河北异小杆线虫一品系的分类鉴定及其对蛴螬致病力的测定

昆虫病原线虫是一种有应用潜力的地下害虫生物防治因子。本研究利用形态学特征和ITS-rDNA分析方法对从河北省沧州分离的异小杆线虫一品系进行了鉴定, 并在室内测定比较了其对蛴螬的致病力。通过对该线虫侵染期幼虫和雄性成虫主要形态学特征的参数测量, 发现其与嗜菌异小杆线虫Heterorhabditis bacteriophora的形态特征最为相近;同时ITS1-rDNA序列比对和系统发育学分析结果显示其与嗜菌异小杆线虫亲缘关系最近。结合形态学和分子生物学特征, 确定该线虫为嗜菌异小杆线虫沧州品系。该线虫对蛴螬（华北大黑鳃金龟Holotrichia oblita、暗黑鳃金龟H. parallela和铜绿丽金龟Anomala corpulenta 3种金龟子的2龄幼虫）的致病力研究结果表明：处理72 h后, 暗黑鳃金龟幼虫死亡率显著高于另外两种金龟子幼虫 (P<0.05);处理120 h后, 暗黑鳃金龟和铜绿丽金龟幼虫的死亡率分别达到93.3%和80.0%, 二者无显著差异 (P>0.05), 可见该线虫对它们有较强的致病力。不同线虫对暗黑鳃金龟幼虫的致病力结果显示, 嗜菌异小杆线虫沧州品系侵染96 h后, 幼虫的死亡率显著高于Steinernema feltiae和S. longicaudum两种线虫的处理 (P<0.05) , 说明嗜菌异小杆线虫沧州品系的致病力显著高于另外两种线虫。     

嗜线虫致病杆菌血腔毒素Tp40的纯化和特性分析

[目的]嗜线虫致病杆菌是一种昆虫病原线虫共生菌,它能够产生多种杀虫毒素.本研究旨在从嗜线虫致病杆菌Xenorhabdus nematophila HB310菌株的细胞内纯化新的杀虫蛋白毒素,并对其进行基因克隆和序列分析.[方法]应用盐析和制备型非变性凝胶电泳等方法纯化蛋白,再通过对5龄大蜡螟幼虫血腔注射进行活性筛选.对获得的目的蛋白与已知蛋白进行同源分析,克隆出该目的蛋白的基因序列,从而进行相应的基因和氨基酸序列分析.[结果]本研究纯化的Tp40蛋白对大蜡螟LD50为68.54 ng/头,其SDS-PAGE电泳图谱只显示出一条分子量约为42 kDa的多肽.Western印迹分析表明Tp40与已知的Txp40为同源蛋白,并且仅存在于细胞内.编码该蛋白的基因开放读码框全长1107bp(GenBank登录号:EU095326),编码368个氨基酸残基,预测分子量为41.5 kDa,等电点为8.66,与GenBank中的其余13株昆虫病原线虫共生菌所包含的相似基因核苷酸序列及推导的氨基酸序列比较,同源性分别为85%～99%和70%～99%.[结论]Tp40蛋白具有很高的血腔杀虫活性,其基因序列具有较强的保守性,是昆虫病原线虫共生菌复合体杀虫过程中的一种关键因子.     

拟双角斯氏线虫D43品系鞘蛋白对大蜡螟幼虫的免疫抑制作用

侵染期的拟双角斯氏线虫Steinernema ceratophorum D43品系体外都包裹着一个透明的体鞘。为探明体鞘对线虫侵染力的影响, 了解鞘蛋白（sheath proteins, SPs）对大蜡螟Galleria mellonella 幼虫的免疫抑制作用, 本研究通过化学方法使拟双角斯氏线虫D43脱鞘, 以对寄主的致死率和侵入点数量为指标, 与包鞘线虫比较对大蜡螟幼虫的侵染力; 采用乙醇提取的方法获得线虫鞘蛋白, 利用双向电泳和质谱技术对鞘蛋白进行鉴定分析; 从血细胞数量和酚氧化酶活力两个方面评价鞘蛋白对大蜡螟幼虫免疫反应的抑制作用。结果表明： 0.5%次氯酸钠处理20 min可以保证95%以上的线虫存活和脱鞘。与包鞘线虫相比, 脱鞘线虫对大蜡螟幼虫的致死率显著降低, 致死时间延后, 节间膜侵入点数量显著减少。以35%乙醇提取的鞘蛋白提取物可鉴定出6种鞘蛋白, 其中一个被鉴定为丝氨酸蛋白酶。此外, 血腔注射鞘蛋白提取物可导致试虫血细胞数量明显降低, 酚氧化酶活力受到显著抑制。由此说明, 体鞘对拟双角斯氏线虫D43的侵染力具有显著影响, 鞘蛋白在抑制寄主昆虫免疫反应中发挥重要作用。     

