A new approach to the investigation on the tonogenic groups of root cell walls

Acid-base properties of wheat, lupin, pea root cell walls were investigated. The roots of etiolated and green plants of different age were analysed by the potentiometric method. The ion exchange capacity of root cell walls (S_i) was estimated at various pH values (pH_i 2 to pH_i 12) and constant ion strength of the solution (10 mM). To analyse polysigmoid curves pH_i =f (S_i), Gregor's equation was used. It was shown that Gregor's model fits fairly well the experimental data. The total quantities of cation-exchange (S_t ^cat) and anion-exchange (S_t ^an) groups were determined in the root cell walls. It was shown that the quantity of anion exchange groups is varied through a small range (60–185 μmol/g dry wt.) in plant species tested, and that the S_t ^cat differs widely from 550 to 1300 μmol/g dry wt. For leguininous plants the quantity of acidic groups (fixed anions) is nearly twice as large as that for cereals. It was found that in seedlings as well as in plants, there are 3 cation-exchange groups and one anion-exchange group in root cell walls. The quantity of functional groups of each type (S^j) was estimated, and the corresponding values of n^j and pK_a ^j were calculated. It can be assumed that the groups with the pK_a ¹ ≈ 3.2 are amine groups, the ones with PK_a ² ≈ 5 are groups of galacturonic acid, the ones with pK_a ≈ 7.5 are the carboxyl groups of the second species, and the ones with pK_a ⁴ ≈ 40 are the phenolic groups. The values of dissociation constants (pK_a ^j) and S^j indicate that the root cell walls of wheat, lupin and pea are identical in qualitative structure of ionogenic groups but vary in the quantity of each ionogenic group. It was demonstrated that the summarized quantity of carboxyl groups (S² + S³) should be connected directly with the pH gradient in the extracellar space at the membrane surface. The gradient arises from ion-exchange reactions between cations of an outer medium and protons of the ionized carboxyl groups of the cell walls. The results suggest that, S_t ^cat and S_t ^an allow the quantitative estimation of ion exchange properties of the cell walls. The resulting parameters (S^j, pK_a ^j and n^j) allow prediction of changes in an ionic composition of a medium that bathes the cell membrane, during the first step of mineral nutrition uptake. This revised version was published online in June 2006 with corrections to the Cover Date.     

Confidence intervals for demographic projections based on products of random matrices

This work is concerned with the growth of age-structured populations whose vital rates vary stochastically in time and with the provision of confidence intervals. In this paper a model Y_{t + 1}(ω) = X_{t + 1}(ω)Y_t(ω) is considered, where Y_t is the (column) vector of the numbers of individuals in each age class at time t, X is a matrix of vital rates, and ω refers to a particular realization of the process that produces the vital rates. It is assumed that {X_i} is a stationary sequence of random matrices with nonnegative elements and that there is an integer n₀ such that any product X_{j + n0} ··· X_{j + 1}X_j has all its elements positive with probability one. Then, under mild additional conditions, strong laws of large numbers and central limit results are obtained for the logarithms of the components of Y_t. Large-sample estimators of the parameters in these limit results are derived. From these, confidence intervals on population growth and growth rates can be constructed. Various finite-sample estimators are studied numerically. The estimators are then used to study the growth of the striped bass population breeding in the Potomac River of the eastern United States.     

New amide linked dimeric 1,2,3-triazoles bearing aryloxy scaffolds as a potent antiproliferative agents and EGFR tyrosine kinase phosphorylation inhibitors

A search for potent antiproliferative agents has prompted to design and synthesize aryloxy bridged and amide linked dimeric 1,2,3-triazoles (7a–j) by using 1,3-dipolar cycloaddition reaction between 2-azido-N-phenylacetamides (4a–e) and bis(prop-2-yn-1-yloxy)benzenes (6a–b) via copper (I)-catalyzed click chemistry approach with good to excellent yields. All the newly synthesized compounds have been screened for their in vitro antiproliferative activities against two human cancer cell lines. The compounds 7d, 7e, 7h, 7i and 7j have revealed promising antiproliferative activity against human breast cancer cell line (MCF-7), whereas, the compounds 7a, 7b, 7c, 7i and 7j were observed as potent antiproliferative agents against human lung cancer cell line (A-549). The active compounds against MCF-7 have been also analysed for their mechanism of action by the enzymatic study, which shows that the compounds 7d, 7h and 7j were acts as active EGFR tyrosine kinase phosphorylation inhibitors. In support to this biological study, the molecular docking as well as in silico ADME properties of all the newly synthesized hybrids were predicted.     

