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PubMed2007

Incidence of ALS in Lombardy, Italy.

OBJECTIVE: To assess the incidence and trends of ALS in a large population at risk. METHODS: This study was performed in nine provinces of Lombardy in Northern Italy (population 4,947,554). Patients with newly diagnosed ALS were enrolled during the period 1998 to 2002 through a prospective regional register. For each patient, the main demographic and clinical information was collected by the caring physicians and reviewed by a panel of experts according to the original and revised El Escorial diagnostic criteria. Overall, age- and sex-specific and standardized annual incidence rates were calculated for the entire population and for each year and province separately. RESULTS: We studied 517 patients (M:F ratio 1.3) aged 18 to 92 years (mean 63.6). Onset of symptoms was bulbar in 29% of cases. ALS was definite in 45%, probable in 27%, probable laboratory supported in 3.5%, possible in 15%, and suspected in 10%. Mean disease duration at diagnosis was 10.6 months. The standardized incidence rate was 2.09 per 100,000/year (95% CI: 1.17 to 3.18). The rate, which was 2.43 in men and 1.76 in women, tended to increase up to ages 65 to 74 and to decrease thereafter. The rate was unchanged over time and presented moderate variations across provinces. The incidence rate of definite ALS was 0.93 (spinal-onset ALS 1.35; bulbar-onset ALS 0.74) and was consistently higher in men with spinal-onset ALS vs men with bulbar-onset ALS and women. CONCLUSIONS: The incidence of ALS varied according to age, sex, and site of onset. No temporal and geographic clusters were detected over a 5-year period.

Adolescent↗
PubMed1998

Decreased N-acetylaspartate in motor cortex and corticospinal tract in ALS.

The primary objectives of this study were to test whether 1) N-acetylaspartate (NAA), a neuronal marker, is reduced in motor cortex and corticospinal-tract (CST) brain regions of ALS patients; and 2) motor cortex NAA correlates to a clinical measurement of upper motor neuron function in ALS patients. Ten probable or definite ALS patients and nine neurologically normal control subjects were studied. Three axial planes of two-dimensional 1H MRSI data were collected, using a single spin-echo multislice sequence (TE140/TR2000). Two of the 1H MRSI planes were positioned superior to the lateral ventricles, and one plane was positioned at the level of the internal capsule. Spectroscopy voxels were selected from motor cortex, frontal cortex, parietal cortex, medial gray matter, centrum semiovale white matter, anterior internal capsule, and posterior internal capsule. Peak integrals were obtained for the three major 1H MRSI singlet resonances, NAA, creatine and phosphocreatine (Cr), and cholines (Cho). Maximum finger-tap rate was used as a clinical measurement of upper motor neuron function. In ALS, brain NAA/(Cho+Cr) was reduced 19% (p=0.024) in the motor cortex and 16% (p=0.021) in the CST (centrum semiovale and posterior internal capsule) regions. NAA/ (Cho+Cr) was not reduced in frontal cortex, parietal cortex, medial gray matter, or anterior internal capsule. There was a significant relation between ALS motor cortex NAA/(Cho+Cr) and maximum finger-tap rate (r=0.80; p=0.014). NAA/(Cho+Cr) was reduced in motor cortex and CST regions and unchanged in other brain regions of ALS patients when compared with controls. These findings are consistent with the known distribution of neuronal loss in ALS. The positive correlation between motor cortex NAA/(Cho+Cr) and maximum finger-tap rate suggests that reduced NAA/(Cho+Cr) is a surrogate marker of motor cortex neuron loss in ALS. These findings support the study of 1H MRSI NAA measurement as an objective and quantitative measurement of upper motor neuron dysfunction in ALS.

Adult↗
PubMed2001

Marked increase in cyclooxygenase-2 in ALS spinal cord: implications for therapy.

