Hydrogen bonding and dipolar interactions between quinolines and organic solvents. Nuclear magnetic resonance and ultraviolet-visible spectroscopic studies

Solvatochromic studies on quinoline (Q), 3-cyanoquinoline (CNQ), 3-bromoquinoline (BrQ) and 8-hydroxyquinoline (OHQ) in pure solvents and alcohol-cyclohexane mixtures have been performed. The results are compared with Proton Nuclear Magnetic Resonance, 1H NMR. studies and AMI calculations. Taft and Kamlet's solvatochromic comparison method was used to disclose solvent effects in pure solvents. These studies shows that the hydrogen bond acceptor ability of the Q ring is diminished and its polarity is increased by the presence of the cyano group in CNQ and the bromo group in BrQ. In OHQ, intramolecular hydrogen bonding has been observed. This interaction is weakened by the interaction with protic solvents. The studies in binary mixtures, alcohol-cyclohexane, show solute-solvent interactions, which compete with solvent self-association in the preferential solvation phenomena. Alcohols with strong ability to self-associate have less preference toward solvation of these compounds. The association constants for solute-ethanol systems were determined by 1H NMR. The results show that the solvent hydrogen bond donor ability is the main factor involved in the interaction with these solutes at the aza aromatic site.     

Influence of dipolar interactions on radical pair recombination reactions subject to weak magnetic fields

Monte Carlo simulations of the effects of weak magnetic fields on the recombination of interacting radical pairs undergoing free diffusion in solution have been performed, with the aim of determining the influence on the low field effect of the magnetic dipolar coupling between the radicals. The suppression of singlet-triplet interconversion in the radical pair by the dipolar interaction is found to be pronounced at magnetic field strengths comparable to the hyperfine interactions in the radicals, to the extent that the low field effect is completely abolished. The averaging of the dipolar coupling by the translational diffusion of the radicals around one another is relatively efficient in the presence of strong magnetic fields but becomes ineffective in weak applied fields where the strength of the dipolar interaction is independent of the orientation of the inter-radical vector. Low field effects are only likely to be observed if the motion of the radical pair is restricted in some way so as to increase the likelihood that, having separated to the large distance required for the dipolar interaction to have a negligible effect, the radicals subsequently encounter and have the opportunity to recombine.     

Solute-solvent interactions. VII. Proton magnetic resonance and infrared study of ion solvation in dipolar aprotic solvents

The solvation of a variety of ions by the dipolar aprotic solvents acetonitrile, sulfolane, and dimethylsulfoxide was studied through the influence of salts on the proton magnetic resonance chemical shifts of the solvents. In the case of acetonitrile the results were supplemented with infrared measurements, which showed that in general anions affect only the C–H and cations both the C–C and particularly the CN stretching frequencies of acetonitrile. The results are discussed in conjunction with transport and other data already in the literature. Current views on the structure of these solvents are summarized.From the Ph.D. thesis of this author, University of Pittsburgh, 1972.     

Heitler-London renormalization for long-range many-molecule interactions

It is shown that the group function formalism of McWeeny leads in a natural way to a renormalization of the perturbation expansion of the partition function in terms of intramolecular correlation functions.     

Exchange and dipolar interactions in a solid nitroxide radical

The ESR linewidths of solid samples of the di-t-butylnitroxide radical have been measured over an extended temperature range at three different Zeeman frequencies. The magnitude of both the exchange and dipolar interactions can be determined through an analysis of the linewidths. Both of these interactions are found to have a complex temperature dependence.     

Measurement of long-range 1H-1H dipolar couplings in weakly aligned proteins

Measurement of 1H-1H dipolar couplings in macromolecules, weakly oriented by a dilute liquid crystalline medium, is generally limited to the largest such interactions. By removing dipolar couplings to nearest neighbors, either by decoupling, deuteration, or both, more remote interactions become accessible. The approach is demonstrated for measurement of amide-amide interactions in the proteins calmodulin and ubiquitin and permits observation of direct dipolar couplings between protons up to 7 A apart. Quantitative evaluation of 1H-1H dipolar couplings measured in ubiquitin shows excellent agreement with its solution structure.     

