Syntheses and properties of organocyanamide, cyanoguanidine and dinitrogen complexes of rhenium. Crystal structure of mer-[ReCl2(NCNEt2) (PMePh2)3]

Treatment of a THF solution of trans-[ReCl(N₂)L₄] (L = PMePh₂) with a cyanamide, NCNR₂ (R = Me, Et or H) or with cyanoguanidine, NCNC(NH₂)₂ , yields mer-[ReCl(N₂)(NCNR₂)L₃] (1) or mer-[Re(N₂)[Re(N₂){NCNC(NH₂)₂}₂L₃]Cl (2), respectively, which, to our knowledge, are the first mixed dinitrogen-cyanamide-type complexes to be reported. The former products (1, R=Me or Et) can also be obtained from reaction of the benzoyldiazenido complex [ReCl₂(NNCOPh)L₃] with NCNR₂ in refluxing methanol; the Re(II) complex mer-[ReCl₂(NCNEt₂)L₃] (3) is also formed (conceivably via an unusual homolysis of the C---N bond of the benzoyldiazenido ligand) and its crystal structure is reported. It shows an unusual pyramidal conformation at the amine N atom of the diethylcyanamide ligand which also exhibits a significant structural trans influence on the phosphine, behaving as a stronger net electron donor than the latter ligand.     

Comparison of Various Oxidants for Alum Hematoxylin

Oxidation of 100 mg of hematoxylm in 40 ml of a 3% solution of EAI(SO₄),₂. 12H₂O with 20 mg iodine, 4.5 mg of NaIO₃. 3.5 mg of H₅IO₆, 3.5 mg of NaIO₄ or 9 mg KMnO₄ gives equivalent results as shown by both staining and absorbance measurements Placing the prepared solutions at 55 C for 18 hours increased absorbance by 1/4 to 1/3 over those kept at room temperature. Two months after preparation, solutions initially placed at 55 C for 18 hours, with no air space in the bottle, had not increased in absorbancy. In simiiar preparations kept at room temperature the absorbance increased from initial values to that of those that had been heated. Solutions in bottles with air space also showed this increase and also had a scum on the surface and sufficient precipitate to require filtering before use.     

不同盐碱类型胁迫对红地球/贝达葡萄植株离子分布的影响

以盆栽红地球/贝达葡萄为试材,定量浇灌NaCl、Na₂SO₄、NaHCO₃、NH₄Cl和(NH₄)₂SO₄,筛选导致葡萄叶片黄化的盐、碱离子,研究不同盐碱类型胁迫对葡萄植株离子分布的影响.结果表明： NaHCO₃对植株影响最大,叶片在处理14 d时出现黄化症状,而NaCl和NH₄Cl处理28 d时出现黄化症状.NaHCO₃和NaCl处理均显著增加了植株各器官中Na^+含量,NaHCO₃处理根中Na⁺含量是对照的 6.4倍;这两种盐处理均降低了除叶片外其他器官中的K⁺含量,NaHCO₃处理显著降低了各器官中K/Na,根中K/Na仅为0.1,NaCl处理降低了除茎外其他器官中K/Na;这两种盐处理还降低了Ca²⁺、Mg²⁺、Fe²⁺向地上部的运输.NH₄Cl、(NH₄)₂SO₄和Na₂SO₄处理降低了植株各器官中K/Na,以NH₄Cl处理显著.碱性盐NaHCO₃对葡萄叶片黄化影响最大,其次是中性盐NaCl,再次是NH₄Cl,而(NH₄)₂SO₄和Na₂SO₄影响较小.     

