Effects of inorganic salts on the properties of aqueous poly(vinylpyrrolidone) solutions

Cloud point curves and temperatures have been determined for aqueous solutions of poly(vinylpyrrolidone) at several concentrations for a variety of inorganic salts (phosphates, monohydrogen phosphates, sulfates, carbonates, dihydrogen phosphates and fluorides). The resulting dependency of the critical temperatures (mostly between 289 and 350 K) on the molar concentration can be expressed as sequences showing the decreasing effect of anion species or cation species in salting out the polymer. The decreasing order of effectiveness of the anions in reducing the temperatures is PO ₄ ^3– >HPO ₄ ^2– >SO ₄ ^2– CO ₃ ^2– >H₂PO ₄ ^– >F^–. The order for cation is Na⁺>K⁺. The changes brought about in temperatures by the salts were found to be the results of the changes taking place in the hydrophilic and hydrophobic interactions among polymer, solvent and additive salts and of the change of water structure by structure making or structure breaking ions, and of the influence of salts on the hydration sheath of the polymer.Deceased     

Pressure tuning spectroscopy of the metal-metal quadruple bond

The results obtained from the application of high pressure in optical absorption studies of compounds with metal-metal quadruple bonds are reviewed. The different degrees of balance between intermolecular and intramolecular effects of compression in different cases are highlighted. A consistent effect observed for [Re₂Cl₈]^2–, [Mo₂Cl₈]^4– , and related compounds is a continuous shift to Iower energy (red) in the to * excitation with increasing pressure. This observation is interpreted in terms of significant van der Waals interactions between the molecular chromophore and its surroundings, leading to relative stabilization of the more polarizable excited state. Changes in the intensity of the to * peak are not correlated with the changes in position. The intensity changes become consistent only at relatively high pressures, and this falloff is attributed largely to compression and deformation of the cell gasket. In certain cases, such as [Re₂ I ₈]^2– and Re₂(piv)₄X₂, piv = pivalate, X= CI, Br, rearrangement to a new species is observed upon the application of high pressure. These rearrangements are all reversible upon pressure release, but they involve different degrees of interaction between adjacent molecules.     

On the possibility of existence of η5-π-complexes of C60 fullerene: π-complexes with silicon

Qualitative estimates of possibility of the formation of fullerene ⁵--complexes have been carried out by the MNDO/PM3 method. It was shown, as exemplified by the C₆₀ cluster, that the introduction of five univalent functional groups R (R = H, Cl, Br) to -positions of a separate pentagon of C₆₀ with the formation of [R₅C₆₀]^– anions results in a pronounced increase in the -electron density on the atoms of this five-membered cycle and more favorable conditions for the formation of -bonds with the ⁵-ligand. The nature of the interaction between the atoms of the separate cycle in [R₅C₆₀]^– anion and ⁵-ligand was analyzed by the example of hypothetical sandwich systems R₅C₆₀SiCp. Half-sandwich complexes R₅C₆₀SiX (X = H, Cl) were also investigated. The local energy minima were found on the potential energy surfaces (PES) of systems R₅C₆₀SiCp and R₅C₆₀SiX with C_5p symmetry. These systems transform barrirlessly into q5-7E-complexes with the angular structure if the symmetry restrictions are removed. The most favorable conditions for ⁵--complexes of R₅C₆₀ to form are realized for R = H. The results obtained were compared to those of semiempirical and nonempirical calculations of bis (cyclopentadienyl) silicon.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2422–2429, October, 1996.     

Properties of aqueous salt solutions of poly(ethylene oxide). Cloud points, θ temperatures

The determination of the properties of aqueous salt solutions of poly(ethylene oxide) has been extended to the cloud point, and temperature measurements have been made at several concentrations for various salts (flourides, iodides, acetates, formates, phosphates, bromides, thiosulfates and perchlorates). The resulting dependency of the critical temperatures (mostly between 290–350 K) on the molar concentration can be expressed as sequences showing the decreasing effect of anion species or cation species in salting out the polymer. The decreasing order of effectiveness of the anions in reducing the temperature is PO ₄ > HPO ₄ > S₂O ₃ > H₂PO ₄ ^– >F^– > HCOO^– > CH₃COO^– > Br^– > I^–. The order for cations is K⁺ Rb⁺ Na⁺ Cs⁺ > Sr⁺⁺ > Ba⁺⁺ Ca⁺⁺ > NH ₄ ⁺ > Li⁺. The changes brought about in temperatures by the salts were found to be the results of the changes taking place in the hydrophilic and hydrophobic interactions among polymer, solvent and additive salts and of the change of water structure by structure making or structure breaking ions, and of the influence of salts on the hydration sheath of the polymer.     

