Oligomers In Solution Research Articles

Hydrolysis of tin(II) neo-pentoxide: syntheses, characterization, and X-ray structures of [Sn(ONep)(2)](infinity), Sn(5)(mu(3)-O)(2)(mu-ONep)(6), and Sn(6)(mu(3)-O)(4)(mu-ONep)(4) where ONep = OCH(2)CMe(3).

The reaction of [Sn(NMe(2))(2)](2) (1) with 4 equiv of HOCH(2)CMe(3) (HONep) leads to the isolation of [Sn(ONep)(2)](infinity) (2). Each Sn atom is four coordinated with mu-ONep ligands bridging the metal centers; however, if the free electrons of the Sn(II) metal center are considered, each Sn center adopts a distorted trigonal bipyramidal (TBP) geometry. Through (119)Sn NMR experiments, the polymeric compound 2 was found to be disrupted into smaller oligomers in solution. Titration of 2 with H(2)O led to the identification of two unique hydrolysis products characterized by single-crystal X-ray diffraction as Sn(5)(mu(3)-O)(2)(mu-ONep)(6) (3) and Sn(6)(mu(3)-O)(4)(mu-ONep)(4) (4). Compound 3 consists of an asymmetrical molecule that has five Sn atoms arranged in a square-based pyramidal geometry linked by four basal mu-ONep ligands, two facial mu(3)-O, and two facial mu-ONep ligands. Compound 4 was solved in a novel octahedral arrangement of six Sn cations with an asymmetric arrangement of mu(3)-O and mu-ONep ligands that yields two square base pyramidal and four pyramidal coordinated Sn cations. These compounds were further identified by multinuclear ((1)H, (13)C, (17)O, and (119)Sn) solid-state MAS and high resolution, solution NMR experiments. Because of the complexity of the compounds and the accessibility of the various nuclei, 2D NMR experiments were also undertaken to elucidate the solution behavior of these compounds. On the basis of these studies, it was determined that while the central core of the solid-state structures of 3 and 4 is retained, dynamic ligand exchange leads to more symmetrical molecules in solution. Novel products 3 and 4 lend structural insight into the stepwise hydrolysis of Sn(II) alkoxides.

ChemInform Abstract: Excited‐State Interactions for [Au(CN)2‐]n and [Ag(CN)2‐]n Oligomers in Solution. Formation of Luminescent Gold—Gold Bonded Excimers and Exciplexes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis and Properties of Coil-Shaped 2,3-Thienylene-Ethynylene Oligomers

A series of 2,3-thienylene-ethynylene oligomers have been synthesized by repeated application of the Pd-catalyzed coupling reaction of terminal alkynes and thienyl iodides as the key building steps. The analytical GPC molecular weights, much deflated relative to the actual molecular weights, strongly suggest a coil shape for the conformation of the oligomers in solution. Their electronic absorption and emission spectral features are discussed.

Synthesis and Properties of Coil-Shaped 2,3-Thienylene-Ethynylene Oligomers

A series of 2,3-thienylene-ethynylene oligomers have been synthesized by repeated application of the Pd-catalyzed coupling reaction of terminal alkynes and thienyl iodides as the key building steps. The analytical GPC molecular weights, much deflated relative to the actual molecular weights, strongly suggest a coil shape for the conformation of the oligomers in solution. Their electronic absorption and emission spectral features are discussed.

Surface Modification of Cellulose and Polyester by Oligomeric Fluoroalkylating Agents Having Oxime-blocked Isocyanate Groups.

