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Lanthanide metal clusters excel in combining molecular and material chemistry properties. Here, we report an efficient cooperative sensitization UC phenomenon of a Eu3+/Yb3+nonanuclear lanthanide cluster in CD3OD. The synthesis and characterization of the heteronuclear cluster in the solid state and solution are described together with the UC phenomenon showing Eu3+luminescence in the visible region upon 980 nm NIR excitation of Yb3+at concentrations as low as 100 nM. Alongside being the Eu/Yb cluster to display UC (with a quantum yield value of 4.88 × 10–8upon 1.13 W cm–2excitation at 980 nm), the cluster exhibits downshifted light emission of Yb3+in the NIR region upon 578 nm visible excitation of Eu3+, which is ascribed to sensitization pathways for Yb through the 5D0energy levels of Eu3+. Additionally, a faint emission is also observed at ca.500 nm upon 980 nm excitation, originating from the cooperative luminescence of Yb3+. The [Eu8Yb(BA)16(OH)10]Cl cluster (BA = benzoylacetonate) is also a field-induced single-molecular magnet (SMM) under 4K with a modest Ueff/kBof 8.48 K, thereby joining the coveted list of Yb-SMMs and emerging as a prototype system for next-generation devices, combining luminescence with single-molecular magnetism in a molecular cluster.

The lead–acid battery is still widely used today and will continue to be one of the benchmarks for diverse scenarios and applications. Although their energy densities are lower than more modern chemistries, the economic advantages of lead–acid batteries outweigh the disadvantages for numerous applications in transportation and stationary markets, uninterruptible power supply, and energy storage for wind or solar-based renewable systems. Nevertheless, optimizing their utility requires the continuous assessment of the state of health (SoH). The existing SoH estimation techniques use extrinsic quantities such as current, voltage, impedance, and temperature obtained through invasive (i.e., probing) methods. However, probing methods do not facilitate seamless cell-level charging to balance the SoH of the entire battery. Our study explored the non-invasive estimation of the battery SoH using acoustic energy. This method used sound both as an emitted and received signal propagating across the internal structure of a battery cell element unit (CEU) during its operation. Information from the received signals is analyzed relative to the aging degree of the lead–acid battery. The patterns of the received sound contain information on the CEU structure, which a data-driven algorithm subsequently encoded into a binary classifier of SoH levels: above 80% and below 80%. Results show that the binary classifier can distinguish between the two classes. A non-invasive SoH estimation technique can support the seamless operation of cell-level charging for lead–acid batteries. Balancing the SoH among all cells is needed to sustain the use life of the entire battery.

Bispidine (3,7-diazabicyclo[3.3.1]nonane) provides a rigid and preorganized scaffold that is particularly interesting for the stable and inert complexation of metal ions, especially for their application in medical imaging. In this study, we present the synthesis of two bispidine ligands with N-methanephosphonate (H4L1) and N-methanecarboxylate (H3L2) substituents as well as the physico-chemical properties of the corresponding Mn2+and Zn2+complexes. The two complexes [Mn(L1)]2–and [Mn(L2)]−have relatively moderate thermodynamic stability constants according to potentiometric titration data. However, they both display an exceptional kinetic inertness, as assessed by transmetallation experiments in the presence of 50 equiv excess of Zn2+, showing only ∼40 and 20% of dissociation for [Mn(L1)]2–and [Mn(L2)]–, respectively, after 150 days at pH 6 and 37 °C. Proton relaxivities amount to r1= 4.31 mM–1s–1([Mn(L1)]2–) and 3.64 mM–1s–1([Mn(L2)]–) at 20 MHz, 25 °C, and are remarkable for Mn2+complexes with one inner-sphere water molecule (q= 1); they are comparable to that of the commercial contrast agent [Gd(DOTA)(H2O)]−. The presence of one inner-sphere water molecule and an associative water exchange mechanism was confirmed by temperature-dependent transverse 17O relaxation rate measurements, which yielded kex298= 0.12 × 107and 5.5 × 107s–1for the water exchange rate of the phosphonate and the carboxylate complex, respectively. In addition, radiolabeling experiments with 52Mn were also performed with H2(L1)2–showing excellent radiolabeling properties and quantitative complexation at pH 7 in 15 min at room temperature as well as excellent stability of the complex in various biological media over 24 h.