OBJECTIVE: To evaluate the hypothesis that cyclooxygenase-2 (COX-2) is linked to the pathology of ALS by determining whether COX-2 mRNA levels are upregulated in ALS spinal cord. METHODS: Spinal cord from 11 ALS cases and 27 controls consisting of 15 cases of Alzheimer disease (AD), six cases of Parkinson disease (PD), three cases of cerebrovascular disease, and three control cases were analyzed. Total RNA was extracted and reverse transcriptase-PCR analysis performed for the mRNA of COX-2, COX-1, the microglial marker CD11b, and the housekeeping gene cyclophilin. RESULTS: In ALS compared with non-ALS spinal cord, COX-2 mRNA was upregulated 7.09-fold (p < 0.0001), COX-1 1.14-fold (p = 0.05), and CD11b 1.85-fold (p = 0.0012). COX-2 mRNA levels in AD, PD, cerebrovascular disease, and control cases were each significantly lower than in ALS and were not significantly different from each other. Western blots of the protein products were in general accord with the mRNA data, with COX-2 protein levels being upregulated 3.79-fold compared with non-ALS cases (p = 0.015). CONCLUSIONS: The strong upregulation of COX-2 mRNA in ALS is in accord with studies in the superoxide dismutase transgenic mouse model in which COX-2 upregulation occurs. Taken in conjunction with evidence of a neuroprotective effect of COX-2 inhibitors in certain animal models and in organotypic cultures, the data are supportive of a possible future role for COX-2 inhibitors in the treatment of ALS.

Aged↗
PubMed2001

Changes in Ca, Cu, Fe, Mg, and Zn contents in mouse brain tissues after prolonged oral ingestion of brick tea liquor containing a high level of Al.

A study was conducted to analyze the regional distribution of Ca, Cu, Fe, Mg, and Zn contents in brain tissues after animals were given liquor of brick tea that contained a high Al content. In 25 normal adult male mice given either water or 0.9% NaCl for 1 mo or 2 mo, the metal concentrations in the serum, liver, frontal cortex, hippocampus, cerebellum, and brain stem were comparable (p > 0.05). When the drinking water was replaced by a 1% brick tea liquor, which contained a high Al content, serum Al concentration was increased significantly 1 mo after the onset of the experiment and remained high at the end of the second month. The level of Al was also elevated in both the cortex and hippocampus at 1 mo after replacing tea for drinking water. In addition to Al, there were a significant increase in hippocampal Zn and a decrease in Cu contents. There was no change in tissue Mg or Fe contents, but there was a significant increase in Ca content in every brain region studied. It was suggested that the increase in Ca might be the result of the effect of other components in tea. Unlike the brain, there was no change in the concentration of any of the metals, including Al, in the liver, which further demonstrated that the changes observed in the brain was specific. The results of the present study confirmed that Al, when given orally in the form of tea, could be absorbed into the bloodstream. The absorbed Al could accumulate in selected brain regions. The presence of Al might also change the tissue content of endogenous trace metals.

Aluminum↗
PubMed2001

The pathogenesis of ALS: implications for treatment strategies.

Besides the free radical hypothesis raised by the identification of Superoxide Dismutase I mutations in a subset of familiar Amyotrophic Lateral Sclerosis (ALS) patients, three etiopathogenic hypotheses for sporadic ALS, namely autoimmune, neurofilament, and glutamate toxicity, have attracted interest in the last few years. The role of autoimmunity in ALS has been seriously questioned. The excitotoxic hypothesis for ALS spurred two clinical trials with riluzole. The results of both studies showed a modest benefit in prolonging survival that was statistically significant. Riluzole was the first drug made available for ALS patients. It began a new era in both basic and clinical research. Various human recombinant neurotrophic molecules (CNTF, BDNF, IGF-I) were administered to ALS patients. IGF-I slowed the progression of functional impairment in patients with ALS with no adverse effects. The recent demonstration of the specific viral echovirus 7 RNA sequences in the spinal cord of ALS patients refocused research on the viral hypothesis of the disease and antiviral drugs are ready to be used in clinical settings. New treatment strategies are today under study: intrathecal infusion with BDNF, intrathecal capsules for neurotrophic factor secretion or in vivo gene therapy using viral vectors. New research findings are, more than for other diseases, immediately transferred to clinical ground for the desperate need of a curative treatment of the patients affected by ALS.

