Copolymers and elastomers with alternating dioxysilphenylene and silane units

Copolymers with alternating dioxysilphenylene and diorganosilane units were investigated as a source of high-temperature elastomers for the aerospace industry. A copolymer with dimethylsilane units alternating with dioxysilphenylene had a glass transition temperature of ?63°C and exceptional thermal stability; a polymer with diphenylsilane units alternating with dioxysilphenylene had a glass transition temperature of 0°C and slightly higher thermal stability. Both were cured to elastomers at room temperature with ethyl silicate in combination with dibutyltin diacetate. Both had tensile strengths (ultimate) above 4000 psi even without reinforcing fillers. Reinforced elastomers of the dimethyl copolymer had tensile strengths (ultimate) up to 16,000 psi.     

Tetradehydroadamantane-1,3,5,7-di- and tetracations and their helium and hydride inclusion complexes: spherical aromaticity and evidence for a bonding interaction between carbon and helium

The unusual stability of the experimentally known 1,3-dehydro-5,7-adamantyl dication was previously explained by four-center two-electron aromaticity with three-dimensional (tetrahedral) topology. Magnetic criteria (ACID and ring-current analysis) now demonstrate that there is also a very strong contribution from hyperconjugation with all six methylene bridges. The delocalized system of electrons thus includes all valence electrons, and the structure, therefore, should rather be described as a spherically aromatic 50-electron system. The corresponding Td-symmetric tetracation with 48 electrons is antiaromatic and not a minimum structure. With a He atom or a hydride ion at the center of the cage, the tetracation is predicted to form a kinetically stable complex. Magnetic criteria demonstrate that the antiaromaticity is greatly reduced, and a bond analysis hints at bonding interactions between He (and H-) and the carbon atoms of the adamantane cage.     

Tricalixarenes and pentacalixarenes: synthesis and complexation studies

Tricalix[4]arene 4, tricalix[5]arene 14, and pentacalix[4]arene 10 have been synthesized from O-alkylcalixarene mono- and dialdehydes by a two-step conversion to the corresponding monoethynyl ketones or diethynyl ketones followed by aryne trimerization in refluxing DMF containing a dialkylamine. The tricalixarenes 4 and 14 were converted, in turn, to calixarenes 6 and 16, which carry OH groups on the lower rim and methylenes as the bridging moieties to the benzene ring. Complexation studies with the tricalix[5]arene 16 show that it forms (a) a 1:3 complex with N,N-dimethylethylenediamine in which each calixarene unit contains a molecule of the amine, (b) a 1:1 complex with tris(aminomethyl)amine in which each calixarene unit contains one of the three arms of the guest, and (c) a 1:1 complex with C60 in which the guest presumably resides in the cavity provided by the three calixarene units acting cooperatively.     

Kinetics and mechanisms of chlorine dioxide and chlorite oxidations of cysteine and glutathione

Chlorine dioxide oxidation of cysteine (CSH) is investigated under pseudo-first-order conditions (with excess CSH) in buffered aqueous solutions, p[H+] 2.7-9.5 at 25.0 degrees C. The rates of chlorine dioxide decay are first order in both ClO2 and CSH concentrations and increase rapidly as the pH increases. The proposed mechanism is an electron transfer from CS- to ClO2 (1.03 x 10(8) M(-1) s(-1)) with a subsequent rapid reaction of the CS* radical and a second ClO2 to form a cysteinyl-ClO2 adduct (CSOClO). This highly reactive adduct decays via two pathways. In acidic solutions, it hydrolyzes to give CSO(2)H (sulfinic acid) and HOCl, which in turn rapidly react to form CSO3H (cysteic acid) and Cl-. As the pH increases, the (CSOClO) adduct reacts with CS- by a second pathway to form cystine (CSSC) and chlorite ion (ClO2-). The reaction stoichiometry changes from 6 ClO2:5 CSH at low pH to 2 ClO2:10 CSH at high pH. The ClO2 oxidation of glutathione anion (GS-) is also rapid with a second-order rate constant of 1.40 x 10(8) M(-1) s(-1). The reaction of ClO2 with CSSC is 7 orders of magnitude slower than the corresponding reaction with cysteinyl anion (CS-) at pH 6.7. Chlorite ion reacts with CSH; however, at p[H+] 6.7, the observed rate of this reaction is slower than the ClO2/CSH reaction by 6 orders of magnitude. Chlorite ion oxidizes CSH while being reduced to HOCl, which in turn reacts rapidly with CSH to form Cl-. The reaction products are CSSC and CSO3H with a pH-dependent distribution similar to the ClO2/CSH system.     