Ab initio study of hydrazoic acid

SCF and CI calculations were carried out on the ground^1A state of HN₃. The equilibrium geometry and vibration frequencies were computed. The results point to a planar structure (groupC _s) but to a non-linear (170 °) N-N-N conformation. The calculated vibration frequencies are in fair agreement with experimental assignments.The dissociation path of the molecule to NH and N₂ products was investigated and compared to the isoelectronic reaction of diazomethane. The dissociation energy of hydrazoic acid is estimated to be about –8 kcal/mole, with a potential barrier to dissociation of about 30 kcal/mole.Boursier IRSIA     

Photobleaching of γ-Glycidoxypropyltrimethoxysilane-Chelated Metal Alkoxide Gel Films

Thick photosensitive inorganic-organic hybrid gel films are fabricated using a silica–PEO(poly(ethylene oxide)) polymeric network and several chelated metal alkoxides: Ti(OEt)₄, Al(OBu^sec)₃, Zr(OPr ⁿ )₄. The -glycidoxypropyltrimethoxysilane (GPTS) and the metal alkoxides stabilized by -ketoester or -diketone are used as precursors. The chelated metal complex in the gel films are photodecomposed and forms the oxide network by UV exposure. The photodecomposition of the chelate ring and the photobleaching of the UV absorption bands are investigated as a function of UV exposure time. The photobleaching rates with respect to chelating agents, metal alkoxides and photon energy are compared.     

Organomineral sorbents based on clinoptilolite-containing tuffs

The anion-exchange properties of a new organomineral sorbent obtained by modification of clinoptilolite-containing tuffs by polyhexamethyleneguanidine have been studied after different periods of storage (time after synthesis) and numbers of sorption-regeneration cycles. The sorbent can be used as a cation- and an anion-exchanger simultaneously. Selectivity coefficients (exchange constants) for F^–, SO₄ ^2–, and HPO₄ ^2– ionsvs. Cl^– ions on modified clinoptilolite-containing tuffs have been determined. The modification improves the mechanical properties of clinoptilolite tuffs.For part 1, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1554–1556, September, 1994.     

Molecular Interactions and Inclusion Phenomena in Substituted β-Cyclodextrins. Simple Inclusion Probes: H2O, C, CH4, C6H6, NH4 +, HCOO−

Using a simple molecular mechanics approach interaction energy profiles of simple probes (C, CH₄, C₆H₆, H₂O, NH₄ ⁺, and HCOO^-) passing through the center of the -CD ring cavity along the main molecular symmetry axis were first evaluated. Molecular Electrostatic Potential (MEP) values along the same path were also evaluated. The effect of the flexibility of the host -CD molecule together with solute-solvent (H₂O) interactions have been represented by averaging structures of MD calculations for -CD alone and -CD surrounded by 133 H₂O molecules. The effect of various substitutions of -CD has also been evaluated. Small symmetric hydrophobic probes (such as C, CH₄, C₆H₆) are predicted to form stable inclusion complexes with non-substituted and substituted -CDs, the probe position typically being near the cavity center. The stability of the inclusion complexes will increase with increasing size and aliphatic character of the probe. Small polar and charged probes (such as H₂O, NH₄ ⁺, HCOO^-) are predicted to prefer the interaction with the solvent (water) in the bulk phase rather than the formation of inclusion complexes with non-substituted and substituted -CDs. Guest–host interactions in the stable inclusion complexes with hydrophobic probes are almost entirely dominated by dispersion interactions. The MEP reaches magnitudes close to zero in the center of the non-substituted -CD ring cavity and in most of the studied substituted -CDs and shows maximum positive or negative values outside of the cavity, near the ring faces. Substitution of -CD by neutral substituents leads to enhanced binding of hydrophobic probes and significant changes in the MEP profile along the -CD symmetry axis.     