嗜线虫致病杆菌HB310菌株杀虫蛋白的纯化及活性鉴定

嗜线虫致病杆菌Xenorhabdus nematophila HB310是从河北省土壤中筛选出的一株昆虫病原线虫体内分离纯化获得的共生菌,该菌的发酵液对多种昆虫有较高的杀虫活性。利用85％饱和度的硫酸铵盐析分别获得胞内蛋白提取物和上清液中胞外蛋白提取物,生测结果表明这两种蛋白提取物中都含有胃毒素和血腔毒素。通过制备型非变性凝胶电泳对蛋白提取物进行分离和纯化,得到了3种有杀虫活性的毒素蛋白（毒素Ⅰ、毒素Ⅱ和毒素Ⅲ）,胞内的毒素蛋白与分泌到胞外上清液中的毒素蛋白是同种蛋白。毒素Ⅰ和毒素Ⅱ对棉铃虫初孵幼虫有明显的胃毒活性,但没有血腔毒性;毒素Ⅲ对大蜡螟幼虫有很强的血腔毒性,LD₅₀为0.18 μg/头。SDS-PAGE图谱显示毒素Ⅰ和毒素Ⅱ是由多个多肽组成的复合蛋白,而毒素Ⅲ只分离出一条多肽。毒素Ⅱ在50℃处理10 min,其杀虫活性没有显著变化;70℃处理10 min对毒素Ⅲ杀虫活性没有显著影响。     

腰带长体茧蜂寄生对亚洲玉米螟幼虫体内酚氧化酶活性的影响

通过对被腰带长体茧蜂Macrocentrus cingulum Brischke寄生的5龄亚洲玉米螟Ostrinia furnacalis Guenée幼虫体内不同组织中酚氧化酶活性的测定,采用体外注射腰带长体茧蜂雌性成蜂的萼液成分、毒液成分、萼液与毒液混合物的方法,研究了寄生蜂各种主要生理因子对寄主血清中酚氧化酶活性的影响。结果表明： 寄生蜂寄生可明显抑制寄主体内的酚氧化酶活性,减少黑色素产生;被寄生组FITC标记的血细胞阳性百分率低于未被寄生组,差异极显著( P<0.01）;萼液成分可明显地抑制亚洲玉米螟幼虫血清中酚氧化酶的活性 （P<0.01）;萼液与毒液混合物对酚氧化酶活性也有明显抑制作用（P<0.01）。研究认为寄生蜂产卵时注入的萼液、毒液可对寄主昆虫酚氧化酶活性产生明显的抑制作用,其中萼液是抑制寄主免疫能力的主要因素。     

不同培养基上繁殖的昆虫病原线虫格氏线虫表皮蛋白的差异

表皮蛋白(surface coat proteins, SCPs)是格氏线虫Steinernema glaseri克服寄主免疫系统的关键因素, 能够抑制昆虫免疫反应, 促进线虫的侵染。为了进一步研究表皮蛋白抑制昆虫免疫的作用机理和线虫与寄主间的相互关系, 我们比较分析了不同培养基繁殖的格氏线虫表皮蛋白的差异。我们用人工培养基和大蜡螟Galleria mellonella末龄（5龄）幼虫分别培养得到格氏线虫侵染期幼虫, 利用酒精提取表皮蛋白。SDS-PAGE和非变性PAGE分析显示, 大蜡螟来源的格氏线虫的表皮蛋白具有更多的蛋白条带。体外和体内的裂解血细胞实验表明, 大蜡螟来源的格氏线虫的表皮蛋白表现出强烈的裂解血细胞活性, 而人工培养基来源的格氏线虫的表皮蛋白活力不明显; 且具有裂解血细胞活性的表皮蛋白为诱导表达型蛋白。不同培养基来源的格氏线虫的表皮蛋白组成的差异和活性的不同, 表明格氏线虫表皮蛋白的产生受线虫培养条件影响较大。     