Amyotrophic Lateral Sclerosis↗
PubMed2001

Beyond denial and despair: ALS and our heroic potential for hope.

Because the patient with amyotrophic lateral sclerosis (ALS) knows at the outset that he or she is facing an incurable and always fatal illness, the experience of hope may be different in the ALS community from that in the general palliative care community. Although the word "hope" is frequently and passionately used by both patients and professionals in the ALS community, to date there has been little published on the subject. Hopelessness and despair are a very real part of the ALS experience. But true hope, of a kind more powerful than mere physical survival, can also be part of the ALS journey. What is this "hope" the professional is expected to engender and the patient is encouraged not to lose? How can professionals help the ALS patient find hope and meaning? This article is an exploration of hope by someone who has experienced ALS, first as an occupational therapist, then as the daughter and caregiver of an ALS patient. Based on literature review and personal experience, factors leading to both hope and hopelessness are explored. Finally, the author offers several strategies that palliative care professionals can use to help ALS patients find hope.

Adaptation, Psychological↗
PubMed2006

Auto-antibodies against proteins of spinal cord cells in cerebrospinal fluid of patients with amyotrophic lateral sclerosis (ALS).

Aetiology and pathogenesis of amyotrophic lateral sclerosis (ALS) is still a mystery. Among several hypotheses autoimmune mechanisms are also taken into account. We report here our investigations of auto-antibodies against proteins of spinal cord cells in the cerebrospinal fluid (CSF) and serum of ALS patients. The results were correlated with the severity of disease course. The subjects were 57 ALS patients (29 severe, 28 mild) and 10 normal controls. The major finding in CSF was the presence of antibodies against a 70 kD protein in the majority of ALS patients. This protein was identified as neurofilament 68. The second protein of high reactivity and frequency of appearance was a 82 kD protein, which was identified as a-actinin. Less reactive and less frequent were antibodies directed against 55 kD and 40 kD proteins. They were immunologically defined to be related to desmin and actin, resp. The difference between the reactivity of anti-neurofilament and anti-desmin related protein in the severe and mild ALS groups was significant. More frequent were the anti-neurofilament antibodies in the severe ALS cases as compared to the milder ones. In normal CSF, antibodies directed against 55 kD, 70 kD and 82 kD proteins were present in traces and appeared in 5%, 20% and 10% of cases, respectively. In the serum of 30% of severe ALS patients traces of antibodies against 70 kD protein were detected. The morphological studies in the presence of CSF of ALS patients revealed pronounced immunoreactivity of spinal cord neurons, mainly within anterior horns. The significance of the presence of auto-antibodies in CSF of ALS patients against cellular proteins of the spinal cord is hard to define. It is conceivable that they appear as a secondary immunological consequence of neuronal death. It is also possible that they may accelerate the course of neuronal degeneration.

Actinin↗
PubMed1993

[Effect of parathyroidectomy (PTX) on aluminum (Al) induced bone disease].

Al-treated or untreated decalcified sections of bone matrix were implanted subcutaneously into the abdominal wall of parathyroidectomized (PTX) or control rats for 21 or 28 days. The bone remodeling and Al, Ca content in the implants were measured by using histomorphometry and atomic absorption spectrum method. The results showed that bone area, osteoclast number, osteoblast number and bone mineralization rate of Al-treated or untreated bone in PTX rats and of Al-treated bone in control rats were significantly lower than those of untreated bone in control rats (P < 0.05). There was no marked difference between these parameters of Al-treated bone in control rats and untreated bone in PTX rats (P > 0.05), and these of Al-treated bone in PTX rats were the lowest (P > 0.05- < 0.05). Ca contents were consistent with the histological parameters. Bone Al removing rate between PTX and control rats was not markedly different. In conclusion, both PTX and Al impair bone formation and mineralization, bone biopsy and removal of Al from bone is necessary before PTX treatment in uremic patients with secondary hyperparathyroidism.

Aluminum↗
PubMed2005

Detection of serum reverse transcriptase activity in patients with ALS and unaffected blood relatives.

