Synthesis of Functionalized trans‐A2B2‐Porphyrins Using Donor–Acceptor Cyclopropane‐Derived Dipyrromethanes

meso‐Substituted trans‐A₂B₂‐porphyrins bearing specific patterns of substituents are crucial building blocks in porphyrin‐based biomimetic systems and molecular materials and can be used for the construction of well‐defined porphyrin‐based architectures. A new stepwise and rational synthesis of functionalized trans‐A₂B₂‐porphyrins is reported in which for the first time donor–acceptor‐substituted cyclopropane precursors (d–a cyclopropanes) are exploited. The three presented d–a cyclopropanes are readily accessible in a multi‐gram scale and serve as aldehyde equivalents in the reaction with an excess of pyrrole to afford the corresponding dipyrromethanes (DPMs). The three DPMs were synthesized in yields of 60–74%. They are stable in purified form in the absence of light and air and were subsequently condensed with a wide range of aliphatic and aromatic aldehydes bearing electron‐donating or electron‐withdrawing substituents followed by oxidation to form the corresponding trans‐A₂B₂‐porphyrins. Fourteen functionalized porphyrins were synthesized in yields of 14–31%, indicating the broad scope of the synthetic procedure. The possibility to introduce key functional groups is emphasized, which enables subsequent modification of these porphyrins with moieties inducing biological activity. Modification of the tetrapyrroles may occur by addition to one of the porphyrin peripheral double bonds, the use of substituents of the aryl groups or via the methoxycarbonyl group at two of the meso‐substituents. Three examples of porphyrins were converted into the corresponding 7,8‐dihydroxychlorins by osmium‐mediated dihydroxylation and one of the resulting chlorins was subjected to saponification to give a highly polar chlorin dicarboxylic acid. A 4‐bromophenyl‐substituted d–a cyclopropane was prepared by rhodium‐catalyzed cyclopropanation and then transformed into a DPM which was subsequently condensed to a porphyrin. Its Zn complex allowed a Heck reaction to afford the functionalized bis(alkenyl)‐substituted trans‐A₂B₂‐Zn‐porphyrin.     

Are Available Models Reliable for Predicting the FRP Contribution to the Shear Resistance of RC Beams?

In this paper the trustworthiness of the existing theory for predicting the fiber-reinforced plastic contribution to the shear resistance of reinforced concrete beams is discussed. The most well-known shear models for external bonded reinforcement are presented, commented on, and compared with an extensive experimental database. The database contains the results from more than 200 tests performed in different research institutions across the world. The results of the comparison are not very promising and the use of the additional principle in the actual shear design equations should be questioned. The large scatter between the predicted values of different models and experimental results is of real concern bearing in mind that some of the models are used in present design codes.     

Failure Load Test of a CFRP Strengthened Railway Bridge in ?rnsk?ldsvik, Sweden

The results obtained when performing a load test to failure of an existing structure are valuable when assessing calculation models, updating finite element models, and investigating the true structural behavior. In this paper a destructive testing and monitoring of a railway bridge in ?rnsk?ldsvik, Sweden is presented. In this particular test the shear capacity of the concrete girders was of primary interest. However, for any reasonable placement of the load (a line load placed transverse to the track direction) a bending failure would occur. This problem was solved by strengthening for flexure using carbon fiber reinforced polymer (CFRP) rectangular rods epoxy bonded in sawed up slots, e.g., near surface mounted reinforcement. The strengthening was very successful and resulted in a desired shear failure when the bridge was loaded to failure. The load-carrying capacity in bending for the unstrengthened and strengthened bridge as well as the shear capacity was predicted with Monte Carlo simulations. The particular calculation presented showed that there was a 25% probability of a bending failure instead of a shear failure. Monitoring showed that the strengthening reduced the strain in the tensile steel reinforcement by approximately 10%, and increased the height of the compressed zone by 100 mm. When the shear failure occurred, the utilization of the compression concrete and CFRP rods were 100 and 87.5%, respectively. This indicates that a bending failure indeed was about to occur, even though the final failure was in shear.     

