Coalgebras Research Articles

Carbonyl Tilting and Bending Potential Energy Surface of Carbon Monoxyhemes

The CO tilting (τ) and bending (β) potential energy surface of carbon monoxyheme has been investigated with local density functional calculations. The calculations indicate that τ and β are strongly coupled and that simultaneous, in-phase displacements along these coordinates represent a low-energy pathway across the surface. Calculations on two small model complexes indicate that strong τ−β coupling also occurs in these systems. Accordingly, this feature appears to be a general characteristic of the Fe−CO unit in a square-planar coordination geometry. In-phase τ−β CO deformations (τ + β) of as much as 25° can take place with the expenditure of relatively small amounts of energy (2 kcal/mol or less). However, very large distortions of 45−60° are energetically demanding and unreasonable. The calculations also rule out the possibility that the coordination geometry of the proximal histidine is the major determinant of the CO orientation. Both a full vibrational analysis on a small model complex and a limited analysis on a tetraatomic model yield calculated frequencies and isotope shifts for the Fe−CO unit in excellent agreement with those observed for carbon monoxyhemes. Collectively, our calculated τ−β potential energy surface provides a plausible explanation for the wide variation in CO orientations reported for carbon monoxymyoglobin and also account for the unusual vibrational characteristics of the Fe−CO unit.

A Nonlocal Density Functional Study of the Pd(II)-Assisted Copolymerization of Ethylene and CO

We study the homogeneous catalytic copolymerization of olefin and carbon monoxide.1-4 The catalytic center is modeled by Pd(II) coordinated to PH2CHCHPH2. C2H4 is used as a model for the olefin. We investigate the chain propagation mechanism for alternating copolymerization as well as the side reactions resulting from multiple insertion of olefin and CO, respectively. We find that strictly alternating copolymerization is kinetically favored over homopolymerization of olefin and thermodynamically as well as kinetically favored over successive multiple insertions of CO. Insertion of one C2H4−CO unit into the Pd−ethyl bond yields −219 kJ/mol, whereas insertion of a C2H4−C2H4 segment yields exactly −200 kJ/mol. Insertion of a CO−CO segment yields only −88 kJ/mol. Therefore, multiple successive CO insertions are by comparison so unfavorable as to be ruled out completely. We explain the experimentally observed preference of strictly alternating copolymerization over multiple olefin insertions by the higher adduct formation energy of CO (−78 kJ/mol) as opposed to only −51 kJ/mol for C2H4. Furthermore, the activation barriers for the insertion of a CO/C2H4 unit into the chain are only 48 and 58 kJ/mol, respectively, whereas the barrier for C2H4 insertion is 65 kJ/mol. All acyl species encountered are only weakly stabilized by agostic interactions, whereas Pd-alkyl species are strongly stabilized by agostic interactions. The acyl species can stabilize itself by −31 kJ/mol over the most favorable agostic conformation by adopting a η2-carbonyl conformation. The growing polyketone chain is strongly stabilized by forming chelate bonds between the carbonyl oxygens and Pd. The strictly alternating copolymerization pattern originates from a combination of effects: On the one hand, the number of CO units incorporated into the chain is maximized, because CO (as the better π acceptor) stabilizes the reactive center more than ethylene during the adduct formation proceeding insertion and CO also faces a lower barrier during insertion into the chain. On the other hand, subsequent multiple insertions of CO are avoided since they are kinetically as well as thermodynamically highly unfavorable.

Structural models for lithium intermediates during carboxamide-directed metallations

Structural models for Li intermediates during metallations of two different organic precursors having –NH–CO units are isolated and structurally characterised, and shown to be complexed mono- and di-meric azaenolates with (–NC–OLi·xB)n(B = Lewis base) groupings; contrary to earlier assumptions, the structures imply that the N-(rather than the O-) centres of these species would direct second lithiations to nearby C–H bonds although it has proved impossible thus far to detect the proposed dilithiated systems.