黄河口不同恢复阶段湿地土壤N2O产生过程对氮输入的响应

以黄河口生态恢复前后未恢复区(R₀)、2007年恢复区(R₂₀₀₇)和2002年恢复区(R₂₀₀₂)的芦苇湿地为研究对象,研究了不同形态氮输入对湿地土壤N₂O产生过程的影响与贡献.结果表明: 硝态氮(NO₃^--N)输入对恢复区湿地土壤N₂O总产生量的影响远远大于铵态氮(NH₄⁺-N),但两者均抑制了R₀土壤的N₂O总产生量.尽管NO₃^--N输入对R₂₀₀₂表层土壤N₂O总产生量的影响明显大于R₂₀₀₇,但二者的N₂O产生量均随氮输入量的增加而增加.恢复区湿地土壤的反硝化作用和硝化细菌反硝化作用受NO₃^--N输入的影响明显,而R₀土壤产生N₂O的生物过程受其影响并不显著.尽管NH₄⁺-N输入对湿地土壤N₂O的总产生量影响不大,但其输入整体促进了R₀ 土壤的硝化细菌反硝化作用、R₂₀₀₇土壤的硝化作用和R₂₀₀₂土壤的非生物作用.比较而言,NO₃^--N输入对R₀、R₂₀₀₇和R₂₀₀₂湿地土壤N₂O产生的非生物作用主要表现为抑制,NH₄⁺-N输入则整体提高了R₀和R₂₀₀₂湿地土壤非生物作用的N₂O产生量,这与不同形态氮输入对土壤pH的调节作用密切相关.研究发现,NO₃^--N输入大大增加了湿地土壤的N₂O总产生量,改变了原有湿地土壤生物作用和非生物作用的贡献模式,故生态恢复工程导致的营养盐输入(NO₃^--N)应受到特别关注.     

Synthesis and ligand substitution reactions of [Ta(CO)5NH3]

Protonation of Na₃[Ta(CO)₅] in liquid ammonia provides the thermally unstable Na[Ta(CO)₅NH₃], which may be isolated as the crystalline and deep violet salt [Ph₄As][Ta(CO)₅NH₃]. Sodium amminepentacarbonyltantalate(1−) reacts with PMe₃, PPh₃, P(OMe)₃, AsPh₃, SbPh₃, CNtBu and CN⁻ at about 0°C in NH₃/THF to give exclusively the corresponding [Ta(CO)₅L]^z. These have been isolated as tetraethylammonium salts in 54–84% yields.     

盐增强培养对弗氏链霉菌产新霉素的影响

目的:弗氏链霉菌(Streptomyces fradiae)作为氨基糖苷类抗生素新霉素的主要生产菌株,其新霉素B具有抗菌活性强、抗癌、抗HIV等作用,提高新霉素B的效价具有重要意义.方法:在满足微生物正常生长所需盐离子的条件下,通过盐增强培养的方式向培养基中添加不同种类、浓度无机盐来改变细胞壁附近的理化特性、渗透压以及...     

The response of soil respiration to different N compounds addition in a saline–alkaline grassland of northern China

不同形态氮化合物添加对中国北方盐渍化草地土壤呼吸的影响 持续增加的氮沉降在提高陆地生态系统生产力的同时也会对土壤微生物产生显著影响;土壤呼吸由植物根系呼吸和土壤微生物呼吸组成,因此影响植物生产力和微生物的因子都会影响到土壤呼吸。以往氮富集对土壤呼吸的研究主要在土壤中性的草地生态系统开展,而对于盐渍化草地土壤呼吸是如何响应氮沉降的研究尚不多见,这限制了全球变化陆地生态系统土壤呼吸模型预测的准确性和完整性。本研究以中国北方农牧交错带盐渍化草地为研究对象,通过3年(2017–2019年)野外监测土壤呼吸及相关生物和非生物因子的变化,探讨了不同形态氮化合物添加(NH₄NO₃、(NH₄)₂SO₄和NH₄HCO₃)对盐渍化草地土壤呼吸的影响及其调控机制。结果表明：(i)土壤呼吸受大气温度、土壤温度及降水的调控,呈现双峰的季节动态变化趋势和显著的年际差异。(ii)与对照相比,经过3年的处理,土壤呼吸在NH₄NO₃、(NH₄)₂SO₄和NH₄HCO₃添加处理下分别提高了19.9%、13.0%和16.6%。(iii)NH₄NO₃添加对土壤呼吸较高的促进作用与较高的地上生物量、地下生物量以及土壤NO₃⁻含量有关。(iv)在NH₄HCO₃ 添加处理下,土壤碳排放(土壤呼吸)显著增加而碳输入(净生产力)无显著改变,表明NH₄HCO₃添加会降低土壤碳的固持。(v)净地下生产力(BNPP)是盐渍化草地土壤呼吸的最主要调控因子,并且土壤阳离子浓度和pH值通过影响土壤微生物间接影响土壤呼吸。上述研究结果表明,草地添加NH₄NO₃的研究高估了氮沉降对土壤呼吸的影响,并且在碳循环预测模型中应充分考虑盐渍化草地土壤碳动态。     