异小杆线虫XJZL1409(Heterorhabditis bacteriophora)共生菌的分离及致病性研究

本研究分离了来自新疆和田地区间作绿豆的4年枣0-40 cm根际土壤中的昆虫病原线虫XJZL1409Heterorhabditis bacteriophora的共生菌,并进行致病性测定。通过侵染期线虫和线虫致死的大蜡螟幼虫血腔直接分离,采用传统形态学观察结合分子生物学方法对菌株进行鉴定。同时大蜡螟Galleria mellonella 5龄幼虫接种菌株细胞发酵液测定致病性。菌株形态学特性结合16S r DNA序列系统发育分析,线虫XJZL1409的共生菌被鉴定为发光杆菌属Photorhabdus luminescens subsp. laumondii。室内菌液注射毒性测定结果显示,侵染致死的幼虫体色呈灰绿色;接种48 h后,每头幼虫接种菌液量为500 CFU时校正死亡率就可以达到100%; 48 h时致死中浓度LC50为10. 74 CFU/m L。同时菌液口服杀虫毒性结果表明,第5天时待测菌株菌液对大蜡螟幼虫的校正死亡率为21. 21%,体重抑制率为20. 02%。因此,昆虫病原线虫XJZL1409的共生菌为P. luminescens subsp. laumondii对大蜡螟幼虫具有很强的注射毒性,为研究线虫的致病机制及发掘新抗性基因奠定基础。     

病原线虫对桔小实蝇种群的控制作用

通过室内和田间实验研究了昆虫病原线虫对桔小实蝇Bactrocera (Bactrocera) dorsalis (Hendel)的控制作用。室内实验结果表明,供试的3种线虫的4个品系（小卷蛾斯氏线虫Steinernema carpocapsae All品系与A24品系,夜蛾斯氏线虫Steinernema feltiae SN品系和嗜菌异小杆线虫Heterorhabditis bacteriophora H06品系）,以小卷蛾斯氏线虫All品系对桔小实蝇的侵染力最强,其3天的LD₅₀和LD₉₅分别为35.0和257.1条/cm²土壤。按300条/cm²土壤的量施用,小卷蛾斯氏线虫All品系对当代桔小实蝇的控制效果为86.3%。用以虫期作用因子组建的生命表方法评价了小卷蛾斯氏线虫All品系对田间桔小实蝇下代种群的控制作用,结果表明,按300条/cm²土壤的量施用线虫,对照杨桃园的桔小实蝇种群趋势指数为105.9,而处理杨桃园的桔小实蝇种群趋势指数下降为15.5;小卷蛾斯氏线虫All品系对桔小实蝇的干扰控制指数为0.146,即线虫处理果园的下代种群密度仅为对照果园的14.6%。     

红脉穗螟寄生蜂寄主选择研究

[目的]优化红脉穗螟寄生蜂繁育技术,为该虫的生物防治提供参考。[方法]通过室内饲养研究了红脉穗螟幼虫寄生蜂褐带卷蛾茧蜂和蛹寄生蜂周氏啮小蜂(海南种)对4种昆虫的寄生效果,并对最佳接种比例进行筛选。[结果]褐带卷蛾茧蜂对大蜡螟幼虫寄生效果优于米蛾幼虫,且对黄粉虫和大麦虫幼虫不表现寄生特性,褐带卷蛾茧蜂和大蜡螟幼虫的最佳接种比例为1∶1和2∶1,其中在2∶1接种比例处理中的寄生率和单寄主产蜂量分别为76.67%和34.60头;4种昆虫蛹均可用于繁育周氏啮小蜂,从寄主的繁育成本和寄生效果分析,以黄粉虫蛹效果较最佳,接种蜂虫比以2∶1为宜,此时的单寄主产蜂量为148.60头。[结论]寄主和接种比例不同会影响寄生蜂的寄生效果,本研究中褐带卷蛾茧蜂适宜寄主为大蜡螟,最优蜂虫比为1∶1和2∶1,周氏啮小蜂(海南种)适宜寄主为黄粉虫,最优接种蜂虫比为2∶1。     

