Evaluation of some derivatives of 4-quinazolones as antioxidants and antirads in rubber

Derivatives of 4-quinazolones were compounded with rubber. The relation between their efficiencies as antioxidants and antirads was studied. It was found that their efficiencies as antioxidants and antirads fall in the same order but differ in degree.     

Low-swelling chitosan derivatives as biosorbents for basic dyes

In this study, three different chitosan microsphere derivatives were prepared as sorbents for basic dyes. Preparation was succeeded by a novel cross-linking method based on ionic gelation with tripolyphosphate and subsequent covalent cross-linking with glutaraldheyde in order to address the large amount of swelling of the powdered form of the respective derivatives. Basic blue 3G (dye) was selected as the sorbate, and chitosan microsheres grafted with acrylamide and acrylic acid were used as biosorbents. Techniques such as FTIR spectroscopy, SEM, and swelling measurements facilitated the evaluation of the materials. Sorption-desorption experiments over the whole pH range were carried out to reveal the optimum value of sorption-desorption. The Langmuir isotherm model was used to fit the equilibrium experimental data, giving a maximum sorption capacity of 0.808 mmol/g at 338 K. An intraparticle diffusion model was employed to fit the kinetic data, and the resulting diffusion coefficients were in the range of (1-10) x 10(-11) m(2)/s. Thermodynamic analysis showed that the sorption process was spontaneous and endothermic with an increased randomness. In addition, sorption experiments were realized with a mixture of three basic dyes at various concentrations of sorbents.     

Laboratory testing of rubber durability

One aim of the ever-increasing standardization of test methods for assessing the resistance of rubber to various tyoes of degradation and other potential failure processes is to give a nore reliable laboratory estimate of service performance. If this aim is to succeed, those developing, and using, such tests should be aware of the limitations of laboratory testing, and be acquainted with the factors that can affect the properties being determined. In his search for a quick estimate the user must recognise that an increase in test severity can also change the nature of the processes involved, and that a test conducted at a single set of conditions cannot be expected to provide the relevant data for a product which may be exposed to a widely varying environment. He also needs to take account of differences in size between the test piece and the intended product.The paper is illustrated by a discussion of the factors influencing resistance to ozone cracking, fatigue in tension, creep and stress relaxation, and liquids.     

Thermo-oxidative evaluation of new cardol derivatives as antioxidants for mineral oils

In this study, the thermo-oxidative stability of two new phosphorylated derivatives of cardol, a compound from the cashew (Anacardium occidentale L.) industry waste CNSL (cashew nutshell liquid), were evaluated. The antioxidant capacity of these new molecules upon two mineral oils, NH10 and NH20 were also studied by thermogravimetric analysis (TG/DTG), observing the onset and offset temperatures variation. The results showed that both MP and DP Cardol increased considerably the onset and offset temperatures of NH10 and NH20 oils.     

Pyrocatechol and its derivatives as antioxidants and prooxidants

The effect of pyrocatechol and its derivatives (4,5-dichloro- and 4,5-dibromo pyrocatechols, veratrol, 4,5-dichloro- and 4,5-dibromoveratrol) on the free-radical oxidation of propan-2-ol in aqueous solutions, initiated by γ-radiation. Pyrocatechol and dihalocatechols exhibit antioxidant properties, whereas dihaloveratrols exhibit prooxidant properties. Dibromoveratrol showed more expressed prooxidant properties.     

Effect of some structural parameters on the efficiency of some aromatic amino compounds as antioxidants in rubber

The relation between the chemical structure of some aromatic amino compounds as anti-oxidants in rubber and their efficiency was studied. A study of the effect of three different structural parameters was carried out. These parameters are: the type of the radical attached directly to the amino group, the position of the carbonyl group with respect to the amino group, and the type of the substituent at the para-position of the aromatic ring. All these parameters confirm that the lability of the hydrogen of the NH group is responsible for the efficiency of these compounds as anti-oxidants. A relation between σ_Hammett of the substituent and the efficiency of these compounds was found.     

l-Isofucoselenofagomine and derivatives: dual activities as antioxidants and as glycosidase inhibitors

The synthesis of a series of l-fuco-configured selenosugars, isosters of the potent glycosidase inhibitor isofucofagomine has been accomplished by a double nucleophilic displacement of a dimesylated derivative with selenide anion generated in situ. Se-Alkylation and oxidation of the corresponding selenane afforded a selenonium and a selenoxide, respectively. The biological activities of such compounds have been evaluated, finding a dual activity caused by the presence of the selenium atom: the selenane exerted a good glutathione peroxidase mimicry by efficiently scavenging H₂O₂ in the presence of thiols, whereas the stable selenoxide derivative was found to be the first example of a selenosugar acting as a good α-l-fucosidase inhibitor.     

3,5-Di-tert-butyl-4-hydroxybenzaldehyde derivatives as antioxidants in cumene oxidation

A series of 4-hydroxy-3,5-di-tert-butylbenzaldehyde derivatives were prepared, and their antioxidant properties were studied.     

