The Na⋅⋅⋅B Bond in NaBH3−: A Different Type of Bond

A newly introduced Na−B bond in NaBH₃⁻ has been a challenge for the chemical bonding community. Here, a series of MBH₃⁻ (M=Li, Na, K) species and NaB(CN)₃⁻ are studied within the context of quantum chemical topology approaches. The analyses suggest that M–B interaction cannot be classified as an ordinary covalent, dative, or even simple ionic interaction. The interactions are controlled by coulombic forces between the metals and the substituents on boron, for example, H or CN, more than the direct M–B interaction. On the other hand, while the characteristics of the (3, −1) critical points of the bonds are comparable to weak hydrogen bonds, not covalent bonds, the metal and boron share a substantial sum of electrons. To the best of the author's knowledge, the characteristics of these bonds are unprecedented among known molecules. Considering all paradoxical properties of these bonds, they are herein described as ionic-enforced covalent bonds.     

Effect of 1,1,2,2-tetrachloroethane on IR spectra of HCl complexes withN,N-dimethylformamide and 1-methyl-2-pyrrolidone formed by a strong quasi-symmetric hydrogen bond

The effect of 1,1,2,2-tetrachloroethane (TCE) on the IR spectra of HCl complexes withN,N-dimethylformamide (DMF) and 1-methyl-2-pyrrolidone (N-MP) with strong quasisymmetric hydrogen bonds was studied using Multiple Attenuated Total Reflection (MATR) IR spectroscopy. The addition of TCE does not change the background absorption spectra, but results in a change in the extinction coefficients of some bands of these complexes. The analysis of the spectra shows that the HCl−DMF complexes interact only with one molecule of TCE, and the HCl−N-MP complexes interact with two molecules of TCE. It is shown that the neutral component of the system (TCE) has no effect on the parameters of the strong quasi-symmetric H-bond in the complexes studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 956–960, May, 1997.     

Photophysical characterization of mixed micelles of n-butanol/SDS and n-hexanol/SDS. A study at low alcohol concentrations

 The effect of the addition of n-butanol (BuOH) and n-hexanol (HexOH) on the micellization of sodium dodecylsulfate (SDS) has been investigated using fluorescence quenching methods. The binding constants were calculated using an expression which relates the total concentration of alcohols and the micelle concentration. The values of K were 4.67 and 17.6 M^-1 for BuOH/SDS and HexOH/SDS, similar to values obtained by other methods. The cmc of SDS decreases on addition of alcohols and goes through a minimum for the BuOH/SDS system. Micellar aggregation numbers (N) were determined from linear plots of Ln (I ⁰/I) against [Quencher] at low alcohol concentrations. For 15 mM SDS, in the presence of BuOH the N values decrease on addition of alcohol up to 0.2 M. For HexOH, N can be assumed to be constant up to 4.8 mM, after which N decreases. The polarity of the micellar core containing alcohol was evaluated from the I ₁/I ₃ ratio of monomeric pyrene. The effect of addition of the alcohol causes a decrease in the I ₁/I ₃, which corresponds to a decrease in the polarity of the pyrene solubilization site. Received: 28 October 1996 Accepted: 10 January 1997     

Elution order in gas chromatography

The retention behavior of a heterogeneous group of solutes has been examined on seven different stationary phases under isothermal and temperature-programmed conditions. Both ΔH_v (enthalpy of solute vaporization from the stationary phase) and ΔS_v (entropy of solute vaporization from the stationary phase) values were determined for each solute – stationary phase combination under isothermal conditions. Both program rate and carrier gas velocity were shown to affect solute elution order. Unless these and other experimental factors discussed are controlled, column equivalency studies based on solute elution order have dubious value.     

Protein—Protein Interactions in Aqueous Ammonium Sulfate Solutions. Lysozyme and Bovine Serum Albumin (BSA)

Osmotic pressures have been measured to determine lysozyme—lysozyme,BSA—BSA, and lysosyme—BSA interactions for protein concentrations to 100 g-L^–1in an aqueous solution of ammonium sulfate at ambient temperature, as a functionof ionic strength and pH. Osmotic second virial coefficients for lysozyme, forBSA, and for a mixture of BSA and lysozyme were calculated from theosmotic-pressure data for protein concentrations to 40 g-L^–1. The osmotic second virialcoefficient of lysozyme is slightly negative and becomes more negative withrising ionic strength and pH. The osmotic second virial coefficient for BSA isslightly positive, increasing with ionic strength and pH. The osmotic second virialcross coefficient of the mixture lies between the coefficients for lysozyme andBSA, indicating that the attractive forces for a lysozyme—BSA pair areintermediate between those for the lysozyme—lysozyme and BSA—BSA pairs. For proteinconcentrations less than 100 g-L^–1, experimental osmotic-pressure data comparefavorably with results from an adhesive hard-sphere model, which has previouslybeen shown to fit osmotic compressibilities of lysozyme solutions.     

