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Kraevsky, Sergey V., Nikolay A. Barinov, Olga V. Morozova, Vladimir V. Palyulin, Alena V. Kremleva i Dmitry V. Klinov. "Features of DNA–Montmorillonite Binding Visualized by Atomic Force Microscopy". International Journal of Molecular Sciences 24, nr 12 (6.06.2023): 9827. http://dx.doi.org/10.3390/ijms24129827.
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In the present work, complexes of DNA with nano-clay montmorillonite (Mt) were investigated by means of atomic force microscopy (AFM) under various conditions. In contrast to the integral methods of analysis of the sorption of DNA on clay, AFM allowed us to study this process at the molecular level in detail. DNA molecules in the deionized water were shown to form a 2D fiber network weakly bound to both Mt and mica. The binding sites are mostly along Mt edges. The addition of Mg2+ cations led to the separation of DNA fibers into separate molecules, which bound mainly to the edge joints of the Mt particles according to our reactivity estimations. After the incubation of DNA with Mg2+, the DNA fibers were capable of wrapping around the Mt particles and were weakly bound to the Mt edge surfaces. The reversible sorption of nucleic acids onto the Mt surface allows it to be used for both RNA and DNA isolation for further reverse transcription and polymerase chain reaction (PCR). Our results show that the strongest binding sites for DNA are the edge joints of Mt particles.
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Gotch, Albert J., R. Nathan Pribble, Frederick A. Ensminger i Timothy S. Zwier. "The Spectroscopy and Photophysics of π Hydrogen-Bonded Complexes: Benzene–CHCl3". Laser Chemistry 13, nr 3-4 (1.01.1994): 187–205. http://dx.doi.org/10.1155/1994/41604.
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A vibronic level study of the spectroscopy and photophysics of the C6H6–CHCl3 complex has been carried out using a combination of laser-induced fluorescence and resonant two-photon ionization (R2PI). In C6H6-CHCl3, the S1–S0 origin remains forbidden while the 1610 transition is weakly induced. Neither 610 nor 1610 are split by the presence of the CHCl3 molecule. On this basis, a C3vstructure is deduced for the complex, placing CHCl3 on the six-fold axis of benzene. The large blue-shift of the complex’s absorption relative to benzene (+178 cm–1) and the efficient fragmentation of the complex following one-color R2PI reflect a hydrogen-bonded orientation for CHCl3 relative to benzene’ π cloud. Dispersed fluorescence scans place a firm upper bound on the ground state binding energy of the complex of 2,024 cm–1. Both the 61and 61 11 levels do not dissociate on the time-scale of the S1 fluorescence and show evidence of extensive state mixing with van der Waals’ levels primarily built on the 00 level of benzene. The C6H6–(CHCl3)2 cluster shows extensive intermolecular structure beginning at +84 cm–1, a strong origin transition, and splitting of 61. A structure which places both CHCl3 molecules on the same side of the benzene ring is suggested on this basis. The vibronic level scheme used to deduce the structure of C6H6–CHCl3 is tested against previous data on other C6H6–X complexes. The scheme is found to be capable, in favorable cases, of deducing the structures of C6H6–X complexes based purely on vibronic level data. Finally, the results on C6H6–CHCl3 are compared with those on C6H6–HCl and C6H6-H2O to evaluate the characteristics of the n hydrogen bond.
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Bowmaker, Graham A., Dip Singh Gill, Brian W. Skelton, Neil Somers i Allan H. White. "Syntheses, Structures and Vibrational Spectroscopy Studies of Copper(I) Perchlorate : Benzonitrile Adducts (1 : n) of n = 2, 3, 4, 5 Stoichiometry". Zeitschrift für Naturforschung B 59, nr 11-12 (1.12.2004): 1307–13. http://dx.doi.org/10.1515/znb-2004-11-1249.
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Abstract Syntheses and room-temperature single crystal X-ray structure determinations are recorded for an array of complexes formed between copper(I) perchlorate and benzonitrile of CuClO4 : PhCN (1:n) stoichiometry. Copper(I) perchlorate crystallized from neat benzonitrile solution yields a 1:5 CuClO4 : PhCN adduct, shown by the X-ray study to be of the form [Cu(NCPh)4](ClO4). PhCN, and, on recrystallization from dichloromethane, the 1:4 adduct, shown to be [Cu(NCPh)4](ClO4), the copper(I) atom in both the n = 4,5 adducts being in a quasi-tetrahedral four-coordinate environment, < Cu−N > 1.99 Å . Heating of either of the above materials under vacuum to 70 - 80◦ or 85 - 90 ◦C (Care!) yields 1:3 and 1:2 adducts respectively which may be crystallized from dichloromethane. The 1:3 adduct is shown to be of the form [(PhCN)3Cu(OClO3)], the CuN3 array quasi-trigonal planar (Σ N-Cu-N 358.0 ◦; Cu-N 1.906(4)-1.958(4), <> 1.93 Å ), with a long unidentate perchlorate oxygen approach (Cu. . .O 2.404(4) Å). The 1:2 adduct comprises a pair of quasi-linear [(PhCN)Cu(NCPh)] moieties (Cu-N 1.884(6), 1.866(5) Å ; N-Cu-N 158.6(3)◦] linked about an inversion centre by a pair of oxygen atoms from centrosymmetrically related perchlorate groups, so that a weakly bound fourmembered Cu(μ-O)2Cu central ring is obtained (Cu. . .O 2.445(4), 2.502(6) Å ). The structural data provide a basis for a comprehensive vibrational spectroscopic study across the whole array. These spectra show features that can be attributed to the structural changes that are observed with the change in the number of benzonitrile molecules in the compounds. The vibrational spectra of the acetonitrile complex [Cu(NCMe)4](ClO4) have also been recorded and used to assist in the assignment of the spectra of the various stoichiometries of the benzonitrile compounds.
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Jimenez-Fabian, Issac, Abraham Jalbout i Abderahim Boutalib. "Conformational study on the structures and energies of the weakly bound complexes of AlCl3 with diatomic molecules". Open Chemistry 5, nr 4 (1.12.2007): 1007–18. http://dx.doi.org/10.2478/s11532-007-0046-4.
