed. Furthermore, we showed that the M93A mutant did not form the decamer but only the dimer in the dark state. These results indicate that the formation of the decamer and the conformational change around the Met residue are important factors that control the regulation of the downstream signal transduction by the PixD photoreceptor.

Nitrenes, Carbenes, Diradicals, and Ylides. Interconversions of Reactive Intermediates

Rearrangements of aromatic and heteroaromatic nitrenes and carbenes can be initiated with either heat or light. The thermal reaction is typically induced by flash vacuum thermolysis, with isolation of the products at low temperatures. Photochemical experiments are conducted either under matrix isolation conditions or in solution at ambient temperature. These rearrangements are usually initiated by ring expansion of the nitrene or carbene to a seven-membered ring ketenimine, carbodiimide, or allene (that is, a cycloheptatetraene or an azacycloheptatetraene when a nitrogen is involved). Over the last few years, we have found that two types of ring opening take place as well. Type I is an ylidic ring opening that yields nitrile ylides or diazo compounds as transient intermediates. Type II ring opening produces either dienylnitrenes (for example, from 2-pyridylnitrenes) or 1,7-(1,5)-diradicals (such as those formed from 2-quinoxalinylnitrenes), depending on which of these species is better stabilized by resonance. In this Account, we describe our achievements in elucidating the nature of the ring-opened species and unraveling the connections between the various reactive intermediates. Both of these ring-opening reactions are found, at least in some cases, to dominate the subsequent chemistry. Examples include the formation of ring-opened ketenimines and carbodiimides, as well as the ring contraction reactions that form five-membered ring nitriles (such as 2- and 3-cyanopyrroles from pyridylnitrenes, N-cyanoimidazoles from 2-pyrazinyl and 4-pyrimidinylnitrenes, N-cyanopyrazoles from 2-pyrimidinylnitrenes and 3-pyridazinylnitrenes, and so forth). The mechanisms of formation of the open-chain and ring-contraction products were unknown at the onset of this study. In the course of our investigation, several reactions with three or more consecutive reactive intermediates have been unraveled, such as nitrene, seven-membered cyclic carbodiimide, and open-chain nitrile ylide. It has been possible in some cases to observe them all and determine their interrelationships by means of a combination of matrix-isolation spectroscopy, photochemistry, flash vacuum thermolysis, and computational chemistry. These studies have led to a deeper understanding of the nature of reactive intermediates and chemical reactivity. Moreover, the results indicate new directions for further exploration: ring-opening reactions of carbenes, nitrenes, and cyclic cumulenes can be expected in many other systems.

Allobetulin and its derivatives: synthesis and biological activity.

This review covers the chemistry of allobetulin analogs, including their formation by rearrangement from betulin derivatives, their further derivatisation, their fusion with heterocyclic rings, and any further rearrangements of allobetulin compounds including ring opening, ring contraction and ring expansion reactions. In the last part, the most important biological activities of allobetulin derivatives are listed. One hundred and fifteen references are cited and the relevant literature is covered, starting in 1922 up to the end of 2010.

Elimination of Allergens in South American Shrimp by Protease Hydrolysis

In order to eliminate the allergens in South American shrimp,proteases such as trypsin,papain and bromelain were individually used to hydrolyze South American shrimp proteins.General immunity experiments in allergic guinea pigs and allergic contraction experiments of isolated ileum were used to evaluate the allergenicity of hydrolysates.The results showed that hydrolysates from South American shrimp proteins digested by each of the three proteases could result in an obvious attenuation of general allergic reactions (Compared with the group of South American shrimp protein,0.01P0.05 or P 0.01).Meanwhile,a reduced allergic contraction reaction of isolated ileum smooth muscle was observed in hydrolyzed South American shrimp proteins (Compared with the group of South American shrimp protein,0.01 P 0.05 or P 0.01).Comprehensive evaluation exhibited that papain hydrolysates could provide an excellent elimination effect on allergens and higher food safety.

ChemInform Abstract: Expansion and Contraction Reactions with BN Four- and Six-Membered Rings.

ChemInform Abstract: Expansion and Contraction Reactions with BN Four- and Six-Membered Rings.