Bulk properties and hydration numbers of ammonium nitrate and ammonium chloride in solution: A structural and thermodynamic analysis

The apparent volumes of the salts in the systems H₂O-NH₄Cl (298 K) and H₂O-NH₄NO₃ (273 K, 298 K, and 323 K) are reproduced with an accuracy of 0.03–0.01 cm³/mol by the equation ? = ?⁰ + Aw ₂ ^0.5 + Bw ₂, where w ₂ is the salt content (mass fractions). The study shows that there is a correspondence between the critical (for determining the hydration number) structural parameters-the intrinsic volume of the electrolyte and the volume of water in ion hydration shells-and the limiting (at w ₂ = 1) partial molar volumes of the components. The hydration numbers at infinite dilution are 6.9 for NH₄Cl at 298 K and 9.1, 6.7, and 6.4 for NH₄NO₃ at 273 K, 298 K, and 323 K. The water volume in ion hydration shells decreases in the sequence: No ₃ ^? , Cl^?, and NH ₄ ⁺ . The hydration numbers decrease with increasing salt concentration. The study shows that within a simpler model ? = ?⁰ + aw ₂ ^0.5 , the hydration numbers are temperature independent.     

Influence of the exchangeable cations on SO<Subscript>2</Subscript> adsorption capacities of clinoptilolite-rich natural zeolite

The sulfur dioxide adsorption on clinoptilolite-rich tuff from Bigadiç region of Western of Turkey and its modified forms (Na⁺, K⁺, Ca²⁺ and Mg²⁺) have been studied at 273 K and 293 K up to 100 kPa. The structural properties of clinoptilolites were studied by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR). The quantitative XRD analysis demonstrated that the Natural-B sample is mainly constituted by clinoptilolite (80–85%) with minor contents of quartz (7–8%), feldspar (5–6%) and mica-illit (4–5%). It was found out that the adsorption capacity and the affinity of SO₂ with clinoptilolite samples depended mainly on the type of exchanged cations and decreased as Na-B > K-B > Mg-B > Natural-B > Ca-B for both temperature. These results show that clinoptilolite-rich zeolites are considered potentially good adsorbents for SO₂ removal.     

Boronate Covalent and Hybrid Organic Frameworks Featuring PIII and P=O Lewis Base Sites

Two covalent organic frameworks comprising Lewis basic P^III centers and Lewis acidic boron atoms were prepared by poly-condensation reactions of newly obtained tris(4-diisopropoxyborylphenyl)phosphine with 2,3,6,7,10,11-hexahydroxytriphenylene and 2,3,6,7-tetrahydroxy-9,10-dimethylanthracene. Obtained materials exhibit significant sorption of dihydrogen (100 cm³ g⁻¹ at 1 bar at 77 K), methane (20 cm³ g⁻¹ at 1 bar at 273 K) and carbon dioxide (50 cm³ g⁻¹ at 1 bar at 273 K). They were exploited as solid-state ligands for coordination of Pd⁰ centers. Alternatively, in a bottom-up approach, boronated phosphine was treated with Pd₂dba₃ and poly-condensated, yielding hybrid materials where the polymer networks are formed by means of covalent boronate linkages and coordination P−Pd bonds. In addition, the analogous materials based on phosphine oxide were synthesized. The DFT calculations on framework–guest interactions revealed that the behavior of adjacent boron and phosphorus/phosphine oxide centers is reminiscent of that found in Frustrated Lewis Pairs and may improve sorption of selected molecules.     

Effective enhancement of selectivities and capacities for CO2 over CH4 and N2 of polymers of intrinsic microporosity via postsynthesis metalation

A series of metalized C-PIM-M (M = Na⁺, Mg²⁺, Al³⁺, PIMs = polymers of intrinsic microporosity) materials were prepared from a carboxyl-functionalized PIM (C-PIMs). The C-PIM-Na exhibited a high CO₂ adsorption capacity of 2.44 mmol/g and extreme low CH₄ uptake of 0.28 mmol/g at 273 K and 101 kPa among three metallated PIMs. It showed remarkably high CO₂/CH₄ and CO₂/N₂ selectivities at both 273 and 293 K due to an advantageous pore-blocking effect of Na⁺ cation.     

