Showing papers by "Polytechnic University of Valencia published in 2002"
TL;DR: This review is focused on the use of solid Lewis acids to promote catalytic oxidations, and the core of the review is organized to show the evolution from the simplest strategy for heterogeneizing homogeneous catalysts, to the more elaborate ones in which the active sites are part of the solid structure.
Abstract: This review is focused on the use of solid Lewis acids to promote catalytic oxidations. While the concept of using Lewis acids to promote the reaction of organic substrates with oxidizing reagents is widely accepted in homogeneous catalysis, this concept has not become evident and generally used in heterogeneous catalysis until recent days. Certainly the development of new Lewis acid solids active and selective for catalytic oxidations is an urgent need and a challenging scientific target for some substrates especially using environmentally friendly oxidants. Since the replacement of current stoichiometric oxidations for the production of fine chemicals by environmentally benign catalytic oxidations is one of the major tasks in green chemistry, solid Lewis acids are called to play a crucial role to accomplish this goal. In the review, we will see the still important role that stoichiometric oxidations play in our daily life, and how they are being substituted by catalytic oxidations. At this point, three general mechanisms in which Lewis acids are involved will be described, and the material has been organized starting from homogeneous and ending with solid catalysts for heterogeneous oxidations. A bridge between the two will be established by presenting catalytic systems that can fill the gap between the two systems helping to rationalize the nature of the catalytic active sites in solid systems. This review is obviously focused on solid oxidation catalysts, and the core of the review is organized to show the evolution from the simplest strategy for heterogeneizing homogeneous catalysts, i.e., supporting the active species on large surface area solids, to the more elaborate ones in which the active sites are part of the solid structure. Given the importance of metallosilicates, and more specifically titanosilicates, as catalysts in commercial processes, special attention has been paid to these types of materials. Although sufficient references are provided to early seminal work, special emphasis has been given to most recent contributions to this area, particularly of the last 10 years. Patent literature has also been extensively covered in this review. Examples to illustrate the concepts have been selected among recent publications, and an effort has been made to present a series of commercial and near commercial processes based on catalytic oxidations. Finally, two * E-mail: acorma@itq.upv.es. 3837 Chem. Rev. 2002, 102, 3837−3892
578 citations
TL;DR: The synthesis of ITQ-21 is reported, a zeolite with a three-dimensional pore network containing 1.18-nm-wide cavities that exhibits high catalytic activity and selectivity for valuable products in preliminary oil refining tests.
Abstract: Crude oil is an important feedstock for the petrochemical industry and the dominant energy source driving the world economy, but known oil reserves will cover demand for no more than 50 years at the current rate of consumption1. This situation calls for more efficient strategies for converting crude oil into fuel and petrochemical products. At present, more than 40% of oil conversion is achieved using catalysts based on faujasite; this zeolite requires extensive post-synthesis treatment to produce an ultrastable form2,3, and has a large cavity accessible through four 0.74-nm-wide windows and thus limits the access of oil molecules to the catalytically active sites. The use of zeolites with better accessibility to their active sites should result in improved catalyst efficiency. To date, two zeolites with effective pore diameters exceeding that of faujasite have been reported4,5, but their one-dimensional pore topology excludes use in oil refining. Similarly, zeolites with large pores and a three-dimensional pore topology have been reported6,7,8, but in all these materials the pore openings are smaller than in faujasite. Here we report the synthesis of ITQ-21, a zeolite with a three-dimensional pore network containing 1.18-nm-wide cavities, each of which is accessible through six circular and 0.74-nm-wide windows. As expected for a zeolite with this structure, ITQ-21 exhibits high catalytic activity and selectivity for valuable products in preliminary oil refining tests.
508 citations
TL;DR: The results of this work confirm the xanthoxin→abscisic aldehyde→ABA transition as the last steps of the major ABA biosynthetic pathway.