Synthesis and Antimicrobial Activity of New Pyridothienopyrimidines and Pyridothienotriazines

5‐Acetyl‐3‐amino‐4‐aryl‐6‐methylthieno[2,3‐b]pyridine‐2‐carboxamides ( 5a,b ) were reacted with triethyl orthoformate or nitrous acid to give the corresponding pyrimidinones 6a,b and triazinones 7a,b . The reaction of 5a,b with acetic anhydride was carried out and its products were identified as a mixture of 8‐acetyl‐9‐aryl‐2,7‐dimethylpyrido[3′,2′:4,5]thieno[3,2‐d]pyrimidine‐4(3H)‐one ( 9a,b ) and related 5‐acetyl‐4‐aryl‐3‐biacetylamino‐6‐methylthieno[2,3‐b]pyridine‐2‐carbonitrile ( 10a,b ). Reaction of 7a with some halocompounds afforded the N‐alkylated triazinones 8a‐c . Chlorination of 6a,b and 9a,b with phosphorus oxychloride produced 4‐chloropyrimidines 11a‐d which were used as precursors for the rest of the target heterocycles. Some of the prepared compounds were tested in vitro for their antimicrobial activities.     

Order and composition of methyl-carboxyl and methyl-hydroxyl surface-chemical gradients

A detailed infrared and XPS characterization of surface-chemical gradients of dodecanethiol with 11-mercaptoundecanol or 11-mercaptoundecanoic acid self-assembled on gold, is reported. Gradients were prepared using a simple, two-step process previously reported from our laboratory, which involves a controlled immersion of a polycrystalline gold substrate in a dilute (5 microM) solution of one component and a subsequent back-filling with the other. FTIR measurements show that a single-component gradient of dodecanethiol is composed of disordered, liquidlike alkyl chain conformations. Such a gradient, when back-filled with a complementary thiol, having either a hydroxyl or carboxyl end-group, yields two-component gradients that show similar changes in wettability along their lengths. However, while gradients composed of methyl and hydroxyl end-groups show a well-ordered alkyl chain structure over their entire length, methyl-carboxyl gradients exhibit a greater conformational disordering toward the carboxyl-rich end.     

Determination of clomipramine and its hydroxylated and demethylated metabolites in plasma and urine by liquid chromatography with electrochemical detection

A procedure for the determination of clomipramine and its 8-hydroxy, demethyl, 8-hydroxydemethyl and didemethyl metabolites in plasma and urine by high-performance liquid chromatography with electrochemical detection is described. A 1-ml plasma or urine sample is made alkaline with a carbonate buffer (pH 9.8) and extracted with 20% ethyl acetate in n-heptane. After back-extraction into an acid phosphate buffer (pH 2.4), an aliquot is injected into a 5-microns ion-paired reversed-phase column and eluted with a mobile phase containing a phosphate buffer with tetramethylammonium chloride-acetonitrile (57:43). The detection is coulometric with a first cell at +0.40 V, a second at +0.73 V and a guard cell set at 0.75 V for oxidation of the mobile phase. The method provides recoveries in the general range of 80-110% and a day-to-day precision of 3.7-8.8%, depending on the compound. The minimum quantifiable level for all compounds was 0.2 ng/ml with a 20-microliters injection. Steady-state plasma concentration data and urinary levels are reported for 24 depressed patients receiving daily either 75-150 mg orally or 50-75 mg by infusion.     

Synthesis and Reactions of Enediynes and Enyne-Allenes

The thermal cycloaromatization reactions of (Z)-3-hexene-1,5-diynes (enediynes) and (Z)-1,2,4-heptatrien-6-ynes (enyne-allenes) provide easy entries to a variety of carbon biradicals. Several new synthetic routes to these highly unsaturated compounds were developed by using multifunctional reagents properly substituted with combinations of boron, silicon, and tin appendages. Condensation of γ-(trialkylsilyl)allenylboranes 1 and 2 with conjugated acetylenic and allenic aldehydes followed by the elimination step of the Peterson olefination reaction furnished enediynes and enyne-allenes with high geometric purity. Convenient procedures for the synthesis of enediynes and enyne-allenes were also developed by using alkenylboronic ester 28 and the trimethyltin-substituted alkenylboranes 34 for cross-coupling reactions. On heating, acyclic enyne-allene 22 underwent a sequence of intramolecular transformations through biradical intermediates to form 26 , providing a new example of a one-step 0 → ABCD ring construction of the tetracyclic-steroidal skeleton.     

