Effect of methyl iodide fumigation on soil urease activity

R E V I E W Effects of antioxidant supplementation on the aging processDomenico Fusco1 Giuseppe Colloca1Maria Rita Lo Monaco1 Matteo Cesari1,21Department of Gerontology, Geriatrics and Physiatry; Catholic University of Sacred Heart, Rome, Italy; 2Department of Aging and Geriatric Research, College of Medicine, Institute on Aging, University of Florida, Gainesville, FLCorrespondence: Matteo Cesari Department of Gerontology, Geriatrics and Physiatry; Catholic University of Sacred Heart; Largo F. Vito, 100186 Rome, ItalyT el + 39 06 3015 4341Fax + 39 06 3051 911Email macesari@ Abstract:The free radical theory of aging hypothesizes that oxygen-derived free radicals are responsible for the age-related damage at the cellular and tissue levels. In a normal situation, a balanced-equilibrium exists among oxidants, antioxidants and biomolecules. Excess generation of free radicals may overwhelm natural cellular antioxidant defences leading to oxidation and further contributing to cellular functional impairment. The identifi cation of free radical reactions as promoters of the aging process implies that interventions aimed at limiting or inhibiting them should be able to reduce the rate of formation of aging changes with a consequent reduction of the aging rate and disease pathogenesis. Even if antioxidant supplementation is receiving growing attention and is increasingly adopted in Western countries, supporting evidence is still scarce and equivocal. Major limitations in literature are still needed to be addressed to better evaluate the potential benefi ts from antioxidant supplementation: 1) an improved understand-ing of oxidation mechanisms possibly at the basis of the aging process, 2) the determination of reliable markers of oxidative damage and antioxidant status, 3) the identifi cation of a therapeu-tic window in which an eventual antioxidant supplementation may be benefi cial, 4) a deeper knowledge of the antioxidant molecules which in several conditions act as pro-oxidants.In the present paper, after a preliminary introduction to the free radical theory of aging and the ratio-nale of antioxidant supplementation as an anti-aging intervention, we will present an overview of evidence relating antioxidant supplementations with clinical conditions typical of older age (ie, cardiovascular disease, Alzheimer’s disease, cancer). We will also discuss studies that have evaluated whether antioxidant supplementation might improve major outcomes of interest in older persons (ie, physical performance, muscle strength, longevity). Given the large amount of data available on the antioxidant supplementation topic, this overview is not intended to be exhaustive. The aim of this paper is to provide the main basis from which future studies should start and indicate which the main limitations that need to be addressed are.Keywords: aging, anti-aging medicine, antioxidant supplementation, oxidative damage The free radical theory of agingMore than 300 theories have been proposed to explain the ageing process (Medvedev 1990), but none has yet been generally accepted by gerontologists. However, the initial proposal by Denham Harman that free radicals are causally related to the basic aging process (Harman 1957) is receiving growing acceptance as a possible explanation of the chemical reactions at the basis of ageing (De La Fuente 2002). The free radical theory of aging hypothesizes a single common process, modifi able by genetic and environmental factors, in which oxygen-derived free radicals are responsible (due to their high reactivity) for the age-associated damage at the cellular and tissue levels. In fact, the accumulation of endogenous oxygen radicals generated in cells and the consequent oxidative modifi cation of biological molecules (lipids, proteins and nucleic acid) have been indicated as responsible for the aging and death of all living beings (Finkel and Holbrook 2000; Harman 1957).© 2007 Dove Medical Press Limited. A ll rights reservedClinical Interventions in Aging 2007:2(3) 377–387377Fusco et alThe free radical theory was revised in 1972 (Harman 1972) when mitochondria were identifi ed as responsible for the initia-tion of most of the free radical reactions occurring in the cells. It was also postulated that the life span is determined by the rate of free radical damage to the mitochondria. In fact, mitochondria, in which there is a continuous generation of free radicals throughout cell life, and especially mitochondrial DNA, are key targets of the free radical attack. Cells which use oxygen, and consequently produce reactive oxygen species, had to evolve complex anti-oxidant defence systems to neutralize reactive oxygen species and protect themselves against free radical damage. Thus, the increasing oxidative stress in ageing seems to be a consequence of the imbalance between free radical production and antioxidant defences with a higher production of the former (Sastre et al 2000). An ideal “golden triangle” of oxidative balance, in which oxidants, antioxidants and biomolecules are placed at each apex, has been described (Carmeli et al 2002). In a normal situation, a balanced-equilibrium exists among these three elements. Excess generation of free radicals may overwhelm natural cellular an-tioxidant defences leading to oxidation and further contributing to cellular functional impairment (Bowles et al 1991; Meydani et al 1993).The identifi cation of free radical reactions as promoters of the aging process implies that interventions aimed at limiting or inhibiting them should be able to reduce the rate of forma-tion of aging changes with a consequent reduction of the aging rate and disease pathogenesis (Harman 2003). In fact, the free radical theory of aging fostered a important body of research investigating the potential role of antioxidant nutrients in thera-peutic or preventive strategies (Mayne 2003). However, even if antioxidant supplementation is receiving growing attention and is increasingly adopted in Western countries, supporting evidence is still scarce and equivocal.Oxidative damageThe simplest free radical is an atom of the element hydrogen, with one proton and a single electron. Free radicals may also be nitrogen- or carbon-centered but O2-centered radicals are the most important ones in aerobic organisms. Reactive oxygen species are mainly produced in mitochondria, whichutilize most of the O2consumed for substrate metabolismand ATP production, reducing O2to water. Reactive oxy-gen species, produced under normal aerobic metabolism, are essential for cell signalling and for bacterial defence. In respiring cells, there appears to be a leakage of electrons from the mitochondrial electron transport chain, to eventually yield a variety of such free radicals and active oxygen derivatives that are collectively called reactive oxygen species.Under normal conditions about 1% of reactive oxygen species daily escapes the control of the endogenous anti-oxidant defences and contributes to oxidative damage of surrounding tissues, consequently promoting and developing the aging process. Reactive oxygen species can attack any biochemical component of the cell. If the body or cell capac-ity to neutralise reactive oxygen species is altered, then they will produce acute damage to vital proteins, lipids and DNA. In humans, unbalance between reactive oxygen species pro-duction and endogenous antioxidants has been involved in the generation or worsening of more than a hundred pathologic conditions (Gutteridge 1993).Measuring the free radical activity in vivo (ie, increased reactive oxygen production) is confronted with practical and analytical problems: we are left with the surrogate determina-tions of the end products of oxidation. In fact, the oxidative damage is commonly determined by the quantity of nucleic acid that is damaged with the Comet assay (Hartmann et al 2003), the amount of end products of lipid peroxidation (Cesari et al 2005; Sakamoto et al 2002), or of protein oxida-tion (Cesari et al 2005).Physical activity and oxidative damageThe increased production of free radicals during physical exercise has been attributed to several factors, including the increase of catecholamines undergoing auto-oxidation, muscle transient hypoxia and re-oxygenation, lactic acid-induced free iron release from myoglobin, and/or infl ammation-related neutrophil func-tion (Ji et al 1998). There is a substantial lack of data regarding the effects of acute or chronic exercise in aging animals or humans. Inconsistent results (partly also due to methodological limitations in the reactive oxygen species measurements) do not allow a clear interpretation of studies regarding exercise-related DNA and protein oxidation, and lipid peroxidation. However, current literature seems to show an increased resistance to oxi-dative damage with chronic exercise and increased lipid, DNA or protein oxidation after an acute bout of maximal exercise (Polidori et al 2000).Regular physical activity and exercise are recommended for the maintenance of an optimal health status and the pre-vention or management of chronic diseases (Department of Health and Human Services, Centers for Disease Control and Prevention, and National Center for Chronic Disease Prevention and H ealth Promotion 1996; Pate et al 1995). Physical activity (especially if begun in mid-life), quitting cigarette smoking, maintaining normal blood pressure, and avoiding obesity are independently associated with reducedClinical Interventions in Aging 2007:2(3)378Antioxidant supplementation and aging processcardiovascular and overall mortality (Paffenbarger et al 1993). Regular physical activity has shown to reverse age-re-lated body composition modifi cations in older subjects (ie, by increasing lean mass and reducing adipose tissue) (Fiatarone Singh 1998; Fiatarone et al 1994; Polidori et al 2000), and to confer signifi cant protection against several age-related diseases (eg, non-insulin-dependent diabetes (Hughes et al 1995); cancer (Ji et al 1991); hypertension (Dengel et al 1998); and osteoporosis (Evans 1999)).Animal (Zerba et al 1990) as well as human (Quindry et al 2003; Tozzi-Ciancarelli, Penco and Di Massimo 2002; Watson et al 2005) models have demonstrated that acute bouts of eccentric exercise produce higher oxidative damage to muscles in