Complex Formation Behavior Research Articles

Self-assembly via hydrogen bonding of bis(18-crown-6)-1,3-distyrylbenzene and [2 + 2] photocycloaddition: Stereoselective synthesis of [2.2]metacyclophanes and butterfly-type thermal isomerization

The photochemistry of bis(18-crown-6)-containing 1,3-distyrylbenzene and its 2 : 2 bis-pseudo-sandwich complex with ethane-1,2-diammonium was studied. The UV irradiation of the supramolecular complex resulted in the formation of three geometric isomers of tetracrown-containing dicyclobutano[2.2]metacyclopane, differing in the orientation of the cyclobutane moieties, with the unsymmetrical isomer (>50 %) predominating. The diammonium cations used as the template could be removed after photolysis by simple extraction, and the product was obtained in high yield (82 %). The 1H NMR signals of a mixture of geometric isomers of [2.2]metacyclophane derivative were assigned resorting to quantum chemistry methods (DFT). The kinetic and thermodynamic parameters of thermal isomerization between the endo,endo- and exo,exo-isomers were measured. Tetracrown-containing dicyclobutano[2.2]metacyclophanes are homotetratopic ligands that contain four binding sites for metal and ammonium cations, which is of interest for the design of photo- and thermo-switchable supramolecular devices with a variable complex formation behavior and supramolecular machines owing to the butterfly-type thermal isomerization.

Iodine-complex formation behavior of vinyl alcohol-vinyl acetate copolymers as studied by X-ray diffraction and vibrational spectroscopic data analyses

The iodine complex formation behavior of a series of vinyl alcohol-vinyl acetate copolymers (P(VA-co-VAc), -[CH2CH(OH)+CH2CH(OCOCH3)]n-) has been studied systematically on the basis of X-ray diffraction and IR/Raman spectroscopic data. The VA segments in the copolymers were found to start to crystallize for the first time when the sequential segmental length is beyond the critical sequential length of 3–4 VA monomeric units. Below this critical length, the OH units on VA segments exist as isolated groups or as being connected with O=C bonds of VAc segments. The latter type of hydrogen bonds, –C=O⋯HO-, was found to be formed in the copolymers of a wide range of VA content of 30–90 mol%. The immersion of these VA-VAc copolymers into the iodine solution gave the crystalline iodine complexes. In the VA range of 0–40%, the PVAc-I5- complex (β form) is formed mainly. Once when the VA content is beyond the critical sequential length, the PVA-I3- complex of form II starts to be created and develops into the larger and regular crystalline complex in addition to the PVAc-iodine complex.

A new ITO-based Aβ42 biosensor for early detection of Alzheimer's disease

In this study, a novel label-free impedimetric immunosensor was fabricated for rapid, selective, and sensitive quantitative analysis of Aβ42 protein for use in the diagnosis of Alzheimer's disease. The immunosensor was fabricated using inexpensive and disposable indium tin oxide polyethylene terephthalate (ITO-PET) electrodes. After the electrodes were modified with 3-glycidoxypropyldimethoxymethylsilane (GPDMMS), the antibody specific to the Aβ42 protein (anti-Aβ42) was immobilized. The affinity interaction between anti-Aβ42 and Aβ42 in the immobilization steps in immunosensor fabrication and in the quantitation of Aβ42 were analyzed using Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) techniques. Additionally, the morphological changes occurring on the electrode surface during each immobilization step were imaged using scanning electron microscopy (SEM). The linear detection range of the immunosensor was determined as 1–100 pg/mL with the limit of detection value of 0.37 pg/mL. Analytical properties of the biosensor, including reproducibility, repeatability, storage stability, selectivity, and regeneration were investigated. The kinetic behavior of antibody-antigen complex formation was determined for the first time using single frequency impedance (SFI) analysis on an Aβ42 biosensor. The potential for use of the immunosensor in clinical studies was demonstrated by analysis of Aβ42 in commercially purchased human serum.

