Fluorescence studies on the interaction of hydrophobic ligands with Momordica charantia (bitter gourd) seed lectin

The interaction of Momordica charantia (bitter gourd) seed lectin (MCL) with several nucleic acid bases has been investigated by monitoring changes induced in the protein fluorescence by ligand binding. Values of the binding constant, K_a were obtained as 1.1 × 10⁴, 1.56 × 10⁴ and 2.2 × 10³ M^?1 for adenine, cytosine and uracil, respectively. In addition, binding of 8-anilinonaphthalene 1-sulfonate (ANS) with MCL was investigated by fluorescence spectroscopy. Interaction with MCL at low pH results in a large enhancement of the fluorescence intensity of ANS with a concomitant blue shift in the emission λ_max, whereas at neutral and basic pH changes in both fluorescence intensity and emission maximum were very small, clearly suggesting that the MCL–ANS interaction is stronger at lower pH values. When excited at 295 nm in the presence of ANS, the protein fluorescence decreased with a concomitant increase in the emission intensity of ANS, suggesting resonance energy transfer from the tryptophan residues of MCL to ANS. Gel filtration profiles of MCL at pH values 2.0 and 7.4 are similar indicating that the tetrameric nature of MCL is retained even at low pH. Addition of lactose or adenine to MCL–ANS mixture did not alter the change in ANS fluorescence suggesting that lactose, adenine and ANS bind to MCL at independent and non-interacting sites. These results are relevant to understanding the functional role of MCL in the parent tissue.     

Solvent Versatility of Immobilized Amylose and Cellulose-Based Chiral Stationary Phases in Enantioselective LC Separation and Monitoring of Bio-Catalyzed Resolutions of Acidic Drugs in Non-Standard Organic Solvents

The solvent versatility of Chiralpak IA (amylose tris(3,5-dimethylphenylcarbamate)), Chiralpak IB (cellulose tris(3,5-dimethylphenylcarbamate)) and Chiralpak IC (cellulose tris(3,5-dichlorophenylcarbamate)) immobilized onto silica gel, are investigated for the enantioselective separation of a set of acidic drugs in liquid chromatography. Non-standard LC organic solvents like dichloromethane, ethyl acetate, tetrahydrofuran, methyl-tert-butyl ether were used in mobile phase compositions and/or diluent agent for the analyte on all new columns. Furthermore, the enantioselective separations of the reported compounds were compared on both immobilized columns (Chiralpak IA and IB) and their conventionally coated versions (Chiralpak AD-H and Chiralcel OD-H, respectively), using a mixture of n-hexane/2-PrOH/TFA (80:20:0.1 v/v/v). The versatility of the immobilized Chiralpak IB in monitoring reactions performed in non-standard solvent was studied on a representative example consisting of the lipase-catalyzed enantioselective esterification of flurbiprofen with n-butanol in methyl-tert-butyl ether as organic solvent.     

Active learning for spectroscopic data regression

In this work, we introduce an active learning approach for the estimation of chemical concentrations from spectroscopic data. Its main objective is to opportunely collect training samples in such a way as to minimize the error of the regression process while minimizing the number of training samples used, and thus to reduce the costs related to training sample collection. In particular, we propose two different active learning strategies developed for regression approaches based on partial least squares regression, ridge regression, kernel ridge regression, and support vector regression. The first strategy uses a pool of regressors in order to select the samples with the greatest disagreements among the different regressors of the pool, while the second one is based on adding samples that are distant from the current training samples in the feature space. For support vector regression, a specific strategy based on the selection of the samples distant from the support vectors is proposed. Experimental results on three different real data sets are reported and discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Microscopical study of the formation of adiabatic shear bands in 4340 steel during dynamic loading

In this study, optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and electron probe microanalyser were used to analyse the changes in microstructure of AISI 4340 steel specimens caused by impact at high strain rates and large strains. The structures of the steel prior to dynamic deformation and after dynamic deformation were examined to understand on a microscale level, the mechanism of formation of adiabatic shear bands (ASBs). The study also includes the structural changes that occur during post-deformation annealing processes which may relate to understanding of the mechanism of formation of ASBs. Prior to deformation, the tempered steel specimens consisted of lenticular laths of α-ferrite with precipitated platelet and spherical M₃C carbides. After impact, the structure inside the shear band was characterized by refined and recrystallized grains immersed in dense dislocation structures. In addition, residual carbide particles were observed inside the shear bands due to deformation induced carbide dissolution. Regions away from the shear bands developed ‘knitted’ dislocation walls, evolving gradually into sub-boundaries and highly misoriented grain boundaries at increasing strains, leading to grain refinement of the ferrite. After impact, annealing the shear bands at 350?°C resulted in an increase in hardness regardless of the heat treatment before impact, amount of deformation and the time of annealing. This is because of the occurrence of extensive reprecipitation of dissolved carbides that existed in the steel structure prior to deformation. It is concluded that dynamic recovery/recrystallization, development of dislocation structures and carbide dissolution all contribute simultaneously to the formation of ASBs in quench-hardened steels.     

