凋落物去除和氮添加对亚热带阔叶林土壤不同组分碳、氮的影响

人类活动显著增加了氮沉降,对森林生态系统产生了不同程度的影响;凋落物在其分解过程中输入的大量有机碳、氮也会影响土壤碳氮的形成、稳定及转化.本研究选择亚热带常绿阔叶林,对样地进行8年氮添加[对照(0)、低氮(75 kg·hm^-2·a^-1)、高氮(150 kg·hm^-2·a^-1)]和控制凋落物处理(保留凋落物、去除凋落物),之后采集土壤样品,通过K₂SO₄、Na₂B₄O₇、Na₄P₂O₇、NaOH、H₂SO₄、Na₂S₂O₄、HF等化学试剂逐级浸提土壤,测定各浸提液和残渣中的碳、氮含量,研究凋落物及氮添加对土壤矿物结合态碳、氮的影响.结果表明: 整体上,胡敏素(humin,H)组分的土壤碳、氮含量均为最高,分别占土壤全量的33.5%和33.3%.Na₂B₄O₇溶液提取的土壤可溶性碳、氮含量最高,其次是NaOH和Na₄P₂O₇溶液,3种试剂提取的土壤可溶性总碳、可溶性总氮以及可溶性有机氮分别占提取总量的46.2%、47.9%和76.5%.与对照相比,氮添加增加了Na₂S₂O₄和H组分碳、氮含量;与保留凋落物比较,去除凋落物降低了Na₂B₄O₇、H₂SO₄、Na₂S₂O₄和H组分的碳含量,以及NaOH、HF和H组分的氮含量.保留凋落物和氮添加显著增加了K₂SO₄组分氮含量.可见,保留凋落物和外源氮通过影响化学稳定性不同的土壤组分的碳氮变化来改变土壤碳氮过程.     

Histochemical Demonstration of Pyrophosphatase

Fresh tissue slices were fixed in 5% formalin containing 0.9% NaCl for 10-20 min and frozen sections therefrom floated for 3 hr at 37°C on an incubating mixture made as follows. Sodium pyrophosphate (Na₄P₂O₇-12H₂O), 1.088 gm was dissolved in 20-30 ml of distilled water and to this was added ferric chloride (FeCl₃-6H₂O), 0.61 gm dissolved in 10-15 ml of water. The precipitate was just dissolved by cautiously adding 5-10% aqueous Na₂CO₃ solution and the pH adjusted to 7.2 with 1N HCl. The volume was made up to 100 ml and 0.9 gm of NaCl added. Before use, 1 ml of 10% Mg(NO₃) was added. After incubation, sections were washed 10-15 min in 0.9% NaCl, then mounted on glass slides and air-dried. When dry, the slides were immersed in 0.9% NaCl containing 0.2-0.5% ammonium sulfide for 2-3 min, then dehydrated rapidly through graded alcohols, cleared, and covered in balsam. Sites of pyrophosphatase activity stained in various shades of green. Acid pyrophosphatase also was histochemically demonstrated by the same principle, excepting that the substrate solution was adjusted to pH 3.7-4.0 with acetate buffer. The pattern of distribution of pyrophosphatase and glycerophosphatase was almost identical.     

Ca2+参与H2O2促进盐碱混合胁迫下燕麦种子的萌发和成苗

盐碱胁迫是制约作物高产优质的重要因素,Ca²⁺和H₂O₂作为信号分子参与作物逆境响应调节。为了解Ca²⁺是否参与H₂O₂对盐碱胁迫下植物种子萌发和成苗的调控,以燕麦（Avena nude）为试验材料,采用隶属函数分析方法,研究了胞外游离Ca²⁺螯合剂EGTA、质膜Ca²⁺通道阻断剂LaCl₃和液泡膜Ca²⁺释放抑制剂钌红（RR）与H₂O₂共处理对盐碱混合（NaCl：Na₂SO₄：NaHCO₃：Na₂CO₃=12：8：9：1）胁迫下种子萌发和成苗的影响。结果表明,25~200 mmol·L^-1盐碱混合胁迫显著抑制燕麦的种子萌发和成苗,抑制程度随浓度提高而增强;0.001~2 mmol·L^-1 H₂O₂能够促进燕麦种子的萌发和成苗,且0.5 mmol·L^-1 H₂O₂可以显著缓解75 mmol·L^-1盐碱混合胁迫对燕麦种子萌发和成苗的抑制作用;而EGTA、LaCl₃和RR均能消减H₂O₂对盐碱混合胁迫下燕麦种子萌发和成苗的促进作用。表明Ca²⁺参与H₂O₂促进盐碱混合胁迫下燕麦种子萌发和成苗的信号转导过程。     

