Instantaneous strain recovery elasticity and endothermic heat change in nylon-6 monofilaments and silicone rubbers

The instantaneous elastic moduli for a nylon-6 monofilament were derived on strain recoveries right after creep, stress relaxation, and rapid elongation,E _c ,E _s andE _e , respectively. It was found that during strain recoveryE _s (>E _e ) andE _e increase monotonically with increasing load,m ₁, on the sample. The extrapolated value of E_s atm ₁=0 g is almost equal to Young's modulus, 4.06 GPa. The value ofE _c also increased with increasingm ₁, and atm ₁=600 g (1.93 t cm^–2) reached about 14 GPa. The endothermic heat change right after creep, stress relaxation or rapid elongation,Q, was negligibly small. For comparison,E _s ,E _c andQ were also investigated for silicone rubber. It was found thatE _s (53.8 M Pa at the draw ratioD=1.2) decreased abruptly atD=1.3. In the range ofD=1.4–1.9,E _s was only 22.6 MPa. In the case of stress relaxation,Q increased with increasingD from 4 J mol^–1 (atD=1.2) to 56 J mol^–1 (atD=1.9). FurthermoreE _c (5.58 MPa atm ₁=133.8 g (429.4 kg cm^–2)) increased gradually with increasing m₁ and attained 16.6 MPa atm ₁=548.4 g (1.76 t cm^–2). In the case of creep,Q was in the range of 0–11.5 J mol^–1 and larger when larger loads,m ₂ were removed during the later stages of creep.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayThe author wishes to thank Mr. Keizi Igarashi and Mr. Tetsuya Yasui for helping in the experiments.     

Solvent effects on ligand-field intensities in some anionic complexes of 3d ions

Ligand-field spectra of tetrahedral CoX ₄ ^2– and octahedral Cr(NCS) ₆ ^3– were measured in a number of solvents. Care was taken to ensure complete formation of the anionic species to be investigated. Considerable variations in intensity were found for complexes with highly polarizable ligands. For Co(NCS) ₄ ^2– the oscillator strength of the⁴T₁(P) transition in aqueous solution was only about 1/5 that in a number of organic solvents, with little variation in these solvents. For Cr(NCS) ₆ ^3– the intensities are highest in aqueous solution, and some variation is observed for the nonaqueous solvents. These data for the chromium complex correlate at least qualitatively with variations of the excited state lifetimes in these solvents. Nonlinear changes of intensities in solvent mixtures can be taken as an indication of preferential solvation of the anionic complex by nonaqueous solvent molecules. The reported results are a strong indication of large differences in solvent/solute interactions between water and the nonaqueous solvents.     

Zum Selbstdiffusionskoeffizienten des Wassers im Polymer (Feststoff)-Wasser-System

Zusammenfassung Wählt man zur Beschreibung einfacher färberischer Systeme die Thermodynamik der irreversiblen Prozesse, so erhält man Gleichungen für den Diffusionsprozeß. Man hat es in diesem vereinfachten Modell mit drei unabhängigen Diffusionskoeffizienten zu tun, wobei einer davon den SelbstdiffusionskoeffizientenD von Wasser im Substrat beschreibt. Durch experimentelle Untersuchungen mittels Tracer-Technik wurdeD bei verschiedenen Polymeren in der Größenordnung von 4 · 10^–10 cm² · sec^–1 bestimmt. Dieser Befund wird durch eine parakristalline Wasserstruktur im Polymer interpretiert. Die scheinbaren AktivierungsenergienE _a für diesen Diffusionsprozeß liegen mit ca. 6 kcal · Mol^–1 etwas höher als im Wasser (4,2 kcal · Mol^–1) und sprechen dafür, daß wegen der Kleinheit des diffundierenden Teilchens die Bewegung der Kettensegmente des Polymers nicht inE _a enthalten ist.

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Summary If the thermodynamics of irreversible processes is used to describe simple dyeing systems, equations for the diffusion process are obtained. This simplified model contunius three independent diffusion coefficients, one. of them describing the self-diffusion coefficientD of water in the substrate. By means of experimental investigations using tracer technics for diverse polymersD was found to be about 4 · 10^–10 cm² · sec 1. This result is interpreted by means of a paracrystalline structure of the water in the polymer. The apparent activation energiesE _a of this diffusion process, being about 6 kcal · Mol^–1, are a little greater than in water (4,2 kcal · Mol^–1), indicating that the movement of the chain-segments of the polymer is not contained inE _a , because of the smallness of the diffusing particles.