Surface modification of cellulose and polyester by the oligomeric fluoroalkylating agents having oxime-blocked isocyanate groups was studied by measuring the contact angle, surface free energy, FT-IR(ATR) and XPS spectra. In the case of cellulose, the modified surface changed to oil-repellent. The dispersion components of the surface free energy γsd were 21-25mJ/m2 and the polar components γsp were 2-6mJ/m2 at above 2 wt% of treatment concentration of oligomer solution. There existed a linear relationship between the treatment concentration and the AC=O/AC-O peak ratios in FT-IR(ATR). Moreover, the surface free energy decreased with increase in the values of F1s/O1s peak area ratios in XPS and became constant above 0.2 of F1s/O1s peak area ratios. In the case of polyester, the contact angles of dodecane were 10-30o and those of water were about 80o even above 5 wt% of treatment concentration. The values of F1s/O1s peak area ratios increased with increase in the treatment concentration and became constant at above 5 wt% of treatment concentration. Based on the FT-IR(ATR) and XPS results, the structures of the modified layer were interpreted in terms of the modification mechanism. In the case of cellulose, the oligomer reacted at the surface, and some parts would diffuse into the inner region. On the other hand, the oligomers were thermally anchored at the polyester surface.

Grafting of functional maleimides onto oligo- and polyolefins

In this paper the modification of polyolefins, especially polypropylene (PP), with maleimides is discussed. As there are many problems associated with the analysis of the grafting reaction, commercially available squalane and eicosane were used as model compounds for ethylene-propylene-copolymer (EPR) and polyethylene (PE). 2,4,6,8-Tetramethylnonane (TMN) was synthesized as a novel model compound for PP. N-Phenylmaleimide and maleimido benzoic acid were grafted onto the oligomers in solution using 2,5-dimethyl-2,5-di-(tert-butyl-peroxy)-3-hexyne (Luperox 130) as radical initiator. The grafting efficiency was determined by NMR-, UV-spectroscopy, gravimetry and gas-chromatography. The influence of several reaction parameters on homopolymerformation, amount of modified oligomer and grafting efficiency could be elaborated. NMR-spectroscopy and SEC were used to analyse the nature of the grafts. Grafting yields were almost quantitative using up to more than 10 mol% monomer, but dropped at higher monomer concentrations to about 60%. The amount of modified oligomer could be increased with higher monomer concentrations or reaction temperatures. Grafting of polymers was done by reactive extrusion. Products were analysed by IR-spectroscopy. Optimal grafting yields could be achieved with 1 wt% monomer and 0.5 wt% peroxide concentration.

PH-dependent oligomerization of BPTI in undersaturated and supersaturated solutions studied by dynamic light scattering

Bovine pancreatic trypsin inhibitor (BPTI), a small protein molecule, is reported to form several types of oligomers in solution including a decamer. We investigate in this work the relation between the oligomerization and crystallization. The oligomerization and interaction between BPTI molecules in NaCl and NaH 2PO 4/K 2HPO 4 solutions were investigated by dynamic light scattering (DLS). In the NaCl solutions, we found that strong electrostatic interaction among BPTI and chloride ions led to the decamer formation only at an acidic pH, whereas the protein solutions were monomeric at a neutral or basic pH, where the electrostatic interaction seemed to be unimportant. The single crystals with a hexagonal truncated bipyramidal shape grew only in the decameric solutions at an acidic pH in the presence of NaCl. On the other hand, the electrostatic interaction was weak in the presence of NaH 2PO 4/K 2HPO 4 at all the pH values investigated, and the solutions were always monomeric. In contrast with the NaCl solutions, single crystals with a rod-like shape appeared at a neutral and basic pH in the NaH 2PO 4/K 2HPO 4 solutions. These results suggest that the crystallization mechanism in the presence of NaCl, where electrostatic interactions seem to drive crystallization, is totally different from that in the presence of NaH 2PO 4/K 2HPO 4 where another interaction such as hydrophobic interaction or hydrogen bonding might cause crystallization.

Photo-Assisted ImmobilizedFenton Degradation up to pH 8 of Azo Dye Orange II Mediated by Fe3+/Nafion/Glass Fibers

