Five-membered Ring Structure Research Articles

Synthesis, Characterization, and Aqueous Solution Behavior of Electrolyte- and pH-Responsive Carboxybetaine-Containing Cyclocopolymers

A novel pH- and salt-responsive carboxybetaine monomer, 4-(N,N-diallyl-N-methylammonio)butanoate (2), was prepared and cyclocopolymerized with the cationic monomer N,N-diallyl-N,N-dimethylammonium chloride (3) in 0.5 M NaCl aqueous solution (pH = 7.0) using 2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone (Irgacure 2959) as the free-radical photoinitiator. The molar feed ratio of 2:3 was varied from 100:0 to 0:100 with the total monomer concentration held constant at 2.5 M. Cyclopolymerization to five-membered ring structures common to diallylammonium salts was confirmed by 13C NMR spectroscopy. Reactivity ratio studies indicate that 2 and 3 copolymerize in a nearly ideal fashion (r1 = 0.86, r2 = 0.99). Weight-average molecular weights and second virial coefficients vary from (6.0 to 12.8) × 104 g mol-1 and (1.62 to 5.36) × 10-4 mL mol g-2, respectively. Dilute solution viscosity behavior depends on copolymer composition, ionic strength, and pH. Copolymers with a large excess charge exhibit typi...

On the entanglement density of differently N-substituted alternating styrene-maleimide copolymers

Abstract Differently N-substituted maleimides were copolymerized with styrene to yield alternating styrene-maleimide copolymers (SMI-R) with different chain diameters. The polymers were obtained by free radical polymerization and characterized by NMR and size exclusion chromatography / differential viscometry. Glass transition temperatures were measured by differential scanning calorimetry. An increase in chain diameter and chain stiffness is accompanied by a decrease in the entanglement density, reflected in lower values of the plateau modulus, which were corrected for the low molecular weight portion using the Wasserman/Graessley model. Increasing the chain diameter by a factor of two results in a decrease of the entanglement density to one third. SMI-Me showed a much lower entanglement density than polystyrene (PS) although they have the same chain diameter. SMIMe however is more rigid than PS because of the maleimide five-membered ring structure in the main chain. SMI-Me and SMI-PhOPh show the same glass transition temperature. However, because of the larger chain diameter of SMIPhOPh, it has a much lower entanglement density. Thus, both the chain flexibility and the chain diameter, two parameters that are strongly related, affect the entanglement density.

DFT Study of Solvent Coordination Effects on Titanium-Based Epoxidation Catalysts. Part Two: Reactivity of Titanium Hydroperoxo Complexes in Ethylene Epoxidation

Density functional theory has been used to study the effects of solvent coordination on the reactivity of titanium hydroperoxo complexes in the epoxidation of the model olefin ethylene. Complexes possessing a variety of coordination environments have been modeled with unconstrained single coordination sphere clusters using a B3LYP/ECP methodology. The Gibbs free energy of activation for ethylene epoxidation with a nonligated titanium hydroperoxo species is 25.7 kcal/mol. Addition of a single solvent ligand to the titanium center has little effect on the activation barrier unless that ligand participates in a hypervalent ω bond with the proximal oxygen (Oα) of the hydroperoxo moiety; in that case, the ω bond inhibits the heterolytic cleavage of the Ti−Oα bond and increases the activation barrier for transfer of Oα to ethylene by 6−7 kcal/mol. Hydrogen bonding of the hydroperoxo moiety with a protic solvent ligand via a monodentate five-membered ring structure does not enhance the reactivity of the titanium hydroperoxo complex. The presence of two solvent ligands on the titanium center increases the activation barrier 11−16 kcal/mol by sterically hindering the attack of ethylene at Oα. The activation barrier is not affected by the presence of a hydrogen-bonded protic solvent molecule bridging the hydroperoxo moiety and a protic ligand on titanium. NBO analysis indicates that changes in the electrophilicity of the peroxo group caused by solvent coordination do not control the observed reactivity of the titanium hydroperoxo complexes. The activation barriers for ethylene epoxidation with titanium hydroperoxo, methylperoxo, and trifluoromethylperoxo oxidants decrease with increasing positive charge on the atom bonded to the distal peroxo oxygen (Oβ) through stabilization of the developing negative charge on Oβ. Comparison of the Gibbs activation barriers for the formation of the titanium hydroperoxo intermediate and its subsequent reaction with ethylene indicates that the oxygen transfer step is the rate-determining step for the overall epoxidation mechanism.

