Removal of Cr(VI) from Wastewater Using Graphene Oxide Chitosan Microspheres Modified with α–FeO(OH)

Graphene oxide and chitosan microspheres modified with α–FeO(OH) (α–FeO(OH)/GOCS) are prepared and utilized to investigate the performance and mechanism for Cr(VI) removal from aqueous solutions and the possibility of Fe secondary pollution. Batch experiments were carried out to identify the effects of pH, mass, and volume ratio (m/v), coexisting ions, time (t), temperature (T), and Cr(VI) initial concentration (C₀) on Cr(VI) removal, and to evaluate adsorption kinetics, equilibrium isotherm, and thermodynamics, as well as the possibility of Fe secondary pollution. The results showed that Cr(VI) adsorption increased with C₀, t, and T but decreased with increasing pH and m/v. Coexisting ions inhibited Cr(VI) adsorption, and this inhibition increased with increasing concentration. The influence degrees of anions and cations on the Cr(VI) adsorption in descending order were SO₄²⁻ > PO₄²⁻ > NO₃⁻ > Cl⁻ and Ca²⁺ > Mg²⁺ > Mn²⁺, respectively. The equilibrium adsorption capacity of Cr(VI) was the highest at 24.16 mg/g, and the removal rate was 97.69% under pH = 3, m/v = 1.0 g/L, T = 298.15 K, and C₀ = 25 mg/L. Cr(VI) adsorption was well fitted to a pseudo-second-order kinetic model and was spontaneous and endothermic. The best fit of Cr(VI) adsorption with the Langmuir and Sips models indicated that it was a monolayer and heterogeneous adsorption. The fitted maximum adsorption capacity was 63.19 mg/g using the Sips model under 308.15 K. Cr(VI) removal mainly included electrostatic attraction between Cr(VI) oxyanions with surface Fe–OH₂⁺, and the adsorbed Cr(VI) was partially reduced to Cr(III) and then precipitated on the surface. In addition, there was no Fe secondary pollution during Cr(VI) adsorption.     

K(pin)-Torsors and the Interpretation of "Triple" Cohomology

A categorical, semi-simplicial interpretation theory for “triple” cohomology is outlined which uses the groups TORS_Uⁿ[X;π] of connected components of certain categories of K(π,n)-torsors (higher dimensional generalizations of locally trivial principal fiber bundles) to interpret the cohomology groups, i.e., TORS_Uⁿ[X;π] [unk] Hⁿ(X;π), n ≥ 1.     

Humidity-Sensing Properties of an 1D Antiferromagnetic Oxalate-Bridged Coordination Polymer of Iron(III) and Its Temperature-Induced Structural Flexibility

A novel one-dimensional (1D) oxalate-bridged coordination polymer of iron(III), {[NH(CH₃)(C₂H₅)₂][FeCl₂(C₂O₄)]}_n (1), exhibits remarkable humidity-sensing properties and very high proton conductivity at room temperature (2.70 × 10⁻⁴ (Ω·cm)⁻¹ at 298 K under 93% relative humidity), in addition to the independent antiferromagnetic spin chains of iron(III) ions bridged by oxalate groups (J = −7.58(9) cm⁻¹). Moreover, the time-dependent measurements show that 1 could maintain a stable proton conductivity for at least 12 h. Charge transport and magnetic properties were investigated by impedance spectroscopy and magnetization measurements, respectively. Compound 1 consists of infinite anionic zig-zag chains [FeCl₂(C₂O₄)]_nⁿ⁻ and interposed diethylmethylammonium cations (C₂H₅)₂(CH₃)NH⁺, which act as hydrogen bond donors toward carbonyl oxygen atoms. Extraordinarily, the studied coordination polymer exhibits two reversible phase transitions: from the high-temperature phase HT to the mid-temperature phase MT at T ~213 K and from the mid-temperature phase MT to the low-temperature phase LT at T ~120 K, as revealed by in situ powder and single-crystal X-ray diffraction. All three polymorphs show large linear thermal expansion coefficients.     

