Molar Entropy and Enthalpy of CO Adsorbed in Zeolites as Derived from VTIR Data: Role of Intermolecular Modes.

Detailed analysis of recently reported variable-temperature IR (VTIR) spectra of carbon monoxide adsorbed in alkaline zeolites shows how, not only the corresponding values of standard adsorption enthalpy ( ΔH0 ) and entropy ( ΔS0 ) can be obtained, but also the thermodynamic values of molar entropy and enthalpy which characterize the adsorbed gas phase. In addition, it is shown that the so obtained molar entropy data can lead to new insights into soft molecular modes, which would be hardly accessible by conventional IR spectroscopic techniques.

Non-Linear Enthalpy-Entropy Correlation for Nitrogen Adsorption in Zeolites.

The thermodynamics of dinitrogen adsorption in faujasite-type zeolites, Na-Y, Ca-Y and Sr-Y, were investigated by means of variable-temperature infrared spectroscopy, a technique that affords determination of the standard adsorption enthalpy (ΔH°) and entropy (ΔS°) from an analysis of the IR spectra recorded over a range of temperatures. The results obtained, taken together with previously reported values for N2 adsorption on protonic zeolites, revealed a non-linear correlation between ΔH° and ΔS°. Implications of such a correlation for gas separation and purification by adsorption in porous solids are highlighted.

Von Willebrand Factor: Multimeric Structure and Functional Activity in Patients With Atrial Fibrillation With and Without Oral Anticoagulation.

von Willebrand factor (vWF) is a multimeric glycoprotein present in blood plasma. It is synthesized in megakaryocytes and endothelial cells, secreted into circulation in the form of high-molecular-weight multimers (HMWMs), and cleaved into shorter, less active multimers by ADAMTS13. It is essential for platelet adhesion and aggregation. Previous studies have investigated the relationship between vWF levels and thromboembolic events with little regard to vWF multimeric structure. Patients with atrial fibrillation (AF) exhibit higher plasma vWF and lower ADAMTS13 levels. One hundred seven patients with AF, 51 anticoagulated and 56 nonanticoagulated, were eligible for the study. Plasma samples were analyzed for vWF antigen, vWF activity, and ADAMTS13; vWF multimers were analyzed by Western blot in 1% to 1.3% sodium dodecyl sulfate agarose gel electrophoresis. Patients with AF without oral anticoagulation (OAC) had significantly higher vWF plasma levels (154.00 [75-201] UI/dL) and vWF activity (60.00% [20%-210%]) compared to patients with OAC (133.50 [90-192] UI/dL, P = <.001; 50.00% [20%-160%], P = .02). Both were specially decreased in patients treated with acenocumarin. Patients without OAC also showed lower ADAMTS13 levels and presence of vWF HMWMs. Patients with AF show higher plasma levels and vWF activity. Moreover, treatment with traditional OAC (acenocumarin) significantly reduced vWF levels. Patients without OAC might have an increased risk of thrombotic events showing lower ADAMTS13 and higher vWF levels. Patients with stroke had higher plasma levels, vWF activity, and HMWMs. Our study suggests that increased vWF levels and presence of HMWMs could be related to cerebrovascular disease and may represent useful biomarkers for stroke in AF.

Probing Gas Adsorption in Zeolites by Variable-Temperature IR Spectroscopy: An Overview of Current Research.

The current state of the art in the application of variable-temperature IR (VTIR) spectroscopy to the study of (i) adsorption sites in zeolites, including dual cation sites; (ii) the structure of adsorption complexes and (iii) gas-solid interaction energy is reviewed. The main focus is placed on the potential use of zeolites for gas separation, purification and transport, but possible extension to the field of heterogeneous catalysis is also envisaged. A critical comparison with classical IR spectroscopy and adsorption calorimetry shows that the main merits of VTIR spectroscopy are (i) its ability to provide simultaneously the spectroscopic signature of the adsorption complex and the standard enthalpy change involved in the adsorption process; and (ii) the enhanced potential of VTIR to be site specific in favorable cases.