Abstract: Mutants able to germinate and perform early growth in medium containing a high NaCl concentration were identified during the course of two independent screenings and named salt resistant ( sre ) and salobreno ( san ). The sre and san mutants also were able to germinate in high-osmoticum medium, indicating that they are osmotolerant in a germination assay. Complementation analyses revealed that sre1-1 , sre1-2 , san3-1 , and san3-2 were alleles of the abscisic acid (ABA) biosynthesis ABA2 gene. A map-based cloning strategy allowed the identification of the ABA2 gene and molecular characterization of four new aba2 alleles. The ABA2 gene product belongs to the family of short-chain dehydrogenases/reductases, which are known to be NAD- or NADP-dependent oxidoreductases. Recombinant ABA2 protein produced in Escherichia coli exhibits a K m value for xanthoxin of 19 � M and catalyzes in a NAD-dependent manner the conversion of xanthoxin to abscisic aldehyde, as determined by HPLC‐mass spectrometry. The ABA2 mRNA is expressed constitutively in all plant organs examined and is not upregulated in response to osmotic stress. The results of this work are discussed in the context of previous genetic and biochemical evidence regarding ABA biosynthesis, confirming the xanthoxin → abscisic aldehyde → ABA transition as the last steps of the major ABA biosynthetic pathway.
424 citations
TL;DR: The catalytic activity of Sn-Beta zeolite in the Meerwein-Ponndorf-Verley reduction of carbonyl compounds with secondary alcohols was performed with quantitative yields to the corresponding alcohol.
Abstract: The catalytic activity of Sn-Beta zeolite in the Meerwein−Ponndorf−Verley (MPV) reduction of carbonyl compounds with secondary alcohols was performed with quantitative yields to the corresponding alcohol. This heterogeneous catalyst exhibits activities and selectivities not observed before with other Me-zeolites.
378 citations
Proceedings Article•
08 Jul 2002TL;DR: This paper shows how a single decision tree can represent a set of classifiers by choosing different labellings of its leaves, or equivalently, an ordering on the leaves, and proposes a novel splitting criterion which chooses the split with the highest local AUC.
Abstract: ROC analysis is increasingly being recognised as an important tool for evaluation and comparison of classifiers when the operating characteristics (i.e. class distribution and cost parameters) are not known at training time. Usually, each classifier is characterised by its estimated true and false positive rates and is represented by a single point in the ROC diagram. In this paper, we show how a single decision tree can represent a set of classifiers by choosing different labellings of its leaves, or equivalently, an ordering on the leaves. In this setting, rather than estimating the accuracy of a single tree, it makes more sense to use the area under the ROC curve (AUC) as a quality metric. We also propose a novel splitting criterion which chooses the split with the highest local AUC. To the best of our knowledge, this is the first probabilistic splitting criterion that is not based on weighted average impurity. We present experiments suggesting that the AUC splitting criterion leads to trees with equal or better AUC value, without sacrificing accuracy if a single labelling is chosen.
332 citations
TL;DR: Physico-chemical and chemical characteristics of 13 coconut coir dust samples from Asia, America and Africa were evaluated as peat alternatives, and all properties studied differed significantly between and within sources, and from the control Sphagnum peat.
322 citations
266 citations
TL;DR: A new IR sensor based on the light intensity back-scattered from objects and able to measure distances of up to 1 m is described and the expected errors in distance estimates are analysed and modelled.
260 citations
TL;DR: Sn-Beta is used as a heterogeneous catalyst for the Baeyer-Villiger reaction with hydrogen peroxide, and shape-selective oxidations are observed for isomeric reactants with different molecular shapes.
Abstract: Sn-Beta is used as a heterogeneous catalyst for the Baeyer-Villiger reaction with hydrogen peroxide. Cyclic ketones are transformed into the corresponding lactones, while unsaturated ketones are oxidized to the corresponding unsaturated lactones with very high chemoselectivity. The catalyst is also selective for the oxidation of aromatic aldehydes with H2O2, producing the formate ester or the corresponding hydrolyzed product, that is the alcohol. Shape-selective oxidations are observed for isomeric reactants with different molecular shapes. The catalytic Sn sites have been characterized by 119Sn MAS-NMR spectroscopy, and tetrahedral incorporation into the zeolite framework has been demonstrated. In situ IR spectroscopy and 18O labeling experiments have shown that the oxidation mechanism involves an intermediate of the Criegee type.
250 citations
TL;DR: A chromogenic reagent for cyanide determination in water based on the reaction of this anion with a squaraine derivative functionalized with ether chains has been developed.
218 citations
TL;DR: In this paper, the problem of using future multivariate observations with missing data to estimate latent variable scores from an existing principal component analysis (PCA) model is addressed, and several methods for estimating the scores of new individuals with missing observations are presented.
