Polymethylene Chain Research Articles

Towards Continuous Flow, Highly Enantioselective Allylic Amination: Ligand Design, Optimization and Supporting

AbstractA family of enantiopure diphenylphosphinooxazolines (PHOX) containing in their structures a sterically tunable alkoxymethyl group (‐CH2OR) has been optimized for the palladium‐catalyzed asymmetric allylic amination. The optimal catalyst (R=CH3), depicting very high catalytic activity and broad scope applicability, has been further modified to include an ω‐alkynyloxy substituent of variable length for polymer supporting via click chemistry, and has been anchored onto slightly cross‐linked azidomethyl poly(styrene). The length of a polymethylene chain connecting the PHOX unit with the 1,2,3‐triazole linker has been optimized, and the first polymer‐supported PHOX ligands for the highly enantioselective allylic amination have been prepared in this manner. Conditions for catalyst recovery and reuse in microwave‐promoted amination reactions have been established, and the system has been finally adapted to continuous flow operation.

Binuclear copper(II) complexes with acyldihydrazones of saturated carboxylic acids and pyruvic acid

Copper(II) binuclear complexes with acyldihydrazones of saturated carboxylic acids and pyruvic acid in which the coordination polyhedra are connected by polymethylene chains of different length (1 to 5 units) were synthesized and studied by chemical and thermogravimetric analysis, IR spectroscopy, and EPR. The structure of binuclear copper(II) complex with succinic acid acyldihydrazone [Cu2L · 4Py] · 2Py was determined by X-ray diffraction. The crystals are monoclinic: a = 14.3795(6), b = 8.8736(4), c = 15.9147(7) A, β = 101.062(3)°, space group P21/c, Z = 2. The number of independent reflections with I > 2σ(I) = 2804, R = 0.042, Rw = 0.087. The copper atoms are spaced by a chain of seven σ bonds at 8.922 A. The coordination polyhedron can be described as a tetragonal pyramid highly distorted toward a trigonal bipyramid. The EPR spectra of solutions of complexes based on malonic, succinic, glutaric, and adipinic acids exhibit a poorly resolved signal of seven HFS lines with a constant of (26.3–27.0) × 10−4 cm−1, which attests to the presence of weak exchange interactions between paramagnetic centers. An increase in the length of the polymethylene spaur suppresses exchange interactions, and the EPR spectrum of the complex based on pimelic acid acyldihydrazone shows a signal of four HFS lines with a constant of 43.8 × 10−4 cm−1 typical of monomeric copper(II) complexes.

Characterization of Bulgarian oil shale kerogen revealed by oxidative degradation

A 13-step alkaline permanganate degradation of Bulgarian oil shale kerogen concentrate at ambient temperature was carried out. A high yield of oxidation products (90.1%) and a low yield of gaseous products (2.79%) were obtained. IR and 1H NMR spectroscopic studies have shown that two significantly different types of high molecular products are present in kerogen. Further oxidation of these structures leads to the formation of low molecular aliphatic and aromatic acids, proven by gas chromotography (GC) and gas chromatography-mass spectrometry (GC-MS). The data obtained at these mild conditions allow us to acquire detailed information about the aromatic structures and polymethylene chain lengths in kerogen. The 5-step oxidation of the kerogen at 90 °C provides information about stable aromatic structures. Soluble and insoluble polyfunctional acids in acid medium have close molecular masses and spectral characteristics. The amount of benzene and naphthalene carboxylic acids is 11.3% of the organic matter of the oil shale.