Evaluation of clopidogrel response variability and identification of the CYP2C19 polymorphism in Mexican patients / Evaluación de la variabilidad en la respuesta a clopidogrel e identificación del polimorfismo CYP2C19 en pacientes mexicanos

Abstract Objective Drug inhibition of platelet P2Y12 adenosine diphosphate receptor has reduced the incidence of adverse cardiovascular events after percutaneous coronary interventions. The analysis of the phosphorylation status of vasodilator-stimulated phosphoprotein by flow cytometry has shown a predictive value for adverse events and stent thrombosis. Polymorphisms of CYP2C19 in high risk patients may also relate to adverse cardiovascular events. Methods Ninety patients were enrolled. Patients received a 600 mg clopidogrel loading dose. Blood samples were obtained at the time of the procedure and 24 h later, platelet reactivity was assessed by vasodilator-stimulated phosphoprotein phosphorylation measurement using flow cytometry. Low response to clopidogrel was defined as a platelet reactivity index ≥ 50%. The presence of CYP2C19*2 was identified with the restriction enzyme Smal. Results Mean platelet reactivity index: 53.45 ± 22.48% in the baseline sample and 57.14 ± 23.08% at 24 h (p = 0.183); 40% of patients behaved as good responders, the rest behaved as non-responders with 38% of patients showing platelet reactivity indexes between 50-70% and 22% showing indexes above 70%. The CYP2C19*2 polymorphism was found in 17% of patients, with a 3.9% AA homozygous genotype carriers. Conclusion Response to the clopidogrel loading dose showed a wide variability among patients with 40% responding to the drug according to previously established cut-off values. Our results showed that 3.9% of patients show the AA genotype. To our knowledge, this is the first study involving clopidogrel response by flow citometry and genotype typification in Mexican Mestizo population.

Resumen Objetivo La inhibición del receptor plaquetario P2Y12 se ha asociado con reducción en incidencia de eventos cardiovasculares mayores en pacientes sometidos a intervenciones coronarias percutáneas. El estudio de la fosfoproteína estimulada por vasodilatadores mediante citometría de flujo tiene valor predictivo para desarrollo de eventos adversos y trombosis del stent. Los polimorfismos del CYP2C19 en pacientes de alto riesgo pueden también asociarse con eventos adversos. Método 90 pacientes, dosis de carga de clopidogrel: 600 mg. Se obtuvieron muestras de sangre basales y post-24 horas. La reactividad plaquetaria se estudió mediante medición de fosfoproteína estimulada por vasodiatadores por citometría de flujo. Se consideró baja respuesta al clopidogrel un índice de reactividad plaquetaria ≥50%. La presencia del CYP2C19*2 se identificó con enzima de restricción Smal. Resultados La media del índice de reactividad plaquetaria fue: 53.45 ± 22.48% en muestras basales y 57.14 ± 23.08% a 24 h (p = 0.183); 40% de los pacientes repondieron a clopidogrel, el resto de comportó como no-respondedores, un 38%, mostró índices de reactividad plaquetaria entre 50 -70% y 22%, índices > 70%. El polimorfismo CYP2C19*2 se encontró en 17% pacientes, con un 3.9% portadores de genotipo homozigótico AA. Conclusiones La respuesta a clopidogrel mostró amplia variabilidad entre pacientes, el 40% presentó respuesta de acuerdo con puntos de corte pre establecidos. Un 3.9% de los pacientes presentó genotipo AA. Consideramos que este es el primer estudio realizado en población mestizo-mexicana utilizado citometría de flujo para evaluar la respuesta a clopidogrel así como la tipificación genética de los pacientes.

Evaluation of clopidogrel response variability and identification of the CYP2C19 polymorphism in Mexican patients.

