Crystallization of Arthrobacter sp. strain 1C N-(1-D-carboxyethyl)-L-norvaline dehydrogenase and its complex with NAD+

The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres.     

Multiplicity structure of proton and kaon diffractive dissociation in 10 and 16 GeV/c K-p interactions

A new method to calculate diffractive mass spectra has been developed. It is applied to K^-p interactions at 10 and 16 GeV/c. Cross sections and mass spectra are given for the difractive dissociation processes p→(N+iπ) and K^-p→(K+iπ) for i = 1 to 5 and also summed over all multiplicities. In addition to the diffractive peak at low mass coming from low multiplicities, a long tail extending to high masses and high multiplicities has been found. The multiplicity structure of diffraction dissociation can be understood in the context of the two-step dynamical picture of Pokorsky and Van Hove.     

Study of proton dissociation into ΛK+ in 3-body final states at 10 and 16 GeV/c

Results are presented for p → (ΛK⁺) dissociation in the reactions K^?p → ΛK⁺K^? and and π^±p → ΛK⁺π^±at 10 and 16 GeV/c. The cross sections for the low-mass ΛK⁺ enhancement are compatible with the energy dependence σ ∝ p_lab^?0.3. The t′ spectra or the (ΛK⁺) threshold enhancement are exponential in shape. Its decay angular distribution reveals neither s-channel nor t-channel helicity conservation. The relative probabilities of the processes $\text{p}\text{→}\text{p, p}\text{→ (}\text{N}\text{π)}{}_{\mathrm{<mtext>I=</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{and p}\text{→ (Λ}\text{K}{}^{\mathrm{+}}\text{)}$ dissociation are in the ratios 100 : 10 : 0.2, independent of the nature of the incident particle.     

Spin and lifetime of the ω− hyperon

A total of 101 ω^? decays have been found in K^?p interactions at 10 and $\text{16 GeV}\text{c}$. The decay angular distribution has been fitted under the assumptions that the ω^? has spin either $\text{1}\text{2}\text{or}\text{3}\text{2}$. It has been found that the probability of isotropy (spin$\text{1}\text{2}\text{)}$ is less than one in a thousand, whereas the probability for spin $\text{3}\text{2}$ is about 70%. Thus, we exclude the spin $\text{1}\text{2}$ assignment. The lifetime of the ω^? is found to be (1.41_?0.24^+0.15) × 10^?10s, in agreement with our earlier result based on about $\text{1}\text{5}$ of the present sample.     

Strange particle production in three- and four-body final states of 16 GeV/cπ±p reactions

Three- and four-body final states with strange particles are studied in π⁺p and π^?p interactions at 16 GeV/c. We present cross sections and investigate their energy dependence. Production mechanism, resonance production and quantum number transfer are discussed. Strong Y¹(1385) production is found in the reaction π⁺p → ΛK⁺π⁺, while the corresponding π^?p reaction is dominated by production of K¹(890). In the $\text{NK}\text{K}\text{π}$ channels, the K and $\text{K}$ are produced mainly at the same vertex, i.e. non-strangeness exchange ΔS = 0 is dominant (about 75% of the cases), whereas in the ΛKππ channels, the Λ and K are more frequently produced at opposite vertices, i.e. |ΔS| = 1 exchange is important (about 60% of the cases). Results on the polarization of the lambdas produced in the π⁺p reactions are given.     

Determination of the α decay parameter of ω-

A determination of the decay α parameter of the omega^? → K^? λ decay mode on the basis of fifteen omega-events from K^?p interactions at 10 GeV/c yields the value $\text{αomega = -0.66}{}^{\mathrm{+36}}{}_{\mathrm{?0.30}}$.     

Intercalation of Toluidines into α-Zirconium Hydrogenphosphate

Intercalates of o-, m-, and p-toluidine into α-Zr(HPO₄)₂ · H₂O were prepared and characterized by powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. As follows from IR, toludine molecules are protonated in the interlayer space. Toluidine molecules are arranged in a bimolecular way in the intercalates containing more than 1.5 toluidine molecules per Zr atom. On the other hand, a monolayer of the toluidine molecules is supposed in the intercalates with less than one toluidine molecule per Zr atom.     

The free energy of a reaction coordinate at multiple constraints: a concise formulation

The free energy as a function of the reaction coordinate (rc) is the key quantity for the computation of equilibrium and kinetic quantities. When it is considered as the potential of mean force, the problem is the calculation of the mean force for given values of the rc. We reinvestigate the PMCF (potential of mean constraint force) method which applies a constraint to the rc to compute the mean force as the mean negative constraint force and a metric tensor correction. The latter allows for the constraint imposed to the rc and possible artefacts due to multiple constraints of other variables which for practical reasons are often used in numerical simulations. Two main results are obtained that are of theoretical and practical interest. First, the correction term is given a very concise and simple shape which facilitates its interpretation and evaluation. Secondly, a theorem describes various rcs and possible combinations with constraints that can be used without introducing any correction to the constraint force. The results facilitate the computation of free energy by molecular dynamics simulations.     

Study of the reactions K−p → K+K−Λ and K−p → ppΛ, at 10 and 16 GeV/c

The reactions (1) K^?p → K⁺K^?Λ and (2) $\text{K}{}^{\mathrm{?}}\text{p}\text{→}\text{p}\text{p}\text{Λ}$ have been studied on samples of 109 and 64 events, respectively, at 10 GeV/c and 125 and 69 events at 16 GeV/c, reasonably free from contaminations. The investigation of the first reaction uses also 84 events of the $\text{K}{}^0\text{K}{}^0\text{Λ}$ final state at 10 GeV/c. Analysis of the Van Hove plots indicates that the K⁺K^?Λ and $\text{p}\text{p}\text{Λ}$ final states are produced by two main mechanisms: (i) a ΔQ = 0 process, with a strong diffractive component near threshold, involving the dissociations p → K⁺Λ in reaction (1) and $\text{K}{}^{\mathrm{?}}\text{→}\text{p}\text{Λ}$ in reaction (2) and (ii) a ΔQ = 1 process involving hypercharge exchange, and producing K⁺K^? and $\text{p}\text{p}$ systems in reactions (1) and (2), respectively, recoiling off the Λ. With increasing energy, this hypercharge exchange process decreases slowly when K⁺K^? is produced, but fast where the production of $\text{p}\text{p}$, violating the Zweig rule, occurs.