Dimethylacetamide Solution Research Articles

Mössbauer spectroscopic studies of the six‐coordinate heme—nitric oxide complex of iron(III) octaethylporphyrin N‐methylimidazole, the first model of the nitrophorin—no complexes

AbstractThe NO, N‐methylimidazole complex of isotopically enriched octaethylporphyrinatoiron(III) chloride, [OEP57Fe(NO)(N‐MeIm)+Cl− has been prepared in dimethylacetamide solution and studied by low‐temperature Mössbauer spectroscopy in the presence and absence of a magnetic field. This complex is a model for the Fe(III)‐NO complexes of the nitrophorins of the blood‐sucking insect, Rhodnius prolixus, where NO is released from the histidine‐coordinated ferrihemin center of each of the proteins upon the insect's injection of the saliva into the victim. The [OEPFe(NO)(N‐MeIm)]+Cl− complex is EPR silent and behaves as a diamagnetic species, with quadrupole splitting ΔEQ = 1.64 mm s−1, asymmetry parameter η = 0.4, isomer shift δ = 0.02 mm s−1, and linewidth Γ= 0.3 mm s−1. Two electron configurations, Fe(III)‐NO (low‐spin d5, strongly antiferromagnetically coupled to NO), or Fe(II)‐NO+ (low‐spin d6, purely diamagnetic), are possible. Which is the actual configuration cannot be determined until detailed molecular calculations are carried out. The low‐spin OEPFe(III)‐bis‐N‐methylimidazole complex also present in this sample has EPR g‐values, quadrupole splitting, isomer shift, and hyperfine splittings typical of rhombic low‐spin ferriheme centers.

A novel preparation of polyimide/clay hybrid films with low coefficient of thermal expansion

A novel polyimide (PI)/clay hybrid nanocomposite, designated as PI (PAAS)/CM, has been developed from the poly(amic acid) salt of triethylamine and organomontmorillonite (CM) using a mixture solution of tetrahydrofuran (THF) and methanol (MeOH). For comparison, two other PI/clay hybrids derived from poly(amic acid) and CM in THF/MeOH solution and N,N′-dimethylacetamide (DMAc) solution, denoted as PI/CM (T/M) and PI/CM (DMAc), respectively, were also prepared. Dispersion of CM in polymer matrix, tensile properties, and thermal expansion properties of the three hybrids were investigated. Results show that PI (PAAS)/CM has the best dispersion of CM in polymer matrix, highest elongation, and lowest coefficient of thermal expansion values in all hybrids presented in this report. In addition, PI/CM (T/M) has better dispersion of CM and lower coefficient of thermal expansion value than PI/CM (DMAc). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 289–294, 2001

Control of adriamycin cytotoxic activity using thermally responsive polymeric micelles composed of poly( N-isopropylacrylamide- co- N, N-dimethylacrylamide)- b-poly( d,l-lactide)

Adriamycin (ADR)-loaded thermally responsive polymeric micelles composed of poly( N-isopropylacrylamide- co- N, N-dimethylacrylamide)- b-poly( d,l-lactide) were prepared by dialysis from its dimethylacetamide solution against water. Microfiltration was successfully applied to removal of block copolymer associates, which were smaller than micellar structures. By this microfiltration polymeric micelles showing a lower critical solution temperature (LCST) at 40°C in phosphate buffered saline was obtained with a monodispersed size distribution of 69.2 nm in cumulant average diameter. ADR-loaded micelles released more ADR at 42.5°C (above the LCST) than at 37°C (below the LCST). ADR-loaded micelles did not show much cytotoxic activity against bovine aorta endothelial cells at 37°C, in contrast to high cytotoxicity at 42.5°C. On the other hand, free ADR expressed high cytotoxicity at both the incubation temperatures. Thus, thermally responsive polymeric micelles showed distinct control of ADR cytotoxic activity by temperature, while free ADR did not. From these results, an effective target therapy against solid tumors is feasible for these polymeric micelles by a combination of selective delivery to tumor sites based on stable micellar structures at 37°C and enhanced cytotoxic activity of these drug-loaded micelles at 42.5°C by local heating at tumor sites.

