Studies of the pyrolysis of tetraethylammonium tetrahydroborate

Tetraethylammonium tetrahydroborate, Et₄NBH₄, in suspension in refluxing decane-dodecane mixtures has been pyrolysed at temperatures between 175 and 190 °C. Et₃NBH₃, which is produced by partial decomposition of Et₄NBH₄, reacts with Et₄NBH₄ to give the intermediate Et₄NB₃H₈. Et₄NBH₄ and Et₃NBH₃ are also involved in the conversion of Et₄NB₃H_8. to (Et₄N)₂B₉H₉, (Et₄N)₂B₁₀H₁₀, Et₄NB₁₁H₁₄ and (Et₄N)₂B₁₂H₁₂ which are formed in varying proportions during the pyrolysis. A 1:1 Et₄NBH₄Et₃NBH₃ mixture gives the same mixture of final products in the same proportions as Et₄NBH₄ alone, but the reaction time is shorter.Results obtained under various conditions, for instance without solvent at 10⁻² torr (50% yield), are explained by the transfer of BH₃ groups occurring not only through Et₃NBH₃, but also by solid—solid reactions involving Et₄NBH₄. A more complete reaction of Et₃NBH₃ is obtained, giving quantitative yields, only when Et₃N is evacuated from the reaction mixture. Optimum conditions for the formation of each hydroborate are examined.     

Preparation of benzophenone imine complexes of transition metals

Benzophenone imine [M(η¹-NHCPh₂)(CO)_nP_5-n]BPh₄ [M = Mn, Re; n = 2, 3; P = P(OEt)₃, PPh(OEt)₂, PPh₂OEt, PPh₃] complexes were prepared by allowing triflate M(κ¹-OTf)(CO)_nP_5-n compounds to react with an excess of the imine. Hydride-imine [MH(η¹-NHCPh₂)P₄]BPh₄ (M = Ru, Os), triflate-imine [Os(κ¹-OTf)(η¹-NHCPh₂)P₄]BPh₄ and bis(imine) [Ru(η¹-NHCPh₂)₂P₄](BPh₄)₂ [P = P(OEt)₃] derivatives were also prepared. The complexes were characterized spectroscopically (IR, ¹H, ³¹P, ¹³C NMR) and a geometry in solution was also established. Hydride-benzophenone imine [IrHCl(η¹-NHCPh₂)L(PPh₃)₂]BPh₄and [IrHCl(η¹-NHCPh₂)L(AsPh₃)₂]BPh₄ [L = P(OEt)₃ and PPh(OEt)₂] complexes were prepared by reacting hydride IrHCl₂L(PPh₃)₂ and IrHCl₂L(AsPh₃)₂ precursors with an excess of imine. Dihydride IrH₂(η¹-NHCPh₂)(PPh₃)₃ complex was also obtained and a geometry in solution was proposed.     

Organic derivatives of aluminium. Part I. Reactions of alkanolamines with aluminium isopropoxide

Reactions of alkanolamines [R₁R₂NXOH; R₁ = H, CH₃, C₂H₅; R₂ = H, CH₃, C₂H₅ and X = -CH₂CH₂-, -CH₂CH₂CH₂-, -CH₂CHCH₃, -C₆H₄CH₂CH₂-] with aluminium isopropoxide in different molar ratios (1 to 3) yield compounds of the type Al(OPrⁱ)_3?n(OXNR₁R₂)_n, where ‘n’ can be 1, 2 and 3. Most of the derivatives are distillable liquids, soluble in common organic solvents and susceptible to hydrolysis even by atmospheric moisture. The new derivatives are characterized by elemental analysis, IR and ¹H NMR spectra. Molecular weight measurements of Al(OPrⁱ)_3?n(OXNR₁R₂)_n reveal them to be tetrameric in nature.     

