Effects of ionization on the phase behavior of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide-co-acrylic acid) and poly(<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diethylacrylamide-co-acrylic acid) in water

Phase transitions of poly(N-isopropylacrylamide-co-acrylic acid) (PiPA-AA) and poly(N,N- diethylacrylamide-co-acrylic acid) (PdEA-AA) in water have been investigated by means of turbidimetry, Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The phase transition temperatures (T_p) of these copolymers increase with the degree of ionization () of the acrylic acid (AA) units, which in turn is dependent on the pH of the solutions. Apparent values of pK_a for the AA units, determined from the pH dependencies of T_p, are 4.7 and 5.4 for PiPA-AA and PdEA-AA, respectively. Differences between T_p for PiPA-AA and T_p for PiPA homopolymer (T_p) are +1.5 and –0.2 °C/mol% of AA at =1 and 0, respectively. The values of T_p for PdEA-AA are +2.6 (ionic) and –0.5 (nonionic)°C/mol%, indicating that the incorporated AA units have a larger effect on PdEA than on PiPA. DSC measurements performed with each of these copolymers at different pH values show a linear relationship between T_p and the enthalpy of transition (H). IR measurements of PiPA-AA show that the profiles of IR bands from both iPA and AA units exhibit critical changes at T_p of the copolymer. Heating the solution above T_p leads to shifts of the amide II, C–H stretch, and C–H bend bands from the iPA units toward lower wavenumbers, as well as a shift of the amide I band from the iPA units toward higher wavenumbers. A decrease in the intensity of the symmetric C=O stretch IR band from carboxylate anions (1560 cm^–1), and an increase in the intensity of the C=O stretch band from COOH groups (1705 cm^–1) suggest that a partial protonation of the carboxylate groups (COO^–+H⁺COOH) takes place upon the phase transition.     

Splitting of the <Emphasis Type="Italic">d</Emphasis><Superscript><Emphasis Type="Italic">N</Emphasis></Superscript> atomic states in icosahedral 3<Emphasis Type="Italic">d</Emphasis> metal endofullerenes M@C<Subscript>60</Subscript>

Group-theoretical and quantum-chemical investigations of the spectrum of low-lying excited states have been performed by the ROHF and FCI-RAS (Full CI in Restricted Active Space) methods for 3d metal endofullerenes (MEFs) M@C₆₀ (M =Mn, Cr, and Fe) in different charged states. The major purpose of this study is quantum-chemical verification of the anomalous (“non-Bethe’s”) character of splitting of the d ^N atomic states in an electrostatic field with icosahedral symmetry, predicted previously within the theory of integral invariants theory. The interrelation between the integral invariants theory and the quantumchemical methods applied in this work is considered in detail. Our calculations suggest that the d ^N atomic states in the icosahedral field generated by fullerene C60 (I _h ) on a metal atom (ion) remain non-split for different charged states of the metal and C₆₀. Reasons for this phenomenon and other possible approaches to verification of the prediction are discussed. It is demonstrated that the d ^N states of the encapsulated metal are split in icosahedral 3d MEFs only under very strong compression of these structures.     

The group-theoretical structure of the atomic g shell: connection with the alternating group <Emphasis Type="Italic">A</Emphasis><Subscript>6</Subscript> as <Emphasis Type="Italic">L</Emphasis><Subscript>2</Subscript>(9)

The special projective linear groups PSL(2ℓ + 1) or L ₂(2ℓ + 1) of order 2ℓ(2ℓ + 1)(ℓ + 1) can be used to study atomic shells of electrons with angular momentum quantum number ℓ corresponding to the atomic p, d, f, and g shells for ℓ = 1, 2, 3, 4, respectively. For the atomic g shell the group L ₂(9) is isomorphic with the alternating group A ₆ on six objects of order 360 or the symmetry group of the 5-dimensional simplex, a 5-dimensional analogue of the tetrahedron with 6 vertices and 15 edges. This leads to the subgroup chain SO(9) ⊃ SO(5) ⊃ L ₂(9) for the atomic g shell analogous to the subgroup chain SO(7) ⊃ G ₂ ⊃ L ₂(7) ≈⁷ O for the atomic f shell. In the L ₂(9) group only the representations of spherical harmonics or sums thereof, Γ(Y_ℓ), with dimensions dim Γ(Y_ℓ) or dim Γ(Y_ℓ) ± 1 divisible by 9 are found to be individually reducible to irreducible representations (irreps) or sums of irreps of L ₂(9). This leads to term groupings such as S, PD, G, PF, DH, L, PK, DI, FH, M, FI, PO, DN, HK, R, etc., of increasing total dimension for the irreps of SO(9) for various g ⁿ configurations in the atomic g shell.     