Abstract: This paper addresses the problem of using future multivariate observations with missing data to estimate latent variable scores from an existing principal component analysis (PCA) model. This is a critical issue in multivariate statistical process control (MSPC) schemes where the process is continuously interrogated based on an underlying PCA model. We present several methods for estimating the scores of new individuals with missing data: a so-called trimmed score method (TRI), a single-component projection method (SCP), a method of projection to the model plane (PMP), a method based on the iterative imputation of missing data, a method based on the minimization of the squared prediction error (SPE), a conditional mean replacement method (CMR) and various least squared-based methods: one based on a regression on known data (KDR) and the other based on a regression on trimmed scores (TSR). The basis for each method and the expressions for the score estimators, their covariance matrices and the estimation errors are developed. Some of the methods discussed have already been proposed in the literature (SCP, PMP and CMR), some are original (TRI and TSR) and others are shown to be equivalent to methods already developed by other authors: iterative imputation and SPE methods are equivalent to PMP; KDR is equivalent to CMR. These methods can be seen as different ways to impute values for the missing variables. The efficiency of the methods is studied through simulations based on an industrial data set. The KDR method is shown to be statistically superior to the other methods, except the TSR method in which the matrix to be inverted is of a much smaller size.
TL;DR: In this paper, the authors carried out the synthesis of ITQ-7 in the presence of Ge and found that the incorporation of Ge reduced the crystallization time from 7 days to less than 12 hours.
Abstract: ITQ-7 is a tri-dimensional twelve-membered ring zeolite which presents double four-membered ring units (D4MR) in its structure. On the basis of theoretical ab initio calculations, which indicate that isomorphic substitution of Ge for Si atoms in the double four-membered ring units stabilizes such small cages, we have carried out the synthesis of ITQ-7 in the presence of Ge. It is found that the incorporation of Ge reduces the crystallization time from 7 days to less than 12 h, while a detailed analysis of the 19F and 29Si MAS NMR leads to the conclusion that Ge selectively occupies positions at the D4MR. An hypothesis has been introduced which assumes that the increase in the crystallization rate is due to the preferential occupancy of D4MR sites by Ge, and this allows relaxation of the constrained T−O−T bonds of these small D4MR cages.
TL;DR: In this paper, the sugar cane bagasse ashes (SCBA) have been chemically, physically and mineralogically characterized, in order to evaluate the possibility of their use as a cement-replacing material in the concrete industry.
Abstract: Sugar cane bagasse is an industrial waste which is used worldwide as fuel in the same sugar-cane industry. The combustion yields ashes containing high amounts of unburned matter, silicon and aluminium oxides as main components. These sugar-cane bagasse ashes (SCBA) have been chemically, physically and mineralogically characterized, in order to evaluate the possibility of their use as a cement-replacing material in the concrete industry. Determination of parameters such as carbon content (by thermal analysis methods), presence of crystalline material (by X-ray diffractometry), granulometric distribution (by laser diffraction in water suspensions), morphology of particles (by scanning electron microscopy) and reactivity towards lime (pozzolanic activity by thermogravimetric monitoring in lime/SCBA and cement/SCBA pastes) have been carried out.
TL;DR: An increase in the expression of the arginine decarboxylase 2 (ADC2) gene in response to mechanical wounding and methyl jasmonate treatment in Arabidopsis was detected by using DNA microarray and RNA gel-blot analysis, providing the first direct evidence of a function of polyamines in the wound-response.
Abstract: Polyamines are small ubiquitous molecules that have been involved in nearly all developmental processes, including the stress response. Nevertheless, no direct evidence of a role of polyamines in the wound response has been described. We have studied the expression of genes involved in polyamine biosynthesis in response to mechanical injury. An increase in the expression of the arginine decarboxylase 2 ( ADC2 ) gene in response to mechanical wounding and methyl jasmonate (JA) treatment in Arabidopsis was detected by using DNA microarray and RNA gel-blot analysis. No induction was observed for the ADC1 gene or other genes coding for spermidine and spermine synthases, suggesting that ADC2 is the only gene of polyamine biosynthesis involved in the wounding response mediated by JA. A transient increase in the level of free putrescine followed the increase in the mRNA level for ADC2 . A decrease in the level of free spermine, coincident with the increase in putrescine after wounding, was also observed. Abscisic acid effected a strong induction on ADC2 expression and had no effect on ADC1 expression. Wound-induction of ADC2 mRNA was not prevented in the JA-insensitive coi1 mutant. The different pattern of expression of ADC2 gene in wild-type and coi1 mutant might be due to the dual regulation of ADC2 by abscisic acid and JA signaling pathways. This is the first direct evidence of a function of polyamines in the wound-response, and it opens a new aspect of polyamines in plant biology.
