Unraveling the Intrinsic Color of Chlorophyll

The exact color of light absorbed by chlorophyll (Chl) pigments, the light‐harvesters in photosynthesis, is tuned by the protein microenvironment, but without knowledge of the intrinsic color of Chl it remains unclear how large this effect is. Experimental first absorption energies of Chl a and b isolated in vacuo and tagged with quaternary ammonium cations are reported. The energies are largely insensitive to details of the tag structure, a finding supported by first‐principles calculations using time‐dependent density functional theory. Absorption is significantly blue‐shifted compared to that of Chl‐containing proteins (by 30–70 nm). A single red‐shifting perturbation, such as axial ligation or the protein medium, is insufficient to account even for the smallest shift; the largest requires pigment–pigment interactions.     

Effect of the nature of organic solvents on their interaction with metal halides

Journal of Radioanalytical and Nuclear Chemistry - A systematic study has been carried out on the extraction of thallium halides with aromatic hydrocarbons, TBP and Amberlite LA2. Extraction has...     

Effect of the nature of organic solvents on their interaction with metal halides

The radioactive tracer technique was used for studying the extraction and predicting the best conditions of separation of arsenic halides by organic solvents of different nature. Sulphuric acid was found to enhance the extraction of arsenic halides. Extraction of AsI₃ increases in the order cyclohexane <CCL₄ toluene <o-xylene <CHCl₄ and is quantitative by benzene and nitrobenzene. For a given extraction increases in the order AsCl₃<AsBr₃< <AsI₃. Spectral measurements were made on some solvents; at maximum absorption there was a linearity between absorbance and AsI₃ concentration up to 2·10⁻⁴ M for o-xylene and to 2.5·10⁻⁴ M for nitrobenzene.     

Intrinsic interaction mode of an inhalation anesthetic with globular proteins: a comparative study on ligand recognition

Interaction mode of an inhalation anesthetic halothane with water-soluble globular proteins, myoglobin (Mgb) and lysozyme (Lys), was studied by differential scanning calorimetry (DSC) and viscometry, and the results were compared with those of bovine serum albumin (BSA). The anesthetic sensitivity was markedly different among the proteins: Mgb was destabilized, Lys was slightly destabilized, and BSA was conversely stabilized. Further, the interaction mode was quite different from those of specific binders for the proteins. The anesthetic sensitivity was highly correlated with the hydrophilicity on the protein surface (Mgb?<?Lys?<?BSA) and the rigidity of the protein structure (BSA????Mgb?<?Lys). We showed that the anesthetic sensitivity among globular proteins can be roughly classified into four categories, and proteins with small hydrophilicity and soft structure are suitable as model proteins of anesthesia. By contrast, the binding of the specific binders was characterized by the lower effective concentrations. The molar ratio of the binder to the protein at the effective concentration was well consistent with the binding number determined from the X-ray structural analysis. Moreover, the interaction mode of the binder was not necessarily in accord with the mode expected from the change in the protein structure. Considering the above facts, we can systematically interpret the effect of an anesthetic on globular proteins by four factors: (1) hydrophobicity of an anesthetic, (2) hydrophilicity of a protein surface, (3) rigidity of a protein structure, and (4) molar ratio of an anesthetic to a protein at the effective concentration.     

Cross bridging proteins in nature and their utilization in bio- and nanotechnology

Cross-linking and cross-bridging are highly versatile methods of creating composite protein structures with desired mechanical properties such as deformation endurance, elasticity, extensibility, and stability under intensive and repetitive sheering forces. Cross-linking and cross-bridging are distinguished by the bonds that hold the structural components together. Cross-linking implies a covalent association, whereas cross-bridging depends on biological recognition, in which hydrogen bonding, ionic, and hydrophobic interactions predominate. Cross-bridged structures are found in all living systems. Cytoskeletal interaction, cell invasion by pathogens, fertilization, and cellulosomal degradation of cellulose are all examples of biological processes in which cross-bridging proteins play a key role. This article will review the different types of biological cross-bridging proteins that are known and discuss their emerging nano- and biotechnological applications.     

