Reverse atom transfer radical polymerization of methyl methacrylate in the presence of Azo-functionalized carbon nanotubes: a grafting from approach

After oxidation of carbon nanotubes (CNT), its carboxyl groups were subsequently converted to acyl chloride and hydroxyl functionalities. Subsequently, 4,4′-azobis (4-cyanopentanoic acid) (ACPA) was attached to the hydroxyl groups of nanotubes by an esterification reaction to yield azo initiator-anchored nanotubes (CNTAzo). Then, grafting from reverse atom transfer radical polymerization of methyl methacrylate in the presence of CNTAzo in different weight percents was carried out. Appearance of N_1s band in the spectrum of CNTAzo originates from the covalent attachment of ACPA on CNT. Successful functionalization of CNT with EG, ACPA, and PMMA was also proved by FTIR. SEC results show that molecular weight and PDI values of the attached chains are higher. XRD and Raman spectroscopy were used to study the structural characteristics of the CNTs. Graft density of modifier and PMMA in various CNTs was evaluated by TGA. Finally, morphology of the CNTs was studied by scanning and transmission electron microscopies.     

Synthesis,characterization, spectrophotometric and electrochemistry studies,and DNA cleavage of copper(II) complexes of a new azacrown bis-macrocycle and its mono-cyclic analogue

A new azacrown bis-macrocycle (5) and its mono–cyclic analogue (7) were synthesized and characterized by FT-IR, ¹H NMR, ¹³C NMR, DEPT ¹³C NMR, MS, and elemental analysis. The reaction with copper(II) nitrate yielded the corresponding complexes, formulated as Cu(5)(NO₃)₂·3H₂O (8), and Cu(7)(NO₃)₂·2.5H₂O (9). Also the stoichiometries of the complexes were determined in alcoholic solution and the results show that for both complexes the ratio of ligand to metal was 1:1 in methanol. The redox behavior of both complexes has been studied by cyclic voltammetry in DMF. Cyclic voltamogram of 8 shows quasi-reversible Cu^II/Cu^I redox couple whereas 9 shows a reversible Cu^II/Cu^I redox couple. Mono- and bis-macrocycle copper(II) complexes (8 and 9 respectively) cleaved plasmid pGS2 DNA by using an oxidative mechanism with 3- mercaptopropionic acid (MPA) as the reductant under aerobic conditions. The bis-macrocycle copper(II) complex 8 showed higher cleavage efficiency than their mono-macrocycle analogue 9 at the same Cu²⁺ concentration.     

One-pot synthesis of 2-amino-3-cyanopyridine derivatives under solvent-free conditions

A series of 2-amino-3-cyanopyridines were obtained from aryl aldehydes, substituted acetophenones, malononitrile and ammonium acetate in good to excellent yields by proceeding through a simple, mild and efficient procedure utilizing N,N,N′,N′-tetrabromobenzene-1,3-disulfonamide [TBBDA] and poly(N-bromo-N-ethylbenzene-1,3-disulfonamide) [PBBS] as catalysts.     

Effects of Ag or Si on precipitation in the alloy Al-2.5 mass% Cu-1.5 mass% Mg

Calorimetric measurements and electron microscopy observations were performed on Al-2.5?mass% Cu-1.5?mass% Mg alloys containing also 0.4, 1 or 2% Ag or 0.5% Si, in order to improve understanding of the relationships between precipitation processes and age hardening. The analogous behaviour of calorimetric and hardness data confirms that the first hardening stage is initiated in all alloys by GPB zone formation which occurs via a nucleation and growth controlled mechanism. The vacancy-trapping effect of Mg is increased by Ag and Si additions and leads to slower precipitation kinetics. Consequently, refined GPB zones sizes are obtained leading to an increase in hardness with respect to the ternary alloy. During the second hardening stage, the formation of the more stable S′ phase increases the total amount of strengthening precipitates in the ternary alloy. Phases typical for binary Al–Cu alloys form additionally in the Si-containing alloy. In the Ag-bearing alloys, precipitation of the hardening X′ phase occurs the earlier the higher the Ag content; it is followed by S′ precipitation. During heating of the ternary alloy, the S′ phase forms after substantial dissolution of GPB zones and of the S′′ phase identified by high resolution electron microscopy; this contradicts the concept of a continuous precipitation sequence.     

