Cu(II)–poly(L-arginine) complexes. Potentiometric and spectral characterization of amine and peptide nitrogen ligands

The study of Cu(II)–poly(L -arginine) complexes by potentiometric titration, as well as by optical, circular dichroism, and infrared spectra, provides information about the nature of ligands and the coordination sphere around the metal ion. Three different complexes have been identified. The first, which is formed below pH 8, contains two guanidinium nitrogens and two water molecules at the corners of the coordination square. The constant of the overall process as determined by the Gregor method equals 2.0 ± 0.1 × 10^?9. The two other complexes form between pH 8 and 10.5 and they contain two guanidinium and two peptide nitrogens as nearest ligands. One of them is a monomer and the other probably a dimer, which differ in the symmetry of the coordination sphere around the cupric ion. The optical spectra of the three complexes show an absorption band at 260 nm that we have assigned to a charge-transfer transition between a σ metal nitrogen (amine) molecular orbital and a d_x2_?y2 metal orbital. The spectra of the two complexes containing peptide nitrogens exhibit another absorption band at 320 nm, which we have assigned to a charge transfer from a π orbital of the amide group to the d_x2_?y2 metal orbital.     

Comparison of the structures and electronic properties of sodalites containing alkali metals and alkali-earth metals and their hydrates

The effects of different alkali and alkali-earth metal ions on the electronic structures and properties of sodalite M_n[AlSiO₄]₆ (M-SOD) and their hydrates M_n[AlSiO₄]₆?8H₂O (M=Li, Na, K, n = 6; M=Ca, n = 3) were studied using density functional theory method. Theoretical calculations predicted that the Al–O–Si bond angle and cation-framework oxide distance in sodalites with alkali metal cations are correlated with cell volumes. The reduced bandwidths in M-SOD (M=Li, Na and K) show that the inter-atomic orbital overlap in sodalites is weaker than those in the hydrate phases. Frontier molecular orbital analysis indicated that oxygen atoms in the frameworks and most metal ions of SOD and their corresponding hydrates exhibit high reactivity. The interactions existing in sodalites and hydrates were qualitative described. The calculated combination energies of metal ions with framework of sodalites are in the order of K⁺< Na⁺< Li⁺< Ca²⁺. This finding confirms the experimental observation for ion exchange.     

Sn‐Alloy Foil Electrode with Mechanical Prelithiation: Full‐Cell Performance up to 200 Cycles

Self‐supporting Sn foil is a promising high‐volumetric‐capacity anode for lithium ion batteries (LIBs), but it suffers from low initial Coulombic efficiency (ICE). Here, mechanical prelithiation is adopted to improve ICE, and it is found that Sn foils with coarser grains are prone to cause electrode damage. To mitigate damage and prepare thinner lithiated electrodes, 3Ag0.5Cu96.5Sn foil is used that has more refined grains (5–10 µm) instead of Sn (50–100 µm), where the abundant grain boundaries (GBs) offer more sliding systems to release stress and reduce deep fractures. Thus, the thickness of Li_x3Ag0.5Cu96.5Sn can be reduced to 50 µm, compared to 100 µm Li_xSn. When the foils contact open air, the Sn‐Li‐O(H) products are more stable than Li‐O(H), thus Li_x3Ag0.5Cu96.5Sn shows outstanding air stability. The as‐prepared 50 µm foil anode achieves stable 200 cycles in LiFePO₄//Li_x3Ag0.5Cu96.5Sn full cell (≈2.65 mAh cm^?2) and the capacity retention is 95%. Even at 5C, the capacity of Li_x3Ag0.5Cu96.5Sn is still up to ≈1.8 mAh cm^?2. The cycle life of NCM523//Li_x3Ag0.5Cu96.5Sn full cell exceeds that of NCM523//Li. Furthermore, 70 µm Li_x3Ag0.5Cu96.5Sn is used as double‐sided anode for a 3 cm × 2.8 cm pouch cell and its actual volumetric capacity density is 674 mAh cm^?3 after 50 cycles.     