Receptor of the serpentine-type and heterotrimeric G protein as targets of action of polylysine dendrimers

Molecular processes of the action of polycationic peptides that represent polylysine homo- and heterodendrimers on the functional activity of the biogenic amine- and peptide hormone-sensitive adenylyl cyclase signaling system (AC system) in rat myocardium and brains were studied. An intended use of these peptides is that of highly effective polymer carriers for biologically active substances. The polylysine homodendrimers of the third [(NH₂)₁₆(Lys)₈(Lys)₄(Lys)₂Lys-Ala-NH₂] (I), fourth [(NH₂)₃₂(Lys)₁₆(Lys)₈(Lys)₄(Lys)₂Lys-Ala-NH₂] (II), and fifth [(NH₂)₆₄(Lys)₃₂(Lys)₁₆(Lys)₈(Lys)₄(Lys)₂Lys-Ala-NH₂] (III) generations, as well as polylysine heterodendrimers of the fifth generation, [(NH₂)₆₄(Lys-Glu)₃₂(Lys-Glu)₁₆(Lys-Glu)₈(Lys-Glu)₄(Lys-Glu)₂Lys-Ala-Ala-Lys(ClAc)-Ala-NH₂] (IV), [(NH₂)₆₄(Lys-Ala)₃₂(Lys-Ala)₁₆(Lys-Ala)₈(Lys-Ala)₄(Lys-Ala)₂Lys-Ala-Lys(ClAc)-Ala-Ala-NH₂] (V) and [(NH₂)₆₄(Lys-Gly-Gly)₃₂(Lys-Gly-Gly)₁₆(Lys-Gly-Gly)₈(Lys-Gly-Gly)₄(Lys-Gly-Gly)₂Lys-Gly-Gly-Lys(ClAc)-Ala-Ala-NH₂] (VI), interact with the C-terminal regions of α subunits of the heterotrimeric G proteins, preferably of the inhibitor type, and stimulate its activity in respector-independent manner. The most effective G-protein activators were homodendrimers II and III and heterodendrimer V. The polylysine dendrimers disturbed the functional coupling of receptors of biogenic amines and peptide hormones with G_i proteins and, to a lesser extent, G_s proteins. This was manifested as a decrease in the regulatory effects of the hormones on AC activity and the GTP binding of the G protein, as well as by a decrease in the affinity of receptors to agonists in the presence of polylysine dendrimers, which is a consequence of the dissociation of the receptor-G protein complex. It has also been shown that, based on their molecular mechanisms and selectivity of action on G proteins, polylysine dendrimers are similar to mastoparan and melittin, which are natural toxins of insect venom.     

Modeling aspects of hydrodesulfurization by molybdenum hydride compounds: Desulfurization of thiophene and benzothiophene and C-S bond cleavage of dibenzothiophene

The molybdenum hydride complexes Mo(PMe₃)₅H₂ and Mo(PMe₃)₄H₄ are capable of cleaving the C-S bonds of thiophene, benzothiophene and dibenzothiophene. For example, Mo(PMe₃)₅H₂ reacts with thiophene to give the η⁵-thiophene and butadiene-thiolate complexes, (η⁵-C₄H₄S)Mo(PMe₃)₃ and (η⁵-C₄H₅S)Mo(PMe₃)₂(η²-CH₂PMe₂). These complexes are also obtained from the reaction between Mo(PMe₃)₄H₄ and thiophene under photochemical conditions, whereas at elevated temperatures thiophene is desulfurized to liberate but-1-ene. Similarly, Mo(PMe₃)₄H₄ desulfurizes benzothiophene at elevated temperatures to liberate ethylbenzene, while the arylthiolate complex Mo(PMe₃)₄(SC₆H₄Et)H₃ is obtained photochemically. Furthermore, Mo(PMe₃)₄H₄ cleaves the C-S bond of dibenzothiophene to give [η⁶,κ¹-C₆H₅C₆H₄S]Mo(PMe₃)₂H.     

