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1.
A series of six deuterium-labelled analogs of isopententyl diphosphate (IPP) was prepared to investigate the detailed stereochemical course of addition of C5 units during rubber biosynthesis in Hevea brasiliensis and Parthenium argentatum. These analogs were incorporated into the cis-polyisoprene chain by rubber transferase in rubber particles, and the stereochemistry was determined by 2H-NMR analysis of the polymer or of levulinic acid derivatives obtained from its ozonolytic degradation. Results indicate that rubber chain elongation occurs with loss of the pro-S hydrogen of IPP, addition of the allylic diphosphate to the si face of IPP and inversion of stereochemistry at the carbon bearing the diphosphate. 相似文献
2.
Enzymatic Formation of a Skipped Methyl‐Substituted Octaprenyl Side Chain of Longestin (KS‐505a): Involvement of Homo‐IPP as a Common Extender Unit
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Dr. Taro Ozaki Dr. Sandip S. Shinde Lei Gao Ryo Okuizumi Dr. Chengwei Liu Dr. Yasushi Ogasawara Prof. Dr. Xiaoguang Lei Prof. Dr. Tohru Dairi Dr. Atsushi Minami Prof. Dr. Hideaki Oikawa 《Angewandte Chemie (International ed. in English)》2018,57(22):6629-6632
Longestin (KS‐505a), a specific inhibitor of phosphodiesterase, is a meroterpenoid that consists of a unique octacyclic terpene skeleton with branched methyl groups at unusual positions (C1 and C12). Biochemical analysis of Lon23, a methyltransferase involved in the biosynthesis of longestin, demonstrated that it methylates homoisopentenyl diphosphate (homo‐IPP) to afford (3Z)‐3‐methyl IPP. This compound, along with IPP, is selectively accepted as extender units by Lon22, a geranylgeranyl diphosphate (GGPP) synthase homologue, to yield dimethylated GGPP (dmGGPP). The absolute configuration of dmGGPP was determined to be (4R,12R) by degradation and chiral GC analysis. These findings allowed us to propose an enzymatic sequence for key steps of the biosynthetic pathway of the unusual homoterpenoid longestin. 相似文献
3.
Hiroshi Ochiai Kunihiko Gekko Hitoshi Yamamura 《Journal of Polymer Science.Polymer Physics》1971,9(9):1629-1640
The sorption properties of atactic polypropylene (APP) and isotactic polypropylene (IPP) were studied by equilibrium sorption of various organic solvents. The variation of the Flory-Huggins interaction parameter χ for the APP-CCl4 system at 25°C was expressed as a function of the volume fraction v2 of polymer by the relation: x = 0.113 exp {1.879 v2}. The average molecular weight M c of the polymer chains between successive crystallites for IPP subjected to different thermal treatments was calculated to be 250 to 350 by the equation of Flory and Rehner. From the variation of M c with solvent concentration, we estimated the number fraction of polymer chains actually contributing to elastic deformation. The clustering function for solvent in the polymer calculated by the method of Zimm and Lundberg decreased linearly from a positive value to ?1 with increasing solvent concentration. Clustering of solvent molecules was found to occur more easily in APP than in IPP. 相似文献
4.
Takafumi Sato Tadafumi Adschiri Kunio Arai 《Journal of Analytical and Applied Pyrolysis》2003,70(2):735-746
The decomposition of 2-propylphenol (PP) at 673 K and a water density of 0–0.5 g cm−3 yielded 2-isopropylphenol (IPP), phenol and 2-cresol. Gas products were methane, carbon dioxide, ethylene and propene. The decomposition was found to occur through rearrangement and alkylation, that is, (1) rearrangement of the propyl functional group from PP to IPP, (2) dealkylation of PP to phenol, (3) dealkylation of PP to 2-cresol. The decomposition probably occurred by a free-radical mechanism. The reaction rate constants of each pathway were determined and it was found that these were invariant over all the water densities studied at the given temperature. 相似文献
5.