Volumes ofN,N-dimethylacetamide solvated metal cations. Variation within the manganese(II) to zinc(II) series

Densities and apparent molar volumes for Mn(ClO4)2,Co(ClO4)2 , Ni(ClO4)2,Cu(ClO4)2 , and Zn(ClO4)2in N, N -dimethylacetamide (DMA) solutions at T= 298.15 K are reported. Densities and apparent molar volumes of tetrabutylammonium tetraphenylborate and tetrabutylammonium perchlorate were determined, and used to obtain the partial molar volume for the ClO4−anion. The partial molar volumes of the DMA-solvated cations are derived, and their variation within the Mn2+toZn2+ series is discussed in terms of structure and stability of the coordination clusters. The ligand field effect on the partial molar volume is demonstrated.

Synthesis and properties of phosphorus containing polyester-amides derived from 1,4-bis(3-aminobenzoyloxy)-2-(6-oxido-6H-dibenz?c,e??1,2?oxaphosphorin-6-yl) phenylene

A series of polyester-amides that contain phosphorus were synthesized by low temperature solution condensation of 1,4-bis(3-aminobenzoyloxy)-2-(6-oxido-6H-dibenz〈c,e〉〈1,2〉oxaphosphorin-6-yl) phenylene (III) with various aromatic acid chlorides in N-methyl pyrrolidone (NMP). All polyester-amides are amorphous and readily soluble in many organic solvents such as dimethylacetamide (DMAc), NMP, dimethylsulfoxide, and dimethylformamide at room temperature or on heating. Light yellow and flexible films of these polyester-amides could be cast from the DMAc solutions. The polymers with an inherent viscosity of 0.26–0.72 dL/g were obtained in quantitative yields. These polyester-amides have good mechanical properties (G′ of ∼ 109 Pa up to 200°C) and good thermal and flame retardant properties. The glass transition temperatures of these polyester-amides ranged from 250 to 273°C. The degradation temperatures (Td 5%) in nitrogen ranged from 466 to 478°C and the char yields at 800°C were 59.6–65.2%. The limiting oxygen indexes of these polyester-amides ranged from 35 to 43. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 891–899, 1999

Inverse Chemical Vapor Deposition: A Novel Single Stage Synthesis of Highly Reflective and Conductive Silvered Polymeric Films

Highly reflective and surface conductive flexible polyimide films have been prepared by the incorporation of silver(I) acetate and 1,1,1-trifluoro-2,4-pentanedione into a dimethylacetamide solution of the poly(amic acid) formed from 3,3‘,4,4‘-benzophenone tetracarboxylic acid dianhydride and 4,4‘-oxydianiline. Thermal curing of the silver(I)-containing poly(amic acid) leads to cycloimidization of the polyimide precursor with concomitant silver(I) reduction, yielding a reflective and conductive silver surface approaching that of the native metal. The metalized films retain the essential mechanical and thermal properties of the parent film. Films were characterized by X-ray diffraction, transmission and scanning electron microscopy, tapping mode atomic force microscopy, X-ray photoelectron spectroscopy, and conductivity, reflectivity, thermal, and mechanical measurements.

Characterization of Cellulose Fibers Extracted from Water Plants, Elodea nuttallii.

Cellulose fibers were extracted from water plants, Elodea Nuttallii, and the structure of the fibers and the anisotropic texture of the regenerated cellulose films were investigated. Wide-angle X-ray powder diffractions revealed that the coarse fibers extracted showed crystal structure of cellulose Iβ and the crystallinity of the fibers was 36.0%. The coarse fibers were refined by the treatment with 17.5% sodium hydroxide aqueous solution and were dissolved in LiCl/ dimethylacetamide (DMAc) solution. The cotton cellulose/LiCl/DMAc solution were prepared for comparison. The texture of the regenerated film for the refined cellulose of the water plants obtained by heating a drop of the solution on a cover glass showed extremely small anisotropic domains as compared with the regenerated cotton cellulose film.