Contribution of Intracellular Calcium and pH in Ischemic Uncoupling of Cardiac Gap Junction Channels Formed of Connexins 43, 40, and 45: A Critical Function of C-Terminal Domain

Ischemia is known to inhibit gap junction (GJ) mediated intercellular communication. However the detail mechanisms of this inhibition are largely unknown. In the present study, we determined the vulnerability of different cardiac GJ channels formed of connexins (Cxs) 43, 40, and 45 to simulated ischemia, by creating oxygen glucose deprived (OGD) condition. 5 minutes of OGD decreased the junctional conductance (G_j) of Cx43, Cx40 and Cx45 by 53±3%, 64±1% and 85±2% respectively. Reduction of G_j was prevented completely by restricting the change of both intracellular calcium ([Ca²⁺]_i) and pH (pH_i) with potassium phosphate buffer. Clamping of either [Ca²⁺]_i or pH_i, through BAPTA (2 mM) or HEPES (80 mM) respectively, offered partial resistance to ischemic uncoupling. Anti-calmodulin antibody attenuated the uncoupling of Cx43 and Cx45 significantly but not of Cx40. Furthermore, OGD could reduce only 26±2% of G_j in C-terminus (CT) truncated Cx43 (Cx43-Δ257). Tethering CT of Cx43 to the CT-truncated Cx40 (Cx40-Δ249), and Cx45 (Cx45-Δ272) helped to resist OGD mediated uncoupling. Moreover, CT domain played a significant role in determining the junction current density and plaque diameter. Our results suggest; OGD mediated uncoupling of GJ channels is primarily due to elevated [Ca²⁺]_i and acidic pH_i, though the latter contributes more. Among Cx43, Cx40 and Cx45, Cx43 is the most resistant to OGD while Cx45 is the most sensitive one. CT of Cx43 has major necessary elements for OGD induced uncoupling and it can complement CT of Cx40 and Cx45.     

Ion exchange properties of plant root cell walls

Acid-base properties and the swelling capacity of wheat, lupin and pea root cell walls were investigated. Roots of seedlings and green plants of different age were analysed by the potentiometric method. The ion exchange capacity (S _i) and the swelling coefficient (K ^cw) of root cell walls were estimated at various pH values (from 2 to 12) and at different ionic strength (between 0.3 and 1000 mM). To analyse the polysigmoid titration curves pH_i = f (S _i), the Gregor's equation was employed. It was shown that the Gregor's model fits well the experimental data. The total number of the cation exchange (S _t ^cat) and the anion exchange (S _t ^an) groups were determined in the root cell walls. The number of the functional group of each type (S ^j) was estimated, and the corresponding values of pK _a ^j were calculated. It was shown that for all types of cation exchangeable groups arranged in the cell wall structure the acid properties are enhanced by the increasing concentration of electrolyte. For each ionogenic group the coefficients of Helfferich's equation [pK _a ^j = f (C ^K+)] were determined. It was found that the swelling of root cell walls changes with pH, C ^K+ and strongly depends on plant species. Within the experimental pH and C ^K+ range the swelling coefficient changes as follows: lupin > pea > wheat. The obtained results show that for the plant species under investigation the differences in the swelling coefficients originate from (a) the differences in the cross-linking degrees of polymeric chains arranged in the cell wall structure, (b) the differences in the number of carboxyl groups and (c) the differences in the total number of functional groups. Based on the estimated swelling coefficients in water it could be inferred that for wheat the cross-linking degree of the polymeric chains in the root cell walls is higher than those for lupin or pea. It has been emphasized that the calculated parameters (S ^j, pK _a ^j, K ^cw), the equation {pK _a ^j = f (C^K+)} and the dependencies {K ^cw = f (C^K+, pH)} allow to estimate quantitatively the changes in the ion exchange capacity of the root cell walls in response to the changes in an ionic composition of an outer solution. The results of these estimations allow to suggest that (a) the root apoplast is a compartment where the accumulation of cations takes place during the first stage of cation uptake from an outer medium, and (b) the accumulation degree is defined by pH and ionic composition of an outer solution. On the basis of the literature review and the results of the present experimental study it was proposed that the changes in the cell wall swelling in response to variances of environmental or experimental conditions could lead to a change of the water flow through a root apoplast. It has been supported that there is direct relationship between the swelling of root cell walls and the water flow within the plant root apoplast.     