Oscillatory velocity response of premixed flat flames stabilized in axial acoustic fields

This article describes a combined theoretical-experimental investigation of the processes that drive axial instabilities in solid propellant rocket motors. In this study, the solid propellant flame has been simulated by a premixed flat flame that has been stabilized on the porous side-wall of a duct. The driving processes have been investigated by studying the interaction of the premixed flame with an axial acoustic field. Using experimentally determined acoustic pressures, burner surface admittances, and steady-state flame temperature distributions as input data, the developed model was used to determine the characteristics of the velocity field in the flame region under a variety of test conditions. The predicted velocity field was then compared with LDV velocity measurements to check the validity of the model and determine the flame driving. These studies reveal that the investigated flame responds to the presence of an axial acoustic field by producing an oscillatory velocity component, ν′, normal to the duct wall, that can drive or damp the acoustic field. Comparison of the measured data with the model predictions reveal satisfactory agreement. These studies also showed that driving and damping of the acoustic field occur simultaneously in different regions of the flame. The net effect of the flame upon the acoustic field depends upon the relative magnitudes of these opposing tendencies. It is also shown that the flame driving depends upon the acoustic admittance of the side-wall surface and the frequency of the acoustic field.     

Growth hormone-releasing factor stimulates milk production and sustains growth hormone release in Holstein cows

Serum growth hormone was determined in lactating cows following repeated intravenous injections of growth hormone-releasing factor. A given dose was injected every 4 h for 24 h in a 4 (cow) X 4 (d) Latin square. Growth hormone increased similarly above controls after 10, 20, or 40 micrograms releasing factor/100 kg body weight. In another experiment the effects on lactational performance and growth hormone responses of cows to repeated injections of releasing factor for 10 d were determined in a 2 (cow) X 2 (period) Latin square crossover. Administration of 20 micrograms releasing factor/100 kg body weight to 16 Holstein cows (lactating 4.5 to 7.5 mo) every 4-h for 10 d increased milk yield from 25.4 to 27.7 kg/d and increased total fat, protein, and lactose 11% above controls. Releasing factor did not affect milk composition or feed intake. Peak growth hormone response to releasing factor was similar between d 1 (19.9 ng/ml) and 10 (24.4 ng/ml). Exogenous growth hormone-releasing factor administered to lactating Holstein cows at the doses tested: 1) increases growth hormone consistently, although the response is not dose dependent, 2) is galactopoietic, 3) causes an apparent increase in feed to milk conversion, and 4) increases growth hormone to at least the same magnitude on d 10 as on d 1.     

Looking for the answer

Metabotropic glutamate receptors (mGluRs) were identified in olfactory receptor neurons of the channel catfish, Ictalurus punctatus, by polymerase chain reaction. DNA sequence analysis confirmed the presence of two subtypes, mGluR1 and mGluR3, that were coexpressed with each other and with the putative odorant receptors within single olfactory receptor neurons. Immunocytochemical data showed that both mGluR subtypes were expressed in the apical dendrites and some cilia of olfactory neurons. Pharmacological analysis showed that antagonists to each mGluR subtype significantly decreased the electrophysiological response to odorant amino acids. alpha-Methyl-L-CCG1/(2S,3S,4S)-2-methyl-2-(carboxycyclopropyl++ +)glycine (MCCG), a known antagonist to mGluR3, and (S)-4-carboxyphenylglycine (S-4CPG), a specific antagonist to mGluR1, each significantly reduced olfactory receptor responses to L-glutamate. S-4CPG and MCCG reduced the glutamate response to 54% and 56% of control, respectively, which was significantly greater than their effect on a neutral amino acid odorant, methionine. These significant reductions of odorant response by the antagonists, taken with the expression of these receptors throughout the dendritic and ciliated portions of some olfactory receptor neurons, suggest that these mGluRs may be involved in olfactory reception and signal transduction.