OBJECTIVE: Drug inhibition of platelet P2Y12 adenosine diphosphate receptor has reduced the incidence of adverse cardiovascular events after percutaneous coronary interventions. The analysis of the phosphorylation status of vasodilator-stimulated phosphoprotein by flow cytometry has shown a predictive value for adverse events and stent thrombosis. Polymorphisms of CYP2C19 in high risk patients may also relate to adverse cardiovascular events. METHODS: Ninety patients were enrolled. Patients received a 600mg clopidogrel loading dose. Blood samples were obtained at the time of the procedure and 24h later, platelet reactivity was assessed by vasodilator-stimulated phosphoprotein phosphorylation measurement using flow cytometry. Low response to clopidogrel was defined as a platelet reactivity index≥50%. The presence of CYP2C19*2 was identified with the restriction enzyme SmaI. RESULTS: Mean platelet reactivity index: 53.45±22.48% in the baseline sample and 57.14±23.08% at 24h (p=0.183); 40% of patients behaved as good responders, the rest behaved as non-responders with 38% of patients showing platelet reactivity indexes between 50-70% and 22% showing indexes above 70%. The CYP2C19*2 polymorphism was found in 17% of patients, with a 3.9% AA homozygous genotype carriers. CONCLUSION: Response to the clopidogrel loading dose showed a wide variability among patients with 40% responding to the drug according to previously established cut-off values. Our results showed that 3.9% of patients show the AA genotype. To our knowledge, this is the first study involving clopidogrel response by flow citometry and genotype typification in Mexican Mestizo population.

A rapid microwave-assisted synthesis of a sodium-cadmium metal-organic framework having improved performance as a CO2 adsorbent for CCS.

We report on a facile and rapid microwave-assisted method for preparing a sodium-cadmium metal-organic framework (having coordinatively unsaturated sodium ions) that considerably shortens the conventional synthesis time from 5 days to 1 hour. The obtained (Na,Cd)-MOF showed an excellent volumetric CO2 adsorption capacity (5.2 mmol cm(-3) at 298 K and 1 bar) and better CO2 adsorption properties than those shown by the same metal-organic framework when synthesized following a more conventional procedure. Moreover, the newly prepared material was found to display high selectivity for adsorption of carbon dioxide over nitrogen, and good regenerability and stability during repeated CO2 adsorption-desorption cycles, which are the required properties for any adsorbent intended for carbon dioxide capture and sequestration (CSS) from the post-combustion flue gas of fossil fuelled power stations.

Measuring the Brønsted acid strength of zeolites--does it correlate with the O-H frequency shift probed by a weak base?

Brønsted-acid zeolites are currently being used as catalysts in a wide range of technological processes, spanning from the petrochemical industry to biomass upgrade, methanol to olefin conversion and the production of fine chemicals. For most of the involved chemical processes, acid strength is a key factor determining catalytic performance, and hence there is a need to evaluate it correctly. Based on simplicity, the magnitude of the red shift of the O-H stretching frequency, Δν(OH), when the Brønsted-acid hydroxyl group of protonic zeolites interacts with an adsorbed weak base (such as carbon monoxide or dinitrogen) is frequently used for ranking acid strength. Nevertheless, the enthalpy change, ΔH(0), involved in that hydrogen-bonding interaction should be a better indicator; and in fact Δν(OH) and ΔH(0) are often found to correlate among themselves, but, as shown herein, that is not always the case. We report on experimental determination of the interaction (at a low temperature) of carbon monoxide and dinitrogen with the protonic zeolites H-MCM-22 and H-MCM-56 (which have the MWW structure type) showing that the standard enthalpy of formation of OH···CO and OH···NN hydrogen-bonded complexes is distinctively smaller than the corresponding values reported in the literature for H-ZSM-5 and H-FER, and yet the corresponding Δν(OH) values are significantly larger for the zeolites having the MWW structure type (DFT calculations are also shown for H-MCM-22). These rather unexpected results should alert the reader to the risk of using the O-H frequency shift probed by an adsorbed weak base as a general indicator for ranking zeolite Brønsted acidity.