Mechanisms of alkyne trimerisation at molybdenum and tungsten centres leading to novel metallacycles: crystal and molecular structures of two isomeric forms of [Mo{C(CF3)C(CF3)C(CF3)C(CF3)C(CO2Me)C(CO2Me)(SPri)}(η5-C5H5)

The η2-C,C vinyl complexes [M{η3-C(CF3)C(CF3)SR}(CF3CCCF3)(η5-C5H5)]1(M = Mo, R = Pri; M = W, R = Me, Et or Pri) reacted with dimethyl acetylenedicarboxylate R′CCR′(R′= CO2Me) to give products of alkyne trimerisation containing two different oligomerisation sequences depending on whether R′CCR′ occupies a terminal or central position in the alkyne trimer chain, i.e. C(CF3)C(CF3)C(CF3)C(CF3)C(R′)C(R′) and C(CF3)C(CF3)C(R′)C(R′)C(CF3)C(CF3). With M = Mo, kinetic 19F NMR studies established a reaction sequence proceeding above ca.–30 °C via two different butadienyl complexes [M{η2-C(CF3)C(CF3)C(R′)C(R′)SPri}(CF3CCCF3)(η5-C5H5)]2 and 3 to give isomeric trienyl derivatives [Mo{η6-C(CF3)C(CF3)C(CF3)C(CF3)C(R′)C(R′)SPri}(η5-C5H5)]4 and [Mo{η5-C(CF3)C(CF3)C(CF3)C(CF3)C(R′)SPriC(R′)}(η5-C5H5)]5 which were isolated at room temperature. X-Ray diffraction studies established that in each case the trienyl ligand is bound to the metal via an η2-C,C alkenyl linkage, and two σ carbon–metal bonds. In 4 this is accompanied by co-ordination of a CO unit of a carbomethoxy carbonyl whereas in 5 the thiolate sulfur is bonded to the metal. Above room temperature 5 isomerises to give species 6 and ultimately 7 which appears to result from thiolate transfer to the metal to give a seven-membered metallacycle. With M = W, the reactions also proceed via a butadienyl complex 2 but this isomerises via two other intermediates to give trienyl products [W{η6-C(CF3)C(CF3)C(R′)C(R′)C(CF3)C(CF3)SR}(η5-C5H5)] and [WF{η5-C(CF2)C(CF3)C(R′)C(R′)C(CF3)C(CF3)SR}(η5-C5H5)]. X-Ray diffraction studies established that the trienyl ligand in the former is co-ordinated via one σ, two π alkene linkages and a thiolate sulfur. Two isomeric forms were structurally characterised which differ only in the orientation of the thiolate isopropyl substituent which can adopt syn or anti positions. In the fluoride a CF3 fluorine has been transferred to the metal and this has generated a hexatrienyl attachment via a quasi π-allylic interaction and through W–C and W–S σ bonds.

A Note on Inner Coalgebra Measuring and Derivations.

A Note on Inner Coalgebra Measuring and Derivations.

Graded coalgebras and Morita-Takeuchi contexts

Graded coalgebras and Morita-Takeuchi contexts

Alternating Olefin/Carbon Monoxide Polymers: A New Family of Thermoplastics

Abstract Significant technological advances by Shell over the past decade have led to the development of a new family of thermoplastics. These new materials are perfectly alternating olefidcarbon monoxide polymers which provide a superior combined balance of performance properties not found in other commercial materials. Shell will market these new polymers under the trade mark CARILON® Polymers. CARILON® polymers are semicrystalline thermoplastics derived from simple and abundant raw materials of carbon monoxide and ethylene (or other a-olefins.) These new materials have resulted, in part, from a high activity catalyst invention which enables the polymer to be produced with perfectly alternating units of CO and olefin. The excellent physical, chemical, and barrier properties of these aliphatic polyketone polymers places them in the broad class of materials known as “engineering thermoplastics” which are widely used in industrial, automotive, appliance, and electrical applications.

Factors influencing acid-base status during acute severe hypothermia in unanesthetized rats

Blood acid-base changes were studied during acute hypothermia (4–6 h) induced by cold exposure in the unanesthetized rat. Stewart's quantitative analysis was applied as a complementary approach to determine the relative contributions of several non-respiratory components to the arterial acid-base response. Acute decrease in body temperature (T B) lowered Pa CO 2 (32.5 to 14.5 mmHg) and [HCO 3 −]a (24.20 mEq/L to 17.56 mEq/L), increased pHa (7.481 to 7.608) and diminished the [ OH −] [ H +] ratio, but had no significant effect on [SID] or [A tot], although both total phosphorus [P T] and inorganic phosphate [Pi] increased. The acid-base changes found were intermediate between those predicted by α-stat and pH-stat hypotheses. Deviation from the regulative α-imidazole strategy was more apparent in the plasma than in the intraerythrocyte compartment. We conclude that blood pH changes observed were mainly caused by increased relative ventilation (lung ventilation per unit of CO 2 removed) and by resulting changes in P CO 2 , with a minor metabolic component but without significant contribution from ionic shifts or changes in plasma protein concentration.