Specificity of the interaction of DNA-platinum, amount of platinum, and pH measurement]

Interaction between the sodium salt of a DNA extracted from salmon sperm (41% GC) with [Pt(NH₃)₄]Cl₂, [Pt(NH₂? (CH₂)₂? NH? (CH₂)₂? NH₂Cl]Cl, cis-Pt(NH₂? (CH₂)₂? NH₂)Cl₂, cis-Pt(NH₃)₂Cl₂, trans-Pt(NH₃)₂Cl₂, K[Pt(C₂H₄)Cl₃], and K₂[PtCl₄) indicates at least three types of complexation. A correlation is found between the change of pH and the number of platinum atoms fixed per (AT + GC) unit. The first binding site is located on the G-C pairs (guanine–cytosine), most likely the N-7(G) site, as it was shown in a previous study of the guanosine-platinum salts. The fixation of the second platinum atom by the pair (AT + GC) takes place with liberation of protons. In the case of the complexes cis-Pt(NH₂? (CH₂)₂? NH₂)Cl₂, cis-Pt(NH₃)₂Cl₂, and trans-Pt(NH₃)₂Cl₂ the second interaction seems to involve simultaneously the N-7(A) and the N-1(G) and N-3(C) sites. This latter intercrosslink between guanine and cytosine obviously liberates protons and the decrease of pH is related in this case to the trans effect of the platinum compounds. The first two platinum atoms in the reaction of K₂PtCl₄] or the Zeise salt, K[Pt(C₂H₄)Cl₃] with DNA are fixed on the G-C pairs. A maximum of six platinum atoms per (AT + GC) unit were fixed in this case. Preliminary experiments with a DNA extracted from bacteria Micrococcus lysodeikticus (72% GC) give similar results.     

Enhancement of BKCa channel activity induced by hydrogen peroxide: Involvement of lipid phosphatase activity of PTEN

Large-conductance calcium and voltage-dependent potassium (BK_Ca) channel is an important determinant of vascular tone. It is activated by hydrogen peroxide (H₂O₂) which occurs in various physiological and pathological processes. However, the regulation mechanism is not fully understood. In the present study, the mSlo in the presence or absence of hβ1 were cotransfected with the PTEN_wt, PTEN_C124S, PTEN_G129E in HEK 293 cells. Typical BK_Ca channel currents could be recorded in cell-attached configurations. We found that PTEN_wt reduced the H₂O₂-induced BK_Ca channel activation during the initial 10 min treatment. In contrast, coexpression with catalytically inactive PTEN_C124S/PTEN_G129E mutants that lack lipid phosphatase activity produced no regulation on the H₂O₂-induced BK_Ca channel activation. These results demonstrated that PTEN regulated the H₂O₂-induced BK_Ca channel activation through phosphatidylinositol 3-phosphatse. However, the inhibitory effect of PTEN on the H₂O₂-induced BK_Ca channel activation was attenuated when cells were treated with H₂O₂ at concentrations higher than 100 μM or at 100 μM for long-term treatment. In addition, the p-AKT expression level in PTEN_wt overexpressing cells was lower than that in control cells, and the increase of cytoplasmic free calcium concentration ([Ca²⁺]_i) induced by H₂O₂ was also inhibited. These findings may elucidate a new mechanism for H₂O₂-induced BK_Ca channel activation and provide some evidences for the role of PTEN on vasodilation induced by H₂O₂.     

Distribution of endogenous gibberellins in vegetative and reproductive organs of Brassica

Recognizing the physiological diversity of different plant organs, studies were conducted to investigate the distribution of endogenous gibberellins (GAs) in Brassica (canola or oilseed rape). GA₁ and its biosynthetic precursors, GA₂₀ and GA₁₉, were extracted, chromatographically purified, and quantified by gas-chromatography-selected ion monitoring (GC-SIM), using [²H₂]GAs as internal standards. In young (vegetative) B. napus cv. Westar plants, GA concentrations were lowest in the roots, increased acropetally along the shoot axis, and were highest in the shoot tips. GA concentrations were high but variable in leaves. GA₁ concentrations also increased acropetally along the plant axis in reproductive plants. During early silique filling, GA₁ concentrations were highest in siliques and progressively lower in flowers, inflorescence stalks (peduncles plus pedicels), stem, leaves, and roots. Concentrations of GA₁₉ and GA₂₀ showed similar patterns of distribution except in leaves, in which concentrations were higher, but variable. Immature siliques were qualitatively rich in endogenous GAs and GA₁, GA₃, GA₄, GA₈, GA₉, GA₁₇, GA₁₉, GA₂₀, GA₂₄, GA₂₉, GA₃₄, GA₅₁, and GA₅₃ were identified by GC-SIM. In whole siliques, GA₁₉, GA₂₀, GA₁, and GA₈ concentrations declined during maturation due to declining levels in the maturing seeds; their concentrations in the silique coats remained relatively constant and low. These studies demonstrate that GAs are differentially distributed in _Brassica with a general pattern of acropetally increasing concentration in shoots and high concentration in actively growing and developing organs.     