The McClure and Weiss models of Fe–O2 bonding for oxyhemes, and the HbO2 + NO reaction

For the Fe–O₂(S = 0) linkages of oxyhemes, valence bond (VB) structures are re-presented for the McClure [Fe^II(S = 1) + O₂(S = 1)], Pauling–Coryell [Fe^II(S = 0) + O₂*(S = 0)], and Weiss [Fe^III(S = ½) + O₂ ^?(S = ½)] models of bonding. The VB structures for the McClure and Weiss models are of the increased-valence type, with more electrons participating in bonding than occur in their component Lewis structures. The Fe–O bond number and O–O bond order for the McClure structure are correlated with measured Fe–O and O–O bond lengths for oxymyoglobin. Back-bonding from O ₂ ^? to Fe^III of the Weiss structure gives a restricted form of the McClure structure. The McClure and Weiss increased-valence structures are used to provide VB formulations of mechanisms for the oxyhemoglobin + NO reaction. The products of these two formulations are Hb⁺ and NO₃ ^? (where Hb is hemoglobin) and Hb⁺ and OONO^?, respectively. Because Hb⁺ and NO₃ ^? are the observed products, they provide an experimental procedure for distinguishing the McClure and Weiss models. It is also shown that the same type of agreement between McClure-type theory and experiment occurs for oxycoboglobin + NO, cytochrome P450 monooxygenases, and related hydrogen atom transfer reactions. In the appendices, the results of density functional theory and multireference molecular orbital calculations for oxyhemes are related to one formulation of the increased-valence wavefunction for the McClure model, and theory is presented for the calculation of approximate weights for the Lewis structures that are components of the McClure increased-valence structure.     

One‐Step Controllable Synthesis of Catalytic Ni4Mo/MoOx/Cu Nanointerfaces for Highly Efficient Water Reduction

Currently, in addition to the electroactive non‐noble metal water‐splitting electrocatalysts, a scalable synthetic route and simple activity enhancement strategy is also urgently needed. In particular, the well‐controlled synthesis of the well‐recognized metal–metal nanointer face in a single step remains a key challenge. Here, the synthesis of Cu‐supported Ni₄Mo nanodots on MoO_x nanosheets (Ni₄Mo/MoO_x) with controllable Ni₄Mo particle size and d‐band structure is reported via a facile one‐step electrodeposition process. Density functional theory (DFT) calculations reveal that the active open‐shell effect from Ni‐3d‐band optimizes the electronic configuration. The Cu‐substrate enables the surface Ni–Mo alloy dots to be more electron‐rich, forming a local connected electron‐rich network, which boosts the charge transfer for effective binding of O‐related species and proton–electron charge exchange in the hydrogen evolution reaction. The Cu‐supported Ni₄Mo/MoO_x shows an ultralow overpotential of 16 mV at a current density of 10 mA cm^?2 in 1 m KOH, demonstrating the smallest overpotential, at loadings as low as 0.27 mg cm^?2, among all non‐noble metal catalysts reported to date. Moreover, an overpotential of 105 mV allows it to achieve a current density of 250 mA cm^?2 in 70 °C 30% KOH, a remarkable performance for alkaline hydrogen evolution with competitive potential for applications.     

Spectroscopic investigation on glutamic acid by Coulomb-attenuating and double hybrid density functional theory methods

This study deals with the identification of glutamic acid by means of quantum chemical approach. FT-IR, FT-Raman and UV–vis spectra were recorded in the region 4000–400, 4000–50 cm^? 1 and 200–600 nm, respectively. CAM-B3LYP/6-31G(d,p) and B2PLYP/6-31G(d,p) calculations were performed to obtain the optimised molecular structures, vibrational frequencies and corresponding vibrational assignment, thermodynamic properties and natural bonding orbital (NBO) analysis. The results show that the obtained optimised geometric parameters (bond lengths, bond angles and bond dihedrals) and vibrational frequencies were found to be in good agreement with the experimental results. The calculations of the electronic spectra were compared with the experimental ones. Furthermore, highest occupied molecular orbital and lowest unoccupied molecular orbital analyses and UV–vis spectral analysis were also performed to determine the energy band gaps and transition states. NBO analysis, calculated using density functional theory methods (CAM-B3LYP/6-31G(d,p) and B2PLYP/6-31G(d,p)), was induced to find inter-molecular atoms. ¹³C and ¹H NMR isotropic chemical shifts were calculated and the assignments made were compared with the ChemDraw Ultra values.     