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AbstractIn this work we present the results of high level ab initio calculations on weakly bound complexes of aluminium trichloride and hydrogen halides, HX, halogens, X2 and diatomic interhalogens, XY (where X, Y = F, Cl, Br). Based upon these calculations we have predicted that all structures in the staggered conformation (except for Cl3AlFH and Cl3AlClH) are stable minima while those in the eclipsed configurations are transition state structures. In the XH complexes the strength of interaction with the Cl3Al group is FH > ClH > BrH. In the case of X2 species it is Br2 > F2 > Cl2, and finally in the XY (YX) group it is: FBr > ClBr > FCl > BrCl > BrF > ClF.
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Jimenez-Fabian, Isaac, Abraham Jalbout i Abderahim Boutalib. "Conformational study on the structures and energies of the weakly bound complexes of AlCl3 with diatomic molecules". Open Chemistry 6, nr 1 (1.03.2008): 133. http://dx.doi.org/10.2478/s11532-007-0057-1.
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Ritschel, Thomas, Lutz Zülicke i Philip J. Kuntz. "Cationic Van-der-Waals Complexes: Theoretical Study of Ar2H+ Structure and Stability". Zeitschrift für Physikalische Chemie 218, nr 4 (1.04.2004): 377–90. http://dx.doi.org/10.1524/zpch.218.4.377.29196.
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AbstractThe electronic and geometric structure, stability and molecular properties of the cationic van-der-Waals complex Ar2H+ in its ground electronic state are studied by means of two ab-initio quantum-chemical approaches: conventional configuration interaction (multi-reference and coupled-cluster methods) and a diatomics-in-molecules model with ab-initio input data. To ensure consistency between the two approaches, one and the same one-electron atomic basis set (aug-cc-pVTZ by Dunning) is employed in both. The topography of the ground-state potential-energy surface is examined with respect to the nature of the binding and the stability of structures corresponding to stationary points. In accordance with most earlier theoretical work, there are two local minima at linear arrangements: a strongly bound centro-symmetric moiety, (Ar–H–Ar)+, and a weakly bound van-der-Waals complex, Ar···ArH+. These are separated by a low barrier. Only the centro-symmetric molecule is significantly stable (De = 0.68eV) against fragmentation into Ar + ArH+ and should have structural and dynamical relevance. A fairly simple diatomics-in-molecules model taking into account only the few lowest electronic fragment states yields a qualitatively correct description of the ground state but shows quantitative deviations from the more accurate configuration-interaction data in detail. Nevertheless, it should provide a good starting point for the treatment of larger complexes ArnH+ with n > 2.
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Palazzetti, Federico, Cecilia Coletti, Alessandro Marrone i Fernando Pirani. "Potential Energy Surfaces for Noble Gas (Ar, Kr, Xe, Rn)–Propylene Oxide Systems: Analytical Formulation and Binding". Symmetry 14, nr 2 (27.01.2022): 249. http://dx.doi.org/10.3390/sym14020249.
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Multidimensional potential energy surfaces for heavy noble gas–propylene oxide systems are obtained by applying the phenomenological method successfully used to describe homologous systems involving He and Ne atoms. Such potential energy surfaces, where the interaction exclusively arises from the anisotropic van der Waals interaction components, are given in an analytical form. Therefore, they can be easily used as force fields to carry out molecular simulations to evaluate spectroscopic features and the dynamical selectivity of weakly bound complexes formed by propylene oxide (a prototype chiral species) with a noble gas atom (a prototype isotropic partner) by two-body collisions under a variety of conditions. Several potential energy minima are identified on the surfaces, which are confirmed and characterized by high level ab initio calculations. The next step to further generalize this methodology is its extension to systems involving propylene oxide-diatomic molecules (as H2, O2 and N2), as well as to propylene oxide dimers.
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Stănciuc, Nicoleta, Gabriela Râpeanu, Gabriela Elena Bahrim i Iuliana Aprodu. "The Interaction of Bovine β-Lactoglobulin with Caffeic Acid: From Binding Mechanisms to Functional Complexes". Biomolecules 10, nr 8 (23.07.2020): 1096. http://dx.doi.org/10.3390/biom10081096.
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In this study, the interaction of native and transglutaminase (Tgase) cross-linked β-lactoglobulin (β-LG) with caffeic acid (CA) was examined, aiming to obtain functional composites. Knowledge on the binding affinity and interaction mechanism was provided by performing fluorescence spectroscopy measurements, after heating the native and cross-linked protein at temperatures ranging from 25 to 95 °C. Regardless of the protein aggregation state, a static quenching mechanism of intrinsic fluorescence of β-LG by CA was established. The decrease of the Stern–Volmer constants with the temperature increase indicating the facile dissociation of the weakly bound complexes. The thermodynamic analysis suggested the existence of multiple contact types, such as Van der Waals’ force and hydrogen bonds, between β-LG and CA. Further molecular docking tests indicated the existence of various CA binding sites on the β-LG surface heat-treated at different temperatures. Anyway, regardless of the simulated temperature, the CA-β-LG assemblies appeared to be unstable. Compared to native protein, the CA-β-LG and CA-β-LGTgase complexes (ratio 1:1) exhibited significantly higher antioxidant activity and inhibitory effects on α-glucosidase, α-amylase, and pancreatic lipase, enzymes associated with metabolic syndrome. These findings might help the knowledge-based development of novel food ingredients with valuable biological properties.
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Dong, Luning, Yaping Mai, Qiang Liu, Wannian Zhang i Jianhong Yang. "Mechanism and Improved Dissolution of Glycyrrhetinic Acid Solid Dispersion by Alkalizers". Pharmaceutics 12, nr 1 (20.01.2020): 82. http://dx.doi.org/10.3390/pharmaceutics12010082.
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The purpose of this study was to increase the dissolution of glycyrrhetinic acid (GA) by preparing ternary solid dispersion (TSD) systems containing alkalizers, and to explore the modulating mechanism of alkalizers in solid dispersion systems. GA TSDs were prepared by hot melt extrusion (HME) with Kollidon® VA64 as the carrier and L-arginine/meglumine as the alkalizers. The in vitro release of the TSD was investigated with a dissolution test, and the dissociation constant (pKa) was used to describe the ionization degree of the drug in different pH buffers. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), Fourier Transform Infrared Spectroscopy (FTIR), Raman spectra, X-ray photoelectron spectroscopy (XPS), and a molecular model were used for solid-state characterizations and to study the dissolution mechanism of the TSDs. It was evident that the dissolution of GA significantly increased as a result of the TSD compared to the pure drug and binary solid dispersion. SEM, DSC, and XPRD data showed that GA transformed into an amorphous form in TSD. As illustrated by FTIR, Raman, XPS, and molecular docking, high binding energy ion-pair complexes formed between GA and the alkalizers during the process of HME. These can destroy the H-bond between GA molecules. Further, intermolecular H-bonds formed between the alkalizers and Kollidon® VA64, which can increase the wettability of the drug. Our results will significantly improve the solubility and dissolution of GA. In addition, the lower pKa value of TSD indicates that higher ionization is beneficial to the dissolution of the drug. This study should facilitate further developments of TSDs containing alkalizers to improve the dissolution of weakly acidic drugs and gain a richer understanding of the mechanism of dissolution.