Conformation of cyclo(Gly-L-Pro-L-Pro-Gly-L-Pro-L-Pro)(2)Mg complex crystallized from CH(3)CN solution

The cyclic hexapeptides (Gly-L-Pro-L-Pro-Gly-L-Pro-L-Pro) in the (peptide—Mg—peptide)²⁺ complex have nearly identical asymmetric conformations. Each has two cis Pro-Pro linkages and lacks any intraring hydrogen bonds. The Mg²⁺ ion forms six ligands in a regular octahedral array with the carbonyl oxygen atoms of the two Gly residues and one Pro residue of each peptide. The “sandwich” complex has an approximate 2-fold rotation axis through the Mg²⁺ relating the two peptide moieties. Cyclo(Gly-Pro-Pro-Gly-Pro-Pro)₂Mg(ClO₄)₂· 4C²H₃CN crystallizes in space group P3₁ with a = b = 15.744(4) Å, c = 24.002(6) Å, γ = 120°, and Z = 3. A highlight of the structure determination is the ready location of the Mg self-vector in a Harker section and the development of the entire structure by use of the tangent formula starting with the known position of the Mg atom.     

Structural effects in solvolytic reactions; carbon-13 NMR studies of carbocations: Effect of increasing electron demand on the carbon-13 NMR shifts in substituted tert-cumyl and 1-aryl-1-cyclopentyl carbocations-correlation of the data by a new set of substituent constants, sigma

The cationic carbon substituent chemical shifts (ΔδC⁺) for nine representative meta-substituted tert-cumyl carbocations are correlated satisfactorily by the σ_m⁺ substituent constants (slope ρ+ = -18.18, correlation coefficient r = 0.990). However, the substituent chemical shifts (ΔδC⁺) for the corresponding para derivatives are not correlated by the σ_p⁺ substituent constants. The possibility of developing a set of substituent constants capable of correlating such ¹³C NMR shifts was examined. The slope of the line defined by the meta substituents (ρ+ = -18.18) was utilized to calculate σ^C+ constants for both meta and para substituents. The utility of these constants was then tested by their ability to correlate the ¹³C NMR shifts in the cations for a different system, the 1-aryl-1-cyclopentyl cations. Indeed, these σ^C+ values correlate very well with the ΔδC⁺ values, yielding ρ^C+ = -16.84, r = 0.999.     

GABA(A)-current rundown of temporal lobe epilepsy is associated with repetitive activation of GABA(A) "phasic" receptors

A study was made of the “rundown” of GABA_A receptors, microtransplanted to Xenopus oocytes from surgically resected brain tissues of patients afflicted with drug-resistant human mesial temporal lobe epilepsy (mTLE). Cell membranes, isolated from mTLE neocortex specimens, were injected into frog oocytes that rapidly incorporated functional GABA_A receptors. Upon repetitive activation with GABA (1 mM), “epileptic” GABA_A receptors exhibited a GABA_A-current (I_GABA) rundown that was significantly enhanced by Zn²⁺ (≤250 μM), and practically abolished by the high-affinity GABA_A receptor inverse agonist SR95531 (gabazine; 2.5–25 μM). Conversely, I_GABA generated by “control” GABA_A receptors microtransplanted from nonepileptic temporal lobe, lesional TLE, or authoptic disease-free tissues remained stable during repetitive stimulation, even in oocytes treated with Zn²⁺. We conclude that rundown of mTLE epileptic receptors depends on the presence of “phasic GABA_A receptors” that have low sensitivity to antagonism by Zn²⁺. Additionally, we found that GABA_A receptors, microtransplanted from the cerebral cortex of adult rats exhibiting recurrent seizures, caused by pilocarpine-induced status epilepticus, showed greater rundown than control tissue, an event also occurring in patch-clamped rat pyramidal neurons. Rundown of epileptic rat receptors resembled that of human mTLE receptors, being enhanced by Zn²⁺ (40 μM) and sensitive to the antiepileptic agent levetiracetam, the neurotrophin brain-derived neurotrophic factor, and the phosphatase blocker okadaic acid. Our findings point to the rundown of GABA_A receptors as a hallmark of TLE and suggest that modulating tonic and phasic mTLE GABA_A receptor activity may represent a useful therapeutic approach to the disease.     