Photovoltaic Materials and Devices Based on the Alloyed Kesterite Absorber (AgxCu1–x)2ZnSnSe4

The photovoltaic absorber Cu₂ZnSn(S_xSe_1–x)₄ (CZTSSe) has attracted interest in recent years due to the earth‐abundance of its constituents and the realization of high performance (12.6% efficiency). The open‐circuit voltage in CZTSSe devices is believed to be limited by absorber band tailing caused by the exceptionally high density of Cu/Zn antisites. By replacing Cu in CZTSSe with Ag, whose covalent radius is ≈15% larger than that of Cu and Zn, the density of I–II antisite defects is predicted to drop. The fundamental properties of the mixed Ag‐Cu kesterite compound are reported as a function of the Ag/(Ag + Cu) ratio. The extent of band tailing is shown to decrease with increasing Ag. This is verified by comparing the optical band gap extrapolated from transmission data with the position of the room‐temperature photoluminescence peak; these values converge for the pure‐Ag compound. Additionally, the pinning of the Fermi level in CZTSSe, attributed to heavy defect compensation and band tailing, is not observed in the pure‐Ag compound, offering further evidence of improved electronic structure. Finally, a device efficiency of 10.2% is reported for a device containing 10% Ag (no antireflection coating); this compares to ≈9% (avg) efficiency for the baseline pure‐Cu CZTSe.     

A Dual Role by Incorporation of Magnesium in YbZn2Sb2 Zintl Phase for Enhanced Thermoelectric Performance

1‐2‐2‐type Zintl phase compounds have promising thermoelectric properties because of their complex crystal structures and multiple valence‐band structures. In this work, a series of single phase (Yb_0.9Mg_0.1)Mg_xZn_2?xSb₂ (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) compounds are prepared by alloying YbZn₂Sb₂ with 10 at% MgZn₂Sb₂ and different amounts of YbMg₂Sb₂. The incorporation of Mg at the Yb site, as well as at the Zn site, not only leads to an effective orbital alignment confirmed by the dramatically enhanced density of states effective mass and Seebeck coefficients, but also increases the point defect scattering, contributing to a low lattice thermal conductivity ≈0.54 W m^?1 K^?1 at 773 K. Combined with the optimization of the carrier concentration by Ag doping at the Zn site, a highest ZT value ≈1.5 at 773 K is achieved in (Yb_0.9Mg_0.1)Mg_0.8Zn_1.2Ag_0.002Sb₂, which is higher than that of all the previously reported 1‐2‐2‐type Zintl phase compounds.     

Partial Purification and Characterization of Chromate Reductase of a Novel Ochrobactrum sp. Strain Cr-B4

Hexavalent chromium contamination is a serious problem due to its high toxicity and carcinogenic effects on the biological systems. The enzymatic reduction of toxic Cr(VI) to the less toxic Cr(III) is an efficient technology for detoxification of Cr(VI)-contaminated industrial effluents. In this regard, a chromate reductase enzyme from a novel Ochrobactrum sp. strain Cr-B4, having the ability to detoxify Cr(VI) contaminated sites, has been partially purified and characterized. The molecular mass of this chromate reductase was found to be 31.53 kD, with a specific activity 14.26 U/mg without any addition of electron donors. The temperature and pH optima for chromate reductase activity were 40°C and 8.0, respectively. The activation energy (E_a) for the chromate reductase was found to be 34.7 kJ/mol up to 40°C and the activation energy for its deactivation (E_d) was found to be 79.6 kJ/mol over a temperature range of 50–80°C. The frequency factor for activation of chromate reductase was found to be 566.79 s^?1, and for deactivation of chromate reductase it was found to be 265.66 × 10³ s^?1. The reductase activity of this enzyme was affected by the presence of various heavy metals and complexing agents, some of which (ethylenediamine tetraacetic acid [EDTA], mercaptoethanol, NaN₃, Pb²⁺, Ni²⁺, Zn²⁺, and Cd²⁺) inhibited the enzyme activity, while metals like Cu²⁺ and Fe³⁺ significantly enhanced the reductase activity. The enzyme followed Michaelis–Menten kinetics with K_m of 104.29 µM and a V_max of 4.64 µM/min/mg.     