BACKGROUND: Retroviral involvement in the etiology of sporadic ALS has been suspected for several years since the recognition that both murine and human retroviruses can cause motor neuron disease-like syndromes. In a pilot study, an increased prevalence of a retroviral marker (reverse transcriptase [RT] activity) was demonstrated in the serum of British patients with ALS. The current investigation was designed to confirm and extend these findings in a geographically distinct patient cohort under blinded testing conditions. METHODS: A highly sensitive product-enhanced RT assay was employed to test coded sera obtained from 30 American patients with sporadic ALS and from 14 of their blood relatives, 16 of their spouses, and 28 nonrelated, nonspousal control subjects. RESULTS: Serum RT activity was detected in a higher proportion of ALS patients (47%) than in non-blood-related controls (18%; p = 0.008). The prevalence of RT activity in the serum of spousal controls (13%) was similar to that in other non-blood-related controls. Unexpectedly, the prevalence of serum RT activity in blood relatives of ALS patients (43%) approached that in the ALS patients themselves. CONCLUSIONS: These results confirm that patients with ALS have a significantly higher prevalence of serum reverse transcriptase (RT) activity than that seen in unrelated control subjects. The finding of a similarly increased prevalence in blood relatives of ALS patients raises the possibility that the observed RT activity might be due to an inherited endogenous retrovirus.

Adult↗
PubMed1998

The effects of hydrolysis and oligomerization upon the NMR shieldings of Be+2 and Al+3 species in aqueous solution.

The 9Be and 27Al NMR shieldings have been calculated for the species Be(OH2)+24, Be(OH2)3OH+1, Be3(OH)3(OH2)+36, Be2(OH)2(OH2)+24, Be2(OH)(OH2)+36, Al(OH2)+36, Al(OH2)5OH+2, and Al2(OH)2(OH2)+48 using a 6-31G* basis set and the gauge-including atomic orbital (GIAO) method. Our results indicate that although hydrolysis deshields the Be and Al nuclei, oligomerization shields them. Since experiment indicates that the most stable Be+2 and Al+3 species in aqueous solution at moderate concentration and pH are Be3(OH)3(OH2)+36 and Al2(OH)2(OH2)+48, respectively, which are both hydrolyzed and oligomerized, their shieldings are little different from those of their unhydrolyzed, unpolymerized parent species Be(OH2)+24 and Al(OH2)+36. The calculated deshielding of Be3(OH)3(OH2)+36 with respect to Be(OH2)+24 is only 0.8 ppm (compared to 0.61 ppm observed experimentally) while the calculated deshielding of Al2(OH)2(OH2)+48 compared to Al(OH2)+36 is 2.1 ppm (compared to 3.5 ppm observed experimentally). The corner sharing Be dimer, Be2(OH)(OH2)+36 is about 0.1 ppm more strongly shielded than Be(OH2)+24. The hydrolyzed monomeric species Be(OH2)3OH+1 and Al(OH2)5OH+2 are calculated to be deshielded by 1.97 and 8.8 ppm, respectively, vs their parent ions. Such species may be observable at very low concentration, but their quadrupole coupling constants are large and they may have large linewidths. Calculated changes in average 1H NMR shieldings for the hydrolyzed, oligomerized species derived from aqueous Be+2 are also in accord with experimental NMR data. Calculated energetics for the formation of oligomeric species from the hydrolyzed ions are consistent with the greater relative stability of oligomerized species in the Be case compared to Al.

Aluminum Compounds↗
PubMed1988

Skeletal muscle amyloid deposition in AL- (primary or myeloma-associated), AA- (secondary), and prealbumin-type amyloidosis.