Hydrogen-Bonding Interaction in a Complex of Amino Acid with <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dimethylformamide Studied by DFT Calculations

Theoretical studies on hydrogen-bonded complexes between amino acids (glycine, alanine and leucine) and N,N-dimethylformamide (DMF) in gas phase have been carried out using density functional theory (DFT) and ab initio calculations at the B3LYP/6-311++G** and MP2/6-311++G** theory levels. The structures, binding energy, stretching frequency and bond characteristics of the mentioned complexes were calculated. The NH₂ and COOH groups of amino acids form different types of hydrogen bonds with the DMF molecule, as well as alkyl side chains. High binding energy suggests multiple hydrogen bonds present in one complex. The nearly linear OH???O and NH???O contacts are stronger than a conventional hydrogen bond interaction with their H???O separation between 1.74 and 2.14 Å. The weaker CH???O H-bond is also discussed as being a crucial interaction in biological systems involving amino acids. The formation of this interaction results in a blue shift in the CH stretching frequency.     

Quantum-chemical investigation of structure and stability of [<Emphasis Type="Italic">n</Emphasis>]-prismanes and [<Emphasis Type="Italic">n</Emphasis>]-asteranes

The study by DFT [B3LYP/6-311G(2df,p)] method of structural and energy characteristics peculiar to [n]-prismanes and [n]-asteranes demonstrated that prismanes of n = 3–10 and asteranes of n = 3–7 possessed a stable structure of D_nh-symmetry; the D_nh-geometry was distorted in the subsequent terms of the series.     

Theoretical study of structure and properties of hexuronic acid and <Emphasis Type="SmallCaps">d</Emphasis>-glucosamine structural units of glycosaminoglycans

The Becke3LYP functional of DFT theory was used to investigate molecular structure and sodium affinity of the systems CH₃CO₂Na (1), CH₃–O–SO₃Na (2), CH₃–NH–SO₃Na (3), saccharide_1Na₂ (4), saccharide_2Na (5), saccharide_3Na₃ (6), saccharide_4Na₂ (7), and saccharide_5Na₂ (8), respectively, which are models of N- and O-sulfate glycosaminoglycans. Interaction enthalpies, entropies and Gibbs energies of the sodium-coordinated systems in the gas phase were determined with the B3LYP/6-311+G(d,p) and B3LYP/6-31+G(d) methods. The computed Gibbs energies, ΔG ^o , of model systems 1–3 are negative and span a rather broad energy interval (from −500 to −1,500 kJ mol⁻¹). Gibbs interaction energies for sodium acetate, sodium sulfate and sodium sulfamate functions of the five saccharides, systems 4–8 are always lower than those values found for the model compounds 1–3. The ionization of sodium salts of saccharides studied in gas phase is in most cases connected with considerable conformational rearrangement of the ionic species. This rearrangement causes an additional energetic stabilization of anionic species and is connected with the substantial release of entropy.     

Complex amidoboranes M<Superscript>2</Superscript>[M<Superscript>1</Superscript>(NH<Subscript>2</Subscript>BH<Subscript>3</Subscript>)<Subscript>4</Subscript>] (M<Superscript>1</Superscript> = Al,Ga; M<Superscript>2</Superscript> = Li,Na, K,Rb, Cs)

Structural, spectral, and thermodynamic characteristics of complex amidoboranes M²[M¹(NH₂BH₃)₄] (M¹ = Al, Ga; M² = Li, Na, K, Rb, Cs) were calculated by the B3LYP/def2-SVPD quantum-chemical method. The procedure for the synthesis of these compounds by reactions of alkali metal amidoboranes with aluminum and gallium chlorides was suggested and experimentally tested. Reaction products were characterized by the NMR and IR spectroscopy and X-ray phase analysis.     