PURIFICATION AND CHARACTERIZATION OF PHOSPHODIESTERASE I FROM Walterinnesia aegyptia VENOM

A phosphodiesterase I (EC 3.1.4.1; PDE-I) was purified from Walterinnesia aegyptia venom by preparative native polyacrylamide gel electrophoresis (PAGE). A single protein band was observed in analytical native PAGE and sodium dodecyl sulfate (SDS)-PAGE. PDE-I was a single-chain glycoprotein with an estimated molecular mass of 158 kD (SDS-PAGE). The enzyme was free of 5′-nucleotidase and alkaline phosphatase activities. The optimum pH and temperature were 9.0 and 60°C, respectively. The energy of activation (Ea) was 96.4, the V_max and K_m were 1.14 µM/min/mg and 1.9 × 10^?3 M, respectively, and the K_cat and K_sp were 7 s^?1 and 60 M ^?1 min^?1 respectively. Cysteine was a noncompetitive inhibitor, with K_i = 6.2 × 10^?3 M and an IC₅₀ of 2.6 mM, whereas adenosine diphosphate was a competitive inhibitor, with K_i = 0.8 × 10^?3 M and an IC₅₀ of 8.3 mM. Glutathione, o-phenanthroline, zinc, and ethylenediamine tetraacetic acid (EDTA) inhibited PDE-I activity whereas Mg²⁺ slightly potentiated the activity. PDE-I hydrolyzed thymidine-5′-monophosphate p-nitrophenyl ester most readily, whereas cyclic 3′-5′-AMP was least susceptible to hydrolysis. PDE-I was not lethal to mice at a dose of 4.0 mg/kg, ip, but had an anticoagulant effect on human plasma. These findings indicate that W. aegyptia PDE-I shares various characteristics with this enzyme from other snake venoms.     

[(B3O3H3)nM]+(n = 1, 2;M = Cu, Ag, Au): a new class of metal-cation complexes

A density functional theory (DFT) investigation into the structures and bonding characteristics of [(B₃O₃H₃)_nM]⁺(n?=?1, 2;M?=?Cu, Ag, Au) complexes was performed. DFT calculations and natural bond orbital (NBO) analyses indicate that the ΙB metal complexes of boroxine exhibit intriguing bonding characteristics, different from the typical cation–π interactions between ΙB metal-cations and benzene. The complexes of [B₃O₃H₃M]⁺ and [(B₃O₃H₃)₂?M]⁺ (M?=?Cu, Ag, and Au) favor the conformation of perfectly planar structures with the C_2v and D_2h symmetry along one of the threefold molecular axes of boroxine, respectively. Detailed natural resonance theory (NRT) and canonical molecular orbitals (CMOs) analyses show that interaction between the metal cation and the boroxine in [B₃O₃H₃M]⁺ (M?=?Cu, Ag, and Au) is mainly ionic, while the ΙB metal-cations←π donation effect is responsible for the binding site. In these complexes, boroxine serves as terminals η¹-B₃O₃H₃ with one O atom of the B₃O₃ ring. The infra-red (IR) spectra of [B₃O₃H₃M]⁺ were simulated to facilitate their future experimental characterization. The complexes all give two IR active modes at about 1,300 and 2,700 cm^?1, which are inactive in pure boroxine. Simultaneously, the B–H stretching modes of the complexes are red-shifted due to the interaction between the metal-cation and boroxine. To explore the possibility of the structural pattern developed in this work forming mesoporous materials, complexes [(B₃O₃H₃M)₆]⁶⁺ (M?=?Cu, Ag, and Au) were also studied, which appear to be unique and particular interesting: they are all true minima with D_6h symmetries and pore sizes ranging from 12.04 Å to 13.65 Å.

Biophysical and computational comparison on the binding affinity of three important nutrients to β-lactoglobulin: folic acid,ascorbic acid and vitamin K3

Small globular protein, β-lactoglobulin (βLG), which has significant affinity toward many drugs, is the most abundant whey protein in milk. In this study, the interaction of βLG with three important nutrients, ascorbic acid (ASC), folic acid (FOL), and vitamin K3 (VK3) was investigated by spectroscopic methods (UV–visible and fluorescence) along with molecular docking technique. The results of fluorescence measurements showed that studied nutrients strongly quenched βLG fluorescence in static (FOL and ACS) or static–dynamic combined quenching (VK3) mode. The values of binding constants (K_βLG-ASC ~ 4.34 × 10⁴ M^?1, K_βLG-FOL ~ 1.67 × 10⁴ M^?1and K_βLG-VK3 ~ 13.49 × 10⁴ M^?1 at 310 K) suggested that VK3 and FOL had stronger binding affinity toward βLG than ASC. Thermodynamic analysis indicated that hydrophobic interactions are the major forces in the stability of FOL–βLG complex with enthalpy- and entropy-driving mode while, hydrogen bonds and van der Waals interactions play a major role for βLG–ASC and βLG–VK3 associations. The results of 3D fluorescence FT-IR and UV–Visible measurements indicated that the binding of above nutrients to βLG may induce conformational and micro-environmental changes of protein. Also, there is a reciprocal complement between spectroscopic techniques and molecular docking modeling. The docking results indicate that the ASC, FOL, and VK3 bind to residues located in the subdomain B of βLG. Finally, this report suggests that βLG could be used as an effective carrier of above nutrients in functional foods.     