氮磷肥配施对冬小麦灌浆期光合参数及产量的影响

在西北绿洲生态条件下, 实验设4个处理, 即165(N₁)和225 kg·hm^-2(N₂)2个氮素(纯氮)水平及105(P₁)和165 kg·hm^-2(P₂)2个磷素(P₂O₅)水平, 研究了氮磷肥配施对冬小麦(Triticum aestivum)品种临抗2号光合特性及产量的影响。结果表明, 低氮(165 kg·hm^-2)处理组的净光合速率(P_n)、气孔导度(G_s)及蒸腾速率(T_r)日变化均呈双峰曲线, 有光合“午休”现象; 高氮(225 kg·hm^-2)处理可减弱甚至使光合“午休”现象消失; 高磷(165 kg·hm^-2)和低磷(105 kg·hm^-2)处理对光合特性的影响差异不显著。N₂P₂具有最高的群体叶面积指数(LAI)、群体光合速率(CAP)、穗粒数、亩穗数、千粒重及产量, 且与N₁P₁和N₁P₂的差异均达显著水平, 与N₂P₁则无显著差异。但N₂P₂水分利用效率(WUE)低于N₂P₁, 显著高于N₁P₁和N₁P₂ (N₁P₁高于N₁P₂, 但无显著差异)。氮肥对光合“午休”的影响大于磷肥, 二者互作效应差异不显著。该实验条件下, 当N、P分别为225和105 kg·hm^-2时有利于提高冬小麦的光合速率及产量。     

水杨酸诱发的丹参悬浮培养细胞内H2O2迸发与其培养基碱化的关系

水杨酸(salicylic acid,SA)处理可诱导丹参悬浮培养细胞内H2O2产生及其培养基碱化。利用NADPH氧化酶抑制剂咪唑(imidazole,IMD)、H2O2淬灭剂二甲基硫脲(dimethylthiourea,DMTU)、质膜H+-ATPase抑制剂钒酸钠(Na3VO4)及激活剂壳梭孢菌素(fusicoccin,FC)处理丹参悬浮培养细胞,探讨SA诱导的H2O2迸发与培养基碱化之间的关系。结果表明,H2O2可促发培养基碱化,IMD和DMTU抑制SA诱发的培养基碱化,说明H2O2参与SA诱发的培养基碱化过程;SA抑制质膜H+-ATPase活性,Na3VO4引发培养基碱化并使H2O2迸发时间提前,FC处理逆转了SA诱导的培养基碱化及H2O2迸发,说明质膜H+-ATPase调控培养基pH值变化,培养基碱化促进了H2O2产生。因此,丹参悬浮培养细胞内H2O2水平与其培养基碱化程度之间相互关联、共同作用,协同响应SA的诱导。     

外源H2O2对盐碱混合胁迫下裸燕麦幼苗生长和抗性生理的影响

为探讨信号分子过氧化氢（H₂O₂）增强裸燕麦盐碱耐性的作用及其生理机制,以裸燕麦品种‘定莜6号’为材料,在日光温室内用珍珠岩培养幼苗至三叶一心期时叶面喷施0.01 mmol·L^-1 H₂O₂的同时根部浇灌75 mmol·L^-1盐碱混合溶液（NaCl：Na₂SO₄：NaHCO₃：Na₂CO₃=12：8：9：1）或添加H₂O₂淬灭剂二甲基硫脲（DMTU）,研究对幼苗生长及叶片光合色素含量、活性氧代谢和渗透调节物质积累的影响。结果表明：喷施H₂O₂能够缓解盐碱混合胁迫对裸燕麦幼苗生长的抑制,提高幼苗根长、株高和植株干重及叶片叶绿素a、叶绿素b、总叶绿素、类胡萝卜素含量和超氧化物歧化酶、过氧化物酶、过氧化氢酶、抗坏血酸过氧化物酶活性,降低超氧阴离子、H₂O₂、丙二醛、抗坏血酸、谷胱甘肽和游离氨基酸含量,促进抗氧化物质类黄酮、总酚和原花青素及渗透调节物质可溶性蛋白质、可溶性糖和脯氨酸积累。添加DMTU部分或完全逆转了H₂O₂的上述作用。采用隶属函数综合评价显示,喷施H₂O₂提高了盐碱混合胁迫下裸燕麦幼苗的综合评价值D,添加DMTU完全逆转了H₂O₂对D值的提升作用。表明外源H₂O₂通过参与活性氧代谢和渗透调节物质积累等生理代谢调控缓解盐碱混合胁迫诱导的氧化伤害和生长抑制,从而提高裸燕麦对盐碱胁迫的适应能力。     

