Recognition properties of an acyclic biphenyl-based receptor toward carbohydrates

Biphenyl-based receptor 1, incorporating four heterocyclic recognition units, was synthesized, and its binding properties toward neutral sugars were determined. Receptor 1 is a representative of a new series of acyclic carbohydrate-binding receptors, which were designed to recognize disaccharides. The compound 1 has been established as a highly effective receptor for dodecyl beta-D-maltoside, showing successive 1:1 and 2:1 receptor/substrate complexation behavior toward the disaccharide. Both hydrogen bonding and interactions of the sugar CH's with the aromatic units of the receptor contribute to the stabilization of the receptor-maltoside complexes.     

Synthesis and supramolecular properties of glycoluril tetramer

Synthesis of glycoluril tetramer bearing hydrogen atoms on its convex face and framed by two xylylene units is reported. This tetramer forms dimeric aggregates in the solid state. Host–guest properties of the tetramer with various ammonium and pyridinium guests were determined using ¹H NMR spectroscopy. The results were compared with structurally related host molecules.     

Recognition of caffeine by a water-soluble acyclic phane compound

Caffeine (1,3,7-trimethylxanthine) is a chemical substance associated with everyday human life. In order to recognize caffeine in water, six water-soluble acyclic phane compounds composed of three aromatic rings were examined as artificial receptors. ¹H NMR titration experiments revealed that 6,6′-[1,3-phenylenebis(carbonylimino)]bis-1,3-naphthalenedisulfonate had the highest binding ability for caffeine, with a binding constant (K_b) of 127±5 M⁻¹ at 300 K. While this phane compound also formed a complex with theophylline (1,3-dimethylxanthine) at around half the value of the binding constant for caffeine (K_b=64±4 M⁻¹), it showed weak or little complexation for adenosine, guanosine, inosine, and their 5′-phosphates (sodium salts of adenylic acid, guanylic acid, and inosinic acid).     

Liquid properties of oligomers. Comparison of relaxational properties of propylene glycol oligomers with those of ethylene glycol oligomers

Liquid properties such as dielectric relaxation and viscous flow of the two structurally homologous propylene glycol oligomers HO(CH(CH₃)CH₂O)_nH (n=1, 2, 3, 4, 5 and 34) and ethylene glycol oligomers HO(C₂H₄O)_nH (n=1, 2, 3, 4, 5 and 6) are studied in pure liquid state to clarify the degree of polymerization dependences of chain molecules on their liquid properties. These oligomers are, at room temperature, viscous liquid which shows dielectric relaxations in the frequency range from 10 Hz to 3 MHz. Propylene glycol oligomers (n=from 1 to 5) show the Davidson-Cole-type relaxations, but the higher glycol (n=34) shows superposition of the two different relaxations, i. e., small Debye-type relaxation in the lower-frequency region and large principal Havriliak-Negami-type relaxation in the higher-frequency region. Relaxation times vs. degree of polymerization do not increase linearly, but vary in zigzag lines. Above all, the dimers (dipropylene glycol and diethylene glycol) show longer relaxation times than the other glycols. This dielectric result does not agree with the degree of polymerization dependence of viscous flow.     

Conformational properties of thiophene oligomers

The molecular geometries and the torsional potentials about the inter‐ring C‐C bond in α‐oligothiophenes (α‐nTh, n=2–4) have been calculated by means of conventional ab initio and density functional theory (DFT) calculations employing the hybrid B3LYP and BH&HLYP functionals. The position and the energetics of the critical points in the potential energy curve generated by rotation about the inter‐ring C? C bond are shown to be dependent on the computational method. DFT calculations, in comparison with MP2 calculations, favour conjugative interactions, while steric and coulombic interactions are equally treated by both methods. On oligomerization the electron delocalisation increases slightly, the p‐charge being preferentially confined within the rings, although it is sufficient to move the molecular structure towards co‐planarization and to increase the barrier through the perpendicular conformation. The IR and Raman spectra on the relevant rotamers of α‐2Th have been computed at HF/6–31G* and B3LYP/6–31G* levels. The comparison with the experiment is excellent. It has been found that small twisting from the planar conformation has no apparent effects, while 90° twisting and isomerization to the syn‐gauche form produce significant frequency and intensity variations which could be useful probes in conformational studies. The simulated IR and Raman spectra of the α‐2Th rotamers are consistent with a smallπ‐electron delocalisation between the rings.     

