Natural spin orbital analysis of diatomic molecular wave functions in terms of generalized diatomic orbitals

The original idea of the model applied to HeH⁺ excited states is: One electron occupies a diatomic orbital similar to the HeH⁺⁺ ground state 1s function. The other electron occupies an orbital which can be represented by a linear combination of functions similar to H ₂ ⁺ excited state functions. One or two screening parameters are variationally optimized to compensate for the smallness of the one-electron basis.CI calculations have been performed for five excited HeH⁺ states covering a wide range of internuclear distances. The CI wave functions have been submitted to a natural spin orbital analysis. The strongly occupied NSOs are compared with the original model functions.Dedicated to Professor Hermann Hartmann on occasion of his 65th birthday on May 4th, 1979.     

A comparative study of NMR chemical shifts of sparteine thiolactams and lactams

The ¹³C and ¹H NMR spectra of the four possible thiolactams of sparteine (1) were recorded and the thiolactam group effects were determined. Most of the effects are greater than those of the lactam group in the oxo analogs. A good linear correlation between the ¹³C chemical shifts of CS and those of CO was found. The effects could help in assignment of the spectra and determination of conformation of thiolactams and related thiocarbonyl compounds.     

A theoretical study of Zn++ interacting with models of ligands present at the thermolysin active site

Summary The binding energy and the geometrical arrangements of the complexes formed by the zinc dication with OH^–, one, four, five or six water molecules, SH^–, H₂S, formic acid, the formate anion, imidazole, its anion and formamide are calculated using the MNDO method. The comparison of the results obtained with those of ab initio computations on the same complexes induced us to propose for Zn⁺⁺ a set of parameters different from the one determined by Dewar for the neutral metal atom. Using the two MNDO parametrizations, similar calculations are carried out for Zn⁺⁺ interacting with two molecules of 2-aminoethanethiol and with models of the four ligands which are present at the thermolysin active site, in order to evaluate the possibilities and limitations of this semiempirical method for theoretical studies concerning zinc metalloenzymes. In the last case, the results obtained suggest that, in the crystal state, the water molecule could be deprotonated. This finding is discussed in relation with the mechanism of action of the enzyme which has been proposed.This laboratory is part of UA 506 of the C.N.R.S.     

Binding/antibinding analyses for diatomic interactions. the HeH2= system

On the basis of the Berlin diagram, the region-functional contribution of the electron density has been quantitatively examined for the Is, 2p, and 2p states of HeH²⁺ system. The binding and antibinding contributions and the dynamic behaviours of the electron density during the interaction processes are discussed in comparison with the previous results for homonuclear H ₂ ⁺ system. The effect of coordinate-dependence of the Berlin diagram on the regional partitioning has also been studied.     

Photoswitch based on remarkably simple naphthopyrans

Photochromic switches built around 5-carbonyl-3,3-diphenyl-3H-naphtho[2,1-b]pyran unit have been synthesized. Their open forms are constituted of a 1:1 ratio of TC and TT-isomers according to ¹⁹F and ¹H NMR investigations. Electrocyclization of TT isomers back to the closed form is efficiently achieved upon visible irradiation whereas it has been found to be a particularly unfavoured thermal process. These simple 2H-chromenes could act as molecular photoswitch at ambient temperature.     

Possibilities of multinuclear NMR in the chemistry of heteroorganic compounds

Results of multinuclear NMR studies of some heteroorganic compounds have been presented.According to a report at the conference «Current problems of organometallic chemistry» (May 8–13,1994, Moscow).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 614–616, April, 1994.     

Microwave-assisted synthesis of spherical monodispersed magnesium fluoride

Spherical monodispersed magnesium fluoride has been obtained using the microwave-assisted precipitation technique from magnesium nitrate and ammonium fluoride solutions. Studies aimed at optimizing synthesis conditions from the point of view of preparing spherical MgF₂ particles of possibly high monodispersity were performed. Spherical MgF₂ particles of 0.25-0.36 μm in diameter have been obtained with relative standard deviation from the average value ranging from 7 to 15%. It has been established that a certain optimal range of Mg(NO₃)₂ and NH₄F concentrations exists that enables a highly monodispersed MgF₂ to be prepared. The range is narrow (0.01-0.03 mol dm⁻³) for both precursors. Spherical MgF₂ particles have been characterized by SEM, XRD, DTG/DTA and FTIR techniques.     