Raluca Nicoleta Darie Mihai Brebu Cornelia Vasile Marek Kozlowski 《Polymer Degradation and Stability》2003,80(3):551-566
Binary isotactic polypropylene (IPP)/polyamide 6 (PA6) and ternary IPP/PA6/ethylene–propylene diene terpolymer (EPDM) blends in various ratios were obtained in a Haake Rheocord mixer. Processing behaviour was changed in the presence of IPP functionalized with bismaleimide (BMI), maleic anhydride (MA) and acrylic acid (AA) as reactive compatibilizing agents. The thermal and thermo-oxidative behaviour of blends was studied by differential scanning calorimetry and thermogravimetry. The functionalized IPPs modify the crystallinity degree and the decomposition behaviour of both IPP and PA6 as a result of chemical reactions of functional groups with those of the PA6. The changes depend on the IPP/PA6 or IPP/PA6/EPDM ratio, the chemical nature and amount of the functionalized IPP. On the basis of the processing and thermal data one can conclude that the compatibilizing agent effect increases in the following order: IPP-AA 相似文献
6.
Substrate analogues for isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), where the C3 methyl groups were replaced by chlorine, were synthesized and evaluated as substrates for avian farnesyl diphosphate synthase (FPPase). The IPP analogue (3-ClIPP) was a cosubstrate when incubated with dimethylallyl diphosphate (DMAPP) or geranyl diphosphate (GPP) to give the corresponding chlorinated analogues of geranyl diphosphate (3-ClGPP) and farnesyl diphosphate (3-ClFPP), respectively. No products were detected in incubations of 3-ClIPP with 3-ClDMAPP. Incubation of IPP with 3-ClDMAPP gave 11-ClFPP as the sole product. Values of K(M)(3-ClIPP) (with DMAPP) and K(M)(3-ClDMAPP) (with IPP) were similar to those for IPP and DMAPP; however, values of k(cat) for both analogues were substantially lower. These results are consistent with a dissociative electrophilic alkylation mechanism where the rate-limiting step changes from heterolytic cleavage of the carbon-oxygen bond in the allylic substrate to alkylation of the double bond of the homoallylic substrate. 相似文献
7.
The effect of stereoregularity on the thermo-oxidative degradation of poly(propylene)s, isotactic (IPP) and syndiotactic (SPP), was compared with that of high density polyethylene (HDPE) by means of chemiluminescence (CL). SPP is extremely stable to thermal oxidation and CL signals appeared much later than in IPP and even later than in HDPE. For example, at 160°C the maximum intensity of CL was measured after only 13 min for IPP, 60 min for HDPE and 260 min for SPP. IR spectroscopic results support the conclusions drawn from CL results. 相似文献
8.
I. K. Mehta D. S. Sood B. N. Misra 《Journal of polymer science. Part A, Polymer chemistry》1989,27(1):53-62
Acrylonitrile (AN) has been graft copolymerized onto isotactic polypropylene (IPP) by the preirradiation method using Co60 as the source of gamma rays in the presence of ethanol, n-propanol, isopropanol, n-butanol, tert. butyl alcohol, and n-pentanol. Alcohols vary in their ability to influence grafting of AN onto IPP and the following reactivity order was found: n-pentanol > n-butanol > tert.-butanol > n-propanol > ethanol > isopropanol. An attempt has been made to explain the observed reactivity pattern shown by different alcohols. Thermal behavior of the graft copolymer has been compared with that of IPP and irradiated IPP and it was observed that grafted IPP is thermally more stable than IPP and irradiated IPP. 相似文献
9.
Zhaoyun Ding Liguo Zhou Shimin Fang 《Journal of Dispersion Science and Technology》2013,34(9):1342-1349
Effect of surfactants [polyglycerol diisostearate ethoxylates (PGDIS-E31, PGDIS-E36 and PGDIS-E40) and Tween-80], alcohols (1,2-propandiol, ethanol, 1-propanol, 1-butanol, 2-butanol and 1-pentanol), oils [isopropyl palmitate (IPP), isooctyl palmitate (IOP), dioctyl carbonate (DOC), and dioctyl hexanediate (DOH)], temperature and sodium chloride on the microemulsion formation of the surfactant/alcohol/oil/water system has been investigated by the pseudo-ternary phase diagrams. The capacities of the four surfactants in the microemulsion formation of the surfactant/alcohol/IPP/water system at surfactant/alcohol of 2:1 are in the order of PGDIS-E31 > PGDIS-E36 > Tween-80 > PGDIS-E40, whatever alcohol (ethanol, 1-propanol, and 1-butanol) is used. PGDIS-E31 and 1-butanol exhibit best synergism in the microemulsion formation. In addition, the volume, structure and polarity of oil all influence the microemulsion formation. At the optimum weight ratio 2:1 of PGDIS-E31/1-butanol, the microemulsion region of the PGDIS-E31/1-butanol/IPP/water system is the largest among the studied systems. The microemulsion system of PGDIS-E31/1-butanol/IPP/water is not sensitive to lower temperature such as 40°C. It is also not sensitive to sodium chloride when the concentration of sodium chloride is in the range of 0 to 1.0%. 相似文献
10.