Competition between dipolar and steric interactions in swallow-tailed compounds

A new class of swallow-tailed mesogen with the longitudinal dipole moment in the direction of the non-branched 'head' is presented. Mixtures of these compounds with 'conventional' swallow-tailed substances were investigated by polarization microscopy and dielectric measurements. In the mixtures, dipolar and steric interactions favour opposite arrangements of the molecules in the short range order.     

Strong magnetic interactions through weak bonding interactions in organometallic radicals: combined experimental and theoretical study

The magnetic properties of a series of three neutral radical organometallic complexes of general formula [CpNi(dithiolene)]. have been investigated by a combination of X-ray crystal structure analysis and magnetic susceptibility measurements, while the assignment of the exchange coupling constants to the possible exchange pathways has been accomplished with the help of calculations based on density functional theory (DFT). The syntheses and X-ray structures of [CpNi(adt)] (adt=acrylonitrile-2,3-dithiolate) and [CpNi(tfd)] (tfd=1,2-bis(trifluoromethyl)ethene-1,2-dithiolate) complexes are described, while [CpNi(mnt)] (mnt=maleonitriledithiolate) was reported earlier. In the three complexes, we observed strong antiferromagnetic coupling that could not be explained solely by short SS intermolecular contacts. Our calculations indicated that spin density in these complexes is strongly delocalized on the NiS2 moiety, with up to 20% on the Cp ring. As a consequence, CpCp and Cpdithiolene overlap interactions have been identified as responsible for antiferromagnetic couplings. The [CpNi(adt)] complex thus has a value J=-369.5 cm(-1) for an exchange interaction through a pi stacking due to the CpCp overlap.     

Magnetic dipolar interactions in solid gold nanosphere dimers

We report the first observation of a magnetic dipolar contribution to the nonlinear optical (NLO) response of colloidal metal nanostructures. Second-order NLO responses from several individual solid gold nanosphere (SGN) dimers, which we prepared by a bottom-up approach, were examined using polarization-resolved second harmonic generation (SHG) spectroscopy at the single-particle level. Unambiguous circular dichroism in the SH signal was observed for most of the dimeric colloids, indicating that the plasmon field located within the interparticle gap was chiral. Detailed analysis of the polarization line shapes of the SH intensities obtained by continuous polarization variation suggested that the effect resulted from strong magnetic-dipole contributions to the nanostructure's optical properties.     

Observation of 2izsz order in NMR relaxation studies for measuring cross-correlation of chemical shift anisotropy and dipolar interactions

The cross-correlation spectral density of chemical shift anisotropy and dipolar interactions in isotropic solution of methyl formate is measured using a novel NMR technique designed to monitor the appearance of longitudinal two-spin order 2I_zS_z during inversion recovery. The result is tentatively interpreted in terms of the orientation of the ¹³C-¹H internuclear vector with respect to the principal axes of the ¹³C chemical shift anisotropy tensor of the carboxyl group.     

Monodisperse fluorene oligomers exhibiting strong dipolar coupling interactions

Well-defined fluorene oligomers (n = 1 to 6) were prepared step by step using Suzuki and Yamamoto couplings, while absorption and photoluminescence properties evidenced very large dipolar coupling interactions between fluorene moieties.     

Effect of long-range interactions on the surface tension

The effect of long-range interactions on the surface tension at a liquid-gas interface was considered. An analytical expression for the correction to the surface tension for the cutoff of the particle interaction potential at the distance r _c was derived based on a step density profile. For the Lennard-Jones fluid, this correction was calculated numerically from the results of computer simulations of the density profiles. It was established that, in the vicinity of the triple point, the correction is as great as ～6% at the potential cutoff radius r _c=6.78 molecular diameters, a quantity insensitive to the form of the density profile in the interfacial layer.     