aged mice and men compared to young animals or human subjects. However, physical activity may still play an important role in limiting the free radical production and oxidative damage. In fact, even if exercise is associated with an abnormal production of free radicals, physically active older persons benefi t from exercise-induced adaptations in the cel-lular antioxidant defence systems (Fulle et al 2004).Physical exercise may lead to an increase in antioxidant defences of the organism in younger as well as in older subjects (Lawler and Powers 1998; Leeuwenburgh and Heinecke 2001). Nevertheless, the equilibrium between free radical produc-tion and antioxidant defence induction by physical exercise intervention in elders may be more unstable than in younger subjects. This is probably due to the higher rate of oxidative stress occurring in older persons (Ames 1989; Facchini et al 2000; Greco et al 2000; Olinski et al 2003), partly explained by increased number of concurrent clinical conditions and the sed-entary lifestyle. Moreover, although age-related modifi cations occurring in antioxidant defences and repairing systems are not yet fully clarifi ed (Beckman and Ames 1998), a decrease of major antioxidants levels with aging has been suggested (Pinzani et al 1997; Poulsen et al 1996).An acute bout of exercise increases antioxidant activities in skeletal muscle, heart, and liver with a threshold and magnitude of activation that differs among antioxidant enzymes, tissues, and type of exercise organisms (Ji et al 1998). No signifi cant difference in the antioxidant enzyme response between old and young animals has been suggested (Fiebig et al 1994; Ji 1996; Lawler and Powers 1998). Moreover, endurance training has shown to increase antioxidant enzyme activities even in the senescent muscle (Ji et al 1991).AntioxidantsAntioxidants are substances, which inhibit or delay oxidation of a substrate while present in minute amounts. Endogenous antioxidant defences are both non-enzymatic (eg, uric acid, glutathione, bilirubin, thiols, albumin, and nutritional fac-tors, including vitamins and phenols) and enzymatic (eg, the superoxide dismutases, the glutathione peroxidases [GSHPx], and catalase). In the normal subject the endogenous antioxi-dant defences balance the reactive oxygen species produc-tion, but for the above-mentioned 1% daily leak. The most important source of antioxidants is provided by nutrition, many belonging to the phenol family.Nutritional antioxidants act through different mechanisms and in different compartments, but are mainly free radical scav-engers: 1) they directly neutralise free radicals, 2) they reduce the peroxide concentrations and repair oxidized membranes, 3) they quench iron to decrease reactive oxygen species produc-tion, 4) via lipid metabolism, short-chain free fatty acids and cholesteryl esters neutralise reactive oxygen species (Berger 2005). The body antioxidant defence can be approximated by measuring antioxidant plasma levels (micronutrients, enzymes, other antioxidant), keeping in mind that the circulating com-partment only refl ects the fl ow between organs and tissues. The tissue levels of the various antioxidants remains limited to research protocols as tissue biopsies are required.Vitamin C is the major water-soluble antioxidant and acts as fi rst defence against free radicals in whole blood and plasma. It is a powerful inhibitor of lipid peroxidation and regenerates vitamin E in lipoproteins and membranes. A strong inverse association has been shown between plasma ascorbic acid and isoprostanes (Block et al 2002). Isoprostanes represent a family of prostaglandin isomers which, in contrast to classic prostaglandins formed through an enzymatic action of the prostaglandin-H-synthase from arachidonic acid, result from a free radical-catalyzed mechanism (Morrow et al 1990). For this reason, isoprostanes provide an optimal estimate of oxida-tive damage to cellular lipids (Morrow 2005) and represent an excellent biomarker of lipid peroxidation for aging studies (Cesari et al 2005).Bagi et al (Bagi et al 2003) have shown that chronic vitamin C treatment is able to decrease high levels of isoprostanes in animal models. Ascorbic acid combined to α-tocopherol is particularly effective in inhibiting oxida-tion (Niki et al 1995). Vitamin C reduces α-tocopheroxyl radicals rapidly in membranes and LDL to regenerate α-tocopherol and possibly inhibits α-tocopheroxyl radical-mediated propagation.Vitamin E is a lipid-soluble vitamin found in cell mem-branes and circulating lipoproteins. It protects against oxidative damage by acting directly with a variety of oxygen radicals. Its antioxidant function is strongly supported by regenerationClinical Interventions in Aging 2007:2(3)379Fusco et alpromoted by vitamin C (Maxwell 1995). Vitamin E is thought to have a role in the prevention of atherosclerosis through inhibition of oxidative modifi cations of LDLs (Steinberg 1997; Witztum 1994). The formation of isoprostanes increases signifi cantly in animals defi cient in vitamin E (Morrow and Roberts 1997). Moreover, inhibition of isoprostanes forma-tion by vitamin E supplementation has been shown in humans (Upritchard et al 2003) as well as in animal models (Liu et al 1999). α-tocopherol is quantitatively the major form of vitamin E in humans and has been extensively studied. In contrast, γ-tocopherol, even if representing the most abundant form of vitamin E in the US diet, has received less attention (Jiang et al 2001). Compared with α-tocopherol, γ-tocopherol is a slightly less potent antioxidant with regard to electron-donat-ing propensity, but is superior in detoxifying electrophiles, such as reactive nitrogen oxide species (Jiang et al 2001). The interaction of α-tocopherol with β-carotene is not as evident as the one reported with vitamin C, but it has been shown that α-tocopherol and β-carotene exert a cooperative effect by residing and scavenging radicals at different positions in the lipophilic compartment (Niki et al 1995).Carotenoids are lipid-soluble antioxidants. Plasma levels of carotenoids are negatively correlated with levels of isoprostanes (Block et al 2002). Carotenoids levels are inversely associated with infl ammation (H u et al 2004), atherosclerosis (Prince et al 1988), cardiovascular disease (Gaziano et al 1995), sarcopenia (Semba et al 2003), and mortality (H u et al 2004), and positively correlated with physical performance (Cesari et al 2004). Improvements in antioxidant status and reduction of lipid peroxidation have been shown after carotenoids supplementation (Upritchard et al 2003). The most known and studied carotenoid is the β-carotene, a potent antioxidant able to quench singlet oxy-gen rapidly (Di Mascio et al 1991). β-carotene, α-carotene, β-cryptoxanthin, lycopene, and lutein/zeaxanthin have all been found associated with infl ammation (H u et al 2004; Kritchevsky et al 2000). The association between low serum levels of β-carotene and increased risk for mortality was recently reported (Hu et al 2004).Vitamin C, vitamin E, and carotenoids have shown to synergistically interact against lipid peroxidation (Niki et al 1995). Higher serum levels of antioxidants are associated with higher strength and physical performance measures (Cesari et al 2004; Semba et al 2003), suggesting that oxida-tive damage may play an important role for the onset of the disabling process.Melatonin is a mammalian hormone synthesized from serotonin, mainly in the pineal gland. Besides of its widely documented action regulating the circadian rhythm, it has been reported that melatonin contributes to the reduction of oxidative damage in both the lipid and the aqueous environments of the cell (Aydogan et al 2006). The powerful antioxidant capacity of melatonin (Pieri et al 1995) is exerted by stimulating the expression and activity of glutathione peroxidase, superoxide dismutase, NO synthetase (Nishida 2005). Interestingly, melatonin concentrations are particu-larly high in mitochondria and the cell nucleus (Aydogan et al 2006), where major oxidation reactions occur.The balance between oxidant and reducing forces is subtle (Abuja 1998). Trace elements with antioxidant prop-erties such as copper and selenium (Terada et al 1999), may become strongly pro-oxidant both in vivo and in vitro, as a consequence of their physical properties. This is also the case with vitamins A, C, E, which may become pro-oxidant under defi ned conditions (Berger 2005).Vitamin E can also become a pro-oxidant in isolated lipoprotein suspensions (eg, parenteral nutrition solutions in clinical conditions (Neuzil et al 1995). The pro-oxidant effects of selenium have been investigated on cultured vas-cular cells exposed to parenteral nutrition containing vari-ous forms and quantities of selenium (Terada et al 1999). In a recent study, Nakamura and colleagues (Nakamura et al 2006) suggested that Vitamin C may play an important role to prevent the pro-oxidant effect of Vitamin E in LDL oxidation.Antioxidant supplementationThe last 50 years have been characterized by the understanding of the impact of nutrition and dietary patterns on health (Caballero 2003). An important part of the population is exposed to the risk of trace element and vitamin defi ciency for multiple reasons (eg, changes in eating habits in Western Countries, lower food concentration of micronutrients due to intensive agricultural techniques). Children, young women and elders are the most exposed (Caballero 2002; Johnson et al 2002; Ramakrishnan 2002). Efforts to fi ght nutrient defi ciencies have centred on supplemental nutrient administration and on addition of selected nutrients to the food chain in the form of food fortifi cation (Caballero 2003). Supplementation and fortifi cation has also been proposed in healthy individuals with the aim of reducing their risk of future diseases (eg, cardiovascular diseases, diabetes and cancer). Nevertheless, with our increasing understanding of the genetic heterogeneity of human nutrient requirements, it is likely that certain groups or even populations may benefi t from higher intakes of certain nutrients. However, the latterClinical Interventions in Aging 2007:2(3)380Antioxidant supplementation and aging processconcept is getting closer to the therapeutic modulation of nutrient intake.Antioxidant supplementationand clinical