Effect of pH on the Encapsulation of the Salicylic Acid / Salicylate System by Hydroxypropyl-β-Cyclodextrin at 25 °c. A Fluorescence Enhancement Study in Aqueous Solutions

The encapsulation of the acid/base conjugated system salicylic acid(HSA)/salicylate (SA^-) by hydroxypropyl--cyclodextrin (HPBCD) has beenstudied through fluorescence emission enhancement measurements in aqueoussolutions at 25 °C. With the aim of analyzing the crucial importance ofa proper and cautious choice of the pH of the medium (i.e. choice of thebuffer), the study has been carried out at pH = 1, 2, 4 and 7. Since the pK_a of the HSA/SA^- system is 2.95 at 25 °C, the presence of the protonated(HSA) and non-protonated (SA^-) forms suitable for inclusion by cyclodextrinvary appreciably within the different pH conditions: 99% HSA,1% SA^- at pH = 1, 90% HSA, 10% SA^- at pH = 2,10% HSA, 90% SA^- at pH = 4, and 0% HSA,100% SA- at pH =7. The association constants K CD : HSA and K _{CD: SA-} have been determined in all cases by using a nonlinear regressionanalysis of the experimental data at three different ^em. The effectof the pH of the medium on all the equilibria involved as well as in the Kvalues is fully discussed. The 8-anilino-1-naphthalene sulfonate (ANS) +-cyclodextrin (-CD) system, widely reported in literature, hasinitially been studied to check the experimental protocol and the numericalmethod.     

Thermodynamic and magnetic resonance studies on the hydration of polymers: I. Interactions of water in a synthetic cation-exchange resin

Measurements of NMR spin-lattice relaxation times T ₁ were performed for sorbed H₂O and D₂O in a sulfonated ion-exchange resin at varying degrees of hydration with alkaline cations as counter ions. From the sorption isotherms at three different temperatures the partial molar enthalpies and entropies of sorption show a minimum for all alkaline cations at water concentrations of n 0.8, i.e., there are 0.8 water molecules per –SO ₃ ^– group. The first water molecules sorbed in the ion-exchange resin matrix are characterized by anisotrtopic rotational diffusion processes with correlation times of the order of ₁ 50 ns and ₂ 30 ps, respectively. This indicates that they are located in the electrostatic field between the corresponding ion pair. Although these two correlation times are very similar at a given temperature for all alkaline cations studied in the present investigation, the existence of a second spin-lattice relaxation time for sorbed H₂O at n=0.8 indicates that for Cs about 50% of the sorbed water diffuses between locations in the resin. This fraction decreases with ionic radii and with falling temperatures. For Li the amount is less than 20%.     

Kinetic-fluorimetric determination of microamounts of cerium(IV) by means of sodium 4,8-diamino-1,5-dihydroxyanthraquinone-2,6-disulphonate

Summary A kinetic method for determination of traces of Ce(IV), based on the oxidation of sodium 4,8-diamino-1,5-dihydroxyanthraquinone-2, 6-disulphonate is described. The reaction is monitored by means of the fluorescence of the oxidation product ( _ex=525nm, _em=585 nm), and allows determination of 0.02–0.37 ppm Ce(IV). The proposed method has few interferences.

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Kinetisch-fluorimetrische Bestimmung von Mikromengen Cer(IV) mit Natnum-4,8-diamino-1,5-dihydroxyanthrachinon-2,6-disulfonat

Zusammenfassung Eine kinetische Methode zur Bestimmung von Spuren Cer(IV) mit Hilfe von Natrium-4,8-diamino-1,5-dihydroxyanthrachinon-2,6-disulfonat wurde beschrieben. Dabei wird ein fluoreszierendes Oxydationsprodukt gebildet, das bei 525 nm angeregt mit einer maximalen Emission bei 585 nm fluoresziert. Die Reaktion ermöglicht die Bestimmung von 0,02–0,37 ppm Cer(IV). Die vorgeschlagene Methode wird nur durch wenige Störungen eingeschränkt.

