The diffusion NMR studies of crown ethers–cyclodextrin complexation process

Formation of complexes between crown ethers and cyclodextrins has been studied using diffusion measurements. The structures of the complexes have been proposed on the basis of the theoretical calculations and the results obtained. Relation between the structural parameters (rings' diameter and symmetry) and the tendency of molecules' interactions are discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Core‐shell nanoparticles with hyperbranched poly(arylene‐oxindole) interiors

Core‐shell type star polymers composed of poly(tert‐butyl acrylate) (poly(t‐BuA)) arms and 100% hyperbranched poly(arylene‐oxindole) interiors were synthesized via the “core‐first” method. Atom transfer radical polymerization of t‐BuA initiated by 2‐bromopropionyl terminal groups of the hyperbranched core was applied for the synthesis of the stars. The resultant star structures were characterized by gel permeation chromatography with triple detection. Polymers of molar masses M_n up to 1.68 × 10⁵ g/mol were obtained. The obtained star polymers compared with the linear counterparts of the same molar mass have a much more compact structure in solution. The intrinsic viscosities of the stars are also significantly lower than their linear counterparts. Light scattering experiments were performed to provide information about the size of these macromolecules in solution. Preliminary characterization of the thermal properties of these novel materials is also reported. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1120–1135, 2009     

New Reactions of Sulfur-Centered 1,3-Dipoles Generated from Thioketones in Three-Component Reactions with Phenyl Azide and an Electron-Deficient Dipolarophile

ABSTRACT:

Reactions of cycloaliphatic thioketones with phenyl azide in the presence of an electron-deficient C-C-dipolarophile have been studied. It was shown that the course of the reactions and the structures of the products depend strongly on the type of the dipolarophile used. Only in the case of fumaronitrile the interception product of the intermediate thiocarbonyl-S-imide was obtained.     

Cycloadditions of `Thiocarbonyl Ylides' with Tetracyanoethylene (=Ethenetetracarbonitrile): Interception of Intermediates

Thiocarbonyl ylides (=sulfonium ylides) belong to the most nucleophilic 1,3‐dipoles (high HO energy). In their reactions with tetracyanoethylene (TCNE=ethenetetracarbonitrile; low LU energy), a borderline crossing from the concerted mechanism to a two‐step pathway via a 1,5‐zwitterion was observed. Steric hindrance at one or both termini of the 1,3‐dipole is an additional requirement. The ylides 3 and 13 , set free by N₂ elimination of dihydro‐1,3,4‐thiadiazoles, underwent electrocyclization or 1,4‐H shift. Ylides 3 and 13 are bases and afforded MeOH adducts of different regiochemistry. Whereas 3 and TCNE in abs. THF at 45° furnished the (3+2) cycloadduct 20 , a MeOH content of 0.5 – 5 vol‐% in THF gave rise to a seven‐membered lactim ether 22 and thiolane 20 in a 65: 35 ratio (Scheme 4). Water (0.5 – 1 vol‐%) in THF led to lactam 24 and adduct 20 in the same ratio. The zwitterion 26 , assumed to be the first intermediate, enters competing reactions: the irreversible ring closure to thiolane 20 and the reversible formation of a strained, cyclic seven‐membered `ketene imine' 28 , which is intercepted by MeOH or H<sub>2</sub>O. The gauche‐conformation 32 of an analogous zwitterion, produced from the tetrasubstituted `thiocarbonyl ylide' 13 with TCNE (Scheme 5), led to the thiolane derivative 35 , while the anti‐conformation 33 afforded the thioxo compound 5 and cyclopropane derivative 36 by intramolecular nucleophilic substitution.     

Synthesis and Hemostatic Activity of New Amide Derivatives

Eight dipeptides containing antifibrinolytic agents (tranexamic acid, aminocaproic acid, 4-(aminomethyl)benzoic acid, and glycine—natural amino acids) were synthesized in a three-step process with good or very good yields. DMT/NMM/TsO⁻ (4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium toluene-4-sulfonate) was used as a coupling reagent. Hemolysis tests were used to study the effects of the dipeptides on blood components. Blood plasma clotting tests were used to examine their effects on thrombin time (TT), prothrombin time (PT), and the activated partial thromboplastin time (aPTT). The level of hemolysis did not exceed 1%. In clotting tests, TT, PT, and aPTT did not differentiate any of the compounds. The prothrombin times for all amides 1–8 were similar. The obtained results in the presence of amides 1–4 and 8 were slightly lower than for the other compounds and the positive control, and they were similar to the results obtained for TA. In the case of amide 3, a significantly decreased aPTT was observed. The aPTTs observed for plasma treated with amide 3 and TA were comparable. In the case of amide 6 and 8, TT values significantly lower than for the other compounds were found. The clot formation and fibrinolysis (CFF) assay was used to assess the influence of the dipeptides on the blood plasma coagulation cascade and the fibrinolytic efficiency of the blood plasma. In the clot formation and fibrinolysis assay, amides 5 and 7 were among the most active compounds. The cytotoxicity and genotoxicity of the synthesized dipeptides were evaluated on the monocyte/macrophage peripheral blood cell line. The dipeptides did not cause hemolysis at any concentrations. They exhibited no significant cytotoxic effect on SC cells and did not induce significant DNA damage.     

Trapping of a Thiocarbonyl Ylide with Imidazolethiones,Pyrimidinethione, and Thioamides

The reactions of 1,1,3,3-tetramethyl-8-thia-5,6-diazaspirol[3.4]oct-5-en-2-one ( 1a ) with imidazole-2-thiones 3 and pyrimidine-2(1H)-thione ( 6 ) in CHCl₃ at 40 – 50° yield 2,2,4,4-tetramethylcyclobutanone dithioacetals of type 4 and 7 , respectively, by interception of the intermediate thiocarbonyl ylide 2a (Scheme 2). Thiirane 5 is formed as a minor product by 1,3-dipolar electrocyclization of 2a . When thioacetamide ( 8a ) and thiobenzamide ( 8b ) are used as trapping reagents, the primary adduct 10 undergoes a spontaneous cyclization by intramolecular nucleophilic addition of the imino group at the carbonyl group to yield bicyclic products of type 9 . The structure of 9a has been established by X-ray crystallography.     

Long-Term Potentiodynamic Testing and Tribometric Properties of Amorphous Alloy Coatings under Saline Environment

Protective coatings for harsh environments are always welcome, but they must overcome profound challenges, including corrosion and wear resistance. The purpose of this study is to look into the long-term potentiodynamic polarization measurements and dry tribometric behavior of plasma-sprayed amorphous coatings on AISI 1035 mild steel. To investigate the impact of unique active polarization potentials on the electrochemical studies of the iron-based amorphous layer, which compares favorably to AISI 1035 mild steel, the active potential polarization curve and friction coefficient tests were performed. Scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) analyses were used to investigate the coating’s corrosion behavior. Their mechanical (Tribometric tests at higher sliding speeds) and chemical properties (electrochemical potentiodynamic polarization investigations) have also been thoroughly investigated. There is enough validation that these protective coatings can be used in hostile environments. The effects of long-term corrosion for 24 and 48 h were thoroughly examined. Tribometric examinations revealed that amorphous layers are highly resistant under dry conditions, as they offered a very low and stable friction coefficient less than 4 μ with micro Vickers hardness 1140 ± 22.14 HV, which is more than twice as compared to mild steel AISI 1035. The corrosion resistance of coatings in 3.5 wt % NaCl solution displays active transition characteristics of activation, passivation, over passivation, and pitting, as shown by the potentiodynamic polarization curves.