conditions Atherosclerosis and cardiovascular diseaseIn Western Countries, atherosclerotic disease is the major cause of death in the elderly population. Several antioxidants, such as polyphenols and lycopene, have been proposed to delay the progression of this disease. At the beginning of the Nineties, Renaud and de Lor-geril created the so-called “French Paradox”, describing how, despite the high intake of saturated fat, the French population presents a low incidence of coronary heart disease events (Renaud and de Lorgeril 1992). Even if their study raised a huge controversy, it has been sug-gested that beneficial effects from red wine consumption might be related to its high content of antioxidants (Heller et al 1998). Resveratrol, a phytoalexin found in several plants (in particular, red grapes), has shown to be able to up-regulate the nuclear Liver X receptor α and its target genes in macrophages, and to reduce the expression of lipoprotein lipase and scavenger receptor AII (Sevov et al 2006). Through these mechanisms, resveratrol seems to limit cholesterol accumulation in human macrophages.A recent study conducted in cultured human coronary artery endothelial cells has also demonstrated a beneficial effect of polyphenols (ie, catechin and quercetin) on the expression of the plasminogen activator inhibitor-1 gene, potentially providing a further biological explanation to the cardiovascular protective role of these molecules (Pasten et al 2007). However, no definite conclusion can still be drawn given the complex mechanisms in which polyphenols (eg, resveratrol) are involved and which may influence the net results of their supplementation (Iannelli et al 2006).A number of prospective cohort studies and case-control studies have reported that increased intake of dietary anti-oxidants including vitamin E, vitamin C, and β-carotene, are associated with reduced risk of atherosclerotic diseases (Kaliora et al 2006). Thus, antioxidants seem to prevent the development and progression of arteriosclerosis (Nakamura et al 2006). From this evidence, a growing interest has been posed into antioxidants as potential inhibitors of the proatherogenic and prothrombotic oxidative events occur-ring in the artery wall and underlying the atherosclerotic process. In 1999, an American Heart Association Science Advisory recommended that the general population con-sume a balanced diet with emphasis on antioxidant-rich fruits, vegetables, and whole grains (Krauss et al 2000). Given the absence of data from randomized, controlled clinical trials at the time, no recommendations were made regarding the use of antioxidant supplementation. In a more recent American Heart Association Science Advisory (Kris-Etherton et al 2004), current evidence about the benefi cial effects of antioxidant vitamins (such as vitamin E, vitamin C, and β-carotene) on cardiovascular risk has been revised and discussed. Consistently with previous recommenda-tions from the American Heart Association (Mosca et al 2004) and the American College of Cardiology (Gibbons et al 2003), scientifi c data do not yet justify the use of antioxidant vitamin supplements for cardiovascular risk reduction. However, the controversial results on this topic require further research.A recent randomized controlled trial, enrolling more than 35,000 healthy women aged 45 years and older, showed no beneficial effect from vitamin E supplementa-tion (600 IU on alternate days for a mean of 10.1 years) for the prevention of major cardiovascular events, cancer, total mortality, and cardiovascular mortality (Lee et al 2005). Similar results were also obtained from the HOPE and the HOPE-TOO trials (The HOPE and HOPE-TOO Trial Investigators 2005), where a possible increased risk of heart failure was also hypothesized in the intervention group (vitamin E 400 IU daily).Recently, Pham and Plakogiannis (Pham and Plakogiannis 2005) have reviewed evidence on the effects of vitamin E supplementation and cardiovascular and cancer prevention. Their meta-analysis showed that contradicting results regarding the benefi ts of vitamin E in the prevention of cardiovascular disease and cancer from the considered stud-ies. Authors assured the presence of adequate evidence from large, well-designed studies to discourage the use of vitamin E in the primary prevention of cardiovascular disease. For what concerns secondary prevention, more adequate clini-cal trials with selected populations are required to examine protective effects of vitamin E in cardiovascular disease.It is important to underline how positive fi ndings are mostly from observational studies, so that the relationship between vitamin E supplementation (the most promising antioxidant in the prevention of atherosclerotic disease) and lower rates of cardiovascular disease may just refl ect an over-all healthy lifestyle and dietary intake of supplement users rather than a real protective effect. Nevertheless, a role forClinical Interventions in Aging 2007:2(3)381Fusco et aloxidative mechanisms underlying the human atherosclerosis pathogenesis can not be ruled out.Alzheimer’s diseaseA number of studies have shown that aging and particularly brain aging are associated with free radicals action. Evidence suggests that reactive oxygen species in brain may play a role in the development of age-related neuronal impairments. The increase in the concentration of the pro-infl ammatory cytokines in aged brain tissue may also represent a contributory factor.The accumulation of oxidative damages to neuronal components with age underlies the molecular basis of brain aging and neurodegeneration (Kolosova et al 2006). Oxida-tive stress has been implicated in mechanisms leading to neuronal cell injury in various pathological states of the brain (Calabrese et al 2003).Alzheimer’s disease is a progressive disorder with cogni-tive and memory decline, speech loss, personality changes and synapse loss. The heterogeneity of the etiologic factors of Alzheimer’s disease makes it diffi cult to defi ne the major clini-cal determinants for the onset and progression of the disease. However, increasing evidence has recently indicated oxidative damage as a potential cause of Alzheimer’s disease pathogenesis (Nunomura et al 2006; Onyango and Khan 2006). Moreover, subjects with dementia attributed to Alzheimer’s disease have shown an altered balance between oxidant and antioxidant levels (Sinclair et al 1998). Recently, increasing interest has been fo-cused on identifying dietary compounds that can inhibit, retard or reverse the multi-stage pathophysiological events underly-ing Alzheimer’s disease pathology. Alzheimer’s disease also involves a chronic infl ammatory response associated with both brain injury and beta-amyloid associated pathology.Animal models have demonstrated that dietary supple-mentation with antioxidant vitamins can prevent or reverse the age-related changes in antioxidant defences in the central nervous system and decrease oxidative stress (O’Donnell and Lynch 1998). In a recent review, Vina and colleagues (Vina et al 2004) demonstrate that the cognitive function in Alzheimer’s disease patients is inversely correlated with sys-temic oxidative stress. They also confi rm the idea that vitamin E may be considered as an effective treatment of Alzheimer’s disease. However, the effect of vitamin E on Alzheimer’s disease patients shows considerable variations both in its antioxidant function and in its capacity to improve cognitive functions. Therefore, consistently with previous recommenda-tions (Kris-Etherton, and for the Nutrition Committee of the American Heart Association Council on Nutrition Physical Activity and Metabolism 2004), Authors suggest that the determination of the oxidant-antioxidant status of the patient is particularly important to test the effect of antioxidants on given functions.A major limitation present in most of the intervention studies exploring the effects of antioxidants supplementa-tion (eg, vitamin E) on Alzheimer’s disease outcomes is that they have been conducted on subjects who already have been diagnosed with this clinical condition. There-fore, it is diffi cult to assess the full potential of the specifi c substances in the prevention of Alzheimer’s disease. More-over, antioxidants are often tested as single agents, while it is becoming clearer that combinations of antioxidants are more effective. As for evidence related to cardiovascular disease, a large part of studies on the topic (mostly from epidemiologic reports) has shown that individuals, who consume higher amounts of fruits and vegetables, as well as vitamin supplement users, have lower rates of Alzheimer’s disease. Some reports have suggested that combinations of vitamins with antioxidant properties (in particular, vitamin C and vitamin E) have shown the greatest benefi ts (Frank and Gupta 2005).CancerWhile the exact role of free radicals in carcinogenesis and cancer progression is still under investigation, increasing evidence has demonstrated that some antioxidants are associated with a lower incidence of specifi c types of can-cers. Vitamin E, for example, has been shown in some trials to reduce the incidence of breast, lung, and colon cancers, but the most signifi cant results have been obtained with prostate cancer. For example, in the the alpha-tocopherol beta-carotene cancer prevention study (Albanes et al 1995), in which the participants were all male smokers, α-tocoph-erol supplementation decreased prostate cancer incidence and mortality. Recently, the supplementation en vitamines et mineraux antioxydants (SU.VI.MAX) study, a randomised, double-blind, placebo-controlled primary prevention trial, tested the effi cacy of supplementation with a combination of antioxidant vitamins and minerals, at nutritional doses, in reducing the incidence of cancer in a general population not selected for risk factors (Hercberg et al 2004). After a 7.5-year follow-up, antioxidant supplementation was associated with a reduction in cancer incidence in men only. However, Authors discussed that antioxidant supplementa-tion may have benefi cial effects on cancer incidence only in healthy subjects, who are not exposed to cancer risk, and with a particularly low baseline antioxidant levels (Hercberg et al 2006). Authors also warned that high dosage antioxi-Clinical Interventions in Aging 2007:2(3)382。