     

Study of the oxygen distribution in YBa2Cu3O7−x ceramics by (n, α) radiography technique

A technique to determine the oxygen distribution in high T_c superconducting YBa₂Cu₃O_7–x ceramics has been developed which is based on the (n, ) radiography method. The technique enables the non-destructive study of superconducting ceramics as well as monocrystal samples with spatial resolution not worse than 1 m at a relative standard deviation of 1.5%. This technique is used to study the influence of radiation-stimulated diffussion of oxygen on the formation of the superconducting phase in an yttrium ceramic. The oxygen distribution in the samples with a narrow transition (T1 K) and with a transition widened (T10 K) by thermal and thermo-radiative treatment is compared in the experiment. The oxygen distribution radiographs of irradiated and unirradiated samples provide strong evidence for the influence of irradiation on the ordering of superconducting ceramics structure.     

Amperometric determination ot bivalent tin with dichromate

Summary An amperometric determination of tin with potassium dichromate has been described. The advantage of the cathodic polarograms of Cr₂O² ₇- and Sn²⁺ in formate media was taken and titrations were performed at –0.8 V vs. S.C.E. at pH 3.0. It is shown that tin upto 10 mg may be determined accurately within the limits of experimental errors.

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Zusammenfassung Eine Methode wird beschrieben zur amperometrischen Bestimmung von Zinn mit Kaliumdichromat unter Ausnutzung des kathodischen Polarogramms von C₂O₇ ^2– und Sn²⁺. Die Titration wird bei –0,8 V (gegen S.K.E.) und PH 3,0 ausgeführt. Zinn kann in Mengen bis zu 10 mg mit guter Genauigkeit bestimmt werden. Die Fehler liegen inner-halb der experimentellen Grenzen.

     

Magnetische Messungen an ternären Fe/Ni-Telluriden mit NiAs-Struktur

The hexagonal NiAs-type phase in the ternary system Fe–Ni–Te was investigated by thermal, X-ray and susceptibility measurements from 100 up to 1000K. The high temperature phase -FeTe (Fe₂Te₃), which is stable only above 520°C was stabilized at lower temperatures by the partial substitution of iron by nickel. Alloys containing less iron than two thirds of the total metal amount were found to be stable even down to room temperature. Due to the continuous addition of iron the weak constant paramagnetism of -NiTe increased and became temperature dependent. The variation of the magnetic susceptibilities with temperature in specimens with a high iron content was indicative of magnetic interactions between iron atoms. It was concluded that at low temperatures Fe₂Te₃ exhibits an antiferromagnetic order which is destroyed somewhere between room temperature and 520°C.     

Zur katalytischen Reduktion aromatischer Stickstoffverbindungen und Diazene in Gegenwart von Übergangsmetallverbindungen

The NaBH₄ reduction of nitrosobenzene to hydrazobenzene/aniline3 : 1, phenylhydroxylamine to aniline, azoxybenzene to hydrazobenzene, azobenzene to hydrazobenzene, and hydrazobenzene to aniline is catalysed by bis(dimethylglyoximato)cobalt compounds (cobaloximes), CoCl₂, and some other salts of transition metals. The NaBH₄–CoCl₂ system is a convenient and mild reducing agent which effects the reduction of e.g.trans-azobenzene to hydrazobenzene even at –60°C. The diazene configuration has no effect on the reduction of the N=N group;cis-fixed benzo[c]cinnoline is smoothly converted into 2.2-diaminobiphenyl. Aliphatic diazeneslike 2.3-diazanorbornene andtrans-di-1-adamantyldiazene do not react.     

Kinetics of the periodate oxidation of octacyanomolybdate(IV) in ethanol-water solvent mixtures

The kinetics of the oxidation of Mo(CN) ₈ ^4– by IO ₄ ^– has been studied in ethanol—water solvent mixtures over a temperature range of 15–35 °C. The effect of solvent composition on the reaction rate and the mechanism has been investigated. Activation parameters are given. An inner-sphere mechanism, consistent with the kinetic results, is proposed.