The coordination properties of the ligand 2,2′-bipyrimidine-4,4′-dicarboxylic acid (H2bpd) with lanthanide(III) ions (Ln = Eu, Tb, or Lu) were investigated. The syntheses of the H2bpdligand and its salts, [K2(bpd)(H2O)2] (1) and [(AlkNH)Lu(bpd)2] (Alk= Et, Hex, or en), are described. In the presence of LnCl3salts (Ln = Lu, Eu, or Tb), the formation of [Ln(bpd)2]−and [Ln(bpd)(H2O)x]+species was assessed by 1H nuclear magnetic resonance (NMR), spectrophotometry, and spectrofluorometric titrations in aqueous solution. The solid state structure of 1, [K(H2O)2][Lu(bpd)2] (2), and [(Et3NH)Lu(bpd)2] (3) could be determined by X-ray diffraction, showing the ligand to act as a tetradentate unit with formation of three five-membered chelate rings around the central Ln(III). With the aim of building polynuclear assemblies, the coordination between [Lu(bdp)2]−and [Lu(tta)3(H2O)] units (tta = thenoyltrifluoroacetylacetonate) was also investigated. In methanol, 1H NMR titration experiments revealed the formation of complex mixtures from which two new species could be identified, [Lu2(bpd)(tta)4] (4) and H[Lu(bpd)(tta)2] (5), as confirmed by their solid state structure analysis. Using highly lipophilic cations in chloroform, the octametallic complex [enH]4[Lu8(bpd)4(tta)18] (6) could be isolated and its X-ray structure determined.

Ligands L1and L2, respectively based on a cyclam and a cross-bridged cyclam scaffold functionalized at N1 and N8 by 6-phosphonic-2-methylene pyridyl groups, are described. While complexation of lanthanide (Ln) cations with L2was not possible, a family of complexes has been prepared with L1, of the general formulae [LnL1H2]Cl (Ln3+= Lu, Tb, Yb) or [LnL1H] (Ln3+= Eu). The solution, structural, potentiometric, and photophysical data for these novel ligands and their complexes have been investigated, including a solid-state study by X-ray diffraction (L1, L2, and [EuL1H]), 1H NMR complexation investigations (Lu3+), as well as UV–vis absorption and luminescence spectroscopy in water and D2O (pH ≈ 7). L1forms 1:1 metal–ligand stoichiometric octadentate complexes in solution. Importantly, the pyridyl phosphonate functions are capable of simultaneous chelation to the metal center and of interaction with a second metal center. 1H NMR (Lu3+) and spectrophotometric titrations of the isolated [TbL1]−complex by EuCl3salts demonstrated the formation of high-order (hetero)polymetallic species in aqueous solution (H2O, pH = 7). Global analysis of the luminescence titration experiment points to the formation of 4:1, 3:1, and 3:2 [TbL1]/Eu heteropolynuclear assemblies, exhibiting a strong preference to forming [TbL1]3Eu2at increased europium concentrations, with energy transfer occurring between the kinetically inert terbium complex and added europium cations.

The adsorption behavior and inhibition mechanism of (1, 4, 7-Tris [hydrogen (6-methylpyridin-2-yl) phosphonate] -1, 4, 7-triazacyclononane) (TPP) on the corrosion of mild steel in 1 M HCl were investigated by weight loss technique, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) methods for different concentrations at 25°C. The results show that the inhibition efficiency values depend on the amount of immersion times and the concentration. A 90% efficiency is found at the highest concentration of the studied compound according to weight loss measurements. The adsorption of the investigated inhibitor on the mild steel surface was well supported using an AFM study. For the assignment of the absorption sites, we performed quantum chemical calculations with (DFT) method. The interaction between the inhibitor and iron surface were performed by molecular dynamic (MD) simulations. In this paper, experimental methods and results used to assess the efficiency of the studied compound are presented.

Here we present the synthesis and characterization of a new bispidine (3,7-diazabicyclo[3.3.1]nonane) ligand with N-methanephosphonate substituents (L2). Its physicochemical properties in water, as well as those of the corresponding Cu(II) and Zn(II) complexes, have been evaluated by using UV–visible absorption spectroscopy, potentiometry, 1H and 31P NMR, and cyclic voltammetry. Radiolabeling experiments with 64CuIIhave been carried out, showing excellent radiolabeling properties. Quantitative complexation was achieved within 60 min under stoichiometric conditions, at room temperature and in the nanomolar concentration range. It was also demonstrated that the complexation occurred below pH 2. Properties have been compared to those of the analogue bispidol bearing a N-methanecarboxylate substituent (L1). Although both systems meet the required criteria to be used as new chelator for 64/67Cu in terms of the kinetics of formation, thermodynamic stability, selectivity for Cu(II), and kinetic inertness regarding redox- or acid-assisted decomplexation processes, substitution of the carboxylic acid function by the phosphonic moiety is responsible for a significant increase in the thermodynamic stability of the Cu(II) complex (+2 log units for pCu) and also leads to an increase in the radiochemical yields with 64CuIIwhich is quantitative for L2.