Effect of antioxidants on aging of the chloroprene rubber/butadiene rubber (CR/BR) blends

Thermal degradation of blends containing chloroprene rubber (CR) and butadiene rubber (BR) cross-linked with copper(II) oxide (CuO) with the addition of anti-aging substance ((N-(1.3-dimethylbutyl)-N-phenyl-p-phenylenediamine (6PPD), polymerized 2.2.4-trimethyl-1.2-dihydroquinoline (TMQ), or 2-mercaptobenzimidazole (MBI)) under high temperature was investigated using a Fourier Transform Infrared spectroscopy (FTIR) spectroscopy and color measurement. Additionally, changes in mechanical properties (such as tensile strength, elongation at break, hardness, tear resistance) causes by aging factors have also been investigated. The results indicated that the 6PPD and the MBI provided better protection of the CR/BR/CuO vulcanizates against degradation at elevated temperature than the TMQ. As a result of thermo-oxidative aging, in an infrared spectrum, a peak assigned to stretching vibration of carbonyl groups was observed. Differences in protection against thermo-oxidative aging by the anti-aging substance are caused by their different structure, consequently, by the differences in their protection mechanism.     

壳聚糖及其衍生物作为疫苗佐剂的研究进展

疫苗佐剂能够增强机体对抗原的免疫应答反应或改变免疫应答反应类型,延长疫苗在体内作用时间,提高疫苗效力。壳聚糖能有效地将疫苗递送到靶抗原递呈细胞或组织,激活抗原提呈细胞,诱导产生免疫应答,促进Th1/Th2应答反应的平衡,因此,壳聚糖作为疫苗佐剂具有一定的潜力。为了解决壳聚糖在中性和碱性溶液中溶解性差,以及进一步提高其黏膜黏附性和靶向性等问题,通过对壳聚糖进行化学改性,生成一系列壳聚糖衍生物,提高其佐剂性能。本论文就近年来有关壳聚糖及其衍生物作为疫苗佐剂和递送系统在疫苗中的应用进行了综述,总结并提出了壳聚糖及其衍生物在疫苗佐剂应用领域所面临的问题以及其未来的发展方向,使读者对其有全面的了解。     

Synthesis of cyanoethyl chitosan derivatives

Cyanoethyl chitosan derivatives with various substitution degrees have been synthesized by the nucleophilic addition of acrylonitrile to the functional groups of chitosan. The process proceeds under homogeneous conditions without any catalyst at various pH values and reagent concentrations in the temperature range of 273–333 K. The formation of cyanoethyl chitosans is established by a gain in the weight of chitosan, a change in its content of nitrogen, and the appearance of an absorption band at 2250 cm^?1 in the IR spectrum which corresponds to the stretching vibrations of a-C≡N group. It has been shown that the most efficient addition of acrylonitrile occurs at 273 K and pH 5.5. Cyanoethyl chitosan samples show better mechanical parameters and are characterized by a lower ordering than the parent chitosan.     

Thiophosphate esters of cashew nutshell liquid derivatives as new antioxidants for poly(methyl methacrylate)

In this work, poly(methyl methacrylate) films 1% additivated with new thiophosphate esters antioxidants derived from technical Cashew Nutshell Liquid (CNSL), a byproduct of the cashew nut (Anacardium occidentale L.) industry, were investigated by thermogravimetry (TG/DTG) and differential scanning calorimetry (DSC) measurements under inert (N₂) and oxidative (synthetic air) atmospheres. Three new products were synthesized and characterized by GC/MS, ¹H and ³¹P NMR. The analyses were focused on the onset (T _e) and offset temperature (T _o) of degradation of the films, and on the maximum degradation temperature (T _MAX). It was observed that the thermal stability of the films increased with the addition of the thiophosphate ester antioxidants, which indicates that CNSL could be used as a natural source of phenolic material for the synthesis of antioxidants.     

Mechanisms of antioxidant action: The role of mercaptobenzthiazole and its derivatives as antioxidants

Mercaptobenzthiazole (MBT) and its zinc complex (ZMBT) are compared as antioxidants for paraffin oil at 140°. The latter is much more effective than the former at comparable molar concentrations. Autoxidation studies at lower temperatures indicate that MBT is superior to ZMBT both as a hydroperoxide decomposer and as a chain-breaking antioxidant. However, products formed from them by reaction with hydroperoxides are much more effective than either MBT or ZMBT. Both are oxidised to bis-2-benzthiazole disulphide (MBTS) are benthiazole sulphinic acid (BTS) which decomposes to give benzthiazole (BT) and sulphur dioxide. In addition, MBT gives benzthiazole sulphonic acid (BTSO) and ZMBT gives the very stable zinc benzthiazole sulphimate (ZBTS) which also behaves as a reservoir for sulphur oxides. The difference in behaviour at 140° appears to be associated with the relative instability of BTSO compared with ZBTS.     