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Kinetik der Periodat-Oxidation von Octacyanomolybdat(IV) in Ethanol-Wasser

Zusammenfassung Die Kinetik der Oxidation von Mo(CN) ₈ ^4– mit IO_4/– wurde in Ethanol—Wasser über einen Temperaturbereich von 15–35 °C untersucht. Der Effekt der Lösungsmittelzusammensetzung auf die Reaktionsgeschwindigkeit und der Mechanismus der Reaktion werden diskutiert. Die Aktivierungsparameter sind angeführt. Es wird ein Inner-Sphere-Mechanismus vorgeschlagen, der mit den kinetischen Ergebnissen konsistent ist.

     

Structural Development of Single Phase (Type I) Mullite Gels

Single phase (type I) mullite gels were prepared by sol-gel techniques starting from alkoxides (Al-butylate, tetraethylorthosilicate) and alkoxides plus nitrates (tetraethylorthosilicate, Al(NO₃)₃·9H₂O). After drying at 150°C the aluminosilicate gels are non-crystalline and remain so up to 900°C. Above 900°C the gels transform into Al₂O₃-rich mullite plus a coexisting SiO₂ phase. Structural studies on temperature-dependent dehydroxylation and condensation of the gels were carried out by large angle X-ray scattering, by infrared spectroscopy and by²⁹ Si NMR spectroscopy. Heat-treatment (<150°C) of dried gels first causes removal of the H₂O and organic residuals weakly bound at the open pore surfaces of the gels while the stronger, structurally bound OH groups are not affected. At temperatures <600°C OH groups are released and recombine to molecular H₂O. If the temperature does not exceed 800°C the newly formed H₂O is trapped in closed nanopores of the gel-network. Corresponding electron microscopical investigations reveal agglomerates of 10 nm sized primary particles virtually unaffected by the heat-treatment below 900°C. NMR investigation provided a new structural model on type and distribution of coordination polyhedra in aluminium silicate gel networks. Unlike Si, which according to ²⁹Si NMR is always 4-fold coordinated with O, ²⁷Al NMR spectroscopy revealed that Al cordination is more complex and is influenced by thermal treatment. Al occurs six-fold (octahedrally) and four-fold (tetrahedrally) coordinated. A third ²⁷Al NMR signal which has been attributed to five-fold-coordinated Al in the literature increased in intensity with the heat-treatment. A comparison of NMR data of the gels with those of mullite suggests that tetrahedra triclusters (3 tetrahedra having one oxygen atom in common) occur as major structural units in aluminium silicate gels rather than five-fold-coordinated Al. Triclusters of tetrahedra may compensate the excess negative charge in the network caused by Si⁴⁺ Al³⁺ substitution. The charge compensation model is supported by aluminosilicate gels doped with network modifiers (e.g., Na⁺). Since equimolar addition of Na⁺ compensates Si⁴⁺ Al³⁺ substitution the formation of triclusters is no longer required which actually can be deduced from²⁷ Al NMR studies.     

Wet Coating Deposition of ITO Coatings on Plastic Substrates

In₂O₃:Sn (ITO) transparent conducting coatings of high optical quality have been obtained on glass and several plastic substrates by spin and dip coating processes followed by a low temperature processing (T < 130°C). The sols are made of crystalline nanoparticles redispersable in an alcohol and modified by adding a binder to favour the coalescing of the particles and to allow the deposition of thick single layers (>400 nm). The smallest stable resistivity so far obtained is = 9 × 10^–2cm (sheet resistance of 1.6 k for a 570 nm thick single layer). The transparency in the visible range is high, T 87%, the abrasion resistance is in agreement with DIN 58-196-G10 and the hardness according to ASTM D 3363-92a is 1H. A spray process allows to obtain antiglare-conducting coatings with an adjustable gloss of 60 to 80 GU and an optical resolution >8 lines/mm.     