Convenient Synthesis of Thiol Esters from Acyl Chlorides and Disulfides Using Zn/AlCl3

Summary.  Various thiol esters were prepared by condensation of acyl chlorides with disulfides in the presence of Zn/AlCl₃. The advantages of this method are high yields under relatively mild conditions, simple work-up, lack of toxicity, and low costs. Received July, 20, 2001. Accepted September 24, 2001     

Diastereoselective and enantioselective alkaline-hydrolysis of 2-aryl-1-cyclohexyl acetate: a CAL-B catalyzed deacylation/acylation tandem process

Candida antarctica lipase proved to be a particularly efficient lipase for the resolution of racemic 2-arylcyclohexyl acetate in hydrolysis reaction with Na₂CO₃ in an organic medium. The (1R,2S)-trans-2-arylcyclohexanols 2a–2d were obtained with high ee values (up to >99%) and the selectivity reached E > 200. The influence of the enol ester and the solvent on (±)-trans-2-arylcyclohexanol in the CAL-B catalyzed acylation was also studied and compared with the deacylation. The CAL-B exhibits a better affinity for the alkaline hydrolysis reaction compared with acylation with the enol esters in the same organic solvents. The best conditions were applied to resolve a stereoisomeric mixture cis/trans-2-phenyl-1-cyclohexanol and its corresponding acetate by acylation and deacylation. The obtained results show a highly enantio- and diastereoselectivity of the CAL-B during the acylation and the deacylation in favor of the trans-(R)-enantiomer product. The resolution of a mixture of cis/trans-2-arylcyclohexanols was an easy, convenient approach to provide only one stereoisomer of a mixture of four with high enantiomeric excess.     

Self-assembled monolayers of organosulfur derivative on gold nanoparticles as electrochemical sensor for determination of isoprenaline

In this paper, the use of molecular self-assembled monolayers of 5-(1,3-dithiolan-2-eyl)-3-methyl banzen-1,2-diol (DMD) on gold nanoparticles was described (DMD-AuNPs). The redox properties of modified electrode at various scan rates were investigated by cyclic voltammetry. A pair of well-defined quasi-reversible redox peaks of DMD were obtained at the modified electrode. Dramatically enhanced electrocatalytic activity was exemplified at the DMD-AuNPs, as an electrochemical sensor to investigate the electro-oxidation of isoprenaline (IP). With this modified electrode, the oxidation potential of the IP was shifted about 235 mV toward a less positive potential value than that of an unmodified electrode. The values of electron transfer coefficients (α = 0.5), catalytic rate constant (ks = 9.2 s^?1) and diffusion coefficient (D = 8.9 × 10^?5 cm² s^?1) were calculated for IP. The response of catalytic current with IP concentration showed a linear relation in the range from 0.5 to 800 µM with a detection limit of 0.21 µM. Finally, this modified electrode was used for the determination of IP in IP injections.     

Virtual screening of some heterocyclic structures toward novel antibacterial agents

Infectious diseases and their treatment are among the most important issues in global health and economy. Moreover, increasing prevalence of antibiotic-resistant pathogenic bacteria necessitates the considerable need for discovering new drugs. Some heterocyclic structures with dihydropyridine (DHP) scaffold have been reported as antimicrobial agents. Herein, we report a structure-based virtual screening of a pool of 3,5-disubstituted DHPs and a post-analysis of virtual hits through in vitro antibacterial assessment. Four top-ranked DHP structures (6a–d) were found to interact with the relevant target active sites and exhibited superior stereoelectronic features within their enzyme inhibition. Selected compounds were synthesized and assessed for their antibacterial activity via microdilution method. Results of this study represented a significant application of multi-step virtual screening strategy in identifying privileged DHP structures as good starting points for further developments toward more potent antibacterial agents.