Frameworks of Transition Metals and Linkers with Two or More Functional Groups

2000 ◽  
Vol 658 ◽  
Author(s):  
Slavi C. Sevov
Keyword(s):  
Amino Acids ◽  
Transition Metals ◽  
Functional Groups ◽  
Organic Molecules ◽  
Layered Structures ◽  
Amino Groups ◽  
Effect Of Ph ◽  
Open Framework ◽  
Acidic Conditions ◽  
New Compounds

ABSTRACTHybrid inorganic/organic materials with open-framework or layered structures are known for many transition metals linked by functionalized organic molecules such as organic diphosphonates, polycarboxylates, polynitriles, etc., species with more than one equivalent functional groups. We have studied the effect of pH on such a system of cobaltmethylenediphosphonate and report three new compounds, Na3Co[(O3PCH2PO3)(OH)],Na2Co(O3PCH2PO3)•H2O, and Co2[(O3PCH2PO3)(H2O)], that form at very basic, moderately basic, and acidic conditions, respectively. More interestingstructural chemistry should be expected from linkers with two or more different functionalities. Both the carboxylic and phosphonic groups in carboxyethylphosphonic acid are used to coordinate to cobalt or calcium atoms in the new compounds Co3(O3PCH2CH2COO)2•6H2O and Ca(O3PCH2CH2COOH)•H2O. Taking one more step further in complexity we have also studied linkers with three different functional groups, phosphonated amino acids. The structures of two new compounds, Zn(O3PCH2CH(NH3)COO) and Zn(O3PCH2CH2CH(NH3)COO), are threedimensional frameworks made of zinccoordinated by both the carboxylic and phosphonic ends of the organic molecules. The amino groups are protonated and terminal in the voids of the frameworks.

Immobilisation of acid pectinase on graphene oxide nanosheets

2014 ◽  
Vol 68 (6) ◽  
Author(s):  
Yang Liu ◽  
Qiang Li ◽  
Yuan-Yuan Feng ◽  
Geng-Sheng Ji ◽  
Tian-Cheng Li ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Functional Groups ◽  
Recent Progress ◽  
Catalytic Efficiency ◽  
Cross Linking ◽  
Carboxyl Group ◽  
Large Specific Surface Area ◽  
Graphene Oxide Nanosheets ◽  
Amino Groups ◽  
Acidic Conditions

AbstractRecent progress in nanotechnology has prompted research interest in immobilised enzymes on graphene oxide (GO) nanosheets for their large specific surface area and abundant functional groups. In the present work, acid pectinase was immobilised on the GO via the cross-linking of amino groups on pectinase and functional groups (e.g. carboxyl group) on the GO surface. Acid pectinase was effectively immobilised on the support and high loading densities were obtained (2400 mg per g of support). In addition, the immobilised enzyme achieved a better catalytic efficiency (K cat/K m) than its free counterpart; 3.7 mg−1 min−1 mL for immobilised pectinase, 3.5 mg−1 min−1 mL for free pectinase. Under acidic conditions, pectinase immobilised on GO will be agglomerated, but the addition of surfactant PEG 6000 could solve the problem and afford higher catalytic activity and catalytic efficiency.

scholarly journals ON PHOSPHOTUNGSTIC ACID STAINING. II

1971 ◽  
Vol 19 (11) ◽  
pp. 648-653 ◽  
Author(s):  
G. QUINTARELLI ◽  
J. A. CIFONELLI ◽  
R. ZITO
Keyword(s):  
Amino Acids ◽  
Phosphotungstic Acid ◽  
Hydroxyl Groups ◽  
Amino Groups ◽  
Ionic Interaction ◽  
Neutral Sugars ◽  
Acidic Conditions ◽  
Heparin Oligosaccharides ◽  
Positively Charged ◽  
Acid Glycosaminoglycans

Phosphotungstic acid (PTA) used at different concentrations in water was combined with various compounds (amino acids, proteins, acid glycosaminoglycans, glycoproteins and simple sugars). The results obtained indicated that PTA interacts with positively charged groups, that the sugar-hydroxyls do not take part in the interaction and that the type of binding involves electrostatic forces. To substantiate these findings further, heparin and heparin oligosaccharides were N-desulfated, combined with PTA and the precipitates were analyzed. It was found that the interaction had taken place only between the metal and the desulfated hexosamine amino groups and that when the N-desulfated product was acetylated no PTA binding occurred. When PTA was used at higher concentrations and in extremely acidic conditions, a precipitation of proteins, amino acids, acid glycosaminoglycans and neutral sugars ensued. This complex formation was interpreted as due to ionic interaction between the polyacid and the protonated hydroxyl groups.

Hydration Free Energies of Organic Molecules in the FreeSolv Database Calculated with Polarized Atom In Molecules Atomic Charges and the GAFF Force Field.