Structure‐Lipophilicity and Structure‐Polarity relationships of amino acids and peptides

AbstractThe objectives of this study were to gain insights into the structure‐lipophilicity relationships of peptides and to propose an improved model for estimating their lipophilicity. First, existing databases were extended to obtain the distribution coefficients of a total of 208 free or protected peptides (di‐ to pentapeptides). The polarity parameters (Λ) of 23 free amino acids and 19 protected amino acids (AcNHCHRCONH2) and of their side chains were calculated from experimental distribution coefficients and computed molecular volumes. An analysis of the polarity parameters revealed that the hydrophobicity of the amino‐acid side chains is largely reduced due to the polar field of the backbone. The polarity parameters of the peptides were then obtained in a similar manner and shown to be highly correlated with the sum of the polarity parameters of their side chains, i.e., the lipophilicity of peptides can be calculated from their molecular volume and the sum of their side‐chain polarities using the regression established for each individual series of peptides (Fig. 1). This last restriction is essential since the polarity and lipophilic increment of a NHC*HCO unit were shown to decrease with increasing length of backbone.

Chain conformation in polyretropeptides: Quantum mechanical and empirical force field calculations on 2,6,8‐trioxo‐3,5,9‐triazadecane, a model compound for poly(retro‐glycine)

AbstractWe report here our results on semiempirical AM1 calculations for the conformational preferences of 2,6,8‐trioxo‐3,5,9‐triazadecane, a model compound for polymers made of retropeptide units. We have evaluated the effect of applying symmetry constraints between chemically equivalent torsion angles. These results suggest that preferred conformations around the NHCH2NH group are quite independent from those on the COCH2CO unit, so all possible combinations generate the complete set of energy minima for the model compound.We have analyzed the implications of the different minimum energy conformation in an infinite chain model and we have explored the conformational space of regular polyretropeptides. This shows a close relation to that of regular polypeptides but with significant differences arising from the change of orientation of the peptide units along the polymer molecule. The energy calculations also support previously proposed models for the crystal structure of the simplest polyretropeptide, poly(retro‐glycine). Finally, we discuss the consequences of retropeptide‐peptide copolymerization as well as the expected conformations for regular alternate terpolymers. © 1995 John Wiley & Sons, Inc.

Nonassociative coalgebras

Nonassociative coalgebras

Graded coalgebras

Graded coalgebras

Skolem-noether theorems and coalgebra actions

Skolem-noether theorems and coalgebra actions

Aquatic biomass resources and carbon dioxide trapping

Intensively managed microalgal production facilities are capable of fixing several-fold more carbon dioxide per unit area than trees or crops. Although CO 2 is still released when fuels derived from algal biomass are burned, integration of microalgal farms for flue gas capture approximately doubles the amount of energy produced per unit of CO 2 released. Materials derived from microalgal biomass also can be used for other long-term uses, serving to sequester CO 2. Flue gas has the potential to provide sufficient quantities of CO 2 for such large-scale microalgae farms. Viewing microalgae farms as a means to reduce the effects of a greenhouse gas (carbon dioxide, CO 2) changes the view of the economics of the process. Instead of requiring that microalgae-derived fuel be cost competitive with fossil fuels, the process economics must be compared with those of other technologies proposed to deal with the problem of CO 2 pollution. However, development of alternative, environmentally safer energy production technologies will benefit society whether or not global climate change actually occurs. Microalgal biomass production has great potential to contribute to world energy supplies, and to control CO 2 emissions as the demand for energy increases. This technology makes productive use of arid and semi-arid lands and highly saline water, resources that are not suitable for agriculture and other biomass technologies.

