Proteins at liquid interfaces : III. Molecular structures of adsorbed films

The rates of change of film pressure (π) and surface concentration (Γ) of protein during the adsorption of β-casein, bovine serum albumin (BSA), and lysozyme at the air-water interface have been monitored by the Wilhelmy plate and surface radioactivity methods, respectively. The increases in π and Γ for the relatively flexible β-casein molecule occur simultaneously with both parameters attaining their steady-state values at about the same time. In contrast, π and Γ follow different time courses for the globular lysozyme molecule; Γ can reach a steady state value while π is still increasing significantly. The kinetics indicate that initially adsorption is diffusion-controlled but at higher surface coverages there is an energy barrier to adsorption. Under these conditions, the ability of the protein molecules to create space in the existing film and penetrate and rearrange in the surface is rate-determining. Two kinetic regions exist: the relaxation time τ₁ (typically 2 hr when Γ 2 mg m⁻²) describes the adsorption when both π and Γ are increasing whereas τ₂ (in the range 1–8 hr for all three proteins) relates to the situation when π is increasing at constant Γ because the protein molecules are changing conformation in the surface.     

Size selective assembly of colloidal particles on a template by directed self-assembly technique

We report a simple and effective approach to organize micron- and submicron-sized particles in a size selective manner. This approach utilizes the template assisted directed self-assembly technique. A topographically patterned photoresist surface is fabricated and used to create an ordered array of colloidal particles from their aqueous suspensions. Assembly of particles on this template is then achieved by using a conventional spin coating technique. Feasibility of this technique to form a large area of patterned particle assemblies has been investigated. To arrange the particles on the template, the physical confinement offered by the surface topography must overcome a joint effect of centrifugal force and the hydrophobic nature of the photoresist surface. This concept has been extended to the size selective sorting of colloidal particles. The capability of this technique for sorting and organizing colloidal particles of a particular diameter from a mixture of microspheres is demonstrated.     

Protein folding simulations of 2D HP model by the genetic algorithm based on optimal secondary structures

In this paper, based on the evolutionary Monte Carlo (EMC) algorithm, we have made four points of ameliorations and propose a so-called genetic algorithm based on optimal secondary structure (GAOSS) method to predict efficiently the protein folding conformations in the two-dimensional hydrophobic–hydrophilic (2D HP) model. Nine benchmarks are tested to verify the effectiveness of the proposed approach and the results show that for the listed benchmarks GAOSS can find the best solutions so far. It means that reasonable, effective and compact secondary structures (SSs) can avoid blind searches and can reduce time consuming significantly. On the other hand, as examples, we discuss the diversity of protein GSC for the 24-mer and 85-mer sequences. Several GSCs have been found by GAOSS and some of the conformations are quite different from each other. It would be useful for the designing of protein molecules. GAOSS would be an efficient tool for the protein structure predictions (PSP).     

Recognition of secondary structures in proteins by a diiron(III) complex via a hydrolytic pathway

The diiron(III) complex Fe(2)(DTPB)(mu(2)-O)(mu(2)-OAc)Cl(BF(4))(2) [DTPB = 1,1,4,7,7-pentakis(2'-benzimidazol-2-yl-methyl)triazaheptane, OAc = acetate] exhibits a similar affinity for proteins belonging to different structural patterns. However, this diiron complex is sensitive to secondary structures in a protein when it is used to promote the protein hydrolysis, indicating that some metal complexes, such as artificial proteolytic agents, could become a new hydrolytic probe of protein structures.     

Staphylococcus Aureus Antigens. Part III1: Synthesis of Artificial Disaccharidic Antigens

Two artificial antigens related to S.aureus have been synthesized to elucidate the influence of the phosphodiester bond in the immunogenicity of the natural ribitol teichoic acid.     

Preparation of amphiphilic polyisobutylenes-b-polyethylenamines by mannich reaction. III. Synthesis of polyisobutylenes-b-polyethylenamines

Copolymers associating α-phenololigoisobutylene and triethylenetetramine blocks in the same chain are prepared by reacting aqueous formaldehyde with α-phenololigoisobutylene and triethylenetetramine. When para-formaldehyde is used instead of monomeric formaldehyde, the reaction does not take place, contrary to what is observed when low molecular weight models are used instead of oligomers. The ability of these copolymers to disperse sludges in motor oil was evaluated by the “spot-test” method. When oil does not contain water, the efficiency of the copolymers is comparable to that of commercial compounds. When oil contains water (1% w) the efficiency of the dispersive agent is drastically reduced. We show that this is due to the presence of phenol group. © 1993 John Wiley & Sons, Inc.     

The History of Ozone. Part III

The introduction of ozone into organic chemistry is due to the work of C. D. Harries, first in Berlin but mainly in Kiel, during the period 1903–1916. He established experimental procedures for ozonolysis, demonstrated the generality of the reaction of unsaturated compounds with ozone, and showed that ozone could be used for the synthesis of a variety of sensitive compounds. Most important for the future development of organic chemistry, he established that ozonolysis could be an important tool for determining the structures of organic compounds. He also initiated investigations into the mechanism of ozone reactions with alkenes, which culminated about forty years later in the Criegee mechanism for ozonolysis.     

