Preparation and x-ray characterization of four new crystal forms of Jacalin, a lectin from Artocarpus integrifolia

Four new crystal forms of the anti-T lectin from jackfruit (Artocarpus integrifolia) have been prepared and characterized. Three of them, two monoclinic (P21, A = 59·4 Å, B = 83·3 Å, C = 63·5 Å, β = 107·7°; C2, A = 106·1,Å, B = 53·9 Å, C = 128·0 Å, β = 95·0 Å) and one orthorhombic (C2221, A = 98·1 Å, B = 67·3 Å, C = 95·1 Å) were grown with 2-methylpentan-2,4-diol (MPD) as the precipitant while the fourth, an hexagonal from (P6122, A = b = 129·6 Å, C = 157·9 Å), was obtained in the presence of methyl-ga-Image -galactopyranoside with polyethylene glycol 4000 as the precipitant. The reported relative molecular mass (Mr) of the lectin was found to be inconsistent with the solvent content of the crystals estimated using measured densities. The Mr was redetermined using size-exclusion chromatography in the presence of methyl-α-Image -galactopyranoside and Ferguson-plot analysis of mobilities in polyacrylamide gel electrophoresis. The redetermined Mr (66,000) is consistent with the measured crystal densities. The orthorhombic and the hexagonal forms, which have one half molecule and one molecule, respectively, in the asymmetric unit, are suitable for high-resolution X-ray analysis.

New Solid State Forms of the Anti-HIV Drug Efavirenz. Conformational Flexibility and High Z ` Issues

Structural information on the solid forms of efavirenz, a non-nucleoside reverse transcriptase inhibitor, is limited, although various polymorphic forms of this drug have been patented. We report here structural studies of four new crystal forms a pure form, a cyclohexane solvate, and cocrystals with 1,4-cyclohexanedione and 4,4'-bipyridine. Temperature dependent single-crystal to single-crystal phase transitions are observed for the pure form and for the cyclohexane solvate with an increase in the number of symmetry independent molecules, Z', upon a lowering of temperature. Other issues related to these solid forms, such as thermal stability, conformational flexibility, and high Z' occurrences, are addressed by using a combined experimental and computational approach.

Structures of new crystal forms of Mycobacterium tuberculosis peptidyl-tRNA hydrolase and functionally important plasticity of the molecule

The X-ray structures of new crystal forms of peptidyl-tRNA hydrolase from M.similar to tuberculosis reported here and the results of previous X-ray studies of the enzyme from different sources provide a picture of the functionally relevant plasticity of the protein molecule. The new X-ray results confirm the connection deduced previously between the closure of the lid at the peptide-binding site and the opening of the gate that separates the peptide-binding and tRNA-binding sites. The plasticity of the molecule indicated by X-ray structures is in general agreement with that deduced from the available solution NMR results. The correlation between the lid and the gate movements is not, however, observed in the NMR structure.

New solid forms of the anti-HIV drug etravirine: salts, cocrystals, and solubility

Thirteen new solid forms of etravirine were realized in the process of polymorph and cocrystal/salt screening to improve the solubility of this anti-HIV drug. One anhydrous form, five salts (hydrochloride, mesylate, sulfate, besylate, and tosylate), two cocrystals (with adipic acid and 1,3,5-benzenetricarboxylic acid), and five solvates (formic acid, acetic acid, acetonitrile, and 2:1 and 1:1 methanolates) were obtained. The conformational flexibility of etravirine suggests that it can adopt four different conformations, and among these, two are sterically favorable. However, in all 13 solid forms, the active pharmaceutical ingredient (API) was found to adopt just one conformation. Due to the poor aqueous solubility of the API, the solubilities of the salts and cocrystals were measured in a 50% ethanol water mixture at neutral pH. Compared to the salts, the cocrystals were found to be stable and showed an improvement in solubility with time. All the salts were dissociated within an hour, except the tosylate, which showed 50% phase transformation after 1 h of the slurry experiment. A structure property relationship was examined to analyze the solubility behavior of the solid forms.

New structural forms of a mycobacterial adenylyl cyclase Rv1625c

Rv1625c is one of 16 adenylyl cyclases encoded in the genome of Mycobacterium tuberculosis. In solution Rv1625c exists predominantly as a monomer, with a small amount of dimer. It has been shown previously that the monomer is active and the dimeric fraction is inactive. Both fractions of wild-type Rv1625c crystallized as head-to-head inactive domain-swapped dimers as opposed to the head-to-tail dimer seen in other functional adenylyl cyclases. About half of the molecule is involved in extensive domain swapping. The strain created by a serine residue located on a hinge loop and the crystallization condition might have led to this unusual domain swapping. The inactivity of the dimeric form of Rv1625c could be explained by the absence of the required catalytic site in the swapped dimer. A single mutant of the enzyme was also generated by changing a phenylalanine predicted to occur at the functional dimer interface to an arginine. This single mutant exists as a dimer in solution but crystallized as a monomer. Analysis of the structure showed that a salt bridge formed between a glutamate residue in the N-terminal segment and the mutated arginine residue hinders dimer formation by pulling the N-terminal region towards the dimer interface. Both structures reported here show a change in the dimerization-arm region which is involved in formation of the functional dimer. It is concluded that the dimerization arm along with other structural elements such as the N-terminal region and certain loops are vital for determining the oligomeric nature of the enzyme, which in turn dictates its activity.