Imaging single molecules and nanoparticles in complex biological media is highly challenging notably due to autofluorescence of cells and tissues. Lanthanides and lanthanide complexes, with their particularly long luminescence lifetimes, offer the possibility to perform time-gated imaging and thus to strongly reduce the autofluorescence background. However, their very low brightness and photon flux have limited their use in single-molecule imaging. Here, we encapsulate high amounts of Europium complexes into poly(methyl methacrylate)-based particles of 10, 20, and 30 nm size. The resulting particles contain up to 5000 copies of the complex with a quantum yield of ≥0.2, resulting in a per particle brightness of up to 4 × 107M–1cm–1. They can be imaged at the single-particle level using low illumination intensities (0.24 W cm–2) and low acquisition times (300 ms) and internalize well into living cells, where they can be monitored through time-gated imaging at illumination conditions compatible with living specimen. These Eu-complex-loaded nanoparticles can thus be applied for highly sensitive and autofluorescence-free imaging and have the potential to become very performant probes for fast intracellular tracking of single biomolecules.

Piling up excited states to reach upconversion (UC) is severely restricted by vibrational quenching mechanisms, especially when one looks at discrete molecular entities in solution. By carefully controlling the supramolecular assembly processes resulting from the strong electrostatic interactions between negatively charged Yb complexes and Tb3+cations in aqueous solutions, we engineered the formation of heteropolynuclear complexes of [(YbL)2Tbx] compositions (x= 1 and 2). These edifices display a phenomenon of cooperative photosensitization UC with green emission of the Tb cations upon NIR excitation at 980 nm in the Yb absorption band. The photophysical properties of the complexes were carefully investigated by steady-state and time-resolved luminescence experiments in D2O, allowing one to quantify the impact of the composition and pD of the solution on the emission intensity as well as clarifying the exact cooperative photosensitization upconversion mechanism. Using optimized conditions, the energy transfer UC process could be observed for the first time in nondeuterated water with discrete molecular compounds.

A series of polynuclear assemblies based on ligand L (1,4,7-tris[hydrogen (6-methylpyridin-2-yl)phosphonate]-1,4,7-triazacyclononane) has been developed. The coordination properties of ligand L with LnIII(Ln = La, Eu, Tb, Yb, Lu) have been studied in water (pH = 7.0) and in D2O (pD = 7.0) by UV-absorption spectrometry, spectrofluorimetry, 1H and 31P NMR, DOSY, ESI-mass spectrometry, and X-ray diffraction. This nonadentate ligand forms highly stable mononuclear complexes in water and provides a very efficient shielding of the Ln cations, as emphasized by the very good luminescence properties of the Yb complex in D2O, especially regarding its lifetime (τD2O= 10.2 μs) and quantum yield (ϕD2O= 0.42%). In the presence of excess LnIIIcation, polynuclar complexes of [(LnL)2Lnx] stoichiometry (x = 1 and x = 2) are observed in solution. In the solid state, a dinuclear complex of La could be isolated and structurally characterized by X-ray diffraction, unraveling the presence of strong hydrogen bonding interactions between a La(H2O)93+cation and the [LaL]3–complex.

Lanthanide complexes featuring luminescent and/or single-molecule magnet (SMM) characteristic(s) are proposed candidates to develop molecule-based spintronics, memory, and quantum information processing (QIP) device architectures. Herein, we report on the luminescent and/or SMM characteristic(s) of charge-neutral binuclear lanthanide complexes─[Ln2Cl6(4-picNO)4(μ2-4-picNO)2]·2H2O (Ln3+= Tb3+([Tb2]) or Dy3+([Dy2]); 4-picNO = 4-picoline-N-oxide). The Dy and Tb complexes show 4-picNO-sensitized luminescence with quantum yields in the solid state of 0.14% and 88%, respectively. The luminescent Dy complex is an SMM with a magnetization reversal barrier (Ueff) = 20.6(4) cm–1under zero applied magnetic field, whereas the Tb complex is not an SMM. The facile preparation of [Ln2Cl6(4-picNO)4(μ2-4-picNO)2]·2H2O complexes showing high luminescence quantum yield (Tb3+) and SMM characteristics (Dy3+) might prove useful toward the designing of analogue luminescent-SMM hybrids suitable for technological applications.