Microwave-assisted synthesis and biological evaluation of new thiazolylhydrazone derivatives as tyrosinase inhibitors and antioxidants

In this work, we have synthesized a series of 2-thiazolylhydrazone derivatives ( 1–27 ) and investigated their biological activities as tyrosinase inhibitors and antioxidants. Some compounds showed potent tyrosinase inhibitory activities and 4-(2-(2-(1-(4-Aminophenyl)ethylidene)-hydrazinyl)thiazol-4-yl) phenol ( 26 ) showed more potent inhibitory effect than the standard tyrosinase inhibitor kojic acid (IC₅₀: 9.8 μM vs. 23.6 μM). Compounds 2 , 14 , and 26 exhibited high antioxidant activities in 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays. The structure–activity relationship (SAR) indicated that the substitutions of bromine, hydroxyl group, and amino groups cause great effect to the inhibition effect against tyrosinase. The mechanism and kinetic studies demonstrated that the inhibitory effect of compound 26 on the tyrosinase by acting as the reversible and uncompetitive inhibitor. Docking studies suggests that compound 26 interacts strongly with mushroom tyrosinase via hydrogen bonding.     

异相法制备磺酸基取代壳聚糖衍生物

用3-氯-2-羟基丙磺酸钠与壳聚糖在较低温度下进行非均相反应制备了一系列取代度,结构新颖的改性壳聚糖.实验表明化学改性能极大的提高壳聚糖在水溶液中的溶解性能.研究了不同的反应条件对壳聚糖取代度的影响并用核磁共振表征了它们的结构.反应可在中性、较为温和的条件下进行,通过改变反应时间和反应物比例能有效的控制改性壳聚糖的取代度.改性后的壳聚糖能溶解于中性的水溶液中,浊度实验表明产物具有明显的两性聚电解质特征,其等电点约在pH=5.7.该方法为制备化学改性壳聚糖的一种有效的方法.     

Radiolysis of chitosan derivatives exhibiting antimutagenic activity

The radiolysis of antimutagens extracted from natural biopolymer chitosan was studied by the EPR method. It was shown that addition of gallic acid (2 mol %) to quaternized chitosan results in a 2.5-fold decrease in the radiation-chemical yield of radicals and a nearly complete inhibition of the formation of ion radicals. Gallic acid units likely play the role of a stabilizer that protects the polycation from radiation damage and, hence, the structure of the cationogenic units from changes, thereby improving the antimutagenic properties of the system.     

The effect of antioxidants on styrenebutadiene rubber vulcanized by alkylphenolformaldehyde resin

Styrene-butadiene rubber was compounded with various phenolic- and amino-type antioxidants and model compounds, and then vulcanized by a p-octylphenolformaldehyde resin. Vulcanization characteristics were evaluated by the Monsanto Oscillating Disc Rheometer and other techniques. It was found that phenolic-type antioxidants have no practical effect on the vulcanization, while amino-type compounds retard it. The retardation effect of the latter depends on the electron density of the nitrogen atom and on the number of hydrogen atoms linked to it.     

Mechanisms of antioxidant action. The role of nitroxyl radicals as chain-breaking acceptor antioxidants in the mechanodegradation of rubber

It is shown that 4-hydroxy-2,2,6,6-tetramethylpiperidinoxyl (HTMPO) becomes partially attached to natural rubber during mechano-oxidation in a shearing mixer at ambient temperatures. It is concluded that the main mechanism responsible for the antidegradant activity of HTMPO under shearing conditions is direct oxidation of mechanochemically produced macroalkyl radicals to species containing conjugated unsaturation.     

Novel nanoparticles composed of chitosan and β-cyclodextrin derivatives as potential insoluble drug carrier

This research was aim to develop novel cyclodextrin/chitosan(CD/CS) nanocarriers for insoluble drug delivery through the mild ionic gelation method previously developed by our lab. A series of different bcyclodextrin(β-CD) derivatives were incorporated into CS nanoparticles including hydroxypropyl-bcyclodextrin(HP-β-CD), sulphobutylether-β-cyclodextrin(SB-β-CD), and 2,6-di-O-methy-β-cyclodextrin(DM-β-CD). Various process parameters for nanoparticle preparation and their effects on physicochemical properties of CD/CS nanoparticles were investigated, such as the type of CD derivatives,CD and CS concentrations, the mass ratio of CS to TPP(CS/TPP), and p H values. In the optimal condition,CD/CS nanoparticles were obtained in the size range of 215–276 nm and with the zeta potential from30.22 m V to 35.79 m V. Moreover, the stability study showed that the incorporation of CD rendered the CD/CS nanocarriers more stable than CS nanoparticles in PBS buffer at p H 6.8. For their easy preparation and adjustable parameters in nanoparticle formation as well as the diversified hydrophobic core of CD derivatives, the novel CD/CS nanoparticles developed herein might represent an interesting and versatile drug delivery platform for a variety of poorly water-soluble drugs with different physicochemical properties.