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Singh, Swapnil, Mateusz Majer, Mirosław Antoni Czarnecki, Yusuke Morisawa i Yukihiro Ozaki. "Solvent Effect on Assembling and Interactions in Solutions of Phenol: Infrared Spectroscopic and Density Functional Theory Study". Applied Spectroscopy 76, nr 1 (20.10.2021): 28–37. http://dx.doi.org/10.1177/00037028211052302.
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This work provides new insight into assembling of phenol in various solvents and competition between different kinds of interactions. To examine both weak and strong interactions, we selected a series of non-aromatic and aromatic solvents. Infrared spectra were measured at low (0.05 M) and high (2 M) phenol content. In addition, we performed density functional theory calculations of the structures and harmonic vibrational spectra of 1:1 complexes of phenol with the solvents and the associates of phenol from dimer to tetramer. Based on these results, we divided the solvents into three groups. The first group consists of non-aromatic solvents weakly interacting with phenol. Depending on the concentration, molecules of phenol in these solvents remain non-bonded or self-associated. In diluted solutions of phenol in chlorinated non-aromatic solvents do not appear free OH groups, since they are involved in a weak OH···Cl interaction. It is of note that in diluted solutions of phenol in tetramethyl ethylene both the non-bonded and bonded OH coexists due to solvent–solvent interactions. The second group consists of aromatic solvents with methyl or chlorine substituents. At low concentration, the molecules of phenol are involved in the phenol–solvent OH···π interaction and the strength of these interactions depends on the solvent properties. At a higher phenol content an equilibrium exists between phenol–solvent OH···π and phenol–phenol OH···OH interactions. Finally, the third group includes the aromatic and non-aromatic solvents with highly polar group (C≡N). In these solvents, regardless of the concentration all molecules of phenol are involved in the solute–solvent OH···NC interaction. Comparison of the experimental and theoretical band parameters reveals that molecules of phenol in non-aromatic solvents prefer the cyclic associates, while in the aromatic solvents they tend to form the linear associates.
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Kutsevol, N., Yu Kuziv, V. Zorin, I. Kravchenko, T. Zorina, A. Marynin i L. Bulavin. "Evaluation of a Dextran-Poly(N-Isopropylacrylamide) Copolymer as a Potential Temperature-Dependent Nanocarrier for Photosensitizers with Different Properties". Ukrainian Journal of Physics 65, nr 7 (15.07.2020): 638. http://dx.doi.org/10.15407/ujpe65.7.638.
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Thermosensitive polymer poly-N-isopropylacrylamide (PNIPAM) having a conformational transition in the interval of physiological temperatures was discussed last years as a novel drug delivery system. Chlorin e6 (Ce6) is a photosensitizer used in the photodynamic anticancer therapy. The comparative study of the encapsulation of Ce6 and its derivative, dimethylether of chlorine e6 (DME Ce6), into a water-soluble star-like PNIPAM-based copolymer to prevent the aggregation of a photosensitizer in the water medium is carried out. The photophysical properties of the copolymer/photosensitizer complexes as functions of the temperature in the region of the conformational transition of the polymer matrix have been studied and discussed. It is shown that Ce6 at low temperatures interacts weakly with the polymer phase. As a result, the absorption and fluorescence properties of Ce6 in aqueous and polymer solutions are practically identical. Fluorescence characteristics of Ce6 in a copolymer solution remain unchanged, when it is heated, which indicates the lack of a possibility for this sensitizer to bind in the bulk of the polymer phase. Following fluorescence data, all DME Ce6 molecules are bound with the polymer matrix, when a temperature is higher than the Lower Critical Solution Temperature (LCST) of the polymer. The formed complexes are quite stable. In the presence of serum proteins, the molecules of the photosensitizer remain associated for a long time with the polymer. At temperatures below LCST, DME Ce6 is not bound by the polymer. Moreover, the cooling of a solution of DME Ce6/polymer complexes leads to the rapid dissociation of photosensitizer molecules with subsequent aggregation or binding to biological structures in an aqueous medium. The obtained results show that the possibility of using the polymer PNIPAM as a temperature-dependent nanocarrier strongly depends on the properties of the loaded drug.
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Varadwaj, Pradeep R. "Does Oxygen Feature Chalcogen Bonding?" Molecules 24, nr 17 (30.08.2019): 3166. http://dx.doi.org/10.3390/molecules24173166.
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Using the second-order Møller–Plesset perturbation theory (MP2), together with Dunning’s all-electron correlation consistent basis set aug-cc-pVTZ, we show that the covalently bound oxygen atom present in a series of 21 prototypical monomer molecules examined does conceive a positive (or a negative) σ-hole. A σ-hole, in general, is an electron density-deficient region on a bound atom M along the outer extension of the R–M covalent bond, where R is the reminder part of the molecule, and M is the main group atom covalently bonded to R. We have also examined some exemplar 1:1 binary complexes that are formed between five randomly chosen monomers of the above series and the nitrogen- and oxygen-containing Lewis bases in N2, PN, NH3, and OH2. We show that the O-centered positive σ-hole in the selected monomers has the ability to form the chalcogen bonding interaction, and this is when the σ-hole on O is placed in the close proximity of the negative site in the partner molecule. Although the interaction energy and the various other 12 characteristics revealed from this study indicate the presence of any weakly bound interaction between the monomers in the six complexes, our result is strongly inconsistent with the general view that oxygen does not form a chalcogen-bonded interaction.
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Aoyagi, Youko, Elisabeth E. Adderson, Craig E. Rubens, John F. Bohnsack, Jin G. Min, Misao Matsushita, Teizo Fujita, Yoshiyuki Okuwaki i Shinji Takahashi. "L-Ficolin/Mannose-Binding Lectin-Associated Serine Protease Complexes Bind to Group B Streptococci Primarily through N-Acetylneuraminic Acid of Capsular Polysaccharide and Activate the Complement Pathway". Infection and Immunity 76, nr 1 (15.10.2007): 179–88. http://dx.doi.org/10.1128/iai.00837-07.