Strong effect of NaBr on self-assembly of quaternary ammonium gemini surfactants at air/water interface and in aqueous solution studied by surface tension and fluorescence techniques

The effects of NaBr on the adsorption of alkanediyl-bis-(dimethyl dodecyl- ammonium bromide) (referred to as C12-s-C12 2Br) at the air/water interface and on the micellization in the solution have been investigated by surface tension and fluorescence techniques. The results showed that the addition of NaBr greatly enhances their efficiency and effectiveness in surface tension reduction as well as the ability of micellization, even induces strong premicellar aggregation before the cmc. These were attributed to the unique molecular structure of gemini surfactant, where the flexible polymethylene chain was the spacer linking the two quaternary ammonium heads. By a short spacer, the charges of the two quaternary ammonium head groups are concentrated. Even for a long spacer (s = 12), since it is bent toward the alkyl tails, the similar effect is also produced. This results in the high sensitivity of their ionic head groups to salt. Besides, the addition of salt also effectively promotes the hydrophobic interaction between the alkyl tails of gemini surfactants.

Theoretical studies of a singlet oxygen-releasing dioxapaddlane (1,4-diicosa naphthalene-1,4-endoperoxide).

Theoretical calculations have been used to examine singlet oxygen release from a naphthalene endoperoxide which bears a flexible (CH(2))(22) polymethylene "lid". Monte Carlo and ONIOM calculations that incorporated semi-empirical and density functional theory predicted the conformational influence of the polymethylene chain in the cycloreversion of dioxapaddlane, 1,4-diicosa naphthalene-1,4-endoperoxide, to (1)O(2) and 1,4-diicosa naphthalene. This study attempts to build a connection between (1)O(2) generation and "jump rope" dynamics of the dioxapaddlane. The polymethylene chain appears to function as a gatekeeper for the oxygen. Instead of coming full circle, a semi-circle rotation of the polymethylene bridge protected the peroxide group, limiting the dissociation of (1)O(2) from the naphthalene site.

Stereoselective [2+2] photocycloaddition in bispseudosandwich complexes of bis(18-crown-6) stilbene with alkanediammonium ions

Due to hydrogen bonding, bis(18-crown-6) stilbene forms 1 : 1, 1 : 2, and 2 : 2 complexes with H3N+(CH2)nNH3+ 2ClO4− salts (n = 2—10, 12). The length of the polymethylene chain in the diammonium ions affects the phototransformation direction of stilbene and the composition of the products. In the 2: 2 bispseudosandwich complexes with relatively short alkanediammonium ions (n = 2—4), the stereoselective reaction of [2+2] photocycloaddition proceeds to form mainly the rctt-isomer of the cyclobutane derivative. The structure of rctt-cyclobutane derivative as a complex with H3N+(CH2)4NH3+2ClO4- was confirmed by X-ray diffraction analysis.

Biodegradable gemini surfactants. Correlation of area per surfactant molecule with surfactant structure

Values of the area per surfactant molecule of various single chain and gemini quaternary ammonium surfactants containing biodegradable amide and ester groups are obtained from the surface tension measurements and they are mutually compared. It was found that surfactant molecules with the ester group in their structure occupy smaller area at the air/water interface than the corresponding molecules with the amide group, mainly due to the higher conformational flexibility of ester groups. In decreasing the area per surfactant molecule value, hydrogen bonding (both inter- and intramolecular) plays a significant role when amide groups are present in the spacer of a gemini molecule. They must be separated by a polymethylene chain or a flexible group such as cyclohexane which is short enough to allow intramolecular hydrogen bonds. The flexible cyclohexane group with the amide group in single chain surfactants may lead to the formation of intermolecular hydrogen bonds among surfactant molecules which also results in the reduction of the area per surfactant molecule.