Farnesyl diphosphate (FPP) synthase catalyzes the consecutive head-to-tail condensations of isopentenyl diphosphate (IPP, C5) with dimethylallyl diphosphate (DMAPP, C5) and geranyl diphosphate (GPP, C10) to give (E,E)-FPP (C15). The enzyme belongs to a genetically distinct family of chain elongation enzymes that install E-double bonds during each addition of a five-carbon isoprene unit. Analysis of the C10 and C15 products from incubations with avian FPP synthase reveals that small amounts of neryl diphosphate (Z-C10) and (Z,E)-FPP are formed along with the E-isomers during the C5 --> C10 and C10 --> C15 reactions. Similar results were obtained for FPP synthase from Escherichia coli, Artemisia tridentata (sage brush), Pyrococcus furiosus, and Methanobacter thermautotrophicus and for GPP and FPP synthesized in vivo by E. coli FPP synthase. When (R)-[2-2H]IPP was a substrate for chain elongation, no deuterium was found in the chain elongation products. In contrast, the deuterium in (S)-[2-2H]IPP was incorporated into all of the products. Thus, the pro-R hydrogen at C2 of IPP is lost when the E- and Z-double bond isomers are formed. The synthesis of Z-double bond isomers by FPP synthase during chain elongation is unexpected for a highly evolved enzyme and probably reflects a compromise between optimizing double bond stereoselectivity and the need to exclude DMAPP from the IPP binding site. 相似文献
11.
[reaction: see text] Type II isopentenyl diphosphate:dimethylallyl diphosphate (IPP:DMAPP) isomerase from Synechocystis PCC 6803 catalyzes the interconversion of IPP and DMAPP. Upon incubation of the enzyme with IPP or DMAPP in 2H2O, one deuterium is incorporated into the C2 methylene of IPP, two deuteriums are incorporated at C4, and three deuteriums are incorporated into the (E)-methyl of DMAPP. 相似文献
12.
The effect of isobutylene-isoprene rubber (IIR) on the crystallizing behavior of isotactic polypropylene (IPP) as well as the morphology of the blends in relation with its properties have been studied by DSC, WAXD, polarized light microscope, SEM and mechanical properties test. The experimental results show that IIR has slight influence on melting point, crystallinity, crystallization rate of IPP. It seems certain that IIR has not entered into IPP phase in melt state. IIR has retarding action on the growth of IPP crystal and is an effective nucleating agent of IPP spherulites. The impact strength of the blend increases rapidly with IIR content more than 30 parts; the tensile strength of the blend, however, decreases as IIR content increases. The temperature and time of alter heat-treatment also have great influence on the impact strength of the blend. The impact strength of IPP/IIR (100/20) heat-treated at about 130℃for 2h is 5 times as high as that of the untreated blend. 相似文献
13.
The charge on oxygen for a series of compounds was obtained using Mulliken population, natural population analysis (NPA), integrated projected electron population (IPP) analysis, and Bader's topological density analysis, “integrated Bader populations” (IBP). The orbital-based methods (Mulliken and NPA) predict oxygen charges of about –0.6 whereas the spatial-based methods (IPP and IBP) predict charges of about – 1.2 to – 1.3. The differences are ascribed primarily to the nuclear-centered basis sets used in the orbital methods that minimize local atomic polarization effects. Accordingly, such population analyses should be used for electronic structure considerations only with due circumspection. The IPP method as an approximation to IBP shows gross similarities; small but significant differences vary in a nonsystematic manner and IPP values must also be used with care. 相似文献
14.
[chemical reaction: see text]. To study the catalysis of isopentenyl diphosphate (IPP) isomerase type II from Staphylococcus aureus, which is a flavoprotein catalyzing the interconversion of IPP and dimethylallyl diphosphate, we have chemically synthesized (S)- and (R)-[2-2H]IPP and carried out stereochemical analysis of the reaction. Our results show that the C-2 deprotonation of IPP by this enzyme is pro-R stereospecific, suggesting a similar stereochemical course as the type I enzyme. 相似文献
15.