Binding of the inhibitor NH3 to the oxygen-evolving apparatus of spinach chloroplasts

Experiments are described on flash-induced luminescence of isolated spinach chloroplasts after addition of NH₄Cl. The results indicate a binding of NH₃, presumably in competition with water, in the oxidation states S₂ and S₃, i.e. the states reached upon illumination of dark-adapted material with one and two flashes, respectively. In the initial state S₁, no binding of NH₃ occurs. In state S₂ the binding of ammonia is rapid (half-time about 0.5 s) and rapidly reversible; in state S₃ the binding is slower (half-time about 10 s) and slowly reversible. NH₃ bound to S₄ prevents the oxidation of water. NH₃ bound to S₂ decreases the rate of the back reaction of reduced primary acceptor (Q⁻), indicating a charge stabilization, i.e. a decrease in the redox potential of S₂ due to interaction with ammonia. In Tris-washed chloroplasts, the stability of the positive charge generated in a flash is much smaller than in normal chloroplasts and not increased by NH₃. On the basis of these observations it is postulated that, in the absence of NH₃, states S₂ and S₃ are stabilized by manganese-coordinated, bound water.     

CO2浓度升高对水体硝化、反硝化作用的影响研究进展

大气CO₂浓度升高潜移默化地影响着水体生态系统的碳循环过程.然而,该过程如何影响与其耦合的氮循环过程仍不明确.水体硝化、反硝化过程作为水体氮循环的重要环节,必然会对大气CO₂浓度升高产生一系列的响应.本文总结了国内外关于大气CO₂浓度升高对水体理化性质、硝化作用、反硝化作用及N形态转化影响方面的研究工作,发现大气CO₂浓度升高会降低水体的pH,增加水中CO₂和HCO₃^-含量,但对富营养化与寡营养化水体中硝化、反硝化作用的影响具有明显差异.大气CO₂浓度升高抑制寡营养化水体的硝化作用和反硝化作用,降低N₂O的释放通量,抑制富营养化水体的硝化作用,但当水体pH在7~9时,可能促进反硝化作用,增加N₂O的释放通量,最终可能导致水体中NH₄⁺的积累及NO₃^-浓度的降低,影响水体中微生物的多样性.在此基础上提出目前相关研究存在的瓶颈问题及值得深入探讨的科学问题,为进一步深入理解温室效应背景下全球CO₂浓度升高对水体生态系统N循环的影响提供参考.     

Effects of NH+4-N and NO+3-N on growth and metabolism of Sphagnum magellanicum

Photosynthetic CO₂-fixation, chlorophyll content, growth rate and nitrate reductase activity were used to examine the influence of NH⁺₄-N and NO⁻₃-N on Sphagnum magellanicum cultivated under defined conditions in phytotrons. NO⁻₃-concentrations up to 322 μ M were found to be favourable. Increased NH⁺₄ concentrations, however, resulted in growth inhibition and decreased chlorophyll content at concentrations ≧ 255 μ M ; e.g. 600 μ M NH⁺₄ caused a 20% reduction of nitrate reductase activity and net photosynthesis. For raised bog Sphagna an improved standard nutrient solution is proposed with the following ion concentrations (μ M ): 55 Na⁺; 17 K⁺; 95 NH⁺₄; 22 Ca²⁺; 22 Mg²⁺; 2 Fe³⁺; 20 Cl⁻; 100 NO⁻₃; 57 SO^2-₄; 7.4 H₂PO⁻₄; trace elements: A-Z solution (Hoagland) 50 μl 1000 ml⁻¹; pH 5.8.     

