Increase of both order and disorder in the first hydration shell with increasing solute polarity

Monte?Carlo simulations of a small model solute in an aqueous solution are used to examine the effects of solute polarity on hydration structure. A judicious definition of the orientational order parameter leads to reinterpretation of the conventional picture of hydration. As the solute varies from hydrophobic to hydrophilic the ordered first shell water simultaneously fractionates into a more highly ordered and a more disordered component. The hydrogen-bond network rearranges such that the more ordered component relaxes to configurations of optimal intermolecular angles, the other fraction being released from the network.     

A Note on a Matrix Version of the Farkas Lemma

A linear polyomial non-negative on the non-negativity domain of finitely many linear polynomials can be expressed as their non-negative linear combination. Recently, under several additional assumptions, Helton, Klep, and McCullough extended this result to matrix polynomials. The aim of this article is to study which of these additional assumptions are really necessary.     

Haloalkane dehalogenase catalysed desymmetrisation and tandem kinetic resolution for the preparation of chiral haloalcohols

Six different bacterial haloalkane dehalogenases were recombinantly produced in Escherichia coli, purified, and used to catalyse the conversion of prochiral short-chain dihaloalkanes and a meso dihaloalkane, yielding enantioenriched haloalcohols. A two-reaction one-enzyme process was established in which the desymmetrisation of a dihaloalkane is followed by kinetic resolution of the chiral haloalcohol that is produced in the first step. In case of 1,3-dibromo-2-methylpropane and 1,3-dibromo-2-phenylpropane, an increase of the enantiomeric excess of the respective haloalcohol was observed in time, leading to ee values of >97%, with analytical yields of 24 and 52%, respectively. The results show that haloalkane dehalogenases can be used for the production of highly enantioenriched haloalcohols and that in some cases product enantiopurity can be improved by allowing a two-step one-enzyme tandem reaction.     

Hydrolysis and Solvolysis of Methyltriethoxysilane Catalyzed with HCl or Trifluoroacetic Acid: IR Spectroscopic and Surface Energy Studies

The aim of this study was, at first, to re-consider the IR spectra of methyltriethoxysilane (MTEOS) catalysed with HCl (hydrolysis) and to compare them with IR spectra of MTEOS catalysed with trifluoroacetic acid (TFAcOH). TFAcOH as a strong carboxylic acid performs non-hydrolytic sol-gel process based on the condensation between the alkoxide and the acid function, liberating ester molecules (solvolysis). We assessed from the time-dependent IR attenuated reflection spectroscopic (IR ATR) measurements the solvolysis and hydrolysis reactions, formation of the oligomeric species and final condensation products. Additional evidence for the formation of these species was obtained from the spectra of films dip-coated from sols aged to different extent. The results of the IR spectral analysis showed that the structure of both xerogels consisted of irregular T_n (n = 8, 10, 12) cube-like species bridged via the ladder-like oligomers (in the case of MTEOS/TFAcOH) and open-chain trisiloxane species (for MTEOS/HCl). ²⁹Si NMR spectra of MTEOS/TFAcOH showed only signals of T³ while MTEOS/HCl spectra showed beside T³ also T² signals, in agreement with IR spectra results. From the XRD peaks at low Bragg angles (∼ 9–10°) we inferred that both xerogels consisted of nanocrystalline CH₃-SiO_3/2 species. In addition, the surface energy values of the films deposited from the corresponding sols were measured and the dispersive and polar portions correlated with the spectral features noted in the films.     

Characterization of incipient cavitation in axial valve by hydrophone and visualization

As the effects of cavitation in valves are devastating, the choice of the correct valve for a given operating range is crucial. For this, the valve characteristic is needed, whereby one side of the operating range depends on the determination of the incipient cavitation.In this paper, the visualization method for incipient cavitation detection is presented. For the purpose of comparison, pressure oscillations inside the pipeline were simultaneously measured with a hydrophone. The effect of operating pressure was studied for two different openings of the valve.For each operating point of incipient cavitation, corresponding points were measured for developed cavitation and no-cavitation state, based on a constant-portion change of volumetric flow rate with regard to the incipient cavitation volumetric flow rate. The visualization and hydrophone signals were compared.The visualization method proved efficiency over hydrophone measurements because it is more sensitive to cavitation and the signal is independent of the operating pressure. The main drawback is the preparation of the observation window.     

Effect of bioengineering lacticin 3147 lanthionine bridges on specific activity and resistance to heat and proteases

Lacticin 3147 is a lantibiotic with seven lanthionine bridges across its two component peptides, Ltnα and Ltnβ. Although it has been proposed that the eponymous lanthionine and (β-methyl)lanthionine (Lan and meLan) bridges present in lantibiotics make an important contribution to protecting the peptides from thermal or proteolytic degradation, few studies have investigated this link. We have generated a bank of bioengineered derivatives of lacticin 3147, in which selected bridges were removed or converted between Lan and meLan, which were exposed to high temperature or proteolytic enzymes. Although switching Lan and meLan bridges has variable consequences, it was consistently observed that an intact N-terminal lanthionine bridge (Ring A) confers Ltnα with enhanced resistance to thermal and proteolytic degradation.     

The total synthesis of (±)-colorata-4(13), 8-dienolide

The total synthesis of (±)-colorata-4(13),8-dienolide ($\text{1}$), a sesquiterpene with a rearranged drimane skieleton, is described using 6β, 8aβ-dimethyl-5-methylene-3,4,4aα, 5,6,7,8,8a-octahydro-1(2H)-naphtalenone ($\text{10}$) as a key intermediate. A new annelation method for butenolides via hydrolysis of a thiohenyl furan is reported.