Timing the Emergence of Resistance to Anti-HIV Drugs with Large Genetic Barriers

New antiretroviral drugs that offer large genetic barriers to resistance, such as the recently approved inhibitors of HIV-1 protease, tipranavir and darunavir, present promising weapons to avert the failure of current therapies for HIV infection. Optimal treatment strategies with the new drugs, however, are yet to be established. A key limitation is the poor understanding of the process by which HIV surmounts large genetic barriers to resistance. Extant models of HIV dynamics are predicated on the predominance of deterministic forces underlying the emergence of resistant genomes. In contrast, stochastic forces may dominate, especially when the genetic barrier is large, and delay the emergence of resistant genomes. We develop a mathematical model of HIV dynamics under the influence of an antiretroviral drug to predict the waiting time for the emergence of genomes that carry the requisite mutations to overcome the genetic barrier of the drug. We apply our model to describe the development of resistance to tipranavir in in vitro serial passage experiments. Model predictions of the times of emergence of different mutant genomes with increasing resistance to tipranavir are in quantitative agreement with experiments, indicating that our model captures the dynamics of the development of resistance to antiretroviral drugs accurately. Further, model predictions provide insights into the influence of underlying evolutionary processes such as recombination on the development of resistance, and suggest guidelines for drug design: drugs that offer large genetic barriers to resistance with resistance sites tightly localized on the viral genome and exhibiting positive epistatic interactions maximally inhibit the emergence of resistant genomes.

Y3-xBa3+xCu6O14+δ system: A new family of superconductors

Compounds of the Y3-x Ba3+x Cu6O14+δ system, which YBa2Cu3O7-δ (x = 1) is member, have been prepared. A relatively low temperature nitrate decomposition method gives almost single phase compounds with tetragonal structure. The phases are metastable and show superconducting transitions (zero-resistance) around 50K.

ABOUT FORMS OF ELECTRONIC AND IONIC DEVICES WITH THERMIONIC CATHODES.

The miniaturization of electronic and ionic devices with thermionic cathodes and thc improvement of their vacuum properties are questions of very great interest to the electronic engineer. However there have bcen no proposals so far to analyse the problem of miniaturization of such devices In a fundamental way. The present work suggests a choice of the geometrical shape of the cathode, the anode and the envelope of the device, that may help towards such a fundamcnlal approach.It is shown that a design, in which the cathode and the envelope of the tube are made of thm prismatic shape and the anode coincides with the cnvclope, offers a slriknrg advantage over the conventional cylindrical design, in respect of over-all size. The use of the prismatic shape will lead to considerable economy in msterials and may facilitate simpler prodoct~ont echn~ques. I n respect of the miin criteria of vacuum, namely the grade of vacuum, the internal volume occupied by residual gases, the evolution of gases in the internal space and the diffusion of gases from outside into the devicc, it is shown that the prismatic form is at least as good as, if not somewhat superior lo, the cylindrical form.In the actual construction of thin prismatic tubes, manv practical problems will arise, the most important being the mechanical strength and stablity of the structure. But the changeover from the conventional cylindrical to the new prirmaiic form, with its basic advantages, is a development that merits close attention.

A New Synthesis Of Dibenzo[Aj]Xanthene Derivatives

Oxidation of mu-H/alkylbisnaphthols (4a-g) gives the 14-substituted dibenzo[aj]xanthenes (5a-g) as the sole product while that of mu-arylbisnaphthols (4h-j) gives the xanthenes (5h-j) along with the corresponding spironaphthalenones (1h-j). A probable mechanism for the formation of the products has been suggested.

A New Class Of Photo-Cross-Linkable Side-Chain Liquid Crystalline Polymers Containing Bis(Benzylidene)Cyclohexanone Units