Scorpion digestive lipase: kinetic study using monomolecular film technique

Using the classical emulsified system and the monomolecular film technique, we compared the interfacial properties of the scorpion digestive lipase (SDL) with those of higher animals'. In the absence of bile slats, SDL does not hydrolyse efficiently pure tributyrin, as well as dicaprin films maintained at low surface pressure. The preincubation of bile salts with tributyrin seems to be a better substrate for SDL than the pure tributyrin. A kinetic study on the surface pressure dependency, stereospecificity and regioselectivity of SDL was performed using monomolecular films of either three dicaprin isomers or three pairs of didecanoyl-deoxyamino-O-methyl glycerol enantiomers (DDG) containing a single hydrolysable decanoyl ester bond. With all diacylglycerol isomers, SDL has a surface pressure threshold of about 15 m Nm(-1), below which enzymatic activity is undetectable. SDL seems to prefer vicinal ester groups of the diacylglycerol isomers, with preference for sn-1 position at both 15 and 23 m Nm(-1). Furthermore, the maximum SDL activity is measured with DDG having a primary ester bond (1,3DDG, SII). This shows that SDL has a preference for the sn-1 position of this diacylglycerol analogue. Moreover, this was in line with the fact that SDL is inactive on sn-2 position of both DDG isomers and a triacylglycerol. With diacylglycerol analogue isomers, SDL shows a preference for distal isomers contrary to what has been observed with diacylglycerol isomers. SDL interacts with egg-phosphatidyl choline (egg-PC) monomolecular films. The critical surface pressure value (13 m Nm(-1)) is comparable to those of pancreatic lipases.     

Numerical study of viscous dissipation effect on free convection heat and mass transfer of MHD non-Newtonian fluid flow through a porous medium

The problem of free convection heat with mass transfer for MHD non-Newtonian Eyring–Powell flow through a porous medium, over an infinite vertical plate is studied. Taking into account the effects of both viscous dissipation and heat source. The temperature and concentration are of periodic variation. The governing non-linear partial differential equations of this phenomenon are transformed into non-linear algebraic system utilizing finite difference method. Numerical results for the velocity, temperature and concentration distributions as well as the skin friction, heat and mass transfer are obtained and reported in tabular form and graphically for different values of physical parameters of the problem. Also, the stability condition is studied.     

Cyclic block designs with block size 3 from Skolem-type sequences

A Skolem-type sequence is a sequence (s ₁, . . . , s _t ) of positive integers \({i\in D}\) such that for each \({i\in D}\) there is exactly one \({j\in \{1, \ldots , t - i\}}\) such that s _j  = s _j+i  = i. Positions in the sequence not occupied by integers \({i\in D}\) contain null elements. In 1939, Peltesohn solved the existence problem for cyclic Steiner triple systems for v ≡ 1, 3(mod 6), v ≠ 9. Using the same technique in 1981, Colbourn and Colbourn extended the solution to all admissible λ > 1. It is known that Skolem-type sequences may be used to construct cyclic Steiner triple systems as well as cyclic triple systems with λ = 2. The main result of this paper is an extension of former results to cyclic triple systems with λ > 2. In addition we introduce a new kind of Skolem-type sequence.     

Biodiversity of Secondary Metabolites Compounds Isolated from Phylum Actinobacteria and Its Therapeutic Applications

The current review aims to summarise the biodiversity and biosynthesis of novel secondary metabolites compounds, of the phylum Actinobacteria and the diverse range of secondary metabolites produced that vary depending on its ecological environments they inhabit. Actinobacteria creates a wide range of bioactive substances that can be of great value to public health and the pharmaceutical industry. The literature analysis process for this review was conducted using the VOSviewer software tool to visualise the bibliometric networks of the most relevant databases from the Scopus database in the period between 2010 and 22 March 2021. Screening and exploring the available literature relating to the extreme environments and ecosystems that Actinobacteria inhabit aims to identify new strains of this major microorganism class, producing unique novel bioactive compounds. The knowledge gained from these studies is intended to encourage scientists in the natural product discovery field to identify and characterise novel strains containing various bioactive gene clusters with potential clinical applications. It is evident that Actinobacteria adapted to survive in extreme environments represent an important source of a wide range of bioactive compounds. Actinobacteria have a large number of secondary metabolite biosynthetic gene clusters. They can synthesise thousands of subordinate metabolites with different biological actions such as anti-bacterial, anti-parasitic, anti-fungal, anti-virus, anti-cancer and growth-promoting compounds. These are highly significant economically due to their potential applications in the food, nutrition and health industries and thus support our communities’ well-being.     

Improved Results on Geometric Hitting Set Problems

We consider the problem of computing minimum geometric hitting sets in which, given a set of geometric objects and a set of points, the goal is to compute the smallest subset of points that hit all geometric objects. The problem is known to be strongly NP-hard even for simple geometric objects like unit disks in the plane. Therefore, unless P = NP, it is not possible to get Fully Polynomial Time Approximation Algorithms (FPTAS) for such problems. We give the first PTAS for this problem when the geometric objects are half-spaces in ?³ and when they are an r-admissible set regions in the plane (this includes pseudo-disks as they are 2-admissible). Quite surprisingly, our algorithm is a very simple local-search algorithm which iterates over local improvements only.