Study on Concrete Deterioration in Different NaCl-Na2SO4 Solutions and the Mechanism of Cl− Diffusion

The diffusion of sulfate (SO₄²⁻) and chloride (Cl⁻) ions from rivers, salt lakes and saline soil into reinforced concrete is one of the main factors that contributes to the corrosion of steel reinforcing bars, thus reducing their mechanical properties. This work experimentally investigated the corrosion process involving various concentrations of NaCl-Na₂SO₄ leading to the coupled erosion of concrete. The appearance, weight, and mechanical properties of the concrete were measured throughout the erosion process, and the Cl⁻ and SO₄²⁻ contents in concrete were determined using Cl⁻ rapid testing and spectrophotometry, respectively. Scanning electron microscopy, energy spectrometry, X-ray diffractometry, and mercury porosimetry were also employed to analyze microstructural changes and complex mineral combinations in these samples. The results showed that with higher Na₂SO₄ concentration and longer exposure time, the mass, compressive strength, and relative dynamic elastic modulus gradually increased and large pores gradually transitioned to medium and small pores. When the Na₂SO₄ mass fraction in the salt solution was ≥10 wt%, there was a downward trend in the mechanical properties after exposure for a certain period of time. The Cl⁻ diffusion rate was thus related to Na₂SO₄ concentration. When the Na₂SO₄ mass fraction in solution was ≤5 wt% and exposure time short, SO₄²⁻ and cement hydration/corrosion products hindered Cl⁻ migration. In a concentrated Na₂SO₄ environment (≥10 wt%), the Cl⁻ diffusion rate was accelerated in the later stages of exposure. These experiments further revealed that the Cl⁻ migration rate was higher than that of SO₄²⁻.     

Magnetic and Electrical Behaviors of the Homo- and Heterometallic 1D and 3D Coordination Polymers Based on the Partial Decomposition of the [Cr(C2O4)3]3− Building Block

One-dimensional (1D) oxalate-bridged homometallic {[Mn(bpy)(C₂O₄)]·1.5H₂O}_n (1) (bpy = 2,2’-bipyridine) and heterodimetallic {[CrCu₃(bpy)₃(CH₃OH)(H₂O)(C₂O₄)₄][Cu(bpy)Cr(C₂O₄)₃]·CH₂Cl₂·CH₃OH·H₂O}_n (2) coordination polymers, as well as the three-dimensional (3D) heterotrimetallic {[CaCr₂Cu₂(phen)₄(C₂O₄)₆]·4CH₃CN·2H₂O}_n (3) (1,10-phenanthroline) network, have been synthesized by a building block approach using a layering technique, and characterized by single-crystal X-ray diffraction, infrared (IR) and impedance spectroscopies and magnetization measurements. During the crystallization process partial decomposition of the tris(oxalato)chromate(III) happened and 1D polymers 1 and 2 were formed. The antiferromagnetic interactions between the manganese(II) ions were mediated by oxalate ligands in the chain [Mn(bpy)(C₂O₄)]_n of 1, with intra-chain super-exchange interaction 𝐽 = (−3.134 ± 0.004) K; magnetic interaction between neighbouring chains is negligible making this system closer than other known Mn-chains to the ideal 1D Heisenberg antiferromagnet. Compound 2 comprises a 1D coordination anion [Cu(bpy)Cr(C₂O₄)₃]_nⁿ⁻ (Cr2–Cu4) with alternating [Cr(C₂O₄)₃]³⁻ and [Cu(bpy)]²⁺ units mutually bridged through the oxalate group. Another chain (Cr1–Cu3) is similar, but involves a homodinuclear unit [Cu(bpy)(H₂O)(µ-C₂O₄)Cu(bpy)(CH₃OH)]²⁺ (Cu1–Cu2) coordinated as a pendant group to a terminal oxalate oxygen. Magnetic measurements showed that the Cu1−Cu2 cationic unit is a strongly coupled antiferromagnetic dimer, independent from the other magnetic ions within ferromagnetic chains Cr1–Cu3 and Cr2–Cu4. A 3D polymer {[CaCr₂Cu₂(phen)₄(C₂O₄)₆]·4CH₃CN·2H₂O}_n (3) comprising three different metal centers (Ca²⁺, Cr³⁺ and Cu²⁺) oxalate-bridged, contains Ca²⁺ atoms as nodes connected with four Cr³⁺ atoms through oxalate ligands. The network thus formed can be reduced to an underlying graph of diamondoid (dia) or (6⁶) topology. Magnetization of 3 shows the ferromagnetic oxalate-bridged dimers [Cu^IICr^III], whose mutual interaction could possibly originate through the spin polarization of Ca²⁺ orbitals. Compounds 1 and 3 exhibit lower electrical conductivity at room temperature (RT) in comparison to compound 2.     