Optical and electrical measurements on CO2 covered copper films

Thin polycrystalline copper films are deposited in a special UHV cell on glass substrates and are covered step by step with CO₂. The optical and electrical properties of the films are studied in-situ by means of ellipsometry and resistivity measurements. The properties of the clean films correspond to literature data. In the case of monolayer adsorption of CO₂, the changes in the ellipsometrical angles are +1° and +0.1°, similar to the Cu/O and Cu/CO systems. Three-dimensional island growth leads to a drastical increase of and by several orders of magnitude. The resistivity first quickly decreases and then slowly reapproaches the initial value. This marked kinetics is quantitatively interpreted on the basis of a diffusion model.     

Zum Spingleichgewicht5T2−1A1 in Fe(II)py 2 phen(NCS) 2

Zusammenfassung Die magnetischen, spektralen und strukturellen Eigenschaften des gemischten Amminkomplexes [Fe(II)py ₂ phen(NCS)₂] werden diskutiert. Der Orbitalparamter liegt mit 11 700 cm^–1 nahe der Spinpaarungsenergie für den mittleren kovalenten Fall 11 000 bis 12 000 cm^–1 und erlaubt so ein Spingleichgewicht zwischen den Spektralzuständen⁵T₂–¹A₁. Dieses Gleichgewicht wird durch magnetische Messungen bei verschiedenen Temperaturen nachgewiesen.

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On the spin equilibrium⁵T₂–¹A₁ in [Fe(II)py₂phen(NCS)₂]

The magnetic, spectral and structural properties of the mixed ammine [Fe(II)py ₂ phen(NCS)₂] are discussed. The orbital parameter of about 11 700 cm^–1 near to the spin-pairing energy for the mean covalent case 11 000 to 12 000 cm^–1 allows a spin equilibrium between the spectral states⁵T₂–¹A₁, put in evidence by the magnetic measurements at different temperatures.

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Mit 3 Abbildungen

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Herrn Prof. Dr.H. Nowotny gewidmet.     

Sorption of gold, silver and mercury on cellulose

Summary Distribution coefficients of Au³⁺ on cellulose in 0.1 M NaNO₃ are rather high in the pH range 2 to 8 (D 5·10³ ml/g). They are appreciably lower in presence of NaCl or NaCN. Distribution coefficients of Ag⁺ are relatively low in 0.1 M NaNO₃, appreciably higher in presence of NH₄NO₃ (D 10³ ml/g in weakly acid media) and low in presence of NaCl, Na₂S₂O₃ or NaCN. Distrubution coefficients of Hg²⁺ are low in 0.1 M NaNO₃, and in presence of NaCN, but higher in 0.5 M NaCl (D 2·10² ml/ g). Responsible for the equilibria are mainly the special interactions between the predominant species with the sorbent under the given conditions, and less the complex equilibria in solution.

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Sorption von Gold, Silber und Quecksilber an Cellulose

Zusammenfassung Die Verteilungskoeffizienten von Au³⁺ an Cellulose in 0,1 M NaNO₃ sind ziemlich hoch im pH-Bereich 2 bis 8 (D 5·10³ ml/g). Sie sind erheblich niedriger in Gegenwart von NaCl oder NaCN. Die Verteilungskoeffizienten von Ag⁺ sind verhältnismäßig niedrig in 0,1 M NaNO₃, erheblich höher in Gegenwart von NH₄NO₃ (D 10³ mol/g in schwach saurem Medium) und niedrig in Gegenwart von NaCl, Na₂S₂O₃ oder NaCN. Die Verteilungskoeffizienten von Hg²⁺ sind niedrig in 0,1 M NaNO₃ sowie in Gegenwart von NaCN, aber höher in 0,5 NaCl (D 2·10² ml/g). Verantwortlich für die Sorption sind in erster Linie die speziellen Wechselwirkungen der vorherrschenden Spezies mit dem Sorbens unter den gegebenen Bedingungen, weniger die Komplexbildungsgleichgewichte in Lösung.

