Lactic acid demineralization of green crab (Carcinus maenas) shells: effect of reaction conditions and isolation of an unusual calcium complex

Chitin and chitosan are potentially useful and environmentally friendly biopolymers with a wide range of value-added applications. Effective and green technologies for isolation of these materials are potentially important. Here, we report the use of lactic acid for the demineralization of green crab shells. Green crab shells and lactic acid, produced during cheese making, are two waste streams that could be tapped for large-scale chitin and chitosan processing. We have studied the effect of concentration and temperature on the demineralization of green crab shells. An unusual calcium lactate/lactic acid complex was also isolated and crystallographically characterized. The results have implications not only for the use of weak acids in the isolation of chitin and chitosan but also for the use of lactic acid as a solvent in green chemistry.     

Novel copolymers of styrene. 3. Some ring-substituted propyl 2-cyano-3-phenyl-2-propenoates

Novel trisubstituted ethylenes, ring-substituted propyl 2-cyano-3-phenyl-2-propenoates, RPhCH?C(CN)CO₂C₃H₇ (where R is 2-C₆H₅CH₂O, 3-C₆H₅CH₂O, 4-C₆H₅CH₂O, 4-CH₃COO, 3-CH₃CO, 4-CH₃CONH, 2-CN, 3-CN, 4-CN, 4-(CH₃)₂N, 4-(C₂H₅)₂N) were prepared and copolymerized with styrene. The monomers were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-substituted benzaldehydes and propyl cyanoacetate, and characterized by CHN analysis, IR, ¹H and ¹³C-NMR. All the ethylenes were copolymerized with styrene (M₁) in solution with radical initiation (ABCN) at 70°C. The compositions of the copolymers were calculated from nitrogen analysis and the structures were analyzed by IR, ¹H and ¹³C-NMR. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200–500°C range with residue (2.7–8.6% wt.), which then decomposed in the 500–800°C range.     

Multimetallic assemblies using piperazine-based dithiocarbamate building blocks

Treatment of cis-[RuCl2(dppm)2] (dppm = bis(diphenylphosphino)methane) with dithiocarbamates, NaS2CNR2 (R = Me, Et) and [H2NC5H10][S2CNC5H10], yields cations [Ru(S2CNR2)2(dppm)2](+) and [Ru(S2CNC5H10)2(dppm)2](+), respectively. The zwitterions S2CNC4H8NHR (R = Me, Et) react with the same metal complex in the presence of base to yield [Ru(S2CNC4H8NR)(dppm)2](+). Piperazine or 2,6-dimethylpiperazine reacts with carbon disulfide to give the zwitterionic dithiocarbamate salts H2NC4H6(R2-3,5)NCS2 (R = H; R = Me), which form the complexes [Ru(S2CNC4H6(R2-3,5)NH2)(dppm)2](2+) on reaction with cis-[RuCl2(dppm)2]. Sequential treatment of [Ru(S2CNC4H8NH2)(dppm)2](2+) with triethylamine and carbon disulfide forms the versatile metalla-dithiocarbamate complex [Ru(S2CNC4H8NCS2)(dppm)2] which reacts readily with cis-[RuCl2(dppm)2] to yield [{Ru(dppm)2}2(S2CNC4H8NCS2)]. Reaction of [Ru(S2CNC4H8NCS2)(dppm)2] with [Os(CH=CHC6H4Me-4)Cl(CO)(BTD)(PPh3)2] (BTD = 2,1,3-benzothiadiazole), [Pd(C6H4CH2NMe2)Cl]2, [PtCl2(PEt3)2], and [NiCl2(dppp)] (dppp = 1,3-bis(diphenylphosphino)propane) results in the heterobimetallic complexes [(dppm)2Ru(S2CNC4H8NCS2)ML(n))](m+) (ML(n) = Os(CH=CHC6H4Me-4)(CO)(PPh3)2](+), m = 1; ML(n) = Pd(C,N-C6H4CH2NMe2), m = 1; ML(n) = Pt(PEt3)2, m = 2; ML(n) = Ni(dppp), m = 2). Reaction of [NiCl2(dppp)] with H2NC4H8NCS2 yields the structurally characterized compound, [Ni(S2CNC4H8NH2)(dppp)](2+), which reacts with base, CS2, and cis-[RuCl2(dppm)2] to provide an alternative route to [(dppm)2Ru(S2CNC4H8NCS2)Ni(dppp)](+). A further metalla-dithiocarbamate based on cobalt, [CpCo(S2CNC4H8NH2)(PPh3)](2+), is formed by treatment of CpCoI2(CO) with S2CNC4H8NH2 followed by PPh3. Further reaction with NEt3, CS2, and cis-[RuCl2(dppm)2] yields [(Ph3P)CpCo(S2CNC4H8NCS2)Ru(dppm)2](2+). Heterotrimetallic species of the form [{(dppm)2Ru(S2CNC4H8NCS2)}2M](2+) result from the reaction of [Ru(S2CNC4H8NCS2)(dppm)2] and M(OAc)2 (where M = Ni, Cu, Zn). Reaction of [Ru(S2CNC4H8NCS2)(dppm)2] with Co(acac)3 and LaCl3 results in the formation of the compounds [{(dppm)2Ru(S2CNC4H8NCS2)}3Co](3+) and [{(dppm)2Ru(S2CNC4H8NCS2)}3La](3+), respectively. The electrochemical behavior of selected examples is also reported.     