过氧亚硝基阴离子调控谷氨酸脱氢酶的催化功能【摘要】目的：观看过氧亚硝基阴离子（ONOO-）对谷氨酸脱氢酶（GDH）的硝基化修饰及功能调控. 方式： GDH与ONOO-体外反映，测定酶活性及别构调剂效应，Western Blot检测GDH硝基化修饰；制备含“去硝基化酶”的脾脏蛋白，观看可否逆转ONOO-作用. 结果：4~12 μmol/L ONOO-不阻碍GDH活性和二磷酸腺苷(ADP)别构激活作用，但使三磷酸鸟苷（GTP， 10 μmol/L）别构抑制作用由（49±4）%降低至（69±7）%和（75±3）%；36~108 μmol/L ONOO-使GDH活性由（±） kat/kg降低至（±）和（±） kat/kg，使GTP（10 μmol/L）别构抑制作用降低至（83±4）%和（95±7）%；324 μmol/L ONOO-使GDH完全失活. Western Blot检测到ONOO-使GDH发生硝基化修饰．脾脏蛋白可部份逆转上述作用. 结论： ONOO-可通过硝基化修饰调控GDH催化功能.【关键词】谷氨酸脱氢酶；过氧亚硝酸；酪氨酸硝基化修饰；别构调剂0引言谷氨酸脱氢酶（glutamate dehydrogenase，GDH）催化L谷氨酸与α酮戊二酸彼此转化，是联系氨基酸和糖代谢的枢纽. GDH在细胞内可能会发生酪氨酸硝基化修饰［1］，但该修饰对酶催化功能的阻碍尚少见报导. 鉴于体内蛋白硝基化要紧通过过氧亚硝基阴离子(peroxynitrite, ONOO-)介导［2］，同时GDH催化功能被别构激活剂二磷酸腺苷(adenosine 5′diphosphate, ADP)和抑制剂三磷酸鸟苷（guanosine 5′triphosphate, GTP）调剂［3］，本研究观看ONOO-对GDH催化活性和别构调剂的阻碍.1材料和方式材料牛肝脏GDH纯酶（Type I, ammonium sulfate suspension, ≥40 units/mg protein），还原型辅酶I（βNADH），α酮戊二酸，脂多糖(from Escherichia coli 055:B5) (美国Sigma公司)；抗硝基化蛋白mAb(anti nitrotyrosine, anti NT，美国Cayman Chemical 公司)；硫酸铵，ADP，GTP(美国Amresco公司)；SmartSpec 3000型分光光度计(美国Bio rad公司).方式合成与定量硝酸化的双氧水与亚硝酸钠，以三通管迅速推入氢氧化钠溶液，得黄色产物，以消光系数 (mmol/L)-1 ·cm-1定量［4］.与ONOO-反映GDH透析除去硫酸铵，蛋白浓度调整为 mg/mL，取300 μL置于 mL离心管，另取1 μL ONOO-置于离心管内壁，使反映体系中ONOO-的终浓度为0，4，12，36，108和324 μmol/L，快速震荡10 s，加入300 μL缓冲液终止反映，当即进行酶活性测定和硝基化修饰检测.催化活性测定依照参考文献［5］的方式进行测定，反映体系为250 μL，包括50 mmol/L磷酸钠缓冲液(pH , 50 mmol/L硫酸铵, 160 μmol/L βNADH, 5 mmol/L α酮戊二酸和5 μL GDH酶溶液；记录 3 min内340 nm吸光度改变量. 以βNADH的消光系数(mmol/L)-1·cm-1计算底物消耗速度，由公式［(△A 340 nm/min)/］×250 μL×10-3÷μg计算每1 μg GDH每分钟转换底物的速度，每分钟转换1 μmol底物概念为1单位，将单位值折算为比催化活性kat/kg.别构调剂效应测定为测定ADP的别构激活效应，在反映体系中加入新鲜配置的ADP，使其终浓度为300 μmol/L，并以氢氧化钠调整pH , 然后测定GDH催化活性；为测定GTP的别构抑制效应，在反映体系中加入10 μmol/L GTP，然后测定GDH催化活性［5］.Blot检测GDH硝基化修饰ONOO-处置后的GDH当即进行SDS PAGE分离，每泳道上样量为50 ng；其中一块凝胶用于银染以确保上样量一致，另一块凝胶进行湿法转膜，硝酸膜用50 g/L脱脂奶粉封锁1 h后，与anti NT（1∶5000）反映留宿，加入辣根过氧化物酶标记的二抗（1∶10 000）进行检测.脾脏蛋白对GDH修饰的阻碍依照参考文献［6］的方式制备脾脏蛋白，雄性SD大鼠，腹腔注射脂多糖20 mg/kg，24 h后，取脾脏，以Tris HCl(pH 匀浆，105 000 g离心，1 h，保留上清得脾脏蛋白，其中含有较高浓度的“去硝基化酶”［6］. ONOO-处置后的GDH,蛋白浓度调整为 mg/mL，与等体积的脾脏蛋白（6 mg/mL）室温反映2 h，取 50 μL与等体积的2×电泳上样缓冲液混合，每泳道上样20 μL，进行Western Blot 检测硝基化修饰的改变，同时取50 μL检测催化活性. 作为对照，将脾脏蛋白煮沸5 min，以灭活“去硝基化酶”，进行平行实验. 以上实验均重复6次.统计学处置：计量数据以x±s表示，以软件包进行方差分析(ANOVA)，多重比较采纳Student Newman Keuls查验法. 2结果对GDH催化活性和别构调剂的阻碍ONOO-在4~12 μmol/L时不阻碍GDH催化比活性，但在36~108 μmol/L时，可显著抑制其催化比活性(P< vs 对照组). 在324 μmol/L时，GDH被完全灭活，其活性检测不到．GDH可被别构激活剂ADP激活倍,该效应不受ONOO-阻碍，可是GTP的别构抑制效应那么显著降低(4~108 μmol/L vs 对照组，P<. 含有“去硝基化酶”的脾脏蛋白，可部份逆转36 μmol/L ONOO-对GDH催化比活性的抑制作用，可是关于108 μmol/L ONOO-处置的样品和完全失活的GDH那么没有作用. 通过煮沸灭活“去硝基化酶”，脾脏蛋白的作用那么完全消失（表1）.表1ONOO-对GDH活性的阻碍及脾脏蛋白的逆转作用（略）bP< vs 对照.致使GDH发生硝基化修饰 0 μmol/L ONOO-处置的GDH与anti NT抗体不发生反映（泳道1），而4～324 μmol/L ONOO-处置的GDH可被anti NT抗体识别，而且免疫反映的信号强度随ONOO-浓度增加而增大（泳道2~6，图1）.1： 0 μmol/L ONOO-； 2~6： 4，12，36，108，324 μmol/L ONOO-.图1Western Blot 法检测ONOO-致使的GDH硝基化修饰（略）脾脏蛋白可部份逆转ONOO-对GDH的硝基化修饰4~36 μmol/L ONOO-处置的GDH与anti NT抗体发生免疫反映（泳道1，4，7），样品经脾脏蛋白处置后，免疫信号被部份逆转（泳道2，5，8），而煮沸灭活的脾脏蛋白那么不阻碍免疫反映强度（泳道3，6，9）（图2A）. 0 μmol/L ONOO-处置的GDH不与anti NT 反映（泳道1），同时加入脾脏蛋白也不与anti NT反映（泳道2和3），而108，324 μmol/L ONOO-处置的GDH与anti NT有明显的反映条带（泳道4和7），脾脏蛋白（泳道5和8）不能逆转这种反映，煮沸的脾脏蛋白（泳道6和9）也没有作用（图2B）.A： 1，4，7: 4，12，36 μmol/L ONOO-； 2，5，8: 4，12，36 μmol/L ONOO- +脾脏蛋白； 3，6，9: 4，12，36 μmol/L ONOO- +煮沸的脾脏蛋白. B： 1，4，7: 0，108，324 μmol/L ONOO-； 2，5，8: 0，108，324 μmol/L ONOO- +脾脏蛋白； 3，6，9: 0，108，324 μmol/L ONOO- +煮沸的脾脏蛋白.图2Western Blot 法检测脾脏蛋白对ONOO-诱导GDH硝基化修饰的逆转作用（略）3讨论目前已有逾百种硝基化蛋白被鉴定［1］，但针对特定蛋白的功能调控尚知之甚少. 本研究第一次报导，硝化剂ONOO-对GDH这一典型的别构酶［7］具有功能调控作用.本研究发觉，ONOO-的作用与浓度紧密相关：低浓度（4~12 μmol/L ）ONOO-不阻碍GDH催化活性，但使GTP的别构抑制作用显著降低，从而可间接地使GDH的总催化活性升高；中等浓度（36~108 μmol/L）ONOO-，一方面可显著抑制GDH催化活性，另一方面使GTP的别构抑制作用降低，二者综合的结果可使GDH总的催化活性或升高，或降低，或不变；高浓度（324 μmol/L）ONOO-，可使GDH完全灭活，别构调剂作用也完全丧失. GDH这些功能改变与酪氨酸硝基化呈正相关．由此能够推测GDH硝基化可能是机体的一种感受机制，当内环境发生改变致使ONOO-过量产生时，GDH通过硝基化的方式来调控其总催化活性（升高，降低，或不变）；当内环境改变超出了机体的反馈能力后，GDH的硝基化那么成为一种损伤机制（完全灭活）.硝基化一样致使蛋白功能丧失［2］. 但本研究发觉，GDH硝基化可使其催化功能间接地升高，这与微粒体谷胱甘肽S转移酶1（MGST1）的硝基化具有类似的地方［8］. 二者不同的地方在于，GDH 在活性调控上比MGST1更具有灵活性：前者总的催化活性可升可降亦可不变，后者的催化活性只是升高；前者的修饰可被逆转，后者修饰的逆转性尚未确立；另外，MGST1被ONOO-修饰，还可形成蛋白二聚体和三聚体［8］，而本研究未发觉GDH存在这些修饰.值得指出，高浓度（324 μmol/L）ONOO-诱发的硝基化不能被“去硝基化酶”逆转，提示ONOO-可能还致使GDH发生了其他修饰，例如羰基化等，引发酶构象发生改变，从而不能被“去硝基化酶”识别．作者初步研究结果支持这一推测，咱们发觉，108~324 μmol/L ONOO-处置GDH样品，可别离检测到（±）和（±） nmol/mg羰基基团，而0~36 μmol/L ONOO-处置的样品检测不到，提示高浓度ONOO-不仅致使硝基化，同时引发了羰基化修饰.综上所述，本研究说明ONOO-可通过酪氨酸硝基化调控GDH 的催化功能.【参考文献】［1］ Aulak KS, Miyagi M, Yan L, et al. Proteomic method identifies proteins nitrated in vivo during inflammatory challenge ［J］. Proc Natl Acad Sci USA, 2001,98(21):.［2］池泉，黄开勋. 蛋白质酪氨酸硝化的研究［J］. 化学进展，2006，18（7/8）：1019-1025.［3］ Choudhury R, Punekar NS. Competitive inhibition of glutamate dehydrogenase reaction. ［J］. FEBS Lett, 2007,581(14):2733-2736.［4］ Lai HH, Yen GC. Inhibitory effect of isoflavoneson peroxynitrite mediated low density lipoprotein oxidation ［J］. Biosci Biotechnol Biochem, 2002,60(1):22-28.［5］ Kanavouras K, Mastorodemos V, Borompokas N, et al. Properties and molecular evolution of human GLUD2 (neural and testicular tissue specific) glutamate dehydrogenase［J］. J Neurosci Res, 2007,85(5):1101-1109.［6］ Irie Y, Saeki M, Kamisaki Y, et al. Histone is a substrate for denitrase, an activity that reduces nitrotyrosine immunoreactivity in proteins ［J］. Proc Natl Acad Sci USA,2003,100(10):5634-5639.［7］ Smith TJ, Peterson PE, Schmidt T, et al. Structures of bovine glutamate dehydrogenase complexes elucidate the mechanism of purine regulation ［J］. J Mol Biol, 2001,307(2):707-720.［8］ Ji Y, Neverova I, Van Eyk JE, et al. Nitration of tyrosine 92 mediates the activation of rat microsomal glutathione s transferase by peroxynitrite［J］. J Biol Chem, 2006,281(4):1986-1991.。