Fe3+ Ions have been immobilized into very thin Nafion films cast onto a glass-fiber mat immersed in an alcoholic solution of Nafion oligomers. This immobilized Fenton catalyst was used to abate/mineralize the azo dye Orange II, taken as a model organic compound. The abatement of Orange II on the Fe3+/Nafion/glass fibers was observed to proceed within the same time period as when Nafion alone was used to immobilize the Fe3+ ions during the photo-Fenton reaction. The amount of Nafion in the Nafion Fe3+/Nafion/glass fibers was ca. 15 times less per unit surface area compared to Fe3+-exchanged on conventional Nafion membranes used to immobilize Fe3+ ions. Orange II solutions under visible-light irradiation in the presence of H2O2 were mineralized up to pH 8 with a kinetics comparable to that found during the degradation runs at pH 3. Repetitive mineralization cycles mediated by the Fe3+/Nafion/glass fibers under visible light did not show any decrease in the activity of the immobilized catalysts. A reaction mechanism consistent with the experimental data is suggested. The morphology of the Fe3+/Nafion/glass fibers was characterized by scanning electron microscopy (SEM) showing thin Nafion films cast deposited on the glass fibers. Transmission-electron-microscopy (TEM) micrographs reveal Fe3+-oxy-hydroxide particles of 3 – 6 nm before and after repetitive Orange II photodegradation. X-Ray photoelectron spectroscopy (XPS) provided the evidence for the existence of Fe clusters on the topmost layer of the catalyst mainly as FeIII. The improvements brought by the glass fibers are a) the use of low quantities of expensive Nafion supported on glass mats to achieve dye degradation rates comparable to Nafion alone and b) Fenton-mediated degradation of azo dyes at pH 8 without the costly initial acidification usually needed for this type of treatment.

Electrical properties of water solutions of polyelectrolytes for electrodeposition

The specific electric conductivity and the electrophoretic mobility of two different polycondensed film-forming substances (alkyd and alkydepoxide oligomers) that are used as binders for anodic electrodeposition have been studied. These electric characteristics were investigated in a broad range of concentrations. By conductometric method the availability of four critical micelle concentrations (CMCs) in aqueous solutions of polyelectrolytes was shown. These CMCs are caused by structural transitions and intermicellar interactions in the oligomer solutions. Characteristic for these transitions alterations were also detected on concentration dependence of electrophoretic mobility.

Amorphous Poly-2,7-fluorene Networks

We have developed a novel strategy for the synthesis of emitters, based on amorphous poly-2,7-fluorene (2,7-PF) networks which exhibit high glass transition temperatures and good photoluminescence properties and are suitable for incorporation into multilayer lightemitting diodes (LEDs). The materials design includes nickel(0)-mediated copolymerization of 2,7-dibromo-9,9-dihexylfluorene with a tetrafunctional spiro-compound, 2,2′,7,7′-tetrabromo-9,9-spirobifluorene, and 4-bromostyrene as end-capping reagent. The introduction of the spiro-bifluorene leads to a 90° branch of the growing 2,7-PF chain, the number of which can be controlled via the feed ratio of monomers used. The termination of the growing network with 4-phenylethenyl end groups limits the molecular weight, hence keeps the material soluble and processable. The oligomer solution can be cast into thin films and thermally cross-linked leading to new amorphous 2,7-PF networks. The amorphous 2,7-PF networks were incorporated in bilayer and trilayer LED devices which emitted colorfast blue light.

Development and characterization of cross-linked poly(malate) microspheres with dipyridamole

Biodegradable cross-linked microspheres containing up to 63 wt.% of the active substance were obtained in a polycondensation process between d,l-malic acid and the tetrahydroxy compound dipyridamole. The in vitro release mechanism from biodegradable cross-linked microspheres has been studied. It was found that dipyridamole was released due to two-step hydrolysis of the ester bonds of the network. Initially, the only product of the hydrolytic degradation was found to be an oligomeric ester fraction with M w=1000 Da. The release of the free drug started after 8 days due to a further hydrolysis of the oligomers in solution. It was found that blood plasma enzymes in rats did not affect the hydrolytic processes. Biodegradable poly(malate) microspheres containing an anti-aggregating agent dipyridamole can be considered as a novel drug delivery system for a prolonged period of time implying a future parenteral application.

