Kinetics of urethane formation from isophorone diisocyanate: The alcohol nature effect

The kinetics of the noncatalytic reactions of isophorone diisocyanate with n-propanol, isopropanol, 1,3-diazidopropan-2-ol, propargyl alcohol, and phenol in toluene in the temperature range from 20 to 90°C at the stoichiometric ratio of reactive groups has been investigated by IR spectroscopy. The apparent rate constants for the reactions of the aliphatic and cycloaliphatic isocyanate groups of isophorone diisocyanate with all of the alcohols have been measured. The activation parameters of the reactions of isophorone diisocyanate with n-propanol, isopropanol, and 1,3-diazidopropan-2-ol have been determined. The data obtained are considered in terms of the alcohol structure and molecular organization of solutions.     

Thermospray mass spectrometry of aliphatic diamines derivatized with trifluoroethyl chloroformate,with special reference to the biological monitoring of hexamethylenediisocyanate (HDI) and isophoronediisocyanate (IPDI)

Chromatographia - 1,6-Diaminohexane (DAH, 1,6-hexamethylene diamine) and isophorone diamine (IPDA) have been derivatized with trifluoroethyl chloroformate (TFECF) using a two-phase procedure....     

Castor oil as a way to fast-cured polyurethane ureas

Polyurethane urea networks have been synthesized in bulk from castor oil, isophorone diisocyanate and methylene bis-methyl ethyl aniline. The kinetics of prepolymer formation have been studied by gel permeation chromatography. Calorimetric and dynamic mechanical properties have been studied for various stoichiometric ratios. A wide range of moduli can be obtained, with short reaction times.     

相转移催化合成香料烟酮及中间体异佛尔酮

报道了香料烟酮（2-羟基-3，5，5-三甲基-2-环戊烯酮）及中间体异佛尔酮的合成，首先用4-甲基-3-戊烯-2-酮与乙酰乙酸乙酯，在相转移催化剂Et3N^ CH2PhCl^-和EtONa/EtOH条件下合成中间体异佛尔酮，异佛尔酮在碱性条件下被H2O2氧化成2,3-环氧异佛尔酮，2，3-环氧异佛尔酮在酸性条件下反应生成烟酮，对烟酮的IR，^1H NHR谱进行了分析。     

The Solubilization of Isophorone in Ionic Surfactant Solutions

Solubilization of isophorone was studied in an anionic and a cationic surfactant solution of SDS and BKC respectively. Solubility of isophorone increases with increase in the surfactant concentrations due to solubilization in micelles. FT NMR spectroscopy was used to understand the location and orientation of isophorone at the micellar interface.     

Heterogeneously catalyzed asymmetric C=C hydrogenation: origin of enantioselectivity in the proline-directed Pd/isophorone system

We have studied the proline-directed, Pd-catalyzed enantioselective hydrogenation of isophorone in the liquid state using a variety of methods. Our results unambiguously reveal the true reaction pathway and demonstrate that all earlier mechanistic hypotheses are wrong: although a proline/isophorone condensation product is formed, it is merely a spectator and not a key reaction intermediate in subsequent heterogeneous hydrogenation. Enantioselectivity is the result of kinetic resolution-a process that occurs homogeneously in solution and not at the metal surface. Racemic 3,3,5-trimethylcyclohexanone (TMCH) is produced by initial heterogeneous hydrogenation of isophorone; proline then reacts homogeneously, preferentially with one enantiomer of TMCH, leaving an excess of the other. Thus in complete contrast to the case of ketoester asymmetric hydrogenation, the metal surface is not involved in the crucial enantio-differentiation step. The mechanism we propose also explains why the maximum attainable yield of enantiopure TMCH cannot exceed 50%.     