Effect of the nature of phospholipids on the degree of their interaction with isobornylphenol antioxidants

The parameters of complexation between natural phospholipids (lecithin, sphingomyelin, and cephalin) with antioxidants of a new class, isobornylphenols (IBPs), were determined by UV and IR spectroscopy. The self-organization of phospholipids (PLs) was studied depending on the structure of IBPs by dynamic light scattering. The nature of phospholipids and the structure of IBPs was found to produce a substantial effect both on the degree of complexation and on the size of PL aggregates in a nonpolar solvent. Based on the obtained data it was concluded that the structure of biological membranes mainly depends on the complexation of IBP with sphingomyelin.     

Design of silica microparticles with oligopeptide brushes and their interaction with proteins

Synthesis of small oligopeptide brushes (oligo(S-benzyl-l-cysteine)) onto polyelectrolyte functionalized silica microparticles was developed. Poly(vinyl amine) (PVAm) adsorbed from salt-free and KCl 10⁻¹ mol L⁻¹ aqueous solution onto silica microparticles was chemically and naturally cross-linked by epichlorohydrin and CO₂, respectively. After the adsorption of PVAm onto microporous silica particles and stabilization by cross-linking, five repeated coupling reactions of Boc-S-benzyl-l-cysteine were performed. To test the protein interactions with the newly designed surface, human serum albumin (HSA) has been selected as a model protein. X-ray photoelectron spectroscopy, total organic carbon, potentiometric and polyelectrolyte titrations, and electrokinetic analysis were employed to obtain information about the polyelectrolyte adsorption and the amount of the amino acid S-benzyl-l-cysteine that was covalently bound to the solid surface and for determination of the protein amount adsorbed onto functionalized surface. The amount of HSA adsorbed onto modified silica microparticles decreased in order: silica/PVAm-cross-linked (silica/PVAm-C) (8.00 mg g⁻¹) > silica/PVAm-C/S-benzyl-l-cysteine (6.34 mg g⁻¹) > silica (4.86 mg g⁻¹) > silica/PVAm-C/(S-benzyl-l-cysteine)₅ (1.86 mg g⁻¹).     

Calcium adsorption and displacement: characterization of lipid monolayers and their interaction with membrane-active peptides/proteins

Background  

The first target of antimicrobial peptides (AMPs) is the bacterial membrane. In the case of Gram-negative bacteria this is the outer membrane (OM), the lipid composition of which is extremely asymmetric: Whereas the inner leaflet is composed of a phospholipid mixture, the outer leaflet is made up solely from lipopolysaccharides (LPSs). LPS, therefore, represents the first target of AMPs. The binding and intercalation of polycationic AMPs is driven by the number and position of negatively charged groups of the LPS. Also, proteins other than cationic AMPs can interact with LPS, e.g. leading eventually to a neutralization of the endotoxic effects of LPS. We compared different biophysical techniques to gain insight into the properties of the electrical surface potentials of lipid monolayers and aggregates composed of LPSs and various phospholipids and their interaction with peptides and proteins.     

Effect of the nature of organic solvents on their interaction with metal halides. Further investigations on antimony

A study is given on the extraction of trivalent antimony halides by nonpolar solvents, nitrobenzene, Amberlite LA-2 from sulphuric and orthophosphoric acids. These two acids, because of their dehydration action, were found to have an enhancing effect on the extraction of Sb(III) halides. Extraction by nonpolar solvents and nitrobenzene was also studied as a function of the antimony concentration.     

On the nature of the interaction between H2 and metal-organic frameworks

The mechanism of adsorption of molecular hydrogen (H₂) on IRMOF-1 is studied at the MP2 level. The role of the two principal MOF components, the inorganic connector and the organic linker, for H₂ adsorption is evaluated. Correlation methods and large basis sets are necessary to describe correctly the weak interactions (London dispersion) and to account for the polarisability of H₂. We proof that the electrostatic interactions have a negligible contribution to the interaction energy and the adsorption mechanism is governed by London dispersion (3–5 kJ mol^?1).     