Gibberellins in Embryo-Suspensor of Phaseolus coccineus Seeds at the Heart Stage of Embryo Development

Gibberellins (GAs) in suspensors and embryos of Phaseolus coccineus seeds at the heart stage of embryo development were analyzed by combined gas chromatography-mass spectrometry (GC-MS). From the suspensor four C₁₉-GAs, GA₁, GA₄, GA₅, GA₆, and one C₂₀ GA, GA₄₄, were identified. From the embryo, five C₁₉-GAs GA₁, GA₄, GA₅, GA₆, GA₆₀ and two C₂₀ GAs, GA₁₉ and GA₄₄ were identified. The data, in relation to previous results, suggest a dependence of the embryo on the suspensor during early stages of development.     

Fluorescence excitation spectra of drought resistant and sensitive genotypes of triticale and maize

An influence of soil drought (7 or 14 d) and 7 d recovery on changes of leaf fluorescence excitation spectra at wavelengths of 450, 520, 690, and 740 nm (F₄₅₀, F₅₂₀, F₆₉₀, F₇₄₀) for drought resistant and sensitive genotypes of triticale and maize was compared. In non-stressed plants the differences between maize and triticale were observed for F₄₅₀ and F₅₂₀, but not for F₆₉₀ and F₇₄₀. Drought caused the increase in F₄₅₀, F₅₂₀, and F₆₉₀ and this increase was more distinct for drought sensitive genotypes. After re-hydration, chlorophyll fluorescence mostly recovered to values of control plants. Drought caused significant increase in F₆₉₀/F₇₄₀ but not in F₄₅₀/F₆₉₀ and F₄₅₀/F₅₂₀. For triticale, highest increase in F₆₉₀/F₇₄₀ was observed in the 4^th and 7^th leaves of resistant genotype and contrarily in maize for the sensitive one. After recovery, the F₄₅₀/F₅₂₀, F₄₅₀/F₆₉₀, and F₆₉₀/F₇₄₀ ratios mostly returned to values of control plants.     

Inhibition of dark‐induced stomatal closure by fusicoccin involves a removal of hydrogen peroxide in guard cells of Vicia faba

Fusicoccin (FC) treatment prevents dark‐induced stomatal closure, the mechanism of which is still obscure. By using pharmacological approaches and laser‐scanning confocal microscopy, the relationship between FC inhibition of dark‐induced stomatal closure and the hydrogen peroxide (H₂O₂) levels in guard cells in broad bean was studied. Like ascorbic acid (ASA), a scavenger of H₂O₂ and diphenylene iodonium (DPI), an inhibitor of H₂O₂‐generating enzyme NADPH oxidase, FC was found to inhibit stomatal closure and reduce H₂O₂ levels in guard cells in darkness, indicating that FC‐caused inhibition of dark‐induced stomatal closure is related to the reduction of H₂O₂ levels in guard cells. Furthermore, like ASA, FC not only suppressed H₂O₂‐induced stomatal closure and H₂O₂ levels in guard cells treated with H₂O₂ in light, but also reopened the stomata which had been closed by darkness and reduced the level of H₂O₂ that had been generated by darkness, showing that FC causes H₂O₂ removal in guard cells. The butyric acid treatment simulated the effects of FC on the stomata treated with H₂O₂ and had been closed by dark, and on H₂O₂ levels in guard cells of stomata treated with H₂O₂ and had been closed by dark, and both FC and butyric acid reduced cytosol pH in guard cells of stomata treated with H₂O₂ and had been closed by dark, which demonstrates that cytosolic acidification mediates FC‐induced H₂O₂ removal. Taken together, our results provide evidence that FC causes cytosolic acidification, consequently induces H₂O₂ removal, and finally prevents dark‐induced stomatal closure.     