Assessment of the elastic properties of amorphous calcium silicates hydrates (I) and (II) structures by molecular dynamics simulation

Based on Hamid model of 11Å tobermorite, amorphous calcium silicates hydrates (or C-S-H) structures (Ca₄Si₆O₁₄(OH)₄?2H₂O as the C-S-H(I) and (CaO)_1.67(SiO₂)(H₂O)_1.75 as the C-S-H(II)) with the Ca/Si ratio of 0.67 and 1.7 are concerned. Then, as the representative ‘globule’ C-S-H, two amorphous C-S-H structures with the size of 5.352 × 4.434 × 4.556 nm³ during the stretch process are simulated at a certain strain rate of 10^?3 ps^?1 by LAMMPS program for molecular dynamics simulation, using ClayFF force field. The tensile stress–strain curves are obtained and analysed. Besides, elastic modulus of the ‘globule’ C-S-H is calculated to assess the elastic modulus of C-S-H phases (the low-density C-S-H – LD C-S-H – and the high-density C-S-H – HD C-S-H), where the porosity is a critical factor for explaining the relationship between ‘globule’ C-S-H at nanoscale and C-S-H phases at microscale. Results show that: (1) The C-S-H(I) structure has transformed from crystalline to amorphous during the annealing process, Young’s moduli in x, y and z directions are almost the same. Besides, the extent of aggregation and aggregation path for water molecules in the structure is different in three directions. (2) Young’s modulus of both amorphous C-S-H(I) and C-S-H(II) structures with a size of about 5 nm under strain rate of 10^?3 ps^?1 at 300 K in three directions is averaged to be equal, of which C-S-H(II) structure is about 60.95 GPa thus can be seen as the elastic modulus of the ‘globule’ C-S-H. (3) Based on the ‘globule’ C-S-H, the LD C-S-H and HD C-S-H can be assessed by using the Self-Consistent Scheme (separately 18.11 and 31.45 GPa) and using the Mori–Tanaka scheme (29.78 and 37.71 GPa), which are close to the nanoindentation experiments by Constantinides et al. (21.7 and 29.4 GPa).     

Atomic‐Scale Spacing between Copper Facets for the Electrochemical Reduction of Carbon Dioxide

Copper (Cu) offers a means for producing value‐added fuels through the electrochemical reduction of carbon dioxide (CO₂), i.e., the CO₂ reduction reaction (CO₂RR), but designing Cu catalysts with significant Faradaic efficiency to C₂₊ products remains as a great challenge. This work demonstrates that the high activity and selectivity of Cu to C₂₊ products can be achieved by atomic‐scale spacings between two facets of Cu particles. These spacings are created by lithiating CuO_x particles, removing lithium oxides formed, and electrochemically reducing CuO_x to metallic Cu. Also, the range of spacing (d_s) is confirmed via the 3D tomographs using the Cs‐corrected scanning transmission electron microscopy (3D tomo‐STEM), and the operando X‐ray absorption spectra show that oxidized Cu reduces to the metallic state during the CO₂RR. Moreover, control of d_s to 5–6 Å allows a current density exceeding that of unmodified CuO_x nanoparticles by about 12 folds and a Faradaic efficiency of ≈80% to C₂₊. Density functional theory calculations support that d_s of 5–6 Å maximizes the binding energies of CO₂ reduction intermediates and promotes C–C coupling reactions. Consequently, this study suggests that control of d_s can be used to realize the high activity and C₂₊ product selectivity for the CO₂RR.     