Studies on the interaction of metals and their hydrous oxide sols with proteins: Interaction of aluminium,chromium, iron and their hydrous oxide sols with casein

Summary Metal ion binding to anionic casein has been measured by potentiometric titration of Al³⁺, Cr³⁺, Fe³⁺ and their hydrous oxide sols with the protein.C _P (the amount of hydrogen ions bound in presence of metal ions) has been plotted against p_H of the metal-protein mixtures. These curves deviate markedly from linearity and a characteristic hump has been realised in case of Al-casein and Cr-casein system between p_H 4.5 to 6.5, indicating the binding of metal ions to the carboxyl groups of protein. If the extent of deviation from linearity inC _P-p_H curve is taken to be a measure of metal ion binding to protein, then casein exhibits greater binding capacity to Cr³⁺ than to Al³⁺. On the other hand, ferric ions appear to combine either withE-amino groups or phenolic groups of casein. Results on viscosity measurements further support the above viewpoint.

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Zusammenfassung Es wurde die metallionische Bindung an anionisches Casein durch potentiometrische Titration von Al³⁺, Cr³⁺, Fe³⁺ und ihren Hydroxid-Solen mit dem Protein untersucht.C _P (der Betrag der gebundenen Wasserstoffionen in Gegenwart von Metallionen) ist gegen den p_H-Wert der Metall-Protein-Mischung aufgetragen. Diese Kurven weichen deutlich vom linearen Verlauf ab, und ein wesentlicher Buckel ist im Fall der Al-Casein- und Cr-Casein-Systeme im Bereich p_H 4,5–6,5 sichergestellt, der die Bindung von Metallionen an die Carboxylgruppen des Proteins anzeigt. Wenn der Betrag der Abweichung von der Linearen inC _P/p_H als Ma\ für die metallionische Bindung an das Protein angesehen wird, dann zeigt Casein eine grö\ere Bindungskapazität für Cr³⁺ als für Al³⁺. Andernfalls scheinen Eisenionen weder mit den Eiwei\-Amino-Gruppen noch den phenolischen Gruppen des Caseins zu kombinieren. Viskosimetrische Messungen unterstützen die oben dargelegte Deutung.

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Abstracted from a thesis submitted byM. Muzaffaruddin to Aligarh Muslim University, Aligarh, in fulfilment of the requirement for the degree of Doctor of Philosophy, March 1964.     

Dipolar waves map the structure and topology of helices in membrane proteins

Dipolar waves describe the structure and topology of helices in membrane proteins. The fit of sinusoids with the 3.6 residues per turn period of ideal alpha-helices to experimental measurements of dipolar couplings as a function of residue number makes it possible to simultaneously identify the residues in the helices, detect kinks or curvature in the helices, and determine the absolute rotations and orientations of helices in completely aligned bilayer samples and relative rotations and orientations of helices in a common molecular frame in weakly aligned micelle samples. Since as much as 80% of the structured residues in a membrane protein are in helices, the analysis of dipolar waves provides a significant step toward structure determination of helical membrane proteins by NMR spectroscopy.     

Intrinsic electrophilic properties of nucleosides: photoelectron spectroscopy of their parent anions

The nucleoside parent anions 2(')-deoxythymidine(-), 2(')-deoxycytidine(-), 2(')-deoxyadenosine(-), uridine(-), cytidine(-), adenosine(-), and guanosine(-) were generated in a novel source, employing a combination of infrared desorption, electron photoemission, and a gas jet expansion. Once mass selected, the anion photoelectron spectrum of each of these was recorded. In the three cases in which comparisons were possible, the vertical detachment energies and likely adiabatic electron affinities extracted from these spectra agreed well with the values calculated both by Richardson et al. [J. Am. Chem. Soc. 126, 4404 (2004)] and by Li et al. [Radiat. Res. 165, 721 (2006)]. Through the combination of our experimental results and their theoretical calculations, several implications emerge. (1) With the possible exception of dG(-), the parent anions of nucleosides exist, and they are stable. (2) These nucleoside anions are valence anions, and in most cases the negative charge is closely associated with the nucleobase moiety. (3) The nucleoside parent anions we have generated and studied are the negative ions of canonical, neutral nucleosides, similar to those found in DNA.     