Chemistry of the azine phosphine ligand Z,E-PPh2CH2C(Bu)=N-N=CMe(C6H4NO2-4): crystal structure of [Mo(CO)4{PPh2CH2C(Bu)=N-N=CMe(C6H4NO2-4)}]

Condensation of Z-PPh₂CH₂C(Bu^t)=NNH₂ with 4-nitroacetophenone gave the azine phosphine Z,E-PPh₂CH₂C(Bu^t)=N-N=CMe(C₆H₄NO₂-4) (I). The corresponding phsophine oxide II was prepared by treatment of I with H₂O₂. The phosphine I with [Mo(CO)₄(nbd)] (nbd=norbornadiene) gave [Mo(CO)₄{PPh₂CH₂C(Bu^t)=N-N=CMe(C₆H₄NO₂-4)}] (1a); the corresponding tungsten 1b and chromium 1c complexes were made similarly. The crystal structure of 1a was determined by X-ray diffraction and showed the presence of a six-membered chelate ring with the bulky 4-nitrophenyl group held close to the metal. Oxidation of 1a with bromine gave the seven-coordinate molybdenum (II) complex 2. Treatment of [PtMe₂(cod)] (cod=cycloocta-1,5-diene) with I at 20°C gave the dimethyl-platinum (II) complex [PtMe₂{PPh₂CH₂C(Bu^t)=N-N=CMe(C₆H₄NO₂-4)}] (3a) which with MeI gave the iodotrimethylplatinum(IV) complex 4. Treatment of 3a with C≡O opened the chelate ring to give the dimethyl(carbonyl)platinum(II) complex 5 containing a monodentate phosphine ligand. When 3a was heated in toluene solution at 110°C it gave the cyclometallated methylplatinum(II) complex [PtMe{PPh₂CH₂C(Bu^t)=N-N=CMe(C₆H₃NO₂-4)}] (6). Treatment of 6 with MeI gave the platinum(IV) complex 7. The dichloropalladium(II) complex [PdCl₂{PPh₂CH₂C(Bu^t)=N-N=CMe(C₆H₄NO₂-4)}] (3b) was prepared by treatment of [PdCl₂(NCPh)₂] with I in CH₂Cl₂. Treatment of [PtCl₂(NCMe)₂] with 2 equiv. of I gave the trans-bis(phosphine) complex 8. When 2 equiv. of I were treated with [PtCl₂(cod)] followed by NH₄PF₆ this gave the salt 9a containing two six-membered chelate rings; the analogous palladium(II) 9b) salt was also prepared. Treatment of 2 equiv. of I with [PtCl₂(cod)] followed by NH₄PF₆ gave the PF₆ salt 10 containing a six-membered chelate ring and a monodentate ligand. When 10 was treated with AgNO₃ followed by NH₄PF₆ this gave the bis-chelate complex 11 containing five- and six-membered chelate rings. Treatment of [IrCl(CO)₂(p-toluidine)] with I gave the cyclometallated iridium(III) hydride complex [IrHClCO{PPh₂CH₂C(Bu^t)=N-N=CMe(C₆H₃NO₂-4)}] (12). [RuCl₂(PPh₃)₃] with the phosphine I resulted in the Ru(II) complex 13 in which the ortho hydrogens of the 4-nitrophenyl group are agostically interacting with ruthenium. Proton, Phosphorus-31, some carbon-13 NMR and IR data have been obtained. Crystals of 1a are orthorhombic, space group Pna2₁, with a = 1819.3(2), b = 1050.0(1), c = 1614.8(2) pm and Z = 4; final R = 0.0191 for 2616 observed reflections.     