TL;DR: The motivation of the present contribution was to illustrate that a muscle-like molecule may be stretched or contracted using electrochemistry and coordination chemistry, the main body of the work is organic synthesis.
Abstract: Copper(I)-induced assembly of two self-complementary identical units, which consist of a ring that incorporates a 1,10-phenanthroline group attached to a small filament containing a second 1,10-phenanthroline (phen) group, leads quantitatively to a doubly threaded complex. Each copper(I) center is four-coordinate and is located inside a ring and bound to a phen from the macrocyle. The two other coordination sites are occupied by a phen from the filament connected to the other ring. An X-ray structure of the dicopper(I) complex unambiguously demonstrates the doubly threaded nature of the system. The molecule has C(2) symmetry in the crystal. This is an extended form with a Cu small middle dot small middle dot small middle dotCu separation of 18.3 A and an overall length close to 40 A. Further synthetic work, which utilizes the two terminal phenolic functions of the previous dicopper(I) complex, gives rise to a more complex system in which both filaments have been prolonged in opposite directions by 2,2':6',2"-terpyridine (terpy) motifs and bulky stoppers. The organic backbone is that of a rotaxane dimer. Although redox cycling of Cu(I) to Cu(II) did not lead to intramolecular rearrangement, simple chemical reactions induced large conformational changes. The rotaxane dimer was set in motion as follows. The dicopper(I) complex, which is in an extended conformation, was demetallated by using KCN. From the free ligand, the dizinc complex was formed quantitatively at room temperature. (1)H NMR data show that a new conformation is obtained: each Zn(II) is five-coordinate (phen + terpy), and the molecule is in a contracted conformation. This process is reminiscent of biological muscles in the sense that the two filaments of this system can be moved along one another in a gliding motion that keeps the whole system together, but which converts a stretched compound (overall length approximately equal to 83 A) into a contracted species (overall length approximately equal to 65 A, according to CPK models). The motion is quantitatively reversed by the addition of an excess of copper(I) to the dizinc complex; this regenerates the extended starting form. Although the motivation of the present contribution was to illustrate that a muscle-like molecule may be stretched or contracted using electrochemistry and coordination chemistry, the main body of the work is organic synthesis. This is testified by the fact that the dicopper(I) rotaxane dimer was obtained in 23 steps from commercially available compounds.
TL;DR: The data demonstrate the existence of a metabolon involving at least the last two steps of polyamine biosynthesis in Arabidopsis, and indicate that SPMS is a novel spermine synthase.
Abstract: The conversion of putrescine to spermidine in the biosynthetic pathway of plant polyamines is catalyzed by two closely related spermidine synthases, SPDS1 and SPDS2, in Arabidopsis. In the yeast two-hybrid system, SPDS2 was found to interact with SPDS1 and a novel protein, SPMS (spermine synthase), which is homologous with SPDS2 and SPDS1. SPMS interacts with both SPDS1 and SPDS2 in yeast and in vitro. Unlike SPDS1 and SPDS2, SPMS failed to suppress the speΔ3 deficiency of spermidine synthase in yeast. However, SPMS was able to complement the speΔ4 spermine deficiency in yeast, indicating that SPMS is a novel spermine synthase. The SPDS and SPMS proteins showed no homodimerization but formed heterodimers in vitro. Pairwise coexpression of hemagglutinin- and c-Myc epitope–labeled proteins in Arabidopsis cells confirmed the existence of coimmunoprecipitating SPDS1-SPDS2 and SDPS2-SPMS heterodimers in vivo. The epitope-labeled SPDS and SPMS proteins copurified with protein complexes ranging in size from 650 to 750 kD. Our data demonstrate the existence of a metabolon involving at least the last two steps of polyamine biosynthesis in Arabidopsis.
TL;DR: Different aspects related to iron-fortified foods is reviewed, including used iron compounds, considering its bioavailability and organoleptic problems, food vehicles and possible interactions.