Rotational molecular motion and solvation of Na+ and Cs+ in water-dimethylacetamide. A nuclear magnetic relaxation study

Nuclear magnetic relaxation by intra- and intermolecular quadrupoleelectric field gradient interaction has been used for the study of the systems DMA-water-NaI and DMA-water-CsI at 25°C.¹⁴N relaxation of DMA and²H relaxation of D₂O measured over the complete mixture range reveal the behavior of the rotational molecular motion of the two solvent components. For both solvent components a marked maximum of the reorientational correlation time has been found, reflecting hydrophobic effects and strong DMA-water interaction. The quadrupolar relaxation rates of²³Na⁺ and¹³³Cs⁺ in pure DMA were evaluated giving an indication that the electric solvent dipoles in the solvation shell are not located on positions of cubic symmetry. A quantitative study of preferential solvation of the cations in the mixed solvent has been performed by using the H₂O-D₂O isotope effect on²³Na⁺ and¹³³Cs⁺ relaxation. For both cations an obviously typical change in the selectivity occurs. In the range l>x _{H2 O}>0.7 we find weak preferential hydration, but in the range 0.7>xH ₂ O>0 strong preferential solvation by DMA is reflected.     

Solvation of Na+ in N,N-dimethylformamide + methanol solutions. A nuclear magnetic relaxation study using dynamic solvent isotope effects

Inter- and intramolecular nuclear magnetic quadrupole relaxation measurements have been used to study the system methanol (CH₃OH)+ N,N-dimethylformamide (DMF)+NaI at 25°C. The dynamic behavior of the solvent molecules was investigated, throughout the composition range of the binary mixtures, by means of ¹⁴ N relaxation of DMF and ² H of methanol-d ₁ (CH ₃ OD). The intermolecular relaxation of ²³ Na⁺ in pure DMF was used to obtain information about the symmetry of the solvent electric dipole arrangement in the solvation sphere of the ion. The investigation of preferential solvation around Na⁺ in the binary mixtures was carried out by means of ²³ Na⁺ relaxation measurements using, for the first time, both the CH ₃ OH/CD ₃ OD and the DMF/DMF-d ₇ dynamic isotope effect. The results show that, throughout the composition range, there is preferential solvation by DMF. Furthermore, the use of the isotope effects of both components allowed for the first time a basic check of the reliability of the method since we obtained two independent sets of data for the composition of the Na⁺ solvation shell in the mixtures. The consistency of the two separate data sets demonstrates that the application of the dynamic isotope effect represents a powerful tool in preferential solvation studies.     

The Kinetics of Uptake of Cu++ Ions in Ionac SR-5 Cation Exchange Resin

The kinetics of sorption of Cu⁺⁺ ions in a typical cation exchange resin (IONAC SR-5) have been studied by two methods; the traditional batch method which involves following the change in Cu⁺⁺ concentration in a solution of finite volume in contact with the resin, and by removing and sectioning individual resin particles to follow the progress of the adsorption front. The results obtained by both methods are consistent. The equilibrium isotherm for this system is of highly favorable (Langmuir) form and the uptake kinetics show a clear transition from linear Fickian behavior at low concentrations to irreversible (shrinking core) behavior at high concentrations. The addition of ammonia to the system has little effect on the equilibrium isotherm but the intraparticle diffusivity is increased by a factor of about four. This may be due to reduction in the degree of hydration of the cuprammonium ion in comparison with uncomplexed Cu⁺⁺.     

HeH+ under Spatial Confinement

In the present study, the influence of spatial confinement on the bond length as well as dipole moment, polarizability and (hyper)polarizabilities of HeH+ ion was analyzed. The effect of spatial confinement was modelled by cylindrically symmetric harmonic oscillator potential, that can be used to mimic high pressure conditions. Based on the conducted research it was found that the spatial confinement significantly affects the investigated properties. Increasing the confinement strength leads to a substantial decrease of their values. This work may be of particular interest for astrochemistry as HeH+ is believed to be the first compound to form in the Universe.     