Self-association of caffeine in aqueous solution. Study of dilute solutions by normal and second derivative UV absorption spectroscopy.

The concentration dependence of the spectral parameters of caffeine bands at ∼205 and 273 nm has been studied in aqueous solution by normal and second derivative spectroscopy. The concentration range was 5 x 10⁻⁶ − 5 x 10⁻³ M and thirty-five different concentrations were used.Discontinuities in parameter variation of these two bands at ∼7.5 x 10⁻⁵, ∼2 x 10⁻⁴, and ∼1 x 10⁻³M were observed as concentration was increased. These “limiting” concentrations define three quite differenciated hyper- or hipochromic effects: the first one can be explained as caffeine-water molecule interaction and the second and third as dimer and (dimer + polymer) stacking, respectively. Apparent self-association constants using the isodesmic model have been obtained K= 160 M⁻¹ (for the second hypochromic effect) and K= 13.6 M⁻¹ (for the third hypochromic effect), for the 273 nm band.It is noteworthy that the three “limiting” concentrations coincide with changes in DNA-caffeine interaction modes (H. Lang , 1976) and biological activity (I.B. Syed , 1976).     

Synthesis of cyanoethyl chitosan derivatives

Cyanoethyl chitosan derivatives with various substitution degrees have been synthesized by the nucleophilic addition of acrylonitrile to the functional groups of chitosan. The process proceeds under homogeneous conditions without any catalyst at various pH values and reagent concentrations in the temperature range of 273–333 K. The formation of cyanoethyl chitosans is established by a gain in the weight of chitosan, a change in its content of nitrogen, and the appearance of an absorption band at 2250 cm^?1 in the IR spectrum which corresponds to the stretching vibrations of a-C≡N group. It has been shown that the most efficient addition of acrylonitrile occurs at 273 K and pH 5.5. Cyanoethyl chitosan samples show better mechanical parameters and are characterized by a lower ordering than the parent chitosan.     

Radioactivity concentrations in sediment and mussel of Bosphorus and Golden Horn

In the present study, mussel (Mytilus galloprovincialis, Lamarck, 1819) and sediment samples were collected from the Bosphorus strait and the Golden Horn estuary in 2008 and 2009. Activity concentrations of ¹³⁷Cs, ⁴⁰K, ²³²Th and ²³⁸U were measured using a gamma spectrometer equipped with HPGe detector. Sediment samples were separated into <63 μm and >63 μm particle fractions. Analysis of radionuclides was carried out on these two fractions of sediment as well as the soft and shell tissues of mussels. Ranges of radioactivity concentrations in the soft parts of mussels were as follows: ¹³⁷Cs, 0.86–2.43; ⁴⁰K: 261.1–496.7; ²³²Th: 0.49–3.58; and ²³⁸U: BDL (below detection limit)-1.38 Bq kg⁻¹ in dry weight. Ranges of radioactivity concentrations in the <63 and >63 sediment fractions were as follows: ¹³⁷Cs, 8.58–67.92 and 1.12–26.40, ⁴⁰K, 341.4–683.0 and 281.9–662.2; ²³²Th, 10.97–20.16 and 7.18–19.18 and ²³⁸U, 13.97–27.25 and 6.41–18 Bq kg⁻¹ in dry weight, respectively. The effect of some physical–chemical parameters on the radionuclide accumulation was also examined in the sediment samples. All data in the current study were compared with data in the literature.     

Dynamics of 3′-Cytidine Monophosphate Bound to Ribonuclease A — A Molecular Dynamic Simulation Study

Molecular dynamic simulations of the 3′-cytidine monophosphate (3′-CMP)/RNase A complex were carried out at three temperatures, 273 K, 300 K and 323 K. The trajectories obtained allowed us to calculate the dynamics of 3′-CMP in protein complex. The O-P bond was found to exert angular fluctuations with an average magnitude of 20° 26°, and 30° at 273 K, 300 K, and 323 K, respectively. These values compare quite favorably with those obtained from lineshape simulation of the ³¹P NMR powder patterns. The magnitude of the translational fluctuation of the center of mass of the ligand was found to be in the range of 0.17 A to 0.21 Å. On the other hand, the phosphate atom was found to fluctuate with amplitude ranging from 0.22 Å to 0.42 Å, depending on orientation. Fluctuation of the dihedral angle, defined by P-O₃-C₃-C₄′ bonds of the ligand, was more restricted in the protein complex as compared to that in free form. The average number of hydrogen bonds formed between the phosphate group and the protein moiety was 1.6 at 273 K and 1.2 at 323 K.     