Metal ions control product specificity of isoprenyl diphosphate synthases in the insect terpenoid pathway

Isoprenyl diphosphate synthases (IDSs) produce the ubiquitous branched-chain diphosphates of different lengths that are precursors of all major classes of terpenes. Typically, individual short-chain IDSs (scIDSs) make the C₁₀, C₁₅, and C₂₀ isoprenyl diphosphates separately. Here, we report that the product length synthesized by a single scIDS shifts depending on the divalent metal cofactor present. This previously undescribed mechanism of carbon chain-length determination was discovered for a scIDS from juvenile horseradish leaf beetles, Phaedon cochleariae. The recombinant enzyme P. cochleariae isoprenyl diphosphate synthase 1 (PcIDS1) yields 96% C₁₀-geranyl diphosphate (GDP) and only 4% C₁₅-farnesyl diphosphate (FDP) in the presence of Co²⁺ or Mn²⁺ as a cofactor, whereas it yields only 18% C₁₀ GDP but 82% C₁₅ FDP in the presence of Mg²⁺. In reaction with Co²⁺, PcIDS1 has a K_m of 11.6 μM for dimethylallyl diphosphate as a cosubstrate and 24.3 μM for GDP. However, with Mg²⁺, PcIDS1 has a K_m of 1.18 μM for GDP, suggesting that this substrate is favored by the enzyme under such conditions. RNAi targeting PcIDS1 revealed the participation of this enzyme in the de novo synthesis of defensive monoterpenoids in the beetle larvae. As an FDP synthase, PcIDS1 could be associated with the formation of sesquiterpenes, such as juvenile hormones. Detection of Co²⁺, Mn²⁺, or Mg²⁺ in the beetle larvae suggests flux control into C₁₀ vs. C₁₅ isoprenoids could be accomplished by these ions in vivo. The dependence of product chain length of scIDSs on metal cofactor identity introduces an additional regulation for these branch point enzymes of terpene metabolism.     

Mechanism(s) of Chloride Transport in Human Distal Colonic Apical Membrane Vesicles