DFT Study of Solvent Coordination Effects on Titanium-Based Epoxidation Catalysts. Part One: Formation of the Titanium Hydroperoxo Intermediate

Density functional theory has been used to study the effects of solvent coordination on the structure and formation of the titanium hydroperoxo species believed to be the active intermediate in oxidation reactions with Ti(IV)−H2O2 catalytic systems. Titanium hydroperoxo intermediates possessing a variety of coordination environments have been modeled with unconstrained single coordination sphere clusters using a B3LYP/ECP methodology. Titanium hydroperoxo intermediates bearing one or two solvent ligands may assume several degenerate structures with the hydroperoxo moiety coordinated to titanium in a monodentate or bidentate manner. Hydrogen bonding of the hydroperoxo moiety with a protic solvent ligand via a monodentate five-membered ring structure does not confer any significant additional stabilization to the titanium hydroperoxo intermediate. The presence of a single solvent ligand on the titanium center lowers the Gibbs free energy of activation for the formation of titanium hydroperoxo intermediates by 4−8.5 kcal/mol. Hydrogen-bonded protic molecules can facilitate proton transfer from a hydrogen peroxide ligand on titanium and thereby lower the Gibbs activation barrier for intermediate formation by 5−6 kcal/mol. NBO analysis provides an enriched understanding of how solvent ligands alter structural and electronic properties and reduce activation barriers. Consideration of thermodynamic and kinetic results indicates that the most abundant titanium hydroperoxo intermediates formed under liquid-phase reaction conditions will most likely possess a single solvent ligand on titanium and possibly a hydrogen-bonded protic solvent molecule.

The structure of water near platinum and its significance in water-adsorbent system: molecular dynamics study

Water structure around hydrophilic adsorbents is expected to differ from normal water structure. In some cases, a change of water structure seems to significantly affect phenomena involved in water-adsorbent systems. To investigate this, we have performed molecular dynamic simulations of three systems, water between (111) surfaces of Pt, water between (100) surfaces of Pt, and pure water at 298 K. For the analysis of water structure, we concentrated on the five-membered ring (R5) structure and six-membered ring (R6) structure, which are the most probable in nature. For both (111) and (100) of Pt, the ratio of hexameric ring/pentameric ring (R6/R5) in semibound regions was higher than that of bulk water, as expected. The function of adsorbent ceramics was explained in terms of the change of water structure when they are used as biomaterials, support materials, etc. The obscure mechanisms for the effects of medicine stones, antioxidants, etc., were also discussed from this point of view.

Utilization of Folin-Ciocalteu phenol reagent for the detection of certain nitrogen compounds.

To determine in more detail the reaction of Folin-Ciocalteu phenol reagent with nitrogen compounds, a number of hydroxylamine-related compounds and a large number of guanidine-containing compounds were tested. In general, guanidine compounds did not react strongly unless they were hydroxyamino or hydrazino derivatives. The non-hydroxyamino paralytic shellfish poison saxitoxin, however, reacted to a significant extent. This may be due to the presence of a five-membered ring structure and its analogy to 2-aminopurines, which react strongly. A number of simpler amines were also tested. Tertiary aliphatic amines, but not primary, secondary, or quaternary amines, reacted strongly with the reagent. Primary, secondary, and tertiary aromatic amines all reacted strongly with the reagent. Reactivity was extended to pyrroles and indole derivatives but not to imidazole and benzimidazole derivatives. Defining the reactivity of Folin-Ciocalteau phenol reagent with nitrogen compounds extends the usefulness of the reagent for the detection and determination of certain nitrogen compounds in basic extracts by colorimetric means and by thin-layer chromatography.