Mixed Micelles in the Presence of Macrocyclic Additives: A Host–Guest Conductometric Study

The conductances of sodium dodecylsulphate (SDS) + sodium decylsulfate (SDeS) and decyltrimethylammonium bromide (DeTAB) + tetradecyltrimethylammonium bromide (TTAB) over the entire mole fraction range of SDS (_SDS) or DeTAB (_DeTAB) were measured in water, 18-crown-6 ether + water (CR + W) and -cyclodextrin + water (CYC + W) mixtures at fixed 4 mM and 8 mM of CR or CYC in their respective binary mixtures at 30 °C. The conductivity plots for SDS + SDeS mixtures show a single break whereas two breaks are observed at most of the _DeTAB for DeTAB + TTAB mixtures. From the break in the conductivity data, the mixed critical micellar concentration (cmc) and degree of counter-ion association () were computed. The first break corresponds to the classical cmc of TTAB is termed as the first cmc (C₁) and the second break which is observed at concentrations about 4 times the first one, corresponding to the classical cmc of DeTAB and is considered to be the second cmc (C₂). The non-ideality in SDS + SDeS mixtures has been evaluated by using the regular solution theory and it has been observed that the mixture is close to ideal in the absence and presence of additives. The variation in C₁, C₂ and ₁, ₂ for DeTAB + TTAB has been discussed in terms of the mixed micelle formation which are predominantly rich in the TTAB and DeTAB monomers respectively.     

Interactions of sodium dodecyl sulfate with acrylamide –N-isopropylacrylamide) statistical copolymer

 Poly(N-isopropylacrylamide) (PNIPAM) precipitates out of water around 32 °C. This critical temperature is raised when hydrophilic acrylamide sequences are present on the polymer chain. We have used neutron scattering to study the structural properties of a statistical copolymer containing acrylamide and N-isopropylacrylamide segments at different temperatures and its interactions with an anionic surfactant, sodium dodecyl sulfate (SDS). At low temperatures, the copolymer behaves as a swollen polymer coil. With an increase in temperature, intermolecular attractions are observed, and close to the critical temperature of the copolymer, microphase separation is observed. Here, the structure consists of dense nodules of hydrophobic sequences stabilized by hydrophilic sequences. In the presence of a small amount of SDS, additional colloidal stability is observed: the nodule size is decreased. At high SDS concentration, the copolymer is completely solubilized at all temperatures studied and the structure of the polymer–surfactant complex resembles the “necklace” structure obtained for the homopolymer PNIPAM–SDS system. Received: 11 November 1999 Accepted: 15 December 1999     

An integrative approach for analyzing metal–polyelectrolyte interactions

An integrative approach based on the combined use of both experiments and modelling is discussed here aimed at investigating metal–polyelectrolyte interactions in solution. Electrochemical techniques are applied because of their potential to measure the actual speciation without disturbing the solution physico–chemical equilibrium. The experimental methodologies are complementary since the ranges of applicability depend on the solution composition itself. To complement and interpret the results of these experimental techniques, a physico–chemical association model, based on the so-called ‘chemical model’ of counterion condensation theory, is used. The model considers that, in addition to the usual electrostatic interactions and entropic effects, territorial affinity and chemical bonding interactions take place between the small counterions in solution and the polyelectrolyte. A number of particular cases of metal/polyelectrolyte systems are discussed aimed at showing that the integrative approach leads to additional information about the solution system which can not be deduced from experimental results solely. Future challenges with respect to the applications in the study of natural aquatic systems are pointed out.     

Organoelement Compounds with Al?Al,Ga?Ga,and In?In Bonds

In the attempt to synthesize compounds with aluminum in a low oxidation state and an Al Al bond, by the reduction of alkylaluminum halides with alkali metals, analogous to a Wurtz coupling, in general the deposition of elemental aluminum and the formation of the corresponding trialkylaluminum compounds is observed. Thus, tetrasubstituted dialuminum compounds R₂Al AlR₂, apart from a few poorly characterized examples, were for a long time considered part of an unverified class of substances. Only with the sterically very highly shielded tetrakis[bis(trimethylsilyl)methyl]dialuminum did we achieve the synthesis of the first completely characterized organoelement compound with unlimited stability, which shows aluminum in the oxidation state + II and has an Al Al bond. In the meantime, corresponding compounds for the elements gallium and indium have been obtained. With the simple access to tetrasubstituted dimetal compounds, a fascinating new research area has opened for preparative chemistry, in which the particular interest will naturally lie in the reactive properties of the metal-metal bond.