This paper reports a new class of photo-cross-linkable side chain liquid crystalline polymers (PSCLCPs) based on the bis(benzylidene)cyclohexanone unit, which functions as both a mesogen and a photoactive center. Polymers with the bis(benzylidene)cyclohexanone unit and varying spacer length have been synthesized. Copolymers of bis(benzylidene)cyclohexanone containing monomer and cholesterol benzoate containing monomer with different compositions have also been prepared. All these polymers have been structurally characterized by spectroscopic techniques. Thermal transitions were studied by DSC, and mesophases were identified by polarized light optical microscopy (POM). The intermediate compounds OH-x, the monomers SCLCM-x, and the corresponding polymers PSCLCP-x, which are essentially based on bis(benzylidene)cyclohexanone, all show a nematic mesophase. Transition temperatures were observed to decrease with increasing spacer length. The copolymers with varying compositions exhibit a cholesteric mesophase, and the transition temperatures increase with the cholesteric benzoate units in the copolymer. Photolysis of the low molecular weight liquid crystalline bis(benzylidene)-cyclohexanone compound reveals that there are two kinds of photoreactions in these systems: the EZ photoisomerization and 2 pi + 2 pi addition. The EZ photoisomerization in the LC phase disrupts the parallel stacking of the mesogens, resulting in the transition from the LC phase to the isotropic phase. The photoreaction involving the 2 pi + 2 pi addition of the bis(benzylidene)cyclohexanone units in the polymer results in the cross-linking of the chains. The liquid crystalline induced circular dichroism (LCICD) studies of the cholesterol benzoate copolymers revealed that the cholesteric supramolecular order remains even after the photo-cross-linking.

Preparation of lamellar and hexagonal forms of mesoporous silica and zirconiaby the neutral amine route: lamellar-hexagonal transformation in the solid state

The chain length of the surfactant and the solvent composition are two of the factors that determine whether the lamellar or the hexagonal form of mesoporous SiO2 (or ZrO2) is formed by the neutral amine route; a lamellar-hexagonal transformation occurs on removal of the amine from the former.

Novel Functionalised Troger's Bases: Synthesis of a New Class of Troger's Base Analogues Containing Dicarboxyl Functionality

The synthesis of three new Troger's base analogues, each functionalized with two carboxyl groups, is described. Copyright.

Detection of the protein dimers, multiple monomeric states and hydrated forms of Plasmodium falciparum triosephosphate isomerase in the gas phase

Dimeric and monomeric forms of the enzyme triosephosphate isomerase (TIM) from Plasmodium falciparum (Pf) have been detected under conditions of nanoflow by electrospray mass spectrometry. The dimer (M = 55 663 Da) exhibits a narrow charge state distribution with intense peaks limited to values of 18(+) to 21(+), maximal intensity being observed for charge states 19(+) and 20(+). A monomeric species with a charge state distribution ranging from 11(+) to 16(+) is also observed, which may be assigned to folded dissociated subunits. Complete dimer dissociation results under normal electrospray condition. The effects of solution pH and source temperature have been investigated. The observation of four distinct charge state distributions which may be assigned to a dimer, folded monomer, partially folded monomer and unfolded monomer is reported. Circular dichromism and fluorescence studies of Pf TIM at low pH support the retention of substantial secondary and tertiary structures. Satellite peaks in mass spectra corresponding to hydrated species are also observed and isotope shift upon deuteration is demonstrated. The analysis of all available independent crystal structures of Pf TIM and TIMs from other organisms permits identification of structurally conserved water molecules. Hydration observed in the dimer and folded monomeric forms in the gas phase may correspond to these conserved sites.

Conformational flexibility in androgenic steroids - the structure of a new form of (+)-17-beta-hydroxy-19-nor-4-androsten-3-one (19-nortestosterone), c18h26o2

The structure and conformation of a second crystalline modification of 19-nortestosterone has been determined by X-ray methods. M r = 274, monoclinic P2 l, a=9.755(2), b= 11.467(3), c= 14.196(3)/L fl=101.07(2) ° , V=1558.4 (8) A 3, Z=4, Ox= I. 168 g cm -3, Mo Ka, 2 = 0.7107 ,/k, ~ = 0.80 cm -l, F(000) = 600, T= 300 K. R = 0.060 for 2158 observed reflections. The two molecules in the asymmetric unit show significant differences in the A-ring conformation from that of the previously reported form of the title compound [Precigoux, Busetta, Courseille & Hospital (1975). Acta Cryst. B31, 1527-1532]. The l a,2fl-half-chair conformation of the A ring increases its conformational freedom compared with testosterone.

Anthranilate Hydroxylase from Aspergillus niger: New Type of NADPH-Linked Nonheme Iron Monooxygenase

Anthranilate hydroxylase from Aspergillus niger catalyzes the oxidative deamination and dihydroxylation of anthranilic acid to 2,3-dihydroxybenzoic acid. This enzyme has been purified to homogeneity and has a molecular weight of 89,000. The enzyme is composed of two subunits of 42,000 with 2 gram-atoms of nonheme iron per mol. Fe2+-chelators like alpha,alpha'-dipyridyl and o-phenanthroline are potent inhibitors of the enzyme activity. Absorption and fluorescence spectra of the enzyme offer no evidence for the presence of other cofactors like flavin. Flavins and flavin-specific inhibitors like atebrin have no effect on the activity of the enzyme. The enzyme incorporates one atom of oxygen each from 18O2 and H218O into the product 2,3-dihydroxybenzoic acid. Based on these studies, it is concluded that anthranilate hydroxylase from A. niger is a new type of NADPH-linked nonheme iron monooxygenase.