Flash photolysis resonance fluorescence investigation of the reaction of OH radicals with dimethyl sulfide

Rate constants for the reaction of OH radicals in a homogeneous gas phase reaction with dimethyl sulfide have been determined using the flash photolysis resonance fluorescence technique over the temperature range 273–400 K. The data (combined with the results of another recent study) can be fit to the Arrhenius expression k = (6.08 ± 2.54) × 10^?12 exp[(134 ± 135)/T] cm³ molecule^?1 s^?1 applicable from 273–426 K. The results are discussed in terms of reaction mechanisms and in light of recent suggestions that dimethyl sulfide plays an important role in the transport of natural sulfur to the earth's atmosphere.     

Characterization of Brazilian commercial milks by instrumental neutron activation analysis

Aiming at the determination of toxic and essential elements in Brazilian commercial bovine milk, 25 ultra high temperature (UHT) milk samples were acquired in the local market of Piracicaba, SP. The samples were freeze-dried and analyzed by instrumental neutron activation analysis (INAA) allowing the determination of Br, Ca, Co, Cs, Fe, K, Na, Rb and Zn. When the results were expressed as concentration (mg·l⁻¹) no significant differences were found. However, considering the dry matter, results showed a clear difference between the mass fractions (mg·kg⁻¹ d.w.) of skim milk and whole milk for the elements Br, Ca, K, Na, Rb and Zn, indicating that the removal of fat caused a concentration effect in the dry matter of skim milks. Discrepancies were found between the concentrations of Ca and Na measured by INAA and the values informed in the labels. Ca showed variations within 30% for most samples, while concentrations of Na were up to 190% higher than informed values. The sample preparation and the INAA procedure were appropriate for the determination of Br, Ca, Co, Cs, Fe, K, Na, Rb and Zn in milk samples.     

A Robust 3D Cage‐like Ultramicroporous Network Structure with High Gas‐Uptake Capacity

A three‐dimensional (3D) cage‐like organic network (3D‐CON) structure synthesized by the straightforward condensation of building blocks designed with gas adsorption properties is presented. The 3D‐CON can be prepared using an easy but powerful route, which is essential for commercial scale‐up. The resulting fused aromatic 3D‐CON exhibited a high Brunauer–Emmett–Teller (BET) specific surface area of up to 2247 m² g^?1. More importantly, the 3D‐CON displayed outstanding low pressure hydrogen (H₂, 2.64 wt %, 1.0 bar and 77 K), methane (CH₄, 2.4 wt %, 1.0 bar and 273 K), and carbon dioxide (CO₂, 26.7 wt %, 1.0 bar and 273 K) uptake with a high isosteric heat of adsorption (H₂, 8.10 kJ mol^?1; CH₄, 18.72 kJ mol^?1; CO₂, 31.87 kJ mol^?1). These values are among the best reported for organic networks with high thermal stability (ca. 600 °C).     

Novel features in the stereochemistry of octacyanides: Phase transition in tetra-n-butylammonium octacyanotungstate(V)

Tetra-n-butylammonium octacyanotungstate(V) has been found to exist in three phases at the temperature range 90–353 K. The IR and ¹H-NMR spectra as well as thermogravimetric and powder diffraction studies support these structural changes. The phase transitions were found in the temperature range 273–283 K (T₁) and 333–343 K (T₂).     