Distributivity and processivity in multisite phosphorylation can be distinguished through steady-state invariants

Multisite protein phosphorylation and dephosphorylation are key cellular regulatory mechanisms but their system properties have been difficult to study in vivo and in vitro. Here we show by mathematical analysis that steady-state invariants enable the mechanism of the kinase or the phosphatase to be determined from steady-state measurements. Invariants exist when both enzymes act distributively (i.e., nonprocessively), making at most one modification in each molecular encounter. For instance, in the sequential case, in any experiment involving the same ingredients, the quantity [S_i−1][S_i+1]/[S_i]² always has the same value, where [S_i] denotes the steady-state concentration of the i-th phospho-form. For a two-site substrate, if either enzyme exhibits processivity, so that more than one modification can be made in each molecular encounter, the degree of processivity can be estimated from changes in this invariant. We discuss the experimental and theoretical challenges in extending these results.     

Interspecific competition among metapopulations with space-limited subpopulations

A model of the dynamics of a single metapopulation with space-limited subpopulations (J. Roughgarden and Y. Iwasa, 1986, Theor. Pop. Biol. 29, 235–261) is extended to include interspecific competition for space. The location and stability of steady states for the regional competition community are analyzed; a necessary condition for stable regional coexisitence of many species, and the condition for successful invasion of a new species into a region, are derived. General results are (1) the number of species that can coexist in a regional competition community is less than or equal to the number of distinct types of local habitats in the region and (2) for any pair of species coexisting in a regional community, say species-i and species-j, there is at least one place where species-i has a higher productivity relative to its larval mortality rate than species-j, and at least one place where species-j has a higher productivity relative to its larval mortality rate than species-i. A regional competition community consisting of two species competing for the space in two local habitats is analyzed using a graphical classification. If both local habitats are net “sources” of larvae for the regional populations of both species, then the qualitative results of interspecific competition on a regional scale are the same as those of the classical two-species Lotka-Volterra competition equations. If one of the local habitats is a net “sink” for larvae of one or more of the metapopulations, then additional results are possible: (1) The existence of a species may require the presence of its competitor. (2) A species which cannot invade an empty regional community may be able to invade if another species is present, and may then displace the first species leaving a regional community that again has one species. (3) A second species may invade a regional community containing one species with the end result that both become extinct.     

Fixation probabilities and effective population numbers in diploid populations with overlapping generations

A finite diploid population, observed at times t = 0, 1, 2,…, is studied. An individual is said to be in age group i at time t if its age is between i and i + 1 units at that time, where i ? 1. It is assumed that the number of individuals in a particular age-sex class is the same for every t and that the probability that a male offspring was produced by a mating of a male in age group i and a female in age group j is p_ij^m (with a corresponding probability p^f_ij for a female offspring), regardless of when the individual is born. The probability of ultimate fixation of an allele A₁ and the inbreeding effective number, for large populations, is calculated under the further assumptions that A₁ is neutral and that mating is random, given the ages of the mates.     

Structure and magnetic properties of a tetranuclear Cu4O4 open-cubane in [Cu(L)]4·4H2O with L = (E)-N′-(2-oxy-3-methoxybenzylidene)benzohydrazide

The in-situ formed hydrazone Schiff base ligand (E)-N′-(2-oxy-3-methoxybenzylidene)benzohydrazide (L²⁻) reacts with copper(II) acetate to a tetranuclear open cubane [Cu(L)]₄ complex which crystallizes as two symmetry-independent (Z′ = 2) S₄-symmetrical molecules in different twofold special positions with a homodromic water tetramer. The two independent (A and B) open- or pseudo-cubanes with Cu₄O₄ cores of 4 + 2 class (Ruiz classification) each have three different magnetic exchange pathways leading to an overall antiferromagnetic coupling with J_1B = J_2B = −17.2 cm⁻¹, J_1A = −36.7 cm⁻¹, J_2A = −159 cm⁻¹, J_3A = J_3B = 33.5 cm⁻¹, g = 2.40 and ρ = 0.0687. The magnetic properties have been analysed using the H = −Σ_i,jJ_ij(S_iS_j) spin Hamiltonian.     