基于不同饲料的洋虫水提液对小鼠的抗衰老作用

为了评价洋虫Martianus dermestoides成虫和幼虫水提液的抗衰老作用,用高级饲料红花、枸杞、大枣、核桃仁的混合饲料)、大米、麦麸饲料饲养洋虫成虫和幼虫,并用幼虫水提液对D-半乳糖致衰老小鼠灌胃, 测定小鼠血清中超氧化物歧化酶(SOD)、 谷胱甘肽过氧化物酶(GSH-Px)和过氧化氢酶（CAT)的活力及丙二醛（MDA)含量。结果表明：3种饲料饲养的洋虫成虫水提液均能提高小鼠血清中SOD,GSH-Px和CAT活力(P<0.05或P<0.01),且显著降低MDA含量(P<0.05);高级饲料组作用优于大米及麦麸饲料组,但三者差异不显著。高级饲料饲养组,其幼虫水提液对小鼠血清中SOD和CAT活力作用显著强于成虫水提液（P<0.05);对GSH-Px活力及MDA含量影响差异不显著。揭示洋虫成虫和幼虫水提液均有一定的抗氧化作用,是一种有效的抗衰老保健食品,且幼虫抗氧化作用优于成虫,饲料种类对洋虫的抗氧化作用无显著影响。     

Synthesis and luminescence properties of a blue-emitting Sr(3.5) Y(6.5) O(2) (PO(4) )(1.5) (SiO(4) )(4.5) :Eu(2+) phosphor

A novel blue‐emitting Sr_3.5Y_6.5O₂(PO₄)_1.5(SiO₄)_4.5:Eu²⁺ phosphor was synthesized via a solid‐state reaction. Powder X‐ray diffraction (XRD) analysis demonstrated that the Sr_3.5Y_6.5O₂(PO₄)_1.5(SiO₄)_4.5 host had a hexagonal crystal structure in the space group P6₃/m and unit cell parameters a = 9.418 Å, c = 6.900 Å. The as‐prepared phosphor showed a blue emission and all the main emission peaks were located at around 466 nm for different excitation wavelengths of 297, 333 and 391 nm. The temperature dependence of the photoluminescence property was investigated in the range 20–250 °C, and the emission intensity decreased to 71% of the initial value at room temperature on increasing the temperature to 150 °C. According to the classical theory of fluorescent thermal quenching, the activation energy (ΔE) for the thermal quenching luminescence of the as‐prepared Sr_3.45Y_6.5O₂(PO₄)_1.5(SiO₄)_4.5:0.05Eu²⁺ phosphor was determined to be 0.20 eV. Copyright © 2011 John Wiley & Sons, Ltd.     

Collagen-like triple helix formation of synthetic (Pro-Pro-Gly)10 analogues: (4(S)-hydroxyprolyl-4(R)-hydroxyprolyl-Gly)10, (4(R)-hydroxyprolyl-4(R)-hydroxyprolyl-Gly)10 and (4(S)-fluoroprolyl-4(R)-fluoroprolyl-Gly)10.

For the rational design of a stable collagen triple helix according to the conventional rule that the pyrrolidine puckerings of Pro, 4-hydroxyproline (Hyp) and 4-fluoroproline (fPro) should be down at the X-position and up at the Y-position in the X-Y-Gly repeated sequence for enhancing the triple helix propensities of collagen model peptides, a series of peptides were prepared in which X- and Y-positions were altogether occupied by Hyp(R), Hyp(S), fPro(R) or fPro(S). Contrary to our presumption that inducing the X-Y residues to adopt a down-up conformation would result in an increase in the thermal stability of peptides, the triple helices of (Hyp(S)-Hyp(R)-Gly)(10) and (fPro(S)-fPro(R)-Gly)(10) were less stable than those of (Pro-Hyp(R)-Gly)(10) and (Pro-fPro(R)-Gly)(10), respectively. As reported by B?chinger's and Zagari's groups, (Hyp(R)-Hyp(R)-Gly)(10) which could have an up-up conformation unfavorable for the triple helix, formed a triple helix that has a high thermal stability close to that of (Pro-Hyp(R)-Gly)(10). These results clearly show that the empirical rule based on the conformational preference of pyrrolidine ring at each of X and Y residues should not be regarded as still valid, at least for predicting the stability of collagen models in which both X and Y residues have electronegative groups at the 4-position.     