Time Evolution of Ultrasmall Gold Nanoparticle-Protein Interactions.

To date, much effort has been devoted toward the study of protein corona formation onto large gold nanoparticles (GNPs). However, the protein corona concept breaks down for GNPs in the ultrasmall size regime (<3 nm), and, as a result, our understanding of ultrasmall GNP (usGNP)-protein interactions remains incomplete. Herein, we used anionic usGNPs and six different proteins as model systems to systematically investigate usGNP-protein interactions, with particular focus on the time evolution and long-term behavior of complex formation. The different proteins comprised chymotrypsin (Cht), trypsin (Try), thrombin (Thr), serum albumin (HSA), cytochrome c (Cyt c), and factor XII (FXII). We used a range of biochemical and biophysical methods to estimate binding affinities, determine the effects of usGNPs on protein structure and function, assess the reversibility of any protein structural and functional changes, and evaluate usGNP-protein complex stability. Among the main findings, we observed that prolonged (24 h)─but not short-term (10 min)─interactions between proteins and usGNPs permanently altered protein function, including enzyme activities (Try, Thr, and FXIIa), peroxidase-like activity (Cyt c), and ligand-binding properties (HSA). Remarkably, this occurred without any large-scale loss of the native global conformation, implying time-dependent effects of usGNPs on local protein conformation or dynamics. We also found that both short-(10 min) and long-term (24 h) interactions between proteins and usGNPs yielded short-lived complexes, i.e., there was no time-dependent "hardening" of the interactions at the binding interface as usually seen with large GNPs. The present study increases our fundamental understanding of nano-bio interactions in the ultrasmall size regime, which may assist the safe and effective translation of usGNPs into the clinic.

Complex Formation Behavior of Silica Nanoparticles and Xanthan

AbstractPolyion complex formation between negatively charged polysaccharide, xanthan, and positively charged silica nanoparticles, Ludox CL is investigated in an acetate buffer at pH 5.0. Appreciable precipitate is found in the composition range cx/cSiNP from 0.056 to 0.58, where cx and cSiNP are the mass concentrations of xanthan and silica nanoparticles, respectively. The sign change of the ζ potential for the mixed solutions is observed in the cx/cSiNP range. Significantly high scattering intensity is detected for the mixed solutions in a wider cx/cSiNP range, clearly showing the complex formation. The scattering profile measured by the small‐angle X‐ray scattering reveals that silica nanoparticles are packed loosely in the complex both when xanthan forms double helix and single chain conformations.

Bioactive Ni(II), Cu(II) and Zn(II) complexes with an N3 functionalized Schiff base ligand: Synthesis, structural elucidation, thermodynamic and DFT calculation studies

Some novel Ni(II), Cu(II) and Zn (II) metal complexes with new triaza Schiff base ligand (N-(2quinolylmethylidene)-4X-2-aminobenzene)imine (where X = Me, Cl, NO2)) have been synthesized. Various spectral techniques such as elemental analysis, magnetic susceptibility, conductivity, 1HNMR, IR, UV–Vis spectra, Mass spectrometry, powder XRD and EDX were used to confirm the structures. It has been found that the Schiff base behaves as a tridentate ligand forming chelates with 1:1 metal:ligand stoichiometry. The prepared Schiff base compounds were screened in vitro for their antibacterial activity against a number of pathogenic Gram positive and Gram negative bacteria, namely S.aureas and E.coli. The complexes show more potent activities than their free ligands. Spectrophotometric method and SQUAD program were applied to extract thermodynamic parameters to explain the complex formation behavior in solution at 25 °C in constant ionic strength (I = 0.1 M NaClO4). Also, density functional theory calculations at different level of DFT and basis set were employed to investigate optimized geometry, vibrational frequency analysis, electronic structure (energy of the HOMO and LUMO, Mulliken atomic charge, dipole moment, hardness and softness, electrophilicity and spectral properties) of the prepared Schiff base compounds. The DFT results showed that proposed structure and stability in ligands and their complexes are in accord with the experimental outcomes.