A mass spectrometric method to determine activities of enzymes involved in polyamine catabolism

An analytical method for the determination of three polyamines (putrescine, spermidine, and spermine) and five acetylpolyamines [N¹-acetylspermidine (N¹AcSpd), N⁸-acetylspermidine (N⁸AcSpd), N¹-acetylspermine, N¹,N⁸-diacetylspermidine, and N¹,N¹²-diacetylspermine] involved in the polyamine catabolic pathway has been developed using a hybrid tandem mass spectrometer. Heptafluorobutyryl (HFB) derivatives of these compounds and respective internal standards labeled with stable isotopes were analyzed simultaneously by TOF MS, based on peak areas appearing at appropriate m/z values. The isomers, N¹AcSpd and N⁸AcSpd were determined from their fragment ions, the acetylamidopropyl and acetylamidobutyl groups, respectively, using MS/MS with ¹³C₂-N¹AcSpd and ¹³C₂-N⁸AcSpd which have the ¹³C₂-acetyl group as an internal standard. The TOF MS method was successfully applied to measure the activity of enzymes involved in polyamine catabolic pathways, namely N¹-acetylpolyamine oxidase (APAO), spermine oxidase (SMO), and spermidine/spermine N¹-acetyltransferase (SSAT). The following natural substrates and products labeled with stable isotopes considering the application to biological samples were identified; for APAO, [4,9,12-¹⁵N₃]-N¹-acetylspermine and [1,4,8-¹⁵N₃]spermidine (¹⁵N₃-Spd), respectively; for SMO, [1,4,8,12-¹⁵N₄]spermine and ¹⁵N₃-Spd, respectively; and for SSAT, ¹⁵N₃-Spd and [1,4,8-¹⁵N₃]-N¹-acetylspermidine, respectively.     

ResonSense: simple linear fluorescent probes for quantitative homogeneous rapid polymerase chain reaction

Here we report a strand-specific fluorescent homogeneous assay format for rapid polymerase chain reaction (PCR). A number of similar assays are commonly used for research applications and are an ideal solution for a closed tube quantitative PCR. These assays use fluorescent resonant energy transfer (FRET) between donor and acceptor fluorescent moieties as the reporting mechanism. However, for different reasons these assays do not report amplification when very rapid cycling times are used. This is because current assays, such as TaqMan^®, are limited, in terms of assay speed, by the 5′-3′ exonuclease activity of Taq DNA polymerase. Other assays based on hybridisation require either a complex de-conformational event to occur, or require more than one probe to report amplification. Reducing the complexity of the experiment reduces costs in terms of design, optimisation and manufacture. Here, we describe ResonSense^® chemistries that use a simple linear fluorescent-labelled probe and a DNA minor-groove binding dye as either donor or acceptor moieties in a homogeneous assay format on the LightCycler^®. This assay format will provide for rapid analysis of samples and so it is particularly well suited to point-of-use testing.     

A N NMR study of tautomerism in dimethyl dihydro-1,2,4,5-tetrazine-3,6-dicarboxylate

Dimethyl dihydro-1,2,4,5-tetrazine-3,6-dicarboxylate can exist either in 1,2- or 1,4-dihydro tautomeric forms. The ¹⁵N NMR spectra of dimethyl dihydro-1,2,4,5-tetrazine-3,6-dicarboxylate were measured at the ¹⁵N natural abundance level as well as in ¹⁵N doubly labelled selectively and in ¹⁵N completely labelled compounds (20% ¹⁵N). The J(¹⁵N,¹⁵N) value was determined in ¹⁵N completely labelled compounds (20% ¹⁵N) using 1D ¹⁵N INADEQUATE and was found to be 12.2 ± 0.2 Hz in deuteriochloroform, acetonitrile-d₃, DMSO-d₆ and CD₃OH. Very similar ¹⁵N chemical shifts and ¹J(¹⁵N,¹H) values were also observed in all the solvents. This indicates that compound 1 exists completely in the 1,4-dihydro tautomeric form (i.e., as dimethyl 1,4-dihydro-1,2,4,5-tetrazine-3,6-dicarboxylate) in all the solvents tested.     