Comparison of fractionation of groundnut proteins by two different methods

The salt-soluble proteins of groundnut meal were fractionated by precipitation with (NH₄)₂SO₄ by increasing the (NH₄)₂SO₄ saturation in steps of 10%. The sharp separation into arachin and conarachin claimed by earlier workers was not achieved, as protein was precipitated at each stage from 20 to 100% saturation with (NH₄)₂SO₄. The fractions so obtained were examined by disc electrophoresis on polyacrylamide gel and the amino acid compositions were determined by ion-exchange chromatography. Differences in both electrophoretic pattern and amino acid composition were found. The protein precipitated by CaCl₂ solution was similar in yield, nitrogen content, electrophoretic pattern, and amino acid composition to the fraction precipitating at 10–20% (NH₄)₂SO₄ saturation. The main differences in amino acid composition of the various fractions precipitated by (NH₄)₂SO₄ were found in the amino acids cystine, methionine, and lysine, which increased with increase in (NH₄)₂SO₄ saturation. The electrophoretic pattern and amino acid composition of “conarachin” varied according to the method of preparation.     

Characterization of ribonucleoprotein subparticles from 50 S ribosomal subunits of Escherichia coli.

Large ribonucleoprotein subparticles were recovered upon ribonuclease digestion of the 50 S ribosomal subunits of Escherichia coli, partially deproteinized by LiCl. Both their RNA and their protein compositions were analysed. The subunits, treated with LiCl at a concentration of 5.5 m, released an homogeneous subparticle containing proteins L₃, L₄, L₁₃, L₁₇, L₂₂ and L₂₉, about 70% of the 13 S fragment of 23 S RNA and about 50% of the 18 S one. Slightly larger species of subparticles were obtained from 50 S subunits treated with LiCl at concentrations between 3 m and 5 m; they contained in addition proteins L₂₀, L₂₁ and L₂₃ or L₂, L₁₄, L₂₀, L₂₁ and L₂₃ and a few small 23 S RNA fragments. No large subparticle was recovered from the 6 m-LiCl-treated 50 S subunits which contain only proteins L₃, L₁₃ and L₁₇. These LiCl subparticles were compared with those obtained from intact, unfolded and sodium doecyl sulphatetreated 50 S subunits.These studies reveal that in the presence of 0.10 m-magnesium acetate there is a very compact area within 50 S subunits consisting of proteins L₃, L₄, L₁₃, L₁₇, L₂₂ and L₂₉ and of about 60% of 23 S RNA; this area probably has an essential structural role. The results also show that 23 S RNA has a more folded conformation when within the 50 S subunit than when isolated, this conformation being stabilized by some of the 50 S proteins, in particular proteins L₄, L₂₂, L₂₀ and L₂₁. Finally these data permit a more definite localization of the primary and/or secondary binding sites of proteins L₂, L₃, L₄, L₁₄, L₁₇, L₂₀, L₂₁ and L₂₂ on 23 S RNA.     

Investigation of the effect of naringenin on oxidative stress‐related alterations in testis of hydrogen peroxide‐administered rats

Testis tissue is prone to oxidation because its plasma membrane contains many polyunsaturated fatty acids. Naringenin is a plant‐derived natural flavonoid. We investigated the possible ameliorative role of naringenin on the hydrogen peroxide (H₂O₂)‐induced testicular damage in Wistar rats. Animals received 12 mg/kg H₂O₂ by intraperitoneal injection, and 50 mg/kg naringenin via orogastric gavage for 4 weeks. In the H₂O₂ group, the testis malondialdehyde level increased, while the amount of reduced glutathione, glutathione transferase activities, and the testis weight decreased. There were severe testicular damages in the H₂O₂ group otherwise their grade were less in the naringenin + H₂O₂ group. However, the serum testosterone concentrations decreased in both the H₂O₂ and the naringenin + H₂O₂ groups. The testicular zinc and calcium levels reduced in the H₂O₂‐treated rats. In conclusion, the administration of H₂O₂ caused oxidative stress in the testes and naringenin supplementation decreased the H₂O₂‐induced effects, except for changes in testosterone levels.     