Amyloid deposition in the quadriceps femoris muscle was investigated in 12 cases of systemic amyloidosis including 6 of AL-(primary or myeloma-associated) type, 2 of AA- (secondary) type, and 4 of prealbumin- (familial or sporadic) types. Clinically, muscle weakness was found in 7 patients. Among the 7 patients, one of the AL-type suffered from systemic myopathy showing progressive muscular stiffness, pseudohypertrophy, and weakness. The other 6 presented with polyneuropathy. Pathologically, no amyloid was found to be deposited in the AA-type. In all of the AL- and prealbumin-types, amyloid deposition was found in the blood vessels and peri- and endomysium. The degrees of amyloid deposition were marked in one case of the AL-type, which was considered to be suffering from amyloid myopathy, moderate in one of the AL-type, and slight in the rest of the AL-type and all of the prealbumin-type. Our observations and descriptions in the literature indicate that the presence and degrees of amyloid deposition in the skeletal muscles would be related to the types of amyloid proteins in amyloidosis. It seems likely that the affinity of amyloid to the skeletal muscles is variable in AL-type, probably depending on the molecular heterogeneity of AL protein, is low in prealbumin-type, and is almost absent in AA-type.

Adult↗
PubMed2006

A P300-based brain-computer interface: initial tests by ALS patients.

OBJECTIVE: The current study evaluates the effectiveness of a brain-computer interface (BCI) system that operates by detecting a P300 elicited by one of four randomly presented stimuli (i.e. YES, NO, PASS, END). METHODS: Two groups of participants were tested. The first group included three amyotrophic lateral sclerosis (ALS) patients that varied in degree of disability, but all retained the ability to communicate; the second group included three non-ALS controls. Each participant participated in ten experimental sessions during a period of approximately 6 weeks. During each run the participant's task was to attend to one stimulus and disregard the other three. Stimuli were presented auditorily, visually, or in both modes. RESULTS: Two of the 3 ALS patient's classification rates were equal to those achieved by the non-ALS participants. Waveform morphology varied as a function of the presentation mode, but not in a similar pattern for each participant. CONCLUSIONS: The event-related potentials elicited by the target stimuli could be discriminated from the non-target stimuli for the non-ALS and the ALS groups. Future studies will begin to examine online classification. SIGNIFICANCE: The results of offline classification suggest that a P300-based BCI can serve as a non-muscular communication device in both ALS, and non-ALS control groups.

Adult↗
PubMed2006

Flux-assisted wetting and spreading of Al on TiC.

The effect of a K-Al-F-based flux on the spreading of Al on TiC, at temperatures up to 900 degrees C, in Ar and in air has been studied. Whilst obtuse contact angles were observed without flux, the flux facilitated rapid spreading to a perfect wetting condition, in both Ar and in air. The atmosphere was found to have a weak effect on the spreading kinetics as the liquid flux provides a locally protective atmosphere by spreading over the TiC surface and also on the solid surface of Al. The flux dissolves the aluminium oxide, covering Al, so that when Al melts, and the oxide layer has been removed or weakened, intimate contact occurs between liquid Al and the TiC substrate facilitating spontaneous spreading and instantaneous wetting of liquid Al on TiC. Since flux-assisted spreading is very rapid and occurs without the formation of a reaction layer at the Al/TiC interface, this process is very different to the reactive wetting behaviour previously reported in the Al-TiC system.

Journal Article↗
PubMed2006

The growth plate sparing effects of the selective glucocorticoid receptor modulator, AL-438.

Long-term use of glucocorticoids (GC) can cause growth retardation in children due to their actions on growth plate chondrocytes. AL-438, a non-steroidal anti-inflammatory agent that acts through the glucocorticoid receptor (GR) retains full anti-inflammatory efficacy but has reduced negative effects on osteoblasts compared to those elicited by prednisolone (Pred) or dexamethasone (Dex). We have used the murine chondrogenic ATDC5 cell line to compare the effects of AL-438 with those of Dex and Pred on chondrocyte dynamics. Dex and Pred caused a reduction in cell proliferation and proteoglycan synthesis, whereas exposure to AL-438 had no effect. LPS-induced IL-6 production in ATDC5 cells was reduced by Dex or AL-438, showing that AL-438 has similar anti-inflammatory efficacy to Dex in these cells. Fetal mouse metatarsals grown in the presence of Dex were shorter than control bones whereas AL-438 treated metatarsals paralleled control bone growth. These results indicate that the adverse effects Dex or Pred have on chondrocyte proliferation and bone growth were attenuated following AL-438 exposure, suggesting that AL-438 has a reduced side effect profile on chondrocytes compared to other GCs. This could prove important in the search for new anti-inflammatory treatments for children.