The atomic structure of calcium-silicate-hydrate (C1.67–S–Hx) has been studied. Atomistic C–S–H models suggested in our previous study have been revised in order to perform a direct comparison of energetic stability of the different structures. An extensive set of periodic structures of C–S–H with variation of water content was created, and then optimized using molecular dynamics with reactive force field ReaxFF and quantum chemical semiempirical method PM6. All models show organization of water molecules inside the structure of C–S–H. The new geometries of C–S–H, reported in this paper, show lower relative energy with respect to the geometries from the original definition of C–S–H models. Model that corresponds to calcium enriched tobermorite structure has the lowest relative energy and the density closest to the experimental values.

The main product of Portland cement hydration is C-S-H. Despite constituting more than half of the volume of hydrated pastes and having an important role in strength development, very little is known about the factors that determine its morphology. To investigate the relationship between the chemical composition, silicate anion structure and morphology of C-S-H, samples were synthesised via silica-lime reactions and by the hydration of C3S under controlled lime concentrations and with/without accelerators. The silicate anion structure of the samples was studied by 29Si magic angle spinning nuclear magnetic resonance spectroscopy and the morphology and chemical composition by TEM and SEM. All samples prepared via silica-lime reactions with bulk Ca/Si up to 1.5 were foil-like. The hydration of C3S at fixed lime concentration yielded foil-like C-S-H for [CaO]<22 mmol L−and fibrillar C-S-H for [CaO]>22 mmol L−1. A relationship between the silicate anion structure and the morphology of C-S-H was found for the samples fabricated with accelerators.

The main product of Portland cement hydration is C-S-H. Despite constituting more than half of the volume of hydrated pastes and having an important role in strength development, very little is known about the factors that determine its morphology. To investigate the relationship between the chemical composition, silicate anion structure and morphology of C-S-H, samples were synthesised via silica-lime reactions and by the hydration of C3S under controlled lime concentrations and with/without accelerators. The silicate anion structure of the samples was studied by 29Si magic angle spinning nuclear magnetic resonance spectroscopy and the morphology and chemical composition by TEM and SEM. All samples prepared via silica-lime reactions with bulk Ca/Si up to 1.5 were foil-like. The hydration of C3S at fixed lime concentration yielded foil-like C-S-H for [CaO]<22 mmol L-and fibrillar C-S-H for [CaO]>22 mmol L-1. A relationship between the silicate anion structure and the morphology of C-S-H was found for the samples fabricated with accelerators.

Numerous aspects of the physical chemistry of colloidal systems are conditioned by the solid–liquid interface, and this is also the case for hydrated cement systems. Estimating the surface area is thus essential for studying the kinetics of cement hydration and admixture adsorption. Proton nuclear magnetic resonance (NMR) relaxation techniques have already proven useful for this objective, but, for hydrating cements at early ages, it is necessary to know the surface relaxivities of all of the individual phases present to correctly interpret the relaxation data. This paper reports the results of a comparison of NMR relaxometry and Brunauer–Emmett–Teller gas adsorption measurements on various synthetic cement hydrates with the aim of evaluating their individual surface relaxivities. We observe that all of the tested phases (anhydrous and hydrated) except for ettringite have surface relaxivities typical of common natural rocks. We also find that the amount of paramagnetic species as measured by electron spin resonance is not a first-order parameter in determining surface relaxivity. The strong relaxivity of ettringite can be explained by the influence of the dimensionality of diffusive exploration on the relaxation rate. The structure of ettringite essentially provides only 1D access to the paramagnetic species, so the water protons only explore a reduced volume and stay in close proximity to paramagnetic ions, maintaining the dipolar pair correlation for a much longer time compared with that observed for the 2D diffusion, which is typical of the other cement hydrates studied.

