Composites of Montmorillonite and Titania Nanoparticles Prepared by Inverse Microemulsion Method: Physico-Chemical Characterization

TiO₂/montmorillonite composites were synthesized using inverse micellar route for the preparation of titania nanoparticles (4-6 nm diameter) in 1-hexanol and for the dispersion of one of the clay components. Two series of composites were obtained: one derived from cetyltrimethylammonium organomontmorillonite (CTA-Mt), exfoliated in 1-hexanol, and the other from sodium form of montmorillonite (Na-Mt) dispersed by formation of an inverse microemulsion in 1-hexanol. The TiO₂ content ranged from 16 to 64 wt.%. The composites were characterized with X-ray diffraction, scanning/transmission electron microscopy/energy dispersive X-ray spectroscopy, thermal analysis, and N₂ adsorption-desorption isotherms. The Na-Mt-derived component was shown to undergo transformation to CTA-Mt, as indicated by basal spacing of 17.5 nm, due to the interaction with the CTABr surfactant in inverse microemulsion. It was also better dispersed and intermixed with TiO₂ nanoparticles. As a result, the TiO₂/Na-Mt series displayed superior textural properties, with specific surface area up to 256 m²g^-1 and pore volume up to 0.247 cm³g^-1 compared with 208 m²g^-1 and 0.231 cm³g^-1, respectively, for the TiO₂/CTA-Mt counterpart. Members of both series were uniformly mesoporous, with the dominant pore size around 5 nm, i.e., comparable with the dimensions of titania nanoparticles. The advantage of the adopted synthesis method is discussed in the context of other preparative procedures used for manufacturing of titania-clay composites.

Influence of Dry Milling on Phase Transformation of Sepiolite upon Alkali Activation: Implications for Textural, Catalytic and Sorptive Properties

Activation of natural sepiolite by means of grinding in a planetary mill followed by wet NaOH activation was studied for the purpose of endowing the product with enhanced basicity for potential catalytic/sorptive applications. Synthesized solids were characterized with X-ray powder diffraction (XRD), N₂ adsorption/desorption, scanning electron microscopy (SEM), energy dispersive (EDX), atomic absorption (AAS), Fourier-transform infrared (FTIR) and ²⁹Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies. Surface basicity was determined by titration with benzoic acid. Grinding changed the pathway of sepiolite phase transformation upon NaOH treatment. The as-received sepiolite evolved to Na-sepiolite (loughlinite) with a micropore system blocked by nanocrystalline Mg(OH)₂, while ground samples yielded magnesium silicate hydrate phase (MSH), with well-developed microporous texture. In unmilled sepiolite desilication involved preferential leaching of Si from the center of the structural ribbons, while in ground samples additional loss of Si from ribbon-ribbon corner linkages was observed. In all cases treatment with NaOH led to enhancement of surface basicity. Synthesized materials were tested as catalysts in a base-catalyzed aldol self-condensation of acetone and oxidation of cyclohexanone to ε-caprolactone, as well as CO₂ sorbents. Catalytic trends depended not only on samples’ basicity, but also on texture and phase composition of the catalysts. Grinding combined with alkali activation proved a simple and effective method for boosting CO₂-sorption capacity of sepiolite to the level comparable to amine-functionalized, acid-activated sepiolite sorbents.

Synthesis of Nanocrystalline Mg-Al Hydrotalcites in the Presence of Starch-the Effect on Structure and Composition

The study describes the synthesis of Mg-Al hydrotalcite (Ht) with the use of starch as a structure controlling biotemplate. Syntheses were carried out at room temperature, by co-precipitation at pH = 10. The investigated synthesis parameters included the nature of the precipitating agent (NaOH/Na₂CO₃ or NH₃aq/(NH₄)₂CO₃), the nature of starch (potato, corn and cassava), the method of starch addition to reagents, the method of drying and the effect of washing. The materials were examined with X-ray diffraction, scanning electron microscopy/energy dispersive X-ray spectroscopy and infrared spectroscopy. The data show that synthesis of Ht materials in the presence of starch, with use of the ammonia-based precipitant, enabled preparation of nanocrystalline Ht with very fine (<50 nm) particle size. All investigated starches had a similar effect on the crystallinity and the grain size of Ht precipitates. Ht with the smallest nanocrystals was obtained when starch was present in all solutions used for synthesis, and the final product subjected to freeze drying. Washing with water was found to enhance recrystallization and exchange of nitrates for carbonates. Infrared spectra showed that an interaction exists between the biopolymer template and the Ht particles, resulting in a higher degree of order within the Ht-adhering starch component.