Synthesis and characterization of novel aromatic poly(amide–imide)s with alternate (amide–amide) and (imide–imide) sequences

Diamine amic acids were synthesized by reacting aromatic diamines with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride in dimethylacetamide and were characterized by melting points, elemental analyses, IR, 1H-NMR and HPLC. Poly(amide–amic acid)s were prepared by low temperature solution polycondensation of diamine amic acids with isophthaloyl chloride in dimethylacetamide. Poly(amide–imide)s with alternate (amide–amide) and (imide–imide) sequences were obtained by cycloimidization of poly(amide–amic acid)s with Et 3N–Ac 2O mixture in dimethylacetamide solution. They were characterized by solubilities, inherent viscosities, IR and 1H-NMR. Thermal properties of the polymers were measured by differential scanning calorimetry and thermogravimetric analyses.

Polyethersulfone-[silicon oxide] hybrid materials viain situ sol-gel reactions for tetra-alkoxysilanes

Polyethersulfone (PES)–[silicon oxide] hybrids were derived via sol–gel reactions for tetraethoxysilane (TEOS) and tetramethoxysilane (TMOS) in dimethylacetamide solutions of the polymer. In one scheme, water was initially present, and condensation reactions between SiOR groups competed with their reactions with —OH groups at PES chain ends. In a second scheme, water addition was delayed; TMOS molecules reacted with chain ends before competing TMOS–TMOS reactions occurred. A third study involved parallel experiments, as follows: 1) introduction of EtOH to PES–TEOS solutions for a time before water addition; and 2) reactions occurring for a time in non-EtOH-containing PES–TEOS solutions before water addition. Infrared (IR) spectroscopy uncovered signatures of Si–O–Si bridges in silicon oxide phases and PES endgroup modifications (Si–O–Ph). Composites prepared according to the latter two schemes contain more Si–O–Ph linkages than those generated via the first. Differential scanning calorimetry showed that Tg can be raised, and thermogravimetric analysis revealed how the PES thermal degradation profile can be modified via these inorganic incorporations. The schemes for late water addition produced composites having increased elongation-to-break and lowered strength relative to unfilled PES. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1799–1810, 1998

Highly Reflective and Surface Conductive Silver-Polyimide Films Fabricated Via Reduction of Silver(I) in a Thermally Curing Poly(Amic Acid) Matrix

AbstractHighly reflective and surface conductive silvered polyimide films have been prepared by the incorporation of the (1,1,1-trifluoro-2,4-pentanedionato)silver(I) complex into a dimethylacetamide solution of the poly(amic acid) formed from 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA) and 4,4'-oxydianiline (ODA). Thermal curing of the silver(I)- containing poly(amic acid) films leads to cycloimidization with concomitant silver(I) reduction yielding a reflective and conductive silvered film surface.

Novel wholly aromatic polyamide-hydrazides: 6. Dependence of membrane reverse osmosis performance on processing parameters and polymer structural variations