Controlling the adsorption enthalpy of CO(2) in zeolites by framework topology and composition.

Zeolites are often investigated as potential adsorbents for CO(2) adsorption and separation. Depending on the zeolite topology and composition (Si/Al ratio and extra-framework cations), the CO(2) adsorption heats at low coverages vary from -20 to -60 kJ mol(-1), and with increasing surface coverage adsorption heats either stay approximately constant or they quickly drop down. Experimental adsorption heats obtained for purely siliceous porous solids and for ion-exchanged zeolites of the structural type MFI, FER, FAU, LTA, TUN, IMF, and -SVR are discussed in light of results of periodic density functional theory calculations corrected for the description of dispersion interactions. Key factors influencing the stability of CO(2) adsorption complexes are identified and discussed at the molecular level. A general model for CO(2) adsorption in zeolites and related materials is proposed and data reported in literature are evaluated with regard to the proposed model.

Variable-temperature IR spectroscopic and theoretical studies on CO2 adsorbed in zeolite K-FER.

Adsorption of CO(2) in K-FER zeolite is investigated by a combination of variable-temperature IR spectroscopy and periodic DFT calculations augmented for description of dispersion interactions. Calculated adsorption enthalpies for CO(2) adsorption complexes on single extra-framework K(+) sites and on dual-cation sites where CO(2) interacts simultaneously with two extra-framework K(+) cations (-40 and -44 kJ mol(-1), respectively) are in excellent agreement with experimental values. The analysis of effects on the frequency of the asymmetric CO(2) stretching mode ν(3) shows that polarization of CO(2) by the K(+) cation leads to an increase in ν(3), while the interaction of CO(2) with the zeolite framework leads to a decrease in ν(3). In the case of K-FER, the latter effect is slightly larger than the former, and thus a small redshift in ν(3) results (-3 cm(-1) with respect to free CO(2)). For adsorption complexes on dual K(+) sites, where CO(2) interacts with one K(+) cation on each end of the molecule, the polarization of CO(2) molecules on both sides results in a blueshift of ν(3). The origin of the redshift in ν(3) when CO(2) is adsorbed in purely siliceous FER is also investigated computationally. Calculations show that the dispersion interaction does not affect the vibrational frequency of adsorbed CO(2).

Ammonia-solvated ammonium species in the NH(4)-ZSM-5 zeolite.

Interaction of gaseous ammonia with a NH(4)-ZSM-5 zeolite (Si/Al=11.5) was studied by means of infrared (IR) spectroscopy both at constant ambient temperature and in the temperature range 373-573 K. H-bonding of NH(3) molecules to the NH(4) (+) species takes place. The interaction is weak and reversible, resembling a solvation process. Spectral evidence shows that only one N--H moiety is actually available, indicating that ammonium ions are tricoordinated to the zeolite inner surface. H-bonded NH(3) has an absorption band at 1712 cm(-1), which grows with increasing pressure in two steps: a monosolvated ammonium species is initially formed, evolving to a disolvated species for pressures above 5 mbar. Coordination of the second NH(3) molecule takes place at the already coordinated NH(3) molecule and not at the ammonium cation. From the changes in intensity of the 1712 cm(-1) band with changing temperature under a moderate NH(3) equilibrium pressure, the calculated standard enthalpy and entropy of the monosolvation reaction were ΔH(0)=-34(±5) kJ mol(-1) and ΔS(0)=-88(±10) J mol(-1) K(-1), respectively. The enthalpy of the second solvation step was calculated from the corresponding equilibrium constant under the assumption of (nearly) the same entropy change for both solvation processes. In agreement with the overall picture, this enthalpy change is small (-15 kJ mol(-1) at the most). Since in a previous work (M. Armandi, B. Bonelli, I. Bottero, C. O. Areán, E. Garrone, J. Phys. Chem. C 2010, 114, 6658) the thermodynamic features of the reaction between bare Brønsted acid sites and NH(3) yielding NH(4) (+) species were determined, the data reported herein allow the study of the coexistence of different species in the NH(3)/H-ZSM-5 zeolite system: 1) unreacted acid Brønsted sites, 2) bare ammonium ions, and 3) variously solvated ammonium species. The relevant description is particularly simple when the overall average coverage is one molecule per site.