Preparation and characteristics of hydroxypropyl-β-cyclodextrin polymeric nanocapsules loading nimodipine

Nimodipine loaded hydroxypropyl-β-cyclodextrin polymeric nanocapsules were prepared by interfacial polyaddition of hydroxypropyl-β-cyclodextrin and isophorone diisocyante in a miniemulsion system. The effects of ultrasonicate times on the preparation of miniemulsion, the total amount of hydroxypropyl-β-cyclodextrin and isophorone diisocyante, and the molar ratio of isophorone diisocyante to hydroxypropyl-β-cyclodextrin on the capsule size and drug release behavior from capsule were investigated. The chitosan based polymeric nanocapsules were prepared as a control to study the effect of hydroxypropyl-β-cyclodextrin molecules in capsule matrix on the drug release. The results indicated that the droplet size of miniemulsion and capsule size decreased with increasing sonicate times. When the total amount of hydroxypropyl-β-cyclodextrin and isophorone diisocyante, and the molar ratio of isophorone diisocyante to hydroxypropyl-β-cyclodextrin were increased, the capsule as well, but the drug release rates from capsules became slower. The drug release behaviors from hydroxypropyl-β-cyclodextrin polymeric nanocapsules were affected by the drug diffusion through the polymer matrix and the formation of inclusion complex between drug and hydroxypropyl-β-cyclodextrin.     

Liquid crystalline dimeric compounds with an alkylene spacer

Two series of compounds with dimeric molecules have been synthesized and characterized. These molecules consist of two non-mesogenic units linked by an alkylene spacer through an ester linkage. The effects of varying the terminal as well as the spacer chain length on the mesomorphic properties have been studied. For compounds with an even number of carbon atoms in the spacer chains, the observed textures in the mesophases are reminiscent of those seen for the smectic phases of banana-shaped molecules.     

Liquid crystalline dimeric compounds with an alkylene spacer

Two series of compounds with dimeric molecules have been synthesized and characterized. These molecules consist of two non-mesogenic units linked by an alkylene spacer through an ester linkage. The effects of varying the terminal as well as the spacer chain length on the mesomorphic properties have been studied. For compounds with an even number of carbon atoms in the spacer chains, the observed textures in the mesophases are reminiscent of those seen for the smectic phases of banana-shaped molecules.     

Synthesis and surface properties of semi-fluorinated gemini surfactants with two reactive bromo pendant groups

This paper presents a series of semi-fluorinated gemini surfactants with two bromo pendant groups. It reviews the effect of the number of methylene units in the spacer group between the two hydrophilic quaternary ammonium heads. Critical micelle concentration (cmc) and free energy of micellization (ΔG(M)(0)) of the title surfactants, in aqueous solution, have been investigated as a function of the number n of carbon atoms in the hydrocarbon spacer. We have pointed out a different behaviour as compared to Gemini hydrocarbon homologues. In the present study, when the number of methylene units (n) in the spacer increases, the cmc first decreases and reaches an optimum for (n=6), then it increases linearly from n≥6. Variations of cmc have been interpreted in terms of conformation changes of the surfactant ion and progressive penetration of the alkyl chain spacer in the micelle hydrophobic core. In this series, the increase of the hydrophobicity seems not to favour the micellisation process as expected, probably impacted by the mutual phobicity of the perfluorinated tails and the hydrocarbon spacer. A minimum is reached for a spacer with six methylene units which seems to be the optimal conformation. The free energy of micellization (ΔG(M)(0)) confirm this tendency.     

Determination of isophorone in food samples by solid-phase microextraction coupled with gas chromatography-mass spectrometry

A simple and sensitive method for the determination of isophorone in food samples was developed by headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS). Isophorone was separated within 10 min by GC-MS using a DB-1 capillary column and detected with selective ion monitoring mode. The HS-SPME using a polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber provided effective sample enrichment, and was carried out by fiber exposition at 60 degrees C for 45 min. The extracted isophorone was easily desorbed by fiber exposition in the injection port of a capillary GC-MS system, and carryover was not observed. Using this method, the calibration curve of isophorone was linear in the range 20-1000 pg/mL, with a correlation coefficient 0.9996 (n = 18), and the detection limit (S/N = 3) was 0.5 pg/mL. The HS-SPME/GC-MS method showed 25,000-fold higher sensitivity than the direct injection method (1 microL injection). The within-day and between-day precisions (relative standard deviations) at the concentration of 1 ng/mL isophorone were 3.9% and 6.1% (n=5), respectively. This method was successfully applied to the analysis of food samples without interference peaks. The recoveries of isophorone spiked into food sample were above 84% for a 50 or 500 pg/mL spiking concentration. The analytical results of the contents of isophorone in various food samples were presented.     

