Synthesis and Molecular Structure of β‐Phosphinoyl Carboxamides: An Unexpected Case of Chiral Discrimination of Hydrogen‐Bonded Dimers in the Solid State

A series of N,P,P‐trisubstituted aminophosphanes react with diphenylcyclopropenone to afford an easily separable mixture of two diastereomeric α,β‐diphenyl‐β‐phosphinoyl carboxamides in good yields. X‐ray crystal structures reveal that these compounds associate into dimers, formed from two enantiomeric units linked by two bifurcated hydrogen bonds, whereby the oxygen atom of the phosphoryl group acts as a dual acceptor for the vicinal NH and CH of a carbonyl group of a neighbouring molecule. Studies on the interconversion between diastereomeric phosphinoyl carboxamides in basic solution show that the thermodynamically most stable isomer depends on the nature of the substituent at the nitrogen atom. Simple computational calculations explain this phenomenon.     

Conversion of [Pt(SRf)2(PPh2 -n(C6F5)n+ 1)2]( n = 0 or 1, Rf=C6HF4-4) through carbon-fluorine bond activation to [Pt(SRf)2(1,2-C6F4(SRf)-(PPh2))] and chiral [Pt(SRf)2(1,2-C6F4(SRf)(PPh(C6F5)))

Treatment of trans-[PtCl(2)(PPh(2 - n)(C(6)F(5))(n + 1))(2)](n = 0 or 1) with Pb(SC(6)HF(4)-4)(2) yields a mixture of monometallic cis/trans [Pt(SC(6)HF(4)-4)(2)(PPh(2 - n)(C(6)F(5))(n + 1))(2)], thiolate-bridged bimetallic cis/trans [Pt(2)(mu-SC(6)HF(4)-4)(2)(SC(6)HF(4)-4)(2)(PPh(2 - n)(C(6)F(5))(n + 1))(2)] and [Pt(SC(6)HF(4)-4)(2)(1,2-C(6)F(4)(SC(6)HF(4)-4)(PPh(2 - n)(C(6)F(5))(n))].     

Stereochemical studies, 73. Saturated heterocycles, 60

N-Substituted-2-carboxamido-1-cycloalkanols were cyclized with 1,1-carbonyldiimidazole to synthesizecis- andtrans-N-alkyl-,N-aralkyl- andN-aryl-2,4-dioxo tri- and tetramethyleneperhydro-1,3-oxazines. The structures of the compounds and theircis ortrans ring anellation were confirmed by IR,¹H- and¹³C-NMR spectroscopy, and thecis andtrans pairs of isomers were compared to establish the predominant conformation of the flexiblecis isomers. It was found that—similarly to the 1,3-oxazin-2- and -4-ones studied earlier—the O-endo conformers are preferred, in which the 1-oxygen atom isaxial to the alicyclic ring; this is independent of the number of ring atoms in the alicycle, and of the presence of an oxazinedione ring, even though this is more flexible that the ring of oxazinones.

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Synthese und Konformation voncis undtrans 2-substituierten kondensierten 1,3-Oxazin-2,4-dionen

Zusammenfassung cis- undtrans-N-Alkyl-,N-Aralkyl- undN-Aryl-2,4-dioxo-, tri- und tetramethylen-perhydro-1,3-oxazine wurden aus 2-Carboxamido-1-cycloalkanolen und 1,1-Carbonyldiimidazol dargestellt. Mit Hilfe der IR,¹H- und¹³C-NMR Spektroskopie wurden die Struktur, diecis- odertrans-Annellierung der Ringe und die bevorzugte Konformation der flexiblencis-Isomeren im Vergleich zumcis-trans Isomerenpaar nachgewiesen. Ähnlich zu den früher untersuchten 1,3-Oxazine-2- und -4-onen ist hier ebenfalls das O-endo Konformere bevorzugt; in diesem ist der Sauerstoffaxial angeordnet, und zwar unabhängig von der Zahl der alicyklischen Ringatome und dem flexibleren Oxazindionring.

     

A Simple Synthesis of 2′,5′-Disubstituted-Spiro [Dihydroacridine 9(10H), 4′-Thiazolines] by the Reaction of Corresponding 3-(Acridin-9-Yl)-Thioureas with Methyl Bromoacetate and Bromoacetonitrile

A convenient method has been devised for the preparation of the spirodihydro-acridinethiazolines 5a-j by the treatment of thioureas 3a-e with methyl bromoacetate and bromoacetonitrile via non-isolable isothioureas 4a-j and their subsequent cyclization with methanolic sodium methoxide.     

New Type of Spiro Heterocycles. A Convenient Synthesis of Spiro[dihydroacridine 9(10H), 4′-Thiazolines]

A new type of heterocycles, spiro[dihydroacridine 9(10H), 4′-thiazolines] has been prepared in good yields by the addition of sodium alkoxides to 9-isothiocyanatoacridines and subsequent cyclization of obtained iminothiocarbonates with alkyl bromoacetates at mild conditions.     