正、反向共沉淀法对Pr_2Zr_2O_7纳米粒子表观活化能的影响

以氨水作为沉淀剂,采用正、反向共沉淀法制备Pr2Zr2O7纳米粒子。利用XRD、SEM、TEM、TG-DTA等测试手段表征了样品物相及形貌;研究其制备过程中合成动力学和晶粒生长动力学,采用Doyle-Ozawa法和Kissinger法分别计算正、反向沉淀粒子在主要反应阶段的表观活化能。结果表明:反向沉淀的滴定速率为2 mL·min-1、母盐溶液初始浓度0.05 mol·L-1、反应体系温度273 K、pH值11、煅烧温度为1 173 K,保温2 h的条件下获得的样品形貌近球形、无团聚现象、一次粒径约60 nm。Pr2Zr2O7前驱体的分解过程分为3个阶段,正、反向粒子各阶段平均表观活化能分别为:71.2、97.8、183.2 kJ·mol-1和45.37、84.34、152.16kJ·mol-1;晶粒生长活化能分别为19.02和11.95 kJ·mol-1,后者比前者的晶粒生长活化能降低了7.07 kJ·mol-1;反向共沉淀制备工艺优于正向共沉淀法。     

Microporous Polymers from a Carbazole‐Based Triptycene Monomer: Synthesis and Their Applications for Gas Uptake

Two kinds of novel organic microporous polymers TCP s ( TCP‐A and TCP‐B ) were prepared by two cost‐effective synthetic strategies from the monomer of tricarbazolyltriptycene ( TCT ). Their structure and properties were characterized by FT‐IR, solid ¹³C NMR, powder XRD, SEM, TEM, and gas absorption measurements. TCP‐B displayed a high surface area (1469 m² g^?1) and excellent H₂ storage (1.70 wt % at 1 bar/77 K) and CO₂ uptake abilities (16.1 wt % at 1 bar/273 K), which makes it a promising material for potential application in gas storage.     

正、反向共沉淀法对Pr2Zr2O7纳米粒子表观活化能的影响

以氨水作为沉淀剂,采用正、反向共沉淀法制备Pr₂Zr₂O₇纳米粒子。利用XRD、SEM、TEM、TG-DTA等测试手段表征了样品物相及形貌;研究其制备过程中合成动力学和晶粒生长动力学,采用Doyle-Ozawa法和Kissinger法分别计算正、反向沉淀粒子在主要反应阶段的表观活化能。结果表明：反向沉淀的滴定速率为2mL·min^-1、母盐溶液初始浓度0.05mol·L^-1、反应体系温度273K、pH值11、煅烧温度为1173K,保温2h的条件下获得的样品形貌近球形、无团聚现象、一次粒径约60nm。Pr₂Zr₂O₇前驱体的分解过程分为3个阶段,正、反向粒子各阶段平均表观活化能分别为：71.2、197.8、183.2kJ·mol^-1和45.37、84.34、152.16kJ·mol^-1;晶粒生长活化能分别为19.02和11.95kJ·mol^-1,后者比前者的晶粒生长活化能降低了7.07kJ·mol^-1;反向共沉淀制备工艺优于正向共沉淀法。     

Porphyrin‐based covalent triazine frameworks: Porosity,adsorption performance,and drug delivery

Two porous porphyrin‐based covalent triazine frameworks (PCTFs), in which porphyrin is incorporated as building block, have been synthesized by the Friedel–Crafts reaction. The copolymer PCTFs show large Brunauer–Emmett–Teller specific surface area of up to 1089 m² g^?1, high CO₂ uptake capacity reaching 139.9 mg g^?1 at 273 K/1.0 bar, and good selectivity for CO₂/CH₄ adsorption attaining 6.1 at 273 K/1.0 bar. The resulting porous solids also can be used as matrices for drug delivery of ibuprofen in vitro. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 2594–2600     

Metal Microporous Aromatic Polymers with Improved Performance for Small Gas Storage