Model liquid crystalline dimers in a slit pore: Monte Carlo simulation study

ABSTRACT

In this work, we present results from (isobaric–isothermal) Monte Carlo Simulation studies of liquid crystalline dimer systems confined in a slit pore. Liquid crystalline dimer systems of various spacer numbers have been considered. Surface-induced conformational and alignment properties of these systems at different pressures under homeotropic anchoring condition have been investigated. We have used easily manageable coarse grained force fields to model both monomer–monomer and monomer–substrate interaction potentials. According to the simulated result, the anchoring of dimers to the surface and orientation of mesogenic units with respect to the surface normal seem to depend on the spacer number for messogen attractive confinement. Dimers with lower spacer number are able be adsorbed to the surface and most of their mesogens are oriented along the surface normal even at lower pressure. Those with larger spacer number are distributed throughout the volume at lower pressure. In the case of mesogen repulsive confinement, most of the dimers are adsorbed to the surface and most mesogens are randomly oriented at low pressure. As the pressure gets higher, the adsorption and orientability increase depending on the type of confinement and spacer number. As a result, clear submolecular partitioning and smectic A like structure have been identified.     

Stepwise assembly of acceptor--sigma spacer--donor monolayers: preparation and electrochemical characterization

Self-assembled monolayers comprising benzoquinone--methylene spacer--ferrocene molecules have been prepared on gold surfaces using a stepwise assembly procedure. A base monolayer of cystamine is formed on a gold surface. Benzoquinone is then attached to the amine end of the cystamine monolayer by a Michael's addition reaction. Subsequently, a diaminoalkane spacer of varying length is introduced. Finally, ferrocene is attached to the diamonoalkane spacer through an amide bond to complete the acceptor--sigma spacer--donor assembly. The distance between the two redox moieties has been varied systematically by altering the length of the alkyl chain spacer present between them. The quinone attachment to the cystamine monolayer leads to two different redox forms, a mono- and a diamino derivative. The pKa values have been evaluated for both of the derivatives. The monomolecular layer assembly has been characterized extensively using electrochemical techniques and the electrochemical kinetic parameters have been evaluated at different stages of modification.     

Encapsulation of electron donor-acceptor dyads in beta-cyclodextrin cavity: unusual planarization and enhancement in rate of electron-transfer reaction

Interaction of beta-cyclodextrin (beta-CD) with a few novel electron donor acceptor dyads 1a-c and 2a-c, having aryl and flexible methylene spacer groups, has been investigated through photophysical, chiroptical, electrochemical, NMR, and microscopic techniques. Dyads 1a and 1c, with p-tolyl and biphenyl spacer groups, respectively, exhibited significantly decreased fluorescence quantum yields and lifetimes in the presence of beta-CD, while negligible changes were observed for dyad 1b with an o-tolyl spacer. In contrast, spacer-length-dependent significant enhancement in fluorescence quantum yields and lifetimes was observed for dyads 2a-c, with flexible polymethylene (n = 1, 3, 11) spacer groups. Association constants of beta-CD encapsulated complexes have been determined and the contrast behavior observed in these systems is explained through an electron transfer (kET) mechanism based on calculated favorable change in free energy (DeltaGET = -1.27 eV) and the redox species characterized through laser flash photolysis studies. Rates of kET have been estimated and are found to increase ca. 2-fold in the case of dyads 1a and 1c when encapsulated in beta-CD, while significantly decreased kET values were observed for the dyads 2a-c with flexible spacer (ca. 9-fold for 2c). As characterized through cyclic voltammetry, 2D NMR [correlated (COSY) and nuclear Overhauser enhancement (NOESY) spectroscopy], and laser flash photolysis studies, the beta-CD encapsulation of dyads with aliphatic spacer groups leads to the conformational unfolding of a sandwich type of structure, whereas dyads with rigid aryl spacer groups undergo unusual planarization as compared to the uncomplexed dyads, resulting in enhanced electron-transfer reaction between the donor and acceptor moieties.     