Torque Generation of Enterococcus hirae V-ATPase

V-ATPase (V_oV₁) converts the chemical free energy of ATP into an ion-motive force across the cell membrane via mechanical rotation. This energy conversion requires proper interactions between the rotor and stator in V_oV₁ for tight coupling among chemical reaction, torque generation, and ion transport. We developed an Escherichia coli expression system for Enterococcus hirae V_oV₁ (EhV_oV₁) and established a single-molecule rotation assay to measure the torque generated. Recombinant and native EhV_oV₁ exhibited almost identical dependence of ATP hydrolysis activity on sodium ion and ATP concentrations, indicating their functional equivalence. In a single-molecule rotation assay with a low load probe at high ATP concentration, EhV_oV₁ only showed the “clear” state without apparent backward steps, whereas EhV₁ showed two states, “clear” and “unclear.” Furthermore, EhV_oV₁ showed slower rotation than EhV₁ without the three distinct pauses separated by 120° that were observed in EhV₁. When using a large probe, EhV_oV₁ showed faster rotation than EhV₁, and the torque of EhV_oV₁ estimated from the continuous rotation was nearly double that of EhV₁. On the other hand, stepping torque of EhV₁ in the clear state was comparable with that of EhV_oV₁. These results indicate that rotor-stator interactions of the V_o moiety and/or sodium ion transport limit the rotation driven by the V₁ moiety, and the rotor-stator interactions in EhV_oV₁ are stabilized by two peripheral stalks to generate a larger torque than that of isolated EhV₁. However, the torque value was substantially lower than that of other rotary ATPases, implying the low energy conversion efficiency of EhV_oV₁.     

Specific Features of Albumin Interactions with Hemiacetals of Aflatoxins and Sterigmatocystin

Aflatoxin B_2a (AB_2a), aflatoxin G_2a (AG_2a), and the hemiacetal of sterigmatocystin have been shown to form immunoreactive conjugates with albumin. The conjugates were formed following incubation of solution mixtures at room temperature for 1 h, as demonstrated by spectrophotometry and enzyme immunoassay. Anti-AB_2a antibodies reacted with AB_2a, aflatoxin B₁, and aflatoxin B₂ (100, 8.8, and 5.9%, respectively); a similar result was obtained for anti-AG_2a antibodies reacting with AG_2a, aflatoxin G₁, and aflatoxin G₂ (100, 2.5, and <1.0%, respectively). Binding of anti-AB_2a and anti-AG_2a antibodies to solid-phase conjugates of AB_2a or AG_2a exhibited similar analytical characteristics.     

Characterisation of neuropeptides of the AKH/RPCH-family from corpora cardiaca of Coleoptera

Summary Extracts of corpora cardiaca from two members of the family Tenebrionidae,Zophobas rugipes andTenebrio molitor, from one member of the Chrysomelidae,Leptinotarsa decemlineata, and from three members of the Scarabaeidae,Pachnoda marginata, P. sinuata andMelolontha hippocastani, were assayed for adipokinetic and hypertrehalosaemic activity in acceptor locusts (Locusta migratoria) and cockroaches (Periplaneta americana), respectively. All corpus cardiacum material tested, except that from the cockchafer,M. hippocastani, gave positive bioassay results. Biological activities of corpus cardiacum extracts from all species investigated can be resolved on reversed-phase high performance liquid chromatography (RP-HPLC). Gland extracts from the two tenebrionid species each show a single peak of biological activity associated with a single peak of UV absorbance having an identical retention time in both species. The two biologically active fractions from the corpora cardiaca of the potato beetle,L. decemlineata, coelute with exogenous (synthetic) hypertrehalosaemic hormones I and II of the American cockroach. The two species of the genusPachnoda contain two active compounds in their glands; compound I of each species is more abundant and elutes just ahead of the (synthetic) hypertrehalosaemic hormone of the cockroachBlaberus discoidalis. The gland material ofM. hippocastani exhibits and absorbance peak with the same retention time as the major peak from thePachnoda-species; however, this peak material does not elicit biological activity in the assays used here. After fractionation by RP-HPLC the main biologically active compounds were subjected to amino acid analyses. All factors are peptidic and contain 8 amino acid residues. The peptides from the tenebrionid species have the amino acid residues Asx₍₂₎, Glx₍₁₎, Ser₍₁₎, Pro₍₁₎, Leu₍₁₎, Phe₍₁₎ and Trp_(i), whereas the main peptide from corpora cardiaca ofP. marginata contains the residues Asx₍₂₎, Glx₍₁₎, Ser₍₁₎, Pro₍₁₎, Tyr₍₁₎, Leu₍₁₎ and Trp₍₁₎. Amino acid composition analyses of the two active fractions fromL. decemlineata reveal the residues Asx₍₂₎, Glx₍₁₎, Ser₍₁₎, Pro₍₁₎, Val₍₁₎, Phe₍₁₎ and Trp₍₁₎ for compound I and Asx₍₁₎, Glx₍₁₎, Thr₍₂₎, Pro₍₁₎, Leu₍₁₎, Phe₍₁₎ and Trp₍₁₎ for compound II.     