Previous studies from our laboratory have demonstrated the presence of an electroneutral Cl^–/HCO₃ ^– exchange process across the human proximal colonic apical membrane vesicles (AMV). However, very little is known about the mechanism(s) of chloride transport in the apical membrane of the human distal colon. Utilizing AMV purified from organ donor distal colonic mucosa and a rapid Millipore filtration technique, the mechanisms of ³⁶Cl^– uptake into these vesicles were examined. Outwardly directed OH^– and HCO₃ ^– gradients markedly increased the uptake of ³⁶Cl^– into these vesicles, demonstrating a transient accumulation over the equilibrium uptake. Voltage clamping in the presence of K⁺/valinomycin reduced the OH^– and HCO₃ ^– gradient-stimulated ³⁶Cl^– uptake into these vesicles by 30% indicating that the conductive Cl^– uptake pathway was present in these vesicles along with the electroneutral exchange process. Under voltage-clamped conditions, the inhibitors the bicarbonate transporters, DIDS and SITS (1 mM), inhibited OH^– and HCO₃ ^– gradient-stimulated ³⁶Cl^– uptake by 50%. Acetazolamide showed small but significant inhibition of chloride uptake. Amiloride, bumetanide, and furosemide failed to inhibit ³⁶Cl^– uptake. Chloride uptake into these vesicles exhibited saturation kinetics with an apparent K _m for chloride of 16.7 mM and a V _max of 5.9 nmol/mg/15 sec. Chloride, acetate, nitrate, but not sulfate (50 mM each), inhibited 5 mM ³⁶Cl^– uptake. Inwardly directed gradients of Na⁺, K⁺ or both together did not stimulate chloride uptake into these vesicles indicating that the uptake of Cl^– and Na⁺ in human distal colonic AMV does not involve Na-Cl or Na-K-2Cl cotransport. In conclusion, these studies demonstrate that Cl^– transport across the apical membranes of human distal colon involves both conductive pathway and electroneutral Cl^–/HCO₃ ^– (OH^–) exchange processes. In view of our previous demonstration of a Na⁺/H⁺ exchange process in these AMV, we propose that the operation of dual ion exchange mechanisms of Na⁺/H⁺ and Cl^–/HCO₃ ^– is the primary mode of electroneutral NaCl absorption across the apical membranes of the enterocytes of the human distal colon.     

NMR study of chloride ion interactions with thylakoid membranes

The role of Cl^- in photosynthetic O₂ evolution has been investigated by observing the ³⁵Cl NMR linewidth under a variety of conditions in aqueous suspensions of chloroplasts, primarily for the halophytes Avicennia germinans, Avicennia marina, and Aster tripolium but also for spinach. The line broadening shows there is weak, ionic binding of Cl^- to thylakoids, the bound Cl^- exchanging rapidly (>>10⁴ sec^-1) with free Cl^- in solution. The binding is necessary for O₂ evolution to occur. Michaelis-Menten constants obtained from the Cl^- dependence of the O₂ evolution rate are ≈15-70 mM for the halophytes compared with 0.6 mM for spinach (0.5 mM with Br^-). There appear to be two types of Cl^- binding sites in halophytes, of which the stronger is the activator, at lower [Cl^-], of O₂ evolution. The ³⁵Cl line broadening includes a nonspecific interaction, which becomes apparent at high Cl^- concentrations (≥0.5 M).     

The Kv channel blocker 4-aminopyridine enhances Ag+ uptake: a scanning electrochemical microscopy study of single living cells

We report that silver ion (Ag⁺) uptake is enhanced by 4-aminopyridine (4-AP), a well known voltage-sensitive potassium ion channel (K_v) blocker. Both bacterial (Escherichia coli) and mammalian (3T3 fibroblast) cells were used as model systems. Ag⁺ uptake was monitored with a scanning electrochemical microscope with an amperometric Ag⁺ ion-selective electrode (Ag⁺-ISE) and the respiration rates of E. coli cells were measured by oxygen reduction at an ultramicroelectrode. The results showed that not only the amount but also the rate of silver uptake by the cells increased significantly when 4-AP was added to the solution. For fibroblasts, the Ag⁺ uptake rate was 4.8 × 10⁷ ions per cell per sec without 4-AP compared with 1.0 × 10⁸ ions per cell per sec with 0.2 mM 4-AP. For E. coli cells, the uptake rate was 1.5 × 10⁴ ions per cell per sec without 4-AP vs. 3.5 × 10⁴ ions per cell per sec with 0.5 mM 4-AP and 5.9 × 10⁴ ions per cell per sec with 1 mM 4-AP. Thus, 4-AP might be useful where silver is used as antimicrobial agent to speed its uptake.     