第24卷第2期2004年2月生 态 学 报A CTA ECOLO G I CA S I N I CA V o l .24,N o.2Feb .,2004茉莉酮酸甲酯对水稻化感物质的诱导效应孔垂华1,2,胡　飞1,张朝贤3,徐效华2(1.华南农业大学热带亚热带生态研究所,广州　510642;2.南开大学元素有机化学国家重点实验室,天津　300071;3.中国农业科学研究院植物保护研究所,北京　100094)基金项目:国家自然科学基金资助项目(30070130);国家“十五”科技攻关计划资助项目(2001BA 509B07);广东省自然科学基金重点资助项目(021045)收稿日期:2003204209;修订日期:2003207214作者简介:孔垂华(1962～),男,安徽省铜陵市人,博士,研究员,主要从事化学生态学研究。

E 2m ail :chkong @scau .edu .cnFoundation ite m :N ati onal N atural Science Foundati on of Ch ina (N o .30070130),T he N ati onal “T enth F ive 2year P lan ”Key P rogram of Science and T echno logy (N o .2001BA 509B 07),T he Key P ro ject of N atural Science Foundati on of Guangdong P rovince ,Ch ina (N o .021045)Rece ived date :2003204209;Accepted date :2003207214Biography :KON G Chui 2H ua ,Ph .D .,P rofesso r ,p ri m arily engaged in the chem ical eco logy .E 2m ail :chkong @scau .edu .cn摘要:在室内和田间条件下,外源茉莉酮酸甲酯均能显著地诱导水稻化感物质的合成,而且这种诱导效应与施用茉莉酮酸甲酯的浓度和诱导时间显著相关。