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ABSTRACT Group B streptococci (GBS) are the most common cause of neonatal sepsis and meningitis. Most infants who are colonized with GBS at birth do not develop invasive disease, although many of these uninfected infants lack protective levels of capsular polysaccharide (CPS)-specific antibody. The lectin pathway of complement is a potential mechanism for initiating opsonization of GBS with CPS-specific antibody-deficient serum. In this study, we determined whether mannose-binding lectin (MBL)/MBL-associated serine protease (MASP) complexes and L-ficolin/MASP complexes bind to different strains of GBS to activate the lectin pathway, and we identified the molecules recognized by lectins on the GBS surface. We found that MBL did not bind to any GBS examined, whereas L-ficolin bound to GBS cells of many serotypes. L-ficolin binding to GBS cells correlated with the CPS content in serotypes Ib, III (restriction digestion pattern types III-2 and III-3), and V but not with the group B-specific polysaccharide (GBPS) content or with the lipoteichoic acid (LTA) content. L-ficolin bound to purified CPS and GBPS in a concentration-dependent manner but not to purified LTA. All strains to which L-ficolin/MASP complexes bound consumed C4. When N-acetylneuraminic acid (NeuNAc) was selectively removed from GBS cells by treatment with neuraminidase, the reduction in L-ficolin binding was correlated with the amount of NeuNAc removed. Additionally, L-ficolin was able to bind to wild-type strains but was able to bind only weakly to unencapsulated mutants and a mutant strain in which the CPS lacks NeuNAc. We concluded that L-ficolin/MASP complexes bind to GBS primarily through an interaction with NeuNAc of CPS.
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Ehrlich, Lisa, Robert Gericke, Erica Brendler i Jörg Wagler. "(2-Pyridyloxy)silanes as Ligands in Transition Metal Coordination Chemistry". Inorganics 6, nr 4 (31.10.2018): 119. http://dx.doi.org/10.3390/inorganics6040119.
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Proceeding our initial studies of compounds with formally dative TM→Si bonds (TM = Ni, Pd, Pt), which feature a paddlewheel arrangement of four (N,S) or (N,N) bridging ligands around the TM–Si axis, the current study shows that the (N,O)-bidentate ligand 2-pyridyloxy (pyO) is also capable of bridging systems with TM→Si bonds (shown for TM = Pd, Cu). Reactions of MeSi(pyO)3 with [PdCl2(NCMe)2] and CuCl afforded the compounds MeSi(µ-pyO)4PdCl (1) and MeSi(µ-pyO)3CuCl (2), respectively. In the latter case, some crystals of the Cu(II) compound MeSi(µ-pyO)4CuCl (3) were obtained as a byproduct. Analogous reactions of Si(pyO)4, in the presence of HpyO, with [PdCl2(NCMe)2] and CuCl2, afforded the compounds [(HpyO)Si(µ-pyO)4PdCl]Cl (4), (HpyO)2Si[(µ-pyO)2PdCl2]2 (5), and (HpyO)2Si[(µ-pyO)2CuCl2]2 (6), respectively. Compounds 1–6 and the starting silanes MeSi(pyO)3 and Si(pyO)4 were characterized by single-crystal X-ray diffraction analyses and, with exception of the paramagnetic compounds 3 and 6, with NMR spectroscopy. Compound 2 features a pentacoordinate Si atom, the Si atoms of the other complexes are hexacoordinate. Whereas compounds 1–4 feature a TM→Si bond each, the Si atoms of compounds 5 and 6 are situated in an O6 coordination sphere, while the TMCl2 groups are coordinated to pyridine moieties in the periphery of the molecule. The TM–Si interatomic distances in compounds 1–4 are close to the sum of the covalent radii (1 and 4) or at least significantly shorter than the sum of the van-der-Waals radii (2 and 3). The latter indicates a noticeably weaker interaction for TM = Cu. For the series 1, 2, and 3, all of which feature the Me–Si motif trans-disposed to the TM→Si bond, the dependence of the TM→Si interaction on the nature of TM (Pd(II), Cu(I), and Cu(II)) was analyzed using quantum chemical calculations, that is, the natural localized molecular orbitals (NLMO) analyses, the non-covalent interaction (NCI) descriptor, Wiberg bond order (WBO), and topological characteristics of the bond critical points using the atoms in molecules (AIM) approach.
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Birnbaum, George I., Dennis D. Klug, John A. Ripmeester i John S. Tse. "Crystal structure and infrared spectra of an inclusion compound of cyclotriveratrylene and water". Canadian Journal of Chemistry 63, nr 11 (1.11.1985): 3258–63. http://dx.doi.org/10.1139/v85-539.
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A crystal grown by slow evaporation from a solution of cyclotriveratrylene (CTV) in toluene was found to be an inclusion compound with water as the only encaged guest. Its stoichiometry is C27H30O6•xH2O (x = 0.16) and it belongs to the monoclinic space group C2/c, with a = 24.216(21), b = 9.636(2), c = 23.117(4) Å, β = 118.08(5)°, Z = 8. X-ray intensity data were measured with a diffractometer and the structure was solved by direct methods. Least-squares refinement, which included all hydrogen atoms of the host molecule, converged at R = 0.046 for 3986 observed reflections. The geometry of the host molecule is compared to that of analogous structures and to cyclononatriene. Significant differences are ascribed to the effects of homoaromaticity and steric strain. Both the X-ray analysis and an FTIR study of the OH stretching show that the water molecules are weakly bound to the methoxy oxygen atoms of CTV. The molecular packing of CTV clathrates is discussed on the basis of crystallographic and spectroscopic evidence.
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Altun, Bleda i Trindle. "Production of Carbamic Acid Dimer from Ammonia-Carbon Dioxide Ices: Matching Observed and Computed IR Spectra". Life 9, nr 2 (23.04.2019): 34. http://dx.doi.org/10.3390/life9020034.
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The production of complex molecules in ammonia–carbon dioxide ices is presumed to pass through species of formula H3N:CO2 with further addition of ammonia and carbon dioxide. One possible landmark, carbamic acid, H2NCOOH, has been implicated among the products of warming and irradiation of such ices. Experimental study of the IR spectra of residues has suggested the presence of related species, including weakly bound 1:1 and 2:1 complexes of ammonia with carbon dioxide, zwitterionic carbamic acid, ammonium carbamate, and the dimer of carbamic acid. We computed the energetics and vibrational spectra of these species as well as the complex between ammonia and carbamic acid for gas and condensed phases. By means of a new spectrum-matching scoring between computed and observed vibrational spectra, we infer species that are most probably present. The leading candidates are ammonium carbamate, the carbamic acid–ammonia complex, and the carbamic acid dimer.