Influence of chelators and iron ions on the production and degradation of H2O2 by beta-amyloid-copper complexes

β-Amyloid peptide (Aβ) 1–42, involved in the pathogenesis of Alzheimer’s disease, binds copper ions to form Aβ · Cu_n complexes that are able to generate H₂O₂ in the presence of a reductant and O₂. The production of H₂O₂ can be stopped with chelators. More reactive than H₂O₂ itself, hydroxyl radicals HO (generated when a reduced redox active metal complex interacts with H₂O₂) are also probably involved in the oxidative stress that creates brain damage during the disease. We report in the present work a method to monitor the effect of chelating agents on the production of hydrogen peroxide by metallo-amyloid peptides. The addition of H₂O₂ associated to a pre-incubation step between ascorbate and Aβ · Cu_n allows to study the formation of H₂O₂ but also, at the same time, its transformation by the copper complexes. Aβ · Cu_n peptides produce but do not efficiently degrade H₂O₂. The reported analytic method, associated to precipitation experiments of copper-containing amyloid peptides, allows to study the inhibition of H₂O₂ production by chelators. The action of a ligand such as EDTA is probably due to the removal of the copper ions from Aβ · Cu_n, whereas bidentate ligands such as 8-hydroxyquinolines probably act via the formation of ternary complexes with Aβ · Cu_n. The redox activity of these bidentate ligands can be modulated by the incorporation or the modification of substituents on the quinoline heterocycle.     

DNA Single Strand Breakage by H2O2 and Ferric or Cupric Ions: Its Modulation by Histidine

The role of histidine on DNA breakage induced by hydrogen peroxide (H₂O₂) and ferric ions or by H₂O₂ and cupric ions was studied on purified DNA. L-histidine slightly reduced DNA breakage by H₂O₂ and Fe³⁺ but greatly inhibited DNA breakage by H₂O₂ and Cu²⁺. However, only when histidine was present, the addition of EDTA to H₂O₂ and Fe³⁺ exhibited a bimodal dose response curve depending on the chelator metal ratio. The enhancing effect of histidine on the rate of DNA degradation by H₂O₂ was maximal at a chelator metal ratio between 0.2 and 0.5, and was specific for iron. When D-histidine replaced L-histidine, the same pattern of EDTA dose response curve was observed. Superoxide dismutase greatly inhibited the rate of DNA degradation induced by H₂O₂, Fe³⁺, EDTA and L-histidine involving the superoxide radical.

These studies suggest that the enhancing effect of histidine on the rate of DNA degradation by H₂O₂ and Fe³⁺ is mediated by an oxidant which could be a ferrous-dioxygen-ferric chelate complex or a chelate-ferryl ion.     

A Copper Sulfate-Silver Nitrate Method for Nerve Fibers of Planarians

For staining in toto, planarians are fixed in a mixture of 10 ml of commercial formalin, 45 ml of 95% ethanol and 2 ml of glacial acetic acid. After treatment with 70% ethanol 3-10 days, they are washed in distilled water and immersed in 10% CuSO₄. 5H₂O for 3 hr at 50° C, transferred without washing to 1% AgNO₃ for 1.0-1.5 hr at 50° C; and then developed in: 10 ml of 1% pyrogallol, 100 ml of 56% ethanol and 1 ml of 0.2% nitric acid. Gold toning, 5% Na₂S₂O₃ and dehydration follow as usual. For staining sections, material is fixed in the same fixative, embedded in paraffin and sectioned at 10 μ. After bringing sections to water, they are immersed in 20% CuSO₄. 5H₂O for 48 hr at 37° C; then rinsed briefly in distilled water and placed in 7% AgNO₃ for 24 hr at 37° C. They are washed briefly in distilled water and reduced in: hydroquincne, 1 gm; Na₂SO₃, 5 gm and distilled water 100 ml. Gold toning, followed by 5% Na₂S₂O₃ and dehydration completes the process. Any counterstaining may follow.     