Reactions of (Me2C)(Me2Si)[(η-C5H3)Mo(CO)3]2 with nitrile and subsequent cleavage of the CN bond by cooperation of molybdenum and ruthenium

Reaction of the doubly bridged dinuclear molybdenum complex (Me₂C)(Me₂Si)[(η⁵-C₅H₃)Mo(CO)₃]₂ (1) with benzonitrile in refluxing xylene afforded complexes (Me₂C)(Me₂Si)[(η⁵-C₅H₃)₂Mo₂(CO)₄(μ-η²-η²(⊥)-NCPh)] (2) (50%) and (Me₂C)(Me₂Si)[(η⁵-C₅H₃)₂Mo₂(CO)₄(μ-η¹-η²-NCPh)] (3) (6%) with different coordination of nitrile. The corresponding μ-η²-η² acetonitrile and propionitrile complexes 4 and 5 could be obtained from the reactions of (Me₂C)(Me₂Si)(C₅H₄)₂ with (RCN)₃Mo(CO)₃ (R = Me, Et) in refluxing xylene. Reactions of 1 with isonitriles generated μ-η¹-η²-CNR (R = ^tBu, Ph, C₆H₁₁) bridged complexes 6-8 in 53-63% yields. Subsequent reaction of 4 with Ru₃(CO)₁₂ yielded two CN bond cleavaged MoRu clusters (Me₂C)(Me₂Si)(η⁵-C₅H₃)₂Mo₂Ru₃(CO)₁₀(μ-CO)(μ₃-CMe)(μ₄-N) (9) (7%) and [(Me₂C)(Me₂Si)(η⁵-C₅H₃)₂]₂Mo₄Ru₆(CO)₁₆(μ-CO)(μ₄-CO)₂(μ₃-η¹-η²-η²-NCMe)(μ₃-CMe)(μ₅-N) (10) (8%). All the new complexes have been fully characterized. The molecular structures of 2, 4, 6, 9, and 10 have been determined by X-ray diffraction analysis.     

Synthesis,Structure and Property of Oxo-Bridged Binuclear Iron(III) Complex [Fe(phen)(H<Subscript>2</Subscript>O)<Subscript>3</Subscript>]<Subscript>2</Subscript>O⋅2SO<Subscript>4</Subscript>

An oxo-bridged binuclear iron(III) complex, [Fe(phen)(H₂O)₃]₂O2SO₄, has been synthesized and structurally characterized by elemental analysis (EA), IR, TG-DSC and X-ray. Its crystal structure has been determined by X-ray crystallography. It crystallizes in the orthorhombic system, space group P2₁2₁2, with lattice parameters a = 17.650(4), b = 8.5133(17), c = 9.971(2) Å; V = 1498.2(5) ų, _calcd = 1.763 g/cm³ and Z = 4 for R₁ = 0.0601. The crystal structure indicated that two octahedrally coordinated iron(III) ions bridged with oxygen atoms formed a non-linear complex. The bond angle of Fe–O–Fe is 163.9(4). The data of EA and IR are in good agreement with the crystal structure. The thermal gravity (TG) data indicate that there are four decomposition steps with three endothermic peaks. The final product of the thermal decomposition may be Fe(C₂H₈N₂)SO₄.     

Phosphorus-supported multidentate coumarin-containing fluorescence sensors for Cu

