Structural studies of poly(phosphazenes). 1. Molecular and crystal structures of poly(dichlorophosphazene)

Chatani, Yôzô; Yatsuyanagi, Koh

doi:10.1021/ma00171a028

Cited by 41 publications

(29 citation statements)

References 5 publications

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“…9). The P-N distances of distorted PNP, 1.8 Å and 1.5 Å, agree remarkably well with singleand double-bond P-N distances of 1.44 -1.49 and 1.77 Å, respectively (37,38). Consequently, we speculate that a PϭN double bond tends to localize at the leaving group P2, with a P-N single bond at the electrophilic P1.…”

Section: Metal Content and Inhibition By Fluoridesupporting

confidence: 72%

A Trimetal Site and Substrate Distortion in a Family II Inorganic Pyrophosphatase

Fabrichniy

Lehtiö

Tammenkoski

et al. 2007

Journal of Biological Chemistry

111

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We report the first crystal structures of a family II pyrophosphatase complexed with a substrate analogue, imidodiphosphate (PNP). These provide new insights into the catalytic reaction mechanism of this enzyme family. We were able to capture the substrate complex both by fluoride inhibition and by site-directed mutagenesis providing complementary snapshots of the Michaelis complex. The universally present inorganic pyrophosphatase (PPase, EC 3.6.1.1) 4 is a central enzyme of phosphorus metabolism.PPases are essential enzymes, because they hydrolyze the inorganic pyrophosphate (PP i ) generated during a number of ATPdependent cellular processes and thus provide the necessary thermodynamic pull for them (1). PPases require divalent metal cations for catalysis. Soluble PPases comprise two families, which differ completely in both sequence (2, 3) and structure (4, 5). Family I PPases (reviewed in Ref. 6) occur in all types of cells from bacteria to man, whereas family II PPases occur almost exclusively in bacteria. Of the 57 known family II PPases, 53 occur in eubacteria, 3 in archaebacteria, and 1 in a unicellular eukaryote (Giardia lamblia). Three Vibrio species, including Vibrio cholerae, have genes for both family I and family II PPases. The frequent occurrence of family II PPase in human pathogens (e.g. Streptococcus agalactiae causes neonatal pneumonia, sepsis, and meningitis; Streptococcus mutans, dental caries; and V. cholerae, cholera) makes studies of this enzyme medically important. In addition, family II PPases belong to the "DHH" family of phosphoesterases, named after the characteristic DHH amino acid signature (7). All of these enzymes have similar structures (5, 8) and presumably related catalytic mechanisms.In contrast to family I PPases, which have a simple cup-like single-domain structure, family II PPases have two domains, with the active site at the domain interface (4, 5) (Fig. 1A). The C-terminal domain of family II PPase contains the high affinity substrate-binding site, whereas the catalytic site that binds the nucleophile-coordinating metal cations is located in the N-terminal domain. Closure of the C-terminal domain onto the N-terminal one creates the catalytically competent conformation by bringing the electrophilic phosphate of substrate into the catalytic site (9). The trigger for domain closure is substrate binding to the C-terminal domain in the open conformation (9).The two PPase families catalyze the hydrolysis of PP i in what initially appeared to be similar active sites (4, 5) (Fig. 1B), but their functional properties are significantly different. The natural metal cofactor of family I PPases is Mg 2ϩ , binding to the enzyme with micromolar affinity, whereas family II enzymes are best activated by Mn 2ϩ or Co 2ϩ , which bind with nanomolar affinity. With these metal ions, family II PPases are ϳ10-fold more active than family I PPases (k cat of 1700 -3300 s Ϫ1 versus 110 -330 s Ϫ1 ) (10 -12). Interestingly, Mg 2ϩ confers lower activity but greater substrate-binding affinity on fam...

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Section: Metal Content and Inhibition By Fluoridesupporting

confidence: 72%

A Trimetal Site and Substrate Distortion in a Family II Inorganic Pyrophosphatase

Fabrichniy

Lehtiö

Tammenkoski

et al. 2007

Journal of Biological Chemistry

111

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“…We see that (1) the chain backbone is at least as flexible as sp 3 carbon-chain polymers and (2) it carries two identical side groups on every second chain atom, except in the case of the polysilylenes where longer skeletal bonds allow each main-chain atom to be doubly substituted; as a result, we have a considerable and regular side-group crowding around the chain skeleton; (3) in the mesophase the chain backbone is generally less extended than in the crystalline state, typically with a 10% contraction along the chain axis direction (cf. l crys and l meso ), whereas the chain diameter is expanded with respect to the crystalline state; [26][27][28] (4) increasing the size of the side groups for a given main chain structure yields both an increasing chain diameter D and a larger persistence length P. These characteristics may be interpreted by a model in which the main chain of polymers giving rise to class 2 mesophases acts as a sort of entropic spring that pulls together the side groups giving rise to a compact cylindrical organization of the macromolecule and the side chains around the chain axis (see Figure 2). Indeed, the distance D between neighboring chain axes is large enough as to ensure that interdigitation between their side groups …”

