Effect of fusion conditions ofβ-polypropylene on the new crystallization

The new crystallization of -modification of polypropylene (-PP) was studied after melring as a function of the final temperature of fusion (T _F ). The new crystallization, thermal characteristics, polymorphic composition, and structure of recrystallized samples were highly influenced by theT _F level. As a function ofT _F , three characteristic regions were outlined: Region I below the melting point of -modification, region II between the melting points of - and -modifications, and region III above the melting point of -modification. In the vicinity of the melting points of both modifications, two narrow transition regions are observed where the crystallization and structural characteristics changed abruptly withT _F . AtT _F values in region I, recrystallization of -modification proceeded without any change in the modification. IfT _F fell in region II, the sample crystallized newly into -modification. The optically negative -ring-spherulites were replaced by positive microclusters of -modification and a marked structural memory effect was observed. In region III, the above characteristic became invariant withT _F (region of blank melt). These observations may be interpreted by the role of self nuclei.     

Solubilization of Homologous ω-Phenylalkanols into Gel and Liquid-Crystalline Liposome Membranes of Dipalmitoylphosphatidylcholine

The gel-to-liquid-crystalline phase transition temperature T _m of dipalmitoylphosphatidylcholine (DPPC) liposome membrane was measured in the presence of homologous -phenylalkanols (phenol to 8-phenyl-1-octanol). The decrease in T _m induced by the alkanols allowed us, by applying the van't Hoff equation for freezing-point depression, to estimate two partition coefficients of each alkanol: gel membrane/bulk water K _x ^g and liquid-crystalline membrane/bulk water K _x ¹ . Shorter alkyl chain alkanols were solubilized only in the liquid-crystalline membrane, i.e., K _x ^g =0, whereas longer-chain alkanols were solubilized not only in the liquid-crystalline membrane but also in the gel membrane. The former result suggests that the fraction of liquid-crystalline phase in the liposome membrane is 0.83 at T _m. From the latter result, the values of the free energy changes of transfer of the alkanol molecules from bulk water to liposome membrane were estimated to be – 3.46 kJ-mol^–1 (liquid-crystalline membrane) and – 3.85 kJ-mol^–1 (gel membrane) per CH₂ group in the alkanol molecules.     

Calorimetric studies on the electrorefining process of copper

Calorimetric measurements were carried out on the electrorefining of copper using different current densities with a Calvet type microcalorimeter at room temperature. The ratio (R) of the measured heat (Q _m orW _m) to the input electric energy (Q _in orW _in) and the excess heat (Q _ex orW _ex), i.e. the difference betweenQ _m (orW _m) andQ _in (orW _in) during the electrorefining process were discussed in terms of general thermodynamics. It was found thatR andQ _ex were related to the current density employed in the experiment and varied as a logarithmic function. The results obtained here indicate that the heat generation under different conditions, such as different currents or voltages, may be caused partially by the irreversibility of the process or by some unknown processes.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthdayThe authors would like to acknowledge the extreme encouragements and help of Professor Shuyi Liu (University of Science and Technology of China) and Professors Fu Tan and Guoquan Liu (Institute of Chemistry, Academia Sinica).This study was supported by the National Nature Science Foundation of China.     

Synthesis of 5′-amino- and 5′-azido-2′,5′-dideoxy nucleosides from thieno[2,3-d]pyrimidine-2,4(1H,3H)-dione