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Faisal, Zelma, Sándor Kunsági-Máté, Beáta Lemli, Lajos Szente, Dominik Bergmann, Hans-Ulrich Humpf i Miklós Poór. "Interaction of Dihydrocitrinone with Native and Chemically Modified Cyclodextrins". Molecules 24, nr 7 (4.04.2019): 1328. http://dx.doi.org/10.3390/molecules24071328.
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Citrinin (CIT) is a nephrotoxic mycotoxin produced by Aspergillus, Penicillium, and Monascus genera. It appears as a contaminant in grains, fruits, and spices. After oral exposure to CIT, its major urinary metabolite, dihydrocitrinone (DHC) is formed, which can be detected in human urine and blood samples. Cyclodextrins (CDs) are ring-shaped molecules built up from glucose units. CDs can form host-guest type complexes with several compounds, including mycotoxins. In this study, the complex formation of DHC with native and chemically modified beta- and gamma-cyclodextrins was tested at a wide pH range, employing steady-state fluorescence spectroscopic and modeling studies. The weakly acidic environment favors the formation of DHC-CD complexes. Among the CDs tested, the quaternary-ammonium-γ-cyclodextrin (QAGCD) formed the most stable complexes with DHC. However, the quaternary-ammonium-β-cyclodextrin (QABCD) induced the strongest enhancement in the fluorescence signal of DHC. Our results show that some of the chemically modified CDs are able to form stable complexes with DHC (logK = 3.2–3.4) and the complex formation can produce even a 20-fold increase in the fluorescence signal of DHC. Considering the above-listed observations, CD technology may be a promising tool to increase the sensitivity of the fluorescence detection of DHC.
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Bazett-Jones, D. P., i M. J. Hendzel. "High resolution mapping of nucleic acid containing complexes in vitro and in situ". Proceedings, annual meeting, Electron Microscopy Society of America 54 (11.08.1996): 48–49. http://dx.doi.org/10.1017/s0424820100162703.
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Structural analysis of combinations of nucleosomes and transcription factors on promoter and enhancer elements is necessary in order to understand the molecular mechanisms responsible for the regulation of transcription initiation. Such complexes are often not amenable to study by high resolution crystallographic techniques. We have been applying electron spectroscopic imaging (ESI) to specific problems in molecular biology related to transcription regulation. There are several advantages that this technique offers in studies of nucleoprotein complexes. First, an intermediate level of spatial resolution can be achieved because heavy atom contrast agents are not necessary. Second, mass and stoichiometric relationships of protein and nucleic acid can be estimated by phosphorus detection, an element in much higher proportions in nucleic acid than protein. Third, wrapping or bending of the DNA by the protein constituents can be observed by phosphorus mapping of the complexes. Even when ESI is used with high exposure of electrons to the specimen, important macromolecular information may be provided. For example, an image of the TATA binding protein (TBP) bound to DNA is shown in the Figure (top panel). It can be seen that the protein distorts the DNA away from itself and much of its mass sits off the DNA helix axis. Moreover, phosphorus and mass estimates demonstrate whether one or two TBP molecules interact with this particular promoter TATA sequence.
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Fritsch, Emmanuel, Etienne Balan, Sabine Petit i Farid Juillot. "Vibrational spectroscopic study of three Mg–Ni mineral series in white and greenish clay infillings of the New Caledonian Ni-silicate ores". European Journal of Mineralogy 33, nr 6 (17.12.2021): 743–63. http://dx.doi.org/10.5194/ejm-33-743-2021.
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Abstract. This study presents and discusses infrared spectroscopic data of well characterised, naturally occurring trioctahedral layer silicates of the serpentine (Srp), talc (Tlc), and sepiolite (Sep) mineral groups, which are found in reactivated faults and sequences of white and green clay veins (deweylite and garnierite) of the New Caledonian Ni-silicate ores. Bands assigned to the OH stretching vibrations of these 1:1 and 2:1 layer silicates in both the fundamental and first overtone regions of mid- and near-infrared (MIR and NIR) spectra, respectively, are compared to those reported in the literature for synthetic Mg–Ni series of the Srp and Tlc mineral groups. They are also presented according to the sequences of infillings recognised in the white and green veins of the Ni-silicate ores. The study reveals that serpentine-like (SL) minerals of the first sequences of clay infillings are residues of larger crystals of serpentines (lizardite, chrysotile, and antigorite) and that the newly formed talc-like (TL) minerals and Sep are the main Ni-bearing carriers of the Ni-silicate ores. Decreasing crystal size and order in serpentine species have major effects on vibrational bands. They favour the broadening of the OH stretching bands, the degradation of the signals assigned to the interlayer OH, and the enhancement of the signal related to weakly bound water molecules. The replacement of Mg by Ni in octahedral sites of the 2:1 layer silicates (TL, Sep) of the greenish clay infillings can be traced by specific OH stretching bands related to the Mg3OH, Mg2NiOH, MgNi2OH, and Ni3OH configurations in the fundamental (MIR) and first overtone (NIR) regions of the spectra. The dominance of the Mg3OH and Ni3OH configurations with respect to mixed configurations in the Mg–Ni mineral series of the clay infillings (mostly in the dominant TL minerals) suggests that Mg and Ni segregation is related to separate Mg-rich and Ni-rich mineral phases rather than to a cationic clustering within the individual particles. This segregation of Mg and Ni in discrete mineral phases is related to Mg–Ni oscillatory zoning patterns (banded patterns) and is reproduced at the scale of the Ni-silicate ores between the white (deweylite) and greenish (garnierite) veins of the reactivated faults.
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Fathy, Amany, Ahmed B. M. Ibrahim, S. Abd Elkhalik, Alexander Villinger i S. M. Abbas. "Trivalent Cobalt Complexes with NNS Tridentate Thiosemicarbazones: Preparation, Structural Study and Investigation of Antibacterial Activity and Cytotoxicity against Human Breast Cancer Cells". Inorganics 10, nr 9 (19.09.2022): 145. http://dx.doi.org/10.3390/inorganics10090145.
