Cellulose Iβ investigated by IR-spectroscopy at low temperatures

Highly crystalline oriented Halocynthia roretzi cellulose Iβ films were investigated by IR-spectroscopy between ?180 and +10 °C. Changes in the IR-spectra induced by temperature were compared to published changes induced by mechanical stretching. This made it possible to conclude that frequency shifts in the O–H stretching region of the IR-spectra due to temperature were not predominantly an indirect effect of thermal expansion leading to greater O–O distances, but were due directly to the effect of temperature on the O–H···O hydrogen bonds. Temperature induced frequency shifts of C–H stretching bands were consistent with the presence of weak inter-sheet C–H···O bonds. Furthermore, no phase transition in cellulose Iβ was found between ?180 and +10 °C.     

Chemical Probing of the Human Sirtuin 5 Active Site Reveals Its Substrate Acyl Specificity and Peptide‐Based Inhibitors

Sirtuins are NAD⁺‐dependent deacetylases acting as sensors in metabolic pathways and stress response. In mammals there are seven isoforms. The mitochondrial sirtuin 5 is a weak deacetylase but a very efficient demalonylase and desuccinylase; however, its substrate acyl specificity has not been systematically analyzed. Herein, we investigated a carbamoyl phosphate synthetase 1 derived peptide substrate and modified the lysine side chain systematically to determine the acyl specificity of Sirt5. From that point we designed six potent peptide‐based inhibitors that interact with the NAD⁺ binding pocket. To characterize the interaction details causing the different substrate and inhibition properties we report several X‐ray crystal structures of Sirt5 complexed with these peptides. Our results reveal the Sirt5 acyl selectivity and its molecular basis and enable the design of inhibitors for Sirt5.     

Synthesis of water‐soluble allyl‐functionalized oligochitosan and its modification by thiol–ene addition in water

A novel, straightforward and versatile chemical pathway has been studied to functionalize water‐soluble chitosan oligomers. This metal‐free methodology is based on the epoxy‐amine reaction of the allyl glycidyl ether with chitosan, followed by thiol‐ene radical coupling reaction of ω‐functional mercaptans, using 4,4′‐Azobis(4‐cyanovaleric acid) as a free radical initiator. Both reactions were entirely carried out in water. In a preliminary step, chitosan depolymerization was carried out using H₂O₂ in an acetic medium under 100 W microwave irradiation, optimizing the yield of water‐soluble oligomers. Functionalization by six different thiols bearing alcohol, carboxylic acid, ester, and amino groups was then performed, leading to a range of functional oligochitosans with different grafting efficiencies. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 39–48     

Single‐Molecule Methods to Study Membrane Receptor Oligomerization

Membrane receptors control fundamental cellular processes. Binding of a specific ligand to a receptor initiates communication through the membrane and activation of signaling cascades. This activation process often leads to a spatial rearrangement of receptors in the membrane at the molecular level. Single‐molecule techniques contributed significantly to the understanding of receptor organization and rearrangement in membranes. Here, we review four prominent single‐molecule techniques that have been applied to membrane receptors, namely, stepwise photobleaching, Förster resonance energy transfer, sub‐diffraction localization microscopy and co‐tracking. We discuss the requirements, benefits and limitations of each technique, discuss target labeling, present a selection of applications and results and compare the different methodologies.     

Nanosecond CO photodissociation and excited-state character of [Ru(X)(X')(CO)2(N,N'-diisopropyl-1,4-diazabutadiene)] (X=X'=Cl or I; X=Me, X'=I; X=SnPh3, X'=Cl) studied by time-resolved infrared spectroscopy and DFT calculations

The character and dynamics of the low-lying excited states of [Ru(X)(X')(CO)2(iPr-dab)] (X=X'=Cl or I; X=Me, X'=I; X=SnPh3, X'=Cl; iPr-dab=N, N'-diisopropyl-1,4-diazabutadiene) were studied experimentally by pico- and nanosecond time-resolved IR spectroscopy (TRIR) and (for X=X'=Cl or I) computationally using density functional theory (DFT) and time-dependent DFT (TD-DFT) techniques. The lowest allowed electronic transition occurs between 390 and 460 nm and involves charge transfer from the Ru(halide)(CO) 2 unit to iPr-dab, denoted (1)MLCT/XLCT (metal-to-ligand/halide-to-ligand charge transfer). The lowest triplet state is well modeled by UKS-DFT-CPCM calculations, which quite accurately reproduce the excited-state IR spectrum in the nu(CO) region. It has a (3)MLCT/XLCT character with an intraligand (iPr-dab) (3)pipi* admixture. TRIR spectra of the lowest triplet excited state show two nu(CO) bands that are shifted to higher energies from their corresponding ground-state positions. The magnitude of this upward shift increases as a function of the ligands X and X' [(I)2 < (Sn)(Cl) < (Me)(I) < (Cl)2] and reveals increasing contribution of the Ru(CO)2-->dab MLCT character to the excited state. The lowest triplet state of [Ru(Cl)2(CO)2(iPr-dab)] undergoes a approximately 10 ps relaxation that is followed by CO dissociation, producing cis(CO,CH 3CN),trans(Cl,Cl)-[Ru(Cl)2(CH 3CN)(CO)(iPr-dab)] with a unity quantum yield and 7.2 ns lifetime and without any observable intermediate. To our knowledge, this is the first example of a "slow" CO dissociation from a thermally equilibrated triplet charge-transfer excited state.     