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Mit 3 Abbildungen und 1 Tabelle     

Calcul par double perturbation de l'interaction dipolaire spin-spin dans les molécules

Résumé Les paramètres D et E de molécules dans l'état triplet sont calculés par double perturbation au premier ordre par rapport à l'hamiltonien de corrélation de P. S. Epstein, et à l'hamiltonien d'interaction dipolaire spin-spin. On montre que les seules configurations diexcitées triplets fournissant une contribution non nulle sont celles où les orbitales occupées par un seul électron dans le plus bas triplet deviennent vides ou doublement occupées. On trouve ainsi pour le naphtalène D= 0,090 cm^–1, E=–0,014 cm^–1 (exp = D=0,100 cm^–1, E=–0,014 cm^–1). La polarisation de spin seule donne D=0,113 cm^–1, E= –0,027 cm^–1. La contribution du 2ème ordre par rapport à la perturbation due à la corrélation est évaluée à 10% de D total.

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Calculation of the dipolar spin-spin interaction by double perturbation theory in moleculesApplication to the triplet states of hydrocarbons

A double perturbation calculation of D and E parameters of molecular triplet states is performed in first order with respect both to correlation (as defined by P. S. Epstein) and dipolar spin-spin interaction. A non zero contribution is obtained from diexcited triplet configurations only if the singly occupied orbitals of the lowest triplet configuration become either empty or doubly occupied. Results are for Naphtalene: D=0.090 cm^–1, E=–0.014 cm^–1 (exp: D=0.100 cm^–1, E=–0.014 cm^–1). Spin polarization alone yields D=0.113 cm^–1, E=–0.027 cm^–1. The correlation second order contribution for D is estimated to 10% of the over-all value.

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Zusammenfassung Es wird eine Berechnung des D- und E-Parameters molekularer Triplettzustände im Rahmen einer zweifachen Störungsrechnung bis zur ersten Ordnung durchgeführt, und zwar sowohl in bezug auf die Korrelation (wie definiert von P. S. Epstein) als auch die dipolare Spin-Spin-Wechselwirkung. Der Beitrag zweifach angeregter Triplettkonfigurationen ist nur dann von Null verschieden, wenn die beiden in der Grundkonfiguration einfach besetzten Orbitale entweder gar nicht oder doppelt besetzt sind. Die Ergebnisse für Naphthalin sind: D=0,090 cm^–1, E=–0,014 cm^–1 (exp.: D=0,100 cm^–1, E=–0,014 cm^–1), während die Spinpolarisation allein D=0,113 cm^–1, E=–0,027 cm^–1 liefert. Der Beitrag der Korrelation zu D in zweiter Ordnung wird auf 10% des Gesamtwertes geschätzt.

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Travail effectué dans les cadres de la Convention N-67-34217-00-480-75-01 de la Direction des Recherches et Moyens d'Essais (Responsable: Prof. B. Pullman).     

Synthesis,structure and electrochemistry of a copper(II) complex with 1,2-di{o-[o-hydroxy(naphthylideneimino)]phenoxy}ethane

The title Schiff base ligand, H₂L, and its complex [CuL] have been prepared and characterized by elemental analysis and i.r. spectroscopy. The electrochemical properties of the single crystal [CuL]·0.5C₂H₄Cl₂ have been investigated by cyclic voltammetry (c.v.). Upon scanning at negative and positive potentials, two reduction and two oxidation waves were observed at E _1/2 ⁰ = –0.47 and –0.77 V and E _1/2 ⁰ = 1.10 and 1.39 V, respectively. Two K _com values for the reduction and oxidation process are 1.2×10⁵ and 8.0×10⁴, respectively, and indicate that the deprotonated ligand, L, has the ability to stabilize the mixed valent states of both Cu^IICu^I and Cu^IICu^III. The crystal structure has been solved by X-ray diffraction, with a final R = 0.0653. Wound around a copper atom, the effectively tetradentate chain ligand, L, coordinates only via its two imino and two phenolate groups at both ends of the chain. The geometry, D _2d symmetry, is best described as trans 'N₂O₂' square-planar with slight tetrahedral distortion. The reason, why the mononuclear [CuL] unit can display two c.v. waves in each process, has been explained on the basis of configuration interchange between mono- and dinuclear units in c.v. electrolyte solution.     