Tandem multi-step synthesis of C-carboxyazlactones promoted by N-heterocyclic carbenes

Cascade reaction sequences incorporating N-heterocyclic carbene-based organocatalysis have been developed that allow the direct preparation of a range of (+/-)-4-phenoxycarbonylazlactones in good isolated yields (66-84%) from the corresponding N-p-anisoyl amino acids.     

New synthetic routes to a disulfidodinickel(II) complex: characterization and reactivity of a Ni2(mu-eta2:eta2-S2) core

Activation of elemental sulfur by the monovalent nickel complex [PhTt (tBu)]Ni(CO) [PhTt(tBu)=phenyl{tris[(tert-butylmethyl)thio]methyl}borate] generates the disulfidodinickel(II) complex 2. This species is alternatively accessible via thermal decomposition of [PhTt (tBu)]Ni(SCPh3). Spectroscopic, magnetic, and X-ray diffraction studies establish that 2 contains a mu-eta(2):eta(2)-S2 ligand that fosters antiferromagnetic exchange coupling between the Ni (II) ions. This observation is in contrast to the lighter congener, oxygen, which strongly favors the bis(mu-oxo)dinickel(III) structure. 2 oxidizes PPh 3 to SPPh3 and reacts with O2, generating several products, one of which has been identified as [(PhTt (tBu))Ni]2(mu-S) (3).     

Separation of fluorescent phosphatidyl inositol phosphates by CE

Phosphatidyl inositol 4,5-bisphosphate (PIP2) and phosphatidyl inositol 3,4,5-trisphosphate (PIP3) labeled with 4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-propionic acid (BODIPY FL) on the acyl chain or a phosphatidyl ethanolamine head group were separated by CE with LIF detection. Several methods and capillary-coating procedures were tested for the separation of these phosphatidyl inositol phosphates (PIPs) at 20 degrees C. Separation of the PIPs in less than 20 min with excellent resolution was achieved using a buffer containing sodium deoxycholate (SDC), 1-propanol, MgCl2 and the polymer coating reagent, EOTrol LR. The efficiency of the optimized method was as high as 1.3x10(5) plates. The dependence of the separation on the concentration of 1-propanol, SDC, and MgCl2 was determined. The separation of PIP2 and PIP3 was primarily due to differential binding of the lipids to Mg2+ rather than to different solubilities in the micellar phase. The role of the SDC was to prevent adsorption of the hydrophobic lipids to the capillary wall and thus enhance the efficiency. The fluorescent PIPs are of value for both in vitro and in vivo assays of phospholipid metabolism. In particular, the use of these lipids with the optimized capillary-based separation will be of utility for drug screening as well as cell-based assays.     