TL;DR: In this article, the authors determined the relaxation times of the cooperative conformational rearrangements of the amorphous phase in semi-crystalline poly(ethylene terephthalate) (PET) and compared them with those calculated in amorphoung PET.
22 Sep 2002
TL;DR: This work investigates the design of on-chip interconnection networks for clustered microarchitectures and proposes point-to-point interconnects together with an effective latency-aware instruction steering scheme and shows that they achieve much better performance than bus-based interConnects.
Abstract: Clustering is an effective microarchitectural technique for reducing the impact of wire delays, the complexity, and the power requirements of microprocessors. In this work, we investigate the design of on-chip interconnection networks for clustered microarchitectures. This new class of interconnects has different demands and characteristics than traditional multiprocessor networks. In a clustered microarchitecture, a low inter-cluster communication latency is essential for high performance. We propose point-to-point interconnects together with an effective latency-aware instruction steering scheme and show that they achieve much better performance than bus-based interconnects. The results show that the connectivity of the network together with latency-aware steering schemes are key for high performance. We also show that these interconnects can be built with simple hardware and achieve a performance close to that of an idealized contention-free model.
TL;DR: It is shown that viroids that replicate and accumulate in the chloroplast are also targets of PTGS and this process may control viroid titer.
Abstract: In plants, posttranscriptional gene silencing (PTGS) has been reported for cytoplasmic RNAs from endogenous nuclear genes, transgenes, viruses, and, recently, for a viroid with nuclear replication and accumulation. However, phenomena of this kind have not been described for mitochondrial or chloroplastic RNAs. Here we show that viroids that replicate and accumulate in the chloroplast are also targets of PTGS and this process may control viroid titer.
TL;DR: Porous pure and doped silicas with pore sizes at two length scales (meso/macroporous) were prepared and shaped both as powders and monoliths through a one-pot surfactant assisted procedure by using a simple template agent and starting from atrane complexes as inorganic precursors as discussed by the authors.
TL;DR: Low-spin, high-spin and spin-transition behaviours have been observed for the doubly interpenetrating three-dimensional bimetallic compounds and influence of pressure--as well as light-induced excited spin-state trapping (LIESST) on the thermal 50% spin transition of the microcrystalline sample has been investigated.
Abstract: Low-spin, high-spin and spin-transition behaviours have been observed for the doubly interpenetrating three-dimensional bimetallic compounds {Fe I I (pz)[Ag(CN) 2 ] 2 }.pz (pz = pyrazine), {Fe I I (4,4'-bipy) 2 [Ag(CN) 2 ] 2 } (4,4'-bipy = 4,4'-bipyridine), and {Fe I I -(bpe) 2 [Ag(CN) 2 ] 2 } (bpe = bispyridyl-ethylene), respectively. The single crystals of the bpe derivative undergo a spin transition with a large hysteresis loop at about 95 K. After several warming and cooling cycles, the single crystals become a microcrystalline powder with 50% spin transition. Influence of pressure- as well as light-induced excited spin-state trapping (LIESST) on the thermal 50% spin transition of the microcrystalline sample has also been investigated. Thermal spin-transition behaviour has also been induced at pressures higher than 1 bar for the 4,4'-bipy derivative. Both the 4,4'-bipy and bpe derivatives show strong pressure dependence of the spin state at 300 K.
TL;DR: The surface and bulk structures of hydrogel contact lenses that contain siloxane moieties, Purevisiontrade mark (balafilcon A) and Focus(R)Night&Day trade mark (lotrafilcon A), were investigated and a macroporous structure was observed on the front and back surfaces, and in their bulk.
Abstract: The surface and bulk structures of hydrogel contact lenses that contain siloxane moieties, Purevision™ (balafilcon A) and Focus®Night&Day™ (lotrafilcon A), were investigated. Standard hydrogel lenses of low (Seequence®), medium (Acuvue®), and high water content (Precision UV®) were used as controls. All the lenses were dehydrated in a series of ethanol solutions of increased concentration, critical-point dried in CO2, and sputter coated with gold/palladium before they were examined by scanning electron microscopy. Of all lenses examined, only the balafilcon lenses presented, in addition to the polymer network porosity characteristic of all hydrogels, a macroporous structure that was observed on the front and back surfaces, and in their bulk. The average diameter of the macropores appears to be much larger, from one to several orders of magnitude, than the network porosity of standard hydrogel lenses. The macropores might contribute to the gas and water permeability of these lenses, as well as to their mobility on the cornea. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 319–325, 2002
TL;DR: In this review, a summary of the current knowledge is presented, and possible future explorations are suggested.