Comparison of temperature,pressure and isotope effects on the proton jump between the hydroxide and oxonium ion

The limiting molar conductances ° of potassium deuteroxide KOD in D₂O and potassium hydroxide KOH in H₂O were determined at 5 and 45°C as a function of pressure to clarify the difference in the temperature, pressure and isotope effects on the proton jump between an OD^– (OH^–) and a D₃O⁺ (H₃O⁺) ion. The excess conductances of the OD^– ion in D₂O and the OH^– ion in H₂O, _E ⁰ (OD^-) and _E ⁰ (OH^-), increase with increasing temperature and pressure as in the case of the excess deuteron and proton conductances, _E ⁰ (D⁺) and _E ⁰ (H⁺). However, the temperature effect on the excess conductance is larger for the OD^–(OH^–) ion than for the D₃O⁺ (H₃O⁺) ion but the pressure effect is much smaller for the OD^– (OH^–) ion than for the D₃O⁺ (H₃O⁺) ion. These findings are correlated with larger activation energies and less negative activation volumes found for the OD^– (OH^–) ion than for the D₃O⁺ (H₃O⁺) ion. Concerning the isotope effect, the value of _E ⁰ (OH^-)/ _E ⁰ (OD^-) deviates considerably from at each temperature and pressure in contrast with that of _E ⁰ (H⁺)/ _E ⁰ (D⁺), although both of them decrease with increasing temperature and pressure. These results are discussed mainly in terms of the difference in repulsive force between the OD^– (OH^–) or the D₃O⁺ (H₃O⁺) ion and the adjacent water molecule, the difference in strength of hydrogen bonds in D₂O and H₂O, and their variations with temperature, pressure, and isotope.     

Laser and radiofrequency spectroscopy of the 5d 4 6s 6 D multiplet in Ta I

The hyperfine structure (hfs) of¹⁸¹Ta has been investigated using laser radio-frequency double resonance and high resolution laser spectroscopy on collimated atomic beams. The magnetic dipole and electric quadrupole hyperfine structure coupling constants of the 5d ^{4 6} s 6D _{3/2, 5/2, 7/2, 9/2} metastable states have been determined using radio-frequency spectroscopy. In the 5d ⁴ 6s ⁶ D _1/2 metastable state and the excited 5d ³ 6s 6p ⁴ D _3/2,⁶ D _{5/2, 9/2} as well as the unidentified 28 182.6 cm^–1 and 30 021.2 cm^–1 states, hfs constants have been obtained from high resolution laser spectroscopy. A radio-frequency converter has been developed in order to reach the frequency region 2.7–10 GHz.     

Enthalpies of alkyl sulfonates in water,heavy water,and water-alcohol mixtures and the interaction of water with methylene groups

The heats of solution of the sodium n-alkyl sulfonates from methyl to octyl have been measured at 25°C in water, D₂O, and three alcohol-rich mixtures with water, all at solute concentrations low enough so that solute-solute interaction is negligible. Methylene-group contributions to the enthalpies of transfer are readily identified. Collation with the results of earlier studies of enthalpies of transfer leads to the conclusion that methylene-group enthalpies of transfer can be identified as follows: 0.87 kcal-mole^–1 for transfers to the gas phase from water and –0.035 kcal-mole^–1 for transfers to D₂O from H₂O, independent of the solute type provided only that methylene-group contributions can be identified in the data. Compared to other solvents, water is about as lipophilic as dimethylsulfoxide or a mixture of 27 moles of water with 73 moles of methanol. However, the range of the interactions between different groups on a given solute molecule seems to be much greater in water than in any of the other solvents studied, making it more difficult to identify group contributions to solvation in water. Another example of the complexity of the solvation of alkyl groups in water is encountered when one compares the solvation enthalpy of hexane in various solvents with some of the above results.     