Pseudo-raft rhenium–platinum clusters. Synthesis and crystal structure of the anions [PtRe3(µ-H)(CO)13]2–and [PtRe4(CO)17]2–, containing a central Pt atom surrounded by a folded stripe of Re atoms

The redox condensation between [{Pt3(CO)6}n]2–(n≈ 10) and rhenium carbonyl anions gives two novel mixed-metal species, [PtRe3(µ-H)(CO)13]2– and [PtRe4(CO)17]2–, containing a Pt–CO unit interacting with three and four Re(CO)4 moieties, respectively, arranged as a stripe folded around the Pt atom and whose formation confirms the tendency of Re atoms to cluster around Pt, giving structures based on Re2Pt triangles with a low Pt: Re ratio.

CO clusters on MgO studied by low-temperature UV-visible diffuse reflectance spectroscopy

A silica cell specially designed for low-temperature measurements of UV-visible diffuse reflectance spectra of adsorbed species has been used to study the interaction of CO with well-outgassed MgO. Spectra recorded with the cell jacket cooled to 77 K show that CO reacts rapidly with MgO to produce strong UV absorption at 360 nm and 290 nm. The bands are attributed to adsorbed CO 2 2− and to ketenic CO dimer/trimer anions, respectively. Larger CO-derived anions containing several CO units (telomers) form at room temperature and produce absorption in the visible with λ max = 450 nm. The formation of these clusters at ambient temperature is greatly assisted by pre-conditioning in CO at low temperature, confirming that CO 2 2− and ketenic species are precursors of the telomeric CO anions.

Atomic-resolution scanning tunneling microscopy and infrared spectroscopy as combined in situ probes of electrochemical adlayer structure: carbon monoxide on rhodium (111)

Abstract : In-situ scanning tunneling microscopy (STM) has been combined with infrared reflection-absorption spectroscopy (IRRAS) to yield detailed atomic- level adlayer structures for saturated coverages of CO on ordered Rh(111) in aqueous solutions. Two distinctly different structures were obtained in CO- containing 0.1 M NaC104, depending on the electrode potential. At higher potentials, ca -0.1 to 0.3 V vs SCE, atomic-resolution STM images were obtained that indicated the presence of a (2 x 2)-3CO unit cell, having a CO coverage in agreement with electrochemical and IRRAS measurements. The corresponding in-situ infrared spectra indicate the presence of two atop (or near-atop) and one twofold bridging CO in the unit cell. A real-space structure is suggested that is related to the corresponding (2 x 2)-3CO adlattice on Rh(111) in uhv as deduced previously by low-energy electron diffraction and vibrational spectroscopy.

Two probable different FeCO geometries in carbonmonoxide myoglobin model systems

Unexpected NMR shifts observed for one bis-ansa iron(II)_carbonmonoxide porphyrin system are considered to be inconsistent with a linear FeCO unit lying perpendicular to the porphyrin plane and rather are deemed to be consonant with the hypothesis that reduced CO affinities in myoglobin complexes may indicate deformations in the actual porphyrin cores.

Coordination behavior of cinoxacine: Synthesis and crystal structure of tris (cinoxacinate) cobaltate(II) of sodium hexahydrate (HCx = 1-ethyl-4(1H) -oxo-(1,3) dioxolo-(4,5g) cinnoline-3-carboxylic acid)

The synthesis, crystal, and molecular structure of Co(Cx)3Na6H2O are reported. The Cobalt(II) compound crystallizes in the trigonal system, space group R 3 with Z = 6, in a cell of dimensions a= 18.688(7) (Å), c= 20.142(6) Å. Least-squares refinement of 1331 reflections [I≥3σ(I)] gave a final R = 0.088 for all observed reflections.The structure consists of anionic monomeric units of (Co(Cx)3−) and sodium cations. Three Cinoxacinate ions are chelated through Oceto and Ocarbox atoms. The Co(II) ion positioned on the third axis is bonded to six oxygen atoms in a slightly distorted octahedral environment.

Electron transfer. 108. Reductions of pyridinecarboxylic acids with vitamin B12s (Cob(I)alamin)

Vitamin B 12s (cob(I)alamin) is oxidized to its Co(II) analogue by pyridinemonocarboxylic and -dicarboxylic acids in buffered aqueous media. With B 12s in excess, the 3- and 4-substituted acids and the 2,4- and 3,5-diacids consume 6 units of Co(I). With the oxidants in excess, conversions are mainly to dihydro derivatives which, in the case of the 3-carboxylic acid, appear to be predominantly 1,6-dihydro species. Further partial conversion to tetrahydro compounds is reflected in biphasic kinetic profiles from which rate constants for both reaction steps have been estimated