Role of tfdC(I)D(I)E(I)F(I) and tfdD(II)C(II)E(II)F(II) gene modules in catabolism of 3-chlorobenzoate by Ralstonia eutropha JMP134(pJP4)

The enzymes chlorocatechol-1,2-dioxygenase, chloromuconate cycloisomerase, dienelactone hydrolase, and maleylacetate reductase allow Ralstonia eutropha JMP134(pJP4) to degrade chlorocatechols formed during growth in 2,4-dichlorophenoxyacetate or 3-chlorobenzoate (3-CB). There are two gene modules located in plasmid pJP4, tfdC(I)D(I)E(I)F(I) (module I) and tfdD(II)C(II)E(II)F(II) (module II), putatively encoding these enzymes. To assess the role of both tfd modules in the degradation of chloroaromatics, each module was cloned into the medium-copy-number plasmid vector pBBR1MCS-2 under the control of the tfdR regulatory gene. These constructs were introduced into R. eutropha JMP222 (a JMP134 derivative lacking pJP4) and Pseudomonas putida KT2442, two strains able to transform 3-CB into chlorocatechols. Specific activities in cell extracts of chlorocatechol-1,2-dioxygenase (tfdC), chloromuconate cycloisomerase (tfdD), and dienelactone hydrolase (tfdE) were 2 to 50 times higher for microorganisms containing module I compared to those containing module II. In contrast, a significantly (50-fold) higher activity of maleylacetate reductase (tfdF) was observed in cell extracts of microorganisms containing module II compared to module I. The R. eutropha JMP222 derivative containing tfdR-tfdC(I)D(I)E(I)F(I) grew four times faster in liquid cultures with 3-CB as a sole carbon and energy source than in cultures containing tfdR-tfdD(II)C(II)E(II)F(II). In the case of P. putida KT2442, only the derivative containing module I was able to grow in liquid cultures of 3-CB. These results indicate that efficient degradation of 3-CB by R. eutropha JMP134(pJP4) requires the two tfd modules such that TfdCDE is likely supplied primarily by module I, while TfdF is likely supplied by module II.     

Induction of in vitro flowering in Dendrobium Madame Thong-In (Orchidaceae) seedlings is associated with increase in endogenous N(6)-(Delta (2)-isopentenyl)-adenine (iP) and N (6)-(Delta (2)-isopentenyl)-adenosine (iPA) levels

We analysed the endogenous cytokinin levels of Dendrobium Madame Thong-In seedlings grown in vitro during vegetative and flowering-inductive periods. HPLC was used to fractionate the extracts and radioimmunoassay (RIA) was used for assay of zeatin (Z), dihydrozeatin (DZ), N(6)-(Delta(2)-isopentenyl)-adenine (iP) and their derivatives. Coconut water used in experiments was found to contain high level (>136 pmol ml(-1)) of zeatin riboside (ZR). Protocorms and seedlings cultured in medium with coconut water were found to contain 0.5-3.9 pmol g(-1) FW of the cytokinins analysed. Seedlings (1.0-1.5 cm) cultured in flowering-inductive liquid medium containing 6-benzyladenine (BA, 4.4 muM) and coconut water (CW, 15%) contained up to 200 and 133 pmol g(-1) FW of iP and iPA, respectively. These levels were significantly higher than all other cytokinins analysed in seedlings of the same stage and were about 80- to 150-folds higher than seedlings cultured in non-inductive medium. During the transitional (vegetative to reproductive) stage, the endogenous levels of iP (178 pmol g(-1) FW) and iPA (63 pmol g(-1) FW) were also significantly higher than cytokinins in the zeatine (Z) and dihydrozeatin (DZ) families in the same seedlings. Seedlings that grew on inductive medium but remained vegetative contained lower levels of iPA. The importance of the profiles of iP and its derivatives in induction of in vitro flowering of D. Madame Thong-In is discussed.     

Biology of Bactrocera (Zeugodacus) tau (Walker) (Diptera: Tephritidae)

The biology of the fruit fly Bactrocera tau, an important horticultural pest, was studied under laboratory conditions at 25°C and 60–70% relative humidity on Cucurbita maxima. The duration of mating averaged 408.03 ± 235.93 min. After mating, the female fly had a preoviposition period of 11.7 ± 4.49 days. The oviposition rate was 9.9 ± 8.50 eggs and fecundity was 464.6 ± 67.98 eggs/female. Eggs were elliptical, smooth and shiny white, turning darker as hatching approached, and measured 1.30 ± 0.07 mm × 0.24 ± 0.04 mm. The chorion has polygonal microsculpturing and is species-specific with polygonal walls. The egg period lasts for 1.3 ± 0.41 days. The duration of the larval period is 1.2 ± 0.42, 1.7 ± 0.48 and 4.0 ± 0.94 days for first, second and third instars, respectively. Pupation occurs in the sand or soil and pupal periods are 7.0 ± 0.47 days. The life cycle from egg to adult was completed in 14.2 ± 1.69 days; the longevity of mated females and males was 130.33 ± 14.18 and 104.66 ± 31.21 days, respectively. At least two to three generations were observed from June 2008 to June 2009.     