Some structural aspects in binary aqueous mixtures of simple amides from rotational molecular motions

Nuclear magnetic relaxation rates of²D and¹⁴N in binary aqueous mixtures of formamide,N-methylformamide (NMF), andN,N-dimethylformamide (DMF) are reported as a function of the mixture composition. From these intramolecular quadrupolar relaxation data separate rotational correlation times for the two components of the mixture can be determined. The relative variation of the single correlation time as a function of the composition is interpreted in terms of structural changes caused by hydrogen bonding and hydrophobic effects. The results also clearly reflect the expected characteristic variation of these effects on the rotational molecular motions in going from formamide to NMF and DMF. The maximum correlation time retardation of DMF in the aqueous mixture is compared with those of other hydrophobic solvents. A correlation between this maximum retardation and the excess enthalpy of mixing of hydrophobic solvents in aqueous solution can be established graphically.     

Separation of 44Sc from 44Ti in the Context of A Generator System for Radiopharmaceutical Purposes with the Example of [44Sc]Sc-PSMA-617 and [44Sc]Sc-PSMA-I&T Synthesis

Today, ⁴⁴Sc is an attractive radionuclide for molecular imaging with PET. In this work, we evaluated a ⁴⁴Ti/⁴⁴Sc radionuclide generator based on TEVA resin as a source of ⁴⁴Sc. The generator prototype (5 MBq) exhibits high ⁴⁴Ti retention and stable yield of ⁴⁴Sc (91 ± 6 %) in 1 mL of eluate (20 bed volumes, eluent—0.1 M oxalic acid/0.2 M HCl) during one year of monitoring (more than 120 elutions). The breakthrough of ⁴⁴Ti did not exceed 1.5 × 10⁻⁵% (average value was 6.5 × 10⁻⁶%). Post-processing of the eluate for further use in radiopharmaceutical synthesis was proposed. The post-processing procedure using a combination of Presep^® PolyChelate and TK221 resins made it possible to obtain ⁴⁴Sc-radioconjugates with high labeling yield (≥95%) while using small precursor amounts (5 nmol). The proposed method takes no more than 15 min and provides ≥90% yield relative to the ⁴⁴Sc activity eluted from the generator. The labeling efficiency was demonstrated on the example of [⁴⁴Sc]Sc-PSMA-617 and [⁴⁴Sc]Sc-PSMA-I&T synthesis. Some superiority of PSMA-I&T over PSMA-617 in terms of ⁴⁴Sc labeling efficiency was demonstrated (likely due to presence of DOTAGA chelator in the precursor structure). It was also shown that microwave heating of the reaction mixture considerably shortened the reaction time and improved radiolabeling yield and reproducibility of [⁴⁴Sc]Sc-PSMA-617 and [⁴⁴Sc]Sc-PSMA-I&T synthesis.     

Nuclear magnetic relaxation and ionic solvation of23Na+ and81Br− in aqueous mixtures of simple amides

Ion-solvent interactions of Na⁺ and Br^– in binary aqueous mixtures of formamide,N-methylformamide (NMF), andN,N-dimethylformamide (DMF) are studied by use of²³Na and⁸¹Br magnetic relaxation times, extrapolated to zero salt concentration. The relaxation times, which are controlled by quadrupolar interaction, have been measured over the complete mixture range and are compared with a simplified theoretical formula. It turned out that the²³Na⁺ relaxation in H₂O-formamide and H₂O-NMF mixtures is in excellent agreement with theoretical predictions, implying nonpreferential solvation of Na⁺ in these systems. Small deviations of experimental from theoretical results in H₂O+DMF possibly indicate weak selective hydration of the cation. In the case of the anionic nuclei⁸¹Br^–, deviations from the theoretical curve occur which are to be expected, especially for systems where hydrophobic effects play a role. On the other hand, it is demonstrated that these deviations can easily be explained within the electrostatic theory by differences in structural details of the anionic solvation sphere in the mixtures compared to the pure solvents.     