Design,synthesis and in vitro anti-tuberculosis activity of benzo[6,7]cyclohepta[1,2-b]pyridine-1,2,3-triazole derivatives

A series of novel benzo[6,7]cyclohepta[1,2-b]pyridine-1,2,3-triazole hybrids (7a–j & 8a–j) have been designed and synthesized in excellent yields by Huisgen’s [3+2] cyclo addition reaction of 3-(azidomethyl)-2-methyl-6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-b]pyridine (5) with various alkynes 6 in presence of copper sulphate and sodium ascorbate and their structures were confirmed by IR, ¹H NMR, ¹³C NMR and HRMS. The newly synthesized compounds 7a–j & 8a–j were evaluated for their in vitro anti-mycobacterial activity against Mycobacterium tuberculosis H37Rv (ATCC 27294). Among the compounds tested, the compounds 7i and 8g displayed most potent activity with MIC value of 1.56?µg/mL with low cytotoxicity.     

Dependence of the energy lifetime on the type of anomalous losses in stellarators

A relatively simple model of transport process in stellarators that was proposed earlier by the author on the basis of neoclassical theory makes it possible to determine the density and temperature profiles of the plasma components, the ambipolar electric field profile, and the particle and energy lifetimes from the given device parameters and given particle and energy sources with allowance for anomalous losses. The results of numerical simulations carried out with this model for the L-2M, ATF, CHS, and LHD stellarators over broad ranges of plasma densities and absorbed powers showed that the plasma energy lifetimes in these devices coincide to within factors on the order of two with those found from empirical scalings. A specific model of anomalous losses was chosen for calculations. Results are presented from simulations with a more general form of the anomalous thermal conductivity. Namely, the thermal conductivity is chosen to be K _j ^(a) ≈ N ^α T _j ^β B ₀ ^?γ , where N(r) is the plasma density and T _j (r) is the temperature of the jth plasma component (j = e, i). The parameters α, β, and γ are set equal to α = 1, β = 2, and γ = 1; α = 0.5, β = 2.5, and γ = 1; α = 1.5, β = 2, and γ = 2; α = 1, β = 2.5, and γ = 2; and α = 1.5, β = 2.5, and γ = 2. The simulations have been done for the L-2M and LHD stellarators. It is found that, in all the five models, the calculated energy lifetimes τ _c are essentially independent of the functional form of the anomalous thermal conductivity and coincide to within a factor on the order of two with those following from the LHD scaling.     

Kinetic Theory Model for Ion Movement through Biological Membranes: II. Interionic Selectivity

The equation presented in the previous paper for steady-state membrane ionic current as a function of externally applied electric field strength is numerically analyzed to determine the influence of ionic and membrane molecule parameters on current densities. The model displays selectivity between different ions. A selectivity coefficient S_i, defined as the ratio of current carried by an ionic species i at a given field strength to the current carried by a reference species at the same field strength, has the following properties: (a) S_i is a function of electric field strength except for ion-membrane molecule interactions yielding velocity independent collision frequencies; (b) for ion-membrane molecule interactions characterized by a collision frequency that is a decreasing (increasing) function of increasing ionic velocity, ions whose S_i > 1 (<1) at zero field strength will show maxima (minima) (minima[maxima]) in their S_i vs. electric field strength curves.     