Phosphorus hydrazides PhP(O)[N(Me)NH₂]₂, (S)P[N(Me)NH₂]₃, and N₃P₃[N(Me)NH₂]₆ were condensed with 7-diethylaminocoumarin-3-aldehyde (RCHO) to afford the corresponding hydrazones PhP(O)[N(Me)NCHR]₂ (1), (S)P[N(Me)NCHR]₃ (2), and N₃P₃[N(Me)NCHR]₆ (3). The structural characterization of 1-3 was carried out by their HRMS, ¹H and ³¹P{¹H} NMR spectra. The molecular structure of 2 was established by a single-crystal X-ray analysis. Interaction of 1 and 2 with various transition metal ions revealed substantial fluorescence enhancement upon interaction with Cu²⁺ enabling a selective detection mechanism for this metal ion. However, such a fluorescence enhancement was not observed in the case of 3. A 1:1 complex [2·Zn][ClO₄]₂·4CH₂Cl₂ was isolated in the reaction of 2 with Zn(ClO₄)₂·6H₂O. The molecular structure of this complex revealed that the Zn^II is encapsulated by the ligand utilizing a 3N, 3O coordination set.     

Exohedral η5-π-complexes of fullerene C20

The problem of stabilization of polyhedral carbon clusters, which do not obey the isolated pentagon rule, is discussed taking a dodecahedral fullerene C₂₀ as an example. Ab initio MO LCAO calculations in the HF/3-21G approximation showed that fullerene C₂₀ as well as its C₂₀H₅ hydrides with C _5v symmetry can form stable 2⁵--complexes of the CpFeC₂₀FeCp and H₅C₂₀FeC₂₀H₅ types. The energies of the ⁵-Fe--C₂₀ -bonds in these complexes were compared with those of the Fe--Cp bond in ferrocene and the Fe--C₆₀ bond in the ⁵--C₆₀H₅FeCp complex.     

Convergent synthesis of 2′,3′-dideoxy-3′-mercapto nucleosides — Potential anti-HIV agents

Summary Methyl 3-benzoylthio-5-O-tert-butyldiphenylsilyl-2,3-dideoxy--D-erythro-pentofuranoside (4) and its corresponding anomer5 were synthesized in four steps from 2-deoxy-D-ribose and used as substrates for the synthesis of nucleosides by condensation with silylated thymidine and N⁶-isobutyryladenine. The nucleosides were deprotected by treatment with Bu₄NF inTHF followed by reaction with MeONa in MeOH to give 3-deoxy-3-mercaptothymidine (8), 2,3-dideoxy-3-mercaptoadenosine (15) and its corresponding anomer16. In the latter reactions it was important to use degassed solvents to minimize formation of the corresponding disulfides of purine nucleosides. Using Bu₄NF, without subsequent reaction with MeONa in the deprotection reaction, resulted in intermolecular transesterification reactions.On leave from Chemistry Department, Faculties of Science and Education, Tanta University, Tanta, Egypt     

Metal-betaine interactions. Part 17: A study of intradimer Cu · · · Cu distance variation in copper(II) betaine complexes containing [Cu2 (carboxylato-O,O′)4L2]n+ species

Four copper(II) complexes of betaines, [Cu₂(BET)₄Cl₂][Cu(BET)₂Cl₂]Cl₂ (2), [Cu₂(pyBET)₄Cl₂]₃[CuCl₄]₂Cl₂ (3), [Cu, (pyBET)₄ (H₂O)₂] (NO₃)₄ · 2H₂O (4), and [Cu₂(ppBET)₄(H₂O)₂](ClO₄)₄ · 4H₂O (5), (BET = Me₃N⁺CH₂COO^–; pyBET = C₅H₅N⁺CH₂COO^–; ppBET=C₅H₅N⁺CH₂CH₂COO^–), have been prepared and characterized by X-ray crystallography. These complexes all contain dimeric [Cu₂ (carboxylato-O,O)₄L₂] structures [basal Cu-O=1.955(4) 1.991(2), Cu Cu=2.602(1) 2.759(1) Å] with the apical ligand L=Cl^– in (2) and (3) [Cu-Cl=2.415(1) 2.436(3) Å] and L = H₂O in (4) and (5) [Cu-OH₂=2.158(4) 2.192(3) Å]; also present are a discrete [Cu(BET)₂Cl₂] molecule with a compressed tetrahedral CuO₂Cl₂ chromophore involving two unidentate carboxylate ligands [Cu-O=1.916(2), Cu-Cl=2.254(1) Å] in (2), and a discrete C_3v [CuCl₄]^2– anion in (3). Generally the intradimer Cu Cu distance may be correlated to the electronic repulsion of the metal-ligand bonds in the CuO₄L chromophore, as well as the steric interaction between the carboxylate moieties and the apical ligand.     