Integrally skinned phase inversion membranes were successfully cast from dimethylacetamide solutions of a series of novel wholly aromatic polyamide-hydrazides for reverse osmosis performance. All the membranes were characterized for their salt rejection (percentage) and water permeability (cm3 cm−2 day−1) of 0.5 N aqueous sodium chloride feed solution at 3924 kPa operating pressure. The effect of polymer structural variations together with several processing parameters to achieve the best combination of high selectivity and permeability were discussed. The polymers structural variations were obtained by varying their para- and meta-oriented phenylene rings content. The latter was changed from 0 to 50 mol%. The processing variables included temperature and period of the solvent evaporation of the cast membranes, coagulation temperature of the thermally treated membranes and annealing of the coagulated membranes, casting solution composition, membrane thickness and the operating pressure. During the thermal treatment step the asymmetric structure of the membranes with a thin dense skin surface layer supported on a more porous layer was established. The former layer seems to be responsible for the separation performance. The results revealed that the membrane performance depended strongly on the conditions of its processing as well as the structure of the polymer from which it is cast. Under identical preparation condition, substitution of p-phenylene rings for m-phenylene ones within the polymer series resulted in an increase in salt rejection capability of the membranes. This may be attributed to an increase in their chain symmetry associated with increased molecular packing and rigidity through enhanced intermolecular hydrogen bonding. This produces a barrier with much smaller pores that would efficiently prevent the solute particles from penetration. For a given membrane, the higher the temperature and the longer the period of the solvent evaporation would result in a membrane of lower solvent content and with a thicker skin layer and consequently led to higher salt rejection at lower water permeability. Further, annealing in deionized water at 100°C produced membranes with optimum salt rejection. Upon annealing, the membrane shrinks resulting in decreasing its pore size particularly in the skin layer. This membrane morphology change improved the salt rejection. Addition of lithium chloride to the casting solution produced a membrane with increased porosity and improved its water permeability. The effects of coagulation temperature and thickness of the membrane on the separation efficiency were also discussed. The optimum salt separation of the membranes was attained at nearly 4000 kPa operating pressure. Membranes showed rejection up to 99.5% at water permeability 13 cm3 cm−2 day−1. © 1997 Elsevier Science Ltd.

Fabrication of Highly Reflective Composite Polyimide Films via in Situ Reduction of Matrix Constrained Silver(I)

Optically reflective composite polyimide films have been prepared by casting a dimethylacetamide solution of silver(I) acetate, hexafluoroacetylacetone, and the poly(amic acid) derived from 3,3‘,4,4‘-benzophenone tetracarboxylic acid dianhydride (BTDA) and 4,4‘-oxydianiline (4,4‘-ODA) onto an fully imidized parent BTDA/4,4‘-ODA base. Thermal curing of the silver(I)-containing poly(amic acid) topcoat leads to imidization with concomitant silver(I) reduction followed by silver(0) migration/aggregation yielding a reflective, but not conductive, silver surface. This “film-on-film” composite approach minimizes the silver required for the formation of a reflective surface and preserves the essential mechanical and thermal properties of the parent polymer. The metallized films exhibit outstanding metal−polymer and polymer−polymer adhesion, with the strong metal−polymer adhesion attributable to mechanical interlocking and/or encapsulation. Films were characterized by X-ray, DSC, TGA, XPS, TEM, and AFM.

Investigation of the Properties of Phthalocyanine Resin Containing Bismaleimide Groups

A bisphthalonitrile monomer containing bismaleimide groups was synthesized using 4,4′-bismaleimidodiphenylmethane and 4-aminophenoxyphthalonitrile. The structure of the monomer was confirmed by elemental analysis and IR spectroscopy. With this monomer, a phthalocyanine resin containing bismaleimide groups was obtained by catalytic thermal polymerization. The structure of the resin was confirmed by IR spectroscopy. The characteristic absorption peak of nitrile groups at 2200cm-1 disappeared in the IR spectra, showing that polymerization of monomer was complete. Thermogravimetry of the resin in air and N2 was investigated; the results show that this resin has excellent thermal and thermo-oxidative stabilities, and a high char yield in nitrogen (82·7%). In addition, a monomer solution in dimethylacetamide was flow-coated on a glass strip to form a resin film. The adhesion between film and glass strip was firm, and the resin film had strong resistance to saturated alkali solution. A solubility test showed that the resin possessed good chemical inertness. Copper and aluminium strips were bonded using monomer solution. The single-lap shear strength of samples was tested after curing. The results demonstrated that the adhesion between resin and copper strips was stronger than with aluminium strips. The resin can be used as a heat-resistant adhesive. © of SCI.