Mechanism of hydrolysis of dicholine esters with long polymethylene chain by human butyrylcholinesterase

Human butyrylcholinesterase hydrolyzes long chain dicholine esters more rapidly than short chain dicholine esters. The active site of butyrylcholinesterase is deeply buried within the enzyme molecule and there is limited space for binding of large compounds. Our goal was to understand how butyrylcholinesterase accommodates long chain dicholine esters to make them better substrates than short chain dicholine esters. For this purpose we studied the rate of hydrolysis of adipyldicholine ( n = 4) and sebacyldicholine ( n = 8) with mass spectrometry, a method that allowed monitoring the dicholine substrates, the monocholine intermediates, the dicarboxylic acid and choline products. It was shown that hydrolysis of adipyldicholine involves two consecutive steps, dicholine ester hydrolysis followed by relatively slow monocholine ester hydrolysis. However, sebacyldicholine was hydrolyzed at both choline ester sites, though hydrolysis of dicholine was faster than hydrolysis of monocholine. Sebacyldicholine was completely converted to sebacic acid and choline within 90 min, whereas only 15% of the adipyldicholine was converted to adipic acid in this time. Molecular modeling indicated that these dicholine esters can bind to butyrylcholinesterase in two energetically equivalent alternative conformations that may theoretically lead to hydrolysis. The long chain dicholine ester makes closer contact than the short chain ester between one of its carbonyl carbons and the catalytic Ser198, thus explaining why long-chain dicholine esters are hydrolyzed more rapidly by butyrylcholinesterase.

13C NMR Spectroscopy to Determine Structure and Composition of Waxes and Glycerides

13C nuclear magnetic resonance spectroscopy has been successfully applied to determine the structures of natural derivatives of long-chain fatty acids and in particular, waxes and glycerides. The term wax is used to indicate esters of aliphatic acids with alcohols other than glycerol. 13C chemical shifts of unsaturated carbons in long-chain esters and acids were explained in terms of long-range σ-inductive interactions through saturated C-C bonds in polymethylene chains. A mathematical model was proposed to predict NMR shifts at sp2 carbons of mono- and non-conjugated polyenoic acids and esters. 13C NMR was also applied for studying the structure of glycerides. Unsaturation degree, cis-trans isomerization, and positional isomerism of fatty acids were determined along with their distribution between the 1,3- and 2-positions of glycerol backbone. The compositional data of the two fatty acid pools which esterify 1,3- and 2-glycerol positions, opened a new frontier in the knowledge of glyceride structures. Positional data of triglycerides enabled the set-up of new analytical methodologies which apply quantitative 13C NMR spectroscopy to determine the composition of natural mixtures of triacylglycerols, i.e. vegetable oils.

Structure and properties of macrocyclic compounds containing a pyrimidine fragment

The structure of a series of macrocyclic compounds consisting of a pyrimidine or 1,3,5-triazine ring and an aza-or thiapolymethylene bridge connecting the N1 and N3 atoms of the heteroring is discussed. Some macroheterocycles undergo methylation at the sulfur atom by the action of methyl p-toluenesulfonate. The length of the polymethylene bridge determines conformation of the macroring. Compounds with a shorter bridge both in crystal and in solution are characterized by closely located structural fragments, while extension of the polymethylene chain gives rise to an unfolded structure. Conformational changes in solution are promoted by protonation of the bridging nitrogen atom, and deprotonation restores the initial structure of the macroring. The basicity of the bridging nitrogen atom depends on the geometric parameters of the macroring.

Temperature-Dependent Self-Assembly and Mixing Behavior of Symmetrical Single-Chain Bolaamphiphiles

