Aqueous channels within apolar peptide aggregates: solvated helix of the &#945;-aminoisobutyric acid (Aib)-containing peptide Boc-(Aib-Ala-Leu)<SUB>3</SUB>-Aib-OMe.2H<SUB>2</SUB>O.CH<SUB>3</SUB>OH in crystals

Although the peptide Boc-Aibl-Ala2-Leu3- Aib4-Ala5-Leu6-Aib7-Ala8-Leu9-Aib10-OMe [with a t-butoxycarbonyl (Boc) blocking group at the amino terminus, a methyl ester (OMe) at the carboxyl terminus, and four &#945;-aminoisobutyric (Aib) residues] has a 3-fold repeat of residues, the helix formed by the peptide backbone is irregular. The carboxyl-terminal half assumes an &#945;-helical form with torsion angles ) and &#968; of approximately -60&#176; and -45&#176;, respectively, whereas the amino-terminal half is distorted by an insertion of a water molecule between the amide nitrogen of Ala5 [N(5)] and the carbonyl oxygen of Ala2 [0(2)]. The water molecule W(1) acts as a bridge by forming hydrogen bonds N(5).W(1) (2.93 A) and W(1)---0(2) (2.86 A). The distortion of the helix exposes the carbonyl oxygens of Aib1 and Aib4 to the outside environment, with the consequence that the helix assumes an amphiphilic character despite having all apolar residues. Neighboring helices in the crystal run in antiparallel directions. On one side of a helix there are only hydrophobic contacts with efficient interdigitation of leucine side chains with those from the neighboring helix. On the other side of the helix there are hydrogen bonds between protruding carbonyl oxygens and four water molecules that separate two neighboring helices. Along the helix axis the helices bind head-to-tail with a direct hydrogen bond N(2)-0(9) (3.00 A). Crystals grown from methanol/water solution are in space group P21, with a = 15.778 &#177; 0.004 A, b = 11.228 &#177; 0.002 A, c = 18.415 &#177; 0.003 A, &#946; = 102.10 &#177; 0.02&#176; and two formula units per cell for C49H88N1003. 2H2O.CH3OH. The overall agreement factor R is 7.5% for 3394 reflections observed with intensities &gt; 3&#963;(F), and the resolution is 0.90 A

Solvated helical backbones: X-ray diffraction study of Boc-Ala-Leu-Aib-Ala-Leu-Aib-OMe &#183; H<SUB>2</SUB>O

A second example of insertion of a water molecule into the helical backbone of an apolar peptide is presented here and compared to a similar occurrence in a longer peptide with the same type of sequence of residues, i.e., Boc-Aib-(Ala-Leu-Aib)3-OMe. The backbone of the title compound assumes an approximate 310-helical form with three 4 &#8594; 1 hydrogen bonds. In the place of a fourth 4 &#8594;1 hydrogen bond, a water molecule is inserted between O(1) and N(4), and acts as a bridge by forming hydrogen bonds N(4) W(1) (2.95 &#197;) and W(1) O(1) (2.81&#197;). The water molecule participates in a third hydrogen bond with a neighboring peptide molecule, W(1) O(4) (2.91 &#197;). The insertion of the water molecule causes the apolar peptide to mimic an amphiphilic helix. Crystals grown from ethyl acetate/petroleum ether (reported here) or from methanol/water solution are in space group P212121 with a = 12.024(4) &#197;, b = 15.714(6) &#197;, c = 21.411(7) &#197;, Z = 4 and dcalc = 1.124 g/cm3 for C32H58N6O9 &#183; H2O. The overall agreement factor R is 6.3% for 2707 reflections observed with intensities &gt; 3&#963;(F) and the resolution is 0.90 &#197;

Optimizing H1 cavities for the generation of entangled photon pairs

We report on the theoretical investigation of photonic crystal cavities etched on a suspended membrane for the generation of polarization entangled photon pairs using the biexciton cascade in a single quantum dot. The implementation of spontaneous emission enhancement effect increases the entanglement visibility, while the concomitant preferential funneling of the emission in the cavity mode increases the collection of both entangled photons. We demonstrate and quantify that standard cavity designs present a polarization dependent emission diagram, detrimental to entanglement. The optimization of H1 cavities allows to obtain both high collection efficiencies and polarization independent emission, while keeping high Purcell factors necessary for high quality entangled photon sources

THE EFFECT OF EXOGENOUS FACTORS ON THERMAL POWER PLANT EFFICIENCY

This study focuses on the relationship between exogenous factors (that cannot be directly impacted by the actions of an economic agent) and combined heat and power (CHP) plant efficiency. As a measure of fuel utilization efficiency this paper proposes to use the Сoefficient of Fuel Utilization (CFU), which is the Russian equivalent of the Primary Energy Factor indicator. Climate conditions and fuel type were used as the exogenous factors in this article. Climate conditions were measured via climate zone proxies. The cause-effect relationships were analyzed using a linear regression model. The findings of the study showcase that the plants, which use natural gas as their primary fuel, show higher fuel utilization efficiency compared to coil plants. Climate conditions were also proven to be a statistically significant factor with plants situated in the third climate zone (mostly regions of the Central and North-Western federal districts) showing the highest average CFU of about 71%. The research shows that the exogenous factors account for close to 20% of CHP plant fuel utilization efficiency in Russia. The authors conclude that climate conditions and fuel type should be taken into account when constructing various energy efficiency models applicable to the Russian context

Helix construction using &#945;-aminoisobutyryl residues in a modular approach to synthetic protein design. Conformational properties of an apolar decapeptide in two different crystal forms and in solution

A modular strategy for the assembly of synthetic protein mimics is outlined. This approach is based on the ability of α -aminoisobutyric acid (Aib) to promote helical folding in peptides. The design of apolar, peptide helices with a high solubility in organic solvents facilitates structural design based on stereochemical constraints imposed by chosen non-protein residues. The design of individual helices is illustrated by the analysis of the decapeptide Boc-Aib-Ala-Leu-A!a-Aib-Aib-Leu-~Ala-Leu-Aib-OMe. Crystal structures of two polymorphic forms reveal an almost completely α-helical backbone. These high-resolution structures permit detailed characterization of the helix. H NMR and CD studies demonstrate maintenance of the helical conformation in solution, a feature that is a consequence of the limited flexibility of Aib residues in φ, ψ space