Thermodynamics of hydrogen adsorption on metal-organic frameworks.

Interaction between adsorbed hydrogen and the coordinatively unsaturated Mg(2+) and Co(2+) cationic centres in Mg-MOF-74 and Co-MOF-74, respectively, was studied by means of variable-temperature infrared (VTIR) spectroscopy. Perturbation of the H(2) molecule by the cationic adsorbing centre renders the H--H stretching mode IR-active at 4088 and 4043 cm(-1) for Mg-MOF-74 and Co-MOF-74, respectively. Simultaneous measurement of integrated IR absorbance and hydrogen equilibrium pressure for spectra taken over the temperature range of 79-95 K allowed standard adsorption enthalpy and entropy to be determined. Mg-MOF-74 showed ΔH(0)=-9.4 kJ mol(-1) and ΔS(0)=-120 J mol(-1) K(-1), whereas for Co-MOF-74 the corresponding values of ΔH(0)=-11.2 kJ mol(-1) and ΔS(0)=-130 J mol(-1) K(-1) were obtained. The observed positive correlation between standard adsorption enthalpy and entropy is discussed in the broader context of corresponding data for hydrogen adsorption on cation-exchanged zeolites, with a focus on the resulting implications for hydrogen storage and delivering.

Thermodynamics of carbon dioxide adsorption on the protonic zeolite H-ZSM-5.

Adsorption of carbon dioxide on H-ZSM-5 zeolite (Si:Al=11.5:1) was studied by means of variable-temperature FT-IR spectroscopy, in the temperature range of 310-365 K. The adsorbed CO(2) molecules interact with the zeolite Brønsted-acid OH groups bringing about a characteristic red-shift of the O-H stretching band from 3610 cm(-1) to 3480 cm(-1). Simultaneously, the nu(3) mode of adsorbed CO(2) is observed at 2345 cm(-1). From the variation of integrated intensity of the IR absorption bands at both 3610 and 2345 cm(-1), upon changing temperature (and CO(2) equilibrium pressure), the standard adsorption enthalpy of CO(2) on H-ZSM-5 is DeltaH(0)=-31.2(+/-1) kJ mol(-1) and the corresponding entropy change is DeltaS(0)=-140(+/-10) J mol(-1) K(-1). These results are discussed in the context of available data for carbon dioxide adsorption on other protonic, and also alkali-metal exchanged, zeolites.

Computational and variable-temperature infrared spectroscopic studies on carbon monoxide adsorption on zeolite Ca-A.

Carbon monoxide adsorption on LTA (Linde type 5A) zeolite Ca-A is studied by using a combination of variable-temperature infrared spectroscopy and computational methods involving periodic density functional calculations and the correlation between stretching frequency and bond length of adsorbed CO species (nu(CO)/r(CO) correlation). Based on the agreement between calculated and experimental results, the main adsorption species can be identified as bridged Ca(2+)...CO...Ca(2+) complexes formed on dual-cation sites constituted by a pair of nearby Ca(2+) cations. Two types of such species can be formed: One of them has the two Ca(2+) ions located on six-membered rings of the zeolite framework and is characterized by a C-O stretching frequency in the range of 2174-2179 cm(-1) and an adsorption enthalpy of -31 to -33 kJ mol(-1), whereas the other bridged CO species is formed between a Ca(2+) ion located on an eight-membered ring and another one on a nearby six-membered ring and is characterized by nu(CO) in the range 2183-2188 cm(-1) and an adsorption enthalpy of -46 to -50 kJ mol(-1). Ca(2+)...CO monocarbonyl complexes are also identified, and at a relatively high CO equilibrium pressure, dicarbonyl species can also be formed.