GC–MS Analysis and In Vivo and Ex Vivo Antidiarrheal and Antispasmodic Effects of the Methanolic Extract of Acacia nilotica

This present study evaluated and rationalized the medicinal use of the fruit part of Acacia nilotica methanolic extract. The phytochemicals were detected using gas chromatography–mass spectrometry (GC–MS) while the in vivo antidiarrheal test was done using Swiss albino mice. To determine the details of the mechanism(s) involved in the antispasmodic effect, isolated rat ileum was chosen using different ex vivo assays by maintaining a physiological environment. GC–MS results showed that A. nilotica contained pyrogallol as the major polyphenol present (64.04%) in addition to polysaccharides, polyphenol, amino acid, steroids, fatty acid esters, and triterpenoids. In the antidiarrheal experiment, A. nilotica inhibited diarrheal episodes in mice significantly (p < 0.05) by 40% protection of mice at 200 mg/kg, while 80% protection was observed at 400 mg/kg by the orally administered extract. The highest antidiarrheal effect was observed with loperamide (p < 0.01), used as a control drug. In the ex vivo experiments, A. nilotica inhibited completely in increasing concentrations (0.3 to 10 mg/mL) the carbachol (CCh; 1 µM) and high K⁺ (80 mM)-evoked spasms in ileum tissues at equal potencies (p > 0.05), similar to papaverine, a dual inhibitor of the phosphodiesterase enzyme (PDE) and Ca⁺⁺ channels. The dual inhibitory-like effects of A. nilotica on PDE and Ca⁺⁺ were further validated when A. nilotica extract (1 and 3 mg/mL)-pre-incubated ileum tissues potentiated and shifted isoprenaline relaxation curves towards lower doses (leftward), similar to papaverine, thus confirming the PDE inhibitory-like mechanism whereas its CCB-like effect of the extract was confirmed at 3 and 5 mg/mL by non-specific inhibition of CaCl₂-mediated concentration response curves towards the right with suppression of the maximum peaks, similar to verapamil, used as standard CCB. Thus, this study characterized the chemical composition and provides mechanistic support for medicinal use of A. nilotica in diarrheal and hyperactive gut motility disorders.     

The relationship of spherical nano-Ni(OH)2 microstructure with its voltammetric behavior

The spherical nano-Ni(OH)₂ has been characterized by a series of spectra methods such as the scanning electron microscope (SEM), the transmission electron microscope (TEM) and the X-ray diffraction (XRD). The electrochemical behavior of spherical nano-Ni(OH)₂, attached to a graphite electrode and adjacent to an aqueous KOH-KCl electrolyte solution, has been studied by cyclic voltammetry. Spherical nano-Ni(OH)₂ exhibits a pair of quasi-reversible redox peaks. The relationship of the granularity and the potential was investigated, as well as the effect of different pH conditions. Moreover, the cycling experiments have been set up using spherical nano-Ni(OH)₂ and traditional analytical grade Ni(OH)₂, respectively, and their cycling performances were evaluated as well. The capacity of spherical nano-Ni(OH)₂ is ca. ten times higher than the one with the traditional material under the same conditions, which shows its better electrochemical properties.     

Texture of spherical aluminum phosphate particles

Spherical aluminum phosphate particles with a mean particle diameter of 477±16 nm, produced from aging of a solution containing Al(NO₃)₃, Na₂HPO₄ and HNO₃ at 100°C for 19 h in 20-cm³ Teflon-lined screw-capped Pyrex test tube without agitation, were characterized by various means. It was revealed from x-ray diffraction measurement and transmission electron microscope observation that amorphous particles are formed by agglomeration of small primary particles. The particles exhibited a high selective adsorption of H₂O though they adsorbed small amount of N₂ and CO₂. This characteristic phenomenon was explained by rehydration of Al³⁺ ions by H₂O molecules that were penetrated into the particles.