Questions and answers

The aim of this paper is twofold. First, we shall derive the Fermi-Dirac (FD) and Bose-Einstein (BE) distributions from the classical Maxwell-Boltzmann (MB) distribution by introducing into the classical system the consequences of quantum mechanical indistinguishability in a direct and simple manner. Next, we go through a brief introduction to feedback systems and see how the FD and BE systems may be viewed as classical systems with appropriate feedback. We shall see that the resemblance to feedback systems is more than formal and that a feedback mechanism does exist in systems obeying quantum statistical mechanics.     

Practical synthesis of a dithiane-protected 3',5'-dialkoxybenzoin photolabile safety-catch linker for solid-phase organic synthesis.

The solution-phase preparation of the 3',5'-dialkoxybenzoin photolabile safety-catch linker 16 is described. Pivotal to this convenient synthesis is the selection of appropriate orthogonal protecting groups for the alkoxy functionalities present. The new linker can be readily loaded onto any standard amine-terminating resin under peptide-coupling conditions, without the need to protect the secondary alcohol functionality, and subsequently loaded with substrate. Alternatively, the loading efficiency of sterically hindered substrates can be enhanced by preloading the semiprotected linker variant 10 in solution prior to immobilization onto the resin. This second generation of benzoin photolabile safety-catch linkers provides greater control of both linker loading and resin attachment and should prove to be a more versatile and convenient form of the linker.     

Multidimensional free-energy calculations using the weighted histogram analysis method

The recently formulated weighted histogram analysis method (WHAM)¹ is an extension of Ferrenberg and Swendsen's multiple histogram technique for free-energy and potential of mean force calculations. As an illustration of the method, we have calculated the two-dimensional potential of mean force surface of the dihedrals gamma and chi in deoxyadenosine with Monte Carlo simulations using the all-atom and united-atom representation of the AMBER force fields. This also demonstrates one of the major advantages of WHAM over umbrella sampling techniques. The method also provides an analysis of the statistical accuracy of the potential of mean force as well as a guide to the most efficient use of additional simulations to minimize errors. © 1995 John Wiley & Sons, Inc.     

Synthesis of tetrazole analogues of amino acids using Fmoc chemistry: isolation of amino free tetrazoles and their incorporation into peptides

An efficient synthesis of tetrazole analogues of amino acids starting from N^α-Fmoc amino acid in a three-step protocol is reported. The free amino tetrazoles were obtained in good yields and with excellent purity after removal of the Fmoc group. The synthesis of analogues of aspartic and glutamic acids in which the 5-tetrazolyl moiety is inserted at the β/γ carboxyl group starting from Fmoc-Asn and Fmoc-Gln and the incorporation of these tetrazoles into peptides are also described.     

Phase behaviour of the discotic mesogen 2,3,6,7,10,11-hexahexylthiotriphenylene (HHTT) under hydrostatic pressure

The phase behaviour of the discotic mesogen 2,3,6,7,10,11-hexahexylthiotriphenylene (HHTT) was investigated under hydrostatic pressures up to 500 MPa using high pressure optical and DTA measurements. The known enantiotropic phase transitions of HHTT, i.e. crystal (Cr)-helical phase (H), H-hexagonal columnar phase (Col_h) and Col_h-isotropic liquid (I) were observed up to 32 MPa. Application of hydrostatic pressures above 32 MPa results in the H and Col_h phases becoming monotropic, depending upon the applied pressure. The H phase was observed as a monotropic phase in the pressure region between 32 and about 180 MPa. Thus, the I →Col_h →H →Cr transition sequence appeared only on cooling under these pressures, while the Cr →Col_h →I transition occurred on heating. Further increases in pressure above a second limiting value leads to the Col_h phase becoming monotropic. Thus the I →Col_h →Cr transition sequence appeared on cooling, while the Cr →I transition was observed on heating. The T vs. P phase diagram based on the data obtained in the heating mode contains two triple points; one is estimated as 40 MPa, 77.2°C for the Cr-H-Col_h triple point and the other is extrapolated as 285 MPa, 118.3°C for the Cr-Col_h-I triple point. These triple points define the upper limits for the appearance of the stable H and Col_h phases, respectively.     

Cp*RhIII-Catalyzed Sterically Controlled C(sp3)−H Selective Mono- and Diarylation of 8-Methylquinolines with Organoborons**

Herein, the Rh^III-catalyzed selective monoarylation and diarylation (symmetrical and unsymmetrical) of 8-methylquinolines with organoboron reagents are disclosed. The selective monoarylation of primary C(sp³)−H bonds is achieved by using 7-substituted 8-methylquinolines or by changing the quantity of the aryl boronic acids. The method is also applicable for the arylation of 2-ethylpyridines, and the heteroarylation with thiophene-2-ylboronic acids. Symmetrical and unsymmetrical diarylation of 8-methylquinolines have been carried out in one-pot and sequential manner, respectively. Late-stage monoarylation of oxime derivatives and gram-scale synthesis of monoarylated products has also been carried out. A mechanistic study revealed that the current reaction is first order with respect to both reactants and a five-membered rhodacycle intermediate may be involved in the catalytic cycle.     

Multifunctional silk fibroin/PVA bio-nanocomposite films containing TEMPO-oxidized bacterial cellulose nanofibers and silver nanoparticles

Cellulose - Silk fibroin (SF) has been intensively studied as a biobased renewable material for biomedical and other applications. However, its relatively low mechanical properties have limited its...     

A Tachyonic Scalar Field with Mutually Interacting Components

We investigate the tachyonic cosmological potential V(?) in two different cases of the quasi-exponential expansion of universe and discuss various forms of interaction between the two components—matter and the cosmological constant—of the tachyonic scalar field, which lead to the viable solutions of their respective energy densities. The distinction among the interaction forms is shown to appear in the O _m (x) diagnostic. Further, the role of the high- and low-redshift observations of the Hubble parameter is discussed to determine the proportionality constants and hence the correct form of matter–cosmological constant interaction.