Preparation and Characterization of Branched β-Cyclodextrins Having Manno-Oligosaccharide Side Chains Derived from Yeast Mannan and Study of Their Functions

Branched -cyclodextrins (-CDs) having manno-oligosaccharide side chains were investigated. Three kinds of monobranched -CDs and five kinds of dibranched -CDs were chemically synthesized using the trichloroacetimidate method. Their structures were analyzed by HPLC, MS, and NMR spectroscopies. The specific interaction between those compounds and mannose-binding lectins (Concanavalin A and Pisum sativum agglutinin) was investigated by inhibition tests of hemagglutinating activity and by using an optical biosensor of the IAsys apparatus with a resonant mirror detector. The results showed that all branched -CDs interactedwith lectins. The binding affinity was 6¹,6⁴-(Man₃)₂- 6¹,6⁴-(Man₂)₂- > 6¹,6⁴-(Man₄)₂--CD when the derivatives were compared on the basis of side chain length and 6¹,6³- 6¹,6⁴- > 6¹,6²-(Man₂)₂--CD when compared on the basis of side chain position.     

Facile hydrosilylation of norbornadiene by silanes R3SiH and R2SiH2 with molybdenum catalysts

Photochemically activated [Mo(CO)₆] and [Mo(CO)₄(η⁴-nbd)] have been demonstrated to be very effective catalysts for hydrosilylation of norbornadiene (nbd) by tertiary (Et₃SiH, Cl₃SiH) and secondary (Et₂SiH₂ and Ph₂SiH₂) silanes to give 5-silyl-2-norbornene, which under the same reaction conditions transform in ring-opening metathesis polymerization (ROMP) to unsaturated polymers and to a double hydrosilylation product, 2,6-bis(silyl)norbornane. The yield of a particular reaction depends very strongly on the kind of silane involved. The reaction products were identified by means of chromatography (GC–MS) and ¹H and ¹³C NMR spectroscopy. In photochemical reaction of [Mo(CO)₄(η⁴-nbd)] and Ph₂SiH₂ in cyclohexane-d₁₂, η²-coordination of the SiH bond to the molybdenum atom is supported by ¹H NMR spectroscopy due to the detection of two equal-intensity doublets with ²J_HH = 5.4 Hz at δ 6.12 and −5.86 ppm.     

Charge-transfer complexes betweenp-toluidine and iodine in solution: A kinetic study

The kinetics of charge-transfer interaction betweenp-toluidine and iodine in methylene chloride was investigated in depth. Thethermal process of formation of theinner complex was found to proceed to an equilibrium. Thephotochemical process follows a different reaction coordinate, going through the formation of an exciplex between the excitedouter complex and the amine ground state. In both cases the same ionic complex (Am ₂I⁺I ₃ ^– , whereAm stands forp-toluidine) was detected as the final product.

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Kinetische Untersuchung der Charge-Transfer-Komplexe zwischenp-Toluidin und Jod

Zusammenfassung Die Kinetik der Charge-Transfer-Wechselwirkung zwischenp-Toluidin und Jod in Methylenchlorid wurde ausführlich untersucht. Derthermische Prozeß, der zur Bildung desinner-Komplexes führt, geht bis zu einem Gleichgewicht. Derphotochemische Prozeß folgt einer unterschiedlichen Reaktionskoordinate und verläuft über die Bildung eines Exziplexes zwischen dem angeregtenouter-Komplex und dem Amin im Grundzustand. In beiden Fällen wurde derselbe ionische Komplex (Am ₂I⁺I ₃ ^– , wobeiAm fürp-Toluidin steht) als Endprodukt festgestellt.

     

Synthesis and properties of 2,2′-dipyridyl and 4,4′-dipyridyl complexes with thulium salts

Summary New complexes of 2,2-dipyridyl and 4,4-dipyridyl with thulium salts TmX ₃ (whereX=Cl^–, Br^–, NO ₃ ^– , NCS^–, and ClO ₄ ^– ) have been prepared and their solubilities in water at 21 °C were determined. The IR spectra of these compounds are discussed. The conditions of thermal decomposition of the complexes were also studied.