Abstract: Fruit dehiscence is a strategy that many fruits adopt to achieve seed dispersal. The dehiscence process involves the differentiation of specialized cell types and a tight co-ordination of molecular and biochemical events that eventually lead to a cell separation process that frees the seeds once they have matured. In the last few years, great progress has been made in identifying the molecular mechanisms underlying fruit dehiscence in the model plant Arabidopsis thaliana. In this review, a summary of our current knowledge is presented, and possible future explorations are suggested.
TL;DR: Novel colorimetric reagents for fluoride sensing containing anthraquinone as chromogenic signalling subunit and thiourea and urea binding sites have been characterised, and a selective colour change from orange to brown was observed upon addition of fluoride to CH3CN solutions of L1 and to DMSO solutions.
TL;DR: A coherent explanation for all Ppz‐dependent phenotypes is provided and evidence for a causal relationship between intracellular cation homeostasis and a potential cell cycle checkpoint is provided.
Abstract: The yeast Ppz protein phosphatases and the Hal3p inhibitory subunit are important determinants of salt tolerance, cell wall integrity and cell cycle progression. We present several lines of evidence showing that these disparate phenotypes are connected by the fact that Ppz regulates K+ transport. First, salt tolerance, cell wall integrity and cell cycle phenotypes of Ppz mutants are dependent on the Trk K+ transporters. Secondly, Ppz mutants exhibit altered activity of the Trk system, as measured by rubidium uptake. Thirdly, Ppz mutants exhibit altered intracellular K+ and pH, as expected from H+ efflux providing electrical balance during K+ uptake. Our unifying picture of Ppz phenotypes contends that activation of Trk by decreased Ppz activity results in plasma membrane depolarization (reducing uptake of toxic cations), increased intracellular K+ and turgor (compromising cell integrity), and increased intracellular pH (augmenting the expression of pH-regulated genes and facilitating α-factor recovery). In addition to providing a coherent explanation for all Ppz-dependent phenotypes, our results provide evidence for a causal relationship between intracellular cation homeostasis and a potential cell cycle checkpoint.
TL;DR: In this article, a prediction technique based on non-linear dynamics is proposed, comparing its performance with a seasonal AutoRegressive and Moving Average (sARIMA) methodology, dealing with short and medium term forecasting.
Abstract: Successful planning and operation of a solid waste management system depends on municipal solid waste (MSW) generation process knowledge and on accurate predictions of solid waste quantities produced. Conventional analysis and prediction models are based on demographic and socioeconomic factors. However, this kind of analysis is related to mean generation data. Dynamic MSW generation analysis can be done using time series data of solid waste generated quantities. In this paper some tools for time series analysis and forecasting are proposed to study MSW generation. A prediction technique based on non-linear dynamics is proposed, comparing its performance with a seasonal AutoRegressive and Moving Average (sARIMA) methodology, dealing with short and medium term forecasting. Finally, a practical implementation consisting of the study of MSW time series of three cities in Spain and Greece is presented.
TL;DR: A series of heterogeneous catalysts with Lewis and Bronsted basic sites, and acid-base bifunctional pairs has been used in order to perform organic reactions as discussed by the authors, which allows to select the most appropriate catalyst for a specific reaction.
Abstract: A series of heterogeneous catalysts with Lewis and Bronsted basic sites, and acid–base bifunctional pairs has been used in order to perform organic reactions. By changing the chemical composition and activation conditions it is possible to have predominantly Lewis or Bronsted base catalysts within a large range of well defined basicities. This allows to select the most appropriate catalyst for a specific reaction. Thus, MgO, calcined hydrotalcites, rehydrated hydrotalcites and grafted quaternary organic ammonium hydroxides on MCM-41, have been used as catalysts in Knoevenagel condensation, aldolization and Michael additions. Catalysts containing mild acid–base pairs such as those existing in amorphous aluminophosphates (ALPOs) allow to achieve high selectivities with still very reasonable activities.