The secondary structure of a membrane-modifying peptide in a supramolecular assembly studied by PELDOR and CW-ESR spectroscopies.

The new technique of pulsed electron-electron double resonance in electron spin-echo (PELDOR) in combination with the CW-ESR method has been used to investigate the secondary structure of a double spin-labeled peptide (the [TOAC-1,8]-analogue of the peptaibol antibiotic trichogin GA IV) that is hidden into a tetrameric supramolecular assembly of unlabeled peptide molecules. The magnetic dipole-dipole relaxation of spin labels has been experimentally studied in glassy solutions of the double-labeled peptide frozen to 77 K in a mixture of chloroform-toluene with an excess of unlabeled peptide. The PELDOR signal oscillations have been observed at high degrees of dilution with unlabeled peptide. The intramolecular distance between the spin labels of the peptide molecule in the aggregate has been determined from the oscillation frequency to be 15.7 A which is close to the value of (approximately equal to) 14 A calculated for a 3(10)-helical structure. Estimation of the fraction of this ordered secondary structure shows that about 19% of the peptide molecules in aggregates are folded in the 3(10)-helical conformation. The present experimental results are consistent with our molecular model presented in J. Am. Chem. Soc. 2000, 122, 3843-3848, wherein four amphiphilic 3(10)-helical peptide molecules form a vesicular system with the polar amino acid side chains pointing to the interior, and the apolar side chains, to the exterior of the cluster. The experimental data were compared with the results obtained with other techniques.     

The effect of dendritic pendants on the folding of amphiphilic copolymers via supramolecular interactions

The supramolecular folding of amphiphilic heterograft copolymers equipped with dendritic pendants is investigated using a combination of proton nuclear magnetic resonance (¹H NMR) spectroscopy, small‐angle X‐ray scattering, and circular dichroism spectroscopy. Hereto, the linear poly(ethylene glycol) pendants normally used to convey water compatibility are partially substituted with branched analogues. For one set of copolymers, second‐generation polyglycerol dendrons are directly attached to the polymer backbone, while for the other a hydrophilic linker is placed in between. The results show that the branching of the hydrophilic pendants affects the local structure of the folded copolymer but does not influence the overall conformation and single‐chain character of the folded copolymers in solution. All copolymers fold into 4–5 nm single‐chain polymeric nanoparticles with a very compact spherical morphology, independent of the dendritic content of the copolymer. Intriguingly, the incorporation of the dendritic pendants affects the formation of a structured interior even at low incorporation ratios. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 411–421     

Monolayer vanadia on titania systems from alkoxide precursors. Part III. Activity in secondary alcohol oxidation

The activity of V⁵⁺ ion monolayer supported on anatase, rutile, and anatase-rutile mixed carrier and of bulk V₂O₅ was examined in isopropyl alcohol and cyclohexanol oxidation. Catalysts exhibited remarkable activity in ketone formation. At higher temperatures benzene was the predominant product of cyclohexanol reaction.

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V⁵⁺, , - V₂O₅, . . .

     

Intrinsically stable secondary structure elements of proteins: a comprehensive study of folding units of proteins by computation and by analysis of data determined by X-ray crystallography

Different protein architectures show strong similarities regardless of their amino acid composition: the backbone folds of the different secondary structural elements exhibit nearly identical geometries. To investigate the principles of folding and stability properties, oligopeptide models (that is, HCO-(NH-L-CHR-CO)(n)-NH(2)) have been studied. Previously, ab initio structure determinations have provided a small amount of information on the conformational building units of di- and tripeptides. A maximum of nine differently folded backbone types is available for any natural alpha-amino acid residue, with the exception of proline. All of these conformers have different relative energies. The present study compiles an ab inito database of optimized HCO-(L-Xxx)(n)-NH(2) structures, where 1相似文献   

The gas-phase decomposition of methylsilane. Part III. Kinetics

The homogeneous gas-phase decomposition kinetics of methylsilane and methylsilane-d₃ have been investigated by the comparative-rate-single-pulse shock-tube technique at total pressures of 4700 torr in the 1125–1250 K temperature range. Three primary processes occur: CH₃SiH₃ → CH₃SiH + H₂ (1), CH₃SiH₃ → CH₄ + SiH₂ (2), and CH₃SiH₃ → CH₂ = SiH₂ + H₂ (3). The high-pressure rate constants for the primary processes in CH₃SiH₃ obtained by RRKM calculations are log (k₁ + k₃) (s^?1) = 15.2 - 64,780 Cal/θ and log k₂ (s^?) = 14.50 - 67,600 → 2800 Cal/θ. For CH₃SiD₃ these same rate constants are log k₁ (s^?) = 14.99 - 64,700 cal/θ log k₂ (s^?) = 14.68 – 66,700 → 2000 cal/θ, and log k₃ (s^?) = 14.3 ? 64,700 cal/θ.     