Design of open-framework germanates by combining different building units

Open-framework germanates with extra-large channels are built from two different types of clusters. The two different clusters are connected in such a way to form a pseudo-body-centered cluster aggregate (PBCCA). The different packing of PBCCAs resulted in different 3D open-framework germanates.     

An EPR, ENDOR and EIE study of gamma-irradiated poly (lactide-co-glycolide) polymers

Gamma radiation of poly (lactide-co-glycolide) raw polymers and processed microspheres under vacuum and at 77 K results in the formation of a series of free radicals. The resulting powder electron paramagnetic resonance (EPR) spectrum contains a distribution of several different radicals, depending on the annealing temperature, and is therefore difficult to interpret. By utilising the selectivity of the electron nuclear DOuble resonance (ENDOR) and associated ENDOR induced EPR (EIE) techniques, a more direct approach for the deconvolution of the EPR spectrum can be achieved. Using this approach, the radiolytically induced CH3 *CHC(O)R- chain scission radical was identified at 120 K by simulation of the EIE spectrum. At elevated temperatures (250 K), this radical decays considerably and the more stable radicals -O*CHC(O)-, CH3 *C(OR)C(O)- and CH3 *C(OH)C(O)- predominate. This work demonstrates the utility of the EIE approach to supplement and aid the interpretation of powder EPR spectra of radicals in a polymer matrix.     

Cooperative Brønsted acid-type organocatalysis: alcoholysis of styrene oxides

We present a mild and efficient method for the completely regioselective alcoholysis of styrene oxides utilizing a cooperative Br?nsted acid-type organocatalytic system comprised of mandelic acid (1 mol %) and N,N'-bis-[3,5-bis-(trifluoromethyl)phenyl]-thiourea (1 mol %). Various styrene oxides are readily transformed into their corresponding beta-alkoxy alcohols in good to excellent yields at full conversion. Simple aliphatic and sterically demanding, as well as unsaturated and acid-sensitive alcohols can be employed.     

Photoinduced intramolecular tryptophan oxidation and excited-state behavior of [Re(L-AA)(CO)3(α-diimine)](+) (L = pyridine or imidazole, AA = tryptophan, tyrosine, phenylalanine)

Re(I) carbonyl-diimine complexes [Re(L-AA)(CO)(3)(N,N)](+) (N,N = bpy, phen) containing an aromatic amino acid (AA), phenylalanine (Phe), tyrosine (Tyr), or tryptophan (Trp), linked to Re by a pyridine-amido or imidazole-amido ligand L have been synthesized and their excited-state properties investigated by nanosecond time-resolved IR (TRIR) and emission spectroscopy. Near-UV optical excitation populates a Re(I)(CO)(3)→N,N (3)MLCT excited state *[Re(II)(L-AA)(CO)(3)(N,N(?-))](+). Decay to the ground state (50-300 ns lifetime) is the only excited-state deactivation process observed in the case of Phe and Tyr complexes, whereas the Trp-containing species undergo a Trp(indole)→*Re(II) electron transfer (ET) producing a charge-separated (CS) state, [Re(I)(L-Trp(?+))(CO)(3)(N,N(?-))](+). The ET occurs with a 8-40 ns lifetime depending on L, N,N, and the solvent. The CS state is characterized by ν(CO) IR bands shifted to lower wavenumbers from their respective ground-state positions and two bands at 1278 and 1497 cm(-1) tentatively attributed to Trp(?+). The amido bridge is affected by both the MLCT excitation and the subsequent ET, manifested by the shifts and intensity changes of the amide-I IR band at about 1680 cm(-1). The CS state decays to the ground state by a N,N(?-)→Trp(?+) back-ET the rates of which are comparable to those of the forward ET, 30-60 ns. This study independently demonstrates that Trp can act as an electron-hopping intermediate in photodriven ET systems based on Re-labeled proteins and supramolecules. Photoinduced ET in Trp-containing Re complexes also can be used to generate Trp(?+) and investigate its spectral properties and reactivity.     

Affinity capillary electrophoresis applied to the studies of interactions of a member of heat shock protein family with an immunosuppressant

The bioaffinity of receptor-ligand interactions is investigated by determining the binding constant (association constant or dissociation constant) of the resulting complex utilizing affinity capillary electrophoresis (ACE). The ACE binding assay was established with a potent immunosuppressant, deoxyspergualin (DSG), that binds specifically to Hsc70, a constitutive or cognate member of heat shock protein 70 (Hsp70) family. Quantitative determination of binding constants under different running buffer systems provide comparative results. The association constants for the interaction between Hsc70 protein and DSG were found to be 5.7·10⁴ M⁻¹ in a buffer with pH 6.95 and 6.3·10⁴ M⁻¹ in a buffer with pH 5.30 (or corresponding dissociation constants, 18 and 16 μM, respectively) based on Scatchard analyses. Binding of DSG to a synthetic peptide, SINPDEAVAYGAAV-QAAILSGDK, one of the DSG-binding fragments found from tryptic digest of Hsc70 protein, provides further detailed information for the understanding of Hsc70 binding domain. The applicability of using coated capillaries was also evaluated for probing Hsc70-DSG interaction.