2018 ◽  
Author(s):  
Maximiliano Riquelme ◽  
Alejandro Lara ◽  
David L. Mobley ◽  
Toon Vestraelen ◽  
Adelio R Matamala ◽  
...  
Keyword(s):  
Force Field ◽  
Functional Groups ◽  
Electrostatic Interactions ◽  
Organic Molecules ◽  
Force Fields ◽  
Chemical Elements ◽  
Atomic Charges ◽  
Free Energies ◽  
Molecular Systems ◽  
Solvent Model

<div>Computer simulations of bio-molecular systems often use force fields, which are combinations of simple empirical atom-based functions to describe the molecular interactions. Even though polarizable force fields give a more detailed description of intermolecular interactions, nonpolarizable force fields, developed several decades ago, are often still preferred because of their reduced computation cost. Electrostatic interactions play a major role in bio-molecular systems and are therein described by atomic point charges.</div><div>In this work, we address the performance of different atomic charges to reproduce experimental hydration free energies in the FreeSolv database in combination with the GAFF force field. Atomic charges were calculated by two atoms-in-molecules approaches, Hirshfeld-I and Minimal Basis Iterative Stockholder (MBIS). To account for polarization effects, the charges were derived from the solute's electron density computed with an implicit solvent model and the energy required to polarize the solute was added to the free energy cycle. The calculated hydration free energies were analyzed with an error model, revealing systematic errors associated with specific functional groups or chemical elements. The best agreement with the experimental data is observed for the MBIS atomic charge method, including the solvent polarization, with a root mean square error of 2.0 kcal mol<sup>-1</sup> for the 613 organic molecules studied. The largest deviation was observed for phosphor-containing molecules and the molecules with amide, ester and amine functional groups.</div>

scholarly journals Peculiarities of promiscuous l-threonine transaldolases for enantioselective synthesis of β-hydroxy-α-amino acids

2021 ◽  
Author(s):  
Shan Wang ◽  
Hai Deng
Keyword(s):  
Amino Acids ◽  
Organic Molecules ◽  
Stereoselective Synthesis ◽  
Enantioselective Synthesis ◽  
General Mechanism ◽  
Future Developments ◽  
Key Points ◽  
Biomaterial Science ◽  
One Step ◽  
Harsh Conditions

Abstract The introduction of β-hydroxy-α-amino acids (βHAAs) into organic molecules has received considerable attention as these molecules have often found widespread applications in bioorganic chemistry, medicinal chemistry and biomaterial science. Despite innovation of asymmetric synthesis of βHAAs, stereoselective synthesis to control the two chiral centres at Cα and Cβ positions is still challenging, with poor atomic economy and multi protection and deprotection steps. These syntheses are often operated under harsh conditions. Therefore, a biotransformation approach using biocatalysts is needed to selectively introduce these two chiral centres into structurally diverse molecules. Yet, there are few ways that enable one-step synthesis of βHAAs. One is to extend the substrate scope of the existing enzyme inventory. Threonine aldolases have been explored to produce βHAAs. However, the enzymes have poor controlled installation at Cβ position, often resulting in a mixture of diastereoisomers which are difficult to be separated. In this respect, l-threonine transaldolases (LTTAs) offer an excellent potential as the enzymes often provide controlled stereochemistry at Cα and Cβ positions. Another is to mine LTTA homologues and engineer the enzymes using directed evolution with the aim of finding engineered biocatalysts to accept broad substrates with enhanced conversion and stereoselectivity. Here, we review the development of LTTAs that incorporate various aldehyde acceptors to generate structurally diverse βHAAs and highlight areas for future developments. Key points • The general mechanism of the transaldolation reaction catalysed by LTTAs • Recent advances in LTTAs from different biosynthetic pathways • Applications of LTTAs as biocatalysts for production of βHAAs

scholarly journals Chiroptical activity of hydroxycarboxylic acids with implications for the origin of biological homochirality

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Jana Bocková ◽  
Nykola C. Jones ◽  
Uwe J. Meierhenrich ◽  
Søren V. Hoffmann ◽  
Cornelia Meinert
Keyword(s):  
Amino Acids ◽  
Lactic Acid ◽  
Organic Molecules ◽  
Building Blocks ◽  
Aliphatic Chain ◽  
Monocarboxylic Acids ◽  
Hydroxycarboxylic Acids ◽  
Polarised Light ◽  
Suitable Target ◽  
Anisotropy Spectra

AbstractCircularly polarised light (CPL) interacting with interstellar organic molecules might have imparted chiral bias and hence preluded prebiotic evolution of biomolecular homochirality. The l-enrichment of extra-terrestrial amino acids in meteorites, as opposed to no detectable excess in monocarboxylic acids and amines, has previously been attributed to their intrinsic interaction with stellar CPL revealed by substantial differences in their chiroptical signals. Recent analyses of meteoritic hydroxycarboxylic acids (HCAs) – potential co-building blocks of ancestral proto-peptides – indicated a chiral bias toward the l-enantiomer of lactic acid. Here we report on novel anisotropy spectra of several HCAs using a synchrotron radiation electronic circular dichroism spectrophotometer to support the re-evaluation of chiral biomarkers of extra-terrestrial origin in the context of absolute photochirogenesis. We found that irradiation by CPL which would yield l-excess in amino acids would also yield l-excess in aliphatic chain HCAs, including lactic acid and mandelic acid, in the examined conditions. Only tartaric acid would show “unnatural” d-enrichment, which makes it a suitable target compound for further assessing the relevance of the CPL scenario.