The temperature-dependent self-assembly and the mixing behavior of symmetrical single-chain bolaamphiphiles with different polymethylene chain lengths and different headgroup structures were investigated in water by differential scanning calorimetry (DSC), cryo transmission electron microscopy (cryo-TEM), and small angle neutron scattering (SANS). The even-numbered polymethylene-1,omega-bis(phosphocholines) (PC-C n-PC) are known to form nanofibers composed of stretched molecules with an all- trans alkyl chain conformation (Drescher, S.; Meister, A.; Blume, A.; Karlsson, G.; Almgren, M.; Dobner, B. Chem.Eur. J. 2007, 13, 5300-5307). The odd-numbered analogues were synthesized to study a possible even-odd effect of these bolaamphiphiles during their aggregation in water. In addition to these bolaamphiphiles with phosphocholine headgroups, a new series of polymethylene-1,omega-bis(phosphodimethylethanolamines) (Me2PE-Cn-Me2PE) with smaller headgroup sizes was synthesized. These bolaamphiphiles show an additional fiber-fiber transition when the alkyl chain length exceeds 26 carbon atoms. The mixing behavior of both types of bolaamphiphiles indicates that differences in the alkyl chain length up to six carbon atoms are tolerated within the fiber structure. The mixing of two Me2PE-Cn-Me2PE or PC-Cn-PC type bolaamphiphiles with different alkyl chain lengths offers the possibility to adjust the temperature, where the cross-linking of the fibers is disrupted and where the fibers break apart. As a consequence, temperature switchable hydrogels are obtained that can be fine-tuned for drug delivery applications. The comparison with dotriacontane-1,32-diyl-bis[2-(methylammonio)-ethylphosphate] (MePE-C32-MePE), a new bolaamphiphile with even smaller phosphomonomethylammonio headgroups, illustrates the importance of the headgroup size for the aggregation behavior. This bolaamphiphile self-assembles exclusively into lamellar structures, and this aggregate type persists in mixtures with the fiber forming Me2PE-C32-Me2PE.

A steered molecular dynamics study on the elastic behaviour of knotted polymer chains

In this paper the influence of a knot on the structure of a polymethylene (PM) strand in the tensile process is investigated by using the steered molecular dynamics (SMD) method. The gradual increasing of end-to-end distance, R, results in a tighter knot and a more stretched contour. That the break in a knotted rope almost invariably occurs at a point just outside the 'entrance' to the knot, which has been shown in a good many experiments, is further theoretically verified in this paper through the calculation of some structural and thermodynamic parameters. Moreover, it is found that the analyses on bond length, torsion angle and strain energy can facilitate to the study of the localization and the size of a knot in the tensile process. The symmetries of torsion angles, bond lengths and bond angles in the knot result in the whole symmetry of the knot in microstructure, thereby adapting itself to the strain applied. Additionally, the statistical property of the force-dependent average knot size illuminates in detail the change in size of a knot with force f, and therefore the minimum size of the knot in the restriction of the potentials considered in this work for a PM chain is deduced. At the same time, the difference in response to uniaxial strain, between a knotted PM strand and an unknotted one is also investigated. The force-extension profile is easily obtained from the simulation. As expected, for a given f, the knotted chain has an R significantly smaller than that of an unknotted polymer. However, the scaled difference becomes less pronounced for larger values of N, and the results for longer chains approach those of the unknotted chains.

Copper N 2S 2 Schiff base macrocycles: The effect of structure on redox potential

A series of bis-salicylidene based N 2S 2 copper macrocycles were prepared, structurally characterised and subjected to electrochemical analysis. The aim was to investigate the effects of length of polymethylene chains between either the imine donors or the sulfur donors on redox state and potential of the metal. The complexes structurally characterised had either distorted square planar or tetrahedral geometries depending on their oxidation state (Cu 2+ or Cu +, respectively), and the N–(CH 2) n –N bridge was found to be most critical moiety in determining the redox potential and oxidation state of the copper macrocycles, with relatively little change in these properties caused by lengthening the S–(CH 2) n –S bridge from two to three carbons. In fact, a weakness was observed in the complexes at the sulfur donor, as further lengthening of the S–(CH 2) n –S methylene bridge to four carbons caused fission of the carbon–sulfur bond to give dimeric rings and supramolecular assemblies. Cu + complexes could be oxidised to Cu 2+ by tert-butylhydroperoxide, with a corresponding change in the spectrophotometric properties, and likewise Cu 2+ complexes could be reduced to Cu + by treatment with β-mercaptoethylamine. However, repeated redox cycles appeared to compromise the stability of the macrocycles, most probably by a competing oxidation of the ligand. Thus the copper N 2S 2 macrocycles show potential as redox sensors, but further development is required to improve their performance in a biochemical environment.