Measuring the Relative Hydrogen‐Bonding Strengths of Alcohols in Aprotic Organic Solvents

Voltammetric experiments with 9,10‐anthraquinone and 1,4‐benzoquinone performed under controlled moisture conditions indicate that the hydrogen‐bond strengths of alcohols in aprotic organic solvents can be differentiated by the electrochemical parameter ΔE_p^red=|E_p^red(1)?E_p^red(2)|, which is the potential separation between the two one‐electron reduction processes. This electrochemical parameter is inversely related to the strength of the interactions and can be used to differentiate between primary, secondary, tertiary alcohols, and even diols, as it is sensitive to both their steric and electronic properties. The results are highly reproducible across two solvents with substantially different hydrogen‐bonding properties (CH₃CN and CH₂Cl₂) and are supported by density functional theory calculations. This indicates that the numerous solvent–alcohol interactions are less significant than the quinone–alcohol hydrogen‐bonding interactions. The utility of ΔE_p^red was illustrated by comparisons between 1) 3,3,3‐trifluoro‐n‐propanol and 1,3‐difluoroisopropanol and 2) ethylene glycol and 2,2,2‐trifluoroethanol.     

Redox properties of hydrogenated quinoline derivatives — inhibitors in oxidation processes of hydrocarbons

Half-wave potentials of the one-electron electrochemical oxidation (E _1/2 ^ox) of hydroquinolines with different degrees of heterocycle hydrogenization as well as containing substituents of various natures in the benzene ring and heterocycle have been measured. Linear correlations betweenE _1/2 ^ox and the values of the Hammett polar -constants form- andp-substituents in dihydroquinolines and related sulfur-containing dithiolthiones were established. The character of the variation ofE _1/2 ^ox in the series of hydroquinolines was found to correlate with the characteristic features of the inhibiting action of these compounds in the liquid-phase oxidation of various hydrocarbons. However, in contrast to phenolic antioxidants for hydroquinolines, there is no dependence of the retardation period onE _1/2 ^oxin the oxidation of hydrocarbons at temperatures higher than 100 °C.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 610–613, April, 1994.     

Study of a hollow cathode arc discharge in the presence of chromium oxide

A hollow cathode arc discharge in hydrogen has been used for the purpose of chromium oxide reduction, the solid oxide being placed inside the anode. Mass transport from the oxide to the gas phase and excitation conditions in the plasma have been investigated. The results show that a substantial amount of oxide is transferred to the gas phase with subsequent reduction and deposition inside the cathode cavity, in the form of a pure metal. The residual part condenses on the discharge chamber wall as an amorphous substance, containing 50–60% of Cr metal, and on the anode surface under the form of a mixture of chromium oxide and metal crystals (10%). From spectroscopic investigations it follows that, inside the anode zone, total Cr concentration in the gas phase is of the order of 10¹⁴ cm^–3, the excitation temperature of the atoms and ions being 4500 and 5500 K, respectively, and the ionization temperature being about 6000 K.Notation I absolute spectral line intensity (W cm^–2 sr^–1) - emission coefficient (W cm^–3 sr^–1) - A relative absorption - absorption coefficient (cm^–1) - L plasma diameter (mm) - f _tk oscillator strength - _D full Doppler width (cm^–1) - S( ₀ L) Ladenburg-Levy function - wave number (cm^–1) - k _pl mass transport rate (mol cm^–2 s^–1) - k _th thermal reduction rate (mol cm^–2 s^–1) - u ion mobility (mm V^–1 s^–1 ) - E electric field strength (V mm^–1) - drift velocity (cm s^–1)     

Thermodynamic parameters of liquid ternary Fe1−x(Ni5/6Cr1/6)x alloys

Summary Computer-aidedKnudsen cell mass spectrometry is used for thermodynamic investigations on liquid ternary Fe_1–x(Ni_5/6Cr_1/6)_x alloys. The thermodynamic excess properties have been determined by means of the Digital Intensity-Ratio (DIR) method. Liquid ternary Fe_1–x(Ni_5/6Cr_1/6)_x alloys are characterized by exothermic molar heats of mixingH ^E, negative molar excessGibbs energiesG ^E, and negative molar excess entropiesS ^E. At 1850 K, the minimumH ^E value is –3120 J/mol (42.3 at.% Fe), the minimumG ^E value is –2540 J/mol (30 at.% Fe), and the minimumS ^E value is –0.44 J/(mol K) (60 at.% Fe). At 1850 K, the thermodynamic activities of Fe show slight negative deviations from the ideal behaviour for alloys with a Fe-content of less than 75 at.%, and ideal behaviour for the Fe-rich alloys (x _Fe>0.75).