SAXS and dynamic viscoelastic studies on segmented polyurethaneurea solutions

The microstructure and dynamic mechanical properties of segmented polyurethaneurea (SPUU) in concentrated dimethyl acetamide (DMAc) solutions have been investigated by means of small-angle X-ray scattering (SAXS) and viscoelastic measurements, respectively. Kratky plots of SAXS intensity functions indicated the following: (1) Formation of hard segment domains introduced mainly by hydrogen bondings is promoted with increasing ratio of isocyanate to hydroxyl groups ([NCO]/[OH]) and polymer concentration, C p. (2) The degree of completion of the hard segment domains increases with temperature up to 55°C and then gradually decreases by further increase of temperature. An analogy was found between [NCO]/[OH] dependence of the dynamic storage G′( ω) and loss shear moduli G″( ω) for SPUU in DMAc and time dependence of those for a chemically gelling system. G′( ω) and G″( ω) indicated that the properties of SPUU solutions change from sol-like to gel-like with increasing [NCO]/[OH]. By varying [NCO]/[OH], a relationship of G′( ω) ≈ G″( ω) ≈ ω k was observed around [NCO]/[OH] = 1.6. The exponent k is evaluated to be 0.67, which was similar to the literature value obtained at the gelation point. This corresponds to the ‘gelation threshold’ of the chemical gelation process.

Control of Reflectivity and Surface Conductivity in Metallized Polyimide Films Prepared via in Situ Silver(I) Reduction

Optically reflective and surface-conductive polyimide films have been prepared by the incorporation of silver(I) acetate and trifluoroacetylacetone into a dimethylacetamide solution of the poly(ami...

Novel functional polymers: Poly(dimethylsiloxane)-polyamide multiblock copolymer. IV. Gas permeability and thermomechanical properties of aramid-silicone resins

Poly(dimethylsiloxane) (PDMS) and aromatic polyamide (aramid) multiblock copolymers (PASs) ranging from 26 wt % to 75 wt% in PDMS content were prepared and cast into transparent, ductile, and elastomeric films from N,N′-dimethylacetamide solutions. The gas permeation properties and dynamic thermomechanical properties of the PAS films were investigated. It was found that the PASs containing < 75 wt % of PDMS had two-phase morphologies due to the great difference between the solubility parameters of the two components, in spite of the relatively low molecular weight of each segment. PASs containing ≥ 35 wt % of PDMS showed the PDMS continuous phase and interfacial mixing occurred clearly between the two phases at the higher PDMS contents. PAS containing ≥ 53 wt % of PDMS showed high enough gas permeability compared with conventional silicone rubbers. The gas permeation properties can be well predicted by the PDMS contribution to the continuous phase rather than by the modulus behaviors alone. © 1996 John Wiley & Sons, Inc.

Novel functional polymers: poly(dimethylsiloxane)-polyamide multiblock copolymer. V. The interaction between biomolecules and the surface of aramid-silicone resins.

Multiblock copolymers consisting of aromatic polyamide(aramid) and poly(dimethylsiloxane) (PDMS) aramid-silicone resins (PASs) were synthesized by low temperature solution polycondensation, and PAS films were prepared by casting from an N,N'-dimethylacetamide solution. In this study, we investigated bovine serum albumin (BSA) adsorption, L929 cell adhesion, and tissue reaction on the surface of PAS in order to clarify the interaction between PAS and biomolecules. It was found that the amount of adsorbed biomolecules on PAS was extremely low in contrast with those on aramid and nylon films, and it was comparable to SILASTIC 500-1 film. This suppression of adsorption of biomolecules onto PAS seemed to be due to the low surface free energy of the outermost surface of PAS, where PDMS block was condensed.

Pharmacokinetics of Highly Lipophilic Antitumor Agent Palmitoyl Rhizoxin Incorporated in Lipid Emulsions in Rats.