Preparation and properties of some new 6-heteropoly-tellurate compounds of tungsten and molybdenum containing vanadium

Methods for preparing the following compounds (NH₄)₇TeW₅VO₂₄·5H₂O, (NH₄)₈TeW₄V₂O₂₄·xH₂O, (NH₄)₉TeV₃W₃O₂₄·xH₂O and (NH₄)₇TeMo₅VO₂₄·8H₂O are described. The compounds thus prepared were examined for thermal behavior, IR, Raman, UV, X-ray, NMR and reaction with base.     

Proton magnetic resonance studies of the conformational changes of dideoxynucleoside ethyl phosphotriesters

PMR investigations on the diastereomeric phosphate methyl protons of the dinucleoside ethyl phosphotriesters Tp(C₂H₅)T, dA, and dIp(C₂H₅)dI have been used to study the conformational changes of these dimersin solution. In D₂O (273°K), the diastereomeric phosphate-methly groups of Tp(C₂H₅)T appear as a triplet. The methyl resonances of dIp(C₂H₅)dI and dAp(C₂H₅)dA appear as two sets of triplets and their chemical shift differences (δ₁ ? δ₂), decrease with increasing temperature, finally becoming zero at 292°K and 333°K, respectively. The same phenomenon is observed for dAp(C₂H₅)dA in CD₃OD; in this detacking solvent, the difference (δ₁ ? δ₂) diminishes to zero at a lower temperature (261°K). At room temperature in D₂O, the chemical shift of the phosphate methyl of Tp(C₂H₅)T appears at lower field than those of dIp(C₂H₅)dI or dAp(C₂H₅)dA. The differences between the chemical shifts of these groups (δ_I ? δ_T or δ_A ? δ_T) increase with increasing temperature, and reach maximal values at 301°K and 333°K, respectively. The results suggest that at low temperature the largest fraction of the dimer population exists in a stacked state, with the phosphate-ethyl groups outside the stack. Increasing temperature causes an oscillation of the bases and a shift in the dimer population away from the stacked state. Finally at high temperature, the planar bases rorate with respect to one another and in the case of dIp(C₂H₅)dI and dAp(C₂H₅)dA, the ethyl groups experience shielding by the anisotropic ring current of the five-membered ring of the bases. Thus, the current pmr studies and those reported earlier from our laboratory support an “oscillation-rotation model” for the unstacking process of the dimers. The relationship of this model and the “two-state model” is discussed.     

Complexes of formamidines and ethyl formimidate

Formamidines and formimidates (L = (p-MeC₆H₄ NH)(p-MeC₆H₄N=)CH; L′ = (p-MeC₆H₄N=) (EtO)CH are shown to yield metal complexes, not obtained directly before. The following complexes were characterized through spectral and magnetic data: L₂Ag⁺, L₂AgNO₃, L₂ZnBr₂, L₂CdBr₂, L₃Cd₂Br₄, LHgCl₂, L₂CoCl₂, [LH]₂[CoCl₄], cis-(CO)₂RhClL as well as L′₂Ag⁺ and cis-(CO)₂RhClL′. I.r. and n.m.r. spectra allow to distinguish these complexes from the derivatives of the isomer carbene ligands, (RNH)₂C: and (RNH)(R′O)C:.