Photocontrol of DNA binding specificity of a miniature engrailed homeodomain

Control of DNA binding of HDH-3, a 18-residue polypeptide based on the recognition helix of the Q50K engrailed homeodomain, has been achieved. HDH-3 was linked to an azobenzene cross-linker through two cysteine residues in an i, i + 11 spacing. For the thermodynamically stable trans configuration of the cross-linker, the dark-adapted peptide (dad-HDH-3) adopted a mainly alpha-helical structure as judged by circular dichroism (CD) spectroscopy. After irradiation with light of 360 nm, the helical content of the peptide (irrad-HDH-3) was reduced significantly and the CD spectrum of the irradiated peptide resembled that of the largely unstructured, unalkylated peptide. Despite lacking helices-1 and -2 and the N-terminal arm of Q50K engrailed, dad-HDH-3 bound to its natural DNA target sequence TAATCC (QRE) with high affinity (K(D) = 7.5 +/- 1.3 nM). The binding affinity for the mutant DNA sequence, TAATTA (ERE), was reduced significantly (K(D) = 140 +/- 11 nM). Unlike irrad-HDH-3, which like the unalkylated parent peptide displayed only marginal DNA binding specificity, dad-HDH-3 specified base pairs 5 and 6 of QRE with an accuracy rivaling that of the intact wild-type Q50K engrailed homeodomain, making dad-HDH-3 the most specific designed DNA binding miniature homeodomain reported to date. Moreover, DNA binding affinity and specificity of HDH-3 could be controlled externally by irradiation with light.     

Synchrotron Radiation Provides a Plausible Explanation for the Generation of a Free Radical Adduct of Thioxolone in Mutant Carbonic Anhydrase II

Thioxolone acts as a prodrug in the presence of carbonic anhydrase II (CA II), whereby the molecule is cleaved by thioester hydrolysis to the carbonic anhydrase inhibitor, 4-mercaptobenzene-1,3-diol (TH0). Thioxolone was soaked into the proton transfer mutant H64A of CA II in an effort to capture a reaction intermediate via X-ray crystallography. Structure determination of the 1.2 ? resolution data revealed the TH0 had been modified to a 4,4'-disulfanediyldibenzene-1,3-diol, a product of crystallization conditions, and a zinc ligated 2,4-dihydroxybenzenesulfenic acid, most likely induced by radiation damage. Neither ligand was likely a result of an enzymatic mechanism.     

A prochelator peptide designed to use heterometallic cooperativity to enhance metal ion affinity

A peptide has been designed so that its chelating affinity for one type of metal ion regulates its affinity for a second, different type of metal ion. The prochelator peptide (PCP), which is a fusion of motifs evocative of calcium loops and zinc fingers, forms a 1 : 2 Zn : peptide complex at pH 7.4 that increases its affinity for Zn²⁺ ∼3-fold in the presence of Tb³⁺ (log β₂ from 13.8 to 14.3), while the 1 : 1 luminescent complex with Tb³⁺ is brighter, longer lived, and 20-fold tighter in the presence of Zn²⁺ (log K from 6.2 to 7.5). This unique example of cooperative, heterometallic allostery in a biologically compatible construct suggests the possibility of designing conditionally active metal-binding agents that could respond to dynamic changes in cellular metal status.     

Lithol Red: a systematic structural study on salts of a sulfonated azo pigment

The first systematic series of single-crystal diffraction structures of azo lake pigments is presented (Lithol Red with cations=Mg(II), Ca(II), Sr(II), Ba(II), Na(I) and Cd(II)) and includes the only known structures of non-Ca examples of these pigments. It is shown that these commercially and culturally important species show structural behaviour that can be predicted from a database of structures of related sulfonated azo dyes, a database that was specifically constructed for this purpose. Examples of the successful structural predictions from the prior understanding of the model compounds are that 1) the Mg salt is a solvent-separated ion pair, whereas the heavier alkaline-earth elements Ca, Sr and Ba form contact ion pairs, namely, low-dimensional coordination complexes; 2) all of the Lithol Red anions exist as the hydrazone tautomer and have planar geometries; and 3) the commonly observed packing mode of alternating inorganic layers and organic bilayers is as expected for an ortho-sulfonated azo species with a planar anion geometry. However, the literature database of dye structures has no predictive use for organic solvate structures, such as that of the observed Na Lithol Red DMF solvate. Interestingly, the Cd salt is isostructural with the Mg salt and not with the Ca salt. It is also observed that linked eight-membered [MOSO](2) rings are the basic coordination motif for all of the known structures of Ca, Sr and Ba salts of sulfonated azo pigments in which competing carboxylate groups are absent.