Fine-Tuning of Molybdenum Imido Alkylidene Complexes for the Cyclopolymerization of 1,6-Heptadiynes To Give Polyenes Containing Exclusively Five-Membered Rings

Diethyl dipropargylmalonate (1) was cyclopolymerized by various well-defined molybdenum-based Schrock initiators to produce polymers exclusively based on 1,2-cyclopent-1-enylenvinylene units. For this purpose, variations in both the imido and alkoxy ligand in molybdenum alkylidene complexes of type Mo(NAr‘)(CHCMe2Ph)(OR)2 (Ar‘ = 2,6-i-Pr2C6H3; 2,6-Me2C6H3; OR = OCH(CF3)2, OCH(CH3)2, OC(CH3)3) were carried out. Polymers containing >95% 1,2-cyclopent-1-enylenvinylene units were obtained by low-temperature-initiated cyclopolymerization of 1 by Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(OCH(CH3)2)2 (2). In the presence of quinuclidine, >95% five-membered ring structures were realized at room temperature using Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(OC(CH3)3)2 (3) and Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(OC(CH3)3)2 (4). In contrast, molybdenum initiators containing electron-withdrawing alkoxides such as Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(OCH(CF3)2)2(quinuclidine) (5) or the nonfluorinated analogue Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(OCH(CH3)2)2(quinuclidin...

Borate esters used as lubricant additives

AbstractBorate esters possess friction‐reducing, antiwear, and anti‐oxidant characteristics when blended in lubricating oils. However, borate esters are susceptible to hydrolysis. The formation of a stable five‐member ring structure in the ester molecules, involving coordination of nitrogen with boron, contributes substantially to the resistance to hydrolysis of borate esters. The susceptibility of borates to hydrolysis can be reduced by introducing N,N‐dialkylaminoethyl groups with alkyl radicals containing more than three carbon atoms. X‐ray photo‐electron spectroscopy and X‐ray diffraction reveal that the borate ester can be adsorbed on the rubbing surface, and some of the adsorbed borate film degrades and forms boron nitride. Four‐ball wear tests indicate that the combination of oil‐soluble copper, tin, and cadmium compounds with organoborates gives better antiwear properties than the components separately. An antiwear synergistic mechanism is postulated in which borates with electron‐deficient boron p orbitals catalyse the tribo‐reduction of the metal compounds on the rubbing surfaces, producing elemental metals.

Photo-induced intra-complex reactions in Mg+-2,2,2-trifluoroethanol

We induced the intra-complex reactions in Mg+-2,2,2-trifluoroethanol by photons in the spectral region of 240–410 nm. We observed the nonreactive channel product Mg+ and a number of reactive channel products throughout the whole excitation region. The reactive photoproducts originate from the scission of the C–O or C–F bond, as well as from the simultaneous rupture of both bonds. The action spectrum consists of two broad peaks between the atomic transition of Mg+(3 2P←3 2S). Ab initio calculations show a minimum-energy structure, in which Mg+ attaches to the O atom and one of the three F atoms of 2,2,2-trifluoroethanol, forming a five-membered ring. The calculated absorption spectrum corresponding to the minimum-energy structure agrees nicely with the experimental action spectrum. The branching fractions of the photoproducts are approximately constant in a given spectral range, but they change significantly across the spectral ranges. The constant branching fractions point to the ground state reactions following traversals from the initially accessed excited states through conical intersections. On the other hand, the observation of the electronic state-specific branching fractions is explained by the orbital alignments of the excited electron, which is dictated by the five-membered ring structure of the complex.