Synthesis of new visnagen and khellin furochromone pyrimidine derivatives and their anti-inflammatory and analgesic activity

6-[(4-Methoxy/4,9-dimethoxy)-7-methylfurochromen-5-ylideneamino]-2-thioxo-2,3-dihydropyrimidin-4-ones 1a,b were prepared by reaction of 6-amino-2-thiouracil with visnagen or khellin, respectively. Reaction of 1a,b with methyl iodide afforded furochromenylideneaminomethylsulfanylpyrimidin-4-ones 2a,b. Compounds 2a,b were reacted with secondary aliphatic amines to give the corresponding furochromen-ylideneamino-2-substituted pyrimidin-4-ones 3a-d. Reaction of 3a-d with phosphorus oxychloride yielded 6-chlorofurochromenylidenepyrimidinamines 4a-d, which were reacted with secondary amines to afford furochromenylideneamino-2,6-disubstituted pyrimidin-4-ones 5a-d. In addition, reaction of 5a-d with 3-chloropentane-2,4-dione gave 3-chloro-furochromenylpyrimidopyrimidines 6a-d. The latter were reacted with piperazine and morpholine to give 1-(furochromenyl)-pyrimidopyrimidine-3,6,8-triylpiperazines or -3,6,8-triylmorpholines 7a-d. The chemical structures of the newly synthesized compound ware characterized by IR, 1H-NMR, 13C-NMR and mass spectral analysis. These compounds were also screened for their analgesic and anti-inflammatory activities. Some of them, particularly 3-7, exhibited promising activities.     

Photochromism and electrical transport characteristics of a dyad and a polymer with diarylethene and quinoline units

The synthesis of a series of photochromic compounds incorporating a phenylquinoline unit and the photophysical and electric transport properties are described. The dyad and polymer with a quinoline unit show a high quantum yield due to the enforced antiparallel conformation of the dithienylethene moieties. High carrier conductivity was observed in the closed form of the diarylethene with a phenylquinoline unit.     

Highly efficient and mild copper-catalyzed N- and C-arylations with aryl bromides and iodides

Mild, efficient, copper-catalyzed N-arylation procedures for nitrogen heterocycles, amides, carbamates, and C-arylation procedures for malonic acid derivatives have been developed that afford high yields of arylated products with excellent selectivity. The N-arylation of imidazole with aryl bromides or iodides was found to be greatly accelerated by inexpensive, air-stable catalyst systems, combining catalytic copper salts or oxides with a set of structurally simple chelating ligands. The reaction was shown to be compatible with a broad range of aryl halides, encompassing sterically hindered, electron-poor, and electron-rich ones, providing the arylated products under particularly mild conditions (50-82 degrees C). The lower limit in ligand and catalyst loading and the scope of Ullmann-type condensations catalyzed by complexes bearing those ligands with respect to the nucleophile class have also been investigated. Chelating Schiff base Chxn-Py-Al (1c) generates a remarkably general copper catalyst for N-arylation of pyrrole, indole, 1,2,4-triazole, amides, and carbamates; and C-arylation of diethyl malonate, ethyl cyanoacetate, and malononitrile with aryl iodides under mild conditions (50-82 degrees C). The new method reported here is the most successful to date with regard to Ullmann-type arylation of some of these nucleophiles.     

Dynamic and steady-shear melt rheology of and ethylene-methacrylic acid copolymer and its salts

Studies have been made on the dynamic and steady-shear melt rheology of an ethylene–methacrylic acid copolymer and two of its salts obtained by partial neutralization with sodium and with calcium bases. Measurements were made with a Weissenberg rheogoniometer over a broad range of shear rates and frequency in the temperature interval mainly from 100 to 160°C. The temperature coefficients of dynamic and steady shear viscosity are evaluated at both constant shear rate and constant stress. Likewise, complex dynamic viscosities and apparent high steady-flow viscosities and intercompared at equivalent frequencies and shear rates. The un-ionized acid copolymer shows good correlation between the frequency dependence of the complex viscosity and the shear rate dependence of the apparent viscosity. This is not true for either the sodium salt or the calcium salt. These results are consistent with the two-phase structural model for these materials, i.e., a matrix of hydrocarbon in which are embedded ionic domains.     

