Cross linking and rheological characterization of adsorbed protein layers at the oil-water interface

The dilatational rheological properties of cross-linked protein layers adsorbed at the oil-water interface were investigated with help of a modified drop tensiometer allowing successive replacements of the external phase. This setup enables one to perform cross-linking reactions at the interface only, that is, without any contact between the cross-linking agent and protein molecules in solution, under continuous monitoring of the interfacial tension. The mechanical properties of the resulting interface were investigated with dilatational large strain experiments. Measured rheological properties were related to the expected stability of an emulsion against disproportionation by considering the ratio of the interfacial elasticity to the interfacial tension. In an attempt to increase this ratio to improve the resistance against disproportionation, experiments were performed with densified protein layers obtained via reduction of the droplet area prior to cross linking. To highlight the influence of the protein morphology on the dilatational rheological properties of the cross-linked adsorbed layers, experiments were performed with random coil (beta-casein) as well as globular (beta-lactoglobulin) proteins. Glutaraldehyde was used as a cross-linking agent. Experiments were performed at 55 degrees C and pH 7.0 in 20 mM imidazole buffer for later comparison with enzymatically cross-linked adsorbed protein layers. The present work demonstrated substantial qualitative and quantitative differences in the interfacial rheological properties of cross-linked random coil and globular proteins.     

The reaction of some 3- and 4-fluorooexetanes with acids

Several oxetanes prepared from hexafluoroacetone and hydrofluoroolefins were treated with aluminum chloride. Substitution of fluorine by chlorine occured on the 3-and 4-carbon atoms as well as cleavage of the ether leakage to give chloroalkyl carbinols or in, some cases, vinyl carbinols. Individual samples of the and -3,4-difluorooxetanes formed roughly equivalent amounts of the 3-fluoro-4-chlorooxetane stereoisomers, indicating a common carbonium intermediate. Treatment of the 4-fluorooxetane with sulfuric acid gave a dioxetane, a dioxene and an unsaturated aldehyde.     

The reaction of 3-(1-imidazolyl)-2-alken-1-ones with nucleophiles

Generally 3-hetero-substituted 2-alken-1-ones were prepared from 1,3-alkanediones, 3-chloro-2-alken-1-ones, or conjugated ynones. The preparation of 3-hetero-substituted 2-alken-1-ones was subjected to some limitations by these methods. By the reaction of 3-(1-imidazolyl)-2-alken-1-ones (I) and 3-(3-oxo-1-alkenyl)-1-methylimidazolium iodides (II) with nucleophiles, 3-hetero-substituted 2-alken-1-ones could be obtained regioselectively in good yield under mild conditions. These results suggested that compounds I and II were concluded to be useful intermediates for the organic synthesis.     

The Lewis acid-catalyzed nazarov reaction of 2-(n-methoxycarbonylamino)-1,4-pentadien-3-ones

[reaction: see text] A highly efficient carbonylative Suzuki-Miyaura coupling reaction of lactam-derived vinyl triflates and alkenylboronic acids afforded 2-(N-methoxycarbonylamino)-1,4-pentadien-3-ones as suitable substrates for the Nazarov reaction. The most competent Lewis acids for the Nazarov reaction were Cu(OTf)(2) (2 mol %) and Sc(OTf)(3) (3 mol %) in DCE, which provided the Nazarov products in excellent yield. As both the carbonylative coupling and the subsequent Nazarov reaction were high yielding, the overall methodology is a concise and efficient route to [1]pyrindine systems.     

The reaction of 3- and 4-aminopyridines with isocyanates and isothiocyanates

The reaction of 3-and 4-aminopyridines with some isocyanates and isothiocyanates has been studied, and it has been shown that in the majority of cases aryl isothiocyanates form symmetrical diaryl- and dipyridylthioureas. The hypothesis has been put forward on the possible occurrence of the reaction of the isothiocyanates with 3- and 4-aminopyridines.     

The reaction of 4-(p-nitrobenzyl)pyridine with some electrophiles

The nucleophile 4-(p-nitrobenzyl)pyridine was allowed to react with four carcinogenic alkylating agents, chloromethyl methyl ether, bis(chloromethyl) ether, glycol sulfate and propane sultone, one carcinogenic acylating agent, N,N-dimethylcarbamyl chloride, and one noncarcinogenic electrophile, perchlorocyclobutenone. The structures of the major products formed, which are substituted pyridinium salts or 1,4-dihydropyridines, were determined.     