Dependence on solution conditions of aggregation and amyloid formation by an SH3 domain

The formation of amyloid fibrils by the SH3 domain of the α-subunit of bovine phosphatidylinositol-3′-kinase (PI3-SH3) has been investigated under carefully controlled solution conditions. NMR and CD characterisation of the denatured states from which fibrils form at low pH show that their properties can be correlated with the nature of the resulting aggregates defined by EM and FTIR spectroscopy. Compact partially folded states, favoured by the addition of anions, are prone to precipitate rapidly into amorphous species, whilst well-defined fibrillar structures are formed slowly from more expanded denatured states. Kinetic data obtained by a variety of techniques show a clear lag phase in the formation of amyloid fibrils. NMR spectroscopy shows no evidence for a significant population of small oligomers in solution during or after this lag phase. EM and FTIR indicate the presence of amorphous aggregates (protofibrils) rich in β-structure after the lag phase but prior to the development of well-defined amyloid fibrils. These observations strongly suggest a nucleation and growth mechanism for the formation of the ordered aggregates. The morphologies of the fibrillar structures were found to be highly sensitive to the pH at which the protein solutions are incubated. This can be attributed to the effect of small perturbations in the electrostatic interactions that stabilise the contacts between the protofilaments forming the amyloid fibrils. Moreover, different hydrogen bonding patterns related to the various aggregate morphologies can be distinguished by FTIR analysis.

Structure of the insecticidal bacterial delta-endotoxin Cry3Bb1 of Bacillus thuringiensis.

The coleopteran-active delta-endotoxin Cry3Bb1 from Bacillus thuringiensis (Bt) strain EG7231 is uniquely toxic to Diabrotica undecimpunctata, the Southern corn rootworm, while retaining activity against Leptinotarsa decemlineata, the Colorado potato beetle. The crystal structure of the delta-endotoxin Cry3Bb1 has been refined using data collected to 2.4 A resolution, with a residual R factor of 17.5% and an R(free) of 25.3%. The structure is made up of three domains: I, a seven-helix bundle (residues 64-294); II, a three-sheet domain (residues 295-502); and III, a beta-sandwich domain (residues 503-652). The monomers in the orthorhombic C222(1) crystal lattice form a dimeric quaternary structure across a crystallographic twofold axis, with a channel formed involving interactions between domains I and III. There are 23 hydrogen bonds between the two monomers conferring structural stability on the dimer. It has been demonstrated that Cry3Bb1 and the similar toxin Cry3A form oligomers in solution. The structural results presented here indicate that the interactions between domains I and III could be responsible for the initial higher order structure and have implications for the biological activity of these toxins. There are seven additional single amino-acid residues in the sequence of Cry3Bb1 compared with that of Cry3A; one in domain I, two in domain II and four in domain III, which also shows the largest conformational difference between the two proteins. These changes can be implicated in the selectivity differences noted for these two delta-endotoxins.

Analysis of Structures of Oligomeric Siloxanes from Dimethoxydimethylsilane under Heat Treatment by FT-IR

The structures of dimethoxydimethylsilane oligomers were investigated before and after heat treatment. FT-IR CIRCLE was used to analyze the structures of siloxane oligomers in solution before annealing, and diffuse reflectance was used to analyze them after annealing. Linear siloxane components were predominant in oligomer solution, while half the volume fraction was changed into ring form after annealing. Ring formation proceeded further with increasing molecular weight of the oligomer in solution. When hydrochloric acid (HCl) was used as catalyst for the reaction, the fraction of linear siloxane component was higher and ring formation was easier than without catalyst or with basic DMF catalyst.

Synthesis and Characterization of Novel Alumina-Pillared γ-Zirconium Phosphates

The preparation of alumina-pillared γ-zirconium phosphate materials was carried out for the first time by thermal hydrotreatment at 473 K of stable aqueous colloidal suspensions of γ-zirconium phosphate and aluminum oligomeric solutions. The nature of the resulting porous materials depends on the delamination processes used. 31P MAS NMR data suggest the existence of P−O−Al groups, and 27Al NMR analysis by means of the two-dimensional five-quanta MQMAS technique reveals the coexistence, in some cases, of octahedral, tetrahedral, and pentacoordinate aluminum. The samples, fresh and after heating at 673 K, were fully characterized by chemical analysis, X-ray diffraction analysis, thermogravimetric−differential thermal analysis, X-ray photoelectron spectroscopy, temperature-programmed desorption of NH3, pyridine adsorption coupled to IR spectroscopy, and nitrogen adsorption−desorption at 77 K.