日光温室番茄-西瓜轮作系统不同水氮处理氨挥发特征

为探究黄土高原地区日光温室果蔬栽培中氨挥发特征,在陕西省杨凌区选择当地典型的日光温室,设置4个不同的水氮处理,采用密闭式间歇抽气法监测番茄-西瓜轮作季的氨挥发特征.结果表明: 日光温室栽培土壤氮素转化快,施氮处理施肥后第1～2天氨挥发出现峰值,氨挥发峰值为0.26～2.02 kg N·hm^-2·d^-1,7 d左右各处理氨挥发通量相近;施氮处理间氨累积排放量无显著差异;相同施氮量条件下,降低灌溉量氨累积排放量两季平均增加了46.7%;不同种植季氨平均排放通量和累积排放量均表现为西瓜季高于番茄季,西瓜季高温促进了氨排放;土壤铵态氮含量、土壤孔隙含水量、0～5 cm地温和温室气温均对氨排放通量有极显著影响,而土壤pH值与氨挥发通量呈显著负相关关系.不同种植季氨挥发通量和累积排放量存在差异,降低施氮量可减少氨排放,相同施氮量条件下降低灌溉量增加了氨排放.     

大气CO2浓度升高对稻田土壤氮素的影响

利用中国稻/麦轮作FACE(Free-Air Carbon=Dioxide Enrichment)试验平台,研究大气CO₂浓度升高200 μmol·mol^-1(周围大气中CO₂浓度约370 μmol·mol^-1)对稻季各生育期不同深度土壤溶液NH₄⁺-N和NO₃^--N浓度的影响.结果表明：高CO2浓度条件下耕层土壤溶液NH₄⁺-N浓度在水稻生育前期有所增加,但在生育后期明显下降;大气CO₂浓度升高增加了稻季5、15、30、60和90 cm处土壤溶液NO₃^--N浓度,分别比对照平均提高了46.5%、36.8%、23.3%、103.7%和42.7%,在60和90 cm处差异分别达到统计上的极显著和显著水平.     

Saccharomyces cerevisiae: the effect of different forms and concentrations of iodine on uptake and yeast growth

The essentiality of iodine for humans, especially in the early stages of life, is well recognized. The chemical forms of iodine in food supplements, infant formulae and iodated salt are either iodide (KI) or iodate (KIO₃). Because there are no or rare data about iodine uptake by yeasts, we investigated the influence of different sources of iodine, as KI, KIO₃ and periodate (KIO₄), on its uptake in and growth of the model yeast Saccharomyces cerevisiae . KIO₃ inhibited the growth of the yeast the most and already at a 400 μM initial concentration in the growth medium; the OD was reduced by 23% in comparison with the control, where no KIO₃ was added. The uptake of different iodine sources by the yeast S. cerevisiae was minimal, in total <1%. Tracer experiments with radioactive ¹³¹I added as KI showed that the yeast S. cerevisiae does not have the ability to transform KI into volatile species. We investigated the specificity of iodine uptake added as KIO₃ in the presence of Na₂SeO₄ or ZnCl₂ or K₂CrO₄ in the growth medium, and it was found that chromate had the most influence on reduction of KIO₃ uptake.     