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New complexes of trivalent cobalt with substituted thiosemicarbazone ligands having an NNS donor system {HL1 = 4-(4-nitrophenyl)-1-((pyridin-2-yl)methylene)thiosemicarbazide and HL2 = 4-(2,5-dimethoxyphenyl)-1-((pyridin-2-yl)methylene)thiosemicarbazide} were synthesized via the in situ oxidation of divalent cobalt chloride accompanying its addition to the ligands. The complexes C1 and C2 were characterized via elemental (CHNS) analysis and 1H NMR, FT-IR and UV-Vis. spectroscopic data. Further, conductometric studies on the DMF solutions of the complexes indicated their 1:1 nature, and their diamagnetism revealed the low-spin trivalent oxidation state of the cobalt in the complexes. The X-ray diffraction analysis of complex C1 indicated that it crystallizes in the triclinic space group P-1. The metal exhibits an octahedral environment built by two anionic ligands bound via pyridine nitrogen, imine nitrogen and thiol sulfur atoms. The complex is counterbalanced by a chloride ion. In addition, two lattice water molecules were detected in the asymmetric unit of the unit cell. The ligand HL2 (20 mg/mL in DMSO) displayed inhibition zones of 10 mm against both S. aureus and E. coli, and the same concentration of the respective complex raised this activity to 15 and 12 mm against these bacterial strains, respectively. As a comparison, ampicillin inhibited these bacterial strains by 21 and 25 mm, respectively. Screening assay by HL1 on four human cancer cells revealed the most enhanced activity against the breast MCF-7 cells. The induced growth inhibitions in the MCF-7 cells by all compounds (0–100 μg/mL) have been detected. The ligands {HL1 and HL2} and complex C2 gave inhibitions with IC50 values of 52.4, 145.4 and 49.9 μM, respectively. These results are more meaningful in comparison with similar cobalt complexes, but less efficient compared with the inhibition with IC50 of 9.66 μM afforded by doxorubicin. In addition, doxorubicin, HL1 and HL2 induced cytotoxicity towards healthy BHK cells with IC50 values of 36.42, 54.8 and 110.6 μM, but surviving fractions of 66.1% and 62.7% of these cells were detected corresponding to a concentration of 100 μg/mL of the complexes (136.8 μM of C1 and 131.4 μM of C2).
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Piepenbrink, Kurt H., Oleg Y. Borbulevych, Ruth F. Sommese, John Clemens, Kathryn M. Armstrong, Clare Desmond, Priscilla Do i Brian M. Baker. "Fluorine substitutions in an antigenic peptide selectively modulate T-cell receptor binding in a minimally perturbing manner". Biochemical Journal 423, nr 3 (12.10.2009): 353–61. http://dx.doi.org/10.1042/bj20090732.
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TCR (T-cell receptor) recognition of antigenic peptides bound and presented by MHC (major histocompatibility complex) molecules forms the basis of the cellular immune response to pathogens and cancer. TCRs bind peptide–MHC complexes weakly and with fast kinetics, features which have hindered detailed biophysical studies of these interactions. Modified peptides resulting in enhanced TCR binding could help overcome these challenges. Furthermore, there is considerable interest in using modified peptides with enhanced TCR binding as the basis for clinical vaccines. In the present study, we examined how fluorine substitutions in an antigenic peptide can selectively impact TCR recognition. Using a structure-guided design approach, we found that fluorination of the Tax peptide [HTLV (human T-cell lymphotropic virus)-1 Tax11-19] enhanced binding by the Tax-specific TCR A6, yet weakened binding by the Tax-specific TCR B7. The changes in affinity were consistent with crystallographic structures and fluorine chemistry, and with the A6 TCR independent of other substitutions in the interface. Peptide fluorination thus provides a means to selectively modulate TCR binding affinity without significantly perturbing peptide composition or structure. Lastly, we probed the mechanism of fluorine's effect on TCR binding and we conclude that our results were most consistent with a ‘polar hydrophobicity’ mechanism, rather than a purely hydrophobic- or electrostatic-based mechanism. This finding should have an impact on other attempts to alter molecular recognition with fluorine.
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Craig, Donald C., Ian G. Dance, Philip AW Dean, James M. Hook, Hilary A. Jenkins, Christopher W. Kirby, Marcia L. Scudder i Umarani Rajalingam. "A synthetic, structural, and 113Cd NMR study of cadmium complexes of 1,3-thiazolidine-2-thionate, including the structures of Cd(C3H4NS2)2, (Cd(C3H4NS2)2(C5H5N)3·C5H5N, and (Ph4P)2[I2Cd(µ-C3H4NS2)2CdI2]". Canadian Journal of Chemistry 83, nr 2 (1.02.2005): 174–84. http://dx.doi.org/10.1139/v04-177.
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The crystallization of cadmium bis(1,3-thiazolidine-2-thionate), Cd(C3H4NS2)2 (1), is reported. Freshly prepared 1 reacts with Ph4P+X in a 1:2 ratio to give (Ph4P)2[Cd2(C3H4NS2)2X4] (X = I (4) or Br (5)). Crystallization of 1 from pyridine produces a solvate 7, which loses pyridine readily. X-ray analyses show that 1 has a polymeric sheet structure in which the C3H4NS2 ligands act as bidentate bridges through N and the exocyclic S and the Cd has a CdN2S2 kernel; 5 is isomorphous with 4, which contains a dimeric anion again with bridging through the N and exocyclic S of the heterocyclic ligands; and 7 is Cd(C3H4NS2)2(C5H5N)3·C5H5N, containing trigonal bipyramidal Cd(C3H4NS2)2(C5H5N)3 molecules, in which the C3H4NS2 ligands, both of which are monodentate and in equatorial positions, occur as a unique combination of S- and N-bound. Cadmium-113 NMR data for 1 in pyridine solution and solid-state CP-MAS 113Cd data for 1, 7, bis(pyridinium-4-thiolate)cadmium, and tetrakis(pyridinium-2-thiolate)cadmium nitrate are reported and discussed. The compound 1 has chemical and NMR spectroscopic properties that make it a useful standard for solid-state CP-MAS 113Cd NMR spectroscopy. Key words: cadmium, 1,3-thiazolidine-2-thionate, X-ray analysis, solid-state 113Cd NMR, 113Cd NMR standard compound.