Preparation,Structural Characterization and the Molecular Structure of 2,3,5-Trinitro-<Emphasis Type="Italic">p</Emphasis>-xylene

2,3,5-trinitro-p-xylene (TPX) is synthesized by nitration of p-xylene in mixed acid of nitric and sulfuric acid. Single crystal of TPX is cultured from DMF solution using a slow cooling method. The compound is characterized by FT-IR, ¹H NMR and MS techniques. The crystal structure is determined by X-ray⁴ single-crystal diffraction analysis. The crystal belongs to the monoclinic system with space group P_n. Its unit cell parameters are as follows: a = 0.8271(2), b = 0.6011(1), c = 1.0487(2) nm, β = 105.42(2)^∘, V = 0.50263(2) nm³, D_c = 1.593 g/cm³, Z = 2, F(0 0 0) = 248. The molecular structures of TPX have been calculated at the B3LYP/6-31G^** and B3LYP/6-311G^** levels of theory, and its frequencies analysis have also been accomplished at the same level of theory. The thermal decomposition process of the compound was studied using DSC and TG-DTG techniques. The predicted nitro group vibrations with B3LYP/6-311G^** calculation considerably agree with the observed frequencies. The calculated results propose that the structural parameters from the theory are close to those of the crystal structure from the experiments.     

The <Emphasis Type="Italic">r</Emphasis><Subscript>0</Subscript> structural parameters of equatorial and axial chlorocyclobutane,conformational stability from temperature dependent infrared spectra of xenon solutions,and vibrational assignments

Variable temperature (?55 to ?100 °C) studies of the infrared spectra (4,000–400 cm^?1) of chlorocyclobutane, c-C₄H₇Cl, dissolved in liquid xenon have been carried out. The infrared spectrum (4,000–100 cm^–1) of the gas has also been recorded. For this puckered ring molecule the enthalpy difference between the more stable equatorial conformer and the axial form, has been determined to be 361 ± 17 cm^?1 (4.32 ± 0.20 kJ/mol). This stability order is consistent with that predicted by ab initio calculations but the ?H is much lower than the average energy value of 646 ± 73 cm^?1 obtained from the MP2 ab initio calculations or 611 ± 28 cm^?1 from the B3LYP density functional theory calculations. The percentage of the axial conformer present at ambient temperature is estimated to be 15 ± 1%. By utilizing previously reported microwave rotational constants for both conformers combined with ab initio MP2(full)/6–311+G(d,p) predicted structural values, adjusted r ₀ parameters have been obtained. The determined heavy atom structural parameters for the equatorial conformer are: the distances C–Cl = 1.783(5), C₁–C₄ = 1.539(3), C₄–C₆ = 1.558(3) Å, and angles ∠C₆C₄C₁ = 86.9(5), ∠C₄C₁C₅ = 89.7(5)°, and for the axial conformer are: the distances C–Cl = 1.803(5), C₁–C₄ = 1.547(3), C₄–C₆ = 1.557(3) Å, and angles ∠C₆C₄C₁ = 86.3(5), ∠C₄C₁C₅ = 88.9(5) and the puckering angles for the equatorial and axial conformers are 30.7(5)° and 22.3(5)°, respectively. The conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios and vibrational frequencies have been obtained for both conformers from MP2(full)/6-31G(d) ab initio calculations and compared to experimental values where available. The results are discussed and compared to the corresponding properties of some similar molecules.     

Kinetics of Na|CF<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> and Li|CF<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> systems

Properties of CF _x /Li and CF _x /Na cells were examined while using galvanostatic charging/discharging, electrochemical impedance spectroscopy and scanning electron microscopy (SEM). The capacity during the first cycle was as high as ca. 1000 mAh g^?1. Such an electrode is suitable for primary CF _x /Li and CF _x /Na batteries. SEM images of CF _x cathode showed that during discharging it was transformed into amorphous carbon and LiF or NaF crystals (of diameter of ca. 5–20 μm). These systems (C?+?LiF or C?+?NaF) cannot be reversibly converted back into CF _x /Li or CF _x /Na, respectively. Exchange current densities are between 10^?7 Acm^?2 and 10^?9 Acm^?2 when working with LiPF₆ and NaPF₆ electrolytes (1.12?×?10^?7 Acm^?2 and 6.82?×?10^?9 Acm^?2, respectively). Those values are low and indicate that the charge transfer process may be the rate-determining step. Activation energies for the charge transfer process were 57 and 72 kJ mol^?1 for CF _x /LiPF₆ and CF _x /NaPF₆ systems, respectively. Higher activation energy barrier for the CF/Na⁺?+?e^??→?C?+?NaF reaction results in lower observed exchange current density in comparison to the system with lithium ions.     