Section: Mesophases Of Flexible Polymers: General Thermodynamic Consimentioning

confidence: 99%

Mesomorphic Phases of Flexible Polymers: The Self-Compacting Chain Model

Allegra

Meille

2004

Macromolecules

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Correlations are established between structural, thermal, and flexibility data of crystalline, locally flexible polymers giving rise to mesomorphic phases, which can be usefully organized in two classes. While in all mesophases the chain conformation is substantially disordered, in class 1 chain packing is characterized by orientation-dependent attractive interactions, so that the transition enthalpy ∆HML from the mesophase to the liquid is of the same order of magnitude as the crystal f mesophase transition enthalpy ∆HCM. Conversely, in mesophases belonging to class 2 and in the corresponding melts nonbonded intermolecular interactions and conformational statistics are roughly similar, so that the M f L transition involves very little enthalpy (∆HML ∼ 0). Consistent with the absence of specific interchain interactions, class 2 mesophases exhibit hexagonal packing and density lower than the corresponding crystalline phase. Polymers giving rise to this type of mesophase are characterized by numerous, regularly spaced side groups, often chemically different from the chain skeleton. The key factor stabilizing class 2 mesophases over the melt appears to be a higher entropy of the side groups, making mesogenic groups unnecessary. Optimization of the intrachain arrangement in class 2 mesophases usually requires a local contraction along the chain axis direction with respect to the extension found in the crystal and the confinement of individual chains within tubes that have a diameter D substantially larger than the average diameter D C in the crystal. With a simple statistical model based on continuum elasticity (the self-compacting chain), applicable to flexible polymers, we show that, consistent with the available experimental data, the persistence length P is proportional to D 2 . As a consequence, the aspect ratio P/D, which is normally assumed to control mesophase stability, is proportional to D. According to our approach, we thus may estimate by simple diffraction measurements of D the persistence length and the class 2 mesophase stability of flexible polymers. In the case of systems which experimentally give rise to class 2 mesophases, relatively large values of P are found despite the relatively low T g.

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“…Therefore,t he birefringence PNCl 2 is only about 0.01 ! [13][14][15][16][17][18][19] Preliminary experiments have confirmed the stability of these compounds including Mg 2 PN 3 ,L i 2 PNO 2 and PNF 2 . [20] An ew PN(OH) 2 structure could be designed using the replacement of (OH) À with F À as in some actual cases.…”

Section: Angewandte Chemiementioning

confidence: 78%

“…Remarkably,the PN bonds are arranged in the same polar orientation along the chained direction so the micro SHG responses for each PN unit are summated to produce alarge macro SHG effect. [19] It can be prepared by polymerization of hexachlorophosphazene in industry.Because of the The large optical anisotropy of the PN motif makes it able to achieve the DUV PM output down to its DUV absorption edge (approximately 142 nm).…”

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confidence: 99%

Poly(difluorophosphazene) as the First Deep‐Ultraviolet Nonlinear Optical Polymer: A First‐Principles Prediction

et al. 2019

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An ovel concept to obtain the deep-ultraviolet (DUV) nonlinear optical (NLO) materials is proposed based on the assembling of one-dimensional (1D) polar motifs into quasi-1D polymer patterns.B ased on the first-principles calculations,w eh ave successfully discovereda ne xcellent DUV NLO polymer,i.e., poly(difluorophosphazene), with the chemical formula of (PNF 2 ) n .C alculations reveal that PNF 2 has alarger band gap,astronger second harmonic generation effect, al arger birefringence,a nd as horter phase-matching cutoff than KBe 2 BO 3 F 2 .T hese findings not only demonstrate that the PNF 2 is the first reported DUV NLO polymer,but also could open an ew direction to discover novel DUV NLO materials in polymer systems.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

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Structural studies of poly(phosphazenes). 1. Molecular and crystal structures of poly(dichlorophosphazene)

Cited by 41 publications

References 5 publications

A Trimetal Site and Substrate Distortion in a Family II Inorganic Pyrophosphatase

A Trimetal Site and Substrate Distortion in a Family II Inorganic Pyrophosphatase

Mesomorphic Phases of Flexible Polymers: The Self-Compacting Chain Model

Poly(difluorophosphazene) as the First Deep‐Ultraviolet Nonlinear Optical Polymer: A First‐Principles Prediction

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