"One-pot" methylation of N-Nosyl-alpha-amino acid methyl esters with diazomethane and their coupling to prepare N-methyl dipeptides

N-Nosyl-alpha-amino acid methyl esters are methylated quantitatively with diazomethane. After proper deprotection of the amino function by treatment with the reagent system mercaptoacetic acid/sodium methoxide, the obtained N-methyl amino acid methyl esters are coupled with N-Fmoc amino acid chlorides to afford the corresponding dipeptides. The obtained products do not show any detectable extent of racemization by (1)H NMR and HPLC.     

Limits to Perception by Quantum Monitoring with Finite Efficiency

We formulate limits to perception under continuous quantum measurements by comparing the quantum states assigned by agents that have partial access to measurement outcomes. To this end, we provide bounds on the trace distance and the relative entropy between the assigned state and the actual state of the system. These bounds are expressed solely in terms of the purity and von Neumann entropy of the state assigned by the agent, and are shown to characterize how an agent’s perception of the system is altered by access to additional information. We apply our results to Gaussian states and to the dynamics of a system embedded in an environment illustrated on a quantum Ising chain.     

Copolymerization of styrene with (Z)-1,3-pentadiene in the presence of a syndiotactic-specific catalyst

Copolymerization of styrene with (Z)-1,3-pentadiene affords copolymers mostly containing 1,2 pentadiene units. Both the styrene and the pentadiene units are in syndiotactic arrangement but the comonomer sequence distribution is far from bernoullian. Interestingly, the behavior of (Z)-1,3-pentadiene does not change much when polymerization temperature raises from −20 to +20°C, notwithstanding that (Z)-1,3-pentadiene affords a 1,2-syndiotactic homopolymer at −20°C but a prevailingly 1,4 cis homopolymer at +20°C. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2697–2702, 1997     

Linear response and quasiparticle calculations as probes of the Kohn-Sham eigenvalues in metals

The Kohn-Sham eigenvalues were formally introduced into density functional theory as Lagrange multipliers in the implementation of the minimum principle for the total energy of a many-electron system. No general results are available concerning the physical significance of these one-electron eigenvalues (with the exception of the highest occupied level, which equals the Fermi energy). Recent ab initio calculations of dynamical response in metals make explicit use of the Kohn-Sham band structure, and associated wave functions, through the use of spectral representations. This opens up the possibility of examining the significance of the eigenvalues at an “empirical” level, i.e., through direct comparison with the results of spectroscopic measurements. A particularly interesting example is afforded by new inelastic x-ray scattering experiments on A1. For a special wave vector transfer, q_o ≈︂ 1.5k_F, the measured spectrum provides a direct mapping of the Kohn-Sham noninteracting spectrum. For a range of wave vectors about q_o, the bare Kohn-Sham spectrum still reproduces all the main features of the measurements; this suggests that, in this metal, the Kohn-Sham eigenvalues are good approximations to the quasiparticle energies. We also discuss the interplay between Kohn-Sham bands and the energy of the “anomalous” plasmon in Cs, whose dispersion bears a signature of the excited-state band structure. Finally, and in a more formal framework, we outline the results of a first-principles comparison between quasiparticle amplitudes and Kohn-Sham wave functions at a jellium surface; the latter turn out to be excellent approximations to the former. © 1996 John Wiley & Sons, Inc.     

Highly Conducting Polyaniline Gels

An improved method, based on mechanical stirring and a controlled solvent evaporation process, is proposed to obtain PANI(CSA)_0.5/m‐cresol solutions, which lead to gels with conductivities in the range 3 to 150 S/cm, preserving the elasticity associated to the gel network. Such high conductivity values have only been found for brittle films cast from PANI solutions. According to our experimental results, there is no justification for an analogy between the elastic modulus and the conductivity of physical networks.     

N‐(2‐Amino‐1,6‐di­hydro‐5‐nitro­so‐6‐oxopyrimidin‐4‐yl)‐l‐isoleucine–water (4/1): interplay of molecular and supramolecular structures

In the title compound, 2C₁₀H₁₅N₅O₄·0.5H₂O, there are two independent mol­ecules of the pyrimidinyl­isoleucine in general positions and a water mol­ecule lying on a twofold rotation axis. The bond lengths within the organic moieties demonstrate significant polarization of the electronic structure. Each of the organic mol­ecules participates in 12 intermolecular hydrogen bonds, of O—H?O and N—H?O types, while the water mol­ecule acts as a double donor and as a double acceptor of O—H?O hydrogen bonds. The organic components are linked by the hydrogen bonds into a single three‐dimensional framework, reinforced by the water mol­ecules.     

4-(4-Chlorophenyl)-3,7,7-trimethyl-1-[2-(4-nitrobenzoyl)ethyl]-4,7,8,9-tetrahydro-1H-pyrazolo[3,4-b]quinolin-5(6H)-one–ethanol (1/1)

Molecules of the title compound, C₂₈H₂₇ClN₄O₄·C₂H₆O, form a C(6) chain via an N—H⋯O hydrogen bond along the c axis by the operation of a c-glide plane, with N⋯O = 2.761 (3) Å and N—H⋯O = 165°. The mol­ecules are further linked by a weak C—H⋯O interaction, with C⋯O = 3.344 (4) Å and C—H⋯O = 150°. Pendant hydrogen-bonded ethanol solvent mol­ecules are attached to the chains by O—H⋯N hydrogen bonds, with O⋯N = 2.904 (3) Å and O—H⋯N = 175°.     

Variable selection in discriminant analysis based on the location model for mixed variables

Non-parametric smoothing of the location model is a potential basis for discriminating between groups of objects using mixtures of continuous and categorical variables simultaneously. However, it may lead to unreliable estimates of parameters when too many variables are involved. This paper proposes a method for performing variable selection on the basis of distance between groups as measured by smoothed Kullback–Leibler divergence. Searching strategies using forward, backward and stepwise selections are outlined, and corresponding stopping rules derived from asymptotic distributional results are proposed. Results from a Monte Carlo study demonstrate the feasibility of the method. Examples on real data show that the method is generally competitive with, and sometimes is better than, other existing classification methods.     

Reaction of 4,5-diamino-1,6-dihydropyrimidin-6-ones with two equivalents of chalcones

The reaction of 4,5-diamino-1,6-dihydropyrimidin-6-ones 1 with two equivalents of the chalcones 2 leads in an acidic medium to the formation of the 2,3,6,7-tetrahydro-1H-pyrimido[4,5-b][1,4]diazepin-6-one derivatives 3a-d . The structure elucidation of the products is based on nmr measurements and an X-ray diffraction.