Synthesis of Superhard and Elastic Carbon Nitride Films by Filtered Cathodic Vacuum arc Combined with Radio Frequency Ion Beam Source

Superhard and elastic carbon nitride films with hardness and elastic recovery of 47 GPa and 87.5%, respectively, were synthesized by using a double-bend filtered cathodic vacuum arc combined with radio-frequency nitrogen ion beam source. The bombardment of energetic nitrogen atom onto the growing film surface results in the high atomic ratio of N/C (0.4), which contributes to the high sp2 content and the formation of a five-membered ring structure in the carbon nitride film at room temperature. The buckling of the five-membered ring basal planes may facilitate cross-linking between the planes through sp3 coordinated carbon atoms. A rigid three-dimensional network is formed, which contributes to the high hardness and elastic recovery of the deposited films.

Poly(ethylene carbonate)s, part II : degradation mechanisms and parenteral delivery of bioactive agents

The degradation and drug carrier properties of poly(ethylene carbonate) (PEC) were investigated in vitro and in rats and rabbits. PEC was found to be specifically degraded in vivo and in vitro by superoxide radical anions O 2 −·, which are, in vivo, mostly produced by inflammatory cells. No degradation of PEC was observed in the presence of hydrolases, serum or blood. PEC is biodegraded by surface erosion without significant change in the molecular weight of the residual polymer mass. The non-hydrolytic biodegradation by cells producing O 2 −· is unique among the polymers used as biodegradable drug carriers. The main degradation product of PEC in aqueous systems is ethylene glycol, formed presumably by hydrolysis of ethylene carbonate. The splitting off of a five-membered ring structure from the polymer chain indicates a chain reaction mechanism for the biodegradation. PEC is a suitable drug carrier, particularly for labile drugs. Using human interleukin-3 and octreotide as model drugs, surface erosion of the PEC formulations was indicated by a 1:1 correlation between drug release and polymer mass loss.

Ultrafast Spectroscopy of the Protonated Schiff Bases of Free and C13C14 Locked Retinals

In this study, the ultrafast pump−probe spectroscopy of the all-trans protonated Schiff base of retinal (trans-PSB) in solution, is compared to that of two retinal analogues, trans-PSB5.12 and 13-cis-PSB5.13, in which C13C14 torsional motion is inhibited by a rigid five-membered ring structure. The objective is to obtain measures of internal conversion (IC) dynamics in these polyenes. Contrasting the results with those obtained for the same pigments when attached to their opsin protein, serve to appreciate the protein role in catalyzing energy transduction in bacteriorhodopsin. Several major features appear to be common to all three PSBs: (i) A 50−100 fs process due to a primary relaxation out of the Franck−Condon (FC) region, (ii) A subsequent biexponential decay (t1 = 1−2 ps and t2 = 4−7 ps) of the fluorescent state (FS) assumed to be due to IC, and (iii) Spectral modulations in the FS emission. The three are only marginally effected by locking of the C13C14 bond. With respect to features (i) and (iii) the PSB model compounds behave analogously to the related retinal protein bacteriorhodopsin (bR). However, this does not apply to the FS decay. While in bR, the IC takes place with a 0.5 ps decay time, locking of the C13C14 bond in bR markedly increases the FS lifetime to ∼15 ps. These observations demonstrate the crucial role played by the protein in directing the isomerization action to the active double bond and enhancing the rate of IC. They also prove that these coordinates are not exclusive pathways of IC in the isolated PSB of retinal. The mechanism of ground-state repopulation in the PSBs is discussed in light of these results.

Azido-mediated ferromagnetic exchange interaction in the M(II)–oxine complexes

We report the synthesis of ferromagnetically ordered mononuclear compounds [M(II)(oxine)(N 3) x ] containing different metal ions, viz. M(II)=Co ( 1), Cr ( 2), Fe ( 3) and Ni ( 4), using azido as the main bridging ligand and oxine (8-hydroxy quinoline) as a new auxiliary ligand. Oxine was chosen because it is known to form a five-membered ring structure around the bivalent metal ions. A one-pot synthesis was carried out in each case. The compounds were characterised and their magnetic behaviour is studied. Ac susceptibility ( χ′ and χ″) measurements, hysteresis plots (VSM) and χT behaviour indicate the onset of long-range ferromagnetic ordering below 18, 17, 9 and 34 K for the compounds 1, 2, 3 and 4, respectively.

