Structures of three substituted pentacyclo[5.4.0.02, 6.03, 10.05, 9]undecanes and a computational analysis of bond lengths

5-Methyl-2-phenylpentacyclo[5.4.0.0^{2, 6}.0^{3, 10}.0^{5, 9}]undecane-8, 11-dione,5-methyl-2-phenylpentacyclo [5.4.0.0^2,6.0^3,10.0^5,9]undecane-8-one-11-ol,and 5-methyl-2-phenylpentacyclo[5.4.0.0^2,6.0^3,10.0^5,9]undecane-8,11-diol are three cage compounds which differ only in the oxidation state at C(8) and C(11). The three compounds contain a four-membered, a six-membered, and four five-membered rings fused into a cagelike structure. An X-ray structure analysis shows the C(1)-C(7) and C(9)-C(10) bonds in the diketo cage to be 1.606(2) and 1.586(2) Å, which are significantly longer than in the other two molecules. In order to assess the effects of strain, steric, and electronic factors in these compounds, we investigated the unsubstituted parent cage compounds and a series of derivatives by molecular mechanics (MM3), AMPAC (AM1), MOPAC (PM3), and GAUSSIAN 90 calculations. These data suggest that dipolar through space interactions are responsible for the bond elongation and not a _– ^* interaction, which has been postulated in parallel-systems originating from a common bond. A small degree of _– ^* through-bond interaction may contribute to the lengthening in the dimethylene cage analogues.     

Picosecond time-resolved cars in isotopically mixed crystals of benzene

Time-resolved coherent anti-Stokes Raman experiments are reported for the benzene crystal 991 cm^?1 mode and in mixed C₆H₆/C ₆D₆ crystals. Addition of C₆D₆ results in an increase in the rate at which the excitation is trapped. This is explained by the recent theory of Velsko and Hochstrasser which predicts that the trapping rate should undergo a maximum at some isotopic impurity concentration, consistent with observations from time and frequency domain studies. A proper convolution procedure for CARS experiments in the time domain is presented.     

Preparation and photocrosslinking behaviors of polyesters derived from trans-2,2′-dihydroxystilbene

The monomer, trans-2,2′-dihydroxystilbene (DHS), has been prepared by asymmetric photocleavage (254 nm) of coumarin dimer acid derived from coumarin dimer. Four new polyesters are successfully synthesized by interfacial polycondensation of the DHS with adipoyl chloride, azelaoyl chloride, sebacoyl chloride, and dodecanedioyl dichloride, respectively. The reduced viscosities of the polyesters decrease from 0.32 to 0.11 dL/g as the number of methylene unit in diacid chlorides increases from 4 to 10. From DSC investigation, it is found that the polyesters are semi-crystalline polymers with T_m = 39–192°C. Under 350 nm light, photocrosslinking behavior in solution and film-state is investigated by UV spectral change with irradiation time (350 nm). The photoreactive stilbene chromophores in the main chain dimerize to form cyclobutane derivatives, and lead to crosslinking of the polyesters. Photosensitivity in the film state has also been evaluated by their characteristic curves. Polyester from dodecanedioyl dichloride ( 5d ) exhibits the highest initial reaction rate and ultimate crosslinking ratio. © 1995 John Wiley & Sons, Inc.     

A Straightforward Synthesis of Polythiophene-fused-3-sulfolenes from Methyl 3-Hydroxy-4,6-dihydrothieno[3,4-b]thiophene-2-carboxylate

A straightforward synthesis of substituted polythiophene-fused-3-sulfolenes from the readily prepared methyl 3-hydroxy-4,6-dihydrothieno[3,4-b]thiophene-2-carboxylate will be presented. Upon thermolysis in the presence of N-phenylmaleimide, these new substrates serve as precursors of reactive polythiophene o-quinodimethanes to give the corresponding Diels-Alder adducts in high yields.     

Remarks on the Convergence Rate of the Spectral Distributions of Wigner Matrices

In this remark, we show that under the assumption of the finite fourth moment elements in the empirical spectral distribution of a large Wigner matrix converges to the Wigner semicircular law in probability of the order O(n ^–1/3).     

Transient conjugated mixed-convective heat transfer in a vertical plate channel with one wall heated discretely

 This study presents a numerical solution of the unsteady conjugated mixed-convection heat transfer in a vertical plate channel with one wall suddenly subjected to either isoflux or isothermal discrete heat sources. The effects of the dimensionless heat source length H ₁, the dimensionless spacing between heat sources H ₂, the dimensionless channel length L, the dimensionless heated-plate thickness B _l, the wall-to-fluid conductivity ratio K and the ratio of Grashof number to Reynolds number Gr/Re on the interface heat flux, Nusselt number and bulk fluid temperature are discussed in detail. Results show that the discrete heating can cause the heat transfer direction conversely from the fluid to the heated plate during the transient period, which is more significant for the cases with larger L and H ₂. For the system with isoflux discrete heat sources, the time required to reach the steady-state is shorter for larger H ₂. While the trend is reverse for system with isothermal discrete heat sources. Additionally, a higher ratio of the input energy is axially conducted through the plate wall from heated sections to unheated regions for a larger H ₂ and B _l or smaller L. Received on 9 November 1998     

Circular Dichroism Measurements on C-Terminal Fragment of Heat Shock Protein from Rat

The secondary structure of the C-terminal fragment (10 kDa) of rat hsc70 (a. a. #546–646) was analyzed according to circular dichroism spectra. In the pH range 5–9 and at concentrations of Na+ up to 0.18 M, the protein is estimated to contain 32-34% a helix, 18–16% of β sheet, approximately 25% for both turns and disordered structures. This protein is most stable at pH between 6 and 7 in solution with 0.055 M Na⁺ concentration. However, all T_m are relatively large (57–73 °C) and alterations from one condition to another are small. Thus, the C-fragment (10 kDa) of hsc70 is a stably folded protein under physiological conditions.     

Photochemical Activities of N‐Nitroso Carboxamides and Sulfoximides and Their Application to DNA Cleavage

N‐Nitroso compounds containing benzene, fluorene or fluorenone rings were synthesized. Photolysis of these compounds with 312‐nm UV light provided the NO ^. species, the presence of which was corroborated by use of an EPR method and of 2‐phenyl‐4,4,5,5‐tetramethylimidazolin‐1‐oxyl 3‐oxide (PTIO) as a trapping agent. During irradiation of N‐methyl‐N‐nitroso‐9‐fluorenone carboxamide ( 14 c ) in the absence of PTIO, it underwent decomposition followed by recombination to give the heterocyclic nitric oxide radical 15 . Incorporation of intercalating moieties endowed the N‐nitroso compounds with DNA‐cleaving ability through single‐strand scission upon UV irradiation in a phosphate buffer (pH 5.0–8.0) under aerobic conditions.