THE KINETICS OF PENETRATION : I. EQUATIONS FOR THE ENTRANCE OF ELECTROLYTES

When the only solute present is a weak acid, HA, which penetrates as molecules only into a living cell according to a curve of the first order and eventually reaches a true equilibrium we may regard the rate of increase of molecules inside as See PDF for Equation where P_M is the permeability of the protoplasm to molecules, M_o, denotes the external and M_i the internal concentration of molecules, A_i denotes the internal concentration of the anion A^- and See PDF for Equation (It is assumed that the activity coefficients equal 1.) Putting P_MF_M = V_M, the apparent velocity constant of the process, we have See PDF for Equation where e denotes the concentration at equilibrium. Then See PDF for Equation where t is time. The corresponding equation when ions alone enter is See PDF for Equation. where K is the dissociation constant of HA, P_A is the permeability of the protoplasm to the ion pair H⁺ + A^-, and A_ie denotes the internal concentration of A_i at equilibrium. Putting P_AKF_M = V_A, the apparent velocity constant of the process, we have See PDF for Equation and See PDF for Equation When both ions and molecules of HA enter together we have See PDF for Equation where S_i = M_i + A_i and S_ie is the value of S_i at equilibrium. Then See PDF for Equation V_M, V_A, and V_MA depend on F_M and hence on the internal pH value but are independent of the external pH value except as it affects the internal pH value. When the ion pair Na⁺ + A^- penetrates and Na_i = BA_i, we have See PDF for Equation and See PDF for Equation where P _NaA is the permeability of the protoplasm to the ion pair Na⁺ + A^-, Na_o and Na_i are the external and internal concentrations of Na⁺, See PDF for Equation, and V _Na is the apparent velocity constant of the process. Equations are also given for the penetration of: (1) molecules of HA and the ion pair Na⁺ + A^-, (2) the ion pairs H⁺ + A^- and Na⁺ + A^-, (3) molecules of HA and the ion pairs Na⁺ + A^- and H⁺ + A^-. (4) The penetration of molecules of HA together with those of a weak base ZOH. (5) Exchange of ions of the same sign. When a weak electrolyte HA is the only solute present we cannot decide whether molecules alone or molecules and ions enter by comparing the velocity constants at different pH values, since in both cases they will behave alike, remaining constant if F_M is constant and falling off with increase of external pH value if F_M falls off. But if a salt (e.g., NaA) is the only substance penetrating the velocity constant will increase with increase of external pH value: if molecules of HA and the ions of a salt NaA. penetrate together the velocity constant may increase or decrease while the internal pH value rises. The initial rate See PDF for Equation (i.e., the rate when M_i = 0 and A_i = 0) falls off with increase of external pH value if HA alone is present and penetrates as molecules or as ions (or in both forms). But if a salt (e.g., NaA) penetrates the initial rate may in some cases decrease and then increase as the external pH value increases. At equilibrium the value of M_i equals that of M_o (no matter whether molecules alone penetrate, or ions alone, or both together). If the total external concentration (S_o = M_o + A_o) be kept constant a decrease in the external pH value will increase the value of M_o and make a corresponding increase in the rate of entrance and in the value at equilibrium no matter whether molecules alone penetrate, or ions alone, or both together. What is here said of weak acids holds with suitable modifications for weak bases and for amphoteric electrolytes and may also be applied to strong electrolytes.     

Uncertainty in partner recognition and the tail-up display in a monogamous butterflyfish

Many monogamous birds and fish perform displays towards mates that are either identical or very similar to threat displays. Uncertainty in partner recognition may be a key to explaining this behaviour in the monogamous butterflyfishChaetodon lunulatus . From a causal perspective, when partner recognition is uncertain, the butterflyfish may follow the same decision rules as in territorial interactions with nonpartners. From this hypothesis, I derived three predictions of the frequencies of social behaviours, that is, solo displays, mutual displays, attacks and rejoinings. If the frequencies areS , M, A and R, respectively, the predictions are that (1) M/ (M+A) andM/ (M+S) should be higher in rejoining situations than in a pair-swimming situation; (2) (M+S)/R and (M+A) /R should increase with the duration of separation; and (3) M/ (M+A) should be larger than M/ (M+S). To test the predictions, I made field observations. The results supported all of these predictions. Therefore, I suggest that uncertainty of partner recognition causes the butterflyfish to perform the tail-up display, which is usually used in territorial interactions, towards the partner. From a functional perspective, this hypothesis implies that the display serves to reduce the risk of failure to recognize a partner, which could result in an attack. The display causes the conspecific to hesitate before attacking, providing sufficient time for partner recognition. Field data indicated that more than 70% of dangerous attacks were prevented by a tail-up display.     

Estimation of Fitness Components in DROSOPHILA MELANOGASTER . I. Heterozygote Viability Indices

We examine the assumption of "dominance" with regard to viability of the Cy and Pm marker chromosomes in D. melanogaster . This assumption is often invoked for the extraction of wild-type second chromosomes from natural populations and for the calculation of relative viability indices. Significant genotypic variances for viability are found among both Cy/+_j and Pm/+_i heterozygotes in California and Japanese populations. The magnitude of the Pm/+ _i genotypic variance is substantially less than that of the Cy/+_j heterozygotes (less than one half). Significant reciprocal effects are also found to influence Cy/+_j, Pm/+_i and +_i/+_j viabilities. We conclude that viability indices of heterozygotes based on the Curly method are biased. We suggest that viability indices in the future be expressed relative to the viability of the Cy/Pm genotype (Curly-Plum method) or possibly that of the Pm/+_i genotype (Plum method).     