A Holocene environmental record from the southern Yangtze River delta, eastern China

The Holocene sedimentary record of core ZX-1, recovered west of mid-Holocene Chenier ridges on the monsoon-controlled Southern Yangtze delta, eastern China, consists of lagoon, salt marsh, upper tidal flat, and limnic facies, reflecting low-energy depositional environments. Holocene deposits mainly originated from the surrounding Tai Lake drainage basin. The temporal variation of most geochemical element percentages corresponds with the climatic phases inferred from the pollen record, i.e., the relatively low values of SiO₂, Na₂O, CaO and high values of Al₂O₃, K₂O, MgO, Fe₂O₃, FeO, FeO + Fe₂O₃ and TiO₂ generally concur with the warm and humid climate, and vice versa. Three geochemical indices − Al₂O₃/Na₂O, K₂O/Na₂O, and CaO/K₂O − are found to be sensitive to past precipitation in the monsoon-controlled southern Yangtze River delta. Based on fine sediment analysis of core ZX-1, the samples deposited under a dry climate with a mean annual precipitation (MAP) < 500–900 mm tend to have Al₂O₃/Na₂O values less than 12.2, and the samples deposited under a moist climate with an MAP 1000–1800 mm mostly have Al₂O₃/Na₂O values higher than 12.2. Similarly, the K₂O/Na₂O boundary value is 2.0. However, for CaO/K₂O, the dry climate sediments likely show values higher than 0.9, and those wet climate ones generally have values less than 0.9. This geochemical response suggests the potential application of these indices in the interpretation of palaeoclimate variation of monsoon-controlled eastern China.

Holocene climatic variation history is reconstructed for the southern Yangtze delta. From 8000 to 7000 yr BP, regional climate demonstrated frequent fluctuations, with warm and wet periods (8000–7700; 7500–7200 yr BP) alternating with cool and less humid periods (7700–7500; 7200–7000 yr BP). From 7000 to 6000 yr BP, the climate was relatively warm and humid. Since then, it had turned cool and dry, climaxing in an intense cold event around 4000 yr BP. After the cold event, it became warm and humid until around 2500 yr BP.     

A Glutaraldehyde-Dichromate-Silver Sequence for Differentiating Norepinephrine Cells from Epinephrine Cells in Neonatal and Adult Rats—Paraffin Sections

A glutaraldehyde-K₂Cr₂O₇ procedure intensified by silver staining enabled norepinephrine and epinephrine cells to be distinguished readily in paraffin sections of the adrenal glands of rats 8 days after birth. The technique involved fixation in 0.1 M cacodylate-buffered 5% glutaraldehyde (6-24 hr), treatment with 3.5% K₂Cr₂O₇ (6-12 hr) and routine preparation of paraffin sections. The sections were deparaffinised, brought to water and immersed in Fontana's solution (24 hr), prepared by adding concentrated NH₄OH drop by drop to 5% AgNO₃ until the precipitate formed just redissolved; more 5% AgNO₃ was then added until a permanent cloudiness just developed. After a rinse in distilled water, the sections were treated with 0.5% gold chloride (5 min) and Na₂S₂O₃ (5 min), then mounted in Depex. This sequence resulted in an intense black cytoplasmic colouration in norpinephrine-containing cells of both the adult and 8-day-old animals whereas epinephrine-containing cells remained colourless. The glutaraldehyde-K₂CrO₇ procedure, without intensification, gave very clear results in the adult: a yellow cytoplasmic colour in the norepinephrine cells with epinephrine cells colourless. A glutaraldehyde-OsO₄ sequence gave a less well defined separation of these cell types in the adult and failed to distinguish the cell types in the neonate.     

Silicon and iron levels in tissues of animals treated with a “ferrimagnetic ceramic” with oncotherapeutic potential (anti-tumor) value

The stability in a biological environment of an injectable cement with oncotherapeutic potential — consisting of a glass powder of SiO₂ (35.6%), CaO (42.4%), P₂O₅ (17%), Na₂O (5%) and 30% of its weight of Fe₃O₄ dissolved in (NH₄)₂HPO₄ plus NH₄H₂PO₄ — was evaluated referring to the release of silicon and iron. The experimental model was the rat, and organs (liver, kidney, spleen, lung, heart, and brain) of the implanted and control animals were collected for quantification of these elements by electrothermal atomization atomic absorption spectrometry methods. In most of the analysed organs no significant difference in the contents of silicon and iron between the implanted and the control animals was found.     