Electrostatic interactions of charged dipolar proteins in reverse micelles

The electrostatic interactions in a reverse micelle containing a small-ionized protein are studied by Monte Carlo simulation. The electrostatic contribution to the potential of mean force of the protein in the reverse micelle is determined for a neutral protein, a uniformly charged protein, and a uniformly charged protein with a dipole moment. The effect of addition of a simple electrolyte is studied. While symmetrically distributed micellar charge exerts no force on enclosed ionic species, the protein is driven to the micellar wall due to interactions with simple ions. Protein binding to the inner wall of the micelle can be regulated by added salt. The presence of a dipole drives the protein further to the wall. These effects are studied for several proteins characterized by different charges and dipole moments. For a weakly charged protein with a strong dipole moment the contribution of dipolar interaction to the free energy can represent a major driving force for protein solubilization in the microemulsion.     

Theoretical and experimental studies of the structure and intermolecular interactions in 2-biphenylmethanole

The crystalline structure of 2-biphenylmethanol has been investigated by the radiographic method at room temperature, and its IR transmission spectra were measured in the 400–4000 cm^?1 range. Structural-dynamic models of free molecules of 2-biphenylmethanol, biphenyl and methanol, hydrogen-bonded complexes of 2-biphenylmethanol with methanol and a tetramer of methanol molecules have been built by the density functional method (B3LYP/6-31G*). The structure, the energy, mechanical and electro-optical parameters, the frequency and intensity of normal vibrations in IR spectra of each of the mentioned molecular systems were calculated. The crystalline structure of 2-biphenylmethanol, its features determined by the hydrogen bond formation in the crystal has been found, its structure-forming role and energy were assessed, and IR spectra interpreted on the basis of single crystal X-ray diffraction data, the analysis of measured IR spectra, and results of molecular modeling.     

13C-detected IPAP-INADEQUATE for simultaneous measurement of one-bond and long-range scalar or residual dipolar coupling constants

The sensitivity of cryoprobes, which are rapidly becoming available, means that the measurement of coupling constants involving 13C, 13C pairs at the natural abundance of 13C can now, in principle, be done by using tens rather then hundreds of milligrams of compounds. However, a robust method that would yield reliable values of small long-range carbon--carbon coupling constants is still missing. In this Communication, we describe a novel 13C-detected incredible natural-abundance double-quantum transfer experiment (INADEQUATE) experiment for simultaneous correlation of one-bond and long-range 13C- 13C pairs and the measurement of both types of coupling constants in 13C natural abundance samples. This method yields accurate values of one-bond and long-range coupling constants by manipulation of pure phase in-phase (IP) and antiphase (AP) doublets, and is referred to as 13C-detected IPAP-INADEQUATE. It is illustrated by the measurement of interglycosidic (3)J(CCOC) coupling constants in a disaccharide molecule providing important information about the conformation of the glycosidic linkage. Owing to the simplicity of INADEQUATE spectra the carbon-carbon coupling constants are particularly suitable for studies of partially oriented molecules through the measurement of carbon-carbon residual dipolar couplings (RDCs). An example of this approach is presented. We expect the method to find a variety of applications in the conformational analysis of small molecules, determination of diastereoisomers and enantiomers, and studies of molecules in aligned media.     

自旋交叉和长程磁有序共存的非均相复合材料

采用一种简单的室温沉淀转化方法,有效制备了同时具有自旋交叉和长程磁有序性能的异质结构复合材料FeTrz@PB,其由[Fe(Htrz)₂(trz)]BF₄(Htrz=1H-1,2,4-三氮唑)和普鲁士蓝KFe^Ⅲ[Fe^Ⅱ(CN)₆](PB)构成。通过扫描电子显微镜、透射电子显微镜、粉末X射线衍射、FTIR、X射线光电子能谱、能量色散X射线分析、热重分析和磁性研究,对这些异质结构复合材料的可控生长过程进行了充分表征。复合材料中,PB颗粒的大小和FeTrz@PB的外观可以通过控制反应时间来进行有效调节。随着反应时间的增加,FeTrz@PB复合材料中PB相的比例逐渐增加。值得注意的是,磁性研究发现,这类材料具有室温以上自旋交叉(362～392 K)和低温下长程磁有序(约5.6 K)的共存。高自旋(HS)组分和场冷/零场冷的强度随着反应时间的增加而逐渐增加,而自旋交叉热滞回线的高度逐渐减小。