New fluorinating reagents - I. The first enantioselective fluorination reaction

Crystalline, optically pure N-fluoro sultams (−)-3 and (+)-5 are the first examples of enantioselective fluorinating reagents. Thus unprecedented enantiomeric excesses up to 70% are observed when various prochiral metal enolates are fluorinated by using these new reagents.     

Azide telechelics chain extended by click reaction: Synthesis,characterization, and cross‐linking

Azide telechelics of poly(dimethylsiloxane) (PDMS), polypropylene oxide (PPO), and polyethylene oxide (PEO) were synthesized from the corresponding epoxy telechelics and characterized. These oligomeric azides were chain extended by reaction with bispropargyl ether of bisphenol A (BPEBA) through a copper‐catalyzed azide‐alkyne cycloaddition (CuAAC) reaction. PDMS manifested a faster reaction in contrast to PPO or PEO. The chain‐extended polymers underwent cross‐linking above 170°C through thermal cleavage of residual (terminal) azide groups. This was manifested in their rheograms and was further substantiated by FTIR and NMR spectroscopic analyses. Dynamic mechanical analyses of the cross‐linked polymers exhibited characteristic transitions of hard and soft segments, implying microphase separation in the system. Microscopic evaluation of the thermally cross‐linked sample revealed a porous morphology with microsized to nanosized pores.     

N-(2-氯乙基)苯甲醛亚胺的Friedel - Crafts反应

研究了N-(2-氯乙基)苯甲醛亚胺与苯和甲苯的Friedel-Crafts烷基化反应,生成的亚胺(2),经酸水解生成2-芳乙胺(3)。     

Cross double Mannich reaction catalyzed by I2: Synthesis of highly substituted 4-piperidones

Cross double Mannich reaction and tandem cyclization were achieved under iodine catalyzed conditions,yielding a series of highly substituted 4-piperidones.Among the possible diastereomers,only one diastereomer was isolated,which could be ascribed to the chair-like transition state in six-membered ring,in which all of the hindered groups are located in the pseudoequatorial orientation.     

The reaction of 1-(N-phenacylidene)amino-1,2,3-triazoles with diphenylnitrilimine

Diphenylnitrilimine reacts with 1-(N-phenacylidene)amino-1,2,3-triazoles 1 to give mainly 1,2,4- and 2H-1,2,3-triazoles 2 and 3 . CNDO/2 calculations were made on the compounds 1 and the cycloaddition was also examined on the basis of the interacting frontier molecular orbitals.     

The reaction of uranyl ions with 4-(2-pyridylazo)resorcinol

The uranyl ion and 4-(2-pyridylazo)resorcinol (PAR) form only 1:1 chelates in solutions of pH < 8.5, UO(2),(PAR)H(+) being formed at pH > 3 and UO(2),(PAR) at pH > 5.5. Equilibrium constants and spectrophotometric data for both chelates are given. Solid, non-stoichiometric crystalline species in which the mole ratio of PAR to uranium is more than 1:1 are precipitated up to pH 6. The medium of 0.1-0.2M triethanolamine at pH 8 recommended by other workers proved satisfactory for the sensitive spectrophotometric determination of uranium, as did pH 3.6 in the presence of < 0.1M formate or 20-30% v/v dimethylformamide.     

Modification of poly(vinyl chloride). XXIX. Cross linking of poly(vinyl chloride) with 2-dibutylamino-4,6-dithiol-s-triazine and MGO

Thermal crosslinking of poly(vinyl chloride) (PVC) with 2-dibutylamino-4,6-dithiol-s-triazine (DB) and MgO has been studied to determine the kinetic parameters such as induction period (t₀), rate constant (k), and activation energy (E), and to elucidate the structure of crosslink and the crosslinking mechanism. The thermal crosslinking was treated as a pseudo-first-order reaction. In the crosslinking, k and t₀ were about 0.075 min^?1 and 6.8 min at 180°C, respectively, and E was 16.6 and 14.2 kcal/mole for k and 1/t₀, respectively. The structure of crosslink was confirmed to be indicated as the following scheme (I) from the results of model reactions and IR spectra of crosslinked products The crosslinking reaction was found to proceed through the following three processes: (1) formation of DB-Mg from DB and MgO; (2) formation of DB-Mg pendants by the reaction of PVC with DB-Mg; and (3) formation of crosslink by the reaction of PVC with DB-Mg pendants.     