Two new tripodal heptadentate ligands, H4dpaba (N,N′‐bis[(6‐carboxypyridin‐2‐yl)methyl]aspartic acid) and H3mpatcn(1,4‐bis(methoxycarbonyl)‐7‐[(6‐carboxypyridin‐2‐yl)methyl]‐1,4,7‐triazacyclononane), which bear one or two picolinate pendant arms, have been synthesised. Their lanthanide complexes have been characterised by NMR and fluorescence spectroscopy and potentiometry. Both ligands gave rise to water soluble 1:1 complexes with an increased thermodynamic stability (pGddpaba= 13.3, pGdmpatcn= 11.8, with pGdL= –log [Gd]freeat pH 7.4, [Gd]total= 1 μMand [L]total= 10 μM) with respect to the analogous bisaqua complex [Gd(tpaa)(H2O)2] [H3tpaa = α,α′,α″‐nitrilotri(6‐methyl‐2‐pyridinecarboxylic acid), pGdtpaa= 11.2). The two inner‐sphere water molecules confer sizeable relaxivities (r1) to the complexes at high field at physiological pH: r1= 8.90 and r1= 7.35 mM–1s–1have been measured in HOD at 200 MHz for [Gd(dpaba)(HOD)2]–and [Gd(mpatcn)(HOD)2], respectively. Their relaxometric properties have been investigated by NMRD (Nuclear Magnetic Relaxation Dispersion) and 17O NMR spectroscopy. The formation of ternary complexes with physiological anions, such as acetate, hydrogen carbonate, hydrogen phosphate and citrate, has been monitored by 1H NMR spectroscopy at 200 MHz and pH 7.4. The addition of a large excess (0.6 M) of acetate, hydrogen phosphate and citrate led to the formation monoaqua ternary complexes. Even under these conditions, the average relaxivity remains higher or similar than most currently used contrast agents. Only hydrogen carbonate interacts strongly with the complexes and coordinates in a bidentate mode by displacing both water molecules to induce a twofold decrease in the relaxivity. Both complexes interact with serum albumin to form a macromolecular adduct with increased relaxivity. In particular, a twofold increase of relaxivity has been measured for [Gd(dpaba)(H2O)2]–in bovine serum, which suggests that anion binding does not significantly affect the relaxivity under these conditions.

Three new complexes of cobalt, manganese, and zinc have been synthesized using a hydrazone Schiff base ligand {(E)-N'-[1-(2-hydroxyphenyl)ethylidene]acetohydrazide} (LH2) produced by the 1:1 condensation of acetic hydrazide and 2-hydroxyacetophenone. The ligand has shown three different coordination modes in the three complexes: a monoanionic tridentate coordination mode with the CoIIcomplex ([Co(LH)2]·CH3OH, 1), a dianionic tridentate coordination mode with the MnIVcomplex ([Mn(L)2], 2), and monoanionic µ2-phenoxo-bridged tridentate coordination mode with the ZnIIcomplex ([Zn(LH)(OOCCF3)]2, 3). All three complexes show interesting supramolecular architectures, especially for 3a nanoporous supramolecular (4, 4) grid 2D framework is formed. The ligand and the complexes are well characterized by elemental analysis, IR and UV–vis spectroscopy. The spin states of the CoIIand MnIVmetal ions and hence the coordination modes of the ligand in these complexes are in good agreement with the EPR spectroscopic data. The fluorescence emission spectra of LH2and the zinc complex 3are measured in acetonitrile solution as well as in solid state.

The most important phase in Portland cement is tricalcium silicate, which leads during its hydration to the nucleation and growth of calcium silicate hydrate [referred to as C–S–H, (CaO)x–SiO2–(H2O)y]. The development of this hydrate around the cement grains is responsible for the setting and hardening of cement pastes. The general term for designating the tricalcium silicate in cements is alite. This name relates to all polymorphs containing various foreign ions inserted in their structure. These ions may influence the intrinsic reactivity, and once released during the dissolution, they may interact also with C–S–H. One of the most likely species to be inserted in the alite structure is aluminium. In order to investigate if aluminium plays an important role in C3S reactivity, alite containing 0·1 wt-% aluminium has been synthesised. Alite hydration was followed and compared with pure tricalcium silicate one. The ion concentration evolution at a very early age shows the formation of a C–S–H containing aluminium ions, and it has been evidenced that this hydrate does not act as nuclei to C–S–H growth that induces a delay before acceleration of hydration commonly named ‘dormant period’.