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Mézière, C., M. Viguier, H. Dumortier, R. Lo-Man, C. Leclerc, J. G. Guillet, J. P. Briand i S. Muller. "In vivo T helper cell response to retro-inverso peptidomimetics." Journal of Immunology 159, nr 7 (1.10.1997): 3230–37. http://dx.doi.org/10.4049/jimmunol.159.7.3230.
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Abstract Peptide analogues containing reversed peptide bonds between each residue along the peptide sequence (retro-inverso modification) have been analyzed for their antigenic and in vivo immunogenic properties in the MHC II and Th cell response context. Two antigenic peptides were selected for this study, namely peptide 103-115 of poliovirus VP1, which is involved in the production of Abs that neutralize the infectivity of the virus, and peptide 435-446 from the third constant region of mouse heavy chain IgG2a allopeptide gamma 2ab, which mimics a corneal Ag implicated in autoimmune keratitis. In a competition assay performed in vitro using reference hybridomas of known MHC class II restriction, both retro-inverso analogues bound (although more weakly in our test) to I-Ad and/or I-Ed class II molecules. However, in both cases, this lower affinity was apparently largely compensated in vivo, as a T cell response (with IL-2 secretion), equivalent to that obtained with the wild-type peptides, was observed following immunization of BALB/c mice with the retro-inverso analogues. Moreover, these T cells proliferated and produced IL-2 in response to the cognate peptides. It is concluded that the T cell receptors of T cells primed in vivo with the retro-inverso analogues readily cross-react with parent and retro-inverso analogue-MHC complexes. The approach of using pseudopeptides containing changes involving the backbone, and not the orientation of side chains, may thus be promising to design potent immunogens for class II-restricted T cells.
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Lee, Calvin W. Z., M. Qadri E. Mubarak, Anthony P. Green i Sam P. de Visser. "How Does Replacement of the Axial Histidine Ligand in Cytochrome c Peroxidase by Nδ-Methyl Histidine Affect Its Properties and Functions? A Computational Study". International Journal of Molecular Sciences 21, nr 19 (27.09.2020): 7133. http://dx.doi.org/10.3390/ijms21197133.
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Heme peroxidases have important functions in nature related to the detoxification of H2O2. They generally undergo a catalytic cycle where, in the first stage, the iron(III)–heme–H2O2 complex is converted into an iron(IV)–oxo–heme cation radical species called Compound I. Cytochrome c peroxidase Compound I has a unique electronic configuration among heme enzymes where a metal-based biradical is coupled to a protein radical on a nearby Trp residue. Recent work using the engineered Nδ-methyl histidine-ligated cytochrome c peroxidase highlighted changes in spectroscopic and catalytic properties upon axial ligand substitution. To understand the axial ligand effect on structure and reactivity of peroxidases and their axially Nδ-methyl histidine engineered forms, we did a computational study. We created active site cluster models of various sizes as mimics of horseradish peroxidase and cytochrome c peroxidase Compound I. Subsequently, we performed density functional theory studies on the structure and reactivity of these complexes with a model substrate (styrene). Thus, the work shows that the Nδ-methyl histidine group has little effect on the electronic configuration and structure of Compound I and little changes in bond lengths and the same orbital occupation is obtained. However, the Nδ-methyl histidine modification impacts electron transfer processes due to a change in the reduction potential and thereby influences reactivity patterns for oxygen atom transfer. As such, the substitution of the axial histidine by Nδ-methyl histidine in peroxidases slows down oxygen atom transfer to substrates and makes Compound I a weaker oxidant. These studies are in line with experimental work on Nδ-methyl histidine-ligated cytochrome c peroxidases and highlight how the hydrogen bonding network in the second coordination sphere has a major impact on the function and properties of the enzyme.
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Sang, Peng, Yong-Qin Chen, Meng-Ting Liu, Yu-Ting Wang, Ting Yue, Yi Li, Yi-Rui Yin i Li-Quan Yang. "Electrostatic Interactions Are the Primary Determinant of the Binding Affinity of SARS-CoV-2 Spike RBD to ACE2: A Computational Case Study of Omicron Variants". International Journal of Molecular Sciences 23, nr 23 (26.11.2022): 14796. http://dx.doi.org/10.3390/ijms232314796.
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To explore the mechanistic origin that determines the binding affinity of SARS-CoV-2 spike receptor binding domain (RBD) to human angiotensin converting enzyme 2 (ACE2), we constructed the homology models of RBD-ACE2 complexes of four Omicron subvariants (BA.1, BA.2, BA.3 and BA.4/5), and compared them with wild type complex (RBDWT-ACE2) in terms of various structural dynamic properties by molecular dynamics (MD) simulations and binding free energy (BFE) calculations. The results of MD simulations suggest that the RBDs of all the Omicron subvariants (RBDOMIs) feature increased global structural fluctuations when compared with RBDWT. Detailed comparison of BFE components reveals that the enhanced electrostatic attractive interactions are the main determinant of the higher ACE2-binding affinity of RBDOMIs than RBDWT, while the weakened electrostatic attractive interactions determine RBD of BA.4/5 subvariant (RBDBA.4/5) lowest ACE2-binding affinity among all Omicron subvariants. The per-residue BFE decompositions and the hydrogen bond (HB) networks analyses indicate that the enhanced electrostatic attractive interactions are mainly through gain/loss of the positively/negatively charged residues, and the formation or destruction of the interfacial HBs and salt bridges can also largely affect the ACE2-binding affinity of RBD. It is worth pointing out that since Q493R plays the most important positive contribution in enhancing binding affinity, the absence of this mutation in RBDBA.4/5 results in a significantly weaker binding affinity to ACE2 than other Omicron subvariants. Our results provide insight into the role of electrostatic interactions in determining of the binding affinity of SARS-CoV-2 RBD to human ACE2.
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Lishko, Valeryi K., i Tatiana P. Ugarova. "Evidence That Fibrinogen Inhibits Leukocyte Adhesion to Fibrin Clot and Immobilized Fibrinogen by Binding to the Substrate but Not to Integrins." Blood 106, nr 11 (16.11.2005): 2631. http://dx.doi.org/10.1182/blood.v106.11.2631.2631.