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Thermodynamische Parameter flüssiger ternärer Fe_1–x(Ni_5/6Cr_1/6)_x-Legierungen

Zusammenfassung Die Thermodynamik flüssiger ternärer Fe_1–x(Ni_5/6Cr_1/6)_x-Legierungen wurde mit Hilfe der computerunterstützten Knudsenzellen-Massenspektrometrie studiert. Die thermodynamische Auswertung der experimentellen Untersuchungen erfolgte nach der digitalen Intensitätsverhältnismethode (DIR). Flüssige ternäre Fe_1–x(Ni_5/6Cr_1/6)_x-Legierungen zeigen exotherme molare MischungswärmenH ^E, negative molareGibbssche ZusatzenergienG ^E, und negative molare ZusatzentropienS ^E. Bei 1850 K sind die Minimumswerte fürH ^E –3120 J/mol (42.3 At.% Fe), fürG ^E –2540 J/mol (30 At.% Fe) und fürS ^E –0.44 J/(mol K) (60 At.% Fe). Bei 1850 K zeigen die thermodynamischen Aktivitäten von Fe bei Legierungen mit einem Fe-Gehalt von höchstens 75 At.% leichte negative Abweichungen vom idealen Verhalten, die Fe-reichsten Legierungen (x _Fe>0.75) verhalten sich hingegen nahezu ideal.

     

Self-Diffusion of Co2+ Ions in CoBr2, CoI2 and Electrolyte-Diffusion of ZnSO4 in Agar Gel Medium

Self-diffusion of Co²⁺ ions in CoBr₂ and CoI₂ is reported in the concentration range of 10^–5 to 0.25M in 1% agar gel at 25 °C. The deviations observed between the experimental and theoretical values of diffusion coefficients are explained by considering different types of interactions occurring in the ion-gel water system. The applicability of the transition state theory to the diffusion of ZnSO₄ in agar gel medium is tested by varying the temperature as well as the gel concentration at high concentration of the electrolyte. The activation energy E and D ₀ value decrease with increasing gel concentration in agreement with the theory.     

Aquation of α-cis-chloroaquoethylenediamine-N,N'-diacetatocobalt(III) in aqueous and in mixed solvents: A mechanistic study

Summary The displacement of chloride ligands from -cis-chloro-aquoethylenediamine-N,N-diacetatocobalt(III) in nonacidic aqueous solutions was followed conductimetrically at 30–45° and the products of aquation were characterised by conductance, spectral and ion-exchange techniques. The rate constants for aquation in aqueous media and in 1 : 4 v : v mixed solvents at 25° are: 4.0 × 10^–5 s^–1 in H₂O, 2.71 × 10^–5 s^–1 in MeOH : H₂O, 2.74 × 10^–5 s^–1 in EtOH: H₂,O and 2.58 × 10^–5 s^–1 n in Me₂CO : H₂O. The corresponding H* and S* values have also been evaluated. Solvent polarity has a marked influence on the rate of chloride ion release. The aquation rate constants and the activation parameters have been correlated with solvent parameters,e.g. D, Y-values, Dimroth's E_T and Kosower's Z-values and, based on these correlations, a dissociative interchange (I_d) mechanism is proposed rather than dissociative as observed for some other cobalt(III) complexes.Senior author.     

Polarographische Bestimmung der 2,2′-Dicinchoninsäure

Zusammenfassung Eine polarographische Methode zur Bestimmung der 2,2-Dicinchoninsäure in 15%iger Ammoniumacetatlösung als Grundelektrolyt wurde ausgearbeitet. Der zweistufigen Reduktion entsprechen zwei polarographische Stufen, deren Halbstufenpotentiale gegen die gesättigte KalomelelektrodeE _1/2=–0,74 V undE _1/2=–1,28 V betragen.Die charakteristischen zwei Maxima wurden mit 0,5%iger Gelatinelösung beseitigt und der Sauerstoff mit elektrolytisch hergestelltem Wasserstoff entfernt.Die lineare Abhängigkeit des Diffusionsstromes für beide Stromstufen der Säure in zwei Konzentrationsbereichen —von 1·10^–4- bis 3·10^–4-m und von 0,5·10^–3-bis 3·10^–3-m —wurde festgestellt.