Karyomorphology and nuclear DNA content of sixteen Ophrys L. taxa from Turkey

Karyotypes in 16 representative taxa of the Ophrys genus are compared, based on Feulgen-stained somatic metaphase chromosomes. The karyotypes of O. omegaifera subsp. israelitica, O. ulupinara, O. lycia, O. argolica subsp. lucis, O. argolica subsp. lesbis, O. climacis and O. reinholdii subsp. reinholdii are described for the first time. Karyological analyses indicate relationships among the species with respect to their asymmetry indices. All Ophrys taxa studied were diploid with 2n = 2x = 36 chromosomes. One B chromosome has been detected among the chromosomes of O. argolica subsp. lucis. All karyotypes are symmetrical, consisting of metacentric and submetacentric chromosomes. The longest chromosomes of all the investigated specimens contain a secondary constriction. It is determined that there is a correlation between the total number of chromosomes having secondary constrictions and the evolutionary development order of the taxa. Based on nuclear DNA content, analysis was carried out by flow cytometer using propodium iodide as fluorochrome, 2C nuclear DNA content of 16 Ophrys species varying between 20.80 pg (O. argolica subsp. lucis) and 23.11 pg (O. omegaifera subsp. israelitica). Karyotype asymmetry relationships are discussed according to the bidimensional scatter plots of A₁–A₂, CV_CL–CV_CI, CV_CL–M_CA and CV_CI–M_CA.     

Molecular dynamics study of methane in water: diffusion and structure

In this study, theoretical analysis on the geometries and electronic properties of various conjugated oligomers based on thiophene (Th) or bicyclic non-classical Th units is reported. The dihedral angle, bond length, bond-length alternation, bond critical point (BCP) properties, nucleus-independent chemical shift (NICS) and Wiberg bond index (WBIs) are analysed and correlated with conduction properties. The changes of bond length, BCP properties, NICS and WBIs all show that the conjugational degree is increased systematically with main chain extension. As a result, the highest occupied molecular orbital–lowest unoccupied molecular orbital energy separation (E _g) is decreased upon chain elongation. The E _g of oligomers based on bicyclic non-classical Th unit is much lower than that of Th-based oligomers due to the narrower E _g of bicyclic non-classical Ths compared to Th, which indicates that the narrow E _g of the bicyclic non-classical Ths can be carried over to their polymers by using them as building blocks for the polymers. The band structures and density of states analysis show that the four polymers all have small band gap ( < 0.9 eV), wide highest occupied bandwidth and relatively small effective mass of hole, which indicate that those proposed polymers may be potential conductors.     

Preliminary results on the photoluminescence and optically stimulated luminescence in Cu‐doped and Ag‐doped ZnB2X4 (B = Li,Na, K: X = Cl,Br) compounds

Photoluminescence, and optically stimulated luminescence in ZnB₂X₄ (B; Li,Na,K: X; Cl,Br) compounds doped with Cu⁺ or Ag⁺ were studied. Double humped emission bands attributable to the activators were observed in all the samples. The observed photoluminescence of Cu⁺ and Ag⁺ could be identified with 3d⁹4s¹?3d¹⁰ and 4d⁹5s¹?5d¹⁰ transitions respectively. The longer wavelength band (400–500 nm range) could be attributed to the Cu⁺ or Ag⁺ ion replacing alkali ion at the octahedral alkali site whereas short wavelength band (340–400 nm range) is attributed to a Cu or Ag ion at tetrahedral zinc site. The short wavelength band was found to be intense compared with long wavelength and gave an indication that most of the Cu or Ag ions prefered a tetrahedral Zn site compared with the octahedral alkali site. All the samples exhibit optically stimulated luminescence (OSL). The sensitivity was found to be lattice dependent. The lowest sensitivity of about 1% compared with Al₂O₃:C was observed in lithium lattices whereas highest the sensitivity of about 290% was observed in the case of Cu‐doped ZnNa₂Br₄.     

Dynamical heterogeneity and anomalously dynamical slowdown in liquid alumina

Molecular dynamics simulations of liquid alumina with various temperatures ranging from 2400 to 4000 K were carried out to investigate dynamical properties. The evolution of structural AlO_x units (where x = 3–6) for different times were examined. We have also traced the time evolution of breakage and formation of AlO_x units in the cluster of 30 neighbouring AlO_x units. The simulation shows that AlO₄ units link together to form the clusters and AlO₅ units are connected to form the poly-units expanding all over the network structure. Dynamical heterogeneity in liquid alumina is caused by less mobile regions containing clusters of AlO₄ units and more mobile regions containing major AlO₅ units. The diffusivity of the aluminium atom is realised through the AlO_x ? AlO_x+1 transition. We also found that the dynamical slowdown in liquid alumina is determined by two terms: The first one relates to the frequency of AlO_x ? AlO_x+1 transitions and the second term mainly relates to the spatial arrangement of AlO_x ? AlO_x+1 transitions. The investigation reveals that the anomalously slow dynamics near the melting temperature is mainly caused by the localisation of AlO_x ? AlO_x+1 transitions.     