Electrospray mass spectrometry determination of linear and cyclic oligomers of polyamide-6

Analysis of linear and cyclic polyamide-6 (PA-6) oligomer mixtures is an often needed task, that requires expensive equipment and/or chemicals or involved chemical procedures. We present an analytical method using electrospray ionization-mass spectrometry (ESI-MS) that has none of the mentioned difficulties. Measurements were performed on simple acidic aqueous solutions of oligomers. The method allowed qualitative and quantitative characterization of cyclic and linear oligomers up to octamer. Scanning for both the positive, as well as negative ion fragments was used. Signal vs. concentration responses were determined for a number of lower oligomers. The method has the advantage of short analysis times and the use of relatively accessible instrumentation.

Self-assembly of 2-(guanidiniocarbonyl)-pyrrole-4-carboxylate in dimethyl sulfoxide: an entropy driven oligomerization

The self-assembly of 2-(guanidiniocarbonyl)-pyrrole-4-carboxylate (2), which is a heteroditopic zwitterion with self-complementary binding groups, was studied in DMSO. Through intermolecular ion pairing between the carboxylate of one and the guanidinium group of another molecule, 2 forms linear chain like oligomers in solution as can be seen from the corresponding shift changes in the NMR spectrum. Concentration dependent NMR studies at different temperatures allowed us to calculate the corresponding binding constants and thermodynamic parameters for this association process. These data show that the oligomerization is endothermic and therefore an entropy-driven process. The release of ordered solvent molecules into the bulk solution during complexation is hence responsible for the oligomerization.

New fluorene based tetramers for luminescence applications

Fluorene based polymers have been receiving much attention as promising component in luminescence devices. In this frame the related oligomers reached relevance either as polymeric models or as active layers. On these basis, three fluorenic-core tetramers have been synthetized via organosynthetic routes. The molecular, optical and electrochemical characterization of such oligomers in solution has been performed, furthermore, their high photoluminescence quantum yields (PLQY) render them attractive for electroluminescent device preparations. In this view the optical investigations with both absorption and emission techniques were also carried out in the solid state samples in thin films (up to 80nm thick) obtained by solution casting or evaporation using ultra high vacuum apparatus. Detailed structural analyses from XRD data allowed packing determination, hence the optical properties are related to the different type of aggregation in the solid state.

The conformational study of chitin and chitosan oligomers in solution

The inter-residual dihedral angles φ and ϕ of chitin and chitosan oligomers were determined from experimental 3JC-H constants and ROESY cross peaks.

Structural Analysis of the Protein/Lipid Complexes Associated with Pore Formation by the Bacterial Toxin Pneumolysin

Pneumolysin, a major virulence factor of the human pathogen Streptococcus pneumoniae, is a soluble protein that disrupts cholesterol-containing membranes of cells by forming ring-shaped oligomers. Magic angle spinning and wideline static (31)P NMR have been used in combination with freeze-fracture electron microscopy to investigate the effect of pneumolysin on fully hydrated model membranes containing cholesterol and phosphatidylcholine and dicetyl phosphate (10:10:1 molar ratio). NMR spectra show that the interaction of pneumolysin with cholesterol-containing liposomes results in the formation of a nonbilayer phospholipid phase and vesicle aggregation. The amount of the nonbilayer phase increases with increasing protein concentration. Freeze-fracture electron microscopy indicates the coexistence of aggregated vesicles and free ring-shaped structures in the presence of pneumolysin. On the basis of their size and analysis of the NMR spectra it is concluded that the rings are pneumolysin oligomers (containing 30-50 monomers) complexed with lipid (each with 840-1400 lipids). The lifetime of the phospholipid in either bilayer-associated complexes or free pneumolysin-lipid complexes is > 15 ms. It is further concluded that the effect of pneumolysin on lipid membranes is a complex combination of pore formation within the bilayer, extraction of lipid into free oligomeric complexes, aggregation and fusion of liposomes, and the destabilization of membranes leading to formation of small vesicles.