Synthesis and characterization of non‐symmetric chiral dimers

A new class of cholesterol‐based non‐symmetric dimers have been synthesized and characterized. They comprise O‐alkylated cinnamic acid and pro‐mesogenic cholesterol segments interlinked covalently through a methylene spacer varying in its length and parity. All the dimers and some of the key precursors have been studied for their phase behaviour. All the intermediates show mesomorphism. Importantly, the thermal properties of dimers are found to be critically dependent on the parity of the flexible spacer. The dimers with odd‐parity spacer display chiral nematic and/or twist grain boundary phases. In contrast, the dimers with even‐parity spacer are either crystalline or exhibit metastable chiral nematic and/or twist grain boundary phases with the exception of one compound for which two unknown mesophases have been observed. The odd–even effect was found to be indistinct for selective reflection wavelengths of the chiral nematic phase. For some dimers, a variation in the pitch of the chiral nematic phase as a function of temperature was observed. Cyclic voltammetry experiments revealed the electrochemical properties of a representative liquid crystal dimer.     

Chemisorption of Glycidyl Spacer on Magnetic Nanoparticles and Immobilization of Albumin and Quinacrine

Chemisorption of a glycidyl spacer on the surface of magnetic nanoparticles from three solvents has been performed. It has been shown that the chemisorption from benzene is the most efficient. Human albumin and quinacrine as a model pharmaceutical have been immobilized via a glycidyl spacer. A mechanism of the interaction of albumin and quinacrine with glycidyl groups has been suggested.     

不同异氰酸酯固化的蓖麻油／酚氧树脂聚氨酯的力学性能

以ＢＦ３·ＯＥｔ２为催化剂，４，４－二羟基二苯基丙烷与环氧氯丙烷反应，生成端羟基的酚氧树脂（Ａ），Ａ与蓖麻油（Ｂ）混合，用３种异氰酸酯（ＴＤＩ、ＩＰＤＩ和ＨＤＩ）作为固化剂，制得交联聚氨酯。研究了这３种聚氨酯的力学性能及形态与组成和二异氰酸酯结构的关系；改变ＮＣＯ／ＯＨ摩尔比及Ｂ与Ａ的质量比，可以制得具有较好力学性能的聚氨酯材料。蓖麻油，酚氧树脂，聚氨酯，力学性能     

Liquid crystalline properties and dependence of transition temperatures on the length of the flexible alkylene spacer of symmetric dimers composed of bent-core units

Three new series of symmetric dimers composed of bent-core molecules connected by a flexible alkylene spacer have been synthesized and their mesomorphic properties studied. The effect of varying the length of the terminal chains for fixed odd and even spacers, as well as varying the spacer length for a fixed terminal chain length, on the mesomorphic properties has been investigated. Remarkably, all the dimers investigated show the same type of mesophase, which has been characterized as a Col_obP_F phase, on the basis of X-ray diffraction and electro-optical measurements. It is found that for a fixed spacer length, the thermal range of the mesophase increases with increase in the number of methylene units in the terminal chain. On the other hand, interestingly an odd-even effect is observed when the length of the flexible spacer is varied; dimers having an odd number of methylene units possess higher clearing points.     

Influence of spacer length on dielectric properties of polymeric liquid crystals

For a liquid-crystalline side chain polymer with cyanobiphenyl mesogenic groups and a spacer length of four methylene groups the dielectric properties over a wide frequency range are studied. They are compared with a previously published analogous compound with six spacer groups in order to get the spacer length dependence of dielectric relaxations. Both compounds have been analysed in terms of theoretical relaxation curves. The δ-relaxation is more asymmetrically broadened and shifted to longer relaxation times for shorter spacer. This is consistent with its molecular interpretation as end-to-end rotation around the short molecular axis. The relaxation in perpendicular orientation is strongly shifted to longer relaxation times and shows another temperature dependence for shorter spacer. This behaviour is attributed to superposition of up to three separate relaxation processes.     

Liquid crystalline dimers with bent-core mesogenic units

Two series of dimers, in which two identical aromatic bent core mesogenic units are connected via an organosiloxane or an alkylene spacer, have been investigated. The dimers with a spacer consisting of a trisiloxane central group and relatively long alkylene groups show an intercalated tilted smectic structure. The layer spacings appear to be very weakly dependent on the terminal chain lengths. In these dimers the smectic phase is stabilized for the compounds with a short terminal chain. Dimers with an aliphatic alkylene spacer are liquid crystalline only when the spacer is relatively short and the terminal chains are long. For these dimers a monolayer tilted smectic phase is observed.