Animals↗
PubMed2004

Vibrational frequencies and structural determination of Al(8)S(12).

The normal mode frequencies and corresponding vibrational assignments of Al(8)S(12) in T(h) symmetry are examined theoretically using the Gaussian98 set of quantum chemistry codes. All normal modes were successfully assigned to one of four types of motion (Al-S stretch, Al-S-Al bend, S-Al-S bend, and Al-S-Al wag) predicted by a group theoretical analysis. Normal mode frequencies are predicted and calculated infrared intensities and Raman activities are presented. The thermodynamics of the reaction 2Al(4)S(6)-->Al(8)S(12) are examined.

Aluminum↗
PubMed2005

Tetrakis(thiadiazole)porphyrazines. 4. Direct template synthesis, structure, general physicochemical behavior, and redox properties of Al(III), Ga(III), and In(III) complexes.

Monometallic derivatives of tetrakis(1,2,5-thiadiazole)porphyrazine, [TTDPzH2], with main group tervalent metal ions having the formulae [TTDPzMX] (TTDPz = tetrakis(1,2,5-thiadiazole)porphyrazinato dianion; M = Al(III), X = Cl-, Br-, OH-; M = Ga(III), X = Cl-, OH-; M = In(III), X = AcO-) were prepared and investigated by single-crystal X-ray analysis and IR and UV-vis spectroscopy as well as cyclic voltammetry and spectroelectrochemistry. The complexes [TTDPzMX] (M = Al(III), X = Cl-, Br-; M = Ga(III), X = Cl-) were obtained by direct autocyclotetramerization of the precursor 3,4-dicyano-1,2,5-thiadiazole in hot quinoline in the presence of MX3 salts (M = Al(III), Ga(III); X = Cl-, Br-) and were hydrolized to form the corresponding hydroxide derivatives, [TTDPzMOH]. The In(III) complex, [TTDPzIn(OAc)], was obtained from the free-base macrocycle [TTDPzH2] with In(OH)(OAc)2 in CH3COOH. A single-crystal X-ray study was made at 173 K on the two isostructural species [TTDPzMCl] (M = Al(III), Ga(III)), which have space group P, with a = 12.470(14), b = 12.464(13), and c = 13.947(12) angstroms, alpha = 70.72(3), beta = 79.76(3), and gamma = 90.06(3) degrees, V = 2009.3(3) angstroms3, and Z = 4 for [TTDPzAlCl] and a = 12.429(3), b = 12.430(3), and c = 13.851(3) angstroms, alpha = 70.663(6), beta = 79.788(8), and gamma = 89.991(9) degrees, V = 1983.3(7) angstroms3, and Z = 4 for [TTDPzGaCl]. Square pyramidal coordination exists about the M(III) centers, with Cl- occupying the apical position (Al-Cl = 2.171(5) and Ga-Cl = 2.193(1) angstroms). Al(III) and Ga(III) are located at distances of 0.416(6) and 0.444(2) angstroms from the center of the N4 system. The molecular packing consists of stacked double layers with internal and external average interlayer distances of 3.2 and 3.3 angstroms, respectively. IR spectra show nu(Al-Cl) at 345 cm(-1) for [TTDPzAlCl], nu(Al-Br) at 330 cm(-1) for [TTDPzAlBr], and nu(Ga-Cl) at 382 cm(-1) for [TTDPzGaCl]. The UV-vis spectra in weakly basic (pyridine, DMF, DMSO) and acidic solvents (CF3COOH, H2SO4) show the typical intense pi --> pi transition bands in the Soret (300-400 nm) and Q-band regions (640-660 nm), the bands evidencing some dependence on the nature of the solvent, particularly in acidic solutions. Cyclic voltammetry, differential pulse voltammetry, and thin-layer spectroelectrochemical measurements in pyridine and dimethylformamide of the species [TTDPzMX] indicate reversible first and second one-electron reductions, whereas additional ill-defined reductions are observed at more negative potentials. The examined species are much easier to reduce than their phthalocyanine or porphyrin analogues as a result of the remarkable electron-attracting properties of the TTDPz macrocycle which contains annulated strongly electron-deficient thiadiazole rings.