The effects of i.v. formulations on the pharmacokinetics were examined for two antitumor agents with different lipophilicities: rhizoxin and palmitoyl-rhizoxin (RS-1541). Blood disposition and tissue distributions in rats were evaluated using three formulations: polyethylene glycol 400 (PEG)/dimethylacetamide (DMA) solution, colloidal solution, and lipid emulsions composed of dioctanoyl decanoyl glycerol (ODO) and polyoxyethylene-(60)-hydrogenated castor oil (HCO-60). The effects of emulsion particle size on the pharmacokinetics were also investigated. Rhizoxin rapidly disappeared from the plasma and showed high distribution in the tissues, and in vitro rapidly degraded in the plasma independent of the formulations used. In in vitro plasma, rhizoxin was easily released from the emulsion particles. In contrast to rhizoxin, the pharmacokinetics of RS-1541 with greater lipophilicity changed considerably depending on the formulations. The emulsions showed high and sustained plasma concentrations for RS-1541. RS-1541 was stably incorporated in the emulsion droplets and protected from the degradation when it was applied as an emulsion. Tissue distributions of RS-1541 in rats after an injection as lipid emulsion were strongly affected by the emulsion particle size. Small size emulsions (100-110 nm) showed the highest plasma concentrations of RS-1541, though they were unable to suppress distributions of the drug in peripheral tissues. Emulsions larger than 200 nm (approx.) in size, on the contrary, effectively inhibited the drug from entering the bone marrow, small intestine and other non-reticuloendothelial system (non-RES) organs, where many cytotoxic compounds showed undesired toxicities. These results indicate that the lipid emulsions composed of ODO and HCO-60 could be a promising and effective DDS carrier for RS-1541, which is highly lipophilic and stabilized in the emulsions. This was not the case for rhizoxin, however, which was less lipophilic than palmitoyl analogue RS-1541. The work described herein has demonstrated that by properly selecting the particle size, these lipid emulsions can control the behavior of a drug in the body.

Syntheses and properties of aromatic polyamides and polyimides based on 3,3-bis[4-(4-aminophenoxy)phenyl]- phthalimidine

3,3-Bis[4-(4-aminophenoxy)phenyl]phthalimidine ( 2) was used as the monomer with various aromatic dicarboxylic acids and tetracarboxylic dianhydrides to synthesize polyamides and polyimides, respectively. The diamine 2 was derived by a nucleophilic substitution of 3,3-bis(4-hydroxyphenyl)phthalimidine with p-chloronitrobenzene in the presence of K 2CO 3 and then reduced by hydrazine and catalyst. Polyamides ( 4a–g) having inherent viscosities of 0.94 – 2.08 dl g −1 were prepared by direct polycondensation of the diamine 2 with various aromatic diacids using triphenyl phosphite and pyridine as condensing agents. All the aromatic polyamides were amorphous and readily soluble in various polar solvents such as N,N- dimethylacetamide (DMAc), N,N-dimethylformamide, dimethylsulfoxide and N-methyl-2-pyrrolidone (NMP). Transparent and flexible films of these polymers could be cast from the DMAc solutions. These aromatic polyamides had glass transition temperatures in the range of 307–338°C and 10% weight loss occurred up to 460°C. The polyimides were synthesized from diamine 2 and various aromatic dianhydrides via a two-stage procedure that included ring-opening polyaddition in DMAc to give poly(amic acid)s, followed by thermal or chemical conversion to polyimides. Most of the aromatic polyimides obtained by chemical cyclization were found to be soluble in NMP, m-cresol and o-chlorophenol. These polyimides showed almost no weight loss up to 500°C in air or nitrogen atmosphere.

Exceptional active site H-bonding in enzymes? Significance of the ‘oxyanion hole’ in the serine proteases from a model study

For a series of secondary (N-butyl) and corresponding tertiary (N,N-tetramethylene) 5-substituted salicylamides, phenolic pKa values have been measured in order to assess the energetic dependence of intramolecular carboxamide-NH hydrogen bonding upon the basicity of an acceptor oxyanion. The results are summarized in a Bronsted-type α coefficient of 0.12 (slope for ΔpKa, tertiary minus secondary, versus phenolic pKa of tertiary amide). Relative acidities of the same salicylamides in dimethylacetamide solution indicate that offsetting differences in anion hydration are not hidden in this coefficient. It is concluded that rather less transition-state stabilization from hydrogen bonding may be available within the active site of serine proteases than has previously been inferred from directed point mutations involving the enzymes.