Summary Thieno[2,3-d]pyrimidine-2,4(1H,3H)-dione (4) was silylated and condensed with methyl 5-azido-2,5-dideoxy-3-O-(4-methylbenzoyl)-D-erythro-pentofuranoside (2) in the presence ofTMS triflate to afford the corresponding protected nucleoside6 and acyclic nucleoside7. Deprotection of6 with MeONa/MeOH at room temperature gave 1-(5-azido-2,5-dideoxy--D-erythro-pentofuranosyl)-thieno[2,3-d]pyrimidine-2,4(1H,3H)-dione (8) and the corresponding anomer9, whereas compound7 yielded 5-azido-2,5-dideoxy-1-(2,4-dioxo-1,2,3,4-tetrahydrothieno[2,3-d]pyrimidin-1-yl)-1-O-methyl-D-erythro-pentitol (10) under the same reaction conditions. 1-(5-Amino-2,5-dideoxy--D-erythro-pentofuranosyl)thieno[2,3-d]pyrimidine-2,4(1H,3H)-dione (11) was obtained on treating9 with Ph₃P in pyridine followed by hyrolysis with NH₄OH. The anomeric nucleosides14 and15 and the corresponding acyclic nucleoside16 were obtained when4 was trimethylsilylated and condensed with methyl 2-deoxy-3,5-di-O-(4-methylbenzoyl)-D-erythro-pentofuranoside (3) followed by deprotection with MeONa in MeOH. Compounds8 and9 were also obtained when the anomeric mixture14/15 was treated with a mixture of NaN₃, Ph₃P, and CBr₄ in dryDMF at room temperature.On leave from Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt     

Three New <Emphasis Type="Italic">in situ</Emphasis> Syntheses of <Emphasis Type="Italic">N</Emphasis>-Acyl-α-triphenylphosphonioglycinates

Summary. N-Acyl--hydroxyglycinates were transformed into N-acyl--triphenylphosphonioglycinates by (i) phosphorylation with Ph ₃PBr₂ in the presence of Et ₃N or (ii) in reaction with DCC and Ph ₃P·HBF₄ in the presence of catalytic amounts of Ph ₃P as well as (iii) by a new kind of Mitsunobu reaction with Ph ₃P·HBF₄ as a nucleophile conjugated acid. The N-acyl--triphenylphosphonioglycinates can be effectively used without isolation for a nucleophilic displacement of the triphenylphosphonium group to obtain corresponding -substituted -amino acid derivatives.     

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.

     

Zur Reaktion von Permethylcyclosilanen mit Halogenen

The series of ,-diiodopermethylpolysilanes, I(SiMe ₂) _n I, (n=4–6) andX(SiMe ₂)₄ X, (X=Cl, Br) has been prepared by the action of halogen on the corresponding cyclic compounds (SiMe ₂) _n . The mass spectra, NMR-, IR- andRaman-spectra of these compounds have been recorded.

Herrn Prof. Dr.Josef Schurz zum 60. Geburtstag gewidmet.     

Studies of the energy spectrum of α, ω- substituted polymethine chains. II. Polymethine chains with odd number of methine groups

The analysis of the experimental data for the energy of the longest wavelength optical transitions _n,opt of substituted polymethines X (CH)_2n+1 X shows that in the asymptotic case (n) _,opt does not tend to zero, as it follows from the empirically established correlations, but has a finite, non-zero value. It is shown that the energy gap of odd polymethines is the same as that of the even polymethines - the polyenes (E 2 eV). The substituents (X N, O, B) are responsible for the appearance of levels in the gap. These, depending on the substituent character, are vacant (X B) or occupied (X N, O). The transition from or to such a level determines the longest wavelength optical transition energy of polymethines.     

Determination of the equilibrium melting point of the β-form of polypropylene

The melting behavior of the -form of isotactic polypropylene (-iPP) was investigated as a function of crystallization time and temperature. Calcium suberate, a selective -nucleating agent was used to produce samples that consist entirely of -form i-PP. The experimental melting points were recorded at different crystallization times and were extrapolated to the start of the crystallization process in order to eliminate the effect of lamellar thickening. Using the non-linear Hoffman—Weeks approach to correlate these extrapolated experimental melting temperatures with the corresponding crystallization temperatures, an equilibrium melting point of 209°C was obtained for -iPP. The equilibrium melting point estimated through the non-linear Hoffman—Weeks analysis is about 30°C higher than that (T _m ⁰=177°C) obtained on the basis of the linear extrapolation. These results are consistent with earlier claims that a linear extrapolation of T _m–T _c data leads to an underestimation of the equilibrium melting point. The results obtained for -iPP exemplify the importance of accounting for both the isothermal lamellar thickening effects and the non-linearity in the T _m–T _c correlation, when the determination of an equilibrium melting point is carried out using a procedure based on the predictions of the Lauritzen—Hoffman secondary nucleation theory.This revised version was published online in November 2005 with corrections to the Cover Date.     