Complex Formation behavior of Copper-Tin Alloys at its Molten State

Complex Formation behavior of Copper-Tin Alloys at its Molten State

Liquefaction Susceptibility Assessment Using Geotechnical and Geological Manners of Northern Thailand

Soil site investigations such as boring logs, basic soil properties, spectral analysis of surface wave, and the examinations of geologic and geomorphologic were performed in Mae Lao area to investigate the susceptibility of liquefaction after the 6.2 Mw Chiang Rai Earthquake 2014. The study area was found to lay on a complex geological formation and geotechnical behavior with a condition of the high groundwater table. Being located on a high seismicity area (intensity V-VII Mercalli) governs the study area as a concern for high liquefaction hazards. Liquefaction susceptibility-based compositional criteria, soil resistance, and geologic criteria have been established, and consequently, the character of liquefaction potential is defined.

Emulsifiers efficiently prevent hardening of pancakes under refrigerated conditions via inclusion complexes with starch molecules

Pancakes served as a dessert with creams and fruits toppings nowadays stored under refrigerated conditions are often subjected to significant changes in physical properties recognized as quality deterioration, which is efficiently prevented by including small molecule emulsifiers into commercial pancakes formulations. In order to reveal these molecular prevention mechanisms in the real multicomponent wheat-based products, small molecule emulsifiers with various HLB values and head group size were formulated into pancake samples and their physical properties evaluated. Starch retrogradation, emulsifier-starch inclusion complex formation and gelatinization behaviors were followed by the texture profile analysis, differential scanning calorimetry, iodine colorimetry and confocal laser scanning microscopy. Hardening of the pancake samples varied with the type of emulsifiers, which in general reduced the retrogradation of starch. This reduction was dominantly attributed to the emulsifier-starch complex formation, particularly with amylose molecules, probably leading to less leaching of the starch molecules from the starch granules. These findings are of practical use in selecting effective emulsifiers that prevent hardening of pancakes. The degree of complexation was partially explained by the HLB and head group size of the emulsifiers, while it can be also significantly affected by interactions between the emulsifier and other components in the pancake mixture, like milk and eggs.

Host-guest interactions between p-sulfonatocalix[4]arene and p-sulfonatothiacalix[4]arene and group IA, IIA and f-block metal cations: a DFT/SMD study.

The molecular recognition in aqueous solution is extremely important because most biological processes occur in aqueous solution. Water-soluble members of the calix[n]arene family (e.g., p-sulfonato substituted) can serve as model systems for studying the nature and manner of interactions between biological receptors and small ions. The complex formation behavior of water-soluble p-sulfonatocalix[4]arene and thiacalix[4]arene and group IA, IIA and f-block metal cations has been investigated computationally by means of density functional theory computations in the gas phase and in aqueous environment. The calculated Gibbs free energy values of the complex formation reaction of these ligands with the bare metal cations suggest a spontaneous and energy-favorable process for all metal cations in the gas phase and only for Na+, Mg2+, Lu3+ cations in water environment. For one of the studied cations (La3+) a supramolecular approach with explicit solvent treatment has been applied in the study of the effect of metal hydration on the complexation process. The La3+ binding to the p-sulfonatocalix[4]arene host molecule (now in the metal’s second coordination shell) is still exergonic as evidenced by the negative Gibbs free energy values (ΔG1 and ΔG78). The combination of implicit/explicit solvent treatment seems useful in the modeling of the p-sulfonatocalix[4]arene (and thiacalix[4]arene) complexes with metal cations and in the prediction of the thermodynamic parameters of the complex formation reactions.