Molecular structure of NiO<Subscript>2</Subscript>N<Subscript>2</Subscript>C<Subscript>16</Subscript>H<Subscript>14</Subscript> from gas-phase electron diffraction and quantum chemical data

Gas-phase electron diffractometry was used to study the molecular structure of N,N′-ethylenebis(salicylaldiminato)nickel(II), NiO₂N₂C₁₆H₁₄, [hereinafter Ni(salen)] at 583(5) K. The molecule has C ₂ symmetry with a practically planar structure of the NiN₂O₂ coordination unit and with internuclear distances r _α (Ni-O) = 1.882(21) Å and r _α (Ni-N) = 1.889(22) Å. The results of B3LYP/CEP-31G molecular structure calculations are in good agreement with experimental data, whereas the RHF/CEP-31G method significantly overestimates the Ni-N internuclear distance and gives worse results for other structural parameters. According to 3LYP/CEP-31G calculations, the ¹ A low-spin state is 28 kJ/mole lower in energy than the ³ B high-spin state.     

<Emphasis Type="Italic">Ab initio</Emphasis> and phenomenological simulation of the phonon spectra Be<Emphasis Type="Italic">M</Emphasis>N<Subscript>2</Subscript> (<Emphasis Type="Italic">M</Emphasis> = C,Si, Ge,Sn) crystals

Phonon spectra of hypothetic BeMN₂ (M = C, Si, Ge, Sn) crystals with a chalcopyrite lattice are calculated by the ab initio density functonal method in the center of the Brillouin zone and interpolated over the whole Brillouin zone using the phenomenological Keating model. Interaction parameters are found by comparing IR and Raman active frequencies obtained in the phenomenological model with calculations performed by the ab initio method. Numerical values of short-range constants and charges are in accordance with the ab initio calculated characteristics of the chemical bond. These parameters have the obvious physical meaning and the chemical nature and can be further used for both qualitative estimates of any physical and physicochemical values and quantitative calculations of the phonon spectra of isostructural compounds.     

Fabrication of a novel Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MoO<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> film modified electrode and its application as an electrochemical sensor of iodate

A novel organic gel film modified electrode was simply and conveniently fabricated by casting Li_xMoO_y and polypropylene carbonate (PPC) onto the surface of a gold electrode. The cyclic voltammetry and amperometry studies demonstrated that the Li_xMoO_y film modified electrode has a high stability and a good electrocatalytic activity for the reduction of iodate. In amperometry, a good linear relationship between the steady current and the concentration of iodate was obtained in the range from 3×10^–7 to 1×10^–4 mol L^–1 with a correlation coefficient of 0.9997 and a detection limit of 1×10^–7 mol L^–1.     

Mechanochemical synthesis of <Emphasis Type="Italic">N</Emphasis>-triethylborazine

Reactions of ethylamine hydrochloride C₂H₅NH₂HCl with MBH₄ (M = Li, Na, K) under mechanical activation of mixtures of crystalline substances in a vacuum vibratory ball mill are studied. The step-by-step pyrolysis of the reaction products at 90 and 240°C is found to yield N-triethylborazine. The maximum yields of N-triethylborazine are 78.9, 60.3, and 73.8% for LiBH₄, NaBH₄, and KBH₄, respectively. The target product is characterized by various physicochemical methods. The melting point, density, refractive index, and other properties correspond to the literature data for N-triethylborazine.     

<Emphasis Type="Italic">N</Emphasis>-allyl and <Emphasis Type="Italic">N</Emphasis>-propargyl trifluoromethanesulfonimides. Theoretical analysis

Tautomers of N-allyl- and N-propargyl-substituted trifluoromethanesulfonimides (CF₃SO₂)₂NR (R = CH₂CH=CH₂, Z/E-CH=CHMe, CH₂C≡CH, CH=CH=CH₂, C≡CCH₂) were calculated by the DFT (B3LYP, wB97XD, PBE1PBE), MP2, and CBS-QB3 methods. The results were compared with the theoretical data for the corresponding amines and amides NHRR¹ (R¹ = H, CF₃SO₂). It was shown that there is no conjugation between the nitrogen atom and C=C bond and that conjugation exists with the C≡C bond with electron density displacement toward the nitrogen atom. The calculations of anions derived from N-allyl- and N-propargyl-trifluoromethanesulfonimides revealed the possibility of their rearrangement with elimination of trifluoromethanesulfinate anion and formation of its H-complex with N-(prop-2-en-1-ylidene)trifluoromethanesulfonamide or N-(prop-2-yn-1-ylidene)trifluoromethanesulfonamide.     