The tripodal hexadentate picolinate ligand dpaa3−(H3dpaa=N,N′‐bis[(6‐carboxypyridin‐2‐yl)methyl]glycine) has been synthesised. It can form 1:1 and 1:2 lanthanide/ligand complexes. The crystal structure of the bis(aquo) lutetium complex [Lu(dpaa)(H2O)2] has been determined by X‐ray diffraction studies. The number of water molecules was determined by luminescence lifetime studies of the terbium and europium complexes. The tris(aquo) terbium complex shows a fairly high luminescence quantum yield (22 %). The [Gd(dpaa)(H2O)3] complex displays a high water solubility and an increased stability (pGd=12.3) with respect to the analogous bis(aquo) complex [Gd(tpaa)(H2O)2] (pGd=11.2). Potentiometric and relaxometric studies show the formation of a soluble GdIIIhydroxo complex at high pH values. A unique aquohydroxo gadolinium complex has been isolated and its crystal structure determined. This complex crystallises as a 1D polymeric chain consisting of square‐shaped tetrameric units. In heavy water, the [Gd(dpaa)(D2O)3] complex shows a quite high HOD proton relaxivity at high field (11.93 s−1mM−1at 200 MHz and 298 K) because of the three inner‐sphere water molecules. The formation of ternary complexes with physiological anions has been monitored by relaxometric studies, which indicate that even under conditions favourable to the formation of adducts with oxyanions, the mean relaxivity remains higher than those of most of the currently used commercial contrast agents except for the citrate. However, the measured relaxivity (r̄1=7.9 s−1mM−1) in a solution containing equimolar concentrations of [Gd(dpaa)(D2O)3] and citrate is still high. The interaction with albumin has been investigated by relaxometric and luminescence studies. Finally, a new versatile method to unravel the geometric and dynamic molecular factors that explain the high‐field relaxivities has been developed. This approach uses a small, uncharged non‐coordinating probe solute, the outer‐sphere relaxivity of which mimics that of the water proton. Only a routine NMR spectrometer and simple mathematical analysis are required.

The new potentially octadentate ligand, 1‐(carboxymethyl)‐4,7‐bis[(6‐carboxypyridin‐2‐yl)methyl]‐1,4,7‐triazacyclononane (H3bpatcn), in which two picolinate arms and one acetate arm are connected to the 1,4,7‐triazacyclonane core, has been prepared. Potentiometric studies show an increased stability of the GdIIIcomplex of H3bpatcn (logKGdL=15.8(2)) with respect to the GdIIIcomplex of the analogous ligand 1,4,7‐triazacyclononane‐N,N′,N′′‐triacetic acid (H3nota) (logKGdL=13.7), associated with an increased selectivity of H3bpatcn for gadolinium over calcium. The H3bpatcn ligand sensitises the terbium ion very efficiently, leading to a long‐lived and highly luminescent terbium complex (quantum yield=43 %), in spite of the presence of a coordinated water molecule. 1H proton NMR studies indicate that the metal ion is rigidly encapsulated by the three arms of the octadentate ligand H3bpatcn and that the macrocycle framework remains bound (through the five nitrogen and the three oxygen atoms) even at high temperature. A new theoretical method for interpreting the water proton relaxivity is presented. It is based on recent progresses in the description of the electronic spin relaxation and on an auxiliary probe solute. It replaces the Solomon, Bloembergen and Morgan (SBM) framework, which is questionable at low field, while avoiding resorting to simulations and/or sophisticated theories with additional unknown zero‐field splitting (ZFS) parameters. The inclusion of two picolinate groups on a triazacyclononane framework affords the mono‐aquo gadolinium complex [Gd(bpatcn)(H2O)] with favourable electron‐relaxation properties (${\tau {{{\rm eff}\hfill \atop {\rm S0}\hfill}}}$=125 ps). The optimisation of the electronic relaxation by ligand design is especially important to achieve high relaxivity in the new generation macromolecular complexes with long rotational correlation times.