Structural Transformations of Hydrolysates Obtained from Ti-, Zr-, and Ti, Zr-Solutions Used for Clay Pillaring: Towards Understanding of the Mixed Pillars Nature

Structural characteristics of hydrolysates formed from the aqueous Ti-, Zr-, and Ti, Zr-pillaring solutions prepared from inorganic precursors (TiCl₄ and ZrOCl₂), was investigated and compared with that of precipitates obtained from the same solutions after a slight alkalization of pH to the values reported for the conditions of clay pillaring. The materials were recovered by lyophilization and subsequently subjected to calcination at 500, 800 and 1000 °C. Of special interest was the effect of pH on the possible formation of mixed Ti, Zr-oxide species. Powder X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscope/energy dispersive spectrometer (SEM/EDS) analysis showed that even a relatively moderate alteration of pH in Ti-, Zr-, or Ti, Zr-precursor solutions caused substantial changes in the outcome of hydrolytic transformations, manifested by different phase and/or chemical composition of the resulting hydrolysates. Analysis of thermal evolution of hydrolysates showed that alkalization facilitated the transformation of anatase into rutile in materials obtained from Ti-pillaring solution, but retarded tetragonal to monoclinic zirconia conversion in samples derived from Zr-pillaring agent. The most striking effect was observed for the mixed Ti, Zr-pillaring solution, where an increase of pH enabled the formation of zirconium titanate as the only crystalline phase, rather than a multiphase mixture of anatase, monoclinic zirconia and zirconium titanate obtained from the more acidic precursor. The finding supports the model of mixed Ti-O-Zr network in props generated in Ti, Zr-pillared montmorillonites.

The expression of autophagy-related proteins within the corpus luteum lifespan in pigs

Autophagy is a cellular process that involves the degradation of intracellular components. Recent studies suggested a role for autophagy in corpus luteum (CL) regression; however, a complete understanding of its contribution to CL function remains unclear. The present research using porcine CLs obtained from gilts at the early (CL1, n = 5), middle (CL2, n = 5), and late (CL3, n = 5) luteal phase of the estrous cycle aimed to assess the incidence of autophagy during CL development. The stages of collected CLs were verified through morphological analysis and intraluteal progesterone concentration. The presence of autophagosomes was assessed using transmission electron microscopy, and the expression of autophagic markers was examined at mRNA (BECN1 and Lamp1) and protein (Beclin 1, LC3-II, and Lamp 1) levels. Lamp 1 immunolocalization was also performed in luteal tissue. Double-membrane autophagosomes and autophagy-related proteins were found in all examined CLs. Interestingly, there was a greater expression of Beclin 1 (P = 0.005 and P = 0.025) and Lamp 1 (P = 0.009 and P = 0.032) protein in CL3 as compared with CL1 and CL2. In addition, the presence of autolysosomes in CL3 indicated advanced autophagy at that developmental stage. Overall, the occurrence of autophagy throughout CL development and regression suggests it has a role in the regulation of CL lifespan in pigs. In the early and mature CL, autophagy is proposed to promote luteal formation and function, whereas in the late CL, it may participate in luteal regression.

Spinocerebellar ataxia type 7 associated with pigmentary retinal dystrophy

Spinocerebellar ataxia type 7 (SCA7) is an autosomal-dominant, late-onset, slowly progressive disorder, primarily characterized by gradual loss of motor coordination, resulting from dysfunction and degeneration of the cerebellum and its connecting pathways. The disease is caused by expansion of a CAG trinucleotide repeat within the SCA7 gene, which encodes a polyglutamine tract within a novel protein, termed ataxin-7. The expansion of polyglutamine-encoding CAG repeats in dissimilar genes underlies eight neurodegenerative conditions besides SCA7, including a number of dominant ataxias related to SCA7. Although elongated polyglutamine itself can initiate neuronal dysfunction and death, its toxicity is modulated by the context of the disease proteins, as evidenced by the differing clinical and pathological presentation of the various disorders. In this respect, it is exciting that SCA7 constitutes the only polyglutamine disorder, in which the photoreceptors of the retina are also severely affected, leading to retinal degeneration and blindness. Since the discovery of the SCA7 mutation, numerous studies attempted to pinpoint the molecular mechanisms underlying the unique features of SCA7, particularly the retinal involvement. Here we summarize the clinical, pathological, and genetic aspects of SCA7, and review the current understanding of the pathogenesis of this disorder.