Journal Article↗
PubMed1998

Characterization of Calcium Aluminate Hydrates and Related Hydrates of Cement Pastes by (27)Al MQ-MAS NMR.

27Al multi quantum (MQ) MAS NMR spectroscopy was used for the first time to characterize calcium aluminate hydrates, which are of importance in the chemistry of high alumina and Portland cements. Substitution sites of silicon by aluminum in the calcium silicate hydrates (C-S-H) which are the main component of Portland cement paste were studied too. Synthetic samples of Ca(3)Al(OH)(12), [CaAl(OH)(4)][OH(H(2)O)(1.5)], [Ca(2)Al(OH)(6)](OH).3H(2)O, [Ca(2)Al(OH)(6)](2)(CO(3)).5H(2)O, [Mg(2)Al(OH)(6)](CO(3))(0.5).3H(2)O, Al(OH)(3), and C-S-H substituted by aluminum were prepared. In most of the samples, the two dimension 3Q-MAS NMR spectra allow one, more easily than the MAS-only NMR spectra, to obtain the chemical shift, delta(iso), and the quadrupolar parameters nu(Q) and eta, which label each site and bring information on its symmetry and environment. The distributions of the aluminum environments were observed for each site. In [Ca(2)Al(OH)](6)(OH).3H(2)O, (27)Al MAS spectrum demonstrates the presence of two octahedral aluminum sites. In the C-S-H substituted with Al, tetrahedral aluminum is observed, in bridging and nonbridging sites of the silicate chains, mostly in the bridging sites for the sample investigated.

Journal Article↗
PubMed2002

Ab initio studies on Al(+)(H(2)O)(n), HAlOH(+)(H(2)O)(n-1), and the size-dependent H(2) elimination reaction.

We report computational studies on Al(+)(H(2)O)(n), and HAlOH(+)(H(2)O)(n-1), n = 6-14, by the density functional theory based ab initio molecular dynamics method, employing a planewave basis set with pseudopotentials, and also by conventional methods with Gaussian basis sets. The mechanism for the intracluster H(2) elimination reaction is explored. First, a new size-dependent insertion reaction for the transformation of Al(+)(H(2)O)(n), into HAlOH(+)(H(2)O)(n-1) is discovered for n > or = 8. This is because of the presence of a fairly stable six-water-ring structure in Al(+)(H(2)O)(n) with 12 members, including the Al(+). This structure promotes acidic dissociation and, for n > or = 8, leads to the insertion reaction. Gaussian based BPW91 and MP2 calculations with 6-31G* and 6-31G** basis sets confirmed the existence of such structures and located the transition structures for the insertion reaction. The calculated transition barrier is 10.0 kcal/mol for n = 9 and 7.1 kcal/mol for n = 8 at the MP2/6-31G** level, with zero-point energy corrections. Second, the experimentally observed size-dependent H(2) elimination reaction is related to the conformation of HAlOH(+)(H(2)O)(n-1), instead of Al(+)(H(2)O)(n). As n increases from 6 to 14, the structure of the HAlOH(+)(H(2)O)(n-1) cluster changes into a caged structure, with the Al-H bond buried inside, and protons produced in acidic dissociation could then travel through the H(2)O network to the vicinity of the Al-H bond and react with the hydride H to produce H(2). The structural transformation is completed at n = 13, coincident approximately with the onset of the H(2) elimination reaction. From constrained ab initio MD simulations, we estimated the free energy barrier for the H(2) elimination reaction to be 0.7 eV (16 kcal/mol) at n = 13, 1.5 eV (35 kcal/mol) at n = 12, and 4.5 eV (100 kcal/mol) at n = 8. The existence of transition structures for the H(2) elimination has also been verified by ab initio calculations at the MP2/6-31G** level. Finally, the switch-off of the H(2) elimination for n > 24 is explored and attributed to the diffusion of protons through enlarged hydrogen bonded H(2)O networks, which reduces the probability of finding a proton near the Al-H bond.

Journal Article↗