Low-temperature thermodynamic properties of <Emphasis Type="Italic">L</Emphasis>-cysteine

Heat capacity C _p(T) of the orthorhombic polymorph of L-cysteine was measured in the temperature range 6–300 K by adiabatic calorimetry; thermodynamic functions were calculated based on these measurements. At 298.15 K the values of heat capacity, C _p; entropy, S _m⁰(T)-S _m⁰(0); difference in the enthalpy, H _m⁰(T)-H _m⁰(0), are equal, respectively, to 144.6±0.3 J K⁻¹ mol⁻¹, 169.0±0.4 J K⁻¹ mol⁻¹ and 24960±50 J mol⁻¹. An anomaly of heat capacity near 70 K was registered as a small, 3–5% height, diffuse ‘jump’ accompanied by the substantial increase in the thermal relaxation time. The shape of the anomaly is sensitive to thermal pre-history of the sample.     

Corannulene vs. C60-fullerene in metal binding reactions: a direct DFT and X-ray structural comparison

DFT calculations and X-ray crystallography were used to directly compare the reactivity of the convex carbon surfaces of C(20)H(10)-corannulene and the C(60)-fullerene toward the diruthenium(i,i) metal cluster.     

Heteronuclear Mn-Ca/Sr complexes, and Ca/Sr EXAFS spectral comparisons with the oxygen-evolving complex of photosystem II

Heterometallic Mn-Ca and Mn-Sr complexes have been prepared and employed as model complexes for Ca and Sr EXAFS spectral comparisons with the Oxygen-Evolving Complex (OEC) of Photosystem II (PS II); these have revealed similarities that support the presence of at least one O atom bridge between the Mn and Ca/Sr in the OEC.     

Preparation and characterization of dense films of poly(amidoamine) dendrimers on indium tin oxide

Indium tin oxide (ITO) substrates were modified with a layer of poly(amidoamine) (PAMAM) dendrimers to change their surface properties and, in particular, the substrates' work function. The functionalization procedure involved the electrostatic adsorption of positively charged PAMAM dendrimers of generation five onto negatively polarized ITO surfaces. Three different PAMAM dendrimers were used: PAMAM-NH2 and PAMAM-OH with terminal amine and hydroxyl groups, respectively, as well as Q-PAMAM-NH2, which had been prepared from PAMAM-NH2 by quaternization of the dendrimer's terminal and internal amine groups with methyl iodide. The resulting organic films were analyzed by contact angle goniometry, X-ray photoelectron spectroscopy, ellipsometry, and Kelvin probe force microscopy to confirm the presence of a dense layer. A Langmuir isotherm was derived from surface densities of fluorescence-labeled PAMAM-NH2 dendrimers from which we deduced an equilibrium binding constant, K(eq), of (1.3 +/- 0.3) x 10(5) M(-1). Kelvin probe measurements of the contact potential difference revealed a high reduction of the work function from 4.9 eV for bare ITO to 4.3 eV for ITO with a dense film of PAMAM-NH2 of generation five. PAMAM-OH and Q-PAMAM-NH2 resulted in slightly smaller work function changes. This study illustrates that the work function of ITO can be tuned by adlayers composed of PAMAM dendrimers.     

The problem of small negatively ionized water clusters

Structures of the negatively charged water clusters (H₂O)⁻_n with n up to 6 were optimized at the UHF/4–31 + + G** level without any geometrical restriction. There was found a chainlike structure for the trimer anion and both chainlike and cyclic geometries for the larger clusters. According to the MP2 energy estimates, all the clusters with n ≥ 3 are more stable than the combinations of separated water molecules and a free electron. The energy of the cycles is lower than that of the chains of the same size. However, the latter species are energetically closer to the neutral oligomers of the same geometry. The energy of vertical detachment of an electron from the chainlike hexamer anion is already about zero. Addition of a diffuse s function centered equidistantly between the oxygen atoms proved metastability, in particular, of the cyclic (H₂O)⁻₄ structure. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 737–748, 1997     

Absorption of ionic amphiphils by oppositely charged polyelectrolyte gels

Slightly cross-linked polyelectrolytes absorb oppositely charged surfactants in aqueous media. Transfer of amphiphilic ions from solution into the swollen network proceeds as a frontal heterogeneous cooperative reaction causing a collapse of the original polyelectrolyte gel. Small and wide angle X-ray diffraction data show that electrostatic complex formed as a result of the reaction consists of lamellar type surfactant micelles embedded in a polyelectrolyte network. It is also shown that such complexes contain equimolar amount of surfactant ions and ionized polyelectrolyte units paired with amphiphil head groups. In other words a charged network is not able to bind surplus oppositely charged surfactant ions. However, it is still able to solubilize a substantial amount of a nonionized surfactant. Chemical structure of surfactants strongly affect internal structure of lamellae and stability of the complexes.     

Highly regioselective synthesis of trifluoromethyl derivatives of pyrazolo[1,5-a]pyrimidines bearing fused cycloalkane rings using (2-ethoxycycloalkenyl)-2,2,2-trifluoroethanones

8-Trifluoromethyl-6,7-dihydro-5H-1,4,8a-triaza-s-indacene and 9-trifluoromethyl-5,6,7,8-tetrahydropyrazolo[5,1-b]quinazolines were efficiently generated by condensation of 5(3)-aminopyrazoles with (2-ethoxycycloalkenyl)-2,2,2-trifluoroethanones and isolated in excellent yields. The regiochemistry of the prepared compounds was established by ¹H, ¹³C and ¹⁹F NMR spectroscopy and X-ray diffraction analysis.     

Thin Film Exfoliation in the Zone of Trapped Elastic Wave Localization

In modern constructions, thin-layer coats are often used as protecting or strengthening elements. Deformations of such constructions may cause significant stresses on the interface between the base and the coat because of the difference in their physical mechanical properties, which leads to the destruction or detachment of the cover. The impact of static or shock loads on the emergence and development of delamination in multilayer constructions has been studied fairly well, but much less is known about destructions of this type under nonstationary (vibrational) loads. The interest in the latter is caused by the fact that even small variable actions may cause the localization of oscillations in a neighborhood of inhomogeneities (such as inclusions, defects, construction elements, etc.) [1] (and lead to the emergence and growth of defects, which strongly affects the reliability and functionality of the whole construction. The possibility of the localization of oscillations near initial delamination and the impact of localization on the growth of the delamination are studied and a model for analyzing conditions under which a detachment zone grows or ceases to grow is suggested. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Competition between non-classical and classical hydrogen bonded sites in [BH3CN]: Spectral, energetic, structural and electronic features

Interaction of the salt (Ph₃PNPPh₃)BH₃CN with the various OH and NH proton donors in low polar media was studied by variable temperature (200–290 K) IR spectroscopy and theoretically by DFT calculations. The formation of two types of complexes containing non-classical dihydrogen bond to the hydride hydrogen (DHB) and classical hydrogen bond (HB) to nitrogen lone pair was shown in solution. The 1:1 complexes of both types (XHH and XHN) coexist in the presence of equimolar amount of proton donor. The addition of excess XH-acid leads to the increase of the classical HB content and appearance of the 1:2 complexes, where two basic sites work simultaneously. The structure, spectral characteristics, energy and electron redistribution were studied by DFT (B3LYP) method. The comparison DHB parameters of [BH₃CN]⁻ with those of the unsubstituted analogue [BH₄]⁻ allowed analyzing the electronic effects of the CN group on the basic properties of boron hydride moiety. The electronic influence of the BH₃ group on CN⁻HX hydrogen bond was also established by comparison with the corresponding classical HB to the CN⁻ anion.