Spectroscopic investigations of Er(3+) :CdO-Bi(2) O(3) -B(2) O(3) glasses

This article reports on the optical properties of Er³⁺ ions doped CdO–Bi₂O₃–B₂O₃ (CdBiB) glasses. The materials were characterized by optical absorption and emission spectra. By using Judd–Ofelt theory, the intensity parameters Ω_λ (λ = 2, 4, 6) and also oscillatory strengths were calculated from the absorption spectra. The results were used to compute the radiative properties of Er³⁺:CdBiB glasses. The concentration quenching and energy transfer from Yb³⁺–Er³⁺ were explained. The stimulated emission cross‐section, full width at half maximum (FWHM) and FWHM × values are also calculated for all the Er³⁺:CdBiB glasses. Copyright © 2011 John Wiley & Sons, Ltd.     

Cationic (tripyrrinato)palladium(II) complexes

The formation of cationic palladium(II)complexes [TrpyPd^II]⁺X⁻ by salt metathesis of the respective trifluoroacetates with different salts of weakly coordinating anions X⁻ was investigated. With non-hydrolizable counterions, cationic mono- and dinuclear complexes are observed depending on the nature of the anion X⁻ and the solvent. The mononuclear cations, which are only formed with X = BAr^F, most probably carry a weakly bound molecule of dichloromethane at the fourth coordination site of Pd^II. When treated with diazoalkanes, only these are sufficiently reactive to form carbene complexes. Four- and five coordinate Lewis base adducts [TrpyPd^IIL]⁺ with L = CH₃NC, tBuNH₂, PMe₃, PEt₃ and PiPr₃ and [TrpyPd^IIL₂]⁺ with L = PMe₃ were prepared from the mononuclear cations [TrpyPd^II]⁺BAr^F−. From structural studies it becomes apparent, that the formation of stable five coordinate Pd^II species is restricted to medium size ligands and depends on the delicate balance between the steric influence of L and the strain, which is induced on the TrpyPd^II unit.     

Copper (II) and cobalt (II) complexes of chiral tetrathiafulvalene-oxazoline (TTF-OX) and tetrathiafulvalene-thiomethyl-oxazoline (TTF-SMe-OX) derivatives

Synthesis and single crystal X-ray structures of the first paramagnetic transition metal complexes containing chiral ethylenedithio-tetrathiafulvalene-oxazoline (EDT-TTF-OX) 1a-c and ethylenedithio-tetrathiafulvalene-thiomethyloxazoline 2 (EDT-TTF-(SMe)OX) ligands based on copper (II) and cobalt (II) are described. The racemic [EDT-TTF-OX][Cu(hfac)₂] complex 3a crystallizes in the triclinic centrosymmetric space group , whereas the enantiopure counterparts 3b-c crystallize in the triclinic non-centrosymmetric space group P1. Cu(II) adopts a distorted square pyramidal coordination geometry, a much weaker Cu?S_TTF interaction also being identified. The same coordination pattern around Cu(II) is observed in the complex [(rac)-EDT-TTF-(SMe)OX][Cu(hfac)₂] (4) in spite of the bidentate nature of the redox active ligand. DFT theoretical calculations afforded two equilibrium configurations for a corresponding model complex, in which the metal centre establishes secondary coordination either with one S_TTF or with the SMe group. The same ligand coordinates the cobalt (II) to afford the octahedral complex [(rac)-EDT-TTF-(SMe)OX][Co(hfac)₂] (5). In all these novel complexes, the paramagnetic centres are structurally and magnetically isolated. Cyclic voltammetry measurements show the stability of the radical cation species.     

The helix-coil transitions of poly (dA)-poly (dT) and poly (dA-dT)-poly (dA-dT)

Helix–coil transition curves are calculated for poly (dA) poly(dT) and poly (dA-dT) poly (dA-dT) using the integral equation approach of Goel and Montroll.⁵ The transitions are described by the loop entropy model with the exponent of the loop entropy factor, k, remaining an arbitrary constant. The theoretical calculations are compared with experimental transition curves of the two polymers. Results indicate that the stacking energies for these two polymers differ by about 1 kcal/mole of base pairs. Also, a fit between theory and experiment was not possible for k > 1.70.