功能化离子液体催化合成甘油单月桂酸酯王松;张争艳;常欠欠;李三喜;张林楠【期刊名称】《化工学报》【年(卷),期】2015(066)0Z1【摘要】合成了由吡啶、N-甲基咪唑、N-甲基-2-吡咯烷酮提供有机阳离子,磷钨酸、对甲苯磺酸提供阴离子的6种离子液体.使用NMR、FT-IR和TG对离子液体表征,并考察它们催化甘油与月桂酸酯化的催化效果.结果表明,这些离子液体都具有较好的热稳定性,以1-(丁基-4-磺酸基)-3-甲基咪唑磷钨酸盐离子液体的热稳定性最好.在最佳条件使用离子液体催化甘油与月桂酸反应时,阴离子的种类对月桂酸的转化率影响较大,以对甲苯磺酸为阴离子的离子液体催化反应时,月桂酸转化率较以磷钨酸为阴离子的离子液体的高;1-(丁基-4-磺酸基)-3-甲基咪唑对甲苯磺酸盐离子液体做催化剂时甘油单月桂酸酯的产率最高.催化剂重复使用性方面,离子液体重复使用5次催化活性没有明显变化.%Six ionic liquids based on pyridine (Py), 1-methylimidazole (MIM),N-methyl-2-pyrrolidinone(NMP) cations were prepared by coupling corresponding SO3H-functionalized zwitterion ionic complex with different counterpart anions including H3PW12O40 andp-toluenesulfonic acid (PTSA). The obtained ionic liquids were well characterized by FT-IR, TG,1H NMR,13C NMR methods and then these ionic liquids were deployed in the esterification reaction of glycerol with lauric acid under the condition without organic solvent. The effects of various key reaction parameters including reaction temperature,glycerol/lauric acid molar ratio, molar ratio of ionic liquid to lauric acid andthe type of catalysts on the acid conversion and yield of glycerol monolaurate were discussed. The results indicated that all the ionic liquids exhibit good thermal stability and compared with other ionic liquids, [MIMBS]3PW12O40 ionic liquid has the best thermal stability. When [MIMBS][PTSA] ionic liquid was used to optimize esterification reaction parameters, the optimum reaction conditions were established as follows: glycerol/lauric acid ratio of 4, amount of catalyst of 1% molar to lauric acid, reaction time of 3 h at 130℃. When us ed under the optimized reaction condition, all the ionic liquids exhibit excellent catalytic activity, the acid conversions are all above 92% and the highest yield of glycerol monolaurate of 64.6% has been achieved. In addition, comparing the structure of the investigated ionic liquids, it can be found that under the condition of lauric acid being catalyzed by the ionic liquids with PTSA anion, the conversion is higher than that when lauric acid was catalyzed by ionic liquids with H3PW12O40 anion. With respect to the yield of glycerol monolaurate, when the reaction was catalyzed by ionic liquids, [MIMBS][PTSA] gives the highest yield. As to the reusability behavior of these ionic liquids, the results indicated that all these catalysts can be reused up to five times without noticeable loss of catalytic activity.【总页数】7页(P209-215)【作者】王松;张争艳;常欠欠;李三喜;张林楠【作者单位】沈阳工业大学理学院,辽宁沈阳 110870;沈阳工业大学理学院,辽宁沈阳 110870;沈阳工业大学理学院,辽宁沈阳 110870;沈阳工业大学理学院,辽宁沈阳110870;沈阳工业大学理学院,辽宁沈阳 110870【正文语种】中文【中图分类】O643.3【相关文献】1.响应面法优化月桂酸单甘油酯的催化合成工艺 [J], 周军;李湘洲;徐雷涛;熊曼;郭颂2.固定化脂肪酶催化椰子油制备月桂酸单甘油酯 [J], 查宝萍;郑联合;王莉;王韧;陈正行;王涛3.离子交换树脂催化月桂酸单甘油酯的合成 [J], 宋国胜;郭祀远;蔡妙颜;肖凯军4.酸功能化离子液体催化合成三乙酸甘油酯 [J], 李红娟;于世涛;刘福胜;李红亮;解从霞5.响应面法优化月桂酸单甘油酯的酶催化合成工艺 [J], 邓成龙;张桂菊;吴望波;王瑞;徐宝财;珠峰因版权原因，仅展示原文概要，查看原文内容请购买。