A precise potentiometric method for determination of algal activity in an open CO2 system

Abstract. The activity of the green alga Scenedesmus obliquus was studied in simplified nutrient solutions (20 mol m₋₃ NaNO₃, 20 mol m₋₃ NH₄C1, 20 mol m₋₃ NH₄NO₃, and 20 mol m₋₃ NaCl, respectively) at 25 °C. The experiments were performed under welldefined incident photon density fluxes ranging from 10 to 200 μmol m₂ s₋₁, Light-dependent changes in pH and alkalinity (A) were followed by means of a potentiometric method using a glass electrode. In the experiments, carbon dioxide with known partial pressure was bubbled through the algal suspension, and during dark periods ul intervals of 1 h, the solution was allowed to equilibrate with the gas phase. This technique was applied to calculate equilibrium values of pH and alkalinity at regular intervals during a 12-h period. Results obtained in NaNO₃, solution show a linear increase in A with time, at each level of illumination studied. After an initial drop, A also increases in NH₄NO₃, solution in a similar way to that in NaNO₃ solution. The change in A with time was also found to increase linearly with the photon density flux studied and no saturation level could be defined. In experiments in NaCl solution, no changes in A were registered while measurements in NH₄Cl solution showed a decrease in A with time.     

High pH effect on S-state turnover in chloroplasts studied by thermoluminescence. Short-time alkaline incubation reversibly inhibits S3-to-S4 transition

The influence of high pH on the functioning of the oxygen-evolving system was studied with isolated thylakoids by measuring flash oxygen yield in parallel with thermoluminescence B band which originates in the recombination between the positive charges on S₂ and S₃, the oxidized states of the water-oxidizing enzyme, and the negative charges on Q⁻_B, the semireduced form of the secondary quinone acceptor of Photosystem II. It was found that a mild alkaline incubation of thylakoids (3 min at pH = 8.8–9.1 in darkness) largely inhibits O₂ evolution, while much less the B-band amplitude. The flash-induced period-four oscillation of the B band was abolished at high pH, showing normal oscillatory response only after the 1st and 2nd flashes, but no more oscillation after the 3rd flash. These observations indicated an inhibition of S₃-to-S₄ transition by high pH and were correlated primarily with the liberation of the 33 kDa peripheral protein followed by release of functional Mn. The above phenomena were largely reversed when the pH was returned to neutral. A possible mechanism of high pH inhibition of oxygen-evolving system is discussed.     

亚适宜温光环境下不同硝铵比营养液对黄瓜幼苗生长、氮吸收和代谢的影响

以‘中农26’黄瓜为试材,研究亚适宜温光(18 ℃/10 ℃,180±20 μmol·m^-2·s^-1)下不同硝铵比(26:2、21:7和14:14)营养液对黄瓜幼苗生长和生理特性的影响.结果表明:硝铵比为21:7处理的黄瓜总根长最长、根体积和根表面积最大、根尖数最多;根中H⁺-ATPase活性最高;硝态氮转运蛋白(NRT)和铵转运蛋白(AMT)基因表达量也升高,提高了根系的氮吸收能力;叶中硝酸还原酶(NR)、谷氨酰胺合成酶(GS)和谷氨酸合酶(GOGAT)活性较高,提高了体内氮代谢能力,使黄瓜氮含量和干物质积累显著增加.亚适宜温光下,营养液中硝铵比为21:7时,黄瓜幼苗干质量分别比26:2和14:14处理增加14.0%和19.3%.亚适宜温光下,可通过调整营养液中硝铵比,提高黄瓜氮吸收与代谢能力,缓解亚适宜温光对黄瓜幼苗的不利影响,促进黄瓜生长.     

Effects of sulfate and nitrate on K+ uptake and growth of wheat and cucumber

The uptake of K⁺ ion was studied in the roots of wheat ( Triuicum aestivum L. cv. GK Szeged) and cucumber ( Cucumis sativus L. cv. Budai csemege) seedlings grown in nutrient solution under nitrogen and sulfate stress conditions. Seedlings pretreated with 1 or 10 m M NaNO₃, absorbed more K⁺ than those treated with 0.1 m M NaNO₃. However, the posteffect of NaNO₃ was considerably influenced by the Na₂SO₄, treatment. The results suggest that, at least partly, a feed-back regulation of K⁺ uptake may occur. However, due to the high Na⁺ contents of the roots, a Na⁺ effect in this process cannot be excluded. The growth and dry matter yields of the roots and shoots were strongly influenced by the SO²⁻/₄ and NO⁻/₃ supply of the plants. Appreciable differences were experienced between wheat and cucumber seedlings. The optimum SO²⁻/₄ concentration of the growth solution for maximal growth varied considerably between the species, and was also different for the roots and the shoots in a given species.     

