Neutron scattering and compressibility measurements for the study of hydration effects on polymeric aqueous solutions

Summary The present paper reports the results of compressibility and incoherent quasi-elastic neutron scattering measurements performed on polymeric systems and on their aqueous solutions. From the compressibility data, the temperature evolution of the polymer hydration number can be derived. On the other hand, neutron data show that the translational diffusion coefficientD _T turns out to be higher in the case of ethylene glycol + water, with respect to that of pure, suggesting that the water molecules act as a ?structure breaker? of the intermolecular connectivity existing into the pure. Furthermore the dynamical properties of the H₂O molecules in the presence of poly(ethylene glycol) deeply differ from those in the bulk, and show that we are in the presence of entangled water. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Extremal Betti numbers of graded ideals

The possible extremal Betti numbers of graded ideals in the polynomial ring K[x₁,…,x_n] in n variables with coefficients in a field K are studied, completing our results in [7]. In case char(K) = 0 we determine, given any integers r < n, the conditions under which there exists a graded ideal I ? K[x₁,…, x_n] with extremal Betti numbers $\beta_{k_{i}k_{i}+\ell_{i}}\ {\rm for}\ i=1,\cdots,r$ . We also treat a similar problem for squarefree lexsegment ideals.     

A FT-IR absorption analysis of vibrational properties of water encaged in NaA zeolites: evidence of a “structure maker” role of zeolitic surface

Linear polyisoprenes having dimethylamine end groups were prepared by high vacuum anionic polymerization techniques using 3-dimethylaminopropyllithium as the initiator. The amine group was reacted with 2-cholesteryl-2-oxo-1,3,2-dioxaphospholane to provide polymer chains having end zwitterionic groups chemically connected with cholesterol. The association behavior of these end-functionalized polymers was studied in cyclohexane by low angle laser light scattering, dynamic light scattering, and viscometry. The aggregation numbers, N _w were found to decrease by increasing the molecular weight of the precursor polymer, due to excluded volume repulsions. The ability of cholesterol to form liquid crystal mesophases facilitated the association process leading to higher N _w values. The hydrodynamic behavior of the aggregates was similar to that of star polymers. The dependence of the N _w values on the molecular weight of the base polymer, the polydispersity of the associates and the absence of critical micelle concentration, cmc are compatible with the linear head-packing model. Received 29 April 2002 and Received in final form 13 November 2002 Published online: 11 March 2003     

Development and characterization of beta-secretase monolithic micro-immobilized enzyme reactor for on-line high-performance liquid chromatography studies

beta-Site APP cleavage enzyme 1 (BACE-1) is a transmembrane aspartyl protease that cleaves the amyloid-beta precursor protein (APP), which is abundant in neurons. BACE-1 is required for the generation of amyloid-beta (Abeta) peptides implicated in the pathogenesis of Alzheimer's disease (AD). It is widely believed that halting the production of Abeta peptide, by inhibition of BACE-1, is an attractive therapeutic modality for the treatment of Alzheimer's disease. BACE-1 has never been immobilized before. In the present study, for the first time, human recombinant beta-secretase micro-immobilised enzyme reactor (hrBACE-1-micro-IMER) was prepared by using an in situ immobilisation procedure on an ethylendiamine monolithic convective interaction media (EDA-CIM) disk. The activity and kinetic parameters of the hrBACE-1-micro-IMER were investigated by insertion in a HPLC system with fluorescent and mass detection. The micro-IMER was characterized in terms of units of immobilised hrBACE-1 and best mobile phase conditions for activity, by using as substrate casein-FITC and JMV2236, a peptide mimicking the Swedish-mutated APP (amyloid precursor protein) sequence. The characterization of the hrBACE-1-micro-IMER in terms of number of enzymatic active units after covalent linking to the solid matrix was performed by using the JMV2236 peptide as substrate in a HPLC-MS system. JMV2236 was injected into the hrBACE-1-micro-IMER and enzymatically cleaved; the product of the enzymatic cleavage and the remaining non-cleaved substrate were collected on a C18 column trap and switched to the LC-electrospray ionization MS system for kinetic constants determination. Inhibition studies were carried out. The effect of donepezil and pepstatin A, as BACE-1 inhibitors, was evaluated by simultaneous injection of the compounds with the peptidic substrate. The relative IC(50) values were found in agreement with that derived by the conventional fluorescence method, confirming the applicability of this new IMER for on-line inhibition studies. The main advantages of the hrBACE-1-micro-IMER approach over the conventional methods were found to be the increased enzyme efficiency, stability and the decreased time of analysis.     