A Review of: “HPLC of Biological Macromolecules (Methods and Applications) K.M. Goodring F.E. Regnier,Eds Marcel Dekker,New York, 1990; hardbound, 676 pages, $150”

An ionically unbound and thermostable polyphenol oxidase (PPO) was extracted from the leaf of Musa paradisiaca. The enzyme was purified 2.54-fold with a total yield of 9.5% by ammonium sulfate precipitation followed by Sephadex G-100 gel filtration chromatography. The purified enzyme exhibited a clear single band on native polyacrylamide gel electrophoresis (PAGE) and sodium dodecyl sulfate (SDS) PAGE. It was found to be monomeric protein with molecular mass of about 40 kD. The zymographic study using crude extract as enzyme source showed a very clear band around 40 kD and a faint band at around 15 kD, which might be isozymes. The enzyme was optimally active at pH 7.0 and 50°C temperature. The enzyme was active in wide range of pH (4.0–9.0) and temperature (30–90°C). From the thermal inactivation studies in the range 60–75°C, the half-life (t_1/2) values of the enzyme ranged from 17 to 77 min. The inactivation energy (Ea) value of PPO was estimated to be 91.3 kJ mol^?1. It showed higher specificity with catechol (K_m = 8 mM) as compared to 4-methylcatechol (K_m = 10 mM). Among metal ions and reagents tested, Cu²⁺, Fe²⁺, Hg²⁺, Mn²⁺, Ni²⁺, protocatechuic acid, and ferrulic acid enhanced the enzyme activity, while K⁺, Na⁺, Co²⁺, kojic acid, ascorbic acid, ethylenediamine tetraacetic acid (EDTA), sodium azide, β-mercaptoethanol, and L-cysteine inhibited the activity of the enzyme.     

Is Ag(I) an adequate probe for Cu(I) in structural copper–metallothionein studies?

The binding abilities of silver(I) to mammalian MT 1 have been studied and compared with those of copper(I), recently reported [Bofill et al. (2001) J Biol Inorg Chem 6:408–417], with the aim of analyzing the suitability of Ag(I) as a Cu(I) probe in Cu–MT studies. The Zn/Ag replacement in recombinant mouse Zn₇–MT 1 and corresponding Zn₄-MT 1 and Zn₃-MT 1 fragments, as well as the stepwise incorporation of Ag(I) to the corresponding apo-MTs, have been followed in parallel by various spectroscopic techniques including electronic absorption (UV–vis), circular dichroism (CD) and electrospray mass spectrometry coupled to capillary zone electrophoresis (CZE-ESI-MS). A comparative analysis of the sets of data obtained in the titration of Zn₇–MT 1, Zn₄–MT 1 and Zn₃-MT 1 with AgClO₄ at pH 7.5 and 2.5 has led to the reaction pathways followed during the incorporation of silver to these proteins under these specific conditions, disclosing unprecedented stoichiometries and structural features for the species formed. Thus, the Zn/Ag replacement in Zn₇–MT 1 at pH 7.5 has revealed the subsequent formation of Ag₄Zn₅–MT, Ag₇Zn₃–MT, Ag₈Zn₃–MT, Ag₁₀Zn₂–MT, Ag₁₂Zn₁–MT, Ag_x–MT, x=14–19, whose structure consists of two additive domains only if Zn(II) remains coordinated to the protein. A second structural role for Zn(II) has been deduced from the different folding found for the Ag_x–MT species of the same stoichiometry formed at pH 7.5 or 2.5. Comparison of the binding features of Cu(I) and Ag(I) to the entire MT at pH 7.5 shows that, among all the _xZn_y–MT (0y<7) species found, only M^I₄Zn₅–MT [(Zn₄)(₄Zn₁)] and M^I₇Zn₃–MT [(₃Zn₂)(₄Zn₁)], which form during the first stages of the Zn(II)/M(I) metal replacement, show comparable 3D structures; thus, they are the only species where Ag(I) ions can be predicted to be an adequate probe for Cu(I).Electronic Supplementary Material Supplementary material is available in the online version of this article at .