Layer-by-layer assembly of human serum albumin and phospholipid nanotubes based on a template

The preparation of nanotubes from human serum albumin (HSA) and mixtures of L-alpha-dimyristoylphosphatidic acid (DMPA)/HSA is described. The nanotubes were prepared via alternate adsorption of HSA of different/opposite charges (by variation of the pH) or by sequential adsorption of DMPA and HSA, respectively, onto the inner surfaces of porous anodic alumina templates. This simple layer-by-layer assembly results in a monodisperse size distribution and a uniform orientation. The nanotubes allow the specific incorporation of lipophilic components such as channels or receptors and may thus serve as probes or sensors for biological systems.     

The characterization of biomolecular secondary structures by surface plasmon resonance

Recently there has been considerable interest in using surface plasmon resonance (SPR) for the measurement of conformational changes of immobilized biomolecules that are induced by an exogenous analyte. While a number of studies have shown the analytical utility of such measurements, there has been no report which characterizes the specific secondary structure that actuates the change in SPR signal. The use of SPR to indicate the type of secondary structure present in two immobilized polypeptides, poly-L-lysine (PL) and poly-L-glutamic acid (PGA), and a globular protein, concanavalin A (Con A) is described in this report. The PL, PGA and Con A were modified with N-succinimidyl 3-(2-pyridyldithiol) propionate (SPDP) to introduce disulfide groups to facilitate the attachment onto gold-coated surfaces via self-assembly. Ethanol and 2,2,2-trifluoroethanol (TFE) were used to induce changes in the secondary structure of the immobilized polypeptides and the protein respectively. Using both circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopies, it has been demonstrated that it is possible to correlate the signal changes observed in SPR to the secondary conformation of the biomolecule. Both CD and FTIR showed that a decrease in SPR signal corresponded to a high content of beta, turn or unordered structures while an increase corresponded to a high alpha-helical content. The sensitivity of the SPR technique is comparable to that obtained in solution with CD and FTIR spectroscopies. These results are the first demonstration that SPR can be used to characterize secondary structures. There is potential, therefore, for SPR to be used as a technique to study secondary conformational changes of immobilized polypeptides and proteins.     

The dependence of catalytic activities of secondary functional beta-cyclodextrins on cavity structures.

Secondary imidazole-appended beta-cyclodextrin 5 with a nondistorted cavity synthesized from a novel intermediate 3-amino-3-deoxy-beta-cyclodextrin exhibits much greater catalytic activity in the ester hydrolysis than its isomer 6 with a distorted cavity, indicating that the catalytic activities of secondary functional cyclodextrins are dependent on cavity structures.     

The Construction of New Proteins and Enzymes-a Prospect for the Future?

Only a vanishingly small proportion of the almost infinite number of possible proteins occur in nature. Can this remaining potential of structural and functional diversity be used in the construction of new proteins? Is a “second evolution” of proteins and enzymes about to occur? These questions have suddenly become of interest because the recombinant DNA technique allows the synthesis of any given amino acid sequence. Examples of enzyme models demonstrate clearly that the unusual catalytic properties of enzymes are associated with the presence of a specifically folded polypeptide chain which has a complex three-dimensional form. The critical hurdle in the path of artificial proteins is thus the design of amino acid sequences which are able to fold into tertiary structures. — Recent studies on the topology and the mechanism of folding have provided considerable insight into the occurrence of, and the rules governing the three-dimensional architecture of proteins. Secondary structures apparently play a key role in the folding process; helices and “β-structures” act as nucleation centers directing folding and account for the surprisingly small number of different folding topologies. The problem of secondary structure formation can be investigated directly by means of conformational studies on model peptides. Oligopeptides with tailormade physicochemical, structural and conformational properties can already be designed. The theoretical and experimental basis for the construction of polypeptides with stable tertiary structures is therefore established. The path to macromolecules with an immense variety of novel properties lays before us.     

The thiolate anion as a nucleophile Part III. Reactions with various fluorobenzenes

The reactions of the fluorobenzenes, C₆F₅H, o-C₆H₂F₄, m-C₆H₂F₄, p-C₆H₂F₄, 1,3,5-C₆F₃H₃, 1,2,4-C₆F₃H₃, o-C₆F₂H₄, m-C₆F₂H₄, p-C₆F₂H₄ and C₆F₅H with thiolate anion nucleophiles RS^? (primarily MeS^?), have been studied in ethylene glycol/pyridine mixtures as a solvent. Multiple replacement of fluorine atoms was observed in the more highly fluorinated compounds, but in all cases two aromatic fluorine atoms were not replaced. Difluorobenzene and fluorobenzene did not react. The product orientations have been deduced from their NMR spectra. The mass spectra of the isomeric products C₆F₂H₃(SMe), C₆F₃H₂(SMe) and C₆F₂H₂(SMe)₂ have been examined.