Effects of increasing polymer hydrophobicity on distribution ratios of TcO4 in polyethylene/poly(propylene glycol)-based aqueous biphasic systems

The partitioning behavior of the pertechnetate anion was studied in aqueous biphasic systems (ABS) formed from (NH₄)₂SO₄ and four types of polymers – poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), Pluronic (a PEG/PPG block copolymer), and polyvinylpyrrolidone (PVP). Phase diagrams are reported for five (NH₄)₂SO₄-polymer ABS systems including the polymers PEG-2000, PEG-3400, PEG-12 000, Pluronic-L64 (average molecular mass ≈ 2900), and PVP-K15 (average M_r≈10 000). Distribution ratios for the TcO₄⁻ anion in each of these ABS were investigated as a function of increasing salt concentration. In addition, the water-insoluble polymer PPG-2000 was studied. Pertechnetate partitions nearly quantitatively to the polymer-rich phase in each ABS, however, distribution ratios of near one were found for the PPG system. The relative ordering of the distribution ratios is PPGPVP-2000PEG-3400>PEG-12 000, exhibiting the expected increase in phase incompatibility with increasing polymer M_r. Investigation of pertechnetate partitioning in two additional ABS based on K₃PO₄ and NaOH with Pluronic-L64 revealed trends similar to those reported for PEG-2000; the distribution ratio (D) values increase in the order NaOH<(NH₄)₂SO₄3PO₄. Despite the higher distribution ratios from Pluronic-L64 at lower concentrations than found for PEG, the limited useable range of salt concentrations available may limit the practical utilization of this polymer in ABS separations.     

Systematic synthesis, structural characterization, and reactivity studies of vanadium(V)–citrate anions [VO2(C6H6O7)]2, isolated from aqueous solutions in the presence of different cations

The aqueous chemistry of vanadium with physiologically relevant ligands constitutes a subject of burgeoning research, extending from bacterial metalloenzymic functions to human-health physiology. Vanadium, in the form of VCl₃ and V₂O_5, reacted expediently with citric acid, in a 1:2 molar ratio in water at pH4, and, in the presence of various cations, afforded crystalline materials bearing the general formula (Cat)₂[V₂O₄(C₆H₆O₇)₂]·nH₂O (A) (Cat⁺=Na⁺, NH₄ ⁺, n=2; Me₄N⁺, K⁺, n=4). Exploration of the reactivity of A toward H₂O₂ yielded the peroxo-containing complexes (Cat)₂[V₂O₂(O₂)₂(C₆H₆O₇)₂]·2H₂O (B) (Cat⁺=K⁺, NH₄ ⁺). Both classes of compounds were characterized analytically and spectroscopically. The X-ray structures of complexes A and B emphasize the exceptional stability of the dimeric rhombic unit V^V ₂O₂, which is retained upon H₂O₂ reaction, and the preserved mode of coordination of the citrate ligand as a doubly deprotonated moiety. In these complexes, typical six and eight coordination numbers were observed for the Na⁺ and K⁺ counter-ions, respectively. The variety of synthetic approaches leading to A, along with the stepwise and direct assembly and isolation of peroxo-compounds (B), denotes the significance of reaction pathways and intermediates in vanadium(III–V)–citrate synthetic chemistry. Hence, a systematic investigation of reactivity modes in aqueous vanadium–citrate systems emerges as a crucial tool for the establishment of chemical interconnectivity among low MW complex species, potentially participating in the intricate biodistribution of that metal ion in biological fluids.