The main source of cohesion in cement paste is the nanoparticles of calcium silicate hydrate (C−S−H), which are formed upon the dissolution of the original tricalcium silicate (C3S). The interaction between highly charged C−S−H particles in the presence of divalent calcium counterions is strongly attractive because of ion−ion correlations and a negligible entropic repulsion. Traditional double-layer theory based on the Poisson−Boltzmann equation becomes qualitatively incorrect in these systems. Monte Carlo (MC) simulations in the framework of the primitive model of electrolyte solution is then an alternative, where ion−ion correlations are properly included. In addition to divalent calcium counterions, commercial Portland cement contains a variety of other ions (sodium, potassium, sulfate, etc.). The influence of high concentrations of these ionic additives as well as pH on the stability of the final concrete construction is investigated through MC simulations in a grand canonical ensemble. The results show that calcium ions have a strong physical affinity (in opposition to specific chemical adsorption) to the negatively charged silicate particles of interest (C−S−H, C3S). This gives concrete surprisingly robust properties, and the cement cohesion is unaffected by the addition of a large variety of additives provided that the calcium concentration and the C−S−H surface charge are high enough. This general phenomenon is also semiquantitatively reproduced from a simple analytical model. The simulations also predict that the affinity of divalent counterions for a highly and oppositely charged surface sometimes is high enough to cause a “charge reversal” of the apparent surface charge in agreement with electrophoretic measurements on both C3S and C−S−H particles.

Atomic force microscopy has been used to investigate the force at the origin of the cohesion of cement. The cohesion of cement grains is caused by surface forces acting between calcium silicate hydrate nanoparticles in interstitial electrolytic solution. Direct measurement of the interaction between two calcium silicate hydrate surfaces is performed in air and different aqueous solutions. In dry air, starting with the van der Waals forces, the interaction area between calcium silicate hydrate nanoparticles can be estimated. In electrolytic solution, the evolution of these forces is extensively dependent on both surface and solution chemistry. The roles of the calcium hydroxide concentration, pH, and ionic strength are investigated. The force measurements allow us to confirm the pre-eminence of ionic correlation forces in the cohesion of cement.

It is generally agreed that the cohesion of cement paste occurs through the formation of a network of nanoparticles of a calcium−silicate−hydrate (“C−S−H”). However, the mechanism by which these particles develop this cohesion has not been established. Here we propose a dielectric continuum model which includes all ionic interactions within a dispersion of C−S−H particles. It takes into account all co-ions and counterions explicitly (with pure Coulomb interactions between ions and between ions and the surfaces) and makes no further assumptions concerning their hydration or their interactions with the surface sites. At high surface charge densities, the model shows that the surface charge of C−S−H particles is overcompensated by Ca²⁺ ions, giving a reversal of the apparent particle charge. Also, at high surface charge densities, the model predicts that the correlations of ions located around neighboring particles causes an attraction between the particle surfaces. This attraction has a range of approximately 3 nm and a magnitude of 1 nN, values that are in good agreement with recent AFM experiments. These predictions are stable with respect to small changes in surface−surface separation, hydrated ion radius, and dielectric constant of the solution. The model also describes the effect of changes in cement composition through the introduction of other ions, either monovalent (Na) or multivalent (aluminum or iron hydroxide).

The sorption of cesium at the calcium silicate hydrates (CSH) surface was investigated, both through sorption isotherm data and by solid-state NMR experiments. The sorption ability of CSH towards cesium is favored for low solid Ca/Si molar ratios, in agreement with the negative surface charge they develop then. A significant proportion of these sorbed cesium cations remains tightly bound to the surface sites forming, in dehydrated CSH, inner-sphere complexes, which can not be removed by alcohol washing. Chloride seems to present a lower affinity for CSH, even for high Ca/Si molar ratios, where the surface charge becomes positive.

In this paper, an original approach is used to study the calcium silicate hydrate (C−S−H) layer formation on the surface of grains of anhydrous silicate during tricalcium and dicalcium silicate hydration from the variation of the rate of hydration with lime concentration. The effects of C−S−H nucleation and growth on the curves for the degree of reaction against time have been separated in both experimental study of the rate of hydration in controlled conditions and numerical simulation of the growth of C−S−H on a surface from a particle aggregation model. The influence of the number of nuclei and of the different growth modes has been quantified.

An investigation into the interaction between alkaline cations and calcium silicate hydrates (CSH) was conducted by electrokinetic measurements, which provided information on the nature of the interface between the solid and its equilibrium solution. Calcium constitutes for the CSH surface a potential-determining cation. A model of the CSH surface could be proposed, accounting for the experimental evolution of the CSH zeta potential. The necessity of studying the zeta-potential evolution of the system as a function of the calcium activity, instead of its concentration, was underlined. The results obtained suggest a specific interaction between cesium and the CSH surface, whereas sodium and lithium may behave as indifferent cations toward the interface.