Randić index and lexicographic order

Let T be a tree and consider the Randi index (T)= ), where v _i –v _j runs over all edges of T and (v _i ) denotes the degree of the vertex v _i . Using counting arguments we show that the Randi index, is monotone increasing over the well (lexicographic order) ordered sequence of trees with unique branched vertex.     

Struik law for enthalpy retardation at the glass transition in poly(n-alkylmethacrylates) measured by DSC aging experiments

Results of calorimetric (DSC) experiments on a series of poly (n-alkylmethcrylates), from methyl to pentyl, after different aging timest _e at different aging temperaturesT _e are presented. The aging behavior is quite different from that in other polymers, for example PS. For all poly(n-alkylmethacrylates) investigated the aging peak temperatureT _max is shifted parallel to the aging temperatureT _e in a large temperature interval below the glass temperature. The results are discussed with respect to shear and entropy response in the splitting region.     

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     

Ab initio studies of the low-lying π-states of borazine

Self-consistent-field and configuration-interaction studies were performed on borazine, using a double-zeta basis set augmented by six diffuse -functions. Low-lying singlet and triplet states of the A ₁ , A ₂ and E species were calculated, corresponding to ^* excited valence and Rydberg states. A selection out of singly and doubly excited configurations relative to a set of reference configurations was made for each species. Calculated vertical excitation energies (in eV) are 7.12 for ¹ A ₂(V), 8.45 for ¹ E (3p-R), 8.57 for ¹ A ₁(V), 8.9 for ¹ E(V-R), 9.55 for ¹ E(3d-R), 6.98 for ³ A ₁(_V), 7.27 for ³ E(V), 7.82 for ³ A ₂(V), 8.30 for ³ E(3p-R), and 9.5 for ³ E(3d-R), where V and R refer to valence or Rydberg character. The results are compared with experimental excitation energies, previous ab initio studies of borazine, and with recent ab initio studies of benzene.Dedicated to Professor Dr. H. Hartmann on the occasion of his 65th birthday.     

Synthesis,crystal structure and conformation of N-acetyl-Cα,α-diethylglycine-N′-methylamide

Summary Synthesis and X-ray structure analysis of N-acetyl-^,-diethylglycine-N-methylamide [CH₃-Co-NH-C(C₂H₅)₂-CO-NHCH₃] are described. The compound was obtained from the corresponding N-acetyl derivative [CH₃-CO-NH-C(C₂H₅)₂-COOH] through the mixed anhydride procedure. It crystallizes as monohydrate (C₉H₁₈N₂O₂·H₂O) in space group P2₁/c,a=7.139(1),b=11.823(2),c=15.778(3) Å, =122.23(1)°,V=1126.53 ų,D _m=1.20 Mgm^–3 (room temperature),R=0.046 for 1523 reflections. The crystal packing is dominated by two strong hydrogen bonds between the water molecule and two carbonyl oxygen atoms and two weak H-bonds to two amide-N-atoms of symmetry-equivalent molecules. The molecular conformation is closer to a 3₁₀-helix then ana-helix.

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Synthese, Kristallstruktur und Konformation von N-Acetyl-^,-diethylglycin-N-methylamid

Zusammenfassung Es wird über Synthese und die röntgenographische Strukturbestimmung von N-Acetyl-^,-diethylglycin-N-methyl-amid [CH₃-CO-NH-C(C₂H₅)₂-CO-NH-CH₃] berichtet. Die Verbindung wurde unter Anwendung der Methode der gemischten Anhydride aus dem entsprechenden N-Acetylderivat [CH₃-CO-NH-C(C₂H₅)₂-COOH] erhalten. Sie kristallisiert als Monohydrat (C₉H₁₈N₂O₂·H₂O) in der Raumgruppe P2₁/c mita=7.139(1),b=11.823(2),c=15.778(3) Å, =122.23(1)°,V=1126.53 ų,D _m=1.20 Mgm^–3,D _x=1.204 Mgm^–3 (Raumtemperatur).R=0.046 für 1523 Reflexe. Die Kristallpackung ist dominiert durch zwei starke H-Brücken vom Wassermolekül zu zwei Carbonylsauerstoffatomen sowie zwei schwachen H-Brücken zu zwei Amid-N-atomen symmetrieequivalenter Moleküle. Die Konformation des Peptidgerüstes ist näher einer 3₁₀ als einera-Helix.