A novel metal‐doping strategy was developed for the construction of iron‐decorated microporous aromatic polymers with high small‐gas‐uptake capacities. Cost‐effective ferrocene‐functionalized microporous aromatic polymers (FMAPs) were constructed by a one‐step Friedel–Crafts reaction of ferrocene and s‐triazine monomers. The introduction of ferrocene endows the microporous polymers with a regular and homogenous dispersion of iron, which avoids the slow reunion that is usually encountered in previously reported metal‐doping procedures, permitting a strong interaction between the porous solid and guest gases. Compared to ferrocene‐free analogues, FMAP‐1, which has a moderate BET surface area, shows good gas‐adsorption capabilities for H₂ (1.75 wt % at 77 K/1.0 bar), CH₄ (5.5 wt % at 298 K/25.0 bar), and CO₂ (16.9 wt % at 273 K/1.0 bar), as well as a remarkably high ideal adsorbed solution theory CO₂/N₂ selectivity (107 v/v at 273 K/(0–1.0) bar), and high isosteric heats of adsorption of H₂ (16.9 kJ mol^?1) and CO₂ (41.6 kJ mol^?1).     

Heat capacity of poly(trimethylene terephthalate)

The heat capacity of poly(trimethylene terephthalate) (PTT) has been measured using adiabatic calorimetry, standard differential scanning calorimetry (DSC), and temperature-modulated differential scanning calorimetry (TMDSC). The heat capacities of the solid and liquid states of semicrystalline PTT are reported from 5 to 570 K. The semicrystalline PTT has a glass transition temperature of 331 K. Between 340 and 480 K, PTT can show exothermic ordering depending on the prior degree of crystallization. The melting endotherm of semicrystalline samples occurs between 480 and 505 K, with a typical onset temperature of 489 K (216°C). The heat of fusion of the semicrystalline samples is about 15 kJ mol⁻¹. For 100% crystalline PTT the heat of fusion is estimated to be 30 ± 2 kJ mol⁻¹. The heat capacity of solid PTT is linked to an approximate group vibrational spectrum and the Tarasov equation is used to estimate the heat capacity contribution due to skeletal vibrations (θ₁ = 550.5 K and θ₂ = θ₃ = 51 K, N_skeletal = 19). The calculated and experimental heat capacities agree to better than ±3% between 5 and 300 K. The experimental heat capacities of liquid PTT can be expressed by: $ C^L_p(exp) $ = 211.6 + 0.434 T J K⁻¹ mol⁻¹ and compare to ±0.5% with estimates from the ATHAS data bank using contributions of other polymers with the same constituent groups. The glass transition temperature of the completely amorphous polymer is estimated to be 310–315 K with a ΔC_p of about 94 J K⁻¹ mol⁻¹. Knowing C_p of the solid, liquid, and the transition parameters, the thermodynamic functions enthalpy, entropy, and Gibbs function were obtained. With these data one can compute for semicrystalline samples crystallinity changes with temperature, mobile amorphous fractions, and resolve the question of rigid-amorphous fractions.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2499–2511, 1998     

Characterization of the PSD of activated carbons from peach stones for separation of combustion gas mixtures

Controlled series of microporous carbons were prepared through chemical activation with phosphoric acid from peach stones as the precursor material, corresponding to different preparation conditions. Adsorption isotherms of N₂ at 77 K and of CO₂ at 273 K were measured to be used in the characterization of the samples. The recently proposed mixed-geometry model (MGM), which assumes that the activated carbon is better represented by a mixture of slit and triangular geometry pores, is used to obtain the PSDs of the samples, on the basis of Grand Canonical Monte Carlo (GCMC) simulated ideal isotherms, both for N₂ at 77 K and of CO₂ at 273 K. Our results emerging from the analysis of two families of activated carbons reveal a consistent picture supporting the thesis that the PSDs of the same sample obtained trough N₂ and CO₂ adsorption are different, a still controversial issue in the literature. Comparison of predictions from the MGM with those of the pure slit geometry model (PSGM) shows that the former gives a more consistent picture and more similar PSDs for the two adsorbates used.     

Spin trapping of radicals in tritiated methanol

The radicals in [methyl-³H]-methanol have been detected by spin trapping with PBN. Two radicals observed in deaerated samples at 273 K are methoxy and hydroxymethyl radicals. The relative contribution of these two radicals changes with the storage time, finally only the PBNCH₂OH adduct being observed. This behaviour is hypothetically explained as resulting from the secondary reactions with a product formed in methanol by internal β-radiolysis or otherwise, whose steadily increasing concentration accelerates the decay of the PBNCH₃O adduct.