Molecular and Crystal Structures of TeCl4-Allylalcohol and -Allylacetate Adducts

1,2-electrophilic addition of TeCl4 to the C=C bond of allylalcohol is observed, while with allylacetate, 1,3-addition occurs, due to migration of the acetate group. The allylalcohol adduct comprises two different kinds of molecules in the solid state, Cl3Te[CH2CH(Cl)CH2OH→] and Cl2Te[CH2CH(Cl)CH2CH-], with dative Te←O and covalent Te-O bonds, five-membered ring structures and Cl-Te⋯Cl and O-H⋯O bridges linking the different molecules. In the allylacetate adduct, Cl3Te[CH2CH(CH2Cl)OC(CH3)=O→], a six-membered ring is formed via an intramolecular dative Te←O interaction, the molecules being linked via C-Cl⋯Te bridges. Multinuclear NMR spectroscopy and 1H-1H-NOESY combined with ab initio (MP2/LANL2DZP) geometry optimisation show the geometry of the ring structures in solution to be similar to those in the solid state.

Modification of cyclosporin A and conjugation of its derivative to HPMA copolymers.

Cyclosporin A (CsA) was epoxidized with m-chloroperoxybenzoic acid in the presence of sodium carbonate or with tert-butyl hydroperoxide in the presence of dioxomolybdenum iminodiethanoxide. The CsA epoxide was not stable and rearranged into a compound with a more stable five-member ring structure. An amino group containing cyclosporin A derivative (CsA amine) was obtained by the reaction of CsA epoxide with excess ethylenediamine. The yield of the CsA amine was 30--40% based on the CsA. An HPMA copolymer--CsA conjugate was prepared by the reaction of the CsA amine with an HPMA and MA-Gly-Phe-Leu-Gly-ONp copolymer. The content of CsA amine in the conjugate was 8.7 wt %. The CsA amine was released from the copolymer by enzymatic hydrolysis with papain.

Five-membered ring formation in unimolecular reactions of peptides: a key structural element controlling low-energy collision-induced dissociation of peptides.

Unimolecular fragmentation reactions of peptides in low-energy collision-induced dissociation are reviewed in the mechanistic context of five-membered ring formation. This structure of intermediates or of fragment ions is recognized as a key element that governs unimolecular peptide fragmentation within the structural framework determined by the peptide backbone and its side-chains. A collection of collision-induced dissociation reactions is presented covering (i) b-ion formation, (ii) the fragmentation of N-terminally acylated peptides, (iii) neutral loss of the C-terminal amino acid in alkali or silver cationized peptides, (iv) the fragmentation of isoAsp-containing peptides and (v) the fragmentation of negatively charged Asp- or Glu-containing peptides. It appears that for all possible nucleophile-electrophile interactions leading to a five-membered ring structure an associated unimolecular peptide fragmentation reaction can be observed.

Possibilities and limitations of the prediction of the Si/Al ratios of zeolites from the batch composition

In earlier studies, it was shown that the Si/Al ratio of faujasite and some related zeolites crystallizing from batches with the composition NaAlO 2: n(Na m H 4– m SiO 4): pH 2O can be described by (A) ( Si/ Al) zeolite =1+b([ SiO 2]/[ OH −]) Solution , where [OH −] is the total alkali content and [SiO 2], the silica content of the solution phase in the batch. From Eq. (A) with some assumptions (B) ( Si/ Al) Product ≈ (b+m)n b+nm can be obtained, containing only the parameters n and m of the batch composition and the fitting parameter b from Eq. (A). For a large number of faujasite batches and for other large pore zeolites with four- and six-membered rings in the structure, a good agreement was obtained between the experimental Si/Al ratios and the values obtained from Eq. (B) using b=2. For zeolites with five-membered ring structures values of b=7–10 proved to be suitable. For high template contents, no common description can be obtained by Eq. (B). It could, however, be shown that this equation would be a good help for planning syntheses of mordenite, template-free ZSM-5 and BETA. The experiments with BETA were best described with b=14. From kinetic studies, Eq. (A) and the parameter b can be at least qualitatively explained by a model assuming that an amorphous layer is formed in an equilibrium reaction at the crystallizing surface. The formation of the final structure occurs by a reorganization of this layer under the influence of cations and templates. This reaction step is rate determining. The Si/Al ratio is determined in the attachment reaction. From an analysis of the alkalinity in the solution phase, it can be seen that, for the zeolites with four- and six-membered rings, the attachment of monomer silicate and the silico-aluminate species with about one silicate ligand can be expected. For the five-membered ring zeolites oligomer silicates and silico-aluminate complexes with two or more ligands are more probable. A borderline between the two situations can be drawn at about ( nm) 55.5/p≈[ OH]≈1 mol/l .