The phase behaviors of adsorbed polymethylene chains

The phase behaviors of a single adsorbed polymethylene chain are investigated by using molecular dynamics simulations. In the free space, it is confirmed in our calculation that the isolated polymer chain exhibits a disordered coil state at high temperatures, and collapses into a condensed state at low temperatures, i.e., the coil-to-globule transition, and finite chain length effects are considered since the critical region may depend on the chain length. When the chain is adsorbed on an attractive surface, however, the equilibrium properties may not only depend on chain length but also depend on the adsorption energy. For short chain of N=40 monomers, a coil-to-globule transition is found for weak adsorption energy of w=2.5kcal/mol, but the critical temperature is lower than the free chain, and for strong adsorptions of w=3.5 and 4.5kcal/mol, the structures at low temperatures are adsorbed hairpin like, so we may call the transition process coil-to-hairpin transition. For long chains of N=80 monomers and N=120 monomers, the critical regions are the same for the free chains both at T=265K, and for the adsorption energies of w=2.5, 3.5, and 4.5kcal/mol, the curves of the heat capacities are smooth when T>200K, and while T<200K, the values of the heat capacities decrease as the temperatures decreasing, so the transition may be from loose globular structures to compact globular structures, and for more stronger adsorption energy of w=6.5 and 8.5kcal/mol, the critical regions are obvious and they are coil-to-crystal like transitions.

Synthesis and Photophysical Properties of Bispsoralen Derivatives Linked by a Bisamide-polymethylene Chain

New bispsoralen derivatives 5-10, 8-MOP-NHCO(CH2)nCONH-8-MOP (BPSBA-Cn, n = 0, 1, 2, 3, 4 and 5) in which 5 position of an 8-methoxypsoralen (8-MOP) is linked by various lengths of bisamide polymethylene chain to 5 position of the other 8-MOP, have been synthesized by the amidation of 5-amino-8-methoxypsoralen (12) with α,ω-alkanoyl dichloride. Photophysical properties of their derivatives including π?π stacking interaction between the two aromatic moieties were investigated by UV absorption and fluorescence emission spectra. Efficient ring-ring stacking interactions have been observed in BPSBA-C4 (9) from the percent hypochromism (%H) of the models.

Synthesis, Characterization and Thermodynamic Parameters of Anionic Gemini Surfactants with Different Spacer Groups

Abstract The aim of this work is to investigate the micellization and adsorption thermodynamics (ΔmicH°, ΔmicG°, ΔmicS°, ΔadsH°, ΔadsG°, ΔadsS°) for three novel anionic Gemini surfactants with the same structure except the spacer length of the polymethylene chain have been synthesized based on nonylphenol (NP). The surface tension at cmc (γcmc) and critical micelle concentration (cmc) of the surfactants in aqueous solutions have been investigated. C20 values (surfactant concentration in the solution phase that will reduce the surface tension of the solvent by 20 mNm−1) were also obtained. The critical micellar concentration (cmc) and the minimum average area per surfactant molecule (Amin) at the air-water interface of Gemini surfactant decrease with increasing number of methylene moieties in the spacer and, consequently, with the enhanced hydrophilic character of the molecule. The results were discussed with particular emphasis on the effect of the length spacer on the hydrophilic character of the spacer group. The surface studies of the molecules confirm that the exothermic values of the differential enthalpy of micellization (ΔmicH°) decrease as the methylene moieties are lengthened. Moreover, the values of the free energy (ΔmicG°) and entropy (ΔmicS°) of micellization indicate an entropy driven phenomenon for all surfactants. The effect of length spacer on surfactant adsorption for Gemini surfactants was utilized to calculate such thermodynamic parameters as the free energy of adsorption (ΔadsG°) and the heat of adsorption (ΔadsH°). The low value of ΔadsH° is an evidence for the physical adsorption of anionic surfactants. The relatively large value of entropic contribution (TΔadsS°) indicates that the adsorption of anionic surfactants is entropically governed.