Syntheses and structures of P-anilino-P-chalcogeno- and P-anilino-P-iminodiazasilaphosphetidines and their group 12 and 13 metal compounds

The P-anilino-P-chalcogeno(imino)diazasilaphosphetidines [Me(2)Si(mu-N(t)Bu)(2)P=E(NHPh)] (E = O (3), S (4), Se (5), N-p-tolyl (6)) were synthesized by oxidizing the P-anilinodiazasilaphosphetidine [Me(2)Si(N(t)Bu)(2)P(NHPh)] (2) with cumene hydroperoxide, sulfur, selenium, and p-tolyl azide, respectively. The lithium salt of 4 reacted with thallium monochloride to produce ([Me(2)Si(mu-N(t)Bu)(2)P=S(NPh)-kappaN-kappaS]Tl)(7), which features a two-coordinate thallium atom. Treatment of 4-6 with AlMe(3) gave the monoligand dimethylaluminum complexes ([Me(2)Si(mu-N(t)Bu)(2)P=E(NPh)-kappaN-kappaE]AlMe(2)) (E = S (8), Se (9), N-p-tolyl (10)), respectively. In these complexes the aluminum atom is tetrahedrally coordinated by one chelating ligand and two methyl groups, as a single-crystal X-ray analysis of 8 showed. A 2 equiv amount of 4-6 reacted with diethylzinc to produce the homoleptic diligand complexes ([Me(2)Si(mu-N(t)Bu)(2)P=E(NPh)-kappaN-kappaE](2)Zn)(E = S (11), Se (12), N-p-tolyl (13)). A crystal-structure analysis of 11 revealed a linear tetraspirocycle with a tetrahedrally coordinated, central zinc atom.     

Homopolymers and copolymers of acrylates and methacrylates of homoterpenylmethyl carbinol and α-campholenol

Acrylates and methacrylates of homoterpenylmethyl carbinol and α-campholenol were homopolymerized. Copolymers with each other and acrylonitrile were studied. Terpolymers of the acrylate of homoterpenylmethyl carbinol and the acrylate of α-campholenol with butadiene and styrene or acrylonitrile were also prepared. The lactone ring in the homopolymer of methacrylate of homoterpenylmethyl carbinol was opened up under basic conditions at room temperature, yielding a water-soluble polymer. Films of this polymer were cast from a water solution. The acrylate of homoterpenylmethyl carbinol gave a high molecular weight copolymer with acrylonitrile which could be molded into a transparent, extremely tough, film. The terpolymers of the acrylate of homoterpenylmethyl carbinol with butadiene and styrene or acrylonitrile were obtained in high yield and could be molded into strong, rubbery films. Several polymers were epoxidized and cured with p-phenylenediamine.     

Synthesis and characterization of triphenylphosphine adducts of ferrocene-based palladacycles and their performance in the Suzuki and Sonogashira reactions with bromo- and chloroarenes

A new triphenylphosphine adduct of cyclopalladated ferrocenylpyridazine containing a chloride anion, 2a, has been synthesized from the reaction of the chloride-bridged palladacyclic dimer 1a with triphenylphosphine. The corresponding adducts 3a,b containing iodide anion have been readily prepared through anion exchange reactions of 2a,b with NaI in acetone. These complexes were characterized by elemental analysis, IR and 1H-NMR. Additionally, their crystal structures have been determined by X-ray diffraction and intermolecular C-H···X (Cl, Br, I) bonds were found in the crystals. The use of these palladacycles as catalysts for the Suzuki and Sonogashira reactions was examined. The complexes 2a,b exhibited higher catalytic activity than the corresponding 3a,b in the Suzuki reaction. However, the order of activity of adducts with varying halogen anions is 3a~3b > 2a~>2b in the Sonogashira reaction.     

Electronic structures and reactivities of methyl-substituted thienothiazoles and thieno- and furopyridines

The electronic structures of a number of methyl-substituted heterocyclces containing a thiophene or furan ring condensed with a thiazole or pyridine ring and of their quaternary salts and methylene bases were calculated by the Pariser-Parr-Pople method. The features of the electronic structures of the investigated molecules were ascertained. It is shown that methyl-substituted thienothiazoles and thieno- and furopyridines and their quaternary salts are appreciably inferior to the corresponding benzothiazoles and quinoline derivatives used for the synthesis of polymethine dyes with respect to the reactivity of the methyl group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1202–1206, September, 1976.     