Experimental and theoretical determination of the accurate interaction energies in benzene-halomethane: the unique nature of the activated CH/pi interaction of haloalkanes

The CH/pi interaction energies between benzene and halomethanes (CH(2)Cl(2) and CHCl(3)) were accurately determined. Two-color ionization spectroscopy was applied to the benzene-CH(2)Cl(2) and -CHCl(3) clusters, and the binding energies in the neutral ground state, i.e. the CH/pi interaction energies in these model cluster systems, were precisely evaluated on the basis of the dissociation threshold measurements of the clusters in the cationic state and the ionization potential value of the bare molecule. The experimentally determined interaction energies were 3.8 +/- 0.2 and 5.2 +/- 0.2 kcal mol(-1) for benzene-CH(2)Cl(2) and -CHCl(3) respectively, and the remarkable enhancement of the CH/pi interaction energy with chlorine-substitution was quantitatively confirmed. The experimental interaction energies were well reproduced by the high-level ab initio calculations. The theoretical calculations clarified the unique nature of the activation of the CH/pi interaction by the chlorine-substitution.     

Studying the nature of interaction between nanohydroxyapatite and albumins by radionuclide-microscopy diagnostics

Multistage character of adsorption isotherms of human and bovine serum albumins on hydroxyapatite nanoparticles from aqueous solution have been developed by the radionuclide-microscopy method. Such a character of isotherms indicated the number of physicalchemical processes: formation of the peptide-nanohydroxyapatite complex and following by aggregation in liquid and solid phases. This hypothesis was confirmed by X-ray and dynamic light-scattering analysis, It was shown, that when hydroxyapatite is formed in albumin solution the peptide-nanohydroxyapatite complex formation is followed by morphology and structure exchange of hydroxyapatite nanocrystals.     

Intrinsic Z-DNA is stabilized by the conformational selection mechanism of Z-DNA-binding proteins

Z-DNA, a left-handed isoform of Watson and Crick’s B-DNA, is rarely formed without the help of high salt concentrations or negative supercoiling. However, Z-DNA-binding proteins can efficiently convert specific sequences of the B conformation into the Z conformation in relaxed DNA under physiological salt conditions. As in the case of many other specific interactions coupled with structural rearrangements in biology, it has been an intriguing question whether the proteins actively induce Z-DNAs or passively trap transiently preformed Z-DNAs. In this study, we used single-molecule fluorescence assays to observe intrinsic B-to-Z transitions, protein association/dissociation events, and accompanying B-to-Z transitions. The results reveal that intrinsic Z-DNAs are dynamically formed and effectively stabilized by Z-DNA-binding proteins through efficient trapping of the Z conformation rather than being actively induced by them. Our study provides, for the first time, detailed pictures of the intrinsic B-to-Z transition dynamics and protein-induced B-to-Z conversion mechanism at the single-molecule level.     

Unraveling the evolving nature of gaseous and dissolved carbon dioxide in champagne wines: A state-of-the-art review,from the bottle to the tasting glass

In champagne and sparkling wine tasting, the concentration of dissolved CO₂ is indeed an analytical parameter of high importance since it directly impacts the four following sensory properties: (i) the frequency of bubble formation in the glass, (ii) the growth rate of rising bubbles, (iii) the mouth feel, and (iv) the nose of champagne, i.e., its so-called bouquet. In this state-of-the-art review, the evolving nature of the dissolved and gaseous CO₂ found in champagne wines is evidenced, from the bottle to the glass, through various analytical techniques. Results obtained concerning various steps where the CO₂ molecule plays a role (from its ingestion in the liquid phase during the fermentation process to its progressive release in the headspace above the tasting glass) are gathered and synthesized to propose a self-consistent and global overview of how gaseous and dissolved CO₂ impact champagne and sparkling wine science.