CLC Cl /H+ transporters constrained by covalent cross-linking

CLC Cl⁻/H⁺ exchangers are homodimers with Cl⁻-binding and H⁺-coupling residues contained within each subunit. It is not known whether the transport mechanism requires conformational rearrangement between subunits or whether each subunit operates as a separate exchanger. We designed various cysteine substitution mutants on a cysteine-less background of CLC-ec1, a bacterial CLC exchanger of known structure, with the aim of covalently linking the subunits. The constructs were cross-linked in air or with exogenous oxidant, and the cross-linked proteins were reconstituted to assess their function. In addition to conventional disulfides, a cysteine–lysine cross-bridge was formed with I₂ as an oxidant. The constructs, all of which contained one, two, or four cross-bridges, were functionally active and kinetically competent with respect to Cl⁻ turnover rate, Cl⁻/H⁺ exchange stoichiometry, and H⁺ pumping driven by a Cl⁻ gradient. These results imply that large quaternary rearrangements, such as those known to occur for “common gating” in CLC channels, are not necessary for the ion transport cycle and that it is therefore likely that the transport mechanism is carried out by the subunits working individually, as with “fast gating” of the CLC channels.     

Primary electron transfer reactions in modified reaction centers from Rhodopseudomonas sphaeroides

Absorption spectra were measured by means of an optical multichannel analyzer in Rhodopseudomonas sphaeroides R-26 reaction centers (RCs) modified by treatment with NaBH₄ at various times (≥1 ps) after the onset of a short excitation flash at 880 nm. Most of these RCs (75-95%) have only one “monomeric” bacteriochlorophyll-800 (B₁) molecule and are as active as the original RCs. The duration of the excitation and measuring pulses was ≈33 ps. If the center of the excitation pulse preceded the center of the measuring pulse by 36-40 ps, the formation of a state P^E (early state), which is converted to the state P^F (P⁺ bacteriopheophytin^-) in 4 ± 1 ps (1/e time), was observed. Also the kinetics and the spectrum of the stimulated emission (reflecting the kinetics and the emission spectrum of the excited state P^*) were determined. The difference spectrum of the state P^E approximately equals the sum of the spectra of the states P^* (≈65%) and ¹[P⁺B₁^-] (≈35%). This indicates that B₁^- is an intermediate in the electron transfer from P^* to bacteriopheophytin, H₁, transferring this electron with a rate constant of (4 × 0.35 ps)^-1 = 7 × 10¹¹ s^-1.     

Nonenzymatic and enzymatic hydrolysis of alkyl halides: A theoretical study of the SN2 reactions of acetate and hydroxide ions with alkyl chlorides

The S_N2 displacements of chloride ion from CH₃Cl, C₂H₅Cl, and C₂H₄Cl₂ by acetate and hydroxide ions have been investigated, using ab initio molecular orbital theory at the HF/6–31+G(d), MP2/6–31+G(d), and MP4/6–31+G(d) levels of theory. The central barriers (calculated from the initial ion–molecule complex) of the reactions, the differences of the overall reaction energies, and the geometries of the transition states are compared. Essential stereochemical changes before and after the displacement reactions are described for selected cases. The gas phase reactions of hydroxide with CH₃Cl, C₂H₅Cl, and C₂H₄Cl₂ have no overall barrier, but there is a small overall barrier for the reactions of acetate with CH₃Cl, C₂H₅Cl, and C₂H₄Cl₂. A self-consistent reaction field solvation model was used to examine the S_N2 reactions between methyl chloride and hydroxide ion and between 1,2-dichloroethane and acetate in solution. As expected, the reactions in polar solvent have a large barrier. However, the transition state structures determined by ab initio calculations change only slightly in the presence of a highly polar solvent as compared with the gas phase. We also calibrated the PM3 method for future study of an enzymatic S_N2 displacement of halogen.     