POTENTIOMETRIC STUDY OF RHENIUM(V) COMPLEX FORMATION WITH AZATHIOPRINE AND CEFTRIAXONE

The behavior of complex formation of Re(V) metal ion with azathioprine (AZ) and ceftriaxone (CE) as medicinal drugs has been investigated potentiometrically in 0.3 M hydrochloric acid. The stability constant of the prepared complexes has been determined and calculated at various temperatures. The obtained results showed that Re(V)-AZ system showed the formation 1:2, 1:3 and 1:4 complexes, while Re(V)-CE showed only 1:1 and 1:2 complexes. The complex formation suggests a successive displacement of the chloride molecules from the coordination sphere of the central ion by the AZ ligand. In addition, the effect of temperature on the complexes formation of Re(V) with AZ and CE was investigated. The entropy and enthalpy changes showed a favorable and exothermic process, respectively. The kinetic parameters of the formation complex process were calculated and discussed.

Characterization of dispersed titania nanosheet under aqueous conditions and its complex formation behavior with cationic porphyrin

Abstract Cation exchange capacity (CEC) of titania nanosheet (TNS) and the complex formation behavior with the cationic porphyrin were investigated. It is turned out that the CEC value of TNS is 1.5 × 10 −3 eq g −1 according to a thermogravimetric analysis. The maximum adsorption ratio of the cationic porphyrin onto dispersed TNS surface was almost 100% versus CEC in aqueous conditions under the optimized concentration of the exfoliating reagent. This result indicates that cationic porphyrins adsorb densely without molecular aggregation.

Structure, electronic, inclusion complex formation behavior and spectral properties of pillarplex

Electronic structure, vibrational and NMR spectra of metal-Pillarplex (metal = Cu, Ag and Au) and its inclusion complex with 1,8-diaminooctane (DAO) are investigated by using density functional theory. The coordinated metal atoms tune the cavity size and the height of metal-Pillarplex and form a rigid cavity thereby reducing their structural deformation. Cu-Pillarplex undergoes a large deformation both on the host and guest molecule. The calculated Gibbs free energy for the formation of inclusion complex were negative indicating their facile formation at the room temperature. Computed binding energies with various functionals and energy decomposition analysis, shows that dispersion correction is essential in these systems. The low binding energy, and the physical adsorption of guest molecule and HOMO–LUMO spatial diagram indicates, that the Au and Ag-Pillarplex can be used as reversible host for linear alkanes Complexation of guest engenders frequency shift in the vibrational spectra. Calculated 1H NMR reveal that guest protons which are closer to the metal sites experience larger shielding possibly due to C–H→LP* metal interaction. The 15N signal observed for the DAO is nearly identical to that observed for the DAO@metal-Pillarplex. NBO and AIM analysis indicate that metal centers in host, play a major role in stabilizing the guest inside the cavity than the amino group on the guest molecule.

Polysaccharide based bionanocomposite hydrogels reinforced with cellulose nanocrystals: Drug release and biocompatibility analyses

Cellulose nanocrystals (CNCs) reinforced, bionanocomposite (BNC) has shown great potential in tissue engineering and drug delivery applications due to the low toxicity, low density, and high aspect ratio. In this work, BNC hydrogels reinforced with CNCs were fabricated from xanthan (XG) solutions and chitosan (CS) in presence of green acidifying agent through electrostatic and hydrogen bonding interactions. As developed BNC hydrogels were characterized for complex formation, morphology, and mechanical behavior. The mechanical performance of BNC hydrogels was improved significantly as increased CNC content (from 2 to 10wt%). 5-Flurouracil as model chemotherapeutic agent was loaded into these BNC hydrogels for evaluating their drug release properties. The BNC hydrogels showed excellent cytocompatability and ability to release of chemotherapeutic agent that shows the suitability to be used in tissue engineering as well as drug delivery applications.