The Generation of Ferryl or Hydroxyl Radicals During Interaction of Haemproteins with Hydrogen Peroxide

The oxidation of 2-keto-4-thiomethyl butyric acid (KTBA) and methionine to ethylene has been used to evaluate generation of ferryl species or hydroxyl radicals by H₂O₂-_-activated haemproteins or free ferric ions. Hydrogen peroxide was generated by a glucose oxidase-glucose system at a rate of 1 μM/min. Free ferric in the presence of H₂O₂ oxidizes KTBA, and this was highly inhibited by hydroxyl radical scavengers, caeruloplasmin, superoxide dismutase (SOD) and EDTA. However, when metmyoglobin, methaemoglobin (MtHb) or horseradish peroxidase (HRP) were tested in the same model system, hydroxyl radical scavengers suppressed partially KTBA oxidation and caeruloplasmin, SOD and EDTA failed to inhibit the reaction. Cytochrome-c was found to be a weak promoter of KTBA oxidation in the presence of H₂O₂. Methionine was oxidized to ethylene by an active system which generates hydroxyl radicals, but not by H₂O₂-_-activated metmyoglobin. Ferric ions chelated to membranes or ADP in the presence of H₂O₂ generated enzymatically, initiated membranal lipid peroxidation only in the presence of ascorbic acid, and this was inhibited by EDTA. In contrast, metmyoglobin and methaemoglobin activated by H₂O₂ generated by the same system, initiated membranal lipid peroxidation and this was not inhibited by EDTA. It is concluded that ferryl and not HO. is the main oxidant in systems containing myoglobin and haemoglobin activated by low concentrations of H₂O₂.     

Thiosulfate-Schiff Reagent

Na₂S₂O₃ and HCl can be used as the reducing system to make Schiff reagent, the sulfur produced by the reaction acting as the adsorbent and consequently eliminating the need of decolorizing charcoal. To 100 ml of a 0.02% solution of basic fuchsin add 8 gm of dry Na₂S₂O₃ shake for 3 min, add 0.5 ml of cone. HCl (final concentration 0.05 N). Do not heat. Store in a refrigerator (4° C) overnight, and filter. The filtrate is water-clear, and will remain stable for 24 hr at room temperature. Periodic acid-Schiff and Feulgen reactions can now be performed, preferably at refrigerator temperature, although the times required are notably prolonged (6-8 hr). Background color is slight, and specificity good.     

A Comparison Of Iron Histochemical Methods For Use On Glycol Methacrylate Embedded Tissues

Four histochemical tests for iron and four procedures for its removal were investigated in regard to their suitability for glycol methacrylate embedded tissues. The HCl-ferrocyanide and chlorate hematoxylin methods were easily modified for plastic sections. The latter does not use iron-containing reagents. Desiderization was complete both after a fifteen minute exposure in 1% Na₂S₂O₄ in 0.1 M acetate-HCl buffer (pH 4.5) and, if an acid method is preferred, after twelve hours in 5% oxalic acid. A six hour treatment in 3.7 N H₂SO₄ also removed all histochemical iron but was accompanied by a relatively greater loss of tissue basophilia.     

钨酸钠对苹果幼苗15N吸收利用、13C积累及果实品质的影响

分别以1年生苹果砧木M9T337幼苗和5年生烟富3/SH6/平邑甜茶为试材,开展盆栽和田间试验,并结合¹⁵N、¹³C同位素示踪技术,研究不同浓度(0、0.5、1、1.5 mmol·L^-1,分别用CK、T₁、T₂和T₃表示)硝酸还原酶(NR)抑制剂钨酸钠对苹果幼苗¹⁵N吸收利用、¹³C积累和成熟期果实品质的影响。结果表明: 盆栽试验中,喷施0.5~1.0 mmol·L^-1钨酸钠可显著抑制幼苗地上部生长,但对根系生长影响不显著;当钨酸钠浓度达到1.5 mmol·L^-1时可显著抑制根系生长。同一时期各处理叶片NR活性与钨酸钠浓度呈负相关,均表现为CK>T₁>T₂>T₃。随处理时间的延长,叶片硝态氮含量总体表现为先升高后降低的趋势,同一时期各处理硝态氮含量与钨酸钠浓度呈正相关,均表现为T₃>T₂>T₁>CK。喷施钨酸钠可不同程度地降低幼苗各器官¹⁵N吸收量和¹⁵N利用率,且钨酸钠浓度越高,抑制幼苗氮素吸收和利用的效果越显著。随钨酸钠浓度的提高,地上部¹³C积累量呈先升高后降低的趋势,在T₂处理时达到最高;幼苗整株¹³C积累量呈相似的规律。田间试验结果表明,喷施钨酸钠可降低成熟期叶片和果实的氮含量,果皮花青苷含量、果实可溶性固形物、可溶性糖含量和糖酸比均不同程度提高,其中T₂处理的效果最好。综上,T₂处理(1.0 mmol·L^-1钨酸钠)可有效抑制幼苗地上部生长,降低¹⁵N吸收利用,提高¹³C积累,有利于果实品质的提高。     