Multisite and multivalent binding between cyanovirin-N and branched oligomannosides: calorimetric and NMR characterization

Binding of the protein cyanovirin-N to oligomannose-8 and oligomannose-9 of gp120 is crucially involved in its potent virucidal activity against the human immunodeficiency virus (HIV). The interaction between cyanovirin-N and these oligosaccharides has not been thoroughly characterized due to aggregation of the oligosaccharide-protein complexes. Here, cyanovirin-N's interaction with a nonamannoside, a structural analog of oligomannose-9, has been studied by nuclear magnetic resonance and isothermal titration calorimetry. The nonamannoside interacts with cyanovirin-N in a multivalent fashion, resulting in tight complexes with an average 1:1 stoichiometry. Like the nonamannoside, an alpha1-->2-linked trimannoside substructure interacts with cyanovirin-N at two distinct protein subsites. The chitobiose and internal core trimannoside substructures of oligomannose-9 are not recognized by cyanovirin-N, and binding of the core hexamannoside occurs at only one of the sites on the protein. This is the first detailed analysis of a biologically relevant interaction between cyanovirin-N and high-mannose oligosaccharides of HIV-1 gp120.     

Affinity and nuclease activity of macrocyclic polyamines and their CuII complexes

The stability constants of Cu(II) complexes that consist of either an oxaaza macrocycle with two triamine moieties linked by dioxa chains, or two macrocyclic ligands with a polyamine chain which are connecting the 2 and 9 positions of phenanthroline, have been determined by means of potentiometric measurements. The results are compared to those reported for other ligands with a similar molecular architecture. Of the complexes that contain phenanthroline in their macrocycle, the Cu(II) ion of the complex with the smallest and most rigid macrocycle (L3) has an unsaturated coordination sphere, while in the complex with the largest macrocycle (L5) the Cu(II) ion is coordinatively almost saturated. These results are corroborated by the crystal structure of the [CuL5](ClO4)2 complex. The affinity of the ligands and the complexes towards nucleic acids was studied by measuring the changes in the melting temperature, which showed that the affinity of the macrocyclic ligands towards double-stranded DNA or RNA is generally smaller than that of their linear analogues that bear a similar charge, with a strong preference for polyA-polyU, a model for RNA. However, the complexes of two of the changed macrocyclic ligands which contain a phenanthroline unit (L4, L5) showed a distinctly larger increase in their melting temperature deltaTm with DNA (polydA-polydT), which is reversed again in favor of RNA upon metallation to the dinuclear copper complex with L5. Experiments with supercoiled plasmid DNA showed a particularly effective cleavage with a mononuclear Cu(II) complex that contains a phenanthroline unit (L6). Related ligands showed less activity towards DNA, but not so towards the biocidic bis(p-nitrophenyl)phosphate (BNPP). In both cases (with DNA and BNPP) the activity seemed to increase with decrease of coordinative saturation of the Cu(II) ion, with the exception of one particular ligand (L6). Experiments with radical scavengers in the DNA experiments showed some decrease in cleavage, which indicates the participation of redox processes.     

Thermodynamic and kinetic characterization of host-guest association between bolaform surfactants and alpha- and beta-cyclodextrins

The thermodynamics and kinetics of formation of host-guest complexes between a series of bolaform surfactants of type C n Me 6 (2+)2Br (-) ( n = 8, 10, and 12) and alpha-cyclodextrin and beta-cyclodextrin were studied with the aid of isothermal titration calorimetry (ITC) at 298.15 and 308.20 K. The association constant, the enthalpy, and the entropy of formation were determined. The obtained thermodynamic parameters are compared with parameters for the micelle formation of a related cationic surfactant. The difference in magnitude and sign between the parameters of the alpha-CD and beta-CD complexes is discussed based on the curvature of the cavity of the CD. We suggest that the water molecules inside the alpha-CD cavity are not able to maintain their hydrogen bond network. Upon complex formation these water molecules are expelled and reform their hydrogen bond network. The situation is different in the larger beta-CD cavity where water has the possibility of a more extensive hydrogen bonding. The kinetics for alpha-CD is slow, associated with high activation energies for both association and dissociation of the complex. The rates increased with a decrease in the number of methylene groups in the hydrocarbon chain. The slow kinetics is argued to originate from the fact that the charged headgroup needs to be pushed through a relative nonpolar cavity. A comparison is made with the Born energy.     

Efficient and reliable numerical integration of exchange-correlation energies and potentials

An adaptive numerical integrator for the exchange-correlation energy and potential is presented. It uses the diagonal elements of the exchange-correlation potential matrix as a grid generating function. The only input parameter is the requested grid tolerance. In combination with a defined cell function the adaptive grid generation scales almost linear with the number of basis functions in a system. With the adaptive numerical integrator the self-consistent field energy error, which is due to the numerical integration of the exchange-correlation energy, converges with increasing adaptive grid size to a reference value. The performance of the adaptive numerical integration is analyzed using molecules with first, second, and third row elements. Especially for transition metal systems the adaptive numerical integrator shows considerably improved performance and reliability.