     

Homolytic addition of polyhaloalkanes to α-vinyloxy-ω-trialkylstannoxy-alkanes as a new route to 2-perhaloalkylmethyl-substituted 1,3-dioxacyclanes

Photoinduced reactions of -vinyloxy--trialkylstannoxyalkanes, CH₂=CHO(CH₂) _n OSnEt₃ (n = 2 to 4), with polyhaloalkanes result in 2-perhaloalkylmethyl-substituted 1,3-dioxacyclanes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1824–1826, September, 1995.     

Some peculiarities of hydrosilylation of α,ω-divinyloligosilanes

The stability of Si-Si bonds in linear and cyclic permethyloligosilanes and in ,-divinyloligosilanes under conditions of hydrosilylation in the presence of the Speier's catalyst was studied. Polycarbosilanes containing silylene fragments in their backbone chains were prepared by the reaction of 1,4-bis(dimethylsilyl)benzene with ,-divinyloligosilanes. It was found that the structure of these polymers is disturbed due to the side reaction involving the cleavage of the Si-Si bond in vinyloligosilanes under the action of H₂PtCl₆.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2547–2549, October, 1996.     

Synthesis of α,ω-dichloropermethyloligosilanes by reactions of polydimethylsilane with metal chlorides

The reactions of high-molecular-weight polydimethylsilane with metal chlorides in variable oxidation states at high temperature in the absence of a solvent afford mixtures of ,-dichloropermethyloligosilanes Cl(Me₂Si) _m Cl (m= 2—9). The influence of the reaction conditions (temperature, reaction time, and the reagent ratio) on the composition and yields of the reaction products was examined.     

Synthesis and X-Ray Crystal Structure Study of ]2-Methyl-4-(2-methylbenzoyl)-phenoxy] Acetic Acid Hydrazide

Benzophenone analog 3 has been synthesized and characterized by the X-ray diffraction (XRD) method. The compound crystallizes in a monoclinic space group P2₁/c with cell parameters a = 7.701(8) Å, b = 7.151(5) Å, c= 28.323(3) Å, = 104.639(4)°, Z = 4. The structure exhibits intra- and intermolecular hydrogen bonding of the type N–HO, C–HO, and N–HN. The molecules are interlinked through hydrogen bonds forming an infinite chain. This polymeric-like structure may play an important role in biological activity.     

Low/high temperature relationships in dinitramide salts by DEA/DSC and study of oxidation of aluminum powders by DSC/TG

The dinitramide salts of ammonia (ADN), hexamethylenetetramine (HDN), potassium (KDN), and sodium (NaDN) showed a linear relationship between the DSC rate of decomposition at the peak maximum and the DEA tan value at the low temperature transition peak. As the cation basicity increased in the series ADN相似文献   

Effects of α-tocopherol and its acetate on the hydrolytic activity of phospholipase D in egg yolk phosphatidylcholine bilayers

Effects of -tocopherol (Toc) and -tocopherol acetate (TocA) on the hydrolysis activity of phospholipase D (fromStreptomyces chromofuscus) were studied in small unilamellar vesicles (SUV) of egg yolk phosphatidylcholine (PC). Choline produced in the reaction was monitored by use of a choline oxidase — oxygen electrode. Addition of 18 mol% Toc into SUV (2 mM PC) brought about a twofold rate of choline production. On the other hand, the effect of 18 mol% TocA in SUV was very small. The apparent maximum velocity,V _max(app), increased by addition of Toc in SUV. The apparent Michaelis constant,K _m(app), was unchanged by addition of Toc and TocA in SUV. The Toc and TocA molecules did not have significant effects when PC was solubilized in the micelles of heptaethylene glycol dodecyl ether. The effects of Toc and TocA are, therefore, not due to specific ones on the enzyme itself, but rather upon the bilayer-organization of the substrate. Measurements of spreading pressure showed complete miscibility of PC and Toc, and limited mutual solubility of PC and TocA, suggesting stronger attractive interactions between Toc and PC than those between TocA and PC in the bilayers.