生态环境 2007, 16(4): 1261-1265 Ecology and Environment E-mail: editor@基金项目：国家自然科学基金项目（30100107）；教育部博士点基金项目（20060564017） 作者简介：董桃杏（1982－），女，硕士，从事农业生态、作物逆境生理生态的研究工作。

*通讯作者，蔡昆争，Tel: +86-020-********；Email: kzcai@ 收稿日期：2006-11-10茉莉酸甲酯（MeJA）对水稻幼苗的抗旱生理效应董桃杏，蔡昆争*，张景欣，荣 辉，谢国政，曾任森华南农业大学热带亚热带生态研究所，广东 广州 510642摘要：茉莉酸类物质（Jas ）是植物体内广泛存在的生长调节物质，它作为内源信号分子参与植物在机械伤害、病虫害、干旱、盐胁迫、低温等条件下的抗逆反应。

选用抗旱性存在明显差异的两个水稻(Oryza sativa L.)品种中二欧六和丰华占作为实验材料，通过设置对照、干旱、干旱+茉莉酸甲酯（MeJA ）三种处理研究了茉莉酸甲酯对水稻幼苗的抗旱生理效应。

研究结果表明，干旱胁迫后两个水稻品种幼苗叶片水势均显著降低，而干旱后喷施茉莉酸甲酯能明显增加叶片的水势，改善叶片的水分状况，抗旱性强的品种水势增加幅度较大。

干旱胁迫后水稻叶片的抗氧化酶活性，包括超氧化物歧化酶（SOD ）、过氧化物酶（POD ）及过氧化氢酶（CAT ）和有机渗透调节物质，包括可溶性糖、脯氨酸及游离氨基酸含量均大幅度上升，而干旱+茉莉酸甲酯处理则能降低了这些物质的含量，两个水稻品种的变化趋势表现一致。

研究结果表明外施茉莉酸甲酯在一定程度上能减缓干旱胁迫对水稻幼苗造成的伤害，有效地提高抗旱性，但这这种增强效应在不同水稻品种间存在一定差异。

关键词：茉莉酸甲酯；水分胁迫；水稻；抗旱性中图分类号：Q946.81 文献标识码：A 文章编号：1672-2175（2007）04-1261-05茉莉酸（Jasmonic acid, JA ）及其甲酯（methyl jasmonate, MeJA ）广泛存在于高等植物体内。