The preparation of 5-(2-bromoethyl)-2-iminooxazolidines via the von braun cyanogen bromide reaction

The reaction of certain 1-alkyl-3-pyrrolidinols with cyanogen bromide in ether solution produced 3-alkyl-5-(2-bromoethyl)-2-iminooxazolidines. 5-(2-Bromoethyl)-2-ethyl-2-imino-5-phenyloxazolidine was tested for and found devoid of anorectic activity.     

酶促合成油酸香茅醇酯的超临界连续反应-分离过程

将固定床动态酶促反应过程和超临界二氧化碳萃取分离过程相耦合,设计并建立了一套超临界相反应分离一体化的实验装置。在该装置上初步考察了反应压力和温度对脂肪酶催化油酸甲酯和外消旋香茅醇酯交换反应的影响。结果表明,我们所建立的反应装置能有效地实现反应分离一体化过程;当体系压力接近二氧化碳的临界压力时反应速率最高;9MPa压力下反应温度为328K时反应转化率最高,而在14MPa压力下反应转化率在308K～328K之间随着温度的升高而增大。     

Molecular level understanding of the role of aldehyde in vegetable‐aldehyde–collagen cross‐linking reaction

The role of formaldehyde (HCHO) in vegetable‐aldehyde–collagen cross‐linking reaction was investigated at the B3LYP/6‐31+G(d) level, where lysine (LYS) was used as model of collagen and catechin (EC) as model of condensed vegetable tannin. Atomic charge and Frontier molecular orbital analysis show that intermediates formed by HCHO reacting with LYS or EC, that is, M_LYS, M_EC‐6, and M_EC‐8, still have both nucleophilic and electrophilic sites, which are elements to form ternary cross‐linking in vegetable‐aldehyde–collagen system. The analysis of energy gap between HOMO (highest occupied molecular orbit) and LUMO (lowest unoccupied molecular orbit) indicate that the intermediate of HCHO–LYS residues (M_LYS) can further react with free HCHO to form product P‐N(CH₂OH)₂ (P‐N‐represents amino acid residue; N represents nitrogen atom on side chain), but the reaction of intermediate M_LYS with free EC is difficult to take place. So, the probability of forming ternary cross‐linking structure of amino acid residue–HCHO–EC is small, if HCHO is added before vegetable tannin in vegetable‐aldehyde–collagen system. However, the reactions of EC–HCHO intermediates (M_EC‐6 and M_EC‐8) with free amino acids, HCHO–amino acid residue intermediate (M_LYS), as well as with other EC–HCHO intermediates (M_EC‐6 and M_EC‐8), are very easy to take place. The reaction enthalpy also shows that the cross‐linking tendency is favorable in thermodynamics. So, it can be deduced that covalent cross‐linking among amino side chain of collagen and vegetable tannin may take place when aldehyde is added after vegetable tannin. In this way, a multiple point cross‐linking reaction occurs to create a high stabilization of collagen. © 2011 Wiley Periodicals, Inc.     

Organometallic synthons: The wittig reaction of tricarbonyl [(3,4,5,6-η)-1,3,5-cycloheptatriene-1-carboxaldehyde] iron

The utility of the Wittig reaction in synthesis of organometallic compounds is exemplified by its application to the preparation of a series of tetraene—Fe(CO)₃ complexes from aldehyde 9 and a variety of triphenylphosphoranes. Reaction of 9 with triphenylmethylene phosphorane afforded unexpectedly a $\text{1}\text{1}$ isomeric mixture of 8-methylheptafulveneiron tricarbonyl (12), probably via a (1,9) hydrogen shift of intermediate 11. Triphenylbenzylidene phosphorane condensed with 9 to give the cis and trans isomers of cycloheptatrienyl—styrene complex 14. The triphenylphosphoranes of carbomethoxymethylene, carboethoxymethylene and cyanomethylene react with 9 yielding the appropriate trans condensation products exclusively. Tetracyanoethylene (TCNE) and N-phenyltriazolinedione (NPTD) readily react periselectively with the unrearranged Wittig reaction products at the free diene moiety, affording the corresponding 4+2 cycloadducts. Heptafulvene complex 12, upon reaction with TCNE, gave the 8+2 cycloadduct 26.