Effects of biopolymer ratio and heat treatment on the complex formation between whey protein isolate and soluble fraction of Persian gum

ABSTRACTProteins and polysaccharides are the two most important natural ingredients with unique functional properties. Their interactions can be considered as a route to produce new materials of various technological applications. In this study, the effect of pH (3–7) as well as the mixing ratio of whey protein isolate (WPI)/soluble part of Persian gum (PG) (1:3, 1:1, 3:1, 6:1, and 9:1% w/w WPI/PG) on the complex formation behavior of the two polymers were studied using spectrophotometric and dynamic light scattering techniques, soluble protein measurement, and microscopic observations. Investigating the curves of turbidity versus pH showed that pHc and pHϕ1, which are associated with the formation of soluble and insoluble complexes, moved toward higher pH values by increasing WPI:PG ratio. Increased solubility was observed at pHc > pH > pHϕ1 for all biopolymers mixtures. In addition, lowering the pH toward pHϕ1 resulted in a decrease in the size of complexes, while further decrease of pH beyond this point led to larger particles. No significant difference was noticed between pHc and pHϕ1 of heated and unheated WPI/PG mixtures, although the turbidity of heated samples increased due to the formation of larger aggregates.

Binding interactions between lysozyme and injectable hydrogels derived from albumin-pH/thermo responsive poly(amino urethane) conjugates in aqueous solution

Injectable hydrogels are alternative materials for drug and protein delivery in biomedical applications, which can potentially eliminate the need of surgical implantation in the treatment procedures. Prior to administration, such hydrogels, in a liquid state, must demonstrate good interactions with the incorporated molecules to maintain the sustain release of active agents and to avoid unappreciative burst release. The injectable hydrogels derived from BSA-pH/temperature responsive poly(amino urethane) conjugates have been reported to demonstrated good sustainability for delivery of lysozyme, both in vitro and in vivo. However, the interactions between such conjugates and the loading lysozyme were not fully understood. In this present work, we reported the binding interactions between the studied complex systems, BSA-pH/temperature responsive poly(amino urethane) conjugates (CONJ1 and CONJ2) and lysozyme. Fluorescence spectroscopy in a combination with thermodynamic analysis exhibited that the binding between the conjugates and lysozyme occurred through static quenching and the binding interactions in the complexes were mainly van der Waals forces and hydrogen bonds. The binding constants (KA) determined at 300, 308 and 318K of CONJ1 to lysozyme were 7.96ÿ104, 6.45ÿ104 and 3.20ÿ104M⿿1, respectively and those of CONJ2 to lysozyme were 2.63ÿ104, 2.53ÿ104 and 1.19ÿ104M⿿1, respectively. FTIR analysis showed that the complexes between the conjugates and lysozyme demonstrated sufficiently small deviation in the conformational structures from the native lysozyme. In addition, the morphology revealed by TEM and AFM imaging portrayed the behavior of complex formation in such a way that the conjugates, before complex formation, displayed the core-shell structures. After the complex formation, a number of lysozyme particles were noticeably entrapped as if they penetrated into the preformed core-shell conjugates.

Effect of pH and chemical mechanical planarization process conditions on the copper–benzotriazole complex formation

Benzotriazole (BTA) has been used to protect copper (Cu) from corrosion during Cu chemical mechanical planarization (CMP) processes. However, an undesirable Cu–BTA complex is deposited after Cu CMP processes and it should be completely removed at post-Cu CMP cleaning for next fabrication process. Therefore, it is very important to understand of Cu–BTA complex formation behavior for its applications such as Cu CMP and post-Cu CMP cleaning. The present study investigated the effect of pH and polisher conditions on the formation of Cu–BTA complex layers using electrochemical techniques (potentiodynamic polarization and electrochemical impedance spectroscopy) and the surface contact angle. The wettability was not a significant factor for the polishing interface, as no difference in the contact angles was observed for these processes. Both electrochemical techniques revealed that BTA had a unique advantage of long-term protection for Cu corrosion in an acidic condition (pH 3).

