A Series of Iron(II)-NHC Sensitizers with Remarkable Power Conversion Efficiency in Photoelectrochemical Cells**

A series of six new Fe(II)NHC-carboxylic sensitizers with their ancillary ligand decorated with functions of varied electronic properties have been designed with the aim to increase the metal-to- surface charge separation and light harvesting in iron-based dye-sensitized solar cells (DSSCs). ARM130 scored the highest efficiency ever reported for an iron-sensitized solar cell (1.83 %) using Mg²⁺ and NBu₄I-based electrolyte and a thick 20 μm TiO₂ anode. Computational modelling, transient absorption spectroscopy and electrochemical impedance spectroscopy (EIS) revealed that the electronic properties induced by the dimethoxyphenyl-substituted NHC ligand of ARM130 led to the best combination of electron injection yield and spectral sensitivity breadth.     

Ammonium Sulphate—Magnesium Promoted Selective Reduction of Aromatic Nitro Compounds

Various nitroarenes and 2,1,3-benznooxadiazole-1-oxides were selectively and rapidly reduces to their corresponding amino and diamino compounds respectively in high yields using (NH₄SO₄-Mg/A1/Bi, a new reduction system.     

One Way Traffic: Base-to-Backbone Hole Transfer in Nucleoside Phosphorodithioate

The directionality of the hole-transfer processes between DNA backbone and base was investigated by using phosphorodithioate [P(S⁻)=S] components. ESR spectroscopy in homogeneous frozen aqueous solutions and pulse radiolysis in aqueous solution at ambient temperature confirmed initial formation of G^.+-P(S⁻)=S. The ionization potential of G-P(S⁻)=S was calculated to be slightly lower than that of guanine in 5′-dGMP. Subsequent thermally activated hole transfer from G^.+ to P(S⁻)=S led to dithiyl radical (P-2S^.) formation on the μs timescale. In parallel, ESR spectroscopy, pulse radiolysis, and density functional theory (DFT) calculations confirmed P-2S^. formation in an abasic phosphorodithioate model compound. ESR investigations at low temperatures and higher G-P(S⁻)=S concentrations showed a bimolecular conversion of P-2S^. to the σ²-σ*¹-bonded dimer anion radical [-P-2S 2S-P-]⁻ [ΔG (150 K, DFT)=−7.2 kcal mol⁻¹]. However, [-P-2S 2S-P-]⁻ formation was not observed by pulse radiolysis [ΔG° (298 K, DFT)=−1.4 kcal mol⁻¹]. Neither P-2S^. nor [-P-2S 2S-P-]⁻ oxidized guanine base; only base-to-backbone hole transfer occurs in phosphorodithioate.     

Hyperpolarization of Amino Acids in Water Utilizing Parahydrogen on a Rhodium Nanocatalyst

NMR offers many possibilities in chemical analysis, structural investigations, and medical diagnostics. Although it is broadly used, one of NMR spectroscopies main drawbacks is low sensitivity. Hyperpolarization techniques enhance NMR signals by more than four orders of magnitude allowing the design of new contrast agents. Parahydrogen induced polarization that utilizes the para-hydrogen's singlet state to create enhanced signals is of particular interest since it allows to produce molecular imaging agents within seconds. Herein, we present a strategy for signal enhancement of the carbonyl ¹³C in amino acids by using parahydrogen, as demonstrated for glycine and alanine. Importantly, the hyperpolarization step is carried out in water and chemically unmodified canonical amino acids are obtained. Our approach thus offers a high degree of biocompatibility, which is crucial for further application. The rapid sample hyperpolarization (within seconds) may enable the continuous production of biologically useful probes, such as metabolic contrast agents or probes for structural biology.     

Synthesis and Characterization of Ferrocene Derived Cyclic Carbaphosphazenes

Dialkylamino substituted cyclic carbaphosphazenes, (R 2 NCN) 2 (NPCl 2 ) were prepared and reacted with the ferrocene derived hydroxymethyl phosphine sulfide FcCH(CH 3 )P(S)(CH 2 OH) 2 after dilithiation to yield a series of new spirocyclic derivatives of cyclic carbaphosphazenes having ferrocenyl pendant groups. To confirm the formation of six membered spirocycles and to compare their spectral features, transesterification reactions of FcCH(CH 3 )P(S)(CH 2 OH) 2 also were carried out with P(NR 2 ) 3 , yielding the six membered heterocycles FcCH 2 P(S)(CH 2 O) 2 PNR 2 (R = Me, Et). The compounds were characterized by 1 H, 31 P, 13 C NMR, mass spectra, and elemental analysis.     

Synthesis and Characterization of Four-Arm Star Poly(ϵ-caprolactone)-Block-Poly(cyclic-carbonate methacrylate) Copolymers by Combining Ring-Opening Polymerization With Atom Transfer Radical Polymerization

Well-defined four-arm star poly(?-caprolactone)-block-poly(cyclic carbonate methacrylate) (PCL-b-PCCMA) copolymers were synthesized by combining ring-opening polymerization (ROP) with atom transfer radical polymerization (ATRP). First, a four-arm poly(?-caprolactone) (PCL) macroinitiator [(PCL-Br)₄] was prepared by the ROP of ?-CL catalyzed by stannous octoate at 110°C in the presence of pentaerythritol as the tetrafunctional initiator followed by esterification with 2-bromoisobutyryl bromide. The sequential ATRP of CCMA monomer was carried out by using the (PCL-Br)₄ tetrafunctional macroinitiator (MI) and in the presence of CuBr/2, 2′-bipyridyl system in DMF at 80°C with [(MI)]:[CuBr]:[bipyridyl] = 1:1:3 to yield block polymers with controlled molecular weights (M_n (NMR) = 10700 to 27300 g/mol) by varying block lengths and with moderately narrow polydispersities (M_w/M_n = 1.2–1.4). Block copolymers with different PCL: PCCMA copolymer composition such as 50:50, 70:30 and 74:26 were prepared with good yields (48-74%). All these block copolymers were well characterized by NMR, FTIR and GPC and tested their thermal properties by DSC and TGA.     

Designing a safer process for the reaction of TFA with sodium borohydride in THF by calorimetric technique

Reaction of TFA with sodium borohydride in THF is a loss of thermal control involving the evolution of Hydrogen gas. The investigation of the process by RC1e and ARSST showed that the criticality class of the reaction is dependant on the addition of TFA. Heat of reaction (Q _r), adiabatic temperature rise (ΔT _ad), and MTSR data are obtained from RC1e experiment. Exothermic onset temperature, Pressure rise, and self heat rate data are obtained from ARSST experiments. The correlation of these data was utilized to define the criticality class of the reaction under different conditions. The reaction with uncontrolled addition of TFA falls in the undesirable criticality class 5. Vent size data are obtained from the adiabatic calorimeter for undesirable reaction. The criticality class can be changed to class 2 with controlled addition. Accordingly, interlock system to control the undesired reaction and appropriate vent relief system are provided.     

RuCl3 · xH2O: A New Efficient Catalyst for Facile Preparation of 1,1‐Diacetates from Aldehydes

An efficient, facile preparation of aldehyde 1,1‐diacetates (acylals) in excellent yields catalyzed by RuCl₃ · xH₂O is described. Ketones do not react under these conditions.