Soluble lanthanide-transition-metal clusters Ln36Co12 as effective molecular electrocatalysts for water oxidation

2021 ◽  
Vol 57 (29) ◽  
pp. 3611-3614
Author(s):  
Rong Chen ◽  
Chao-Long Chen ◽  
Ming-Hao Du ◽  
Xing Wang ◽  
Cheng Wang ◽  
...  
Keyword(s):  
Transition Metal ◽  
Transition Metals ◽  
Synergistic Effect ◽  
Water Oxidation ◽  
Metal Clusters ◽  
Bond Formation ◽  
Transition Metal Clusters ◽  
Oxidation Activity ◽  
Acidic Conditions ◽  
Effective Water

The stable 48-metal Ln36Co12 clusters show an effective water oxidation activity under weak acidic conditions because of the synergistic effect between lanthanide and transition metals in O–O bond formation.

The potential mechanism of atmospheric new particle formation involving amino acids with multiple functional groups

2021 ◽  
Author(s):  
Jiarong Liu ◽  
Ling Liu ◽  
Hui Rong ◽  
Xiuhui Zhang
Keyword(s):  
Amino Acids ◽  
Aspartic Acid ◽  
Functional Groups ◽  
Atmospheric Aerosols ◽  
Potential Role ◽  
Particle Formation ◽  
Potential Mechanism ◽  
New Particle Formation

Amino acids are recognized as significant components of atmospheric aerosols. However, its potential role in the atmospheric new particle formation (NPF) is poorly understood, especially aspartic acid (ASP), one of...

scholarly journals Simple and efficient modifications of well known techniques for reliable growth of high-quality crystals of small bioorganic molecules

2014 ◽  
Vol 47 (4) ◽  
pp. 1435-1442 ◽  
Author(s):  
Denis A. Rychkov ◽  
Sergey G. Arkhipov ◽  
Elena V. Boldyreva
Keyword(s):  
Amino Acids ◽  
Secondary School ◽  
Organic Molecules ◽  
Poor Quality ◽  
Chemical Degradation ◽  
School Level ◽  
Chemistry Curriculum ◽  
High Quality ◽  
Small Organic Molecules ◽  
Secondary School Level

A number of modifications to traditional techniques are suggested in order to overcome problems that frequently arise when growing crystals from solution. These improvements, and their combination, help to avoid problems such as poor nucleation, the spontaneous precipitation of many poor-quality small powder-like crystals, crystals adhering to the crystallization vessel or to each other, and chemical degradation of the solution. The proposed techniques can be used to crystallize desirable metastable polymorphs reliably. None of the suggested methods demands the usage of any special or expensive equipment, or specific skills, and they can be implemented in the chemistry curriculum even at secondary school level. Examples are given for the crystallization of small organic molecules such as carboxylic acids, amino acids, pharmaceuticals etc., but the same techniques are applicable to other classes of compound.

scholarly journals The principle of formaldehyde, alcohol, and acetone titrations. With a discussion of the proof and implication of the zwitterion conception

1934 ◽  
Vol 115 (792) ◽  
pp. 121-141 ◽  
Keyword(s):  
Amino Acids ◽  
Carboxyl Groups ◽  
Recent Discussion ◽  
Amino Groups ◽  
Chemical Methods ◽  
Titration Method ◽  
Physico Chemical ◽  
Empirical Argument ◽  
Chemical Evidence

Consideration of the implications of the zwitterion hypothesis of Bjerrum (1923) makes it desirable to state afresh the principles underlying the methods commonly employed in the titration of amino-acids. Deductions of considerable theoretical importance, cf., e. g ., Calvery (1933) are still being made on the supposition that the alkalimetric formaldehyde titration method of Sørensen (1907) and the corresponding alcohol method of Foreman (1920) and of Willstätter and Waldschmidt-Leitz (1921) estimate the carboxyl groups of amino-acids whilst the acidimetric acetone titration of Linderstrøm-Lang (1928) estimates the amino-groups. Yet the zwitterion hypothesis indicates that this assumption is the reverse of the truth. Discussion is greatly facilitated by collective consideration of recent physico-chemical evidence clarifying the principles upon which these common bio-chemical methods rest. In a recent discussion of two of the titrimetric methods (Van Slyke and Kirk, 1933) the existence of this evidence is ignored, so that it becomes necessary to systematize and elaborate the empirical argument of these authors in the light of the relevant investigations of Grünhut (1919), Cray and Westrip (1925), Michaelis and Mizutani (1925), Birch and Harris (1930, b ), and Levy (1933). At the same time new and useful developments are indicated.

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