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Summary A polarographic method has been developed for the determination of 2,2-dicinchonic acid in 15% ammonium acetate solution as fundamental electrolyte. The two-stage reduction is shown by two polarographic stages, whose half-stage potentials as referred to the saturated calomel electrode amount toE _1/2=–0.74 V andE _1/2=–1.28 V.The two characteristic maxima were removed by 0.05% gelatin solution and the oxygen was eliminated by means of hydrogen produced electrolytically. The linear dependence of the diffusion current for both current stages of the acid were established in two concentration ranges —from 1·10^–4 to 3·10^–4 M and from 0.5·10^–3 to 3·10^–3 M.

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Résumé Mise au point d'une méthode polarographique pour doser l'acide dicinchonine-2, 2 en solution dans l'acétate d'ammonium à 15% comme électrolyte support. La réduction en deux temps correspond à deux vagues polarographiques, dont les potentiels de demi-vague par rapport à l'électrode au calomel saturée s'élèvent àE _1/2= – 0,74 V etE _1/2=–1,28 V.On élimine les deux maximums caractéristiques par une solution de gélatine à 0,05% et l'oxygène par l'hydrogène préparé électrolytiquement. Mise en évidence d'un rapport linéaire entre le courant de diffusion pour les deux vagues de courant de l'acide dans les deux domaines de concentration: de 1·10^–4 à 3·10^–4 M et de 0,5·10^–3 à 3·10^–3 M.

     

Radioluminescence of Europium(III) in POCl3–SnCl4–235UO2+ 2–Eu3+, and D2O–235UO2+ 2–Eu3+ Solutions

Results of studying the spectral and luminescent properties of Eu³⁺ ions upon homogeneous excitation of POCl₃–SnCl₄–^-UO²⁺ ₂–Eu³⁺ and D₂O–²³⁵UO²⁺ ₂–Eu³⁺ solutions by -particles are presented. It was found that the radioluminescence intensity of Eu³⁺ ions in both solvents increases proportionally to the energy input by -particles. The yield of radioluminescence photons from europium ions in the POCl₃–SnCl₄–UO²⁺ ₂–Eu³⁺ solutions is more than nine times as high as that in D₂O–UO²⁺ ₂–Eu³⁺. The radiation-chemical yields of excited ⁵ D ₀ states of Eu³⁺ ions are 0.74 ± 0.07 and 0.18 ± 0.02 ions/100 eV in POCl₃–SnCl₄–UO²⁺ ₂–Eu³⁺ and D₂O–UO²⁺ ₂–Eu³⁺ solutions, respectively.     

Conformational dependence of the intrinsic acidity of the aspartic acid residue sidechain in N-acetyl- -aspartic acid-N′-methylamide

The sidechain conformational potential energy hypersurfaces (PEHS) for the γ_L, β_L, α_L, and α_D backbone conformations of N-acetyl- -aspartate-N′-methylamide were generated. Of the 81 possible conformers initially expected for the aspartate residue, only seven were found after geometric optimizations at the B3LYP/6-31G(d) level of theory. No stable conformers could be located in the δ_L, _L, γ_D, δ_D, and _D backbone conformations. The ‘adiabatic’ deprotonation energies for the endo and exo forms of N-acetyl- -aspartic acid-N′-methylamide were calculated by comparing their optimized relative energies against those found for the seven stable conformers of N-acetyl- -aspartate-N′-methylamide. Sidechain conformational PEHSs were also generated for the estimation of ‘vertical’ deprotonation energies for both endo and exo forms of N-acetyl- -aspartic acid-N′-methylamide. All backbone–sidechain (N–H⁻O–C) and backbone–backbone (N–HO=C) hydrogen bond interactions were analyzed. A total of two backbone–backbone and four backbone–sidechain interactions were found for N-acetyl- -aspartate-N′-methylamide. The deprotonated sidechain of N-acetyl- -aspartate-N′-methylamide may allow the aspartyl residue to form strong hydrogen bond interactions (since it is negatively charged) which may be significant in such processes as protein–ligand recognition and ligand binding. As a primary example, the molecular geometry of the aspartyl residue may be important in peptide folding, such as that in the RGD tripeptide.     

