Zur Umsetzung des 3,4,5,6-Tetrahydro-6-hydroxy-4,4,6-trimethyl-1,3-thiazin-2-thions mit sekundären Aminen

Tetrahydro-6-hydroxy-trimethyl-1,3-thiazine-2-thione (1) reacts with secondary amines via the dialkylammonium-3-oxoalkyldithiocarbamate3, either via isothiocyanates6 to 4-dialkylaminodihydro-2(1H)-pyridinethiones7 or to dialkylammonium dithiocarbamates (13), depending on the amine used and the reaction conditions. Subsequently, 6-dialkylaminotetrahydro-1,3-thiazine-2-thiones11 or tetrahydro-6-mercapto-1,3-thiazine-2-thione10 are formed. On being heated to reflux,11 reacts to pyridinethione7 and 4-dialkylaminodihydrothiopyranthione19. With secondary amines only13 is formed from tetrahydro-6-hydroxytetramethyl-1,3-thiazine-2-thione20. The reaction of dihydrotrimethyl-1,3-thiazine-2-thione21 with secondary amines leads to N,N-dialkylthioureas16 or dialkylammonium thiocyanates17 and with dialkylformamides 4-dialkylaminodihydropyridinethiones7 are formed. Dihydrotetramethyl-1,3-thiazine-2-thione24 reacts neither with secondary amines nor with dialkylformamides.     

Koordinationschemie von Dinitroresorcin mit Kupfer-, Kobalt-, Nickel-, Eisen- und Zinksalzen

The reactions of the bidentate dinitrosoresorcinol (DNR) with copper, cobalt, nickel, iron and zinc salts were investigated. This ligand was found to react with these metal salts in aqueous media where hydrogen ion was confirmed to be liberated except in case of iron. The solid complexes were prepared in alcoholic media. Chemical analyses, magnetic and spectral data were compatible to determine the structure of these complexes and their mode of chelation.

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Beiträge zur Chemie der Pyrrolpigmente, 19. Mitt.: Die elektrochemische Oxidation von Pyrromethenonen und Pyrromethenen (Gallenpigment-Partialstrukturen)

The electrochemical oxidation of arylmethylene-pyrrolinones, pyrromethenones and pyrromethenes as representative bile pigment partial structure models was investigated by means of a rotating disc platinum electrode using acetonitrile as the solvent. Two different oxidation reactions were found. The first reaction being a reversible one-electron oxidation with compounds of the arylmethylene-pyrrolinone series and pyrromethenones which are unsubstituted in position 5 of the pyrrole ring. A two step reaction (the first one reversible, the second irreversible) on the other hand was found to be typical for pyrromethenones bearing a methyl group in this position.Through protonation the first step is at a higher potential, whereas the second one is lowered and becomes reversible. The resulting oxidation pattern can be interpreted analogous to the oxidation of hydroquinones in aprotic solvents.The geometrical isomers of a pyrromethenone were oxidized at appr. the same potential, but there is a strong dependence of the potential of the first oxidation step on the substitution: a higher degree of alkylation favours oxidation by lowering the oxidation potential.

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Synthesis of Phosphaformamidines and Phosphaformamidinates

A large‐scale synthetic route to a variety of phosphaformamidines and phosphaformamidinates, a type of derivative that was not accessible by the methods previously known for preparing phosphaamidines and phosphaamidinates, is reported. Thermally stable ethyl N‐arylformimidates 1 (ArN?CH(OEt), Ar=2,4,6‐(Me)₃Ph or 2,6‐(iPr)₂Ph) readily reacted with lithium dialkyl‐ and diarylphosphanides to afford the corresponding N‐aryl phosphaformamidines in 80 and 60 % yield, respectively, whereas with lithium (aryl)(silyl)phosphanide, the N‐aryl‐N‐silylphosphaformamidine (60 % yield) was obtained. Addition of primary lithium arylphosphanides to 1 followed by addition of a stoichiometric amount of nBuLi gave rise to the respective phosphaformamidinates (70–88 % yield). Methanolysis of the products afforded the N‐aryl‐N‐hydrogenophosphaformamidines (90–95 % yield). The solid‐state structure of one of the phosphaformamidinates is also presented.     