Characterization of reversible and pseudo-irreversible acetylcholinesterase inhibitors by means of an immobilized enzyme reactor

The aim of the present study was the application of a human AChE-CIM-IMER (enzyme reactor containing acetylcholinesterase immobilized on a monolithic disk) for the rapid evaluation of the thermodynamic and kinetic constants, and the mechanism of action of new selected inhibitors. For this application, human recombinant AChE was covalently immobilized onto an ethylenediamine (EDA) monolithic Convective Interaction Media (CIM) disk and on-line studies were performed by inserting this IMER into a HPLC system. Short analysis time, absence of backpressure, low nonspecific matrix interactions and immediate recovery of enzyme activity were the best characteristics of this AChE-CIM-IMER. Mechanisms of action of selected reversible inhibitors (tacrine, donepezil, edrophonium, ambenonium) were evaluated by means of Lineweaver-Burk plot analysis. Analyses were performed on-line by injecting increasing concentrations of the tested inhibitor and substrate and by monitoring the product peak area. AChE-CIM-IMER kinetic parameters (Km(app) and vmax(app)) were derived as well as inhibitory constants (Ki(app)) of selected compounds. Moreover, noteworthy results were obtained in the application of the AChE-CIM-IMER to the characterization of the carbamoylation and decarbamoylation steps in pseudo-irreversible binding of carbamate derivatives (physostigmine and rivastigmine). AChE-CIM-IMER appeared to be a valid tool to determine simultaneously the kinetic constants in a reliable and fast mode. The obtained values were found in agreement with those obtained with the classical methods with the free enzyme. Furthermore, after inactivation by carbamates, activity could be fully recovered and the AChE-CIM-IMER could be reused for further studies. Results showed that the AChE-CIM-IMER is a valid tool not only for automated fast screening in the first phase of the drug discovery process but also for the finest characterization of the mode of action of new hit compounds with increased accuracy and reproducibility and with saving of time and materials.     

Dynamical response and H-bond effects in confined liquid water

An analysis of Rayleigh wing and Raman scattering data performed in water confined in a nanoporous GelSil matrix, is presented. In the restricted translational region, the results show a strong modification of the vibrational dynamics of water in the confined state, with the disappearance of the 60 cm⁻¹ and 170 cm⁻¹ lattice bands in the VDOS. Furthermore, the collective contribution to the polarised OH stretching band comes down indicating that the tetrabonded network is destroyed.     

The effect of hydrogen bond on the vibrational dynamics of genistein free and complexed with β‐cyclodextrins

Inclusion, or host–guest, complexes are supramolecular assemblies in which two or more molecules hold together and organize by means of intermolecular noncovalent bonds. In the pharmaceutical field, inclusion complexation of drugs with unsubstituted and derivative β‐cyclodextrins (β‐CDs) has proven to be a successful method to improve the dissolution of water insoluble drugs. Genistein (Gen), an isoflavone constituent of Onodis spinosae radix, turned out to be a suitable guest molecule for the encapsulation into β‐CD, resulting in a significant improvement of its aqueous solubility. In the present study, the modifications of the vibrational spectrum of Gen caused by its inclusion into β‐CDs cavity have been characterized by means of Raman scattering experiments. These changes have been interpreted by comparing the experimental data with the vibrational wavenumbers and Raman intensities obtained by simulation for the free and complexed guest molecule. Following this strategy, we have obtained a deeper understanding of the host–guest interactions involved in the formation and stabilization of the complexes, with particular regard to the role played by the guest chemical groups, as well as to disentangle the effects directly related to the complexation process from those ascribed to other factors, such as formation of intra‐ and intermolecular hydrogen bonds. Copyright © 2009 John Wiley & Sons, Ltd.     