The Azure Dyes their Purification and Physicochemical properties. II. Purification of Azure B

A method is described for the purification of the dye azure B in quantities sufficient for biological staining experiments on a larger scale. The method is based on the use of column chromatography. Two columns are employed. In column A with silica gel as adsorbent the azure B fraction is isolated from a suitable substrate ('technical' azure B gained by a modification of Bernthsen's synthesis of methylene blue, or plychrome methylene blue) using an acetate-formate mixture as eluent. In column B, on an Amberlite polyineric adsorbent (XAD-2) the acetate-formate anions are exchanged for chloride. Regeneration of both columns is possible: KMnO₄, Na₂S₂O₄ and water are run through column A, 5% NaOH, methanol and water through column B. Purification of azure B on economic terms is thus attained. The opinion is expressed that this method is also applicable to the purification of other cationic dyes.     

A HYDROXYL-DEPENDENT SILVER METHOD FOR NERVE AXOPLASM

Axoplasm is selectively impregnated by the following steps: (1) fixation in 10% formalin or in 10% formalin with added sucrose, 15%, and concentrated NH₄OH, 1%, for 1-7 days; (2) frozen sections; (3) extraction of the sections in 95% ethyl alcohol, absolute alcohol, xylene, and 95% ethyl alcohol and absolute alcohol, 1 hr each; (4) distilled water, 3 changes of 10 min each; (5) 20% AgNO₃ (aq.) at 25°C, 30 min; (6) distilled water, 3 changes of 1-2 sec each; (7) 6.9% K₂CO₃, 1 hr; (8) water, 3 changes of about 1 min each; (9) 0.2%AuCl₃, 2 min; (10) distilled water; (11) 5% Na₂S₂O₃, 2 min; (12) washing, clearing and mounting. This procedure is proposed as a simplified stain for axoplasm, with other tissue components remaining unstained. The few reagents necessary suit this method for histochemical investigation of the mechanism of silver staining.     

Interaction of metal compounds with ‘double-hydrophilic’ block copolymers in aqueous medium and metal colloid formation

The interaction of a ‘double-hydrophilic’ polyethyleneoxide-polyethyleneimine block copolymer (PEO-b-PEI) with AuCl₃, PdCl₂, Na₂PdCl₄, H₂PtCl₆·6H₂O, Na₂PtCl₆·6H₂O, and K₂PtCl₄ in aqueous medium was studied. Micellar structure formation was observed for all metal compounds except Na₂PdCl₄ where additional protonation of the polymer was required to induce micelle formation. The characteristics of the micelles formed depended strongly on the metal type, the molar ratio polymermetal compound, and the type of reducing agent. Micellization in the presence of AuCl₃·H₂O is accompanied with reduction of the salt and the formation of gold colloid without reducing agent induced by oxidation of the PEI block. The interaction with PtCl₆²⁻ ions results in narrowly distributed micelles wi size depending on the metal compound loading. In the case of loading with H₂PtCl₆, it was found that the size and shape of the colloids can be controlled by changing the molar ratio PEI:metal salt. The lower is the metal loading, the smaller are the particles. In addition, differently shaped Pt colloids were observed. This phenomenon can be controlled by the relative ratio of reactants.     

Modification of the in vitro Cytotoxicity of Hydrogen Peroxide by Iron Complexes

The effect of a range of iron chelates on the cytotoxicity of H₂O₂ was studied on a mammalian epithelial cell line. Iron complexes which were internalised enhanced the cytotoxicity of H₂O₂ measured by delayed thymidine incorporation. Iron complexed to 8-hydroxyquinoline (Fe/8-HQ) potentiated the cytotoxicity of 50 µM by 38% and Fe/dextran by 23%. Pre-exposure of cells to Fe/dextran at 4°C did not result in any potentiation of H₂O₂-induced cytotoxicity which we ascribe to failure of the Fe/dextran to be endocytosed at low temperature. Iron complexes which are slowly taken up or remain extracellular protected the cells from H₂O₂-induced cytotoxicity. Thus, Fe/EDTA inhibited the cytotoxicity of 50 µM H₂O₂ by 33%; Fe/ADP by 80% and Fe/ATP by 88%, suggesting mutual extracellular detoxification.