Fourth generation CP violation effects on B-->Kpi, phiK, and rhoK in next-to-leading-order perturbative QCD

We study the effect from a sequential fourth generation quark on penguin-dominated two-body nonleptonic B meson decays in the next-to-leading order perturbative QCD formalism. With an enhancement of the color-suppressed tree amplitude and possibility of a new CP phase in the electroweak penguin amplitude, we can account better for A(CP)(B(0)-->K+ pi-)-A(CP)(B+-->K+ pi0). Taking |V(t's)V(t'b)| approximately 0.02 with a phase just below 90 degrees, which is consistent with the b-->sl+ l- rate and the B(s) mixing parameter Deltam(B)(s), we find a downward shift in the mixing-induced CP asymmetries of B(0)-->K(S)(pi 0) and phi(K)(S). The predicted behavior for B(0)-->rho(0)(K)(S) is opposite.     

Observable azacyclobutenone ylides with antiaromatic character from 2-diazoacetyl-azaaromatics

Azacyclobutenone ylides 2 and 11 were generated in solution by laser flash photolysis of 2-diazoacetylpyridine (1) and 3-diazoacetylpyridazine (10), respectively, together with the corresponding ketenes. The ylides were identified by their characteristic IR and UV spectra: 2, nu (CH3CN) 1725 cm(-1), lambdamax 360 and 550 (br) nm; 11, nu (CH3CN) 1776 cm(-1), lambdamax 370 and 550 (br) nm. 2-Triisopropylsilyldiazoacetylpyridine 20 upon photolysis at 5 degrees C in CH3CN forms the ylide 21 as a rather persistent (T1/2 2 h at 25 degrees C) purple solution, nu (CH3CN) 1718 cm(-1), lambdamax 245, 378 and 546 (br) nm, but no ketene is observed. Quinolyl ylide 14 and pyridyl ylides 17 and 19 with Me and 2-pyridyl substituents, respectively, with characteristic IR and UV spectra were also generated. The 1H NMR spectrum of the pyridyl ring of 21 shows substantial upfield shifts relative to those of 20. Calculated nucleus-independent chemical shifts (NICS) for 2, 11, and 21 are comparable to those for benzocyclobutadiene (22) and benzocyclobutenone enolate (23), with substantial positive values for the 4-membered rings, while the NICS values for the 6-membered rings are significantly more positive than for benzene or pyridine. Significant bond alternation is also found in the calculated ylide structures, and these results suggest strong antiaromatic character for the 4-membered rings of 2, 11, 14, 17, 19, and 21, and greatly reduced aromatic character for the 6-membered rings.     

Modulation of optical properties of dissolved humic substances by their molecular complexity

In this study, we show that several UV-Vis absorbance, steady-state and time-resolved fluorescence parameters of a series of dissolved humic substances (DHS) from different sources (e.g. terrestrial fulvic and humic acids, and humic acid-like molecules extracted from composted and vermicomposted wastes) correlate with the molar absorptivity at 280 nm per mole of organic carbon (ε(280)), which in turn is proportional to the molecular complexity (e.g. molecular size, aromaticity and oxidation degree) of the DHS. Both absorbance and fluorescence spectral responses were sensitive to the molecular complexity associated with the maturation degree of the DHS. Depending on the DHS, different emitting responses by excitation at the UVA (340 nm) and VIS (460 nm) regions of the absorption spectra were observed. The results were explained in terms of the extent of intramolecular electronic interactions between electron donor groups, such as polyhydroxylated aromatics and indoles, and more oxidized acceptor groups (e.g. quinones or other oxidized aromatics) as the molecular complexity of the DHS increased.     

Optimal conflict-avoiding codes of length <Emphasis Type="Italic">n</Emphasis> ≡ 0 (mod 16) and weight 3

A conflict-avoiding code of length n and weight k is defined as a set of binary vectors, called codewords, all of Hamming weight k such that the distance of arbitrary cyclic shifts of two distinct codewords in C is at least 2k−2. In this paper, we obtain direct constructions for optimal conflict-avoiding codes of length n = 16m and weight 3 for any m by utilizing Skolem type sequences. We also show that for the case n = 16m + 8 Skolem type sequences can give more concise constructions than the ones obtained earlier by Jimbo et al.      

Fourier Transform Infrared Study of the Dissolution Mechanism of Poly(methyl methacrylate) in CO2‐Expanded Ethanol

Both CO ₂ and ethanol are nonsolvents for poly(methyl methacrylate) (PMMA) at 303 K, but PMMA dissolves in CO₂‐expanded ethanol (red spectrum, see figure). The dissolution process consists of swelling of the PMMA by the CO₂, which allows the ethanol to penetrate the PMMA and interact with the polymer through carbonyl–hydroxyl hydrogen bonds to separate the polymer chains.