The Surface of Nanoparticle Silicon as Studied by Solid-State NMR

The surface structure and adjacent interior of commercially available silicon nanopowder (np-Si) was studied using multinuclear, solid-state NMR spectroscopy. The results are consistent with an overall picture in which the bulk of the np-Si interior consists of highly ordered (“crystalline”) silicon atoms, each bound tetrahedrally to four other silicon atoms. From a combination of ¹H, ²⁹Si and ²H magic-angle-spinning (MAS) NMR results and quantum mechanical ²⁹Si chemical shift calculations, silicon atoms on the surface of “as-received” np-Si were found to exist in a variety of chemical structures, with apparent populations in the order (a) (Si–O–)₃Si–H > (b) (Si–O–)₃SiOH > (c) (HO–)_nSi(Si)_m(–OSi)_4−m−n ≈ (d) (Si–O–)₂Si(H)OH > (e) (Si–O–)₂Si(–OH)₂ > (f) (Si–O–)₄Si, where Si stands for a surface silicon atom and Si represents another silicon atom that is attached to Si by either a Si–Si bond or a Si–O–Si linkage. The relative populations of each of these structures can be modified by chemical treatment, including with O₂ gas at elevated temperature. A deliberately oxidized sample displays an increased population of (Si–O–)₃Si–H, as well as (Si–O–)₃SiOH sites. Considerable heterogeneity of some surface structures was observed. A combination of ¹H and ²H MAS experiments provide evidence for a substantial population of silanol (Si–OH) moieties, some of which are not readily H-exchangeable, along with the dominant Si–H sites, on the surface of “as-received” np-Si; the silanol moieties are enhanced by deliberate oxidation. An extension of the DEPTH background suppression method is also demonstrated that permits measurement of the T₂ relaxation parameter simultaneously with background suppression.     

Characterisation at the Bonding Zone between Fly Ash Based Geopolymer Repair Materials (GRM) and Ordinary Portland Cement Concrete (OPCC)

In recent years, research and development of geopolymers has gained significant interest in the fields of repairs and restoration. This paper investigates the application of a geopolymer as a repair material by implementation of high-calcium fly ash (FA) as a main precursor, activated by a sodium hydroxide and sodium silicate solution. Three methods of concrete substrate surface preparation were cast and patched: as-cast against ordinary Portland cement concrete (OPCC), with drilled holes, wire-brushed, and left as-cast against the OPCC grade 30. This study indicated that FA-based geopolymer repair materials (GRMs) possessed very high bonding strength at early stages and that the behavior was not affected significantly by high surface treatment roughness. In addition, the investigations using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy have revealed that the geopolymer repair material became chemically bonded to the OPC concrete substrate, due to the formation of a C–A–S–H gel. Fundamentally, the geopolymer network is composed of tetrahedral anions (SiO₄)⁴⁻ and (AlO₄)⁵⁻ sharing the oxygen, which requires positive ions such as Na⁺, K⁺, Li⁺, Ca²⁺, Na⁺, Ba²⁺, NH⁴⁺, and H₃O⁺. The availability of calcium hydroxide (Ca(OH)₂) at the surface of the OPCC substrate, which was rich in calcium ions (Ca²⁺), reacted with the geopolymer; this compensated the electron vacancies of the framework cavities at the bonding zone between the GRM and the OPCC substrate.     

Axial Presentations of Regular Arcs on M(n)

THEOREM 1. Let M_n be a Riemannian manifold of class C^m, m > 0. On M_n let g be a simple compact, sensed, regular arc whose local coordinates are functions of class C^m of the algebraic arc length s, measured along g from a prescribed point of g. There then exists a presentation (F: U, X) [unk] [unk]M_n such that g [unk] X, and each point p(s) of g is represented in the euclidean domain U by coordinates (x¹,...,xⁿ) = (s,0,...,0).     

Structure and charging of hydrophobic material/water interfaces studied by phase-sensitive sum-frequency vibrational spectroscopy

We have studied the hydrophobic water/octadecyltrichlorosilane (OTS) interface by using the phase-sensitive sum-frequency vibrational spectroscopy (PS-SFVS), and we obtained detailed structural information of the interface at the molecular level. Excess ions emerging at the interface were detected by changes of the surface vibrational spectrum induced by the surface field created by the excess ions. Both hydronium (H₃O⁺) and hydroxide (OH⁻) ions were found to adsorb at the interface, and so did other negative ions such as Cl⁻. By varying the ion concentrations in the bulk water, their adsorption isotherms were measured. It was seen that among the three, OH⁻ has the highest adsorption energy, and H₃O⁺ has the lowest; OH⁻ also has the highest saturation coverage, and Cl⁻ has the lowest. The result shows that even the neat water/OTS interface is not neutral, but charged with OH⁻ ions. The result also explains the surprising observation that the isoelectric point appeared at ∼3.0 when HCl was used to decrease the pH starting from neat water.     