一种合成Frutinone A及其衍生物的新方法张娜;陈志卫【摘要】以4-羟基香豆素和水杨醛为原料，在哌啶催化下，甲苯中回流反应，得到具抗真菌活性的天然化合物Frutinone A及其类似物，该方法具有步骤少、环境友好、收率较高等优点。

%The natural fungicidal compounds, Frutinone A and its derivatives, were synthesized by refluxing 4-hydroxyxoumarins and salicylaldehyde in toluene. The catalyst was piperidine. This method has the advantages of brief reaction steps, environmental friendliness and higher yield.【期刊名称】《浙江化工》【年(卷),期】2014(000)008【总页数】3页(P14-16)【关键词】Frutinone A;4-羟基香豆素;水杨醛;哌啶【作者】张娜;陈志卫【作者单位】浙江工业大学药学院，浙江杭州 310014;浙江工业大学药学院，浙江杭州 310014【正文语种】中文香豆素是具有苯骈α-吡喃酮母核的一类天然产物的总称，其衍生物是一类重要的有机杂环化合物，由于具有抗菌[1]、抗氧化[2]、抗肿瘤[3]、抗凝[4]和抗HIV[5]等多种生物活性而倍受人们的关注。

1989 年，Paolo 等人首次从远志科植物金露梅的叶和根中提取得到Frutinone A、B、C 三种色原酮香豆素类化合物，结构如图1 所示，活性测试实验表明Frutinone A 对黄瓜黑星病菌（Cladosporium cucumerinum）具有强烈的杀菌活性[6]。

1997 年，Bergeron 等人从非洲植物P.gazensis Bak 和P.teretifoliaL 中也提取分离得到了化合物Frutinone A，同时发现其对白色念珠菌表现出抗菌活性[7]。

含有孤对电子的路易斯碱作为金化学蒸气发生的催化增敏剂的结构特征及增敏效果卜范龙;郭文丽;段旭川【期刊名称】《理化检验-化学分册》【年(卷),期】2014(050)004【总页数】3页(P500-502)【作者】卜范龙;郭文丽;段旭川【作者单位】天津师范大学生命科学学院,天津市动植物抗性重点实验室,天津300387;天津市产品质量监督检测技术研究院,天津300384;天津师范大学生命科学学院,天津市动植物抗性重点实验室,天津300387【正文语种】中文【中图分类】O657.31某些路易斯碱可催化增敏硼氢化钠和过渡与贵金属元素的化学蒸气光度计对乙醚、四氢呋喃和三乙胺对金的化学蒸气发生（CVG）效率增强进行了初步验证［1］。

研究结果显示：某些带有孤对电子的路易斯碱对硼氢化钠与金的化学蒸气发生效率具有明显的增强作用，这些路易斯碱主要是醚、胺等及杂环化合物。

为了继续探索这些路易斯碱的催化增敏效果与结构特征，本工作继续以下几方面的研究：①选取的胺类路易斯碱有三甲胺、吡啶、咪唑、N，N－二甲基苯胺；②醚类路易斯碱有乙醚、四氢呋喃、二乙二醇二甲醚；③含硫原子的路易斯碱有甲硫醚、二甲亚砜、氨基硫脲、硫脲；④含磷原子的路易斯碱有次亚磷酸钠和亚磷酸；⑤含有氮氧硫杂环的路易斯碱有铜试剂、铋试剂、乙基黄原酸钾。

通过研究上述的路易斯碱催化硼氢化钠与金的化学蒸气发生效率，进一步探索总结具有催化增敏效果的路易斯碱的结构特点，研究比较带有孤对电子的元素相同但相对分子质量或分子结构不同的路易斯碱对金蒸气发生反应的催化增敏效率的影响；分子结构或相对分子质量相近，但带有孤对电子的元素不同的路易斯碱对金蒸气发生反应的催化增敏效率的影响。

1 试验部分1.1 仪器与试剂PF6型无色散原子荧光光度仪（AFS），HAF－2型金高性能空心阴极灯。

金标准储备溶液：1.000g·L－1，称取纯度为99.99%金1.000g于烧杯中，加入盐酸10mL和硝酸5 mL 溶解，在水浴上蒸发近干，用盐酸－硝酸（3＋1）溶液溶解，移入1L容量瓶中，用水稀释至刻度，摇匀。

过氧磷钨酸季铵盐催化合成环氧柏木烷高炜琳;朱凯【摘要】以钨酸钠、磷酸、过氧化氢(H2O2)和十六烷基三甲基氯化铵为原料制备了过氧磷钨酸季铵盐催化剂.通过FT-IR、TG对催化剂进行了结构和热稳定性的表征.在H2O2为氧化剂,无溶剂条件下,采用过氧磷钨酸季铵盐催化α-柏木烯环氧化合成环氧柏木烷.考察了各反应条件对环氧化反应的影响.结果表明,在反应温度60℃,反应时间3.5 h,H2O2与α-柏木烯摩尔比为1∶2,催化剂过氧磷钨酸季铵盐用量3.0％(以H2O2质量计,下同),助剂Na2HPO4用量1.6％条件下,环氧柏木烷的收率为65.7％,α-柏木烯的转化率为90.1％,环氧产物选择性可达72.9％.【期刊名称】《日用化学工业》【年(卷),期】2019(049)002【总页数】5页(P108-112)【关键词】环氧柏木烷;磷钨酸盐;α-柏木烯【作者】高炜琳;朱凯【作者单位】南京林业大学化学工程学院江苏省农林生物质化学与利用国家重点实验室培育点,江苏南京210037;南京林业大学化学工程学院江苏省农林生物质化学与利用国家重点实验室培育点,江苏南京210037【正文语种】中文【中图分类】TQ655柏木油是从柏木中提取得到的一种重要的植物芳香精油 [1， 2]，带有甜而柔和的柏木香韵。

目前，国内市场的柏木油大部分是作为香原料直接出口，附加值较低。

柏木油的主要成分是柏木烯、柏木醇及少量萜类化合物[3-5]，经过一系列的化学深加工可合成高附加值的柏木系香料[6-8]，如甲基柏木酮、乙酸柏木酯、甲基柏木醚和环氧柏木烷等。

其中环氧柏木烷是一种具有良好木香，微带樟脑样香韵的高级香料。

香味较为持久，被广泛应用于日用化妆品及烟草等香精产品中，安全性高、稳定性好，市场前景广。

目前，环氧柏木烷的合成方法有多种，主要不同在于氧化剂。

有过氧乙酸氧化[9]，无机过氧酸盐（过硼酸钠或过碳酸钠）进行环氧化[10]，H2O2进行环氧化[11]。