Variable-temperature infrared spectroscopy studies on the thermodynamics of CO adsorption on the zeolite Ca-Y.

Variable temperature FT-IR spectroscopy (in the range of 298-380 K) is used to study the thermodynamics of formation of Ca(2+)...CO carbonyl species upon CO adsorption on the faujasite-type zeolite Ca-Y, and also the (temperature-dependent) isomerization equilibrium between carbonyl and isocarbonyl (Ca(2+)...OC) species. The standard enthalpy and entropy changes involved in formation of the monocarbonyl species resulted to be DeltaH(0)=-50.3 (+/-0.5) kJ mol(-1) and DeltaS(0)=-186 (+/-5) J mol(-1) K(-1), respectively. Isomerization of the (C-bonded) Ca(2+)...CO carbonyl to yield the (O-bonded) Ca(2+)...OC isocarbonyl involves an enthalpy change DeltaH(iso)(0)=+11.4 (+/-1.0) kJ mol(-1). These results are compared with previously reported data for the CO/Sr-Y system; and also, a brief analysis of enthalpy-entropy correlation for CO adsorption on zeolites and metal oxides is given.

Materials for hydrogen storage: current research trends and perspectives.

Storage and transport of hydrogen constitutes a key enabling technology for the advent of a hydrogen-based energy transition. Main research trends on hydrogen storage materials, including metal hydrides, porous adsorbents and hydrogen clathrates, are reviewed with a focus on recent developments and an appraisal of the challenges ahead. .

The vibrational dynamics of carbon monoxide in a confined space-CO in zeolites.

Based on theoretical calculations, and a survey of infrared spectra of CO adsorbed on different cation exchanged zeolites, a model is proposed to explain the influence of the zeolite framework on the vibrational behaviour of CO confined into small void spaces (zeolite channels and cavities). The concepts developed should help to understand a number of details relevant to both, precise interpretation of IR spectra and a better understanding of the vibrational dynamics of small molecules in a confined space.

Variable temperature infrared spectroscopy: a convenient tool for studying the thermodynamics of weak solid-gas interactions.

This tutorial review describes the use of variable temperature infrared spectroscopy of adsorbed species (VTIR), a recent method for studying the thermodynamics of weak solid-gas interactions. Examples show how a fundamental relationship of thermodynamics (the van't Hoff equation, used long since in several fields of physical chemistry) can describe equilibrium processes at the solid-gas interface. The VTIR method is fully exploited by measuring absorbance of an IR band, temperature and pressure over a wide temperature range: an estimation of the interaction energy is, however, possible even ignoring the equilibrium pressure. Precise thermodynamic characterization of solid-gas interactions is required in several fields: on the applied side, gas sensing, separation and storage, which involve such areas as work-place security, air pollution control and the energy sector; regarding fundamental knowledge, weak solid-gas interactions are relevant to a number of fields, including hydrogen bonding, coordination chemistry and surface phenomena in a broad sense. Infrared (IR) spectroscopy of (gas) molecules adsorbed on a solid is frequently used to characterize both, the adsorbed species and the adsorbing centres at the solid surface. The potential of the technique can be greatly enhanced by obtaining IR spectra over a temperature range, and simultaneously measuring IR absorbance, temperature and equilibrium pressure. When this is done, variable temperature infrared (VTIR) spectroscopy can be used not only for a more detailed surface characterization, but also for precise studies on the thermodynamics of solid-gas interactions. Furthermore, when weak interactions are concerned, the technique shows favourable features compared to adsorption calorimetry, or to other classical methods. The potential of the VTIR method is highlighted by reviewing recently reported studies on dihydrogen, dinitrogen and carbon monoxide adsorption on zeolites. To facilitate understanding, an outline of the basis of the method is also given, together with an appraisal of the critical points involved in its practical use.