Zur Synthese der 4-Dialkylamino-5,6-dihydro-2(1H)-pyridinthione sowie entsprechender 4-Alkylamino- bzw. 4-Arylaminoverbindungen

The rearrangement of 1-alkyl- and 1-aryldihydro-6-methyl-2(1H)-pyrimidinethiones (1 a) or-ones (1 b) and of methylene compounds (2a, 2b) resp., to 4-alkylamino- and 4-arylaminodihydro-2(1H)-pyridinethiones (4 a) or-ones (4 b) takes place via the corresponding 3-alkylamino- and 3-aryl-amino-3-butenylisothiocyanates (3 a) or-isocyanates (3 b). Dialkylamino-dihydro-2(1H)-pyridinethiones (10) are formed by heating dihydro-6-methyl-2(1H)-pyrimidinethiones (6 a) and 3,4-dihydro-6-methyl-1,3-thiazin-2-thiones (6 b) with dialkylformamides and by the reaction of secondary amines with tetrahydro-6-hydroxy-6-methyl-1,3-thiazin-2-thiones (5 a), with N,N-dialkyl-N-(3-oxobutyl)-thioureas (7) and 3-oxobutyl isothiocyanates (8). A general method for the preparation of10 is the reaction of dialkylammoniumrhodanides12, N,N-dialkylthioureas13 and dialkylammonium chlorides and KCNS, resp., with 3-alken-2-ones14 and 4-hydroxy-2-alkanones15, resp. Methyl ketones such as acetone, which readily undergo the aldol condensation, behave analogously. The reactions described take place via the intermediate aminoalkenyl isothiocyanates (9).     

N-Monobromamide: Darstellung durch Bromierung mit „Dibromisocyanursäure”, Eigenschaften

By reaction of primary carboxamides with “dibromoisocyanuric acid” (DBI) N-monobromoamides can be readily obtained as well as the N,N-dibromoamides described in an earlier paper¹. Reactions, some of them new, and properties of these compounds are described and compared with those of the N,N-dibromoamides. Like other compounds bearing the NHBr group^{2, 3} the N-monobromocarboxamides disproportionate at room temperature according to: 2 RCONHBr ? ? RCONH₂+RCONBr₂. For CH₃CONHBr the equilibrium constant was found to beK=0.02. In aqueous solution they behave as weak acids. The dissociation constants of eight compounds [R=?CH₃, ?C₂H₅, ?CH₂Cl, ?CHCl₂, ?CCl₃, ?CF₃, ?C(CH₃)₃ and ?C₆H₅] were measured: they differ from those of the corresponding carboxylic acids by about three powers of ten.     

An injectable chitosan-based hydrogel reinforced by oxidized nanocrystalline cellulose and mineral trioxide aggregate designed for tooth engineering applications

The complex anatomy of teeth limits the accessibility and efficacy of regenerative treatments. Therefore, the application of well-known inducers as injectable hydrogels for the regeneration of the dentin-pulp complex is considered a promising approach. In this regard, this study aimed to develop an injectable hydrogel containing mineral trioxide aggregate (MTA). The injectable chitosan/oxidized-nanocrystalline cellulose/MTA (CS/OCNC/MTA) hydrogels were prepared, and the physicochemical properties of these hydrogels were evaluated by TGA, FTIR, Rheological analysis, and SEM. Moreover, the effect of MTA on the swelling and degradability of scaffolds was assessed. The proliferative effects of synthesized hydrogels were also determined on human dental pulp stem cells (hDPSCs) by MTT assay. For induction of differentiation and biomineralization in these cells, the alkaline phosphatase activity and Alizarin Red S staining tests were performed in the presence of fabricated scaffolds. The proliferation of hDPSCs was significantly increased in the presence of these hydrogels. Moreover, the addition of MTA to hydrogel structure dramatically improved the differentiation of hDPSCs. These results suggested that this novel injectable hydrogel provides appropriate physiochemical properties and can be considered a promising scaffold for regenerative endodontic procedures.