     

An ESR and Optical Spectroscopic Study of the Mechanism of Photostimulated Reactions in Hydrogen Cyanide γ-Irradiated at 77 K

Changes in the electronic absorption spectra and ESR spectra in the course of photobleaching of radiolyzed solid HCN with light of different wavelengths (236–600 nm) were studied by ESR and optical spectroscopy. Two bands at 270 and 290 nm in the optical spectrum were attributed to the presence of H₂C=N and HC=NH radicals, respectively (the molar absorption coefficients are k ₂₇₀ 2.7 × 10²l mol^–1cm^–1and k ₂₉₀ 1.5 × 10²l mol^–1cm^–1, respectively). Structureless broad bands with maximums at 313 and 465 nm, which were detected after the exposure of a sample to light with 300 nm, can belong to the cyanide ions (CN^–) and H₂C=N⁺cations (the molar absorption coefficients of the ions are k _ion= (0.4–1.0) × 10²l mol^–1cm^–1). In the photobleaching of -irradiated HCN ( = 236–280 nm), H₂C=N⁺radicals were additionally formed by the photoinduced reaction of electron transfer from the CN^–anion to the H₂C=N⁺cation. The amount of these radicals generated in the course of photobleaching is several times greater than that of the same radicals formed in the radiolysis via hydrogen atom addition to the multiple bond of HCN molecules.     

Mischligandenderivate des 1:1-Th(IV)—DTPA-Chelates mit Milchsäure,Mandelsäure und o-Hydroxynaphthoesäuren

Potentiometric studies of the mixed ligand derivatives of 11-Th(IV)—DTPA chelate (whereDTPA=diethylene-triamine pentaacetic acid) with certain secondary ligands, such as lactic, mandelic and o-hydroxynaphthoic acids have been carried out. The pH-titrations of the reaction mixtures containing 111 molar ratio of metal ion toDTPA to secondary ligand have shown the formation of 111 ternary complexes at higher pH (8). The equilibrium constants of the resulting mixed complexes have been determined at 30±1°C and =0.1 (KNO₃) and the order of stability in terms of secondary ligands has been found to be o-hydroxy naphthoic acids>mandelic acid>lactic acid.

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Mit 1 Abbildung     

Conformation analysis of diphosphine

Extended basis set ab initio computations are performed on HF, PNO-CI and CEPA level to determine the structure of P₂H₄ and the potential curve E() for rotation around the P-P axis. The structure parameters are optimized for dihedral angles of 0 ° (cis), 50 °, 80 ° (gauche or semi-eclipsed), 130 °, and 180 ° (trans). It turns out that P₂H₄ has a gauche equilibrium structure, a local minimum for trans which is 2.5 kJ/mol above gauche, a rather large cis barrier of 20 kJ/mol and a gauche trans barrier of 3.5 kJ/mol. The potential E() is extremely flat in the region 50 ° < < 310 °, where E() varies by less than 5 kJ/mol. Electron correlation tends to reduce the barriers but has no drastic effect on E().     

Heats of solution and neutralization ofLewis acids and bases in acetic anhydride

Heats solution of someLewis acids and bases in acetic anhydride have been determined and the following order of their relative strengths is proposed: SbCl₅>SO₃>SnCl₄>TiCl₄>AsCl₃ and piperidine> n-butylamine>potassium acetate>sodium acetate -picoline>quinoline. Heats neutralization of theseLewis acids and bases in acetic anhydride suggest that the major enthalpy change in these neutralization reactions is due to the combination of a proton and the (CH₂COOCOCH₃)-ion, resulting in the formation of acetic anhydride.

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Lösungs- und Neutralisationswärmen von Lewis-Säuren und-Basen in Essigsäureanhydrid

Zusammenfassung Es wurden die Lösungswärmen einigerLewis-Säuren in Essigsäureanhydrid bestimmt und folgende Reihung nach ihrer relativen Stärke vorgeschlagen: SbCl₅>SO₃>SnCl₄>TiCl₄>AsCl₃ und Piperidin> n-Butylamin>KAc>NaAc-Picolin>Chinolin. Die Neutralisationswärmen dieserLewis-Säuren und-Basen legen nahe, daß der Hauptanteil daran auf die Reaktion eines Protons mit (CH₂–COOCOCH₃)-zurückzuführen ist.