Adsorption of<Emphasis Type="Italic"> N</Emphasis>-dodecyl-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethyl-3-ammonio-1-propanesulfonate (DDAPS), a model zwitterionic surfactant,on the Au(111) electrode surface

Electrochemical measurements including cyclic voltammetry, differential capacity, and chronocoulometry have been used to characterize the adsorption behaviors of the zwitterionic surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS) on the Au(111) electrode surface. The thermodynamics of the ideally polarized electrode have been employed to determine the Gibbs excess and the Gibbs energy of adsorption. The results show that the adsorption of DDAPS has a multistate character. The first two states are observed at potentials close to zero charge. At low bulk DDAPS concentrations, it corresponds to the formation of a film of nearly flat adsorbed molecules. At higher concentrations it is converted into a hemimicellar state. The second state is formed at negative potentials and charge densities close to 0 C cm^–2. It corresponds to a film of tilted molecules oriented with the hydrocarbon tail towards the metal and the polar head toward the solution.Dedicated to Professor Zbigniew Galus on the occasion of his 70^th birthday and in recognition of his many contributions to electrochemistry.     

Formation of a Hydroxo-bridged Dinuclear Ru(III)/Ru(III) Complex from <Emphasis Type="Italic">N</Emphasis>-Methylimidazole and [Ru<Emphasis Type="Italic">Cp</Emphasis>(CH<Subscript>3</Subscript>CN)<Subscript>3</Subscript>]<Superscript>+</Superscript>

Summary. The reaction of [RuCp(CH₃CN)₃]PF₆ with 1 equiv of N-Me-imidazole results in the quantitative formation of [RuCp(¹N-N-Me-imidazole)(CH₃CN)₂]PF₆ (1) featuring a ¹N rather than a ¹C bound N-Me-imidazole ligand. According to DFT/B3LYP calculations, ¹N coordination of N-Me-imidazole is preferred over ¹C coordination by 25.5kJ/mol. Upon exposure to air 1 reacts with oxygen and water to afford the novel hydroxo-bridged dinuclear complex of [Ru₂Cp₂(¹N-N-Me-imidazole)₂(-OH)₂](PF₆)₂ (2) featuring a metal-metal single bond. The dimeric nature of 2 was confirmed by a single-crystal X-ray structure analysis.     

Hexafluoroacetone as Protecting and Activating Reagent. A New Approach to <Emphasis Type="Italic">N</Emphasis>-Glycosides

Summary. N-Glycosides of Asn and homologues have been synthesized starting from hexafluoroacetone-protected -activated Asp, Glu, and Aad derivatives and glycosylamines. The synthetic value of the new building blocks was demonstrated by the concise incorporation of N-glycosylated Asn, Gln, and Aad -amides into glycopeptides.     

<Emphasis Type="Italic">O</Emphasis>-vinylacetoxime as a hydrogen bond acceptor

According to quantum chemical calculations (B3LYP/6-311G*) and IR spectroscopy the basicity of oxygen atom of O-vinylacetoxime is substantially lower than that of O-ethylacetoxime and is comparable to the basicity of phenyl vinyl and diphenyl ethers. In CCl₄ solution, O-vinylacetoxime gives H-complexes wit methanol by formation of N···HO bonds. With phenol and trifluoroacetic acid under these conditions it enters in the reaction of electrophilic addition. O-Ethylacetoxime in inert media forms with methanol and phenol two types of H-complexes with the N···HO or O···HO bonds.     

Alkaloids of <Emphasis Type="Italic">Arundo donax</Emphasis> L.

The structure of a new dimeric indole alkaloid, arundarine, isolated from the roots of the plant Arundo donax L. (Poaceae) was determined. On the basis of spectroscopic data, arundarine was identified as 5-[3-(2-dimethylaminoethyl)indol-1-yl]-6-hydroxy-N ²-methyl-1,2,3,4-tetrahydro--carboline.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1697–1699, August, 2004.For Part 14, see Ref. 1.