One-Pot Self-Assembly of Dinuclear,Tetranuclear, and H-Bonding-Directed Polynuclear Cobalt(II), Cobalt(III), and Mixed-Valence Co(II)/Co(III) Complexes of Schiff Base Ligands with Incomplete Double Cubane Core

The reaction of 2,6-diformyl-4-methylphenol (DFMF) with 1-amino-2-propanol (AP) and tris(hydroxymethyl)aminomethane (THMAM) was investigated in the presence of Cobalt(II) salts, (X = ClO₄⁻, CH₃CO₂⁻, Cl⁻, NO₃⁻), sodium azide (NaN₃), and triethylamine (TEA). In one pot, the variation in Cobalt(II) salt results in the self-assembly of dinuclear, tetranuclear, and H-bonding-directed polynuclear coordination complexes of Cobalt(III), Cobalt(II), and mixed-valence Co^IICo^III: [Co₂^III(H₂L⁻¹)₂(AP⁻¹)(N₃)](ClO₄)₂ (1), [Co₄(H₂L⁻¹)₂(µ₃-1,1,1-N₃)₂(µ-1,1-N₃)₂Cl₂(CH₃OH)₂]·4CH₃OH (2), [Co₂^IICo₂^III(HL⁻²)₂(µ-CH₃CO₂)₂(µ₃-OH)₂](NO₃)₂·2CH₃CH₂OH (3), and [Co₂^IICo₂^III (H₂L1²⁻)₂(THMAM⁻¹)₂](NO₃)₄ (4). In 1, two cobalt(III) ions are connected via three single atom bridges; two from deprotonated ethanolic oxygen atoms in the side arms of the ligands and one from the1-amino-2-propanol moiety forming a dinuclear unit with a very short (2.5430(11) Å) Co-Co intermetallic separation with a coordination number of 7, a rare feature for cobalt(III). In 2, two cobalt(II) ions in a dinuclear unit are bridged through phenoxide O and μ₃-1,1,1-N₃ azido bridges, and the two dinuclear units are interconnected by two μ-1,1-N₃ and two μ₃-1,1,1-N₃ azido bridges generating tetranuclear cationic [Co₄(H₂L⁻¹)₂(µ₃-1,1,1-N₃)₂(µ-1,1-N₃)₂Cl₂(CH₃OH)₂]²⁺ units with an incomplete double cubane core, which grow into polynuclear 1D-single chains along the a-axis through H-bonding. In 3, HL²⁻ holds mixed-valent Co(II)/Co(III) ions in a dinuclear unit bridged via phenoxide O, μ-1,3-CH₃CO₂⁻, and μ₃-OH⁻ bridges, and the dinuclear units are interconnected through two deprotonated ethanolic O in the side arms of the ligands and two μ₃-OH⁻ bridges generating cationic tetranuclear [Co₂^IICo₂^III(HL⁻²)₂(µ-CH₃CO₂)₂(µ_3-OH)₂]²⁺ units with an incomplete double cubane core. In 4, H₂L1⁻² holds mixed-valent Co(II)/Co(III) ions in dinuclear units which dimerize through two ethanolic O (μ-RO⁻) in the side arms of the ligands and two ethanolic O (μ₃-RO⁻) of THMAM bridges producing centrosymmetric cationic tetranuclear [Co₂^IICo₂^III (H₂L1⁻²)₂(THMAM⁻¹)₂]⁴⁺ units which grow into 2D-sheets along the bc-axis through a network of H-bonding. Bulk magnetization measurements on 2 demonstrate that the magnetic interactions are completely dominated by an overall ferromagnetic coupling occurring between Co(II) ions.