Copper(II) bromide complexes with acyclic and cyclic pyrimidine-containing phane ligands

Complexes of copper(II) bromide with cyclic and isostructural acyclic phane ligands containing derivatives of pyrimidine nucleobases (cytosine and uracil) were synthesized and characterized. In two cyclic pyrimidinophanes used, the macrocycles included two 6-methylthiocytosine and one 6-methyluracil units linked by polymethylene chains (L3) and two 6-methyluracil units linked by N-containing bridges (L5). Ligand L3 and its isostructural acyclic analogs are coordinated by the Cu2+ ion through the same donor sites (the ring N atoms of the thiocytosine units). The coordination polyhedra of the Cu atom in complexes with cyclic and acyclic ligands are different. Ligand L5 and its isostructural acyclic analog also form copper(II) complexes with different coordination polyhedra involving different donor sites. The acyclic ligand is coordinated by the Cu2+ ion via the bridging N atom, while cyclic ligand L5, via the uracil CO groups (the bridging N atoms become protonated). The resulting complexes are dielectrics.

Bivalent ligand approach on 4-[2-(3-methoxyphenyl)ethyl]-1-(2-methoxyphenyl)piperazine: Synthesis and binding affinities for 5-HT 7 and 5-HT 1A receptors

We here report on the synthesis and binding properties at 5-HT 7 and 5-HT 1A receptors of ligands 3– 12, that were designed according to the ‘bivalent ligand’ approach. Two moieties of the 5-HT 7/5-HT 1A ligand 4-[2-(3-methoxyphenyl)ethyl]-1-(2-methoxyphenyl)piperazine ( 1) were linked through their 3-methoxy substituent by polymethylene chains of variable length, with the aim to increase the affinity for 5-HT 7 receptor and the selectivity over 5-HT 1A receptors. In the best cases, the dimers showed affinities for 5-HT 7 receptors as high as the monomer with no improvement in selectivity. Some dimers displayed 5-HT 1A receptor affinities slightly higher than monomer 1.

Synthesis and Spectral Properties of Amphiphilic Lipids with Linear Conjugated Polyene and Phenylpolyene Fluorescent Groups

AbstractLipophilic fluorescent groups with a chain‐like linear conformation emitting in the visible range and with high photostability are presently unavailable. These structures would be of great interest as labels for long‐chain fatty acids and phospholipids lacking intrinsic fluorescent groups. With this aim in mind, we report the synthesis and the spectroscopic characterization of a series of emitting amphiphilic lipids that may approach that ideal fluorescent tag. Each lipid was constructed by attaching a linear, all‐(E) conjugated pentaene, tetraenyne, ω‐phenyltetraene, or ω‐phenyltrienyne chromophore to a hydrophilic head‐group through a polymethylene chain spacer. The key steps of the synthesis were the Pd0‐mediated cross‐coupling reaction between bromopolyenes and terminal acetylenic compounds, yielding tetraenynes or ω‐phenyltrienynes, and the subsequent triple‐bond partial reduction, producing the corresponding pentaenes or ω‐phenyltetraenes in good overall yields. This method represents a further successful example of the so‐called “acetylenic approach” to the indirect high‐yield synthesis of polyene systems. In the case of ω‐phenyltrienynes, a higher proportion of the all‐(E) isomer was obtained using an alternative method based on the reaction of an ω‐phenyldienylphosphonate with an α‐acetylenic aldehyde. Some of the resulting compounds exhibit spectral and photochemical properties that warrant their use as emitting lipophilic tags. Thus, the ω‐phenyltetraene and ω‐phenyltrienyne members of the series show intense absorption bands in the 320–370 nm range with fluorescence emission centered at 475 nm and quantum yields up to 0.25. These parameters are appropriate for the applications noted above. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2007)

Quinoxaline—Benzimidazole Rearrangement in the Synthesis of Benzimidazole‐Based Podands.

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