Separation and quantitation of fructose-6-phosphate and fructose-1 ,6-diphosphate by LC-ESI-MS for the evaluation of fructose-1,6-biphosphatase activity

An LC-ESI-MS method was developed for the identification and quantification of fructose-1,6-biphosphate (F1,6BP) and fructose-6-phosphate (F6P), respectively the substrate and the product of the enzymatic reaction catalysed by fructose-1,6-bisphosphatase (F1,6BPase). F1,6BPase, expressed predominantly in liver and kidney, is one of the rate-limiting enzymes of hepatic gluconeogenesis and has become a target for the development of new drugs for type 2 diabetes. The two sugar phosphates were separated on a Phenomenex Luna NH2 column (150 mm x 2.0 mm id) using the following mobile phase: 5 mM triethylamine acetate buffer/ACN (80:20) v/v in a linear pH gradient (from pH = 9 to 10 in 15 min) at the flow rate of 0.3 mL/min. The detection was performed with an IT mass spectrometer in negative polarity (full scan 100-450 m/z) and in SIM mode on the generated anions at m/z = 339 (F1,6BP) and m/z = 259 (F6P). Under the optimised final conditions, the method was validated for accuracy, specificity, precision (inter- and intradays RSD comprised between 1.0 and 6.3% over the range of concentrations used), linearity (50-400 microM), LODs (0.44 microM) and LOQs (1.47 microM), and the method was applied to F6P determination in the F1,6BPase catalysed hydrolysis of F1,6BP.     

Isosorbide telechelic bio‐based oligomers

This article deals with the preparation of novel co‐oligoethers constituted with 1,3‐propanediol (PDO) and isosorbide units and, prepared according to two different melt processes, without any solvent in the presence of acid catalyst: co‐etherification of PDO and isosorbide (process A) and, trans‐etherification between polytrimethylene ether glycol (PTEG) and isosorbide (process B). Complementary analytical methods: D and 2D ¹H NMR and gas chromatography analysis, coupled with FID and MS‐MALDI‐TOF mass spectrometry, were performed to precisely define the microstructure of the final products. In particular, one can observe that two mechanisms involve during the reaction: etherification and trans‐etherification where isosorbide reacts decreasing the molar mass of polymers chains. This led to oligomers having isosorbide units at each extremity and little inner isosorbide units. Computational calculations have been performed in parallel, and the data well duplicate the experimental results. Finally, it was shown that these new telechelic oligoethers have higher compatibility to water and higher T_g level and thermal stability than PTEG homopolymer. Therefore, such oligomers can be considered as new intermediates for designing new surfactants and/or new copolymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2178–2189     

REACTION BETWEEN 2,2′-DITHIODIANILINE AND ETHYL 2-OXO-1-CYCLOALKANECARBOXYLATES

Abstract

A study has been carried out on the acid-catalysed reaction between 2,2′-dithiodianiline (1) and ethyl 2-oxo-1-cycloalkanecarboxylates (2a–d). While the 1,4-benzothiazines 3a, b and benzothiazoles 6a, b are obtained from the keto esters 2a, b, mixtures of the 1,4-benzothiazines 3c, d and 4c, d and benzothiazolines 5c, d are obtained from the keto esters 2c, d.

The formation of the benzothiazines 4 falls within the general pattern previously proposed for reactions between 2,2′-dithiodi(aryl- or alkylamines) and ketones.

The benzothiazines 3 arise from an acid-catalysed rearrangement of the benzothiazines 4, involving a [1, 3] sulfur migration.