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Synthese und Eigenschaften von 2,2-Dipyridyl- und 4,4-Dipyridylkomplexen mit Thuliumsalzen

Zusammenfassung Es wurden neue 2,2-Dipyridyl- und 4,4-Dipyridyl-Komplexen mit Thuliumsalzen TmX ₃ (X=Cl^–, Br^– No ₃ ^– , NCS^–, ClO ₄ ^– ) dargestellt und ihre Wasserlöslihkeit bei 21 °C bestimmt. Die IR-Spektren werden diskutiert. Das thermische Verhalten der erhaltenen Komplexe wurde untersucht.

     

Molecular and electronic structure of some bowl-shaped unsaturated hydrocarbon molecular systems,possible precursors of C60 fullerene

The AMI calculations of hydrocarbon molecules C₂₀H₁₀ (1) and C₃₀H₁₀ (2) and anions C₂₀H₁₅ ^–4 (3) and C₃₀H₁₅ ^– (4) have been performed with the full energy optimization of the geometric parameters. The chosen topology of the carbon framework of the studied compounds is identical to the topology of the corresponding carbon fragments of C₆₀ fullerene. Analysis of the structure of the frontier orbitals of systems1–4 demonstrated that the tendency of the C₂₀H₁₀ molecule to form sandwich -complexes of the ⁵-type with transition metal atoms is small; however, this tendency is significantly larger than that of C₃₀H₁₀. Moreover, the exclusion of the five-membered cycle of bowlshaped unsaturated hydrocarbon molecules and anions from the conjugated system (as a result of the conversion of five framing C atoms to saturated carbon centers) favors the stabilization of their ⁵-type -complexes with M(C₅H₅) species. The stability of these complexes must approach the stability of classical sandwich complexes of the ferrocene type. The results obtained have been extrapolated to polyhedral C₆₀ and C₇₀ carbon clusters.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 855–858, May, 1995.This work was financially supported by the Russian Foundation for Basic Research (Projects No. 93-03-4101 and 93-03-18725).     

Structure of the β-Cyclodextrin·p-Hydroxybenzaldehyde Inclusion Complex in Aqueous Solution and in the Crystalline State

-Cyclodextrin (-CD) and p-hydroxybenzaldehyde (p-HB) were studied by ¹H-NMR in deuterated aqueous solution and the stoichiometry of the resulting complex (1:1) was determined by the continuous variation method. Inclusion of p-HB in -CD was confirmed by the observation of NMR shifts for the inside H5 protons of the -CD cavity. In the solid state X-ray analysis was carried out and revealed the detailed structure of the inclusion complex. Two -CDs cocrystallize with four p-HB and 9.45 water molecules[2(C₆H₁₀O₅)^7·4C₇H₆O_2·9.45H₂O] in the triclinic space group P1 with unit cell parameters: a = 15.262(2), b = 15.728(1), c = 16.350(1) Å, = 92.67(1)°, = 96.97(1)°, = 103.31(1)°. The anisotropic refinement of 1973 atomic parameters converged at an R-factor = 0.066 for 10157 data with F_o ² > 2 (F_o ²). The 2:4 stoichiometry for the -CD inclusion complex with p-HB in the crystalline state is different from that obtained in solution. -CD forms dimers stabilized by direct O2(m)₁O3(m)₁·O2(n)₂O3(n)₂ hydrogen bonds (intradimer) and by indirect O6(m)₁·O6(n)₂ hydrogen bonds with one or two bridging water molecules joined in between (interdimer). These dimers are stacked like coins in a roll constructing infinite channels where the p-HB molecules are included. The p-HB molecules direct their polar CHO and OH groups into the nonpolar -CD cavities and are hydrogen bonded to each other, yielding infinite, antiparallel chains. In addition, crystals of the complex were also investigated with thermogravimetry, vibrational spectroscopy (FTIR), and ¹³C CP-MAS NMR spectroscopy. The results obtained enabled us to structurally characterize the -CD inclusion complex with p-HB.