Gondolelloid multielement conodont apparatus (Scythogondolella) from the Lower Triassic of Jiangsu,East China,revealed by high-resolution X-ray microtomography

The application of high-resolution X-ray microtomography on conodont natural assemblages has provided new information on the structure of the elements and enabled the three-dimensional reconstruction of apparatuses. We herein report four conodont natural assemblages from uppermost Lower Qinglong Formation, Longtan, Nanjing, East China. Using X-ray microtomography, we reconstructed the apparatus of the end-Smithian (Olenekian, Early Trassic) Scythogondolella milleri. Our result confirms that Scythogondolella has an octomembrate apparatus composed of 15 elements (a single S₀ element, two pairs of S_1–4, M and P_1–2 elements) like other gondolelloid apparatuses that have been tested by their corresponding natural assemblages, including Neogondolella, Novispathodus and Nicoraella. Element morphology of Scythogondolella closely resembles that of Neogondolella apparatus from the Illyrian (Anisian, Middle Triassic) of Monte San Giorgio: an alate (hibbardellan) S₀ element with two long lateral processes that meet at a denticle anterior of the cusp, a bipennate (hindeodellan) S₃ element with a bifurcated anterior process branching from the third denticle anterior of the cusp and an enantiognathiform S₂ element with two dissimilar processes of nearly equal in length. It differs from the latter in the length of the inner-lateral process of M element and the posterior process of S₀ and S_3–4 elements without considering the obvious morphological differences in P elements between them. The element positional homologues of Scythogondolella conforms to those of the standard 15-element plan shared primitively among ozarkodinin, prioniodinin and prioniodontid conodonts, and again confirms that the breviform digyrate elements of cypridodellan and enantiognathiform morphotypes occupy the S₁ and S₂ positions, respectively, within the superfamily Gondolelloidea.     

A family of titanium (IV) alkoxo complexes with N,O and O,O chelating ligands. Crystal structure of [Ti(O-i-Pr)2{2-(−)-menthoxo-pyridine}2]

In view of the wide applicability and versatility of titanium based Lewis acids in selective organic synthesis including asymmetric synthesis, we have synthesized a family of mono and polyatomic titanium derivatives. The polymetallic complexes prepared are bridged by pyridimine, quinone and triazine based ligands. The synthesis of [{Ti(O-i-Pr)₃(Oddbf)}₂] (1), [Ti(O-i-Pr)₂(Oddbf)₂] (2), [{Ti(O-i-Pr)₂(Oddbf)(OMent)}₂] (3) (ddbfO = 2,3-dihydro-2,2-dimethyl-benzofuranoxo; MentO = (1R,2S,5R)-(−)-menthoxo), [{Ti(O-i-Pr)₃(OMenpy)}₂] (4), [Ti(O-i-Pr)₂(OMenpy)₂] (5) (MenpyO = (1S,2S,5R)-(−)-menthoxo-pyridine); [{(Ti(OR)₃)₂L}_n] (RO = isopropoxo, (1R,2S,5R)-(−)-menthoxo) (6-11) and [{(Ti(O-i-Pr)₃)₃L}_n] (12) was accomplished from a Lewis acid such as Ti(O-i-Pr)₄, [{Ti(O-i-Pr)₃(OMent)}₂] or [Ti(OMent)₄] and chelating ligands (ddbfOH = 2,3-dihydro-2,2-dimethyl-benzofuranol; MenpyOH = (1R,2S,5R)-(−)-5-methyl-2-isopropyl-1-(2′-pyridinyl)cyclohexan-1-ol; LH₂ = 4,6-dihydroxy-2,5-diphenyl-pyrimidine, 2,4-dihydroxy-5,6-dimethyl-pyrimidine, 5,8-dihydroxy-1,4-napthoquinone, 2,5-dihydroxy-1,4-benzoquinone and LH₃ = cyanuric acid) that provide a rigid framework for the metal centre. The molecular structure of 5 has been determined by single crystal X-ray diffraction studies.