Graphical abstract

     

Perturbation calculations on the hydrogen bond in the water dimer for different proton acceptor orientations

Using perturbation theory of intermolecular forces (including exchange effects) hydrogen-bond energies are calculated for a simple model representing the water dimer. Several orientations of the proton acceptor with respect to the O...O axis are considered and it is found that the optimum orientation depends sensitively on the oxygen lone-pair hybridization assumed. The main orientation-dependent energy term is found to be the classical electrostatic energy between the unperturbed molecules. The relation of the present results to the structures of the ices I and Ic, and to the results of recent SCF studies are discussed briefly.

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Zusammenfassung Die Energien von Wasserstoffbindungen werden für ein einfaches Modell des dimeren Wassers mit Hilfe der Störungstheorie für intermolekulare Kräfte (mit Austauscheffekten) berechnet. Verschiedene Orientierungen des Protonen-Akzeptors bezüglich der O ... O-Achse werden untersucht; man findet, daß die optimale Orientierung empfindlich von der angenommen Hybridisierung des einsamen Elektronenpaars des Sauerstoffs abhängt. Der hauptsächliche, von der Orientierung abhängige Energieterm ist die klassische elektrostatische Energie zwischen den beiden ungestörten Molekülen. Die Beziehung der vorliegenden Ergebnisse zu den Strukturen von Eis I und Ic sowie zu den Ergebnissen kürzlicher SCF-Rechnungen wird kurz diskutiert.

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For some recent CNDO/2 calculations on (H₂O)₂ which concentrate mainly on rotations of the donor see Ref. [5].     

Untersuchungen über die Fluorescenzerscheinung bei Ketosen in Gegenwart von Zirkoniumoxidchlorid

Ketoses, as fructose and sorbose, react with ZrOCl₂ after slight heating. The reaction mixture exhibits strong fluorescence in UV; increased absorption is shown at 220–230 nm and a characteristic maximum at 335 nm. There is also an increase in conductivity. The stoichiometric composition of the fluorescing ketose-Zirconium chelate compound has been determined by a Job diagram. This compound can be used as a sensitive optical test in the microdetermination of ketoses.     

The electronic structures of pyridine-N-oxide and related compounds

The electronic structures of pyridinen-oxide, 2- and 4-methoxypyridinen-oxide, their conjugate acids, and 2- and 4-pyridone are calculated using the Pariser-Parr-Pople SCF-CI approximation. The results indicate that the¹ B ₁¹ A ₁ transition of pyridinen-oxide lies in the same energy region as the transition previously assigned as beingn -*. The strong electronic transitions in the 250–280 m region of pyridine-n-oxide, 4-methoxypyridinen-oxide, and 4-pyridone are assigned as being¹ A ₁¹ A ₁.

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Zusammenfassung Die elektronischen Strukturen von Pyridin-N-Oxyd, 2- und 4-Methoxypyridin-N-Oxyd, ihrer Kationen, und von 2- und 4-Pyridon wurden nach der Methode von Pariser-Parr-Popple SCF-CI berechnet. Es ergibt sich, daß der¹ B ₁¹ A ₁ Übergang des Pyridin-N-Oxyds etwa die gleiche Energie besitzt, wie die bisher einemn -* Übergang zugeordnete Bande. Der intensitätsstarke Übergang des Pyridin-N-oxyds, 4-Methoxypyridin-N-oxyds und 4-Pyridons im Bereich von 250–280 m wird einem¹A₁¹ A ₁ Übergang zugeordnet.

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Résumé Les structures électroniques de l'oxyde de pyridine, desn-oxydes de 2- et 4-methoxypyridine, leurs cations, et les 2- et 4-pyridone sont calculés par l'approximation Pariser-Parr-Pople SCF-CI. Les résultats obtenus indiquent que la transition¹ B ₁¹ A ₁ dun-oxyde de pyridine est située dans la même région d'énergie que la transition assignée auparavant comme étantn -*. Les transitions électroniques fortes dans la région de 250–280 m dun-oxyde de pyridine, dun-oxyde de 4-methoxypyridine et du 4-pyridone sont assignées comme étant¹ A ₁¹ A ₁.