Addition reactions of aldehydes to lithium enolates of 1,3-dioxolan-4-ones: a configurational reassessment

The results for the addition reactions of chiral lithium (2S)-enolates of 1,3-dioxolan-4-ones to aldehydes and to acetophenone, yielding the corresponding dioxolanone alcohols have been revised. The results reported herein differ from those reported in the literature, both in product distribution and in the stereochemical assignment of the products. In fact, in several cases no stereocontrol was observed at the C5 carbon atom of the lithium enolate. The (2S,5R,1'S)/(2S,5R,1'R) stereochemistry was also reassessed for several dioxolanone alcohols. The major conformers are considered to have an intramolecular hydrogen-bonded five-membered ring structure instead of the six-membered ring structure previously suggested for cyclic dioxolanone alcohols.

Catalytic cyclopolymerization and copolymerization of 1,6-heptadiynes by Mo(CO)6

The catalytic polymerization of a series of 1,6-heptadiynes (1–4) by Mo(CO)6 under simple thermal conditions produces corresponding poly(1,6-heptadiyne)s with highly conjugated polyenes. The number-average molecular weights of the polymers range from 2400 to 110,000. The structures of the polymers depend on the types of monomers employed. Namely, diethyl dipropargylmalonate (DEDPM) and 1 result in a polyene backbone consisting of only five-membered rings, whereas the remaining monomers (2–4) result in a mixture of both five-membered and six-membered ring structures. The copolymerization of DEDPM and phenylacetylene (PA) can also be effected by the same catalysis to yield a polyene backbone consisting of only five-membered rings as well as PA. The relative molar ratio of the two monomers determines the yields and molecular weights of the copolymers. Comparative studies show that Mo(CO)6 exhibits reactivity toward DEDPM alone, thus initially catalyzing metathesis cyclopolymerization of DEDPM followed by copolymerization with PA. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2663–2670, 2000

Water Soluble Polymers. 76. Electrolyte Responsive Cyclocopolymers with Sulfobetaine Units Exhibiting Polyelectrolyte or Polyampholyte Behavior in Aqueous Media

Copolymers of N,N-diallyl-N,N-dimethylammonium chloride (DADMAC) and the zwitterionic monomer 3-(N,N-diallyl-N-methylammonio)propanesulfonate (DAMAPS) have been prepared in a 0.5 M NaCl aqueous solution using 2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone (Irgacure 2959) as the free-radical photoinitiator. The feed ratio of DADMAC:DAMAPS was varied from 100:0 to 0:100 mol % with the total monomer concentration held constant at 2.5 M. 13C NMR data indicate that the resulting polymers maintain the five-membered ring structure in the cis conformation common to diallylammonium salts. Reactivity ratio studies indicate that the sulfobetaine monomer is incorporated randomly along the polymer backbone. Laser light scattering provided molecular weights and second virial coefficients, which varied from 5.16 × 104 to 8.42 × 104 and 5.54 × 10-4 to 1.89 × 10-4 mL mol g-2, respectively. Solution behavior is dependent upon ionic strength as determined by low shear viscosity and dynamic light scattering exper...