Association of ataxin-7 with the proteasome subunit S4 of the 19S regulatory complex

Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder characterized by ataxia and selective neuronal cell loss caused by the expansion of a translated CAG repeat encoding a polyglutamine tract in ataxin-7, the SCA7 gene product. To gain insight into ataxin-7 function and to decipher the molecular mechanisms of neurodegeneration in SCA7, a two-hybrid assay was performed to identify ataxin-7 interacting proteins. Herein, we show that ataxin-7 interacts with the ATPase subunit S4 of the proteasomal 19S regulatory complex. The ataxin-7/S4 association is modulated by the length of the polyglutamine tract whereby S4 shows a stronger association with the wild-type allele of ataxin-7. We demonstrate that endogenous ataxin-7 localizes to discrete nuclear foci that also contain additional components of the proteasomal complex. Immunohistochemical analyses suggest alterations either of the distribution or the levels of S4 immunoreactivity in neurons that degenerate in SCA7 brains. Immunoblot analyses demonstrate reduced levels of S4 in SCA7 cerebella without evident alterations in the levels of other proteasome subunits. These results suggest a role for S4 and ubiquitin-mediated proteasomal proteolysis in the molecular pathogenesis of SCA7.

Isolation of CAG/CTG repeats from within the chromosome 2p21-p24 locus for autosomal dominant spastic paraplegia (SPG4) by YAC fragmentation

Pure autosomal dominant spastic paraplegia (SPG) is a genetically heterogeneous neurodegenerative disorder of the central nervous system clinically characterized by progressive spasticity mainly affecting the lower limbs. Three distinct loci have been mapped to chromosomes 14q (SPG3), 2p (SPG4) and 15q (SPG6). In particular, SPG4 families show striking intrafamilial variability suggestive of anticipation and evidence has been provided that CAG/CTG repeat expansions may be involved. To isolate CAG/CTG repeat containing sequences from within the SPG4 candidate region, a novel approach was developed. Fragmentation vectors were assembled allowing direct fragmentation of yeast artificial chromosomes (YACs) with a short (> or = 21 bp) CAG/CTG sequence as the target site for homologous recombination. We used the CAG/CTG YAC fragmentation vectors to isolate CAG/CTG containing sequences from four YACs spanning the SPG4 candidate region between D2S400 and D2S367. A total of four CAG/CTG containing sequences were isolated of which three were novel. However, none of the four CAG/CTG repeats showed expanded alleles in two Belgian SPG4 families. In addition, we showed that the CAG/CTG alleles detected by the repeat expansion detection (RED) method could be fully explained by two polymorphic nonpathogenic CAG/CTG repeats on chromosomes 17 and 18, respectively. Also, the RED expansions in six SPG families could not be explained by amplification of the CAG/CTG repeats at the SPG4 locus. Together, our data do not support the hypothesis of a CAG/CTG repeat expansion as the molecular mechanism underlying SPG4 pathology.

Molecular genetic analysis of autosomal dominant cerebellar ataxia with retinal degeneration (ADCA type II) caused by CAG triplet repeat expansion

Autosomal dominant cerebellar ataxia with retinal degeneration (ADCAII) was previously mapped by linkage analysis studies to chromosome 3p12-p21.1 (SCA7). Positional cloning efforts have recently identified a novel gene, SCA7 , containing a translated CAG repeat, expanded in SCA7 patients. We cloned the SCA7 gene from a yeast artificial chromosome (YAC) clone contig spanning the SCA7 candidate region. Using a combination of genomic sequencing and cosmid-based exon trapping, two expressed sequence tags were identified. Sequencing of the corresponding cDNA clones and RT-PCR analysis identified the full-length SCA7 cDNA. Together, our sequence data defined the intron/exon boundaries of the first two coding exons of the SCA7 gene, with the first exon containing the expanded CAG repeat. Further, sequence comparison with the published SCA7 cDNA identified one additional putative exon in the 5'-UTR region of the SCA7 gene. The SCA7 gene was mapped on the YAC contig in the 2.5 cM interval between D3S1600 and D3S1287. In one extended Belgian SCA7 pedigree the expanded alleles ranged from 38 to at least 55 repeats with allele lengths being inversely correlated with onset age of ADCAII symptoms. The SCA7 repeats increased in length in successive generations. Normal alleles had from four to 18 repeats, with 10 repeats being the most common allele.

Pure familial spastic paraplegia: clinical and genetic analysis of nine Belgian pedigrees

We ascertained 9 multigeneration Belgian families with pure dominant spastic paraplegia (SPG) for clinical and genetic studies. Linkage was examined using simple tandem repeat (STR) markers located near the 5 loci for familial SPG on chromosomes Xq28 (SPG1), Xq21.3-q22 (SPG2), 2p21-p24 (SPG4), 14q12-q23 (SPG3) and 15q11.1 (SPG6). Positive linkage results were obtained only for markers at the SPG4 locus mapping the SPG4 gene between D2S400 and D2S367, a region of 4 cM. In order to facilitate the positional cloning of the SPG4 gene, we constructed a contiguous YAC map covering the SPG4 candidate region. Our physical mapping data indicate that the SPG4 gene resides within maximal 5 Mb.