PH-Sensitive Supramolecular Assemblies of β-Cyclodextrin and 2-Aminodiphenylamine in Water Medium: Structure, Solubility and Stability

The influence of β-cyclodextrin on the solubility, protolytic properties, and complex formation behavior of 2-aminodiphenylamine was studied using UV spectroscopy. In accordance with the results of the spectrophotometric titration that was carried out in phosphate buffer solutions, the presence of β-cyclodextrin does not change the value of the deprotonation constant of the primary amino group of 2-aminodiphenylamine. This fact confirms that the primary amino group is not involved in the complex formation and interaction between β-cyclodextrin and 2-aminodiphenylamine occurs via the phenylimine moiety. The phase solubility profiles of 2-aminodiphenylamine in the presence of β-cyclodextin, at pH = 1.00 and pH = 5.00, indicate formation of inclusion complexes with limited solubility and can be classified as Higuchi–Connors curves of BI and BS type, respectively. The stoichiometry of the complexes and the apparent stability constants that characterize the β-cyclodextrin complexes with both protonated and neutral forms of 2-aminodiphenylamine were estimated from the dependence of absorbance intensity of the guest molecule at increasing amounts of β-cyclodextrin by the Ketelar equation. The linearity of the plots in the coordinates of the Ketelar equation proves the formation of 1:1 inclusion complexes for both protolytic forms of 2-aminodiphenylamine. It was found that inclusion complex formation is preferable for the neutral form of 2-aminodiphenylamine.

DOES hemopressin bind metal ions in vivo?

Hemopressin is a neuropeptide, derived from the degradation of the α(1)-chain of hemoglobin, and possesses several pharmacologic properties, such as the ability to block cannabinoid CB1 receptor activity, to cause dose-dependent hypotension and to inhibit food intake. Actually, human hemopressin (PVNFKLLSH) is only the precursor of a class of longer peptides, called "Pepcans", which bear additional residues at their amino-terminus and possess slightly different chemical and biological properties with respect to hemopressin. The presence of a histidyl residue and the free terminal amine imparts to hemopressin and its derivatives good binding properties towards transition metal ions. In this paper, we present a wide investigation on the complex-formation equilibria of human hemopressin and three analogues towards the Cu(ii) and Ni(ii) ions. The study showed that the main coordination site is always the amino terminus (if not protected), while the C-terminal histidine acts only as an anchoring site for the metal ions at acidic pH, with the formation of a macrochelate complex. The presence of additional residues in N-terminal position produces significant differences in the protonation and complex-formation behaviors of these peptides, which can be explained in terms of charge of the ligand and coordination environment. Although the participation of metal ions in the biological activity of hemopressin and Pepcans has not yet been demonstrated, the data reported here can help to shed light on the mechanisms governing the action of these neuropeptides in vivo.

Tuning Emission Responses of a Triphenylamine Derivative in Host–Guest Complexes and an Unusual Dynamic Inclusion Phenomenon

A newly synthesized triphenylamine derivative (1Cl3) shows significant differences in inclusion complex formation with two different macrocyclic hosts, cucurbit[7]uril (CB[7]) and β-cyclodextrin (β-CD). Detailed investigations by NMR spectroscopy reveal that CB[7] forms a 1:3 host-guest complex ([1·3{CB[7]}]Cl3) in which three arms of 1Cl3 are bound to three host molecules. On the other hand, β-CD forms a dynamic 1:1 inclusion complex ([1·{β-CD}]Cl3) by binding to only one of the three arms of 1Cl3 at a given time. The formation of a 1:1 host-guest complex with β-CD and 1:3 host-guest complex with CB[7] was also confirmed from the results of the isothermal titration calorimetric studies. Interestingly, 1Cl3 exhibits a rare dual emission property in solution at room temperature with the lower and higher energy bands arising from a locally excited state and an intramolecular charge-transfer transition, respectively. The difference in inclusion complex formation behavior of 1Cl3 with the two macrocyclic hosts results in the stabilization of different emission states in the two inclusion complexes. The fundamental difference in the electrostatic surface potentials, cavity polarities, and shapes of the two macrocyclic hosts could account for the formation of the different inclusion complexes with distinct luminescence responses.