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Abstract The recruitment of phagocytic leukocytes to sites of injured vessel wall plays an important role in thrombus remodeling during normal vascular repair and in the pathophysiology of thrombosis. Fibrin and fibrinogen, present in the thrombus, are potent adhesive substrates for neutrophils and monocytes. They support cellular attachment by binding cell surface receptors that belong to the β2 subfamily of integrins. Adhesive interactions of neutrophils and monocytes with polymerized fibrin and insoluble fibrinogen matrix in vivo occur in the presence of high concentrations of circulating plasma fibrinogen (~2–4 mg/ml). One important property of fibrinogen that would have a major bearing on leukocyte adhesion is its capacity to form complexes with fibrin. Therefore, by virtue of its binding to the fibrin clot and/or immobilized fibrinogen, soluble plasma fibrinogen can influence leukocyte adhesion to these substrates. In this study, the possibility that soluble fibrinogen could protect fibrin from adhesion of leukocytes was examined. Fibrinogen was an efficient inhibitor of adhesion of U937 monocytoid cells and neutrophils to fibrin gel and immobilized fibrin(ogen). An investigation of the mechanism by which fibrinogen exerts its influence on leukocyte adhesion indicated that it did not block integrins but rather associated non-covalently and weakly with fibrin(ogen) substrates. Consequently, leukocyte integrins that engage fibrinogen molecules loosely bound to the fibrin(ogen) matrix are not able to consolidate their grip on the substrate; subsequently, cells detach. This conclusion is based on the evidence obtained in adhesion studies using various β2-integrin bearing cells and performed under static and flow conditions. Furthermore, surface plasmon resonance studies, undertaken to determine the Kd of fibrinogen-fibrin interactions under flow conditions, indicated that fibrinogen formed complexes with fibrin(ogen) with micromolar affinities. Thus, these findings reveal a new role of fibrinogen in integrin-mediated leukocyte adhesion. They also imply that the anti-adhesive effect of fibrinogen may protect the thrombus from an excessive leukocyte accumulation and premature dissolution at the early stages of wound healing when hemostatic plug integrity is critical for preventing blood loss.
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Raoufi, Mojgan, Wenhua Zhou, Enriqueta Guinto, Nick Grafos, Safi Ranzurmal, Robert S. Greenfield, Jacob Rand i Han-Mou Tsai. "A Sensitive Enzyme-Linked Assay of ADAMTS13 Antibodies for Diagnosis of TTP." Blood 106, nr 11 (16.11.2005): 553. http://dx.doi.org/10.1182/blood.v106.11.553.553.
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Abstract Thrombotic thrombocytopenic purpura (TTP), a serious disorder characterized by the development of VWF-platelet rich thrombi in the arterioles and capillaries, requires reliable diagnostic assays for optimal management of the patients. Simple, reliable assays of ADAMTS13 inhibitors or antibodies are not yet widely available. To develop an ELISA for antibodies of ADAMTS13, we analyze the levels of patient IgG bound to immobilized recombinant ADAMTS13 in a microtiter plate format. The mean (±SD) IgG binding value is 5.1 ± 1.5 arbitrary units (AU)/mL among a group of 36 normal subjects and is 5.3 ± 2.7 AU/mL among 31 random patients (P > 0.1). Two (5%) of the normal group and 2 (6%) of the random group are outliers. When applied to patients with thrombotic microangiopathy, this assay yields IgG binding values ranging from 2.0 – 58.3 (median = 5.4) AU/mL in a group of 40 subjects with other thrombotic microangiopathy and 10.1 - > 60.0 (median 49.0) AU/mL in a group of 56 patients with acute TTP. Excluding 2 (5%) outlying samples, the mean (±SD) for the “other TM” group is 5.9 ±2.5 AU/mL, which is not different from the values of the normal and random subjects. In contrast, the IgG binding values are > 10.0 AU/mL in each of the acute TTP patients. Furthermore, heating the plasma samples at 56oC, presumably by dissociating ADAMTS13 from immune complexes, increases IgG binding of 4 weakly positive TTP samples from 10.1 – 12.7 to 28.3 – 154.3 AU/mL. Addition of native ADAMTS13 lacking the tag sequences decreases the binding of TTP IgG to 40% ± 20% of control, but does not affect the binding of 6 outlying non-TTP IgG (120% ± 20% vs. control, P < 0.001), suggesting that the IgG of non-TTP samples do not recognize ADAMTS13. In summary, the ELISA for ADAMTS13 antibodies is highly sensitive for detection of ADAMTS13 antibodies. A subset of the general population contains IgG molecules that react with the recombinant ADAMTS13 fusion protein but not with native ADAMTS13. Blocking with native ADAMTS13 enhances the specificity of the assay for TTP. Figure Left: Binding of IgG to immobilized rADAMTS13-FLAG/His in four groups of study subjects. Right: Suppression of IgG binding by untagged ADAMTS13 in TTP but not in non-TTP samples. Figure. Left: Binding of IgG to immobilized rADAMTS13-FLAG/His in four groups of study subjects. . / Right: Suppression of IgG binding by untagged ADAMTS13 in TTP but not in non-TTP samples.
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Depastas, Theodoros, Alexandros Androutsopoulos i Demeter Tzeli. "Analysis of chemical bonding of the ground and low-lying states of Mo2 and of Mo2Clx complexes, x = 2 - 10." Journal of Chemical Physics, 4.07.2022. http://dx.doi.org/10.1063/5.0091907.
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In the present study, we perform accurate calculations via multireference configuration interaction and coupled cluster methodologies on the dimolybdenum molecule in conjunction with complete series of correlation and weighted core correlation consistent basis sets up to quintuple size. The bonding, dissociation energies, and spectroscopic parameters of the seven states that correlate to the ground state products are calculated. The ground state has a sextuple chemical bond and each of the calculated excited state has one less bond than the previous one. The calculated values for the ground(X1Σg+ ) state of Mo2 have been extrapolated to the complete basis set limits. Our final values, re=1.9324 Å and De(D0)=4.502{plus minus}0.007(4.471{plus minus}0.009) eV, are in excellent agreement with the experimental values of re=1.929, 1.938(9) Å and D0=4.476(10) eV. The Mo2 in 13Σg+ state is a weakly bound dimer, forming 5s...5pz bonds, with De=0.120 eV at re=3.53 Å. All calculated excited states (except 13Σg+) have a highly multireference character (C0=0.25-0.55). The ordering of the molecular bonding orbitals changes as the spin is increased from quintet to septet state. The quite low bond dissociation energy of the ground state is due to the splitting of the molecular bonding orbitals in two groups differing in energy by ~3 eV. Finally, the bond breaking of Mo2, as the multiplicity of spin is increased, is analyzed in parallel with the Mo-Mo bond breaking in a series of Mo2Clx complexes when x is increased. Physical insight into the nature of the sextuple bond and its low dissociation energy is provided.