Effect of Temperature on the Catalytic Ability of Electrochemically Active Biofilm as Anode Catalyst in Microbial Fuel Cells

In this study we report the effect of temperature on the catalytic ability of an electrochemically active biofilm based on mixed‐culture to oxidize acetate and found the optimum temperature showing maximal catalytic activity and power output. Electrochemical characterization of biofilm and power output and internal resistance of microbial fuel cell (MFC) have been investigated at different temperatures. When temperature increased from 30 to 45 °C the catalytic ability of biofilms to oxidize acetate increased following the Arrhenius law with apparent activation energy of 44.85 kJ/mol. At temperatures higher than 48 °C, however, the bioelectrocatalytic current decreased. At 53 °C the bacterial metabolism was in inactivation. The optimum working temperature of the biofilm was 45 °C, producing current of 1339 µA cm^?2. This current was almost three times higher than 527 µA cm^?2 at 30 °C. The MFC performance at different temperatures showed consistent temperature dependence to that of a semi‐batch cell, which implies that anode catalytic ability in MFC is the main limit factor for increasing power output. A maximum power output of 1065 mW m^?2 was also observed at 45 °C and it was 1.5 times higher than 764 mW m^?2 at 30 °C. The increased MFC performance from 30 °C to 45 °C is lower in comparison with about three times higher increase in semi‐batch cells. This could be due to other factors such as proton migration rate in membrane of MFC, which can be seen from that the internal resistance value of 121.5 Ω in the MFC at 45 °C was only slightly lower than 177.6 Ω at 30 °C. Also, some other factors such as cell configuration which would limit the power output and can be further optimized. This work contributes to the study of influence from temperature on anodic electrochemically active biofilm activity and their subsequent influence on MFC performance and reports the optimal temperature for biofilm activity based on mixed‐culture.     

Bimodal dynamics of mechanically constrained hydrogen bonds revealed by vibrational photon echoes

We have investigated the dynamics of the hydrogen bonds that connect the components of a [2]rotaxane in solution. In this rotaxane, the amide groups in the benzylic-amide macrocycle and the succinamide thread are connected by four equivalent N-H???O=C hydrogen bonds. The fluctuations of these hydrogen bonds are mirrored by the frequency fluctuations of the NH-stretch modes, which are probed by means of three-pulse photon-echo peak shift spectroscopy. The hydrogen-bond fluctuations occur on three different time scales, with time constants of 0.1, 0.6, and ≥200 ps. Comparing these three time scales to the ones found in liquid formamide, which contains the same hydrogen-bonded amide motif but without mechanical constraints, we find that the faster two components, which are associated with small-amplitude fluctuations in the strength of the N-H???O=C hydrogen bonds, are very similar in the liquid and the rotaxane. However, the third component, which is associated with the breaking and subsequent reformation of hydrogen bonds, is found to be much slower in the rotaxane than in the liquid. It can be concluded that the mechanical bonding in a rotaxane does not influence the amplitude and time scale of the small-amplitude fluctuations of the hydrogen bonds, but strongly slows down the complete dissociation of these hydrogen bonds. This is probably because in a rotaxane breaking of the macrocycle-axle contacts is severely hindered by the mechanical constraints. The hydrogen-bond dynamics in rotaxane-based molecular machines can therefore be regarded as liquidlike on a time scale 1 ps and less, but structurally frozen on longer (up to at least 200 ps) time scales.     

Dampened circumrotation by CH···π interactions in hydrogen bonded [2]rotaxanes

Establishment of CH···π interactions between the aliphatic axis and the benzylic amide macrocycle of hydrogen-bonded [2]rotaxanes causes a measurable interference in the pirouetting submolecular motion of these interlocked molecules.     

A global approach to automatic solution of jigsaw puzzles

We present a new algorithm for automatically solving jigsaw puzzles by shape alone. The algorithm can solve more difficult puzzles than could be solved before, without the use of backtracking or branch-and-bound. The algorithm can handle puzzles in which pieces border more than four neighbors, and puzzles with as many as 200 pieces. Our overall strategy follows that of previous algorithms but applies a number of new ideas, such as robust fiducial points, “highest-confidence-first” search, and frequent global reoptimization of partial solutions.     

Pushing Disks Together—The Continuous-Motion Case

If disks are moved so that each center—center distance does not increase, must the area of their union also be nonincreasing? We show that the answer is yes, assuming that there is a continuous motion such that each center—center distance is a nonincreasing function of time. This generalizes a previous result on unit disks. Our proof relies on a recent construction of Edelsbrunner and on new isoperimetric inequalities of independent interest. We go on to show analogous results for the intersection and for holes between disks. Received November 6, 1996, and in revised form June 16, 1997, and September 23, 1997.