New phosphorylated glycoluril derivatives

The N-acylation of glycoluril with 1-haloacetyl halides was studied. The optimal conditions and reaction regioselectivity, as well as the effect of reagent molar ratios, base nature, temperature, and reaction time on the yield of the target product were established. It was shown that the chemical modification of the synthesized bis(bromoacetyl) derivative of glycoluril by phosphorylation by the classical Arbuzov reaction gave a previously unknown bis(diethylphosphonoacetyl) derivative of glycoluril. The consecutive silylation and hydrolysis of the latter derivative gave the corresponding bis(phosphonoacetyl) derivative which presents interest as a potentially biologically active compound.     

Synthesis and properties of tetrazole-containing oligomers

Linear, star-shaped, and hyperbranched oligomeric compounds containing tetrazole cycles in the main chains are synthesized via the polycondensation (polyalkylation) of N-H unsubstituted bis(tetrazoles), tris(tetrazoles), and tetrakis(tetrazoles) with compounds containing mobile halogen atoms. Some properties of the oligomers are studied. Some of the oligomers are characterized by high density and a large content of nitrogen.     

Surface properties of liquid reactive oligomers

Spreading coefficients and the work of adhesion of oligomers to different substrates are calculated based on the results of studying the wettability and surface tension of ED-20 epoxy oligomer and oligooxyethyleneoxypropylene triols. It is shown that the addition of surfactant (ethoxylated alkyl phenols) considerably enhances the wettability of the studied oligomers. It is established that the addition of surfactant imparted to the properties of oligomers and surface energy characteristics of composites based on these oligomers nonlinearly depend on the degree of ethoxylation.     

Synthesis and paramagnetic properties of polytelluride oligomers

Organotellurium oligomers with different lengths of the telluride fragments and hydrocarbon chains were synthesized by reactions of tellurium with organic dihalogen derivatives in the system hydrazine hydrate-KOH. Oligomers containing two and three contiguous tellurium atoms in the solid state give rise to strong ESR signals with a g value of 2.005–2.030 and a line width of 180–290 Oe. The possibility for formation of tellurium-centered radicals is discussed. Nitrosodurene as radical scavenger in chloroform solution trapped neither primary radical species nor radical products derived therefrom.     

Effect of glycoluril and its derivatives on the flame resistance and physico-mechanical properties of rubber

The effect of bicyclic bisureas (glycolurils) and their derivatives functionalized with hydroxymethyl, halomethyl, and dimethoxyphoshorylmethyl groups on the flame resistance and physico-chemical properties of synthetic isoprene and divinyl rubbers was studied, and the procedures for preparing these agents were suggested. The rubbers with the addition of the synthesized bicyclic bisureas demonstrated satisfactory levels of flame resistance and physico-mechanical parameters.     

1,6-Dibenzylglycoluril for synthesis of deprotected glycoluril dimer

1,6-Dibenzylglycoluril is not accessible via classical condensation reaction between substituted urea and glyoxal. In this paper 1,6-dibenzylglycoluril was successfully prepared by alkylation of 1,6-diacetylglycoluril with benzylbromide for the first time. 1,6-Dibenzylglycoluril reacted with formaldehyde to give tetrabenzylglycoluril dimer. Deprotection of this dimer and the previously reported o-xylyleneglycoluril dimer was achieved by dissolving metal reduction, whereas propyleneglycoluril dimer was deprotected by action of potassium persulfate.     

Regular acyclic and macrocyclic [AB] oligomers by formation of push-pull chromophores in the chain-growth step

The substrate scope of the [2+2] cycloaddition-cycloreversion (CA-CR) reaction between electron-deficient (2,2-dicyanovinyl)benzene (DCVB) or (1,2,2-tricyanovinyl)benzene (TCVB) derivatives and N,N-dimethylanilino (DMA)-substituted acetylenes was investigated. The structural features of the cyanobutadiene products of these transformations were examined and the rates of selected CA-CR reactions were measured. Rate constants for reactions utilizing pentafluorinated TCVB and DCVB were found to be one to two orders of magnitude larger than those for the unsubstituted analogues. Multiple, consecutive CA-CR reactions were performed with substrates incorporating two reactive 2,2-cyanovinyl or 4-ethynylanilino sites. 1,4-Bis(2,2-dicyanovinyl)-2,3,5,6-tetrafluorobenzene and 1,4-bis[(4'-dihexylamino)phenylethynyl]benzene were selected as suitably reactive monomers for the synthesis of regular [AB] oligomers wherein the push-pull chromophores were formed in the chain-growth step. Oligomers of two types were isolated: macrocyclic [AB](n) and open-chain B[AB](n) oligomers, with n≤4.     