EPR Studies on Branched High‐Spin Arylnitrenes

The UV (λ>305 nm) photolysis of triazide 3 in 2‐methyl‐tetrahydrofuran glass at 7 K selectively produces triplet mononitrene 4 (g=2.003, D_T=0.92 cm^?1, E_T=0 cm^?1), quintet dinitrene 6 (g=2.003, D_Q=0.204 cm^?1, E_Q=0.035 cm^?1), and septet trinitrene 8 (g=2.003, D_S=?0.0904 cm^?1, E_S=?0.0102 cm^?1). After 45 min of irradiation, the major products are dinitrene 6 and trinitrene 8 in a ratio of ～1:2, respectively. These nitrenes are formed as mixtures of rotational isomers each of which has slightly different magnetic parameters D and E. The best agreement between the line‐shape spectral simulations and the experimental electron paramagnetic resonance (EPR) spectrum is obtained with the line‐broadening parameters Γ(E_Q)=180 MHz for dinitrene 6 and Γ(E_S)=330 MHz for trinitrene 8 . According to these line‐broadening parameters, the variations of the angles Θ in rotational isomers of 6 and 8 are expected to be about ±1 and ±3°, respectively. Theoretical estimations of the magnetic parameters obtained from PBE/DZ(COSMO)//UB3LYP/6‐311+G(d,p) calculations overestimate the E and D values by 1 and 8 %, respectively. Despite the large distances between the nitrene units and the extended π systems, the zero field splitting (zfs) parameters D are found to be close to those in quintet dinitrenes and septet trinitrenes, where the nitrene centers are attached to the same aryl ring. The large D values of branched septet nitrenes are due to strong negative one‐center spin–spin interactions in combination with weak positive two‐center spin–spin interactions, as predicted by theoretical considerations.     

Direct electrochemical reduction of hemin in imidazolium-based ionic liquids

The direct electrochemical reduction of hemin, protoporphyrin(IX) iron(III) chloride, ligated with strong or weak heterocyclic bases, was investigated in the ionic liquids (IL), 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([omim][PF₆]), using cyclic voltammetry and chronocoulometry. Hemin complexed with N-methylimidazole (NMI) or with pyridine had E_1/2 values slightly (4–59 mV) more positive in IL (without electrolyte) than in methanol (1.0 M electrolyte) using a gold electrode. NMI-ligated hemin had a lower E_1/2 than pyridine-ligated hemin in either IL, consistent with the stronger electron donor characteristic of NMI. [Bmim][PF₆] solutions consistently yielded E_1/2 values 30 mV more negative than [omim][PF₆] solutions. The diffusion coefficients D_o of hemin in the IL ranged between 1.50 and 2.80×10⁻⁷ cm² s⁻¹, while the heterogeneous electron-transfer rate constants k_s ranged between 3.7 and 14.3×10⁻³ cm s⁻¹. Cyclic voltammetry of hemin adsorbed to a gold surface through 4,4′-bispyridyl disulfide (AT4) linkages showed a large positive shift in the oxidation wave, indicating that adsorption stabilizes the reduced hemin state. The surface concentration Γ_o of the adsorbed hemin was determined to be 1.21×10⁻¹⁰ mol cm⁻², indicating the presence of one or more complete monolayers of hemin. These findings suggest that while hemin is electrochemically active in IL, its behavior is modified by the ligand field strength and surface adsorption phenomena.     

Test study on the excitation spectra of the N<Subscript>2</Subscript>–He van der Waals molecule

We have performed ab initio fourth-order Møller–Plesset perturbation theory calculations in the framework of the supermolecule approach on the vertical excitation spectra of the weakly bound van der Waals N₂–He dimer. They indicate a ``T-shaped' stablest ground N<sub>2</sub>(X<sup>1</sup><sub>g</sub><sup>+</sup>)–He(<sup>1</sup>S) electronic state with a well depth, D<sub>e</sub>, of 21.63 cm<sup>–1</sup> at a minimum distance, R<sub>e</sub>, of 3.44 Å and zero-point vibration correction, D<sub>o</sub>, of 7.07 cm<sup>–1</sup>. They also indicate a ``T-shaped' stablest excited conformer with R_e=3.25 Å, D_e=36.85 cm^–1 and D_o=17.06 cm^–1 for the N₂(B³_g)–He(¹S) triplet electronic level. In order to investigate the use of less-demanding correlation methods, test density functional theory calculations using the mPW1PW exchange–correlation functional are also presented for comparison.