LLDPE/IPP共混物高取向薄膜的附生结晶 总被引:1,自引:0,他引:1
本文用透射电子显微术、电子衍射等方法研究了线性低密度聚乙烯(LLDPE)和等规聚丙烯(IPP)共混物高取向薄膜的形态结构.在熔体拉伸薄膜中统组分的LLDPE与IPP均以高取向的片晶形式存在,片晶生长方向垂直手拉伸方向.当共混物中LLDPE含量较低(小于40%)时,作为分散相的LLDPE在IPP上附生结晶.两种片晶的c轴成45°交角,附生结晶的接触面为LLDPE的(100)和IPP的(010).而在LLDPE含量大于50%时,LLDPE形成独立的相区,则不存在附生结晶现象,结果两种片晶的生长方向均垂直于拉伸方向.在135℃热处理15min,然后自然冷却的LLDPE/IPP共混物薄膜中,当LLDPE含量≤50%时,LLDPE仍然在IPP上附生生长,二者的结构关系与热处理前的相同. 相似文献
16.
Dr. Lin-Fu Liang Prof. Dr. Jeroen S. Dickschat 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(15):e202200095
Five analogs of dimethylallyl diphosphate (DMAPP) with additional or shifted Me groups were converted with isopentenyl diphosphate (IPP) and the fungal variediene synthase from Aspergillus brasiliensis (AbVS). These enzymatic reactions resulted in the formation of several new terpene analogs that were isolated and structurally characterised by NMR spectroscopy. Several DMAPP analogs showed a changed reactivity giving access to compounds with unusual skeletons. Their formation is mechanistically rationalised and the absolute configurations of all obtained compounds were determined through a stereoselective deuteration strategy, revealing absolute configurations that are analogous to that of the natural enzyme product variediene. 相似文献
17.
[formula: see text] Farnesyl diphosphate (FPP) synthase from Escherichia coli catalyzes the condensation of isopentenyl diphosphate (IPP) and geranyl diphosphate (GPP) with selective removal of the pro-R hydrogen at C2 of IPP, the same stereochemistry observed for the pig liver, yeast, and avian enzymes. 相似文献
18.
The E. coli isopentenyl diphosphate isomerase (IDI) catalyzed reaction of isopentenyl diphosphate (IPP) in D(2)O gives a 66% yield of dimethylallyl diphosphate labeled with deuterium at the (E)-methyl group (d-DMAPP) and a 34% yield of IPP labeled with 1 mol of deuterium at C-2 (d-IPP). This shows that the release to D(2)O of the initial product of the IDI-catalyzed reaction (d-DMAPP) is slower than its conversion to d-IPP. Product dissociation is therefore rate determining for isomerization of IPP with a rate constant k(dis) ≈ k(cat) = 0.08 s(-1). The data provide an estimated rate constant of k(as) = 6 × 10(3) M(-1) s(-1) for binding of DMAPP to E. coli IDI that is similar to rate constants determined for the binding of N-protonated 2-amino ethyl diphosphate intermediate analogs to IDI from yeast [Reardon, J. E.; Abeles, R. H. Biochemistry1986, 25, 5609-5616]. We propose that ligand binding to IDI is relatively slow because there is a significant kinetic barrier to reorganization of the initial encounter complex between enzyme, substrate, and an essential Mg(2+) to form the Michaelis complex where the metal cation bridges the protein and the substrate diphosphate group. 相似文献
19.
Diversity of the biosynthesis of the isoprene units 总被引:1,自引:0,他引:1
This review covers the biosynthesis of the starter units of terpenoids, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) via the nonmevalonate pathway together with a new enzyme involved in the conversion of IPP and DMAPP, i.e type 2 IPP isomerase. The biosynthesis of terpenoids produced by actinomycetes is also reviewed. 117 references are cited. 相似文献
20.
氯溴卡宾与系列取代苯甲醛作用均产生CO(即羰基脱氧产物),取代基的电子效应直接影响CO的产率.捕获反应证实,该反应经历0°,0°型羰基叶立德中间体阶段.氟氯(溴)卡宾与四苯基环戊二烯酮(TPCP)反应除得到高产率的CO外,还生成偕氟卤环戊二烯(8)、双键加成物(9)及其重排产物(10).该类反应以脱CO途径为主,这可能是由于中间体羰基叶立德内部存在着"推-拉"稳定效应和不利于分子内电环化和分子间1,3-偶极加成的0°,90°型构象.本文讨论了这两类反应的微观作用机制. 相似文献