Investigation of rheological properties of modified carbamide-formaldehyde oligomers

Comparative results of determining the rheological properties of modified adhesive compositions based on carbamide-formaldehyde binders, main wood species, and flax shive are presented.     

Methylene-bridged glycoluril dimers: synthetic methods

Methylene-bridged glycoluril dimers are the fundamental building blocks of cucurbituril (CB[6]), its homologues (CB[n]), and its derivatives. This paper describes three complementary methods for the synthesis of C- and S-shaped methylene-bridged glycoluril dimers (29-34 and 37-44). For this purpose, we prepared glycoluril derivatives (1a-d) bearing diverse functionalities on their convex face. These glycoluril derivatives were alkylated under basic conditions (DMSO, t-BuOK) with 1,2-bis(halomethyl)aromatics 6-15 to yield 4a-d and 16-24, which contain a single aromatic o-xylylene ring and potentially nucleophilic ureidyl NH groups. Glycoluril derivatives bearing potentially electrophilic cyclic ether groups (5a-f) and 25-28 were prepared by various methods including condensation reactions in refluxing TFA containing paraformaldehyde. The condensation reactions of 4a-d and 16-24 with paraformaldehyde under anhydrous acidic conditions (PTSA, ClCH(2)CH(2)Cl, reflux) give, in most cases, the C-shaped and S-shaped methylene-bridged glycoluril in good to excellent yields. In many cases, the C-shaped compound is formed preferentially with high diastereoselectivity. Cyclic ethers 5a,d-f and 25-26 undergo highly diastereoselective dimerization reactions to yield methylene-bridged glycoluril dimers with the formal extrusion of formaldehyde. Last, it is possible to perform selective heterodimerization reactions using both cyclic ethers and glycoluril derivatives bearing ureidyl NH groups. These reactions deliver the desired C- and S-shaped heterodimers with low to moderate diastereoselectivities. This heterodimerization route is the method of choice in cases where the homodimerization reactions fail. The formation of side products (+/-)-35b and (+/-)-35d helps clarify the electronic requirements for a successful CB[n] synthesis. The X-ray structures of 30C, 38C, and 38S allow for a discussion of the structural features of this class of compounds.     

Synthesis and anion recognition properties of pyrrole-bearing acyclic receptors

A new series of acyclic anion receptors (1-4) based on methyl 5-(aminomethyl)-1H-pyrrole-2-carboxylate were designed and synthesized. The anion recognition properties of these receptors were examined by ¹H NMR spectroscopy and rationalized by density functional theoretical calculation. Receptor 1 displays the highest affinity and selectivity for anionic guests mainly due to the intramolecular hydrogen bonds and rigid molecular geometry.     

Rheological and rheokinetic properties of phosphazene-containing epoxy oligomers

The rheological and rheokinetic properties of a two-component binder consisting of epoxy-diane oligomers and the oligoepoxyphosphazenes PEO-1 (30 wt %) and PEO-2 (40 wt %) are studied. The viscosities of the initial oligomers at 40°C are 130 (PEO-1) and 270 (PEO-2) Pa s; the activation energies of viscous flow in the range 40–70°C are from 122 to 128 kJ/mol. The addition of equivalent amounts of curing agents, such as triethylenetetramine or iso-methyltetrahydrophthalic anhydride, reduces the initial viscosity of a composition, most strongly in the presence of the second curing agent (by a factor of 50–100). The activation energies of the cure process with triethylenetetramine in the range 45–95°C are 89 (PEO-1) and 125 (PEO-2) kJ/mol, and the gelation time at 55°C is 6 min for both oligomers. The time of gelation for the system PEO–iso-methyltetrahydrophthalic anhydride at 90°C is 475 min, and the glass-transition temperatures of the cured compositions are 238 (PEO-1) and 250°C (PEO-2), as evidenced by thermomechanical studies.     

Investigation of rheological properties of modified phenol-formaldehyde oligomers

Comparative results of determining the rheological properties of modified adhesive compositions based on phenol-formaldehyde oligomer, main wood species, and flax shive are presented. Recommendations on the application of modified glues in the production of composite materials are given.